Design and performance of resonant cavities for communication systems. The theory and performance of resonant cavities for application-, in mobile radio and base-stations in the VHF and UHF bands are investigated.

It is often necessary to operate a number of radio communication channels from a single control room without time-sharing between the various channels. Here it is necessary to operate a number of transmitters and receivers simultaneously from the same base station or mobile unit without interference. The best method to achieve this has been found in the use of filters inserted in the transmission line between the antenna and the transmitter(s) on one hand and the receiver(s) on the other hand. The basic unit employed in the design of microwave filters is usually a cavity resonator of which the most important factors are the Q, insertion loss and resonant frequency. However, a problem which frequently arises with cavity resonators is the accurate determination of these resonant characteristics complicated by the presence of coupling port, materials and various design and geometrical deviations. Such cavities have been investigated in several cases and the results have been generalised, but this investigation has been conducted to examine thoroughly most of the problems being met in present practice. Design and development of some common resonant structures are considered. Emphasis is placed on solutions found to special problems especially regarding complicated boundary conditions. Furthermore, investigation includes methods for optimising resonant parameters such as insertion loss and Q, trading of insertion loss with coupled cavity selectivity, frequency tuning and compensation for frequency variations due to wide ranges of operating temperatures. By comparing Q values obtained in practice with theoretical values, it has been possible to establish an appropriate Q loss budget to as to facilitate accurate prediction of coupled cavity unloaded Q. A satisfactory agreement between theory and practice has been obtained. By application of the results of theoretical analysis and experiment, it is shown that microwave filters can be designed to have a desired insertion loss and off-band attenuation slope. Steps leading to designs of any number of cascaded cavities in a two-port network and, subsequently, multi-port networks are discussed in detail

Time – Course of Sodium Arsenate Induced Hepatotoxicity and Nephrotoxicity in Male Wistar Rats

Arsenic exposure has been implicated by several epidemiological studies as an important metalloid that is currently poisoning millions of people globally. In order to investigate the time – course of arsenic exposure on hepatic and renal toxicity, male albino rats (n=45) were exposed to arsenic (100 ppm, 150 ppm and 200 ppm) for 4, 8 and 12 weeks as sodium arsenate in their drinking water. Control animals (n=15) received distilled water for the same period after which blood and vital organs were removed from the animals and analyzed for alanine amino transaminase (ALT), aspartate amino transaminase (AST) gamma amino transaminase (γGT), alkaline phosphatase (ALP), creatinine and urea spectrophotometrically. Histological changes in hepatocytes was also examined. Before the commencement of arsenic exposure, five animals were sacrificed to obtain baseline data. Significant elevation in plasma ALT, AST, γGT and alkaline phosphatase activities characterized the effect of the arsenical at all doses and time interval relative to the controls. Plasma levels of creatinine and urea were also elevated at all-time intervals in the arsenic group. In most of the cases observed, the elevated level of these biochemical marker in circulation are time – and dose – dose dependent. Hepatic histopathology reveals degeneration of cytoplasmic contents, evidence of necrosis, collapse of central vein, cytoplasmic inclusion and enlarged hepatic sinusoids in arsenic – exposed groups. These findings suggest that different dose regimens of sodium arsenate at different time interval caused degenerative changes in hepatic and renal tissues in rats in dose – and time – dependent fashion. Keywords: Arsenic, Time – course, Hepatotoxicity, Nephrotoxicity DOI: 10.7176/JNSR/9-4-0

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population