空间网络数据库中最近邻查询的设计与实现

随着无线通讯技术、位置定位技术以及数据库技术的发展,使得能为移动用户提供相关的位置服务.K近邻查询是位置服务的一个重要功能.本文主要研究了空间网络数据库中的K近邻查询.以提出的集成道路网络距离与欧式距离的道路网络框架为基础,提出了一种新的KNN查询算法,通过网络扩展方法计算最近邻(NN),避免了不必要的磁盘I0s,减少了昂贵的最短路径计算,从而有效地提高了算法效率.实验结果说明,在目标点分布比较密集的情况下,算法显著优于其它的算法.     

Single-chamber atrial pacing is better than single chamber ventricular pacing in patients with sick sinus syndrome. Results of long-term follow up in a prospective randomized study

In a study of 225 patients with sick sinus syndrome randomized to single chamber atrial pacing (n = 110) or ventricular pacing (n = 115), atrial pacing was associated with less atrial fibrillation and thromboembolism after 3.3 years follow-up. To determine whether this beneficial effect of atrial pacing is maintained at long-term, follow-up was extended. Follow-up visits were at 3 months, 12 months, and then once every year, and included physical examination, ECG, and pacemaker check-up. After 5.5 years follow-up, all-cause mortality, cardiovascular deaths, atrial fibrillation, thromboembolism, and heart failure were significantly less in the atrial group. AV block occurred in four patients in the atrial group. The beneficial effect of atrial pacing observed previously is enhanced substantially after extended follow-up. Patients with sick sinus syndrome should be treated with an atrial pacing system.     

Morphine-induced conformational changes in human monocytes, granulocytes, and endothelial cells and in invertebrate immunocytes and microglia are mediated by nitric oxide

We evaluated the contribution of nitric oxide (NO) to morphine-induced rounding of spontaneously activated (mobile) ameboid human monocytes, granulocytes, or arterial endothelial cells and invertebrate immunocytes and microglia. Morphine induced significant rounding and inactivation of ameboid cells within 20 min except for arterial endothelial cells, which became rounded 24 h after morphine exposure. The effects of morphine on cell conformation were blocked in the presence of N-nitro-L-arginine, a nitric oxide synthase inhibitor. Treatment of cells with the NO donor, sodium nitroprusside, induced cell rounding similar to that observed following morphine exposure, suggesting that NO release may mediate morphine-induced changes in cell conformation. The contribution of NO release to morphine-induced cell rounding was determined by direct evaluation of NO concentration in real-time using a NO-specific amperometric probe. Significant increases in NO concentration were observed 2 min after morphine stimulation, whereas morphine-induced NO release was markedly impaired by pretreatment with N-nitro-L-arginine or the opiate alkaloid antagonist, naloxone. In contrast, opioid peptides failed to induce NO release, consistent with our previous observations that demonstrated the failure of opioid peptides to promote cell rounding. Taken together, these data suggest that morphine-induced NO release may be mediated by activation of the opiate alkaloid-selective, opioid peptide-insensitive micro3 receptor, and that functional coupling of morphine to NO production has been conserved during evolution and may modulate cellular activation.     

A novel membrane protein is a mouse mammary tumor virus receptor

Mouse mammary tumor virus (MMTV) infects a number of different cell types, including mammary gland and lymphoid cells, in vivo. To identify the cellular receptor for this virus, a mouse cDNA expression library was transfected into Cos-7 monkey kidney cells, and those transfected cells able to bind virus were selected by using antibody against the virus's cell surface envelope protein, gp52. One clone isolated from a library prepared from newborn thymus RNA, called MTVR, was able to confer virus binding to both monkey and human cells; this binding was blocked by anti-MTVR antibody. Moreover, transfection of MTVR into CV1 cells rendered them susceptible to infection by a murine leukemia virus-based retrovirus vector pseudotyped with the MMTV envelope protein. An epitope-tagged MTVR cofractionated with cellular membranes. Coimmunoprecipitation of the MMTV envelope protein and a MTVR-rabbit Fc fusion protein showed that these two proteins bound to each other. The MTVR sequence clone is unique, shows no homology to known membrane proteins, and is transcribed in many tissues.     

Measurement of the ferric diffusion coefficient in agarose and gelatine gels by utilization of the evolution of a radiation induced edge as reflected in relaxation rate images

A method has been developed to determine the diffusion coefficients of ferric ions in ferrous sulphate doped gels. A radiation induced edge was created in the gel, and two spin-echo sequences were used to acquire a pair of images of the gel at different points of time. For each of these image pairs, a longitudinal relaxation rate image was derived. From profiles through these images, the standard deviations of the Gaussian functions that characterize diffusion were determined. These data provided the basis for the determination of the ferric diffusion coefficients by two different methods. Simulations indicate that the use of single spin-echo images in this procedure may in some cases lead to a significant underestimation of the diffusion coefficient. The technique was applied to different agarose and gelatine gels that were prepared, irradiated and imaged simultaneously. The results indicate that the diffusion coefficient is lower in a gelatine gel than in an agarose gel. Addition of xylenol orange to a gelatine gel lowers the diffusion coefficient from 1.45 to 0.81 mm2 h-1, at the cost of significantly lower Rl sensitivity. The addition of benzoic acid to the latter gel did not increase the Rl sensitivity.     

网络商店的付费机制与信息安全分析

随着因特网的发展与普及,产生了更多的商机,造就出各种不同型态的网络商店,同时也衍生出不同的付费方式,例如电子钱包、网上银行、在线ATM等等。面对众多付费方式的选择时,不同市场必须选搭各种付费制度,当市场导入新制付费制度后,除了增加新制付费制度给予消费者选择外,并能让原来的市场消费者对于新付费机制产生消费学习性,最终消费者会依个人意志选择最利己的付费机制。通过调查分析,网络商店提供付费机制使用的便利性、易用性、实时性、精确性、安全性对消费者态度有显著正向的影响。     

Structure and mechanical properties of a eutectic high-temperature Nb-Si alloy grown by directional solidification

The structure and the short-term high-temperature strength of Ni-18.7 at % Si (Nb-Nb₃Si eutectic) alloys fabricated by vacuum electron-beam zone melting and induction melting in an argon atmosphere are studied. The structure of the samples prepared by vacuum electron-beam zone melting is characterized by the presence of primary Nb₅Si₃ intermetallic precipitates and the absence of its secondary precipitates. The structure of the samples prepared by induction melting in an argon atmosphere has two characteristic zones, namely, eutectic and eutectoid ones.     

陶瓷窑炉的燃料与节能技术

本文对国内外陶瓷工业窑炉的燃料,燃烧现状及其节能技术作了简介,并对窑炉的节能效果进行评价。     

Influence of rat placental lactogen-I on the development of whole rat embryos in culture

Rat placental lactogen-I (rPL-I), the first prolactin-like hormone expressed in the placenta during pregnancy in the rat, is known to influence maternal functions. In the present study, we have investigated the effects of rPL-I on the growth and development of cultured whole rat embryos. Rat embryos, with or without ectoplacental cone (EPC) attached, were explanted at day 9 of gestation. After 48 h of culture, the embryos, enclosed by the yolk sacs, were assessed by the presence of visible heart contractions ('heart beats'), crown-rump length (CRL) and yolk sac diameter (YSD). When intact embryos with EPC were cultured, the concentrations of rPL-I and rPL-II (products of EPC) in the medium were 850+/-841 and 92+/-181 ng/ml respectively (means+/-s.e.m.). In embryo cultures with the EPC removed, rPL-I levels decreased to相似文献