405 research outputs found
Irreversible flow of vortex matter: polycrystal and amorphous phases
We investigate the microscopic mechanisms giving rise to plastic depinning
and irreversible flow in vortex matter. The topology of the vortex array
crucially determines the flow response of this system. To illustrate this
claim, two limiting cases are considered: weak and strong pinning interactions.
In the first case disorder is strong enough to introduce plastic effects in the
vortex lattice. Diffraction patterns unveil polycrystalline lattice topology
with dislocations and grain boundaries determining the electromagnetic response
of the system. Filamentary flow is found to arise as a consequence of
dislocation dynamics. We analize the stability of vortex lattices against the
formation of grain boundaries, as well as the steady state dynamics for
currents approaching the depinning critical current from above, when vortex
motion is mainly localized at the grain boundaries. On the contrary, a
dislocation description proves no longer adequate in the second limiting case
examined. For strong pinning interactions, the vortex array appears completely
amorphous and no remnant of the Abrikosov lattice order is left. Here we obtain
the critical current as a function of impurity density, its scaling properties,
and characterize the steady state dynamics above depinning. The plastic
depinning observed in the amorphous phase is tightly connected with the
emergence of channel-like flow. Our results suggest the possibility of
establishing a clear distinction between two topologically disordered vortex
phases: the vortex polycrystal and the amorphous vortex matter.Comment: 13 pages, 16 figure
Ionospheric effects during first 2 hours after the Chelyabinsk meteorite impact
This paper presents the analysis of ionospheric effects in the region close
to the Chelyabinsk meteorite explosion at 03:20UT 2013 February 15 from the
Institute of Solar-Terrestrial Physics of Siberian Branch of Russian Academy of
Sciences (ISTP SB RAS) EKB radar data, and from the Institute of Geophysics of
Ural Branch of Russian Academy of Sciences (IG UB RAS) PARUS ionosonde data.
Both instruments are located within the IG UB RAS Arti Observatory
approximately 200 km northward from the estimated explosion site. According to
the data obtained, the ionospheric disturbance caused by the meteorite flyby,
explosion, and impact had high dynamics and amplitude. However, it obviously
did not lead to a variation in the ionosphere mean parameters in the region
above the disturbance center during the first 2 hours. Essential effects,
however, were observed at more than 100-200 km from the explosion site and
farther up to 1500 km.Comment: 30 pages, 15 figures, submitted to JAST
Developing willingness of education community to use ICT facilities
The willingness of education community to apply ICT facilities is composed of understanding the specific of devices and skills to exploit them fluently as well as ideas about the most efficient and effective way for training during classesГотовность участников образовательного процесса к задействованию средств ИКТ складывается из понимания особенностей их устройства и навыков свободной эксплуатации, а также из представлений о наиболее рациональном и эффективном для обучения методе их использования в ходе заняти
Precise and ultrafast molecular sieving through graphene oxide membranes
There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries
Multimedia technology in university for foreign language teaching
Multimedia technology is vital and essential for foreign language teaching. It helps to have absolutely innovative, new and interesting lessons at the university. It is obvious, that teaching approaches are more effective and diverse nowadaysМультимедийные технологии являются необходимым средством при изучении иностранных языков. Современное обучение немыслимо без электронных ресурсов и современных технологий. Обучение становится эффективным и разнообразны
Depinning and critical current characteristics of topologically defected vortex lattices
We discuss the role of dislocation assemblies such as grain boundaries in the
dynamic response of a driven vortex lattice. We simulate the depinning of a
field-cooled vortex polycrystal and observe a general enhancement of the
critical current as well as a distinct crossover in the characterisitic of this
quantity as a function of pinning density. The results agree with analytical
predictions for grain boundary depinning. The dynamics of grain boundaries thus
proves an essential mechanism underlying the flow response of defected vortex
lattices and the corresponding transport properties of the superconducting
material. We emphasize the connection between the topological rearrangements of
the lattice and its threshold dynamics. Our theory encompasses a variety of
experimental observations in vortex matter as well as in colloidal crystals.Comment: 7 Figure
Instabilities in the Flux Line Lattice of Anisotropic Superconductors
The stability of the flux line lattice has been investigated within
anisotropic London theory. This is the first full-scale investigation of
instabilities in the `chain' state. It has been found that the lattice is
stable at large fields, but that instabilities occur as the field is reduced.
The field at which these instabilities first arise, ,
depends on the anisotropy and the angle at which the
lattice is tilted away from the -axis. These instabilities initially occur
at wavevector , and the component of along the
average direction of the flux lines, , is always finite. As the
instability occurs at finite the dependence of the cutoff on is
important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The
instabilities only occur for values of the anisotropy appropriate to
a material like BSCCO, and not for anisotropies more appropriate to YBCO. The
lower critical field is calculated as a function of the angle
at which the applied field is tilted away from the crystal axis. The
presence of kinks in is seen to be related to instabilities in
the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic
instabilities. Calculation of the lower critical field is included, and the
presence of kinks in is seen to be related to the elastic
instabilities. 29 pages including 16 figures, LaTeX with epsf styl
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