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.     

Electromagnetic surface waves supported by a half-space of a counterstreaming plasma

The characteristics of electromagnetic surface waves supported by a plane interface separating a semi-infinite region of free space from another semi-infinite region consisting of a plasma counterstreaming parallel to the interface are investigated for the case in which the wave is progressing parallel to the direction of the streams. The behaviour of the surface waves is quite different from the case in which the plasma is stationary. The surface waves exist for all frequencies. The phase velocity of the surface wave is equal to the electromagnetic wave velocity in free space for very low frequencies, decreases monotonically as the frequency is increased and asymptotically approaches the velocity of the stream for very high frequencies. The surface waves are always stable. In contrast to on unbounded counterstreaming plasma which gives rise to instability for the plane longitudinal wave progressing parallel to the streams, a half-space of counterstreaming plasma does not give rise to any instabilities for waves progressing parallel to the streams.     

端到端网络服务健康度的人工免疫评价模型

从网络多维性能出发,建立了端到端网络服务健康度评价模型(ENHMM).该模型支持动态定制服务评价因子,同时给出基于评价因子的网络性能数据的主动测量方法.在评价算法上,利用了一种新的抗体促进与抑制机制的AiNet网络免疫算法.开发了原型系统对现实网络进行评价,得到了网络服务健康度等级.通过对评价结果的线性回归分析,发现该等级能够准确地反映用户感知的网络质量.     

浅谈数字机顶盒的利弊和发展

阐述了数字机顶盒在城市家庭收视使用过程中的优缺点,机顶盒使用的技术参数特性,针对机顶盒使用缺陷的具体改进方案,以及数字机顶盒技术在未来的发展趋势。     

数据挖掘算法的评价标准与方法

文章阐述了数据挖掘的定义及所涉及到的基础理论知识，并根据数据挖掘本身的特点，探讨了选择合适挖掘算法的重要性，同时分析提出了数据挖掘算法的评价标准与评估方法。并结合实例作了分析。