7,213 research outputs found
Energy-momentum conservation in pre-metric electrodynamics with magnetic charges
A necessary and sufficient condition for energy-momentum conservation is
proved within a topological, pre-metric approach to classical electrodynamics
including magnetic as well as electric charges. The extended Lorentz force,
consisting of mutual actions by F=(E, B) on the electric current and G=(H, D)
on the magnetic current, can be derived from an energy-momentum "potential" if
and only if the constitutive relation G=G(F) satisfies a certain vanishing
condition. The electric-magnetic reciprocity introduced by Hehl and Obukhov is
seen to define a complex structure on the tensor product of 2-form pairs (F,G)
which is independent of but consistent with the Hodge star operator defined by
any Lorentzian metric. Contrary to a recent claim in the literature, it does
not define a complex structure on the space of 2-forms itself.Comment: 8 pages, 1 fugur
International capital mobility in an era of globalisation: adding a political dimension to the 'Feldstein–Horioka Puzzle'
The debate about the scope of feasible policy-making in an era of globalisation continues to be set within the context of an assumption that national capital markets are now perfectly integrated at the international level. However, the empirical evidence on international capital mobility contradicts such an assumption. As a consequence, a significant puzzle remains. Why is it, in a world in which the observed pattern of capital flows is indicative of a far from globalised reality, that public policy continues to be constructed in line with more extreme variants of the globalisation hypothesis? I attempt to solve this puzzle by arguing that ideas about global capital market integration have an independent causal impact on political outcomes which extends beyond that which can be attributed to the extent of their actual integration
Seidel elements and mirror transformations
The goal of this article is to give a precise relation between the mirror
symmetry transformation of Givental and the Seidel elements for a smooth
projective toric variety with nef. We show that the Seidel elements
entirely determine the mirror transformation and mirror coordinates.Comment: 36 pages. We corrected several issues as pointed out by the refere
Asymptotic corrections to the eigenvalue density of the GUE and LUE
We obtain correction terms to the large N asymptotic expansions of the
eigenvalue density for the Gaussian unitary and Laguerre unitary ensembles of
random N by N matrices, both in the bulk of the spectrum and near the spectral
edge. This is achieved by using the well known orthogonal polynomial expression
for the kernel to construct a double contour integral representation for the
density, to which we apply the saddle point method. The main correction to the
bulk density is oscillatory in N and depends on the distribution function of
the limiting density, while the corrections to the Airy kernel at the soft edge
are again expressed in terms of the Airy function and its first derivative. We
demonstrate numerically that these expansions are very accurate. A matching is
exhibited between the asymptotic expansion of the bulk density, expanded about
the edge, and the asymptotic expansion of the edge density, expanded into the
bulk.Comment: 14 pages, 4 figure
A Morse-theoretical analysis of gravitational lensing by a Kerr-Newman black hole
Consider, in the domain of outer communication of a Kerr-Newman black hole, a
point (observation event) and a timelike curve (worldline of light source).
Assume that the worldline of the source (i) has no past end-point, (ii) does
not intersect the caustic of the past light-cone of the observation event, and
(iii) goes neither to the horizon nor to infinity in the past. We prove that
then for infinitely many positive integers k there is a past-pointing lightlike
geodesic of (Morse) index k from the observation event to the worldline of the
source, hence an observer at the observation event sees infinitely many images
of the source. Moreover, we demonstrate that all lightlike geodesics from an
event to a timelike curve in the domain of outer communication are confined to
a certain spherical shell. Our characterization of this spherical shell shows
that in the Kerr-Newman spacetime the occurrence of infinitely many images is
intimately related to the occurrence of centrifugal-plus-Coriolis force
reversal.Comment: 14 pages, 2 figures; REVTEX; submitted to J. Math. Phy
The Evolution of Anodic Hydrogen on High Purity Magnesium in Acidic Buffer Solution
Hydrogen evolution (HE) on anodically polarized Mg, commonly referred to as Negative Difference Effect, was studied by galvanodynamic measurements coupled with real-time gravimetric H2 volume collection, the Scanning Vibrating Electrode Technique and potentiodynamic polarization experiments. High purity Mg (99.96% Mg) electrodes were studied in chloride-free 0.1 M citric acid solution buffered at pH with the aim of determining the source of anodic HE and the role of the corrosion film on the process. In such conditions of pH, the typical dark corrosion product exhibited in neutral and alkaline solutions was not found but the HE rate still increased with increasing potential. Evidence that HE on dissolving high purity Mg is associated with the regions dominated by the anodic dissolution reaction is provided. The role of noble impurity enrichment on the electrode surface during anodic polarization and the effect of Fe re-deposition are also discussed
SENSORS: A Novel Lateral Field Excited Acoustic Wave Sensor for Chemical and Biological Agents
Sensors for the sensitive and selective detection of chemical agents and a biological agent are being developed. The sensor structure consists of a piezoelectric platform that is coated with a film that selectively sorbs a chemical or biological agent of interest. The sensitivity of the sensor is embodied in the sensor platform, which consists of a quartz crystal that is excited by a lateral electric field. The exciting electrodes are placed opposite to the sensing surface, and the sensing film is attached directly to the sensor platform. This arrangement is in contrast to the standard quartz microbalance (QCM), where the sensing surface is normally coated with a gold film, and it offers increased sensitivity along with selectivity. The high sensitivity exhibited by this novel lateral-field-excited (LFE) QCM is attributed to the fact that the sensor can measure both electrical and mechanical property changes in the sensing film caused by the sorbed chemical or biological agent. The selectivity of the LFE-QCM sensor is obtained by performing molecular filtering directly in the sensing film. In this specific project the LFE-QCM sensor is being designed to detect two specific chemicals and one biological agent. The target chemicals are dimethyl phosponate (DMMP), which simulates VX and G nerve agents, and an organophosphate pesticide that is chemically similar to many other chemical-warfare agents. The biological agent is E. coli O157:H7, which could appear in food or water supplies. In order to realize the desired chemical and biological sensors, the research team is exploring several issues relating to the LFE-QCM platform and the sensing film. These issues include the optimum electrode geometry in the LFE-QCM platform, the development of novel polymer and silica films for the detection of organophosphates in water, and the coupling of E. coli antibodies to the sensing surface. Homeland security as well as environmental and industrial health concerns dictate that improved chemical and biological sensors must be developed and deployed. After various sorbate-selective films have been attached to the LFE-QCM surface, they will be exposed to the chemical simulants and the biological agent in order to determine the sensing properties. It is anticipated that the proposed work on these organo-phosphorus chemicals and E. coli can be extended to development of selective sensors for other significant chemical and biological agents. In addition, by coupling with existing GK-12 and REU programs, this project will contribute to the education of a number of students and teachers who will participate in the research program
Split structures in general relativity and the Kaluza-Klein theories
We construct a general approach to decomposition of the tangent bundle of
pseudo-Riemannian manifolds into direct sums of subbundles, and the associated
decomposition of geometric objects. An invariant structure {\cal H}^r defined
as a set of r projection operators is used to induce decomposition of the
geometric objects into those of the corresponding subbundles. We define the
main geometric objects characterizing decomposition. Invariant non-holonomic
generalizations of the Gauss-Codazzi-Ricci's relations have been obtained. All
the known types of decomposition (used in the theory of frames of reference, in
the Hamiltonian formulation for gravity, in the Cauchy problem, in the theory
of stationary spaces, and so on) follow from the present work as special cases
when fixing a basis and dimensions of subbundles, and parameterization of a
basis of decomposition. Various methods of decomposition have been applied here
for the Unified Multidimensional Kaluza-Klein Theory and for relativistic
configurations of a perfect fluid. Discussing an invariant form of the
equations of motion we have found the invariant equilibrium conditions and
their 3+1 decomposed form. The formulation of the conservation law for the curl
has been obtained in the invariant form.Comment: 30 pages, RevTeX, aps.sty, some additions and corrections, new
references adde
A Randomized Controlled Study of Parent-assisted Children’s Friendship Training with Children having Autism Spectrum Disorders
This study evaluated Children’s Friendship Training (CFT), a manualized parent-assisted intervention to improve social skills among second to fifth grade children with autism spectrum disorders. Comparison was made with a delayed treatment control group (DTC). Targeted skills included conversational skills, peer entry skills, developing friendship networks, good sportsmanship, good host behavior during play dates, and handling teasing. At post-testing, the CFT group was superior to the DTC group on parent measures of social skill and play date behavior, and child measures of popularity and loneliness, At 3-month follow-up, parent measures showed significant improvement from baseline. Post-hoc analysis indicated more than 87% of children receiving CFT showed reliable change on at least one measure at post-test and 66.7% after 3 months follow-up
- …