Noise reduction studies for the Cessna model 337 (0-2) airplane

A study was undertaken to determine the noise reduction potential of the 0-2 airplane in order to reduce its aural detection distance. Static and flyover noise measurements were made to document the noise signature of the unmodified airplane. The results show that significant reductions in aural detection distance can be achieved by the combination of propeller geometry changes and the addition of engine exhaust mufflers. The best results were estimated for the aircraft equipped with a six-blade propeller operating at 3/4 engine speed in combination with a 3.49 cubic foot exhaust muffler installed on each engine. Detection distance for the modified aircraft is estimated to be reduced from about 4-1/4 miles to about 1-1/2 miles when the aircraft is operating at an altitude of 1,000 ft over grassy terrain. Reducing the altitude to 300 ft over a leafy jungle ground cover should reduce the aural detection distance to 0.9 miles. Reduced aural detection distances were also indicated for a modification utilizing a direct-drive six-blade propeller of reduced radius along with smaller exhaust mufflers

The analysis of reactively loaded microstrip antennas by finite difference time domain modelling

In recent years, much interest has been shown in the use of printed circuit antennas in mobile satellite and communications terminals at microwave frequencies. Although such antennas have many advantages in weight and profile size over more conventional reflector/horn configurations, they do, however, suffer from an inherently narrow bandwidth. A way of optimizing the bandwidth of such antennas by an electronic tuning technique using a loaded probe mounted within the antenna structure is examined, and the resulting far-field radiation patterns are shown. Simulation results from a 2D finite difference time domain (FDTD) model for a rectangular microstrip antenna loaded with shorting pins are given and compared to results obtained with an actual antenna. It is hoped that this work will result in a design package for the analysis of microstrip patch antenna elements

Noise reduction studies for the OV-1 airplane

A study has been conducted to define possible modifications to the OV-1 aircraft to reduce its aural detection distance. This effort involved documenting the noise characteristics of the airplane, devising modifications to reduce the noise, estimating the reduction in detection distance, and evaluating aircraft performance as a result of these modifications. It was found that the main noise source on this aircraft is the propeller and hence modifications only to the propeller and the propeller drive system are proposed. Modifications involving only the propeller are noted to involve no increase in weight but they result in only a modest decrease in aural detection distance. In order to obtain substantial decreases in aural detection distance, modifications involving changes both to the propeller and the engine-propeller gearing are required

Noise reduction studies for the U-10 airplane

A study was undertaken by the NASA Langley Research Center to determine the noise reduction potential of the U-10 airplane in order to reduce its aural detection distance. Static and flyover noise measurements were made to document the basic airplane noise signature. Two modifications to the airplane configuration are suggested as having the best potential for substantially reducing aural detection distance with small penalty to airplane performance or stability and control. These modifications include changing the present 3-blade propeller to a 5-blade propeller, changing the propeller diameter, and changing the propeller gear ratio, along with the use of an engine exhaust muffler. The aural detection distance corresponding to normal cruising flight at an altitude of 1,000 ft over grassy terrain is reduced from 28,000 ft (5.3 miles) to about 50 percent of that value for modification 1, and to about 25 percent for modification 2. For the aircraft operating at an altitude of 300 ft, the analysis indicates that relatively straightforward modifications could reduce the aural detection distance to approximately 0.9 mile. Operation of the aircraft at greatly reduced engine speed (1650 rpm) with a 1.3-cu-ft muffler provides aural detection distances slightly lower than modification 1

Adaptive resistance to Biocides and implications of cross-resistance to Antimicrobial Agents in Foodborne Pathogens.

This study was focused on the potential for adaptive resistance in Salmonella and Escherichia coli to commonly used biocides, to identify resistance strategies and any cross-resistance to antibiotics. Bacteria were serially exposed in sub-inhibitory concentrations of biocides and adaptive resistance was observed in all strains investigated. Erythromycin-resistant Salm. Enteritidis did not cross-resist to biocides, whereas erythromycin-resistant Salm. Typhimurium express cross-resistance to chlorohexidine. Benzalkonium chloride-resistant Salm. Virchow showed an elevated resistance to chlorohexidine, however chlorohexidine-resistant Salm. Virchow did not demonstrate it back

Mechanisms of resistance in Salmonella enterica

The aim of this study was to promote resistance in Salmonella enterica serovar Enteritidis, Typhimurium, and Virchow to commonly used antibacterials and to identify mechanisms underlying any resistance obtained. Strains were exposed to various biocides and following each passage adaptive resistance was recorded. Permeability changes in the outer membrane, including LPS, cell surface charge and hydrophobicity and efflux were investigated as possible resistance mechanism candidates. The outer membrane and LPS bands were analysed by SDS-PAGE and visualised by Coomassie blue and silver staining. The cell surface charge and hydrophobicity were investigated employing microelectrophoresis and microbial adhesion to hydrocarbons assay, respectively. Efflux activity was examined by comparing resistance in pre- and post-adapted strains in the presence of reserpine. The outer membrane and LPS did not reveal any significant changes. Most of the parent strains were not significantly hydrophobic, whereas adapted were. An active efflux system was associated with benzalkonium chloride and chlorohexidine resistance

Use of multiple primers in RAPD analysis of clonal organisms provides limited improvement in discrimination

Randomly amplified polymorphic DNA (RAPD) analysis using two or more primers has been reported to provide additional discriminatory ability over one primer used individually. This may be of particular application in epidemiological typing of clonal organisms, such as Shiga toxin-producing E. coli O157, where strain differentiation can be difficult. Using four arbitrary primers individually, and in all possible permutations, E. coli O157 isolates and other arbitrarily chosen E. coli strains were typed using RAPD analysis. For most nonclonal strains, the use of two primers resulted in increased differentiation between isolates; however, more than two primers did not increase further the discriminatory capacity. E. coli O157 isolates that produced virtually identical profiles using one primer did not show increased differentiation when using two or more primers, demonstrating that in some cases, where strains of an organism are highly related, there is limited advantage to using more than one primer in RAPD analysis

Noise measurement evaluations of various takeoff-climbout profiles of a four-engine turbojet transport airplane

Noise measurement evaluations of various takeoff-climbout profiles of four engine turbojet transport airplan