Joint scheduling and power control supporting multicasting in wireless ad hoc networks

This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem.     

Assessing organo-clay dispersion in polymer layered silicate nanocomposites: A SAXS approach

A SAXS method for the quantitative assessment of the morphology of polymer layered silicate nanocomposites is proposed. Fitting the SAXS patterns, the number of clay layers, the periodicity of the layers in the tactoids, the thickness of the regions interposed between the clay platelets and their distributions can be measured. A good agreement with TEM data was obtained, avoiding the inconsistencies with microscopical observations often reported in the literature.     

XPS studies of directly fluorinated HDPE: problems and solutions

X-ray photoelectron spectroscopy (XPS) applied to the study of fluorinated polymer surfaces presents several problems related both to peak assignment and to degradation. In this work, we analyse extensively the question of XPS peak assignments in this kind of surfaces. We conclude that in this kind of surfaces using binding energy differences between fluorine and carbon is better than using absolute binding energies. Also a useful relation between fluorine photoelectron energy vs. polymer composition expressed through the atomic ratio fluorine/carbon (F/C) was found. A protocol for data treatment is proposed and applied to a XPS study of the degradation induced by X-ray on high-density polyethylene surfaces modified by direct fluorination. Results obtained for the degradation, namely the atomic ratio F/C obtained by two different methods, combined with angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to study the fluorine concentration profile in depth, producing self-consistent results.     

The Effect of Reagents on Ultrafine Iron Ore Vacuum Filtration

Continuous vacuum filters normally carry out the final removal of water from iron ore products. The objective of this investigation is to check the possibility of enhancing the industrial performance of a horizontal belt filter by adding one flocculant and two surfactants to the filtration feed slurry. The mineral sample came from the Iron Quadrangle (State of Minas Gerais, Brazil). X-ray diffraction showed a predominance of hematite and small amounts of quartz and goethite. The filtration tests were performed at laboratory scale using a modified Büchner funnel apparatus, which was connected to a scale/computer system. The results indicated: a) the best filtration condition was achieved near the zero charge condition; b) cake moisture, cake porosity, cake formation time and the specific cake resistance were pronouncedly influenced by the flocculant addition; and c) surfactants tested were not able to significantly reduce the cake moisture.     

Effects of load modeling in security constrained OPF studies

Results of computational experiments carried out on an adaptation of the AEP/IEEE 30 bus test system are reported. Some selected buses were modeled using an exponential type of load model. Three cases are considered. In the first case it is assumed that the specified load at modeled buses is obtained with unity voltage. In the second case it is assumed that the transformer taps have been adjusted to give all industrial-type consumers one per unit at the low-voltage panel when the high-side voltage corresponds to the standard optimal power flow (OPF) solution. The third case differs from the second in that the specified power demand is assumed to take place when the high-side voltages correspond to the intact case of the standard security constrained OPF solution. It is concluded that a decrease in fuel cost can be obtained in some instances when load models are incorporated in security constrained OPF studies during contingencies only. In situations where a decrease in fuel cost is obtained in this manner, the magnitude of decrease depends on the total percentage of load fed by fixed tap transformers and the sensitivity of these loads to modeling     

Insiders Behaving Badly

This column goes beyond previous insider analyses to identify a framework for a taxonomy of insider threats including both malicious and inadvertent actions by insiders that put organizations or their resources at some risk. The framework includes factors reflecting the organization, the individual, the information technology system, and the environment.     

Renewable energy systems: A societal and technological platform

Today, the analysis of renewable energy places the emphasis on the technological and economic attributes with social and environmental impact assessment providing for a rather static, narrow frame of analysis. The participation and response of social actors and other stakeholders is usually of a traditional type, with consultation documents and public meetings, collection of complaints and suggestion schemes. This often encourages parochialism and an over-concentration on relatively trivial issues. It is, therefore, imperative to establish a new participatory planning platform to incorporate the wider socio-economic aspects of renewable energy systems and to provide for an operational analytical decomposition of them. In this work the issue of decomposition analysis is clarified, and a new agenda for the societal and technological decomposition analysis of renewable energy systems is developed. A case study is disclosed to present the relevance of the established platform for integrated (renewable) energy systems planning. Innovative aspects comprise of the simultaneous inclusion of decision analysis and social acceptance methods and tools in concert with the related public participation techniques.     

Performance analysis of concurrency control using locking withdeferred blocking

The concurrency control (CC) method employed can be critical to the performance of transaction processing systems. Conventional locking suffers from the blocking phenomenon, where waiting transactions continue to hold locks and block other transactions from progressing. In a high data contention environment, as an increasing number of transactions wait, a larger number of lock requests get blocked and fewer lock requests can get through. The proposed scheme reduces the blocking probability by deferring the blocking behavior of transactions to the later stages of their execution. By properly balancing the blocking and abort effects, the proposed scheme can lead to better performance than either the conventional locking or the optimistic concurrency control (OCC) schemes at all data and resource contention levels. We consider both static and dynamic approaches to determine when to switch from the nonblocking phase to the blocking phase. An analytical model is developed to estimate the performance of this scheme and determine the optimal operating or switching point. The accuracy of the analytic model is validated through a detailed simulation     

Size exclusion behavior of polymers in amide solvents

Summary The size exclusion chromatography of neutral polymers and polymers containing ionic groups was investigated using N,N-dimethylacetamide (DMA) as mobile phase. As reported previously for N,N-dimethylformamide (DMF), acrylonitrile polymers containing charges, even those at terminal end groups, showed markedly small retention volumes and multimodal peaks by refractive index and 280 nm UV detectors. In DMA containing small amounts of LiBr the peaks of the ionic polymers were shifted to small retention volumes while neutral polymers with analogous chemical structures did not show the same behavior. As in the case of DMF the peculiarities observed in DMA were attributed to the formation of supramolecular structures by the interaction of the ionic groups in the polymer and the ionic species from DMA decomposition.     

Prediction of mean square radius of gyration of tree-like polymers by a general kinetic approach

This paper describes a kinetic method to predict the z-average molecular mean square radius of gyration of tree-like polymers formed by irreversible reactions, assuming Gaussian chains. It is based on the population balance equations for the two-sided molecular distributions of pendant chains associated with every chemically distinguishable kind of bonds. An automated method for the solution of those equations is valid both before as well as after gelation for complex kinetic schemes. Examples of its use are presented with polycondensation systems leading to hyperbranched polymers, the anionic polymerization of mono- and divinyl monomers and a radical polymerization with terminal branching and transfer to polymer.