William E. Johnston

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We have implemented and deployed an access control mechanism that uses digitally-signed certificates to define and enforce an access policy for a set of distributed resources that have multiple, independent and geographically dispersed stakeholders. The stakeholders assert their access requirements in use-condition certificates and designate those trusted(More)
We describe a methodology that enables the real-time diagnosis of performance problems in complex high-performance distributed systems. The methodology includes tools for generating precision event logs that can be used to provide detailed end-to-end application and system level monitoring; a Java agent-based system for managing the large amount of logging(More)
With the advent of service sensitive applications such as remote controlled experiments, time constrained massive data transfers, and video-conferencing, it has become apparent that there is a need for the setup of dynamically provisioned, quality of service enabled virtual circuits. The ESnet on-demand secure circuits and advance reservation system(More)
Information Power Grid (IPG) is the name of NASA’s project to build a fully distributed computing and data management environment – a Grid. The IPG project has near, medium, and long-term goals that represent a continuum of engineering, development, and research topics. The overall goal is to provide the NASA scientific and engineering communities a(More)
As the practice of science moves beyond the single investigator due to the complexity of the problems that now dominate science, large collaborative and multi-institutional teams are needed to address these problems. In order to support this shift in science, the computing and data handling infrastructure that is essential to most of modern science must(More)
BACKGROUND We hypothesized that 1) endogenous adenosine released during ischemia conferred an inherent cardioprotection, and 2) a pretreatment dose of adenosine before ischemia would provide additional protection independent of hemodynamic effects. METHODS AND RESULTS Thirty-six anesthetized New Zealand White rabbits underwent 30 minutes of regional(More)
OBJECTIVE The aim was to test the hypothesis that the cardioprotective effects against ischaemic-reperfusion injury of pretreatment with adenosine are mediated in part by activation of ATP sensitive potassium channels (K+ATP channels). METHODS 42 anaesthetised New Zealand White rabbits underwent 30 min coronary occlusion, followed by 2 h reperfusion. Half(More)
The decrease in left ventricular (LV) stroke volume during positive end-expiratory pressure (PEEP) has been attributed to reduced LV filling and a decreased contractile state. To assess the relative importance of each mechanism, we examined the effects of zero, 5, 10, and 15 cm H2O PEEP on LV end-diastolic volume (EDV) and end-systolic volume (ESV), and on(More)
A mathematical model describing the dynamic interaction between the left and the right ventricle over the complete cardiac cycle is presented. The pericardium-bound left and right ventricles are represented as two coupled chambers consisting of the left and right free walls and the interventricular septum. Time-varying pressure-volume relationships(More)