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Recently, because a renewable power source must operate as a constant rate in accordance with RPS(Renewable Portfolio Standard), the study of the renewable power sources has been ongoing. Especially because of noise of wind turbine, troubleshooting, and urban greening business, research related with small wind turbine are underway. The economics and reliability are important parts for the activation of small wind turbine, such as solar energy. In this paper, by analyzing the temperature variations for each location and efficiency of power conversion devices in accordance with short period wind speed changes in simulation test, we reviewed the safety about temperature variations of wind generator and the method of selection of power converter.

The electrical safety and efficiency is the most important thing of the electric vehicle charging system. The prior system is contact charging system that is contacted directly by human. So, it has riskiness such as electric shock in the case of poor insulation or contact problems. To solve these safety issues and the convenience problems, a wireless power transmission system has been developed and is currently in trial operation. However, because high frequency is used in wireless power transmission system instead of commercial frequency, we need to apply protection measures concerning electric shock and equipment protection. Also, it should be accompanied by measuring efficiency for the effective operation of the wireless power transmission system. Therefore, we structured monitoring system in trial operation area of wireless power transmission system and applied decision algorithm for protection of human and equipment and economic operation of it.

Recently, due to the excessive use of fossil fuels, many studies about the fossil fuels such as solar and fuel cell energy source are progressing. Fuel cell system has high energy conversion efficiency. Also, fuel cell system is environmentally friendly system because the carbon emission is almost not occur. Therefore, the fuel cell system is considered as the core technology of in the fields of the future energy and environmental. Fuel cell system has an effect on distribution power system because another power source of other than large power plants. So, fuel cell system can be reason of power quality in the power system. In this paper, we constructed the system for an assessment on Islanding. The system is composed with power source, Impedance coordination load and linear load, fuel cell system. we are performed assessment on voltage and power quality in customer and the distributed power system during the Islanding of residential fuel cell system. In addition, no change in the impedance of power system, we made a islanding condition only using the actual load, As a variation of generation and load current under islanding, an analysis results based on assessment system showed that the power qualities of distribution system became more aggravation as effect of voltage sag and voltage swell phenomena.

In this paper, carried out for optimal ground system for ensuring safety for electricity used to power equipment in the 20 kHz frequency. Now the grounding system of the mesh electrode, electrode rods are installed for power plant safety and protection against electric shock. However, the electrical equipment grounding system in the 20 kHz were considering the increasing grounding impedance due to the high frequency and the magnetic shielding. But until now, there has been little research on the grounding system. To solve this problem, In this paper was proposed optimal grounding system due to the experiment using a mesh electrode, rod electrode, aluminum plate electrodes. Measurement results, grounding resistance was depending on the material of the electrode grounding resistance. In addition, the leakage current (induced) appeared to be affected depending on the type of electrode.

CdCr2O4 is a cubic spinel with geometrically-frustrated antiferromagnetic interactions between Cr3+ ions. We investigated the structural and magnetic phase transitions in powder samples by using magnetization and neutron diffraction measurements. An antiferromagnetic phase transition was observed at T N = 8.1 K, below which the crystallographic unit cell was tetragonal (c < a = b). Its incommensurate antiferromagnetic ordering below T N resembles dimerized spin chains in the ab planes with the propagation vector k = (0, 0.088, 1). We argue that the Dzyaloshinskii-Moriya interaction and the magnetic frustration play important roles in establishing the observed magnetic ordering.

Syntheses and property analysis of hydropolysilanes were studied. Those hydropolysilanes can be utilized as precursors for amorphous silicon and polycrystallline silicon for the purpose of the solar cell and the thin film transister for the next generation's semiconductors. Most important characteristics of this study are to find optimized conditions for the synthesis and property analysis of soluble hydropolysilanes. Also the possibility of pyrolytic conversion to amorphous and polycrystalline silicon was investigated.

Ag/polyaniline (PANI) nanocomposites were prepared by two different methods using γ-ray irradiation. The morphology of the Ag nanoparticles in the nanocomposites was followed by transmission electron microscopy (TEM). In one of the method ( Method I ), Ag/PANI nanocomposites were prepared by the following sequential steps. PVP-stabilized Ag colloids were prepared by γ-irradiation, aniline was added and oxidatively polymerized. Method II involved the preparation of Ag/PANI nanocomposites by oxidative polymerization of aniline-stabilized Ag colloids prepared by γ-irradiation. The average size of PVP-stabilized Ag sphere-type nanoparticles was 13 nm. The morphology of Ag nanoparticle in Ag/PANI nanocomposites prepared by Method I was sphere-type. On the other hand, the morphology of aniline-stabilized Ag nanoparticle prepared by γ-irradiation was a hexangular-type one. Size of aniline-stabilized Ag nanoparticles was found to depend on the weight ratios of aniline-to-Ag ions used in the preparation. The paper discusses the changes in the morphology of Ag nanoparticles in the Ag/PANI nanocomposites with the method of preparation, source of protection and polymerization.

The one-pot synthesis of nanocomposites of a conductive poly(N-vinylcarbazole) (PVK) with CdS, Ag, Pd50–Ag50, and Pt50–Ru50 nanoparticles was performed with γ irradiation in a tetrahydrofuran–water mixture (3/1 vol %). For comparison, the CdS, Ag, Pd50–Ag50, and Pt50–Ru50 nanoparticles were also prepared with γ irradiation with polyvinylpyrrolidone as a stabilizer. Ultraviolet–visible spectroscopy, transmission electron microscopy, X-ray diffraction analysis, and photoluminescence spectroscopy were used for the characterization of CdS, Ag, Pd50–Ag50, and Pt50–Ru50 nanoparticles and nanocomposites of PVK with CdS, Ag, Pd50–Ag50, and Pt50–Ru50 nanoparticles. The absorption spectrum of the CdS-nanoparticle-based composite revealed a quantum confinement effect. The emission spectrum of the composite with CdS nanoparticles and PVK indicated the block effect of PVK for surface recombination. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1809–1815, 2006

Friedel−Crafts alkylation reactions of biphenyl with (dichloroalkyl)chlorosilanes [Cl3-mMemSi(CnH2n-1Cl2), m = 0−2, n = 1−3] at temperatures ranging from 120 to 160 °C in the presence of a Lewis ac...

Friedel−Crafts alkylations of ferrocene, 1, with allylchlorosilanes in the presence of Lewis acid catalysts under mild conditions gave regiospecific [1-methyl-2-(alkylchlorosilyl)ethyl]ferrocenes in fair to good yields depending upon the substituents on silicon, along with small amounts of dialkylated products. The alkylation of ferrocene with 1.2 equiv of (2-methylallyl)dimethylchlorosilane, 2b, at 0 °C gave monoalkylated ferrocene 3b and an isomeric mixture of dialkylated products in 76% and 4% yields, respectively. The yield of the dialkylated ferrocene mixture increased to 21% when 2 equiv of alkylating agent 2b was used. The two components of the dialkylated product mixture were identified as 1,1‘-dialkylated ferrocene 4b (17%), and 1,3-dialkylated ferrocene 4b‘ (4%). A higher yield of the 1,1‘-diadduct compared to the 1,3-diadduct indicates that the electron-donating alkylsilyl group does not greatly enhance a second alkylation on the same ring. The reactivities of allylchlorosilanes in the ferrocen...

The hydrosilylation of cyclic alkenes and linear alkenes with trialkylsilanes in the presence of Lewis acid catalysts under mild conditions gave the corresponding (trialkylsilyl)alkanes in fair to good yields. The reaction of 1-methylcyclohexene with triethylsilane at −20 °C gave cis-1-triethylsilyl-2-methylcyclohexane with regio- and stereoselectivity via a trans hydrosilylation pathway. Cycloalkenes having an alkyl group at the double-bonded carbon showed better reactivity than nonsubstituted compounds in the Lewis acid-catalyzed hydrosilylation. The catalytic reactivity of Lewis acids decreases in the following order: AlBr3 > AlCl3 > HfCl4 > EtAlCl2 > ZrCl4 > TiCl4. When triorganochlorosilane was used as an activator in the aluminum chloride-catalyzed reaction, the hydrosilylation rate drastically increased. The results are consistent with a stepwise mechanism proceeding via the formation of a trialkylsilylenium ion intermediate.

The ferrimagnetic spinel MnV${}_{2}$O${}_{4}$ undergoes an orbital-induced cubic-to-tetragonal distortion at ${T}_{\mathrm{YK}}=58$ K, below which noncollinear commensurate ferrimagnetic ordering occurs. Using inelastic neutron scattering, we investigated low-energy dynamics in its cubic phase above ${T}_{\mathrm{YK}}$. We observed two types of coexisting short-range magnetic excitations: the dispersive spin waves centered around the Brillouin-zone centers, ${\mathbf{k}}_{0}$ $=$ (0, 0, 0), and quasielastic spin fluctuations centered at incommensurate wave vectors, ${\mathbf{k}}_{\mathrm{incom}}$ $=$ ($\ensuremath{\xi}$, $\ensuremath{\xi}$, 0). The coexistence of the two distinct features can be understood as a dynamic realization of the conical spiral order observed in cubic spinels such as CoCr${}_{2}$O${}_{4}$.

Objectives The purpose of this study was to assess the ability of two new calcium silicate-based pulp-capping materials (Biodentine and BioAggregate) to induce healing in a rat pulp injury model and to compare them with mineral trioxide aggregate (MTA). Materials and Methods Eighteen rats were anesthetized, cavities were prepared and the pulp was capped with either of ProRoot MTA, Biodentine, or BioAggregate. The specimens were scanned using a high-resolution micro-computed tomography (micro-CT) system and were prepared and evaluated histologically and immunohistochemically using dentin sialoprotein (DSP). Results On micro-CT analysis, the ProRoot MTA and Biodentine groups showed significantly thicker hard tissue formation (p < 0.05). On H&E staining, ProRoot MTA showed complete dentin bridge formation with normal pulpal histology. In the Biodentine and BioAggregate groups, a thick, homogeneous hard tissue barrier was observed. The ProRoot MTA specimens showed strong immunopositive reaction for DSP. Conclusions Our results suggest that calcium silicate-based pulp-capping materials induce favorable effects on reparative processes during vital pulp therapy and that both Biodentine and BioAggregate could be considered as alternatives to ProRoot MTA.

We investigated the effect of Al doping in magnetic properties of the Y-type hexaferrite Ba${}_{0.7}$Sr${}_{1.3}$Zn${}_{2}$(Fe${}_{1\ensuremath{-}x}$Al${}_{x}$)${}_{12}$O${}_{22}$ ($0\ensuremath{\le}x\ensuremath{\le}0.12$), which exhibit field-induced magnetoelectric polarization. We find that Al doping increases the pitch of a spin helix and enhances $c$-axis magnetization, stabilizing longitudinal conical phases. These conical phases eventually collapse at $x\ensuremath{\ge}$ 0.10. These results suggest that competitions between easy-axis and easy-plane anisotropy fields play a key role in generating stable magnetoelectric polarization in Y-type hexaferrites.

We studied the multiferroic properties of the incommensurate spiral phase of ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}{\text{WO}}_{4}$ using single-crystal neutron-diffraction and ferroelectric measurements. Whereas the rotational plane of the spin spiral is parallel to the $b$ axis for $x\ensuremath{\le}0.05$, it flops by $90\ifmmode^\circ\else\textdegree\fi{}$ for $x=0.10$. As a result, the direction of the ferroelectric polarization also flops from the $b$ to the $a$ axis. These results show that the orientation of the ferroelectric polarization in ${\text{MnWO}}_{4}$ can be controlled via chemical doping.

We have studied the effect of Co doping on the magnetic properties of multiferroic ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}{\text{WO}}_{4}$ using vibrating sample magnetometry and neutron powder diffraction. We find that Co doping at $x\ensuremath{\gtrsim}0.05$ suppresses the commensurate AF1 phase and stabilizes the incommensurate spiral AF2 phase down to the lowest temperature. As the Co doping concentration increases further, a spin-flop transition occurs with the spiral-basal plane tilting off the $b$ axis. Such magnetic structure expects a ferroelectric polarization component along the $a$ axis. The resulting phase diagram is richer than the case of Fe doping.

In this Letter, we report the effect of replacing Mn2+ ions with Ni2+ on the ferroelectricity of multiferroic MnWO4 single crystals. When the amount of substitution was close to 16%, the sign of ferroelectric polarization spontaneously became negative with respect to initial dc poling field at a few degrees below TC. Neutron diffraction intensities revealed a sudden change in the underlying spiral spin ordering that occurred coincidentally with the observed sign reversal. This unusual behavior in zero magnetic fields suggests that strong competitions between the two different magnetic ions may provide an efficient route to manipulation of existing multiferroics.

We report the cobalt doping dependencies of the ferroelectric polarization and underlying incommensurate spiral magnetic ordering in multiferroic Mn1-xCoxWO4 (0 ≤x 0.15). These consecutive changes were accompanied by simultaneous 90° flops of ferroelectric polarizations. Such doping dependencies are driven by the competitions between the anisotropy fields of MnWO4 and CoWO4, the spatial distributions of which are nearly orthogonal to each other. We propose a model that can consistently describe the two consecutive flops based on a combined picture of magnetic anisotropy and biquadratic exchange.

Tetragonal ferrimagnetic spinel Mn3O4 shows complex magnetic phase transitions due to competing anti ferromagnetic interactions involving Mn2+/3+ ions with difference valences. Using magnetization and neutron diffraction measurements, we propose that its tetragonal lattice possesses an instability towards orthorhombic distortion in zero field well below \(T_{\text{N}}\). The direction of the observed instability suggests that the anomaly is related to lifting of the persistent geometrical frustration via spin–lattice coupling.

A robust long-range antiferromagnetic coupling between ferromagnetic Ga 0.97Mn 0.03As layers has previously been realized via insertion of nonmagnetic Be-doped GaAs spacers between the magnetic lay ...