Circular 19

The turnip maggot, seed-corn maggot and onion maggot are the root maggots of economic importance in Alaska. They feed on crucifers, crucifers and other crops, and onions, respectively. The damage they cause can be materially lessened by properly timed applications of insecticide and certain cultural practices.Cooperating with the United States Department of Agriculture, Agricultural Research Administratio

Experimental study of nonlinear conductance in small metallic samples

We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample

Normal-Metal Aharonov-Bohm Effect in the Presence of a Transverse Electric Field

The effects of transverse electric fields on the conductance fluctuations in an Sb loop have been studied. We show that the electric field can be used to tune the position (or phase) of Aharonov-Bohm oscillations as well as to alter the aperiodic conductance fluctuation patterns. We disucss two mechanisms which might cause the observed dependence of the fluctuation pattern on transverse electric field. The first is the electrostatic Aharonov-Bohm effect, and the second is the spatial shifting of the electron trajectories by the electric field

Evaluation of Bird Response to Propane Exploders in an Airport Environment

Bird-aircraft collisions (bird-strikes) cause serious safety hazards to aircraft, costing civilian aviation at least $496 million annually in the U.S. Non-lethal bird-frightening devices, such as propane exploders, are commonly used to deter birds from airport environments. We conducted a study during August - October 2004 to determine the efficacy of propane exploders utilized with and without concurrent lethal reinforcement activities for altering bird behavior at John F. Kennedy International Airport in Queens, New York. Two groups of 8 propane exploders each were deployed on the airfield. One group of propane exploders was set to “off” (control), whereas the other group was programmed to activate at 15-minute intervals (treatment). This pattern was reversed each week for a 12-week period. In addition, lethal control activities to reduce gull-aircraft collisions were conducted during August and September 2004. We conducted bird observations associated with propane exploders during the lethal control program (8-week period) and following the end of the program (4-week period). The number of bird flocks (≥1 birds) that were within 150 m of treatment (n = 432) and control (n = 442) propane exploders was similar. Simultaneous lethal control activities at the airport did not alter the effectiveness of the propane exploders. Birds responded (e.g., altered flight path) on 3 of 21 (14.3%) occasions when a bird flock was within 150 m of a treatment propane exploder that activated. Our findings suggest propane exploders used in this manner in this airport environment do not significantly alter birds behavior or reduce the threat of bird-strikes. Future research is needed to evaluate techniques such as motion-activated propane exploders to enhance the effectiveness of this tool to reduce wildlife hazards at airports

Temperature Dependence of the Normal-Metal Aharonov-Bohm Effect

The amplitude of h/e periodic oscillations in the magnetoresistance of very small normal-metal (Au) rings, as well as the harmonic h/2e, have been studied as a function of temperature. The amplitudes depend on the temperature T roughly as T-1/2, as expected from the averaging of conduction channels in the absence of inelastic scattering, but may not be entirely consistent with this model. At the lowest T, the size of the fluctuations in the conductance is about ΔG∼e2/h, as predicted recently

Universal scaling of nonlocal and local resistance fluctuations in small wires

Resistance fluctuations in small metal samples result from coherent transport of the carriers. The wave functions of the carriers extend into regions which are not accessible classically. We have directly measured the length dependence of the nonlocal magnetoresistance fluctuations in Sb and Au wires by studying regions of our samples separated from the classical current path by a distance L which varied from 3Lcphi down to 0.2Lcphi (where Lcphi is the phase coherence length for the carriers in the metal). These fluctuations decay exponentially with L/Lcphi. Measurements along the classical current paths scale more slowly with L/Lcphi than predicted by the analytical theory but are in agreement with numerical simulations. We have also studied the length dependence of the magnetic field correlation scale BC, and we find that it is in qualitative agreement with a recent model calculation that accounts for the voltage probes

Interaction Effects Among Two-Dimensional Electrons and Holes

We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory

Truth Be Told: Evidence of Wheelchair Users’ Accuracy in Reporting Their Height and Weight

Objectives To examine whether wheelchair users’ self-reports of height and weight differed significantly from direct measurements and whether weight category classifications differed substantially when based on self-reported or measured values. Design Single group, cross-sectional analysis. Analyses included paired t tests, chi-square test, analysis of variance, and Bland-Altman agreement analyses. Setting A university-based exercise lab. Participants Community-dwelling wheelchair users (N=125). Interventions Not applicable. Main Outcome Measure Participants’ self-reported and measured height, weight, and body mass index. Results Paired t tests revealed that there were significant differences between wheelchair users’ self-reported and measured values for height (difference of 3.1±7.6cm [1.2±3.0in]), weight (−1.7±6.5kg [−3.6±14.2lb]), and BMI (−1.6±3.3). These discrepancies also led to substantial misclassification into weight categories, with reliance on self-reported BMI underestimating the weight status of 20% of the sample. Conclusions Our findings suggest that similar to the general population, wheelchair users are prone to errors when reporting their height and weight and that these errors may exceed those noted in the general population