York University

About: York University is a education organization based out in Toronto, Ontario, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 18899 authors who have published 43357 publications receiving 1568560 citations.

Phase-based disparity measurement

Abstract: The measurement of image disparity is a fundamental precursor to binocular depth estimation. Recently, Jenkin and Jepson (in Computational Processes in Human Vision (V. Pylyshyn, Ed.), Ablex, New Jersey, 1988) and Sanger (Biol. Cybernet, 59, 1988 , 405–418) described promising methods based on the output phase behavior of bandpass Gabor filters. Here we discuss further justification for such techniques based on the stability of bandpass phase behavior as a function of typical distortions that exist between left and right views. In addition, despite this general stability, we show that phase signals are occasionally very sensitive to spatial position and to variations in scale, in which cases incorrect measurements occur. We find that the primary cause for this instability is the existence of singularities in phase signals. With the aid of the local frequency of the filter output (provided by the phase derivative) and the local amplitude information, the regions of phase instability near the singularities are detected so that potentially incorrect measurements can be identified. In addition, we show how the local frequency can be used away from the singularity neighbourhoods to improve the accuracy of the disparity estimates. Some experimental results are reported.

Paradoxes and dilemmas for stakeholder responsive firms in the extractive sector: lessons from the case of Shell and the Ogoni

Abstract: This paper examines some of the paradoxes and dilemmas facing firms in the extractive sector when they attempt to take on a more stakeholder-responsive orientation towards issues of environmental and social responsibility We describe the case of Shell and the Ogoni and attempt to draw out some of the lessons of that case for more sustainable operations in the developing world We argue that firms such as Shell, Rio Tinto and others may well exhibit increasingly stakeholder-responsive behaviours at the corporate, strategic level However for reasons of strategy, lack of competency or institutional will this increasing level of corporate responsiveness may not be mirrored effectively in dealings between subsidiary business units and their most important direct stakeholders: for example local communities and in the developing world We contrast the struggles of Shell to replicate its corporate stakeholder-responsiveness at the local level in Nigeria with the experiences of other firms that seem to have developed managerial capabilities at a somewhat deeper level throughout the firm with consequent benefits both for stakeholders and the business

Penalized Maximal t Test for Detecting Undocumented Mean Change in Climate Data Series

Abstract: In this paper, a penalized maximal t test (PMT) is proposed for detecting undocumented mean shifts in climate data series. PMT takes the relative position of each candidate changepoint into account, to diminish the effect of unequal sample sizes on the power of detection. Monte Carlo simulation studies are conducted to evaluate the performance of PMT, in comparison with the most popularly used method, the standard normal homogeneity test (SNHT). An application of the two methods to atmospheric pressure series recorded at a Canadian site is also presented. It is shown that the false-alarm rate of PMT is very close to the specified level of significance and is evenly distributed across all candidate changepoints, whereas that of SNHT can be up to 10 times the specified level for points near the ends of series and much lower for the middle points. In comparison with SNHT, therefore, PMT has higher power for detecting all changepoints that are not too close to the ends of series and lower power for d...

Hippocampal Atrophy in Normal Aging: An Association With Recent Memory Impairment

Abstract: • Objective. —To estimate the prevalence of radiographically detectable hippocampal atrophy (HA) in a normal aging sample and to test whether such atrophy is associated with memory dysfunction. Design. —One hundred fifty-four medically healthy and cognitively normal elderly persons (aged 55 to 88 years) received magnetic resonance imaging and/or computed tomographic scans designed to identify HA. One hundred forty-five of these subjects also underwent psychometric tests of memory function. Multivariate analyses of variance were used to evaluate differences in memory performance between subjects with and without HA. Setting. —This study was conducted at a research clinic for the investigation of age-associated neuropsychological and neuroradiologic changes. Participants. —Based on the following criteria, 154 subjects were consecutively selected from a larger group of elderly research volunteers participating in a study of normal aging: age of 55 years or greater; Global Deterioration Scale score of 2 or less; and Mini-Mental State examination score of 28 or greater. Subjects with evidence for significant medical, psychiatric, or neurologic disease were excluded. Main Outcome Measure. —Outcome measurements included individual psychometric test scores and computed tomographic—magnetic resonance imaging hippocampal atrophy ratings. Results. —Nearly 33% of the subjects had radiographic evidence for HA. The prevalence of HA increased significantly with age and was more common in male than female subjects. After controlling for age, level of education, and vocabulary, subjects with HA were found to perform more poorly on tests of recent (secondary) verbal memory when compared with subjects without HA ( P Conclusion. —We conclude that HA is a common accompaniment of normal aging and is associated with mild memory impairment. Additional research is needed to determine whether HA constitutes a significant risk for future dementia.