Changes in the Distribution of Income Volatility

Recent research has documented a significant rise in the volatility (e.g., expected squared change) of individual incomes in the U.S. since the 1970s. Existing measures of this trend abstract from individual heterogeneity, effectively estimating an increase in average volatility. We decompose this increase in average volatility and find that it is far from representative of the experience of most people: there has been no systematic rise in volatility for the vast majority of individuals. The rise in average volatility has been driven almost entirely by a sharp rise in the income volatility of those expected to have the most volatile incomes, identified ex-ante by large income changes in the past. We document that the self-employed and those who self-identify as risk-tolerant are much more likely to have such volatile incomes; these groups have experienced much larger increases in income volatility than the population at large. These results color the policy implications one might draw from the rise in average volatility. While the basic results are apparent from PSID summary statistics, providing a complete characterization of the dynamics of the volatility distribution is a methodological challenge. We resolve these difficulties with a Markovian hierarchical Dirichlet process that builds on work from the non-parametric Bayesian statistics literature

WILDCOMS

Disease and contaminants can both pose major risks to wildlife and human populations. Disease is a natural driver regulating the dynamics of wildlife populations, but some diseases warrant particular attention because they (i) cause major mortalities that lead to population crashes, (eg., VHD in rabbits), (ii) threaten wildlife species of high conservation concern (for example squirrelpox virus in red squirrels), or (iii) pose a potential threat to Man (eg., rabies, avian influenza). The wildlife Disease & Contaminant Monoitoring and Surveillance (WILDCOMS) Network is a collaborative project among the major disease and contaminant monitoring schemes for vertebrate wildlife that operate in the United Kingdom. These schemes are run by various government agencies and laboratories, research centres, institutes, and academia. The overall aim is to establish a network which will foster and facilitate knowledge exchange, harmonisation towards best practice, and productive collaboration between: (i) partner organisations; (ii) surveillance schemes and end-users. It will aim to provide end-users with an integrated overview of environmental disease and contaminant risk. The specific objectives will be to develop the network and use it to address common challenges, specifically maximising dissemination of information to stakeholders and harmonisation towards common operational procedures to facilitate interaction and collaboration

The Galactic Center Isolated Nonthermal Filaments as Analogs of Cometary Plasma Tails

We propose a model for the origin of the isolated nonthermal filaments observed at the Galactic center based on an analogy to cometary plasma tails. We invoke the interaction between a large scale magnetized galactic wind and embedded molecular clouds. As the advected wind magnetic field encounters a dense molecular cloud, it is impeded and drapes around the cloud, ultimately forming a current sheet in the wake. This draped field is further stretched by the wind flow into a long, thin filament whose aspect ratio is determined by the balance between the dynamical wind and amplified magnetic field pressures. The key feature of this cometary model is that the filaments are dynamic configurations, and not static structures. As such, they are local amplifications of an otherwise weak field and not directly connected to any static global field. The derived field strengths for the wind and wake are consistent with observational estimates. Finally, the observed synchrotron emission is naturally explained by the acceleration of electrons to high energy by plasma and MHD turbulence generated in the cloud wake.Comment: Uses AAS aasms4.sty macros. ApJ (in press, vol. 521, 20 Aug

Approximation methods for combined thermal/structural design

Two approximation concepts for combined thermal/structural design are evaluated. The first concept is an approximate thermal analysis based on the first derivatives of structural temperatures with respect to design variables. Two commonly used first-order Taylor series expansions are examined. The direct and reciprocal expansions are special members of a general family of approximations, and for some conditions other members of that family of approximations are more accurate. Several examples are used to compare the accuracy of the different expansions. The second approximation concept is the use of critical time points for combined thermal and stress analyses of structures with transient loading conditions. Significant time savings are realized by identifying critical time points and performing the stress analysis for those points only. The design of an insulated panel which is exposed to transient heating conditions is discussed

Reviewing the problem of the U(1) axial symmetry and the chiral transition in QCD

We discuss the role of the U(1) axial symmetry for the phase structure of QCD at finite temperature. We expect that, above a certain critical temperature, also the U(1) axial symmetry will be (effectively) restored. We will try to see if this transition has (or has not) anything to do with the usual chiral transition: various possible scenarios are discussed. In particular, supported by recent lattice results, we analyse a scenario in which a U(1)-breaking condensate survives across the chiral transition. This scenario can be consistently reproduced using an effective Lagrangian model. The effects of the U(1) chiral condensate on the slope of the topological susceptibility in the full theory with quarks are studied: we find that this quantity (in the chiral limit of zero quark masses) acts as an order parameter for the U(1) axial symmetry above the chiral transition. Further information on the new U(1) chiral order parameter is derived from the study (at zero temperature) of the radiative decays of the pseudoscalar mesons in two photons: a comparison of our results with the experimental data is performed.Comment: 27 pages, LaTeX file. Completely revised version including new references and new comments on the result

Preparation of nondegenerate coherent superpositions in a three-state ladder system assisted by Stark Shifts

We propose a technique to prepare coherent superpositions of two nondegenerate quantum states in a three-state ladder system, driven by two simultaneous fields near resonance with an intermediate state. The technique, of potential application to enhancement of nonlinear processes, uses adiabatic passage assisted by dynamic Stark shifts induced by a third laser field. The method offers significant advantages over alternative techniques: (\i) it does not require laser pulses of specific shape and duration and (\ii) it requires less intense fields than schemes based on two-photon excitation with non-resonant intermediate states. We discuss possible experimental implementation for enhancement of frequency conversion in mercury atoms.Comment: 22 pages, 8 figures, 1 table, submitted to PHys. Rev.

Generalized molecular chaos hypothesis and H-theorem: Problem of constraints and amendment of nonextensive statistical mechanics

Quite unexpectedly, kinetic theory is found to specify the correct definition of average value to be employed in nonextensive statistical mechanics. It is shown that the normal average is consistent with the generalized Stosszahlansatz (i.e., molecular chaos hypothesis) and the associated H-theorem, whereas the q-average widely used in the relevant literature is not. In the course of the analysis, the distributions with finite cut-off factors are rigorously treated. Accordingly, the formulation of nonextensive statistical mechanics is amended based on the normal average. In addition, the Shore-Johnson theorem, which supports the use of the q-average, is carefully reexamined, and it is found that one of the axioms may not be appropriate for systems to be treated within the framework of nonextensive statistical mechanics.Comment: 22 pages, no figures. Accepted for publication in Phys. Rev.

Photoionization Suppression by Continuum Coherence: Experiment and Theory

We present experimental and theoretical results of a detailed study of laser-induced continuum structures (LICS) in the photoionization continuum of helium out of the metastable state 2s $^1S_0$. The continuum dressing with a 1064 nm laser, couples the same region of the continuum to the {4s $^1S_0$} state. The experimental data, presented for a range of intensities, show pronounced ionization suppression (by as much as 70% with respect to the far-from-resonance value) as well as enhancement, in a Beutler-Fano resonance profile. This ionization suppression is a clear indication of population trapping mediated by coupling to a contiuum. We present experimental results demonstrating the effect of pulse delay upon the LICS, and for the behavior of LICS for both weak and strong probe pulses. Simulations based upon numerical solution of the Schr\"{o}dinger equation model the experimental results. The atomic parameters (Rabi frequencies and Stark shifts) are calculated using a simple model-potential method for the computation of the needed wavefunctions. The simulations of the LICS profiles are in excellent agreement with experiment. We also present an analytic formulation of pulsed LICS. We show that in the case of a probe pulse shorter than the dressing one the LICS profile is the convolution of the power spectra of the probe pulse with the usual Fano profile of stationary LICS. We discuss some consequences of deviation from steady-state theory.Comment: 29 pages, 17 figures, accepted to PR

The effects of an extra U(1) axial condensate on the radiative decay eta' --> gamma gamma at finite temperature

Supported by recent lattice results, we consider a scenario in which a U(1)-breaking condensate survives across the chiral transition in QCD. This scenario has important consequences on the pseudoscalar-meson sector, which can be studied using an effective Lagrangian model. In particular, generalizing the results obtained in a previous paper (where the zero-temperature case was considered), we study the effects of this U(1) chiral condensate on the radiative decay eta' --> gamma gamma at finite temperature.Comment: 15 pages, LaTeX fil