G.D. van Albada

The implementation of dynamite: an environment for migrating PVM tasks

Parallel programming on clusters of workstations is increasingly attractive, but dynamic load balancing is needed to make efficient use of the available resources. Dynamite provides dynamic load balancing for PVM applications running under Linux and Solaris. It supports migration of individual tasks between nodes in a manner transparent both to the application programmer and to the user, implemented entirely in user space. Dynamically linked executables are supported, as are tasks with open files and with direct PVM connections. In this paper, we describe the technical aspects of migrating message-passing tasks.

A low-cost pose-measuring system for robot calibration

To maintain robot accuracy, calibration equipment is needed. In this paper we present a self-calibrating measuring system based on a camera in the robot hand plus a known reference object in the robot workspace. A collection of images of the reference object is obtained. Using image-processing, image-recognition and photogrammetric techniques, the positions and orientations of the camera are computed. The essential geometrical and optical camera parameters can be derived from the redundancy in the measurements. From each image the positions of markers on the reference object are extracted and the individual markers are identified. The camera positions for all images plus the parameters of the camera are solved together in a non-linear least-squares fitting procedure. Experimental results for this low-cost measuring system are presented.

First Prototype of the CrossGrid Testbed

The CrossGrid project is developing new grid middleware components, tools and applications with a special focus on parallel and interactive computing. In order to support the development effort and provide a test infrastructure, an international grid testbed has been deployed across 9 countries. Through the deployment of the testbed and its supporting services, CrossGrid is also contributing to another important project objective, the expansion of the grid coverage in Europe. This paper describes the status of the CrossGrid testbed.

The Polder Computing Environment: a system for interactive distributed simulation

The paper provides an overview of an experimental, Grid‐like computing environment, Polder, and its components. Polder offers high‐performance computing and interactive simulation facilities to computational science. It was successfully implemented on a wide‐area cluster system, the Distributed ASCI Supercomputer. An important issue is an efficient management of resources, in particular multi‐level scheduling and migration of tasks that use PVM or sockets. The system can be applied to interactive simulation, where a cluster is used for high‐performance computations, while a dedicated immersive interactive environment (CAVE) offers visualization and user interaction. Design considerations for the construction of dynamic exploration environments using such a system are discussed, in particular the use of intelligent agents for coordination. A case study of simulatedabdominal vascular reconstruction is subsequently presented: the results of computed tomography or magnetic resonance imaging of a patient are displayed in CAVE, and a surgeon can evaluate the possible treatments by performing the surgeries virtually and analysing the resulting blood flow which is simulated using the lattice‐Boltzmann method. Copyright

Performance modeling of distributed hybrid architectures

Hybrid architectures are systems where a high performance general purpose computer is coupled to one or more special purpose devices (SPDs). Such a system can be the optimal choice for several fields of computational science. Configuring the system and finding the optimal mapping of the application tasks onto the hybrid machine often is not straightforward. Performance modeling is a tool to tackle and solve these problems. We have developed a performance model to simulate the behavior of a hybrid architecture consisting of a parallel multiprocessor where some nodes are the host of a GRAPE board. GRAPE is a very high performance SPD used in computational astrophysics. We validate our model on the architecture at our disposal, and show examples of predictions that our model can produce.

Toward Grid-Aware Time Warp

The authors study the adaptation of an optimistic Time Warp kernel to cross-cluster computing on the Grid. Wide-area communication, the primary source of overhead, is offloaded onto dedicated routing processes. This allows the simulation processes to run at full speed and thus significantly decreases the performance gap caused by the wide-area distribution. Further improvements are obtained by employing message aggregation on the wide-area links and using a distributed global virtual time algorithm. The authors achieve many of their objectives for a cellular automaton simulation with lazy cancellation and moderate communication. High communication rates, especially with aggressive cancellation, present a challenge. This is confirmed by the experiments with synthetic loads. Even then, a satisfactory speedup can be achieved, provided that the computational grain of events is large enough.

Time Warp cancellation optimizations on high latency networks

We investigate the performance of the time warp kernel APSIS when running on various communication layers, in particular on a wide-area grid. Several cancellation strategies are tried, among them the lazy cancellation and a little known bulk anti-messages optimization. Our experiments with an Ising spin simulation indicate that the slowdown caused by high latency networks, while significant, is not catastrophic; and that it can be significantly reduced using the lazy cancellation. Experiments suggest that further improvements can be expected if a more elaborate communication infrastructure is put in place.

Eye in hand robot calibration

Outlines research work to design a robot calibration system which is portable, accurate and low‐cost. Describes prototype measuring system which is based on a camera in the robot hand, plus a known reference object in the robot workspace. Gives details of the measuring procedure, the camera lens, the reference plate and the possible sources of measurement errors. Concludes that this method, based on photogrammetry to obtain measurements for the calibration of robot systems, has been implemented and tested and provides promising results for practical application.

Measurement of mechanical vibrations excited in aluminum resonators by 0.6 GeV electrons

We present measurements of mechanical vibrations induced by 0.6 GeV electrons impinging on cylindrical and spherical aluminum resonators. To monitor the amplitude of the resonator’s vibrational modes we used piezoelectric ceramic sensors calibrated by standard accelerometers. Calculations using the thermo-acoustic conversion model agree well with the experimental data, as demonstrated by specific variations of the excitation strengths with the absorbed energy, and with the traversing particles’ track positions. For the first longitudinal mode of the cylindrical resonator we measured a conversion factor of 7.4±1.4 nm/J, confirming the model value of 10 nm/J. Also, for the spherical resonator, we found the model values for the L=2 and L=1 mode amplitudes to be consistent with our measurement. We thus have confirmed the applicability of the model, and we note that calculations based on the model have shown that next generation resonant mass gravitational wave detectors can only be expected to reach their int...

Simulation of gravitational wave detectors

A simulation program that provides insight into the vibrational properties of resonant mass gravitational radiation antennas is developed from scratch. The requirements that are set necessitate the use of an explicit finite element kernel. Since the computational complexity of this kernel requires significant computing power, it is tailored for execution on parallel computer systems. After validating the physical correctness of the program as well as the performance on distributed memory architectures, we present a number of “sample” simulation experiments to illustrate the simulation capabilities of the program. The development path of the code, consisting of problem definition, mathematical modeling, choosing an appropriate solution method, parallelization, physical validation, and performance validation, is argued to be typical for the design process of large-scale complex simulation codes.