A novel current-mode four-quadrant CMOS analog multiplier/divider

This paper presents, a new current mode four-quadrant CMOS analog multiplier/divider based on dual translinear loops. Compared with the previous works this circuit has a simpler structure resulting in lower power consumption and higher frequency response. Simulation results, performed using HSPICE with 0.25 μm technology, confirm performance of the proposed circuit.     

Toxic cyanobacterial breakthrough and accumulation in a drinking water plant: a monitoring and treatment challenge

The detection of cyanobacteria and their associated toxins has intensified in recent years in both drinking water sources and the raw water of drinking water treatment plants (DWTPs). The objectives of this study were to: 1) estimate the breakthrough and accumulation of toxic cyanobacteria in water, scums and sludge inside a DWTP, and 2) to determine whether chlorination can be an efficient barrier to the prevention of cyanotoxin breakthrough in drinking water. In a full scale DWTP, the fate of cyanobacteria and their associated toxins was studied after the addition of coagulant and powdered activated carbon, post clarification, within the clarifier sludge bed, after filtration and final chlorination. Elevated cyanobacterial cell numbers (4.7 × 10⁶ cells/mL) and total microcystins concentrations (up to 10 mg/L) accumulated in the clarifiers of the treatment plant. Breakthrough of cells and toxins in filtered water was observed. Also, a total microcystins concentration of 2.47 μg/L was measured in chlorinated drinking water. Cyanobacterial cells and toxins from environmental bloom samples were more resistant to chlorination than results obtained using laboratory cultured cells and dissolved standard toxins.     

Fate of toxic cyanobacterial cells and disinfection by-products formation after chlorination

Drinking water sources in many regions are subject to proliferation of toxic cyanobacteria (CB). Chlorination of source water containing toxic cyanobacterial cells for diverse treatment purposes might cause cell damage, toxin release and disinfection by-products (DBP) formation. There is limited information available on chlorination of different toxic CB cells and DBP formation potentials. This work: (1) determines the extent of lysis and toxins/taste and odor compound release in chlorinated natural water from CB cells (Anabaena circinalis, Microcystis aeruginosa, Cylindrospermopsis raciborskii, and Aphanizomenon issatsckenka) from laboratory cultures and natural blooms; (2) assesses the rates of oxidation of toxins by free chlorine under environmental conditions; (3) studies the DBP formation associated with the chlorination of CB cell suspensions. With chlorine exposure (CT) value of <4.0 mg min/L >60% cells lost viability causing toxin release. Cell membrane damage occurred faster than oxidation of released toxins. Kinetic analysis of the oxidation of toxins in natural water revealed significant differences in their susceptibility to chlorine, saxitoxins being the easiest to oxidize, followed by cylindrospermopsin and microcystin-LR. Furthermore, concentrations of trihalomethanes and haloacetic acids (<40 μg/L) and N-nitrosodimethylamine (<10 ng/L) as chlorination by-products were lower than the guideline values even at the highest CT value (220 mg min/L). However, the DBP concentrations in environmental bloom conditions with very high cell numbers were over the guideline values.     

Removal of Double Oxide Film Defects by Ceramic Foam Filters

In this study, Weibull statistical and statistical image analyses of porosity were employed to determine the efficiency of ceramic foam filters for the removal of double oxide film (bifilm) defects from a pure Al melt. Using these efficiencies and the branch filter model, the average size of the inclusions present in the liquid was estimated, and assuming that most of the inclusions in the melt are in the form of double oxide films, the possible dimensions for these defects were calculated. The results showed that the foam filters can remove oxide defects from the melt and that the efficiency of this filtration depends on the pore size of the filter. The average dimension of the oxide film defects was calculated to be 13.8?×?13.8???m with a maximum thickness of 1???m, if they remained non-convoluted in the metal flow. If they became convoluted because of the turbulence of the liquid flow, then the dimensions of the flat defect before it became curled up in the flow were calculated to be between 37?×?37?×?1 and 370?×?370?×?0.01???m.     

Dynamic observer-based controllers for linear uncertain systems

This paper addresses robust controller design for uncertain linear systems via a dynamic observer-based controller. A dynamic observer is an alternative structure for a classical observer which can be regarded as a general form of a usual observer and has additional degrees of freedom in the observer structure. Using this new observer structure, a new observer-based controller for linear systems is proposed. Some strict linear matrix inequalities (LMIs) have been given to find the dynamic observer parameters and controller gain. It is shown that dynamic observer can be used effectively for tackling the drawbacks of the classical observer-based robust controller design methods. As an advantage, LMIs are derived even in the presence of uncertainties in system, input and output matrices simultaneously, whereas by using the traditional observer, bilinear matrix inequalities (BMIs) are given in the presence of such uncertainties. Moreover, the proposed LMIs do not imply the equality constraint. Simulation results are used to illustrate the effectiveness of the proposed design technique.     

Antimicrobial effect,frictional resistance,and surface roughness of stainless steel orthodontic brackets coated with nanofilms of silver and titanium oxide: a preliminary study

Nano‐silver and nano‐titanium oxide films can be coated over brackets in order to reduce bacterial aggregation and friction. However, their antimicrobial efficacy, surface roughness, and frictional resistance are not assessed before. Fifty‐five stainless‐steel brackets were divided into 5 groups of 11 brackets each: uncoated brackets, brackets coated with 60 µm silver, 100 µm silver, 60 µm titanium, and 100 µm titanium. Coating was performed using physical vapor deposition method. For friction test, three brackets from each group were randomly selected and tested. For scanning electron microscopy and atomic‐force microscopy assessments, one and one brackets were selected from each group. For antibacterial assessment, six brackets were selected from each group. Of them, three were immediately subjected to direct contact with S. mutans. Colonies were counted 3, 6, 24, and 48 h of contact. The other three were stored in water for 3 months. Then were subjected to a similar direct contact test. Results pertaining to both subgroups were combined. Groups were compared statistically. Mean (SD) friction values of the groups 'control, silver‐60, silver‐100, titanium‐60, and titanium‐100' were 0.55 ± 0.14, 0.77 ± 0.08, 0.82 ± 0.11, 1.52 ± 0.24, and 1.57 ± 0.41 N, respectively (p = .0004, Kruskal–Wallis). Titanium frictions were significantly greater than control (p < .05), but silver groups were not (p > .05, Dunn). In the uncoated group, colony count increased exponentially within 48 h. The coated groups showed significant reductions in colony count (p < .05, two‐way‐repeated‐measures ANOVA). In conclusions, all four explained coatings reduce surface roughness and bacterial growth. Nano‐titanium films are not suitable for friction reduction. Nano‐silver results were not conclusive and need future larger studies.     

Influence of Concentrations of KOH and Na_2SiO_3 Electrolytes on the Electrochemical Behavior of Ceramic Coatings on 6061 Al Alloy Processed by Plasma Electrolytic Oxidation

In this study,ceramic coatings were deposited on 6061 Al alloy using a plasma electrolytic oxidation(PEO)technique,and the effect of concentrations of KOH and Na_2SiO_3 as electrolytes for PEO process was studied on microstructure,chemical composition,and electrochemical behavior of PEO coatings formed on the 6061 Al alloy.The results indicated that the increase in concentration of KOH led to rise in electrical conductivity of electrolyte.Consequently,the breakdown voltage reduced,which in turn improved the surface quality and the corrosion behavior.Moreover,the increase in concentration of Na_2SiO_3 resulted in the increase in incorporation of Si in the coating,which led to a higher corrosion potential in the concentration of 4 g L~(-1).According to this investigation,the best protection behavior of coatings can be obtained when the KOH and Na_2SiO_3 concentrations in PEO electrolyte are equal to 4 g L~(-1).     

Comprehensive kinetic study for Fischer–Tropsch reaction over KMoFe/CNTs nano-structured catalyst

The kinetics of the Fischer–Tropsch (FT) reaction was evaluated through detailed experimentation with a KMo bimetallic promoted Fe catalyst supported on carbon nanotubes (CNTs). The kinetic tests were conducted in a fixed-bed reactor under operating conditions of P = 6.9–41.3 bar, T = 543–563 K, H₂/CO = 1, gas hourly specific velocity (GHSV) = 2000 h⁻¹. This study aimed to investigate the mechanism prevailing in CO activation and the rate equation for CO consumption during FT reactions over a 0.5K5Mo10Fe/CNTs catalyst. To evaluate the synergistic effects of Fe, Mo, and K phases on the catalyst activity, both fresh and spent catalysts were thoroughly characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) to ascertain the different phases (active sites) present and relevant interactions. Based on the adsorption of carbon monoxide and hydrogen, 22 possible mechanisms for monomer formation were proposed for FT synthesis in accordance with the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Rideal (ER) adsorption theories. The best fit kinetic model was identified through a multi-variable non-linear regression analysis. The selected mechanistic model was based on carbide formation approach, where H₂-assisted adsorption of CO was considered for the derivation. Kinetic parameters such as activation energy, adsorption enthalpies of H₂, and CO were estimated to be 65.0, −13.0, and −54.0 kJ/mol, respectively. Considering the developed kinetic model, the effects of reaction temperature and pressure were assessed on Fischer–Tropsch synthesis (FTS) product distribution. Additionally, the kinetic model was compared with the typical Anderson–Schulz–Flory model, suggesting the effects of water-gas-shift and the existence of additional formation pathway such as secondary re-adsorption of olefins for heavier hydrocarbons.     

Bidentate salen Cu(II) complex functionalized on mesoporous MCM-41 as novel nano catalyst for the oxidative coupling of thiols into disulfides using urea hydrogen peroxide (UHP)

Functionalized Copper(II) complex into nano dimensional mesoreactor was successfully prepared. The Copper(II) complex with N–O donor Schiff base ligand was readily trapped into mesoporous silica MCM-41 through the post grafting method. N–O Chelating Schiff-base-MCM-41 has been derived from 5-bromo-salicylaldehyde and 3-aminopropyltriethoxysilane which was functionalized on MCM-41 via silicon alkoxide route. This compound was characterized by FT-IR, TGA, small angle X-ray diffraction patterns, ICP/MS analysis and N₂ sorption–desorption analysis. The catalytic property of Cu–salen–MCM-41 was considered for the preparation of disulfides using urea hydrogen peroxide as oxidant. The reaction progress is simple and proceeds under mild and heterogeneous conditions in acetonitrile at the ambient of temperature. The corresponding disulfides have been achieved with high purity and good to excellent yields; also, no over oxidation to sulfoxide or sulfone was observed in all cases. The catalyst can be recovered and reused several times without significant loss of stability and activity.     

Short-Term Wind Speed Forecast Using Measurements From Multiple Turbines in A Wind Farm

Turbine operations in a wind farm benefit from an understanding of the near-ground behavior of wind speeds. This article describes a probabilistic spatial-temporal model for analyzing local wind fields. Our model is constructed based on measurements taken from a large number of turbines in a wind farm, as opposed to aggregating the data into a single time-series. The model incorporates both temporal and spatial characteristics of wind speed data: in addition to using a time epoch mechanism to model temporal nonstationarity, our model identifies an informative neighborhood of turbines that are spatially related, and consequently, constructs an ensemble-like predictor using the data associated with the neighboring turbines. Using actual wind data measured at 200 wind turbines in a wind farm, we found that the two modeling elements benefit short-term wind speed forecasts. We also investigate the use of regime switching to account for the effect of wind direction and the use of geostrophic wind to account for the effects of meteorologic factors other than wind. These at best provide a small performance boost to speed forecast.