GPRS的服务质量及其测量

(GN Nettest)　　一、GPRS简介　　通用分组无线服务 ( GPRS)系统扩展了当前世界上最流行的第二代移动系统一基于语音的 GSM的应用 ,使其能够收发基于分组的数据 ;同时保留了无线接口的基本内容 ,如时分多路复用和频率分配方案 ,以使 GPRS和 GSM能够共存于同一网络上。　　 1 .特性　　传统的 GSM拨号数据接入为用户提供了最大960 0波特的速率。GPRS能够结合多个 GSM时隙 ,在上行链路和下行链路上 ,最多可以使用八个 GSM时隙 ,提供最高 1 70 kbit/sec的带宽。此外 ,GPRS采用全新的 IP网络“一直在线”接入模式 :移动用户开…     

Preservation of refrigerated meats with controlled atmospheres: Treatment and post-treatment effects of carbon dioxide on pork and beef

Whole pork loins were divided into roasts and subjected to air control and carbon dioxide enriched atmospheres at 1°C for up to 21 days. Quintuplicate samples of both control and carbon dioxide treated loins were transferred to air storage at 0,4,7, 14 and 21 days and further held for 0, 3(4), 7 and 10 days at 4°C. Microbiological counts were taken at all time permutations. The results indicated a strong inhibiting effect of the carbon dioxide atmosphere on microbial growth as well as a marked residual effect during post-treatment storage in air. Satisfactory colour and odour were maintained on the loins for extended storage times, with visual and olfactory deterioration preceding microbial spoilage. Beef round wedges were treated in a similar manner. Although bacterial spoilage inhibition was comparable, colour degeneration was rapid and severe, making the method unsuitable for treatment of finished beef cuts.     

Apoptosis in batch cultures of Chinese hamster ovary cells

One of the main problems in the culture of Chinese Hamster Ovary (CHO) cells continues to be the inability to maintain the viability of the cultures over an extended period of time. The rapid decline in viability at the end of the culture is exacerbated by the absence of serum. In trying to reduce the extent of death in these cultures, we first tried to determine the mode of death. We found that more than 80% of the cells in a standard serum-free batch culture of CHO cells in suspension died via apoptosis--as evidenced by condensed chromatin and the appearance of a characteristic DNA ladder. Furthermore, when protein synthesis was inhibited using cycloheximide, the cells underwent rapid apoptosis indicating that death proteins were present in greater abundance than survival proteins in our CHO cells. Cell lysate from CHO cells showed evidence of cysteine protease (caspase) activity. Caspases of the Interleukin-1-beta-Converting Enzyme (ICE) family, e.g., CPP32, Mch-1, etc., have been implicated in the apoptotic process. Surprisingly, a caspase peptide inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoro-methyl-ketone (z-VAD.fmk), was unable to substantially extend the life of a serum-free batch culture of CHO cells. In addition, z-VAD.fmk was only marginally able to extend viability in response to withdrawal of growth and survival factors, insulin and transferrin. In both these instances, z-VAD.fmk was able to prevent cleavage of caspase substrates, but not protect cells from death. However, we found that bcl-2 expression was able to significantly extend viabilities in CHO batch culture. Bcl-2 expression also substantially extended the viability of cultures in response to insulin and transferrin withdrawal. These results provide interesting insights into the pathways of death in a CHO cell.     

用于蛋白快速分离的1-mm内径的高效聚合物整体材料

多年来,整体技术已经成功地从概念阶段发展到表征良好且可重复的商用阶段。不同的整体柱化学材料,包括阴离子交换剂、阳离子交换剂和在ProSwift线性整体柱的反相功能基团,均可用于多种蛋白质的分离。与更大尺寸的色谱柱相比,1-mm内径的色谱柱在灵敏度提高和使用方便二者间达到了很好的协调。由于背压较小,这些整体柱可以在高动力学流速下运行,从而可以在标准的分析型色谱仪器上使用,而不需要微柱或者毛细管柱高效液相色谱系统。     

Clinicopathologic features of dogs with hepatic microvascular dysplasia with and without portosystemic shunts: 42 cases (1991-1996)

A 14 year old girl with double outlet right ventricle, left isomerism, and complicated atrial anatomy had undergone corrective surgery with intra-atrial rerouting at 5 years of age. Cardiac catheterisation eight years after the surgery showed that she had two systemic venous baffle stenoses: between the hepatic vein and caval vein, and the caval vein and right atrium. Two Palmaz stents were successfully implanted percutaneously through a long sheath and a balloon catheter. The stenoses were relieved immediately and her symptoms quickly disappeared.     

Age- and sex-related differences in nuclear lipid content and nucleoside triphosphatase activity in the JCR:LA-cp corpulent rat

The putative role of the nuclear nucleoside triphosphatase (NTPase) is to provide energy to the nuclear pore complex for poly A(+) mRNA export. Previous work has demonstrated that liver nuclear NTPase activity is greater in 6 month old corpulent (cp/cp) female JCR:LA rats, a hyperlipidemic rat model, compared to lean (+/?) animals. This increase appeared to be related to increases in nuclear membrane cholesterol content. The current study extended these initial data to compare NTPase activity as a function of age and sex in isolated JCR:LA-cp rat liver nuclei, to further test the hypothesis that nuclear membrane cholesterol may modulate NTPase activity. NTPase activity was increased in cp/cp female animals compared to +/? females at all ages studied, with Vmax values increased by 60-176%. Membrane integrity of cp/cp female nuclei was reduced compared to +/? female nuclei. Nuclear membrane cholesterol levels increased linearly with age by 50, 150 and 250% in 3, 6 and 9 month old cp/cp females over leans. In contrast, nuclei from cp/cp males exhibited only minor, isolated changes in NTPase activity. Furthermore, there were no significant changes in nuclear cholesterol content or membrane integrity in the less hyperlipidemic male animals at any age. These data suggest that altered lipid metabolism may lead to changes in nuclear membrane structure, which in turn may alter NTPase activity and functioning of the nuclear pore complex.     

Characterization of the copper chaperone Cox17 of Saccharomyces cerevisiae

Assembly of functional cytochrome oxidase in yeast requires Cox17, which has been postulated to deliver copper ions to the mitochondrion for insertion into the enzyme. This role for Cox17 is supported by the observation that it binds copper as a binuclear cuprous-thiolate cluster. X-ray absorption spectroscopy, together with UV-visible absorption and emission spectroscopy, indicates the presence of bound cuprous ions, trigonally coordinated by thiolate ligands. Analysis of the EXAFS shows three Cu-S bonds at 2.26 A, plus a short Cu-Cu distance of 2.7 A, indicating a binuclear cluster in Cox17. The cuprous-thiolate cluster in Cox17 is substantially more labile than structurally related clusters in metallothioneins.     

Protein kinase C in platelets of depressed patients

Though described in 1769, the etiology of Zenker's diverticulum remains unclear. Various primary esophageal motor disorders have been proposed, but no consistent manometric pattern or anatomic etiology has been uniformly recognized. An association with clinical neurologic disease at our institution prompted a review of 12 cases of Zenker's diverticulum in patients over 60 years of age, treated in the last 8 years. Nine patients (75%) underwent cricopharyngeus myotomy and diverticulectomy, with uniformly good results. Ten patients (83%) had an associated neurologic disorder, substantiated by cranial CT or MRI, in most cases. A wide range of neurologic problems were identified, but a strong trend toward brainstem or basilar lesions was present. As expected, the etiology of the neurologic abnormality in most patients in this group was cerebrovascular disease, but two patients had peripheral neuropathies. We suggest that the etiology of Zenker's diverticulum in the elderly may be neurologic in origin. Esophageal motor disorders, including incomplete upper esophageal sphincter opening and increased hypopharyngeal pressures, which may result in Zenker's diverticulum, may be a manifestation of central or peripheral neurologic disease in the elderly.     

Influence of proximal side mutations on the molecular and electronic structure of cyanomet myoglobin: an 1H NMR study

A series of proximal side mutants of sperm whale metmyoglobin (metMb) that involves residues which provide hydrogen bonds to the axial His and heme have been prepared, and the CO binding and solution molecular and electronic structure has been investigated by 1H NMR. These include Ser92(F7), whose O gamma serves as a hydrogen-bond acceptor to the axial His ring NdeltaH and whose O gamma H serves as hydrogen-bond donor to the 7-propionate carboxylate, and His97(FG3) whose ring provides the other hydrogen-bond donor to the 7-propionate carboxylate. 2D NMR data on the S92A-metMbCN, S92P-metMbCN and H97F-metMbCN show that the distal structure is completely conserved and that proximal side structural changes are highly localized. For the S92A-metMbCN, altered dipolar contacts to the F-helix backbone show that the axial His imidazole has rotated clockwise by approximately 10 degrees relative to a stationary heme, while in H97F-metMbCN, the altered heme-E helix backbone contacts reveal that the heme has rotated counterclockwise by approximately 3 degrees relative to a conserved axial His. The pattern of axial His rotation was qualitatively predicted by energy minimization calculations. The assignments and conserved structural elements allow the determination of a set of magnetic axes whose major magnetic axis is unchanged with respect to WT and confirms that local distal, and not proximal, interactions control the orientation of the major magnetic axis and, by inference, the degree and direction of tilt of the Fe-CN from the heme normal. The rhombic magnetic axes in S92A-metMbCN are rotated approximately 10 degrees in the opposite direction from the established approximately 10 degrees rotation for the axial His ring as expected. It is shown, moreover, that the pairwise alpha-, gamma-meso vs beta-, delta-meso-H hyperfine shift differences are well predicted by the change in the location of the rhombic magnetic axes. Carbon monoxide ligation rates experience minor but systematic perturbation for the S92A substitutions which confirms an influence (albeit very small) for axial His orientation on ligand affinity.