4,071 research outputs found
Recent Trends in the Earnings of New Immigrants to the United States
This paper studies long-term trends in the labor market performance of immigrants in the United States, using the 1960-2000 PUMS and 1994-2009 CPS. While there was a continuous decline in the earnings of new immigrants 1960-1990, the trend reversed in the 1990s, with newcomers doing as well in 2000, relative to natives, as they had 20 years earlier. This improvement in immigrant performance is not explained by changes in origin-country composition, educational attainment or state of residence. Changes in labor market conditions, including changes in the wage structure which could differentially impact recent arrivals, can account for only a small portion of it. The upturn appears to have been caused in part by a shift in immigration policy toward high-skill workers matched with jobs, an increase in the earnings of immigrants from Mexico, and a decline in the earnings of native high school dropouts. However, most of the increase remains a puzzle. Results from the CPS suggest that, while average entry wages fell again after 2000, correcting for simple changes in the composition of new immigrants, the unexplained rise in entry wages has persisted.
Q-stars and charged q-stars
We present the formalism of q-stars with local or global U(1) symmetry. The
equations we formulate are solved numerically and provide the main features of
the soliton star. We study its behavior when the symmetry is local in contrast
to the global case. A general result is that the soliton remains stable and
does not decay into free particles and the electrostatic repulsion preserves it
from gravitational collapse. We also investigate the case of a q-star with
non-minimal energy-momentum tensor and find that the soliton is stable even in
some cases of collapse when the coupling to gravity is absent.Comment: Latex, 19pg, 12 figures. Accepted in Phys. Rev.
Searching for better prospects: endogenizing falling job tenure and private pension coverage
Recent declines in job tenure have coincided with a shift away from traditional defined benefit (DB) pensions, which reward long tenure. New evidence also points to an increase in job-to-job movements by workers, and we document gains in relative wages of job-to-job movers over a similar period. We develop a search model in which firms may offer tenure-based contracts like DB pensions to reduce the incidence of costly on-the-job search by workers. Either reduced search costs or an increase in the probability of job matches can, under fairly general conditions, lower the value of deterring search and the use of DB pensions.Pensions ; Unemployment
Searching for Better Prospects: Endogenizing Falling Job Tenure and Private Pension Coverage
Recent declines in job tenure have coincided with a shift away from traditional defined benefit (DB) pensions, which reward long tenure. Recent evidence also points to an increase in job-to-job movements by workers, and we document gains in relative wages of job-to-job movers over a similar period. We develop a search model in which firms may offer tenure-based contracts like DB pensions to reduce the incidence of costly on-the-job search by workers. Reduced search costs can, under fairly general conditions, lower the value of deterring search and the use of DB pensions.
Gravity action on the rapidly varying metrics
We consider a four-dimensional simplicial complex and the minisuperspace
general relativity system described by the metric flat in the most part of the
interior of every 4-simplex with exception of a thin layer of thickness
along the every three-dimensional face where the metric
undergoes jump between the two 4-simplices sharing this face. At this jump would become discontinuity. Since, however, discontinuity of
the (induced on the face) metric is not allowed in general relativity, the
terms in the Einstein action tending to infinity at arise.
In the path integral approach, these terms lead to the pre-exponent factor with
\dfuns requiring that the induced on the faces metric be continuous, i. e. the
4-simplices fit on their common faces. The other part of the path integral
measure corresponds to the action being the sum of independent terms over the
4-simplices. Therefore this part of the path integral measure is the product of
independent measures over the 4-simplices. The result obtained is in accordance
with our previous one obtained from the symmetry considerations.Comment: 10 page
Extended bound states and resonances of two fermions on a periodic lattice
The high- cuprates are possible candidates for d-wave superconductivity,
with the Cooper pair wave function belonging to a non-trivial irreducible
representation of the lattice point group. We argue that this d-wave symmetry
is related to a special form of the fermionic kinetic energy and does not
require any novel pairing mechanism. In this context, we present a detailed
study of the bound states and resonances formed by two lattice fermions
interacting via a non-retarded potential that is attractive for nearest
neighbors but repulsive for other relative positions. In the case of strong
binding, a pair formed by fermions on adjacent lattice sites can have a small
effective mass, thereby implying a high condensation temperature. For a weakly
bound state, a pair with non-trivial symmetry tends to be smaller in size than
an s-wave pair. These and other findings are discussed in connection with the
properties of high- cuprate superconductors.Comment: 21 pages, RevTeX, 4 Postscript figures, arithmetic errors corrected.
An abbreviated version (no appendix) appeared in PRB on March 1, 199
One-dimensional Cooper pairing
We study electron pairing in a one-dimensional (1D) fermion gas at zero
temperature under zero- and finite-range, attractive, two-body interactions.
The binding energy of Cooper pairs (CPs) with zero total or center-of-mass
momentum (CMM) increases with attraction strength and decreases with
interaction range for fixed strength. The excitation energy of 1D CPs with
nonzero CMM display novel, unique properties. It satisfies a dispersion
relation with \textit{two} branches: a\ phonon-like \textit{linear }excitation
for small CP CMM; this is followed by roton-like \textit{quadratic} excitation
minimum for CMM greater than twice the Fermi wavenumber, but only above a
minimum threshold attraction strength. The expected quadratic-in-CMM dispersion
\textit{in vacuo }when the Fermi wavenumber is set to zero is recovered for
\textit{any% } coupling. This paper completes a three-part exploration
initiated in 2D and continued in 3D.Comment: 12 pages, 6 figure
A New Approach to Solve the Low-lying States of the Schroedinger Equation
We review a new iterative procedure to solve the low-lying states of the
Schroedinger equation, done in collaboration with Richard Friedberg. For the
groundstate energy, the order iterative energy is bounded by a finite
limit, independent of ; thereby it avoids some of the inherent difficulties
faced by the usual perturbative series expansions. For a fairly large class of
problems, this new procedure can be proved to give convergent iterative
solutions. These convergent solutions include the long standing difficult
problem of a quartic potential with either symmetric or asymmetric minima.Comment: 54 pages, 3 figures given separatel
Biases in the Experimental Annotations of Protein Function and their Effect on Our Understanding of Protein Function Space
The ongoing functional annotation of proteins relies upon the work of
curators to capture experimental findings from scientific literature and apply
them to protein sequence and structure data. However, with the increasing use
of high-throughput experimental assays, a small number of experimental studies
dominate the functional protein annotations collected in databases. Here we
investigate just how prevalent is the "few articles -- many proteins"
phenomenon. We examine the experimentally validated annotation of proteins
provided by several groups in the GO Consortium, and show that the distribution
of proteins per published study is exponential, with 0.14% of articles
providing the source of annotations for 25% of the proteins in the UniProt-GOA
compilation. Since each of the dominant articles describes the use of an assay
that can find only one function or a small group of functions, this leads to
substantial biases in what we know about the function of many proteins.
Mass-spectrometry, microscopy and RNAi experiments dominate high throughput
experiments. Consequently, the functional information derived from these
experiments is mostly of the subcellular location of proteins, and of the
participation of proteins in embryonic developmental pathways. For some
organisms, the information provided by different studies overlap by a large
amount. We also show that the information provided by high throughput
experiments is less specific than those provided by low throughput experiments.
Given the experimental techniques available, certain biases in protein function
annotation due to high-throughput experiments are unavoidable. Knowing that
these biases exist and understanding their characteristics and extent is
important for database curators, developers of function annotation programs,
and anyone who uses protein function annotation data to plan experiments.Comment: Accepted to PLoS Computational Biology. Press embargo applies. v4:
text corrected for style and supplementary material inserte
Nuclear and Particle Physics applications of the Bohm Picture of Quantum Mechanics
Approximation methods for calculating individual particle/ field motions in
spacetime at the quantum level of accuracy (a key feature of the Bohm Picture
of Quantum Mechanics (BP)), are studied. Modern textbook presentations of
Quantum Theory are used throughout, but only to provide the necessary, already
existing, tested formalisms and calculational techniques. New coherent
insights, reinterpretations of old solutions and results, and new (in principle
testable) quantitative and qualitative predictions, can be obtained on the
basis of the BP that complete the standard type of postdictions and
predictions.Comment: 41 page
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