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Hisayuki Hara

Hisayuki Hara, Akimichi Takemura and Ruriko Yoshida

Hara Hisayuki, Takemura Akimichi, Yoshida Ruriko

A Markov Basis for Conditional Test of Common Diagonal Effect in Quasi-Independence Model for Square Contingency Tables

15 pages

Comput. Statist. Data Anal. (2009), 53, 1006-1014

10.1016/j.csda.2008.11.030

stat.ME

In two-way contingency tables we sometimes find that frequencies along the diagonal cells are relatively larger(or smaller) compared to off-diagonal cells, particularly in square tables with the common categories for the rows and the columns. In this case the quasi-independence model with an additional parameter for each of the diagonal cells is usually fitted to the data. A simpler model than the quasi-independence model is to assume a common additional parameter for all the diagonal cells. We consider testing the goodness of fit of the common diagonal effect by Markov chain Monte Carlo (MCMC) method. We derive an explicit form of a Markov basis for performing the conditional test of the common diagonal effect. Once a Markov basis is given, MCMC procedure can be easily implemented by techniques of algebraic statistics. We illustrate the procedure with some real data sets.

v1 (Tue, 19 Feb 2008 07:36:20 GMT), v2 (Tue, 22 Jul 2008 05:00:49 GMT)

Marc Schartmann

M. Schartmann (1), K. Meisenheimer (1), M. Camenzind (2), S. Wolf (1), K. R. W. Tristram (1) and Th. Henning (1) ((1) MPIA, Heidelberg, Germany (2) ZAH-LSW Heidelberg, Germany)

Schartmann M., Meisenheimer K., Camenzind M., Wolf S., Tristram K. R. W., Henning Th.

Three-dimensional radiative transfer models of clumpy tori in Seyfert galaxies

15 pages, 23 figures, accepted by A&A

10.1051/0004-6361:20078907

astro-ph

Tori of Active Galactic Nuclei are made up of a mixture of hot and cold gas, as well as dust. In order to protect the dust grains from destruction by the hot gas as well as by the energetic radiation of the accretion disk, the dust is often assumed to be distributed in clouds. In our new 3D model of AGN dust tori, the torus is modelled as a wedge-shaped disk in which dusty clouds are randomly distributed, by taking the dust density distribution of the corresponding continuous model into account. We especially concentrate on the differences between clumpy and continuous models in terms of the temperature distributions, the surface brightness distributions and interferometric visibilities, as well as spectral energy distributions. To this end, we employ radiative transfer calculations with the help of the 3D Monte Carlo code MC3D. In a second step, interferometric visibilities are calculated from the simulated surface brightness distributions, which can be directly compared to observations with the MIDI instrument. The radial temperature distributions of clumpy models possess significantly enhanced scatter compared to the continuous cases. Even at large distances, clouds can be heated directly by the central accretion disk. The existence of the silicate 10 micron-feature in absorption or in emission depends sensitively on the distribution, the size and optical depth of clouds in the innermost part of the torus, due to shadowing effects of clouds there. This explains failure and success of previous modelling efforts of clumpy tori. After adapting the parameters of our clumpy standard model to the circumstances of the Seyfert 2 Circinus galaxy, it can qualitatively explain recent mid-infrared interferometric observations performed with MIDI, as well as high resolution spectral data.

v1 (Tue, 19 Feb 2008 20:21:21 GMT)

Wen-Ge Wang

Wen-ge Wang

Wang Wen-ge

Sensitivity of Quantum Motion to Perturbation in Triangle Map

6 pages, 8 figures, published version

Phys. Rev. E 77, 036206 (2008)

10.1103/PhysRevE.77.036206

nlin.CD quant-ph

We study quantum Loschmidt echo, or fidelity, in the triangle map whose classical counterpart has linear instability and weak chaos. Numerically, three regimes of fidelity decay have been found with respect to the perturbation strength $\epsilon$. In the regime of weak perturbation, the fidelity decays as $\exp (-c\epsilon^2 t^{\gamma})$ with $\gamma \simeq 1.7$. In the regime of strong perturbation, the fidelity is approximately a function of $\epsilon t^{2.5}$, which is predicted for the classical fidelity [G. Casati, {\it et al}, Phys.Rev.Lett.{\bf 94}, 114101 (2005)], and decays slower than power-law decay for long times. In an intermediate regime, the fidelity has approximately an exponential decay $\exp (-c' \epsilon t)$.

v1 (Tue, 19 Feb 2008 08:07:40 GMT), v2 (Mon, 24 Mar 2008 12:47:24 GMT)

Wei-Qin Zhao

Zhao Wei-Qin

Wei-Qin Zhao

Two Kinds of Iterative Solutions for Generalized Sombrero-shaped Potential in $N$-dimensional Space

16 pages, 3 figures

10.1088/1751-8113/41/23/235302

quant-ph

Based on two different iteration procedures the groundstate wave functions and energies for N-dimensional generalized Sombrero-shaped potentials are solved. Two kinds of trial functions for the iteration procedure are defined. The iterative solutions are convergent nicely to consistent results for different choices of iteration procedures and trial functions.

v1 (Tue, 19 Feb 2008 08:12:38 GMT)

Zaza Osmanov

Z. Osmanov, A. Mignone, S. Massaglia, G. Bodo, A. Ferrari

Osmanov Z., Mignone A., Massaglia S., Bodo G., Ferrari A.

On the linear theory of Kelvin-Helmholtz instabilities of relativistic magnetohydrodynamic planar flows

8 pages, 9 figures

10.1051/0004-6361:200809605

astro-ph

We investigate the linear stability properties of the plane interface separating two relativistic magnetized flows in relative motion. The two flows are governed by the (special) relativistic equations for a magnetized perfect gas in the infinite conductivity approximation. By adopting the vortex-sheet approximation, the relativistic magnetohydrodynamics equations are linearized around the equilibrium state and the corresponding dispersion relation is derived and discussed. The behavior of the configuration and the regimes of instability are investigated following the effects of four physical parameters, namely: the flow velocity, the relativistic and Alfv\'enic Mach numbers and the inclination of the wave vector on the plane of the interface. From the numerical solution of the dispersion relation, we find in general two separate regions of instability, associated respectively with the slow and fast magnetosonic modes. Modes parallel to the flow velocity are destabilized only for sufficiently low magnetization. For the latter case, stabilization is attained, additionally, at sufficiently large relativistic velocities between the two flows in relative motion. The relevance of these results to the study of the stability of astrophysical jets is briefly commented.

v1 (Tue, 19 Feb 2008 08:14:00 GMT), v2 (Fri, 7 Mar 2008 08:21:05 GMT), v3 (Thu, 14 Aug 2008 06:40:40 GMT)

Luigi Coraggio

L. Coraggio, A. Covello, A. Gargano, N. Itaco, and T. T. S. Kuo

Coraggio L., Covello A., Gargano A., Itaco N., Kuo T. T. S.

Shell-model studies on exotic nuclei around 132Sn

8 pages, 4 tables, invited talk at INPC2007, Tokyo, Japan, June 3-8 2007. To be published in Nuclear Physics A

Nucl.Phys.A805:424-430,2008

10.1016/j.nuclphysa.2008.02.264

nucl-th

The study of exotic nuclei around 132Sn is a subject of current experimental and theoretical interest. Experimental information for nuclei in the vicinity of 132Sn, which have been long inaccessible to spectroscopic studies, is now available thanks to new advanced facilities and techniques. The experimental data which have been now become available for these neutron-rich nuclei may suggest a modification in the shell structure. They are, in fact, somewhat different from what one might expect by extrapolating the existing results for N<82, and as a possible explanation a change in the single-proton level scheme has been suggested. The latter would be caused by a more diffuse nuclear surface, and could be seen as a precursor of major effects which should show up at larger neutron excess. New data offer therefore the opportunity to test the shell model and look for a possible evolution of shell structure when going toward neutron drip line. This is stimulating shell-model studies in this region. Here, we present an overview of recent shell-model studies of 132Sn neighbors, focusing attention on those calculations employing realistic effective interactions.

v1 (Tue, 19 Feb 2008 14:21:19 GMT)

Huawei Zhang

H.W. Zhang, T. Gehren, G. Zhao

Zhang H. W., Gehren T., Zhao G.

NLTE study of scandium in the Sun

10 pages, 6 figures, A&A accepted

10.1051/0004-6361:20078910

astro-ph

We investigate the formation of neutral and singly ionized scandium lines in the solar photospheres. The research is aimed derive solar $\log gf\epsilon_{\odot}$(Sc) values for scandium lines, which will later be used in differential abundance analyses of metal-poor stars. Extensive statistical equilibrium calculations were carried out for a model atom, which comprises 92 terms for \ion{Sc}{i} and 79 for \ion{Sc}{ii}. Photoionization cross-sections are assumed to be hydrogenic. Synthetic line profiles calculated from the level populations according to the NLTE departure coefficients were compared with the observed solar spectral atlas. Hyperfine structure (HFS) broadening is taken into account. The statistical equilibrium of scandium is dominated by a strong underpopulation of \ion{Sc}{i} caused by missing strong lines. It is nearly unaffected by the variation in interaction parameters and only marginally sensitive to the choice of the solar atmospheric model. Abundance determinations using the ODF model lead to a solar Sc abundance of between $\log\epsilon_\odot = 3.07$ and 3.13, depending on the choice of $f$ values. The long known difference between photospheric and meteoritic scandium abundances is confirmed for the experimental $f$-values.

v1 (Tue, 19 Feb 2008 08:45:06 GMT)

Vesna Borka Jovanovi\'c

V. Borka, J. Milogradov-Turin, D. Uro\v{s}evi\'c

Borka V., Milogradov-Turin J., Urošević D.

The Brightness of the Galactic Radio Loops at 1420 MHz: Some Indications for the Existence of Loops V and VI

6 pages, 4 tables, 4 figures. Accepted for publication in Astron. Nachr

10.1002/asna.200610927

astro-ph

In this article we use 1420 MHz data to demonstrate the likely reality of Galactic radio Loops V and VI. We further estimate distances and spectral indices for both these and the four main radio loops. In the cases of Loops I - IV, radio spectral indices are calculated from the mean brightnesses at 1420 and 820/404 MHz. The spectral indices of Loops V and VI are obtained from $T - T$ plots between 1420 and 408 MHz. Using the supernova remnant (SNR) hypothesis for the origin of radio loops, distances are calculated from the surface brightnesses and the angular diameters at 1420 MHz. We also study how results for brightnesses and distances of radio loops agree with current theories of SNR evolution. For this purpose, the ambient density and initial explosion energy of the loops are discussed. We also discuss applications of different $\Sigma - D$ relations. The results obtained confirm a non-thermal origin and nearby locations for the Galactic radio loops. Therefore, we have indications that they are very old SNRs that evolve in low ambient densities, with high initial explosion energies.

v1 (Tue, 19 Feb 2008 08:46:15 GMT)

Michael Ruzhansky

Michael Ruzhansky and Mitsuru Sugimoto

Ruzhansky Michael, Sugimoto Mitsuru

Comparison of estimates for dispersive equations

an expository note; 7 pages

Begehr, H. G. W. (ed.) et al., Further progress in analysis. Proceedings of the 6th international ISAAC congress, Ankara, Turkey, August 13-18, 2007. Hackensack, NJ: World Scientific. 486-494 (2009)

math.AP math.FA

This paper describes a new comparison principle that can be used for the comparison of space-time estimates for dispersive equations. In particular, results are applied to the global smoothing estimates for several classes of dispersive partial differential equations.

v1 (Tue, 19 Feb 2008 09:04:37 GMT)

Sergey Gubin

Sergey Gubin

Gubin Sergey

On Subgraph Isomorphism

Simplified, 6 pages

Polynomial size asymmetric linear model for Subgraph Isomorphism, Proceedings WCECS 2008, ISBN: 978-988-98671-0-2, pp.241-246

cs.DM cs.CC cs.DS math.CO

Article explicitly expresses Subgraph Isomorphism by a polynomial size asymmetric linear system.

v1 (Tue, 19 Feb 2008 09:06:40 GMT), v2 (Thu, 14 Aug 2008 22:22:49 GMT)

Giacomo Beccari

G. Beccari, B.Lanzoni, F.R. Ferraro, L.Pulone, M.Bellazzini, F.Fusi Pecci, R.T.Rood, E.Giallongo, R.Ragazzoni, A.Grazian, A.Baruffolo, N.Bouche, P.Buschkamp, C.De Santis, E.Diolaiti, A.Di Paola, J.Farinato, A.Fontana, S.Gallozzi, F.Gasparo, G.Gentile, F.Pasian, F.Pedichini, R.Smareglia, R.Speziali, V.Testa, E.Vernet

Beccari G., Lanzoni B., Ferraro F. R., Pulone L., Bellazzini M., Pecci F. Fusi, Rood R. T., Giallongo E., Ragazzoni R., Grazian A., Baruffolo A., Bouche N., Buschkamp P., De Santis C., Diolaiti E., Di Paola A., Farinato J., Fontana A., Gallozzi S., Gasparo F., Gentile G., Pasian F., Pedichini F., Smareglia R., Speziali R., Testa V., Vernet E.

The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study

25 pages, 9 figures, accepted for publication on ApJ

10.1086/587689

astro-ph

We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ~60'' (~2 r_c) from the cluster center. This value turns out to be a factor of two smaller than the radius of avoidance (r_avoid, the radius within which all the stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r_avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected. We have also used this data base to construct the radial star density profile of the cluster: this is the most extended and accurate radial profile ever published for this cluster, including detailed star counts in the very inner region. The star density profile is reproduced by a standard King Model with an extended core (~25'') and a modest value of the concentration parameter (c=1.58). A deviation from the model is noted in the most external region of the cluster (at r>6.5' from the center). This feature needs to be further investigated in order to address the possible presence of a tidal tail in this cluster.

v1 (Tue, 19 Feb 2008 19:03:03 GMT)

Kouichi Hagino

F. Minato and K. Hagino

Minato F., Hagino K.

Fission barriers in neutron-proton isospin plane for heavy neutron-rich nuclei

6 pages, 7 figures

Phys.Rev.C77:044308,2008

10.1103/PhysRevC.77.044308

nucl-th

We discuss the sensitivity of fission barrier for heavy neutron-rich nuclei to fission paths in the two dimensional neutron-proton quadrupole plane. To this end, we use the constrained Skyrme-Hartree-Fock + BCS method, and examine the difference of fission barriers obtained with three constraining operators, that is, the neutron, proton, and mass quadrupole operators. We investigate $^{220}$U, $^{236}$U, and $^{266}$U, %from proton-rich to neutron-rich uranium isotopes, that is relevant to r-process nucleosynthesis. We find that the fission barrier heights are almost the same among the three constraining operators even for neutron-rich nuclei, indicating that the usual way to calculate fission barriers with the mass quadrupole operator is well justified. We also discuss the difference between proton and neutron deformation parameters along the fission paths.

v1 (Tue, 19 Feb 2008 09:23:23 GMT)

Jose Natario

Filipe C. Mena, Jose Natario

Mena Filipe C., Natario Jose

Matching stationary spacetimes

13 pages; v2: references added, typos corrected, matches final published version; v3: statement about higher genus stars corrected, reference added; v4: footnote 3 made more precise

J. Geom. Phys. 59 (2009) 448-458

10.1016/j.geomphys.2008.12.002

gr-qc

Using the quasi-Maxwell formalism, we derive the necessary and sufficient conditions for the matching of two stationary spacetimes along a stationary timelike hypersurface, expressed in terms of the gravitational and gravitomagnetic fields and the 2-dimensional matching surface on the space manifold. We prove existence and uniqueness results to the matching problem for stationary perfect fluid spacetimes with spherical, planar, hyperbolic and cylindrical symmetry. Finally, we find an explicit interior for the cylindrical analogue of the NUT spacetime.

v1 (Tue, 19 Feb 2008 09:49:47 GMT), v2 (Wed, 11 Feb 2009 17:09:21 GMT), v3 (Tue, 17 Mar 2009 10:15:24 GMT), v4 (Thu, 8 Oct 2020 10:09:25 GMT)

Alexandre Piriou

A. Piriou, Y. Fasano, E. Giannini, \O. Fischer

Piriou A., Fasano Y., Giannini E., Fischer Ø.

Effect of oxygen-doping on Bi$_{2}$Sr$_{2}$Ca$_{2}$Cu$_{3}$O$_{10 + \delta}$ vortex matter: Crossover from electromagnetic to Josephson interlayer coupling

Erroneous duplicate of arXiv:0802.2617

10.1103/PhysRevB.77.184508

cond-mat.supr-con

Erroneous duplicate of arXiv:0802.2617, removed by arXiv admin

v1 (Tue, 19 Feb 2008 09:51:58 GMT), v2 (Wed, 20 Feb 2008 17:03:26 GMT)

Alexandre Piriou

A. Piriou, Y. Fasano, E. Giannini, \O. Fischer

Piriou A., Fasano Y., Giannini E., Fischer Ø.

Effect of oxygen-doping on Bi-2223 vortex matter: Crossover from electromagnetic to Josephson interlayer coupling

Phys. Rev. B 77, 184508 (2008)

10.1103/PhysRevB.77.184508

cond-mat.supr-con

We study the effect of oxygen-doping on the critical temperature, Tc, the vortex matter phase diagram and the nature of the coupling mechanism between the Cu-O layers in the three-layer Bi2Sr2Ca2Cu3O10+delta (Bi-2223) compound. Contrary to previous reports, in the overdoped (OD) regime we do find a variation of Tc with increasing the oxygen partial-pressure of the post-annealing treatment. This variation is less significant than in the bi-layer parental compound Bi-2212 and does not follow the universal Tc vs.delta relation. Magnetic measurements reveal that increasing delta enlarges the field and temperature stability of the Bragg glass phase. These findings imply that the interlayer coupling between Cu-O layers enhances with delta. The anisotropy parameter estimated from directional first-penetration field measurements monotonously decreases from 50 in the underdoped (UD) to 15 in the OD regimes. However, the in-plane penetration depth presents a boomerang-like behaviour with $\delta$, reaching its minimum value close to optimal doping. These two facts lead to a crossover from a Josephson(OD) to electromagnetic(UD)-dominated coupling of adjacent Cu-O layers in the vicinity of optimal doping.

v1 (Tue, 19 Feb 2008 09:47:24 GMT)

Eduardo de Rafael

Jean-Philippe Aguilar (CPT), Eduardo De Rafael (CPT), David Greynat (IFIC)

Aguilar Jean-Philippe, De Rafael Eduardo, Greynat David

Muon Anomaly from Lepton Vacuum Polarization and The Mellin--Barnes Representation

v2, minor changes in the introduction, typos corrected, two references added; to appear in Phys. Rev. D

Phys.Rev.D77:093010,2008

10.1103/PhysRevD.77.093010

hep-ph

We evaluate, analytically, a specific class of eighth--order and tenth--order QED contributions to the anomalous magnetic moment of the muon. They are generated by Feynman diagrams involving lowest order vacuum polarization insertions of leptons $l=e,\mu$, and $\tau$. The results are given in the form of analytic expansions in terms of the mass ratios $m_e/m_\mu$ and $m_\mu/m_\tau$. We compute as many terms as required by the error induced by the present experimental uncertainty on the lepton masses. We show how the Mellin--Barnes integral representation of Feynman parametric integrals allows for an easy analytic evaluation of as many terms as wanted in these expansions and how its underlying algebraic structure generalizes the standard renormalization group properties. We also discuss the generalization of this technique to the case where two independent mass ratios appear. Comparison with previous numerical and analytic evaluations made in the literature, whenever pertinent, are also made.

v1 (Tue, 19 Feb 2008 09:48:34 GMT), v2 (Fri, 4 Apr 2008 14:31:56 GMT)

Julien Randon-Furling

Satya. N. Majumdar (LPTMS), Julien Randon-Furling (LPTMS), Michael J. Kearney, Marc Yor (PMA)

Majumdar Satya. N., Randon-Furling Julien, Kearney Michael J., Yor Marc

On the time to reach maximum for a variety of constrained Brownian motions

Submitted to J. Phys. A

Journal of Physics A Mathematical and Theoretical 41 (2008) 365005

10.1088/1751-8113/41/36/365005

cond-mat.stat-mech math.PR

We derive P(M,t_m), the joint probability density of the maximum M and the time t_m at which this maximum is achieved for a class of constrained Brownian motions. In particular, we provide explicit results for excursions, meanders and reflected bridges associated with Brownian motion. By subsequently integrating over M, the marginal density P(t_m) is obtained in each case in the form of a doubly infinite series. For the excursion and meander, we analyse the moments and asymptotic limits of P(t_m) in some detail and show that the theoretical results are in excellent accord with numerical simulations. Our primary method of derivation is based on a path integral technique; however, an alternative approach is also outlined which is founded on certain "agreement formulae" that are encountered more generally in probabilistic studies of Brownian motion processes.

v1 (Tue, 19 Feb 2008 09:51:16 GMT)

Kasper Peeters

Kasper Peeters and Anne Taormina

Peeters Kasper, Taormina Anne

Dynamics of icosahedral viruses: what does Viral Tiling Theory teach us?

10 pages, contribution to the proceedings of the `Second Mathematical Virology Workshop', Edinburgh (6-10 August 2007)

Computational and Mathematical Methods in Medicine, 9(03-04), 2008, 211 - 220.

10.1080/17486700802168270

q-bio.BM

We present a top-down approach to the study of the dynamics of icosahedral virus capsids, in which each protein is approximated by a point mass. Although this represents a rather crude coarse-graining, we argue that it highlights several generic features of vibrational spectra which have been overlooked so far. We furthermore discuss the consequences of approximate inversion symmetry as well as the role played by Viral Tiling Theory in the study of virus capsid vibrations.

v1 (Tue, 19 Feb 2008 09:59:35 GMT)

Gokhan Unel

V. E. Ozcan, S. Sultansoy, G. Unel

Ozcan V. E., Sultansoy S., Unel G.

Search for 4th family quarks with the ATLAS detector

Eur. Phys. J. C (2008) 57: 621

10.1140/epjc/s10052-008-0766-4

hep-ex

The pair production of heavy fourth-generation quarks, which are predicted under the hypothesis of flavor democracy, is studied using tree-level Monte Carlo generators and fast detector simulation. Two heavy-quark mass values, 500 and 750$\gev$, are considered with the assumption that the fourth family mixes primarily with the two light families. It is shown that a clear signature will be observed in the data collected by the ATLAS detector, after the first year of low-luminosity running at the Large Hadron Collider.

v1 (Tue, 19 Feb 2008 10:27:32 GMT), v2 (Sat, 8 Mar 2008 20:54:45 GMT)

Itzhak Baum

Itzhak Baum, Gad Eilam, Shaouly Bar-Shalom

Baum Itzhak, Eilam Gad, Bar-Shalom Shaouly

Scalar FCNC and rare top decays in a two Higgs doublet model "for the top"

added two references. 15 pages, 14 figures

Phys.Rev.D77:113008,2008

10.1103/PhysRevD.77.113008

hep-ph

In the so called two Higgs doublet model for the top-quark (T2HDM), first suggested by Das and Kao, the top quark receives a special status, which endows it with a naturally large mass, and also potentially gives rise to large flavor changing neutral currents (FCNC) only in the up-quark sector. In this paper we calculate the branching ratio (BR) for the rare decays t->ch and h->tc (h is a neutral Higgs) in the T2HDM, at tree level and at 1-loop when it exceeds the tree-level. We compare our results to predictions from other versions of 2HDM's and find that the scalar FCNC in the T2HDM can play a significant role in these decays. In particular, the 1-loop mediated decays can be significantly enhanced in the T2HDM compared to the 2HDM of types I and II, in some instances reaching BR~10^-4 which is within the detectable level at the LHC.

v1 (Tue, 19 Feb 2008 10:04:36 GMT), v2 (Mon, 25 Feb 2008 17:47:20 GMT)

Pekka Koskinen Dr

Pekka Koskinen, Sami Malola, Hannu H\"akkinen

Koskinen Pekka, Malola Sami, Häkkinen Hannu

Self-passivating edge reconstructions of graphene

4 pages, 4 figures, 1 table

Phys. Rev. Lett. 101, 115502 (2008)

10.1103/PhysRevLett.101.115502

cond-mat.mtrl-sci

Planar reconstruction patterns at the zigzag and armchair edges of graphene were investigated with density functional theory. It was unexpectedly found that the zigzag edge is metastable and a planar reconstruction spontaneously takes place at room temperature. The reconstruction changes electronic structure and self-passivates the edge with respect to adsorption of atomic hydrogen from molecular atmosphere.

v1 (Tue, 19 Feb 2008 10:13:51 GMT), v2 (Fri, 8 Aug 2008 09:44:12 GMT)

Makoto Nakano

Makoto Nakano, Koji Sugitani, Takahiro Niwa, Yoichi Itoh, and Makoto Watanabe

Nakano Makoto, Sugitani Koji, Niwa Takahiro, Itoh Yoichi, Watanabe Makoto

Clustering of Emission-line Stars in the W5E HII region

16 pages, 7 figures, 3 tables, accepted for publication in PASJ

10.1093/pasj/60.4.739

astro-ph

We have made a new survey of emission-line stars in the W5E HII region to investigate the population of PMS stars near the OB stars by using the Wide Field Grism Spectrograph 2 (WFGS2). A total of 139 H-alpha emission stars were detected and their g'i'-photometry was performed. The spatial distribution of them shows three aggregates, i.e., two aggregates near the bright-rimmed clouds at the edge of W5E HII region (BRC 13 and BRC 14) and one near the exciting O7V star. The age and mass of each H-alpha star were estimated from the extinction corrected color-magnitude diagram and theoretical evolutionary tracks. We found, for the first time in this region, that the young stars near the exciting star are systematically older (4 Myr) than those near the edge of the HII region (1 Myr). This result supports that the formation of stars proceed sequentially from the center of HII region to the eastern bright rim. We further suggest a possibility that the birth of low mass stars near the exciting star of HII region precede the production of massive OB stars in the pre-existing molecular cloud.

v1 (Tue, 19 Feb 2008 11:08:20 GMT)

Ali Ayad

Ali Ayad

Ayad Ali

A note on the computation of Puiseux series solutions of the Riccatti equation associated with a homogeneous linear ordinary differential equation

math.CA

We present in this paper a detailed note on the computation of Puiseux series solutions of the Riccatti equation associated with a homogeneous linear ordinary differential equation. This paper is a continuation of [1] which was on the complexity of solving arbitrary ordinary polynomial differential equations in terms of Puiseux series.

v1 (Tue, 19 Feb 2008 14:02:29 GMT)

E. V. Ferapontov

P.A. Burovskiy, E.V. Ferapontov and S.P. Tsarev

Burovskiy P. A., Ferapontov E. V., Tsarev S. P.

Second order quasilinear PDEs and conformal structures in projective space

37 pages. In the new version the correct acknowledgement of grant support for SPT is added

nlin.SI math.DG

We investigate second order quasilinear equations of the form f_{ij} u_{x_ix_j}=0 where u is a function of n independent variables x_1, ..., x_n, and the coefficients f_{ij} are functions of the first order derivatives p^1=u_{x_1}, >..., p^n=u_{x_n} only. We demonstrate that the natural equivalence group of the problem is isomorphic to SL(n+1, R), which acts by projective transformations on the space P^n with coordinates p^1, ..., p^n. The coefficient matrix f_{ij} defines on P^n a conformal structure f_{ij} dp^idp^j. In this paper we concentrate on the case n=3, although some results hold in any dimension. The necessary and sufficient conditions for the integrability of such equations by the method of hydrodynamic reductions are derived. These conditions constitute a complicated over-determined system of PDEs for the coefficients f_{ij}, which is in involution. We prove that the moduli space of integrable equations is 20-dimensional. Based on these results, we show that any equation satisfying the integrability conditions is necessarily conservative, and possesses a dispersionless Lax pair. Reformulated in differential-geometric terms, the integrability conditions imply that the conformal structure f_{ij} dp^idp^j is conformally flat, and possesses an infinity of 3-conjugate null coordinate systems. Integrable equations provide an abundance of explicit examples of such conformal structures parametrized by elementary functions, elliptic functions and modular forms.

v1 (Tue, 19 Feb 2008 10:29:03 GMT), v2 (Sat, 20 Sep 2008 18:26:56 GMT), v3 (Sun, 1 Feb 2009 03:37:45 GMT)

Daniela Maionchi

D. O. Maionchi, A. M. C. Souza, H. J. Herrmann, R. N. da Costa Filho

Maionchi D. O., Souza A. M. C., Herrmann H. J., Filho R. N. da Costa

Anderson localization on Falicov-Kimball model with next-nearest-neighbor hopping and long-range correlated disorder

9 figures. submitted to PRB

10.1103/PhysRevB.77.245126

cond-mat.str-el

The phase diagram of correlated, disordered electron systems is calculated within dynamical mean-field theory for the Anderson-Falicov-Kimball model with nearest-neighbors and next-nearest-neighbors hopping. The half-filled band is analyzed in terms of the chemical potential of the system using the geometric and arithmetic averages. We also introduce the on-site energies exhibiting a long-range correlated disorder, which generates a system with similar characteristics as the one created by a random independent variable distribution. A decrease in the correlated disorder reduces the extended phase.

v1 (Tue, 19 Feb 2008 10:32:54 GMT)

Mihaita Popinciuc

C. Jozsa, M. Popinciuc, N. Tombros, H. T. Jonkman and B. J. van Wees (Physics of Nanodevices and Molecular Electronics, Zernike Institute for Advanced Materials, The Netherlands)

Jozsa C., Popinciuc M., Tombros N., Jonkman H. T., van Wees B. J.

Electronic spin drift in graphene field effect transistors

4 figures

10.1103/PhysRevLett.100.236603

cond-mat.mes-hall

We studied the drift of electron spins under an applied DC electric field in single layer graphene spin valves in a field effect transport geometry at room temperature. In the metallic conduction regime ($n \simeq 3.5 \times 10^{16}$ m$^{-2}$), for DC fields of about $\pm$70 kV/m applied between the spin injector and spin detector, the spin valve signals are increased/decreased, depending on the direction of the DC field and the carrier type, by as much as $\pm$50%. Sign reversal of the drift effect is observed when switching from hole to electron conduction. In the vicinity of the Dirac neutrality point the drift effect is strongly suppressed. The experiments are in quantitative agreement with a drift-diffusion model of spin transport.

v1 (Tue, 19 Feb 2008 11:42:51 GMT), v2 (Mon, 14 Apr 2008 14:47:05 GMT)

Awadhesh Prasad

Awadhesh Prasad, Manish Agrawal, and Ramakrishna Ramaswamy

Prasad Awadhesh, Agrawal Manish, Ramaswamy Ramakrishna

Strange nonchaotic attractors in driven delay--dynamics

To be appeared as a Book Chapter dedicated to Prof. M Lakshmanan on the occasion of his sixtieth birthday

nlin.CD

Strange nonchaotic attractors (SNAs) are observed in quasiperiodically driven time--delay systems. Since the largest Lyapunov exponent is nonpositive, trajectories in two such identical but distinct systems show the property of {\it phase}--synchronization. Our results are illustrated in the model SQUID and R\"ossler oscillator systems.

v1 (Tue, 19 Feb 2008 11:00:55 GMT)

Leonardo Campanelli

L. Campanelli, P. Cea, G.L. Fogli and L. Tedesco

Campanelli L., Cea P., Fogli G. L., Tedesco L.

Inflation-Produced Magnetic Fields in R^n F^2 and I F^2 models

5 pages, 2 figures. Minor revisions. References added. Accepted for publication in Phys. Rev. D

Phys.Rev.D77:123002,2008

10.1103/PhysRevD.77.123002

astro-ph

We re-analyze the production of seed magnetic fields during Inflation in (R/m^2)^n F_{\mu \nu}F^{\mu \nu} and I F_{\mu \nu}F^{\mu \nu} models, where n is a positive integer, R the Ricci scalar, m a mass parameter, and I \propto \eta^\alpha a power-law function of the conformal time \eta, with \alpha a positive real number. If m is the electron mass, the produced fields are uninterestingly small for all n. Taking m as a free parameter we find that, for n \geq 2, the produced magnetic fields can be sufficiently strong in order to seed dynamo mechanism and then to explain galactic magnetism. For \alpha \gtrsim 2, there is always a window in the parameters defining Inflation such that the generated magnetic fields are astrophysically interesting. Moreover, if Inflation is (almost) de Sitter and the produced fields almost scale-invariant (\alpha \simeq 4), their intensity can be strong enough to directly explain the presence of microgauss galactic magnetic fields.

v1 (Tue, 19 Feb 2008 11:12:05 GMT), v2 (Thu, 1 May 2008 08:53:00 GMT)

Oleg Kochukhov

O. Kochukhov

Kochukhov O.

The Paschen-Back effect in the Li I 6708 A line and the presence of lithium in cool magnetic Ap stars

11 pages, 7 figures; accepted for publication in Astronomy & Astrophysics

10.1051/0004-6361:20078856

astro-ph

A number of cool magnetic Ap stars show a prominent feature at lambda 6708 A. Its identification with Li I remains controversial due to a poor knowledge of the spectra of rare-earth elements that are strongly enhanced in peculiar stars and can potentially provide an alternative identification. We suggest to investigate the 6708 line in Ap stars with strong magnetic fields. In these objects the magnetic broadening and splitting provides an additional powerful criterium for line identification, allowing to use the whole line profile instead of a mere coincidence of the observed and predicted wavelength. Due to a small separation of the Li I doublet components, their magnetic splitting pattern deviates from the one expected for the Zeeman effect even in relatively weak fields. We carry out detailed calculations of the transition between the Zeeman and Paschen-Back regimes in the magnetic splitting of the Li I line and compute polarized synthetic spectra for the range of field strength expected in Ap stars. Theoretical spectral synthesis is compared with the high-resolution observations of cool Ap stars HD 116114, HD 166473 and HD 154708, which have a mean field strength of 6.4, 8.6 and 24.5 kG, respectively, and show a strong 6708 A line. High-resolution spectra for the 6708 A region are analysed for 17 magnetic Ap stars. The presence of the 6708 A line is confirmed in 9 stars and reported for the first time in 6 stars. We demonstrate that the observed profiles of the 6708 A line in the strong field stars HD 116114, HD 166473 and HD 154708 correspond rather well to the theoretical calculations assuming the Li I identification. Inclusion of the Paschen-Back effect improves the agreement with observations, especially for HD 154708. Results of our study confirm the Li I identification proposed for the 6708 A line in cool Ap stars.

v1 (Tue, 19 Feb 2008 15:34:17 GMT)

Georgi Ganchev

Georgi Ganchev

Ganchev Georgi

Canonical Weierstrass Representation of Minimal and Maximal Surfaces in the Three-dimensional Minkowski Space

15 pages

math.DG

We prove that any minimal (maximal) strongly regular surface in the three-dimensional Minkowski space locally admits canonical principal parameters. Using this result, we find a canonical representation of minimal strongly regular time-like surfaces, which makes more precise the Weierstrass representation and shows more precisely the correspondence between these surfaces and holomorphic functions (in the Gauss plane). We also find a canonical representation of maximal strongly regular space-like surfaces, which makes more precise the Weierstrass representation and shows more precisely the correspondence between these surfaces and holomorphic functions (in the Lorentz plane). This allows us to describe locally the solutions of the corresponding natural partial differential equations.

v1 (Tue, 19 Feb 2008 11:15:55 GMT)

Dominique Vuillaume

Christophe Novembre (LCEI), David Guerin (IEMN), Kamal Lmimouni (IEMN), Christian Gamrat (LCEI), Dominique Vuillaume (IEMN)

Novembre Christophe, Guerin David, Lmimouni Kamal, Gamrat Christian, Vuillaume Dominique

Gold nanoparticle-pentacene memory-transistors

10.1063/1.2896602

cond-mat.mtrl-sci

We demonstrate an organic memory-transistor device based on a pentacene-gold nanoparticles active layer. Gold (Au) nanoparticles are immobilized on the gate dielectric (silicon dioxide) of a pentacene transistor by an amino-terminated self-assembled monolayer. Under the application of writing and erasing pulses on the gate, large threshold voltage shift (22 V) and on/off drain current ratio of ~3E4 are obtained. The hole field-effect mobility of the transistor is similar in the on and off states (less than a factor 2). Charge retention times up to 4500 s are observed. The memory effect is mainly attributed to the Au nanoparticles.

v1 (Tue, 19 Feb 2008 11:19:07 GMT)

Victor M. Red'kov

Victor M. Red'kov, Andrei A. Bogush and Natalia G. Tokarevskaya

Red'kov Victor M., Bogush Andrei A., Tokarevskaya Natalia G.

On Parametrization of the Linear GL(4,C) and Unitary SU(4) Groups in Terms of Dirac Matrices

This is a contribution to the Proc. of the Seventh International Conference ''Symmetry in Nonlinear Mathematical Physics'' (June 24-30, 2007, Kyiv, Ukraine), published in SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at http://www.emis.de/journals/SIGMA/

SIGMA 4 (2008), 021, 46 pages

10.3842/SIGMA.2008.021

math-ph math.MP

Parametrization of $4\times 4$-matrices $G$ of the complex linear group $GL(4,C)$ in terms of four complex 4-vector parameters $(k,m,n,l)$ is investigated. Additional restrictions separating some subgroups of $GL(4,C)$ are given explicitly. In the given parametrization, the problem of inverting any $4\times 4$ matrix $G$ is solved. Expression for determinant of any matrix $G$ is found: $\det G = F(k,m,n,l)$. Unitarity conditions $G^{+} = G^{-1}$ have been formulated in the form of non-linear cubic algebraic equations including complex conjugation. Several simplest solutions of these unitarity equations have been found: three 2-parametric subgroups $G_{1}$, $G_{2}$, $G_{3}$ - each of subgroups consists of two commuting Abelian unitary groups; 4-parametric unitary subgroup consisting of a product of a 3-parametric group isomorphic SU(2) and 1-parametric Abelian group. The Dirac basis of generators $\Lambda_{k}$, being of Gell-Mann type, substantially differs from the basis $\lambda_{i}$ used in the literature on SU(4) group, formulas relating them are found - they permit to separate SU(3) subgroup in SU(4). Special way to list 15 Dirac generators of $GL(4,C)$ can be used $\{\Lambda_k\} = \{\alpha_i\oplus\beta_j\oplus(\alpha_iV\beta_j = {\boldsymbol K} \oplus {\boldsymbol L}\oplus{\boldsymbol M})\}$, which permit to factorize SU(4) transformations according to $S = e^{i\vec{a}\vec{\alpha}} e^{i\vec{b}\vec\beta}} e^{i{\boldsymbol k}{\boldsymbol K}} e^{i{\boldsymbol l}{\boldsymbol L}} e^{i\boldsymbol m}{\boldsymbol M}}$, where two first factors commute with each other and are isomorphic to SU(2) group, the three last ones are 3-parametric groups, each of them consisting of three Abelian commuting unitary subgroups.

v1 (Tue, 19 Feb 2008 11:20:20 GMT)

Wolfgang Limmer

W. Limmer, J. Daeubler, L. Dreher, M. Glunk, W. Schoch, S. Schwaiger, and R. Sauer

Limmer W., Daeubler J., Dreher L., Glunk M., Schoch W., Schwaiger S., Sauer R.

Advanced resistivity model for arbitrary magnetization orientation applied to a series of compressive- to tensile-strained (Ga,Mn)As layers

14 pages, 11 figures, submitted to Phys. Rev. B

10.1103/PhysRevB.77.205210

cond-mat.mtrl-sci

The longitudinal and transverse resistivities of differently strained (Ga,Mn)As layers are theoretically and experimentally studied as a function of the magnetization orientation. The strain in the series of (Ga,Mn)As layers is gradually varied from compressive to tensile using (In,Ga)As templates with different In concentrations. Analytical expressions for the resistivities are derived from a series expansion of the resistivity tensor with respect to the direction cosines of the magnetization. In order to quantitatively model the experimental data, terms up to the fourth order have to be included. The expressions derived are generally valid for any single-crystalline cubic and tetragonal ferromagnet and apply to arbitrary surface orientations and current directions. The model phenomenologically incorporates the longitudinal and transverse anisotropic magnetoresistance as well as the anomalous Hall effect. The resistivity parameters obtained from a comparison between experiment and theory are found to systematically vary with the strain in the layer.

v1 (Tue, 19 Feb 2008 11:23:06 GMT)

Davit Varron

Davit Varron

Varron Davit

A limited in bandwidth uniformity for the functional limit law of the increments of the empirical process

Published in at http://dx.doi.org/10.1214/08-EJS193 the Electronic Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of Mathematical Statistics (http://www.imstat.org)

Electronic Journal of Statistics 2008, Vol. 2, 1043-1064

10.1214/08-EJS193

math.ST stat.TH

Consider the following local empirical process indexed by $K\in \mathcal{G}$, for fixed $h>0$ and $z\in \mathbb{R}^d$: $$G_n(K,h,z):=\sum_{i=1}^n K \Bigl(\frac{Z_i-z}{h^{1/d}}\Big) - \mathbbE \Bigl(K \Bigl(\frac{Z_i-z}{h^{1/d}}\Big)\Big),$$ where the $Z_i$ are i.i.d. on $\mathbb{R}^d$. We provide an extension of a result of Mason (2004). Namely, under mild conditions on $\mathcal{G}$ and on the law of $Z_1$, we establish a uniform functional limit law for the collections of processes $\bigl\{G_n(\cdot,h_n,z), z\in H, h\in [h_n,\mathfrak{h}_n]\big\}$, where $H\subset \mathbb{R}^d$ is a compact set with nonempty interior and where $h_n$ and $\mathfrak{h}_n$ satisfy the Cs\"{o}rg\H{o}-R\'{e}v\'{e}sz-Stute conditions.

v1 (Tue, 19 Feb 2008 11:30:02 GMT), v2 (Thu, 13 Nov 2008 13:21:09 GMT)

M. Hossein Dehghani

M. H. Dehghani, N. Alinejadi and S. H. Hendi

Dehghani M. H., Alinejadi N., Hendi S. H.

Topological Black Holes in Lovelock-Born-Infeld Gravity

14 pages

Phys.Rev.D77:104025,2008

10.1103/PhysRevD.77.104025

hep-th

In this paper, we present topological black holes of third order Lovelock gravity in the presence of cosmological constant and nonlinear electromagnetic Born-Infeld field. Depending on the metric parameters, these solutions may be interpreted as black hole solutions with inner and outer event horizons, an extreme black hole or naked singularity. We investigate the thermodynamics of asymptotically flat solutions and show that the thermodynamic and conserved quantities of these black holes satisfy the first law of thermodynamic. We also endow the Ricci flat solutions with a global rotation and calculate the finite action and conserved quantities of these class of solutions by using the counterterm method. We compute the entropy through the use of the Gibbs-Duhem relation and find that the entropy obeys the area law. We obtain a Smarr-type formula for the mass as a function of the entropy, the angular momenta, and the charge, and compute temperature, angular velocities, and electric potential and show that these thermodynamic quantities coincide with their values which are computed through the use of geometry. Finally, we perform a stability analysis for this class of solutions in both the canonical and the grand-canonical ensemble and show that the presence of a nonlinear electromagnetic field and higher curvature terms has no effect on the stability of the black branes, and they are stable in the whole phase space.

v1 (Tue, 19 Feb 2008 11:50:20 GMT), v2 (Sat, 24 May 2008 10:13:17 GMT)

Alexei J. Nurmagambetov

Alexei J. Nurmagambetov

Nurmagambetov Alexei J.

Hidden Symmetries of M-Theory and Its Dynamical Realization

This is a contribution to the Proc. of the Seventh International Conference ''Symmetry in Nonlinear Mathematical Physics'' (June 24-30, 2007, Kyiv, Ukraine), published in SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at http://www.emis.de/journals/SIGMA/

SIGMA 4:022,2008

10.3842/SIGMA.2008.022

hep-th gr-qc math-ph math.MP

We discuss hidden symmetries of M-theory, its feedback on the construction of the M-theory effective action, and a response of the effective action when locality is preserved. In particular, the locality of special symmetries of the duality-symmetric linearized gravity constraints the index structure of the dual to graviton field in the same manner as it is required to separate the levels 0 and 1 generators subalgebra from the infinite-dimensional hidden symmetry algebra of gravitational theory. This conclusion fails once matter fields are taken into account and we give arguments for that. We end up outlining current problems and development perspectives.

v1 (Tue, 19 Feb 2008 11:54:05 GMT)

Ruben Farinelli

R. Farinelli, L. Titarchuk, A. Paizis, F. Frontera

Farinelli R., Titarchuk L., Paizis A., Frontera F.

A new Comptonization model for low-magnetized accreting neutron stars in low mass X-ray binaries

15 pages, 8 figures, accepted for publication in ApJ

10.1086/587162

astro-ph

We developed a new model for the X-ray spectral fitting \xspec package which takes into account the effects of both thermal and dynamical (i.e. bulk) Comptonization. The model consists of two components: one is the direct blackbody-like emission due to seed photons which are not subjected to effective Compton scattering, while the other one is a convolution of the Green's function of the energy operator with a blackbody-like seed photon spectrum. When combined thermal and bulk effects are considered, the analytic form of the Green's function may be obtained as a solution of the diffusion Comptonization equation. Using data from the BeppoSAX, INTEGRAL and RXTE satellites, we test our model on the spectra of a sample of six persistently low magnetic field bright neutron star Low Mass X-ray Binaries, covering three different spectral states. Particular attention is given to the transient powerlaw-like hard X-ray (> 30 keV) tails that we interpret in the framework of the bulk motion Comptonization process. We show that the values of the best-fit delta-parameter, which represents the importance of bulk with respect to thermal Comptonization, can be physically meaningful and can at least qualitatively describe the physical conditions of the environment in the innermost part of the system. Moreover, we show that in fitting the thermal Comptonization spectra to the X-ray spectra of these systems, the best-fit parameters of our model are in excellent agreement with those of COMPTT, a broadly used and well established XSPEC model.

v1 (Tue, 19 Feb 2008 11:55:21 GMT)

Anais Sene

Igor A. Lukyanchuk, Laurent Lahoche and Anais Sene

Lukyanchuk Igor A., Lahoche Laurent, Sene Anais

Universal Properties of Ferroelectric Domains

Phys. Rev. Lett. to be published

I. A. Luk'yanchuk, L. Lahoche and A.Sene, Phys. Rev. Lett. 102, 147601 (2009)

10.1103/PhysRevLett.102.147601

cond-mat.mtrl-sci

Basing on Ginzburg-Landau approach we generalize the Kittel theory and derive the interpolation formula for the temperature evolution of a multi-domain polarization profile P(x,z). We resolve the long-standing problem of the near-surface polarization behavior in ferroelectric domains and demonstrate the polarization vanishing instead of usually assumed fractal domain branching. We propose an effective scaling approach to compare the properties of different domain-containing ferroelectric plates and films.

v1 (Tue, 19 Feb 2008 12:04:47 GMT), v2 (Fri, 22 Feb 2008 18:24:28 GMT), v3 (Sat, 14 Mar 2009 13:35:24 GMT)

Stephen Connor

Stephen B. Connor

Connor Stephen B.

Separation and coupling cutoffs for tuples of independent Markov processes

15 pages; Changed content: more general result presented

math.PR

We consider an $n$-tuple of independent ergodic Markov processes, each of which converges (in the sense of separation distance) at an exponential rate, and obtain a necessary and sufficient condition for the $n$-tuple to exhibit a separation cutoff. We also provide general bounds on the (asymmetric) window size of the cutoff, and indicate links to classical extreme value theory.

v1 (Tue, 19 Feb 2008 12:09:27 GMT), v2 (Wed, 12 Aug 2009 13:02:04 GMT), v3 (Thu, 18 Mar 2010 12:57:12 GMT)

Wei Liao

Wei Liao

Liao Wei

Signal of New Physics and Chemical Composition of Matter in Core Crossing Neutrinos

10 pages, 4 figures

Eur.Phys.J.C57:763-768,2008

10.1140/epjc/s10052-008-0702-7

hep-ph

We consider non-standard matter effect in flavor conversion of neutrinos crossing the core of the Earth. We show that oscillation of core crossing neutrinos with $E \gsim 0.5$ GeV can be well described by a first order perturbation theory. We show that due to non-standard matter effect varying chemical composition in the Earth can modify the neutrino flavor conversion by 100%. Effects of CP violating phases in non-standard Neutral Current interactions are emphasized in particular.

v1 (Tue, 19 Feb 2008 12:17:32 GMT), v2 (Sun, 30 Nov 2008 10:00:12 GMT)

Gloria Mateu-Figueras

G. Mateu-Figueras, V. Pawlowsky-Glahn, J.J. Egozcue

Mateu-Figueras G., Pawlowsky-Glahn V., Egozcue J. J.

The normal distribution in some constrained sample spaces

21 pages, 8 figures

stat.ME math.ST stat.TH

Phenomena with a constrained sample space appear frequently in practice. This is the case e.g. with strictly positive data and with compositional data, like percentages and the like. If the natural measure of difference is not the absolute one, it is possible to use simple algebraic properties to show that it is more convenient to work with a geometry that is not the usual Euclidean geometry in real space, and with a measure which is not the usual Lebesgue measure, leading to alternative models which better fit the phenomenon under study. The general approach is presented and illustrated both on the positive real line and on the D-part simplex.

v1 (Tue, 19 Feb 2008 12:30:04 GMT)

Jae Dong Noh

Sang-Woo Kim and Jae Dong Noh

Kim Sang-Woo, Noh Jae Dong

Percolation transition in correlated static model

5 pages, 5 figures

J. Korean Phys. Soc. 52, S145 (2008)

10.3938/jkps.52.145

cond-mat.stat-mech

We introduce a correlated static model and investigate a percolation transition. The model is a modification of the static model and is characterized by assortative degree-degree correlation. As one varies the edge density, the network undergoes a percolation transition. The percolation transition is characterized by a weak singular behavior of the mean cluster size and power-law scalings of the percolation order parameter and the cluster size distribution in the entire non-percolating phase. These results suggest that the assortative degree-degree correlation generates a global structural correlation which is relevant to the percolation critical phenomena of complex networks.

v1 (Tue, 19 Feb 2008 12:25:08 GMT)

Andrew Rosalsky

Han-Ying Liang, Deli Li, Andrew Rosalsky

Liang Han-Ying, Li Deli, Rosalsky Andrew

Complete moment and integral convergence for sums of negatively associated random variables

Submitted to the Probability Surveys (http://www.i-journals.org/ps/) by the Institute of Mathematical Statistics (http://www.imstat.org)

math.PR

For a sequence of identically distributed negatively associated random variables $\{X_n; n\geq 1\}$ with partial sums $S_n=\sum_{i=1}^nX_i, n\geq 1$, refinements are presented of the classical Baum-Katz and Lai complete convergence theorems. More specifically, necessary and sufficient moment conditions are provided for complete moment convergence of the form $$ \sum_{n \ge n_0} n^{r -2 -\frac{1}{pq}} a_n E(\max_{1 \le k \le n}|S_k|^{\frac{1}{q}} - \epsilon b_n^{\frac{1}{pq}})^+ < \infty $$ to hold where $r>1, q>0$ and either $n_0=1, 0<p<2, a_n=1, b_n=n$ or $n_0=3, p=2, a_n=(\log n)^{-\frac{1}{2q}}, b_n=n\log n$. These results extend results of Chow (1988) and Li and Sp\u{a}taru (2005) from the independent and identically distributed case to the identically distributed negatively associated setting. The complete moment convergence is also shown to be equivalent to a form of complete integral convergence.

v1 (Tue, 19 Feb 2008 12:33:00 GMT)

Bernd-Jochen Schaefer

Haris Djapo, Bernd-Jochen Schaefer, Jochen Wambach

Djapo Haris, Schaefer Bernd-Jochen, Wambach Jochen

Hyperon-nucleon single-particle potentials with low-momentum interactions

10 Pages, 11 figures, 4 tables, minor modification, 1 reference added, version accepted for publication in EPJA

Eur.Phys.J.A36:101-110,2008

10.1140/epja/i2008-10542-5

nucl-th hep-ph

Single-particle potentials in Hartree-Fock approximation for different hyperon-nucleon (YN) channels are calculated in the framework of the effective low-momentum YN interaction V_lowk. In contrast to the nucleon-nucleon interaction, the available experimental data for the YN interaction are scarce. As a consequence no unique YN low-momentum potential V_lowk can be predicted from the various bare potentials. The resulting momentum- and density-dependent single-particle potentials for several different bare OBE models and for chiral effective field theory are compared to each other.

v1 (Tue, 19 Feb 2008 12:37:55 GMT), v2 (Thu, 6 Mar 2008 08:14:06 GMT)

Silvia Zane

L.Nobili (1), R.Turolla (1 and 2) and S.Zane (2) ((1)Department of Physics, University of Padova, Italy, (2) Mullard Space Science Laboratory, University College London, UK)

Nobili L., Turolla R., Zane S.

X-ray spectra from magnetar candidates. I. Monte Carlo simulations in the non-relativistic regime

37 pages, 14 figures, 1 table; corrected typos; accepted for publication in MNRAS

10.1111/j.1365-2966.2008.13125.x

astro-ph

The anomalous X-ray pulsars and soft gamma-repeaters are peculiar high-energy sources believed to host a magnetar, i.e. an ultra-magnetized neutron star. Their persistent, soft X-ray emission (~1-10 keV)is usually modeled by the superposition of a blackbody and a power-law tail. It has been suggested that this spectrum forms as the thermal photons emitted by the star surface traverse the magnetosphere. Magnetar magnetospheres are likely different from those of ordinary radio-pulsars, since the external magnetic field may acquire a toroidal component as a consequence of the deformation of the star crust induced by the super-strong interior field. In turn, the magnetosphere will be permeated by currents that can boost primary photons through repeated scatterings. Here we present 3D Monte Carlo simulations of photon propagation in a twisted magnetosphere. Our model is based on a simplified treatment of the charge carriers velocity distribution which, however, accounts for the particle collective motion, in addition to the thermal one. Present treatment is restricted to conservative (Thomson) scattering in the electron rest frame. The code, nonetheless, is completely general and inclusion of the relativistic QED resonant cross section, which is required in the modeling of the hard (~20-200 keV) spectral tails observed in the magnetar candidates, is under way. The properties of emerging spectra have been assessed under different conditions, by exploring the model parameter space, including effects arising from the viewing geometry. Monte Carlo runs have been collected into a spectral archive. Two tabulated XSPEC spectral models, with and without viewing angles, have been produced and applied to the 0.1-10 keV XMM-Newton EPIC-pn spectrum of the AXP CXOU J1647-4552.

v1 (Tue, 19 Feb 2008 13:05:11 GMT), v2 (Wed, 20 Feb 2008 11:01:56 GMT)

Qiang Zhao

Xiao-Hai Liu, Qiang Zhao, and Frank E. Close

Liu Xiao-Hai, Zhao Qiang, Close Frank E.

Search for tetraquark candidate Z(4430) in meson photoproduction

Minor changes with wording; Revised version to appear on Phys. Rev. D

Phys.Rev.D77:094005,2008

10.1103/PhysRevD.77.094005

hep-ph hep-ex

We propose a search for the newly discovered tetraquark candidate Z(4430) in photoproduction. Based on the Belle results we show that if Z(4430) is a genuine resonance, its significantly large coupling to $\psi^\prime\pi$ will cause it to stand out above the background in $\gamma p\to Z^+(4430) n\to \psi^\prime \pi^+ n$. We consider the dependence of the cross section for the quantum numbers ($J^{P}=1^{-}$, $1^{+}$ or $0^{-}$).

v1 (Tue, 19 Feb 2008 13:05:22 GMT), v2 (Sat, 29 Mar 2008 11:55:59 GMT)

Elena Litvinova

E. Litvinova, P. Ring, V. Tselyaev

Litvinova E., Ring P., Tselyaev V.

Relativistic quasiparticle time blocking approximation. Dipole response of open-shell nuclei

43 pages, 3 figures

Phys.Rev.C78:014312,2008

10.1103/PhysRevC.78.014312

nucl-th

The self-consistent Relativistic Quasiparticle Random Phase Approximation (RQRPA) is extended by the quasiparticle-phonon coupling (QPC) model using the Quasiparticle Time Blocking Approximation (QTBA). The method is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticle space with an energy-dependent two-quasiparticle residual interaction. This equation is solved either in the basis of Dirac states forming the self-consistent solution of the ground state or in the momentum representation. Pairing correlations are treated within the Bardeen-Cooper-Schrieffer (BCS) model with a monopole-monopole interaction. The same NL3 set of the coupling constants generates the Dirac-Hartree-BCS single-quasiparticle spectrum, the static part of the residual two-quasiparticle interaction and the quasiparticle-phonon coupling amplitudes. A quantitative description of electric dipole excitations in the chain of tin isotopes (Z=50) with the mass numbers A = 100, 106, 114, 116, 120, and 130 and in the chain of isotones with (N=50) 88-Sr, 90-Zr, 92-Mo is performed within this framework. The RQRPA extended by the coupling to collective vibrations generates spectra with a multitude of '2q+phonon' (two quasiparticles plus phonon) states providing a noticeable fragmentation of the giant dipole resonance as well as of the soft dipole mode (pygmy resonance) in the nuclei under investigation. The results obtained for the photo absorption cross sections and for the integrated contributions of the low-lying strength to the calculated dipole spectra agree very well with the available experimental data.

v1 (Tue, 19 Feb 2008 13:07:41 GMT)

Viktor Maslov Professor

V. P. Maslov

Maslov V. P.

Uniform Asymptotics in the Problem of Superfluidity of Classical Liquids in Nanotubes

Latex, 13pages

cond-mat.stat-mech

In the preceding papers (see [1, 2]), the superfluidity of the classical liquid was proved under the assumption that the parameters $N$ and $r$, where $N$ is the particle number and $r$ it the capillary radius, tend respectively to infinity and to zero so that $\frac 1N \ll \frac rR$, where $R$ is the capillary length. In the present paper, this assumption is removed.

v1 (Tue, 19 Feb 2008 13:35:07 GMT)

Patrick Ingram

Patrick Ingram

Ingram Patrick

Multiples of integral points on elliptic curves

Revised version, correcting a significant error

math.NT

If $E$ is a minimal elliptic curve defined over $\ZZ$, we obtain a bound $C$, depending only on the global Tamagawa number of $E$, such that for any point $P\in E(\QQ)$, $nP$ is integral for at most one value of $n>C$. As a corollary, we show that if $E/\QQ$ is a fixed elliptic curve, then for all twists $E'$ of $E$ of sufficient height, and all torsion-free, rank-one subgroups $\Gamma\subseteq E'(\QQ)$, $\Gamma$ contains at most 6 integral points. Explicit computations for congruent number curves are included.

v1 (Tue, 19 Feb 2008 13:39:08 GMT), v2 (Thu, 14 Aug 2008 20:26:14 GMT)

Douglas Braun

D.C. Braun, A.C. Birch

Braun D. C., Birch A. C.

Surface-focused Seismic Holography of Sunspots: I. Observations

Solar Physics, accepted

10.1007/s11207-008-9152-5

astro-ph

We present a comprehensive set of observations of the interaction of p-mode oscillations with sunspots using surface-focused seismic holography. Maps of travel-time shifts, relative to quiet-Sun travel times, are shown for incoming and outgoing p modes as well as their mean and difference. We compare results using phase-speed filters with results obtained with filters that isolate single p-mode ridges, and further divide the data into multiple temporal frequency bandpasses. The f mode is removed from the data. The variations of the resulting travel-time shifts with magnetic-field strength and with the filter parameters are explored. We find that spatial averages of these shifts within sunspot umbrae, penumbrae, and surrounding plage often show strong frequency variations at fixed phase speed. In addition, we find that positive values of the mean and difference travel-time shifts appear exclusively in waves observed with phase-speed filters that are dominated by power in the low-frequency wing of the p1 ridge. We assess the ratio of incoming to outgoing p-mode power using the ridge filters and compare surface-focused holography measurements with the results of earlier published p-mode scattering measurements using Fourier-Hankel decomposition.

v1 (Tue, 19 Feb 2008 18:09:37 GMT)

Marco Tarzia

M. Tarzia and G. Biroli

Tarzia M., Biroli G.

The Valence Bond Glass phase

EPL 82, 67008 (2008)

10.1209/0295-5075/82/67008

cond-mat.str-el cond-mat.dis-nn

We show that a new glassy phase can emerge in presence of strong magnetic frustration and quantum fluctuations. It is a Valence Bond Glass. We study its properties solving the Hubbard-Heisenberg model on a Bethe lattice within the large $N$ limit introduced by Affleck and Marston. We work out the phase diagram that contains Fermi liquid, dimer and valence bond glass phases. This new glassy phase has no electronic or spin gap (although a pseudo-gap is observed), it is characterized by long-range critical valence bond correlations and is not related to any magnetic ordering. As a consequence it is quite different from both valence bond crystals and spin glasses.

v1 (Tue, 19 Feb 2008 13:55:25 GMT)

Steven Finch

Steven Finch, Pascal Sebah and Zai-Qiao Bai

Finch Steven, Sebah Pascal, Bai Zai-Qiao

Odd Entries in Pascal's Trinomial Triangle

25 pages

math.NT math.CO math.DS

The nth row of Pascal's trinomial triangle gives coefficients of (1+x+x^2)^n. Let g(n) denote the number of such coefficients that are odd. We review Moshe's algorithm for evaluating asymptotics of g(n) -- this involves computing the Lyapunov exponent for certain 2x2 random matrix products -- and then analyze further examples with more terms and higher powers of x.

v1 (Tue, 19 Feb 2008 14:03:03 GMT)

Gilles Stoltz

S\'ebastien Bubeck (INRIA Futurs), R\'emi Munos (INRIA Futurs), Gilles Stoltz (DMA, GREGH)

Bubeck Sébastien, Munos Rémi, Stoltz Gilles

Pure Exploration for Multi-Armed Bandit Problems

math.ST cs.LG stat.TH

We consider the framework of stochastic multi-armed bandit problems and study the possibilities and limitations of forecasters that perform an on-line exploration of the arms. These forecasters are assessed in terms of their simple regret, a regret notion that captures the fact that exploration is only constrained by the number of available rounds (not necessarily known in advance), in contrast to the case when the cumulative regret is considered and when exploitation needs to be performed at the same time. We believe that this performance criterion is suited to situations when the cost of pulling an arm is expressed in terms of resources rather than rewards. We discuss the links between the simple and the cumulative regret. One of the main results in the case of a finite number of arms is a general lower bound on the simple regret of a forecaster in terms of its cumulative regret: the smaller the latter, the larger the former. Keeping this result in mind, we then exhibit upper bounds on the simple regret of some forecasters. The paper ends with a study devoted to continuous-armed bandit problems; we show that the simple regret can be minimized with respect to a family of probability distributions if and only if the cumulative regret can be minimized for it. Based on this equivalence, we are able to prove that the separable metric spaces are exactly the metric spaces on which these regrets can be minimized with respect to the family of all probability distributions with continuous mean-payoff functions.

v1 (Tue, 19 Feb 2008 14:05:22 GMT), v2 (Fri, 13 Jun 2008 07:03:22 GMT), v3 (Tue, 17 Jun 2008 07:07:03 GMT), v4 (Thu, 19 Feb 2009 10:33:29 GMT), v5 (Tue, 26 Jan 2010 10:10:42 GMT), v6 (Wed, 9 Jun 2010 09:08:50 GMT)

Klaus Reinsch

K. Beuermann, E. El Kholy, K. Reinsch

Beuermann K., Kholy E. El, Reinsch K.

Soft X-ray spectral variability of AM Herculis

7 pages, 6 figures, accepted for publication in Astronomy & Astrophysics

10.1051/0004-6361:20079335

astro-ph

Polars (AM Herculis binaries) are a prominent class of bright soft X-ray sources, many of which were discovered with ROSAT. We present a homogenous analysis of all the pointed ROSAT PSPC observations of polars subdivided into two papers that discuss the prototype polar AM Her in detail and summarize the class properties of all other polars. We derive the high-state soft X-ray flux and short-term spectral variability of AM Her using a new detector response matrix and a confirmed flux calibration of the ROSAT PSPC below 0.28 keV. The best-fit mean single-blackbody temperature and integrated bright-phase energy flux of AM Her in its April 1991 high state are 27.2 +/- 1.0 eV and (2.6 +/- 0.6) x 10^-9 erg cm^-2s^-1, respectively. The total blackbody flux of a multi-temperature model that fits both the soft X-ray and the fluctuating far-ultraviolet components is Fbb = (4.5 +/- 1.5) x 10^-9 erg cm^-2s^-1. The total accretion luminosity at a distance of 80 pc, Lbb = (2.1 +/- 0.7) x 10^33 erg s-1, implies an accretion rate of Mdot = (2.4 +/- 0.8) x 10^-10 Msun yr^-1 for an 0.78 Msun white dwarf. The soft X-ray flux displays significant variability on time scales down to 200 ms. Correlated spectral and count-rate variations are seen in flares on time scales down to 1 s, demonstrating the heating and cooling associated with individual accretion events. Our spectral and temporal analysis provides direct evidence for the blobby accretion model and suggests a connection between the soft X-ray and the fluctuating far-ultraviolet components.

v1 (Tue, 19 Feb 2008 14:23:26 GMT)

Dorothea Samtleben

Dorothea Samtleben (for the QUIET Collaboration)

Samtleben Dorothea

Measuring the Cosmic Microwave Background Radiation (CMBR) polarization with QUIET

6 pages, 4 figures, to appear in the Proceedings `A Century of Cosmology', San Servolo (Venezia, Italy), August 2007, to be published by `Il Nuovo Cimento'

Nuovo Cim.B122:1353-1358,2007

10.1393/ncb/i2008-10488-7

astro-ph

A major goal of upcoming experiments measuring the Cosmic Microwave Background Radiation (CMBR) is to reveal the subtle signature of inflation in the polarization pattern which requires unprecedented sensitivity and control of systematics. Since the sensitivity of single receivers has reached fundamental limits future experiments will take advantage of large receiver arrays in order to significantly increase the sensitivity. Here we introduce the Q/U Imaging ExperimenT (QUIET) which will use HEMT-based receivers in chip packages at 90(40) GHz in the Atacama Desert. Data taking is planned for the beginning of 2008 with prototype arrays of 91(19) receivers, an expansion to 1000 receivers is foreseen. With the two frequencies and a careful choice of scan regions there is the promise of effectively dealing with foregrounds and reaching a sensitivity approaching 10$^{-2}$ for the ratio of the tensor to scalar perturbations.

v1 (Tue, 19 Feb 2008 16:24:40 GMT)

Klaus Reinsch

K. Beuermann

Beuermann K.

Soft X-ray in-flight calibration of the ROSAT PSPC

3 pages, 1 figure, accepted for publication in Astronomy & Astrophysics

10.1051/0004-6361:200809458

astro-ph

We present an in-flight calibration of the ROSAT PSPC using the incident spectra of the hot white dwarf HZ43 and the polar AM Her. We derive an absolute flux calibration of the PSPC using the accurately known soft X-ray spectrum of HZ43. Corrections to the PSPC response matrix are derived from a comparison of predicted and observed PSPC spectra of HZ43, supplemented by results for AM Her. The calibration of the PSPC for photon energies E < 0.28 keV is found to be accurate to better than 5% refuting earlier reports of a major miscalibration. Our corrections to the detector response matrices remove systematic residuals in the pulse height spectra of soft sources.

v1 (Tue, 19 Feb 2008 14:33:15 GMT)

Renaud Belmont

R. Belmont and M. Tagger

Belmont R., Tagger M.

The diffuse X-ray emission from the Galactic center with Simbol-X

4 pages, Simbol-X international workshop

astro-ph

Similarly to the larger Galactic ridge, the Galactic center region presents a hard diffuse emission whose origin has been strongly debated for the past two decades: does this emission result from the contribution of numerous, yet unresolved, discrete point sources ? Or does it originate in a truly diffuse, hot plasma ? The Galactic center region (GC) is however different on many respects from the outer parts of the Galaxy, which makes the diffuse emission issue at the Galactic center unique. Although recent observations seem to favour a point sources origin in the far Galactic ridge, the situation is still unclear at the GC and new observations are required. Here we present results on the modeling of the truly diffuse plasma. Interestingly, such a plasma would strongly affect the dynamics of orbiting molecular clouds and thus the central engine activity. Discriminating between the two hypothesis has thus become a crucial issue in the understanding of this central region that makes the link between the inner small accretion disk and the large scale Galactic dynamics. We investigate the new inputs we can expect from Simbol-X on this matter.

v1 (Tue, 19 Feb 2008 14:42:43 GMT)

K. Splittorff

K. Splittorff, J.J.M. Verbaarschot, M.R. Zirnbauer

Splittorff K., Verbaarschot J. J. M., Zirnbauer M. R.

Nonhermitian Supersymmetric Partition Functions: the case of one bosonic flavor

17 pages, 0 figures. Section II extended. Version to appear in Nucl.Phys.B

Nucl.Phys.B803:381-404,2008

10.1016/j.nuclphysb.2008.06.003

hep-th

We discuss the supersymmetric formulation of the nonhermitian $\beta = 2$ random matrix partition function with one bosonic flavor. This partition function is regularized by adding one conjugate boson and fermion each. A supersymmetric nonlinear $\sigma$-model for the resulting Goldstone degrees of freedom is obtained using symmetry arguments only. For a Gaussian probability distribution the same results are derived using superbosonization and the complex orthogonal polynomial method. The symmetry arguments apply to any model with the same symmetries and a mass gap, and demonstrate the universality of the nonlinear $\sigma$-model.

v1 (Tue, 19 Feb 2008 14:51:45 GMT), v2 (Tue, 10 Jun 2008 13:51:23 GMT)

Renaud Belmont

R. Belmont, J. Malzac and A. Marcowith

Belmont R., Malzac J., Marcowith A.

A new code for radiation processes in high energy plasmas

Poster at the international workshop 'Simbol-X: the hard X-ray universe in focus' held in Bologna, 14-16 May 2007. To appear in Memorie della SAIt, 2 pages, 1 figure

astro-ph

Extreme objects such as X-ray binaries, AGN, or $\gamma$-ray bursters harbor high energy plasmas whose properties are not well understood yet. Not only are they responsible of the hard X- and $\gamma$-ray emission we observe but also they have a strong influence on the main dynamics and energetics of these objects themselves. Here we present a new kinetic code that solves the evolution equations for particles and photons around compact objects. It produces spectra that will be compared with observations from Simbol-X to constrain the radiation and acceleration processes in these objects.

v1 (Tue, 19 Feb 2008 15:01:41 GMT)

Renaud Belmont

R. Belmont and M. Tagger

Belmont R., Tagger M.

A note on magnetized coronae

Poster at the international workshop 'Simbol-X: the hard X-ray universe in focus' held in Bologna, 14-16 May 2007. To appear in Memorie della SaIt, 2 pages

astro-ph

X-ray binaries and AGN show observational evidence for magnetized hot plasmas. Despite years of data, very little is known on these {\it coronae} especially on the mechanisms responsible for their heating, and most models simply assume their existence. However, understanding its properties has now become a key issue of the AGN and microquasars modelling. Here we consider the effect of a strong vertical magnetic field on the corona AGN and X-ray binaries and show that its modeling (structure, heating) must be reconsidered. As a first step, we present one mechanism that could extract energy from the accretion disks and deposits it in the coronae: the {\it magnetic pumping

v1 (Tue, 19 Feb 2008 15:07:45 GMT)

Joel Eaton

Joel A. Eaton

Eaton Joel A.

Spurious Eccentricities of Distorted Binary Components

14 pp, 2 tables, 12 fig; under review by ApJ

10.1086/588270

astro-ph

I discuss the effect of physical distortion on the velocities of close binary components and how we may use the resulting distortion of velocity curves to constrain some properties of binary systems, such as inclination and mass ratio. Precise new velocities for 5 Cet convincingly detect these distortions with their theoretically predicted phase dependence. We can even use such distortions of velocity curves to test Lucy's theory of convective gravity darkening. The observed distortions for TT Hya and 5 Cet require the contact components of those systems to be gravity darkened, probably somewhat more than predicted by Lucy's theory but clearly not as much as expected for a radiative star. These results imply there is no credible evidence for eccentric orbits in binaries with contact components. I also present some speculative analyses of the observed properties of a binary encased in a non-rotating common envelope, if such an object could actually exist, and discuss how the limb darkening of some recently calculated model atmospheres for giant stars may bias my resuts for velocity-curve distortions, as well as other results from a wide range of analyses of binary stars.

v1 (Tue, 19 Feb 2008 15:10:26 GMT)

Steven R. Blusk

CLEO Collaboration: M. Artuso, et al

CLEO Collaboration , Artuso M.

Measurement of exclusive D meson decays to eta and eta' final states and SU(3) amplitude analysis

15 pages, accepted to PRD

Phys.Rev.D77:092003,2008

10.1103/PhysRevD.77.092003

hep-ex

Using 281 pb^-1 of data collected with the CLEO-c detector, we present new measurements of Cabibbo-suppressed decays of D0 and D+ mesons to eta and eta' final states. We make first observations of D0-->eta'pi0, eta eta, eta eta', and eta pi+ pi-, and find evidence for D+ --> eta pi+ pi0$, D+ --> eta' pi+ pi0 and D0 --> eta' pi+ pi-. We also report on improved measurements of D0-->eta pi0, D+ --> eta pi+ and D+ --> etap' pi+. Using the measured two-body Cabibbo-suppressed decays, we extract amplitudes for specific flavor topologies and compare them to those from Cabibbo-favored decays.

v1 (Tue, 19 Feb 2008 15:11:01 GMT), v2 (Sat, 26 Apr 2008 12:34:25 GMT)

Paula Coelho

P. Coelho

Coelho P.

Model stars for the modelling of galaxies: $\alpha$-enhancement in stellar populations models

Invited contribution to the XII Latin American IAU Regional Meeting, Isla Margarita, Venezuela. To appear in "Memorias de la Reunion Regional Latino Americana de la UAI (2007)"

astro-ph

Stellar population (SP) models are an essential tool to understand the observations of galaxies and clusters. One of the main ingredients of a SP model is a library of stellar spectra, and both empirical and theoretical libraries can been used for this purpose. Here I will start by giving a short overview of the pros and cons of using theoretical libraries, i.e. model stars, to produce our galaxy models. Then I will address the question on how theoretical libraries can be used to model stellar populations, in particular to explore the effect of $\alpha$-enhancement on spectral observables.

v1 (Tue, 19 Feb 2008 15:11:15 GMT)

Vaneet Aggarwal

Vaneet Aggarwal

Aggarwal Vaneet

Distributed Joint Source-Channel Coding for arbitrary memoryless correlated sources and Source coding for Markov correlated sources using LDPC codes

7 pages, 10 figures, Results have been taken from the Course Project Report for ELE 539B (Instructor: Prof. Robert Calderbank), May 2006

cs.IT math.IT

In this paper, we give a distributed joint source channel coding scheme for arbitrary correlated sources for arbitrary point in the Slepian-Wolf rate region, and arbitrary link capacities using LDPC codes. We consider the Slepian-Wolf setting of two sources and one destination, with one of the sources derived from the other source by some correlation model known at the decoder. Distributed encoding and separate decoding is used for the two sources. We also give a distributed source coding scheme when the source correlation has memory to achieve any point in the Slepian-Wolf rate achievable region. In this setting, we perform separate encoding but joint decoding.

v1 (Tue, 19 Feb 2008 15:33:43 GMT)

Mikhail Zobov

M. Zobov (INFN LNF), P. Raimondi (INFN LNF), D. Shatilov (IYF, Novosibirsk), K. Ohmi (KEK)

Zobov M., Raimondi P., Shatilov D., Ohmi K.

Crab Waist Collision Studies for e+e- Factories

Invited talk at IR07 Workshop (Interaction Regions for the LHC Upgrade, DAFNE and SuperB), 7-9 November 2007, Frascati, Italy

physics.acc-ph

Numerical simulations have shown that the recently proposed "crab waist" scheme of beam-beam collisions can substantially boost the luminosity of existing and future electron-positron colliders. In this paper we describe the crab waist concept and discuss potential advantages that such a scheme can provide. We also present the results of beam-beam simulations for the two currently proposed projects based on the crab waist scheme: the DAFNE upgrade and the Super B-factory project.

v1 (Tue, 19 Feb 2008 15:19:46 GMT)

Shai Gutner

Shai Gutner

Gutner Shai

The complexity of planar graph choosability

Discrete Math. 159 (1996), 119-130

cs.DM cs.CC cs.DS

A graph $G$ is {\em $k$-choosable} if for every assignment of a set $S(v)$ of $k$ colors to every vertex $v$ of $G$, there is a proper coloring of $G$ that assigns to each vertex $v$ a color from $S(v)$. We consider the complexity of deciding whether a given graph is $k$-choosable for some constant $k$. In particular, it is shown that deciding whether a given planar graph is 4-choosable is NP-hard, and so is the problem of deciding whether a given planar triangle-free graph is 3-choosable. We also obtain simple constructions of a planar graph which is not 4-choosable and a planar triangle-free graph which is not 3-choosable.

v1 (Tue, 19 Feb 2008 15:26:19 GMT)

Matthias Jamin

Matthias Jamin, Vicent Mateu

Jamin Matthias, Mateu Vicent

OPE-RchiT matching at order alpha_s: hard gluonic corrections to three-point Green functions

21 pages, 2 figures

JHEP0804:040,2008

10.1088/1126-6708/2008/04/040

hep-ph

In this work we push the matching between the QCD operator product expansion (OPE) and resonance chiral theory (RchiT) to order alpha_s. To this end we compute two- and three-point QCD Green functions (GFs) in both theories and compare the results. GFs which are order parameters of chiral symmetry breaking make this matching more transparent and thus we concentrate on those. On the OPE side one needs to calculate the hard-gluon virtual corrections to the quark condensate, and in particular for three-point GFs this computation was hitherto missing. We also discuss the need for including the infinite tower of hadronic states in the hadronic representation of the GF when non-analytic terms such as logarithms are present in the OPE Wilson coefficients.

v1 (Tue, 19 Feb 2008 15:29:12 GMT), v2 (Fri, 11 Apr 2008 17:27:37 GMT)

Antoine Venaille

Freddy Bouchet (INLN), Julien Barr\'e (JAD), Antoine Venaille (LEGI)

Bouchet Freddy, Barré Julien, Venaille Antoine

Equilibrium and out of equilibrium phase transitions in systems with long range interactions and in 2D flows

Dans DYNAMICS AND THERMODYNAMICS OF SYSTEMS WITH LONG RANGE INTERACTIONS: Theory and Experiments - DYNAMICS AND THERMODYNAMICS OF SYSTEMS WITH LONG RANGE INTERACTIONS: Theory and Experiments, Italie (2007)

10.1063/1.2839113

cond-mat.stat-mech physics.flu-dyn

In self-gravitating stars, two dimensional or geophysical flows and in plasmas, long range interactions imply a lack of additivity for the energy; as a consequence, the usual thermodynamic limit is not appropriate. However, by contrast with many claims, the equilibrium statistical mechanics of such systems is a well understood subject. In this proceeding, we explain briefly the classical approach to equilibrium and non equilibrium statistical mechanics for these systems, starting from first principles. We emphasize recent and new results, mainly a classification of equilibrium phase transitions, new unobserved equilibrium phase transition, and out of equilibrium phase transitions. We briefly discuss what we consider as challenges in this field.

v1 (Tue, 19 Feb 2008 15:42:14 GMT)

Aline Lefebvre-Lepot

Aline Lefebvre-Lepot (CMAP), Bertrand Maury (LM-Orsay), Aline Lefebvre (CMAP)

Lefebvre-Lepot Aline, Maury Bertrand, Lefebvre Aline

Micro-Macro Modelling of an Array of Spheres Interacting Through Lubrication Forces

math.AP

We consider here a discrete system of spheres interacting through a lubrication force. This force is dissipative, and singular near contact: it behaves like the reciprocal of interparticle distance. We propose a macroscopic constitutive equation which is built as the natural continuous counterpart of this microscopic lubrication model. This model, which is of the newtonian type, relies on an elongational viscosity, which is proportional to the reciprocal of the local fluid fraction. We then establish the convergence in a weak sense of solutions to the discrete problem towards the solution to the partial differential equation which we identified as the macroscopic constitutive equation.

v1 (Tue, 19 Feb 2008 15:42:46 GMT), v2 (Wed, 5 Sep 2012 14:56:25 GMT)

Marco Genovese

G.Brida, M.Genovese, A.Meda, E. Predazzi and I.Ruo-Berchera

Brida G., Genovese M., Meda A., Predazzi E., Ruo-Berchera I.

Systematic study of the PDC speckle structure for quantum imaging applications

Int. Journ Quant. Inf. 7 (2009) 139

10.1080/09500340802464665

quant-ph

Sub shot noise imaging of weak object by exploiting Parametric Down Converted light represents a very interesting technological development. A precise characterization of PDC speckle structure in dependence of pump beam parameters is a fundamental tool for this application. In this paper we present a first set of data addressed to this purpose.

v1 (Tue, 19 Feb 2008 15:43:18 GMT), v2 (Tue, 30 Sep 2008 09:05:41 GMT)

Borys Alvarez-Samaniego

Borys Alvarez-Samaniego (I3M), Pascal Azerad (I3M)

Alvarez-Samaniego Borys, Azerad Pascal

Existence of travelling-wave solutions and local well-posedness of the Fowler equation

21 pages

Discrete and Continuous Dynamical Systems-Series B 12 (2009), No. 4, 671-692

10.3934/dcdsb.2009.12.671

math.AP

We study the existence of travelling-waves and local well-posedness in a subspace of $C_b^1(\mathbb{R})$ for a nonlinear evolution equation recently proposed by Andrew C. Fowler to study the dynamics of dunes.

v1 (Tue, 19 Feb 2008 15:44:15 GMT), v2 (Mon, 31 Mar 2008 19:45:12 GMT), v3 (Thu, 12 Mar 2009 17:17:14 GMT)

Benjamin Seibold

Benjamin Seibold

Seibold Benjamin

Minimal positive stencils in meshfree finite difference methods for the Poisson equation

26 pages, 20 figures

Comput. Methods Appl. Mech. Engrg., Vol. 198 (3-4), 2008, pp. 592-601

10.1016/j.cma.2008.09.001

math.NA

Meshfree finite difference methods for the Poisson equation approximate the Laplace operator on a point cloud. Desirable are positive stencils, i.e. all neighbor entries are of the same sign. Classical least squares approaches yield large stencils that are in general not positive. We present an approach that yields stencils of minimal size, which are positive. We provide conditions on the point cloud geometry, so that positive stencils always exist. The new discretization method is compared to least squares approaches in terms of accuracy and computational performance.

v1 (Tue, 19 Feb 2008 15:45:25 GMT), v2 (Thu, 10 Jul 2008 19:08:44 GMT)

Winton Brown

Winton G. Brown, Yaakov S. Weinstein, and Lorenza Viola

Brown Winton G., Weinstein Yaakov S., Viola Lorenza

Quantum pseudo-randomness from cluster-state quantum computation

4 pages, 4 figures, version appearing in Phys. Rev. A

10.1103/PhysRevA.77.040303

quant-ph

We show how to efficiently generate pseudo-random states suitable for quantum information processing via cluster-state quantum computation. By reformulating pseudo-random algorithms in the cluster-state picture, we identify a strategy for optimizing pseudo-random circuits by properly choosing single-qubit rotations. A Markov chain analysis provides the tool for analyzing convergence rates to the Haar measure and finding the optimal single-qubit gate distribution. Our results may be viewed as an alternative construction of approximate unitary 2-designs.

v1 (Tue, 19 Feb 2008 19:46:44 GMT), v2 (Mon, 25 Feb 2008 15:33:54 GMT), v3 (Thu, 15 May 2008 17:53:04 GMT)

Joseph Rynkiewicz

Joseph Rynkiewicz (SAMOS, Ces)

Rynkiewicz Joseph

Estimation and Test for Multidimensional Regression Models

Communication in Statistics - Theory and Methods 36, 14 (2007) 2655-2671

math.ST stat.TH

This work is concerned with the estimation of multidimensional regression and the asymptotic behaviour of the test involved in selecting models. The main problem with such models is that we need to know the covariance matrix of the noise to get an optimal estimator. We show in this paper that if we choose to minimise the logarithm of the determinant of the empirical error covariance matrix, then we get an asymptotically optimal estimator. Moreover, under suitable assumptions, we show that this cost function leads to a very simple asymptotic law for testing the number of parameters of an identifiable and regular regression model. Numerical experiments confirm the theoretical results.

v1 (Tue, 19 Feb 2008 15:49:45 GMT)

John Tobin

John J. Tobin, Lee Hartmann, Nuria Calvet, and Paola D'Alessio

Tobin John J., Hartmann Lee, Calvet Nuria, D'Alessio Paola

Constraining the Envelope Structure of L1527 IRS: Infrared Scattered Light Modeling

50 pages, 14 figures 2 tables, accepted by the Astrophysical Journal. The manuscript with full resolution figures can be downloaded from http://astro.lsa.umich.edu/~jjtobin/L1527.pdf

10.1086/587683

astro-ph

We model Spitzer Space Telescope observations of the Taurus Class 0 protostar L1527 IRS (IRAS 04368+2557) to provide constraints on its protostellar envelope structure. The nearly edge-on inclination of L1527 IRS, coupled with the highly spatially-resolved near to mid-infrared images of this object and the detailed IRS spectrum, enable us to constrain the outflow cavity geometry quite well, reducing uncertainties in the other derived parameters. The mid-infrared scattered light image shows a bright central source within a dark lane; the aspect ratio of this dark lane is such that it appears highly unlikely to be a disk shadow. In modeling this dark lane, we conclude that L1527 IRS is probably not described by a standard TSC envelope with simple bipolar cavities. We find it necessary to model the dark lane and central source as a modified inner envelope structure. This structure may be due either to a complex wind-envelope interaction or induced by the central binary. To fit the overall SED, we require the central source to have a large near to mid-infrared excess, suggesting substantial disk accretion. Our model reproduces the overall morphology and surface brightness distribution of L1527 IRS fairly well, given the limitations of using axisymmetric models to fit the non-axisymmetric real object, and the derived envelope infall rates are in reasonable agreement with some other investigations. IRAC observations of L1527 IRS taken 12 months apart show variability in total flux and variability in the opposing bipolar cavities, suggesting asymmetric variations in accretion. We also provide model images at high resolution for comparison to future observations with current ground-based instrumentation and future space-based telescopes.

v1 (Tue, 19 Feb 2008 15:58:09 GMT)

Satoshi Okamoto

Randy S. Fishman, Satoshi Okamoto, and Fernando A. Reboredo

Fishman Randy S., Okamoto Satoshi, Reboredo Fernando A.

Jahn-Teller Distortion in Bimetallic Oxalates

7 pages, 4 figures, submitted to Journal of the American Chemical Society

10.1103/PhysRevLett.101.116402

cond-mat.other

A C$_3$-symmetric crystal-field potential in the Fe(II)Fe(III) bimetallic oxalates splits the L=2 Fe(II) multiplet into two doublets and a singlet. In compounds that exhibit magnetic compensation, one of the doublets was predicted to lie lowest in energy and carry a non-quenched orbital angular momentum $\pm \ld $, where $\ld $ exceeds a threshold value. In a range of $\ld $, a Jahn-Teller (JT) distortion increases the energy splitting of the low-lying doublet and breaks the C$_3$ symmetry of the bimetallic planes around the ferrimagnetic transition temperature. At low temperatures, the JT distortion disappears in compounds that display magnetic compensation due to the competition with the spin-orbit coupling. A comparison with recent measurements provides strong evidence for this re-entrant, low-temperature JT transition and a prediction for the normal, high-temperature JT transition. The size of the JT distortion is estimated using first-principles calculations, which suggest that the long-range ordering of smaller, non-C$_3$-symmetric organic cations can eliminate magnetic compensation.

v1 (Tue, 19 Feb 2008 15:53:42 GMT)

A. Marin

A. Marin, for CERES Collaboration

Marin A., Collaboration for CERES

Dilepton measurements with CERES

Proceedings of 4th International Workshop on Critical Point and Onset Deconfinement, Darmstadt, Germany, 9-13 Jul 2007

PoSCPOD07:034,2007

nucl-ex

We report on dilepton measurements for central Pb on Au collisions at the top CERN SPS energy with the upgraded CERES experiment. The dilepton mass spectrum of 2000 data with improved mass resolution shows an enhancement over the expectation from hadron decays that is well described by a model including a strong broadening of the $\rho$ spectral function. The measured excess yield excludes the dropping mass scenario. We also report on the $\phi$ meson measured simultaneously both in the $K^+K^-$ and in the dilepton decay channel for the first time in high energy heavy-ion collisions. An excellent agreement is found between the rapidity densities and the shape of the measured tranverse momentum spectrum. The data rule out a possible enhancement of the $\phi$ yield in the leptonic over hadronic channel by a factor larger than 1.6 at 95% CL. CERES results are in agreement with NA49 results.

v1 (Tue, 19 Feb 2008 16:21:25 GMT)

Jose Ramon Espinosa

A. Delgado, J. R. Espinosa, J. M. No and M. Quiros

Delgado A., Espinosa J. R., No J. M., Quiros M.

The Higgs as a Portal to Plasmon-like Unparticle Excitations

12 LaTeX pages, 2 figures

JHEP0804:028,2008

10.1088/1126-6708/2008/04/028

hep-ph

A renormalizable coupling between the Higgs and a scalar unparticle operator O_U of non-integer dimension d_U<2 triggers, after electroweak symmetry breaking, an infrared divergent vacuum expectation value for O_U. Such IR divergence should be tamed before any phenomenological implications of the Higgs-unparticle interplay can be drawn. In this paper we present a novel mechanism to cure that IR divergence through (scale-invariant) unparticle self-interactions, which has properties qualitatively different from the mechanism considered previously. Besides finding a mass gap in the unparticle continuum we also find an unparticle pole reminiscent of a plasmon resonance. Such unparticle features could be explored experimentally through their mixing with the Higgs boson.

v1 (Tue, 19 Feb 2008 16:47:58 GMT)

Davesh Maulik

Davesh Maulik

Maulik Davesh

Gromov-Witten theory of A_n-resolutions

42 pages, 4 figures

Geom. Topol. 13 (2009) 1729-1773

10.2140/gt.2009.13.1729

math.AG

We give a complete solution for the reduced Gromov-Witten theory of resolved surface singularities of type A_n, for any genus, with arbitrary descendent insertions. We also present a partial evaluation of the T-equivariant relative Gromov-Witten theory of the threefold A_n x P^1 which, under a nondegeneracy hypothesis, yields a complete solution for the theory. The results given here allow comparison of this theory with the quantum cohomology of the Hilbert scheme of points on the A_n surfaces. We discuss generalizations to linear Hodge insertions and to surface resolutions of type D,E. As a corollary, we present a new derivation of the stationary Gromov-Witten theory of P^1.

v1 (Tue, 19 Feb 2008 16:52:15 GMT)

Michael J. W. Hall

Michael J.W. Hall

Hall Michael J. W.

Comment on "An Arrow of Time Operator for Standard Quantum Mechanics" - a sign of the time!

Further propeties, generalisation to almost periodic systems, ref added, minor corrections, bad pun

quant-ph

It is shown that the `arrow of time' operator, M_F, recently suggested by Strauss et al., in arXiv:0802.2448v1 [quant-ph], is simply related to the sign of the canonical `time' observable, T (apparently first introduced by Holevo). In particular, the monotonic decrease of < M_F > corresponds to the fact that < sgn T > increases monotonically with time. This relationship also provides a physical interpretation of the property M_F < 1. Some further properties and possible generalisations are pointed out, including to almost-periodic systems.

v1 (Tue, 19 Feb 2008 16:56:59 GMT), v2 (Wed, 20 Feb 2008 16:16:19 GMT)

Jason Locasale W

Jason W. Locasale

Locasale Jason W.

Signal duration and the time scale dependence of signal integration in biochemical pathways

27 pages, 4 figures

q-bio.MN q-bio.SC

Signal duration (e.g. the time scales over which an active signaling intermediate persists) is a key regulator of biological decisions in myriad contexts such as cell growth, proliferation, and developmental lineage commitments. Accompanying differences in signal duration are numerous downstream biological processes that require multiple steps of biochemical regulation. Here, we present an analysis that investigates how simple biochemical motifs that involve multiple stages of regulation can be constructed to differentially process signals that persist at different time scales. We compute the dynamic gain within these networks and resulting power spectra to better understand how biochemical networks can integrate signals at different time scales. We identify topological features of these networks that allow for different frequency dependent signal processing properties. Our studies suggest design principles for why signal duration in connection with multiple steps of downstream regulation is a ubiquitous control motif in biochemical systems.

v1 (Tue, 19 Feb 2008 17:01:22 GMT)

Yijia Fan

Yijia Fan, Abdulkareem Adinoyi, John S Thompson, Halim Yanikomeroglu, H. Vincent Poor

Fan Yijia, Adinoyi Abdulkareem, Thompson John S, Yanikomeroglu Halim, Poor H. Vincent

A Simple Distributed Antenna Processing Scheme for Cooperative Diversity

To appear in the IEEE Transactions on Communications

cs.IT math.IT

In this letter the performance of multiple relay channels is analyzed for the situation in which multiple antennas are deployed only at the relays. The simple repetition-coded decodeand- forward protocol with two different antenna processing techniques at the relays is investigated. The antenna combining techniques are maximum ratio combining (MRC) for reception and transmit beamforming (TB) for transmission. It is shown that these distributed antenna combining techniques can exploit the full spatial diversity of the relay channels regardless of the number of relays and antennas at each relay, and offer significant power gain over distributed space-time coding techniques.

v1 (Tue, 19 Feb 2008 17:05:54 GMT)

Maziar Nekovee

C. J. Rhodes and M. Nekovee

Rhodes C. J., Nekovee M.

The Opportunistic Transmission of Wireless Worms between Mobile Devices

Submitted for publication

10.1016/j.physa.2008.09.017

cs.NI cond-mat.stat-mech cs.CR

The ubiquity of portable wireless-enabled computing and communications devices has stimulated the emergence of malicious codes (wireless worms) that are capable of spreading between spatially proximal devices. The potential exists for worms to be opportunistically transmitted between devices as they move around, so human mobility patterns will have an impact on epidemic spread. The scenario we address in this paper is proximity attacks from fleetingly in-contact wireless devices with short-range communication range, such as Bluetooth-enabled smart phones. An individual-based model of mobile devices is introduced and the effect of population characteristics and device behaviour on the outbreak dynamics is investigated. We show through extensive simulations that in the above scenario the resulting mass-action epidemic models remain applicable provided the contact rate is derived consistently from the underlying mobility model. The model gives useful analytical expressions against which more refined simulations of worm spread can be developed and tested.

v1 (Tue, 19 Feb 2008 17:07:32 GMT)

Iain Martin W

I Martin, H Armandula, C Comtet, M M Fejer, A Gretarsson, G Harry, J Hough, J-M M Mackowski, I MacLaren, C Michel, J-L Montorio, N Morgado, R Nawrodt, S Penn, S Reid, A Remillieux, R Route, S Rowan, C Schwarz, P Seidel, W Vodel, A. Zimmer

Martin I, Armandula H, Comtet C, Fejer M M, Gretarsson A, Harry G, Hough J, Mackowski J-M M, MacLaren I, Michel C, Montorio J-L, Morgado N, Nawrodt R, Penn S, Reid S, Remillieux A, Route R, Rowan S, Schwarz C, Seidel P, Vodel W, Zimmer A.

Measurements of a low temperature mechanical dissipation peak in a single layer of Ta2O5 doped with TiO2

Class.Quant.Grav.25:055005,2008

10.1088/0264-9381/25/5/055005

gr-qc

Thermal noise arising from mechanical dissipation in oxide coatings is a major limitation to many precision measurement systems, including optical frequency standards, high resolution optical spectroscopy and interferometric gravity wave detectors. Presented here are measurements of dissipation as a function of temperature between 7 K and 290 K in ion-beam sputtered Ta2O5 doped with TiO2, showing a loss peak at 20 K. Analysis of the peak provides the first evidence of the source of dissipation in doped Ta2O5 coatings, leading to possibilities for the reduction of thermal noise effects.

v1 (Tue, 19 Feb 2008 17:10:47 GMT)

Daniel Grieser

Daniel Grieser

Grieser Daniel

Thin tubes in mathematical physics, global analysis and spectral geometry

29 pages, 4 figures. To appear in 'Analysis on Graphs and its Applications', Proceedings of the Newton Institute Program 2007, in the series 'Proceedings of Symposia in Pure Mathematics' by the AMS

math.SP math-ph math.MP

A thin tube is an $n$-dimensional space which is very thin in $n-1$ directions, compared to the remaining direction, for example the $\epsilon$-neighborhood of a curve or an embedded graph in $\R^n$ for small $\epsilon$. The Laplacian on thin tubes and related operators have been studied in various contexts, with different goals but overlapping techniques. In this survey we explain some of these contexts, methods and results, hoping to encourage more interaction between the disciplines mentioned in the title.

v1 (Tue, 19 Feb 2008 17:14:53 GMT)

Bartlomiej Waclaw

B. Waclaw, Z. Burda, W. Janke

Waclaw B., Burda Z., Janke W.

Power laws in zero-range processes on random networks

6 pages, EPJ Latex style

Eur. Phys. J. B 65, 565 (2008)

10.1140/epjb/e2008-00361-0

cond-mat.stat-mech cond-mat.other

We study statistical properties of a zero-range process (ZRP) on random networks. We derive an analytic expression for the distribution of particles (also called node occupation distribution) in the steady state of the ZRP in the ensemble of uncorrelated random graphs. We analyze the dependence of this distribution on the node-degree distribution. In particular, we show that when the degree distribution is tuned properly, one can obtain scale-free fluctuations in the distribution of particles. Such fluctuations lead to a power law in the distribution of particles, just like in the ZRP with the hopping rate u(m)=1+b/m on homogeneous graphs.

v1 (Tue, 19 Feb 2008 17:18:56 GMT)

J\'er\'emy Blanc

J\'er\'emy Blanc

Blanc Jérémy

Sous-groupes alg\'ebriques du groupe de Cremona

Text in French, Translated introduction, 35 pages, 1 figure, to appear in Transform. Groups

Transform. Groups 14 (2009), no. 2, 249-285

10.1007/s00031-008-9046-5

math.AG

We give a complete classification of maximal algebraic subgroups of the Cremona group of the plane and provide algebraic varieties that parametrize the conjugacy classes. ----- Nous donnons une classification compl\`ete des sous-groupes alg\'ebriques maximaux du groupe de Cremona du plan et explicitons les vari\'et\'es qui param\`etrent les classes de conjugaison.

v1 (Tue, 19 Feb 2008 17:23:05 GMT), v2 (Sat, 2 Aug 2008 15:26:49 GMT)

Ioana Bena Dr.

Ioana Bena, Michel Droz, Istvan Lagzi, Kirsten Martens, Zoltan Racz, Andras Volford

Bena Ioana, Droz Michel, Lagzi Istvan, Martens Kirsten, Racz Zoltan, Volford Andras

Designer Patterns: Flexible Control of Precipitation through Electric Currents

4 pages, 6 figures

Phys. Rev. Lett. 101, 075701 (2008)

10.1103/PhysRevLett.101.075701

cond-mat.other cond-mat.mtrl-sci nlin.PS physics.chem-ph

Precipitation patterns generated by A^{+}+B^{-} --> C type reaction-diffusion processes are studied. It is shown both theoretically and experimentally that the patterns can be controlled by an appropriately designed, time-dependent electric current in the system. We describe examples of current dynamics yielding periodic bands of prescribed wavelength, as well as more complicated structures. The pattern control is demonstrated experimentally on the reaction-diffusion-precipitation process 2AgNO_3+K_2Cr_2O_7 --> Ag_2Cr_2O_7+2KNO_3 taking place in a gel.

v1 (Tue, 19 Feb 2008 17:48:37 GMT)

Thomas Feierl

Thomas Feierl

Feierl Thomas

The height of watermelons with wall

23 pages, 2 figures; final version accepted for publication

J.Phys.A: Math.Theor. 45 095003 (2012)

10.1088/1751-8113/45/9/095003

math.CO cond-mat.stat-mech math-ph math.MP math.PR

We derive asymptotics for the moments as well as the weak limit of the height distribution of watermelons with p branches with wall. This generalises a famous result of de Bruijn, Knuth and Rice on the average height of planted plane trees, and results by Fulmek and Katori et al. on the expected value, respectively the higher moments, of the height distribution of watermelons with two branches. The asymptotics for the moments depend on the analytic behaviour of certain multidimensional Dirichlet series. In order to obtain this information we prove a reciprocity relation satisfied by the derivatives of one of Jacobi's theta functions, which generalises the well known reciprocity law for Jacobi's theta functions.

v1 (Tue, 19 Feb 2008 17:49:21 GMT), v2 (Wed, 19 Nov 2008 21:27:07 GMT), v3 (Wed, 11 Apr 2012 09:23:20 GMT)

George Jackeli

G. Jackeli and D. I. Khomskii

Jackeli G., Khomskii D. I.

Classical dimers and dimerized superstructure in orbitally degenerate honeycomb antiferromagnet

to appear in Phys. Rev. Lett

Phys. Rev. Lett. 100, 147203 (2008)

10.1103/PhysRevLett.100.147203

cond-mat.str-el cond-mat.stat-mech

We discuss the ground state of the spin-orbital model for spin-one ions with partially filled $t_{2g}$ levels on a honeycomb lattice. We find that the orbital degrees of freedom induce a spontaneous dimerization of spins and drive them into nonmagnetic manifold spanned by hard-core dimer (spin-singlet) coverings of the lattice. The cooperative ``dimer Jahn-Teller'' effect is introduced through a magnetoelastic coupling and is shown to lift the orientational degeneracy of dimers leading to a peculiar valence bond crystal pattern. The present theory provides a theoretical explanation of nonmagnetic dimerized superstructure experimentally seen in Li$_2$RuO$_3$ compound at low temperatures.

v1 (Tue, 19 Feb 2008 17:55:16 GMT), v2 (Tue, 18 Mar 2008 19:52:22 GMT)

Amaury Lambert

Maria-Emilia Caballero, Amaury Lambert (PMA), Geronimo Uribe Bravo

Caballero Maria-Emilia, Lambert Amaury, Bravo Geronimo Uribe

Proof(s) of the Lamperti representation of Continuous-State Branching Processes

Probability Surveys 6 (2009) 62-89

10.1214/09-PS154

math.PR

This paper uses two new ingredients, namely stochastic differential equations satisfied by continuous-state branching processes (CSBPs), and a topology under which the Lamperti transformation is continuous, in order to provide self-contained proofs of Lamperti's 1967 representation of CSBPs in terms of spectrally positive L\'evy processes. The first proof is a direct probabilistic proof, and the second one uses approximations by discrete processes, for which the Lamperti representation is evident.

v1 (Tue, 19 Feb 2008 18:05:56 GMT), v2 (Tue, 15 Sep 2009 07:55:42 GMT)

Eduardo Ibar Mr

Edo Ibar, Michele Cirasuolo, Rob Ivison, Philip Best, Ian Smail, Andy Biggs, Chris Simpson, Jim Dunlop, Omar Almaini, Ross McLure, Sebastien Foucaud, Steve Rawlings

Ibar Edo, Cirasuolo Michele, Ivison Rob, Best Philip, Smail Ian, Biggs Andy, Simpson Chris, Dunlop Jim, Almaini Omar, McLure Ross, Foucaud Sebastien, Rawlings Steve

Exploring the infrared/radio correlation at high redshift

The paper contains 7 figures and 1 table. In press at MNRAS

10.1111/j.1365-2966.2008.13077.x

astro-ph

We have analysed the 24um properties of a radio-selected sample in the Subaru-XMM/Newton Deep Field in order to explore the behaviour of the FIR/radio relation at high redshifts. Statistically, the correlation is described by q24, the ratio between the observed flux densities at 24um and 1.4GHz, respectively. Using 24um data results in considerably more scatter in the correlation than previous work using data at 60-70um. Nevertheless, we do observe a steady correlation as a function of redshift, up to z~3.5, suggesting its validity back to primeval times. We find q24 = 0.30 +/- 0.56 for the observed and q24 = 0.71 +/- 0.47 for the k-corrected radio sample, based on sources with 300uJy < S(1.4GHz) < 3.2mJy and 24um detections. A suitable k-correction given by a M82-like mid-IR template suggests no extreme silicate absorption in the bulk of our radio sample. Using thresholds in q24 to identify radio-excess sources, we have been able to characterise the transition from radio-loud AGN to star-forming galaxies and radio-quiet AGN at faint (<1mJy) radio flux densities. Our results are in broad agreement with previous studies which show a dominant radio-loud AGN population at >1mJy. The rest-frame U-B colours of the expected radio-excess population have redder distribution than those that follow the correlation. This is therefore a promising way to select obscured Type-2 AGN, with a radio loud nature, missed by deep X-ray observations. Spectroscopic follow-up of these sources is required to fully test this method.

v1 (Tue, 19 Feb 2008 19:04:14 GMT), v2 (Tue, 19 Feb 2008 21:00:35 GMT)

Raul Cruz Hidalgo

R.C. Hidalgo, K.Kovacs, I. Pagonabarraga and F. Kun

Hidalgo R. C., Kovacs K., Pagonabarraga I., Kun F.

Universality class of fiber bundles with strong heterogeneities

EPL, 81 (2008) 54005

10.1209/0295-5075/81/54005

cond-mat.stat-mech

We study the effect of strong heterogeneities on the fracture of disordered materials using a fiber bundle model. The bundle is composed of two subsets of fibers, i.e. a fraction 0<\alpha<1 of fibers is unbreakable, while the remaining 1-\alpha fraction is characterized by a distribution of breaking thresholds. Assuming global load sharing, we show analytically that there exists a critical fraction of the components \alpha_c which separates two qualitatively different regimes of the system: below \alpha_c the burst size distribution is a power law with the usual exponent \tau=5/2, while above \alpha_c the exponent switches to a lower value \tau=9/4 and a cutoff function occurs with a diverging characteristic size. Analyzing the macroscopic response of the system we demonstrate that the transition is conditioned to disorder distributions where the constitutive curve has a single maximum and an inflexion point defining a novel universality class of breakdown phenomena.

v1 (Tue, 19 Feb 2008 18:50:25 GMT)

Ewa Krot-Sieniawska

Ewa Krot-Sieniawska

Krot-Sieniawska Ewa

On Characteristic Polynomials of the Family of Cobweb Posets

7 pages, 1 figure

math.CO cs.DM

This note is a response to one of problems posed by A.K. Kwasniewski in one of his recent papers. Namely for the sequence of finite cobweb subposets, the looked for explicit formulas for corresponding sequence of characteristic polynomials are discovered and delivered here. The recurrence relation defining arbitrary family of charactristic polynomials of finite cobweb posets is also derived.

v1 (Tue, 19 Feb 2008 18:53:38 GMT)

Vanessa Andrade

E. P. Spaniol and V. C. de Andrade

Spaniol E. P., de Andrade V. C.

Gravitomagnetism in teleparallel gravity

25 pages. Submitted to International Journal of Modern Physics D. Version 2: some new discussions, references added

Int.J.Mod.Phys.D19:489-505,2010

10.1142/S0218271810016476

gr-qc

The assumption that matter charges and currents could generate fields, which are called, by analogy with electromagnetism, gravitoeletric and gravitomagnetic fields, dates from the origins of General Relativity (GR). On the other hand, the Teleparallel Equivalent of GR (TEGR), as a gauge theory, seems to be the ideal scenario to define these fields, based on the gauge field strength components. The purpose of the present work is to investigate the nature of the gravitational electric and magnetic fields in the context of the TEGR, where the tetrad formalism behind it seems to be more appropriated to deal with phenomena related to observers. As our main results, we have obtained, for the first time, the exact expressions for the gravito-electromagnetic fields for the Schwarzschild solution that in the linear approximation become the usual expected ones. To improve our understanding about these fields, we have also studied the geometry produced by a spherical rotating shell in slow motion and weak field regime. Again, the expressions obtained are in complete agreement with those of electromagnetism.

v1 (Tue, 19 Feb 2008 19:02:32 GMT), v2 (Thu, 2 Jul 2009 13:45:43 GMT), v3 (Fri, 3 Jul 2009 18:08:15 GMT)

Galina L. Klimchitskaya

G. L. Klimchitskaya, U. Mohideen, V. M. Mostepanenko

Klimchitskaya G. L., Mohideen U., Mostepanenko V. M.

Casimir-Polder force between an atom and a dielectric plate: thermodynamics and experiment

10 pages, 1 figure; improved discussion; to appear in J. Phys. A: Math. Theor. (Fast Track Communications)

J. Phys. A: Math. Theor. v.41, 432001-(1-9) (2008)

10.1088/1751-8113/41/43/432001

quant-ph

The low-temperature behavior of the Casimir-Polder free energy and entropy for an atom near a dielectric plate are found on the basis of the Lifshitz theory. The obtained results are shown to be thermodynamically consistent if the dc conductivity of the plate material is disregarded. With inclusion of dc conductivity, both the standard Lifshitz theory (for all dielectrics) and its generalization taking into account screening effects (for a wide range of dielectrics) violate the Nernst heat theorem. The inclusion of the screening effects is also shown to be inconsistent with experimental data of Casimir force measurements. The physical reasons for this inconsistency are elucidated.

v1 (Tue, 19 Feb 2008 19:31:59 GMT), v2 (Thu, 13 Mar 2008 18:31:42 GMT), v3 (Tue, 16 Sep 2008 09:40:57 GMT)

Farhad Jafarpour Hamadani

F. H. Jafarpour and S. R. Masharian

Jafarpour F. H., Masharian S. R.

Repelling Random Walkers in a Diffusion-Coalescence System

5 pages, 1 EPS figure, Accepted for publication in PRE (2008)

10.1103/PhysRevE.77.031115

cond-mat.stat-mech

We have shown that the steady state probability distribution function of a diffusion-coalescence system on a one-dimensional lattice of length L with reflecting boundaries can be written in terms of a superposition of double shock structures which perform biased random walks on the lattice while repelling each other. The shocks can enter into the system and leave it from the boundaries. Depending on the microscopic reaction rates, the system is known to have two different phases. We have found that the mean distance between the shock positions is of order L in one phase while it is of order 1 in the other phase.

v1 (Tue, 19 Feb 2008 19:09:02 GMT)

Alessia Mandini

Alessia Mandini

Mandini Alessia

The cobordism class of the moduli space of polygons in $\mathbb{R}^3$

29 pages, 8 figures, Remark 9 added, circle action specified in main Theorem

J. Symplectic Geom. 7, no. 1 (2009), 1-27

math.SG

For any vector $r=(r_1,..., r_n)$, let $M_r$ denote the moduli space (under rigid motions) of polygons in $\mathbb{R}^3$ with $n$-sides whose lengths are $r_1,...,r_n$. We give an explicit characterization of the oriented $S^1$-cobordism class of $M_r$ which depends uniquely on the length vector $r$.

v1 (Tue, 19 Feb 2008 20:02:49 GMT), v2 (Mon, 4 Aug 2008 20:38:23 GMT)

Lifeng Lai

Lifeng Lai, Hesham El Gamal and H. Vincent Poor

Lai Lifeng, Gamal Hesham El, Poor H. Vincent

Authentication over Noisy Channels

Appeared in the Proceedings of the 45th Annual Allerton Conference on Communication, Control and Computing, Monticello, IL, September 26 - 28, 2007

cs.IT cs.CR math.IT

In this work, message authentication over noisy channels is studied. The model developed in this paper is the authentication theory counterpart of Wyner's wiretap channel model. Two types of opponent attacks, namely impersonation attacks and substitution attacks, are investigated for both single message and multiple message authentication scenarios. For each scenario, information theoretic lower and upper bounds on the opponent's success probability are derived. Remarkably, in both scenarios, lower and upper bounds are shown to match, and hence the fundamental limit of message authentication over noisy channels is fully characterized. The opponent's success probability is further shown to be smaller than that derived in the classic authentication model in which the channel is assumed to be noiseless. These results rely on a proposed novel authentication scheme in which key information is used to provide simultaneous protection again both types of attacks.

v1 (Tue, 19 Feb 2008 20:01:52 GMT)

Gian Paolo Vacca

J. Bartels, M. Salvadore and G.P. Vacca

Bartels J., Salvadore M., Vacca G. P.

Inclusive 1-jet Production Cross Section at Small x in QCD: Multiple Interactions

42 pages, 22 figures, few references and comments added, to appear on JHEP

JHEP0806:032,2008

10.1088/1126-6708/2008/06/032

hep-ph

We study corrections due to two Pomeron exchanges to the inclusive 1-jet production cross section in the Regge limit of perturbative QCD for a finite number of colors. By considering deep inelastic scattering on a weakly bound two-nucleon system, we carefully follow the logic of the AGK cutting rules and show, for the single inclusive cross section, that, due to the reggeization of the gluon, modifications of the AGK cutting rules appear. As our main result, we investigate and calculate the jet production vertex in the presence of a two-Pomeron cut correction. Compared to previous studies, we find a novel structure of the jet vertex which has not been considered before. We discuss a few implications of this new piece.

v1 (Tue, 19 Feb 2008 20:04:52 GMT), v2 (Wed, 4 Jun 2008 10:27:53 GMT)