Assessment of oscillatory stability constrained available transfer capability

This paper utilizes a bifurcation approach to compute oscillatory stability constrained available transfer capability (ATC) in an electricity market having bilateral as well as multilateral transactions. Oscillatory instability in non-linear systems can be related to Hopf bifurcation. At the Hopf bifurcation, one pair of the critical eigenvalues of the system Jacobian reaches imaginary axis. A new optimization formulation, including Hopf bifurcation conditions, has been developed in this paper to obtain the dynamic ATC. An oscillatory stability based contingency screening index, which takes into account the impact of transactions on severity of contingency, has been utilized to identify critical contingencies to be considered in determining ATC. The proposed method has been applied for dynamic ATC determination on a 39-bus New England system and a practical 75-bus Indian system considering composite static load as well as dynamic load models.     

Preparation of bulk ultrafine-grained and nanostructured Zn,Al and their alloys by in situ consolidation of powders during mechanical attrition

Bulk ultrafine-grained (UFG) or nanostructured Zn, Al and their alloys were produced via in situ consolidation of powders by mechanical attrition (MA) at room temperature. In situ consolidation of metal powders during MA may be a promising method to produce bulk UFG or nanostructured materials with full density and less contamination.     

Influence of low-temperature AlGaN intermediate multilayer structures on the growth mode and properties of GaN

GaN growth on the low-temperature (LT) AlGaN intermediate multilayer-coated GaN film was conducted using metal alkyls (trimethylgallium (TMG) and/or trimethylaluminum (TMA)) and ammonia in an inductively heated quartz reactor operated at atmospheric pressure. LT-AlGaN multilayers having certain Al contents and layer thicknesses were found to induce island growth of GaN based upon the observations of scanning electron microscopy (SEM). Cross-sectional transmission electron microscopic (TEM) studies show that the use of LT-AlGaN intermediate multilayers blocks threading dislocations (TDs) coming from the underlying GaN film very efficiently, and thereby results in great reduction of TD density in the GaN islands. The island growth nature of GaN is believed to originate from the lattice mismatch between GaN and LT-AlGaN multilayer structures. These nearly TD-free GaN islands exhibit enhanced room temperature (RT) near band-edge photoluminescence (PL) emissions.     

Homojunction and heterojunction based on CdTe polycrystalline thin films

The reaction growth temperature plays an important role for growing CdTe thin film on a foreign substrate by CVD. If a growth temperature is more than 560 °C, the CdTe film is a p-type. The higher growth temperature, the greater is the carrier concentration. If the growth temperatures are less than 520 °C, the CdTe films are n-type. A p-type CdTe film is firstly grown at a higher temperature, and an n-type CdTe film is then grown at a lower temperature, forming a CdTe homojunction. The properties of as-deposited CdTe homojunction are measured for the first time. In addition, a p-type CdTe film is exposed in an air environment for several weeks, forming a hybrid layer of CdO and TeO₂. An ITO film is then deposited on the oxide layer, forming an n-ITO/i/p-CdTe heterojunction. At the same time, an n-ITO/p-CdTe heterojunction is also deposited by the same processes except without the oxidation treatment. The efficiency of the heterojunction solar cell with the oxidation treatment is much greater than that without the oxidation processing.     

Effect of oxidation on flexural strength and thermal properties of AlN ceramics with residual stress and impedance spectroscopy analysis of defects and impurities

The effect of oxidation in air on the phase composition, microstructure, flexural strength and thermal property of AlN ceramics was investigated. Oxidation was found to produce a continuous oxide layer on the surface of AlN samples. The flexural strength and thermal conductivity of AlN ceramics significantly improved after oxidation at 1000 °C and 1100 °C. Residual stress in the AlN ceramic matrix was enhanced by oxidation. The enhanced residual compressive stresses inhibited crack propagation and reduced interfacial thermal resistance, thereby improving the flexural strength and thermal conductivity of AlN ceramics. Electrochemical impedance spectroscopy was further used to analyze the defects in AlN ceramics. The increase in fitting grain resistance revealed a decrease in aluminum vacancy concentration in oxidized AlN sample, which resulted in high thermal conductivity. Therefore, oxidation at a certain temperature is pretty effective to obtain excellent performance for AlN ceramics.     

Principal component analysis of upgraded Western Canadian coals

Three Western Canadian coals with different ranks have been upgraded by evaporative drying in several atmospheres at temperatures up to 500°C. Data from proximate and ultimate analyses, along with equilibrium moistures and heating values, have been evaluated by principal component analysis. The results indicate that significant changes in the products occur above 400°C for lignite and above 300°C for subbituminous B and high-volatile C bituminous coals. No significant differences are observed when the data for the upgraded coals are compared with published data for naturally occurring Western Canadian and US coals of the same rank.     

Synthesis and structure of a disilver(I) complex of a thiophene-linked Schiff base azacryptand

The synthesis and crystal structure of a mixed anion disilver(I) complex of a thiophene-linked Schiff base azacryptand are reported. The crystalline species is not stable at ambient temperature and the structure reveals a possible mechanism for the breakdown of the crystals.     

Electroless deposition of Ni–Cu–P on a self-supporting graphene with enhanced hydrogen evolution reaction activity

With the increasing issues of the energy crisis and environmental pollution, the development of clean energy has become an urgent task. Herein, self-supporting graphene (SSG) that could serve as the three-dimensional catalyst support is developed by electrochemically intercalating the flexible graphite paper (FGP) in 1 M KOH. Then, the Ni-base alloy is deposited on the SSG by electroless plating. The resulting electrode (Ni–Cu–P/SSG) exhibits excellent hydrogen evolution reaction (HER) electrocatalytic performance in 1 M KOH. The Ni–Cu–P/SSG catalyst just requires the overpotentials of 75 and 219 mV to reach 10 and 100 mA cm⁻², respectively. Besides, the Ni–Cu–P/SSG still maintains superior HER catalytic activity after the stability test of 12 h. The Ni–Cu–P/SSG composite catalyst with high catalytic activity, remarkable stability and facile preparation method has a significant influence on the extension of renewable energy preparation and application.