808 research outputs found
Stabilization of class-B broad-area lasers emission by external optical injection
We theoretically examine the effect of external optical injection on the
spatio-temporal dynamics of class-B broad-area lasers. We demonstrate that
optical injection can efficiently stabilize the intrinsic transverse
instabilities in such lasers associated with both the boundaries of the pumping
area and with the bulk nonlinearities of the active medium. Stabilizing action
of optical injection is shown to be closely related to the suppression of
inherent relaxation oscillations behavior.Comment: 8 pages, 7 figure
Giant magnetoimpedance in crystalline Mumetal
We studied giant magnetoimpedance (GMI) effect in commercial crystalline
Mumetal, with the emphasis to sample thickness dependence and annealing
effects. By using appropriate heat treatment one can achieve GMI ratios as high
as 310%, and field sensitivity of about 20%/Oe, which is comparable to the best
GMI characteristics obtained for amorphous and nanocrystalline soft magnetic
materials.Comment: 8 pages, 3 figure
Position-sensitive detector for the 6-meter optical telescope
The Position-Sensitive Detector (PSD) for photometrical and spectral
observation on the 6-meter optical telescope of the Special Astrophysical
Observatory (Russia) is described. The PSD consists of a position-sensitive
tube, amplifiers of output signals, analog-to-digital converters (ADC) and a
digital logic plate, which produces a signal for ADC start and an external
strob pulse for reading information by registration system. If necessary, the
thermoelectric cooler can be used. The position-sensitive tube has the
following main elements: a photocathode, electrodes of inverting optics, a
block of microchannel plates (MCP) and a position-sensitive collector of
quadrant type. The main parameters of the PSD are the diameter of the sensitive
surface is 25 mm, the spatial resolution is better than 100 (\mu)m in the
centre and a little worse on the periphery; the dead time is near 0.5 (\mu)s;
the detection quantum efficiency is defined by the photocathode and it is not
less than 0.1, as a rule; dark current is about hundreds of cps, or less, when
cooling. PSD spectral sensitivity depends on the type of photocathode and input
window material. We use a multialkali photocathode and a fiber or UV-glass,
which gives the short- wave cut of 360 nm or 250 nm, respectively.Comment: 4 pages, 7 figures, to be published in Nuclear Instruments & Methods
in Physics Researc
Generation of unipolar half-cycle pulse via unusual reflection of a single-cycle pulse from an optically thin metallic or dielectric layer
We present a significantly different reflection process from an optically
thin flat metallic or dielectric layer and propose a strikingly simple method
to form approximately unipolar half-cycle optical pulses via reflection of a
single-cycle optical pulse. Unipolar pulses in reflection arise due to
specifics of effectively one-dimensional pulse propagation. Namely, we show
that in considered system the field emitted by a flat medium layer is
proportional to the velocity of oscillating medium charges instead of their
acceleration as it is usually the case. When the single-cycle pulse interacts
with linear optical medium, the oscillation velocity of medium charges can be
then forced to keep constant sign throughout the pulse duration. Our results
essentially differ from the direct mirror reflection and suggest a possibility
of unusual transformations of the few-cycle light pulses in linear optical
systems
Dielectric responses of the layered cobalt oxysulfide Sr_2Cu_2CoO_2S_2 with CoO_2 square-planes
We have studied the dielectric responses of the layered cobalt oxysulfide
SrCuCoOS with the CoO square-planes. With decreasing
temperature below the N\'eel temperature, the resistivity increases like a
semiconductor, and the thermopower decreases like a metal. The dielectric
constant is highly dependent on temperature, and the dielectric relaxation is
systematically changed with temperature, which is strongly correlated to the
magnetic states. These behaviors suggest that carriers distributed
homogeneously in the paramagnetic state at high temperatures are expelled from
the antiferromagnetically ordered spin domain below the N\'eel temperature.Comment: 3 pages, 4 eps figures, to be published in J. Appl. Phy
Expression of TLR1-10 and caspase-3 alfa at women with early miscarriages
Toll-like receptors (TLR) are the first signal receptors of innate immunity, recognizing bacteria and viruses and promoting development of inflammation through the activation of proinflammatory cytokines secretion (1). In animal models it was shown, that TLRs play role in pathogenesis of miscarriages (2, 3) and can influence to trophoblast apoptosis. The aim of research was to investigate study specialty of mRNA expression of TLR1-10 and caspase-3a in endometrium at patients with early miscarriagesyesBelgorod State Universit
Quantum Size Effect transition in percolating nanocomposite films
We report on unique electronic properties in Fe-SiO2 nanocomposite thin films
in the vicinity of the percolation threshold. The electronic transport is
dominated by quantum corrections to the metallic conduction of the Infinite
Cluster (IC). At low temperature, mesoscopic effects revealed on the
conductivity, Hall effect experiments and low frequency electrical noise
(random telegraph noise and 1/f noise) strongly support the existence of a
temperature-induced Quantum Size Effect (QSE) transition in the metallic
conduction path. Below a critical temperature related to the geometrical
constriction sizes of the IC, the electronic conductivity is mainly governed by
active tunnel conductance across barriers in the metallic network. The high 1/f
noise level and the random telegraph noise are consistently explained by random
potential modulation of the barriers transmittance due to local Coulomb
charges. Our results provide evidence that a lowering of the temperature is
somehow equivalent to a decrease of the metal fraction in the vicinity of the
percolation limit.Comment: 21 pages, 8 figure
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