Search

We report on a program of spectroscopic observations of gravitationally-lensed QSOs with multiple images. We seek to establish whether microlensing is occurring in each QSO image using only single-epoch observations. We calculate flux ratios for the cores of emission lines in image pairs to set a baseline for no microlensing. The offset of the continuum flux ratios relative to this baseline yields the microlensing magnification free from extinction, as extinction affects the continuum and the lines equally. When we find chromatic microlensing, we attempt to constrain the size of the QSO accretion disk. SDSSJ1004+4112 and HE1104-1805 show chromatic microlensing with amplitudes $0.2< |\Delta m| < 0.6$ and $0.2< |\Delta m| < 0.4$ mag, respectively. Modeling the accretion disk with a Gaussian source ($I\propto \exp(-R^2/2r_s^2)$) of size $r_s\propto \lambda^p$ and using magnification maps to simulate microlensing we find $r_s(\lambda 3363)=7\pm3 light-days (18.1\pm7.8 \times 10^{15} cm$) and $p=1.1\pm 0.4$ for SDSS1004+4112, and $r_s(\lambda 3363)=6\pm2 light-days (15.5\pm5.2 \times 10^{15} cm$) and $p=0.7\pm0.1$ for HE1104-1805. For SDSSJ1029+2623 we find strong chromaticity of $\sim 0.4$ mag in the continuum flux ratio, which probably arises from microlensing although not all the available data fit within this explanation. For Q0957+561 we measure B-A magnitude differences of 0.4 mag, much greater than the $\sim$0.05 mag amplitude usually inferred from lightcurve variability. It may substantially modify the current interpretations of microlensing in this system, likely favoring the hypothesis of smaller sources and/or larger microdeflectors. For HS0818+1227, our data yield posible evidence of microlensing., Comment: 45pp, 17figs, ApJ accepted (june 4th 2012)

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA-2010-BLG-477. The measured planet-star mass ratio is $q=(2.181\pm0.004)\times 10^{-3}$ and the projected separation is $s=1.1228\pm0.0006$ in units of the Einstein radius. The angular Einstein radius is unusually large $\theta_{\rm E}=1.38\pm 0.11$ mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range $0.13

Using microlensing measurements from a sample of 27 image-pairs of 19 lensed quasars we determine a maximum likelihood estimate for the accretion disk size of an {{\em}average} quasar of $r_s=4.0^{+2.4}_{-3.1} $ light days at rest frame $<\lambda>=1736$\AA\ for microlenses with a mean mass of $=0.3M_\odot$. This value, in good agreement with previous results from smaller samples, is roughly a factor of 5 greater than the predictions of the standard thin disk model. The individual size estimates for the 19 quasars in our sample are also in excellent agreement with the results of the joint maximum likelihood analysis., Comment: 6 pages, 3 figures, submitted to ApJ

We present the analysis of the light curves of 9 high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For 7 events, we measure the Einstein radii and the lens-source relative proper motions. Among them, 5 events are found to have Einstein radii less than 0.2 mas, making the lenses candidates of very low-mass stars or brown dwarfs. For MOA-2011-BLG-274, especially, the small Einstein radius of $\theta_{\rm E}\sim 0.08$ mas combined with the short time scale of $t_{\rm E}\sim 2.7$ days suggests the possibility that the lens is a free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and thus uniquely determine the physical parameters of the lens. We also find that the measured lens mass of $\sim 0.84\ M_\odot$ is consistent with that of a star blended with the source, suggesting that the blend is likely to be the lens. Although we find planetary signals for none of events, we provide exclusion diagrams showing the confidence levels excluding the existence of a planet as a function of the separation and mass ratio., Comment: 14 pages, 12 figures, 5 tables

Theoretical and numerical modeling of dark-matter halo assembly predicts that the most luminous galaxies at high redshift are surrounded by overdensities of fainter companions. We test this prediction with HST observations acquired by our Brightest of Reionizing Galaxies (BoRG) survey, which identified four very bright z~8 candidates as Y-dropout sources in four of the 23 non-contiguous WFC3 fields observed. We extend here the search for Y-dropouts to fainter luminosities (M_* galaxies with M_AB\sim-20), with detections at >5sigma confidence (compared to >8sigma confidence adopted earlier) identifying 17 new candidates. We demonstrate that there is a correlation between number counts of faint and bright Y-dropouts at >99.84% confidence. Field BoRG58, which contains the best bright z\sim8 candidate (M_AB=-21.3), has the most significant overdensity of faint Y-dropouts. Four new sources are located within 70arcsec (corresponding to 3.1 comoving Mpc at z=8) from the previously known brighter z\sim8 candidate. The overdensity of Y-dropouts in this field has a physical origin to high confidence (p>99.975%), independent of completeness and contamination rate of the Y-dropout selection. We modeled the overdensity by means of cosmological simulations and estimate that the principal dark matter halo has mass M_h\sim(4-7)x10^11Msun (\sim5sigma density peak) and is surrounded by several M_h\sim10^11Msun halos which could host the fainter dropouts. In this scenario, we predict that all halos will eventually merge into a M_h>2x10^14Msun galaxy cluster by z=0. Follow-up observations with ground and space based telescopes are required to secure the z\sim8 nature of the overdensity, discover new members, and measure their precise redshift., Comment: Minor revision: ApJ accepted [17 pages (emulateapj style), 7 figures, 2 tables]

Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of 8 binary lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central perturbations caused by planets. However, the degeneracy between close and wide binary solutions cannot be resolved with a $3\sigma$ confidence level for 3 events, implying that the degeneracy would be an important obstacle in studying binary distributions. The dependence of the degeneracy on the lensing parameters is consistent with a theoretic prediction that the degeneracy becomes severe as the binary separation and the mass ratio deviate from the values of resonant caustics. The measured mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is $q\sim 0.1$, making the companion of the lens a strong brown-dwarf candidate., Comment: 10 figures, 6 tables, 26 pages

X-ray absorption spectroscopy measurements in Pr0.5Ca0.5CoO3 were performed at the Pr M4,5, Pr L3, and Ca L2,3 absorption edges as a function of temperature below 300 K. Ca spectra show no changes down to 10 K while a noticeable thermally dependent evolution takes place at the Pr edges across the metal-insulator transition. Spectral changes are analyzed by different methods, including multiple scattering simulations, which provide quantitative details on an electron loss at Pr 4f orbitals. We conclude that in the insulating phase a fraction [15(+5)%] of Pr3+ undergoes a further oxidation to adopt a hybridized configuration composed of an admixture of atomic-like 4f1 states (Pr4+) and f- symmetry states on the O 2p valence band (Pr3+L states) indicative of a strong 4f- 2p interaction., Comment: 19 pages (.doc), 4 figures, Phys. Rev. B, in press

Light tensor mesons (T = a_2, f_2 and K_2^*) can be produced in decays of tau leptons. In this paper we compute the branching ratios of tau --> T pi nu decays by assuming the dominance of intermediate virtual states to model the form factors involved in the relevant hadronic matrix element. The exclusive f_2(1270) pi^- decay mode turns out to have the largest branching ratio, of O(10^-4) . Our results indicate that the contributions of tensor meson intermediate states to the three-pseudoscalar channels of tau decays are rather small., Comment: 10 pages, 1 figure. Version accepted for publication in PRD, some typos are corrected and comments are added in section 4. Conclusions remain unchanged

We have computed branching ratios of two-body nonleptonic B_c \to X_{c\bar{c}}M decays, where X_{c\bar{c}} is the radially excited charmonium \eta_c(2S) or \psi(2S) meson, and M is a pseudoscalar (P) or a vector (V) or an axial-vector (A(^3P_1)) meson. We have assumed factorization hypothesis and calculated the form factors in the nonrelativistic ISGW2 quark model. We have found that some of these decays have branching ratios of the order of 10^{-3} - 10^{-4}., Comment: 16 pages, 2 figures. Sections 2 and 4 were extended. Two tables and some references were added

In this work, we modify the superparamagnetic clustering algorithm (SPC) by adding an extra weight to the interaction formula that considers which genes are regulated by the same transcription factor. With this modified algorithm that we call SPCTF, we analyze Spellman et al. microarray data for cell cycle genes in yeast, and find clusters with a higher number of elements compared with those obtained with the SPC algorithm. Some of the incorporated genes by using SPCFT were not detected at first by Spellman et al. but were later identified by other studies, whereas several genes still remain unclassified. The clusters composed by unidentified genes were analyzed with MUSA, the motif finding using an unsupervised approach algorithm, and this allow us to select the clusters whose elements contain cell cycle transcription factor binding sites as clusters worth of further experimental studies because they would probably lead to new cell cycle genes. Finally, our idea of introducing available information about transcription factors to optimize the gene classification could be implemented for other distance-based clustering algorithms, Comment: 16 pages, 6 Figures made of a total of 11 figures, 2 tables, supplementary info file containing a list of the 27 most stable clusters of 6 or more genes of the cell cycle, in this approach, with the codes of their component genes in synchronized Sc yeast cultures, available from the authors, or from the Physica A site

We compute important ratios between decay widths of some exclusive two-body nonleptonic and semileptonic B decays, which could be test of factorization hy- pothesis. We also present a summary of the expressions of the decay widths and differential decay rates of these decays, at tree level, including l = 0 (ground state), l = 1 (orbitally excited) and n = 2 (radially excited) mesons in the fi- nal state. From a general point of view, we consider eight transitions, namely H \rightarrow P, V, S, A, A, T, P (2S), V (2S). Our analysis is carried out assuming factorization hypothesis and using the WSB, ISGW and CLFA quark models., Comment: 17 Pages, Version accepted for publication in Rev. Mex. Fis., The title was changed, in section 2 some equations were eliminated, one paragraph was added in section 3, section 5 and the appendix were re-written and section 6 was extended

The gravitational lens system MG J0414+0534 is formed by an elliptical galaxy at redshift ~0.96 and a quasar at z~2.64. The system geometry is typical of lensing by an elliptical galaxy with the QSO close to and inside a fold caustic. It shows 4 images of the background source, and a partial Einstein ring is visible at optical wavelengths. It was observed with a global-VLBI array at 18 cm in June 2008. We present here the imaging results and a preliminary lens model constrained by these observations., Comment: submitted to the proceedings of 10th European-VLBI network Symposium. 6 pages, 1 figure

What is the relationship between the macroscopic parameters of the constitutive equation for a granular soil and the microscopic forces between grains? In order to investigate this connection, we have simulated by molecular dynamics the oedometric compression of a granular soil (a dry and bad-graded sand) and computed the hypoplastic parameters $h_s$ (the granular skeleton hardness) and $\eta$ (the exponent in the compression law) by following the same procedure than in experiments, that is by fitting the Bauer's law $e/e0 = exp(-(3p/hs)\eta)$, where $p$ is the pressure, and $e_0$ and $e$ are the initial and present void ratios. The micro-mechanical simulation includes elastic and dissipative normal forces plus slip, rolling and static friction between grains. By this way we have explored how the macroscopic parameters change by modifying the grains stiffness, V ; the dissipation coefficient, $\gamma_n$; the static friction coefficient, $\mu_s$; and the dynamic friction coefficient, $\mu_k$ . Cumulating all simulations, we obtained an unexpected result: the two macroscopic parameters seems to be related by a power law, $h_s = 0.068(4)\eta^{9.88(3)}$. Moreover, the experimental result for a Guamo sand with the same granulometry fits perfectly into this power law. Is this relation real? What is the final ground of the Bauer's Law? We conclude by exploring some hypothesis., Comment: 8 pages, 7 figures

The ability of grains to rotate can play a crucial role on the collective behavior of granular media. It has been observed in computer simulations that imposing a torque at the contacts modifies the force chains, making support chains less important. In this work we investigate the effect of a gradual hindering of the grains rotations on the so-called critical state of soil mechanics. The critical state is an asymptotic state independent of the initial solid fraction where deformations occur at a constant shear strength and compactness. We quantify the difficulty to rotate by a friction coefficient at the level of particles, acting like a threshold. We explore the effect of this particle-level friction coefficient on the critical state by means of molecular dynamics simulations of a simple shear test on a poly-disperse sphere packing. We found that the larger the difficulty to rotate, the larger the final shear strength of the sample. Other micro-mechanical variables, like the structural anisotropy and the distribution of forces, are also influenced by the threshold. These results reveal the key role of rotations on the critical behavior of soils and suggest the inclusion of rotational variables into their constitutive equations., Comment: 9 pages, 8 figures, Accepted for publication in Computer Physics Communications

Diffraction in time (DIT) is a fundamental phenomenon in quantum dynamics due to time-dependent obstacles and slits. It is formally analogous to diffraction of light, and is expected to play an increasing role to design coherent matter wave sources, as in the atom laser, to analyze time-of-flight information and emission from ultrafast pulsed excitations, and in applications of coherent matter waves in integrated atom-optical circuits. We demonstrate that DIT emerges robustly in quantum waves emitted by an exponentially decaying source and provide a simple explanation of the phenomenon, as an interference of two characteristic velocities. This allows for its controllability and optimization., Comment: 4 pages, 6 figures

We report the new spectroscopic observations of the gravitational lens RXJ 021+4529 with the multi-mode focal reducer SCORPIO of the SAO RAS 6-m telescope. The new spectral observations were compared with the previously observed spectra of components A and B of RXJ 0921+4529, i.e. the same components observed in different epochs. We found a significant difference in the spectrum between the components that cannot be explained with microlensing and/or spectral variation. We conclude that RXJ 0921+4529 is a binary quasar system, where redshifts of quasars A and B are 1.6535 +/- 0.0005 and 1.6625 +/- 0.0015, respectively., Comment: 6 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters

We provide the most general forms of covariant and normalized time operators and their probability densities, with applications to quantum clocks, the time of arrival, and Lyapunov quantum operators. Examples are discussed of the profusion of possible operators and their physical meaning. Criteria to define unique, optimal operators for specific cases are given.

A 2D, hexagonal in geometry, statistical model of fracture is proposed. The model is based on the drying fracture process of the bamboo Guadua angustifolia. A network of flexible cells are joined by brittle junctures of different Young moduli that break at a fixed threshold in tensile force. The system is solved by means of the Finite Element Method (FEM). The distribution of avalanche breakings exhibits a power law with exponent -2.93(9), in agreement with the random fuse model.

The {57}Fe-specific phonon density of states of Ba(Fe(1-x)Co(x))2As2 single crystals (x=0.0, 0.08) was measured at cryogenic temperatures and at high pressures with nuclear-resonant inelastic x-ray scattering. Measurements were conducted for two different orientations of the single crystals, yielding the orientation-projected {57}Fe-phonon density of states (DOS) for phonon polarizations in-plane and out-of-plane with respect to the basal plane of the crystal structure. In the tetragonal phase at 300 K, a clear stiffening was observed upon doping with Co. Increasing pressure to 4 GPa caused a marked increase of phonon frequencies, with the doped material still stiffer than the parent compound. Upon cooling, both the doped and undoped samples showed a stiffening, and the parent compound exhibited a discontinuity across the magnetic and structural phase transition. These findings are generally compatible with the changes in volume of the system upon doping, increasing pressure, or increasing temperature, but an extra softening of high-energy modes occurs with increasing temperature. First-principles computations of the phonon DOS were performed and showed an overall agreement with the experimental results, but underestimate the Grueneisen parameter. This discrepancy is explained in terms of a magnetic Grueneisen parameter, causing an extra phonon stiffening as magnetism is suppressed under pressure.

We estimate the fraction of mass that is composed of compact objects in gravitational lens galaxies. This study is based on microlensing measurements (obtained from the literature) of a sample of 29 quasar image pairs seen through 20 lens galaxies. We determine the baseline for no microlensing magnification between two images from the ratios of emission line fluxes. Relative to this baseline, the ratio between the continua of the two images gives the difference in microlensing magnification. The histogram of observed microlensing events peaks close to no magnification and is concentrated below 0.6 magnitudes, although two events of high magnification, $\Delta m \sim 1.5$, are also present. We study the likelihood of the microlensing measurements using frequency distributions obtained from simulated microlensing magnification maps for different values of the fraction of mass in compact objects, $\alpha$. The concentration of microlensing measurements close to $\Delta m \sim 0$ can be explained only by simulations corresponding to very low values of $\alpha$ (10% or less). A maximum likelihood test yields $\alpha=0.05_{-0.03}^{+0.09}$ (90% confidence interval) for a quasar continuum source of intrinsic size $r_{s_0}\sim 2.6 \cdot 10^{15} \rm cm$. Regarding the current controversy about Milky Way/LMC and M31 microlensing studies, our work supports the hypothesis of a very low content in MACHOS (Massive Compact Halo Objects).

Fundamental low-energy limits to the accuracy of quantum clock and stopwatch models in which the clock hand motion is activated by the presence of a particle in a region of space have been studied in the past, but their relevance for actual atomic clocks had not been assessed. In this work we address the effect of slow atomic quantum motion on Rabi and Ramsey resonance fringe patterns, as a perturbation of the results based on classical atomic motion. We find the dependence of the fractional error of the corresponding atomic clocks on the atomic velocity and interaction parameters., Comment: 7 pages, 5 figures

In this work we have studied hadronic charmless two-body B decays involving p-wave mesons in final state. We have calculated branching ratios of $B\to AT$ decays (where $A$ and $T$ denotes a $^3P_1$ axial-vector and a tensor meson, respectively), using $B \to T$ form factors obtained in the covariant light-front (CLF) approach, and the full effective Hamiltonian. We have obtained that $\mathcal{B}(B^{0} \to a_{1}^{+}a_{2}^{-}) =42.47 \times10^{-6}$, $\mathcal{B}(B^{+} \to a_{1}^{+}a_{2}^{0}) = 22.71 \times10^{-6}$, $\mathcal{B}(B \to f_{1}K_{2}^{*}) = (2.8-4) \times 10^{-6}$ (with $f_{1}=, f_{1}(1285),f_{1}(1420)$) for $\theta_{^{3}P_{1}} = 53.2^{\circ}$, $\mathcal{B}(B \to f_{1}(1420)K_{2}^{*}) = (5.91-6.42) \times 10^{-6}$ with $\theta_{^{3}P_{1}} = 27.9^{\circ}$, $\mathcal{B}(B \to K_{1}a_{2})= (1.7 - 5.7) [1-9.3] \times10^{-6}$ for $\theta_{K_{1}} = -37^{\circ} [-58^{\circ}]$ where $K_1 = K_1(1270), K_1(1400)$. It seems that these decays can be measured in experiments at $B$ factories. Additionally, we have found that $\mathcal{B}(B \to K_{1}(1270)a_{2})/\mathcal{B}(B \to K_{1}(1400)a_{2})$ and $\mathcal{B}(B \to f_1(1420)K_{2}^{*})/\mathcal{B}(B \to f_1(1285)K_{2}^{*})$ ratios could be useful to determine numerical values of mixing angles $\theta_{K_{1}}$ and $\theta_{^{3}P_{1}}$, respectively., Comment: 12 pages

We reanalyzed nonleptonic charmless two-body B decays involving tensor mesons in final state motivated by the disagreement between current experimental information and theoretical predictions obtained in ISGW2 model for some $\mathcal{B}(B \to P(V)T)$ (where $P$, $V$ and $T$ denote a pseudoscalar, a vector and a tensor meson, respectively). We have calculated branching ratios of charmless $B \to PT$ and $B\to VT$ modes, using $B \to T$ form factors obtained in the covariant light-front (CLF) approach and the full effective Hamiltonian. We have considered the $\eta-\eta^{\prime}$ two-mixing angle formalism for $B \to \eta^{(\prime)}T$ channels, which increases branching ratios for these processes. Our predictions obtained in the CLF approach are, in general, greater than those computed in the framework of the ISGW2 model and more favorable with the available experimental data. Specifically, our results for exclusive channels $B \to \eta K_{2}^{*}(1430)$ and $B \to \phi K_{2}^{*}(1430)$ are in agreement with recent experimental information., Comment: 10 pages

Some fundamental and formal aspects of the quantum dwell time are reviewed, examples for free motion and scattering off a potential barrier are provided, as well as extensions of the concept. We also examine the connection between the dwell time of a quantum particle in a region of space and flux-flux correlations at the boundaries, as well as operational approaches and approximations to measure the flux-flux correlation function and thus the second moment of the dwell time, which is shown to be characteristically quantum, and larger than the corresponding classical moment even for freely moving particles., Comment: To appear in "Time in Quantum Mechanics, Vol. 2", Springer 2009, ed. by J. G. Muga, A. Ruschhaupt and A. del Campo

We examine the connection between the dwell time of a quantum particle in a region of space and flux-flux correlations at the boundaries. It is shown that the first and second moments of a flux-flux correlation function which generalizes a previous proposal by Pollak and Miller [E. Pollak and W. H. Miller, Phys. Rev. Lett. {\bf 53}, 115 (1984)], agree with the corresponding moments of the dwell-time distribution, whereas the third and higher moments do not. We also discuss operational approaches and approximations to measure the flux-flux correlation function and thus the second moment of the dwell time, which is shown to be characteristically quantum, and larger than the corresponding classical moment even for freely moving particles., Comment: 7 pages

In this work, we study the numerical optimization of nearest-neighbor concurrence of bipartite one and two dimensional lattices, as well as non bipartite two dimensional lattices. These systems are described in the framework of a tight-binding Hamiltonian while the optimization of concurrence was performed using genetic algorithms. Our results show that the concurrence of the optimized lattice structures is considerably higher than that of non optimized systems. In the case of one dimensional chains the concurrence is maximized when the system begins to dimerize, i.e. it undergoes a structural phase transition (Peierls distortion). This result is consistent with the idea that entanglement is maximal or shows a singularity near quantum phase transitions and that quantum entanglement cannot be freely shared between many objects (monogamy property). Moreover, the optimization of concurrence in two-dimensional bipartite and non bipartite lattices is achieved when the structures break into smaller subsystems, which are arranged in geometrically distinguishable configurations. This behavior is again related to the monogamy property., Comment: 18 pages, 10 figures

We present narrowband images of the gravitational lens system Q~2237+0305 made with the Nordic Optical Telescope in eight different filters covering the wavelength interval 3510-8130 \AA. Using point-spread function photometry fitting we have derived the difference in magnitude versus wavelength between the four images of Q~2237+0305. At $\lambda=4110$ \AA, the wavelength range covered by the Str\"omgren-v filter coincides with the position and width of the CIV emission line. This allows us to determine the existence of microlensing in the continuum and not in the emission lines for two images of the quasar. Moreover, the brightness of image A shows a significant variation with wavelength which can only be explained as consequence of chromatic microlensing. To perform a complete analysis of this chromatic event our observations were used together with Optical Gravitational Lensing Experiment light curves. Both data sets cannot be reproduced by the simple phenomenology described under the caustic crossing approximation; using more realistic representations of microlensing at high optical depth, we found solutions consistent with simple thin disk models ($r_{s}\varpropto \lambda^{4/3}$); however, other accretion disk size-wavelength relationships also lead to good solutions. New chromatic events from the ongoing narrow band photometric monitoring of Q~2237+0305 are needed to accurately constrain the physical properties of the accretion disk for this system., Comment: 9 pages, 9 figures, 2 tables. Matches ApJ published version. Some references added

This study shows that isoscaling, usually studied in nuclear reactions, is a phenomenon common to all cases of fair sampling. Exact expressions for the yield ratio $R_{21}$ and approximate expressions for the isoscaling parameters $\alpha$ and $\beta$ are obtained and compared to experimental results. It is concluded that nuclear isoscaling is bound to contain a component due to sampling and, thus, a words of caution is issued to those interested in extracting information about the nuclear equation of state from isoscaling., Comment: 7 pages, 1 figure

In this paper we introduce a novel 3D Lattice-Boltzmann model that recovers in the continuous limit the Maxwell equations in materials. In order to build conservation equations with antisymmetric tensors, like the Faraday law, the model assigns four auxiliary vectors to each velocity vector. These auxiliary vectors, when combined with the distribution functions, give the electromagnetic fields. The evolution is driven by the usual BGK collision rule, but with a different form for the equilibrium distribution functions. This LBGK model allows us to consider for both dielectrics and conductors with realistic parameters, and therefore it is adequate to simulate the most diverse electromagnetic problems, like the propagation of electromagnetic waves (both in dielectric media and in waveguides), the skin effect, the radiation pattern of a small dipole antenna and the natural frequencies of a resonant cavity, all with 2% accuracy. Actually, it shows to be one order of magnitude faster than the original FDTD formulation by Yee to reach the same accuracy. It is, therefore, a valuable alternative to simulate electromagnetic fields and opens lattice Boltzmann for a broad spectrum of new applications in electrodynamics. In this paper we develop a 3D Lattice-Boltzmann model that recovers in the continuous limit the Maxwell equations for macroscopic mediums. The model can sucessfully reproduces the propagation of the electromagnetic waves in dielectric mediums and waveguide, the skin effect, the electrical dipole radiation and the electromagnetic response of a resonant cavity., Comment: Accepted for publication in Phys. Rev. E

We present a brief discussion about expressions of decay widths of exclusive nonleptonic and semileptonic B decays at tree level including $l=0$ and $l=1$ mesons in final state. Our analysis is carried out assuming factorization hypothesis and using parametrizations of hadronic matrix elements given in WSB and ISGW quark models. Special interest is focused on dynamics of these processes and several important ratios between decay widths to determine form factors and decay constants are given., Comment: 14 pages

We present a systematic study of exclusive charmless nonleptonic two-body B decays including axial-vector mesons in the final state. We calculate branching ratios of B\to PA, VA and AA decays, where A, V and P denote an axial-vector, a vector and a pseudoscalar meson, respectively. We assume naive factorization hypothesis and use the improved version of the nonrelativistic ISGW quark model for form factors in B\to A transitions. We include contributions that arise from the effective \Delta B=1 weak Hamiltonian H_{eff}. The respective factorized amplitude of these decays are explicitly showed and their penguin contributions are classified. We find that decays B^-to a_1^0\pi^-,\barB^0\to a_1^{\pm}\pi^{\mp}, B^-\to a_1^-\bar K^0, \bar B^0\to a_1^+K^-, \bar B^0\to f_1\bar K^0, B^-\to f_1K^-, B^-\to K_1^-(1400)\etap, B^-\to b_1^-\bar K^{0}, and \bar B^0\to b_1^+\pi^-(K^-) have branching ratios of the order of 10^{-5}. We also study the dependence of branching ratios for B \to K_1P(V,A) decays (K_1=K_1(1270),K_1(1400)) with respect to the mixing angle between K_A and K_B., Comment: 28 pages, 2 tables and one reference added, notation changed in appendices, some numerical results and abstract corrected

The influence of microlensing in the profiles of the emission lines generated in a biconical geometry is discussed. Microlensing amplification in this anisotropic model is not directly related to the bicone's intrinsic size but depends on the orientation of the bicone axis and on the cone aperture. The orientation of the projected bicone with respect to the shear of the magnification pattern can induce very interesting effects, like the quasi-periodic enhancements of the red/blue part of the emission line profile or the lack of correlation between the broad line region (BLR) and continuum light curves of QSOs. The emission line profiles of a BLR moving in a high caustic concentration exhibit sharp features that are well defined in wavelength. These features (spikes) correspond to the scanning of the kinematics of the BLR by the caustic clusters. The biconical model can qualitatively reproduce with a transversal (with respect to the shear) movement of the BLR, the recurrent blue-wing enhancement detected in the emission line profile of the A image of the quasar lensed system SDSS J1004+4112. The probability of observing this repetitive event is almost a 2% for a fraction of matter in stars of a 5%. This result would make plausible the detection of the spectral variability in SDSS J1004+4112 under the hypothesis of microlensing of a bicone., Comment: 21 figures, quality severely reduced. ApJ accepted

We present integral field spectroscopic observations of the quadruple-lensed QSO SDSS 1004+4112 taken with the fiber system INTEGRAL at the William Herschel Telescope on 2004 January 19. In May 2003 a blueward enhancement in the high ionization lines of SDSS 1004+4112A was detected and then faded. Our observations are the first to note a second event of similar characteristics less than one year after. Although initially attributed to microlensing, the resemblance among the spectra of both events and the absence of microlensing-induced changes in the continuum of component A are puzzling. The lack of a convincing explanation under the microlensing or intrinsic variability hypotheses makes the observed enhancements particularly relevant, calling for close monitoring of this object., Comment: 4 pages, 5 figures

In this paper we develop a 3D Lattice-Boltzmann model that recovers in the continuous limit the two-fluids theory for plasmas, and consecuently includes the generalizated Ohm's law. The model reproduces the magnetic reconnection process just by given the right initial equlibrium conditions in the magnetotail, without any assumption on the resistivity in the diffusive region. In this model, the plasma is handled like two fluids with an interaction term, each one with distribution functions associated to a cubic lattice with 19 velocities (D3Q19). The electromagnetic fields are considered like a third fluid with an external force on a cubic lattice with 13 velocities (D3Q13). The model can simulate either viscous fluids in the incompressible limit or non-viscous compressible fluids, and sucessfully reproduces both the Hartmann flow and the magnetic reconnection in the magnetotail. The reconnection rate obtained with this model is R=0.109, which is in excellent agreement with the observations., Comment: Submitted to PRE, Computational Physics. 11 pages and 9 figures