The effect of visualization method on the performance of simulated microsurgery tasks

The operating microscopes may be a significant cause of fatigue and discomfort in surgeons. The need for the microscope to be placed over the operating field forces surgeons to remain at the microscope's eyepieces at an uncomfortable posture for the entirety of the surgery. This study compared the effects on microsurgical task performance for four visualization methods: a monocular microscope, a binocular microscope, a three-dimensional (3D) flat-panel television display and a two-dimensional (2D) flat-panel television display. Eleven subjects each performed two microsurgical tasks and their performance was documented by video camera. The statistical analysis performed indicated utilization of the microscope as a visualization method increased subject performance. No significant difference in performance between the 2D and stereoscopic visualization methods.     

TEACHING THE PRODUCTION/OPERATIONS MANAGEMENT CORE COURSE: INTEGRATING LOGISTICS PLANNING ACTIVITIES

This paper discusses the benefits of restructuring the introductory undergraduate production and operations management (pom) course to improve its pedagogical effectiveness and to better convey the importance of integrating logistics planning activities. The introduction of a dynamic integrative semester-long case study which involves students in applying pom concepts and tools through a simulation game is reported.     

The dynamics of hapū research relationships

Abstract

The Whakaki Lake Trust has a long history of being an active kaitiaki of Whakaki Lake and has developed a hapū-based restoration and enhancement programme at the Lake property. Part of this programme has involved working with a range of external agencies and researchers. Research relationships have become an important part of the restoration process to build the capability and capacity of hapū to execute activities associated with restoration. In addition, relationships have provided an opportunity to strengthen and expand the knowledge base that hapū can draw upon to inform ecological restoration and resource management decisions. Some of these relationships have been adversarial and a source of much frustration. As a consequence the Trust has developed very clear expectations and policy around working with others. My experience of developing a doctoral research project with Whakaki Lake Trust is used here to discuss hapū expectations of research and resultant academic dilemmas.     

Penalized Maximum Likelihood Estimator for Normal Mixtures

The estimation of the parameters of a mixture of Gaussian densities is considered, within the framework of maximum likelihood. Due to unboundedness of the likelihood function, the maximum likelihood estimator fails to exist. We adopt a solution to likelihood function degeneracy which consists in penalizing the likelihood function. The resulting penalized likelihood function is then bounded over the parameter space and the existence of the penalized maximum likelihood estimator is granted. As original contribution we provide asymptotic properties, and in particular a consistency proof, for the penalized maximum likelihood estimator. Numerical examples are provided in the finite data case, showing the performances of the penalized estimator compared to the standard one.     

中国古代慈善事业的发展特点

中国古代慈善事业在漫长的历史发展过程中不但逐渐形成了庞杂而丰富的思想体系,而且其慈善主体也实现了从最初单纯的国家慈善到以国家慈善为主、宗族慈善和宗教慈善为重要补充的多元化发展过程。另外,中国古代慈善事业的发展轨迹还明显具备与整个中国古代社会兴衰相表里的重要特点。     

Quantitative posture analysis of 2D, 3D, and optical microscope visualization methods for microsurgery tasks

The purpose of this paper is to present a quantitative posture analysis of microsurgery tasks performed with different visualization methods. Microsurgery is traditionally performed using a binocular microscope; however surgeons are constrained by the optical eyepieces and are forced to assume joint angles that deviate away from neutral postures. This may be especially problematic for the neck and can increase surgeon discomfort and fatigue. Alternative visualization methods may improve surgeon posture by eliminating the constraints imposed by the microscope. This study examines both 2D and 3D heads-up displays as possible alternatives. Six subjects performed microsurgical tasks with each visualization methods for four hours. Quantitative posture analysis was done using Maxtraq software that tracks reflective markers on the subjects. The initial analysis of neck, upper arm, and elbow angles found significant differences between each display. A biomechanical analysis found that the differences in angles can result in loads on the neck joint that are twice as high in the microscope than the headsup displays. Although the alternative displays can result in better postures, improvements the display technology is needed to improve microsurgical task performance.     

Non-parametric Quantile Regression with Censored Data

Abstract.  Censored regression models have received a great deal of attention in both the theoretical and applied statistics literature. Here, we consider a model in which the response variable is censored but not the covariates. We propose a new estimator of the conditional quantiles based on the local linear method, and give an algorithm for its numerical implementation. We study its asymptotic properties and evaluate its performance on simulated data sets.     

Estimating the Effects of Residential Mobility: A Methodological Note

This article reviews the methodological challenges of estimating a causal association between mobility and children's cognitive, social, emotional, and physical development. Utilizing a comprehensive set of empirical articles published in the past 25 years that employ quantitative methods, it describes the limitations of previous studies and the innovative ways that researchers have attempted to deal with them. The concept of mobility is inconsistently operationalized along four dimensions: school versus residential, distance, timing, and frequency. Imprecise operationalization conflates different forms of mobility, which have differential effects on development. Attempts to estimate a causal association between mobility and development suffer from three sources of bias: selection, contextual shifts, and contemporaneous instigating events. (a) Methods that account for unobserved differences between mobile and nonmobile children have consistently shown smaller or even positive effects of mobility. (b) Moving can have a positive or negative effect on children's ecological contexts in ways that are systematically correlated with child development. (c) Moves are frequently catalyzed by changes in family structure and employment. The article concludes with recommendations for future research. Researchers should continue to engage fixed- and random-effect, matching, and instrumental variable techniques, each of which makes the question of causality explicit.