Highly efficient wavelength conversion of Q-switched Nd:YAG lasers into a red wavelength

We report a nanosecond upconversion optical parametric oscillator which can convert the output of a Nd:YAG laser at 1064-nm wavelength into 627 nm with high efficiency. This device is based on a single KTiOAsO/sub 4/ crystal that is simultaneously phase matched for optical parametric generation and sum-frequency generation. Pumped at a wavelength of 1064 nm by a Q-switched Nd:YAG laser in a double-pass configuration, this device produces 14.2-ns-long 5.8-mJ red pulses at a wavelength of 627 nm with 29% energy conversion efficiency. In addition, we developed a theoretical model for this device, whose predictions agree reasonably well with our experimental results. It is possible to scale this device for use with higher energy pump lasers and to shape it into a physically small semi-monolithic configuration.     

Recommendations for ammonia borane composite pellets as a hydrogen storage medium

The perspective of this study describes a new concept for ammonia borane (NH₃BH₃, AB) in the form of pellet composited with CoB catalyst to use as a hydrogen storage medium. For the purpose of this, hydrogen storage capacity and physical-chemical properties of composite pellet are examined and tested to investigate effects of specified environmental conditions by exposing pellets in temperature from 22 °C to 80 °C in a long period of time (1 day–4 months). A statistical strategy is provided to detail the investigation for significant differences between holding conditions and their interactions. These results suggest that the changing in holding time is more important than the temperature. The general point of view, there is no change in hydrogen storage properties when the composite pellets held at low temperature about 22 °C for 3 months, and the same trend is also preserved when the composites are kept at the higher temperature for a week. It is concluded that the composite pellets shown performance at hydrogen storage with easy handling and controlled hydrogen generation for on-board energy applications.     

Sorption isotherms and isosteric heat of sorption for grapes, apricots, apples and potatoes

Moisture sorption isotherms of grapes, apricots, apples and potatoes were determined at 30°C, 45°C, and 60°C using the standard, static-gravimetric method. Six two-parameter and five three-parameter sorption models were tested to fit the experimental data. A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The Halsey equation gave the best fit to the experimental sorption data for all materials tested over the range of temperatures and water activities investigated. The GAB model gave also the closest fit to the sorption data for potatoes and grapes. The agreement between experimental and predicted values of these models was found to be satisfactory. The isosteric heat of desorption and adsorption of water determined from the equilibrium data using the Clausius-Clapeyron equation.     

Effect of ruthenium addition on molybdenum catalysts for syngas production via catalytic partial oxidation of methane in a monolithic reactor

Hydrogen is mainly produced from hydrocarbon resources. Natural gas, mostly composed of methane, is widely used for hydrogen production. As a valuable feedstock for ‘Fischer–Tropsch’ (FT) process and ‘Gas to Liquids’ (GTL) technology, syngas production from catalytic partial oxidation of methane (CPOM) is gaining prominence especially owing to its more desirable H₂/CO ratio; relatively less energy consumption, and lower investment, compared to steam reforming processes (SMR), the leading technology.In the present study, effect of ruthenium (Ru) addition on molybdenum (Mo) catalysts for syngas production from methane (CH₄) via partial oxidation in a monolithic reactor was investigated. Mo based catalysts supported on Nickel (Ni) and Cobalt (Co) metal oxides and Ni-Co bimetallic oxides and their Ru added versions were developed, characterized, and tested for performance in a monolithic type reactor system. Catalyst activity was investigated in terms of H₂ and CO selectivity, CH₄ conversion; and CO₂ emission and it is concluded that addition of Ru over the structure led to increase in catalytic activity and reduction in carbon deposition over the catalyst surface.     

Electron–Electron Interactions in Sb-Doped SnO<Subscript>2</Subscript> Thin Films

Electrical conductivity and Hall-effect measurements on undoped and Sb-doped SnO₂ thin films prepared by the sol–gel technique were carried out as a function of temperature (55 K to 300 K). Structural characterizations of the films were performed by atomic force microscopy (AFM) and x-ray diffraction (XRD). A doping-induced metal–insulator transition (MIT) was observed. On the metallic side of the transition, the experimental data were interpreted in terms of electron–electron interactions (EEI). The existence of EEI was confirmed by excellent agreement between theoretical and experimental data. The experimental data on the insulator side of the transition were analyzed in terms of variable-range hopping (VRH) conduction. A complete set of parameters describing the properties of the localized electrons, including hopping energy, hopping distance, and the value of the density of states at the Fermi level, was determined.     

Magnetic Characterizations of Cobalt Oxide Nanoparticles

Cobalt oxide (Co₃O₄) nanoparticles were synthesized by a novel microwave-assisted decomposition reaction of the cobalt nitrate hexahydrate, Co(NO₃)₂?6H₂O. While most of the traditional methods for the preparation of Co₃O₄ are at relatively high temperature, microwave-assisted decomposition was adapted to have better control in the production of Co₃O₄ nanoparticles. The temperature dependence of the magnetic properties for the Co₃O₄ was investigated by vibrating sample magnetometer (VSM) and electron spin resonance (ESR) techniques. VSM and ESR measurements have shown a phase transition occurring at around 31?K, as the antiferromagnetic transition temperature for the bulk Co₃O₄ crystal exhibits almost the same value. The average particle size of the sample at around the transition temperature is estimated as 2.015?nm. The title compound was characterized and identified by an x-ray powder diffraction (XRD).