The distribution of palladium in a Pd-modified 4130 steel

The addition of palladium to a 4130 steel reduces its sensitivity to stress corrosion cracking and to hydrogen-induced cracking. The atom probe field-ion microscope has been used to study the microstructure and microchemistry of these palladium-modified 4130 steels with particular emphasis on the distribution of palladium between the various phases and internal interfaces. The palladium was found to segregate to the ferrite-ferrite lath boundaries to form a mono-atomically thick adsorbate layer. Palladium-manganese precipitates both at the lath boundaries and in the ferrite matrix were also detected. Most of the palladium was found to remain in solution in the ferrite.     

Analysis of multilayered dielectric waveguides: variationaltreatment

A fast and near exact modal analysis is presented to obtain the propagation constants and electric field profiles for dielectric multilayered channel (rib) waveguides. Calculations are performed for a particular channel configuration and found to be in excellent agreement with those obtained using the finite difference method     

High voltage (>1kV) and high current gain (32) 4H-SiC power BJTs using Al-free ohmic contact to the base

This letter reports the design and fabrication of 4H-SiC bipolar junction transistors with both high voltage (>1kV) and high dc current gain (/spl beta/=32) at a collector current level of I/sub c/=3.83A (J/sub c/=319 A/cm/sup 2/). An Al-free base ohmic contact has been used which, when compared with BJTs fabricated with Al-based base contact, shows clearly improved blocking voltage. A specific on-resistance of 17 m/spl Omega//spl middot/cm/sup 2/ has been achieved for collector current densities up to 289 A/cm/sup 2/.     

Particulate organic matter transport in the lower Colorado river,South-Western USA

The lower Colorado River from Laughlin, Nevada, to the border with Mexico is one of the most regulated rivers in North America. An analysis of particulate organic matter (POM) transport through the system was made to determine POM concentrations, composition and point of origin, as well as to determine the effect dams had on this transport. Particulate organic matter concentrations generally increased from upstream to downstream, and were dominated by very fine organic detritus (< 25μm size fraction). Reservoirs released more POM than they received during spring and summer, but less during autumn and winter. Reservoirs recycled POM, taking in organic detritus and discharging small limnoplankton. Backwater complexes functioned as filters during storm events, trapping coarse material and releasing fine material. Agricultural drains made only minor contributions of POM, but provided important nutrients for in-channel production of POM. Water diversions forced POM off-channel, whereas sluicing operations reduced inorganic loads in the canals. Despite the presence of six mainstem dams, the lower reaches support a diverse assemblage of detritivorous fishes, similar to that found in the lowermost reaches of natural, unregulated rivers. The food base for this fishery stems from autochthonous production of POM.     

News: United Kingdom to set air quality emission standards

Government.     

Occupational stress and dentistry: theory and practice. Part II. Assessment and control

Since dentistry has been identified as being a stressful profession, dentists, with the help of the members of the dental team, must attempt to achieve a relatively stress-free working environment. In addition to recognising potential occupational stressors it is important for dentists to be able to assess their emotional responses to the practice of dentistry and to arrange their daily working lives in such a way as to reduce occupational stress. This paper examines the means by which dentists may assess occupational stress as well as person-centred and/or situation-centred strategies of coping with and controlling occupational stress in general dental practice.     

Trends in glove use by dentists in England and Wales: 1989-1992

The routine wearing of gloves during the dental treatment of patients forms an integral part of the recommended guidelines of many authorities worldwide. Compliance has been variable but there is evidence to show that this is increasing, as are other cross-infection control measures. A survey of glove use by general dental practitioners in England and Wales was carried out in 1989. This paper reports a follow up study in 1991/2 which aimed to identify any differences that had occurred in the interim. The results indicated that there was increasing compliance with recommended cross-infection control measures, although only one fifth of respondents were found to change gloves between patients. Of those practitioners who did not change gloves between patients, half considered that blood contact was not a reason for changing gloves. Comparisons are made with compliance rates in other countries and recommendations made for further education within the dental profession on the subject of cross-infection control.     

The effects of metformin on glycemic control and serum lipids in insulin-treated NIDDM patients with suboptimal metabolic control

The edentulous ridge expansion has been introduced in recent years to reestablish an appropriate alveolar ridge width. This technique consists of the placement of implants in the space formed after the dislocation of the buccal plate in a labial direction. In guided bone regeneration, the quantity of bone regenerated under the membranes has been demonstrated to be directly related to the amount of the space under the membranes. This space can diminish as a result of membrane collapse. To avoid this problem, a new technique of edentulous ridge expansion, which involved the use of a titanium mesh barrier to protect the regenerating tissues and to achieve a rigid fixation of the bone segments, was used in association with autologous bone in 25 patients. At second-stage surgery in all patients, it was possible to see tissue, under the mesh, that had the macroscopic characteristics of mature bone and was superficially covered by a thin soft tissue layer. The microscopic examination showed that all autologous bone particles were embedded in newly formed bone. The use of a rigid mesh can assist bone regeneration in non-space-making defects, since it probably does not interfere with the blood flow to the underlying tissues because of the presence of microholes within the mesh.