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Biomedical subjects

Gary A Williams

Publications and source records attributed to Gary A Williams.

8 recordsLinked to original sources

Properties of luminescence from laser-created bubbles in pressurized water.

The properties of the luminescence pulse from collapsing laser-created bubbles in pressurized water are studied for pressures between 0.25 and 15 bars. The duration of the light pulse is found to be linear in the maximum bubble size, but for a given bubble size it increases with the applied pressure p as p0.38. The number of photons emitted increases quadratically with the bubble size, and increases approximately linearly with pressure. The spectrum of the luminescence is blackbody in form, with a temperature that increases somewhat with pressure, from 8100 K at 1 bar to 9400 K at 10 bars. At higher pressures the blackbody temperature drops, but this is primarily due to the rapid onset above 10 bars of a fission instability, where the bubbles split into two just before the collapse point.

Journal Article↗

Luminescence spectra of laser-induced cavitation bubbles near rigid boundaries.

The luminescence spectra of laser-induced cavitation bubbles near rigid boundaries are measured for various relative distances between the bubble and the boundaries. We find that the luminescence spectra of bubbles collapsing near a single boundary consist only of a blackbody continuum. Luminescence from bubbles collapsing between two parallel rigid boundaries contains O H- emission bands similar to those found in multibubble sonoluminescence. In both cases, the bubble interior temperature deduced from blackbody fits decreases with the distance between bubble and boundary. The shape instabilities of the collapse near a boundary and the consequent presence of high-velocity jets inside the bubble at its minimum volume are discussed in connection with the generation of the O H- radicals.

Journal Article↗

Photoreceptors and photopigments in a subterranean rodent, the pocket gopher (Thomomys bottae).

Pocket gophers (Thomomys bottae) are rodents that spend much of their lives in near-lightless subterranean burrows. The visual adaptations associated with this extreme environment were investigated by making anatomical observations of retinal organization and by recording retinal responses to photic stimulation. The size of the eye is within the normal range for rodents, the lens transmits light well down into the ultraviolet, and the retina conforms to the normal mammalian plan. Electroretinogram recording revealed the presence of three types of photopigments, a rod pigment with a spectral peak of about 495 nm and two types of cone pigment with respective peak values of about 367 nm (UV) and 505 nm (medium-wavelength sensitive). Both in terms of responsivity to lights varying in temporal frequency and in response recovery following intense light adaptation, the cone responses of the pocket gopher are similar to those of other rodents. Labeling experiments indicate an abundance of cones that reach densities in excess of 30,000 mm-2. Cones containing UV opsin are found throughout the retina, but those containing medium-wavelength sensitive opsin are mostly restricted to the dorsal retina where coexpression of the two photopigments is apparently the rule. Rod densities are lower than those typical for nocturnal mammals.

Adaptation, Ocular↗

Dynamics of normal and superfluid fogs using diffusing-wave spectroscopy.

The dynamics of normal and superfluid fogs are studied using the technique of diffusing-wave spectroscopy. For a water fog generated with a 1.75 MHz piezoelectric driver below the liquid surface, the 7 microm diameter droplets are found to have diffusive dynamics for correlation times long compared to the viscous time. For a fog of 10 microm diameter superfluid helium droplets in helium vapor at 1.5 K the motion appears to be ballistic for correlation times short compared to the viscous time. The velocity correlations between the helium droplets are found to depend on the initial velocity with which the droplets are injected from the helium surface into the fog.

Journal Article↗

Vortex fluctuations in the critical Casimir effect of superfluid and superconducting films.

Vortex-loop renormalization techniques are used to calculate the magnitude of the critical Casimir forces in superfluid films. The force is found to become appreciable when the size of the thermal vortex loops is comparable to the film thickness, and the results for T T(c). When applied to a high-T(c) superconducting film connected to a bulk sample, the Casimir force causes a voltage difference to appear between the film and the bulk, and estimates show that this may be readily measurable.

Journal Article↗

Influence of cone pigment coexpression on spectral sensitivity and color vision in the mouse.

The mouse retina contains both middle-wavelength-sensitive (M) and ultraviolet-sensitive (UV) photopigments that are coexpressed in cones. To examine some potential visual consequences of cone pigment coexpression, spectral sensitivity functions were measured in mice (Mus musculus) using both the flicker electroretinogram (ERG) and behavioral discrimination tests. Discrimination tests were also employed to search for the presence of color vision in the mouse. Spectral sensitivity functions for the mouse obtained from ERG measurements and from psychophysical tests each reveal contributions from two classes of cone having peak sensitivities (lambda(max)) of approximately 360 and 509-512 nm. The relative contributions of the two pigment types to spectral sensitivity differ significantly in the two types of measurements with a relationship reversed from that often seen in mammals. Mice were capable of discriminating between some pairs of spectral stimuli under test conditions where luminance-related cues were irrelevant. Since mice can make dichromatic color discriminations, their visual systems must be able to exploit differences in the spectral absorption properties among the cones. Complete selective segregation of opsins into individual photoreceptors is apparently not a prerequisite for color vision.

Animals↗

Change the way you persuade.

You call a meeting to try to convince your boss that your company needs to make an important move. Your argument is impassioned, your logic unassailable, your data bulletproof. Two weeks later, though, you learn that your brilliant proposal has been tabled. What went wrong? It's likely the proposal wasn't appropriately geared toward your boss's decision-making style, say consultants Gary Williams and Robert Miller. Over the course of several years' research, the authors have found that executives have a default style of decision making developed early in their careers. That style is reinforced through repeated successes or changed after several failures. Typically, the authors say, executives fall into one of five categories of decision-making styles: Charismatics are intrigued by new ideas, but experience has taught them to make decisions based on balanced information, not just on emotions. Thinkers are risk-averse and need as much data as possible before coming to decisions. Skeptics are suspicious of data that don't fit their worldview and thus make decisions based on their gut feelings. Followers make decisions based on how other trusted executives, or they themselves, have made similar decisions in the past. And controllers focus on the facts and analytics of decisions because of their own fears and uncertainties. But most business presentations aren't designed to acknowledge these different styles--to their detriment. In this article, the authors describe the various subtleties of the five decision-making styles and how best to persuade executives from each group. Knowing executives' preferences for hearing or seeing certain types of information at specific stages in their decision-making process can substantially improve your ability to tip the outcome in your favor, the authors conclude.

Commerce↗

Rod and cone function in coneless mice.

Transgenic coneless mice were initially developed to study retinal function in the absence of cones. In coneless mice created by expressing an attenuated diphtheria toxin under the control of flanking sequences from the human L-cone opsin gene, a small number of cones (3-5% of the normal complement) survive in a retina that otherwise appears structurally quite normal. These cones predominantly ( approximately 87% of the total) contain UV-sensitive photopigment. ERG recordings, photoreceptor labeling, and behavioral measurements were conducted on coneless and wild-type mice to better understand how the nature of this alteration in receptor complement impacts vision. Signals from the small residual population of UV cones are readily detected in the flicker ERG where they yield signal amplitudes at saturation that are roughly proportional to the number of surviving cones. Behavioral measurements show that rod-based vision in coneless mice does not differ significantly from that of wild-type mice, nor does their rod system show any evidence of age-related deterioration. Coneless mice are able to make accurate rod-based visual discriminations at light levels well in excess of those required to reach cone threshold in wild-type mice.

Animals↗