On the modal expansion of resonator field in the source region

Two field expansions for the electromagnetic field radiated by electric and magnetic currents in a cavity resonator are presented. The first utilizes the cavity resonant modes only, while the other utilizes, in addition, the irrotational modes. The first expansion is shown to be more suitable if the exciting currents have volume distributions. On the other hand, the second expansion is more suitable if the resonator contains surface or filamentary current distributions. Typical examples are given to demonstrate the convergence behavior of the two expansions near and within the source region     

Cyclohexane dehydrogenation on a nickel catalyst: Kinetics and catalyst fouling

The main reaction and deactivation kinetics of cyclohexane dehydrogenation in the presence of hydrogen has been investigated at atmospheric pressure over a nickel kieselguhr catalyst in the temperature range 583–623 K. The rate of reaction for the fresh catalyst increased with increasing temperature, cyclohexane and hydrogen partial pressures whereas it decreased with an increase in the benzene partial pressure. The experimental data could be adequately modelled by a power law rate expression. The catalyst activity decreased with run time due to catalyst fouling by coke deposition. The rate of deactivation was independent of cyclohexane partial pressure, increased with increasing benzene concentration and decreased with increasing hydrogen partial pressure. It is postulated that coke is most likely formed by the successive dehydrogenation of benzene.     

Preparation and Evaluation of Directly-Compressed Indomethacin, Indomethacin Sodium and Indomethacin Meglumine Tablets

A formula containing Compactrol, Ac-Di-Sol, Aerosil 200 and talc was used to prepare directly-compressed tablets of indomethacin and its sodium and meglumine salts. The prepared tablets were evaluated for uniformity of weight and thickness, hardness, friability and content uniformity. Each batch was then divided into two, one was coated with an opaque non-enteric film coat and evaluated for coat thickness uniformity. The dissolution rates of the uncoated and coated tablets and the effect of shelf-storage, at room temperature for 11 months, on drug contents were also studied. Indomethacin meglumine tablets showed the least relative standard deviation of weight and thickness. They exhibited acceptable uniformity of content and coat thickness, and the highest hardness-friability ratio. Also exhibited, uncoated and coated, the best in-vitro release of its drug contents and the maximal stability.     

Load matching to photovoltaic generators

This paper investigates the suitability of a photovoltaic source to a particular load as regards the degree of load matching in systems that do not employ maximum-power-point-trackers. It is shown that, since the load line is independent of the array characteristics, the array interconnection may be selected to suit the load. The paper identifies two situations in which the system performance can be improved: one through a permanent change in array interconnections from a predominantly series mode to a parallel mode or vice versa; and the other through dynamic array switching from one mode to the other, depending on the solar insolation. Transient analysis of the system due to this array switching has shown that, within a few seconds, the system reaches its new steady-state values.     

Burning characteristics of high-ash bangladeshi peat

The combustion characteristics of high-ash Bangladeshi peat was investigated in an atmospheric fluidized-bed combustor at bed temperatures of 750, 800 and 850°C. The particle size was varied from 8.05 mm to 22.76 mm. Combustion of this variety of peat occurred at constant size and thus followed a shrinking core model. Volatile evolution is complete before the particles reached bed temperature and during char combustion the particle temperature exceeded the bed temperature. Combustion times can be represented by power law equations. Results indicated that the burning rate of peat char is a combination of diffusion and kinetic control mechanisms.     

The thermal properties of soils in cold regions

A summary is given of some of the main features associated with the thermal properties of soils in cold regions as described in a USACRREL monograph and report. The main effects of the freezing process in soils are noted and its analogy with the drying process is emphasized. It is shown that the unfrozen water present in frozen fine-grained soils plays an important and effective role in facilitating heat transfer. The influence of the degree of saturation is described and the concept of a “critical” degree of saturation introduced.The methods for calculating the thermal conductivity of frozen soils are compared and some of their trends indicated. The results of an evaluation of these methods show which gives the best agreement with measured thermal conductivity values under certain conditions.     

The synthesis and evaluation of cyclic olefin sulfone copolymers and terpolymers as electron beam resists

Poly(cyclopentene sulfone) (PCPS) and poly(bicycloheptene sulfone) (PBCHS) copolymers have been evaluated as potential positive electron beam resists which have good thermal properties and which show high sensitivity to ionizing radiation. It was found that thin copolymer films could be processed as resists but that films greater than 3000 Å thick cracked in the solvents used to dissolve the radiation-exposed regions. Incorporation of plasticizing additives did not improve the film properties. Films from low molecular weight polymer fractions cracked less in solvents, but higher radiation doses were required to offset the reduced sensitivity. This resulted in the formation of intractable residues in the exposed regions which appear to be crosslinked polymer. Bicycloheptene monomers with specific functional groups did not improve the properties of the copolymer films. Terpolymerization with α-olefins such as butene-1 and cis-2-butene plasticized these films and reduced their tendency to crack in solvents. Poly(cyclopentene sulfone–co–butene-1 sulfone) films were found to have the best properties, and 1.25-μ resist images could be etched in SiO₂ layers at an exposure dose of 4 × 10^?6 C/cm² at 25KV. However, one important limitation of this terpolymer was the low dissolution rate ratio between the exposed and unexposed regions. Since straight-walled relief images are essential to the formation of high-resolution patterns, the usefulness of this terpolymer as an electron beam resist appears to be hindered by the limited choice of good solvents to maximize the dissolution rate ratio. PBCHS block terpolymers containing methyl methacrylate (MMA) or methacrylic acid (MAA) were synthesized to improve the solubility in solvents and to incorporate the properties of methacrylates. PBCHS–MMA films cracked in solvents after irradiation; PBCHS–MAA polymers were too insoluble to form resist films.