Relaxation volumes of microscopic and mesoscopic irradiation-induced defects in tungsten

The low-energy structures of irradiation-induced defects in materials have been studied extensively over several decades, as these determine the available modes by which a defect can diffuse or relax, and how the microstructure of an irradiated material evolves as a function of temperature and time. Consequently, many studies concern the relative energies of possible defect structures, and empirical potentials are commonly fitted to or evaluated with respect to these. But recently [S. L. Dudarev et al., Nucl. Fusion 58, 126002 (2018)], we have shown that other parameters of defects not directly related to defect energies, namely, their elastic dipole tensors and relaxation volumes, determine the stresses, strains, and swelling of reactor components under irradiation. These elastic properties of defects have received comparatively little attention. In this study, we compute relaxation volumes of irradiation-induced defects in tungsten using empirical potentials and compare to density functional theory results. Different empirical potentials give different results, but some clear potential-independent trends can be identified. We show that the relaxation volume of a small defect cluster can be predicted to within 10% from its point-defect count. For larger defect clusters, we provide empirical fits as a function of defect cluster size. We demonstrate that the relaxation volume associated with a single primary-damage cascade can be estimated from the primary knock-on atom energy. We conclude that while annihilation of defects invariably reduces the total relaxation volume of the cascade debris, there is still no conclusive verdict about whether coalescence of defects reduces or increases the total relaxation volume. Published under license by AIP Publishing.Peer reviewe

Screening and Treatment for Subclinical Hypertensive Heart Disease in Emergency Department Patients With Uncontrolled Blood Pressure: A Cost‐effectiveness Analysis

ObjectivesPoorly controlled hypertension (HTN) is extremely prevalent and, if left unchecked, subclinical hypertensive heart disease (SHHD) may ensue leading to conditions such as heart failure. To address this, we designed a multidisciplinary program to detect and treat SHHD in a high‐risk, predominantly African American community. The primary objective of this study was to determine the cost‐effectiveness of our program.MethodsStudy costs associated with identifying and treating patients with SHHD were calculated and a sensitivity analysis was performed comparing the effect of four parameters on cost estimates. These included prevalence of disease, effectiveness of treatment (regression of SHHD, reversal of left ventricular hypertrophy [LVH], or blood pressure [BP] control as separate measures), echocardiogram costs, and participant time/travel costs. The parent study for this analysis was a single‐center, randomized controlled trial comparing cardiac effects of standard and intense (<120/80 mm Hg) BP goals at 1 year in patients with uncontrolled HTN and SHHD. A total of 149 patients (94% African American) were enrolled, 133 (89%) had SHHD, 123 (93%) of whom were randomized, with 88 (72%) completing the study. Patients were clinically evaluated and medically managed over the course of 1 year with repeated echocardiograms. Costs of these interventions were analyzed and, following standard practices, a cost per quality‐adjusted life‐year (QALY) less than $50,000 was defined as cost‐effective.ResultsTotal costs estimates for the program ranged from$117,044 to $119,319. Cost per QALY was dependent on SHHD prevalence and the measure of effectiveness but not input costs. Cost‐effectiveness (cost per QALY less than$50,000) was achieved when SHHD prevalence exceeded 11.1% for regression of SHHD, 4.7% for reversal of LVH, and 2.9% for achievement of BP control.ConclusionsIn this cohort of predominantly African American patients with uncontrolled HTN, SHHD prevalence was high and screening with treatment was cost‐effective across a range of assumptions. These data suggest that multidisciplinary programs such as this can be a cost‐effective mechanism to mitigate the cardiovascular consequences of HTN in emergency department patients with uncontrolled BP.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136283/1/acem13122.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136283/2/acem13122_am.pd

Ab initio scaling laws for the formation energy of nanosized interstitial defect clusters in iron, tungsten, and vanadium

International audienceThe size limitation of ab initio calculations impedes first-principles simulations of crystal defects at nanometer sizes. Considering clusters of self-interstitial atoms as a paradigm for such crystal defects, we have developed an ab initio–accuracy model to predict formation energies of defect clusters with various geometries and sizes. Our discrete-continuum model combines the discrete nature of energetics of interstitial clusters and continuum elasticity for a crystalline solid matrix. The model is then applied to interstitial dislocation loops with (100) and 1/2(111) Burgers vectors, and to C15 clusters in body-centered-cubic crystals Fe, W, and V, to determine their relative stabilities as a function of size. We find that in Fe the C15 clusters were more stable than dislocation loops if the number of self-interstitial atoms involved was fewer than 51, which corresponds to a C15 cluster with a diameter of 1.5nm. In V and W, the 1/2(111) loops represent the most stable configurations for all defect sizes, which is at odds with predictions derived from simulations performed using some empirical interatomic potentials. Further, the formation energies predicted by the discrete-continuum model are reparametrized by a simple analytical expression giving the formation energy of self-interstitial clusters as a function of their size. The analytical scaling laws are valid over a very broad range of defect sizes, and they can be used in multiscale techniques including kinetic Monte Carlo simulations and cluster dynamics or dislocation dynamics studies

Relaxation volumes of microscopic and mesoscopic irradiation-induced defects in tungsten

International audienceThe low energy structures of irradiation-induced defects in materials have been extensively studied overseveral decades, as these determine the available modes by which a defect can diffuse or relax, and how themicrostructure of an irradiated material evolves as a function of temperature and time. Consequently manystudies concern the relative energies of possible defect structures, and empirical potentials are commonlyfitted to, or evaluated with respect to these. But recently [Dudarev et al. Nuclear Fusion 2018], we haveshown that other parameters of defects not directly related to defect energies, namely their elastic dipoletensors and relaxation volumes, determine the stresses, strains and swelling of reactor components underirradiation. These elastic properties of defects have received comparatively little attention. In this studywe compute relaxation volumes of irradiation-induced defects in tungsten using empirical potentials, andcompare to density functional theory results. Different empirical potentials give different results, but someclear potential-independent trends can be identifed. We show that the relaxation volume of a small defectcluster can be predicted to within 10% from its point-defect count. For larger defect clusters we provideempirical fits as a function of defect cluster size. We demonstrate that the relaxation volume associated witha single primary-damage cascade can be estimated from the primary knock-on atom energy. We concludethat while annihilation of defects invariably reduces the total relaxation volume of the cascade debris, thereis still no conclusive verdict about whether coalescence of defects reduces or increases the total relaxation volume

Effect of lower blood pressure goals on left ventricular structure and function in patients with subclinical hypertensive heart disease

© American Journal of Hypertension, Ltd 2020. All rights reserved. For Permissions, please email: [email protected] BACKGROUND Subclinical hypertensive heart disease (SHHD) is a precursor to heart failure. Blood pressure (BP) reduction is an important component of secondary disease prevention in patients with SHHD. Treating patients with SHHD utilizing a more intensive BP target (120/80 mm Hg), may lead to improved cardiac function but there has been limited study of this, particularly in African Americans (AAs). METHODS We conducted a single center, randomized controlled trial where subjects with uncontrolled, asymptomatic hypertension, and SHHD not managed by a primary care physician were randomized to standard (\u3c140/90 mm Hg) or intensive (\u3c120/80 mm Hg) BP therapy groups with quarterly follow-up for 12 months. The primary outcome was the differences of BP reduction between these 2 groups and the secondary outcome was the improvement in echocardiographic measures at 12 months. RESULTS Patients (95% AAs, 65% male, mean age 49.4) were randomized to the standard (n = 65) or the intensive (n = 58) BP therapy groups. Despite significant reductions in systolic BP (sBP) from baseline (−10.9 vs. −19.1 mm Hg, respectively) (P \u3c 0.05), no significant differences were noted between intention-to-treat groups (P = 0.33) or the proportion with resolution of SHHD (P = 0.31). However, on post hoc analysis, achievement of a sBP \u3c130 mm Hg was associated with significant reduction in indexed left ventricular mass (−6.91 gm/m2.7; P = 0.008) which remained significant on mixed effect modeling (P = 0.031). CONCLUSIONS In post hoc analysis, sBP \u3c130 mm Hg in predominantly AA patients with SHHD was associated with improved cardiac function and reverse remodeling and may help to explain preventative effects of lower BP goals