GaAs-double-heterostructure lasers as optical amplifiers

The results of measurements on a GaAs-double-heterostructure (DHS) laser used as an optical amplifier are reported. The laser's amplifying guide is coupled to an optical fiber with a rectangular core. The laser amplifier can be operated either in the traveling-wave or the resonator mode. The gain, noise, and performance of the amplifier when driven hard into saturation were measured as a function of various parameters.     

New non-steroidal anti-rheumatic drugs: selective inhibitors of inducible cyclooxygenase

MODE OF ACTION OF NON-STEROIDAL ANTI-INFLAMMATORY DRUGS: Non-steroidal anti-inflammatory drugs (NSAID) exert their major therapeutic and adverse effects by inhibition of prostanoid synthesis. Also the interactions with antihypertensive drugs and lithium are caused by this mechanism of action. Cyclooxygenation is a key enzymatic step in the synthesis of prostanoids. 1990 2 isoforms of the enzyme cyclooxygenase have been identified: Prostanoids synthesized by the constitutive cyclooxygenase (COX-1) are involved in physiological homeostasis. In contrast, the inducible cyclooxygenase (COX-2) produces large amounts of prostanoids, mainly contributing to the pathophysiological process of inflammation. COX-2 SELECTIVE NSAID: The discovery of the cyclooxgenase-isoenzymes ushered in a new generation of NSAID: A drug with selectivity for COX-2 would inhibit proinflammatory prostanoid synthesis while sparing physiologic prostanoid synthesis. Thus, a selective COX-2 inhibitor should be anti-inflammatory with less or no gastrointestinal or other NSAID-typical adverse effects. The experiences with currently used NSAID, which show an increasing incidence of side effects as COX-1 inhibition increases, and studies with the COX-2 selective NSAID salsalate and meloxicam, which have less adverse effects than nonselective COX inhibitors in equivalent antiphlogistic dosage, prove the concept of selective COX-2 inhibition to avoid the NSAID typical side effects. Newly developed drugs with a very high selectivity for COX-2 are now tested in clinical trials. CONCLUSION: So far the results suggest, that selective and highly selective COX-2 inhibitors have significantly fewer gastrointestinal and renal adverse effects and do not inhibit platelet aggregation.     

Development of a new injury cost scale

The Automobile Technique Research Association at Frankfurt, the Institute for Forensic Medicine at Mainz, the Federal Highway Research Institute at Bergisch-Gladbach, the German Motor Vehicle Inspection Association at Stuttgart, and the German Worker's Compensation at St. Augustin have completed a joint research project dealing with injury costs due to automobile accidents. The data for this social cost analysis were based on costs for administrative expenses, medical treatment, rehabilitation measures, social security payment, and loss of income, which were all paid by Worker's Compensation for single, well-documented injuries to the working population in West Germany (15 to 65 years old). The data base used included 15,407 injured and 1,026 fatal road accident victims. Tables are presented which show the costs associated with various injury levels. The result is an injury cost scale (ICS) that might be a base for establishing priorities of safety measures. The ICS has to be seen as supplemental to the AIS.     

Organization and structure of branches in the rat pulmonary arterial bed

Pulmonary arteries were fixed by perfusion under constant pressure and filled with rubber. The hardened rubber cast delineated the arterial bed, permitting dissection of axial vessels and all branches. Each segment was prepared for scanning electron microscopy and transmission electron microscopy. Branches arising at acute angles from the axial artery and the first two generations of its branches, regardless of diameter, had the same concentric muscle layer structure as parent vessels. Endothelial cells of the parent vessel were oriented into the ostia of these branches. Branches that came off the axial vessel or its branches at right angles had spiral muscle bundles and led to nonmuscular precapillary vessels. Right angle branches also had similar wall structure regardless of diameter. Near the ostia of right angle branches, endothelial cells of the parent vessels did not show orientation of their long axis into the branch lumens. It was concluded that branch arteries arising at acute angles are conduit which carry blood to distant parts of the lung while right angle branches are a histologically different group which distribute the blood to local capillary beds.     

Look, Ma, My homepage is Mobile!

Much of the ongoing research in ubiquitous computing has concentrated on providing context information, e.g. location information, to the level of services and applications. Typically, mobile clients obtain location information from their environment which is used to provide “locally optimal” services. In contrast, it may be of interest to obtain information about the current context a mobile user or device is in, from a client somewhere on the Web, i.e. to use the mobile device as an information provider for Internet clients. As an instance of such services we propose the metaphor of a “location-aware” Web homepage of mobile users providing information about, e.g. the current location a mobile user is at. Requesting this homepage can be as easy as typing a URL containing the mobile user's phone number such ashttp://mhp.net/+49123456789 in an off-the-shelf browser. The homepage is dynamically constructed as Web users access it and it can be configured in various ways that are controlled by the mobile user. We present the architecture and implementation and discuss issues around this example of “inverse” ubiquitous computing.     

On the performance of concatenated convolutional code and Alamouti space-time code with noisy channel estimates and finite-depth interleaving

In this paper, performance of the Alamouti space- time code (STC) [1] and performance of the concatenation between the convolutional code and the Alamouti STC are derived. In order to describe realistic performance issues, we assume that the channel estimates are calculated from linear filters using noisy pilot symbols. We also assume non-quasi- static channels, spatially correlated transmit antennas and finite- depth interleaving. Two types of receivers are investigated for the Alamouti STC, namely, the linear-combining space-time decoder (LC-STD) and the maximum-likelihood space-time decoder (ML- STD). Two types of receivers are investigated for the concatenated system, namely, the LC-STD with the ML convolutional decoder and the joint Alamouti and convolutional ML decoder. The results have shown that the LC-STD is more sensitive to the Doppler spread than the ML-STD. However, since the ML- STD is very sensitive to the channel estimation error, the gains provided by the decoder in fast fading channels will be offset unless an optimized channel estimator is employed. Performance comparisons between the Alamouti systems and the SISO systems indicate that, when the system environment is not ideal, the SISO systems may outperform the Alamouti systems. Lastly, analytical results are compared with simulation results to illustrate the accuracy of the analysis.     

Constant Envelope OFDM

This paper describes a transformation technique aimed at solving the peak-to-average power ratio (PAPR) problem associated with OFDM (orthogonal frequency-division multiplexing). Constant envelope OFDM (CE-OFDM) transforms the OFDM signal, by way of phase modulation, to a signal designed for efficient power amplification. At the receiver, the inverse transformation?phase demodulation?is applied prior to the conventional OFDM demodulator. The performance of CE-OFDM is analyzed in additive white Gaussian noise (AWGN) and fading channels. CE-OFDM is shown to achieve good performance in dense multipath with the use of cyclic prefix transmission in conjunction with a frequencydomain equalizer (FDE). By way of computer simulation and hardware realization, CE-OFDM is shown to compare favorably to conventional OFDM.     

An ion-implanted diamond metal-insulator-semiconductor field-effecttransistor

A p-type conducting layer has been formed in a substrate of semi-insulating natural diamond (type IIa) by boron implantation. Silicon dioxide was deposited over this layer to make an insulated-gate field-effect transistor. Saturation and pinch-off were both observed at room temperature. The transconductance was 3.9 μS-mm^-1 and the output conductance was 60 nS-mm^-1. This is the first reported use of ion implantation to successfully fabricate a field-effect device in diamond