摘要： As suggested by previous results, we show that the conventional analysis of the results of 13C NMR line shifts used for metals do not apply in GICs: an orbital contribution to the shift must be taken into account To evaluate quantitatively this contribution, we apply a recently developed formalism for orbital shifts in crystals to the case of first and second stage GICs (for B // c), in the independent subsystem approximation. It is shown that the sign of the orbital contribution is different for donor and acceptor compounds but its magnitude is almost independent of the charge transfer amplitude. For second stages, the calculation predicts a splitting of the lines though dipolar contribution does not These results explain the experimental data. © 1994, Taylor & Francis Group, LLC. All rights reserved.

关键词： Release   调制解调器   笔记本计算机   PCMCIA卡   存储器卡   扩充卡   向后兼容性   控制器   移动计算   Exchange  

摘要： 笔记本计算机的争夺焦点已移到扩充卡.这些如同信用卡大小的PCMCIA卡可以插入笔记本计算机的扩充槽里,以提高机器的性能.PCMCIA(Personal Computer Memory Card InternationalAssociation)协会目前有300多家厂家,它们正在共同制定PCMCIA技术标准,以保证用户能够把这些卡随便插入任何机器里.1990年底,该协会推出了Release1.0标准,主要内容是移动计算用的存储器卡要求.1991年9月,该协会公布了Re- lease2.0,确定了调制解调器、局域网、蜂窝无线电频率和其他输入/输出外部设备的标准.Release2.0具有向后兼容性,因此,符合Release2.0标准的扩充卡可以正常使用于符合Release1.0标准的插槽.Release2.

关键词： FEM   岩层移动   岩石力学  

摘要： 针对有限单元法（ＦＥＭ）在岩层移动预测和计算中遇到的实际问题，包括怎样从地质模型建立一个合理的计算模型、本构关系及参数的选择、不连续性、冒落过程、地应力场和地下水渗流的模拟等，指出了今后应着重解决的问题和进一步研究的方向。

摘要： From the observation of solid-state C-13 NMR chemical shifts of L-alanine residues which are contained in some peptides, and the C-13 chemical shift calculations employing the coupled-Hartree Fock method with gauge-invariant-atomic-orbital, it was found that the C-13 chemical shift of the C(beta)-carbon in the L-alanine residue is related to the main-chain dihedral angles, phi, psi, but that of the C(alpha)-carbon is affected not only by dihedral angles but also by hydrogen-bonding structure. These results were successfully applied to the structural study of proteins in solution, ribonuclease H from Escherichia coli and basic pancreatic trypsin inhibitor.

关键词： 交互式电视   计算机   交互电视   个人机   移动计算   CATV   电话机   电话设备   信息高速公路   高速信息传输网   节目  

摘要： 近一年多来,全世界都在刮信息超高速公路旋风,至今未见减弱。这是因为它将促使计算机同通信的融合,把我们带入信息化社会。 信息超高速公路的内容和意义 信息超高速公路的正式名称是“全美信息基础设施”。其目标是要在全美国建立高速光纤通信网络,其末端将伸入美国所有的基层单

关键词： 全功能   移动计算   超小型  

摘要： 具有移动计算能力的全功能超小型工作站Ｓｕｎ公司的超小型工作站ＳＰＡＲＣｓｔａｔｉｏｎＶｏｙａｇｅｒ的能力是ＳＰＡＲＣｓｃａｃｉｏｎＬＸ的两倍，而面积仅是它的３５％，能耗也大大降低。具有可上下活动的无闪烁有源矩障ＬＣＤ显示器，工作起来非常安静。这种新系...

关键词： DISTANCE GEOMETRY   H-1 NMR CHEMICAL SHIFT CALCULATION   RING CURRENT EFFECT   BASIC PANCREATIC TRYPSIN INHIBITOR  

摘要： A new method for protein structure determination in solution has been proposed by a combination of distance geometry calculation (DADAS90) and H-1 NMR chemical shift calculation for proteins. When the ring current shielding effect from the aromatic ring in protein on an alpha-CH proton is larger than 0.3 ppm, the distance constraints from the aromatic rings to the alpha-CH protons are incorporated into the process of DADAS calculation using the co-ordinates from the X-ray diffraction analysis. A better structure for BPTI (Basic Pancreatic Trypsin Inhibitor) with a good correlation between calculated and observed alpha-CH chemical shifts, and with a small value of the target function, is obtained by taking into accountsuch a ring-current shielding effect.

关键词： Coda file system   distributed systems   mobile computing systems   personal computing   portable computers   social aspects of automation   transparency of environment  

摘要： The problems, limitations, and potential advantages of mobile computing systems are discussed. It is suggested that the constraints violate many of the assumptions upon which today's distributed systems are based. A key requirement of mobile computing systems will be the ability to access critical data regardless of location, which implies interdependence between the elements of a mobile computing system. The Coda file system, which is an effort to provide transparency of environment to mobile computing systems, is reviewed

关键词： LOCATION INFORMATION   MOBILE COMPUTING   PRIVACY   SCALABILITY  

摘要： Location information is important to mobile computer users for a variety of reasons. While keeping track of and making available location information about 'public' things, such as printers and restaurants, is both acceptable and desirable, the same does not necessarily apply to people. In a system that covers only one friendly administrative domain, security may be accomplished by something as simple as a centralized location database with access controls. Unfortunately this simple approach will not scale to a system that must span multiple administrative domains. Even when individual communications packets do not allow determination of someone's location, an attacker who can observe all communications in the system may be able to employ traffic analysis techniques to deduce it anyway. Traffic analysis can be performed on communications both when they cross traditional 'wired' networks as well as when they are being conveyed by multi-celled wireless media. Exactly how much information an attacker can derive from traffic analysis depends on how much traffic is analyzed.