Effect of rapid solidification on hydrogen solubility in Mg-rich Mg-Ni alloys

The hydrogenation properties of Mg_100−xNi_x alloys (x = 0.5, 1, 2, 5) produced by melt spinning and subsequent high-energy ball milling were studied. The alloys were crystalline and, in addition to Mg matrix, contained finely dispersed particles of Mg₂Ni and metastable Mg₆Ni intermetallic phases. The alloys exhibited excellent hydrogenation kinetics at 300 °C and reversibly absorbed about 6.5 mass fraction (%) of hydrogen. At the same temperature, the as prepared Mg_99.5Ni_0.5 and Mg₉₅Ni₅ powders dissolved about 0.6 mass fraction (%) of hydrogen at the pressures lower than the hydrogen pressure corresponding to the bulk Mg-MgH₂ two-phase equilibrium, exhibiting an extended apparent solubility of hydrogen in Mg-based matrix. The hydrogen solubility returned to its equilibrium value after prolonged hydrogenation testing at 300 °C. We discuss this unusually high solubility of hydrogen in Mg-based matrix in terms of ultrafine dispersion of nanometric MgH₂ precipitates of different size and morphology formed on vacancy clusters and dislocation loops quenched-in during rapid solidification.     

Roughness characterization of silver oxide anodes for use in efficient top-illuminated organic solar cells

In this study, we optimize the process of treating the surface of Ag anodes through exposure to UV-ozone, for the efficient planar heterojuction top-illuminated organic solar cells (OSCs). Several characteristics of Ag anodes such as work function (Ф_Anode), surface roughness (R_a) and sheet resistance are increased proportionally to exposure time following the formation of AgO_x on the surface. Two factors, Ф_Anode and R_a, dominated the performance of the device due to their opposite contributions of power conversion efficiency (PCE). An increase in Ф_Anode flattened the energy barrier level between the anode and copper phthalocyanine, thereby benefiting hole injection and increasing open circuit voltage (V_OC). An increase in R_a led to an increase in the density of localized traps, which obstructed hole injection and degraded the V_OC. It also reduced reflectivity, thereby diminishing the short circuit current density (J_SC). The top-illuminated OSCs in this study were optimized following surface treatment of the anode for 45 s to achieve a maximum PCE of 1.04%, V_OC of 0.48 V, and J_SC of 3.56 mA/cm² with a fill factor of 60.7%.     

Effects on teachers' self-efficacy and job satisfaction: Teacher gender, years of experience, and job stress.

The authors of this study sought to examine the relationships among teachers' years of experience, teacher characteristics (gender and teaching level), three domains of self-efficacy (instructional strategies, classroom management, and student engagement), two types of job stress (workload and classroom stress), and job satisfaction with a sample of 1,430 practicing teachers using factor analysis, item response modeling, systems of equations, and a structural equation model. Teachers' years of experience showed nonlinear relationships with all three self-efficacy factors, increasing from early career to mid-career and then falling afterwards. Female teachers had greater workload stress, greater classroom stress from student behaviors, and lower classroom management self-efficacy. Teachers with greater workload stress had greater classroom management self-efficacy, whereas teachers with greater classroom stress had lower self-efficacy and lower job satisfaction. Those teaching young children (in elementary grades and kindergarten) had higher levels of self-efficacy for classroom management and student engagement. Lastly, teachers with greater classroom management self-efficacy or greater instructional strategies self-efficacy had greater job satisfaction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Controllable p-n junction formation in monolayer graphene using electrostatic substrate engineering

We investigate electric transport in graphene on SiO2 in the high field limit and report on the formation of p-n junctions. Previously, doping of graphene has been achieved by using multiple electrostatic gates, or charge transfer from adsorbants. Here we demonstrate a novel approach to create p-n junctions by changing the local electrostatic potential in the vicinity of one of the contacts without the use of extra gates. The approach is based on the electronic modification not of the graphene but of the substrate and produces a well-behaved, sharp junction whose position and height can be controlled.     

Modification of sputter deposited solid-state electrolyte thin films

All solid-state thin film batteries (TFBs) consisting of amorphous lithium phosphorus oxynitride (LiPON) solid electrolyte, crystalline LiMn₂O₄ cathode and crystalline SnO₂ anode have been fabricated and characterized. All of the thin films are prepared by RF magnetron sputtering. By fabricating under different pressures and applying low temperature post-annealing (200 °C), the performances of the LiPON electrolytes and SnO₂/LiPON/LiMn₂O₄ TFBs are improved. Suitable working pressures results in pinhole-free amorphous LiPON films with smooth surface and dense micro-structure. The TFBs post-annealed at 200 °C show smooth interface contacts between electrode and electrolyte thin films. The low pressure deposited and post-annealed TFBs exhibits lower impedance and higher cycling stability. Initial open-circuit voltage of 3.8 V and initial capacity of 12 μAh/cm² are obtained.     

Effects of mesoscopic poly(3,4-ethylenedioxythiophene) films as counter electrodes for dye-sensitized solar cells

Counter electrode coated with chemically polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) in a dye-sensitized solar cell (DSSC) was studied. The surface morphology and the nature of I⁻/I₃⁻ redox reaction based on PEDOT film were investigated using Atomic Force Microscopy and Cyclic Voltammetry, respectively. The performance of the DSSCs containing the PEDOT coated electrode was compared with sputtered-Pt electrode. We found that the root mean square roughness decreases and conductivity increases as the molar ratio of imidazole (Im)/EDOT in the PEDOT film increases. The DSSC containing the PEDOT coated on fluorine doped tin oxide glass with Im/EDOT molar ratio of 2.0, showed a conversion efficiency of 7.44% compared to that with sputtered-Pt electrode (7.77%). The high photocurrents were attributed to the large effective surface area of the electrode material resulting in good catalytic properties for I₃⁻ reduction. Therefore, the incorporation of a multi-walled carbon nanotube (MWCNT) in the PEDOT film, coated on various substrates was also investigated. The DSSC containing the PEDOT films with 0.6 wt.% of MWCNT on stainless steel as counter electrode had the best cell performance of 8.08% with short-circuit current density, open-circuit voltage and fill factor of 17.00 mA cm⁻², 720 mV and 0.66, respectively.     

State Boundary Surfaces for an Aged Compacted Clay

The yielding and the peak strength of an aged compacted clay were studied by conducting a series of suction-controlled triaxial tests. The test results were interpreted using the framework of intrinsic properties of reconstituted soil. The peak strength envelopes of undisturbed samples lie above those of reconstituted samples. The suction provides additional attractive forces to stabilize the soil structure, which result in the augmentation of the yield stress and peak strength envelope. The shear strength is normalized by the equivalent preconsolidation pressure (pe′) and Hvorslev surfaces are identified from undisturbed samples which expand with suction. A single peak strength envelope and Hvorslev surface will be emerged from the saturated and unsaturated (degree of saturation >80%) samples if the shear strength data are presented in terms of the average skeleton stress. The influence of the soil structure on the shear strength of the aged compacted clay may be measured by the ratio of normalized strengths at the intrinsic critical state which is about 1.26     

Design and Analysis of Shock-Absorbing Structure for Flat Panel Display

In order to protect the fragile panel of a liquid crystal display (LCD) from damage caused by shock, a shock-absorbing structure designed to absorb most of the shock energy can be installed between the panel and the frame. The design methodology proposed in this paper uses the topology optimization technique in designing this shock-absorbing structure. The objective is to minimize the maximal panel stress with the shock-absorbing structure, which is designed to be of minimal weight. An algorithm which integrates three modules-the finite-element software ANSYS/LS-DYNA used as the structural analysis tool, the optimization module based on the differential evolution method, and a topology module - is developed to achieve crashworthiness design. Numerical results show that an optimal layout of the shock-absorbing structure with minimal weight is obtained. And, this shock-absorbing structure is proven to effectively increase LCD shock resistance.     

Electrical Characteristics of Passivated Pseudomorphic HEMTs With $hbox{P}_{hbox{2}}hbox{S}_{hbox{5}}/(hbox{NH}_{hbox{4}})_{hbox{2}}hbox{S}_{hbox{X}}$ Pretreatment

This paper elucidates the dc, pulse I-V, microwave, flicker noise, and power properties of AlGaAs/InGaAs pseudomorphic high electron mobility transistors (pHEMTs) after various ex situ sulfur pretreatments. The pHEMTs were pretreated with NH₄OH, (NH₄)₂S_X, and P₂S₅/(NH₄)₂S_X solutions before SiO₂ passivation to reduce the GaAs native oxide-related surface states. Stable phosphorus oxides and sulfur bound to the Ga and As species can be efficiently obtained using P₂S₅/(NH₄)₂S_X pretreatment; therefore, the leakage current in pHEMT was reduced following this process. Atomic force microscopy measurements indicated that the phosphorus oxides formed by P₂S₅/(NH₄)₂S_X treatment also provided a better surface roughness than obtained following traditional (NH₄)2S_X-only pretreatment, reducing mobility degradation after sulfur pretreatment. Based on the dc and 1 mus pulse I-V measurement results, P₂S₅/(NH₄)₂S_X-treated pHEMT exhibited very similar I_ds trends, especially at high currents; however, NH₄OH, (NH₄)₂S_X treatments clearly reduced the current upon pulse measurement because of the presence of surface traps. Hence, this novel pretreatment method has great potential for highly linear microwave power transistor applications.     

An improved single‐stage Flyback PFC converter for high‐luminance lighting LED lamps

This paper presents a high‐performance LED lamp driver with an improved single‐stage Flyback configuration. A constant current control method is used to regulate the lamp current and brightness. A laboratory prototype has been built and tested. With the prototype, high efficiency, high power factor, and constant lamp current can be achieved under different pieces of LED series connection. Copyright © 2007 John Wiley & Sons, Ltd.