20,969 research outputs found
How labor market policies shape immigrants’ opportunities
When it comes to unemployment and labor force participation rates, immigrants do better in the United States than in most other countries. In 2005, for example, the foreign-born had average unemployment of 4.6 percent in the U.S., well below native-born workers’ 5.2 percent. U.S. immigrants also had higher participation rates. The American experience stands in stark contrast to many other developed nations’. In France and Germany, for example, the foreign-born typically have jobless rates twice as high as native-born workers and lower participation rates. ; What accounts for these differences? Most studies attribute poor labor market outcomes to the immigrants themselves—their education levels, language skills, inexperience, family composition and reasons for migrating. Immigrant characteristics surely matter, but so do the host country’s labor market institutions and policies.Immigrants ; Labor policy ; Employment
A new look at the problem of gauge invariance in quantum field theory
Quantum field theory is assumed to be gauge invariant. However it is well
known that when certain quantities are calculated using perturbation theory the
results are not gauge invariant. The non-gauge invariant terms have to be
removed in order to obtain a physically correct result. In this paper we will
examine this problem and determine why a theory that is supposed to be gauge
invariant produces non-gauge invariant results.Comment: Accepted by Physica Scripta. 27 page
The essential signature of a massive starburst in a distant galaxy
Observations of carbon monoxide (CO) emission in high redshift (z>2) galaxies
indicate the presence of large amounts of molecular gas. Many of these galaxies
contain an active galactic nucleus (AGN) powered by accretion of gas onto a
supermassive black hole, and a key question is whether their extremely high
infrared luminosities result from the AGN, or from bursts of massive star
formation (associated with the molecular gas), or both. In the Milky Way,
high-mass stars form in the dense cores of interstellar molecular clouds; gas
densities are n(H2)>105 cm-3 in the cores. Recent surveys show that virtually
all galactic sites of high-mass star formation have similarly high densities.
The bulk of the cloud material traced by CO observations is at a much lower
density. In galaxies in the local Universe, the HCN(J=1-0) line is an effective
tracer of the high-density molecular gas. Here we report observations of HCN
emission in the early Universe from the infrared luminous 'Cloverleaf' quasar
(at a redshift z=2.5579). The HCN line luminosity indicates the presence of 10
billion solar masses of very dense gas, an essential feature of an immense
starburst that contributes, together with the AGN it harbors, to its high
infrared luminosity.Comment: PDF pape
Impact of Race and Insurance on Door-to-Appendectomy Time among Pediatric Patients
Racial and ethnic disparities in the rate of appendiceal rupture have been widely reported among the pediatric population. The main reasons for this remain largely unknown given that previous explanations pointing to signs of poor health care access have recently been shown to account for only a small percentage of the difference in perforation rates between white and minority children. Because the risk of perforation increases with time, racial disparities in time delay from emergency department presentation to OR appendectomy may help account for the higher appendiceal perforation rates observed among minority children. This is the first study dedicated to analyzing racial differences in door-to-appendectomy time. Insurance status and language barriers were also considered as variables of interest.
Retrospective, observational study using admission and treatment data of 607 consecutive children less than or equal to 18 years of age with surgical confirmation of appendicitis. Patients were admitted from February 2, 2013 (start of electronic medical record use) to April 27, 2017.
A significant association was found between race and perforation rate (p0.05 for all). Door-to-appendectomy times were also not significantly longer for Medicaid/uninsured patients (613 minutes) compared to private insurance patients (597 minutes) (p=0.60), nor for patients with language barriers (545 minutes) compared to patients without (612 minutes) (p=0.23).
While there was a higher appendiceal perforation rate among minority children, it was not due to differences in door-to-appendectomy time. Insurance status and language barriers also did not lead to differential treatment among pediatric patients
High Redshift HCN Emission: Dense Star-Forming Molecular Gas in IRAS F10214+4724
Hydrogen cyanide emission in the J=1-0 transition has been detected at
redshift z=2.2858 in IRAS F10214+4724 using the Green Bank Telescope . This is
the second detection of HCN emission at high redshift. The large HCN line
luminosity in F10214 is similar to that in the Cloverleaf (z=2.6) and the
ultra-luminous infrared galaxies Mrk231 and Arp220. This is also true of the
ratio of HCN to CO luminosities. The ratio of far-infrared luminosity to HCN
luminosity, an indicator of the star formation rate per solar mass of dense
gas, follows the correlation found for normal spirals and infrared luminous
starburst galaxies. F10214 clearly contains a starburst that contributes,
together with its embedded quasar, to its overall infrared luminosity. A new
technique for removing spectral baselines in the search for weak, broad
emission lines is presented.Comment: 9 pages, 2 figures; accepted ApJ(Letters
Chaotic diffusion of particles with finite mass in oscillating convection flows
Deterministic diffusion in temporally oscillating convection is studied for
particles with finite mass. The particles are assumed to obey a simple
dissipative dynamical system and the particle diffusion is induced by the
strange attractor. The diffusion constants are numerically calculated for
convection models with free and rigid boundary conditions.Comment: 5 figure
Coherent pairing states for the Hubbard model
We consider the Hubbard model and its extensions on bipartite lattices. We
define a dynamical group based on the -pairing operators introduced by
C.N.Yang, and define coherent pairing states, which are combinations of
eigenfunctions of -operators. These states permit exact calculations of
numerous physical properties of the system, including energy, various
fluctuations and correlation functions, including pairing ODLRO to all orders.
This approach is complementary to BCS, in that these are superconducting
coherent states associated with the exact model, although they are not
eigenstates of the Hamiltonian.Comment: 5 pages, RevTe
Ground-based measurements of O3, NO2, OClO, and BrO during the 1987 Antarctic ozone depletion event
Near-ultraviolet absorption spectroscopy in the wavelength range from 330 to 370 nm was used to measure O3, NO2, OClO, and BrO at McMurdo Station (78S) during 1987. Visible absorption measurements of O3, NO2, and OClO were also obtained using the wavelength range from about 403 to 453 nm. These data are described and compared to observations obtained in 1986. It is shown that comparisons of observations in the two wavelength ranges provide a sensitive measure of the altitude where the bulk of atmospheric absorption takes place
Some new results concerning the vacuum in Dirac Hole Theory
In Dirac's hole theory the vacuum state is generally believed to be the state
of minimum energy. It will be shown that this is not, in fact, the case and
that there must exist states in hole theory with less energy than the vacuum
state. It will be shown that energy can be extracted from the hole theory
vacuum state through the application of an electric field.Comment: Accepted by Physica Scripta, 19 page
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