The effects of monovacancies on the terrace width during sublimation from the (111) surface of a diamond-like crystal

Using the three-dimensional Monte Carlo model, the effect of monovacancies on the diffusion exchange between the steps on the (111) surface of a diamond-like crystal during sublimation was investigated. The critical terrace width L_cr (the distance from the step edge to the nearest stable vacancy islands) was determined as a function of the relationship between the energy of adatom formation at the smooth terrace E_n and the energy of adatom desorption from the terrace E_d with retention of the sum of these energies E_sub=E_n+E_d, which characterizes the sublimation of a substance. A well-pronounced maximum exists in the dependences L_cr(E_n) obtained. The formula is suggested which well describes the dependences L_cr(E_n) for various values of E_sub. The extrapolation of the dependence L_cr(E_n) to the value E_sub=4.2 eV, which is characteristic of Si, permits us to compare the model results with the experimental data of other authors. The explanation of a threefold increase in the terrace width, which is observed experimentally at about 1500 K, is suggested.     

G-band (140-220-GHz) InP-based HBT amplifiers

We report tuned amplifiers designed for the 140-220-GHz frequency band. The amplifiers were designed in a transferred-substrate InP-based heterojunction bipolar transistor technology that enables efficient scaling of the parasitic collector-base junction capacitance. A single-stage amplifier exhibited 6.3-dB small-signal gain at 175 GHz. Three-stage amplifiers were subsequently fabricated with one design demonstrating 12.0-dB gain at 170 GHz and a second design exhibiting 8.5-dB gain at 195 GHz.     

High power mid-infrared optically pumped PbSe/PbSrSe multiple-quantum-well vertical-cavity surface-emitting laser operation at 325 K

A high power, mid-infrared (/spl lambda/=3.8 /spl mu/m) lead-salt vertical-cavity surface-emitting laser (VCSEL) operating at 325 K is demonstrated. The laser emission is generated in a half-wavelength microcavity consisting of seven pairs of PbSe/PbSrSe multiple-quantum-wells embedded in two mirrors and optically pumped with 5 ns laser pulses.     

Experimental validation of a thermal modelling method dedicated to multichip power modules in operating conditions

In this paper, we present an implementation of a thermal modelling method applied to a multichip module used as a power converter. Analytical functions of thermal impedances, with original formulations for the mutuals are defined. They are derived from 3D thermal simulations and experimental validations with direct chips temperature measurements. Finally, simulations are performed in order to improve the capability of our model to assess, with fast computation, the thermal constraints applied on the multichip module in a real operating condition.     

High-power laser diodes based on asymmetric separate-confinement heterostructures

Asymmetric separate-confinement laser heterostructures with ultrawide waveguides based on AlGaAs/GaAs/InGaAs solid solutions, with an emission wavelength of ～1080 nm, are grown by MOCVD. The optical and electrical properties of mesa-stripe lasers with a stripe width of ～100 μm are studied. Lasers based on asymmetric heterostructures with ultrawide (>1 μm) waveguides demonstrate lasing in the fundamental transverse mode with an internal optical loss of as low as 0.34 cm^?1. In laser diodes with a cavity length of more than 3 mm, the thermal resistance is reduced to 2°C/W, and the characteristic temperature T ₀= 10°C is obtained in the range 0–100°C. A record-breaking wallplug efficiency of 74% and an output optical power of 16 W are reached in CW mode. Mean-time-between-failures testing for 1000 h at 65°C with an operation power of 3–4 W results in the power decreasing by 3–7%.     

Receive antenna selection for closely-spaced antennas with mutual coupling

We investigate the achievable rate of receive antenna selection MIMO systems in the presence of mutual coupling and spatial correlation. For that, we assume the antenna array to consist of dipole antennas placed side-by-side in a linear pattern and in a very limited physical space. In a first step, we will assume perfect channel state information at the receiver side only and a negligible training overhead compared with the payload. We will demonstrate that in contrast to what might be expected based on results for cases without mutual coupling, MIMO receive antenna selection can achieve higher data rates than the system using all antennas provided that the total number of receive antennas is larger than a critical value that we will further discuss. We then propose an optimal antenna selection processing that ensures rate maximization regardless of the number of antennas used. In a later step, we will address the impact of training overhead on the system achievable rate when the training overhead is considerable. We will show that such a rate is reduced dramatically due to the large amount of training overhead arising from the presence of mutual coupling. To overcome this problem, we will thus propose a novel channel estimation method, which reduces the training overhead greatly and improves the system achievable rate performance.     

主被动传感器异地配置下的数据关联

在雷达和ESM传感器异地配置的情况下，分别基于角度统计量和距离统计量提出了二种异类传感器数据关联算法，对算法进行了讨论，进行了计算机仿真。仿真结果表明：二种算法有基本相同的正确关联概率，但基于距离统计量的异类传感器数据关联算法有相对较低的错误关联概率。     

Effects of grain source and enzyme additive on site and extent of nutrient digestion in dairy cows

Four lactating, cannulated Holstein cows were used in a 4 x 4 Latin square design to investigate the effects of grain source and fibrolytic enzyme supplementation on ruminal fermentation, nutrient digestion in the rumen and in the intestine, and milk production. A 2 x 2 factorial arrangement was used; two grains (barley and hull-less barley) were combined with and without enzyme. The enzyme supplement (Pro-Mote; Biovance Technologies Inc., Omaha, NE) contained primarily cellulase and xylanase activities and was applied daily to the total mixed diet. Dry matter intake was not affected by diet, but starch intake was greatest when hull-less barley was fed. Starch from hull-less barley was more digestible in the rumen and in the total tract than was starch from barley, but opposite results occurred for fiber digestion, indicating that hull-less barley depressed fiber digestion. As a result, cows fed the hull-less barley diets tended to produce more milk with a higher milk lactose content than did cows fed the barley diets. Enzyme supplementation had minimal effects on ruminal digestion but increased nutrient digestibility in the total tract and the proportion of microbial N in nonammonia N. Consequently, cows fed diets supplemented with enzyme had a higher milk protein content and tended to produce more 4% fat-corrected milk than did control cows. These results indicate that the use of hull-less barley rather than barley increased the digestible energy intake of dairy cows, resulting in higher milk production. The use of a fibrolytic enzyme mixture enhanced feed digestibility and milk production.     

In vitro and in vivo determinations of sun protection factors of sunscreen lotions with octylmethoxycinnamate

The aim of this work was to evaluate the correlation between in vitro and in vivo determinations of sun protection factors (SPF) of sunscreen lotions containing the synthetic sunscreen octyl methoxycinnamate. Three sunscreen lotions containing either 2, 4.5 or 7.5% octyl methoxycinnamate were prepared. The in vitro SPFs of these sunscreen lotions were determined according to the spectrophotometric method of Mansur et al. The in vivo SPF values were determined according to the Food and Drug Administration (FDA) method. The results indicate that there was a good correlation between the in vitro and in vivo determinations for the sunscreen lotions examined.     

New neural method for bias dependent noise modelling of microwave transistors

A new method for accurate determination of noise parameters of microwave transistors for various bias conditions is proposed in this paper. The proposed model consists of a transistor empirical noise model (modification of Pospieszalski’s noise model) and two artificial neural networks. With the aim to avoid extraction of the empirical model parameters for each bias point, an artificial neural network is used to introduce bias-dependence of the equivalent circuit parameters. Accuracy of such bias-dependent model is further improved by using an additional neural network aimed to correct the noise parameters’ values. The proposed modeling approach is exemplified by modelling of a MESFET device in packaged form. The noise parameters obtained by the simulation agree well with the measured data.