Instantaneous Nature Research Articles

Mechanism of bulk laser damage to CdS-type semiconductors

An investigation was made of the photoconductivity of pure CdS crystals at the moment of appearance of bulk damage and of the kinetics of this damage. An analysis of the experimental data revealed direct multiplication of carriers as a result of bulk damage, dependence of the bulk damage threshold on the amplitude of the optical wave field, and the instantaneous nature of the damage itself. This evidence shows that electron avalanche ionization is the dominant bulk damage mechanism in the case of pure CdS-type semiconductors subjected to nanosecond laser radiation pulses.

Effeciency of bonded joints of composite shells of glass during cyclic loading by external hydrostatic pressure

1. By means of bonded joints it is possible to make closed composite shells of glass which have a considerable capacity to withstand a number of cycles of loading by an external hydrostatic pressure under extremely arduous operating conditions. 2. The high efficiency of the bonded joints is due to the fact that the thin film between the elements being joined does not introduce perceptible disturbances of the stress and strain distribution of the shell. 3. The load-bearing capacity and life of the composite shell is a direct function of the instantaneous nature of the stress and strain distribution. Consequently to provide the optimum indices of the joint efficiency for elements of glass shells it is necessary to locate the joints in the zones with minimum stress disturbance by a voiding if possible the use of structural elements of the type with massive flanges or intermediate rings, etc., which limit movement in the shells under external load. 4. The efficiency of composite glass shells is directly related to the accuracy of machining the surfaces being joined and the conformity of their geometric shape and dimensions. In particular, nonconformity of the external or internal sizes of the shells being joined must not be greater than 0.1 of the mean shell wall thickness. Greater deviations of these dimensions leads to a marked reduction of the load-bearing capacity.

Effect of Osmolality on the Hydraulic Permeability Coefficient of Red Cells

The osmotic water permeability coefficient, L(p), for human and dog red cells has been measured as a function of medium osmolality, and found to depend on the osmolality of the bathing medium. In the case of human red cells L(p) falls from 1.87 x 10(-11) cm(3)/dyne sec at 199 mOSM to 0.76 x 10(-11) cm(3)/dyne sec at 516 mOSM. A similar decrease was observed for dog red cells. Moreover, L(p) was independent of the direction of water movement and the nature of the solute used to provide the osmotic pressure gradient; it depended only on the final osmolality of the medium. Furthermore, L(p) was not affected by pH in the range of 6 to 8 nor by the presence of drugs such as valinomycin (1 x 10(-6)M) and tetrodotoxin (3.2 x 10(-6)M). The instantaneous nature of the response to changes in external osmolality suggests that the hydraulic conductivity of the membrane is controlled by a thin layer at the outer face of the membrane.

Computer model for the prediction of the dispersion of airborne radioactive pollutants.

Presented are two computer programs written for an IBM 1401/7040 digital computer in a FORTRAN IV computer language. The programs are called RADS and ARADS, acronyms for Radiological Atmospheric Dispersion Study and Alternate RADS, respectively. Both programs are designed to investigate the use of various equations formulated to predict the dispersion of radioactive effluents deposited into the atmosphere from a smoke-stack. The release of the effluents may be of either an instantaneous or continuous nature. Predictions of atmospheric concentrations are made for approximately 600 points throughout an observation area surrounding the smoke source, allowing contour lines of equal concentrations to be drawn. The RADS program was designed for one particular effluent release. The program predicts the path of the smoke from the source to one of the boundaries of the observation area. Predictions are then made concerning the dispersion of the smoke. The ARADS program uses average meteorological conditions to predict the air concentrations resulting from long-term releases of a smokestack effluent. The output data for both programs contain a scaled map of the observation area showing the location of the predicted concentrations in order to simplify the drawing of the contour lines. While the authenticity of the prediction equations is not certain, a definite relationship between relative air concentrations with respect to the location of the source was established. The programs permit fast, accurate, and voluminous solutions to the complex equations, and provide a tool with which to examine the prediction equations themselves.

On the Kinetic Theory of Dense Fluids

In this paper we analyze the Rice—Allnatt kinetic equations using a formal perturbation expansion in which the lifetime of dynamical coherence plays a fundamental role. It is shown that: (a) In the limit of short dynamical coherence time, the Rice—Allnatt equations are a valid description of steady-state transport phenomena in a liquid, (b) The Kirkwood time-smoothing hypothesis is a natural expression of the nature of the coherence time expansion, (c) The use of a separable intermolecular potential, the instantaneous nature of rigid-core collisions, and the nature of time smoothing all have interesting consequences for the derivation of Markovian kinetic equations from the Liouville equation.