95 research outputs found
"Unusual" critical states in type-II superconductors
We give a theoretical description of the general critical states in which the
critical currents in type-II superconductors are not perpendicular to the local
magnetic induction. Such states frequently occur in real situations, e.g., when
the sample shape is not sufficiently symmetric or the direction of the external
magnetic field changes in some complex way. Our study is restricted to the
states in which flux-line cutting does not occur. The properties of such
general critical states can essentially differ from the well-known properties
of the usual Bean critical states. To illustrate our approach, we analyze
several examples. In particular, we consider the critical states in a slab
placed in a uniform perpendicular magnetic field and to which two components of
the in-plane magnetic field are then applied successively. We also analyze the
critical states in a long thin strip placed in a perpendicular magnetic field
which then is tilted towards the axis of the strip.Comment: 15 pages including 11 figure
Observation of Flux Reversal in a Symmetric Optical Thermal Ratchet
We demonstrate that a cycle of three holographic optical trapping patterns
can implement a thermal ratchet for diffusing colloidal spheres, and that the
ratchet-driven transport displays flux reversal as a function of the cycle
frequency and the inter-trap separation. Unlike previously described ratchet
models, the approach we describe involves three equivalent states, each of
which is locally and globally spatially symmetric, with spatiotemporal symmetry
being broken by the sequence of states.Comment: 4 pages, 2 figures, submitted for publication in Physical Review
Letter
Electron localization in sound absorption oscillations in the quantum Hall effect regime
The absorption coefficient for surface acoustic waves in a piezoelectric
insulator in contact with a GaAs/AlGaAs heterostructure (with two-dimensional
electron mobility at T=4.2K) via a small
gap has been investigated experimentally as a function of the frequency of the
wave, the width of the vacuum gap, the magnetic field, and the temperature. The
magnetic field and frequency dependencies of the high-frequency conductivity
(in the region 30-210 MHz) are calculated and analyzed. The experimental
results can be explained if it assumed that there exists a fluctuation
potential in which current carrier localization occurs. The absorption of the
surface acoustic waves in an interaction with two-dimensional electrons
localized in the energy "tails" of Landau levels is discussed.Comment: RevTeX 6 pages+6 EPS pic
Molecular dynamics simulations of oxide memory resistors (memristors)
Reversible bipolar nano-switches that can be set and read electronically in a
solid-state two-terminal device are very promising for applications. We have
performed molecular-dynamics simulations that mimic systems with oxygen
vacancies interacting via realistic potentials and driven by an external bias
voltage. The competing short- and long-range interactions among charged mobile
vacancies lead to density fluctuations and short-range ordering, while
illustrating some aspects of observed experimental behavior, such as memristor
polarity inversion.Comment: 15 pages, 5 figure
Detection of Phage-Induced Mobile Genetic Elements in Strains of <i>Vibrio cholerae</i> O1 Biovar El Tor
The acquisition of new mobile genetic elements contributes to the genetic diversity of Vibrio cholerae strains. An important role in this process belongs to the genetic material obtained from phages. The aim of this work was to identify phage-induced PLE islands in strains of V. cholerae O1 serogroup and to determine the resistance of isolates with and without those mobile genetic elements to the lytic activity of the diagnostic cholera El Tor bacteriophage. Materials and methods. Whole genomes nucleotide sequences of toxigenic and non-toxigenic V. cholerae O1 strains presented in the NCBI GenBank were used for the work. Bioinformatic analysis was performed using the BLAST algorithm, MEGA X (or BioEdit v. 7.0.9.0). The test with phages was carried out according A. Gratia technique. Results and discussion. The analysis of 39 toxigenic strains imported to the territory of the Russian Federation and neighboring countries has revealed one strain of V. cholerae O1 of the classical biovar containing the PLE5 island, and 13 strains of V. cholerae O1 of the El Tor biovar containing the PLE4 island. PLE islands have not been found in non-toxigenic strains. It is shown that strains with PLE4 belong to V. cholerae O1 genovariants of the El Tor biovar and have the ctxB1 gene allele. Isolates with this mobile element caused sporadic cases of the disease in 1994–1999, as well as cholera outbreaks in the Russian Federation (in 1993–1994, in 1998 – Dagestan, and 1993 – Tatarstan) and Ukraine (1994–1995). It has been suggested that, perhaps, the presence of the PLE4 island makes a certain contribution to the resistance of V. cholerae O1 strains of the El Tor biovar to the diagnostic cholera El Tor phage (55.6 % of phage-resistant isolates were detected), but there are other mechanisms that have not yet been identified. Thus, the data on the presence of new mobile genetic elements in the genome of earlier imported toxigenic strains of V. cholerae O1, biovar El Tor have been obtained, which expands information about their genetic organization
Does theory of quantum correction to conductivity agree with experimental data in 2D systems?
The quantum correction to the conductivity have been studied in two types of
2D heterostructures: with doped quantum well and doped barriers. The consistent
analysis shows that in the structures where electrons occupy the states in
quantum well only, all the temperature and magnetic field dependencies of the
components of resistivity tensor are well described by the theories of quantum
corrections. The contribution of electron-electron interaction to the
conductivity have been determined reliably in the structures with different
electron density. A possible reason of large scatter in experimental data
concerning the contribution of electron-electron interaction, obtained in
previous papers, and the role of the carriers, occupied the states of the doped
layers, is discussed.Comment: 10 pages with 9 figure
The London theory of the crossing-vortex lattice in highly anisotropic layered superconductors
A novel description of Josephson vortices (JVs) crossed by the pancake
vortices (PVs) is proposed on the basis of the anisotropic London theory. The
field distribution of a JV and its energy have been calculated for both dense
() PV lattices with distance
between PVs, and the nonlinear JV core size . It is shown that the
``shifted'' PV lattice (PVs displaced mainly along JVs in the crossing vortex
lattice structure), formed in high out-of-plane magnetic fields transforms into
the PV lattice ``trapped'' by the JV sublattice at a certain field, lower than
, where is the flux quantum, is the
anisotropy parameter and is the distance between CuO planes.
With further decreasing , the free energy of the crossing vortex lattice
structure (PV and JV sublattices coexist separately) can exceed the free energy
of the tilted lattice (common PV-JV vortex structure) in the case of with the in-plane penetration depth if the low
() or high ()
in-plane magnetic field is applied. It means that the crossing vortex structure
is realized in the intermediate field orientations, while the tilted vortex
lattice can exist if the magnetic field is aligned near the -axis and the
-plane as well. In the intermediate in-plane fields
, the
crossing vortex structure with the ``trapped'' PV sublattice seems to settle in
until the lock-in transition occurs since this structure has the lower energy
with respect to the tilted vortex structure in the magnetic field
oriented near the -plane.Comment: 15 pages, 6 figures, accepted for publication in PR
Strong 3D correlations in vortex system of Bi2212:Pb
The experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO)
reveals remarkable field penetration pattern alteration (flux configuration
change) and superconducting current anisotropy enhancement by the in-plane
field. The anisotropy increases with the temperature rise up to . At an abrupt change in the flux behavior is found; the
correlation between the in-plane magnetic field and the out-of-plane magnetic
flux penetration disappears. No correlation is observed for . The
transition temperature does not depend on the magnetic field strength.
The observed flux penetration anisotropy is considered as an evidence of a
strong 3D - correlation between pancake vortices in different CuO planes at . This enables understanding of a remarkable pinning observed in
Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure
Artificial Brownian motors: Controlling transport on the nanoscale
In systems possessing spatial or dynamical symmetry breaking, Brownian motion
combined with symmetric external input signals, deterministic or random, alike,
can assist directed motion of particles at the submicron scales. In such cases,
one speaks of "Brownian motors". In this review the constructive role of
Brownian motion is exemplified for various one-dimensional setups, mostly
inspired by the cell molecular machinery: working principles and
characteristics of stylized devices are discussed to show how fluctuations,
either thermal or extrinsic, can be used to control diffusive particle
transport. Recent experimental demonstrations of this concept are reviewed with
particular attention to transport in artificial nanopores and optical traps,
where single particle currents have been first measured. Much emphasis is given
to two- and three-dimensional devices containing many interacting particles of
one or more species; for this class of artificial motors, noise rectification
results also from the interplay of particle Brownian motion and geometric
constraints. Recently, selective control and optimization of the transport of
interacting colloidal particles and magnetic vortices have been successfully
achieved, thus leading to the new generation of microfluidic and
superconducting devices presented hereby. Another area with promising potential
for realization of artificial Brownian motors are microfluidic or granular
set-ups.....Comment: 57 pages, 39 figures; submitted to Reviews Modern Physics, revised
versio
Evolution of <I>Vibrio cholerae</I> El Tor and Detection of Their Gene-Variants in the Caucasus
, rstC genes), and 7 strains – to the genotype I. Genotypes I and II (genetically altered ones) are the hybrid variants of the El Tor biovar producing CT of the first type
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