Peso Acceptance Patterns in El Paso

This paper examines the acceptance of peso payments, or currency substitution reverse dollarization, by U.S retail firms near the international border with Mexico. Survey data are drawn from a stratified random sample of 586 retailers located in El Paso, Texas, situated across the border from Ciudad Juarez, Chihuahua, Mexico. Approximately 13 percent of the participant firms accept Mexican pesos in exchange for goods and services. Empirical results indicate that factors such as a firm’s percentage of Spanish speaking employees and distance to the nearest international bridge significantly influence the decision to accept or reject Mexican pesos.Currency Substitution; Mexican Peso; Border Economics; Probit Models

Procrustean Motherhood: The Good Mother during Depression (1930s), War (1940s), and Prosperity (1950s)

Women have long considered home making, parenting, and fashion magazines, addressed directly to them, to be a trusted source for advice and for models of behavior. This trust is problematic given that sample magazine articles from the 1930s, 1940s, and 1950s show cultural portrayals of motherhood that appear more proscriptive than descriptive. They changed little, although real women’s roles in both the domestic and public realms were undergoing significant shifts. During these decades of Great Depression, World War II, and unprecedented post-war prosperity, women went to school and entered the workplace in growing numbers, changed their reproductive choices, and shifted their decisions to marry and divorce, living more of their lives independent of matrimony. All the while, popular culture’s discourse on the Good Mother held to the same sweet but increasingly stale portrait that failed to address the changes in women’s lives beyond the glossy page

Distortion of the Stoner-Wohlfarth astroid by a spin-polarized current

The Stoner-Wohlfarth astroid is a fundamental object in magnetism. It separates regions of the magnetic field space with two stable magnetization equilibria from those with only one stable equilibrium and it characterizes the magnetization reversal of nano-magnets induced by applied magnetic fields. On the other hand, it was recently demonstrated that transfer of spin angular momentum from a spin-polarized current provides an alternative way of switching the magnetization. Here, we examine the astroid of a nano-magnet with uniaxial magnetic anisotropy under the combined influence of applied fields and spin-transfer torques. We find that spin-transfer is most efficient at modifying the astroid when the external field is applied along the easy-axis of magnetization. On departing from this situation, a threshold current appears below which spin-transfer becomes ineffective yielding a current-induced dip in the astroid along the easy-axis direction. An extension of the Stoner-Wohlfarth model is outlined which accounts for this phenomenon.Comment: 8 pages, 6 figure

Frustration Driven Stripe Domain Formation in Co/Pt Multilayer Films

We report microscopic mechanisms for an unusual magnetization reversal behavior in Co/Pt multilayers where some of the first-order reversal curves protrude outside of the major loop. Transmission x-ray microscopy reveals a fragmented stripe domain topography when the magnetic field is reversed prior to saturation, in contrast to an interconnected pattern when reversing from a saturated state. The different domain nucleation and propagation behaviors are due to unannihilated domains from the prior field sweep. These residual domains contribute to random dipole fields that impede the subsequent domain growth and prevent domains from growing as closely together as for the interconnected pattern.Comment: 13 pages, 3 figures, to appear in AP

Does the Brief Self-Control Scale Assess Relatively Stable Individual Differences in Self-Control Among Endurance Athletes?

Endurance athletes are a population where self-control in the form of following training plans, race plans, and pacing schedules is key to performing successfully. A valid and stable measure of self-control has theoretical and applied value through the ability to identify athletes who might be susceptible to poor self-control. The present study reports the test-retest stability of the Brief Self-Control Scale (BSCS). 132 endurance athletes (18-65 years) completed the 13-item BSCS on two occasions, separated by two weeks. Stability was measured by calculating the test-retest differences for each questionnaire item, with a stable item showing 90% of respondents’ test-retest differences within a reference value of ±1. Analyses revealed seven items to be stable with the question, Q11 = “I am able to work effectively toward long-term goals”, demonstrating greatest stability (96.3%). In contrast, six items showed relatively poor stability with test-retest difference scores ranging from 83.4-89.4%. Chi-square tests of independence revealed no associations with categorical levels of age, gender, sport, and training habits. In the context of the current findings, we argue that the six unstable items do not represent dispositional self-control behaviours among endurance athletes. Future researchers are encouraged to assess the stability of individual items rather than favoring a summary statistic, particularly when developing trait measures

FUSE observations of HD 5980: The wind structure of the eruptor

HD 5980 is a unique system containing one massive star (star A) that is apparently entering the luminous blue variable phase, and an eclipsing companion (star B) that may have already evolved beyond this phase to become a Wolf-Rayet star. In this paper we present the results from FUSE observations obtained in 1999, 2000, and 2002 and one far-UV observation obtained by ORFEUS/BEFS in 1993 shortly before the first eruption of HD 5980. The eight phase-resolved spectra obtained by FUSE in 2002 are analyzed in the context of a wind-eclipse model. This analysis shows that the wind of the eruptor obeyed a very fast velocity law in 2002, which is consistent with the line-driving mechanism. Large amplitude line-profile variations on the orbital period are shown to be due to the eclipse of star B by the wind of star A, although the eclipse due to gas flowing in the direction of star B is absent. This can only be explained if the wind of star A is not spherically symmetric, or if the eclipsed line radiation is "filled-in" by emission originating from somewhere else in the system, e.g., in the wind-wind collision region. Except for a slightly lower wind speed, the ORFEUS/BEFS spectrum is very similar to the spectrum obtained by FUSE at the same orbital phase: there is no indication of the impending eruption. However, the trend for decreasing wind velocity suggests the occurrence of the "bi-stability" mechanism, which in turn implies that the restructuring of the circumbinary environment caused by the transition from "fast, rarefied wind" to "slow, dense wind" was observed as the eruptive event. The underlying mechanism responsible for the long-term decrease in wind velocity that precipitated this change remains an open issue.Comment: 19 pages, 13 figure

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

We observed NGC 1624-2, the O-type star with the largest known magnetic field Bp~20 kG), in X-rays with the ACIS-S camera onboard the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Halpha emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterise the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are: (i) The observed spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star Theta 1 Ori C, with only a few photons detected below 0.8 keV. The emergent X-ray flux is 30% lower at the Halpha minimum phase. (ii) Our modelling indicated that this seemingly hard spectrum is in fact a consequence of relatively soft intrinsic emission, similar to other magnetic Of?p stars, combined with a large amount of local absorption (~1-3 x 10^22 cm^-2). This combination is necessary to reproduce both the prominent Mg and Si spectral features, and the lack of flux at low energies. NGC 1624-2 is intrinsically luminous in X-rays (log LX emission ~ 33.4) but 70-95% of the X-ray emission produced by magnetically confined wind shocks is absorbed before it escapes the magnetosphere (log LX ISM corrected ~ 32.5). (iii) The high X-ray luminosity, its variation with stellar rotation, and its large attenuation are all consistent with a large dynamical magnetosphere with magnetically confined wind shocks.Comment: Accepted in MNRAS 13 pages, 10 figures, 4 table

Chandra X-Ray Spectroscopy Of The Very Early O Supergiant HD 93129A: Constraints On Wind Shocks And The Mass-Loss Rate

We present an analysis of both the resolved X-ray emission-line profiles and the broad-band X-ray spectrum of the O-2 If* star HD 93129A, measured with the Chandra High Energy Transmission Grating Spectrometer ( HETGS). This star is among the earliest and most massive stars in the Galaxy, and provides a test of the embedded wind-shock scenario in a very dense and powerful wind. A major new result is that continuum absorption by the dense wind is the primary cause of the hardness of the observed X-ray spectrum, while intrinsically hard emission from colliding wind shocks contributes less than 10 per cent of the X-ray flux. We find results consistent with the predictions of numerical simulations of the line-driving instability, including line broadening indicating an onset radius of X-ray emission of several tenths of R-*. Helium-like forbidden-to-intercombination line ratios are consistent with this onset radius, and inconsistent with being formed in a wind-collision interface with the star\u27s closest visual companion at a distance of 100 au. The broad-band X-ray spectrum is fitted with a dominant emission temperature of just kT = 0.6 keV along with significant wind absorption. The broad-band wind absorption and the line profiles provide two independent measurements of the wind mass-loss rate:. M = 5.2(-1.5)(+1.8) x 10(-6) and 6.8(-2.2)(+2.8) x 10(-6) M-circle dot yr(-1), respectively. This is the first consistent modelling of the X-ray line-profile shapes and broad-band X-ray spectral energy distribution in a massive star, and represents a reduction of a factor of 3-4 compared to the standard H alpha mass-loss rate that assumes a smooth wind

Modeling Ultraviolet Wind Line Variability in Massive Hot Stars

We model the detailed time-evolution of Discrete Absorption Components (DACs) observed in P Cygni profiles of the Si IV lam1400 resonance doublet lines of the fast-rotating supergiant HD 64760 (B0.5 Ib). We adopt the common assumption that the DACs are caused by Co-rotating Interaction Regions (CIRs) in the stellar wind. We perform 3D radiative transfer calculations with hydrodynamic models of the stellar wind that incorporate these large-scale density- and velocity-structures. We develop the 3D transfer code Wind3D to investigate the physical properties of CIRs with detailed fits to the DAC shape and morphology. The CIRs are caused by irregularities on the stellar surface that change the radiative force in the stellar wind. In our hydrodynamic model we approximate these irregularities by circular symmetric spots on the stellar surface. We use the Zeus3D code to model the stellar wind and the CIRs, limited to the equatorial plane. We constrain the properties of large-scale wind structures with detailed fits to DACs observed in HD 64760. A model with two spots of unequal brightness and size on opposite sides of the equator, with opening angles of 20 +/- 5 degr and 30 +/- 5 degr diameter, and that are 20 +/- 5 % and 8 +/- 5 % brighter than the stellar surface, respectively, provides the best fit to the observed DACs. The recurrence time of the DACs compared to the estimated rotational period corresponds to spot velocities that are 5 times slower than the rotational velocity. The mass-loss rate of the structured wind model for HD 64760 does not exceed the rate of the spherically symmetric smooth wind model by more than 1 %. The fact that DACs are observed in a large number of hot stars constrains the clumping that can be present in their winds, as substantial amounts of clumping would tend to destroy the CIRs.Comment: 58 pages, 16 figures, 1 animation. Accepted for publication in The Astrophysical Journal, Main Journal. More information and animations are available at http://alobel.freeshell.org/hotstars.htm

Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers

Proximity effects of 20 \AA thin Fe layers on the spin density waves (SDWs) in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk Cr we observe a SDW with its wave vector Q pointing along only one {100} direction which depends dramatically on the film thickness t_{Cr}. For t_{Cr} < 250 \AA the SDW propagates out-of-plane with the spins in the film plane. For t_{Cr} > 1000 \AA the SDW propagates in the film plane with the spins out-of-plane perpendicular to the in-plane Fe moments. This reorientation transition is explained by frustration effects in the antiferromagnetic interaction between Fe and Cr across the Fe/Cr interface due to steps at the interface.Comment: 4 pages (RevTeX), 3 figures (EPS