Collision-enhanced friction of a bouncing ball on a rough vibrating surface.

We describe experiments and simulations to investigate the dynamics of a ball bouncing on a rough vibrating surface. Directly measuring the impulse due to each bounce we find that the frictional interaction with the surface is strongly enhanced near to the side wall. The enhanced dissipation arises as a consequence of the coupling between the collision, rotation and surface friction. This dissipation, which for our experimental conditions was estimated to be up to three times larger than the more obvious inelastic collision, can result in an enhanced probability density near boundaries and particle-particle spatial correlations. Our findings imply that the effective particle collision properties cannot be considered independently of the surface's frictional properties.

Magnetic Levitation Stabilized by Streaming Fluid Flows.

We demonstrate that the ubiquitous laboratory magnetic stirrer provides a simple passive method of magnetic levitation, in which the so-called "flea" levitates indefinitely. We study the onset of levitation and quantify the flea's motion (a combination of vertical oscillation, spinning and "waggling"), finding excellent agreement with a mechanical analytical model. The waggling motion drives recirculating flow, producing a centripetal reaction force that stabilized the flea. Our findings have implications for the locomotion of artificial swimmers and the development of bidirectional microfluidic pumps, and they provide an alternative to sophisticated commercial levitators.

Instabilities in vertically vibrated fluid-grain systems.

When a bed of fluid-immersed fine grains is exposed to vertical vibration a wealth of phenomena may be observed. At low frequencies a horizontal bed geometry is generally unstable and the bed breaks spatial symmetry, acquiring a tilt. At the same time it undergoes asymmetric granular convection. Fine binary mixtures may separate completely into layers or patterns of stripes. The separated regions may exhibit instabilities in which they undergo wave-like motion or exhibit quasi-periodic oscillations. We briefly review these and a number of related behaviours, identifying the physical mechanisms behind each. Finally, we discuss the magneto-vibratory separation of binary mixtures which results from exposing each component to a different effective gravity and describe the influence of a background fluid on this process.

Enhancement of fibroblast growth factor (FGF) activity by an FGF-binding protein.

Fibroblast growth factor-binding protein (FGF-BP) 1 is a secreted protein that can bind fibroblast growth factors (FGFs) 1 and 2. These FGFs are typically stored on heparan sulfate proteoglycans in the extracellular matrix in an inactive form, and it has been proposed that FGF-BP1 functions as a chaperone molecule that can mobilize locally stored FGF and present the growth factor to its tyrosine kinase receptor. FGF-BP1 is up-regulated in squamous cell, colon, and breast cancers and can act as an angiogenic switch during malignant progression of epithelial cells. For the present studies, we focused on FGF-1 and -2 and investigated interactions with recombinant human FGF-BP1 protein as well as effects on signal transduction, cell proliferation, and angiogenesis. We show that recombinant FGF-BP1 specifically binds FGF-2 and that this binding is inhibited by FGF-1, heparan sulfate, and heparinoids. Furthermore, FGF-BP1 enhances FGF-1- and FGF-2-dependent proliferation of NIH-3T3 fibroblasts and FGF-2-induced extracellular signal-regulated kinase 2 phosphorylation. Finally, in the chicken chorioallantoic membrane angiogenesis assay, FGF-BP1 synergizes with exogenously added FGF-2. We conclude that FGF-BP1 binds directly to FGF-1 and FGF-2 and positively modulates the biological activities of these growth factors.

Survival-time distribution for inelastic collapse.

In a recent publication [Phys. Rev. Lett. 81, 1142 (1998)] it was argued that a randomly forced particle that collides inelastically with a boundary can undergo inelastic collapse and come to rest in a finite time. Here we discuss the survival probability for the inelastic collapse transition. It is found that the collapse-time distribution behaves asymptotically as a power law in time, and that the exponent governing this decay is nonuniversal. An approximate calculation of the collapse-time exponent confirms this behavior and shows how inelastic collapse can be viewed as a generalized persistence phenomenon.

"First-dose" response to mianserin: effects of age.

The effects of single 10 mg oral doses of the antidepressant mianserin on psychomotor performance, subjective sedation and supine and standing blood pressure were compared in ten young and nine elderly healthy volunteers. Immediate and residual sedation following this subtherapeutic dose was readily detected in both groups. In contrast to previous studies with benzodiazepines, the sedation effect was not accentuated in the older subjects. Subjective awareness of sedation was significant in the young but not, however, in the elderly. "First-dose" postural hypotension, presumably due to post-synaptic alpha-blockade also occurred in young subjects only. Caution may be needed on initial dosage of mianserin in young individuals who drive or undertake skilled tasks and in the elderly who may be unaware of psychomotor impairment. The reported alpha 2 receptor selectivity of mianserin might explain the lack of postural effects in the elderly, and might constitute a potentially useful characteristic in the development of new compounds.

Single dose pharmacokinetics and pharmacodynamics of oral loprazolam in the elderly.

The pharmacokinetics of the benzodiazepine hypnotic, loprazolam (1.0 mg orally), and the pharmacodynamic response to single oral doses (0.5 mg and 1.0 mg) have been compared in young and elderly healthy volunteers. No difference between the groups in peak plasma concentration (Cmax) or in the time to peak (tmax) was found, but the elimination half-life t1/2,z and area under the plasma concentration-time curve (AUC) were significantly greater in the elderly group. The immediate effects of loprazolam on all three performance tests used (postural sway, critical flicker fusion threshold (CFFT) and choice reaction time (CRT] and on subjective sedation tended to be more pronounced in the elderly subjects, though intersubject variability in response was high in both groups. The corresponding plasma concentrations did not differ significantly between the two groups. The higher (1.0 mg) dosage was associated with significant residual (11 h) impairment of standing steadiness in the elderly subjects. No other hangover effects were observed. The results are compatible with previous evidence of increased 'sensitivity' to benzodiazepines in the elderly and suggest that a lower (0.5 mg) starting dose of loprazolam would be appropriate for older recipients. Further investigation would be necessary to establish whether clinically relevant accumulation of loprazolam occurs in the elderly following repeated dosage.

Side-effect 'tolerance' in elderly long-term recipients of benzodiazepine hypnotics.

The outcome of long-term benzodiazepine hypnotic therapy has been investigated in a group of elderly patients in the community; 220 receiving nitrazepam and 33 flurazepam. The estimated duration of therapy was as long as 15 years in some cases. More than half were taking doses greater than 5 mg and 15 mg, respectively, the majority on a regular nightly basis in accordance with the instructions on containers. The plasma concentrations of nitrazepam and the active desalkyl metabolite of flurazepam correlated positively with weight-related dose. In the case of desalkyl-flurazepam, but not nitrazepam, the levels were substantially higher than those previously reported in young individuals. There was sustained patient satisfaction with the effectiveness of the hypnotics and, despite the high plasma levels, little subjective or objective evidence of unwanted sedation, confusion or unsteadiness. The findings of the survey suggest the development of both pharmacodynamic tolerance to the unwanted sedative effects of these drugs and a degree of dependence in long-term recipients.

Myotonic muscular dystrophy: abnormalities in fibroblast culture.

Skin fibroblasts in culture, derived from four unrelated patients with myotonic muscular dystrophy, contain abnormally large amounts of material with the staining characteristics of acid mucopolysaccharide. These cells also differ from normal cells in their pattern of growth at a high density in culture.

Susceptibility of human diploid fibroblast strains to transformation by SV40 virus.

A quantitative system has been developed for the study of transformation of human diploid fibroblasts in culture by two oncogenic viruses, SV40 and the E46 strain of adeno 7-SV40 "hybrid" virus. Seven of the eleven cell strains derived from human skin biopsies when infected with SV40 (10(9) tissue culture infective doses per milliliter) gave rise to transformed colonies with approximately the same frequency (0.03 percent). Two strains derived from patients with Fanconi's anemia, an autosomal recessive disease associated with a high incidence of chromosome abnormalities and spontaneous neoplasms, gave values more than ten times higher. Two strains from persons heterozygous for this gene were also considerably more susceptible to viral transformation.