Using M-integral for multi-cracked problems subjected to nonconservative and nonuniform crack surface tractions

AbstractIn this paper, an energy parameter based on the concept of the M-integral is proposed for describing the fracture behavior of a multi-cracked solid subjected to nonconservative and nonuniform crack surface tractions. By using the M-integral with a suitably chosen closed contour, one can evaluate the ‘surface creation energy’ (SCE) required for creation of the stressed cracks. Also, it is demonstrated that the property of path-independence holds even under the action of crack surface tractions. Therefore, the singular stress field in the near-tip areas is not directly involved in the calculation so that a complicated finite element model around the crack tips is not required in evaluation of the M-integral

Experimental application of FRF-based model updating approach to estimate soil mass and stiffness mobilised under pile impact tests

The dynamic response of structures in contact with soil is receiving increasing interest and there is a growing need for more accurate models capable of simulating the behaviour of these systems. This is particularly important in the field of offshore wind turbines, where accurate estimates of system frequency are needed to avoid resonance, and in the structural health monitoring fields, where accurate reference damage models are used. Previous work has shown that there is significant uncertainty in how to specify mobilised soil stiffness for dynamic soil-pile interaction modelling. Moreover, the contribution of soil mass in dynamic motion is often ignored. This paper applies a finite-element iterative model updating approach previously developed by the authors to two experimental piles to ascertain the mobilised soil stiffness and mass profiles from impact test data. The method works by obtaining a frequency response function (FRF) from an impact test performed on a test pile, developing a numerical model of this system, applying initial estimates of soil mass and stiffness, and updating these properties to match the experimental FRF with that generated in the numerical model. A range of elements are investigated including multiple runs of the approach to test repeatability, the influence of different starting estimates for stiffness, the effect of variability in experimental test data, and the influence of the pile length over which masses are distributed. Moreover, potential sources of error are discussed. The method provides reasonably consistent estimates of the soil stiffness and mass acting in the lateral dynamic motion of a given pile tested in this paper. The approach may be useful in the continued improvement of Soil-Structure Interaction (SSI) modelling for dynamic applications

Perceived coach autonomy support and athlete burnout : the role of athletes’ experiential avoidance

Researchers have found that perceived coach autonomy support is negatively related to athlete burnout. However, whether offering such support would be helpful for all athletes or only athletes with certain characteristics is unknown. Following the notion of autonomous goal regulation suggested in self-determination theory, the authors propose that having autonomy support from coaches will be more strongly associated with a decrease in athlete burnout among athletes with lower experiential avoidance than among those with higher experiential avoidance. Experiential avoidance is a tendency to escape, avoid, or modify the frequency of uncomfortable experiences. A total of 141 collegiate student athletes completed surveys at two time points over three months. The results indicate that perceived coach autonomy support is negatively related to athlete burnout. Furthermore, the negative relationship between perceived coach autonomy support and decreased athlete burnout is stronger when experiential avoidance is low rather than high. When the three dimensions of burnout were analyzed individually (i.e., emotional and physical exhaustion, reduced sense of accomplishment and sport devaluation), only emotional and physical exhaustion and overall score were significant. The implications and applications of these results are discussed from an interactionist perspective

An Aircraft Service Staff Rostering using a Hybrid GRASP Algorithm

The aircraft ground service company is responsible for carrying out the regular tasks to aircraft maintenace between their arrival at and departure from the airport. This paper presents the application of a hybrid approach based upon greedy randomized adaptive search procedure (GRASP) for rostering technical staff such that they are assigned predefined shift patterns. The rostering of staff is posed as an optimization problem with an aim of minimizing the violations of hard and soft constraints. The proposed algorithm iteratively constructs a set of solutions by GRASP. Furthermore, with multi-agent techniques, we efficiently identify an optimal roster with minimal constraint violations and fair to employees. Experimental results are included to demonstrate the effectiveness of the proposed algorithm

Usefulness of Cardiac Biomarker Score for Risk Stratification in Stable Patients Undergoing Elective Cardiac Evaluation Across Glycemic Status

Several clinically available cardiac biomarkers have established their prognostic value in patients with acute coronary syndromes. However, their relative prognostic significance in stable subjects has not been prospectively validated, either individually or in combination. The aim of this study was to evaluate the extent to which B-type natriuretic peptide, myeloperoxidase, and high-sensitivity C-reactive protein alone or together could be prognostic biomarkers in 3,635 consecutive stable patients without acute coronary syndrome who underwent elective diagnostic coronary angiography. After adjusting for traditional risk factors and renal function, each of the markers monitored was a significant predictor of incident major adverse cardiovascular events (death, nonfatal myocardial infarction, and stroke) over 3 years. A cardiac biomarker score based on the sum total of “positive” biomarkers provided independent prediction of future risk for incident major adverse cardiovascular events at 3 years (hazard ratio [HR] 7.61, 95% confidence interval [CI] 4.98 to 11.65, p \u3c0.001), even after adjusted for traditional risk factors (HR 6.11, 95% CI 3.98 to 9.38, p \u3c0.001). A positive cardiac biomarker score remained a strong and independent predictor of 3-year risk for major adverse cardiovascular events among those with normal glycemic control (HR 4.24, 95% CI 1.96 to 9.18, p \u3c0.001), those with prediabetes (HR 7.62, 95% CI 3.87 to 15.01, p \u3c0.001), and those with diabetes (HR 5.61, 95% CI 2.55 to 12.33, p \u3c0.001), as well as within subjects without significant angiographic evidence of coronary artery disease (HR 10.82, 95% CI 3.82 to 30.6, p \u3c0.001). In conclusion, an integrated assessment of cardiac biomarkers may provide independent prognostic value for long-term adverse clinical events in stable cardiac patients

Cystatin C Identifies Patients with Stable Chronic Heart Failure at Increased Risk for Adverse Cardiovascular Events

Background—Renal function is a strong predictor of adverse events in heart failure. Current renal function measures are imperfect, and cystatin C (CysC) is promoted as a better marker of glomerular filtration rate. This study compares the prognostic use of CysC and derived glomerular filtration rate estimates with other measures of renal function in patients with chronic heart failure. Methods and Results—We measured serum CysC levels in 823 patients with heart failure undergoing coronary angiography with follow-up of major adverse cardiovascular events (death, myocardial infarction, stroke). CysC levels strongly correlated with creatinine (r=0.73), blood urea nitrogen (r=0.70), and estimated glomerular filtration rate by the 4-variable modification of diet in renal disease equation (r=−0.62) (all P\u3c0.001). However, the correlation was lower in estimated glomerular filtration rate ≥60 mL/min per 1.73 m2. CysC-based measures significantly improved areas under the receiver operating characteristic curve for the prediction of major adverse cardiovascular events, especially in estimated glomerular filtration rate ≥60 mL/min per 1.73 m2 (P\u3c0.01). Net reclassification improvement was 22.2% (P\u3c0.001) in this group. CysC remained an independent predictor of major adverse cardiovascular events (P\u3c0.001) after adjustment for traditional risk factors and brain natriuretic peptide. Conclusions—CysC is an independent predictor of adverse events in chronic heart failure. It adds prognostic value to creatinine, particularly in patients with preserved renal function

Cystatin C Identifies Patients with Stable Chronic Heart Failure at Increased Risk for Adverse Cardiovascular Events

Background—Renal function is a strong predictor of adverse events in heart failure. Current renal function measures are imperfect, and cystatin C (CysC) is promoted as a better marker of glomerular filtration rate. This study compares the prognostic use of CysC and derived glomerular filtration rate estimates with other measures of renal function in patients with chronic heart failure. Methods and Results—We measured serum CysC levels in 823 patients with heart failure undergoing coronary angiography with follow-up of major adverse cardiovascular events (death, myocardial infarction, stroke). CysC levels strongly correlated with creatinine (r=0.73), blood urea nitrogen (r=0.70), and estimated glomerular filtration rate by the 4-variable modification of diet in renal disease equation (r=−0.62) (all P\u3c0.001). However, the correlation was lower in estimated glomerular filtration rate ≥60 mL/min per 1.73 m2. CysC-based measures significantly improved areas under the receiver operating characteristic curve for the prediction of major adverse cardiovascular events, especially in estimated glomerular filtration rate ≥60 mL/min per 1.73 m2 (P\u3c0.01). Net reclassification improvement was 22.2% (P\u3c0.001) in this group. CysC remained an independent predictor of major adverse cardiovascular events (P\u3c0.001) after adjustment for traditional risk factors and brain natriuretic peptide. Conclusions—CysC is an independent predictor of adverse events in chronic heart failure. It adds prognostic value to creatinine, particularly in patients with preserved renal function

Purification and Visualization of Influenza A Viral Ribonucleoprotein Complexes

The influenza A viral genome consists of eight negative-sense, single stranded RNA molecules, individually packed with multiple copies of the influenza A nucleoprotein (NP) into viral ribonulceoprotein particles (vRNPs). The influenza vRNPs are enclosed within the viral envelope. During cell entry, however, these vRNP complexes are released into the cytoplasm, where they gain access to the host nuclear transport machinery. In order to study the nuclear import of influenza vRNPs and the replication of the influenza genome, it is useful to work with isolated vRNPs so that other components of the virus do not interfere with these processes. Here, we describe a procedure to purify these vRNPs from the influenza A virus. The procedure starts with the disruption of the influenza A virion with detergents in order to release the vRNP complexes from the enveloped virion. The vRNPs are then separated from the other components of the influenza A virion on a 33-70% discontinuous glycerol gradient by velocity sedimentation. The fractions obtained from the glycerol gradient are then analyzed on via SDS-PAGE after staining with Coomassie blue. The peak fractions containing NP are then pooled together and concentrated by centrifugation. After concentration, the integrity of the vRNPs is verified by visualization of the vRNPs by transmission electron microscopy after negative staining. The glycerol gradient purification is a modification of that from Kemler et al. (1994)1, and the negative staining has been performed by Wu et al. (2007).