3,173 research outputs found
Regional Science Reconsidered
Because disciplines and their cores and boundaries are subject to change, a periodic introspective assessment can be useful in evaluating the relevance of a changing discipline to the equally dynamic and pressing needs of society. Similar examinations of other disciplines, notably economics, have been conducted in part as a means of minimizing the risks of declining credibility, policy relevance, and societal benefit. With the Southern Regional Science Association celebrating recently its 50th meeting, and as regional science itself approaches its 60th year, this paper provides a reexamination of the core of regional science. We consider the theoretical and methodological underpinnings and current status, the various roles played by space in various representations, and the values that guide our policy advice and recommendations. While cores and boundaries of regional science cannot be unambiguously identified, particularly due to the considerable overlap with and lineage to other disciplines, we conclude that it is precisely the interdisciplinarity of regional science that distinguishes it from other social sciences, and ensures its continued relevance
Supersymmetric Sum Rules for Electromagnetic Multipoles
We derive model independent, non-perturbative supersymmetric sum rules for
the magnetic and electric multipole moments of any theory with N=1
supersymmetry. We find that in any irreducible N=1 supermultiplet the diagonal
matrix elements of the l-multipole moments are completely fixed in terms of
their off-diagonal matrix elements and the diagonal (l-1)-multipole moments.Comment: 10 pages, plain Te
Relationship of social and economic factors to mental disorders among population-based samples of Jamaicans and Guyanese
BACKGROUND: There have been growing concerns about increasing mental health problems in the Caribbean region. This study explores rates and factors associated with selected mental health disorders within 2 Caribbean countries: Jamaica and Guyana. METHODS: Probability samples of 1218 Jamaicans and 2068 Guyanese participants were used. A modified version of the WHO Composite International Diagnostic Interview (WHO CIDI) defined by the Diagnostic Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) was administered in order to assess lifetime mental disorders. Descriptive statistics, χ(2) and hierarchical regression analytic procedures were used to examine rates and factors associated with mental disorders. RESULTS: Rates of mental health conditions were different across contexts and were generally higher for Guyanese compared with Jamaicans for alcohol abuse (3.6% vs 2.2%), drug abuse (1.4% vs 1.3%), substance abuse (4.7% vs 2.7%) and mania (0.4% vs 0.1%). The rate of depression, however, was higher among Jamaicans than Guyanese (7.4% vs 4.1%). There were also noticeable differences in rates in both countries, due to social and economic factors, with social factors playing a larger contributory role in the mental health status of individuals across countries. CONCLUSIONS: The results of this study suggest the need for more indepth analyses of factors contributing to mental health conditions of peoples within the Caribbean region, including the influence of additional sources of stress, quality of care and help-seeking behaviours of individuals
On the possibility of a relativistic correction to the E and B fields around a current-carrying wire
It is well known that electric and magnetic fields may change when they are
observed from different frames of reference. For example, the motion of a
charged probe particle moving parallel to a current-carrying wire would be
described by utilizing different electric or magnetic fields, depending on from
which frame of reference the system is observed and described. To describe the
situation in all frames by utilizing the theory of relativity, one has to first
describe the situation in one particular frame, and this choice in the case of
a current-carrying wire is the topic of this paper. In this study I examine an
alternative to the standard choice, and consider its theoretical and
experimental validity. An outcome of the alternative approach is that in the
rest frame of a wire, running a current introduces also an electric field by
giving rise to a minute charge. Present day experimental sensitivities,
specifically those of cold ions, may be able to differentiate between the
observable signatures predicted by the different approaches
Internal Structure and Apsidal Motions of Polytropic Stars in Close Binaries
We consider a synchronized, circular-orbit binary consisting of a polytrope
with index n and a point-mass object, and use a self-consistent field method to
construct the equilibrium structure of the polytrope under rotational and tidal
perturbations. Our self-consistent field method is distinct from others in that
the equilibrium orbital angular velocity is calculated automatically rather
than being prescribed, which is crucial for obtaining apsidal motion rates
accurately. We find that the centrifugal and tidal forces make perturbed stars
more centrally condensed and larger in size. For n=1.5 polytopes with fixed
entropy, the enhancement factor in stellar radii is about 23% and 4-8% for mu=1
and sim0.1-0.9, respectively, where mu is the fractional mass of the polytrope
relative to the total. The centrifugal force dominates the tidal force in
determining the equilibrium structure provided mu > 0.13-0.14 for n > 1.5. The
shape and size of rotationally- and tidally-perturbed polytropes are well
described by the corresponding Roche models as long as n > 2. The apsidal
motion rates calculated for circular-orbit binaries under the equilibrium tide
condition agree well with the predictions of the classical formula only when
the rotational and tidal perturbations are weak. When the perturbations are
strong as in critical configurations, the classical theory underestimates the
real apsidal motion rates by as much as 50% for n=1.5 polytropes, although the
discrepancy becomes smaller as n increases. For practical uses, we provide
fitting formulae for various quantities including the density concentration,
volume radius, and effective internal structure constant, as functions of mu
and the perturbation parameters.Comment: 48 pages, 17 figures, 9 Tables. To appear in the ApJ (v699 issue
Lorentz-Abraham-Dirac vs Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions)
When the parameters of electron - extreme power laser interaction enter the
regime of dominated radiation reaction, the electron dynamics changes
qualitatively. The adequate theoretical description of this regime becomes
crutially important with the use of the radiation friction force either in the
Lorentz-Abraham-Dirac form, which possess unphysical runaway solutions, or in
the Landau-Lifshitz form, which is a perturbation valid for relatively low
electromagnetic wave amplitude. The goal of the present paper is to find the
limits of the Landau-Lifshitz radiation force applicability in terms of the
electromagnetic wave amplitude and frequency. For this a class of the exact
solutions to the nonlinear problems of charged particle motion in the
time-varying electromagnetic field is used.Comment: 14 pages, 5 figure
A theory of intense-field dynamic alignment and high harmonic generation from coherently rotating molecules and interpretation of intense-field ultrafast pump-probe experiments
A theory of ultra-fast pump-probe experiments proposed by us earlier [F.H.M.
Faisal et al., Phys. Rev. Lett. 98, 143001 (2007) and F.H.M. Faisal and A.
Abdurrouf, Phys. Rev. Lett. 100, 123005 (2008)] is developed here fully and
applied to investigate the phenomena of dynamic alignment and high harmonic
generation (HHG) from coherently rotating linear molecules. The theory provides
essentially analytical results for the signals that allow us to investigate the
simultaneous dependence of the HHG signals on the two externally available
control parameters, namely, the relative angle between the polarizations, and
the delay-time between the two pulses. It is applied to investigate the
characteristics of high harmonic emission from nitrogen and oxygen molecules
that have been observed experimentally in a number of laboratories. The results
obtained both in the time-domain and in the frequency-domain are compared with
the observed characteristics as well as directly with the data and are found to
agree remarkably well. In addition we have predicted the existence of a "magic"
polarization angle at which all modulations of the harmonic emission from
nitrogen molecule changes to a steady emission at the harmonic frequency. Among
other things we have also shown a correlation between the existence of the
"magic" or critical polarization angles and the symmetry of the active
molecular orbitals, that is deemed to be useful in connection with the "inverse
problem" of molecular imaging from the HHG data.Comment: 31 pages, 22 figures, and 140 equation
Canonical and kinetic forms of the electromagnetic momentum in an ad hoc quantization scheme for a dispersive dielectric
An ad hoc quantization scheme for the electromagnetic field in a weakly
dispersive, transparent dielectric leads to the definition of canonical and
kinetic forms for the momentum of the electromagnetic field in a dispersive
medium. The canonical momentum is uniquely defined as the operator that
generates spatial translations in a uniform medium, but the quantization scheme
suggests two possible choices for the kinetic momentum operator, corresponding
to the Abraham or the Minkowski momentum in classical electrodynamics. Another
implication of this procedure is that a wave packet containing a single dressed
photon travels at the group velocity through the medium. The physical
significance of the canonical momentum has already been established by
considerations of energy and momentum conservation in the atomic recoil due to
spontaneous emission, the Cerenkov effect, the Doppler effect, and phase
matching in nonlinear optical processes. In addition, the data of the Jones and
Leslie radiation pressure experiment is consistent with the assignment of one
?k unit of canonical momentum to each dressed photon. By contrast, experiments
in which the dielectric is rigidly accelerated by unbalanced electromagnetic
forces require the use of the Abraham momentum.Comment: 21 pages, 1 figure, aip style, submitted to PR
Prevalence and correlates of physical health conditions in Jamaica and Guyana
The increasing prevalence of non-communicable diseases remains an important source of concern in
the Caribbean and Latin American regions. This study examines rates and the associated socio-
demographic correlates of physical health indicators in Jamaica and Guyana. Area probability cross-
sectional data were collected on 1,218 Jamaicans and 2,068 Guyanese participants in 2005. Physician-
diagnosed hypertension, diabetes mellitus, arthritis, and self-rated oral and general physical health
were assessed using descriptive statistics, chi-square, and hierarchical logistic regression analytic
procedures. Jamaicans generally reported poorer physical health, including diabetes mellitus, arthritis,
and overall perceived oral and physical health compared to Guyanese; Guyanese reported higher rates
of hypertension. Generally, lower social and economic standing was associated with poorer health
conditions but made different contributions across countries. The study highlights the need for greater
awareness and access to health care services for individuals who are especially vulnerable to poorer
health. The results of this study suggest the need for additional studies on factors associated with
physical health conditions, including a better understanding of the role of race/ethnicity in the
Caribbean
Minimal Cooling of Neutron Stars: A New Paradigm
A new classification of neutron star cooling scenarios, involving either
``minimal'' cooling or ``enhanced'' cooling is proposed. The minimal cooling
scenario replaces and extends the so-called standard cooling scenario to
include neutrino emission from the Cooper pair breaking and formation process.
This emission dominates that due to the modified Urca process for temperatures
close to the critical temperature for superfluid pairing. Minimal cooling is
distinguished from enhanced cooling by the absence of neutrino emission from
any direct Urca process, due either to nucleons or to exotica. Within the
minimal cooling scenario, theoretical cooling models can be considered to be a
four parameter family involving the equation of state of dense matter,
superfluid properties of dense matter, the composition of the neutron star
envelope, and the mass of the neutron star. Consequences of minimal cooling are
explored through extensive variations of these parameters. Results are compared
with the inferred properties of thermally-emitting neutron stars in order to
ascertain if enhanced cooling occurs in any of them. All stars for which
thermal emissions have been clearly detected are at least marginally consistent
with the lack of enhanced cooling. The two pulsars PSR 0833-45 (Vela) and PSR
1706-44 would require enhanced cooling in case their ages and/or temperatures
are on the lower side of their estimated values whereas the four stars PSR
0656+14, PSR 1055-52, Geminga, and RX J0720.4-3125 may require some source of
internal heating in case their age and/or luminosity are on the upper side of
their estimated values. The new upper limits on the thermal luminosity of PSR
J0205+6449 and RX J0007.0+7302 are indicative of the occurrence of some
enhanced neutrino emission beyond the minimal scenario.Comment: Version to appear in ApJ Supplements. Minor modifications in text and
discussion of updated data with new figure
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