180 research outputs found
On the Strength of Spin-Isospin Transitions in A=28 Nuclei
The relations between the strengths of spin-isospin transition operators
extracted from direct nuclear reactions, magnetic scattering of electrons and
processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur
Formation of "Lightnings" in a Neutron Star Magnetosphere and the Nature of RRATs
The connection between the radio emission from "lightnings" produced by the
absorption of high-energy photons from the cosmic gamma-ray background in a
neutron star magnetosphere and radio bursts from rotating radio transients
(RRATs) is investigated. The lightning length reaches 1000 km; the lightning
radius is 100 m and is comparable to the polar cap radius. If a closed
magnetosphere is filled with a dense plasma, then lightnings are efficiently
formed only in the region of open magnetic field lines. For the radio emission
from a separate lightning to be observed, the polar cap of the neutron star
must be directed toward the observer and, at the same time, the lightning must
be formed. The maximum burst rate is related to the time of the plasma outflow
from the polar cap region. The typical interval between two consecutive bursts
is ~100 s. The width of a single radio burst can be determined both by the
width of the emission cone formed by the lightning emitting regions at some
height above the neutron star surface and by a finite lightning lifetime. The
width of the phase distribution for radio bursts from RRATs, along with the
integrated pulse width, is determined by the width of the bundle of open
magnetic field lines at the formation height of the radio emission. The results
obtained are consistent with the currently available data and are indicative of
a close connection between RRATs, intermittent pulsars, and extreme nullers.Comment: 24 pages, no figures, references update
Magnetothermopower and Magnetoresistivity of RuSr2Gd1-xLaxCu2O8 (x=0, 0.1)
We report measurements of magnetothermopower and magnetoresistivity as a
function of temperature on RuSr2Gd1-xLaxCu2O8 (x = 0, 0.1). The normal-state
thermopower shows a dramatic decrease after applying a magnetic field of 5 T,
whereas the resistivity shows only a small change after applying the same
field. Our results suggest that RuO2 layers are conducting and the magnetic
field induced decrease of the overall thermopower is caused by the decrease of
partial thermopower decrease associated with the spin entropy decrease of the
carriers in the RuO2 layers.Comment: 21 pages, 6 figure
Disorder Induced Ferromagnetism in Restricted Geometries
We study the influence of on-site disorder on the magnetic properties of the
ground state of the infinite Hubbard model. We find that for one
dimensional systems disorder has no influence, while for two dimensional
systems disorder enhances the spin polarization of the system. The tendency of
disorder to enhance magnetism in the ground state may be relevant to recent
experimental observations of spin polarized ground states in quantum dots and
small metallic grains.Comment: 4 pages, 4 figure
Measurement of the Pion Form Factor in the Energy Range 1.04-1.38 GeV with the CMD-2 Detector
The cross section for the process is measured in the
c.m. energy range 1.04-1.38 GeV from 995 000 selected collinear events
including 860000 events, 82000 events, and 33000
events. The systematic and statistical errors of measuring the
pion form factor are equal to 1.2-4.2 and 5-13%, respectively.Comment: 5 pages, 2 figure
Constraints on Non-Newtonian Gravity from Recent Casimir Force Measurements
Corrections to Newton's gravitational law inspired by extra dimensional
physics and by the exchange of light and massless elementary particles between
the atoms of two macrobodies are considered. These corrections can be described
by the potentials of Yukawa-type and by the power-type potentials with
different powers. The strongest up to date constraints on the corrections to
Newton's gravitational law are reviewed following from the E\"{o}tvos- and
Cavendish-type experiments and from the measurements of the Casimir and van der
Waals force. We show that the recent measurements of the Casimir force gave the
possibility to strengthen the previously known constraints on the constants of
hypothetical interactions up to several thousand times in a wide interaction
range. Further strengthening is expected in near future that makes Casimir
force measurements a prospective test for the predictions of fundamental
physical theories.Comment: 20 pages, crckbked.cls is used, to be published in: Proceedings of
the 18th Course of the School on Cosmology and Gravitation: The Gravitational
Constant. Generalized Gravitational Theories and Experiments (30 April- 10
May 2003, Erice). Ed. by G. T. Gillies, V. N. Melnikov and V. de Sabbata,
20pp. (Kluwer, in print, 2003
Beta-decay in odd-A and even-even proton-rich Kr isotopes
Beta-decay properties of proton-rich odd-A and even-even Krypton isotopes are
studied in the framework of a deformed selfconsistent Hartree-Fock calculation
with density-dependent Skyrme forces, including pairing correlations between
like nucleons in BCS approximation. Residual spin-isospin interactions are
consistently included in the particle-hole and particle-particle channels and
treated in Quasiparticle Random Phase Approximation. The similarities and
differences in the treatment of even-even and odd-A nuclei are stressed.
Comparison to available experimental information is done for Gamow-Teller
strength distributions, summed strengths, and half-lives. The dependence of
these observables on deformation is particularly emphasized in a search for
signatures of the shape of the parent nucleus.Comment: 29 pages, 16 figure
Induced pseudoscalar coupling of the proton weak interaction
The induced pseudoscalar coupling is the least well known of the weak
coupling constants of the proton's charged--current interaction. Its size is
dictated by chiral symmetry arguments, and its measurement represents an
important test of quantum chromodynamics at low energies. During the past
decade a large body of new data relevant to the coupling has been
accumulated. This data includes measurements of radiative and non radiative
muon capture on targets ranging from hydrogen and few--nucleon systems to
complex nuclei. Herein the authors review the theoretical underpinnings of
, the experimental studies of , and the procedures and uncertainties
in extracting the coupling from data. Current puzzles are highlighted and
future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic
Arecibo 430 MHz Pulsar Polarimetry: Faraday Rotation Measures and Morphological Classifications
We have measured Faraday Rotation Measures (RMs) at Arecibo Observatory for
36 pulsars, 17 of them new. We combine these and earlier measurements to study
the galactic magnetic field and its possible temporal variations. Many RM
values have changed significantly on several-year timescales, but these
variations probably do not reflect interstellar magnetic field changes. By
studying the distribution of pulsar RMs near the plane in conjunction with the
new NE2001 electron density model, we note the following structures in the
first galactic longitude quadrant: (1) The local field reversal can be traced
as a null in RM in a 0.5-kpc wide strip interior to the Solar Circle, extending
\~7 kpc around the Galaxy. (2) Steadily increasing RMs in a 1-kpc wide strip
interior to the local field reversal, and also in the wedge bounded by 42<l<52
deg, indicate that the large-scale field is approximately steady from the local
reversal in to the Sagittarius arm. (3) The RMs in the 1-kpc wide strip
interior to the Sagittarius arm indicate another field reversal in this strip.
(4) The RMs in a final 1-kpc wide interior strip, straddling the Scutum arm,
also support a second field reversal interior to the Sun,between the
Sagittarius and Scutum arms. (5) Exterior to the nearby reversal, RMs from
60<l<78 deg show evidence for two reversals, on the near and far side of the
Perseus arm. (6) In general, the maxima in the large-scale fields tend to lie
along the spiral arms, while the field minima tend to be found between them. We
have also determined polarized profiles of 48 pulsars at 430 MHz. We present
morphological pulse profile classifications of the pulsars, based on our new
measurements and previously published data.Comment: Accepted by Astrophysical Journal Supplement, 56 pages, 22 fig
Pathogenetic Effects of Bacteria of the Genus <i>Desulfovibrio</i>. Experimental Study. Part One: Iron Metabolism
The aim of the work was to study specific systemic effect of sulfate-reducing bacteria of the genus Desulfovibrio on organism systems through creating an experimental model of intragastric bacterial invasion against the background of dysbiotic conditions of rodent gastrointestinal tract. Materials and methods. The experimental study was conducted on Wistar rats. Intestinal dysbiosis was modeled with the help of antibiotics, amoxicillin and metronidazole. Typical strain Desulfovibrio desulfuricans subsp. desulfuricans VKM B-1799T was used as an infectious agent. Results and discussion. As a result of the experiment performed, during the period of acute infection (on day 15 of the experiment), a direct correlation between the concentration of the injected D. desulfuricans VKM B-1799T bacteria suspension and the serum iron level was observed: the higher the infectious agent dose, the lower the serum iron concentration. During the phase of remote effects (day 38 of the experiment), the inverse correlation between the concentrations of D. desulfuricans VKM B-1799T in the intestines of rodents was revealed: when the concentration of the infecting agent increased from 103 CFU/g and higher, the iron level decreased from 43.5 μmol/l to 38.5 μmol/l. When comparing the level of transferrin and unsaturated iron binding capacity (UIBC), an increase in those parameters was observed in all groups of rats both during the period of acute infection and the period of long-term effects, and the percentage of transferrin iron saturation decreased, indicating the occurrence of iron deficiency against the background of exposure to the infectious agent. Intestinal dysbiosis promotes colonization by opportunistic flora, including Desulfovibrio sp. Changes in the iron metabolism markers in experimental animals against the background of D. desulfuricans VKM B-1799T infestation above 103 CFU/g and the ability of this microorganism to bind iron into an unavailable form suggest that the bacteria Desulfovibrio sp. are one of the key etiological factors of iron deficiency anemia
- …