采用粉末冶金技术制备的空心微珠分散钛基复合材料的表征及磨损性能(英文)

采用粉末冶金技术制备空心微珠分散的钛基复合材料,并对其磨损和腐蚀行为进行研究。结果表明,所制备的复合材料组织中在α-Ti基体中分散有平均孔径为50~150μm的空心微珠。复合材料的多孔性归因于压制过程中载荷对空心微珠颗粒的破坏及空心微珠本身的空心特性。X射线衍射分析表明复合材料由Al2O3、SiO2、TiO2和α-Ti相组成。基体钛合金的显微硬度为HV 240,而复合材料的显微硬度在HV 1100~HV 1800范围内变化。磨损实验表明,相对于商用Ti-6Al-4V合金,复合材料对硬化钢球和WC球的抗磨损性能得到显著增强。复合材料在3.56%NaCl(质量分数)溶液中的腐蚀行为表明,其耐点蚀性能改善,腐蚀电位向正(更高)方向移动。然而,与商用Ti-6Al-4V合金相比,空心微珠分散钛合金的腐蚀速率增大。     

PRELIMINARY STUDIES ON PHYSICAL AND NUTRITIONAL QUALITIES OF SOME INDIGENOUS AND IMPORTANT RICE CULTIVARS OF NORTH‐EASTERN HILL REGION OF INDIA

ABSTRACT

The northeastern hills of India are endowed with rich source of rice germplasm, which may be safely estimated about 9,000 accessions, excluding the redundancies. Even though much of the germplasm have been collected, studies on nutritional aspects of these local cultivars are still lacking. Fifteen important indigenous rice genotypes collected from different rice growing ecosystem of this region were studied for physical and nutritional qualities. Kernel color of the genotypes varied from white to dark purple. All the genotypes except Manipuri were of bold‐grain type. Most of the genotypes studied have fat contents more than 2.0%. The protein content was found higher in Chahou angouba and Naga special. Five cultivars were identified as high‐protein cultivars of rice, with 10–12.07% protein content. Amylose content varied from 2.27 to 24.5%. Most of long‐grained genotypes recorded lesser amylose than short grained. Chahou varieties were found aromatic and glutinous, which demand higher market prices in local market.

PRACTICAL APPLICATION

The north‐eastern hills of India are endowed with rich source of rice germplasm, and much of the germplasm have been collected, but studies on basic and advanced nutritional aspects of these local cultivars are still lacking. This part of India has valuable rice genotypes of strong aroma, glutinous characters and slender grains with high amount of protein, fat and fiber. Having not known to the rest of the world and even to indigenous end users, some of such cultivars have already been lost, and some more are at the verge of extinction. Quality evaluation done in the present study provided useful information on their commercial exploitation and utilization in breeding programs of nutritional enhancement of rice to fight malnutrition among rice‐consuming population, which is largest in the world.     

DEVELOPMENT OF A HIGH-MOISTURE SHELF-STABLE GRATED CARROT PRODUCT USING HURDLE TECHNOLOGY

Carrot (Daucus carota) can be highly perishable and difficult to preserve fresh for long periods at ambient temperature and humidity. Studies on grated carrots were carried out for the development of a shelf‐stable moist‐preservation process based on infusion of additives using hurdle technology. Additives comprising 3.0% sodium chloride (to reduce water activity [A_w] to 0.94), 0.9% citric acid (to reduce pH to below 4.5), 1.0% sodium citrate and 0.2% sodium benzoate (as antimicrobial agents) were followed by partial dehydration. The product was stored in flexible polymeric pouches. The physical, chemical and pathological stability was monitored during storage at ambient temperatures (19–33C). The partially dehydrated grated carrots (moisture 66.2%) were acceptable for more than six months at ambient temperature with the retention of carotenoid up to 82.5%. The product was microbiologically safe throughout the study.     

Thermal Expansion of CeO2, Ho2O3, and Lu2O3 from 100° to 300°K by an X-Ray Method

Thermal expansion of CeO₂, Ho₂O₈, and Lu₂O₃ was determined from 100° to 300°K by a back-reflection X-ray technique. The variation of thermal expansion with temperature is the same as that of specific heat for CeO₂ and Ho₂O₃; these oxides obey the Grueneisen model of thermal expansion in the temperature range studied.     

Effect of variation of load resistance on amplifier characteristics of complementary composite transistors. II

A configuration has been proposed by which an ideally infinite input impedance can be realized at all frequencies. The advantage of this configuration is that both positive and negative capacitive reactance can be realized just be controlling the gain of the amplifier, the realized capacitance being independent of frequency.     

Compact solid state radio frequency amplifiers in kW regime for particle accelerator subsystems

Radio frequency and Microwave (RFM) infrastructure test facility is under development at RRCAT for evaluating and powering, subsystems of particle accelerator. As a part of this facility, design of 20–30 kW UHF solid state power amplifiers is in progress. For this work, design procedure has been formulated for the development of solid state amplifier modules, radial combiner, divider and directional coupler; with specifications suited to RFM power system for particle accelerator. Methodology has been demonstrated by developing two different compact amplifiers with power output of 2 kW each, operating at 352 MHz and 505.8 MHz, respectively. This paper describes underlying design principles and indigenous development of these amplifiers, consisting of 270–300 W amplifier modules, 8-way 2 kW radial combiner/divider and directional couplers. Design methodology for power combiner has been extended by physically realizing higher power (4 kW) 16-way power combiner and 2-way combiner (8 kW) for higher power (8 kW) amplifier configuration planned. Simple design, indigenous technology, high efficiency and ease of fabrication, are the main features of this design.     

Reactive power deployment and cost benefit analysis in DNO operated distribution electricity markets with D-STATCOM

The aim of this paper is to analyze unbalanced radial distribution systems (UBRDS) with the distribution static compensator (D-STATCOM). The main objectives of this paper are D-STATCOM allocation in UBRDS with an objective of providing reactive power support to enhance voltage profile and reduce line losses of the distribution network, determination of optimal D-STATCOM rating subjected to minimization of total cost, and impact of D-STATCOM placement on improving power factor and savings in cost of energy loss. The analysis is conducted on a large industrial load model with light, medium and high loading scenarios. Further, the impact of load growth is also considered for better planning of the power distribution system. The results are obtained on standard 25-bus UBRDS to check the feasibility of the proposed methodology.     

LOCAL OPTIMAL COORDINATION BASED ADAPTIVE COORDINATION

ABSTRACT

This paper presents the development of an adaptive coordination scheme for the coordination of directional overcurrent relays for large interconnected power systems, using the concept of local optimal coordination under the changed system conditions. In response to a structural change or an operational change in the power system, the developed adaptive local optimal coordination algorithm automatically identifies the local disturbed region and re-coordinates only the settings of the relays which fall inside this identified local region in an on-line manner. The scheme developed is applied to the IEEE 57-bus test power transmission system. The results are validated through a full system coordination study and the usefulness of the reported algorithm is demonstrated.     

A BRIEF HISTORY OF THE BEGINNING OF THE FINITE ELEMENT METHOD

This paper presents summaries of the works of several authors associated with the invention of the analysis technique now referred to as the finite element method. It stresses the notion of first development from which subsequent ideas evolved and gives what is believed to be an accurate record of the historical sequence of published papers in the international literature.     

INNOVATIVE NETWORKING CONCEPTS TESTED ON THE ADVANCED COMMUNICATIONS TECHNOLOGY SATELLITE

This paper describes a program of experiments conducted over the advanced communications technology satellite (ACTS) and the associated T1-VSAT (very small aperture terminal). The experiments were motivated by the commercial potential of low-cost receive-only satellite terminals that can operate in a hybrid network environment, and by the desire to demonstrate frame relay technology over satellite networks. The first experiment tested highly adaptive methods of satellite bandwidth allocation in an integrated voice–data service environment. The second involved comparison of forward error correction (FEC) and automatic-repeat-request (ARQ) methods of error control for satellite communication with emphasis on the advantage that a hybrid architecture provides, especially in the case of multicasts. Finally, the third experiment demonstrated hybrid access to databases and compared the performance of internetworking protocols for interconnecting local area networks (LANs) via satellite. A custom unit termed frame relay access switch (FRACS) was developed by COMSAT Laboratories for these experiments; the preparation and conduct of these experiments involved a total of 20 people from the University of Maryland, the University of Colorado and COMSAT Laboratories, from late 1992 until 1995.