Critical collapse of collisionless matter - a numerical investigation

In recent years the threshold of black hole formation in spherically symmetric gravitational collapse has been studied for a variety of matter models. In this paper the corresponding issue is investigated for a matter model significantly different from those considered so far in this context. We study the transition from dispersion to black hole formation in the collapse of collisionless matter when the initial data is scaled. This is done by means of a numerical code similar to those commonly used in plasma physics. The result is that for the initial data for which the solutions were computed, most of the matter falls into the black hole whenever a black hole is formed. This results in a discontinuity in the mass of the black hole at the onset of black hole formation.Comment: 22 pages, LaTeX, 7 figures (ps-files, automatically included using psfig

Can community care workers deliver a falls prevention exercise program? A feasibility study

Background: Almost half of older people receiving community care fall each year and this rate has not improved in the last decade. Falls prevention programs targeted at this group are uncommon, and expensively delivered by university trained allied health professionals. Purpose: To investigate the feasibility of community care workers delivering a falls prevention exercise program to older clients, at low or medium risk of falling, as part of an existing service provision. Patients and methods: Community care workers from 10 community care organizations participated in the training for, and delivery to their clients of, an 8-week evidence-based falls prevention exercise program. Community care workers included assessment staff (responsible for identifying the need for community care services through completing an assessment) and support workers (responsible for providing support in the home). Clients were surveyed anonymously at the completion of the intervention and workers participated in a semi-structured interview. Results: Twenty-five community care workers participated in the study. The falls prevention program was delivered to 29 clients, with an average age of 82.7 (SD: 8.72) years and consisting of 65.5% female. The intervention was delivered safely with no adverse events recorded, and the eligibility and assessment tools were completed by the majority of community care workers (93.1%). Assessment staff found it difficult to find time to deliver the intervention. Support workers were able to complete the intervention within their current service delivery period, with the initial assessment taking a small amount of additional time. Support workers reported enjoying the additional responsibility afforded by delivering the falls prevention program and seeing changes in their clients. The majority of clients (82%) reported enjoying the exercises, with 59% reporting that they felt it made a positive change in their health. Cl ients completed the exercises on average 4.8 (SD: 2.2) days per week. Conclusion: Community care workers who have completed appropriate training are able to deliver a falls prevention exercise program to their clients as part of their current services. Further research is required to determine whether the program reduces the rate of falls for community care clients and whether integration of a falls prevention program into an existing service is cost-effective

Synthesis and optical properties of ordered-vacancy perovskite cesium bismuth halide nanocrystals

Perovskite-phase cesium bismuth halide (Cs3Bi2X9; X = Cl, Br, I) nanocrystals were synthesized using a hot-injection approach. These nanocrystals adopted ordered-vacancy perovskite crystal structures and demonstrated composition-tunable optical properties. Growth occurred by initial formation of Bi0 seeds, and morphology was controlled by precursor and seed concentration. The Cs3Bi2I9 nanocrystals demonstrated excellent stability under ambient conditions for several months. Contrary to previous reports, we find that photoluminescence originates from the precursor material as opposed to the Cs3Bi2X9 nanocrystals

A talin mutant that impairs talin-integrin binding in platelets decelerates αIIbβ3 activation without pathological bleeding

Tight regulation of integrin affinity is critical for hemostasis. A final step of integrin activation is talin binding to 2 sites within the integrin β cytoplasmic domain. Binding of talin to a membrane-distal NPxY sequence facilitates a second, weaker interaction of talin with an integrin membrane-proximal region (MPR) that is critical for integrin activation. To test the functional significance of these distinct interactions on platelet function in vivo, we generated knock-in mice expressing talin1 mutants with impaired capacity to interact with the β3 integrin MPR (L325R) or NPLY sequence (W359A). Both talin1(L325R) and talin1(W359A) mice were protected from experimental thrombosis. Talin1(L325R) mice, but not talin(W359A) mice, exhibited a severe bleeding phenotype. Activation of αIIbβ3 was completely blocked in talin1(L325R) platelets, whereas activation was reduced by approximately 50% in talin1(W359A) platelets. Quantitative biochemical measurements detected talin1(W359A) binding to β3 integrin, albeit with a 2.9-fold lower affinity than wild-type talin1. The rate of αIIbβ3 activation was slower in talin1(W359A) platelets, which consequently delayed aggregation under static conditions and reduced thrombus formation under physiological flow conditions. Together our data indicate that reduction of talin-β3 integrin binding affinity results in decelerated αIIbβ3 integrin activation and protection from arterial thrombosis without pathological bleeding