Efficient Processing of Spatial Group Keyword Queries

With the proliferation of geo-positioning and geo-tagging techniques, spatio-textual objects that possess both a geographical location and a textual description are gaining in prevalence, and spatial keyword queries that exploit both location and textual description are gaining in prominence. However, the queries studied so far generally focus on finding individual objects that each satisfy a query rather than finding groups of objects where the objects in a group together satisfy a query.

We define the problem of retrieving a group of spatio-textual objects such that the group's keywords cover the query's keywords and such that the objects are nearest to the query location and have the smallest inter-object distances. Specifically, we study three instantiations of this problem, all of which are NP-hard. We devise exact solutions as well as approximate solutions with provable approximation bounds to the problems. In addition, we solve the problems of retrieving top-k groups of three instantiations, and study a weighted version of the problem that incorporates object weights. We present empirical studies that offer insight into the efficiency of the solutions, as well as the accuracy of the approximate solutions.

SOPS: A System for Efficient Processing of Spatial-Keyword Publish/Subscribe

Massive amount of data that are geo-tagged and associated with text information are being generated at an unprecedented scale. These geo-textual data cover a wide range of topics. Users are interested in receiving up-to-date geo-textual objects (e.g., geo-tagged Tweets) such that their locations meet users’ need and their texts are interesting to users. For example, a user may want to be updated with tweets near her home on the topic “dengue fever headache.” In this demonstration, we present SOPS, the Spatial-Keyword Publish/Subscribe System, that is capable of efficiently processing spatial keyword continuous queries. SOPS supports two types of queries: (1) Boolean Range Continuous (BRC) query that can be used to subscribe the geo-textual objects satisfying a boolean keyword expression and falling in a specified spatial region; (2) Temporal Spatial-Keyword Top-k Continuous (TaSK) query that continuously maintains up-to-date top-k most relevant results over a stream of geo-textual objects. SOPS enables users to formulate their queries and view the real-time results over a stream of geotextual objects by browser-based user interfaces. On the server side, we propose solutions to efficiently processing a large number of BRC queries (tens of millions) and TaSK queries over a stream of geo-textual objects.

Mercury (II) removal from aqueous solutions by microporous materials

O Mercúrio é um dos metais pesados mais tóxicos existentes no meio ambiente, é persistente e caracteriza-se por bioamplificar e bioacumular ao longo da cadeia trófica. A poluição com mercúrio é um problema à escala global devido à combinação de emissões naturais e emissões antropogénicas, o que obriga a políticas ambientais mais restritivas sobre a descarga de metais pesados. Consequentemente o desenvolvimento de novos e eficientes materiais e de novas tecnologias para remover mercúrio de efluentes é necessário e urgente. Neste contexto, alguns materiais microporosos provenientes de duas famílias, titanossilicatos e zirconossilicatos, foram investigados com o objectivo de avaliar a sua capacidade para remover iões Hg2+ de soluções aquosas. De um modo geral, quase todos os materiais estudados apresentaram elevadas percentagens de remoção, confirmando que são bons permutadores iónicos e que têm capacidade para serem utilizados como agentes descontaminantes. O titanossilicato ETS-4 foi o material mais estudado devido à sua elevada eficiência de remoção (>98%), aliada à pequena quantidade de massa necessária para atingir essa elevada percentagem de remoção. Com apenas 4 mg⋅dm-3 de ETS-4 foi possível tratar uma solução com uma concentração igual ao valor máximo admissível para descargas de efluentes em cursos de água (50 μg⋅dm-3) e obter água com qualidade para consumo humano (<1.0 μg⋅dm-3), de acordo com a legislação Portuguesa (DL 236/98). Tal como para outros adsorbentes, a capacidade de remoção de Hg2+ do ETS- 4 depende de várias condições experimentais, tais como o tempo de contacto, a massa, a concentração inicial de mercúrio, o pH e a temperatura. Do ponto de vista industrial as condições óptimas para a aplicação do ETS-4 são bastante atractivas, uma vez que não requerem grandes quantidades de material e o tratamento da solução pode ser feito à temperatura ambiente. A aplicação do ETS-4 torna-se ainda mais interessante no caso de efluentes hospitalares, de processos de electro-deposição com níquel, metalúrgica, extracção de minérios, especialmente ouro, e indústrias de fabrico de cloro e soda cáustica, uma vez que estes efluentes apresentam valores de pH semelhantes ao valor de pH óptimo para a aplicação do ETS-4. A cinética do processo de troca iónica é bem descrita pelo modelo Nernst-Planck, enquanto que os dados de equilíbrio são bem ajustados pelas isotérmicas de Langmuir e de Freundlich. Os parâmetros termodinâmicos, ΔG° and ΔH° indicam que a remoção de Hg2+ pelo ETS-4 é um processo espontâneo e exotérmico. A elevada eficiência do ETS-4 é confirmada pelos valores da capacidade de remoção de outros materiais para os iões Hg2+, descritos na literatura. A utilização de coluna de ETS-4 preparada no nosso laboratório, para a remoção em contínuo de Hg2+ confirma que este material apresenta um grande potencial para ser utilizado no tratamento de águas. ABSTRACT: Mercury is one of the most toxic heavy metals, exhibiting a persistent character in the environment and biota as well as bioamplification and bioaccumulation along the food chain. Natural inputs combined with the global anthropogenic sources make mercury pollution a planetary-scale problem, and strict environmental policies on metal discharges have been enforced. The development of efficient new materials and clean-up technologies for removing mercury from effluents is, thus, timely. In this context, in my study, several microporous materials from two families, titanosilicates and zirconosilicates were investigated in order to assess their Hg2+ sorption capacity and removal efficiency, under different operating conditions. In general, almost all microporous materials studied exhibited high removal efficiencies, confirming that they are good ion exchangers and have potential to be used as Hg2+ decontaminant agents. Titanosilicate ETS-4 was the material most studied here, by its highest removal efficiency (>98%) and lowest mass necessary to attain it. Moreover, according with the Portuguese legislation (DL 236/98) it is possible to attain drinking water quality (i.e. [Hg2+]< 1.0 μg⋅dm-3) by treating a solution with a Hg2+ concentration equal to the maximum value admissible for effluents discharges into water bodies (50 μg⋅dm-3), using only 4 mg⋅dm-3 of ETS-4. Even in the presence of major freshwater cations, ETS-4 removal efficiency remains high. Like for other adsorbents, the sorption capacity of ETS-4 for Hg2+ ions is strongly dependent on the operating conditions, such as contact time, mass, initial Hg2+ concentration and solution pH and, to a lesser extent, temperature. The optimum operating conditions found for ETS-4 are very attractive from the industrial point of view because the application of ETS-4 for the treatment of wastewater and/or industrial effluents will not require larges amounts of adsorbent, neither energy supply for temperature adjustments becoming the removal process economically competitive. These conditions become even more interesting in the case of medical institutions liquid, nickel electroplating process, copper smelter, gold ore tailings and chlor-alkali effluents, since no significant pH adjustments to the effluent are necessary. The ion exchange kinetics of Hg2+ uptake is successfully described by the Nernst-Planck based model, while the ion exchange equilibrium is well fitted by both Langmuir and Freundlich isotherms. Moreover, the feasibility of the removal process was confirmed by the thermodynamic parameters (ΔG° and ΔH°) which indicate that the Hg2+ sorption by ETS-4 is spontaneous and exothermic. The higher efficiency of ETS-4 for Hg2+ ions is corroborate by the values reported in literature for the sorption capacity of other adsorbents for Hg2+ ions. The use of an ETS-4 fixed-bed ion exchange column, manufactured in our laboratory, in the continuous removal of Hg2+ ions from solutions confirms that this titanosilicate has potential to be used in industrial water treatment.

An efficient parallel implementation of a least squares problem

Least squares solutions are a very important problem, which appear in a broad range of disciplines (for instance, control systems, statistics, signal processing). Our interest in this kind of problems lies in their use of training neural network controllers.

An efficient parallel implementation of a least squares problem

Least squares solutions are a very important problem, which appear in a broad range of disciplines (for instance, control systems, statistics, signal processing). Our interest in this kind of problems lies in their use of training neural network controllers.

An efficient method for optimal location and sizing of fixed and switched shunt capacitors in large distribution systems

This paper proposes a computationally efficient methodology for the optimal location and sizing of static and switched shunt capacitors in large distribution systems. The problem is formulated as the maximization of the savings produced by the reduction in energy losses and the avoided costs due to investment deferral in the expansion of the network. The proposed method selects the nodes to be compensated, as well as the optimal capacitor ratings and their operational characteristics, i.e. fixed or switched. After an appropriate linearization, the optimization problem was formulated as a large-scale mixed-integer linear problem, suitable for being solved by means of a widespread commercial package. Results of the proposed optimizing method are compared with another recent methodology reported in the literature using two test cases: a 15-bus and a 33-bus distribution network. For the both cases tested, the proposed methodology delivers better solutions indicated by higher loss savings, which are achieved with lower amounts of capacitive compensation. The proposed method has also been applied for compensating to an actual large distribution network served by AES-Venezuela in the metropolitan area of Caracas. A convergence time of about 4 seconds after 22298 iterations demonstrates the ability of the proposed methodology for efficiently handling large-scale compensation problems.

Recycling of pultrusion production waste into innovative concrete-polymer composite solutions

In this study, the added value resultant from the incorporation of pultrusion production waste into polymer based concretes was assessed. For this purpose, different types of thermoset composite scrap material, proceeding from GFRP pultrusion manufacturing process, were mechanical shredded and milled into a fibrous-powdered material. Resultant GFRP recyclates, with two different size gradings, were added to polyester based mortars as fine aggregate and filler replacements, at various load contents between 4% up to 12% in weight of total mass. Flexural and compressive loading capacities were evaluated and found better than those of unmodified polymer mortars. Obtained results highlight the high potential of recycled GFRP pultrusion waste materials as efficient and sustainable admixtures for concrete and mortar-polymer composites, constituting an emergent waste management solution.

An efficient numerical scheme for solving multi-dimensional fractional optimal control problems with a quadratic performance index

The shifted Legendre orthogonal polynomials are used for the numerical solution of a new formulation for the multi-dimensional fractional optimal control problem (M-DFOCP) with a quadratic performance index. The fractional derivatives are described in the Caputo sense. The Lagrange multiplier method for the constrained extremum and the operational matrix of fractional integrals are used together with the help of the properties of the shifted Legendre orthonormal polynomials. The method reduces the M-DFOCP to a simpler problem that consists of solving a system of algebraic equations. For confirming the efficiency and accuracy of the proposed scheme, some test problems are implemented with their approximate solutions.

Scalable and Efficient Configuration of TimeDivision Multiplexed Resources

Consumer-electronics systems are becoming increasingly complex as the number of integrated applications is growing. Some of these applications have real-time requirements, while other non-real-time applications only require good average performance. For cost-efficient design, contemporary platforms feature an increasing number of cores that share resources, such as memories and interconnects. However, resource sharing causes contention that must be resolved by a resource arbiter, such as Time-Division Multiplexing. A key challenge is to configure this arbiter to satisfy the bandwidth and latency requirements of the real-time applications, while maximizing the slack capacity to improve performance of their non-real-time counterparts. As this configuration problem is NP-hard, a sophisticated automated configuration method is required to avoid negatively impacting design time. The main contributions of this article are: 1) An optimal approach that takes an existing integer linear programming (ILP) model addressing the problem and wraps it in a branch-and-price framework to improve scalability. 2) A faster heuristic algorithm that typically provides near-optimal solutions. 3) An experimental evaluation that quantitatively compares the branch-and-price approach to the previously formulated ILP model and the proposed heuristic. 4) A case study of an HD video and graphics processing system that demonstrates the practical applicability of the approach.

Eco-wall modular solutions for buildings

This paper discusses the development of modular solutions for eco low-cost houses based on a pre-fabricated modular wall system environmentally sustainable, socioeconomically competitive and geared towards developing African nations with a housing deficit. The key point to the research of a modular wall solution is a structural layer complemented with local and materials made by non-specialized workforce. This wall also meets also hydrothermal acoustic and mechanical properties. Thus,the solution also offers good safety and interior comfort conditions to its users while maintaining the flexibility to expand the size of the house. Parameters as dimensions, materials and constructive processes of the existing housing stock were studied. Features such as the family size, typology, different uses, common materials, existing regulations, minimal living conditions, safety and comfort have also been considered to achieve the most efficient solution.

Les facilitateurs et les solutions à la pratique optimale des médecins dans le traitement de l’asthme

OBJECTIF : Déterminer les principales solutions qui facilitent la pratique optimale des médecins dans le traitement de l’asthme, incluant la prescription d’un médicament de contrôle à long terme et l’utilisation de plans d’action écrits. MÉTHODOLOGIE: Des entrevues individuelles semi-structurées ont été menées avec des médecins de différentes spécialités (médecins de famille, pédiatres, urgentologues, pneumologues et allergologues). Ces entrevues ont été transcrites puis analysées qualitativement de manière indépendante par deux chercheures qualifiées. RÉSULTATS : Quarante-deux médecins ont été interviewés. Un total de 867 facilitateurs et solutions ont été exprimés, répondant à trois de leurs besoins: (1) avoir du soutien dans la prestation de soins optimaux, (2) être habileté à aider et motiver les patients à suivre leurs recommandations et (3) avoir l’opportunité d’offrir des services efficients. À partir de ces données, une taxonomie de facilitateurs et de solutions comprenant dix catégories a également été développée. CONCLUSION : Les médecins ont proposé une multitude de facilitateurs et de solutions pour soutenir la pratique optimale. Ils varient essentiellement selon la spécialité et le comportement visé (prescription de médicaments de contrôle à long terme, utilisation de plans d’autogestion écrits et la gestion générale de l’asthme). Cela fait ressortir l’importance d’effectuer le choix des interventions en étroite collaboration avec les utilisateurs de connaissances afin d’obtenir des solutions qui soient perçues comme faisables et applicables, ayant ainsi potentiellement plus de chances de mener à un changement de pratique. La nouvelle taxonomie offre la possibilité d’utiliser un langage commun pour classifier les facilitateurs et les solutions.

Efficient tree construction for the multicast problem

A new heuristic for the Steiner Minimal Tree problem is presented here. The method described is based on the detection of particular sets of nodes in networks, the “Hot Spot” sets, which are used to obtain better approximations of the optimal solutions. An algorithm is also proposed which is capable of improving the solutions obtained by classical heuristics, by means of a stirring process of the nodes in solution trees. Classical heuristics and an enumerative method are used CIS comparison terms in the experimental analysis which demonstrates the goodness of the heuristic discussed in this paper.

Efficient tree construction for the multicast problem

A new heuristic for the Steiner minimal tree problem is presented. The method described is based on the detection of particular sets of nodes in networks, the “hot spot” sets, which are used to obtain better approximations of the optimal solutions. An algorithm is also proposed which is capable of improving the solutions obtained by classical heuristics, by means of a stirring process of the nodes in solution trees. Classical heuristics and an enumerative method are used as comparison terms in the experimental analysis which demonstrates the capability of the heuristic discussed

An efficient low power FFT implementation for multiband full-rate ultra-wideband (UWB) receivers

This paper discusses the design, implementation and synthesis of an FFT module that has been specifically optimized for use in the OFDM based Multiband UWB system, although the work is generally applicable to many other OFDM based receiver systems. Previous work has detailed the requirements for the receiver FFT module within the Multiband UWB ODFM based system and this paper draws on those requirements coupled with modern digital architecture principles and low power design criteria to converge on our optimized solution. The FFT design obtained in this paper is also applicable for implementation of the transmitter IFFT module therefore only needing one FFT module for half-duplex operation. The results from this paper enable the baseband designers of the 200Mbit/sec variant of Multiband UWB systems (and indeed other OFDM based receivers) using System-on-Chip (SoC), FPGA and ASIC technology to create cost effective and low power solutions biased toward the competitive consumer electronics market.

An efficient numerical scheme for the Euler equations

A finite difference scheme based on flux difference splitting is presented for the solution of the Euler equations for the compressible flow of an ideal gas. A linearised Riemann problem is defined, and a scheme based on numerical characteristic decomposition is presented for obtaining approximate solutions to the linearised problem. An average of the flow variables across the interface between cells is required, and this average is chosen to be the arithmetic mean for computational efficiency, leading to arithmetic averaging. This is in contrast to the usual ‘square root’ averages found in this type of Riemann solver, where the computational expense can be prohibitive. The method of upwind differencing is used for the resulting scalar problems, together with a flux limiter for obtaining a second order scheme which avoids nonphysical, spurious oscillations. The scheme is applied to a shock tube problem and a blast wave problem. Each approximate solution compares well with those given by other schemes, and for the shock tube problem is in agreement with the exact solution.