This paper presents an algorithm to estimate what parts of the surrounding environment are visible from each of many sample points on a surface, which may be highly folded and may contain holes. The results can be use...
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A method to scale and deform a trimmed NURBS surface while holding the shape and size of specific features (trimming curves) unchanged is presented. The new surface is formed by scaling the given surface according to ...
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Synchronization is an area that exhibits rich hardware-software interactions in multiprocessors. It was studied extensively using microbenchmarks a decade ago. However, its performance implications are not well unders...
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Synchronization is an area that exhibits rich hardware-software interactions in multiprocessors. It was studied extensively using microbenchmarks a decade ago. However, its performance implications are not well understood on modern systems or on real applications. We study the impact of synchronization primitives and algorithms on a modern, 64-processor, hardware-coherent shared address space multiprocessor: the SGI Origin 2000. In addition to the actual results on a modern system, we examine the key methodological issues in studying synchronization, for both microbenchmarks and applications. We find that although the efficient hardware support (Fetch&Op) for synchronization provided on our machine usually helps lock and barrier microbenchmarks, it does not help in improving application performance when compared to good software algorithms that use the processor-provided LL-SC instructions. This is true even in applications that spend a significant amount of time in synchronization operations. More elaborate hardware support is unlikely to have a significant benefit either. From the applications' perspective, it is usually the waiting time due to load imbalance or serialization that dominates synchronization time, not the overhead of the synchronization operations themselves, even in apparently balanced cases where the overhead may be expected to be substantial.
Layered Manufacturing (LM) is an emerging technology that is gaining importance in the manufacturing industry. (See e.g. the book by Jacobs [7].) This technology makes it possible to rapidly build three-dimensional ob...
ISBN:
(纸本)3540668365
Layered Manufacturing (LM) is an emerging technology that is gaining importance in the manufacturing industry. (See e.g. the book by Jacobs [7].) This technology makes it possible to rapidly build three-dimensional objects directly from their computer representations on a desktop-sized machine connected to a workstation. A specific process of LM, that is widely in use, is StereoLithography. The input to this process is the triangulated boundary of a polyhedral CAD model. This model is first sliced by horizontal planes into layers. Then, the object is built layer by layer in the following way. The StereoLithography apparatus consists of a vat of photocurable liquid resin, a platform, and a laser. Initially, the platform is below the surface of the resin at a depth equal to the layer thickness. The laser traces out the contour of the first slice on the surface and then hatches the interior, which hardens to a depth equal to the layer thickness. In this way, the first layer is created; it rests on the platform. Then, the platform is lowered by the layer thickness and the just-vacated region is re-coated with resin. The subsequent layers are then built in the same way.
In this paper we propose a new approach for the generation of visual scales for the visualization of scalar and multivariate data. Based on the specification of only a few correspondences between the data set and elem...
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An application of C/sup 1/ scalar interpolation for 2D vector field topology visualization is presented. Powell-Sabin and Nielson interpolants are considered which both make use of Nielson's Minimum Norm Network f...
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ISBN:
(纸本)078035897X
An application of C/sup 1/ scalar interpolation for 2D vector field topology visualization is presented. Powell-Sabin and Nielson interpolants are considered which both make use of Nielson's Minimum Norm Network for the precomputation of the derivatives in our implementation. A comparison of their results to the commonly used linear interpolant underlines their significant improvement of singularity location and topological skeleton depiction. Evaluation is based upon the processing of polynomial vector fields with known topology containing higher order singularities.
This paper emphasises a navigation method in a virtual environment, which is one of the major interfaces for interactivity between human and virtual environment. It proposes a new navigation method: intelligent cruise...
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This paper emphasises a navigation method in a virtual environment, which is one of the major interfaces for interactivity between human and virtual environment. It proposes a new navigation method: intelligent cruise-control navigation (ICCN) which provides a natural navigation method in a virtual environment and can improve telepresence and immersion; the final goal of virtual reality. The ICCN is composed of 3 major phases: constant velocity navigation (CVN); collision detecting and avoiding; and adjusting path phases. The ICCN can reduce user fatigue and improve user presence and reality in the virtual environments.
Controlling the running movement of a machine with jointed legs is a difficult problem in robotics. The control of a single running stride can be broken down into three phases; takeoff, ballistic, and landing. This pa...
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Controlling the running movement of a machine with jointed legs is a difficult problem in robotics. The control of a single running stride can be broken down into three phases; takeoff, ballistic, and landing. This paper describes the development of an intelligent controller for the landing phase of a simulated jointed leg's running stride. The landing controller takes control when the tool touches the ground after the airborne ballistic phase of the stride. It lears from experience to control the leg so as to recover from the impact with the ground and to reposition the leg for the takeoff of the next running stride. Very accurate control is achieved even during the first attempt at the running stride.
Stereotactic radiosurgery is a minimally invasive procedure that uses a focused beam of radiation as an ablative instrument to destroy brain tumors. To deposit a high dose of radiation in a tumor, while reducing the d...
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Stereotactic radiosurgery is a minimally invasive procedure that uses a focused beam of radiation as an ablative instrument to destroy brain tumors. To deposit a high dose of radiation in a tumor, while reducing the dose to healthy tissue, a large number of beams are crossfired at the tumor from multiple directions. The treatment planning problem (also called the inverse dosimetry problem) is to compute a set of beams that produces the desired dose distribution. So far its investigation has focused on the generation of isocenter-based treatments in which the beam axes intersect at a common point, the isocenter. However this restriction limits the applicability of the treatments to tumors which have simple shapes. This paper describes CARABEAMER, a new treatment planner for a radiosurgical system in which the radiation source can be arbitrarily positioned and oriented by a six-degree-of-freedom manipulator. This planner uses randomized techniques to guess a promising initial set of beams. It then applies space partitioning and linear programming techniques to compute the energy to be delivered along each beam. Finally, it exploits the results of the linear program to iteratively adapt and improve the beam set. Experimental results obtained with CARABEAMER on both patient and synthetic cases are presented and discussed. These results demonstrate that a radiosurgical system with general kinematics can deliver treatments in which the region receiving a high dose closely matches the shape of the tumor, even in complicated cases. They also suggest new research directions which are discussed at the end of the paper.
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