Comparison of Paper- and Electronic-Formatted Hydroacoustic Data Charts used for Salmon Enumeration on the Yukon River near Pilot Station

The Yukon River Sonar Project estimates salmon passage through the river near Pilot Station, Alaska. The hydroacoustic data collected by the sonar is currently printed on paper charts in a series of grey marks called “traces.” Technicians count traces that were generated by fish, and these numbers are used to calculate daily abundance estimates. New technology allows the hydroacoustic data to be presented on electronic charts viewed on a computer. The electronic charts also present the data in a series of grey marks, and fish traces must be identified manually by technicians. However, the electronic charts present the data in greater detail, and settings that are used to optimize the visibility of fish traces are more easily adjusted. Both of these features may improve fish detection, which would result in more accurate estimates. Project leaders are planning to make a complete switchover from paper to electronic charts. The principle aim of this study was to compare the fish counts produced by the paper and electronic formats in order to expose any biases and explain why they occur. Due to variation in the slope of the river bottom, the area of river covered by the sonar is divided into several horizontal strata by distance from the transducer. Due to the properties of sound and the variation in the shape of fish traces at different ranges, it is possible that the level and direction of bias may differ among strata. A sample of 150 electronic files, out of approximately 1,700, from the 2008 season was selected for this comparison. Files were counted using Echotastic, a program written by AYK Regional Sonar Biologist, Carl Pfisterer. The electronic chart counts were higher than the paper chart counts for strata one through four, while the electronic counts were lower than the paper counts for stratum five (linear regression output: stratum one: slope=1.112, y-intercept=44.662, stratum two: slope=1.344, y-intercept=13.615, stratum three: slope=1.098, y-intercept=-7.052, stratum four: slope=1.077, y-intercept=-8.566, stratum five: slope=0.827, y-intercept=-0.688). Both the positive and negative biases are likely a result of improved fish detection on the electronic charts and a high level of subjectivity associated with counting fish using sonar. If project leaders conclude that these biases are acceptable, a transition from paper to electronic charts would be advantageous, although correcting for differences will be necessary to make past and future fish estimates comparable

Design, construction and evaluation of a 12.2 GHz, 4.0 kW-CW high efficiency klystron amplifier

An analytical and experimental program is described, for studying design techniques for optimizing the conversion efficiency of klystron amplifiers, and to utilize these techniques in the development and fabrication of an X-band 4 kW cw klystron, for use in satellite-borne television broadcast transmitters. The design is based on a technique for increasing the RF beam current by using the second harmonic space charge forces in the bunched beam. Experimental analysis was also made of a method to enhance circuit efficiency in the klystron cavities. The design incorporates a collector which is demountable from the tube to facilitate multistage depressed collector experiments employing an axisymmetric, electrostatic collector for linear beam microwave tubes

Trends in physical activity and sedentary behaviour in adolescence: ethnic and socioeconomic differences

Objective: To assess developmental trends in physical activity and sedentary behaviour in British adolescents in relation to sex, ethnicity and socioeconomic status (SES).Design: A 5-year longitudinal study of a diverse cohort of students aged 11 - 12 years at baseline in 1999.Setting: 36 London schools sampled using a stratified random sampling procedure.Participants: A total of 5863 students categorised as white, black or Asian, and stratified for SES using the Townsend Index.Main outcome measures: Number of days per week of vigorous activity leading to sweating and breathing hard. Hours of sedentary behaviour, including watching television and playing video games. Data were analysed using multilevel, linear, mixed models.Results: Marked reductions in physical activity and increases in sedentary behaviour were noticed between ages 11 - 12 and 15 - 16 years. Boys were more active than girls, and the decline in physical activity was greater in girls (46% reduction) than in boys (23%). Asian students were less active than whites, and this was also true of black girls but not boys. Black students were more sedentary than white students. Levels of sedentary behaviour were greater in respondents from lower SES. Most differences between ethnic and SES groups were present at age 11 years, and did not evolve over the teenage years.Conclusions: Physical activity declines and sedentary behaviour becomes more common during adolescence. Ethnic and SES differences are observed in physical activity and sedentary behaviour in British youth that anticipate adult variations in adiposity and cardiovascular disease risk. These are largely established by age 11 - 12 years, so reversing these patterns requires earlier intervention

Overdiagnosis:An unrecognised and growing worldwide problem in healthcare

Overdiagnosis is the diagnosis of deviations, abnormalities, risk factors, and pathologies that in themselves would never cause symptoms (this applies only to risk factors and pathology), would never lead to morbidity, and would never be the cause of death. Therefore, treating an overdiagnosed condition (deviation, abnormality, risk factor, pathology) cannot, by definition, improve the patient’s prognosis, and can therefore only be harmful

Designing Effective Group Projects: Applying Student Feedback to Project Design

By integrating group projects into the curriculum, educators can seize the opportunity to provide students not only with marketable skills, but the chance to deepening their understanding of a given topic or subject matter by learning from one another. Designing an effective group project, however, is a challenging task. In the current paper, I utilize results from a student survey on characteristics of effective groups to design an applied group project and describe six key lessons learned by incorporating student feedback into group project design