Systems integration with reliability in mind

Device sophistication and data-processing ability continue to grow steadily and new processing devices dedicated to special functions such as speech processing or data encryption are regularly being introduced or replaced by more powerful devices. As device manufacturers extend the power and applicability of devices, new system design concepts are needed. Not only are specialist disciplines required but also the question of integration arises, a problem, all too easily overlooked. This paper looks at the problems caused by increased complexity (such as in two-sided cards on buses) and puts forward suggestions as to how to improve reliability, such as protecting the system clock and limiting the amount of parallel I/O, at least on the system card.     

Tolerance to delta9-tetrahydrocannabinol in adapted and nonadapted rabbits

Two groups of New Zealand white rabbits, one which had been adapted to the testing chamber and one which had not been adapted to the testing chamber, were given delta9-tetrahydrocannabinol (delta9-THC; 0.5 mg/kg, IV) daily for 12 days. During vehicle control and on the first and last day of delta9-THC administration, electroencephalograms (EEG's) were recorded from the motor cortex and hippocampus, while standing, sprawling and behavioral activity were recorded concurrently. The results showed that tolerance to the behavioral and EEG effects of delta9-THC occurs in rabbits and that acute and chronic effects produced by delta9-THC are influenced by environmental factors.     

Waveguide-fed spherical dielectric antennas

The results of an experimental investigation into the radiation properties of circular waveguide excited dielectric sphere antennas are reported. The input waveguide had a plain end without a flange or ground plane. The input voltage standing-wave ratio varied from about 1.1 to 2.5 for the sphere sizes used but can usually be reduced to about 1.25 over the 8-12 GHz band by separating the sphere from the waveguide. Separation increases the on-axis gain by 1-3 dB and produces nearly equal beamwidths in bothE- andH- planes. Phase front measurements located a fixed phase center near the end of the waveguide.     

The influence of microstructural characteristics on the failure properties of a polybutadiene system

The stress-strain characteristic of polymeric binders and solid propellants are dependent on the crosslink density, molecular weight between crosslinks, molecular weight distribution in the binder formulation, volume fraction of filler, and the interaction between the binder and filler particles. This investigation is directed toward elucidation of solid propellant microscopic response and failure mechanisms through characterization of the constitutive effects of crosslink density, molecular weight distribution and curing agent ratio in the binder formulation, and filler fraction. This was accomplished on the ERLA/PBAA propellant system through investigation of three binder formulations with the same curing agent ratio but different crosslink densities; five binder formulations with different curing agent ratios; and four formulations with up to 69.9% by volume of filler. Uniaxial stress-strain characteristics were determined on each formulation at displacement rates of 0.2 to 20.0 in/min at isothermal test conditions ranging from 75 to ?90°F. The failure characteristics of a viscoelastic material represent a curve in the three-dimensional space of stress, strain, and time. The ultimate property data on each formulation are presented as projections of this failure curve on the stress-strain, stress-time, and strain-time planes, respectively. Relationships are developed for the dependence of the stress-time, strain-time, and stress-strain failure envelopes on the volume fraction of bound rubber, crosslink density, molecular weight distribution and curing agent ration in the binder component, and the volume fraction of filler.     

Effect of radiation intensity on photo-oxidation of an air-blown bitumen

Xenon-arc irradiation was used to study the influence of a wide range of radiation intensity on the rate of photo-oxidation of a sample of air-blown bitumen as determined by infra-red spectroscopy. The xenon-arc was monitored to provide information on its rate of decay, and its range of intensity was compared with that of total solar radiation in Melbourne. Thermal (dark) oxidation rates were also determined at various temperatures. The information obtained is discussed in terms of the mechanism of photo-oxidation of bitumen and the relation to climatological data. Acceleration factors for oxidation of bitumen in the laboratory for prediction of durability were determined by applying the superposition principle to the data.     

Algebraic Coding and Digital Redundancy

The techniques of coding theory are used to improve the reliability of digital devices. Redundancy is added to the device by the addition of extra digits which are independently computed from the input digits. A decoding device examines the original outputs along with the redundant outputs. The decoder may correct any errors it detects, not correct but locate the defective logic gate or subsystem, or only issue a general error warning. Majority voting and parity bit checking are introduced, and computations are made for several binary addition circuits. A detailed summary of coding theory is presented. This includes a discussion of algebraic codes, binary group codes, nonbinary linear codes, and error locating codes.     

Intrinsic coercive force variation with packing in fine particle assemblies

A formula is given to describe the variation of intrinsic coercive force with packing in elongated single domain (ESD) iron particle assemblies. A similar formula, which describes this variation in barium ferrite particle assemblies, is formally identical to the other one by simply changingp(packing) into1 - p(porosity). Magnetic interactions are considered, and an overall interaction field is defined that may account for intrinsic coercive force variations in the case of ESD iron particles. Experimental results on barium ferrite particle assemblies are presented that suggest the existence of a critical packing factor (p sim 0.15) separating two different, but not specified, modes of interaction.     

Effects of Low Temperature on Structural Metals

Numerous alloys are evaluated for their structural usefulness in terms of ductility and notch toughness at cyrogenic temperatures. Alloys being evaluated include those of aluminum, nickel, steel, titanium and magnesium.     

Easing prefiltering requirements of s.c. filters

A simple technique is presented which eases the requirements of the continuous-time antialiasing prefilter in a switched-capacitor filter.