Dispersion of ZrO2 nanoparticles in polyacrylonitrile: Preparation of thermally-resistant electrically-conductive oxygen barrier nanocomposites

Polyacrylonitrile/zirconium dioxide (PAN/ZrO₂) nanocomposites were synthesized by dispersion of ZrO₂ nanoparticles through the in situ emulsifier-free emulsion polymerization technique. The thermal stability of PAN/ZrO₂ nanocomposites was enhanced with increasing concentrations of ZrO₂ which may be due to dispersion of nanoparticles in PAN matrix. The electrical conductivity of nanocomposites gradually increased with increase in the ZrO₂ loading. The gas barrier property of PAN/ZrO₂ nanocomposites was determined by using gas permeameter and it was found that, the gas barrier property was reduced to about 10 times with increase of ZrO₂ proportions. This is because ZrO₂ nanoparticles in PAN/ZrO₂ nanocomposites created a tortuous path for preventing oxygen permeation. The electrical conductive PAN/ZrO₂ nanocomposites may be used in semiconductor devices and packaging materials.     

An improved PSO technique for short-term optimal hydrothermal scheduling

This paper presents a new approach to the solution of optimal power generation to short-term hydrothermal scheduling problem, using improved particle swarm optimization (IPSO) technique. The practical hydrothermal system is highly complex and possesses nonlinear relationship of the problem variables, cascading nature of hydraulic network, water transport delay and scheduling time linkage that make the problem of finding global optimum difficult using standard optimization methods. In this paper an improved PSO technique is suggested that deals with an inequality constraint treatment mechanism called as dynamic search-space squeezing strategy to accelerate the optimization process and simultaneously, the inherent basics of conventional PSO algorithm is preserved. To show its efficiency and robustness, the proposed IPSO is applied on a multi-reservoir cascaded hydro-electric system having prohibited operating zones and a thermal unit with valve point loading. Numerical results are compared with those obtained by dynamic programming (DP), nonlinear programming (NLP), evolutionary programming (EP) and differential evolution (DE) approaches. The simulation results reveal that the proposed IPSO appears to be the best in terms of convergence speed, solution time and minimum cost when compared with established methods like EP and DE.     

Electron microscopy nanoscale characterization of ball milled Cu-Ag powders. Part II: Nanocomposites synthesized by elevated temperature milling or annealing

Microstructures and phases stabilized at steady state by variable temperature ball milling of Cu₅₀Ag₅₀ powders are characterized using transmission and scanning transmission electron microscopy. Starting from chemically mixed and cold-worked powders obtained by room temperature milling, it is shown that, upon increasing the milling temperature, the material first decomposes into Cu-rich and Ag-rich solid solutions, and then recrystallizes. A similar sequence is observed during the static annealing of the solid solution precursor. In both cases, Cu-Ag nanocomposites are synthesized, at a scale of a few nanometers in the unrecrystallized state, and at a scale ranging from 30 nm after dynamic recrystallization to 75 nm after static recrystallization. These nanocomposites exhibit high hardness values, approaching 6 GPa. Interestingly enough, recrystallization leads to an increase in the hardness of these materials.     

A reinforcement learning approach to automatic generation control

This paper formulates the automatic generation control (AGC) problem as a stochastic multistage decision problem. A strategy for solving this new AGC problem formulation is presented by using a reinforcement learning (RL) approach. This method of obtaining an AGC controller does not depend on any knowledge of the system model and more importantly it admits considerable flexibility in defining the control objective. Two specific RL based AGC algorithms are presented. The first algorithm uses the traditional control objective of limiting area control error (ACE) excursions, where as, in the second algorithm, the controller can restore the load-generation balance by only monitoring deviation in tie line flows and system frequency and it does not need to know or estimate the composite ACE signal as is done by all current approaches. The effectiveness and versatility of the approaches has been demonstrated using a two area AGC model.     

Simulation of a magneto-mechanical damping machine: analysis,discretization, results

This paper presents and analyzes a method for the simulation of the dynamical behavior of a coupled magneto-mechanical system such as a damping machine. We consider a two-dimensional model based on the transverse magnetic formulation of the eddy currents problem for the electromagnetic part and on the motion equation of a rotating rigid body for the mechanical part.The magnetic system is discretized in space by means of Lagrangian finite elements and the sliding mesh mortar method is used to account for the rotation. In time, a one step Euler method is used, implicit for the magnetic and velocity equations. The coupled differential system is solved with an explicit procedure.     

Engine performance and optimum injection timing for 4-cylinder direct injection hydrogen fueled engine

This paper presents the engine performance and optimum injection timing for 4-cylinder direct injection hydrogen fueled engine. The 4-cylinder direct injection hydrogen engine model was developed utilizing the GT-Power commercial software. This model employed one dimensional gas dynamics to represent the flow and heat transfer in the components of engine model. Sequential pulse injectors are adopted to inject hydrogen gas fuel within the compression stroke. Injection timing was varied from 110° before top dead center (BTDC) until top dead center (TDC) timing. Engine speed was varied from 2000 rpm to 6000 rpm, while the equivalence ratio was varied from 0.2 to 1.0. The validation was performed with the existing previous experimental results. The negative effects of the interaction between ignition timing and injection duration was highlighted and clarified. The results showed that optimum injection timing and engine performance are related strongly to the air fuel ratio and engine speed. The acquired results show that the air fuel ratio and engine speed are strongly influence on the optimum injection timing and engine performance. It can be seen that the indicated efficiency increases with increases of AFR while decreases of engine speed. The power and torque increases with the decreases of AFR and engine speed. The indicated specific fuel consumption (ISFC) decreases with increases of AFR from rich conditions to lean while decreases of engine speed. The injection timing of 60° BTDC was the overall optimum injection timing with a compromise.     

Properties and rapid consolidation of ultra-hard tungsten carbide

Extremely dense WC with a relative density of up to 99% was obtained within 3 min under a pressure of 80 MPa using the high frequency induction heating sintering method (HFIHS) method. The average grain size of the WC was about 87 nm. The advantage of this process is not only rapid densification to obtain a near theoretical density but also the prohibition of grain growth in nanostructured materials. The hardness and fracture toughness of the dense WC produced by the HFIHS were investigated.     

Effect of tunneling current on the noise characteristics of a 4H-SiC Read Avalanche diode

Noise characteristics of a Read Avalanche diode are analyzed by incorporating the tunneling mechanism of the electron into the avalanche mechanism.Analytical expressions are presented for the mean square noise voltage and noise measure in MITATT(mixed tunneling and avalanche transit time) mode operation.A wide band gap semiconductor(4H-SiC) based MITATT diode is considered to study the effect of tunneling on the noise characteristics and negative conductance.While exhibiting enough potential for 4H-SiC to be used as a terahertz source of power in the MITATT mode,our results record a noise measure of 35.18 dB at a frequency of 1.5 THz.     

Thermal and Oxygen Barrier Properties of Chitosan Bionanocomposites by Reinforcement of Calcium Carbonate Nanopowder

Chitosan and calcium carbonate nanopowder（chitosan/CaCO3） bionanocomposites were prepared by solution method.Interaction between chitosan and CaCO3 was studied by Fourier transform infrared spectroscopy（FTIR）.Structure and surface morphology of chitosan/CaCO3 bionanocomposites were investigated by X-ray diffraction（XRD） and field emission scanning electron microscopy（FESEM）,respectively.The energy dispersive X-ray spectroscopy（EDS） of chitosan/CaCO3 bionanocomposites was studied in order to establish the elements of composition.Thermal stability of prepared bionanocomposites was studied by thermogravimetric analysis（TGA） and a substantial increase of thermal stability of virgin chitosan was noticed due to incorporation of CaCO3 nanopowder.The oxygen permeability was reduced by three times as compared to the raw chitosan due to the dispersion of nano CaCO3 filler.Biodegradability and resistance towards dilute acid and alkali of the prepared bionanocomposite were investigated.The bionanocomposite having gas barrier and thermal stable property may be suitable for packaging and biomedical applications.     

Synthesis and electrocatalytic activities of β-nickel hydroxide nanosheets and nanocones

The β-Ni(OH)₂ nanosheets and nanocones are fabricated by a hydrothermal method, respectively. The products are characterized in detail by multiform techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The prepared β-Ni(OH)₂ nanosheets and nanocones are used as electrode materials to study the electrocatalytic reduction of hydrogen peroxide (H₂O₂) in 0.5 M NaOH solution. The electrocatalytic activities of the β-Ni(OH)₂ for reduction of H₂O₂ are enhanced by change of the morphology from nanocones to nanosheets. This demonstrates that β-Ni(OH)₂ nanosheets are promising cathode catalysts for fuel cells with H₂O₂ as oxidant, which may be in place of precious metal materials.