29,105 research outputs found
On the scaling rules for the anomaly-induced effective action of metric and electromagnetic field
The anomaly-induced effective action is a useful tool for deriving the
contributions coming from quantum effects of massless conformal fields. It is
well-known that such corrections in the higher derivative vacuum sector of the
gravitational action provide the same exponential inflation (Starobinsky model)
as the cosmological constant term. At the same time, the presence of a
classical electromagnetic field breaks down the exponential solution. In this
paper we explore the role of the anomaly-induced term in the radiation sector
and, furthermore, derive the ``equation of state'' and the scaling laws for all
terms in the Einstein equations. As one could expect, the scaling law for the
vacuum anomaly-induced effective action is the same as for the cosmological
constant.Comment: 12 pages, LaTeX, 4 figure
Knocking on the Door: Barriers to Welfare and Other Assistance for Teen Parents
The 1996 welfare reform legislation, which established the Temporary Assistance for Needy Families (TANF) program, sought, among other purposes, to move recipients off of welfare and into work and to prevent long-term welfare receipt. Policymakers recognized that concentrating on teen parents was an important part of tackling the problem of long-term receipt of welfare: although teen parents represent only about five percent of the overall TANF caseload, historically about 50 percent of adult welfare recipients began parenting as teens. The legislation adopted a new approach for minor teen parents, creating two major requirements -- commonly known as the "living arrangement rule" and the "stay-in-school rule." The first required unmarried, custodial teen parents under age 18 to live at home or in an adult-supervised setting, and the second required that they participate in school or approved training until obtaining a high school diploma or General Educational Development (GED) equivalency diploma.In the years since 1996, some states have reported greater declines in the number of teen parents receiving TANF relative to the general caseload declines. Limited qualitative information indicated that some teens were being turned away at local TANF offices, without having the opportunity to complete applications -- that is, they were knocking on the door but not getting in. Because TANF can have an important role in helping low-income teen parents stay on track towards economic independence, this information alarmed teen parent advocates and led the Center for Impact Research (CIR) to conduct a collaborative survey project in Chicago to determine what was happening to teen mothers who were in need of assistance. The Chicago survey was replicated in Boston and Atlanta, and this report highlights the collective findings across the three sites. In conducting the survey, CIR intended that about half of the respondents in all three sites were current recipients of TANF assistance and half were not
Accessing TANF Assistance: A Survey of Low-Income Young Mothers in Chicago
In 2000-2001, the Center for Impact Research (CIR), in collaboration with other concerned organizations, set out to obtain more information from young mothers about their experiences with TANF (Temporary Assistance for Needy Families) receipt in order to determine if changes in the TANF application process for teens are needed, and whether the Illinois Department of Human Services (IDHS) is effectively engaging teens in the TANF system. Working with community-based organizations, CIR trained young mothers to locate and survey other young mothers in low-income communities. A total of 601 young mothers, ages 13-21, were interviewed. Summary of Findings: CIR found that many young mothers were told they were ineligible for TANF and left TANF offices without having filled out applications; that those who had applied and were not receiving TANF were in need of education and employment; and that the older respondents -- who no longer qualified for the in-depth case management -- were experiencing more hardship than younger respondents
Spin-orbit correlation energy in neutron matter
We study the relevance of the energy correlation produced by the two-body
spin-orbit coupling present in realistic nucleon-nucleon potentials. To this
purpose, the neutron matter Equation of State (EoS) is calculated with the
realistic two-body Argonne potential. The shift occuring in the EoS when
spin-orbit terms are removed is taken as an estimate of the spin-orbit
correlation energy. Results obtained within the Bethe-Brueckner-Goldstone
expansion, extended up to three hole-line diagrams, are compared with other
many-body calculations recently presented in the literature. In particular,
excellent agreement is found with the Green's function Monte-Carlo method. This
agreement indicates the present theoretical accuracy in the calculation of the
neutron matter EoS.Comment: 5 pages, 2 figures, 2 tables; to appear in Phys. Rev.
Neutron matter at low density and the unitary limit
Neutron matter at low density is studied within the hole-line expansion.
Calculations are performed in the range of Fermi momentum between 0.4 and
0.8 fm. It is found that the Equation of State is determined by the
channel only, the three-body forces contribution is quite small, the
effect of the single particle potential is negligible and the three hole-line
contribution is below 5% of the total energy and indeed vanishing small at the
lowest densities. Despite the unitary limit is actually never reached, the
total energy stays very close to one half of the free gas value throughout the
considered density range. A rank one separable representation of the bare NN
interaction, which reproduces the physical scattering length and effective
range, gives results almost indistinguishable from the full Brueckner G-matrix
calculations with a realistic force. The extension of the calculations below
fm does not indicate any pathological behavior of the
neutron Equation of State.Comment: 17 pages, 7 figures. To be published in Phys. Rev.
Photoassociation adiabatic passage of ultracold Rb atoms to form ultracold Rb_2 molecules
We theoretically explore photoassociation by Adiabatic Passage of two
colliding cold ^{85}Rb atoms in an atomic trap to form an ultracold Rb_2
molecule. We consider the incoherent thermal nature of the scattering process
in a trap and show that coherent manipulations of the atomic ensemble, such as
adiabatic passage, are feasible if performed within the coherence time window
dictated by the temperature, which is relatively long for cold atoms. We show
that a sequence of ~2*10^7 pulses of moderate intensities, each lasting ~750
ns, can photoassociate a large fraction of the atomic ensemble at temperature
of 100 microkelvin and density of 10^{11} atoms/cm^3. Use of multiple pulse
sequences makes it possible to populate the ground vibrational state. Employing
spontaneous decay from a selected excited state, one can accumulate the
molecules in a narrow distribution of vibrational states in the ground
electronic potential. Alternatively, by removing the created molecules from the
beam path between pulse sets, one can create a low-density ensemble of
molecules in their ground ro-vibrational state.Comment: RevTex, 23 pages, 9 figure
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