A line-imaging velocity interferometer has been implemented at the OMEGA laser facility of the Laboratory for Laser Energetics, University of Rochester. This instrument is the primary diagnostic for a variety of experiments involving laser-driven shock wave propagation, including high pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh-Taylor experiments, and shock timing experiments for inertial confinement fusion research. Using a laser probe beam to illuminate a target the instrument measures shock breakout times and Doppler shifts in the reflected light. Velocities of interfaces, free surfaces and of shock fronts traveling through transparent media can be measured for velocities ranging from 0.1 to greater than 50 km/s with accuracies ∼ 1% over most of this range. Quantitative measurements of the optical reflectance of ionizing shock fronts can also be obtained simultaneous with the velocity measurements.

The present analysis provides Tb(0.27−0.30)Dy(0.73−0.70)Fe(1.9−2.0) magnetization and magnetostriction states during applied magnetic field and stress processes by minimizing the total magnetic free energy in the presence of a parameter selected inverse exponential magnetic free energy distribution. A comparison between experimental and model results shows that the model provides a qualitatively accurate description of the magnetostriction and magnetization in Tb(0.27−0.30)Dy(0.73−0.70)Fe(1.9−2.0) during applied magnetic field processes for a range of constant uniaxial applied stresses. Therefore, the model appears to be a useful tool for the analysis of Tb(0.27−0.30)Dy(0.73−0.70)Fe(1.9−2.0) applications with constant stress or strain dependent stress states. Furthermore, the good qualitative agreement between model and experiment supports the contention that the magnetostriction and magnetization response of Tb(0.27−0.30)Dy(0.73−0.70)Fe(1.9−2.0) is influenced by a defect induced defocusing of local magnetization direction about the average magnetization direction.

The extent to which motoneuron pool excitability, as measured by the Hoffmann reflex (H-reflex), is affected by an acute bout of whole-body vibration (WBV) was recorded in 19 college-aged subjects (8 male and 11 female; mean age 19 +/- 1 years) after tibial nerve stimulation. H/M recruitment curves were mapped for the soleus muscle by increasing stimulus intensity in 0.2- to 1.0-volt increments with 10-second rest intervals between stimuli, until the maximal M-wave and H-reflex were obtained. After determination of Hmax and Mmax, the intensity necessary to generate an H-reflex approximately 30% of Mmax (mean 31.5% +/- 4.1%) was determined and used for all subsequent measurements. Fatigue was then induced by 1 minute of WBV at 40 Hz and low amplitude (2-4 mm). Successive measurements of the H-reflex were recorded at the test intensity every 30 seconds for 30 minutes post fatigue. All subjects displayed a significant suppression of the H-reflex during the first minute post-WBV; however, four distinct recovery patterns were observed among the participants (alpha = 0.50). There were no significant differences between genders across time (P = 0.401). The differences observed in this study cannot be explained by level or type training. One plausible interpretation of these data is that the multiple patterns of recovery may display variation of muscle fiber content among subjects. Future investigation should consider factors such as training specificity and muscle fiber type that might contribute to the differing H-reflex response, and the effect of WBV on specific performance measures should be interpreted with the understanding that there may be considerable variability among individuals. Recovery times and sample size should be adjusted accordingly.

Extracellular pH markedly influences the ability of yeast cells to discriminate between K+ and Na+, with K+ favored to a greater degree at low pH. Studies of the kinetics of uptake of individual alkali metal cations by fermenting yeast indicate three zones relative to pH. Between pH 6 and 8, H + has no effect. Below pH 4, H + competitively inhibits the transport of each cation. Between pH 4 and 6, H+ acts kinetically as a predominantly non-competitive inhibitor. Both effects can be reversed by increasing the concentrations of cations. However, the concentrations required to reverse the competitive effect are considerably lower than those required to reverse the apparently non-competitive effect. It is suggested that H+ and the alkali metal cations can combine with two sites, a transport or carrier site, and a second, non-transporting site that influences the maximal rate of transport. Because the non-competitive inhibitory effect of H + is considerably greater on the other cations than on K + , the discrimination in favor of K+ is increased severalfold at low pH, beyond that predicted on the basis of the relative affinities for the transport site.The yeast cell possesses a transport system by means of which monovalent cations can be absorbed in large amounts. This transport system requires the presence of an utilizable substrate and, in well starved cells, the cation absorbed is balanced by the excretion of an equivalent amount of hydrogen ion whose source is the metabolism of the cell (3, 9). Kinetically, cation uptake appears to follow a saturation curve that can be adequately described by the Michaelis-Menten equation (5,11). If pairs of ions of the alkali metal series are present, each interferes in a competitive manner with the uptake of the other (5).The uptake of the alkali metal cations is markedly influenced by pH. As the pH is reduced the net rate of potassium uptake not only decreases but also may even become negative at pH levels below 2. Similar effects of pH on the net uptake of other cations have been reported (4). The mechanism by which

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