Noise calibrator for v.h.f. and u.h.f. field-strength-measuring receivers

A simple noise generator, based on a semiconductor diode of the Zener type and suitable for use in the frequency range 30?900 MHz, can be used to check both absolute gain and noise performance of sensitive receivers.     

Factors Associated With Persistence in Science and Engineering Majors: An Exploratory Study Using Classification Trees and Random Forests

Many students who start college intending to major in science or engineering do not graduate, or decide to switch to a non‐science major. We used the recently developed statistical method of random forests to obtain a new perspective of variables that are associated with persistence to a science or engineering degree. We describe classification trees and random forests and contrast the results from these methods with results from the more commonly used method of logistic regression. Among the variables available in Arizona State University data, high school and freshman year GPAs have highest importance for predicting persistence; other variables such as number of science and engineering courses taken freshman year are important for subgroups of the student population. The method used in this study could be employed in other settings to identify faculty practices, teaching methods, and other factors that are associated with high persistence to a degree.     

Semiconductor-diode v.h.f. and u.h.f. noise sources

The v.h.f. and u.h.f. noise properties of silicon and gallium-arsenide diodes are discussed. A formula for calculating the noise output is given.