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.

Recent studies have recognized that plasticity in metals can be controlled by dislocation avalanches. Here the authors examine temperature-dependent microplasticity in bcc Nb and reveal the dominance of athermal screw dislocation activity during intermittent slip.

Circulating extracellular vesicles from patients with acute chest syndrome disrupt adherens junctions between endothelial cells

BACKGROUND

Small cell-derived extracellular vesicles (EVs) can affect endothelial function. We previously found that patients with sickle cell disease (SCD) have greater numbers of circulating EVs than subjects without the disease, and the EVs differentially disrupt endothelial integrity in vitro. Because endothelial disruption is a critical component of acute chest syndrome (ACS), we hypothesized that EVs isolated during ACS would induce greater endothelial damage than those isolated at baseline.

METHODS

Nine pediatric subjects had plasma isolated at baseline and during ACS from which EVs were isolated. Cultured microvascular endothelial cells were treated with EVs and then studied by immunofluorescence microscopy to localize VE-cadherin and F-actin.

RESULTS

The EVs had a diameter of 95 nm. They contained CD63 and flotillin-1, which were increased in SCD patients (5-13-fold compared to control) and further increased between baseline and ACS (24-57%). The EVs contained hemoglobin, glycophorin A, and ferritin. Treatment with baseline EVs caused modest separation of endothelial cells, while ACS EVs caused substantial disruptions of the endothelial cell monolayers. EVs from subjects with ACS also caused a 50% decrease in protein levels of VE-cadherin.

CONCLUSIONS

These results suggest that circulating EVs can modulate endothelial integrity contributing to the development of ACS in SCD patients by altering cadherin-containing intercellular junctions.

IMPACT

Sickle cell disease patients have circulating extracellular vesicles (EVs) that modulate endothelial integrity by altering cadherin-containing intercellular junctions. Disruption is more severe by EVs obtained during acute chest syndrome (ACS). These results expand our knowledge of the pathophysiology of acute chest syndrome and the vasculopathies of sickle cell disease.

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 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.