SGB-620/40G(40GS)型刮板输送机的研制

本文针对40T刮板机承受能力不够这一问题,而研制的40G(40GS)型刮板机。文中介绍了该机型的设计思想及改进措施。     

建立在隐形Markov模型基础上的取机手写体汉字识别

汉字识别的困难在于大量的笔道通常弯曲成一种曲线形状，并存在着一个数量庞大的字符集。要文提出一种建立在隐形Ｍａｒｋｏｖ模型（ＨＭＭ）基础上，能有效处理这类识别问题的识别模型。该模型是一种部首ＨＭＭ和连字符ＨＭＭ的互联网络。借助于ＨＭＭ的各种特征，该模型能在各种弯曲笔道上很限地工作，并具有良好的可伸缩性。为了解决同大量搜索路径引起的识别速度问题，我们利用互不相关的部首ＨＭＭ和连字符ＨＭＭ的组合，形成了     

Corrections for nonuniform sampling distortions in magnetic resonance imagery

A technique for estimating and correcting nonuniform sampling distortions in magnetic resonance imagery is presented. The technique consists of first estimating the sampling grid distortion using a parametric model, and then estimating the uniformly sampled data by interpolation on the nonuniform grid. Parameterized models for two particular sampling grid distortion are presented. Maximum likelihood and maximum a posteriori estimators are developed for these distortions. Using computer simulated data, these estimators are shown to perform well.     

Time-coded aperture tomography: experimental results

In this paper, we discuss the applicability of a time-coded aperture system especially designed for thyroid tomography on the basis of phantom experiments. Our studies show that 1) the quality of the reconstructions is high (e.g., a cold spot of 6 mm diameter in a thyroid phantom can easily be detected), and 2) the reconstruction can be carried out in less than 11 min on a standard 16 bit minicomputer (HP1000). It is therefore concluded that the clinical potentiality of the device is good.     

氟塑料的分析

氟塑料是高品位材料,由于它们有耐高温性能和化学稳定性,以及突出的机械性能和电性能,近几年来越来越稳固地确立了自己的重要地位。然而对这些含氟材料采取完全相同的应用方法会导致差错,为此需要有可靠、快速的分析方法来加以鉴别。在众多的氟聚合物中只有少数几种有实际意义,本文也只限于对这几种材料进行分析研     

Structural and kinetic studies on ligand binding in wild-type and active-site mutants of penicillin acylase

Penicillin acylase catalyses the condensation of Calpha-substituted phenylacetic acids with beta-lactam nucleophiles, producing semi-synthetic beta-lactam antibiotics. For efficient synthesis a low affinity for phenylacetic acid and a high affinity for Calpha-substituted phenylacetic acid derivatives is desirable. We made three active site mutants, alphaF146Y, betaF24A and alphaF146Y/betaF24A, which all had a 2- to 10-fold higher affinity for Calpha-substituted compounds than wild-type enzyme. In addition, betaF24A had a 20-fold reduced affinity for phenylacetic acid. The molecular basis of the improved properties was investigated by X-ray crystallography. These studies showed that the higher affinity of alphaF146Y for (R)-alpha-methylphenylacetic acid can be explained by van der Waals interactions between alphaY146:OH and the Calpha-substituent. The betaF24A mutation causes an opening of the phenylacetic acid binding site. Only (R)-alpha-methylphenylacetic acid, but not phenylacetic acid, induces a conformation with the ligand tightly bound, explaining the weak binding of phenylacetic acid. A comparison of the betaF24A structure with other open conformations of penicillin acylase showed that betaF24 has a fixed position, whereas alphaF146 acts as a flexible lid on the binding site and reorients its position to achieve optimal substrate binding.