1,134 research outputs found
Selfgravitating Gas Spheres in a Box and Relativistic Clusters: Relation between Dynamical and Thermodynamical Stability
We derive a variational principle for the dynamical stability of a cluster as
a gas sphere in a box. Newtonian clusters are always dynamically stable and,
for relativistic clusters, the relation between dynamical and thermodynamical
instabilities is analyzed. The boundaries between dynamically and
thermodynamically stable and unstable models are found numerically for
relativistic stellar systems with different cut off parameters. A criterion
based on binding energy curve is used for determination of the boundary of
dynamical stability.Comment: 10 figure
Динамика альфа-активности электроэнцефалографии у человека при триггерной фотостимуляции в контуре интерфейса мозг — компьютер
Trigger photo stimulation (TPS), based on synchronization of flashes of light with events in a brain, for example, with waves of alpha activity EEG, is widely known as a methodical approach for studying of mechanisms of a brain and also as a method of neurologic diagnostics. In the present work TPS has been used for the first time as an element of the brain — computer interface (BCI) where the start of light flashes determined by crossing of definite level by amplitude of EEG alpha-waves. It has been shown that specific reorganizations of alpha-waves time distribution during BCI-training. It testifies that brain develops a new control path by means of EEG alpha-patterns.Триггерная фотостимуляция (ТФ), основанная на синхронизации вспышек света с событиями в мозгу, например с волнами альфа-активности электроэнцефалографии (ЭЭГ), широко известна как методический прием для изучения механизмов мозга и как метод неврологической диагностики. В настоящей работе ТФ впервые была использована как элемент интерфейса мозг — компьютер (ИМК), определяющего протокол запуска вспышек света в зависимости от амплитуды альфаволн ЭЭГ. Было показано, что в ходе ИМК-тренинга наблюдаются специфические перестройки структурной организации альфа-активности в ЭЭГ испытуемого, что свидетельствует об активном освоении мозгом нового канала управления посредством ЭЭГ
Effective Regge QCD
A new framework for a high energy limit of quantum gauge field theories is
introduced. Its potency is illustrated on a new derivation of the reggeization
of the gluon.Comment: Latex, 9 pages + 2 figures as PS-file, extended version, to appear in
Phys. Rev. Let
Estimation of coupling between oscillators from short time series via phase dynamics modeling: limitations and application to EEG data
We demonstrate in numerical experiments that estimators of strength and
directionality of coupling between oscillators based on modeling of their phase
dynamics [D.A. Smirnov and B.P. Bezruchko, Phys. Rev. E 68, 046209 (2003)] are
widely applicable. Namely, although the expressions for the estimators and
their confidence bands are derived for linear uncoupled oscillators under the
influence of independent sources of Gaussian white noise, they turn out to
allow reliable characterization of coupling from relatively short time series
for different properties of noise, significant phase nonlinearity of the
oscillators, and non-vanishing coupling between them. We apply the estimators
to analyze a two-channel human intracranial epileptic electroencephalogram
(EEG) recording with the purpose of epileptic focus localization.Comment: 22 pages, 7 figures, the paper is to be published in Chaos, 2005,
vol.15, issue 2, see http://chaos.aip.org
Clinical and economic comparison of an individualised immunoglobulin protocol vs. standard dosing for chronic inflammatory demyelinating polyneuropathy
Background The clinical and economic implications of an individualised intravenous immunoglobulin (IVIg) protocol for chronic inflammatory demyelinating polyneuropathy (CIDP) are unknown. Comparison with standard dosing regimens has not been performed. Methods We retrospectively studied 47 IVIg-treated subjects with CIDP over 4 years with an individualised, outcome-measured, dose-modifying protocol. We evaluated responder and remission rates, clinical improvement levels and dose requirements. We compared clinical benefits and costs with those reported with standard dosing at 1 g/kg every 3 weeks. Results The IVIg-responder rate was 83% and the 4-year remission rate was 25.6%. Mean IVIg dose requirements were 22.06 g/week (SD:15.29) in patients on ongoing therapy. Dose range was wide (5.83–80 g/week). Mean infusion frequency was every 4.34 weeks (SD:1.70) and infusion duration of 2.79 days (SD:1.15). Mean Overall Neuropathy Limitation Scale improvement was 2.54 (SD:1.89) and mean MRC sum score improvement of 12.23 (SD:7.17) in IVIg-responders. Mean modified-INCAT (Inflammatory Neuropathy Cause and Treatment) score improvement was similar (p = 0.47) and mean MRC sum score improvement greater (p < 0.001) in our cohort, compared to the IVIg-treated arm of the ICE Study. Mean drug costs were GBP 37,660/patient/year (€ 43,309) and mean infusion-related costs of GBP 17,115/patient/year (€ 19,682), totalling GBP 54,775/patient/year (€ 62,991). Compared to standard dosing using recorded weight, mean savings were of GBP 13,506/patient/year (€ 15,532). Compared to standard dosing using dosing weight, savings were of GBP 6,506/patient/year (€ 7,482). Conclusion Our results indicate that an individualised IVIg treatment protocol is clinically non-inferior and 10–25% more cost-effective than standard dosing regimens in CIDP
Analysis of cross-correlations in electroencephalogram signals as an approach to proactive diagnosis of schizophrenia
We apply flicker-noise spectroscopy (FNS), a time series analysis method
operating on structure functions and power spectrum estimates, to study the
clinical electroencephalogram (EEG) signals recorded in children/adolescents
(11 to 14 years of age) with diagnosed schizophrenia-spectrum symptoms at the
National Center for Psychiatric Health (NCPH) of the Russian Academy of Medical
Sciences. The EEG signals for these subjects were compared with the signals for
a control sample of chronically depressed children/adolescents. The purpose of
the study is to look for diagnostic signs of subjects' susceptibility to
schizophrenia in the FNS parameters for specific electrodes and
cross-correlations between the signals simultaneously measured at different
points on the scalp. Our analysis of EEG signals from scalp-mounted electrodes
at locations F3 and F4, which are symmetrically positioned in the left and
right frontal areas of cerebral cortex, respectively, demonstrates an essential
role of frequency-phase synchronization, a phenomenon representing specific
correlations between the characteristic frequencies and phases of excitations
in the brain. We introduce quantitative measures of frequency-phase
synchronization and systematize the values of FNS parameters for the EEG data.
The comparison of our results with the medical diagnoses for 84 subjects
performed at NCPH makes it possible to group the EEG signals into 4 categories
corresponding to different risk levels of subjects' susceptibility to
schizophrenia. We suggest that the introduced quantitative characteristics and
classification of cross-correlations may be used for the diagnosis of
schizophrenia at the early stages of its development.Comment: 36 pages, 6 figures, 2 tables; to be published in "Physica A
Heavy hexaquarks in a chiral constituent quark model
We discuss the stability of hexaquark systems of type uuddsQ (Q=c or b)
within a chiral constituent quark model which successfully describes the baryon
spectra including the charmed ones. We find these systems highly unstable
against strong decays and give a comparison with some of the previous
literature.Comment: 17 pages, Late
Fermions scattering in a three dimensional extreme black hole background
The absorption cross section for scattering of fermions off an extreme BTZ
black hole is calculated. It is shown that, as in the case of scalar particles,
an extreme BTZ black hole exhibits a vanishing absorption cross section, which
is consistent with the vanishing entropy of such object. Additionally, we give
a general argument to prove that the particle flux near the horizon is zero.
Finally we show that the {\it reciprocal space} introduced previously in
\cite{gm} gives rise to the same result and, therefore, it could be considered
as the space where the scattering process takes place in an AdS spacetime.Comment: 15 pages, RevTex4. Revised version. To be published in Class.
Quantum. Gra
Ground-State Magnetization for Interacting Fermions in a Disordered Potential : Kinetic Energy, Exchange Interaction and Off-Diagonal Fluctuations
We study a model of interacting fermions in a disordered potential, which is
assumed to generate uniformly fluctuating interaction matrix elements. We show
that the ground state magnetization is systematically decreased by off-diagonal
fluctuations of the interaction matrix elements. This effect is neglected in
the Stoner picture of itinerant ferromagnetism in which the ground-state
magnetization is simply determined by the balance between ferromagnetic
exchange and kinetic energy, and increasing the interaction strength always
favors ferromagnetism. The physical origin of the demagnetizing effect of
interaction fluctuations is the larger number of final states available for
interaction-induced scattering in the lower spin sectors of the Hilbert space.
We analyze the energetic role played by these fluctuations in the limits of
small and large interaction . In the small limit we do second-order
perturbation theory and identify explicitly transitions which are allowed for
minimal spin and forbidden for higher spin. These transitions then on average
lower the energy of the minimal spin ground state with respect to higher spin.
For large interactions we amplify on our earlier work [Ph. Jacquod and A.D.
Stone, Phys. Rev. Lett. 84, 3938 (2000)] which showed that minimal spin is
favored due to a larger broadening of the many-body density of states in the
low-spin sectors. Numerical results are presented in both limits.Comment: 35 pages, 24 figures - final, shortened version, to appear in
Physical Review
Variations on the Deuteron
We consider few problems which are related to the deuteron and have simple
analytical solution. Relation is found between the deuteron electric quadrupole
moment and the -scattering amplitude. The degree of circular polarization
of photons is calculated for the radiative capture of longitudinally polarized
thermal neutrons. The anapole, electric dipole and magnetic quadrupole moments
of the deuteron are calculated.Comment: 14 pages, late
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