Semiclassical theory of the tunneling anomaly in partially spin-polarized compressible quantum Hall states

Electron tunneling into a system with strong interactions is known to exhibit an anomaly, in which the tunneling conductance vanishes continuously at low energy due to many-body interactions. Recent measurements have probed this anomaly in a quantum Hall bilayer of the half-filled Landau level, and shown that the anomaly apparently gets stronger as the half-filled Landau level is increasingly spin polarized. Motivated by this result, we construct a semiclassical hydrodynamic theory of the tunneling anomaly in terms of the charge-spreading action associated with tunneling between two copies of the Halperin-Lee-Read state with partial spin polarization. This theory is complementary to our recent work (arXiv:1709.06091) where the electron spectral function was computed directly using an instanton-based approach. Our results show that the experimental observation cannot be understood within conventional theories of the tunneling anomaly, in which the spreading of the injected charge is driven by the mean-field Coulomb energy. However, we identify a qualitatively new regime, in which the mean-field Coulomb energy is effectively quenched and the tunneling anomaly is dominated by the finite compressibility of the composite Fermion liquid.Comment: 24 pages, 2 figures; Final published versio

How Will Defined Contribution Pension Plans Affect Retirement Income?

How has the emergence of defined contribution pension plans, such as 401(k)s, affected the financial security of future retirees? We consider this question using a detailed survey of pension formulas in the Survey of Consumer Finances. Our simulations show that average and median pension benefits are higher under defined contribution plans that for defined benefit plans. Defined benefit plans are slightly better at providing minimum benefits, but for plausible values of risk aversion, a defined contribution plan drawn randomly from those available in 1995 is still preferred to a defined benefit plan drawn randomly from those available in 1983. This result is robust to different assumptions regarding the spending of defined contribution balances between jobs, equity rates of return, and the date of retirement. In short, we suggest that defined contribution plans can strengthen the financial security of retirees.

A Rich Population of X-ray Emitting Wolf-Rayet Stars in the Galactic Starburst Cluster Westerlund 1

Recent optical and IR studies have revealed that the heavily-reddened starburst cluster Westerlund 1 (Wd 1) contains at least 22 Wolf-Rayet (WR) stars, comprising the richest WR population of any galactic cluster. We present results of a senstive Chandra X-ray observation of Wd 1 which detected 12 of the 22 known WR stars and the mysterious emission line star W9. The fraction of detected WN stars is nearly identical to that of WC stars. The WN stars WR-A and WR-B as well as W9 are exceptionally luminous in X-rays and have similar hard heavily-absorbed spectra with strong Si XIII and S XV emission lines. The luminous high-temperature X-ray emission of these three stars is characteristic of colliding wind binary systems but their binary status remains to be determined. Spectral fits of the X-ray bright sources WR-A and W9 with isothermal plane-parallel shock models require high absorption column densities log N$_{H}$ = 22.56 (cm$^{-2}$) and yield characteristic shock temperatures kT_shock ~ 3 keV (T ~ 35 MK).Comment: ApJL, 2006, in press (3 figures, 1 table

Should One Use the Ray-by-Ray Approximation in Core-Collapse Supernova Simulations?

We perform the first self-consistent, time-dependent, multi-group calculations in two dimensions (2D) to address the consequences of using the ray-by-ray+ transport simplification in core-collapse supernova simulations. Such a dimensional reduction is employed by many researchers to facilitate their resource-intensive calculations. Our new code (F{\sc{ornax}}) implements multi-D transport, and can, by zeroing out transverse flux terms, emulate the ray-by-ray+ scheme. Using the same microphysics, initial models, resolution, and code, we compare the results of simulating 12-, 15-, 20-, and 25-M$_{\odot}$ progenitor models using these two transport methods. Our findings call into question the wisdom of the pervasive use of the ray-by-ray+ approach. Employing it leads to maximum post-bounce/pre-explosion shock radii that are almost universally larger by tens of kilometers than those derived using the more accurate scheme, typically leaving the post-bounce matter less bound and artificially more "explodable." In fact, for our 25-M$_{\odot}$ progenitor, the ray-by-ray+ model explodes, while the corresponding multi-D transport model does not. Therefore, in two dimensions the combination of ray-by-ray+ with the axial sloshing hydrodynamics that is a feature of 2D supernova dynamics can result in quantitatively, and perhaps qualitatively, incorrect results.Comment: Updated and revised text; 13 pages; 13 figures; Accepted to Ap.

DIVERSIFICATION OF REGIONAL MARKETING COOPERATIVES

Agribusiness, Marketing,

The Resolution of the Labor Scarcity Paradox

This paper reconciles the apparently contradictory evidence about American and British technology in the first half of the nineteenth century. Past studies have focused on the writings of a number of distinguished British engineers, who toured the United States during the 1850s and commented extensively on the highly mechanized state of the manufacturing sector. Other studies, however, have marshalled evidence that the interest rate was higher, and the aggregate manufacturing capital stock was lower, in the United States relative to Britain. We resolve this paradox by noting that British engineers were most impressed by only a few industries which relied on skilled workers. Using the 1849 Census of Manufactures, we estimate separate production functions for the skilled sector and for the remaining, less skilled manufacturing sector. We find strong relative complementarity between capital and natural resources in the skilled sector, and relative substitutability between skilled labor and capital. Using these parameters in a computable general equilibrium model of the U.S. and British economies indicates greater capital intensity (or labor scarcity) in the skilled manufacturing sector, but overall capital scarcity and higher interest rates, in the U.S. relative to Britain.

Connections of the Mesencephalic Locomotor Region (MLR) in the Cat

The cat entopeduncular nucleus (EN), which is the main output of the basal ganglia, is known to project to the mesencephalic tegmentum. We have been able to elicit antidromic responses in single EN neurons from the region of the mesencephalic locomotor region (MLR), then transect (precollicular-postmamillary) the brainstem and elicit rhythmic movements of the limbs by stimulation of the same site in the same animal. Injections of the fluorescent dye 2,4 diamidino phenylindole 2 HCL (DAPI) into this area induces retrograde labeling of cell bodies in EN and motor cortex. Injections of a tritiated amino acid (leucine) into the motor cortex induce terminal labeling in the area of the MLR. These studies describe convergent projections from EN and motor cortex to the MLR. These connections may be involved in the sequencing and ordering of voluntary movements in which locomotion is necessary

Local Volume Effects in the Generalized Pseudopotential Theory

The generalized pseudopotential theory (GPT) is a powerful method for deriving real-space transferable interatomic potentials. Using a coarse-grained electronic structure, one can explicitly calculate the pair ion-ion and multi-ion interactions in simple and transition metals. Whilst successful in determining bulk properties, in central force metals the GPT fails to describe crystal defects for which there is a significant local volume change. A previous paper [PhysRevLett.66.3036 (1991)] found that by allowing the GPT total energy to depend upon some spatially-averaged local electron density, the energetics of vacancies and surfaces could be calculated within experimental ranges. In this paper, we develop the formalism further by explicitly calculating the forces and stress tensor associated with this total energy. We call this scheme the adaptive GPT (aGPT) and it is capable of both molecular dynamics and molecular statics. We apply the aGPT to vacancy formation and divacancy binding in hcp Mg and also calculate the local electron density corrections to the bulk elastic constants and phonon dispersion for which there is refinement over the baseline GPT treatment.Comment: 11 pages, 6 figure