123 research outputs found
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Welfare Research Perspectives: Past, Present, and Future, 2001 Edition
This is the third in a series of working papers designed to examine what has been learned since the enactment of the Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA) of 1996
Recommended from our members
Welfare Research Perspectives: Past, Present, and Future, 2002 Edition
This is the fourth in a series of working papers designed to examine what has been learned since the enactment of the Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA) of 1996
Recommended from our members
Policies Affecting New York City's Low-Income Families
Since the mid-1990s, policy and program changes at federal, state, and local levels have had a profound impact on the well-being of low-income families in New York City. In 2000, at the request of the New York Community Trust, the National Center for Children in Poverty—a research center affiliated with the Mailman School of Public Health at Columbia University—undertook a review of these changes and their implementation in New York City. This report describes some of the most important policy and program changes affecting New York's low-income families, discusses a number of issues that have arisen in connection with those changes, and suggests several ways in which city, state, and federal governments might enhance the well-being of low-income families. In the aftermath of the tragic events of September 11, 2001, the challenges facing New York City's low-income families are even more urgent
Recommended from our members
Welfare Research Perspectives: Past, Present, and Future, 2000 Edition
This is the second in a series of three working papers designed to examine what has been learned since the enactment of the Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA) of 1996
Spin relaxation in Mn12-acetate
We present a comprehensive derivation of the magnetization relaxation in a
Mn12-acetate crystal based on thermally assisted spin tunneling induced by
quartic anisotropy and weak transverse magnetic fields. The overall relaxation
rate as function of the magnetic field is calculated and shown to agree well
with data including all resonance peaks. The Lorentzian shape of the resonances
is also in good agreement with recent data. A generalized master equation
including resonances is derived and solved exactly. It is shown that many
transition paths with comparable weight exist that contribute to the relaxation
process. Previously unknown spin-phonon coupling constants are calculated
explicitly.Comment: 4 pages,4 EPS figures,LaTeX(europhys.sty);final version accepted for
EP
Haptoglobin Genotype Is a Consistent Marker of Coronary Heart Disease Risk Among Individuals With Elevated Glycosylated Hemoglobin
ObjectivesThis study sought to investigate into the biologically plausible interaction between the common haptoglobin (Hp) polymorphism rs#72294371 and glycosylated hemoglobin (HbA1c) on risk of coronary heart disease (CHD).BackgroundStudies of the association between the Hp polymorphism and CHD report inconsistent results. Individuals with the Hp2-2 genotype produce Hp proteins with an impaired ability to prevent oxidative injury caused by elevated HbA1c.MethodsHbA1c concentration and Hp genotype were determined for 407 CHD cases matched 1:1 to controls (from the NHS [Nurses' Health Study]) and in a replication cohort of 2,070 individuals who served as the nontreatment group in the ICARE (Prevention of Cardiovascular Complications in Diabetic Patients With Vitamin E Treatment) study, with 29 CHD events during follow-up. Multivariate models were adjusted for lifestyle and CHD risk factors as appropriate. A pooled analysis was conducted of NHS, ICARE, and the 1 previously published analysis (a cardiovascular disease case-control sample from the Strong Heart Study).ResultsIn the NHS, Hp2-2 genotype (39% frequency) was strongly related to CHD risk only among individuals with elevated HbA1c (≥6.5%), an association that was similar in the ICARE trial and the Strong Heart Study. In a pooled analysis, participants with both the Hp2-2 genotype and elevated HbA1c had a relative risk of 7.90 (95% confidence interval: 4.43 to 14.10) for CHD compared with participants with both an Hp1 allele and HbA1c <6.5% (p for interaction = 0.004), whereas the Hp2-2 genotype with HbA1c <6.5% was not associated with risk (relative risk: 1.34 [95% confidence interval: 0.73 to 2.46]).ConclusionsHp genotype was a significant predictor of CHD among individuals with elevated HbA1c
Spin Tunneling and Phonon-assisted Relaxation in Mn12-acetate
We present a comprehensive theory of the magnetization relaxation in a
Mn12-acetate crystal in the high-temperature regime (T>1 K), which is based on
phonon-assisted spin tunneling induced by quartic magnetic anisotropy and weak
transverse magnetic fields. The overall relaxation rate as function of the
longitudinal magnetic field is calculated and shown to agree well with
experimental data including all resonance peaks measured so far. The Lorentzian
shape of the resonances, which we obtain via a generalized master equation that
includes spin tunneling, is also in good agreement with recent data. We derive
a general formula for the tunnel splitting energy of these resonances. We show
that fourth-order diagonal terms in the Hamiltonian lead to satellite peaks. A
derivation of the effective linewidth of a resonance peak is given and shown to
agree well with experimental data. In addition, previously unknown spin-phonon
coupling constants are calculated explicitly. The values obtained for these
constants and for the sound velocity are also in good agreement with recent
data. We show that the spin relaxation in Mn12-acetate takes place via several
transition paths of comparable weight. These transition paths are expressed in
terms of intermediate relaxation times, which are calculated and which can be
tested experimentally.Comment: 18 pages, 22 EPS figures, REVTe
Spitzer Survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (SAGE) I: Overview and Initial Results
We are performing a uniform and unbiased, ~7x7 degrees imaging survey of the
Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the
Spitzer Space Telescope in order to survey the agents of a galaxy's evolution
(SAGE), the interstellar medium (ISM) and stars in the LMC. The detection of
diffuse ISM with column densities >1.2x10^21 H cm^-2 permits detailed studies
of dust processes in the ISM. SAGE's point source sensitivity enables a
complete census of newly formed stars with masses >3 solar masses that will
determine the current star formation rate in the LMC. SAGE's detection of
evolved stars with mass loss rates >1x10^-8 solar masses per year will quantify
the rate at which evolved stars inject mass into the ISM of the LMC. The
observing strategy includes two epochs in 2005, separated by three months, that
both mitigate instrumental artifacts and constrain source variability. The SAGE
data are non-proprietary. The data processing includes IRAC and MIPS pipelines
and a database for mining the point source catalogs, which will be released to
the community in support of Spitzer proposal cycles 4 and 5. We present initial
results on the epoch 1 data with a special focus on the N79 and N83 region. The
SAGE epoch 1 point source catalog has ~4 million sources. The point source
counts are highest for the IRAC 3.6 microns band and decrease dramatically
towards longer wavelengths consistent with the fact that stars dominate the
point source catalogs and that the dusty objects, e.g. young stellar objects
and dusty evolved stars that detected at the longer wavelengths, are rare in
comparison. We outline a strategy for identifying foreground MW stars, that may
comprise as much as 18% of the source list, and background galaxies, that may
comprise ~12% of the source list.Comment: Accepted by the Astronomical Journa
Spitzer survey of the Large Magellanic Cloud, surveying the agents of a galaxy's evolution (SAGE). IV. Dust properties in the interstellar medium
The goal of this paper is to present the results of a preliminary analysis of the extended infrared (IR) emission by dust in the interstellar medium (ISM) of the Large Magellanic Cloud (LMC). We combine Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and Infrared Astronomical Satellite (IRAS) data and correlate the infrared emission with gas tracers of H I, CO, and Hα. We present a global analysis of the infrared emission as well as detailed modeling of the spectral energy distribution (SED) of a few selected regions. Extended emission by dust associated with the neutral, molecular, and diffuse ionized phases of the ISM is detected at all IR bands from 3.6 μm to 160 μm. The relative abundance of the various dust species appears quite similar to that in the Milky Way (MW) in all the regions we have modeled. We construct maps of the temperature of large dust grains. The temperature map shows variations in the range 12.1-34.7 K, with a systematic gradient from the inner to outer regions, tracing the general distribution of massive stars and individual H II regions as well as showing warmer dust in the stellar bar. This map is used to derive the far-infrared (FIR) optical depth of large dust grains. We find two main departures in the LMC with respect to expectations based on the MW: (1) excess mid-infrared (MIR) emission near 70 μm, referred to as the 70 μm excess, and (2) departures from linear correlation between the FIR optical depth and the gas column density, which we refer to as FIR excess emission. The 70 μm excess increases gradually from the MW to the LMC to the Small Magellanic Cloud (SMC), suggesting evolution with decreasing metallicity. The excess is associated with the neutral and diffuse ionized gas, with the strongest excess region located in a loop structure next to 30 Dor. We show that the 70 μm excess can be explained by a modification of the size distribution of very small grains with respect to that in the MW, and a corresponding mass increase of ≃13% of the total dust mass in selected regions. The most likely explanation is that the 70 μm excess is due to the production of large very small grains (VSG) through erosion of larger grains in the diffuse medium. This FIR excess could be due to intrinsic variations of the dust/gas ratio, which would then vary from 4.6 to 2.3 times lower than the MW values across the LMC, but X_(CO) values derived from the IR emission would then be about three times lower than those derived from the Virial analysis of the CO data. We also investigate the possibility that the FIR excess is associated with an additional gas component undetected in the available gas tracers. Assuming a constant dust abundance in all ISM phases, the additional gas component would have twice the known H I mass. We show that it is plausible that the FIR excess is due to cold atomic gas that is optically thick in the 21 cm line, while the contribution by a pure H_2 phase with no CO emission remains a possible explanation
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