9,263 research outputs found

### The Long-Run Labour Market Consequences of Teenage Motherhood in Britain

Common wisdom states that teenage childbearing reduces schooling, labour market experience and adult wages. However, the decisions to be a teenage mother, to quit school, and be less attached to the labour market might all stem from some personal or family characteristics. Using the National Child Development Study (NCDS), we find that in Britain teenage childbearing decreases the probability of post-16 schooling by 12% to 24%. Employment experience is reduced by up to three years, and the adult pay differential ranges from 5% to 22%. The negative impact of teen motherhood on various adult outcomes is not due to some pre-motherhood characteristics; hence policies aiming to encourage return to school and participation in the labour market may be an efficient way to reduce the long-term consequences of teenage pregnancy.Teenage pregnancy, schooling decisions, wages

### The Supply of Childcare in Britain: Do Mothers Queue for Childcare?

This paper presents a model of partial observability applied to the childcare market in Britain. We simultaneously estimate the demand and use and calculate the excess demand for childcare. We find a large queue with nearly half of the mothers demanding childcare queuing for it. We also find that formal and informal care are not substitute, implying that policies increasing the supply of formal care lead to an increase in the use of care rather than solely a shift from informal to formal care. This has implication on the efficiency of policies aiming at increasing the labour supply of mothers.supply of childcare

### Towards adiabatic waveforms for inspiral into Kerr black holes: I. A new model of the source for the time domain perturbation equation

We revisit the problem of the emission of gravitational waves from a test
mass orbiting and thus perturbing a Kerr black hole. The source term of the
Teukolsky perturbation equation contains a Dirac delta function which
represents a point particle. We present a technique to effectively model the
delta function and its derivatives using as few as four points on a numerical
grid. The source term is then incorporated into a code that evolves the
Teukolsky equation in the time domain as a (2+1) dimensional PDE. The waveforms
and energy fluxes are extracted far from the black hole. Our comparisons with
earlier work show an order of magnitude gain in performance (speed) and
numerical errors less than 1% for a large fraction of parameter space. As a
first application of this code, we analyze the effect of finite extraction
radius on the energy fluxes. This paper is the first in a series whose goal is
to develop adiabatic waveforms describing the inspiral of a small compact body
into a massive Kerr black hole.Comment: 21 pages, 6 figures, accepted by PRD. This version removes the
appendix; that content will be subsumed into future wor

### Comment on "Canonical and Mircocanonical Calculations for Fermi Systems"

In the context of nuclear physics Pratt recently investigated noninteracting
Fermi systems described by the microcanonical and canonical ensemble. As will
be shown his discussion of the model of equally spaced levels contains a flaw
and a statement which is at least confusing.Comment: Comment on S. Pratt, Phys. Rev. Lett. 84, 4255 (2000) and
nucl-th/990505

### Fluorescence from a few electrons

Systems containing few Fermions (e.g., electrons) are of great current
interest. Fluorescence occurs when electrons drop from one level to another
without changing spin. Only electron gases in a state of equilibrium are
considered. When the system may exchange electrons with a large reservoir, the
electron-gas fluorescence is easily obtained from the well-known Fermi-Dirac
distribution. But this is not so when the number of electrons in the system is
prevented from varying, as is the case for isolated systems and for systems
that are in thermal contact with electrical insulators such as diamond. Our
accurate expressions rest on the assumption that single-electron energy levels
are evenly spaced, and that energy coupling and spin coupling between electrons
are small. These assumptions are shown to be realistic for many systems.
Fluorescence from short, nearly isolated, quantum wires is predicted to drop
abruptly in the visible, a result not predicted by the Fermi-Dirac
distribution. Our exact formulas are based on restricted and unrestricted
partitions of integers. The method is considerably simpler than the ones
proposed earlier, which are based on second quantization and contour
integration.Comment: 10 pages, 3 figures, RevTe

### Identification of an RVB liquid phase in a quantum dimer model with competing kinetic terms

Starting from the mean-field solution of a spin-orbital model of LiNiO$_2$,
we derive an effective quantum dimer model (QDM) that lives on the triangular
lattice and contains kinetic terms acting on 4-site plaquettes and 6-site
loops. Using numerical exact diagonalizations and Green's function Monte Carlo
simulations, we show that the competition between these kinetic terms leads to
a resonating valence bond (RVB) state for a finite range of parameters. We also
show that this RVB phase is connected to the RVB phase identified in the
Rokhsar-Kivelson model on the same lattice in the context of a generalized
model that contains both the 6--site loops and a nearest-neighbor dimer
repulsion. These results suggest that the occurrence of an RVB phase is a
generic feature of QDM with competing interactions.Comment: 8 pages, 12 figure

### Bent-Double Radio Sources as Probes of Intergalactic Gas

As the most common environment in the universe, groups of galaxies are likely
to contain a significant fraction of the missing baryons in the form of
intergalactic gas. The density of this gas is an important factor in whether
ram pressure stripping and strangulation affect the evolution of galaxies in
these systems. We present a method for measuring the density of intergalactic
gas using bent-double radio sources that is independent of temperature, making
it complementary to current absorption line measurements. We use this method to
probe intergalactic gas in two different environments: inside a small group of
galaxies as well as outside of a larger group at a 2 Mpc radius and measure
total gas densities of $4 \pm 1_{-2}^{+6} \times 10^{-3}$ and $9 \pm
3_{-5}^{+10} \times 10^{-4}$ per cubic centimeter (random and systematic
errors) respectively. We use X-ray data to place an upper limit of $2 \times
10^6$ K on the temperature of the intragroup gas in the small group.Comment: 6 pages, 1 figure, accepted for publication in Ap

### Report on the first round of the Mock LISA Data Challenges

The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data analysis tools and capabilities, and demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data output. The first round of MLDCs has just been completed: nine challenges consisting of data sets containing simulated gravitational-wave signals produced either by galactic binaries or massive black hole binaries embedded in simulated LISA instrumental noise were released in June 2006 with deadline for submission of results at the beginning of December 2006. Ten groups have participated in this first round of challenges. All of the challenges had at least one entry which successfully characterized the signal to better than 95% when assessed via a correlation with phasing ambiguities accounted for. Here, we describe the challenges, summarize the results and provide a first critical assessment of the entries

### Searching for Massive Black Hole Binaries in the first Mock LISA Data Challenge

The Mock LISA Data Challenge is a worldwide effort to solve the LISA data
analysis problem. We present here our results for the Massive Black Hole Binary
(BBH) section of Round 1. Our results cover Challenge 1.2.1, where the
coalescence of the binary is seen, and Challenge 1.2.2, where the coalescence
occurs after the simulated observational period. The data stream is composed of
Gaussian instrumental noise plus an unknown BBH waveform. Our search algorithm
is based on a variant of the Markov Chain Monte Carlo method that uses
Metropolis-Hastings sampling and thermostated frequency annealing. We present
results from the training data sets and the blind data sets. We demonstrate
that our algorithm is able to rapidly locate the sources, accurately recover
the source parameters, and provide error estimates for the recovered
parameters.Comment: 11 pages, 6 figures, Submitted to CQG proceedings of GWDAW 11, AEI,
Germany, Dec 200

### Detection of a close supernova gravitational wave burst in a network of interferometers, neutrino and optical detectors

Trying to detect the gravitational wave (GW) signal emitted by a type II
supernova is a main challenge for the GW community. Indeed, the corresponding
waveform is not accurately modeled as the supernova physics is very complex; in
addition, all the existing numerical simulations agree on the weakness of the
GW emission, thus restraining the number of sources potentially detectable.
Consequently, triggering the GW signal with a confidence level high enough to
conclude directly to a detection is very difficult, even with the use of a
network of interferometric detectors. On the other hand, one can hope to take
benefit from the neutrino and optical emissions associated to the supernova
explosion, in order to discover and study GW radiation in an event already
detected independently. This article aims at presenting some realistic
scenarios for the search of the supernova GW bursts, based on the present
knowledge of the emitted signals and on the results of network data analysis
simulations. Both the direct search and the confirmation of the supernova event
are considered. In addition, some physical studies following the discovery of a
supernova GW emission are also mentioned: from the absolute neutrino mass to
the supernova physics or the black hole signature, the potential spectrum of
discoveries is wide.Comment: Revised version, accepted for publication in Astroparticle Physic

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