10,321 research outputs found
On meteor stream spatial structure theory
The classical spatial representation of meteor streams is an elliptical torus with variable cross section. The position of this torus in space is determined by the mean orbit elements that may be obtained directly from observations of individual meteor stream particles when crossed by the Earth. Since the orbits of individual particles of a stream differ from each other, the distance between them on a plane normal to the mean orbit of elliptical torus forms some area, i.e., a cross section. The size and form of these cross sections change with the change of the direction among the mean orbit and are completely defined by the dispersion values of the orbit elements in a stream. An attempt was made to create an analytical method that would permit description of the spatial and time parameters of meteor streams, i.e., the form and size of their cross section, density of incident flux and their variations along the mean orbit and in time. In this case, the stream is considered as a continuous flux rather than a set of individual particles
Full counting statistics of a charge pump in the Coulomb blockade regime
We study the full charge counting statistics of a charge pump based on a
nearly open single electron transistor. The problem is mapped onto an exactly
soluble problem of a g=1/2 non-equilibrium Luttinger liquid with an impurity.
We obtain an analytic expression for the generating function of the transmitted
charge for an arbitrary pumping strength. Even though this model contains
fractionally charged excitations only integer transmitted charges can be
observed during finite observation times.Comment: 4 pages, 1 figur
Andreev tunneling through a double quantum-dot system coupled to a ferromagnet and a superconductor: effects of mean field electronic correlations
We study the transport properties of a hybrid nanostructure composed of a
ferromagnet, two quantum dots, and a superconductor connected in series. By
using the non-equilibrium Green's function approach, we have calculated the
electric current, the differential conductance and the transmittance for
energies within the superconductor gap. In this regime, the mechanism of charge
transmission is the Andreev reflection, which allows for a control of the
current through the ferromagnet polarization. We have also included interdot
and intradot interactions, and have analyzed their influence through a mean
field approximation. In the presence of interactions, Coulomb blockade tend to
localized the electrons at the double-dot system, leading to an asymmetric
pattern for the density of states at the dots, and thus reducing the
transmission probability through the device. In particular, for non-zero
polarization, the intradot interaction splits the spin degeneracy, reducing the
maximum value of the current due to different spin-up and spin-down densities
of states. Negative differential conductance (NDC) appears for some regions of
the voltage bias, as a result of the interplay of the Andreev scattering with
electronic correlations. By applying a gate voltage at the dots, one can tune
the effect, changing the voltage region where this novel phenomenon appears.
This mechanism to control the current may be of importance in technological
applications.Comment: 12 pages, 11 figure
Estimation of the particle-antiparticle correlation effect for pion production in heavy ion collisions
Estimation of the back-to-back pi-pi correlations arising due to evolution of
the pionic field in the course of pion production process is given for central
heavy nucleus collisions at moderate energies.Comment: 6 LaTeX pages + 5 ps figure
Two-photon correlations as a sign of sharp transition in quark-gluon plasma
The photon production arising due to time variation of the medium has been
considered. The Hamilton formalism for photons in time-variable medium (plasma)
has been developed with application to inclusive photon production. The results
have been used for calculation of the photon production in the course of
transition from quark-gluon phase to hadronic phase in relativistic heavy ion
collisions. The relative strength of the effect as well as specific two- photon
correlations have been evaluated. It has been demonstrated that the opposite
side two-photon correlations are indicative of the sharp transition from the
quark-gluon phase to hadrons.Comment: 23 pages, 2 figure
Nonlinear Hysteretic Torsional Waves
We theoretically study and experimentally report the propagation of nonlinear
hysteretic torsional pulses in a vertical granular chain made of cm-scale,
self-hanged magnetic beads. As predicted by contact mechanics, the torsional
coupling between two beads is found nonlinear hysteretic. This results in a
nonlinear pulse distortion essentially different from the distortion predicted
by classical nonlinearities, and in a complex dynamic response depending on the
history of the wave particle angular velocity. Both are consistent with the
predictions of purely hysteretic nonlinear elasticity and the
Preisach-Mayergoyz hysteresis model, providing the opportunity to study the
phenomenon of nonlinear dynamic hysteresis in the absence of other type of
material nonlinearities. The proposed configuration reveals a plethora of
interesting phenomena including giant amplitude-dependent attenuation, short
term memory as well as dispersive properties. Thus, it could find interesting
applications in nonlinear wave control devices such as strong
amplitude-dependent filters
Triple-gap superconductivity of MgB2 - (La,Sr)MnO3 composite. Which of the gaps is proximity induced?
Interplay of superconductivity and magnetism in a composite prepared of the
ferromagnetic half-metallic La_0.67Sr_0.33MnO (LSMO) nanoparticles and the
conventional s-wave superconductor MgB_2 has been studied. A few principal
effects have been found in bulk samples. With an onset of the MgB_2
superconductivity, a spectacular drop of the sample resistance has been
detected and superconductivity has been observed at temperature up to 20K.
Point-contact (PC) spectroscopy has been used to measure directly the
superconducting energy coupling. For small voltage, an excess current and
doubling of the PC's normal state conductance have been found. Conductance
peaks corresponding to three energy gaps are clearly observed. Two of these
gaps we identified as enhanced \Delta_{\pi} and \Delta_{\sigma} gaps
originating from the MgB_2; the third gap \Delta_{tr} is more than three times
larger than the largest MgB_2 gap. The experimental results provide unambiguous
evidences for a new type of proximity effect which follows the phase coherency
scenario of proximity induced superconductivity. Specifically, at low
temperature, the p-wave spin-triplet condensate with pairing energy \Delta_{tr}
is essentially sustained in LSMO but is incapable to display long-range
supercurrent response because of a phase-disordering state. The proximity
coupling to MgB_2 restores the long-range phase coherency of the triplet
superconducting state, which, in turn, enhances superconducting state of the
MgB_2.Comment: 10 pages, 6 figure
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