15,855 research outputs found
The Impact of the 1996 SSI Childhood Disability Reforms: Evidence from Matched SIPP-SSA Data
The Personal Responsibility and Work Opportunity Reconciliation Act of 1996 changed the definition of disability used to determine eligibility for disabled children under the Supplemental Security Income (SSI) program and made other changes in the program. The law required the redetermination of eligibility status for children potentially affected by the new definition of disability. As a result, an estimated 100,000 children were expected to lose SSI benefits. The goal of this paper is to understand the impact of benefit loss on affected children and their families. The analysis draws on data from the 1992, 1993 and 1996 panels of the Survey of Income and Program Participation matched with Social Security Administration records on SSI program participation. The data are used to analyze the impact of the loss of SSI income as a result of the 1996 legislation on family labor supply, welfare program participation, and income and poverty. Compared with families that lost SSI benefits due to normal attrition from the program, the excess benefit loss due to the 1996 childhood disability reforms is associated with lower levels of family labor supply, higher levels of participation in AFDC/TANF and food stamps, and lower levels of family income relative to poverty. For some outcomes, these effects—measured one month after benefit loss—persist for up to 12 months.
Preschool and School Readiness: Experiences of Children With Non-English-Speaking Parents
Examines gaps in school readiness among low-income children, especially those in immigrant and linguistically isolated families; the type of early care and education they receive; and the need for targeted center-based preschool programs to close gaps
First-order nature of the ferromagnetic phase transition in (La-Ca)MnO_3 near optimal doping
Neutron scattering has been used to study the nature of the ferromagnetic
transition in single crystals of La_0.7Ca_0.3MnO_3 and La_0.8Ca_0.2MnO_3, and
polycrystalline samples of La_0.67Ca_0.33MnO_3 and La_5/8Ca_3/8MnO_3 where the
naturally occurring O-16 can be replaced with the O-18 isotope. Small angle
neutron scattering on the x=0.3 single crystal reveals a discontinuous change
in the scattering at the Curie temperature for wave vectors below ~0.065 A^-1.
Strong relaxation effects are observed for this domain scattering, for the
magnetic order parameter, and for the quasielastic scattering, demonstrating
that the transition is not continuous in nature. There is a large oxygen
isotope effect observed for the T_C in the polycrystalline samples. For the
optimally doped x=3/8 sample we observed T_C(O-16)=266.5 K and T_C(O-18)=261.5
K at 90% O-18 substitution. The temperature dependence of the spin-wave
stiffness is found to be identical for the two samples despite changes in T_C.
Hence, T_C is not solely determined by the magnetic subsystem, but instead the
ferromagnetic phase is truncated by the formation of polarons which cause an
abrupt transition to the paramagnetic, insulating state. Application of
uniaxial stress in the x=0.3 single crystal sharply enhances the polaron
scattering at room temperature. Measurements of the phonon density-of-states
show only modest differences above and below T_C and between the two different
isotopic samples.Comment: 13 pages, 16 figures, submitted to Phys. Rev.
Quantum Monte Carlo Calculations of Light Nuclei Using Chiral Potentials
We present the first Green's function Monte Carlo calculations of light
nuclei with nuclear interactions derived from chiral effective field theory up
to next-to-next-to-leading order. Up to this order, the interactions can be
constructed in a local form and are therefore amenable to quantum Monte Carlo
calculations. We demonstrate a systematic improvement with each order for the
binding energies of and systems. We also carry out the first
few-body tests to study perturbative expansions of chiral potentials at
different orders, finding that higher-order corrections are more perturbative
for softer interactions. Our results confirm the necessity of a three-body
force for correct reproduction of experimental binding energies and radii, and
pave the way for studying few- and many-nucleon systems using quantum Monte
Carlo methods with chiral interactions.Comment: 5 pages, 3 figures, 4 tables. Updated references. Cosmetic changes to
figures, tables, and equations; added a sentence clarifying the
correspondence between our real-space cutoffs and momentum-space cutoffs.
Other sentences were reworded for clarit
The Cell Wall Teichuronic Acid Synthetase (TUAS) Is an Enzyme Complex Located in the Cytoplasmic Membrane of Micrococcus luteus
The cell wall teichuronic acid (TUA) of Micrococcus luteus is a long-chain polysaccharide composed of disaccharide repeating units [-4-β-D-ManNAcAp-(1→6)α-D-Glcp−1-]n, which is covalently anchored to the peptidoglycan on the inner cell wall and extended to the outer surface of the cell envelope. An enzyme complex responsible for the TUA chain biosynthesis was purified and characterized. The 440kDa enzyme complex, named teichuronic acid synthetase (TUAS), is an octomer composed of two kinds of glycosyltransferases, Glucosyltransferase, and ManNAcA-transferase, which is capable of catalyzing the transfer of disaccharide glycosyl residues containing both glucose and the N-acetylmannosaminuronic acid residues. TUAS displays hydrophobic properties and is found primarily associated with the cytoplasmic membrane. The purified TUAS contains carotinoids and lipids. TUAS activity is diminished by phospholipase digestion. We propose that TUAS serves as a multitasking polysaccharide assembling station on the bacterial membrane.National Institute of Allergy and Infectious Diseases (Public Health Service Grants AI-08295); American Lung Association (RG-107-N
The use of the Winograd matrix multiplication algorithm in digital multispectral processing
The Winograd procedure for matrix multiplication provides a method whereby general matrix products may be computed more efficiently than the normal method. The algorithm and the time savings that can be effected are described. A FORTRAN program is provided which performs a general matrix multiply according to this algorithm. A variation of this procedure that may be used to calculate Gaussian probability density functions is also described. It is shown how a time savings can be effected in this calculation. The extension of this method to other similar calculations should yield similar savings
Signatures of few-body resonances in finite volume
We study systems of bosons and fermions in finite periodic boxes and show how
the existence and properties of few-body resonances can be extracted from
studying the volume dependence of the calculated energy spectra. Using a
plane-wave-based discrete variable representation to conveniently implement
periodic boundary conditions, we establish that avoided level crossings occur
in the spectra of up to four particles and can be linked to the existence of
multi-body resonances. To benchmark our method we use two-body calculations,
where resonance properties can be determined with other methods, as well as a
three-boson model interaction known to generate a three-boson resonance state.
Finding good agreement for these cases, we then predict three-body and
four-body resonances for models using a shifted Gaussian potential. Our results
establish few-body finite-volume calculations as a new tool to study few-body
resonances. In particular, the approach can be used to study few-neutron
systems, where such states have been conjectured to exist.Comment: 13 pages, 10 figures, 2 tables, published versio
Is a Trineutron Resonance Lower in Energy than a Tetraneutron Resonance?
We present quantum Monte Carlo calculations of few-neutron systems confined
in external potentials based on local chiral interactions at
next-to-next-to-leading order in chiral effective field theory. The energy and
radial densities for these systems are calculated in different external
Woods-Saxon potentials. We assume that their extrapolation to zero
external-potential depth provides a quantitative estimate of three- and
four-neutron resonances. The validity of this assumption is demonstrated by
benchmarking with an exact diagonalization in the two-body case. We find that
the extrapolated trineutron resonance, as well as the energy for shallow well
depths, is lower than the tetraneutron resonance energy. This suggests that a
three-neutron resonance exists below a four-neutron resonance in nature and is
potentially measurable. To confirm that the relative ordering of three- and
four-neutron resonances is not an artifact of the external confinement, we test
that the odd-even staggering in the helium isotopic chain is reproduced within
this approach. Finally, we discuss similarities between our results and
ultracold Fermi gases.Comment: 6 pages, 5 figures, version compatible with published lette
Unusual Coupling Between Field-induced Spin Fluctuations and Spin Density Wave in Intermetallic CeAg2Ge2
We report on the experimental evidences for an unusual coupling between the
magnetic field- induced fluctuations of correlated Ce-ions coinciding with the
discontinuous movement of the underlying spin density wave in the intermetallic
rare earth compound CeAg2Ge2. The measurements performed using neutron
scattering and magnetic Gruneisen ratio methods suggest that the coupling
onsets at H= 2.7 T, T < 3.8 K and persists to the lowest measurement
temperature T ~ 0.05 K. These measurements suggest a new mechanism behind the
spin fluctuations which can affect the intrinsic properties of the system.Comment: 4 pages, 4 figures, Strongly correlated electrons syste
Uncorrelated and correlated nanoscale lattice distortions in the paramagnetic phase of magnetoresistive manganites
Neutron scattering measurements on a magnetoresistive manganite
La(CaSr)MnO show that uncorrelated
dynamic polaronic lattice distortions are present in both the orthorhombic (O)
and rhombohedral (R) paramagnetic phases. The uncorrelated distortions do not
exhibit any significant anomaly at the O-to-R transition. Thus, both the
paramagnetic phases are inhomogeneous on the nanometer scale, as confirmed
further by strong damping of the acoustic phonons and by the anomalous
Debye-Waller factors in these phases. In contrast, recent x-ray measurements
and our neutron data show that polaronic correlations are present only in the O
phase. In optimally doped manganites, the R phase is metallic, while the O
paramagnetic state is insulating (or semiconducting). These measurements
therefore strongly suggest that the {\it correlated} lattice distortions are
primarily responsible for the insulating character of the paramagnetic state in
magnetoresistive manganites.Comment: 10 pages, 8 figures embedde
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