Beyond the Border Buildup: Towards a New Approach to Mexico-U.S. Migration

A proper understanding of the causes of international migration suggests that punitive immigration and border policies tend to backfire, and this is precisely what has happened in the case of the United States and Mexico. Rather than raising the odds that undocumented immigrants will be apprehended, U.S. border-enforcement policies have reduced the apprehension rate to historical lows and in the process helped transform Mexican immigration from a regional to a national phenomenon. The solution to the problems associated with undocumented migration is not open borders, but frontiers that are reasonably regulated on a binational basis

Commentary on "Trajectories for the immigrant second generation in New York City"

This article is commentary on a paper presented at a conference organized by the Federal Reserve Bank of New York in April 2005, "Urban Dynamics in New York City." The goal of the conference was threefold: to examine the historical transformations of the engine-of-growth industries in New York and distill the main determinants of the city's historical dominance as well as the challenges to its continued success; to study the nature and evolution of immigration flows into New York; and to analyze recent trends in a range of socioeconomic outcomes, both for the general population and recent immigrants more specifically.Immigrants - New York (N.Y.) ; Economic conditions - New York (N.Y.) ; Federal Reserve District, 2nd ; Urban economics

The Massive Wolf-Rayet Binary SMC WR7

We present a study of optical spectra of the Wolf--Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double lined WN+O6 spectroscopic binary with an orbital period of 19.56 days. The radial velocities of the He absorption lines of the O6 component and the strong He{\sc ii} emission at $\lambda$4686\AA of the WN component describe antiphased orbital motions. However, they show a small phase shift of $\sim$ 1 day. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He {\sc ii} emission is twice that of the absorption lines. The binary components have fairly high minimum masses, $\sim$ 18 \modot and 34 \modot for the WN and O6 components, respectively.Comment: Accepted by MNRA

An Overview on Urban Education: A Brief History and Contemporary Issues

This paper is designed to provide insights into both the ever-shifting nature-as well as the trajectory of-urban education in the United States. We provide a brief historical synopsis, a contextualization of how education in urban settings is commonly constructed through popular discourses, and a discussion of how the definitions and perceptions of urban schools influence research and policy measures. Lastly, this paper offers a brief exploration of recent movements and complications concerning urban education reform.Educatio

PSF calibration requirements for dark energy from cosmic shear

The control of systematic effects when measuring galaxy shapes is one of the main challenges for cosmic shear analyses. In this context, we study the fundamental limitations on shear accuracy due to the measurement of the Point Spread Function (PSF) from the finite number of stars. In order to do that, we translate the accuracy required for cosmological parameter estimation to the minimum number of stars over which the PSF must be calibrated. We first derive our results analytically in the case of infinitely small pixels (i.e. infinitely high resolution). Then image simulations are used to validate these results and investigate the effect of finite pixel size in the case of an elliptical gaussian PSF. Our results are expressed in terms of the minimum number of stars required to calibrate the PSF in order to ensure that systematic errors are smaller than statistical errors when estimating the cosmological parameters. On scales smaller than the area containing this minimum number of stars, there is not enough information to model the PSF. In the case of an elliptical gaussian PSF and in the absence of dithering, 2 pixels per PSF Full Width at Half Maximum (FWHM) implies a 20% increase of the minimum number of stars compared to the ideal case of infinitely small pixels; 0.9 pixels per PSF FWHM implies a factor 100 increase. In the case of a good resolution and a typical Signal-to-Noise Ratio distribution of stars, we find that current surveys need the PSF to be calibrated over a few stars, which may explain residual systematics on scales smaller than a few arcmins. Future all-sky cosmic shear surveys require the PSF to be calibrated over a region containing about 50 stars.Comment: 13 pages, 4 figures, accepted by A&

Implications of the metallicity dependence of Wolf-Rayet winds

Aims: Recent theoretical predictions for the winds of Wolf-Rayet stars indicate that their mass-loss rates scale with the initial stellar metallicity in the local Universe.We aim to investigate how this predicted dependence affects the models of Wolf-Rayet stars and their progeny in different chemical environments. Methods: We compute models of stellar structure and evolution for Wolf-Rayet stars for different initial metallicities, and investigate how the scaling of the Wolf-Rayet mass-loss rates affects the final masses, the lifetimes of the WN and WC subtypes, and how the ratio of the two populations vary with metallicity. Results: We find significant effects of metallicity dependent mass-loss rates for Wolf-Rayet stars. For models that include the scaling of the mass-loss rate with initial metallicity, all WR stars become neutron stars rather than black holes at twice the solar metallicity; at lower $Z$, black holes have larger masses. We also show that our models that include the mass-loss metallicity scaling closely reproduce the observed decrease of the relative population of WC over WN stars at low metallicities.Comment: 8 pages, 9 figures, accepted by Astronomy & Astrophysic

Deflection resistance indicator

Instrument for nondestructively measuring compression resistance of spray foam used as thermal insulation was developed. Cylindrical indicator has probe with coil spring to provide force and indicating dial. Probe is manually pressed against area to be tested until complete foot area contacts foam surfaces

Contextualising all-African peacekeeping:political and ethical dimensions

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Test of nuclear level density inputs for Hauser-Feshbach model calculations

The energy spectra of neutrons, protons, and alpha-particles have been measured from the d+59Co and 3He+58Fe reactions leading to the same compound nucleus, 61$Ni. The experimental cross sections have been compared to Hauser-Feshbach model calculations using different input level density models. None of them have been found to agree with experiment. It manifests the serious problem with available level density parameterizations especially those based on neutron resonance spacings and density of discrete levels. New level densities and corresponding Fermi-gas parameters have been obtained for reaction product nuclei such as 60Ni,60Co, and 57Fe