Development of ultra light magnesium-lithium alloys

Magnesium-lithium alloys are among the lowest density metallic materials. Addition of lithium, with a relative density of 0·53, in magnesium reduces the density of the alloy significantly. Furthermore, addition of nearly 11 wt.% lithium converts hexagonal close packed structure of pure magnesium to a body centered cubic lattice, markedly improving formability of the alloy. The development of these alloys, however, had been hampered due to the high reactivity of lithium and magnesium in the molten state and also, due to poor creep resistance and instability of mechanical properties at room temperature. In an attempt to indigenize these ultra light alloys for possible applications in Indian satellite programme, detailed research work was initiated in DMRL. The difficulties associated with producing sound cast ingots have been overcome by controlling melting and casting parameters of these alloys. Extensive work has been done on structure-property correlation of alloys with varying lithium content and minor alloying additions. Based on these work, advanced magnesium-lithium alloys have been developed with improved tensile properties, room temperature stability and creep resistance. Wrought products (plates/sheets) of magnesium-lithium alloy have been supplied to ISAC, Bangalore and are being used in their INSAT-2 programme. This paper describes the systematic studies carried out in the laboratory to indigenize these ultra light alloys.     

Dislocations and flux pinning in YBa2Cu3O7

The dislocation structures of bulk textured and epitaxial thin film YBa₂Cu₃O₇ superconductors are examined. Correlations between increases in flux pinning and dislocation densities are noted. A model for flux pinning by individual dislocations is presented. This gives a treatment of strain induced effects and effects of normal state region interactions. It is shown that the values of pinning predicted are in line with experimental observations.     

群时延精确设计的全差分四阶Bessel滤波器

采用MOS管有源电阻,提出了一种全差分R-MOSFET-C四阶Bessel有源低通滤波器,.通过调节工作于亚阈值区的CMOS管的沟道导纳补偿电阻值的大小,能抵消集成电路制造工艺中电阻值的一致偏差,实现Bessel有源滤波器群时延的精确设计.根据无源滤波器的状态方程完成有源滤波器的综合,应用3.3V,0.5μm CMOS工艺完成了群时延大小为0.75μs的四阶Bessel低通滤波器的管极计算机仿真,仿真结果表明所提电路正确有效,适于全集成.     

Evaluation of influence of external magnetic disturbance on superconducting magnet taking conservation of linkage flux into account

External magnetic disturbance influences the quality of the image obtained with a magnetic resonance imaging (MRI) system because it causes magnetic resonance frequency drift. When a superconducting magnet in persistent current mode operation is exposed to external magnetic disturbance coil current varies to keep linkage flux constant. Conventional analysis is usually formulated with constant current and does not provide correct evaluation of drift of magnetic field in the magnet. This paper proposes a method of numerical analysis of magnetic field considering conservation of linkage flux in a superconducting magnet under a persistent current mode operation. This method is applied to evaluate drift of the magnetic field in a superconducting magnet for magnetic resonance imaging due to external magnetic disturbance. Analysis results show good agreement with the experimental results.     

主动阻尼控制中的扩展加速度输出反馈法

正位置反馈(PPF)是一种能够显著提高结构模态阻尼的控制策略，但是这种策略在原理和应用中具有一定的局限性。本文在指出了传统的PPF控制器的优缺点基础上，提出一种扩展的加速度输出反馈控制方法AOEF，同时给出了最优AOEF控制器的设计计算方法。仿真计算和实验表明，在传感器／作动器同相的情况下，采用这种控制器的闭环系统具有无条件的稳定性，在非同相的情况下也能达到优良的控制性能。     

系列尼古丁PVC膜选择性电极的研制

以尼古丁为研究对象 ,研制了一系列含有不同增塑剂 (苯二甲酸二辛酯、苯二甲酸二壬酯和癸二酸二辛酯 )和电活性物质 (尼古丁 四苯硼缔合物、尼古丁 硅钨酸缔合物、尼古丁 磷钨酸缔合物和尼古丁 雷氏盐缔合物 )的PVC膜电极。所有的 8支电极均对尼古丁盐酸溶液有Nernst响应。所制备的电极中 ,以尼古丁 四苯硼缔合物、尼古丁 硅钨酸缔合物、尼古丁 磷钨酸缔合物或尼古丁 雷氏盐缔合物为活性物的电极 ,其线性范围达到 10 - 4～ 10 - 1 mol/L ,以尼古丁 硅钨酸缔合物为活性物的电极线性范围达到 10 - 5～ 10 - 1 mol/L。电极响应的均匀性还在进一步的研究和改善中     

Influence of process variables on the drying of potato slices

Investigation of the effects of varying air velocity, slice thickness, and pre-treatment with sodium chloride solutions and surface active agents on drying potato slices indicated that the drying occurred entirely in the falling rate period and was controlled by the mechanism of liquid diffusion. The rate of drying, and therefore the diffusion coefficients, increased with the addition of sodium chloride and surface active agents. Diffusion coefficients were also influenced by air velocity and slice thickness, suggesting that the rate of drying of potato slices is controlled by a combination of internal and external resistances.     

一种基于自然数线性八叉树的优化构造算法

本文提出了一种基于自然数线性八叉树的优化构造算法。该算法以活动结点表为中间辅助结构，在图像输入过程中直接生成基于Ｎ码的八叉树叶结点．与常规构造算法相比，新提出的优化构造算法省去了Ｎ码的计算及合并过程，从而具有较高的时空效率．     

Monolithic SiGe Up‐/Down‐Conversion Mixers with Active Baluns

The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on‐chip 1 to 6 GHz up‐conversion and 1 to 8 GHz down‐conversion mixers using a 0.8 µm SiGe hetero‐junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up‐conversion mixer was implemented on‐chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up‐conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down‐conversion mixer was implemented on‐chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down‐conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz.     

砂岩储层渗透率表征方法探讨

渗透率是反映储层渗流能力的重要参数，目前对于单一储层的渗透率表征方法，通常是在岩心分析渗透率或测井解释渗透率的基础上进行厚度加权算术平均。这种方法对于均质的储层来说是适用的，但对于非均质严重的储层，不能准确反映该储层的实际渗流能力。本文提出一种应用可动流体体积权衡表征渗透率的方法，经实际资料验证，能较好地反映储层的实际渗透能力。