Electrical conductivity of concrete containing silica fume

The influence of silica fume on concrete properties represents an important technical research. In general, silica fume tends to improve both mechanical characteristics and durability of concrete. Thus the electrical properties of concrete containing silica fume can be studied to clarify its physical performance during hydration. The electrical conductivity of neat cement, mortar and concrete pastes was measured during setting and hardening. The ordinary Portland cement was partially replaced by different amounts of silica fume by weight. The changes in the electrical conductivity were reported during setting and hardening after gauging with water. The results of this study showed that the electrical conductivity can be used as an indication for the setting characteristics as well as the structural changes of the hardened pastes made with and without silica fume.     

Yield response of lentil to directly applied and residual phosphorus in a Mediterranean environment

The response of lentil grown under rainfed conditions to directly applied and residual phosphorus (P) was described by a modified Mitscherlich equation, accounting for the effects of rainfall on (1) potential yield, and (2) the availability of soil-P to the crop. The response of lentil yield to directly applied and residual P was studied in two-course cereal–lentil rotational trials under rainfed conditions in a Mediterranean-type environment. Cereal crops were grown at different P application rates during 4 growing seasons at 3 sites, representing different rainfall zones in northwest Syria. Lentil (Lens culinaris Med.) was grown during 4 seasons at the same sites, each lentil crop following a cereal crop. In 3 out of 4 lentil-growing seasons, additional P was applied to lentil in subplots to compare the residual and direct effects of P application. The initial contents of extractable soil-P (P-Olsen) were low at all sites, in the range of 2–5 ppm P. Under the conditions of the experiments, lentil appeared to benefit slightly more from P applied to the preceding wheat crop (residual P) than from directly applied P. It is shown that the modified Mitscherlich equation could be used as a basis for P fertilizer recommendations for rainfed farming. As for lentil, it was concluded that a single application of P to the wheat crop in a wheat/lentil rotation could reduce the cost of lentil production, without reducing lentil yield.     

A reverse osmosis desalting plant operated by gas turbines

Power plants in Kuwait use gas turbines (GT) only for a few hours to produce power at peak load times. Peak loadoccurs in the summer due to the air-conditioning load. As an example, the average number of operating hours for six gas turbines in the Doha East power plant was 16 in the summer of 2001. There is little concern about efficiency of these GT since they work for a very short time during the year. However, a recent increase in desalted seawater demand suggests the use of these GT to operate reverse osmosis (RO) desalting systems all year around. The summer outside design temperature in Kuwait for air-conditioning calculations is 48°C dry bulb temperature (DBT), and 28°C wet bulb temperature (WBT); but the ambient temperature can easily reach 60°C. Gas turbine power output and efficiency are drastically reduced by the increase in temperature of intake air to the gas turbine's compressor, especially during harsh Kuwaiti summer conditions. Thus, it is essential to investigate cooling of air intake to the GT compressor. The performance of a typical GT unit and its ability to produce desalted waterby a RO desalting system at different ambient temperatures are presented. Calculation of needed capacities for the cooling of intake air to the GT compressor was performed for evaporative cooling, single and multiple mechanical vapor compression cycles, and combined indirect evaporation cooling with the refrigeration system. The improvements of power output and efficiency due to the cooling of air intake of the GT and the resulting increase in desalted water are also presented.     

Time optimization of ultraviolet–ozone pretreatment for improving wool fabrics properties

Wool fabrics were exposed to ultraviolet (UV)–ozone treatment for different periods. After exposure, the fabrics were analyzed by Fourior transform infrared spectroscopy (FTIR). Also, the crystallinity and amorphousity regions were followed by an X‐ray diffraction technique. The results were correlated by mechanical properties measurements. After a certain period of exposure, the dyeability and printability were improved because these abilities are strongly related to the percentage ratio of crystallinity regions to amorphousity regions in wool fabrics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1469–1476, 2002     

Thermal and flammability properties of a silica–poly(methylmethacrylate) nanocomposite

PMMA, poly(metheylmethacrylate), nanocomposites were made by in situ radical polymerization of MMA, methylmethacrylate, with colloidal silica (ca. 12 nm) to study the effects of nanoscale silica particles on the physical properties and flammability properties of PMMA. Transparent samples resulted and the dispersity of the particles was examined by transmission electron microscopy and atomic force microscopy. The addition of nanosilica particles (13% by mass) did not significantly change the thermal stability, but it made a small improvement in modulus, and it reduced the peak heat release rate roughly 50%. Last, the flame‐retardant mechanism provided by the addition of nanosilica particles in PMMA is discussed. Published 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2072–2078, 2003     

Cryptanalysis of an embedded systems’ image encryption

Multimedia Tools and Applications - Recently, a new image encryption-scheme for embedded systems based on continuous third-order hyperbolic sine chaotic system, has been proposed. The...     

Temperature and processing effects on lithium ion conductivity of solution-deposited lithium zirconium phosphate (LiZr2P3O12) thin films

Lithium zirconium phosphate (LiZr₂P₃O₁₂) thin films have been prepared on platinized silicon substrates via a chemical solution deposition approach with processing temperatures between 700°C and 775°C. Films that were subject to a single high-temperature anneal were found to crystallize at temperatures above 725°C. Crystallization was observed in films annealed after each deposited layer at 700°C and above. In both cases, grain size was found to increase with annealing temperature. Ion conductivity was found to increase with annealing temperature in singly annealed films. In per-layer annealed films ion conductivity was found to initially increase then decrease with increasing annealing temperature. A maximum ion conductivity of 1.6 × 10⁻⁶ S/cm was observed for the singly annealed 775°C condition, while a maximum ion conductivity of 5.8 × 10⁻⁷ S/cm was observed for the 725°C per-layer annealed condition. These results are consistent with an increasing influence of cross-plane, internal interface resistance and vapor phase carrier loss in the per-layer annealed samples. This work demonstrates that post-deposition processing methods can strongly affect the ion conducting properties of LiZr₂P₃O₁₂ thin films.     

Great enhancement of mechanical features in PLA based composites containing aligned few layer graphene (FLG), the effect of FLG loading,size, and dispersion on mechanical and thermal properties

Four series of polylactide (PLA) based composite films containing horizontally aligned few layer graphene (FLG) flakes of high aspect ratio and adsorbed albumin are prepared. The mechanical and thermal properties varies with percentage, dispersion degree and size of FLG flakes. Great improvement up to 290% and 360% of tensile modulus and strength respectively were obtained for the composite containing high lateral size of FLG at 0.17% wt, and up to 60% and 80% for the composite with very well dispersed 0.02% wt FLG. The composites of PLA and PEG-PLLA containing very well dispersed FLG flakes at 0.07% wt are ductile showing enhancement of elongation at break up to respectively 80% and 88%. Relatively high electrical conductivity, 5 × 10⁻³ S/cm, is measured for PLA film charged with 3% of FLG.     

Crack growth angle prediction of an internal crack under mixed mode load for unfilled elastomer using the strain energy density factor

This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles.     

Equation of state and the dynamic compression of cerium in the range of the γ-α phase transition

A thermodynamically complete equation of two-phase (γ, α) state of cerium was derived in terms of a pseudobinary solid-solution model developed by Aptekar’ and Ponyatovskii. According to the model, unalloyed cerium is considered to be a substitutional solid solution whose components are represented by atoms with different electron configurations. The free energy of the individual phases (solid-solution components) is represented as a sum of three terms that describe the atomic interaction at T = 0 K, quasi-harmonic lattice vibrations, and the combined contribution of the anharmonicity and thermally excited electrons. The equation of state is shown to adequately describe the unusual behavior of cerium under the effect of static actions. In this work, calculations of the dynamic compression of cerium are performed. The calculations indicate that, up to the completion of the γ-α transition, the formation of the shockwave front in cerium is impossible and compression of cerium occurs in an isentropic wave of simple compression. As the pressure increases, a multiwave configuration with the participation of isentropic and shock waves is realized in cerium. The initial state in which the shock wave is propagated changes depending on the wave intensity; i.e., the initial state “slides” along the leading isentropic wave. The shock adiabat was shown to not pass through the very complex range of metastable existence of α-, α′-, and α″ phases. This provides prerequisites for experimental finding the α-ε transformation which can occur in the shock wave and is not masked with the preceding α-α′ and α′-α″ transformations. When assuming the absence of the α-ε transformation, the calculated coordinates of the point corresponding to the start of melting in the shock wave are p _melt = 11.3 GPa and T _melt = 1130 K.