A Cost-Based Approach to Adaptive Resource Management in Data Stream Systems

Data stream management systems need to adaptively control their resources, since stream characteristics and query workload may vary over time. In this paper, we investigate an approach to adaptive resource management for continuous sliding-window queries that adjusts window sizes and time granularities to keep resource usage within bounds. These two novel techniques differ from standard load shedding approaches based on sampling, as they ensure exact query answers for given user-defined quality of service specifications, even under query reoptimization. In order to quantify the effects of both techniques on the various operations in a query plan, we develop an appropriate cost model for estimating operator resource allocation in terms of memory usage and processing costs. A thorough experimental study not only validates the accuracy of our cost model but also demonstrates the efficacy and scalability of the proposed techniques.     

Influence of age and proximity warning devices on collision avoidance in simulated driving

OBJECTIVE: We conducted a set of experiments to examine the utility of several different uni- and multimodal collision avoidance systems (CASs) on driving performance of young and older adult drivers in a high-fidelity simulator. BACKGROUND: Although previous research has examined the efficacy of different CASs on collision avoidance, there has been a dearth of studies that have examined such devices in different driving situations with different populations of drivers. METHOD: Several different CAS warnings were examined in varying traffic and collision configurations both without (Experiment 1a) and with (Experiment 2) a distracting in-vehicle task. RESULTS: Overall, collision avoidance performance for both potential forward and side object collisions was best for an auditory/visual CAS, which alerted drivers using both modalities. Interestingly, older drivers (60-82 years of age) benefited as much as younger drivers from the CAS, and sometimes they benefited more. CONCLUSION: These data suggest that CASs can be beneficial across a number of different driving scenarios, types of collisions, and driver populations. APPLICATION: These results have important implications for the design and implementation of CASs for different driver populations and driving conditions.     

An Approach for Recovering Distributed System Architectures

Reasoning about software systems at the architectural level is key to effective software development, management, evolution and reuse. All too often, though, the lack of appropriate documentation leads to a situation where architectural design information has to be recovered directly from implemented software artifacts. This is a very demanding process, particularly when involving recovery of runtime abstractions (clients, servers, interaction protocols, etc.) that are typical to the design of distributed software systems. This paper presents an exploratory reverse engineering approach, called X-ray, to aid programmers in recovering architectural runtime information from a distributed system's existing software artifacts. X-ray comprises three domain-based static analysis techniques, namely component module classification, syntactic pattern matching, and structural reachability analysis. These complementary techniques can facilitate the task of identifying a distributed system's implemented executable components and their potential runtime interconnections. The component module classification technique automatically distinguishes source code modules according to the executables components they implement. The syntactic pattern matching technique in turn helps to recognise specific code fragments that may implement typical component interaction features. Finally, the structural reachability analysis technique aids in the association of those features to the code specific for each executable component. The paper describes and illustrates the main concepts underlying each technique, reports on their implementation as a suit of new and off-the-shelf tools, and, to give evidence of the utility of the approach, provides a detailed account of a successful application of the three techniques to help recover a static approximation of the runtime architecture for Field, a publicly-available distributed programming environment.     

Obturation of a C-shaped canal using an improved method of warm lateral condensation

Pilot studies conducted by the authors seem to indicate that obturation of a root canal system by the lateral condensation of gutta-percha using an electrically heated spreader results in a more homogeneous mass of gutta-percha than standard lateral condensation. This article describes an improved variation which prevents inadvertent dislodgement of the mass of gutta-percha during the obturation. The authors refer to this technique as "zap and tap" and a case report describes its use to obturate a C-shaped canal system of a mandibular second molar.     

Analysis of a mixed mode fracture specimen: the asymmetric double cantilever beam

An asymmetric double cantilever beam (ADCB) is a simple but effective specimen for the measurement of polymer/polymer and polymer/non-polymer bimaterial interface fracture toughness. In order to characterize fully the bimaterial interface strength, and to control the crack trajectory, the critical energy release rate, G _c, and the phase angle, , of the applied stress field as functions of loading and geometry of the specimen should be obtained. For most practical cases, has to be evaluated numerically. In this work, a boundary element analysis is carried out to obtain G and for the ADCB specimen at different material and geometry combinations. An expression for the energy release rate, G, based on Kanninen's beam on elastic foundation model is compared with the numerical results. Limitations on the use of the ADCB specimen are also discussed.     

Nonequilibrium theory of dirty,current-carrying superconductors: phase-slip oscillators in narrow filaments near T c

General equations for the dynamic behavior of dirty superconductors in the Ginzburg-Landau regime T _c-T T _care derived from microscopic theory. In the immediate vicinity of T _ca local equilibrium approximation leads to a simple generalized time-dependent Ginzburg-Landau equation. The oscillatory phase-slip solutions presented previously are discussed in greater detail.Supported by the Science Research Council (England) under grant GR/A65218, and by the Deutsche Forschungsgemeinschaft.     

Craze intersections in biaxially-stressed polystyrene

Crazes are produced on two orthogonal planes in both thin film and macroscopic samples of polystyrene by sequentially applying two orthogonal tensile strains ₁ and ₂. Although many crazes produced by the second strain ₂ (secondary crazes) are stopped when they meet a primary craze, some intersections occur. The fraction of craze meetings resulting in intersection increases from 20% at ₁= ₂=3% to 55% at ₁= ₂=5%; intersections also occur preferentially in thin regions of primary crazes. The craze fibril structure in the intersection has a much lower fibril volume fraction, v _f, than either of the two crazes from which it formed. The fibril volume fraction in the intersection is approximately given by the product of the fibril volume fractions of the two crazes, in agreement with a prediction based on the surface drawing mechanism of craze thickening. At higher strain levels the v _fs of the intersections are lower, leading to higher fibril stresses and enhanced fibril fracture; an increasing fraction of intersections breaks down to form large voids at these higher strain levels. Fractography of macroscopic samples containing intersecting crazes demonstrates that voids formed at the intersections can act as nuclei for cracks causing premature fracture of the material.     

Examining cognitive function across the lifespan using a mobile application

Many studies conducted in a laboratory or university setting are limited by funding, personnel, space, and time constraints. In the present study, we introduce a method of data collection using a mobile application that circumvents these typical experiment administration issues. Using the application, we examined cross-sectional age differences in cognitive function. We obtained data from more than 15,000 participants and replicated specific patterns of age-related differences in cognition. Using a subset of these participants, we also examined the processing speed account of age-related cognitive differences, and the association of exercise and leisure activity with cognitive function across the lifespan. We discuss the relative advantages and disadvantages of data collection with a mobile application, and provide recommendations for the use of this method in research.     

Micromechanics of solvent crazes in polystyrene

Double exposure holographic interferometry (DEHI) is used to determine the strain energy release rate, craze opening displacement profile, and craze stress profile ofn-heptane and methanol crazes growing from cracks in polystyrene.n-heptane crazes have strain energy release rates (SERRs) close to those of cracks and their stress profile is almost crack-like in that the tensile stress across the craze falls almost to zero. On the other hand, the SERRs of methanol crazes are only 30 to 55% the SERR of a crack depending on stress intensity factorK _I of the precrack from which they are grown. The stress profile of the methanol craze shows it to be strongly load-bearing away from the craze tip, apparently as a result of the strain hardening of the craze fibrils. The stress concentration in front of the methanol craze tip is only 40% of that in front of then-heptane craze tip. The opening displacements of the methanol craze are almost as large as those of a crack very near its tip but are much less than those of a crack at large distances behind the tip. The Dugdale model of a strip yielding zone provides a poor representation of the craze opening displacements of the growing methanol craze. Dry (static) methanol crazes have larger opening displacements in response to an incremental tensile strain at moderate prestrains than at either low or high prestrains, suggesting that the craze fibrils undergo a yielding/strain-hardening process as the strain is increased similar to that observed in polycarbonate crazes by Kopp and Kambour. Dryn-heptane crazes do not show this response but rather open linearly with increasing prestrain. The opening displacement for long (dry)n-heptane crazes is almost crack-like whereas the largest opening of a dry methanol craze is only 20% of that of a crack. Dry methanol crazes break at aK _IC that is 40% of theK _IC of precracked but uncrazed specimens. The strongest (shortest) dryn-heptane crazes fail at only 7% ofK _IC of uncrazed specimens and theK _IC of the dryn-heptane crazes decreases markedly with increasing craze length.