The role of Al and Mg in the hydrogen storage of electrospun ZnO nanofibers

Pure and doped ZnO nanofibers with Al and Mg were successfully synthesized via an electrospinning method using a sol–gel containing Polyvinylpyrrolidone as a spinning aid and a zinc nitrate precursor. Calcination of the doped and undoped electrospun nanofibers was conducted at 500 °C in air, and the resultant structures were analyzed by X-ray diffraction (XRD) and Raman spectroscopy. The diameter of the doped nanofibers decreased with increasing viscosity and conductivity, as measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) showed that Mg and Al are present in ZnO nanofibers. The pressure composition isotherm (PCI) demonstrated that the capacity of hydrogen storage in pure zinc oxide nanofibers is a factor of two greater than that of zinc oxide nanoparticles. However, Al-doped ZnO nanofibers have the highest capacity of hydrogen storage (2.81 wt%) at room temperature.     

Multiple-step martensitic transformations in the Ni51Ti49 single crystal

Multiple-step martensitic transformations of an aged Ni₅₁Ti₄₉ single crystal using calorimetric method were investigated. Results show that for short aging times (10–45 min) multiple-step martensitic transformations on cooling occur in two steps. Applying intermediate aging times (1.25–4 h) results in three steps and long aging times (more than 8 h) lead to two-step martensitic transformations again. This behavior has not been recognized in NiTi single crystals in literatures. It can be related to the heterogeneity of composition and stress fields around Ni₄Ti₃ precipitates.     

Investigation of Fuel Energy Gain for Tritium-Poor Fuels in Fast Ignition Fusion Approach

One of the most fascinating ignition schemes for the inertial fusion energy that might be feasible is fast ignition.Its targets are ignited on the outside surface so there is no need to low density and high temperature center is required by central hot spot ignition.Fast ignition concept is noteworthy for a simple but fundamental reason:In principle it requires less total energy input to achieve ignition.In this paper,fuel energy and fuel energy gain of nearly pure deuterium capsule are calculated.This capsule is ignited by a deuterium-tritium seed,which would reduce the tritium inventory to a few percentages.The variations of fuel energy gain versus fuel density have been studied and submitted.On the basis of different physical parameters the following results of the investigation are presented and discussed.The energy gain curves for different tritium concentrations are found and limiting gain curves are derived.Finally,tritium-poor fast ignitor is compared to equimolar deuterium-tritium fast ignitor.     

Modelling and analysis of productivity teamwork based on information technology

Organizations are usually represented and evaluated by their output. Therefore, all procedures and models which may affect and improve output attract the attention of researchers. The effects of organizing work teams as one essential resource of organizations, in addition to the structure, size and effectiveness of the team, are also considered important factors. This paper reports on an investigation performed to define a model to explain how the results of teamwork may improve production, while considering the role of IT as an effective parameter. Also, it is shown that if there is a number of IT improvement options, there may be a mix of IT improvement and team size increase that will yield the most cost efficient increase in team output.     

Vacuum Evaporation of Pure Metals

Theories on the evaporation of pure substances are reviewed and applied to study vacuum evaporation of pure metals. It is shown that there is good agreement between different theories for weak evaporation, whereas there are differences under intensive evaporation conditions. For weak evaporation, the evaporation coefficient in Hertz-Knudsen equation is 1.66. Vapor velocity as a function of the pressure is calculated applying several theories. If a condensing surface is less than one collision length from the evaporating surface, the Hertz-Knudsen equation applies. For a case where the condensing surface is not close to the evaporating surface, a pressure criterion for intensive evaporation is introduced, called the effective vacuum pressure, p _eff. It is a fraction of the vapor pressure of the pure metal. The vacuum evaporation rate should not be affected by pressure changes below p _eff, so that in lower pressures below p _eff, the evaporation flux is constant and equal to a fraction of the maximum evaporation flux given by Hertz-Knudsen equation as 0.844 $ \dot{n}_{\hbox{Max} } $ . Experimental data on the evaporation of liquid and solid metals are included.     

Influence of Aging Treatment on In-Situ Electrical Resistance Variation During Aging of Nickel-Rich NiTi Shape Memory Wires

Electrical resistance variations of Ni_50.9Ti_49.1 shape memory wires were studied during aging treatment at different temperatures via in-situ electrical resistance measurement. The results showed that during aging treatment, a cyclic behavior was observed in the electrical resistance variations, which could be related to the precipitation process. The evaluation of transition temperatures was conducted, after aging, using differential scanning calorimetry (DSC) analysis. The precipitation process is found to occur in four different stages. The results show that depending on the stress level around precipitates, two-, three-, or four-step martensitic transformation could be observed in DSC curves. In the points with maximum stress level (during precipitation process), four-step martensitic transformation is observed.     

Design of a 12-bit high-speed CMOS D/A converter using a new 3D digital decoder structure useful for wireless transmitter applications

In this paper a 12-bit Nyquist current-steering digital-to-analog converter (DAC) is implemented using TSMC 0.35 μm standard CMOS process technology. The proposed DAC is an essential part in baseband section of wireless transmitter circuits. Using oversampling ratio (OSR) for it leads to avoid use of an active analog reconstruction filter. The optimum segmentation (75%) has been used to get the best DNL and reduce glitch energy. This segmentation ratio guarantees the monotonicity. Higher performance is achieved using a new 3D thermometer decoding method which reduces the area, power consumption and the number of control signals of the digital section. Using two digital channels in parallel, helps reach 1 GHz sampling frequency. Simulations indicate that the DAC has an accuracy better than 10.7-bit for upcoming higher data rate standards (IEEE 802.16 and 802.11n), and a spurious-free-dynamic-range (SFDR) higher than 64 dB in whole Nyquist frequency band. The post layout four corner Monte-Carlo simulated INL is better than 0.74 LSB while simulated DNL is better than 0.49 LSB. The analog voltage supply is 3.3 V while the digital part of the chip operates with only 2.4 V. Total power consumption in Nyquist rate measurement is 144.9 mW. Active area of chip is 1.37 mm².     

Influence of Mold Preheating and Silicon Content on Microstructure and Casting Properties of Ductile Iron in Permanent Mold

 The effects of the mold preheating and the silicon content of ductile iron on the percentage of carbides, graphite nodule counts and shrinkage volume were investigated. The results showed that the percentage of carbides and the shrinkage volume decreased when the mold preheating increased. The ductile iron with the carbon equivalent of 445 % and the silicon content of 25% without any porosity defects was achieved when the mold preheating was 450 ℃. Increasing the silicon content in the range of 21%-33% led to the increase in graphite nodule count and graphite size and the decrease in percentage of carbides. It is due to the increase in induced expansion pressure during the graphite formation with the increasing of silicon content. The suitable condition for casting a sound product of ductile iron without the riser at the mold preheating temperature of 300 ℃ is the silicon content of 33% and carbon equivalent of 47%.     

Ultra low power frequency divider for 2.45 GHz ZigBee frequency synthesizer

An ultra low power CMOS frequency divider whose modulus can be varied from 481 to 496 is presented. It has been customized to be used in 2.45 GHz Integer-N PLL frequency synthesizers utilized in ZigBee standard. Its based on swallow divider that replaces the swallow counter by a simple digital circuit in order to reduce power consumption and design complexity. Also a low power and high speed divide-by-7/8 is presented. Post layout simulation results exhibit 420 μW power consumption for 4 bit frequency divider in 2.45 GHz ISM frequency band that proves 40 % reduction compared to same previous works. All of the circuits have been designed in 0.18 μm TSMC CMOS technology with a single 1.8 V DC voltage supply.