323 research outputs found
Second harmonic electromagnetic emission of a turbulent magnetized plasma driven by a powerful electron beam
The power of second harmonic electromagnetic emission is calculated for the
case when strong plasma turbulence is excited by a powerful electron beam in a
magnetized plasma. It is shown that the simple analytical model of strong
plasma turbulence with the assumption of a constant pump power is able to
explain experimentally observed bursts of electromagnetic radiation as a
consequence of separate collapse events. It is also found that the
electromagnetic emission power calculated for three-wave interaction processes
occurring in the long-wavelength part of turbulent spectrum is in
order-of-magnitude agreement with experimental results
Homology class of a Lagrangian Klein bottle
It is shown that an embedded Lagrangian Klein bottle represents a non-trivial
mod 2 homology class in a compact symplectic four-manifold with
. (In versions 1 and 2, the last assumption was missing.
A counterexample to this general claim and the first proof of the corrected
result have been found by Vsevolod Shevchishin.) As a corollary one obtains
that the Klein bottle does not admit a Lagrangian embedding into the standard
symplectic four-space.Comment: Version 3 - completely rewritten to correct a mistake; Version 4 -
minor edits, added references; AMSLaTeX, 6 page
Strain-Hardening Stages and Structure Evolution in Pure Niobium and Vanadium upon High Pressure Torsion
High pressure torsion (HPT) is one of the ways to form nanostructured
materials with high strength properties. However, HPT hardening mechanisms vary
from material to material and are poorly understood for some BCC metals,
particularly niobium and vanadium. This work aims to identify strain hardening
stages for Nb and V metals during HPT. Two approaches have been used to
identify the deformation stages during high pressure torsion. The approaches
are based on the application of a "piecewise" model, taking into account the
different deformation mechanisms that determine the type of the forming
structure, and on the analysis of the hardness vs. true strain dependence
according to the law. We compared the identified stages with
the results of the electron microscopic study of the structure. Both models
describe well the structural changes observed microscopically in HPT-deformed
niobium. However, we have shown that only the piecewise model gives an adequate
description of the stages of structure development in vanadium. We have
provided an explanation for the observed difference in the behavior of niobium
and vanadium upon HPT.Comment: 21 pages, 9 figures, 1 tabl
Permian palaeomagnetism of East Kazakhstan and the amalgamation of Eurasia
Most of Kazakhstan belongs to the Ural–Mongol belt, the tectonic evolution of which is poorly understood as demonstrated by disparate tectonic models suggested thus far. We undertook a palaeomagnetic study of Upper Permian basalts and andesites from two localities in east Kazakhstan in order to evaluate the final stages of the evolution of this belt and Eurasian amalgamation. Thermal demagnetization revealed a single pre-tilting characteristic component of ubiquitously reversed polarity from all samples. The mean declination of this remanence from one locality agrees rather well with the Permian European palaeomeridian, whereas that from the other is clockwise rotated by 28°± 8° . The overall mean inclination of −49°± 4° differs by 9.7°± 4.2° from the reference inclination calculated, for our localities, from the Eurasian mean pole for the 245–260 Ma interval and is in agreement with 260–275 Ma data. We account for the observed pattern by either a slightly erroneous rock age (lithologies are somewhat older than indicated by geological data) or non-dipole (octopole) components of the geomagnetic field. Because significant relative motion of the study area with respect to Eurasia is not demonstrated, we conclude that welding of Kazakhstan, Europe and Siberia was essentially completed by Mid-Permian time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73262/1/j.1365-246X.2003.01879.x.pd
Negative cooperativity in adenylate formation catalysed by beef pancreas tryptophanyl-tRNA synthetase Influence of tRNATrp
Chaotic Interaction of Langmuir Solitons and Long Wavelength Radiation
In this work we analyze the interaction of isolated solitary structures and
ion-acoustic radiation. If the radiation amplitude is small solitary structures
persists, but when the amplitude grows energy transfer towards small spatial
scales occurs. We show that transfer is particularly fast when a fixed point of
a low dimensional model is destroyed.Comment: LaTex + 4 eps file
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