4,961 research outputs found
Welfare benefits and family-size decisions of never-married women
Since the 1970s, the out-of-wedlock birthrate has been increasing rapidly in the United States and has prompted several states to propose (and in some cases, enact) legislation to deny access to higher AFDC benefits for families in which the mother gives birth while receiving AFDC. The authors investigate whether AFDC benefit levels are systematically related to the family-size decisions of never-married women. Using a Poisson Regression model, applied to Current Population Survey data from the years 1980-1988, they find that the basic benefit level positively influences family size for white and Hispanic women, but not for black women. Incremental benefits for larger families, however, do not affect family-size decisions, suggesting that reducing (or eliminating) this differential will not necessarily reduce the number of illegitimate births. The basic benefit level positively affects the family-size decision of high school dropouts, but not of high school graduates. This suggests that to discourage nonmarital births, policymakers should consider altering the AFDC benefit structure in such a way as to encourage single mothers to complete high school. However, being a high school dropout might be a proxy for some other underlying characteristic of the woman, and inducing women to complete high school who otherwise would not might have no effect whatsoever on nonmarital births.
Computational Topology Techniques for Characterizing Time-Series Data
Topological data analysis (TDA), while abstract, allows a characterization of
time-series data obtained from nonlinear and complex dynamical systems. Though
it is surprising that such an abstract measure of structure - counting pieces
and holes - could be useful for real-world data, TDA lets us compare different
systems, and even do membership testing or change-point detection. However, TDA
is computationally expensive and involves a number of free parameters. This
complexity can be obviated by coarse-graining, using a construct called the
witness complex. The parametric dependence gives rise to the concept of
persistent homology: how shape changes with scale. Its results allow us to
distinguish time-series data from different systems - e.g., the same note
played on different musical instruments.Comment: 12 pages, 6 Figures, 1 Table, The Sixteenth International Symposium
on Intelligent Data Analysis (IDA 2017
Gradient echo memory in an ultra-high optical depth cold atomic ensemble
Quantum memories are an integral component of quantum repeaters - devices
that will allow the extension of quantum key distribution to communication
ranges beyond that permissible by passive transmission. A quantum memory for
this application needs to be highly efficient and have coherence times
approaching a millisecond. Here we report on work towards this goal, with the
development of a Rb magneto-optical trap with a peak optical depth of
1000 for the D2 transition using spatial and temporal
dark spots. With this purpose-built cold atomic ensemble to implement the
gradient echo memory (GEM) scheme. Our data shows a memory efficiency of % and coherence times up to 195 s, which is a factor of four greater
than previous GEM experiments implemented in warm vapour cells.Comment: 15 pages, 5 figure
Quantum tunneling dynamics of an interacting Bose-Einstein condensate through a Gaussian barrier
The transmission of an interacting Bose-Einstein condensate incident on a
repulsive Gaussian barrier is investigated through numerical simulation. The
dynamics associated with interatomic interactions are studied across a broad
parameter range not previously explored. Effective 1D Gross-Pitaevskii equation
(GPE) simulations are compared to classical Boltzmann-Vlasov equation (BVE)
simulations in order to isolate purely coherent matterwave effects. Quantum
tunneling is then defined as the portion of the GPE transmission not described
by the classical BVE. An exponential dependence of transmission on barrier
height is observed in the purely classical simulation, suggesting that
observing such exponential dependence is not a sufficient condition for quantum
tunneling. Furthermore, the transmission is found to be predominately described
by classical effects, although interatomic interactions are shown to modify the
magnitude of the quantum tunneling. Interactions are also seen to affect the
amount of classical transmission, producing transmission in regions where the
non-interacting equivalent has none. This theoretical investigation clarifies
the contribution quantum tunneling makes to overall transmission in
many-particle interacting systems, potentially informing future tunneling
experiments with ultracold atoms.Comment: Close to the published versio
Effects of non-denumerable fixed points in finite dynamical systems
The motion of a spinning football brings forth the possible existence of a
whole class of finite dynamical systems where there may be non-denumerably
infinite number of fixed points. They defy the very traditional meaning of the
fixed point that a point on the fixed point in the phase space should remain
there forever, for, a fixed point can evolve as well! Under such considerations
one can argue that a free-kicked football should be non-chaotic.Comment: This paper is a replaced version to modify the not-so-true claim,
made unknowingly in the earlier version, of being first to propose the
peculiar dynamical systems as described in the paper. With respect to the
original workers, we present here our original finding
Achieving peak brightness in an atom laser
In this paper we present experimental results and theory on the first
continuous (long pulse) Raman atom laser. The brightness that can be achieved
with this system is three orders of magnitude greater than has been previously
demonstrated in any other continuously outcoupled atom laser. In addition, the
energy linewidth of a continuous atom laser can be made arbitrarily narrow
compared to the mean field energy of a trapped condensate. We analyze the flux
and brightness of the atom laser with an analytic model that shows excellent
agreement with experiment with no adjustable parameters.Comment: 4 pages, 4 black and white figures, submitted to Physical Revie
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