Critical Hysteresis from Random Anisotropy

Critical hysteresis in ferromagnets is investigated through a $N$-component spin model with random anisotropies, more prevalent experimentally than the random fields used in most theoretical studies. Metastability, and the tensorial nature of anisotropy, dictate its physics. Generically, random field Ising criticality occurs, but other universality classes exist. In particular, proximity to $\mathcal{O}(N)$ criticality may explain the discrepancy between experiment and earlier theories. The uniaxial anisotropy constant, which can be controlled in magnetostrictive materials by an applied stress, emerges as a natural tuning parameter.Comment: four pages, revtex4; minor corrections in the text and typos corrected (published version

Failure due to fatigue in fiber bundles and solids

We consider first a homogeneous fiber bundle model where all the fibers have got the same stress threshold beyond which all fail simultaneously in absence of noise. At finite noise, the bundle acquires a fatigue behavior due to the noise-induced failure probability at any stress. We solve this dynamics of failure analytically and show that the average failure time of the bundle decreases exponentially as the stress increases. We also determine the avalanche size distribution during such failure and find a power law decay. We compare this fatigue behavior with that obtained phenomenologically for the nucleation of Griffith cracks. Next we study numerically the fatigue behavior of random fiber bundles having simple distributions of individual fiber strengths, at stress less than the bundle's strength (beyond which it fails instantly). The average failure time is again seen to decrease exponentially as the stress increases and the avalanche size distribution shows similar power law decay. These results are also in broad agreement with experimental observations on fatigue in solids. We believe, these observations regarding the failure time are useful for quantum breakdown phenomena in disordered systems.Comment: 13 pages, 4 figures, figures added and the text is revise

Prevalência e incidência da hepatite C em pacientes submetidos a transplante renal

OBJECTIVE: To detect the prevalence and the seroconversion of the anti-HCV in renal transplants, while evaluating the presence of this antibody at the time of thetransplant, and during a 1-year follow-up, as well as the possibility of transmitting the disease to the recipient of the contaminated organ.PATIENTS AND METHODS: We investigated the prevalence of anti-HCV infection in 48 kidney transplant recipients, and also in their respective donors. Serumspecimens were collected from the organ recipients right before kidney transplant, and 6 and 12 months after transplant; serum specimens were collected from donors at the time of nephroctomy. The 192 samples were stored at -20º C. The anti-HCV tests used were commercial kits based on synthetic HCV peptides (UBI), enzygnost anti-HCV (Boehringer), and Abbot HCV EIA 2nd generation. In patients with a positive anti-hepatitis C UBI test, the presence of HCV-RNA was verified by polymerase chain reaction .RESULTS: Eleven of 40 patients had positive UBI results, and 12 of 48 had positive EIA anti-HCV results before the transplant. Sixteen patients were anti-HCV positive during the 1-year follow-up. Two patients became positive after 6 months, and one after 12 months. One of these patients was also HCV-RNA positive. No transplant recipient patient with positive anti-HCV before transplant seroconverted after 1 year. Fifty percent of the patients who received a kidney were HCV-RNA positive. Three of 40 donors indicated a positive anti-HCV antibody in the UBI test, and 4 of 48 donors indicated a positive anti-HCV antibody in the Boehringer and EIA tests. Two donors were HCV-RNA positive.CONCLUSIONS: The prevalence of anti-HCV before transplant was high, and the serconversion to positive was low during the follow-up; none of the anti-HCV positive patients seroconverted; the HCV-RNA positive patients did not change to negative after transplant, which indicates the persistence of viral replication even after immunosupression; anti-HCV positive donors, even in the presence of HCV-RNA, did not transmit the infection during 1 year after transplant.OBJETIVO: Investigar a prevalência do anti-VHC em 48 receptores renais e seusrespectivos doadores.PACIENTES E MÉTODOS: Foi coletado sangue dos receptores pré-transplante, 6meses e 1 ano pós-transplante; e dos doadores, no momento da nefrectomia. As192 amostras foram conservadas a -20 °C. Os testes anti-VHC utilizados forampeptídeos sintéticos (UBI) e ELISA de segunda geração (Abbott). Nos pacientescom positividade ao anti-VHC pelo teste UBI, foi pesquisado o VHC-ARN por reaçãoem cadeia da polimerase.RESULTADOS: Onze de 40 receptores foram anti-VHC positivos pelo teste da UBIe 12 de 48 pelo teste da Abbott pré-transplante. Dezesseis pacientes apresentarampositividade ao anti-VHC no período de 1 ano pós-operatório. Dois positivaram aos6 meses e um em 1 ano. Um deles apresentou positividade também ao VHC-ARN.Nenhum paciente anti-VHC positivo seroconverteu com 1 ano de seguimento.Verificou-se a presença do VHC-ARN em 50% dos receptores renais. Três de 40doadores foram anti-VHC positivos pelo teste UBI e 4 de 48 pelo teste Abbott. Doisdoadores apresentaram positividade ao VHC-ARN.CONCLUSÕES: 1) A prevalência do anti-VHC pré-transplante foi alta, porém aseroconversão para anti-VHC positivo no seguimento de 1 ano foi baixa; 2) nenhumpaciente anti-VHC positivo seroconverteu; 3) houve manutenção da positividadeao VHC-ARN demonstrando persistência da replicação viral apesar daimunossupressão; 4) os doadores anti-VHC positivos, mesmo com a presença doVHC-ARN não transmitiram a infecção através do enxerto renal no seguimento de1 ano pós-operatório

Non-Linear Stochastic Equations with Calculable Steady States

We consider generalizations of the Kardar--Parisi--Zhang equation that accomodate spatial anisotropies and the coupled evolution of several fields, and focus on their symmetries and non-perturbative properties. In particular, we derive generalized fluctuation--dissipation conditions on the form of the (non-linear) equations for the realization of a Gaussian probability density of the fields in the steady state. For the amorphous growth of a single height field in one dimension we give a general class of equations with exactly calculable (Gaussian and more complicated) steady states. In two dimensions, we show that any anisotropic system evolves on long time and length scales either to the usual isotropic strong coupling regime or to a linear-like fixed point associated with a hidden symmetry. Similar results are derived for textural growth equations that couple the height field with additional order parameters which fluctuate on the growing surface. In this context, we propose phenomenological equations for the growth of a crystalline material, where the height field interacts with lattice distortions, and identify two special cases that obtain Gaussian steady states. In the first case compression modes influence growth and are advected by height fluctuations, while in the second case it is the density of dislocations that couples with the height.Comment: 9 pages, revtex

Correlates of accelerometer-assessed physical activity in pregnancy—The 2015 Pelotas (Brazil) Birth Cohort Study

Objective methods to measure physical activity (PA) have become available and widely used given the high degree of precision to evaluate PA. However, few studies have used accelerometers to measure PA during pregnancy, especially in low- and middle-income countries. We assessed overall PA, moderate, vigorous, and moderate-to-vigorous physical activity (MVPA) objectively measured among pregnant women and their correlates in a population-based study. PA was assessed for seven consecutive days using a raw triaxial wrist-worn accelerometer in women interviewed around 16 and 24 weeks of gestation in the 2015 Pelotas (Brazil) Birth Cohort Study. The average acceleration, which expresses overall PA, was presented in milli-g (1 mg = 0.001 g), and average time (min/day) spent in MVPA (>100 mg) was also analyzed in 5- and 10-min bouts. Analyses were performed using linear regression. In total, 2317 women were included in the analyses. Overall PA was 27.6 mg. Pregnant women spent on average 14 min/day in MVPA and 0.4 min in vigorous PA. Time spent in MVPA and total PA were inversely associated with years in school and income, and were lower among women receiving advice to not exercise. MVPA was also inversely associated with age, lower among women living with a partner, and higher among non-white women. The study indicated low levels of PA among pregnant women. The identified correlates may provide a framework to better understand factors influencing PA during pregnancy and thus inform future interventions