Experimental Study of crack propagation in carbon steel using acoustic emission

Acoustic emission technique has become a significant and powerful structural health monitoring tool for structures. Researches to date have been done on crack location, fatigue crack propagation in materials and severity assessment of failure using acoustic emission technique. Determining severity of failure in steel structures using acoustic emission technique is still a challenge to accurately determine the relationship between the severity of crack propagation and acoustic emission activities. In this study three point bending test on low carbon steel samples along with acoustic emission technique have been used to determine crack propagation and severity. A notch is introduced at the tension face of the loading point to the samples to initiate the crack. The results show that the percentage of load drop of the steel specimen has a reciprocal relationship with the crack opening i.e. crack opening zones are influenced by the loading rate. In post yielding region, common acoustic emission signal parameters such as, signal strength, energy and amplitudes are found to be higher than those at pre-yielding and at yielding.

Data replication and extension: A commentary

Honig and Samuelsson (2014) and Delmar (2015) recently had an exchange in this journal related to a replication-and-extension attempt of two papers which originally arrived at different conclusions based on the same data set. This commentary provides further clarification on the issues and links the debate to broader issues scholarly culture and practices in entrepreneurship research.

Vibration based baseline updating method to localize crack formation and propagation in reinforced concrete members

Structural Health Monitoring (SHM) schemes are useful for proper management of the performance of structures and for preventing their catastrophic failures. Vibration based SHM schemes has gained popularity during the past two decades resulting in significant research. It is hence evitable that future SHM schemes will include robust and automated vibration based damage assessment techniques (VBDAT) to detect, localize and quantify damage. In this context, the Damage Index (DI) method which is classified as non-model or output based VBDAT, has the ability to automate the damage assessment process without using a computer or numerical model along with actual measurements. Although damage assessment using DI methods have been able to achieve reasonable success for structures made of homogeneous materials such as steel, the same success level has not been reported with respect to Reinforced Concrete (RC) structures. The complexity of flexural cracks is claimed to be the main reason to hinder the applicability of existing DI methods in RC structures. Past research also indicates that use of a constant baseline throughout the damage assessment process undermines the potential of the Modal Strain Energy based Damage Index (MSEDI). To address this situation, this paper presents a novel method that has been developed as part of a comprehensive research project carried out at Queensland University of Technology, Brisbane, Australia. This novel process, referred to as the baseline updating method, continuously updates the baseline and systematically tracks both crack formation and propagation with the ability to automate the damage assessment process using output only data. The proposed method is illustrated through examples and the results demonstrate the capability of the method to achieve the desired outcomes.

Testing times for the implementation of curriculum change: Analysis and extension of a curriculum change model

School curriculum change processes have traditionally been managed internally. However, in Queensland, Australia, as a response to the current high-stakes accountability regime, more and more principals are outsourcing this work to external change agents (ECAs). In 2009, one of the authors (a university lecturer and ECA) developed a curriculum change model (the Controlled Rapid Approach to Curriculum Change (CRACC)), specifically outlining the involvement of an ECA in the initiation phase of a school’s curriculum change process. The purpose of this paper is to extend the CRACC model by unpacking the implementation phase, drawing on data from a pilot study of a single school. Interview responses revealed that during the implementation phase, teachers wanted to be kept informed of the wider educational context; use data to constantly track students; relate pedagogical practices to testing practices; share information between departments and professional levels; and, own whole school performance. It is suggested that the findings would be transferable to other school settings and internal leadership of curriculum change. The paper also strikes a chord of concern – Do the responses from teachers operating in such an accountability regime live their professional lives within this corporate and globalised ideology whether they want to or not?

Blended learning extension in a global collaborative learning environment

The advancement of technology and the internet have created global collaborative learning opportunities and changed learning and teaching in any discipline around the world, including in developing countries. The availability of web-based resources and high-speed internet infrastructure has extended the opportunities to conduct blended learning and new ways of distance learning beyond virtual class room webinars. The aim of this exploratory paper is to review the challenges and opportunities for increasing student engagement in virtual learning. A reflective analysis of international collaborative learning case studies, published articles and practices in virtual learning is used to explore the extension of blended learning organised and participated by institutions from multiple countries. The lessons learnt from flexible learning delivery in professional practice courses in Property Education are used to evaluate potential extensions of blended learning implementation in a global context.

Functional and structural of the erector spinae muscle during isometric lumbar extension

Study Design Cross-sectional study. Objectives To compare erector spinae (ES) muscle fatigue between chronic non-specific lower back pain (CNLBP) sufferers and healthy subjects from a biomechanical perspective during fatiguing isometric lumbar extensions. Background Paraspinal muscle maximal contraction and fatigue are used as a functional predictor for disabilities. The simplest method to determine muscle fatigue is by evaluating the evolution during specific contractions, such as isometric contractions. There are no studies that evaluate the evolution of the ES muscle during fatiguing isometric lumbar extensions and analyse functional and architectural variables. Methods In a pre-calibrated system, participants performed a maximal isometric extension of the lumbar spine for 5 and 30 seconds. Functional variables (torque and muscle activation) and architecture (pennation angle and muscle thickness) were measured using a load cell, surface electromyography and ultrasound, respectively. The results were normalised and a reliability study of the ultrasound measurement was made. Results: The ultrasound measurements were highly reliable, with Cronbach’s alpha values ranging from 0.951 0.981. All measured variables shown significant differences before and after fatiguing isometric lumbar extension. Conclusion During a lumbar isometric extension test, architecture and functional variables of the ES muscle could be analised using ultrasound, surface EMG and load cell. In adition, during an endurance test, ES muscle suffers an acute effect on architectural and functional variables.

Ability to discriminate between healthy and low back pain sufferers using ultrasound during maximum lumbar extension

Objective To analyze the ability to discriminate between healthy individuals and individuals with chronic nonspecific low back pain (CNLBP) by measuring the relation between patient-reported outcomes and objective clinical outcome measures of the erector spinae (ES) muscles using an ultrasound during maximal isometric lumbar extension. Design Cross-sectional study with screening and diagnostic tests with no blinded comparison. Setting University laboratory. Participants Healthy individuals (n=33) and individuals with CNLBP (n=33). Interventions Each subject performed an isometric lumbar extension. With the variables measured, a discriminate analysis was performed using a value ≥6 in the Roland and Morris disability questionnaire (RMDQ) as the grouping variable. Then, a logistic regression with the functional and architectural variables was performed. A new index was obtained from each subject value input in the discriminate multivariate analysis. Main Outcome Measures Morphologic muscle variables of the ES muscle were measured through ultrasound images. The reliability of the measures was calculated through intraclass correlation coefficients (ICCs). The relation between patient-reported outcomes and objective clinical outcome measures was analyzed using a discriminate function from standardized values of the variables and an analysis of the reliability of the ultrasound measurement. Results The reliability tests show an ICC value >.95 for morphologic and functional variables. The independent variables included in the analysis explained 42% (P=.003) of the dependent variable variance. Conclusions The relation between objective variables (electromyography, thickness, pennation angle) and a subjective variable (RMDQ ≥6) and the capacity of this relation to identify CNLBP within a group of healthy subjects is moderate. These results should be considered by clinicians when treating this type of patient in clinical practice.

A novel human leucocyte antigen-DRB1 genotyping method based on multiplex primer extension reactions

We have developed and validated a semi-automated fluorescent method of genotyping human leucocyte antigen (HLA)-DRB1 alleles, HLA-DRB1*01-16, by multiplex primer extension reactions. This method is based on the extension of a primer that anneals immediately adjacent to the single-nucleotide polymorphism with fluorescent dideoxynucleotide triphosphates (minisequencing), followed by analysis on an ABI Prism 3700 capillary electrophoresis instrument. The validity of the method was confirmed by genotyping 261 individuals using both this method and polymerase chain reaction with sequence-specific primer (PCR-SSP) or sequencing and by demonstrating Mendelian inheritance of HLA-DRB1 alleles in families. Our method provides a rapid means of performing high-throughput HLA-DRB1 genotyping using only two PCR reactions followed by four multiplex primer extension reactions and PCR-SSP for some allele groups. In this article, we describe the method and discuss its advantages and limitations.

Fatigue crack growth under pulsatile pressure and plaque rupture

Identification of vulnerable plaque pre-rupture is extremely important for patient risk stratification. The mechanism of plaque rupture is still not entirely clear, but it is thought to be a process involving multiple factors. From a biomechanical viewpoint, plaque rupture is usually seen as a structural failure when the plaque cannot resist the hemodynamic blood pressure and shear stress exerted on it. However, the cardiovascular system is naturally a cyclical hemodynamic environment, and myocardial infarction can be a symptomatically quiescent but potentially progressive process when plaque ruptures at stresses much lower than its strength. Therefore, fatigue accumulation is a possible mechanism for plaque rupture. In this study, a crack growth model was developed, and the previously-mentioned hypothesis was tested by conducting a comparative study between 18 symptomatic and 16 asymptomatic patients with carotid stenosis.

Fatigue crack propagation analysis of plaque rupture

Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.

An extension of the continual reassessment method using decision theory

The primary goal of a phase I trial is to find the maximally tolerated dose (MTD) of a treatment. The MTD is usually defined in terms of a tolerable probability, q*, of toxicity. Our objective is to find the highest dose with toxicity risk that does not exceed q*, a criterion that is often desired in designing phase I trials. This criterion differs from that of finding the dose with toxicity risk closest to q*, that is used in methods such as the continual reassessment method. We use the theory of decision processes to find optimal sequential designs that maximize the expected number of patients within the trial allocated to the highest dose with toxicity not exceeding q*, among the doses under consideration. The proposed method is very general in the sense that criteria other than the one considered here can be optimized and that optimal dose assignment can be defined in terms of patients within or outside the trial. It includes as an important special case the continual reassessment method. Numerical study indicates the strategy compares favourably with other phase I designs.

Moral expansiveness: Examining variability in the extension of the moral world

The nature of our moral judgments—and the extent to which we treat others with care—depend in part on the distinctions we make between entities deemed worthy or unworthy of moral consideration— our moral boundaries. Philosophers, historians, and social scientists have noted that people’s moral boundaries have expanded over the last few centuries, but the notion of moral expansiveness has received limited empirical attention in psychology. This research explores variations in the size of individuals’ moral boundaries using the psychological construct of moral expansiveness and introduces the Moral Expansiveness Scale (MES), designed to capture this variation. Across 6 studies, we established the reliability, convergent validity, and predictive validity of the MES. Moral expansiveness was related (but not reducible) to existing moral constructs (moral foundations, moral identity, “moral” universalism values), predictors of moral standing (moral patiency and warmth), and other constructs associated with concern for others (empathy, identification with humanity, connectedness to nature, and social responsibility). Importantly, the MES uniquely predicted willingness to engage in prosocial intentions and behaviors at personal cost independently of these established constructs. Specifically, the MES uniquely predicted willingness to prioritize humanitarian and environmental concerns over personal and national self-interest, willingness to sacrifice one’s life to save others (ranging from human out-groups to animals and plants), and volunteering behavior. Results demonstrate that moral expansiveness is a distinct and important factor in understanding moral judgments and their consequences.

Human error risk management methodology for rail crack incidents

The paper presents an innovative approach to modelling the causal relationships of human errors in rail crack incidents (RCI) from a managerial perspective. A Bayesian belief network is developed to model RCI by considering the human errors of designers, manufactures, operators and maintainers (DMOM) and the causal relationships involved. A set of dependent variables whose combinations express the relevant functions performed by each DMOM participant is used to model the causal relationships. A total of 14 RCI on Hong Kong’s mass transit railway (MTR) from 2008 to 2011 are used to illustrate the application of the model. Bayesian inference is used to conduct an importance analysis to assess the impact of the participants’ errors. Sensitivity analysis is then employed to gauge the effect the increased probability of occurrence of human errors on RCI. Finally, strategies for human error identification and mitigation of RCI are proposed. The identification of ability of maintainer in the case study as the most important factor influencing the probability of RCI implies the priority need to strengthen the maintenance management of the MTR system and that improving the inspection ability of the maintainer is likely to be an effective strategy for RCI risk mitigation.

Evaluation of material crack using acoustic emission technique

Cracks in civil structures can result in premature failure due to material degradation and can result in both financial loss and environmental consequences. This thesis reports an effective technique using Acoustic Emission (AE) technique to assess the severity of the crack propagation in steel structures. The outcome of this work confirms that combination of AE parametric analysis and signal processing techniques can be used to evaluate crack propagation under different loading configurations. The technique has potential application to assess and monitor the condition of civil structures.