Silicon nanowire fabric as a lithium ion battery electrode material

A nonwoven fabric with paperlike qualities composed of silicon nanowires is reported. The nanowires, made by the supercritical-fluid-liquid-solid process, are crystalline, range in diameter from 10 to 50 nm with an average length of >100 μm, and are coated with a thin chemisorbed polyphenylsilane shell. About 90% of the nanowire fabric volume is void space. Thermal annealing of the nanowire fabric in a reducing environment converts the polyphenylsilane coating to a carbonaceous layer that significantly increases the electrical conductivity of the material. This makes the nanowire fabric useful as a self-supporting, mechanically flexible, high-energy-storage anode material in a lithium ion battery. Anode capacities of more than 800 mA h g(-1) were achieved without the addition of conductive carbon or binder.     

Zirconium oxide (NP) - ionic liquid as an efficient media for the domino Knoevenagel hetero Diels-Alder reaction with unactivated alkynes

Immobilized ZrO₂-nanopowder (NP) in ionic liquid and different organic solvents was used as a suitable Lewis-acid for the synthesis of polycyclic heterocycles which contains pyran-based skeletons. Reaction of O-propargylated salicylaldehyde with active methylene compounds in the presence of ZrO₂-NP in ionic liquid proceeds via domino Knoevenagel hetero Diels-Alder reaction of unactivated alkynes to construct the pyran skeleton. Comparison with different ionic liquids and organic solvents showed that the best results were obtained with 1-butyl-3-methylimidazolium nitrate [bmim][NO₃] because of short reaction times and high yields. Carrying out the reaction under these conditions has advantages such as: high yields, short reaction times and easy work-up.     

Optimizing multi-item multi-period inventory control system with discounted cash flow and inflation: Two calibrated meta-heuristic algorithms

A mixed binary integer mathematical programming model is developed in this paper for ordering items in multi-item multi-period inventory control systems, in which unit and incremental quantity discounts as well as interest and inflation factors are considered. Although the demand rates are assumed deterministic, they may vary in different periods. The situation considered for the problem at hand is similar to a seasonal inventory control model in which orders and sales happen in a given season. To make the model more realistic, three types of constraints including storage space, budget, and order quantity are simultaneously considered. The goal is to find optimal order quantities of the products so that the net present value of total system cost over a finite planning horizon is minimized. Since the model is NP-hard, a genetic algorithm (GA) is presented to solve the proposed mathematical problem. Further, since no benchmarks can be found in the literature to assess the performance of the proposed algorithm, a branch and bound and a simulated annealing (SA) algorithm are employed to solve the problem as well. In addition, to make the algorithms more effective, the Taguchi method is utilized to tune different parameters of GA and SA algorithms. At the end, some numerical examples are generated to analyze and to statistically and graphically compare the performances of the proposed solving algorithms.     

Molecular dynamics simulation of a graphite-supported copper nanocluster: thermodynamic properties and gas adsorption

Molecular dynamics simulations were conducted for a cubic Cu cluster supported on a graphite bilayer. The Sutten–Chen and Lennard–Jones potentials were used for metal–metal and metal–graphite interactions, respectively. Heating and cooling processes were performed by NVT simulations at different temperatures in the range 200 to 1800?K. The melting point was identified on the basis of caloric and heat capacity curves. The calculated melting point was 770?K, far below the bulk melting point of crystalline copper. Several phenomena such as the appearance of a hysteresis (irreversibility) in caloric curves, surface melting, and cluster-induced surface wetting were justified from the results. The simulation of cluster in the presence of gas atmosphere showed that the CO gas is adsorbed more than H₂ and it has a greater impact on the cluster's structure.     

Study of titanium adsorption on perfect and defected BC3 nanotubes using density functional theory

Density functional theory calculations were used to study the titanium (Ti) adsorption on perfect and defected (4, 0) BC₃ nanotubes, considering Stone–Wales and vacancy defects. The binding energy values for these nanotubes were larger than the corresponding values for carbon nanotubes. The charge transfer from the Ti atom to nanotube was observed for all systems studied. The most exothermic binding process occurred for the Ti adsorption on a native V_B defect, which showed minimum structural deformation with respect to a perfect BC₃ tube. In the case of a nanotube with a reconstructed carbon vacancy, the adsorption of Ti generated a half-metallic anti-ferromagnet. The results obtained in this paper are relevant for spintronics and hydrogen adsorption applications.     

Capacitated location allocation problem with stochastic location and fuzzy demand: A hybrid algorithm

In this article, a capacitated location allocation problem is considered in which the demands and the locations of the customers are uncertain. The demands are assumed fuzzy, the locations follow a normal probability distribution, and the distances between the locations and the customers are taken Euclidean and squared Euclidean. The fuzzy expected cost programming, the fuzzy β-cost minimization model, and the credibility maximization model are three types of fuzzy programming that are developed to model the problem. Moreover, two closed-form Euclidean and squared Euclidean expressions are used to evaluate the expected distance between customers and facilities. In order to solve the problem at hand, a hybrid intelligent algorithm is applied in which the simplex algorithm, fuzzy simulation, and a modified genetic algorithm are integrated. Finally, in order to illustrate the efficiency of the proposed hybrid algorithm, some numerical examples are presented.     

A comparative studyof heat‐treated Ag:SiO2 nanocomposites synthesized by cosputtering and sol‐gel methods

In this work, we compared formation and properties of heat‐treated Ag nanoparticles in silica matrix synthesized by RF‐reactive magnetron cosputtering and sol–gel methods separately. The sol–gel and sputtered films were annealed at different temperatures in air and in a reduced environment, respectively. The optical UV‐visible spectrophotometry have shown that the absorption peak appears at 456 and 400 nm wavelength indicating formation of silver nanoparticles in SiO₂ matrix for both the sol–gel and sputtering methods at 100 and 800 °C, respectively. XPS measurements showed that the metallic Ag⁰ nanoparticles can be obtained from both the techniques at these temperatures. According to XPS and AFM analysis, by increasing annealing temperature, the concentration of the Ag nanoparticles on the surface decreased and the nanoparticles diffused into the substrate for the sol–gel films, while for the films deposited by cosputtering method, the Ag surface concentration increased by increasing the temperature. Based on AFM observations, the size of nanoparticles on the surface were obtained at about 25 and 55 nm for sputtered and sol–gel films, respectively, supporting our optical data analysis. In comparison, the sputtering technique can produce Ag metallic nanoparticles with a narrower particle size distribution relative to the sol–gel method. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrical and magnetic properties of Gd(Ba2-xLax)Cu3O7+δ

We have studied the structural, electrical, and magnetic properties of the normal and superconducting states Gd(Ba2-xLax)Cu3O7+ [Gd(BaLa)123] samples with 0.0 x 0.8 prepared by the standard solid-state reaction. XRD characterization shows an orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration analysis shows the oxygen content of the samples increase with the increase of La doping. The resistivity curves show that for x0.15, there is metallic behavior, and for x0.2, there is a gradual insulating transition behavior in the normal state. The metal-insulator and superconductor-insulator transitions occur between x=0.35 and x=0.4. The superconducting transition temperature decreases with the increase of La content as two-step curve. The normal-state resistivity is fitted for two and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap (CG) regimes, separately. The results show that the dominant mechanism is CG for x0.35, and VRH for x0.4. The pinning energy U, derived from the thermally activated flux creep (TAFC) model and Ambegaokar-Halperin (AH) theory, shows a power-law relation as UH -. The critical current density decreases with the increase of La doping and magnetic field. The E-J curves show that the induced electric field increases with the increase of magnetic field and La concentration. The magnetization measurements indicate that the critical penetration fields and magnetic current density decrease with La doping.     

Effect of Ni, Pd and Ni-Pd nano-islands on morphology and structure of multi-wall carbon nanotubes

In this research, the effect of Ni, Pd and Ni-Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO₂ (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni-Pd nano-islands were measured about 55, 110, 45 and 50 nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940 °C in CH₄ ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120 nm for Ni, Ni-Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550-1600 and 1250-1450 cm⁻¹ (as a quality factor for the CNTs) for Ni, Pd and Ni-Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni-Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.     

Turbulence control in wall-bounded flows by spanwise oscillations

The feasibility of control of wall turbulence by high frequency spanwise oscillations is investigated by direct numerical simulations of a planar turbulent channel flow subjected either to an oscillatory spanwise crossflow or to the spanwise oscillatory motion of one of the channel walls. Periods of oscillation,T _osc. ⁺ =T _osc. u ² /v, ranging from 25 to 500 were studied. For 25<T _osc. ⁺ <200 production of turbulence is suppressed. The most effective suppression of turbulence occurs atT _osc ⁺ =100, for which the overall turbulence production is reduced by 62% compared to the unperturbed channel and sustained turbulent drag reductions of 40% are obtained. The suppression of turbulence is due to a continual shift of the near wall streamwise vortices relative to the wall layer streaks, which in turn leads to a widening, merging and weakening of the wall layer streaks and an overall reduction in the turbulence production. The turbulence suppression mechanism observed in these studies opens up new possibilities for effective control of turbulence in wall-bounded flows.