In this paper, we discuss the recent ESG's development and implementation efforts concerning its authentication infrastructure. ESG's requirements are to make the user's logon-experience as easy as possible, and to facilitate the integration of the security services and the Grid components for both the developers and system administrators. To meet that goal, we leverage existing primary authentication mechanisms, deploy a "lightweight" but secure OpenID WebSSO, deploy a "lightweight" X.509-PKI, and use autoprovisioning to ease the burden of security configuration management. We're close to finalizing the associated development and deployment.
We introduce and discuss preliminary experience with an application that has vast potential to exploit the Grid for social benefit and offers interesting resource assessment and allocation challenges, having real-time aspects: image registration. Image registration is generally formulated as an optimization problem that satisfies constraints, such as coordinate displacements that are affine or volumepreserving or that obey the laws of elasticity. Three-dimensional registration of high-resolution images is computationally complex and justifies parallel implementation. In turn, ensembles of registration tasks exploit concurrency in the simpler sense of job farming.Registration is an elementary example of a much larger class of large-scale mesh-based computations that are in principle amenable to execution on the Grid, but are sensitive to workload-to-capability balance at synchronization points. While better resource assessment and allocation tools lift all such applications, reducing sensitivity to synchronization within an individual application is a complementary and equally important objective. We therefore examine the potential for weakening the synchronization sensitivity of general mesh-based bulk synchronous computations through less restrictive programming paradigms.Keywords: Medical image registration, asynchronous numerical algorithms, Grid-based processing, MPI-based parallelization Imaging applications are ripe for the Grid. The Globus-based MEDICUS system has already "broken the medical image communication barrier" [17], in the sense that raw images can be shared with unprecedented speed and transparency. The communication breakthroughs of the Grid create opportunities in Grid-enabled processing, as well, by opening up vast possibilities for registration of images that were previously not simultaneously available.Numerical computing on the Grid, of which image registration is an example, is, in turn, only one of several categories of Grid-based applications, and has not so far been a significant driver of the Grid overall. The Grid is yet to be exploited by most computational scientists, though it is potentially very useful for applications requiring real-time solution or exceptional amounts of memory. This potential will be realized after two independent trends, each with its own inertia, converge: better tools for understanding and harnessing the dynamic performance capabilities of the Grid, and better asynchronous algorithms implemented in consistency-relaxed parallel programming models.A basic problem that motivates this work can be posed as follows: given a number of images that require registration, an MPI-based program to perform the registration, and a collection of Grid-enabled compute resources, compute the registrations by a specified time or estimate for the user what portion of the registrations can be completed before a given time. A currently available affine linear registration code has complexity roughly linear in the voxel volume. The target images are 1024 3 . Our test images of 128...
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