Revealing dislocation structure around and underneath indentations in (001) strontium titanate single crystals at room temperature and 350o C

Many crystalline materials exhibit an indentation size effect, i.e., an intrinsic change in hardness with changes in sampled material volume. During indentation testing, the material underneath the indenter is heavily deformed, introducing high local dislocation densities and density gradients. In the present work, dislocation structures around and underneath the Vickers and Berkovich indentations performed at room temperature and 350oC have been resolved in (001) oriented strontium titanate (STO) single crystal via a sequential polishing, etching, and imaging technique. Laser and atomic force microscopy were used to image dislocation etch-pit patterns which were then digitized for calculating dislocation densities, plastic zone sizes, and dislocation spacing at multiple depths within the material. In addition, a simple model for estimating lattice friction stresses from digitized dislocation etch-pit images has been modified to work at large applied loads [1]. At high loads, images consistently exhibited etch-pit arms extending from the indentation aligned along the {010} and {110} directions, regardless of indenter symmetry. However, the size, shape, and density of etch-pits was found to strongly depend on applied load at lower indentation loads, consistent with the idea of a size effect. Interestingly, slip was documented at depths well below indentation depth, where slip was favored. Load-displacement data combined with dislocation etch-pit techniques revealed that incipient plasticity (manifested as sudden indenter displacement bursts) was strongly influenced by pre-existing dislocations. Furthermore, there was a significant decrease in the indentation size effect with an increase in temperature. Results from the model show a significant change in lattice friction stresses between room temperature and 350oC for and slip planes, consistent with compression testing. The above-mentioned results show that STO provides a unique opportunity as a reference material for understanding size effects in crystalline materials. In addition, the sequential polishing, etching, and imaging technique combined with modeling gives rise to estimates of lattice friction stresses from an indentation test

Cardiorespiratory Fitness and the Risk of Serious Ventricular Arrhythmias:A Prospective Cohort Study

Cardiorespiratory fitness (CRF) is an established risk factor for cardiovascular disease outcomes. However, the relationship of CRF with risk of ventricular arrhythmias (VAs) is unknown. We aimed to assess the prospective association of CRF with the risk of serious VAs. Cardiorespiratory fitness, as measured by maximal oxygen uptake, was assessed using a respiratory gas exchange analyzer in 2299 middle-aged men in the Kuopio Ischemic Heart Disease prospective cohort. We corrected for within-person variability in CRF levels using data from repeated measurements 11 years apart. During median follow-up of 25.3 years (interquartile range, 18.7-27.2 years), 73 serious VAs were recorded. The age-adjusted regression dilution ratio of CRF was 0.58 (95% CI, 0.53-0.64). In analysis adjusted for age, the hazard ratio (HR) for serious VAs per 1-SD increase in CRF was 0.64 (95% CI, 0.49-0.84). The association persisted on additional adjustment for body mass index, systolic blood pressure, history of hypertension, prevalent coronary heart disease, smoking, history of diabetes, cholesterol level, alcohol consumption, and physical activity (HR, 0.67; 95% CI, 0.51-0.88). The corresponding adjusted HRs (95% CIs) were 0.29 (0.14-0.59) and 0.32 (0.15-0.65), respectively, comparing the top vs bottom tertiles. The associations were stronger on correction for regression dilution bias, remained consistent on exclusion of men with a history of coronary heart disease, and did not vary importantly in several relevant clinical subgroups. Cardiorespiratory fitness is inversely associated with future risk of serious VAs, independently of several cardiovascular disease risk factors. Further research is needed to assess the causal relevance of these findings. (C) 2018 Mayo Foundation for Medical Education and Researc

Cardiorespiratory Fitness, Inflammation, and Risk of Sudden Cardiac Death in Middle-Aged Men

Peer reviewe

Inflammatory biomarker score and cancer: A population-based prospective cohort study

BACKGROUND: Inflammation is associated with cancer but there are conflicting reports on associations of biomarkers of inflammation with cancer risk and mortality. We investigated the associations of C-reactive protein (CRP) and leukocyte count with cancer risk and mortality using individual biomarkers, and an inflammatory score derived from both biomarkers. METHODS: We conducted this analysis among 2,570 men enrolled in the population-based, prospective Kuopio Ischemic Heart Disease Risk Factor Study in Finland. During an average follow-up period of 26 years, 653 cancer cases and 287 cancer deaths occurred. We computed a z-score for each participant, with the combined z-score being the sum of each individual’s CRP and leukocyte z-scores. Multivariable-adjusted Cox proportional hazard model was used to evaluate associations with cancer risk and mortality. RESULTS: Using individual biomarkers, elevated leukocyte count was associated with an increased risk of cancer (RR = 1.31, 95 % CI 1.04-1.66), and cancer mortality (RR=, 95 % CI 1.39, 0.98-1.97). The corresponding results for CRP were (RR = 1.23, 95 % CI 0.97-1.55) for risk and (RR = 1.15, 95 % CI 0.81-1.64) for cancer mortality. Associations of the biomarkers with cancer appeared to be more robust using the combined z-score. HRs comparing men within the highest z-score quartile to those within the lowest z-score quartiles were 1.47 (95 % CI 1.16-1.88, p-trend < 0.01) for cancer risk, and 1.48 (95 % CI 1.03-2.14, p-trend = 0.09) for cancer mortality. CONCLUSION: Our study suggests that inflammation is associated with cancer risk and mortality, and combining inflammatory biomarkers into a score is a robust method of elucidating this association