Scaling behavior near jamming in random sequential adsorption.

For the random sequential adsorption model, we introduce the "availability" as a variable corresponding to the number of available locations in which an adsorbate can be accommodated. We investigate the relation of the availability to the coverage of the adsorbent surface over time. Power law scaling between the two is obtained both through numerical simulations and analytical techniques for both one- and two-dimensional random sequential adsorption, as well as in the case of competitive random sequential adsorption in one dimension.

Behavioral responsiveness in sleeping older adults.

The control of behavior by stimuli presented during sleep, and related effects on sleep and daytime sleepiness, were investigated in 17 older (age = 60-74 years) adults. Experimental subjects (N = 8) were trained while awake to terminate tone presentations by taking a deep breath. Tones were then presented following sleep onset for four consecutive nights with a mean intertone interval of 4 min. Control subjects (N = 9) slept in the laboratory but did not receive tones. The daytime sleepiness of both groups was assessed by recording latency to sleep onset in a morning and afternoon nap test. It was found that the experimental subjects responded reliably to the tones. Responding, however, was almost invariably accompanied by disruption of sleep and overall sleep structure was markedly altered. Surprisingly, the daytime sleepiness of experimental subjects was not reliably greater than that of control subjects.

Control of masseter muscle tension during sleep.

This study evaluated whether muscle tension could be controlled during sleep. Twelve volunteers were assigned to an experimental condition or to a no treatment control group. Experimental subjects were instructed to reduce the tension in their masseter (jaw) muscle when signalled with an auditory tone. These subjects demonstrated cue-controlled tension reductions during awake training sessions. Although both groups evidenced muscle tension increases in response to the tones presented during sleep, experimental subjects produced significantly smaller increases in response to tone stimuli than did control subjects. More importantly, experimental subjects sustained lower tonic levels of muscle tension throughout the sleep sessions than did control subjects. Sleep was moderately disrupted for subjects in both groups. However, experimental subjects evidenced the greatest tension reductions during those responses in which they shifted to a lighter stage of sleep rather than fully awakening. These data suggest that muscle tension can be moderated during sleep.

The effects of wheat germ agglutinin on the adipocyte insulin receptor.

Treatment of rat adipocytes with wheat germ agglutinin markedly enhances insulin binding by increasing the affinity of the insulin receptor. The structure of adipocyte receptor following wheat germ agglutinin treatment was studied by column chromatography and polyacrylamide gel electrophoresis to determine if aggregates of the insulin receptor are present. Solubilization of the receptor by Triton X-100 and passage of this material over Sepharose 6B revealed two insulin binding activities: a major peak which had a Strokes radius of 87 A and a minor peak with a Strokes radius of 47 A. Wheat germ agglutinin treatment produced an increase in the binding activity of both peaks, but their molecular weights did not change. In addition, 125I-labeled insulin was covalently attached to the adipocyte insulin binding sites by a cross-linking reagent. Column chromatography of the insulin-receptor complex again indicated the presence of two species with Strokes radii of 87 A and 47 A. Heterogeneity in these complexes was also demonstrated by polyacrylamide gel electrophoresis in the presence of Triton X-100. Ferguson plots indicated that the peak of radioactivity had a molecular radius of 60 A, a size found both in the presence and absence of wheat germ treatment of adipocytes. These findings suggest that the increase in receptor affinity produced by wheat germ agglutinin treatment is not caused by the formation of receptor clusters. Instead, it appears that a simple interaction between the plant lectin and the receptor is sufficient to induce the changes in the insulin binding properties of adipocytes.

Effects of wheat germ agglutinin on insulin binding and insulin sensitivity of fat cells.

The plant lectin (wheat germ agglutinin, WGA) produces several alterations in the ability of fat cells to bind and respond to insulin. Although WGA markedly stimulated glucose oxidation, it caused only a modest stimulation of glucose transport. WGA (0.25-20 micrograms/ml) increased the binding of insulin by adipocytes, apparently by increasing the binding affinity of the insulin receptor. With low WGA concentrations (0.25-2.5 micrograms/ml), the elevation in binding was accompanied by an increase in the sensitivity of the adipocytes to insulin stimulation of glucose transport. However, the sensitivity of these cells to vitamin K5 and H2O2 was not altered. With higher WGA concentrations (5-20 micrograms/ml), stimulation of the glucose transport system by insulin, vitamin K5, or H2O2 was markedly inhibited, an effect that is reversed by the addition of ovomucoid. These findings suggest that low WGA concentrations increase the affinity of the insulin receptor and the insulin sensitivity of the cells. At higher concentrations, the lectin appears to act at another site(s) to inhibit the activation of the transport system by insulin or other agents.