Various techniques for object selection in virtual environments have been proposed over the years. Among them, the virtual pointer or ray-casting is one of the most popular method for object selection because it is easy and intuitive to use and allows the user to select objects that are far away. Variants of the virtual pointer metaphor include the Aperture [5], Flashlight [3], and Image plane method [fl as categorized as such by [10]. In a monoscopic environment, these methods are essentially 2D interaction techniques, as the selection is made effectively on the image plane. Such a 2D based selection (or more generally, interaction) method has an added advantage in that it can find many good uses in 3D environments ranging from a simple 2D oriented subtask (object selection on a constrained surface, menu selection) to a siutation where a whole 2D application (e.g. sketching tool, desktop manager) is embedded in the 3D environment. In this paper, we experimentally compare the performance of four different virtual pointer implementations, namely, the direct image plane selection, head-directed pointer, hand directed pointer and head-hand directed pointer. The experimental results revealed that the direct image plane selection produced the best performance among the four in terms ofboth task completion time and the pixel-level pointing error.

We propose a new polygonal approximation method for soft objects. While the conventional polygonization methods decompose space into small-sized cells and compute many pieces of polygons for the cells, this new method polygonizes a soft object by smoothing an initial polygonal approximation using subdivision surface schemes. The initial polygonal approximation is generated by the union of the polygonal approximations of the components that constitute the soft object. Our method has many advantages over the conventional methods: faster computation time, regular-sized polygons, efficient robust results, and multiresolutional representation. These features will lead to an interactive modeling environment using soft objects as well as an efficient polygonal representation that is proper to be used in virtual reality and distributed environments.

We present a fast visualization scheme of soft objects by introducing an efficient evaluation method for a field function. The evaluation of a field function includes distance computation between a point in space and the defining primitives of the soft object. If the unnecessary distance computations between a point in space and the components that do not influence the point can be avoided, the evaluation can be accelerated. For this purpose, we decompose the space into adaptive‐sized cells according to the bounding volume of the components and build a data structure called an interval tree through which the influencing components for a point are sought. The bounding volume of a component is generated by considering the radius of a component and k‐DOPs. The proposed scheme can be used in many applications for soft objects such as modeling and rendering, especially in the interactive modeling process. Copyright © 2003 John Wiley & Sons, Ltd.

A two measurement points pulse techniqque was employed to determine axial dispersion coefficients in a 3/4 inch diameter pipe with four 90 degree bends located at 50 inch intervals. Water velocities corresponding to Reynold numbers of 3,800 to 11,500 were used. It was found that the effect of bends on the overall dispersion coefficient depends on the Reynolds number and a characteristic length. Two mathematical models of a reactor with bends are presented. One model assumed that the bend section is a perfectly mixed reactor with an equivalent length. The second assumed a fixed equivalent length for the bend section and a proportional relationship between the dispersion coefficients in the bend and the straight section.

Real-time applications require an eficient scheduler supporting multiple priority levels and fast preemption. In this paper, we propose a scheduler based on the hardware-supported scheduler of transputers, Though the hardware-supported scheduler of transputers is very eficient in terms of scheduling overhead, it should be extended to support multiple priority levels and fast preemption in order to be used in real-time applications. Many schedulers have been proposed. However, they have several drawbacks in terms of scheduling overhead, preemption latency, and portability. I n reference [3], we have proposed a scheduler featuring low Scheduling overhead and portability while suflering from a long preemption delay. In this paper, we propose an improved scheduler which greatly reduces preemption delay by using ISL (Interrupt Save Location) an transputers. Experimental results show that the improved scheduler overhead is about 13.54psec and its preemption delay is well below 42psec.