Crossover Behavior in Burst Avalanches of Fiber Bundles: Signature of Imminent Failure

Bundles of many fibers, with statistically distributed thresholds for breakdown of individual fibers and where the load carried by a bursting fiber is equally distributed among the surviving members, are considered. During the breakdown process, avalanches consisting of simultaneous rupture of several fibers occur, with a distribution D(Delta) of the magnitude Delta of such avalanches. We show that there is, for certain threshold distributions, a crossover behavior of D(Delta) between two power laws D(Delta) proportional to Delta^(-xi), with xi=3/2 or xi=5/2. The latter is known to be the generic behavior, and we give the condition for which the D(Delta) proportional to Delta^(-3/2) behavior is seen. This crossover is a signal of imminent catastrophic failure in the fiber bundle. We find the same crossover behavior in the fuse model.Comment: 4 pages, 4 figure

Structural disorder in (Bi,M)2(Fe,Mn,Bi)2O6+x (M = Na or K) pyrochlores seen from reverse Monte Carlo analysis of neutron total scattering

The average structures of the polycrystalline pyrochlores (Na0.60Bi1.40)(Fe1.06Mn0.17Bi0.77)O6.87 and (K0.24Bi1.51)(Fe1.07Mn0.15Bi0.78)O6.86 can be refined through Rietveld refinement against Bragg scattering data using cubic space group Fd3 ̅m, with off-centred 96h and 32e positions describing the A2Oʹ network. Investigation of their local structures through neutron total scattering confirms the extent of disorder within these materials, and furthermore shows significant deviation from the average structure, which is not accounted for through analysis of Bragg data alone. Reverse Monte Carlo (RMC) analysis with a 6 × 6 × 6 supercell was used to model accurately this local disorder, revealing ellipsoidal distributions for A-site potassium, distinctly different to the hollow torus-shaped distributions for the sodium and bismuth cations. It is shown through bond valence sum analysis that whilst these atomic displacements allow for the steric preferences of Bi3+, they are also necessary to satisfy the valence of both the bismuth and the alkali metals on the A sites. Analysis of the final RMC configuration showed the BO6 octahedra for the separate B site metals to be more regular (O–B–O ≈ 90°) than those in the Rietveld model (O–B–O ≈ 85/95°) which describes an average of the three different environments

Species-specific calcite production reveals Coccolithus pelagicus as the key calcifier in the Arctic Ocean

Through the production and export of their calcite coccoliths, coccolithophores form a key component of the global carbon cycle. Despite this key role, very little is known about the biogeochemical role of different coccolithophore species in terms of calcite production, and how these species will respond to future climate change and ocean acidification. Here, we present the first study to estimate species-specific calcite production, from samples collected in the Arctic Ocean and subarctic Iceland Basin in June 2012. We show that although the coccolithophorid Coccolithus pelagicus comprised only a small fraction of the total community in terms of abundance (2%), our estimates indicate that it was the major calcite producer in the Arctic Ocean and Iceland Basin (57% of total calcite production). In contrast, Emiliania huxleyi formed 27% of the total abundance and was responsible for only 20% of the calcite production. That C. pelagicus was able to dominate calcite production was due to its relatively high cellular calcite content compared with the other species present. Our results demonstrate, for the first time, the importance of investigating the complete coccolithophore community when considering pelagic calcite production, as relatively rare but heavily calcified species such as C. pelagicus can be the key calcite producers in mixed communities. Therefore, the response of C. pelagicus to ocean acidification and climate change has the potential to have a major impact on carbon cycling within the North Atlantic and Arctic Ocean

Designing prenatal care for low-income, black patients in urban settings using human centered design

Objective: Black and low-income pregnant patients face significant inequities in health care access and outcomes in the United States. Yet, these patients’ voices have been largely absent from designing improved prenatal care models. Our objective was to use Human Centered Design to examine patients’ and health care workers’ experiences with prenatal care delivery in a largely low-income, Black population, to inform future care innovations to improve access, quality, and outcomes. Study Design: Using snowball sampling, we conducted Human Centered Design-informed interviews with low-income, Black patients and health care workers in a large, urban setting. Interview questions addressed the first two Human Centered Design phases: 1) observation: understanding the problem from the end-user’s perspective, and 2) ideation: generating novel potential solutions. We assessed these questions for the three key components of prenatal care: medical care, anticipatory guidance, and psychosocial support. Results: Nineteen patients and 19 health care workers were interviewed. All patients were Black, and the majority had public insurance (17/19, 89.5%). Health care workers included doctors, midwives, breastfeeding counselors, doulas, and social workers. Participants affirmed the three goals of prenatal care. Participants reported failures of current prenatal care delivery and potential solutions for each of the three goals (medical care, anticipatory guidance, and psychosocial support) and two overarching categories: maternity care professionals and care structure. Participants reported in an ideal model, patients would have strong relationships with their maternity care professional who would be at the center of all prenatal care services. Additionally, care would be tailored to individual patients and use care navigators, flexible models, and colocation of services, to reduce barriers. Conclusion: Current prenatal care delivery fails to meet low-income, Black patients’ needs. Ideal prenatal care delivery includes more comprehensive, integrated services tailored to patients’ medical needs and preferences

Iatrogenic Spinal Cord Injury Resulting From Cervical Spine Surgery.

STUDY DESIGN: Retrospective cohort study of prospectively collected data. OBJECTIVE: To examine the incidence of iatrogenic spinal cord injury following elective cervical spine surgery. METHODS: A retrospective multicenter case series study involving 21 high-volume surgical centers from the AOSpine North America Clinical Research Network was conducted. Medical records for 17 625 patients who received cervical spine surgery (levels from C2 to C7) between January 1, 2005, and December 31, 2011, were reviewed to identify occurrence of iatrogenic spinal cord injury. RESULTS: In total, 3 cases of iatrogenic spinal cord injury following cervical spine surgery were identified. Institutional incidence rates ranged from 0.0% to 0.24%. Of the 3 patients with quadriplegia, one underwent anterior-only surgery with 2-level cervical corpectomy, one underwent anterior surgery with corpectomy in addition to posterior surgery, and one underwent posterior decompression and fusion surgery alone. One patient had complete neurologic recovery, one partially recovered, and one did not recover motor function. CONCLUSION: Iatrogenic spinal cord injury following cervical spine surgery is a rare and devastating adverse event. No standard protocol exists that can guarantee prevention of this complication, and there is a lack of consensus regarding evaluation and treatment when it does occur. Emergent imaging with magnetic resonance imaging or computed tomography myelography to evaluate for compressive etiology or malpositioned instrumentation and avoidance of hypotension should be performed in cases of intraoperative and postoperative spinal cord injury