Coupled heat and mass transport phenomena in siliceous aggregate concrete slabs subjected to fire

A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum and energy, and including the effects of evaporation and dehydration processes on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Siliceous aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions. © 1997 John Wiley & Sons, Ltd.     

Comparative study between prepared electrical grease and the imported one

Grease lubrication is a complex mixture of science and engineering, requiring an interdisciplinary approach, and is applied to the majority of bearings worldwide. Grease can be more than a lubricant; it is often expected to perform as a seal, corrosion inhibitor in electrical joints, electrical insulator and electrical connection improver. This work is concerned, therefore, with the comparative study between prepared electrical grease and the imported one. Physicochemical and electrical properties for the prepared grease and the imported one were evaluated. The results of dropping point, penetration, dynamic viscosity, corrosion inhibition, evaporation loss, total acid number and oil separation for the prepared grease under investigation are mostly the same compared with the imported grease. In addition, the results interpreted in terms of the physical and chemical properties of both greases revealed that no remarkable differences. In this respect, calorimetric study shows that the prepared grease, like the imported one, is thermally stable up to about 200 °C then decomposition and degradation started slightly faster and higher than that of the imported one. The electrical and dielectric parameters are very close at and around room temperature then the increase of charge carriers' mobility at higher temperatures explains the deviation from stability in case of the prepared grease. One can conclude that the prepared electrical grease could replace efficiently the imported electrical grease especially in isothermal application at and around room temperature.     

Transdermal Delivery of Tadalafil. I. Effect of Vehicles on Skin Permeation

Transdermal delivery that avoids the presystemic disposition can provide an alternative to oral administration of tadalafil. Accordingly, the aim of this study was to select the best vehicle as the first step in optimization of tadalafil transdermal delivery. The vehicles were used neat or in selected binary combinations and were evaluated for drug solubilization and transdermal delivery. The drug solubility in pure vehicles were ranked as polyethylene glycol (PEG) 400 >?propylene glycol (PG) >?ethanol >?ethyl oleate (EO) >?isopropyl myristate (IPM) >?water. The solubility in binary systems containing ethanol at 2:1 ratios with EO or IPM was greater than that obtained with pure ethanol, EO, or IPM. This effect could be due to the cosolvency effect. The transdermal drug delivery from pure vehicles was ranked as IPM >?EO >?ethanol >?PG >?PEG >?water. The delivery from binary mixtures of ethanol with either IPM or EO was higher than that obtained from pure solvents with the delivery increasing with increasing ethanol concentration in the mixtures. The delivery from binary mixtures was synergistic rather than additive. The study thus demonstrated a potential of tadalafil transdermal delivery. Binary combinations of ethanol with either IPM or EO provided the first step forward toward the development of transdermal delivery system for tadalafil.     

Effects of exposure to oil sands process-affected water from experimental reclamation ponds on Chironomus dilutus

Effective detoxification of oil sands process-affected water (OSPW) is one issue associated with bitumen extraction in the Alberta oil sands. It has been suggested that reclamation ponds can be used to passively treat OSPW, potentially allowing for its safe return to the environment. In this study, OSPW was sampled in two batches (A and B) from the Syncrude Canada Ltd. West In-Pit (WIP) settling pond and from three experimental reclamation ponds - Big Pit, FE5, and TPW. Acute (10 d) and chronic (until adult emergence) exposures of Chironomus dilutus larvae to OSPW were conducted and survival, growth, development, and behavior were assessed. Masses of larvae exposed to WIP-OSPW were 64-77% less than the freshwater control (p < 0.001). Similarly, chronic exposure to WIP-OSPW resulted in significantly (p < 0.05) less pupation than in the freshwater control, with 31% (A) and 71% (B) less pupation of larvae exposed to WIP-OSPW. Rates of emergence were significantly less for larvae exposed to WIP-OSPW, with only 13% (A) and 8% (B) of larvae emerging as adults when exposed to WIP-OSPW, compared to 81% in the freshwater control (p < 0.0001). Pupation and emergence rates were significantly less in TPW than freshwater control (p < 0.05), but there were no differences observed in Big Pit or FE5. Lesser toxicity was observed in reclaimed OSPW compared to fresh OSPW and this coincided with lesser concentrations of NAs. The results presented are consistent with the hypothesis that an organic fraction is the cause of the toxicity of OSPW toward C. dilutus and that OSPW aged in reclamation ponds retains toxicity and therefore, more aggressive, targeted treatment of OSPW is required to accelerate decreases.     

The impact of metallic coagulants on the removal of organic compounds from oil sands process-affected water

Coagulation/flocculation (CF) by use of alum and cationic polymer polyDADMAC, was performed as a pretreatment for remediation of oil sands process-affected water (OSPW). Various factors were investigated and the process was optimized to improve efficiency of removal of organic carbon and turbidity. Destabilization of the particles occurred through charge neutralization by adsorption of hydroxide precipitates. Scanning electron microscope images revealed that the resultant flocs were compact. The CF process significantly reduced concentrations of naphthenic acids (NAs) and oxidized NAs by 37 and 86%, respectively, demonstrating the applicability of CF pretreatment to remove a persistent and toxic organic fraction from OSPW. Concentrations of vanadium and barium were decreased by 67-78% and 42-63%, respectively. Analysis of surface functional groups on flocs also confirmed the removal of the NAs compounds. Flocculation with cationic polymer compared to alum, caused toxicity toward the benthic invertebrate, Chironoums dilutus, thus application of the polymer should be limited.     

Correlation of electrical and swelling properties with nano free‐volume structure of conductive silicone rubber composites

The present study focuses on finding a correlation between the positron annihilation parameters of silicone rubber polydimethylsiloxane (PDMS) composites loaded with different conductive fillers and their swelling and electrical properties. Four types of conductive fillers have been used in this study, i.e., carbon black (CB), graphite (G), copper, and nickel powders. The investigated swelling parameters for PDMS composites such as the maximum degree of swelling Q_m%, the penetration rate, P, and consequently the diffusion coefficient, D, decreased with increasing the filler content due to the reduction of the size of free‐volume, which could be observed through a decrease of the probability of ortho‐positronium (o‐Ps) formation I₃, that has been measured by the positron annihilation spectroscopy (PALS). Accordingly, a positive correlation has been found of 76.78% and 61.1% between Q_m% and the o‐Ps lifetime τ₃, representing the size of free‐volume for the CB and G filled composites, respectively. It is worthwhile, mentioning that the CB filled composites exhibit relatively low values of P, D, and Q_m% as compared to the G filled composites due to the difference in the physical properties of the filler, particle size, surface area as well as the tendency of the filler particles to make aggregates. On the other hand, the variation of the diffusion coefficient with the relative fractional free‐volume F_r is found in good agreement with the Fujita's free‐volume theory. On the other hand, the electrical conductivity increases with increasing the conductive filler content. Positive temperature coefficient of conductivity (PTCC) behavior is detected, except for the composite containing 20 or 25 phr CB, which showed a metallic behavior. Besides, CB filled PDMS composites exhibit higher electrical conductivity as compared to the composites filled with the other three fillers. The electrical conductivity ln (σ) is positively correlated with the probability of free annihilation of positrons at interfaces I₂, thus suggesting an increase in the electron density with the filler content. The activation energy of conduction, E_a, decreases with the increase in the loading of conductive filler. Moreover, it was noticed that E_a varies with the filler type, the values of E_a increase as the particle size of the filler increases. Finally, a correlation between the free‐volume V_f, determined by PALS with the DC electrical conductivity ln(σ) is found to be in accordance with Miyamoto and Shibayma model. POLYM. COMPOS., 34:2105–2115, 2013. © 2013 Society of Plastics Engineers     

Microcontroller implementation of direct torque control

The switching frequency of a conventional direct torque control (DTC) strategy which is based on hysteresis controllers results in a variable switching frequency which depends on the mechanical speed, stator flux, stator voltage, and the hysteresis band of the comparator. In this paper, a DTC scheme using space vector modulator (SVM) and fuzzy logic controller (FLC) is suggested. A comparison with the classical DTC is presented. The suggested control strategy guarantees very good dynamic and steady state characteristics with low sampling rate and a constant switching frequency. The experimental results are presented to validate the scheme. Copyright © 2005 John Wiley & Sons Ltd.     

Mucoadhesive polymeric hydrogels for nasal delivery of acyclovir

The study evaluated different mucoadhesive polymeric hydrogels for nasal delivery of acyclovir. Gels containing poly-N-vinyl-2-pyrrolidone (PVP) were prepared with crosslinking achieved by irradiation with a radiation dose of 15 kGy being as efficient as 20 kGy. Gels containing chitosan and carbopol were also evaluated. The mucoadhesive properties of gels were measured by a modification of a classical tensile experiment, employing a tensile tester and using freshly excised sheep nasal mucosa. Considering the mucoadhesive force, chitosan gel and gel prepared with 3% PVP in presence of polyethylene glycol (PEG) 600 were the most efficient. The in vitro drug release depended on the gel composition. Higher release rates were obtained from PVP gels compared to chitosan or carbopol gels. The release rate of drug from PVP gels was increased further in presence of PEG or glycerol. Histopathological investigations proved that the PVP was a safe hydrogel to be used for mucosal delivery. The PEG in gel formulations caused less damages to the nasal mucosal compared to formulation containing glycerol.     

A unified framework for tree search decoding: rediscovering the sequential decoder

We consider receiver design for coded transmission over linear Gaussian channels. We restrict ourselves to the class of lattice codes and formulate the joint detection and decoding problem as a closest lattice point search (CLPS). Here, a tree search framework for solving the CLPS is adopted. In our framework, the CLPS algorithm is decomposed into the preprocessing and tree search stages. The role of the preprocessing stage is to expose the tree structure in a form matched to the search stage. We argue that the forward and feedback (matrix) filters of the minimum mean-square error decision feedback equalizer (MMSE-DFE) are instrumental for solving the joint detection and decoding problem in a single search stage. It is further shown that MMSE-DFE filtering allows for solving underdetermined linear systems and using lattice reduction methods to diminish complexity, at the expense of a marginal performance loss. For the search stage, we present a generic method, based on the branch and bound (BB) algorithm, and show that it encompasses all existing sphere decoders as special cases. The proposed generic algorithm further allows for an interesting classification of tree search decoders, sheds more light on the structural properties of all known sphere decoders, and inspires the design of more efficient decoders. In particular, an efficient decoding algorithm that resembles the well-known Fano sequential decoder is identified. The excellent performance-complexity tradeoff achieved by the proposed MMSE-DFE Fano decoder is established via simulation results and analytical arguments in several multiple-input multiple-output (MIMO) and intersymbol interference (ISI) scenarios.