A note on element-wise matrix sparsification via a matrix-valued Bernstein inequality

Given a matrix A∈Rn×n, we present a simple, element-wise sparsification algorithm that zeroes out all sufficiently small elements of A and then retains some of the remaining elements with probabilities proportional to the square of their magnitudes. We analyze the approximation accuracy of the proposed algorithm using a recent, elegant non-commutative Bernstein inequality, and compare our bounds with all existing (to the best of our knowledge) element-wise matrix sparsification algorithms.     

Linkages in the construction sector

An important issue regarding the use of construction investment as a public policy tool is the magnitude of its contribution to growth and the nature of its interactions with the other sectors in the economy. Development planners have long used the concepts of backward and forward linkages to examine these interactions. None of the previous analysts, however, has concentrated on the construction sector. In this paper, we discuss the general nature of backward and forward linkages and their role in inducing economic development, present the most commonly used measures for quantifying and understanding the strength and nature of these linkages, and review estimates of backward linkages. In all countries for which estimates exist, we found that gross construction linkages are strong and that the economic impact of construction activities is relatively evenly dispersed over the sectors from which they obtain their inputs.     

Single and combined effects of nickel (Ni(II)) and cobalt (Co(II)) ions on activated sludge and on other aerobic microorganisms: a review

Nickel (N(II)) and cobalt (Co(II)) are often encountered in wastewaters. As conventional wastewater treatment may only partially remove nickel and cobalt, a large fraction of the above metals is released to the aquatic environment. Both metals have been identified as micronutrients, at trace concentrations; however, they are both microbial growth inhibitors, at relatively high concentrations. On the other hand, the combined effects (e.g.: growth stimulation or toxicity) of the above metals have been found to differ from the summation of the effects which occur when the metals are applied individually. Moreover, a number of environmental factors (e.g.: pH, biomedium composition, biomass concentration, presence of other heavy metals) can affect the microbial toxicity of the above metallic species. The present review discusses, in a systematic way, the individual and joint effects of the above heavy metals to the growth of microorganisms grown under aerobic conditions, with focus on the growth of activated sludge. Data on multi-metal toxicity are particularly useful in establishing criteria for heavy metal tolerance levels in the environment.     

Cooperative diversity schemes for asynchronous wireless networks

We construct cooperative diversity coding schemes that mitigate the effects of symbol asynchronicity among network users. We do so by modifying, at the expense of implementation practicality, the signaling complexity of well behaved existing schemes. The modification allows the same good performance (DMT optimality) in the presence of synchronicity, and almost-surely permits full-diversity gains for any event of symbol asynchronicity. This work was in part carried out while Petros Elia was at the University of Southern California. This research is supported in part by NSF-ITR CCR-0326628.     

Spatial and temporal variability of fine particle composition and source types in five cities of Connecticut and Massachusetts

To protect public health from PM_2.5 air pollution, it is critical to identify the source types of PM_2.5 mass and chemical components associated with higher risks of adverse health outcomes. Source apportionment modeling using Positive Matrix Factorization (PMF), was used to identify PM_2.5 source types and quantify the source contributions to PM_2.5 in five cities of Connecticut and Massachusetts. Spatial and temporal variability of PM_2.5 mass, components and source contributions were investigated. PMF analysis identified five source types: regional pollution as traced by sulfur, motor vehicle, road dust, oil combustion and sea salt. The sulfur-related regional pollution and traffic source type were major contributors to PM_2.5. Due to sparse ground-level PM_2.5 monitoring sites, current epidemiological studies are susceptible to exposure measurement errors. The higher correlations in concentrations and source contributions between different locations suggest less spatial variability, resulting in less exposure measurement errors. When concentrations and/or contributions were compared to regional averages, correlations were generally higher than between-site correlations. This suggests that for assigning exposures for health effects studies, using regional average concentrations or contributions from several PM_2.5 monitors is more reliable than using data from the nearest central monitor.     

Dynamic fracture of unidirectional graphite fiber composite strips

An approximate equation of motion is derived and is used in the analysis of a dynamically propagating crack in a highly orthotropic fiber composite infinite strip subjected to constant displacement Mode I loading. With the use of Fourier transforms, the problem is reduced to an equation which is solved by the Wiener-Hopf technique. The dynamic stress intensity factor is derived and is expressed as the product of a velocity correction factor and a static stress intensity factor. The corresponding dynamic energy release rate is derived also and it is found not to be explicitly dependent upon the crack-tip velocity. It is found experimentally that the long strip configuration subjected to constant extensional displacement can simulate constant crack propagation velocities. Accordingly, the model's dynamic energy release rate is used to determine the dynamic fracture energy (toughness) of 90° Hercules AS/3501-6 graphite epoxy composites.

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Résumé On déduit une équation approximative de mouvement et on l'utilise dans l'analyse d'une fissure se propageant de manière dynamique dans une bande infinie en fibres composites à haute orthotropicité sujette à une mise en charge de mode I à déplacement constant. En utilisant les transformées de Fourier, on ramène le problème à une équation qui est solutionable par la technique de Wiener-Hopf. Le facteur d'intensité de contrainte dynamique en est déduit et est exprimé comme le produit d'un facteur de correction de vitesse et d'un facteur d'intensité de contrainte statique. Le taux de relaxation d'énergie dynamique correspondante est également déduit et l'on trouve qu'il n'est pas explicitement dépendant de la vélocité à la pointe de la fissure. On trouve par voie expérimentale que la configuration d'une bande longue soumis à des déplacements constants en traction permet de simuler des vitesses de propagation constante. Dès lors, on utilise le taux de relaxation d'énergie dynamique du modèle à la détermination de l'énergie de rupture dynamique ou ténacité des composites époxygraphites 90° Hercules AS/3501-6.

     

Towards formal open standards: formalizing a standard’s requirements

Open standardization seems to be very popular among software developers as it simplifies the standard’s adoption by the software engineering. Formal specification methods, while very promising, are being adopted slowly as the industry seems to have little motivation to move into this territory. In this paper the authors present (1) the idea of applying formal specification techniques to open standards’ specifications, and (2) an example of a formal specification of the Rich Site Summary (RSS) v2.0 open standard. The authors provide evidence for the advantages of the open standards formal specification over natural language documentations: formal specifications are more concise, less ambiguous, more complete with respect to the original documentation and, when using certain kinds of specification languages, executable and reusable as they support module inheritance. The merging of formal specification methods and open standards allows (1) a more concrete standard design; (2) an improved understanding of the environment under design; (3) an enforced certain level of precision into the specification, and also (4) provides software engineers with extended property checking/verification capabilities, especially if they opt to use any algebraic specification language. The authors showcase how the RSS standard can be formally specified using an algebraic specification language and demonstrate how can that be beneficial.     

The virtual stuntman: dynamic characters with a repertoire of autonomous motor skills

An ambitious goal in the area of physics-based computer animation is the creation of virtual actors that autonomously synthesize realistic human motions and possess a broad repertoire of lifelike motor skills. To this end, the control of dynamic, anthropomorphic figures subject to gravity and contact forces remains a difficult open problem. In this paper, we report on our ongoing development of a virtual stuntman, a dynamic graphical character that possesses a nontrivial repertoire of lifelike motor skills. The repertoire includes basic actions such as balance, protective stepping when balance is disturbed, protective arm reactions when falling, multiple ways of rising upright after a fall, and several more vigorously dynamic motor skills. Our virtual stuntman is the product of a recently proposed framework for integrating motor controllers, which includes among other ingredients an explicit model of pre-conditions; i.e., those regions of a dynamic figure's state space within which a given motor controller is applicable and expected to work properly.     

The influence of build strategies in selective inhibition sintering (SIS)

Selective Inhibition Sintering of metal alloys (SIS-metal) has been proven effective in the additive manufacture (AM) of low resolution bronze parts. Recent advancements in the use of a high-precision inkjet print head represented an order of magnitude improvement in SIS-metal resolution. However, the fabrication of complex three-dimensional metallic parts required new SIS-metal compatible, cross-sectional image generation based on the part boundary profile. In the proposed study, five candidate layer-processing approaches were identified and validated for basic geometries. These approaches were chosen from previous research as well as preliminary investigations and were applied to a modified SIS-metal process for validation. The validation criteria were based upon the amount of powder waste produced, the ability to handle complex geometries, printing speed, extraction (post-processing) speed, and part integrity. Results are discussed for implementation of the five candidate layer processing approaches in the fabrication of basic shapes. A preliminary evaluation is presented for their use on more complex geometries. Two approaches were then chosen for the construction of more complex geometries, the results of which are presented.