254 research outputs found
Percolative shunting on electrified surface
The surface discharge of electrified dielectrics at high humidity is
considered. The percolative nature of charge transport in electrets is
established. Particular attention is given to the phenomena of adsorption and
nucleation of electrically conducting phase in the cause of percolation cluster
growth on electrified surface. The critical index of the correlation lenght for
percolation cluster is found, and its value is in good agreement with the known
theoretical estimations.Comment: 4 pages with 1 figure, revtex, published in Tech. Phys. Lett. 25
(1999) 877-879 with one additional figur
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
Resistive state of superconducting structures with fractal clusters of a normal phase
The effect of morphologic factors on magnetic flux dynamics and critical
currents in percolative superconducting structures is considered. The
superconductor contains the fractal clusters of a normal phase, which act as
pinning centers. The properties of these clusters are analyzed in the general
case of gamma-distribution of their areas. The statistical characteristics of
the normal phase clusters are studied, the critical current distribution is
derived, and the dependencies of the main statistical parameters on the fractal
dimension are found. The effect of fractal clusters of a normal phase on the
electric field induced by the motion of the magnetic flux after the vortices
have been broken away from pinning centers is considered. The voltage-current
characteristics of fractal superconducting structures in a resistive state for
an arbitrary fractal dimension are obtained. It is found that the fractality of
the boundaries of normal phase clusters intensifies magnetic flux trapping and
thereby increases the current-carrying capability of the superconductor.Comment: 15 pages with 8 figures, revtex3, alternative e-mail of author is
[email protected]
Toward An Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights
In this paper we return to the old problem of conal component-pair widths and
profile dimensions. Observationally, we consider a set of 10 pulsars with
prominent conal component pairs, for which well measured profiles exist over
the largest frequency range now possible. Apart from some tendency to narrow at
high frequency, the conal components exhibit almost constant widths. We use all
three profile measures, the component separation as well as the outside
half-power and 10% widths, to determine conal beam radii, which are the focus
of our subsequent analysis. These radii at different frequencies are well
fitted by a relationship introduced by Thorsett (1991), but the resulting
parameters are highly correlated. Three different types of behavior are found:
one group of stars exhibits a continuous variation of beam radius which can be
extrapolated down to the stellar surface along the ``last open field lines''; a
second group exhibits beam radii which asymptotically approach a minimum high
frequency value that is 3--5 times larger; and a third set shows almost no
spectral change in beam radius at all. The first two behaviors are associated
with outer-cone component pairs; whereas the constant separation appears to
reflect inner-cone emission.Comment: 21 pages, 11 figures, accepted for publication in Astrophysical
Journal, uses aaste
New constraints for non-Newtonian gravity in nanometer range from the improved precision measurement of the Casimir force
We obtain constraints on non-Newtonian gravity following from the improved
precision measurement of the Casimir force by means of atomic force microscope.
The hypothetical force is calculated in experimental configuration (a sphere
above a disk both covered by two metallic layers). The strengthenings of
constraints up to 4 times comparing the previous experiment and up to 560 times
comparing the Casimir force measurements between dielectrics are obtained in
the interaction range 5.9 nmnm. Recent speculations about
the presence of some unexplained attractive force in the considered experiment
are shown to be unjustified.Comment: 5 pages, 1 figur
Towards the solution of the anomaly in shell-model calculations of muon capture
Recently many authors have performed shell-model calculations of nuclear
matrix elements determining the rates of the ordinary muon capture in light
nuclei. These calculations have employed well-tested effective interactions in
large scale shell-model studies. For one of the nuclei of interest, namely
Si, there exists recent experimental data which can be used to deduce
the value of the ratio by using the calculated matrix elements.
Surprisingly enough, all the abovementioned shell-model results suggest a very
small value () for , quite far from the PCAC prediction
and recent data on muon capture in hydrogen. We show that this rather
disturbing anomaly is solved by employing effective transition operators. This
finding is also very important in studies of the scalar coupling of the weak
charged current of leptons and hadrons.Comment: Revtex, 6 pages, 2 figs include
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
Comparison of superconductivity in Sr_2RuO_4 and copper oxides
To compare the superconductivity in strongly correlated electron systems with
the antiferromagnetic fluctuations in the copper oxides and with the
ferromagnetic fluctuations in Sr_2RuO_4 a t-J-I model is proposed. The
antiferromagnetic coupling J results in the superconducting state of
d_{x^2-y^2} symmetry and the ferromagnetic coupling constant I results in the
spin-triplet p-type state. The difference in the gap anisotropies provides the
large difference in T_c values, for the typical values of the coupling
constants: T_c of order of 1K for the ruthenate and T_c of order of 100K for
the cuprates.Comment: 4 pages, RevTEX, 3 figs. Submitted to Phys. Rev. Let
Constraints for hypothetical interactions from a recent demonstration of the Casimir force and some possible improvements
The Casimir force is calculated in the configuration of a spherical lens and
a disc of finite radius covered by and thin layers which was used in
a recent experiment. The correction to the Casimir force due to finiteness of
the disc radius is shown to be negligible. Also the corrections are discussed
due to the finite conductivity, large-scale and short-scale deviations from the
perfect shape of the bounding surfaces and the temperature correction. They
were found to be essential when confronting the theoretical results with
experimental data. Both Yukawa-type and power-law hypothetical forces are
computed which may act in the configuration under consideration due to the
exchange of light and/or massless elementary particles between the atoms of the
lens and the disc. New constraints on the constants of these forces are
determined which follow from the fact that they were not observed within the
limits of experimental errors. For Yukawa-type forces the new constraints are
up to 30 times stronger than the best ones known up today. A possible
improvement of experimental parameters is proposed which gives the possibility
to strengthen constraints on Yukawa-type interactions up to times and on
power-law interactions up to several hundred times.Comment: 15 pages, 3 figures, subm. to Phys. Rev.
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
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