Optimal recovery schemes in fault tolerant distributed computing

Clusters and distributed systems offer fault tolerance and high performance through load sharing. When all n computers are up and running, we would like the load to be evenly distributed among the computers. When one or more computers break down, the load on these computers must be redistributed to other computers in the system. The redistribution is determined by the recovery scheme. The recovery scheme is governed by a sequence of integers modulo n. Each sequence guarantees minimal load on the computer that has maximal load even when the most unfavorable combinations of computers go down. We calculate the best possible such recovery schemes for any number of crashed computers by an exhaustive search, where brute force testing is avoided by a mathematical reformulation of the problem and a branch-and-bound algorithm. The search nevertheless has a high complexity. Optimal sequences, and thus a corresponding optimal bound, are presented for a maximum of twenty one computers in the distributed system or cluster.Received: 26 May 2004, Published online: 14 March 2005     

Design automation for customized apparel products

This paper presents solution techniques for a three-dimensional Automatic Made-to-Measure scheme for apparel products. Freeform surface is adopted to represent the complex geometry models of apparel products. When designing the complex surface of an apparel product, abstractions are stored in conjunction with the models using a non-manifold data structure. Apparel products are essentially designed with reference to human body features, and thus share a common set of features as the human model. Therefore, the parametric feature-based modeling enables the automatic generation of fitted garments on differing body shapes. In our approach, different apparel products are each represented by a specific feature template preserving its individual characteristics and styling. When the specific feature template is encoded as the equivalent human body feature template, it automates the generation of made-to-measure apparel products. The encoding process is performed in 3D, which fundamentally solves the fitting problems of the 2D tailoring and pattern-making process. This paper gives an integrated solution scheme all above problems. In detail, a non-manifold data structure, a constructive design method, four freeform modification tools, and a detail template encoding/decoding method are developed for the design automation of customized apparel products.     

Augmented geophysical data interpretation through automated velocity picking in semblance velocity images

Velocity picking is the problem of picking velocity–time pairs based on a coherence metric between multiple seismic signals. Coherence as a function of velocity and time can be expressed as a 2D color semblance velocity image. Currently, humans pick velocities by looking at the semblance velocity image; this process can take days or even weeks to complete for a seismic survey. The problem can be posed as a geometric feature-matching problem. A feature extraction algorithm can recognize islands (peaks) of maximum semblance in the semblance velocity image: a heuristic combinatorial matching process can then be used to find a subset of peaks that maximizes the coherence metric. The peaks define a polyline through the image, and coherence is measured in terms of the summed velocity under the polyline and the smoothness of the polyline. Our best algorithm includes a constraint favoring solutions near the median solution for the local area under consideration. First, each image is processed independently. Then, a second pass of optimization includes proximity to the median as an additional optimization criterion. Our results are similar to those produced by human experts. Accepted: 15 June 2001     

Recent Advancement in Titanium Near-Net-Shape Technology

JOM - Significant advancements in near-net-shape technologies for titanium alloys have been achieved in 1970s. These technologies are now readily applicable as major manufacturing methods of...     

Knowledge in Regional Economic Growth—The Role of Knowledge Accessibility

This paper analyzes the role of knowledge in regional economic growth by focusing on knowledge accessibility. The research question is the following: can the variation in knowledge accessibility between regions in a given period explain the variation in growth performance of regions in subsequent periods? A main assumption in the paper is that knowledge accessibility transforms into potential knowledge flows. Our results show that differences in growth of value-added per employee across regions can be explained by differences in knowledge accessibility. Intra-municipal and intra-regional knowledge accessibilities are significant and capable of explaining a significant share of the variation in growth of value-added per employee between Swedish municipalities. However, inter-regional knowledge accessibility turned out to be insignificant. This is interpreted as a clear indication of spatial dependence in the sense that the knowledge resources in a given municipality tend to have a positive effect on the growth of other municipalities, conditional on that the municipalities belong to the same functional region. Thus, the results of the analysis indicate that knowledge flows transcend municipal borders, but that they tend to be bound within functional regions.     

Mitigating the gateway bottleneck via transparent cooperative caching in wireless mesh networks

Wireless mesh networks (WMNs) have been proposed to provide cheap, easily deployable and robust Internet access. The dominant Internet-access traffic from clients causes a congestion bottleneck around the gateway, which can significantly limit the throughput of the WMN clients in accessing the Internet. In this paper, we present MeshCache, a transparent caching system for WMNs that exploits the locality in client Internet-access traffic to mitigate the bottleneck effect at the gateway, thereby improving client-perceived performance. MeshCache leverages the fact that a WMN typically spans a small geographic area and hence mesh routers are easily over-provisioned with CPU, memory, and disk storage, and extends the individual wireless mesh routers in a WMN with built-in content caching functionality. It then performs cooperative caching among the wireless mesh routers.We explore two architecture designs for MeshCache: (1) caching at every client access mesh router upon file download, and (2) caching at each mesh router along the route the Internet-access traffic travels, which requires breaking a single end-to-end transport connection into multiple single-hop transport connections along the route. We also leverage the abundant research results from cooperative web caching in the Internet in designing cache selection protocols for efficiently locating caches containing data objects for these two architectures. We further compare these two MeshCache designs with caching at the gateway router only.Through extensive simulations and evaluations using a prototype implementation on a testbed, we find that MeshCache can significantly improve the performance of client nodes in WMNs. In particular, our experiments with a Squid-based MeshCache implementation deployed on the MAP mesh network testbed with 15 routers show that compared to caching at the gateway only, the MeshCache architecture with hop-by-hop caching reduces the load at the gateway by 38%, improves the average client throughput by 170%, and increases the number of transfers that achieve a throughput greater than 1 Mbps by a factor of 3.     

WireWarping: A fast surface flattening approach with length-preserved feature curves

This paper presents a novel approach — WireWarping for computing a flattened planar piece with length-preserved feature curves from a 3D piecewise linear surface patch. The property of length-preservation on feature curves is very important to industrial applications for controlling the shape and dimension of products fabricated from planar pieces. WireWarping simulates warping a given 3D surface patch onto plane with the feature curves as tendon wires to preserve the length of their edges. During warping, the surface-angle variations between edges on wires are minimized so that the shape of a planar piece is similar to its corresponding 3D patch. Two schemes — the progressive warping and the global warping schemes are developed, where the progressive scheme is flexible for local shape control and the global scheme gives good performance on highly distorted patches. Experimental results show that WireWarping can successfully flatten surface patches into planar pieces while preserving the length of edges on feature curves.     

Thermal sensation and comfort models for non-uniform and transient environments, part III: Whole-body sensation and comfort

A three-part series presents the development of models for predicting the local thermal sensation (Part I) and local thermal comfort (Part II) of different parts of the human body, and also the whole-body sensation and comfort (Part III) that result from combinations of local sensation and comfort. The models apply to sedentary activities in a range of environments: uniform and non-uniform, stable and transient. They are based on diverse findings from the literature and from body-part-specific human subject tests in a climate chamber. They were validated against a test of automobile passengers. The series is intended to present the models’ rationale, structure, and coefficients, so that others can test them and develop them further as additional empirical data becomes available.A) The whole-body (overall) sensation model has two forms, depending on whether all of the body's segments have sensations effectively in the same direction (e.g warm or cool), or whether some segments have sensations opposite to those of the rest of the body. For each, individual body parts have different weights for warm versus cool sensations, and strong local sensations dominate the overall sensation. If all sensations are near neutral, the overall sensation is close to the average of all body sensations.B) The overall comfort model also has two forms. Under stable conditions, people evaluate their overall comfort by a complaint-driven process, meaning that when two body parts are strongly uncomfortable, no matter how comfortable the other body parts might be, the overall comfort will be near the discomfort level of the two most uncomfortable parts. When the environmental conditions are transient, or people have control over their environments, overall comfort is better than that of the two most uncomfortable body parts. This can be accounted for by adding the most comfortable vote to the two most uncomfortable ones.