Thermodynamic description of the viscosity of liquid solder alloys with minor Co impurities

Because of the increasing complexity and cost of experiments carried out, the data for the multi-component alloy systems have frequently been obtained by numerical modelling. It is clear that the related calculations require reliable data dealing with the pure components and binary alloy systems. Selecting the reliable data concerning the pure components from the literature, the viscosities for the SAC and (SAC)_1?x Co_x solder alloys have been calculated using different viscosity models (geometric and physical). The viscosity decreases as the amount of tin content increases in the SAC387 alloy while the addition of the cobalt to SAC387 solder results in the increasing of the viscosity. Moreover, by computing the root mean square values between theoretical and experimental viscosities, it can be concluded that the lowest value among all models is that of obtained by Kaptay equation.     

Sulphur and oxygen isotopic characters of dissolved sulphate in groundwater from the Pleistocene aquifer in the southern Jordan Valley (Jericho area,Palestine)

Sulphate and chloride concentrations in the shallow Pleistocene aquifer systems in the lower Jordan valley area indicate a general trend of increasing salinity eastward and southward. This study was conducted in one of the important sub-basins feeding the Pleo–Pleistocene aquifer in the Jericho area in the southern part of the valley using S and O isotopes of dissolved sulphate. The results show that sulphate has mainly two contributions to the groundwater. One is the surface seepage, which is present as a salty leachate form with the positive δ³⁴S_sulphate values of primary gypsum in Lisan and Samara formations, and the second is the upwelling saline water which was in contact with a deep secondary gypsum, aragonites and salty rocks and rose up under heavy abstraction with depleted ³⁴S in sulphate and relatively high sulphate and chloride content. The latest was clearly shown in the Arab Project wells to the east that is undergoing a continuous heavy abstraction. The isotopic signatures of S and O in these wells to the east show that this depleted ³⁴S and highly concentrated sulphate might also indicate a dissolved sulphate originating from pyrite oxidation that results from the interaction with a pyrite-rich aquifer, which can well up with salty water under heavy abstraction and is oxidised in the upper aerobic shallow aquifer.     

Structure and Mechanical Properties of 50/50 NR/SBR Blend/Pristine Clay Nanocomposites

A blend/clay nanocomposites of 50/50 (wt%) NR/SBR was prepared via mixing the latex of a 50/50 NR/SBR blend with an aqueous clay dispersion and co‐coagulating the mixture. The structure of the nanocomposite was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Nanocomposites containing less than 10 phr clay showed a fully exfoliated structure. After increasing the clay content to 10 phr, both nonexfoliated (stacked layers) and exfoliated structures were observed in the nanocomposites. The results of mechanical tests showed that the nanocomposites presented better mechanical properties than clay‐free NR/SBR blend vulcanizate. Furthermore, tensile strength, tensile strain at break, and hardness (shore A) increased with increasing clay content, up to 6 phr, and then remained almost constant.     

Formation of silver iodide nanoparticles on silk fiber by means of ultrasonic irradiation

The growth of silver iodide nanoparticles on silk fiber was achieved by sequential dipping in an alternating bath of potassium iodide and silver nitrate under ultrasound irradiation. Some parameters such as effect of pH, concentration and numerous sequential dipping in growth of the nanocrystal have been studied. The samples were characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), ICP, TGA and solid state UV–vis spectroscopy.     

Effect of the spectral profile of a deriving field on the bistability of a dissipative medium

 Through the differential equation describing the behavior of the nonlinear polarization of a medium with respect to an incident field, the Maxwell field equations and the boundary conditions of the field inside a resonator, the relationship between the output and the incident fields is obtained, describing a bistability phenomena. The effect of the spectral profile of the incident field and its spectral halfwidth on the bistability phenomena is studied.     

Influence of tungsten doping concentration on the electronic and optical properties of anatase TiO2

The structural, electronic and optical properties of tungsten-doped TiO₂ have been investigated using density functional theory with plane wave basis sets and ultrasoft pseuodopotential. Substitutional W doping at Ti sites create W 5d states just below the conduction band minimum while interstitial W doping gives isolated W 5d states in the middle of forbidden region. Averaged bond lengths show that W doping at Ti sites produce minimum structural distortion as compared to the interstitial W-doped TiO₂. Substitutional W-doped TiO₂ has better visible light absorption compared to interstitial W-doped TiO₂ and has stable configuration which provide reasonable explanation for the experimental findings. Tungsten doping in TiO₂ with different doping concentrations is investigated as an enabling concept for enhancing the visible light absorption. Optical properties show that optimal W doping concentration would improve the visible light absorption. 2.08% W doping concentration gives strong visible and ultraviolet light absorption among all doped models found consistent with experiments.     

Comparison between standard and counterpoise-corrected optimization using some hydrogen and halogen bonded systems

The effect of the counterpoise correction on the geometries, stabilization energies, and vibrational harmonic frequencies of some hydrogen- and halogen-bonded systems (B?=?CH₃CN,?HCN,?NH₃,?N₂,?CO,?H₂O,?H₂S,?PH₃;?HX?=?HF,?HCl,?HBr,?HCN,?HCF₃; XY?=?Br₂,?BrCl,?BrF,?Cl₂,?ClF,?F₂) has been analysed at the MP2 level of theory using the popular 6-311++G(d,p) basis set. The optimized B?···?H and B?···?X bond lengths increase with counterpoise (CP) correction. In some cases standard values and in other cases CP-corrected values are close to experimental data. The absolute values of complexation energies of CP-corrected structures are higher than standard by inclusion of BSSE correction. The effect of CP correction on intermolecular bond lengths and complexation energies of B?···?XY series are usually higher than B?···?HX. Also, this effect is higher for H₂S and PH₃ groups. The CP correction changes the vibrational harmonic frequencies by 0–100%. The changes are frequently lower than 20% for frequencies higher than 300?cm^?1.     

Computational studies on cyclic [n]paraphenyleneacetylenes using homodesmotic reactions

Cyclic [n]paraphenyleneacetylenes ([n]CPPAs) are potentially useful compounds for molecular electronics. In this article, a homodesmotic reaction scheme coupled with density functional theory has been used to estimate theoretically strain energies and heats of formation of [n]CPPAs. Calculations have been done for a series of [n]CPPAs, containing up to ten phenylacetylene units. Strain energies of [n]CPPAs decrease, while heats of formation increase steadily with the increase in the number of phenylacetylene units using homodesmotic reaction schemes. B3LYP and mPW1PW91 functionals have been used with the Pople basis set 6-31G* to analyze the trends. The results are sensitive to the scheme of homodesmotic reaction chosen, thereby necessitating careful chemical consideration before spending considerable computational resources for higher [n]CPPAs not considered here. Computational estimates for the ring diameter of [n]CPPAs and absolute entropy have also been obtained here. The HOMO-LUMO gaps of the belt shaped [n]CPPAs show an odd–even difference. In addition, the HOMOs of the [3]CPPA, [5]CPPA, [7]CPPA and [9]CPPA are doubly degenerate.     

Laminar natural convection between vertical isothermal heated plates with different temperatures

Numerical investigation of laminar free convection heat transfer in the vertical parallel plate channel with asymmetric heating is presented. Both inlet and exit effects are included into the analysis. A numerical solution is obtained for a Prandtl number of 0.71 and for modified Rayleigh number [`(Ra)]\overline {Ra} = 10⁻¹ ÷ 10⁵, and varying heating ratio T_R = 0 ÷ 1 and aspect ratio A = 10. Fully elliptic Navier-Stokes and energy equations are solved using the finite volume techniques with staggered grid arrangements. The obtained results show a strong influence of the temperature ratio on local and average heat transfer coefficient on the hot and cold plates. With reduction of T_R the heat transfer parameter on the hot wall grows, and on the cold one, on the contrary, it decreases. As a result, the total heat exchange from two plates depends poorly on the parameter T_R.     

Efficient visible-light-induced photocatalytic degradation of MO on the Cr-nanocrystalline titania-S

In order to improve visible light photocatalytic activities of the nanometer TiO₂, a novel and efficient Cr,S-codoped TiO₂ (Cr-TiO₂-S) photocatalyst was prepared by precipitation-doping method. The crystalline structure, morphology, particle size, and chemical structure of Cr-TiO₂-S were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) techniques, respectively. Results indicate that the doping of Cr and S, cause absorption edge shifts to the visible light region (λ > 420 nm) compare to the pure TiO₂, reduces average size of the TiO₂ crystallites, enhances desired lattice distortion of Ti, promotes separation of photo-induced electron and hole pair, and thus improves pollutant decomposition under visible light irradiation. The photocatalytic activities of Cr-TiO₂-S nanoparticles were evaluated using the photodegradation of methyl orange (MO) as probe reaction under the irradiation of UV and visible light and it was observed that the Cr-TiO₂-S photocatalyst shows higher visible photocatalytic activity than the pure TiO₂. The optimal Cr-TiO₂-S concentration to obtain the highest photocatalytic activity was 5 mol% for both of Cr and S.