670 research outputs found
Strong-Pinning Effects in Low-Temperature Creep: Charge-Density Waves in TaS_3
Nonlinear conduction in the quasi-one dimensional conductor o-TaS_3 has been
studied in the low-temperature region down to 30 mK. It was found that at
temperatures below a few Kelvins the current-voltage (I-V) characteristics
consist of several branches. The temperature evolution of the I-V curve
proceeds through sequential freezing-out of the branches. The origin of each
branch is attributed to a particular strong pinning impurity type.
Similar behavior is expected for other physical systems with collective
transport (spin-density waves, Wigner crystals, vortex lattices in type-II
superconductors etc.) in the presence of strong pinning centers.Comment: 11 pages, 3 ps figures, Revtex, To be published in Phys. Rev. Letters
(1997
Unconventional magnetoresistance in long InSb nanowires
Magnetoresistance in long correlated nanowires of degenerate semiconductor
InSb in asbestos matrix (wire diameter of around 5 nm, length 0.1 - 1 mm) is
studied over temperature range 2.3 - 300 K. At zero magnetic field the electric
conduction and the current-voltage characteristics of such wires obey the
power laws , , expected for
one-dimensional electron systems. The effect of magnetic field corresponds to a
20% growth of the exponents , at H=10 T. The observed
magnetoresistance is caused by the magnetic-field-induced breaking of the
spin-charge separation and represents a novel mechanism of magnetoresistance.Comment: To be published in JETP Letters, vol. 77 (2003
Region of Excessive Flux of PeV Cosmic Rays in the Direction Toward Pulsars PSR J1840+5640 and LAT PSR J1836+5925
An analysis of arrival directions of extensive air showers (EAS) registered
with the EAS MSU and EAS-1000 prototype arrays has revealed a region of
excessive flux of PeV cosmic rays in the direction toward pulsars PSR
J1840+5640 and LAT PSR J1836+5925 at significance level up to 4.5sigma. The
first of the pulsars was discovered almost 30 years ago and is a well-studied
old radio pulsar located at the distance of 1.7pc from the Solar system. The
second pulsar belongs to a new type of pulsars, discovered by the space
gamma-ray observatory Fermi, pulsations of which are not observed in optical
and radio wavelengths but only in the gamma-ray range of energies
(gamma-ray-only pulsars). In our opinion, the existence of the region of
excessive flux of cosmic rays registered with two different arrays provides a
strong evidence that isolated pulsars can give a noticeable contribution to the
flux of Galactic cosmic rays in the PeV energy range.Comment: 14 pages; v.2: a few remarks to match a version accepted for
Astronomy Letters added. They can be found by redefining the \NEW command in
the preamble of the LaTeX fil
Self-assembled quasi-1D and 2D nanostructures of fullerenes on silicon
The work was supported by Russian Foundation for Basic Researches (Grant No. 17-02-00577)
Local Inhomogeneity Effects on Nucleation Process in a High External Bias
Quantum nucleation processes in the presence of local moderate
inhomogeneities are studied theoretically at high biases. The quantum
nucleation rate Gamma is calculated for one-dimensional systems in a form Gamma
= A e^(-B/hbar) by using the `bounce' method. The bias-dependence of the
exponent B is shown to be changed by inhomogeneities. This change is explained
by the reduction of the effective spatial dimension of the system. By studying
the system-size dependence of the prefactor A, the condition for the appearance
of inhomogeneity effects is evaluated. Nucleation rates in thermal activation
regimes are also calculated, and compared with quantum tunneling regimes. For
higher-dimensional systems, it is shown that the local approximation of
inhomogeneity does not hold, and that spatial profiles of inhomogeneity become
important.Comment: 10 pages, 6 figure
Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3
In the Peierls state very thin samples of TaS_3 (cross-section area \sim
10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the
threshold field. With approaching the Peierls transition temperature, T_P, the
smearing evolves into smooth growth of conductance from zero voltage
interpreted by us as the contribution of fluctuations to the non--linear
conductance. We identify independently the fluctuation contribution to the
linear conductance near T_P. Both linear and non-linear contributions depend on
temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently
reveal the same process. We reject creep of the {\it continuous} charge-density
waves (CDWs) as the origin of this effect and show that it is spontaneous phase
slippage that results in creep of the CDW. A model is proposed accounting for
both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR
On the angular distribution of extensive air showers
Angular distributions of extensive air showers with different number of
charged particles in the range 2.5x10^5--4x10^7 are derived using the
experimental data obtained with the EAS MSU array. Possible approximations of
the obtained distributions with different empiric functions available in
literature, are analysed. It is shown that the exponential function provides
the best approximation of the angular distributions in the sense of the
chi-squared criterion.Comment: 5 pages including 1 figur
The current status of orbital experiments for UHECR studies
Two types of orbital detectors of extreme energy cosmic rays are being
developed nowadays: (i) TUS and KLYPVE with reflecting optical systems
(mirrors) and (ii) JEM-EUSO with high-transmittance Fresnel lenses. They will
cover much larger areas than existing ground-based arrays and almost uniformly
monitor the celestial sphere. The TUS detector is the pioneering mission
developed in SINP MSU in cooperation with several Russian and foreign
institutions. It has relatively small field of view (+/-4.5 deg), which
corresponds to a ground area of 6.4x10^3 sq.km. The telescope consists of a
Fresnel-type mirror-concentrator (~2 sq.m) and a photo receiver (a matrix of
16x16 photomultiplier tubes). It is to be deployed on the Lomonosov satellite,
and is currently at the final stage of preflight tests. Recently, SINP MSU
began the KLYPVE project to be installed on board of the Russian segment of the
ISS. The optical system of this detector contains a larger primary mirror (10
sq.m), which allows decreasing the energy threshold. The total effective field
of view will be at least +/-14 degrees to exceed the annual exposure of the
existing ground-based experiments. Several configurations of the detector are
being currently considered. Finally, JEM-EUSO is a wide field of view (+/-30
deg) detector. The optics is composed of two curved double-sided Fresnel lenses
with 2.65 m external diameter, a precision diffractive middle lens and a pupil.
The ultraviolet photons are focused onto the focal surface, which consists of
nearly 5000 multi-anode photomultipliers. It is developed by a large
international collaboration. All three orbital detectors have multi-purpose
character due to continuous monitoring of various atmospheric phenomena. The
present status of development of the TUS and KLYPVE missions is reported, and a
brief comparison of the projects with JEM-EUSO is given.Comment: 18 pages; based on the rapporteur talk given by M.I. Panasyuk at
ECRS-2014; v2: a few minor language issues fixed thanks to the editor; to be
published in the proceeding
Prompt photon and associated heavy quark production at hadron colliders with kt-factorization
In the framework of the kt-factorization approach, the production of prompt
photons in association with a heavy (charm or beauty) quarks at high energies
is studied. The consideration is based on the O(\alpha \alpha_s^2) off-shell
amplitudes of gluon-gluon fusion and quark-(anti)quark interaction
subprocesses. The unintegrated parton densities in a proton are determined
using the Kimber-Martin-Ryskin prescription. The analysis covers the total and
differential cross sections and extends to specific angular correlations
between the produced prompt photons and muons originating from the semileptonic
decays of associated heavy quarks. Theoretical uncertainties of our evaluations
are studied and comparison with the results of standard NLO pQCD calculations
is performed. Our numerical predictions are compared with the recent
experimental data taken by the D0 and CDF collaborations at the Tevatron.
Finally, we extend our results to LHC energies.Comment: 14 pages, 10 figure
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