Performing horizontal to vertical ratio testing in stiff soils in and around Grand Teton National Park

Horizontal to vertical spectral ratio (HVSR) testing was completed at two cross sections in and around GTNP. The HVSR testing produced reliable estimates of the fundamental frequencies for many of the sites tested. The goal of the testing was to determine a depth of soil above competent bedrock. However the fundamental frequencies recorded yielded predicted depths that are much shallower than expected. Also the predicted depths did not increase at greater distance from the Teton Range, which would be expected at these sites. Based on these predictions the authors do not believe the frequencies recorded are a good indication of the depth of the soil above bedrock but instead it is believed that the depths correspond with a layer of softer topsoil/overburden above a stiffer gravel layer. Although the goal of measuring the depth of soil above bedrock was not met, HVSR produced results that may be useful to others for determination of a fundamental frequency of resonance at our testing locations. Featured photo by Anna Cressman, taken from the AMK Ranch photo collection. https://flic.kr/p/2jjWZGT

Performance Analysis of Modulation Response of a Designed 1550 nm Oxide Confined Vertical Cavity Surface Emitting Laser

This paper aims to present the impact of using oxidized layer and the effect of oxide aperture size on VCSEL’s modulation performance. After the introduction of oxidized layer, the characteristics of VCSEL have improved immensely, especially in modulation performance. The peak material gain of Al0.06Ga0.24In0.70As/InP MQW VCSEL found from the MATLAB simulation tools has been utilized for investigating the modulation characteristics of the laser model. The optical output power of 27.23 dBm is found at 2.5 mA of current injection. Later, by varying the injection current up to 2.5 mA a maximum frequency of resonance of 10.75 GHz and the equivalent -3dB cut off frequency of 11.85 GHz are achieved. It is seen that with the reduction of oxide aperture size and increase of injection current, the frequency of resonance in addition to the -3dB cut off frequency of the laser increases. The use of oxidized layer and impact of aperture size effect on VCSEL’s -3dB cut off frequency.

A new elastic model for ground coupling of geophones with spikes

Ground coupling are terms that describe the transfer from seismic ground motion to the motion of a geophone. In previous models, ground coupling was mainly considered as a disk lying on top of a half-space, not considering the fact that in current practice geophones are spiked and are buried for optimal response. In this paper we introduce a new model that captures the spike added to the geophone and models the effect of geophone burial. The geophone is modeled as a rigid, movable cylinder embedded in a half-space near or at the surface. The coupling problem is then tackled by a scattering approach using the elastic form of reciprocity; we consider the vertical component only. The main feature in the coupling function is a resonance whose location and shape depend on the different parameters of the geophone and the soil. In accordance with previous models, adding mass reduces the frequency of resonance. However, we show that pure mass loading assumption is too restrictive for standard geophones. Our new model shows that increasing the spike radius and length decreases the frequency of resonance and the resonance is more peaked. Furthermore, burying the geophone decreases the frequency of resonance, but when one takes into account that the soil at depth is more compact, then the behavior is as observed in practice — namely, an increase in frequency of resonance. As for the properties of the soil, the shear-wave velocity has the largest effect; when increased, it shifts the frequency of resonance to the high-frequency end as desired.

Loss of Visual Constancy of a Fixated Target Induced by Rapid Movement of the Head

The possibility that various types of conjugate eye movements are not merely a means of efficient perception but also determine the related visual effects is tested by imposing rapid (saccadic) movements upon the (slow) compensatory mechanism. 10 subjects were asked to shake and nod the head, at separate times, with increasing speed while fixating a stationary target. As the head reaches a frequency of resonance, at around 5 Hz, the fixated target appears to be jumping counter-head-wise.