714 research outputs found
Inequality reversal: effects of the savings propensity and correlated returns
In the last decade, a large body of literature has been developed to explain
the universal features of inequality in terms of income and wealth. By now, it
is established that the distributions of income and wealth in various economies
show a number of statistical regularities. There are several models to explain
such static features of inequality in an unifying framework and the kinetic
exchange models, in particular, provide one such framework. Here we focus on
the dynamic features of inequality. In the process of development and growth,
inequality in an economy in terms of income and wealth follows a particular
pattern of rising in the initial stage followed by an eventual fall. This
inverted U-shaped curve is known as the Kuznets Curve. We examine the
possibilities of such behavior of an economy in the context of a generalized
kinetic exchange model. It is shown that under some specific conditions, our
model economy indeed shows inequality reversal.Comment: 15 pages, 5 figure
Ondansetron does not inhibit the analgesic effect of alfentanil
5-Hydroxytryptamine (5-HT) causes antinociception via presynaptic 5-HT3 (5-HT subtype 3) receptors on primary afferent nociceptive neurones in the spinal cord dorsal horn. Therefore, ondansetron (a 5-HT3 receptor antagonist) may increase the perception of a noxious stimulus or decrease the effects of concurrently administered antinociceptive drugs. Using a randomized, doubleblind, crossover study design, we have tested this hypothesis in eight healthy volunteers who, on three different days, received either ondansetron and placebo, ondansetron and alfentanil or placebo and alfentanil. Experimental pain was induced with heat, cold, mechanical pressure and electrical stimulation. Ondansetron alone did not change the response to any of the experimental tests, but alfentanil and the combination ondansetron- alfentanil significantly changed the response compared with ondansetron alone. There was no difference between alfentanil alone and the combination ondansetron-alfentanil. We conclude that ondansetron does not change the response to pressure, heat, cold or electrical nociceptive stimuli or antagonize the analgesic effect of alfentani
Two subgroups of antipsychotic-naive, first-episode schizophrenia patients identified with a Gaussian mixture model on cognition and electrophysiology
AbstractDeficits in information processing and cognition are among the most robust findings in schizophrenia patients. Previous efforts to translate group-level deficits into clinically relevant and individualized information have, however, been non-successful, which is possibly explained by biologically different disease subgroups. We applied machine learning algorithms on measures of electrophysiology and cognition to identify potential subgroups of schizophrenia. Next, we explored subgroup differences regarding treatment response. Sixty-six antipsychotic-naive first-episode schizophrenia patients and sixty-five healthy controls underwent extensive electrophysiological and neurocognitive test batteries. Patients were assessed on the Positive and Negative Syndrome Scale (PANSS) before and after 6 weeks of monotherapy with the relatively selective D2 receptor antagonist, amisulpride (280.3±159âmg per day). A reduced principal component space based on 19 electrophysiological variables and 26 cognitive variables was used as input for a Gaussian mixture model to identify subgroups of patients. With support vector machines, we explored the relation between PANSS subscores and the identified subgroups. We identified two statistically distinct subgroups of patients. We found no significant baseline psychopathological differences between these subgroups, but the effect of treatment in the groups was predicted with an accuracy of 74.3% (P=0.003). In conclusion, electrophysiology and cognition data may be used to classify subgroups of schizophrenia patients. The two distinct subgroups, which we identified, were psychopathologically inseparable before treatment, yet their response to dopaminergic blockade was predicted with significant accuracy. This proof of principle encourages further endeavors to apply data-driven, multivariate and multimodal models to facilitate progress from symptom-based psychiatry toward individualized treatment regimens.</jats:p
Non BPS noncommutative vortices
We construct exact vortex solutions to the equations of motion of the Abelian
Higgs model defined in non commutative space, analyzing in detail the
properties of these solutions beyond the BPS point. We show that our solutions
behave as smooth deformations of vortices in ordinary space time except for
parity symmetry breaking effects induced by the non commutative parameter
.Comment: 17 pages, 5 figure
Matrix Models
Matrix models and their connections to String Theory and noncommutative
geometry are discussed. Various types of matrix models are reviewed. Most of
interest are IKKT and BFSS models. They are introduced as 0+0 and 1+0
dimensional reduction of Yang--Mills model respectively. They are obtained via
the deformations of string/membrane worldsheet/worldvolume. Classical solutions
leading to noncommutative gauge models are considered.Comment: Lectures given at the Winter School on Modern Trends in
Supersymmetric Mechanics, March 2005 Frascati; 38p
Tachyon Tube and Supertube
We search for tubular solutions in unstable D3-brane. With critical electric
field E=1, solutions representing supertubes, which are supersymmetric bound
states of fundamental strings, D0-branes, and a cylindrical D2-brane, are found
and shown to exhibit BPS-like property. We also point out that boosting such a
{\it tachyon tube} solution generates string flux winding around the tube,
resulting in helical electric fluxes on the D2-brane. We also discuss issues
related to fundamental string, absence of magnetic monopole, and finally more
tachyon tubes with noncritical electric field.Comment: 21 pages, 3 figure
Non-Abelian Chern-Simons Particles and their Quantization
A many--body Schr\"odinger equation for non--Abelian Chern--Simons particles
is obtained from both point--particle and field--theoretic pictures. We present
a particle Lagrangian and a field theoretic Lagrange density, and discuss their
properties. Both are quantized by the symplectic method of Hamiltonian
reduction. An --body Schr\"odinger equation for the particles is obtained
from both starting points. It is shown that the resulting interaction between
particles can be replaced by non--trivial boundary conditions. Also, the
equation is compared with the one given in the literature.Comment: 18 pages, MIT preprint CTP # 227
Forced Topological Nontrivial Field Configurations
The motion of a one-dimensional kink and its energy losses are considered as
a model of interaction of nontrivial topological field configurations with
external fields. The approach is based on the calculation of the zero modes
excitation probability in the external field. We study in the same way the
interaction of the t'Hooft-Polyakov monopole with weak external fields. The
basic idea is to treat the excitation of a monopole zero mode as the monopole
displacement. The excitation is found perturbatively. As an example we consider
the interaction of the t'Hooft-Polyakov monopole with an external uniform
magnetic field.Comment: 18 pages, 3 Postscript figures, RevTe
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