聚氯乙烯增塑剂的吸收行为

通常,认为增塑剂的吸收过程是由扩散机理引起的。在与高聚物的亲合力方面,增塑剂有一种介于溶剂与非溶剂之间的性质。譬如,如果一高聚物能无限量地吸收一种液体,并因此而被溶介,那末,该液体归进为这种高聚物的溶剂一类。相反,如果一种高聚物完全不能吸收该液体,则该液体称为非溶剂。而增塑剂是一种有限度的溶解高聚物的液体。     

Low-field 3-DFT MRI: conceptual, analytical, and experimental aspects

Three-dimensional Fourier transform (3-DFT) magnetic resonance imaging (MRI) offers advantages in terms of signal-to-noise (S/N) per unit of time for the case where a large number of slices is desired. This advantage is enhanced when the relaxation time, T(1 ), is short. Because time limitations in 3-DFT imaging force the use of short time intervals, TR, between excitations of a slice, lesion contrast is often undesirable at mid-and high-field strength even when the S/N is good. At low fields, where T(1) values are short, high S/N and contrast can both be achieved with 3-DFT MR images. The conceptual and analytical aspects of low-field 3-DFT MRI are presented and demonstrated at 640 G.     

Quantization improvement in MRI using dual quantizers

The quantization of magnetic resonance imaging (MRI) data can cause information loss due to quantizer/data mismatch. The authors address a method for improved quantization as well as techniques for measuring the improvement in such methods. A dual quantizer scheme is described and simulated which is fast and more accurately quantizes MRI data than conventional methods. The approach is to use two quantizers, one for the high-level data and one for the low-level data. This adaptive, dual quantization scheme is simple and provides significant improvements in image quality, especially for three-dimensional (3-D) acquisition. Results are given which show how well the low frequencies are represented and indicate the increased fidelity of the high-frequency components. These results show a significant improvement in signal-to-noise ratio as well as in detection tasks for both noiseless data and data which include varying amounts of system noise.     

Recent progress of CERN RD50 Collaboration

The objective of the CERN RD50 Collaboration is to develop radiation hard semiconductor detectors for very high luminosity colliders, in particular, for the upgrade of the large hadron collider （LHC） which itself is scheduled to be operational in 2007. The approach of the RD50 has two major research lines, material engineering and device engineering. These are further subdivided into projects covering defect characterization and engineering, new detector materials, detector characterization, new detector structures and full detector systems. Presently, 264 members from 53 institutes are actively participating in the RD50 Collaboration. Detectors made of defect engineered substrates, e.g. high resistivity magnetic Czochralski （MCz-Si）, epitaxial silicon （Epi-Si） on Czochralski silicon （Cz-Si） substrate, intentionally thermal donor （TD） compensated p-type MCz-Si and oxygen enriched （DOFZ） silicon, have been demonstrated by the RD50 Collaboration. An overview and highlights of the results of these defect engineering techniques were given in this report.     

D2工具钢在气淬和回火过程中的各向异性畸变

分别使用铸造试样及两种不同锻造程度的锻件试样，对高合金冷作模具钢D2在气淬和回火过程中的畸变行为进行了研究。试验结果表明，铸造试样的畸变是等向性的，而锻造试样的畸变显然呈各向异性。各向异性畸变程度随奥氏体化温度的升高而增加。在本试验范围内，不同的锻造程度对各向异性的畸变程度影响不大。回火后各向异性畸变程度有所降低。使用测膨胀方法及金相检验探讨了产生各向异性畸变的可能机制。     

铝电解工须知(4)

现在介绍电解槽中氧化铝加入量过少或过多时的后果。正常生产槽加入氧化铝过少时的后果: 1.电流效率下降理论和实践都证明,当电解质中氧化铝含量为5.0～5.5％时电解槽     

液-液萃取法分离铂族金属

从矿石提取铂族金属,将其精制到所要求的很高纯度,以应多方面的使用,需要大量复杂的操作过程。现在,从铂族混合液中,产出单一铂族金属的最终精制过程,是用选择沉淀来实现,然而,就分离程度而论,其效率是低的。一种改进的方法——液—液萃取法,已发展到中间工场阶段。本文在此法分离的基础上,着重谈某些化学及操作的原理。     

Experimental Study of Microstructure Evolution during Tempering of Quenched Steel and Its Application

LARGE-SIZED FORGINGS are usually intensivelyquenched to obtain the desired microstructuredistribution,high strength and hardness.Becauseresidual stresses are high in quenched large-sizedforgings,tempering processes follow quenchingprocesses to reduce the residual stress and obtain goodmechanical properties.Several differentmicrostructures are generated in quenched steelforgings,such as martensite,bainite and retainedaustenite.Modeling of microstructure evolution inquenched steel during …