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Electrical tree structures generated by the ab-initio discharge-avalanche model
Initially the discharge-avalanche model for electrical tree formation treated the local Poisson fields as being derived from the applied Laplace field via a modification factor that was regarded as a random variable in time and space. Recently we have removed this approximation by calculating the local Poisson fields from the space charge arrangement produced by discharges in the tree tubules and avalanches in the surrounding polymer. This “ab-initio” version of the model has now been fully implemented. The ac-cycle is divided into 16 time segments. In each time segment tube-discharges are allowed to occur if the potential difference along a tube is greater than an onset threshold. Positive space charge is regarded as being deposited on the tube walls in the form of positive ions. Negative charge is allowed to penetrate the polymer where it can be used to initiate avalanches and thereby generate damage. The avalanches compete with a field dependant mobility in rearranging the charge around the tree tips
Aging and Labor Force Participation: A Review of Trends and Explanations
The American population is aging rapidly. Persons 65 and over who now constitute about one-fifth of the population will constitute about two-fifths of the population by 2040. In addition, individuals are living longer. Yet the labor force participation of older Americans has fallen dramatically in recent years. This paper discusses this trend and the principal arguments put forth to explain it. The paper is in two parts. The first part reviews trends in labor force participation and associated trends in Social Security (SS) coverage, firm pension plan coverage, and other factors that are likely to be associated with the labor force participation trends, including demographics. The second part of the paper discusses the incentive effects of SS and retirement plans, with emphasis on firm pension plans.
X ray opacity in cluster cooling flows
We have calculated the emergent x-ray properties for a set of spherically symmetric, steady-state cluster cooling flow models including the effects of radiative transfer. Opacity due to resonant x-ray lines, photoelectric absorption, and electron scattering have been included in these calculations, and homogeneous and inhomogeneous gas distributions were considered. The effects of photoionization opacity are small for both types of models. In contrast, resonant line optical depths can be quite high in both homogeneous and inhomogeneous models. The presence of turbulence in the gas can significantly lower the line opacity. We find that integrated x-ray spectra for the flow cooling now are only slightly affected by radiative transfer effects. However x-ray line surface brightness profiles can be dramatically affected by radiative transfer. Line profiles are also strongly affected by transfer effects. The combined effects of opacity and inflow cause many of the lines in optically thick models to be asymmetrical
Top-Quark Mass and Bottom-Quark Decay
The possibility of a long B-meson lifetime is explored, in which case the weak mixing angles θ_2 and θ_3 are quite small. This allows the derivation of a lower bound on the top-quark mass as a function of the B-meson lifetime, by comparison of the short-distance prediction for the CP-nonconservation parameter ε with its experimental value. The bound is significant for τ_B>4×10^(-13) s
Using deep learning to understand and mitigate the qubit noise environment
Understanding the spectrum of noise acting on a qubit can yield valuable
information about its environment, and crucially underpins the optimization of
dynamical decoupling protocols that can mitigate such noise. However,
extracting accurate noise spectra from typical time-dynamics measurements on
qubits is intractable using standard methods. Here, we propose to address this
challenge using deep learning algorithms, leveraging the remarkable progress
made in the field of image recognition, natural language processing, and more
recently, structured data. We demonstrate a neural network based methodology
that allows for extraction of the noise spectrum associated with any qubit
surrounded by an arbitrary bath, with significantly greater accuracy than the
current methods of choice. The technique requires only a two-pulse echo decay
curve as input data and can further be extended either for constructing
customized optimal dynamical decoupling protocols or for obtaining critical
qubit attributes such as its proximity to the sample surface. Our results can
be applied to a wide range of qubit platforms, and provide a framework for
improving qubit performance with applications not only in quantum computing and
nanoscale sensing but also in material characterization techniques such as
magnetic resonance.Comment: Accepted for publication, 15 pages, 10 figure
Late Pop III Star Formation During the Epoch of Reionization: Results from the Renaissance Simulations
We present results on the formation of Pop III stars at redshift 7.6 from the
Renaissance Simulations, a suite of extremely high-resolution and physics-rich
radiation transport hydrodynamics cosmological adaptive-mesh refinement
simulations of high redshift galaxy formation performed on the Blue Waters
supercomputer. In a survey volume of about 220 comoving Mpc, we found 14
Pop III galaxies with recent star formation. The surprisingly late formation of
Pop III stars is possible due to two factors: (i) the metal enrichment process
is local and slow, leaving plenty of pristine gas to exist in the vast volume;
and (ii) strong Lyman-Werner radiation from vigorous metal-enriched star
formation in early galaxies suppresses Pop III formation in ("not so") small
primordial halos with mass less than 3 10 M. We
quantify the properties of these Pop III galaxies and their Pop III star
formation environments. We look for analogues to the recently discovered
luminous Ly emitter CR7 (Sobral et al. 2015), which has been
interpreted as a Pop III star cluster within or near a metal-enriched star
forming galaxy. We find and discuss a system similar to this in some respects,
however the Pop III star cluster is far less massive and luminous than CR7 is
inferred to be.Comment: 8 pages, 4 figures, 3 tables. Accepted by Ap
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