温室气体CO2低温分离过程的研究

基于一套等温VLE的文献数据,本文首先以状态方程法,分别选用RKS、PSRK、PR、RKS-BM、PR-BM和UNIQUAC等热力学模型进行计算,考察了这些模型对CO2-H2体系适用性.结果发现RKS方程和PR方程适应性较好.对CO2-H2的低温分离工艺进行了模拟,并进行了热力学分析,每生产1 kg CO2需消耗425.83 kJ压缩功和496.79kJ的低温(-125℃)冷量.     

风源热泵空调器除霜技术实验研究

风源热泵空调器的结霜问题和除霜控制技术受到制冷与空调领域学者的广泛关注。文中重点对普遍采用时间温度法除霜控制技术的家用空调器制热运行时 ,结霜和除霜过程进行了深入地实验研究。结果表明 ,在较宽的气候变化范围 ,该控制方法工作不可靠 ,容易出现除霜不净和过早除霜的现象。提出了能适应气候变化的模糊自修正除霜技术的设计思想。     

Designing current-strain-assisted superconductor-ferromagnet multi-bit memories

Current superconducting memory devices lack the basic quality of high memory density for practical memories, mainly due to the size limitations of superconducting quantum interference devices. Here, we propose a superconductor-ferromagnet bilayer device with strain-pulse-assisted multi-bit ladder-type memory, by using strain-engineered ferromagnet domain structure to control carrier concentration in the superconductor, which is simulated by coupled Landau-Lifshitz-Gilbert and Ginzburg-Landau equations. Current- and strain-pulses are observed to deterministically control the resistivity of superconductor for one and two-bit device arrangements. The average carrier concentration of superconductor is observed to have multiple metastable states that can be controllably switched using current-pulse and strain-pulse to determine multiple resistivity states. These findings confirm the eligibility of superconductor-ferromagnet bilayers to be used as ladder-type multibit memories and open a new way for further theoretical and experimental investigations of the cryogenic memories.     

Deformation-induced martensite and nanotwins by cryogenic laser shock peening of AISI 304 stainless steel and the effects on mechanical properties

Laser shock peening (LSP) of stainless steel 304 was carried out at room and cryogenic temperature (liquid nitrogen temperature). It was found that the deformation-induced martensite was generated by LSP only when the laser-generated plasma pressure is sufficiently high. Compared to room temperature laser shock peening (RT-LSP), cryogenic laser shock peening (CLSP) generates a higher volume fraction of martensite at the same laser intensity. This is due to the increase in the density of potential embryos (deformation bands) for martensite nucleation by deformation at cryogenic temperature. In addition, CLSP generates a high density of deformation twins and stacking faults. After CLSP, an innovative microstructure, characterised by networks of deformation twins, stacking faults and composite structure (martensite and austenite phases), contributes to material strength and microstructure stability improvement. The combined effect of higher surface hardness and a more stabilised microstructure results in greater fatigue performance improvement of the CLSP samples compared to that of the RT-LSP samples.     

Thermal stability of nanotwinned and nanocrystalline microstructures produced by cryogenic shear deformation

Nanotwinned microstructures are of significant interest due to their high strength and enhanced thermal stability, attributed to the presence of a dense network of coherent twin interfaces. Propensity for twinning during deformation is known to increase at low temperature and/or high-strain-rate. In this study, we use high-strain-rate (~10^3?s^?1) shear deformation in cutting over a range of strains (γ ~1–5) and temperatures (cryogenic to ambient) to engineer a variety of microstructures in three face-centred cubic (FCC) metals – copper, brass and aluminium. The microstructures include nanocrystalline-equiaxed and densely (nano) twinned types of controllable domain size. The effects of low-temperature deformation and stacking fault energy on the resulting microstructure, hardening, stored energy and associated recrystallization kinetics are established. For copper, the nanotwinned microstructures are found to be thermally more stable and stronger than the equiaxed counterparts comprised of random high-angle grain boundaries. This enhanced effect of nanotwins on microstructure stability is, however, not observed in brass, while aluminium did not show any indications of twinning over the investigated range of deformation conditions.     

低温下氘分子红外吸收特性研究

采用基于第一性原理的从头计算单双取代耦合簇方法并结合cc-PVTZ基组,计算了处于基态的(D2)3分子两种不同构型(D2d和D2h)的各种能量模式及其对应的红外谱图.利用自主研制的低温平面冷冻靶系统和低温红外光谱测量系统获得了低温下液氘的红外吸收谱.结果表明,实验测得的液氘红外吸收最强位置与理论计算得到的基态(D2)3分子的红外强度最大位置基本一致,且均为低模式Q1(0)+S0(0).     

低温Yb:YAG放大器增益与热畸变特性实验研究

为了研究低温条件下Yb:YAG放大器的增益和热特性,搭建了一套液氮冷却的低温放大器,开展了实验研究。测量了不同泵浦强度下的小信号增益以及低温和常温下的介质热致波前畸变。结果表明:低温条件下,可以用更少的泵浦能量得到高于常温的增益;常温下泵浦电流200A、脉冲宽度1200μs的小信号增益为1.59;低温下泵浦电流200A、脉冲宽度400μs的小信号增益为1.82,光光效率显著提高。自发辐射放大(ASE)问题在低温下更加显著,采用短脉冲泵浦有利于降低ASE的影响。低温的热管理效果较常温有显著提高,可以在更高的平均功率下运行。     

Nanoscale chemical analysis of beam-sensitive polymeric materials by cryogenic electron microscopy

Nanoscale chemical analysis of functional polymer systems by electron microscopy, to gain access into degradation processes during the materials life cycle, is still a formidable challenge due to their beam sensitivity. Here a systematic study on the different stages of degradation in a P3HT-PCBM organic photovoltaic (OPV) model system is presented. To this end pristine samples, samples with (reversibly) physisorbed oxygen and water and samples with (irreversibly) chemisorbed oxygen and water are imaged utilizing the full capabilities of cryogenic STEM-EELS. It is found that oxygen and water are largely physisorbed in this system leading to significant effects on the band structure, especially for PCBM. Quantification proves that degradation concomitantly decreases the amount of CC bonds and increases the amount of C O C bonds in the sample. Finally, it is shown that with a pulsed electron beam utilizing a microwave cavity, beam damage can be significantly reduced which likely extends the possibilities for such studies in future.     

Role of remote Coulomb scattering on the hole mobility at cryogenic temperatures in SOI p-MOSFETs

The impacts of remote Coulomb scattering(RCS)on hole mobility in ultra-thin body silicon-on-insulator(UTB SOI)p-MOSFETs at cryogenic temperatures are investigated.The physical models including phonon scattering,surface roughness scattering,and remote Coulomb scatterings are considered,and the results are verified by the experimental results at different temperatures for both bulk(from 300 K to 30 K)and UTB SOI(300 K and 25 K)p-MOSFETs.The impacts of the interfacial trap charges at both front and bottom interfaces on the hole mobility are mainly evaluated for the UTB SOI p-MOSFETs at liquid helium temperature(4.2 K).The results reveal that as the temperature decreases,the RCS due to the interfacial trap charges plays an important role in the hole mobility.     

On the refinement of carbide precipitates by cryotreatment in AISI D2 steel

Refinement of carbide particles by cryotreatment is often proposed as a major factor for the improvement of wear resistance in tool steels. However, this proposition is not substantiated by experimental evidence. This has been examined in this report by (i) detailed micro-structural analyses of the nature, volume fraction, size, population density and distribution of carbide particles, (ii) XRD and EDX micro-analysis on the bulk samples and electrochemically extracted carbides, and (iii) measurement of hardness and wear rate of a series of differently cryotreated AISI D2 steel. The results conclusively establish that (i) cryotreatment, in comparison to conventional treatment, induces precipitation of finer carbides with higher volume fraction and more uniform distribution, and (ii) population density and the size of secondary carbide particles significantly increases with holding time up to a critical duration at 77 K in cryotreatment. The latter observation indicates the pioneering direction towards optimization of cryotreatment design for techno-economic benefit.