The Anticorrelated Nature of the Primary and Secondary Eclipse Timing Variations for the Kepler Contact Binaries

We report on a study of eclipse timing variations in contact binary systems, using long-cadence lightcurves in the Kepler archive. As a first step, 'observed minus calculated' (O-C) curves were produced for both the primary and secondary eclipses of some 2000 Kepler binaries. We find ~390 short-period binaries with O-C curves that exhibit (i) random-walk like variations or quasi-periodicities, with typical amplitudes of +/- 200-300 seconds, and (ii) anticorrelations between the primary and secondary eclipse timing variations. We present a detailed analysis and results for 32 of these binaries with orbital periods in the range of 0.35 +/- 0.05 days. The anticorrelations observed in their O-C curves cannot be explained by a model involving mass transfer, which among other things requires implausibly high rates of ~0.01 M_sun per year. We show that the anticorrelated behavior, the amplitude of the O-C delays, and the overall random-walk like behavior can be explained by the presence of a starspot that is continuously visible around the orbit and slowly changes its longitude on timescales of weeks to months. The quasi-periods of ~50-200 days observed in the O-C curves suggest values for k, the coefficient of the latitude dependence of the stellar differential rotation, of ~0.003-0.013.Comment: Published in The Astrophysical Journal, 2013, Vol. 774, p.81; 14 pages, 12 figures, and 2 table

Exact renormalization-group analysis of first order phase transitions in clock models

We analyze the exact behavior of the renormalization group flow in one-dimensional clock-models which undergo first order phase transitions by the presence of complex interactions. The flow, defined by decimation, is shown to be single-valued and continuous throughout its domain of definition, which contains the transition points. This fact is in disagreement with a recently proposed scenario for first order phase transitions claiming the existence of discontinuities of the renormalization group. The results are in partial agreement with the standard scenario. However in the vicinity of some fixed points of the critical surface the renormalized measure does not correspond to a renormalized Hamiltonian for some choices of renormalization blocks. These pathologies although similar to Griffiths-Pearce pathologies have a different physical origin: the complex character of the interactions. We elucidate the dynamical reason for such a pathological behavior: entire regions of coupling constants blow up under the renormalization group transformation. The flows provide non-perturbative patterns for the renormalization group behavior of electric conductivities in the quantum Hall effect.Comment: 13 pages + 3 ps figures not included, TeX, DFTUZ 91.3

A preliminary optical visibility model

A model is being created to describe the effect of weather on optical communications links between space and ground sites. This article describes the process by which the model is developed and gives preliminary results for two sites. The results indicate nighttime attenuation of optical transmission at five wavelengths. It is representative of a sampling of nights at Table Mountain Observatory from January to June and Mount Lemmon Observatory from May and June. The results are designed to predict attenuation probabilities for optical communications links

Dynamic instabilities of fracture under biaxial strain using a phase field model

We present a phase field model of the propagation of fracture under plane strain. This model, based on simple physical considerations, is able to accurately reproduce the different behavior of cracks (the principle of local symmetry, the Griffith and Irwin criteria, and mode-I branching). In addition, we test our model against recent experimental findings showing the presence of oscillating cracks under bi-axial load. Our model again reproduces well observed supercritical Hopf bifurcation, and is therefore the first simulation which does so

Less-Skilled Workers, Welfare Reform, and the Unemployment Insurance System

The declining economic position over the past two decades of those workers with less skill increases the importance of the unemployment insurance (UI) system in providing a safety net during periods of unemployment. Recent welfare reform legislation, designed to encourage labor market entry of typically very low-skilled workers who are likely to have unstable work patterns at best, potentially makes the UI system an even more critical component of the safety net. This paper seeks to determine how less-skilled workers typically fare in the UI system, estimating their likelihood of becoming eligible for and collecting benefits. We find that many workers who separate from a job, and particularly those with lower levels of skill, will not be compensated by the UI system. Although minimum earnings requirements keep some less-skilled job losers from receiving UI, it is the provision mandating that separations be involuntary that prevents most workers from gaining UI eligibility. These findings suggest that the UI system will provide little additional support to the safety net following welfare reform

Triple-Star Candidates Among the Kepler Binaries

We present the results of a search through the photometric database of eclipsing Kepler binaries (Prsa et al. 2011; Slawson et al. 2011) looking for evidence of hierarchical triple star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O-C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ~1/2-hour Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O-C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called "physical" delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O-C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions.Comment: 19 pages, 13 figures, 3 tables; ApJ, 2013, 768, 33; corrected Fig. 7, updated references, minor fixes to tex

Information about the Integer Quantum Hall Transition Extracted from the Autocorrelation Function of Spectral Determinants

The Autocorrelation function of spectral determinants (ASD) is used to probe the sensitivity of a two-dimensional disordered electron gas to the system's size L. For weak magnetic fields ASD is shown to depend only trivially on L, which is a strong indication that all states are localized. From nontrivial dependence of ASD on L for infinite L at a Hall conductance of 1/2 e^2/h we deduce the existence of critical wave functions at this point, as long as the disorder strength does not exceed a critical value.Comment: 4 pages, one citation correcte

Dynamic behavior of anisotropic non-equilibrium driving lattice gases

It is shown that intrinsically anisotropic non-equilibrium systems relaxing by a dynamic process exhibit universal critical behavior during their evolution toward non-equilibrium stationary states. An anisotropic scaling anzats for the dynamics is proposed and tested numerically. Relevant critical exponents can be evaluated self-consistently using both the short- and long-time dynamics frameworks. The obtained results allow us to clarify a long-standing controversy about the theoretical description, the universality and the origin of the anisotropy of driven diffusive systems, showing that the standard field theory does not hold and supporting a recently proposed alternative theory.Comment: 4 pages, 2 figure

A Nuclear Physics Program at the ATLAS Experiment at the CERN Large Hadron Collider

The ATLAS collaboration has significant interest in the physics of ultra-relativistic heavy ion collisions. We submitted a Letter of Intent to the United States Department of Energy in March 2002. The following document is a slightly modified version of that LOI. More details are available at: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/SM/ionsComment: Letter of Intent submitted to the United States Department of Energy Nuclear Physics Division in March 2002 (revised version

An exactly solvable dissipative transport model

We introduce a class of one-dimensional lattice models in which a quantity, that may be thought of as an energy, is either transported from one site to a neighbouring one, or locally dissipated. Transport is controlled by a continuous bias parameter q, which allows us to study symmetric as well as asymmetric cases. We derive sufficient conditions for the factorization of the N-body stationary distribution and give an explicit solution for the latter, before briefly discussing physically relevant situations.Comment: 7 pages, 1 figure, submitted to J. Phys.