Epitaxial growth of GaN on (0001) Al<Subscript>2</Subscript>O<Subscript>3</Subscript> via solution-cast seed layer formation process using Ga(mDTC)<Subscript>3</Subscript>

This paper reports an alternative method for the growth of GaN epitaxial layer on (0001) Al₂O₃ substrate by hot-wall vapor phase epitaxy technique. Tris (N,N-dimethyldithiocarbamato)-gallium (III), Ga(mDTC)₃ was introduced as a precursor material for the seed layer formation in the growth of GaN. Optimal growth conditions with seed layers formed by the Ga(mDTC)₃ concentration of 0.047 mol/L were identified: Growth temperature was found to be 850 °C, and optimal distance between the reactant outlet and substrate was determined to be 12.5 cm. Characterization results showed that this growth method produce high-crystallinity GaN epitaxial layers at a relatively lower growth temperature compared to the existing growth techniques and simplify the growth process.     

Reward optimization of a repairable system

This paper analyzes a system subject to repairable and non-repairable failures. Non-repairable failures lead to replacement of the system. Repairable failures, first lead to repair but they lead to replacement after a fixed number of repairs. Operating and repair times follow phase type distributions (PH-distributions) and the pattern of the operating times is modelled by a geometric process. In this context, the problem is to find the optimal number of repairs, which maximizes the long-run average reward per unit time. To this end, the optimal number is determined and it is obtained by efficient numerical procedures.     

低噪声晶振16次倍频源

本文介绍了低噪声高次倍频器的设计原理及低相位噪声晶振１６次倍频信号源。     

粒界缓冲型展宽效应对PTC材料温度系数的影响

本文利用相变扩张理论分析了粒界缓冲型展宽效应对BaTiO_3系PTC陶瓷的介电系数及温度系数a_r的影响,指出了晶粒尺寸和温度系数的关系。     

New strategies for separations through reactions

Separations through reactions can provide reliable and economically viable alternatives to established methods of separation, particularly for close boiling substances. New strategies in ‘Dissociation Extraction’ and ‘Dissociation Extractive Crystallization’ for separation of close boiling acidic/basic mixtures have been highlighted. Separations with aqueous solutions of hydrotrope and aqueous micellar solutions have been brought out. Separations by membranes with facilitated transport is potentially attractive. This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday.     

一种新颖的跳频振荡器

摘要本文综合考虑到频率合成技术及单端口体波谐振器HBAR的特点提出了一种基于一阶非线性PLL的锁相频率合成方案。文中对这种跳频方案的原理、性能特点作了详细论述、并通过实验、从不同角度对本方案进行了说明、同时对整机的各项指标作了详尽测试:在HBAR无载Q_N值为4000的情况下,该多模跳频振荡源的捷变范围为770MHz—840MHz、捷变时间小于20μS。杂散分量低于—60dB、二次谐波分量低于—34dB。离散捷变频率点为16点,构成闭环跳频系统后,对开环VCO的短稳改善了三个量级:从1.3×10~(-5)/ms到1.6×10~(-8)/ms及9.56×~(-7)/s到1.69×!0~(-9)/s,尤为重要的是该多模跳频振荡源达到此性能所需的硬件量很小,因此在对体积要求苛刻的场合、此种跳频方案具有极强的竞争力。     

SYNTHESIS OF CHEMICAL REACTION PATHS: ECONOMIC AND SPECIFICATION CONSTRAINTS

The synthesis of alternative reaction paths leading to a desired chemical has received increasing attention in the recent past. A procedure to develop new reaction schemes in a systematic manner was reviewed by the authors ( [ 1 -3] ). The algorithm presented in these earlier papers implied the generation of an infinite number of reaction paths. The thermodynamic feasibility is a preliminary screening which reduces the number of chemical production schemes. Further screening is necessary, taking into account considerations which are related to economics, processing, safety and so on. Some constraints related with role specification, gross added value and demand/supply requirements are analysed in this paper. Examples illustrate the application of the screening procedure, showing that the addition of a few constraints results in a dramatic decrease of alternative reaction paths.     

Shock-induced phase transition of oriented pyrolytic graphite to diamond at pressures up to 15 GPa

In studies of shock-induced phase transition of ordered pyrolytic graphite to a diamond-like phase, the lowest transition onset pressure was observed at 19.6 GPa. The phase transition in that case was considered to be martensitic. In the present study ordered pyrolytic graphite with voids between particles was loaded at pressures up to 15 GPa using a planar shock wave propagating along the basal plane of the graphitic crystal structure. As a result, both diamond-like carbon and diamond were observed in the postshock sample. The phase transition of graphite to diamond was assumed to occur by the release of distortional energy stored in the graphite particles, that is, diffusional-controlled reconstructive mechanism, on the basis of the data by high resolution electron microscopy together with electron energy loss spectroscopy.     

InGaAsP／InP PFBH激光器

采用Ｎ－ＩｎＰ衬底研制ＩｎＧａＡｓＰ／ＩｎＰ激光器和ＤＦＢ激光器在国内已报导过多次，本文介绍用Ｐ－ＩｎＰ衬底研制ＩｎＧａＡｓＰ／ＩｎＰ平面埋层异质结构激光器和ＤＦＢ－ＰＦＢＨ激光器，同时利用晶体生长和晶向的依赖关系，改进埋区的结构，使器件最高激射温度大于１００℃。     

SIMULATION OF MICROMIXING IN A TURBULENT TUBULAR REACTOR WITH CONCENTRIC FEED

Turbulence on the axis of a pipe is isotropic and homogeneous and the rate of turbulent energy dissipation, ε, is known as a function of the velocity, pipe diameter and viscosity. When, however, a concentric feed pipe is introduced (as in a reactor), the ε field does not seem to be known. Evidence from fast, mixing-controlled reactions indicates a disturbance near to and downstream from the feed pipe with an increase in ε. Because of the lack of experimental information, the radial and axial distribution of ε has been modeled. One parameter—ε at the outlet of the feedpipe—is undetermined in this model. It is shown how the radial dispersion and especially the micromixing and reaction of fluid emerging isokinetically from the feed pipe can then be calculated, using a one-dimensional, radially averaged formulation. An application to four coupled, mixing-controlled reactions is included. Simulated and measured product distributions compared satisfactorily at various concentration levels and two solution viscosities. Whereas the new model is plausible, more work is needed to understand how a feed pipe modifies the flow in its vicinity.