37,990 research outputs found
Locally Adaptive Function Estimation for Binary Regression Models
In this paper we present a nonparametric Bayesian approach for fitting unsmooth or highly oscillating functions in regression models with binary responses. The approach extends previous work by Lang et al. (2002) for Gaussian responses. Nonlinear functions are modelled by first or second order random walk priors with locally varying variances or smoothing parameters. Estimation is fully Bayesian and uses latent utility representations of binary regression models for efficient block sampling from the full conditionals of nonlinear functions
Women, Work, and Motherhood: Changing Employment Penalties for Motherhood in West Germany after 1945 -- A Comparative Analysis of Cohorts Born in 1934-1971
This paper deals with the effects of entry into motherhood on women's employment dynamics. Our analysis is based on the complete lifetime working- and income histories of a 1% sample of all persons born between 1934 and 1971 and employed in West Germany sometime between 1975 and 1995. We use the records of women who were employed before the birth of their first child. We apply a semi-parametric hierarchical Bayesian modeling approach simultaneously including several time scales and further covariates whose effects we estimate by MCMC techniques. We investigate short-term consequences of entry into motherhood and their changes over different birth cohorts and thereby take into account the employment histories before the birth of the first child. We conduct two models differentiating between the simple return to the labor market and the return for at least a certain period in order to measure subsequent employment stability. Our results indicate that a higher extent of employment experience, a stronger attachment to the labor market and an employment in white collar jobs reduces the employment penalty for mothers after the birth of their first child
Green's and spectral functions of the small Frolich polaron
According to recent Quantum Monte Carlo simulations the small polaron theory
is practically exact in a wide range of the long-range (Frohlich)
electron-phonon coupling and adiabatic ratio. We apply the Lang-Firsov
transformation to convert the strong-coupling term in the Hamiltonian into the
form of an effective hopping integral and derive the single-particle Green's
function describing propagation of the small Frohlich polaron. One and two
dimensional spectral functions are studied by expanding the Green's function
perturbatively. Numerical calculations of the spectral functions are produced.
Remarkably, the coherent spectral weight (Z) and effective mass (Z')
renormalisation exponents are found to be different with Z'>>Z, which can
explain a small coherent spectral weight and a relatively moderate mass
enhancement in oxides.Comment: RevTeX, 5 pages, 2 postscript figures, LaTeX processing problems
correcte
Inclusion of new LHC data in MMHT PDFs
I consider the effects of including a variety of new LHC data sets into the
MMHT approach for PDF determination. I consider the impact of fitting new LHC
and Tevatron data, which leads to clear improvements in some PDF uncertainties.
There are specific issues with ATLAS 7 TeV jet data and I include a discussion
of the treatment of correlated uncertainties and briefly the effects of NNLO
corrections. I also present preliminary results with the inclusion of the high
precison final ATLAS 7 TeV rapidity-dependent data.Comment: 6 pages. To appear in proceedings of DIS2017 Worksho
Tilted-mirror semiconductor lasers
Broad-area GaAs heterostructure lasers with a tilted mirror were demonstrated for the first time, with the tilted mirror fabricated by etching. These lasers operate in a smooth and stable single lateral mode with a high degree of spatial coherence. The suppression of filamentation manifests itself in a high degree of reproducibility in the near-field pattern
Quantum phase transition in the Dicke model with critical and non-critical entanglement
We study the quantum phase transition of the Dicke model in the classical
oscillator limit, where it occurs already for finite spin length. In contrast
to the classical spin limit, for which spin-oscillator entanglement diverges at
the transition, entanglement in the classical oscillator limit remains small.
We derive the quantum phase transition with identical critical behavior in the
two classical limits and explain the differences with respect to quantum
fluctuations around the mean-field ground state through an effective model for
the oscillator degrees of freedom. With numerical data for the full quantum
model we study convergence to the classical limits. We contrast the classical
oscillator limit with the dual limit of a high frequency oscillator, where the
spin degrees of freedom are described by the Lipkin-Meshkov-Glick model. An
alternative limit can be defined for the Rabi case of spin length one-half, in
which spin frequency renormalization replaces the quantum phase transition.Comment: 1o pages, 10 figures, published versio
Wheel–rail contact: experimental study of the creep forces–creepage relationships
The wheel–rail contact problem plays an important role in the simulation methods used to solve railway dynamics problems. As a consequence, many different mathematical models have been developed to calculate wheel–rail contact forces. However, most of them tackle this problem purely from a theoretical point of view and need to be experimentally validated. Such validation could also reveal the influence of certain parameters not taken into account in the mathematical developments. This paper presents the steps followed in building a scaled test-bench to experimentally characterise the wheel–rail contact problem. The results of the longitudinal contact force as a function of the longitudinal creepage are obtained and the divergences with respect to Kalker's simplified theory are analysed. The influence of lateral creepage, angular velocity and certain contaminants such as cutting fluid or high positive friction modifier is also discussed
Updates of PDFs in the MSTW framework
I present results on updates on PDFs which are obtained within the general
framework which led to the MSTW2008 PDF sets. There are some theory and
procedural improvements and a variety of new data sets, including many relevant
up-to-date LHC data. A new set of PDFs is very close to being finalised, with
no significant changes expected to the preliminary PDFs shown here.Comment: 6 pages, 6 figures,Published in PoS DIS (2014
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Low-energy models for correlated materials: bandwidth renormalization from Coulombic screening
We provide a prescription for constructing Hamiltonians representing the low
energy physics of correlated electron materials with dynamically screened
Coulomb interactions. The key feature is a renormalization of the hopping and
hybridization parameters by the processes that lead to the dynamical screening.
The renormalization is shown to be non-negligible for various classes of
correlated electron materials. The bandwidth reduction effect is necessary for
connecting models to materials behavior and for making quantitative predictions
for low-energy properties of solids.Comment: 4 pages, 2 figure
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