Lasers take up residence in the surgical suite

The fundamental laser/tissue interaction, in which laser light with a time-dependent intensity propagates into a biological tissue where it is absorbed and scattered is described. The uses of laser radiation for detection and treatment of cancer, tissue imaging, tissue ablation, angioplasty, and in ophthalmology are discussed. Ongoing research efforts in laser medicine are outlined     

Characterization of the reflected beam profile of solar mirror materials

The absolute specular reflectance of flat mirrors was obtained as a function of the reflected beam width from 1 mrad to 17 mrad using a bidirectional reflectometer. The characteristics, calibration and advantages of this reflectometer are discussed. The mirror materials studied include samples of silvered glass, metallized plastic films and polished, bulk aluminum obtained from a variety of commerical suppliers. For some of these materials, the reflected beam profile could be described by a single normal distribution. However, for the other materials, the reflected beam profile was described by the sum of two normal distributions. Examples of the curve fitting procedure and data for selected materials are presented.     

Memorial: Professor Neil Birks

Oxidation of Metals -     

Stimulated emission from Ga1-xAlxAs diodes at 77°K

Ga1-xAlxAs was found to be a suitable material for semiconductor lasers. Stimulated emission from Fabry-Perot type of diodes has been observed at 77°K and 273°K. The highest peak energy of the laser line at 77°K so far is 1.65 eV (l = 7500Å). The Ga1-xAlxAs material was obtained by a liquid phase epitaxial method, described in a previous paper.     

A general dynamic simulation model for evaporators and condensers in refrigeration. Part II: simulation and control of an evaporator

A mathematical model of an evaporator based on one-dimensional partial differential equations representing mass conservation, and tube wall energy has been formulated. These equations are then restructured and linked to a program data base of all major refrigerants and refrigerant mixtures. The result is a simulation model of an evaporator that is general and flexible. The model is tested over a wide range of operating conditions and a simple controller is implemented to demonstrate the effectiveness of the model for controller and systems design.

Résumé

On a établi un modèle mathématique d'un évaporateur basé sur des équations aux dérivés partielles unidimensionnelles qui représentent la conservation de masse et l'énergie de la paroi du tube. Ces équations ont été restructurées ensuite, puis reliées à une base de données sur les principaux frigorigènes purs et en mélanges. De cette manière, on obtient un modèle d'évaporateur d'application générale et souple. Ce modèle a été éprouvé dans des conditions de fonctionnement très variées et on a employé un système de régulation simple pour montrer l'efficacité du modèle pour la conception et la régulation des systèmes.     

Na2SO4-induced accelerated oxidation (hot corrosion) of nickel

The Na₂SO₄-induced accelerated oxidation of nickel has been studied at 1000°C. It has been found that low oxygen activities in the Na₂SO₄, which are produced by the formation of NiO, cause the sulfur activity of the Na₂SO₄ to be increased. Nickel and sulfur from the Na₂SO₄ combine to form nickel sulfide and the oxide ion activity of the Na₂SO₄ is increased. The accelerated oxidation of nickel occurs because oxide ions react with NiO to form a nonprotective oxide scale. The accelerated oxidation of nickel is not self-sustaining since oxide ions are not produced when conditions in the Na₂SO₄ are no longer favorable for the formation of nickel sulfide.     

Forming continuous alumina scales to protect superalloys

The development of continuous Al₂O₃ scales on alloys via selective oxidation is an extremely effective approach to obtain high-temperature oxidation resistance. Depending on the alloy system, it may be necessary to optimize the selective oxidation process. For all alloy systems, improvements in oxidation resistance can be obtained by optimizing the type and concentrations of reactive elements and by controlling the concentration of sulfur.     

Theoretical Response Characteristics of the Coherent Optical Particle Spectrometer

The response characteristics for a particle size measurement system based on coherent detection of the scattered light are developed theoretically. The predictions of this theoretical model are compared with data collected on a prototype experimental configuration in our laboratory. Good agreement is found between predicted and measured responses for polystyrene-latex spheres and NaCI aerosol in the size range 0.31–3.0 μm. Using the theoretical model, various configurations for the system are explored. Based on the modeling results, it is apparent that the proposed technique is best suited for studying size distributions of absorbing particles, such as soot and certain metal oxides.