5,389 research outputs found
Dynamic Modelling of Child Mortality in Developing Countries: Application for Zambia
In this paper, we analyse the causes of under five mortality in Zambia, with a particular emphasis on assessing possible time-variations in the effects of covariates, i.e. whether the effects of certain covariates vary with the age of the child. The analysis is based on micro data from the 1992 Demographic and health Survey. Employing a Bayesian dynamic logit model for discrete time survival data and Markov-Chain Monte Carlo methods, we find that there are several variables, including the age of the mother and the breastfeeding duration whose effects exhibit distinct age-dependencies. In the case of breastfeeding, this age dependency is intimately linked with the reasons for stopping breastfeeding. Incorporating such age dependencies greatly improves the explanatory power of the model and yields new insights on the differential role of covariates on child survival
Analysis of the time to sustained progression in Multiple Sclerosis using generalised linear and additive models
The course of multiple sclerosis (MS) is generally difficult to predict. This is due to the great inter-individual variability with respect to symptoms and disability status. An important prognostic endpoint for MS is the expected time to sustained disease progression. Using the Expanded Disability Status Scale (EDSS) this endpoint is here defined as a rise of 1.0 or 0.5 compared to baseline EDSS (5.5) which is confirmed for at least six months. The goal of this paper was threefold. It aimed at identifying covariates which significantly influence sustained progression, determining size and form of the effect of these covariates and estimating the survival curves for given predictors. To this end a piecewise exponential model utilizing piecewise constant hazard rates and a Poisson model were devised. In order to improve and simplify these models a method for piecewise linear parameterization of non-parametric generalized additive models (GAMs) was applied. The models included fixed and random effects, the posterior distribution was estimated using Markov Chain Monte Carlo methods (MCMC) as well as a penalized likelihood approach and variables were selected using Akaikes information criterium (AIC). The models were applied to data of placebo patients from worldwide clinical trials that are pooled in the database of the Sylvia Lawry Centre for Multiple Sclerosis Research (SLCMSR). Only with a pure exponential model and fixed effects, baseline EDSS and the number of relapses in the last 12 month before study entry had an effect on the hazard rate. For the piecewise exponential model with random study effects there was no effect of covariates on the hazard rate other than a slightly decreasing effect of time. This reflects the fact that unstable patients reach the event early and are therefore eliminated from the analysis (selection effect)
Entanglement of mechanical oscillators coupled to a non-equilibrium environment
Recent experiments aim at cooling nanomechanical resonators to the ground
state by coupling them to non-equilibrium environments in order to observe
quantum effects such as entanglement. This raises the general question of how
such environments affect entanglement. Here we show that there is an optimal
dissipation strength for which the entanglement between two coupled oscillators
is maximized. Our results are established with the help of a general framework
of exact quantum Langevin equations valid for arbitrary bath spectra, in and
out of equilibrium. We point out why the commonly employed Lindblad approach
fails to give even a qualitatively correct picture
Intrinsically Legal-For-Trade Objects by Digital Signatures
The established techniques for legal-for-trade registration of weight values
meet the legal requirements, but in praxis they show serious disadvantages. We
report on the first implementation of intrinsically legal-for-trade objects,
namely weight values signed by the scale, that is accepted by the approval
authority. The strict requirements from both the approval- and the
verification-authority as well as the limitations due to the hardware of the
scale were a special challenge. The presented solution fulfills all legal
requirements and eliminates the existing practical disadvantages.Comment: 4 pages, 0 figure
Ptychographic reconstruction of attosecond pulses
We demonstrate a new attosecond pulse reconstruction modality which uses an
algorithm that is derived from ptychography. In contrast to other methods,
energy and delay sampling are not correlated, and as a result, the number of
electron spectra to record is considerably smaller. Together with the robust
algorithm, this leads to a more precise and fast convergence of the
reconstruction.Comment: 12 pages, 7 figures, the MATLAB code for the method described in this
paper is freely available at
http://figshare.com/articles/attosecond_Extended_Ptychographyc_Iterative_Engine_ePIE_/160187
Nonequilibrium Landau-Zener-Stuckelberg spectroscopy in a double quantum dot
We study theoretically nonequilibrium Landau-Zener-St\"uckelberg (LZS)
dynamics in a driven double quantum dot (DQD) including dephasing and,
importantly, energy relaxation due to environmental fluctuations. We derive
effective nonequilibrium Bloch equations. These allow us to identify clear
signatures for LZS oscilations observed but not recognized as such in
experiments [Petersson et al., Phys. Rev. Lett. 105, 246804, 2010] and to
identify the full environmental fluctuation spectra acting on a DQD given
experimental data as in [Petersson et al., Phys. Rev. Lett. 105, 246804, 2010].
Herein we find that super-Ohmic fluctuations, typically due to phonons, are the
main relaxation channel for a detuned DQD whereas Ohmic fluctuations dominate
at zero detuning.Comment: 5 pages, 4 figure
Einsatz des digitalen kieferorthopädischen Präsenz-Archivs 'DokuInforma' in Lehre und Weiterbildung
The End Of Nucleosynthesis: Production Of Lead And Thorium In The Early Galaxy
We examine the Pb and Th abundances in 27 metal-poor stars (-3.1 56) enrichment was produced only by the rapid (r-) nucleosynthesis process. New abundances are derived from Hubble Space Telescope/Space Telescope Imaging Spectrograph, Keck/High Resolution Echelle Spectrograph, and Very Large Telescope/UV-Visual Echelle Spectrograph spectra and combined with other measurements from the literature to form a more complete picture of nucleosynthesis of the heaviest elements produced in the r-process. In all cases, the abundance ratios among the rare earth elements and the third r-process peak elements considered (La, Eu, Er, Hf, and Ir) are constant and equivalent to the scaled solar system r-process abundance distribution. We compare the stellar observations with r-process calculations within the classical "waiting-point" approximation. In these computations a superposition of 15 weighted neutron-density components in the range 23 <= log n(n) <= 30 is fit to the r-process abundance peaks to successfully reproduce both the stable solar system isotopic distribution and the stable heavy element abundance pattern between Ba and U in low-metallicity stars. Under these astrophysical conditions, which are typical of the "main" r-process, we find very good agreement between the stellar Pb r-process abundances and those predicted by our model. For stars with anomalously high Th/Eu ratios (the so-called actinide boost), our observations demonstrate that any nucleosynthetic deviations from the main r-process affect-at most-only the elements beyond the third r-process peak, namely Pb, Th, and U. Our theoretical calculations also indicate that possible r-process abundance "losses" by nuclear fission are negligible for isotopes along the r-process path between Pb and the long-lived radioactive isotopes of Th and U.Deutsche Forschungsgemeinschaft KR 806/13-1Helmholtz Gemeinschaft VH-VI-061U S National Science Foundation AST 07-07447, AST 06-07708Astronom
Single-photon optomechanics in the strong coupling regime
We give a theoretical description of a coherently driven opto-mechanical
system with a single added photon. The photon source is modeled as a cavity
which initially contains one photon and which is irreversibly coupled to the
opto-mechanical system. We show that the probability for the additional photon
to be emitted by the opto-mechanical cavity will exhibit oscillations under a
Lorentzian envelope, when the driven interaction with the mechanical resonator
is strong enough. Our scheme provides a feasible route towards quantum state
transfer between optical photons and micromechanical resonators.Comment: 14 pages, 6 figure
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