24,806 research outputs found
Is the Melting Pot Still Hot? Explaining the Resurgence of Immigrant Segregation
This paper uses decennial Census data to examine trends in immigrant segregation in the United States between 1910 and 2000. Immigrant segregation declined in the first half of the century, but has been rising steadily over the past three decades. Analysis of restricted access 1990 Census microdata suggests that this rise would be even more striking if the native-born children of immigrants could be consistently excluded from the analysis. We analyze panel and cross-sectional variation in immigrant segregation, as well as housing price patterns across metropolitan areas, to test four hypotheses of immigrant segregation. Immigration itself has surged in recent decades, but the tendency for newly arrived immigrants to be younger and of lower socioeconomic status explains very little of the recent rise in immigrant segregation. We also find little evidence of increased nativism in the housing market. Evidence instead points to changes in urban form, manifested in particular as native-driven suburbanization and the decline of public transit as a transportation mode, as a central explanation for the new immigrant segregation.
An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres
The nature of aerosols in hot exoplanet atmospheres is one of the primary
vexing questions facing the exoplanet field. The complex chemistry, multiple
formation pathways, and lack of easily identifiable spectral features
associated with aerosols make it especially challenging to constrain their key
properties. We propose a transmission spectroscopy technique to identify the
primary aerosol formation mechanism for the most highly irradiated hot Jupiters
(HIHJs). The technique is based on the expectation that the two key types of
aerosols -- photochemically generated hazes and equilibrium condensate clouds
-- are expected to form and persist in different regions of a highly irradiated
planet's atmosphere. Haze can only be produced on the permanent daysides of
tidally-locked hot Jupiters, and will be carried downwind by atmospheric
dynamics to the evening terminator (seen as the trailing limb during transit).
Clouds can only form in cooler regions on the night side and morning terminator
of HIHJs (seen as the leading limb during transit). Because opposite limbs are
expected to be impacted by different types of aerosols, ingress and egress
spectra, which primarily probe opposing sides of the planet, will reveal the
dominant aerosol formation mechanism. We show that the benchmark HIHJ,
WASP-121b, has a transmission spectrum consistent with partial aerosol coverage
and that ingress-egress spectroscopy would constrain the location and formation
mechanism of those aerosols. In general, using this diagnostic we find that
observations with JWST and potentially with HST should be able to distinguish
between clouds and haze for currently known HIHJs.Comment: 10 pages, 4 figures, accepted to ApJ Letter
When Are Ghettos Bad? Lessons from Immigrant Segregation in the United States
Recent literature on the relationship between ethnic or racial segregation and outcomes has failed to produce a consensus view of the role of ghettos; some studies suggest that residence in an enclave is beneficial, some reach the opposite conclusion, and still others imply that any relationship is small. This paper presents new evidence on this relationship using data on first-generation immigrants in the United States. Using average group characteristics as instruments for segregation, controlling for individual characteristics and both metropolitan area and country-of-origin fixed effects, we estimate impacts of residential concentration that vary with group human capital levels. Residential concentration can be beneficial, but primarily for more educated groups. The mean impact of residential concentration varies across measures, which may illuminate some of the causal mechanisms relating segregation to outcomes.
Density-Dependent Response of an Ultracold Plasma to Few-Cycle Radio-Frequency Pulses
Ultracold neutral plasmas exhibit a density-dependent resonant response to
applied radio-frequency (RF) fields in the frequency range of several MHz to
hundreds of MHz for achievable densities. We have conducted measurements where
short bursts of RF were applied to these plasmas, with pulse durations as short
as two cycles. We still observed a density-dependent resonant response to these
short pulses. However, the too rapid timescale of the response, the dependence
of the response on the sign of the driving field, the response as the number of
pulses was increased, and the difference in plasma response to radial and
axially applied RF fields are inconsistent with the plasma response being due
to local resonant heating of electrons in the plasma. Instead, our results are
consistent with rapid energy transfer from collective motion of the entire
electron cloud to electrons in high-energy orbits. In addition to providing a
potentially more robust way to measure ultracold neutral plasma densities,
these measurements demonstrate the importance of collective motion in the
energy transport in these systems.Comment: 5 pages, 4 figure
Is the Melting Pot Still Hot? Explaining the Resurgence of Immigrant Segregation
This paper uses decennial Census data to examine trends in immigrant segregation in the United States between 1910 and 2000. Immigrant segregation declined in the first half of the century, but has been rising over the past few decades. Analysis of restricted access 1990 Census microdata suggests that this rise would be even more striking if the native-born children of immigrants could be consistently excluded from the analysis. We analyze longitudinal variation in immigrant segregation, as well as housing price patterns across metropolitan areas, to test four hypotheses of immigrant segregation. Immigration itself has surged in recent decades, but the tendency for newly arrived immigrants to be younger and of lower socioeconomic status explains very little of the recent rise in immigrant segregation. We also find little evidence of increased nativism in the housing market. Evidence instead points to changes in urban form, manifested in particular as native-driven suburbanization and the decline of public transit as a transportation mode, as a central explanation for the new immigrant segregation.
Strong interrelationship between anomalous electric-field induced lattice strain along non-polar direction and domain reorientation in pseudorhombohedral piezoelectric ceramic BiScO3-PbTiO3
The lattice strain and domain switching behaviour was investigated as a
function of cyclic field and grain orientation for a pseudorhombohedral
composition of the high Curie point piezoelectric system xBiScO3 - (1-x)PbTiO3
(x = 0.40) by in-situ electric field diffraction technique with high energy
synchrotron x-rays. Along the field direction, the system exhibts five time
large strain along 100 as compared to the 111 direction. A one-to-one
correspondence between the 200 lattice strain and the 111 domain switching
suggests a strong correlation between the two phenomena.Comment: 11 pages, 7 figure
Triplet proximity effect and odd-frequency pairing in graphene
We study the interplay between proximity-induced superconductivity and
ferromagnetism in graphene by self-consistently solving the Bogoliubov-de
Gennes equations on the honeycomb lattice. We find that a strong triplet
proximity effect is generated in graphene, leading to odd-frequency pairing
correlations. These odd-frequency correlations are clearly manifested in the
local density of states of the graphene sheet, which can be probed via
STM-measurements. Motivated by recent experiments on SNS graphene
Josephson junctions, we also study the spectrum of Andreev-bound states formed
in the normal region due to the proximity effect. Our results may be useful for
interpreting spectroscopic data and can also serve as a guideline for future
experiments.Comment: 4 pages, 3 figures. Submitted to Physical Review
From the ISR to RHIC--measurements of hard-scattering and jets using inclusive single particle production and 2-particle correlations
Hard scattering in p-p collisions, discovered at the CERN ISR in 1972 by the
method of leading particles, proved that the partons of Deeply Inelastic
Scattering strongly interacted with each other. Further ISR measurements
utilizing inclusive single or pairs of hadrons established that high pT
particles are produced from states with two roughly back-to-back jets which are
the result of scattering of constituents of the nucleons as desribed by Quantum
Chromodynamics (QCD), which was developed during the course of these
measurements. These techniques, which are the only practical method to study
hard-scattering and jet phenomena in Au+Au central collisions at RHIC energies,
are reviewed, as an introduction to present RHIC measurements.Comment: To appear in the proceedings of the workshop on Correlations and
Fluctuations in Relativistic Nuclear Collisions, MIT, Cambridge, MA, April
21-23, 2005, 10 pages, 9 figures, Journal of Physics: Conference Proceeding
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