异质结光晶体管的研究与进展

回顾了异质结光晶体管(HPT)在近年来的重要进展,综合分析了HPT的工作原理以及影响其性能的主要参数。综述了不同材料制作的HPT的研究现状,得出了目前限制HPT发展的主要因素及当前应重点解决由于基区表面复合等效应导致的增益下降和由于结电容的充放电限制的响应带宽等问题的结论。     

浅析HPT250轧机中滑移系数对轧制过程的影响

通过HPT250轧机在技术改造中遇到的一个问题，即滑移系数对冷轧元缝钢管在轧制过程中所起的作用。在实际生产中经过不断的技术研究和改进。使闲置多年的HPT250轧机为钢管公司的生产迭拉起到很大的作用。     

高压扭转变形Mg-Zn-Y合金的组织演化和时效行为

采用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)仪和显微硬度计研究了高压扭转(HPT)变形Mg-Zn-Y合金的微观组织演变和时效行为。结果表明,在HPT变形前后,合金中的第二相颗粒是W相和Mg₂₄Y₅相,且在HPT处理后没有观察到任何新沉淀物的形成,说明HPT变形并未导致合金发生相变。同时,发现HPT变形过程是伴随着形变孪晶的产生和大量位错增殖而进行的,其中形变孪晶在HPT处理过程中被第二相颗粒所细分。与未变形合金相比,HPT变形可以加速时效进程,即在更短的时效时间达到相对高的峰值硬度。对HPT变形7圈的试样进行175 ℃×8 h时效处理后,峰值显微硬度达到约114 HV0.1。经过时效处理后,析出相优先在位错和孪晶界处形核,说明位错和孪晶界充当析出相优先形核位点。     

Effect of initial powder type on the hydrogen storage properties of high-pressure torsion consolidated Mg

While severe plastic deformation (SPD) on bulk samples has been widely applied for modifying the H-sorption properties, there has been little attention towards the use of SPD on powder materials. In this context, the aim of the present work was to compare the H-storage properties of high-pressure torsion (HPT) consolidated products obtained from two distinct Mg powder precursors: atomized micro-sized and condensed ultrafine powder particles. The results showed that the nature of the initial powder precursor had a pronounced effect on the H-sorption behavior. The HPT product obtained from the condensed ultrafine powder showed faster absorption kinetics than the consolidated product obtained from the atomized powder. However, the HPT product obtained from atomized powder could absorb more hydrogen and showed faster desorption kinetics corresponding to a lower activation energy. These results are discussed by taking into account the effectiveness of the HPT process to refine the grain sizes and differences in the dispersion of fine MgO oxide particles.     

Validation of the CATHARE2 code against experimental data from Brayton-cycle plants

In recent years the Commissariat à l’Energie Atomique (CEA) has commissioned a wide range of feasibility studies of future-advanced nuclear reactors, in particular gas-cooled reactors (GCR). The thermohydraulic behaviour of these systems is a key issue for, among other things, the design of the core, the assessment of thermal stresses, and the design of decay heat removal systems. These studies therefore require efficient and reliable simulation tools capable of modelling the whole reactor, including the core, the core vessel, piping, heat exchangers and turbo-machinery. CATHARE2 is a thermal-hydraulic 1D reference safety code developed and extensively validated for the French pressurized water reactors. It has been recently adapted to deal also with gas-cooled reactor applications. In order to validate CATHARE2 for these new applications, CEA has initiated an ambitious long-term experimental program. The foreseen experimental facilities range from small-scale loops for physical correlations, to component technology and system demonstration loops.In the short-term perspective, CATHARE2 is being validated against existing experimental data. And in particular from the German power plants Oberhausen I and II. These facilities have both been operated by the German utility Energie Versorgung Oberhausen (E.V.O.) and their power conversion systems resemble to the high-temperature reactor concepts: Oberhausen I is a 13.75-MWe Brayton-cycle air turbine plant, and Oberhausen II is a 50-MWe Brayton-cycle helium turbine plant. The paper presents these two plants, the adopted CATHARE2 modelling and a comparison between experimental data and code results for both steady state and transient cases.     

Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish

Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark.     

RTD/HPT光控单-双稳转换逻辑单元

以光接收器件代替RTD MOBILE(RTD单-双稳转换逻辑单元)电路中的HEMT或HBT,可构成光控MOBILE电路。在比较了四种光控MOBILE结构的基础上,选择RTD/HPT光控结构,重点分析讨论了RTD/HPT光控MOBILE的工作原理,当光控MOBILE的输入光功率超过一个临界值时,MOBILE的输出电压便会从高电平跳变到低电平;由HPT光增益理论分析了提高HPT性能的措施以及HPT设计中应该注意的问题;介绍了以Si光三极管代替HPT,通过模拟实验,验证了RTD/HPT光控MOBILE的逻辑功能。     

高压扭转圈数对碳化硅颗粒铝基复合材料组织和性能的影响

采用高压扭转(high-pressure torsion,HPT)工艺,成功将8.75%体积分数SiC颗粒与Al的混合粉末制成金属基复合材料,并用金相显微镜、显微维氏硬度计、万能材料试验机和扫描电镜等,分析了扭转圈数对SiCp/Al复合材料的显微组织、显微硬度、拉伸性能和拉伸断口形貌的影响。结果显示,扭转圈数从0.5圈增加到4圈,基体的变形抗力降低,SiC颗粒在剪应力的作用下易于与基体协调变形,SiC颗粒分布均匀化程度显著提高;随着扭转圈数增加,试样所受到的剪切作用增大,极易引起位错的运动和增殖,基体晶粒得到细化,单位体积内的晶界增多,使试样显微硬度得到提高;扭转圈数越多,拉伸断口韧窝数量明显增多,且尺寸变小。     

Plutonium Third Phase Formation in the 30% TBP/Nitric Acid/Hydrogenated Polypropylene Tetramer System

Abstract

A study on plutonium third phase formation in 30% TBP/nitric acid/hydrogenated polypropylene tetramer (HPT) was performed. Characterization studies of HPT indicate its composition to be a mixture of many highly branched alkanes with a volatility close to n‐undecane. This composition results in about a factor of two better resistance to Pu(IV) third phase formation than dodecane. At 7 M nitric acid in the aqueous phase, the presence of Pu(VI) was observed to substantially reduce the organic phase metal concentration necessary to induce phase splitting in both diluents. Spectroscopic investigation of mixed valence systems also suggest a prominent role for Pu(VI) in the formation of the dense organic phase. Accumulation of Pu(VI) in the heavy phase, as well as certain spectral features, suggest that Pu(VI) is forming a different species, possibly a plutonyl trinitrato, with a strong tendency to form third phase.