On robust stability with structured time-invariant perturbations

We consider the problem of robust stability for uncertain systems described in terms of multiple scalar structured time-invariant perturbations, which are norm-bounded. The issue we address is the role that the type of perturbation norm plays in the robust stability conditions. To this end, the L^p-induced norm (for 1 ≤ p ≤ ∞) on the perturbations is considered, and it is shown that the structured singular value is the necessary and sufficient condition for robust stability for all these norms. We conclude that for time-invariant perturbations, in contrast to the time-varying case, robust stability conditions are independent of the type of perturbation norms.     

Transparent and conducting ZnO films prepared by reactive pulsed laser deposition

Undoped ZnO films were prepared on glass substrates without any post-deposition heat treatment using a pulsed Nd:YAG laser ablation of Zn target in the presence of oxygen as reactive atmosphere. Structural, optical, and electrical properties of these films have been investigated as functions of oxygen pressure during deposition. Transparent conducting ZnO films, formed at 120 torr of oxygen pressure, showed an electrical resistivity of 0.27 Ωcm, a mean optical transmittance of 80%, and an optical band gap of 3.25 eV.     

Large-Eddy Simulations and Heat-Flux Modeling in a Turbulent Impinging Jet

This article documents the results of an investigation into aspects of the simulation and modeling of turbulent jets that impinge orthogonally on a target surface. The focus is on the case of a jet which issues from a circular pipe into stagnant surrounding at the relatively high value of Reynolds number of 23,000 (based on nozzle diameter and bulk velocity) for which experimental data are available. Large-eddy simulations were performed to obtain details of the mean flows and the turbulence fields including distributions of all components of the turbulent heat fluxes. The outcome of these simulations were used to assess three alternative models for the turbulent heat fluxes which differ from the conventional Fourier's Law by not being based on the assumption of proportionality between the eddy and thermal diffusivities via a constant Prandtl number. It was found that only one of the models considered succeeds in representing the effects on the heat fluxes of the complex strain field associated with the stagnation region and the subsequent development into the wall-jet region. The reasons for this outcome are discussed.     

Hydromechanical Analysis of Upstream Tailings Disposal Facilities

Very large quantities of mined ore materials are processed annually to obtain the various types of minerals that are essential to industrial processes. Due to its execution simplicity and low cost, upstream tailings disposal has been the most common method used for the surface disposal of tailings produced from processing the mined ore materials in spite of it being the most vulnerable to failure. The complex hydromechanical behavior of the upstream tailings disposal facilities (UTDFs) during their staged construction makes the traditional approaches to consolidation, stability, and seepage analyses inadequate for producing accurate and, in many situations, correct design and evaluation of these facilities. Transient coupled nonlinear finite-element analyses are carried out in this paper using the general purpose code ABAQUS to investigate the hydromechanical behavior of the UTDF during its staged construction. The analyses simulate, in combination, a number of realistic features of the UTDFs during construction, including the transient partially saturated flow within the impoundment, the two-dimensional large consolidation and nonlinear material response of the tailings, and the staged construction loading with time. The UTDF response as predicted by the numerical analyses, which are carried out in the form of comparative study on three different impoundment tailings, is qualitatively comparable with the UTDF behavior trends observed and reported in the literature.     

Low power Wallace multiplier design based on wide counters

Multiplication is one of the most basic arithmetic operations. It is used in digital applications, central processing units, and digital signal processors. In most systems, the multiplier lies within the critical path and hence, due to probability and reliability issues, the power consumption of the multiplier has become very important. Moreover, as chips shrink and their power densities increase, power is becoming a major concern for chip designers. The ever increasing demand for portable applications with their limited battery lifetime indicates that power considerations should be a center stone in today's designs and the future's designs. Thus, all this has motivated us to provide a novel circuit design technique for a low power multiplier without compromising the multiplier's speed. This paper presents a new power aware multiplier design based on Wallace tree structure. A new algorithm is proposed using high‐order counters to meet the power constraints imposed by mobility and shrinking technology. Commonly used multipliers of widths 8, 16, and 32 bits are designed based on the proposed algorithm. The new approach has succeeded in reducing the total number of gates used in the multiplier tree. Simulations on Altera's Quartus‐II FPGA simulator showed that the design achieves an average of 18.6% power reduction compared to the original Wallace tree. The design performs even better as the multiplier's size increases, achieving a 5% gate count reduction, a 26.5% power reduction, and a 23.9% better power‐delay product in 32‐bit multipliers. Copyright © 2011 John Wiley & Sons, Ltd.     

Alginate‐Encapsulated Bacteria for the Treatment of Hypersaline Solutions in Microbial Fuel Cells

A microbial fuel cell (MFC) based on a new wild‐type strain of Salinivibrio sp. allowed the self‐sustained treatment of hypersaline solutions (100 g L^?1, 1.71 m NaCl), reaching a removal of (87±11) % of the initial chemical oxygen demand after five days of operation, being the highest value achieved for hypersaline MFC. The degradation process and the evolution of the open circuit potential of the MFCs were correlated, opening the possibility for online monitoring of the treatment. The use of alginate capsules to trap bacterial cells, increasing cell density and stability, resulted in an eightfold higher power output, together with a more stable system, allowing operation up to five months with no maintenance required. The reported results are of critical importance to efforts to develop a sustainable and cost‐effective system that treats hypersaline waste streams and reduces the quantity of polluting compounds released.     

Microstructural analysis of the adhesion mechanism between old concrete substrate and UHPFC

The performance of any repaired concrete structure, and thus its service life, depends on the quality of the interfacial transition zone of the composite system formed by the repair material and the existing concrete substrate. In this work, the properties of the interfacial transition zone between normal concrete (NC) substrate as an old concrete and ultra-high performance fiber-reinforced concrete (UHPFC) as a repair material was investigated. Pull-off and splitting cylinder tensile tests were performed to quantify the bond strength in direct and indirect tensions, respectively. The microstructure of the interfacial transition zone was also studied using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS). Different types of NC substrate surface preparation methods were used. An optical three-dimensional surface metrology device was used to estimate the substrate roughness parameters. Based on the results, high interfacial bond strength was achieved on the 3rd, 7th, and 28th days. The pull-off test results revealed that all failures occurred in the substrate, regardless of the substrate surface roughness. The majority of failures in the split tensile test also occurred in the substrate. SEM/EDS proved that the use of UHPFC as a repair material chemically, physically, and mechanically improved the repaired interfacial transition zone to become stronger and denser, as well as more uniform, and durable. Moreover, the use of UHPFC increased the service life of repaired structures and minimized the number and extent of interventions to the lowest possible level.     

Some Experimental Aspects of Drag Reduction in Thermoplastic Pipes

This paper reports some experimental results of using a new additive solution for reducing drag in thermoplastic pipes. It was found that the amount of drag achieved is very much dependent on the diameter of the pipe, Reynolds number, and concentrations of the additives. In general it was found that the drag is higher in small-diameter thermoplastic pipes. The maximum drag reduction obtained was 29.4%.     

Effects of Pseudomonas chlororaphis and gaseous chlorine dioxide on the survival of Salmonella enterica on tomatoes

Control of Salmonella enterica on tomatoes is important for food safety. The aim of this research was to evaluate the survival of Salmonella enterica serovars Montevideo (SM) and Typhimurium (ST) on tomatoes exposed to gaseous chlorine dioxide and Pseudomonas chlororaphis (Pc). Pc was applied to stem scars of tomatoes prior to inoculations with SM and ST. Tomatoes were treated with gaseous ClO₂ at 0.4 mg L^?1 for 2 and 4 h (90% R.H. 13 °C), respectively. At 4 h of ClO₂ treatment, SM and ST populations were reduced to 0.82 and <0.30 log CFU g^?1, respectively. Tomatoes treated with SM and ST had 5.42 and 5.37 log CFU g^?1 of Salmonella. Tomatoes treated with Pc + Salmonella count was 2.59 (treated) and 5.83 log CFU g^?1 (control). Salmonella survival was similar at 2 and 4 h of ClO₂ treatment. Application of ClO₂ and Pc may reduce contamination of tomatoes by Salmonella serovars.     

Fat oxidation in freeze-dried grouper during storage at different temperatures and moisture contents

The effects of moisture content levels and storage temperature on the lipid oxidation in freeze-dried grouper were studied. Three trends were observed in the changes of PV (peroxide value) depending on the moisture content and storage temperature. An exponential rise of PV was observed (p < 0.05) at lower temperatures (−20 °C and 5 °C for samples at moisture 5 g/100 g; and −20 °C for samples at moisture 20 g/100 g). At temperatures 25 °C for samples at moisture 5 g /100 g, and 5 and 25 °C for samples at 20 g moisture/100 g peaks of PV were observed (p < 0.05). At higher temperatures (40 °C for both moisture content levels) an exponential decay instead of increase were observed (p < 0.05). Moisture content levels had no significant effect (p > 0.05) on PV stored at temperature of −40 °C. The monolayer moisture for freeze-dried grouper was estimated as 6.2 g/100 g dry solids using BET-isotherm. Differential scanning calorimetry (DSC and modulated DSC) thermogram line showed two shifts (i.e. glass transition) and two endothermic peaks, one for melting of oil and another for decomposition. The validity of the water activity and glass transition concepts were evaluated. It is concluded that glass transition concept may be used to explain the process more adequately.