Philip M. Papadopoulos

Inverse Dynamics and Kinematics of Multi- Link Elastic Robots: An Iterative Frequency Domain Approach

A technique is presented and experimentally validated for solving the inverse dynamics and kinematics of multi-link flexible robots. The proposed method finds the joint torques necessary to produce a specified end-effector motion. Since the inverse dynamic problem in elastic manipulators is closely coupled to the inverse kinematic problem, the solution of the first also renders the displacements and rotations at any point of the manipulator, including the joints. Further more the formulation is complete in the sense that it includes all the nonlinear terms due to the large rotation of the links. The Timoshenko beam theory is used to model the elastic characteristics, and the resulting equations of motion are discretized using the finite element method. An iterative solu tion scheme is proposed that relies on local linearization of the problem. The solution of each linearization is carried out in the frequency domain. The performance and capabilities of this technique are tested, first through simulation analysis, and second through experimental validation using feed-forward control. Results show the potential use of this method not only for open-loop control, but also for incorporation in feedback control strate gies. 1. This section contains a revised and corrected formulation of open-chain case. A previous method reported by the first author in: Computed Torque for the Fosition Control of Open-Chain Flexible Robots. Proc. 1988 IEEE International Conference in Robotics and Automation contained an error.

NPACI Rocks: tools and techniques for easily deploying manageable Linux clusters

High‐performance computing clusters (commodity hardware with low‐latency, high‐bandwidth interconnects) based on Linux are rapidly becoming the dominant computing platform for a wide range of scientific disciplines. Yet, straightforward software installation, maintenance, and health monitoring for large‐scale clusters has been a consistent and nagging problem for non‐cluster experts. The NPACI Rocks distribution takes a fresh perspective on management and installation of clusters to dramatically simplify software version tracking and cluster integration.

The OptIPuter

This architecture/infrastructure of parallel optical networks couples data exploration, visualization, and collaboration technologies through IP at multi-gigabit speeds.

A National Human Neuroimaging Collaboratory Enabled by the Biomedical Informatics Research Network (BIRN)

The aggregation of imaging, clinical, and behavioral data from multiple independent institutions and researchers presents both a great opportunity for biomedical research as well as a formidable challenge. Many research groups have well-established data collection and analysis procedures, as well as data and metadata format requirements that are particular to that group. Moreover, the types of data and metadata collected are quite diverse, including image, physiological, and behavioral data, as well as descriptions of experimental design, and preprocessing and analysis methods. Each of these types of data utilizes a variety of software tools for collection, storage, and processing. Furthermore sites are reluctant to release control over the distribution and access to the data and the tools. To address these needs, the biomedical informatics research network (BIRN) has developed a federated and distributed infrastructure for the storage, retrieval, analysis, and documentation of biomedical imaging data. The infrastructure consists of distributed data collections hosted on dedicated storage and computational resources located at each participating site, a federated data management system and data integration environment, an extensible markup language (XML) schema for data exchange, and analysis pipelines, designed to leverage both the distributed data management environment and the available grid computing resources.

NPACI: rocks: tools and techniques for easily deploying manageable Linux clusters

High-performance computing clusters (commodity hardware with low-latency, high-bandwidth interconnects) based on Linux, are rapidly becoming the dominant computing platform for a wide range of scientific disciplines.Yet, straightforward software installation, maintenance, and health monitoring for large-scale clusters has been a consistent and nagging problem for non-cluster experts.The NPACI Rocks toolkit takes a fresh perspective on management and installation of clusters to dramatically simplify software version tracking, and cluster integration.The toolkit incorporates the latest Red Hat distribution (including security patches) with additional cluster-specific software.Using the identical software tools used to create the base distribution, users can customize and localize Rocks for their site.Strong adherence to widely-used (\emph{de facto}) tools allows Rocks to move with the rapid pace of Linux development.Version 2.1 of the toolkit is available for download and installation.To date, 10 clusters spread among 5 institutions have been built using this toolkit.

Design and Evaluation of Opal2: A Toolkit for Scientific Software as a Service

Grid computing provides mechanisms for making large-scale computing environments available to the masses. In recent times, with the advent of Cloud computing, the concepts of Software as a Service (SaaS), where vendors provide key software products as services over the internet that can be accessed by users to perform complex tasks, and Service as Software (SaS), where customizable and repeatable services are packaged as software products that dynamically meet the demands of individual users, have become increasingly popular. Both SaaS and SaS models are highly applicable to scientific software and users alike. Opal2 is a toolkit for wrapping scientific applications as Web services on Grid and cloud computing resources. It provides a mechanism for scientific application developers to expose the functionality of their codes via simple Web service APIs, abstracting out the details of the back-end infrastructure. Services may be combined via customized workflows for specific research areas and distributed as virtual machine images. In this paper, we describe the overall philosophy and architecture of the Opal2 framework, including its new plug-in architecture and data handling capabilities. We analyze its performance in typical cluster and Grid settings, and in a cloud computing environment within virtual machines, using Amazons Elastic Computing Cloud (EC2).

Rolls: modifying a standard system installer to support user-customizable cluster frontend appliances

The Rocks toolkit uses a graph-based framework to describe the configuration of all node types (termed appliances) that make up a complete cluster. With hundreds of deployed clusters, our turnkey systems approach has shown to be quite easily adapted to different hardware and logical node configurations. However, the Rocks architecture and implementation contains a significant asymmetry: the graph definition of all appliance types except the initial frontend can be modified and extended by the end-user before installation. However, frontends can be modified only afterward by hands-on system administration. To address this administrative discontinuity between nodes and frontends, we describe the design and implementation of Rolls. First and foremost, Rolls provide both the architecture and mechanisms that enable the end-user to incrementally and programmatically modify the graph description for all appliance types. New functionality can be added and any Rocks-supplied software component can be overwritten or removed simply by inserting the desired Roll CD(s) at installation time. This symmetric approach to cluster construction has allowed us to shrink the core of the Rocks implementation while increasing flexibility for the end-user. Rolls are optional, automatically configured, cluster-aware software systems. Current add-ons include: scheduling systems (SGE, PBS), grid support (based on NSF Middleware Initiative), database support (DB2), Condor, integrity checking (Tripwire) and the Intel compiler. Community-specific Rolls can be and are developed by groups outside of the Rocks core development group.

HARNESS: Heterogeneous Adaptable Reconfigurable NEtworked SystemS

We describe our vision, goals and plans for HARNESS, a distributed, reconfigurable and heterogeneous computing environment that supports dynamically adaptable parallel applications. HARNESS builds on the core concept of the personal virtual machine as an abstraction for distributed parallel programming, but fundamentally extends this idea, greatly enhancing dynamic capabilities. HARNESS is being designed to embrace dynamics at every level through a pluggable model that allows multiple distributed virtual machines (DVMs) to merge, split and interact with each other. It provides mechanisms for new and legacy applications to collaborate with each other using the HARNESS infrastructure, and defines and implements new plug-in interfaces and modules so that applications can dynamically customize their virtual environment. HARNESS fits well within the larger picture of computational grids as a dynamic mechanism to hide the heterogeneity and complexity of the nationally distributed infrastructure. HARNESS DVMs allow programmers and users to construct personal subsets of an existing computational grid and treat them as unified network computers, providing a familiar and comfortable environment that provides easy-to-understand scoping.

The OptIPuter: high-performance, QoS-guaranteed network service for emerging E-science applications

Emerging large-scale scientific applications have a critical need for high bandwidth and predictable-performance network service. The OptlPuter project is pioneering a radical new type of distributed application paradigm that exploits dedicated optical circuits to tightly couple geographically dispersed resources. These private optical paths are set up on demand and combined with end resources to form a distributed virtual computer (DVC). The DVC provides high-quality dedicated network service to applications. In this article we compare the OptIPuters approach (DVC), which exploits network resources to deliver higher-quality network services, to several alternative service models (intelligent network and asynchronous file transfer). Our simulations show that there are significant differences among the models in their utilization of resources and delivered application services. Key takeaways include that the OptlPuter approach provides applications with superior network service (as needed by emerging e-science applications and performance-critical distributed applications), at an expense in network resource consumption. The other approaches use fewer network resources, but provide lower-quality application service

The PRAGMA Testbed - Building a Multi-Application International Grid

This practices and experience paper describes the coordination, design, implementation, availability, and performance of the Pacific Rim Applications and Grid Middleware Assembly (PRAGMA) Grid Testbed. Applications in high-energy physics, genome annotation, quantum computational chemistry, wildfire simulation, and protein sequence alignment have driven the middleware requirements, and the testbed provides a mechanism for international users to share software beyond the essential, de facto standard Globus core. In this paper, we describe how human factors, resource availability and performance issues have affected the middleware, applications and the testbed design. We also describe how middleware components in grid monitoring, grid accounting, grid Remote Procedure Calls, grid-aware file systems, and grid-based optimization have dealt with some of the major characteristics of our testbed. We also briefly describe a number of mechanisms that we have employed to make software more easily available to testbed administrators.