Computational study of packing a collagen-like molecule: quasi-hexagonal vs "Smith" collagen microfibril model

The lateral packing of a collagen-like molecule, CH3CO-(Gly-L-Pro-L-Pro)4-NHCH3, has been examined by energy minimization with the ECEPP/3 force field. Two current packing models, the Smith collagen microfibril twisted equilateral pentagonal model and the quasi-hexagonal packing model, have been extensively investigated. In treating the Smith microfibril model, energy minimization was carried out on various conformations including those with the symmetry of equivalent packing, i.e., in which the triple helices were arranged equivalently with respect to each other. Both models are based on the experimental observation of the characteristic axial periodicity, D = 67 nm, of light and dark bands, indicating that, if any superstructure exists, it should consist of five triple helices. The quasi-hexagonal packing structure is found to be energetically more favorable than the Smith microfibril model by as much as 31.2 kcal/mol of five triple helices. This is because the quasi-hexagonal packing geometry provides more nonbonded interaction possibilities between triple helices than does the Smith microfibril geometry. Our results are consistent with recent x-ray studies with synthetic collagen-like molecules and rat tail tendon, in which the data were interpreted as being consistent with either a quasi-hexagonal or a square-triangular structure.     

Psychosocial characteristics of pregnant and nonpregnant HIV-seropositive women

Thirty-three HIV-positive women, 12 of whom were pregnant, participated in semistructured interviews to define areas of psychosocial need. Eighty-eight percent of the subjects reported current unemployment. A history of substance abuse was reported by 82 percent, suicide attempts by 52 percent, and sexual problems by 43 percent. Approximately 30 percent reported elevated levels of depressive symptoms on standardized symptom inventories. The pregnant women appeared psychologically healthier than the nonpregnant group. HIV-positive women face multiple psychosocial stressors and may experience significant psychological distress.     

Ultrastructural evidence for an innervation of epithelial enterochromaffine cells in the guinea pig duodenum

The innervation of the duodenal enterochromaffine cells (E.C.) of the guinea pig was studied at the electronmicroscopic level. Pretreatment with 5-OH-dopamine was performed to visualize catecholaminergic (CA) nervous elements. Near the basement membrane of all examined E.C. in the crypts, bundles of unmyelinated nerve processes were observed, only partly ensheathed in a Schwann cell cover. At least 4 types of processes could be observed. 1) Boutons containing only small clear vesicles, probably cholinergic fibres; 2) boutons with small clear vesicles, and in addition large (greater than 200 nm) granules with a dense matrix (P-type-fibres); 3) boutons with small electron-dense vesicles, probably CA-fibres; and 4) processes with few vesicles but having the appearance of dendrites. No typical synaptic arrangements were observed, but the minimal distance between the E.C. and the nerve bundles was 150 to 250 nm, thus well within the functional limits of the "autonomic gap". Thus epithelial E.C. may be influenced by several types of nervous elements, including CA-fibres.     

皮肤Merkel细胞癌的免疫组化和超微结构观察

报道一例罕见的皮肤Ｍｅｒｋｅｌ细胞品。活体组织检查光镜做出正确诊断很困难,需要结合相关免疫组织化学染色结果和超微结构来分析判断。电镜观察癌细胞质内含有神经分泌颗粒,癌细胞有相互交织的树状突起,表面有少数微绒毛,细胞间有少数中间连接,偶见桥粒,其它细胞器多少不定。依其超微结构特征,可以做出正确诊断。     

双星系统对雷达无源定位的可行性分析

双星无源定位系统对地海面雷达辐射进行定位时,存在脉冲信号频差参数提取的模糊问题。提出了一种基于虚拟双星的双时差粗定位方法,可有效解决频差测量的模糊,再结合时差/频差联合定位方法,分析了双星系统对雷达辐射源无源定位的可行性,给出了一些有用的结论。     

辐射源识别系统中分类器设计及其应用

针对辐射源识别系统中分类器设计分析的不足,本文从分类器的两大基本任务拒识和鉴别出发,研究辐射源识别系统中的分类器设计。首先详细分析了拒识和鉴别先后执行顺序对系统性能的影响;然后阐述了拒识分类器和鉴别分类器设计所需要考虑的要点;最后根据当前分类器和工程应用的状况,分析适合于辐射源识别系统的分类器。