Tests for comparing images based on randomization and permutation methods

Tests comparing image sets can play a critical role in PET research, providing a yes-no answer to the question "Are two image sets different?" The statistical goal is to determine how often observed differences would occur by chance alone. We examined randomization methods to provide several omnibus test for PET images and compared these tests with two currently used methods. In the first series of analyses, normally distributed image data were simulated fulfilling the requirements of standard statistical tests. These analyses generated power estimates and compared the various test statistics under optimal conditions. Varying whether the standard deviations were local or pooled estimates provided an assessment of a distinguishing feature between the SPM and Montreal methods. In a second series of analyses, we more closely simulated current PET acquisition and analysis techniques. Finally, PET images from normal subjects were used as an example of randomization. Randomization proved to be a highly flexible and powerful statistical procedure. Furthermore, the randomization test does not require extensive and unrealistic statistical assumptions made by standard procedures currently in use.     

Adapting plans in progress in distributed supervisory work: aspects of complexity, coupling, and control

Distributed supervisory control systems often rely on complex and centralized plans to cope with a variety of unanticipated situations. Replanning requires practitioners to forgo standard procedures in favor of making simple plans without simplifying, managing task coupling, and anticipating team needs to provide decentralized and elaborate plans. This article proposes a plan classification scheme to study what features of plans facilitate or hinder adaptation and a framework to examine how features of plans influence the cognitive processes of replanning. The plan features have been assigned to the categories of plan complexity, coupling, and control. Plans are task networks sharing similar features of complexity and coupling to technical systems. The proposed framework sets out to explore how plan features influence the processes of recognizing plan disruptions, reviewing challenges and different team stances, repairing plans to resolve new risks, and reacting by coordinating team efforts to execute plans. The framework draws on the Extended Control Model (ECOM) to integrate the four processes of replanning into a set of control loops. The benefits of this framework are illustrated in the context of operator training and decision support.     

Spinal neurilemmomas and neurofibromas: central dot sign in postgadolinium MRI

The MR studies of three histologically proven spinal neurilemmomas and neurofibromas were reviewed retrospectively. There were two benign neurilemmomas (schwannomas) and one neurofibroma. The common characteristic of these cases was a central low intensity focus ("dot") seen on postcontrast T1-weighted imaging. The low intensity foci corresponded histologically to a congeries of changes including edema, microcysts, foam cells, hyalinization of blood vessels, old hemorrhage, and dystrophic calcification.     

Chlorpropamide-induced hypoglycemia: successful treatment with diazoxide

A healthy adolescent boy was treated on two occasions for an overdose of chlorpropamide (Diabinese). Glucose therapy alone was not sufficient to control the hypoglycemia, but the administration of glucose plus diazoxide raised the blood sugar to supranormal levels. A bolus of intravenous glucagon briefly raised the blood sugar level to within normal limits, increased the blood ketones but also augmented insulin secretion. An overdose of sulfonylurea may cause prolonged and fatal hypoglycemia. Rational therapy, both in diabetic and normal persons, is glucose plus an "insulin antagonist." The administration of diazoxide was effective in our patient, substantially reducing the plasma insulin level; this agent may be the "insulin-antagonist" of choice for use in sulfonylurea-induced hypoglycemia.     

Integrating operational and risk information with system risk models in air traffic control

Cognition, Technology & Work - The next generation Air Transport Management (ATM) requires performance-based safety management that is fully integrated into seamless operational management. To...     

Managing emergencies and abnormal situations in air traffic control (part II): Teamwork strategies

Team performance has been studied in many safety-critical organizations including aviation, nuclear power plant, offshore oil platforms and health organizations. This study looks into teamwork strategies that air traffic controllers employ to manage emergencies and abnormal situations. Two field studies were carried out in the form of observations of simulator training in emergency and unusual scenarios of novices and experienced controllers. Teamwork strategies covered aspects of team orientation and coordination, information exchange, change management and error handling. Several performance metrics were used to rate the efficiency of teamwork and test the construct validity of a prototype model of teamwork. This is a companion study to an earlier investigation of taskwork strategies in the same field (part I) and contributes to the development of a generic model for Taskwork and Teamwork strategies in Emergencies in Air traffic Management (T²EAM). Suggestions are made on how to use T²EAM to develop training programs, assess team performance and improve mishap investigations.     

Well Supported Approximate Equilibria in Bimatrix Games

In view of the apparent intractability of constructing Nash Equilibria (NE in short) in polynomial time, even for bimatrix games, understanding the limitations of the approximability of the problem is an important challenge.     

Folding pathway of a lattice model for proteins

The folding of a protein-like heteropolymer is studied by using direct simulation of a lattice model that folds rapidly to a well-defined "native" structure. The details of each molecular folding event depend on the random initial conformation as well as the random thermal fluctuations of the polymer. By analyzing the statistical properties of hundreds of folding events, a classical folding "pathway" for such a polymer is found that includes partially folded, on-pathway intermediates that are shown to be metastable equilibrium states of the polymer. These results are discussed in the context of the "classical" and "new" views of folding.     

Kinematic data on primate head and neck posture: implications for the evolution of basicranial flexion and an evaluation of registration planes used in paleoanthropology

Kinematic data on primate head and neck posture were collected by filming 29 primate species during locomotion. These were used to test whether head and neck posture are significant influences on basicranial flexion and whether the Frankfurt plane can legitimately be employed in paleoanthropological studies. Three kinematic measurements were recorded as angles relative to the gravity vector, the inclination of the orbital plane, the inclination of the neck, and the inclination of the Frankfurt plane. A fourth kinematic measurement was calculated as the angle between the neck and the orbital plane (the head-neck angle [HNA]). The functional relationships of basicranial flexion were examined by calculating the correlations and partial correlations between HNA and craniometric measurements representing basicranial flexion, orbital kyphosis, and relative brain size (Ross and Ravosa [1993] Am. J. Phys. Anthropol. 91:305-324). Significant partial correlations were observed between relative brain size and basicranial flexion and between HNA and orbital kyphosis. This indicates that brain size, rather than head and neck posture, is the primary influence on flexion, while the degree of orbital kyphosis may act to reorient the visual field in response to variation in head and neck posture. Regarding registration planes, the Frankfurt plane was found to be horizontal in humans but inclined in all nonhuman primates. In contrast, nearly all primates (including humans) oriented their orbits such that they faced anteriorly and slightly inferiorly. These results suggest that for certain functional craniometric studies, the orbital plane may be a more suitable registration plane than Frankfurt "Horizontal."