Causal Algebras on Chain Event Graphs with Informed Missingness for System Failure

Graph-based causal inference has recently been successfully applied to explore system reliability and to predict failures in order to improve systems. One popular causal analysis following Pearl and Spirtes et al. to study causal relationships embedded in a system is to use a Bayesian network (BN). However, certain causal constructions that are particularly pertinent to the study of reliability are difficult to express fully through a BN. Our recent work demonstrated the flexibility of using a Chain Event Graph (CEG) instead to capture causal reasoning embedded within engineers’ reports. We demonstrated that an event tree rather than a BN could provide an alternative framework that could capture most of the causal concepts needed within this domain. In particular, a causal calculus for a specific type of intervention, called a remedial intervention, was devised on this tree-like graph. In this paper, we extend the use of this framework to show that not only remedial maintenance interventions but also interventions associated with routine maintenance can be well-defined using this alternative class of graphical model. We also show that the complexity in making inference about the potential relationships between causes and failures in a missing data situation in the domain of system reliability can be elegantly addressed using this new methodology. Causal modelling using a CEG is illustrated through examples drawn from the study of reliability of an energy distribution network.     

288例孕前妇女血铅水平及相关因素和健康干预分析

为了解南京建邺地区计划妊娠妇女的血铅水平及其影响因素进行健康干预,采用石墨炉原子吸收光谱法测定了南京市建邺区妇幼保健院孕前门诊健康体检的288例孕前妇女血铅水平,并对其个人生活和饮食习惯等相关因素进行问卷调查,同时对部分铅超标孕前妇女进行健康干预。结果表明,孕前妇女铅中毒发生率为12.01%,经多元逐步回归分析确定,孕前妇女文化水平是妇女铅中毒的保护因素,经常食用皮蛋、膨化食品是妇女铅中毒的危险因素;健康干预方法对于铅超标妇女干预效果前后差异有显著性(P<0.01)。鉴于目前南京市建邺地区孕前妇女铅中毒流行率较高,对危险因素的预防以及健康干预方法能降低孕前妇女铅暴露水平,建议进行健康干预以促进健全婴儿出生,实现优生优育的目标。     

Target Zone Interventions and Coordination of Expectations

Foreign exchange markets display regularly severe bubbles. This paper explores whether or not the so-called target zone interventions are an effective tool for central banks to stabilize the exchange rate. We define such intervention operations as buying/selling an undervalued/overvalued currency when the distance between the exchange rate and its fundamental value exceeds a critical threshold value. On the basis of a nonlinear empirical exchange rate model with chartists and fundamentalists, we find that not only target zone interventions have the power to reduce misalignments but also to earn profits. The idea of this paper was born during the 2003 Complexity Workshop in Aix-en-Provence and the Viennese Workshop on Optimal Control, Dynamic Games, and Nonlinear Dynamics. The paper was presented at the International Conference on Computing in Economics and Finance in Amsterdam and at the Erich-Schneider research seminar at the University of Kiel. We thank Richard Day, Herbert Dawid, Cars Hommes, Blake LeBaron, Thomas Lux, Erik Mosekilde, Barkley Rosser and Jan Tuinstra for stimulating discussions. Also, we thank two anonymous referees and Christophe Deissenberg for helpful comments.     

MRI-guided focused ultrasound treatments

Focused ultrasound (FUS) allows noninvasive focal delivery of energy deep into soft tissues. The focused energy can be used to modify and eliminate tissue for therapeutic purposes while the energy delivery is targeted and monitored using magnetic resonance imaging (MRI). MRI compatible methods to deliver these exposures have undergone rapid development over the past 10 years such that clinical treatments are now routinely performed. This paper will review the current technical and clinical status of MRI-guided focused ultrasound therapy and discuss future research and development opportunities.     

A dynamical model for describing behavioural interventions for weight loss and body composition change

We present a dynamical model incorporating both physiological and psychological factors that predict changes in body mass and composition during the course of a behavioural intervention for weight loss. The model consists of a three-compartment energy balance integrated with a mechanistic psychological model inspired by the Theory of Planned Behaviour. This describes how important variables in a behavioural intervention can influence healthy eating habits and increased physical activity over time. The novelty of the approach lies in representing the behavioural intervention as a dynamical system and the integration of the psychological and energy balance models. Two simulation scenarios are presented that illustrate how the model can improve the understanding of how changes in intervention components and participant differences affect outcomes. Consequently, the model can be used to inform behavioural scientists in the design of optimized interventions for weight loss and body composition change.     

Predicting performance in a first engineering calculus course: implications for interventions

At the University of Louisville, a large, urban institution in the south-east United States, undergraduate engineering students take their mathematics courses from the school of engineering. In the fall of their freshman year, engineering students take Engineering Analysis I, a calculus-based engineering analysis course. After the first two weeks of the semester, many students end up leaving Engineering Analysis I and moving to a mathematics intervention course. In an effort to retain more students in Engineering Analysis I, the department collaborated with university academic support services to create a summer intervention programme. Students were targeted for the summer programme based on their score on an algebra readiness exam (ARE). In a previous study, the ARE scores were found to be a significant predictor of retention and performance in Engineering Analysis I. This study continues that work, analysing data from students who entered the engineering school in the fall of 2012. The predictive validity of the ARE was verified, and a hierarchical linear regression model was created using math American College Testing (ACT) scores, ARE scores, summer intervention participation, and several metacognitive and motivational factors as measured by subscales of the Motivated Strategies for Learning Questionnaire. In the regression model, ARE score explained an additional 5.1% of the variation in exam performance in Engineering Analysis I beyond math ACT score. Students took the ARE before and after the summer interventions and scores were significantly higher following the intervention. However, intervention participants nonetheless had lower exam scores in Engineering Analysis I. The following factors related to motivation and learning strategies were found to significantly predict exam scores in Engineering Analysis I: time and study environment management, internal goal orientation, and test anxiety. The adjusted R² for the full model was 0.42, meaning that the model could explain 42% of the variation in Engineering Analysis I exam scores.     

Applying an alternative mathematics pedagogy for students with weak mathematics: meta-analysis of alternative pedagogies

Student mathematics performance and the need for work-ready graduates to be mathematics-competent is a core issue for many universities. While both student and teacher are responsible for learning outcomes, there is a need to explicitly acknowledge the weak mathematics foundation of many university students. A systematic literature review was undertaken of identified innovations and/or interventions that may lead to improvement in student outcomes for university mathematics-based units of study. The review revealed the importance of understanding the foundations of student performance in higher education mathematics learning, especially in first year. Pre-university mathematics skills were identified as significant in student retention and mathematics success at university, and a specific focus on student pre-university mathematics skill level was found to be more effective in providing help, rather than simply focusing on a particular at-risk group. Diagnostics tools were found to be important in identifying (1) student background and (2) appropriate intervention. The studies highlighted the importance of appropriate and validated interventions in mathematics teaching and learning, and the need to improve the learning model for mathematics-based subjects, communication and technology innovations.     

Wireless MR tracking of interventional devices using phase-field dithering and projection reconstruction

Purpose

Device tracking is crucial for interventional MRI (iMRI) because conventional device materials do not contribute to the MR signal, may cause susceptibility artifacts and are generally invisible if moved out of the scan plane. A robust method for wireless tracking and dynamic guidance of interventional devices equipped with wirelessly connected resonant circuits (wRC) is presented.

Methods

The proposed method uses weak spatially-selective excitation pulses with very low flip angle (0.3°), a Hadamard multiplexed tracking scheme and employs phase-field dithering to obtain the 3D position of a wRC. RF induced heating experiments (ASTM protocol) and balloon angioplasties of the iliac artery were conducted in a perfused vascular phantom and three Thiel soft-embalmed human cadavers.

Results

Device tip tracking was interleaved with various user-selectable fast pulse sequences receiving a geometry update from the tracking kernel in less than 30 ms. Integrating phase-field dithering significantly improved our tracking robustness for catheters with small diameters (4–6 French). The volume root mean square distance error was 2.81 mm (standard deviation: 1.31 mm). No significant RF induced heating (< 0.6 °C) was detected during heating experiments.

Conclusion

This tip tracking approach provides flexible, fast and robust feedback loop, intuitive iMRI scanner interaction, does not constrain the physician and delivers very low specific absorption rates. Devices with wRC can be exchanged during a procedure without modifications to the iMRI setup or the pulse sequence. A drawback of our current implementation is that position information is available for a single tracking coil only. This was satisfactory for balloon angioplasties of the iliac artery, but further studies are required for complex navigation and catheter shapes before animal trials and clinical application.