On the Less Known Effects of Environment and Specimen Geometry on Creep Fracture of Nickel Alloys

Attention has been drawn to the fact that during exposure of nickel to air at elevated temperatures, oxygen diffuses through the grain boundary and reacts with carbon forming gas bubbles of carbon monoxide and/or carbon dioxide. Voids are produced due to the high pressure generated by the gas bubbles which cause creep embrittlement. Alloying nickel with 3.8 weight per cent aluminium, which is a stronger oxide forming element as compared to carbon, could not prevent diffusion of oxygen during exposure of the alloy to air at elevated temperatures. The diffusing oxygen reacts even in the Ni-Al-C system, with carbon and forms gas bubbles of CO and CO/sub 2/ which lead to creep embrittlement. The presence of 15 weight per cent chromium in nickel (Inconel 600 and Inconel alloy X-750), however, plays an interesting role on the kinetics of oxygen diffusion. At temperature 1050 degree Celsius and below, during exposure to air at atmospheric pressure, oxygen can diffuse along the grain boundary and reacts with carbon forming gas bubbles of carbon monoxide, where as at 1120 degree Centigrade and above, the formation of 'barrier' oxide scale, chromium oxide, at the surface prevents diffusion of oxygen. On the other hand, the presence of chromium, as observed in Inconel alloy X-750, does not play an effective role in preventing diffusion of oxygen along the grain boundary in poor vacuum. Circumstantial evidence suggests that diffusing oxygen reacts with carbon and forms gas bubbles of CO with consequential creep embrittlement, reduction in creep life and enhancement in creep rate. It has been shown that exposure of the alloy in poor vacuum has a much more damaging effect on the creep properties than that of an atmospheric pressure. It is, therefore, emphasized that exposure of nickel base superalloys to poor vacuum at elevated temperatures must be avoided; in particular this effect is more pronounced in the alloy with thin section size. It is also shown that even in the absence of oxygen interaction prior to creep testing, section size has considerable influence on the creep properties which is believed to be caused by oxygen interaction during creep deformation. For the same section size, the creep properties may be different in specimens of different geometrices. But for the same ratio of cross-sectional area to perimeter (A/P), rupture lifetime becomes independent of specimen geometry. Failure analysis of an aero engine blade has been presented as a case study to emphasize that while designing a component, utmost care must be excercised to avoid thin sections

Predictability and herding of bourse volatility: an econophysics analogue

Financial Reynolds number works as a proxy for volatility in stock markets. This piece of work helps to identify the predictability and herd behavior embedded in the financial Reynolds number (time series) series for both CNX Nifty Regular and CNX Nifty High Frequency Trading domains. Hurst exponent and fractal dimension have been used to carry out this work. Results confirm conclusive evidence of predictability and herd behavior for both the indices. However, it has been observed that CNX Nifty High Frequency Trading domain (represented by its corresponding financial Reynolds number) is more predictable and has traces of significant herd behavior. The pattern of the predictability has been found to follow a quadratic equation

Kinetics and Jamming Coverage in a Random Sequential Adsorption of Polymer Chains

Using a highly efficient Monte Carlo algorithm, we are able to study the growth of coverage in a random sequential adsorption (RSA) of self-avoiding walk (SAW) chains for up to 10^{12} time steps on a square lattice. For the first time, the true jamming coverage (theta_J) is found to decay with the chain length (N) with a power-law theta_J propto N^{-0.1}. The growth of the coverage to its jamming limit can be described by a power-law, theta(t) approx theta_J -c/t^y with an effective exponent y which depends on the chain length, i.e., y = 0.50 for N=4 to y = 0.07 for N=30 with y -> 0 in the asymptotic limit N -> infinity.Comment: RevTeX, 5 pages inclduing figure

Temporal Trends and Prognosis of Physical Examination Findings in Patients with Acute Decompensated Heart Failure: The ARIC Study Community Surveillance

BACKGROUND: Bedside evaluation of congestion is a mainstay of heart failure (HF) management. Whether detected physical examination signs have changed over time as obesity prevalence has increased in HF populations, or if the associated prognosis differs for HF with reduced or preserved ejection fraction (HFrEF or HFpEF) is uncertain. METHODS: From 2005 to 2014, the ARIC study (Atherosclerosis Risk in Communities) conducted adjudicated hospital surveillance of acute decompensated HF. We analyzed trends in physical examination findings, imaging signs, and symptoms related to congestion, both over time and by obesity class, and associated 28-day mortality risks. RESULTS: Of 24 937 weighted hospitalizations for acute decompensated HF (mean age 75 years, 53% women, 32% Black), 47% had HFpEF. The prevalence of obesity increased from 2005 to 2014 for both HF types. With increasing obesity category, detected edema increased, while jugular venous distension decreased, and rales remained stable. Detected edema also increased over time, for both HF types. Associations between 28-day mortality and individual signs and symptoms of congestion were similar for HFpEF and HFrEF; however, the adjusted mortality risk with all 3 (edema, rales, and jugular venous distension) versus <3 physical examination findings was higher for patients with HFpEF (odds ratio, 2.41 [95% CI, 1.53-3.79]) than HFrEF (odds ratio, 1.30 [95% CI, 0.87-1.93]); P for interaction by HF type =0.02. CONCLUSIONS: In patients hospitalized with acute decompensated HF, detected physical examination findings differ both temporally and by obesity. Combined findings from the physical examination are more prognostic of 28-day mortality for patients with HFpEF than HFrEF

Temporal trends in prevalence and prognostic implications of comorbidities among patients with acute decompensated heart failure: The ARIC study community surveillance

Background: Patients with heart failure (HF) have multiple coexisting comorbidities. The temporal trends in the burden of comorbidities and associated risk of mortality among patients with HF with preserved ejection fraction (HFpEF) and HF with reduced ejection fraction (HFrEF) are not well established. Methods: HF-related hospitalizations were sampled by stratified design from 4 US areas in 2005 to 2014 by the community surveillance component of the ARIC study (Atherosclerosis Risk in Communities). Acute decompensated HF was classified by standardized physician review and a previously validated algorithm. An ejection fraction <50% was considered HFrEF. A total of 15 comorbidities were abstracted from the medical record. Mortality outcomes were ascertained for up to 1-year postadmission by linking hospital records with death files. Results: A total of 5460 hospitalizations (24 937 weighted hospitalizations) classified as acute decompensated HF had available ejection fraction data (53% female, 68% white, 53% HFrEF, 47% HFpEF). The average number of comorbidities was higher for patients with HFpEF versus HFrEF, both for women (5.53 versus 4.94; P<0.0001) and men (5.20 versus 4.82; P<0.0001). There was a significant temporal increase in the overall burden of comorbidities, both for patients with HFpEF (women: 5.17 in 2005-2009 to 5.87 in 2010-2013; men: 4.94 in 2005-2009 and 5.45 in 2010-2013) and HFrEF (women: 4.78 in 2005-2009 to 5.14 in 2010-2013; men: 4.62 in 2005-2009 and 5.06 in 2010-2013; P-trend<0.0001 for all). Higher comorbidity burden was significantly associated with higher adjusted risk of 1-year mortality, with a stronger association noted for HFpEF (hazard ratio [HR] per 1 higher comorbidity, 1.19 [95% CI, 1.14-1.25] versus HFrEF (HR, 1.10 [95% CI, 1.05-1.14]; P for interaction by HF type=0.02). The associated mortality risk per 1 higher comorbidity also increased significantly over time for patients with HFpEF and HFrEF, as well (P for interaction with time=0.002 and 0.02, respectively) Conclusions: The burden of comorbidities among hospitalized patients with acute decompensated HFpEF and HFrEF has increased over time, as has its associated mortality risk. Higher burden of comorbidities is associated with higher risk of mortality, with a stronger association noted among patients with HFpEF versus HFrEF

Racial Differences and Temporal Obesity Trends in Heart Failure with Preserved Ejection Fraction

BACKGROUND/OBJECTIVES: Obesity increases with age, is disproportionately prevalent in black populations, and is associated with heart failure with preserved ejection fraction (HFpEF). An “obesity paradox,” or improved survival with obesity, has been reported in patients with HFpEF. The aim of this study was to examine whether racial differences exist in the temporal trends and outcomes associated with obesity among older patients with HFpEF. DESIGN: Community surveillance of acute decompensated heart failure (ADHF) hospitalizations, sampled by stratified design from 2005 to 2014. SETTING: Atherosclerosis Risk in Communities Study (NC, MS, MD, MN). PARTICIPANTS: A total of 10,147 weighted hospitalizations for ADHF (64% female, 74% white, mean age 77 years), with ejection fraction ≥50%. MEASUREMENTS: ADHF classified by physician review, HFpEF defined by ejection fraction ≥50%. Body mass index (BMI) calculated from weight at hospital discharge. Obesity defined by BMI ≥30 kg/m2, class III obesity by BMI ≥40 kg/m2. RESULTS: When aggregated across 2005–2014, the mean BMI was higher for black compared to white patients (34 vs 30 kg/m2; P <.0001), as was prevalence of obesity (56% vs 43%; P <.0001) and class III obesity (24% vs 13%; P <.0001). Over time, the annual mean BMI and prevalence of class III obesity remained stable for black patients, but steadily increased for white patients, with annual rates statistically differing by race (P-interaction =.04 and P =.03, respectively). For both races, a U-shaped adjusted mortality risk was observed across BMI categories, with the highest risk among patients with a BMI ≥40 kg/m2. CONCLUSION: Black patients were disproportionately burdened by obesity in this decade-long community surveillance of older hospitalized patients with HFpEF. However, temporal increases in mean BMI and class III obesity prevalence among white patients narrowed the racial difference in recent years. For both races, the worst survival was observed with class III obesity. Effective strategies are needed to manage obesity in patients with HFpEF

Trends, management, and outcomes of acute myocardial infarction hospitalizations with in-hospital-onset versus out-of-hospital onset: The aric study

BACKGROUND: Acute myocardial infarction (AMI) with in-hospital onset (AMI-IHO) has poor prognosis but is clinically underap-preciated. Whether its occurrence has changed over time is uncertain. METHODS AND RESULTS: Since 1987, the ARIC (Atherosclerosis Risk in Communities) study has conducted adjudicated surveillance of AMI hospitalizations in 4 US communities. Our analysis was limited to patients aged 35 to 74 years with symptomatic AMI. Patients with symptoms initiating after hospital arrival were considered AMI-IHO. A total of 26 678 weighted hospitalizations (14 276 unweighted hospitalizations) for symptomatic AMI were identified from 1995 to 2014, with 1137 (4%) classified as in-hospital onset. The population incidence rate of AMI-IHO increased in the 4 ARIC communities from 1995 through 2004 to 2005 through 2014 (12.7—16.9 events per 100 000 people; P for 20-year trend 65

Twenty Year Trends and Sex Differences in Young Adults Hospitalized with Acute Myocardial Infarction: The ARIC Community Surveillance Study

Background: Sex differences are known to exist in the management of older patients presenting with acute myocardial infarction (AMI). Few studies have examined the incidence and risk factors of AMI among young patients, or whether clinical management differs by sex. Methods: The Atherosclerosis Risk in Communities (ARIC) Surveillance study conducts hospital surveillance of AMI in 4 US communities (MD MN, MS and NC). AMI was classified by physician review, using a validated algorithm. Medications and procedures were abstracted from the medical record. Our study population was limited to young patients aged 35 to 54 years. Results: From 1995 to 2014, 28 732 weighted hospitalizations for AMI were sampled among patients aged 35 to 74 years. Of these, 8737 (30%) were young. The annual incidence of AMI hospitalizations increased for young women but decreased for young men. The overall proportion of AMI admissions attributable to young patients steadily increased, from 27% in 1995 to 1999 to 32% in 2010 to 2014 (P for trend=0.002), with the largest increase observed in young women. History of hypertension (59% to 73%, P for trend<0.0001) and diabetes mellitus (25% to 35%, P for trend<0.0001) also increased among young AMI patients. Compared to young men, young women presenting with AMI were more often black and had a greater comorbidity burden. In adjusted analyses, young women had a lower probability of receiving lipid-lowering therapies (relative risk [RR]=0.87; 95% confidence interval [CI], 0.80-0.94), nonaspirin antiplatelets (RR=0.83; 95% CI, 0.75-0.91), beta blockers (RR=0.96; 95% CI, 0.91-0.99), coronary angiography (RR=0.93; 95% CI, 0.86-0.99) and coronary revascularization (RR = 0.79; 95% CI, 0.71-0.87). However, 1-year all-cause mortality was comparable for women versus men (HR=1.10; 95% CI, 0.83-1.45). Conclusions: The proportion of AMI hospitalizations attributable to young patients increased from 1995 to 2014 and was especially pronounced among women. History of hypertension and diabetes among young patients admitted with AMI increased over time as well. Compared with young men, young women presenting with AMI had a lower likelihood of receiving guideline-based AMI therapies. A better understanding of factors underlying these changes is needed to improve care of young patients with AMI

Prevalence and Prognostic Significance of Mitral Regurgitation in Acute Decompensated Heart Failure: The ARIC Study

Objectives: This study investigates the prevalence and prognostic significance of mitral regurgitation (MR) in acute decompensated heart failure (ADHF) patients. Background: Few studies characterize the burden of MR in heart failure. Methods: The ARIC (Atherosclerosis Risk In Communities) study surveilled ADHF hospitalizations for residents ≥55 years of age in 4 U.S. communities. ADHF cases were stratified by left ventricular ejection fraction (LVEF): <50% and ≥50%. Odds of moderate or severe MR in patients with varying sex and race, and odds of 1-year mortality in those with higher MR severity were estimated using multivariable logistic regression. Results: From 2005 to 2014, there were 17,931 weighted ADHF hospitalizations of which 49.2% had an LVEF <50% and 50.8% an LVEF ≥50%. Moderate or severe MR prevalence was 44.5% in those with an LVEF <50% and 27.5% in those with an LVEF ≥50%. Moderate or severe MR was more likely in females than males regardless of LVEF; LVEF <50% (odds ratio [OR]: 1.21 [95% confidence interval (CI): 1.11 to 1.33]), LVEF ≥50% (OR: 1.52 [95% CI: 1.36 to 1.69]). Among hospitalizations with an LVEF ≥50%, moderate or severe MR was less likely in blacks than whites (OR: 0.72 [95% CI: 0.64 to 0.82]). Higher MR severity was independently associated with increased 1-year mortality in those with an LVEF <50% (OR: 1.30 [95% CI: 1.16 to 1.45]). Conclusions: Patients with ADHF have a significant MR burden that varies with sex and race. In ADHF patients with an LVEF <50%, higher MR severity is associated with excess 1-year mortality

Epidemiology and Outcomes of Aortic Stenosis in Acute Decompensated Heart Failure: The ARIC Study

Background: Few studies characterize the epidemiology and outcomes of aortic stenosis (AS) in acute decompensated heart failure (ADHF). This study investigates the significance of AS in contemporary patients who have experienced an ADHF hospitalization. Methods: The ARIC study (Atherosclerosis Risk in Communities) surveilled ADHF hospitalizations for residents ≥55 years of age in 4 US communities. ADHF cases were stratified by left ventricular ejection fraction (LVEF). Demographic differences in AS burden and the association of varying AS severities with mortality were estimated using multivariable logistic regression. Results: From 2005 through 2014, there were 3597 (weighted n=16 692) ADHF hospitalizations of which 48.6% had an LVEF <50% and 51.4% an LVEF ≥50%. AS prevalence was 12.1% and 18.7% in those with an LVEF <50% and ≥50%, respectively. AS was less likely in Black than White patients regardless of LVEF: LVEF <50% (odds ratio [OR], 0.34 [95% CI, 0.28-0.42]); LVEF ≥50% (OR, 0.51 [95% CI, 0.44-0.59]). Higher AS severity was independently associated with 1-year mortality in both LVEF subgroups: LVEF <50% (OR, 1.16 [95% CI, 1.04-1.28]); LVEF ≥50% (OR, 1.40 [95% CI, 1.28-1.54]). Sensitivity analyses excluding severe AS patients detected that mild/moderate AS was independently associated with 1-year mortality in both LVEF subgroups: LVEF <50% (OR, 1.23 [95% CI, 1.02-1.47]); LVEF ≥50% (OR, 1.31 [95% CI, 1.14-1.51]). Conclusions: Among patients who have experienced an ADHF hospitalization, AS is prevalent and portends poor mortality outcomes. Notably, mild/moderate AS is independently associated with 1-year mortality in this high-risk population