Mild-to-wild plastic transition is governed by athermal screw dislocation slip in bcc Nb.

Plastic deformation in crystals is mediated by the motion of line defects known as dislocations. For decades, dislocation activity has been treated as a homogeneous, smooth continuous process. However, it is now recognized that plasticity can be determined by long-range correlated and intermittent collective dislocation processes, known as avalanches. Here we demonstrate in body-centered cubic Nb how the long-range and scale-free dynamics at room temperature are progressively quenched out with decreasing temperature, eventually revealing intermittency with a characteristic length scale that approaches the Burgers vector itself. Plasticity is shown to be bimodal across the studied temperature regime, with conventional thermally-activated smooth plastic flow ('mild') coexisting with sporadic bursts ('wild') controlled by athermal screw dislocation activity, thereby violating the classical notion of temperature-dependent screw dislocation motion at low temperatures. An abrupt increase of the athermal avalanche component is identified at the critical temperature of the material. Our results indicate that plasticity at any scale can be understood in terms of the coexistence of these mild and wild modes of deformation, which could help design better alloys by suppressing one of the two modes in desired temperature windows.

Actions of MDMA at glutamatergic neuromuscular junctions.

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") compels mammalian serotonergic neurons to release serotonin (5-HT). In this study, MDMA altered synaptic transmission presynaptically by enhancing quantal release in two model glutamatergic synapses-the neuromuscular junction (NMJ) of the crayfish opener muscle, which is enhanced by exogenous 5-HT application, and the NMJ of a larval body wall muscle in Drosophila melanogaster, which is insensitive to exogenous 5-HT application. At the crayfish NMJ, MDMA mimicked the actions of 5-HT but only at a substantially higher concentration. At the Drosophila NMJ, MDMA altered synaptic transmission but not through a 5-HT receptor. Using simple invertebrate preparations, we have demonstrated an additional non-serotonergic mechanism of MDMA activity that has not yet been addressed in vertebrate systems and that may play an important role in understanding the mechanism of action for a commonly abused drug.

5-HT offsets homeostasis of synaptic transmission during short-term facilitation.

In this study, we approach the topic of vesicle recruitment and recycling by perturbing neurotransmission at the crayfish neuromuscular junction with altered electrical activity and the presence of the neuromodulator serotonin (5-HT). After induction of short-term facilitation (STF) with stimulus pulse trains (40 Hz, 20 pulses), the amount of synaptic transmission can be maintained at a relatively constant level, producing a plateau in the amplitude of the excitatory postsynaptic potentials (EPSPs) throughout the remaining stimuli within a train of a few hundred milliseconds. With an increase in the frequency of the stimuli within a train (60 Hz, 20 pulses), an altered plateau of larger EPSP amplitudes occurs. This suggests that differential rates of vesicle recruitment can be rapidly reached and maintained. Exposure of nerve terminals to 5-HT further enhances the EPSP amplitudes to yet a higher plateau level. The effect of 5-HT is more pronounced for 40-Hz pulse trains than for 60-Hz trains. This suggests that 5-HT can recruit vesicles into the readily releasable pool (RRP) and that the recruitment is limited at higher stimulation frequencies. The attainment of a larger amplitude in the plateaus of the EPSPs at 60 Hz compared with 40 Hz also suggests that the rapid induction of STF enhances the entry of vesicles into the RRP. By direct quantal counts, mean quantal content increases linearly during STF, and 5-HT offsets the linear release. We propose that 5-HT and electrically induced recruitment of vesicles from a reserve pool to the RRP may share similar recruitment mechanisms.

Understanding differences between high and low childhood accident rate areas: the importance of qualitative data.

BACKGROUND: The research discussed in the paper was undertaken for a District Health Authority to aid the development of appropriate policies to achieve the Health of the nation strategic target for reducing the death rate from accidents amongst children under 15. There has been a great deal of quantitative and epidemiological research into childhood accidents which has demonstrated a clear social class gradient in childhood accidents, fatalities and injuries. Less research has been undertaken into the possible reasons for the 'social patterning' of accidents and other aspects of health. Recent sociological research on childhood accidents has adopted a more qualitative approach and studied childhood safety within a family and community context. This approach has been used in the Huddersfield study on parental perspectives on childhood safety. METHODS: In-depth interviews were held with a sample of parents from a high and a low childhood accident rate area. RESULTS: The two focus areas reveal contrasting social profiles. There were significant differences on a number of aspects of parental perceptions on safety and beliefs about accidents, in the two areas. Analysis of accident events revealed that all the families in the high childhood accident rate area sample had children who had had an accident in the past which required hospital treatment. A high proportion of their children had experienced 'near misses'. In contrast, half the families in the low childhood accident rate area had children who had experienced an accident in the past and a much smaller proportion had experienced 'near misses'. All the parents in the sample from both areas developed rules, routines and practices to keep their children safe. The study suggests that there are social class differences in the effective use of these safety rules. CONCLUSION: Qualitatively orientated sociological research into parental perspectives on childhood safety contributes to an understanding of the reasons for the social patterning of childhood accidents. Such information should be of help to professionals in their prevention and safety promotion work.

The effect of daytime running lights on crashes between two vehicles in Saskatchewan: a study of a government fleet.

Keeping vehicle lights on to increase vehicle conspicuity during daytime hours has been found to reduce crashes in Scandinavia and the United States. Crashes of vehicles with and without daytime running lights owned by the Central Vehicle Agency of the Province of Saskatchewan were compared to a random selection of crashes drawn from provincial crash files involving vehicles without daytime running lights for the years 1982 through 1989. Daytime two-vehicle crashes involving vehicles approaching from the front or side were reduced by about 28% for the daytime running-light equipped vehicles. A 28% reduction in daytime running-light relevant daytime two-vehicle crashes corresponds to a 15% reduction in all daytime two-vehicle crashes.

The medical and economic impact of closed cervical spine dislocations.

The current study examined the medical and economic impact of various treatment modalities of unstable cervical spine dislocations. Thirty-five patients with dislocations of the cervical spine were reviewed retrospectively from two large university hospitals. There were 23 unilateral and 12 bilateral facet dislocations. Fourteen patients were treated nonoperatively and 21 patients were treated with early surgery. Nine of the 14 patients treated nonoperatively redisplaced their dislocations while in an orthosis and required late surgery. Analysis of variance shows that it is the amount of injury (unilateral versus bilateral) that results in statistically significant difference in the injury severity score, Glasgow coma scale, trauma motor index, and the number of complications. Of the treatment groups (operative versus nonoperative), the operative group showed a statistically significant difference in the length of hospital stay. Also noted in the operative group was less traction time, earlier erect physical therapy, an average financial savings of $18,407.00, and equal morbidity or mortality to the nonoperative treatment group. Based on this limited experience, it would appear that "diagnosis related groups" are not capable of supporting traumatic spinal care and, if adopted by other states and third party payers, the concept of trauma and/or spinal cord injury centers may be in jeopardy.