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

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

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

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 Sr$_2$Cu$_2$CoO$_2$S$_2$ with the CoO$_2$ 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

Variability in pH, fCO2, oxygen and flux of CO2 in the surface water along a transect in the Atlantic sector of the Southern Ocean

Underway sampling and measurements of pH, fCO2, oxygen and Chlorophyll a (Chl a) were performed in the surface waters from Cape Town (South Africa) to Queen Maud Land (Antarctica) in the Atlantic sector of the Southern Ocean during the austral summer 1997/1998. From direct measurements of these parameters and from calculated fCO2 the oceanic carbon dioxide system was studied and related to hydrological and biological parameters. fCO2 was in general undersaturated relative to the atmosphere and showed a large variability with values ranging from 313 to 377 μatm with a mean value of 346±13 μatm. The undersaturation was more pronounced in areas associated with fronts where high Chl a and high pH in situ values were observed. Using shipboard wind speed data, estimates of the CO2 flux were made along the transect and during three mesoscale surveys on the northward return transect in the area of the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and in the Antarctic Polar Front (APF). The undersaturation observed during the transect caused the ocean to act as a sink for CO2 with a mean sea–air flux for the entire transect of −3±5 mmol m−2 d−1 with a large variability between −20 mmol m−2 d−1 (oceanic uptake) to 1.3 mmol m−2 d−1 (oceanic source). The lowest fCO2 values (largest oceanic uptake of CO2) were found at the southern boundary of the APF at 53°S, which coincided with a supersaturation in oxygen and high pH values. Oxygen concentrations were measured from 50°S to 63°S and varied between 324 and 359 μmol kg−1 with a mean value of 347±9 μmol kg−1. In general only small deviations from equilibrium oxygen saturation were observed (mean value=99±2%). However, in the SIE oxygen was clearly undersaturated, probably an effect of upwelling of oxygen poor deep water which had not yet been compensated for by biological production. Three weeks later, the ice edge had retreated in the SIE region and the Chl a concentration had increased three-fold, suggesting the start of a phytoplankton bloom. This was also seen in the oxygen concentration which had increased and showed supersaturation. This coincided with an increased oceanic uptake of CO2 in the SIE during the mesoscale survey

Temporal dynamic of the phylogenetic diversity of the bird community of agricultural lands in Ukrainian steppe drylands

This study discussed the importance of the phylogenetic components in the structure of bird communities of anthropogenically transformed ecosystems. The investigation was conducted in the landscapes of the south and south-east of Ukraine in the nesting seasons 1988–2018. The bird community in the agricultural landscape was found to be presented by 10 species. The number of species was closely correlated with its phylogenetic analogue – Faith’s index. Both indices were stationary over time, as they do not show a statistically significant time trend. The two axes were extracted as a result of the DPCOA procedure and the permutation test showed their statistical significance. The axis 1 was the most sensitive to the opposite dynamics of the abundance of Coturnix coturnix and Burhinus oedicnemus on the one hand and Alauda arvensis and Melanocorypha calandra on the other. The axis 2 is the most sensitive to the opposite dynamics of Corvus monedula and Melanocorypha calandra on the one hand and Coturnix coturnix and Motacilla flava on the other. Based on phylogenetic diversity, the years can be clustered with the extraction of four relatively homogeneous phylogenetic structures of bird communities. The indicator of the initial period of dynamics (1988–1992) was Burhinus oedicnemus. Sowing or mechanical weeding may be considered as a major factor of nest destruction of Burhinus oedicnemus. The decreasing of the abundance of the trophic recourses because of agricultural activity may have caused the monotonous negative trend over time of the Burhinus oedicnemus populations. The period 1993–2003 was a transitional one, for which there were no clear indicators, as a characteristic feature of this period was the processes of bird community restructuring. The period 2004–2013 was characterized by the loss of Burhinus oedicnemus from the community and a sharp increase in the abundance of Corvus monedula. These species are distinguished by their phylogenetic specificity and are located on the periphery relative to the phylogenetic core of the community. There was growing importance in the community of such species as Alauda arvensis, Anthus campestris, and Melanocorypha calandra between 2014 and 2018. Our results also confirm the assumption that phylogenetic overdispersion is an important requirement for the stability of the bird community in anthropogenically transformed landscapes