Wear of filled and unfilled dental restorative resins

The influence of double-pass sliding on the surface failure of filled and unfilled dental restorative resins was evaluated. Damage was more severe for double-pass than for single-pass sliding. Wear of restorative resins and composites was influenced by the resistance to penetration and by the mode of deformation during sliding.     

A microcomputer-based system for stereogrammetric analysis

A system for the quantitative analysis of stereo-pairs of photomicrographs has been devised using a Commodore ‘PET’ microcomputer coupled to a digitizing pad, plotter and printer. The system need not use any form of stereo-viewer and does not require any particular alignment of the photographs. Height differences, derived from parallax measurements, can be obtained quickly even by operators who might normally experience difficulties with stereoscope-based systems due to either poor stereo vision or inexperience. Three-dimensional coordinates, input from point-pairs, are stored inside the computer and may be sorted to draw line profiles along any operator-selected line. Such profiles may be referred to either the projection of the median plane of the two images or rotated (‘levelled’) to the 0° tilt plane. The operation of the system is described and illustrated using both specially-constructed left- and right-hand ‘images’ from test contours and also real SEM stereo pairs. Finally, both the potential and limitations of such a system for development and application are discussed.     

Life stress and treatment course of recurrent depression: II. Postrecovery associations with attrition, symptom course, and recurrence over 3 years.

Life stress was studied in relation to postrecovery attrition, symptom course, and recurrence of depression over 3 yrs. Participants were 67 individuals with recurrent depression who had responded to treatment. Life stress was assessed for the prior 12 wks at acute treatment entry (T1), initial recovery (T2), and after 17 wks of sustained recovery (T3). Severe life events at T1 predicted greater attrition, a more favorable postrecovery symptom course, and a lower likelihood of recurrence over 3 yrs. Life stress at T2 was not predictive of outcomes. Finally, undesirable life events at T3 tended to predict a worse symptom course and a higher likelihood of recurrence, particularly for individuals on medication. The findings are discussed in terms of (a) different processes influenced by life stress over time and (b) limitations of existing longitudinal research for studying the effects of life stress over prolonged intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of normal alcohols on the abrasive wear of glass

Normal alcohols were used as cutting fluids in a study of friction and wear of soda lime silicate glass against silicon carbide. Abrasion surfaces were 600 grit silicon carbide paper and a roughened plate of hot-pressed silicon carbide. As the alcohol chain length increased, the coefficient of friction decreased. This result was attributed in part to better lubrication of the abrading surfaces by the long chain length alcohols. The wear rate and the coefficient of friction were strongly dependent on pullout of carbide grains from the silicon carbide paper. Wear on fresh abrasive paper was independent of alcohol chain length. As the paper becomes used, long chain length alcohols were more effective cutting fluids. On the silicon carbide plate, the wear rate decreased in a non-linear fashion as the alcohol chain length increased. For all conditions, the highest wear rate and coefficient of friction were obtained in water. Data are explained in terms of classical theories of friction and wear.     

Vaccines against endogenous hormones: a possible future tool in animal production

Vaccines have been widely used by the livestock industry to control and prevent disease. New technologies now permit development of vaccines against hormones that control reproduction, growth, and lactation in domestic farm animals. Results of research projects studying passive and active immunization against such hormones as estrogen, testosterone, LH, FSH, and somatotropin have demonstrated that reproductive efficiencies and growth can be altered through vaccination. Although immunizations against most of the hormones studied have proven effective in most cases, there remain problems related to longevity, consistency, and efficiency of response both within and between animals. When these areas have been clearly defined for individual hormones, standardized immunization regimens can be developed that will optimize antibody production in the animal, thus providing the animal agriculture industry with a powerful and profitable production tool.     

Traffic theory and the Internet

We argue that traffic theory, an essential component in the design of traditional telecommunications networks, should be increasingly applied in the development of the multiservice Internet. We discuss the statistical characteristics of Internet traffic at different time scales. Modeling is facilitated on identifying the notion of flow and distinguishing the categories of streaming and elastic traffic. We review mathematical modeling approaches useful for predicting the relationship between demand, capacity and performance for both streaming and elastic flows. Derived results indicate the limitations of service differentiation as a means for guaranteeing QoS and highlight the importance of traditional traffic engineering approaches in ensuring that the network has sufficient capacity to handle offered demand     

Electrical polarization control of vertical-cavity surface-emittinglasers using polarized feedback and a liquid crystal

We report electrical control of the polarization state of a vertical-cavity surface-emitting laser (VCSEL), The VCSEL is subject to strong external optical feedback (up to 6% of emission), with polarization controlled by a liquid-crystal (LC) element, It is found that the contrast ratio of the complete system can be enhanced compared to the contrast ratio of the LC element alone     

Reliability of large periphery GaN-on-Si HFETs

GaN devices exhibit excellent potential for use in many RF applications. However, commercial acceptance of the technology has been hindered by the scarcity and non-statistical nature of reliability results. In this work we present a full device level reliability study of GaN-on-Si HFETs. Reliability results on this technology include three-temperature DC data that show an activation energy of 1.7 eV and an average failure time >10⁷ h at 150 °C. Additionally, long duration DC lifetest (30 000 device hours) and RF lifetest (4000 device hours) results demonstrate a repeatable low drift process. Environmental tests such as autoclave and ESD demonstrate the ruggedness of the material system and technology. Finally, initial failure analysis is discussed.     

An EM Algorithm for Ion-Channel Current Estimation

Parameter estimation of a continuous-time Markov chain observed through a discrete-time memoryless channel is studied. An expectation-maximization (EM) algorithm for maximum likelihood estimation of the parameter of this hidden Markov process is developed and applied to a simple example of modeling ion-channel currents in living cell membranes. The approach follows that of Asmussen, Nerman and Olsson, and Ryden, for EM estimation of an underlying continuous-time Markov chain.     

740 nm InP/GaInP quantum-dot laser with 190 A cm/sup -2/ room temperature threshold current density

InP quantum-dot lasers grown on GaAs substrates and emitting in the 730-740 nm band with threshold current density as low as 190 A cm/sup -2/ for a 2000 /spl mu/m-long device with uncoated facets are reported.