智能化集成媒体通讯技术

多媒体数字化技术集成了文本、图像、声音、动画、视频等方面，移动媒体技术对多媒体的图像、声音质量、传输带宽等都提出了要求，本书讨论了一些适用于第三代移动媒体终端的方法和技术，主要是面向第三代移动服务。     

Genetic variation in the New World: Ancient teeth,bone, and tissue as sources of DNA

Examination of ancient and contemporary Native American mtDNA variation via diagnostic restriction sites and the 9-pb Region V deletion suggests a single wave of migration into the New World. This is in contrast to data from Torroni et al.³⁴ which suggested two waves of migration into the New World (the NaDene and Amerind). All four founding lineage types are present in populations in North, Central, and South America suggesting that all four lineages came over together and spead throughout the New World. Ancient Native American DNA shows that all four lineages were present before European contact in North America, and at least two were present in South America. The presence of all four lineages in the NaDene and the Amerinds argues against separate migrations founding these two groups, although admixture between the groups is still a viable explanation for the presence of all four types in the NaDene.     

A model for interfacial activation in lipases from the structure of a fungal lipase-inhibitor complex

Lipases are hydrolytic enzymes which break down triacylglycerides into free fatty acids and glycerols. They have been classified as serine hydrolases owing to their inhibition by diethyl p-nitrophenyl phosphate. Lipase activity is greatly increased at the lipid-water interface, a phenomenon known as interfacial activation. X-ray analysis has revealed the atomic structures of two triacylglycerol lipases, unrelated in sequence: the human pancreatic lipase (hPL)4, and an enzyme isolated from the fungus Rhizomucor (formerly Mucor) miehei (RmL). In both enzymes the active centres contain structurally analogous Asp-His-Ser triads (characteristic of serine proteinases), which are buried completely beneath a short helical segment, or 'lid'. Here we present the crystal structure (at 3 A resolution) of a complex of R. miehei lipase with n-hexylphosphonate ethyl ester in which the enzyme's active site is exposed by the movement of the helical lid. This movement also increases the nonpolarity of the surface surrounding the catalytic site. We propose that the structure of the enzyme in this complex is equivalent to the activated state generated by the oil-water interface.     

Local cytoplasmic calcium gradients in living mitotic cells

Cytoplasmic free calcium has been proposed as a regulator of many microtubule-mediated processes, including mitosis. It has been difficult to test this hypothesis because methods for local measurement of free Ca2+ in the living cell have not been available. We have used the fluorescent calcium indicator dye Quin-2 (methoxyquinoline-1bis(o-aminophenoxy)ethane-N,N,N',N' -tetra acetic acid), which allows such observations to be made by digital processing of fluorescent images from the light microscope. Here we report the application of this technique to the study of local Ca2+ concentrations in mitotic endosperm cells of Haemanthus sp., and show that there is transient increase in free Ca2+ at the mitotic spindle poles during anaphase. This locally high Ca2+ may provide a mechanism for the regional control of microtubules and other cytoskeletal elements during anaphase.     

Calcium uptake by sarcoplasmic reticulum from nerve-intact and standard skeletal muscle grafts

A freely grafted rat soleus muscle exhibits a decrease in velocity and capacity of SR calcium uptake. This deficit is not prevented by maintaining neural connections (nerve-intact graft) during grafting. Thus the greater mechanical capability of nerve-intact grafts, relative to standard grafts, is not accompanied by any enhancement of the SR tubules.     

Human gamma-chain genes are rearranged in leukaemic T cells and map to the short arm of chromosome 7

Three gene families that rearrange during the somatic development of T cells have been identified in the murine genome. Two of these gene families (alpha and beta) encode subunits of the antigen-specific T-cell receptor and are also present in the human genome. The third gene family, designated here as the gamma-chain gene family, is rearranged in murine cytolytic T cells but not in most helper T cells. Here we present evidence that the human genome also contains gamma-chain genes that undergo somatic rearrangement in leukaemia-derived T cells. Murine gamma-chain genes appear to be encoded in gene segments that are analogous to the immunoglobulin gene variable, constant and joining segments. There are two closely related constant-region gene segments in the human genome. One of the constant-region genes is deleted in all three T-cell leukaemias that we have studied. The two constant-region gamma-chain genes reside on the short arm of chromosome 7 (7p15); this region is involved in chromosomal rearrangements identified in T cells from individuals with the immunodeficiency syndrome ataxia telangiectasia and observed only rarely in routine cytogenetic analyses of normal individuals. This region is also a secondary site of beta-chain gene hybridization.     

Androstenedione or corticosterone treatment during pregnancy alters estrous cycle of adult female offspring in mice

Female offspring from mice injected with androstenedione during late pregnancy showed lengthened vaginal cycles, persistent estrus and decreased incidence of pro-estrus and diestrus, whilst offspring from mice injected with corticosterone showed increased incidence of diestrus. These observations give qualified support to the hypothesis that stress during pregnancy alters the female offspring reproductive system through the action of adrenal steroids.     

Primary structure and transmembrane orientation of the murine anion exchange protein

The amino-acid sequence of murine band 3, deduced from the nucleotide sequence of a complementary DNA clone, confirms that this integral membrane glycoprotein is composed of two major structural domains which correlate with its dual functions as the anchor for the erythrocyte cytoskeleton and as a plasma membrane anion antiporter. This latter activity resides within a highly hydrophobic domain that crosses the plasma membrane at least 12 times.