General properties of antennas

In antenna design there are some fundamental relationships based on reciprocity. The equivalence of antenna pattern in transmission and reception is well known. Less well known is the time-derivative relationship going from reception to transmission. These relationships are derived here and expressed in various useful forms. Electric and magnetic dipoles are given special consideration, and the combined form constructed as a terminated TEM transmission line (the BTW antenna) is discussed for its transmission and reception properties     

Methods for packet combining in HARQ systems over bursty channels

The performance of ARQ systems can be improved by combining current and prior transmissions at the receiver. Two techniques for combining outputs in a packet-based communication system are presented. In both techniques the fundamental unit of retransmission is a packet, and the fundamental unit of combining is a codeword. The techniques are analyzed for a bursty channel and a system that employs Reed–Solomon coding and bounded-distance errors-and-erasures decoding. Performance results show that the packet-combining schemes provide significant gains in throughput and reductions in error probability when compared with a system that does not employ combining. This revised version was published online in June 2006 with corrections to the Cover Date.     

Breath and blood ethanol following use of a cough-cold preparation

All leaders in health care today are charged with the responsibility of transforming present practices into new and different ones that are needed for the future. The structural side of transforming is ultimately easier than the human side. However, the most frequent failures come from not concentrating sufficiently on the behavioral side of the change. Structural and psychological change must occur simultaneously and embrace each other for best results.     

Comparison between the effects of positive noncatastrophic HBM ESDstress in n-channel and p-channel power MOSFETs

The effect of noncatastrophic positive human body model (HBM) electrostatic discharge (ESD) stress on n-channel power MOSFETs is radically different from that on p-channel MOSFETs. In n-channel transistors, the stress causes negative shifts of the current-voltage characteristics indicative of positive charge trapping in the gate oxide. In p-channel transistors, the stress increases the drain-to-source leakage current, probably due to localized avalanche electron injection from the p-doped drain     

自动实时X射线检测技术在半导体制程控制中的应用

对X光检测的不同技术在半导体制程上的应用作了详细的介绍;着重讨论了全旋倾斜(off-axis)X射线技术的特点和优势。     

Bayesian generation of dependent erasures for frequency-hopcommunications and fading channels

The use of block coding and errors-and-erasures decoding can enhance performance in frequency-hop (FH) communication systems, provided that a good scheme is employed to determine which symbols to erase. The problem of making erasure decisions from collections of receiver outputs is investigated in this paper. Methods to determine which received symbols to erase are derived from Bayesian decision theory. Decision rules are developed for a system with M-ary orthogonal signaling, noncoherent demodulation, and frequency-selective fading. One result is a class of Bayesian schemes in which erasure decisions are made independently from symbol to symbol. Within this class is a rule that uses signal amplitude estimates for improved performance. A second result is a Bayesian technique in which erasure decisions are mutually dependent and are made collectively for each codeword. These techniques are analyzed and compared with the performance of receivers that use erasure techniques that require multiple applications of bounded distance decoding. The performance of the Bayesian techniques for dependent erasures are also compared with the performance of receivers that do not permit erasures. It is found that each of the Bayesian techniques offers substantial performance gains over errors-only decoding, and the dependent erasure scheme provides the best performance among the techniques of lower complexity     

Real-time NMR investigations of triple-helix folding and collagen folding diseases

Folding of the collagen triple helix provides an opportunity to look at multichain molecular assembly. This triple helix also offers unique advantages for the study of folding because the process is very slow compared to globular proteins, and the kinetics of folding can be obtained in real time by NMR. Studies on triple-helical peptides illustrate the ability to observe kinetic folding intermediates directly and the ability to propose detailed mechanisms of folding through the use of real-time NMR methods. Defective collagen folding has been implicated in various connective tissue diseases and the capacity of NMR to look at the folding of specific sites provides a tool for obtaining information about altered folding mechanisms. Comparison of folding in peptides that model normal and diseased collagens could shed light on the molecular perturbation and the etiology of disease.     

Energy storage devices for future hybrid electric vehicles

Powertrain hybridization as well as electrical energy management are imposing new requirements on electrical storage systems in vehicles. This paper characterizes the associated vehicle attributes and, in particular, the various levels of hybrids. New requirements for the electrical storage system are derived, including: shallow-cycle life, high dynamic charge acceptance particularly for regenerative braking and robust service life in sustained partial-state-of-charge usage. Lead/acid, either with liquid or absorptive glass-fibre mat electrolyte, is expected to remain the predominant battery technology for 14 V systems, including micro-hybrids, and with a cost-effective battery monitoring system for demanding applications. Advanced AGM batteries may be considered for mild or even medium hybrids once they have proven robustness under real-world conditions, particularly with respect to cycle life at partial-states-of-charge and dynamic charge acceptance. For the foreseeable future, NiMH and Li-ion are the dominating current and potential battery technologies for higher-functionality HEVs. Li-ion, currently at development and demonstration stages, offers attractive opportunities for improvements in performance and cost. Supercapacitors may be considered for pulse power applications. Aside from cell technologies, attention to the issue of system integration of the battery into the powertrain and vehicle is growing. Opportunities and challenges for potential “battery pack” system suppliers are discussed.     

Pharmacokinetics of newer cephalosporins after subconjunctival and intravitreal injection in rabbits

Pharmacologic considerations suggest that third-generation cephalosporins might penetrate the vitreous humor better after periocular injection and might be eliminated less readily after intravitreous injection than older agents. We studied the sodium salts of ceftizoxime, ceftriaxone, and ceftazidime, and of an investigational cephalosporin, cefepime, in rabbits. After a single subconjunctival injection in animals with normal eyes, vitreous levels ranged from 3 to 13 mg/L. After five subconjunctival injections in rabbits with infected eyes, vitreous concentrations ranged from 12 to 34 mg/L. These concentrations are not appreciably greater than those found with older beta-lactams. The vitreous half-life of the four drugs after intravitreous injection varied from 5.7 to 20 hours in rabbits with uninflamed eyes and from 9.4 to 21.5 hours in rabbits with infected eyes. Except for ceftizoxime, the half-lives were substantially longer than those for older beta-lactams and suggest predominantly anterior route elimination. Vitreous penetration of these new agents after subconjunctival injection does not appear to be sufficient to overcome the need for intravitreous injections in the treatment of endophthalmitis. However, the longer vitreous half-lives of some of the newer agents may be useful if the drugs are to be given intravitreally.