Collecting Statistics over Runtime Executions

By collecting statistics over runtime executions of a program we can answer complex queries, such as “what is the average number of packet retransmissions” in a communication protocol, or “how often does process P₁ enter the critical section while process P₂ waits” in a mutual exclusion algorithm. We present an extension to linear-time temporal logic that combines the temporal specification with the collection of statistical data. By translating formulas of this language to alternating automata we obtain a simple and efficient query evaluation algorithm. We illustrate our approach with examples and experimental results.     

Processing, physical and thermal properties of BlackglasTM matrix composites reinforced with NextelTM fabric

The cure and pyrolysis behavior of a BlackglasTM resin and NextelTM 440 impregnated with BlackglasTM resin were studied. Cure of the BlackglasTM resin is an exothermic process and DSC studies indicate that with an increase of catalyst content from 0.1 to 1.0%, the onset and peak temperature of cure are decreased coupled with an increase in the enthalpy of cure indicating a greater extent of cross linking. However, pyrolysis char yield of the pyrolyzate is relatively insensitive to cure conditions.Cure pressure and pyrolysis environment are variables in the processing of BlackglasTM matrix composite reinforced with NextelTM 440 Plain weave fabric. Variations in cure pressure from 30 to 80 psi had no discernible effect on the chemistry of the pryrolyzate. However, the higher cure pressure resulted in top and bottom ply damage. Pyrolysis in an Ar environment resulted in incorporationj of up to 12 wt % C of which 8 wt % as graphitic in nature in the ceramic matrix. Pyrolysis in NH3 resulted in 3.9 wt % nitrogen and 1.5 wt % carbon in the matrix, with all the nitrogen and carbon bonded to Si. The cured panels have to be pyrolyzed/densified between 6–7 times to achieve required density and porosity content. Oxidation behavior of the composites at 1000°C indicate that the argon pyrolyzed CMC's lose more weight due to decomposition of the pyrolytic carbon, whereas, NH3 pyrolyzed CMC's are stable as both the N and C are bonded to Si in the matrix. Dielectric constants K and K measured at 1 GHz in the as-processed condition are high in the argon pyrolyzed CMC, (K = 11–28) due to the presence of pyrolytic carbon. On the other hand NH3 pyrolyzed CMC exhibit low dielectric constant (K = 4). On oxidation, the dielectric constant in both the Ar and NH3 pyrolyzed panels is approximately 4.0.     

Small-signal conductance vs temperature: A rapid means of determining the nature of current transport in high-doped n-GaAs Schottky barrier diodes

Measurements of small-signal forward conductance vs temperature at a constant bias current, and the reverse conductance vs temperature at a constant bias voltage have been carried out on ion-implanted n-GaAs Schottky barrier diodes fabricated on semi-insulated substrates, for the temperature range of 97–340 K. The results obtained have been interpreted in terms of diode ideality factors and compared with those calculated using the thermionic field emission model for the forward bias case and the pure field emission model for the reverse bias case.     

Computing Optimal Diameter-Bounded Polygon Partitions

The minimum -small partition problem is the problem of partitioning a given simple polygon into subpolygons, each with diameter at most , for a given > 0. This paper considers the version of this problem that disallows Steiner points. This problem is motivated by applications in mesh generation and collision detection. The main result in the paper is a polynomial-time algorithm that solves this problem, and either returns an optimal partition or reports the nonexistence of such a partition. This result contrasts with the recent NP-completeness result for the minimum -small partition problem for polygons with holes (C. Worman, 15th Canadian Conference on Computational Geometry, 2003). Even though the running time of our algorithm is a polynomial in the input size, it is prohibitive for most real applications and we seek faster algorithms that approximate an optimal solution. We first present a faster 2-approximation algorithm for the problem for simple polygons and then a near linear-time algorithm for convex polygons that produces, for any > 0, an (+)-small partition with no more polygons than in an optimal -small partition. We also present an exact polynomial-time algorithm for the minimum -small partition problem with the additional constraint that each piece in the partition be convex.     

Efficient Update of Indexes for Dynamically Changing Web Documents

Recent work on incremental crawling has enabled the indexed document collection of a search engine to be more synchronized with the changing World Wide Web. However, this synchronized collection is not immediately searchable, because the keyword index is rebuilt from scratch less frequently than the collection can be refreshed. An inverted index is usually used to index documents crawled from the web. Complete index rebuild at high frequency is expensive. Previous work on incremental inverted index updates have been restricted to adding and removing documents. Updating the inverted index for previously indexed documents that have changed has not been addressed. In this paper, we propose an efficient method to update the inverted index for previously indexed documents whose contents have changed. Our method uses the idea of landmarks together with the diff algorithm to significantly reduce the number of postings in the inverted index that need to be updated. Our experiments verify that our landmark-diff method results in significant savings in the number of update operations on the inverted index.     

The Effects of Technological Advancement and Violent Content in Video Games on Players' Feelings of Presence, Involvement, Physiological Arousal, and Aggression

The possible impact of technological advancement on video games' effects—particularly in the case of violent games—has often been discussed but has not been thoroughly explored by empirical research. The present investigation employed a 2 × 2 between-subjects factorial experiment to examine the interplay of technological advancement and violence by exposing participants ( N = 120) to either a newer or older version of a violent or nonviolent game and measuring these factors' effects on players' sense of presence, involvement, physiological arousal (measured by skin conductance), self-reported arousal, and affective and cognitive aggression. The results indicate that technological advancement increased participants' sense of presence, involvement, and physiological and self-reported arousal. Neither advancement nor violence had statistically significant effects on accessibility of players' aggressive thoughts, but there is some tentative evidence that violent game content increased players' state hostility. Theoretical and practical implications of findings are discussed, and recommendations are made for future research.     

Multi-Fault Tolerance for Cartesian Data Distributions

Faults are expected to play an increasingly important role in how algorithms and applications are designed to run on future extreme-scale systems. Algorithm-based fault tolerance is a promising approach that involves modifications to the algorithm to recover from faults with lower overheads than replicated storage and a significant reduction in lost work compared to checkpoint-restart techniques. Fault-tolerant linear algebra algorithms employ additional processors that store parities along the dimensions of a matrix to tolerate multiple, simultaneous faults. Existing approaches assume regular data distributions (blocked or block-cyclic) with the failures of each data block being independent. To match the characteristics of failures on parallel computers, we extend these approaches to mapping parity blocks in several important ways. First, we handle parity computation for generalized Cartesian data distributions with each processor holding arbitrary subsets of blocks in a Cartesian-distributed array. Second, techniques to handle correlated failures, i.e., multiple processors that can be expected to fail together, are presented. Third, we handle the colocation of parity blocks with the data blocks and do not require them to be on additional processors. Several alternative approaches, based on graph matching, are presented that attempt to balance the memory overhead on processors while guaranteeing the same fault tolerance properties as existing approaches that assume independent failures on regular blocked data distributions. Evaluation of these algorithms demonstrates that the additional desirable properties are provided by the proposed approach with minimal overhead.     

A multiscale model for polymer crystallization. I: Growth of individual spherulites

In this two-part paper, we present a model for the solidification of semicrystalline thermoplastic polymers that links the microscopic and macroscopic length scales. The model accounts for the important physical phenomena occurring during spherulitic cyrstallization and predicts microstructural evolution. In this first part, we concentrate on the growth of individual spherulites. We present a fast and accurate model that predicts the shape of a spherulite as well as the path of its constitutive lamellae in any thermal situation. In part II of this paper we shall couple this new model for spherulite growth with a nucleation law and a macroscopic heat flow computation, thus enabling us to model realistic crystallization conditions.     

Content-based assembly search: A step towards assembly reuse

The increased use of CAD systems by product development organizations has resulted in the creation of large databases of assemblies. This explosion of assembly data is likely to continue in the future. In many situations, a text-based search alone may not be sufficient to search for assemblies and it may be desirable to search for assemblies based on the content of the assembly models. The ability to perform content-based searches on these databases is expected to help the designers in the following two ways. First, it can facilitate the reuse of existing assembly designs, thereby reducing the design time. Second, a lot of useful designs for manufacturing, and assembly knowledge are implicitly embedded in existing assemblies. Therefore a capability to locate existing assemblies and examine them can be used as a learning tool by designers to learn from the existing assembly designs. This paper describes a system for performing content-based searches on assembly databases. We identify templates for comprehensive search definitions and describe algorithms to perform content-based searches for mechanical assemblies. We also illustrate the capabilities of our system through several examples.     

Thermal decomposition of doped calcium hydroxide for chemical energy storage

Thermal decomposition of Ca(OH)₂ with and without additives has been experimentally investigated for its application as a thermochemical energy storage system. The homogeneous reaction model gives a satisfactory fit for the kinetic data on pure and Ni(OH)₂---, Zn(OH)₂--- and Al(OH)₃---doped Ca(OH)₂ and the order of reaction is 0.76 in all cases except for the Al(OH)₃-doped sample for which the decomposition is zero order. These additives are shown not only to enhance the reaction rate but also to reduce the decomposition temperature significantly. Some models for solid decomposition reactions, and possible mechanisms in the decomposition of solids containing additives, are also discussed.