Terahertz Quantum Well Photodetectors

The terahertz (THz) part of the electromagnetic spectrum promises a wide range of new and novel, some may be disruptive, applications. However, the development of technologies in the THz spectrum or the very far infrared region has been slow mainly because of the lack of convenient detectors and lasers. There are a few competing new approaches for better detectors, and here, we concentrate on one based on quantum wells. We report on the design and simulated performance of quantum-well photodetectors for the terahertz (1-10 THz). Quantum well, barrier, and doping parameters are optimized in terms of operating temperature, absorption, and detectivity. We also report on our experimental demonstration of GaAs/AlGaAs photodetectors with background limited infrared performance. These devices are suited for a variety of applications, especially in conjunction with the newly developed THz quantum cascade lasers. Examples include THz sensing and imaging and free space communication.     

The Effect of Concentration on Lubricating Properties of Aqueous Solutions of Sodium Lauryl Sulfate and Ethoxylated Sodium Lauryl Sulfate

The objective of this study was to formulate new ecological lubricating substances, primarily water-based, and to verify their tribological and physicochemical properties. Initially, simple binary solutions were investigated. Then, various additives were added depending on application targets. Two alkyl sulfates were selected as additives modifying lubricating properties of water: sodium lauryl sulfate (SLS) and ethoxylated sodium lauryl sulfate (ESLS). They have an identical hydrophobic part in the form of an alkyl chain consisting of 12 carbon atoms. The SO₄ ²⁻ anion forms the hydrophilic part in SLS molecules, whereas an ESLS molecule also contains two mers of ethylene oxide which cause an increase in its hydrophilicity relative to SLS. Both SLS and ESLS exhibit high surface activity measured by their surface tension. Micelles form in aqueous solutions of alkyl sulfates at low concentrations of the order of 1%, whereas the presence of liquid crystalline phases can be found at the concentrations of 40 and 70%. High surface activity and formation of structures in the solutions (micelles, mesophases) formed the basis for application of the compounds as additives modifying lubricating properties. Tribological properties of aqueous solutions of alkyl sulfates were verified with a four-ball machine (T02 tester) at a constant load of 2 kN. The values of friction coefficient (μ) were a measure of motion resistance, while the wear scar diameter (d) was a measure of wear. Alkyl sulfates significantly improve tribological properties of water. The coefficient of friction decreased sixfold and the wear scar diameter decreased by as much as twofold relative to the base. Non-monotonic changes in the tribological properties measured were observed as a function of concentration of additives. An attempt was made to relate those atypical changes with the presence of micelles and mesophases in both the surface phase and the bulk phase. In the model proposed the whole concentration range was divided into four areas in which tribological properties correspond well with physicochemical properties, particularly with the structures formed in solutions and at the interface.     

Clinico-electroencephalographic observations in epileptic patients during long-term treatment with benzonal

Benzonal was given to 52 epileptics. In 50 cases the duration of treatment ranged from 3 months to 7 years (mean 18 months) in doses of 100-500 mg daily, in 2 cases it had to be withdrawn after a short-term treatment because of intolerance. In all cases the drug was given together with other anticonvulsants: hydantoin, derivatives, mysodin, Tegretol, pheneturid or Ospolot in place of previously administered phenobarbital. It was found that benzonal reduced significantly the frequency of partial simple seizures (in 6 out of 20 cases) and grand mal seizures (in 24 out of 34 cases), while its action on the partial complex seizures was much weaker (improvement in only 7 out of 20 cases). The drug was usually well tolerated, side effects of greater intensity developed in 2 cases only, transient somnolence was observed in another 6 cases. In EEG records a slight favourable effect was exerted on pathological background activity with absent effect in focal changes and increase of seizure activity. The authors believe that in view of its favourable clinical action and good tolerance the drug may be widely used in properly selected cases of epilepsy.     

From urban terrain models to visible cities

We face the possibility and, in some cases, the results of acquiring accurate digital representations of our cities. The first challenge is to take data from multiple sources, which are often accurate but incomplete, and weave them together into comprehensive models. Because of the size and extent of the data that we can now obtain, this modeling task is daunting and must be accomplished in a semiautomated manner. Once we have comprehensive models, and especially if we can build them rapidly and extend them at will, the next question is what to do with them. Thus, the second challenge is making the models visible. In particular, they must be made interactively visible so users can explore, inspect, and analyze them. We discuss the nature of the acquired data and how we're beginning to meet these challenges and produce visually navigable models. We've developed 3D City, a semiautomated system that supports human intervention at key points to meet the challenge of constructing complete and extended urban models from several data sources. We've already built virtual environments (VEs) for urban planning and emergency response using 3D City.     

The effects of applied stress on the martensitic transformation in TiNi

The deformation behavior of TiNi at 20°C has been investigated as a function of composition and of the prior heat treatment. Wide mechanical property variation and significant differences between the effects of tensile and of compressive loading were observed. Under some conditions anelastic behavior, characterized by a broad hysteresis loop, was reproducibly obtained. The effects of heating the deformed materials aboveA _f on the subsequent stress-strain behavior indicate the anomalies observed to be directly related to the martensitic transformation. The effects of stress application on the martensitic transformation are discussed. It is shown that, under some conditions, the stress-assisted transformation structures may be unstable on the removal of the stress. At test temperatures outside theM _f toA _f range, this can result in anelastic behavior. More complex behavior expected at temperaturesM _f < T < A_f, is discussed in some detail. It is shown that both the anelastic behavior and the “shape memory” can be accounted for by the effects of applied stress. It is also shown that the mechanical properties in this temperature range can vary markedly with the prior heat treatment, even at temperatures not normally considered of significance. Though based on observations made on TiNi, the phenomena discussed are inherent in materials undergoing a martensitic transformation over a narrow range of temperatures.     

Distribution of Methane Concentration in the Ventilating Area of the Longwall

Journal of Mining Science - The paper presents an analysis of experimental data that include space–time distributions of methane concentration at the shearer-exploited longwall. The main...     

Cu/LaCrO3 joining by local melt infiltration through laser cladding

Direct bonding of copper and porous LaCrO₃ without an extra filler interlayer was successfully completed using local and fast Cu‐infiltration through laser cladding. This significantly reduced the susceptibility of the ceramic to cracking. A high‐speed camera investigation into the wetting and infiltration behavior of a Cu‐melt into LaCrO₃ with a porosity of ~63 vol% was performed. By adjusting the focal distance with a constant laser power of 300 W, the Cu‐melt was rapidly infiltrated into the ceramic preform in 10 seconds. This was completed under atmospheric air conditions, without added inert gas. The joining process developed can be used to fabricate ceramic/metal joints with targeted (micro‐) structure properties by adjusting the infiltrated melt and the infiltration depth, which would be suitable for many applications, such as multifunctional devices, solid oxide fuel cells or heating elements.     

Swept away [quantum-well infrared photodetectors]

The ultra high-speed capability of quantum-well infrared photodetectors (QWIPs) is well known, thanks to their intrinsic short carrier lifetime (/spl sim/5 ps). This obviously makes QWIPs well suited for high-speed and high-frequency applications. In the past, for thermal infrared imaging where devices are optimized to have the highest possible detectivity, the absorption quantum efficiency has been low (<10%). For high-speed applications where lasers are usually used, the most important parameter is the absorption efficiency. We show that high absorption (/spl sim/100%) can be easily achieved by simply changing some of the device parameters. We also review the experimental demonstrations of the high-speed capability. At present, QWIPs hold the unique position of having high-speed/-frequency capability and high absorption for the thermal infrared region. There are no competitive alternatives.     

Association between coronary heart disease and cancers of the breast, prostate, and colon

Coronary heart disease (CHD) and cancers of the breast, prostate, and colon are more common in industrialized countries than in the developing world, and to some degree, these conditions appear to share risk factors. To investigate whether there is an association between these cancers and a prior history of CHD, a hospital-based case-control study was conducted at Columbia-Presbyterian Medical Center in New York. The study was based on 252 breast cancer cases, 256 colorectal cancer cases, and 322 benign surgical controls, all of whom underwent biopsy or surgery between January 1989 and December 1992, and on 319 prostate cancer cases and 189 benign prostatic hypertrophy controls diagnosed between January 1984 and December 1986 (prior to widespread use of prostate-specific antigen screening). Medical records were reviewed on each, focusing on the preoperative anesthesia and surgical clearances. No association was found between a history of CHD and breast or colorectal cancer, but an elevated risk was found for prostate cancer (odds ratio, 2.00; 95% confidence interval, 1.18-3.39), using unconditional logistic regression with adjustment for appropriate confounders. No association was found between cigarette smoking and any of the three cancers. Aspirin use was protective for colorectal cancer (odds ratio, 0.35; 95% confidence interval, 0.17-0.73) but had no association with breast or prostate cancer. The study suggests that individuals with CHD are at elevated risk for prostate cancer but not breast or colorectal cancer. Etiological risk factors associated with CHD should be investigated with regard to prostate cancer. Patients with CHD may represent a high-risk group for prostate cancer and potential future targets for prostate cancer screening interventions.