Current and entanglement in a Bose-Hubbard lattice

We study the generation of entanglement for interacting cold atoms in an optical lattice. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The thermalization process between the species is also shown to be closely related to the evolution of the current.Comment: 10 pages, 5 figure

Geometric quantum discord with Bures distance: the qubit case

The minimal Bures distance of a quantum state of a bipartite system AB to the set of classical states for subsystem A defines a geometric measure of quantum discord. When A is a qubit, we show that this geometric quantum discord is given in terms of the eigenvalues of a (2 n_B) x (2 n_B) hermitian matrix, n_B being the Hilbert space dimension of the other subsystem B. As a first application, we calculate the geometric discord for the output state of the DQC1 algorithm. We find that it takes its highest value when the unitary matrix from which the algorithm computes the trace has its eigenvalues uniformly distributed on the unit circle modulo a symmetry with respect to the origin. As a second application, we derive an explicit formula for the geometric discord of two-qubit states with maximally mixed marginals and compare it with other measures of quantum correlations. We also determine the closest classical states to such two-qubit states.Comment: This article contains some material from a previous preprint arXiv:1304.3334v1 [quant-ph], which has been split into two parts, as well as new results. Minor changes in the second version with respect to the first version. 14 pages, 5 figure

Prediction of compliant wall drag reduction, part 1

Computer codes developed to test Bushnell's compliant wall drag reduction model are discussed. One code computes the evolution of mean velocity profiles during the period between bursts as forced by an imposed large-scale pressure pulse due to earlier bursts. Another code computes the local stability characteristics of these computed profiles. The programs use Chebyshev polynomials to resolve the normal boundary layer (y) direction and a staggered grid of mesh points to resolve the x direction. Typically, 257 grid points and 33 Chebyshev polynomials are used in the computations

Prediction of compliant wall drag reduction, part 2

A numerical model of turbulent boundary layer flows over compliant walls was investigated. The model is based on Burton's observation that outer flow structures in turbulent boundary layers produce large scale pressure fluctuations near the wall. The results of calculations indicate that certain small wavelength wall motions can have a significant effect upon the stability of turbulent boundary layers

Stability analysis for laminar flow control, part 2

Topics covered include: (1) optimization of the numerics of the SALLY stability analysis code; (2) relation between temporal and spatial stability theory; (3) compressible flow stability calculations; (4) spectral methods for the boundary layer equations; and (5) numerical study of nonlinear, nonparallel stability of incompressible flows

Hispanics and the Current Economic Downturn: Will the Receding Tide Sink Hispanics?

Explores the progress made by Hispanics during the economic boom of the 1990s, and examines the potential impact of the 2001/2002 economic slowdown on Hispanic workers and families

Does the Social Security Earnings Test Affect Labor Supply and Benefits Receipt?

The Social Security earnings test, a version of which still applies to those ages 62-64, reduces immediate payments to beneficiaries whose labor income exceeds a given threshold. Although benefits are subsequently increased to compensate for any such reduction, the earnings test is typically perceived as a tax on working. As a result, it is considered by many to be an important disincentive to paid work for older Americans. Yet there is little evidence to suggest an economically significant effect of the earnings test on hours of work, and almost no research on the effect of the test on the decision to work at all. We investigate these issues using the significant changes in the structure of the earnings test over the past 25 years, using data over the past 25 years, using data over the 1973-1998 period from the March Supplement to the Current Population Survey (CPS), which provide large samples of observations on the elderly. Our analysis suggests two major conclusions. First, the earnings test exerts no robust influence on the labor supply decisions of men. Neither graphical analyses of breaks in labor supply trends, nor regression estimates that control for underlying trends in labor supply by age group, reveal any significant impact of changes in earnings test parameters on aggregate employment, hours of work, or earnings for men. For women, there is more suggestive evidence that the earnings test is affecting labor supply decisions. Second, loosening the earnings test appears to accelerate benefits receipt among the eligible population, lowering benefits levels, and heightening concerns about the standard of living of these elderly at very advanced ages. Our findings suggest some cause for caution before rushing to remove the earnings test at younger ages.