Transverse optical mode patterns for an RF excited Ar-He-Xe laser

Transverse optical modes for an RF excited Ar-He-Xe laser are studied both experimentally and theoretically. A diffraction model for a waveguide with a nonsaturable gain and refractive index gradients placed between two plane mirrors is formulated. The effects of gain and diffraction index gradients and of diffraction in free space are evaluated for typical experimental conditions. A direct comparison between theoretical mode patterns and experimentally measured ones at distances of 17 and 114 cm from the output mirror demonstrated a satisfactory agreement for various laser wavelengths and gas mixture compositions     

Novel algorithms for the network lifetime problem in wireless settings

One of the major concerns in wireless ad-hoc networks design is energy efficiency. Wireless devices are typically equipped with a limited energy supply sufficient only for a limited amount of time which is reversely proportional to the transmission power of the device. The network lifetime is defined as the time the first device runs out of its initial energy charge. In this paper we study the maximum network lifetime problem for broadcast and data gathering in wireless settings. We provide polynomial time approximation algorithms, with guaranteed performance bounds while considering omnidirectional and unidirectional transmissions. We also consider an extended variant of the maximum lifetime problem, which simultaneously satisfies additional constraints, such as bounded hop-diameter and degree of the routing tree, and minimizing the total energy used in a single transmission. Finally, we evaluate the performance of some of our algorithms through simulations.     

Antiresonant reflecting optical waveguide-type vertical-cavity surface emitting lasers: comparison of full-vector finite-difference time-domain and 3-D bidirectional beam propagation methods

The cold-cavity modal characteristics of an antiresonant optical waveguide-type cylindrical vertical-cavity surface-emitting laser (VCSEL) are investigated through numerical simulations using a three-dimensional (3-D) bidirectional beam propagation method (BD-BPM) and a full-vector axisymmetric finite-difference time-domain (FDTD) method. Good agreement between the BPM- and FDTD-computed radial mode profiles as well as the mode-dependent radiation losses is obtained. The results of this paper establish the accuracy of the BD-BPM technique for simulating this class of devices and confirm effective-index method predictions that antiresonance conditions for cylindrical geometry devices (i.e., VCSELs) differ from those of planar geometry devices (i.e., edge emitters).     

Single-Mode Emission From Vertical-Cavity Surface-Emitting Lasers With Low-Index Defects

Mode confinement to low-index "defect" regions of a two-dimensional square photonic lattice has been studied as a means to realize single-spatial-mode vertical-cavity surface-emitting lasers (VCSELs). A selective etching process with two-step metal-organic chemical vapor deposition is used to fabricate the low-index defect VCSELs. A device with a 9-mum-wide aperture demonstrates 2.9-mW continuous-wave (CW) output power. The near diffraction-limited single-lobe far-field and high-resolution spectral analyses confirm single fundamental defect mode emission. Comparison studies between pulsed and CW operation indicate that thermal effects have a significant impact on the modal performance of the devices. Single-mode emission with more than 8 mW of peak pulsed power has been observed with short pulsewidth operation (0.1 mus, 2%). Improvements in thermal management are required to achieve higher CW single-mode emission in these devices     

Comprehensive above-threshold analysis of antiresonant reflecting optical waveguide edge-emitting diode laser

A three-dimensional (3-D) above-threshold analysis has been performed for laterally antiguided laser structures of the antiresonant-reflecting-optical-waveguide type, of relatively large core width (/spl sim/ 10 /spl mu/m), for high-power, single-spatial-mode operation. A 3-D numerical code has been developed, which takes into account carrier diffusion in the quantum well as well as edge radiation losses. The laser characteristics are calculated as functions of the above-threshold drive level. Within the simulation, 3-5 higher order optical modes on a "frozen background" are computed by the Arnoldi algorithm. Because of the nonuniform gain saturation of the lasing mode, the modal gains for higher order modes increase with the drive current due to increasing overlap of their fields with the two-dimensional gain distribution. The onset of threshold for higher order modes puts an upper limit on the range for stable single-mode operation. The above-threshold analysis is done for various values of the width of the reflector region, below and above the lateral-antiresonance condition. It is found that the maximum intermodal discrimination, which in turn provides the maximum single-mode power, is obtained when the reflector-region width is /spl sim/25 % larger that its value at antiresonance. Then, for 10-/spl mu/m-core devices, stable, single-mode operation is found to occur to drive levels as high as 41 /spl times/ threshold, with single-mode output powers as high as 1.45 W.     

Selective Synthesis of Glyceryl Tris[9,10-(threo)-dihydroxyoctadecanoate]

Elaborating novel triacylglyceride (TAG) based polyester hyperbranched unimolecular encapsulating agents represents an original and promising approach to the selective delivery of hydrophobic biologically active compounds. However, selective modification of double bonds in unsaturated TAG to obtain corresponding pure polyhydroxy derivatives with high yields is still a big challenge. Two novel approaches to synthesize the glyceryl tris[9,10-(threo)-dihydroxyoctadecanoate] were proposed and tested: (1) via the bromination and nucleophilic substitution of secondary halide functions by oxyacetyl groups followed by the hydrolysis of acetyls, and (2) direct transformation of the double bonds by the reaction with peroxoformic acid in an excess of formic acid, and the removal of formyl protective groups. Glycerol trioleate and natural olive oil were used as starting materials. The first synthetic route allowed for successful preparation of the corresponding polyhalide and polyoxyacetyl products; however, a more effective final deacetylation procedure is required. The second proposed approach showed a very good reproducibility in obtaining hydroxy-oxyformyl derivatives. The optimal conditions of the reaction involve the use of diethyl ether as a cosolvent and stirring at room temperature for 30 min. To remove the formyl groups, three original procedures using organic solvent medium at room temperature were proposed: in the presence of cesium carbonate in chloroform–methanol mixture, and two methods using hydrochloric acid in chloroform–methanol mixture or in acetone. All three methods were efficient to carry out the deformylation; nevertheless, TAG esters remained stable only with 15–17 % hydrochloric acid in acetone. Simple isolation procedures and high overall yields (95.6 and 94.9 % for both triolein and olive oil, respectively) allow considering the second approach as a promising method to obtain threo-polyhydroxy derivatives from unsaturated TAG.     

Using SS coal in silicon production

The industrial use of Kuznetsk Basin SS coal in silicon production is considered. The influence of SS coal quality on the operation of electrothermal furnaces is studied.     

Formation of Phases upon the Mechanosynthesis and Subsequent Annealing of Samples of Cementite Composition Alloyed with Chromium and Nickel

Using X-ray, Mössbauer, and magnetic measurements, the formation of phases has been investigated upon mechanosynthesis in a ball planetary mill and upon the subsequent annealing of samples of the cementite composition (Fe_0.95–уСr_0.05Ni _y )₇₅C₂₅, where у = 0–0.20, which contains two alloying elements (chromium and nickel). It has been shown that, in the mechanosynthesis process, cementite alloyed with chromium and a small amount of nickel and an amorphous phase alloyed with chromium and nickel have been formed. Upon heating above 300°С, the amorphous phase is crystallized into nickel-enriched cementite. In the process of annealing at higher temperatures, the most nickel-rich cementite decomposes with the formation of austenite. As a consequence, after annealing at medium temperatures, the composition of the alloys contains cementite alloyed mainly with chromium and some amount of alloyed austenite, which can be found in ferromagnetic or paramagnetic states depending on the Ni content. Annealing at 800°С bring about the complete or partial decomposition of cementite contained in the alloys. The intensity of the decomposition has been determined by the nickel content in the samples.     

Experimental investigations of the effect of new passive safety systems on the temperature state of fuel elements

Results of experiments conducted on a large-scale integral PSB-VVéR bench and directed toward investigation of the performance of new passive safety systems for nuclear plants with a water-cooled power reactor, an additional system for passive flooding of the active zone, and a system for the passive removal of heat from steam generators are presented. __________ Translated from élektricheskie Stantsii, No. 9, September 2007, pp. 7–10.     

Architecture and Physical Implementation of a Third Generation 65 nm, 16 Core, 32 Thread Chip-Multithreading SPARC Processor

This third-generation Chip-Multithreading (CMT) SPARC processor consists of 16 cores with shared memory architecture and supports a total of 32 main threads plus 32 scout threads. It is targeted for high-performance servers, and is optimized for both single- and multi-threaded applications. The 396 mm² chip is fabricated in an 11 metal layer 65-nm CMOS process and operates at a nominal frequency of 2.3 GHz, consuming a maximum power of 250 W at 1.2 V. This paper provides an overview of the architectural highlights and describes the physical implementation challenges and solutions including circuit innovations in memory arrays, register files, and floating-point hardware that boost the performance and circuit robustness with low area overhead.