Экспериментальные исследования периодического способа питания забоя скважин дробью

High power diode lasers have become an established source for numerous direct applications like metal hardening and polymer welding due to their high efficiency, small size, low cost and high reliability. These laser sources are also used for efficient pumping of solid state lasers as Nd:YAG lasers. To increase the output power of diode lasers up to several kilowatts, the emitters are scaled laterally by forming a diode laser bar and vertically by forming a diode laser stack. For most applications like hardening and illumination, though, the undefined far field distribution of most commercially available high power diode laser stacks states a major drawback of these devices. As single emitters and bars can fail during their lifetime, the near field distribution does not remain constant. To overcome these problems, the intensity distribution can be homogenized by a waveguide or by microoptic devices. The waveguide segments the far field distribution by several total internal reflections, and these segments are overlaid at the waveguide's exit surface. By the microoptic device, the near field is divided into beamlets which are overlaid by a field lens. Both approaches are presented, and realized systems are described

Stability Analysis of Asynchronous States in Neuronal Networks with Conductance-Based Inhibition

Oscillations in networks of inhibitory interneurons have been reported at various sites of the brain and are thought to play a fundamental role in neuronal processing. This Letter provides a self-contained analytical framework that allows numerically efficient calculations of the population activity of a network of conductance-based integrate-and-fire neurons that are coupled through inhibitory synapses. Based on a normalization equation this Letter introduces a novel stability criterion for a network state of asynchronous activity and discusses its perturbations. The analysis shows that, although often neglected, the reversal potential of synaptic inhibition has a strong influence on the stability as well as the frequency of network oscillations

First visual orbit for the prototypical colliding-wind binary WR 140

Wolf-Rayet stars represent one of the final stages of massive stellar evolution. Relatively little is known about this short-lived phase and we currently lack reliable mass, distance, and binarity determinations for a representative sample. Here we report the first visual orbit for WR 140(=HD193793), a WC7+O5 binary system known for its periodic dust production episodes triggered by intense colliding winds near periastron passage. The IOTA and CHARA interferometers resolved the pair of stars in each year from 2003--2009, covering most of the highly-eccentric, 7.9 year orbit. Combining our results with the recent improved double-line spectroscopic orbit of Fahed et al. (2011), we find the WR 140 system is located at a distance of 1.67 +/- 0.03 kpc, composed of a WR star with M_WR = 14.9 +/- 0.5 Msun and an O star with M_O = 35.9 +/- 1.3 Msun. Our precision orbit yields key parameters with uncertainties times 6 smaller than previous work and paves the way for detailed modeling of the system. Our newly measured flux ratios at the near-infrared H and Ks bands allow an SED decomposition and analysis of the component evolutionary states.Comment: Complete OIFITS dataset included via Data Conservancy Projec

Neural Network Model for Apparent Deterministic Chaos in Spontaneously Bursting Hippocampal Slices

A neural network model that exhibits stochastic population bursting is studied by simulation. First return maps of inter-burst intervals exhibit recurrent unstable periodic orbit (UPO)-like trajectories similar to those found in experiments on hippocampal slices. Applications of various control methods and surrogate analysis for UPO-detection also yield results similar to those of experiments. Our results question the interpretation of the experimental data as evidence for deterministic chaos and suggest caution in the use of UPO-based methods for detecting determinism in time-series data.Comment: 4 pages, 5 .eps figures (included), requires psfrag.sty (included

LLiST - a new star tracker camera for tip-tilt correction at IOTA

The tip-tilt correction system at the Infrared Optical Telescope Array (IOTA) has been upgraded with a new star tracker camera. The camera features a backside-illuminated CCD chip offering doubled overall quantum efficiency and a four times higher system gain compared to the previous system. Tests carried out to characterize the new system showed a higher system gain with a lower read-out noise electron level. Shorter read-out cycle times now allow to compensate tip-tilt fluctuations so that their error imposed on visibility measurements becomes comparable to, and even smaller than, that of higher-order aberrations.Comment: To be published in "New Frontiers in Stellar Interferometry", W. A. Traub, ed., SPIE Proceedings Series, Vol. 5491, paper [5491-126]; 10 pages, 6 figures, 1 table; Latex spie class, uses packages graphicx and url; bib style spiebib; keywords: interferometry, tip-tilt correctio

The role of inhibitory feedback for information processing in thalamocortical circuits

The information transfer in the thalamus is blocked dynamically during sleep, in conjunction with the occurence of spindle waves. As the theoretical understanding of the mechanism remains incomplete, we analyze two modeling approaches for a recent experiment by Le Masson {\sl et al}. on the thalamocortical loop. In a first step, we use a conductance-based neuron model to reproduce the experiment computationally. In a second step, we model the same system by using an extended Hindmarsh-Rose model, and compare the results with the conductance-based model. In the framework of both models, we investigate the influence of inhibitory feedback on the information transfer in a typical thalamocortical oscillator. We find that our extended Hindmarsh-Rose neuron model, which is computationally less costly and thus siutable for large-scale simulations, reproduces the experiment better than the conductance-based model. Further, in agreement with the experiment of Le Masson {\sl et al}., inhibitory feedback leads to stable self-sustained oscillations which mask the incoming input, and thereby reduce the information transfer significantly.Comment: 16 pages, 15eps figures included. To appear in Physical Review

Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system

Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the youngest and nearest high-mass stars (O5-O7) and also known to be a close binary system. Using new multi-epoch visual and near-infrared bispectrum speckle interferometric observations obtained at the BTA 6 m telescope, and IOTA near-infrared long-baseline interferometry, we trace the orbital motion of the Theta 1 Ori C components over the interval 1997.8 to 2005.9, covering a significant arc of the orbit. Besides fitting the relative position and the flux ratio, we apply aperture synthesis techniques to our IOTA data to reconstruct a model-independent image of the Theta 1 Ori C binary system. The orbital solutions suggest a high eccentricity (e approx. 0.91) and short-period (P approx. 10.9 yrs) orbit. As the current astrometric data only allows rather weak constraints on the total dynamical mass, we present the two best-fit orbits. From these orbital solutions one can be favoured, implying a system mass of 48 M_sun and a distance to the Trapezium cluster of 434 pc. When also taking the measured flux ratio and the derived location in the HR-diagram into account, we find good agreement for all observables, assuming a spectral type of O5.5 for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun). We find indications that the companion C2 is massive itself, which makes it likely that its contribution to the intense UV radiation field of the Trapezium cluster is non-negligible. Furthermore, the high eccentricity of the preliminary orbit solution predicts a very small physical separation during periastron passage (approx. 1.5 AU, next passage around 2007.5), suggesting strong wind-wind interaction between the two O stars.Comment: 13 pages, 9 figures, Accepted for publication in Astronomy & Astrophysic

Detectability of Terrestrial Planets in Multi-Planet Systems: Preliminary Report

We ask if Earth-like planets (terrestrial mass and habitable-zone orbit) can be detected in multi-planet systems, using astrometric and radial velocity observations. We report here the preliminary results of double-blind calculations designed to answer this question.Comment: 10 pages, 0 figure

The Pulsation of Chi Cygni Imaged by Optical Interferometry; a Novel Technique to Derive Distance and Mass of Mira Stars

We present infrared interferometric imaging of the S-type Mira star Chi Cygni. The object was observed at four different epochs in 2005-2006 with the IOTA optical interferometer (H band). Images show up to 40% variation in the stellar diameter, as well as significant changes in the limb darkening and stellar inhomogeneities. Model fitting gave precise time-dependent values of the stellar diameter, and reveals presence and displacement of a warm molecular layer. The star radius, corrected for limb darkening, has a mean value of 12.1 mas and shows a 5.1mas amplitude pulsation. Minimum diameter was observed at phase 0.94+/-0.01. Maximum temperature was observed several days later at phase 1.02+/-0.02. We also show that combining the angular acceleration of the molecular layer with CO (Delta v = 3) radial velocity measurements yields a 5.9+/-1.5 mas parallax. The constant acceleration of the CO molecules -- during 80% of the pulsation cycle -- lead us to argument for a free-falling layer. The acceleration is compatible with a gravitational field produced by a 2.1(+1.5/-0.7) solar mass star. This last value is in agreement with fundamental mode pulsator models. We foresee increased development of techniques consisting in combining radial velocity with interferometric angular measurements, ultimately allowing total mapping of the speed, density, and position of the diverse species in pulsation driven atmospheres.Comment: 36 pages, accepted in Ap