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Bugs in distributed systems are often hard to find. Many bugs reflect discrepancies between a system's behavior and the programmer's assumptions about that behavior. We present Pip 1 , an infrastructure for comparing actual behavior and expected behavior to expose structural errors and performance problems in distributed systems. Pip allows programmers to(More)
Device drivers typically execute in supervisor mode and thus must be fully trusted. This paper describes how to move them out of the trusted computing base, by running them without supervisor privileges and constraining their interactions with hardware devices. An implementation of this approach in the Nexus operating system executes drivers in user space,(More)
Many interesting large-scale systems are distributed systems of multiple communicating components. Such systems can be very hard to debug, especially when they exhibit poor performance. The problem becomes much harder when systems are composed of "black-box" components: software from many different (perhaps competing) vendors, usually without source code(More)
Wide-area distributed applications are challenging to debug, optimize, and maintain. We present Wide-Area Project 5 (WAP5), which aims to make these tasks easier by exposing the causal structure of communication within an application and by exposing delays that imply bottlenecks. These bottlenecks might not otherwise be obvious, with or without the(More)
Creutzfeldt-Jakob disease (CJD) causes diffuse neurological symptoms, but asymmetric lesions have been found on conventional magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI). Less often, position emission tomography (PET) scanning can also reveal asymmetric lesions in patients with CJD. Such imaging may mislead clinicians. The authors(More)
This paper describes the design and implementation of a new operating system authorization architecture to support trustworthy computing. Called <i>logical attestation</i>, this architecture provides a sound framework for reasoning about run time behavior of applications. Logical attestation is based on attributable, unforgeable statements about program(More)
The key principles behind current peer-to-peer research include fully distributing service functionality among all nodes participating in the system and routing individual requests based on a small amount of locally maintained state. The goals extend much further than just improving raw system performance: such systems must survive massive concurrent(More)
Mentoring is deeply rooted in medical practice. More than just a role model, a mentor is invested in the development of the mentee, providing personal and professional support, guidance, and the means for advancement. Mentoring is vital at all levels of medical training and plays an important role in the development of academicians. Increasing clinical(More)
Magnetic resonance imaging (MRI) of rodent brains enables study of the development and the integrity of the brain under certain conditions (alcohol, drugs etc.). However, these images are difficult to analyze for biomedical researchers with limited image processing experience. In this paper we present an image processing pipeline running on a Midas server,(More)