Quantum statistics of the degenerate four-wave mixing process

A quantum mechanical treatment is given of the degenerate four-wave mixing process. The approximate Heisenberg equation of motion for creation and annihilation operators is solved taking into account attenuation and noise. The solution and the statistics of the modes are discussed both below and above the threshold condition.     

Field emission characteristics of screen-printed carbon nanotubes cold cathode by hydrogen plasma treatment

Selective plasma etching and hydrogen plasma treatment were introduced in turn to improve field emission characteristics of screen-printed carbon nanotubes (CNTs) cold cathode, which was prepared by using slurry of mixture of multi-wall CNTs, organic vehicles and inorganic binder, i.e. silicon dioxide sol. The results show that selective plasma etching process could effectively remove parts of surface inorganic vehicle (SiO₂) layer and expose more smooth and clean CNTs on cathode surface, which could significantly decrease the operating field of CNTs cathode. There are some nanoparticles emerging on the out of CNTs wall after hydrogen plasma treatment, which are equivalent to increase field emission point of cathode. At the same time, these nanoparticles can increase the local electric field of CNTs, which can decrease operating voltage of CNTs cathode and improve uniformity field emission.     

Solute transport and composition profile during direct metal deposition with coaxial powder injection

Direct metal deposition (DMD) with coaxial powder injection allows fabrication of three-dimensional geometry with rapidly solidified microstructure. During DMD, addition of powder leads to the interaction between laser and powder, and also the redistribution of solute. The concentration distribution of the alloying element is very important for mechanical properties of the deposited clad material. The evolution of concentration distribution of carbon and chromium in the molten pool is simulated using a self-consistent three-dimensional model, based on the solution of the equations of mass, momentum, energy conservation and solute transport in the molten pool. The experimental and calculated molten pool geometry is compared for model validation purposes.     

Mott transition in modulated lattices and parent insulator of (K,Tl)(y)Fe(x)Se(2) superconductors

The degree of electron correlations remains a central issue in the iron-based superconductors. The parent iron pnictides are antiferromagnetic, and their bad-metal behavior has been interpreted in terms of proximity to a Mott transition. We study such a transition in multiorbital models on modulated lattices containing an ordered pattern of iron vacancies, using a slave-rotor method. We show that the ordered vacancies lead to a band narrowing, which pushes the system to the Mott insulator side. This effect is proposed to underlie the insulating behavior observed in the parent compounds of the newly discovered (K,Tl)(y)Fe(x)Se(2) superconductors.     

Ultrahigh sensitivity electric field detection with a liquid electro-optical film

In this Letter, an electro-optical probe configuration with polar molecule liquids as the sensing film is proposed to improve the voltage sensitivity. This method exhibited increases in intrinsic sensitivities better than 0.1 mV/√Hz, 2 orders of magnitude larger than the normal method using a GaAs probe in the same measurement system. Based on the mechanism of orientation polarization, the electro-optic coefficient was measured to be 250 pm/V by the Teng-Man method at a modulation field of 100 Hz. This technology will be promising in applications of low-frequency field detection.     

Engineering the electronic band structure for multiband solar cells

Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.     

A possible origin of room temperature ferromagnetism in Indium-Tin oxide thin film: Surface spin polarization and ferromagnetism

Room temperature ferromagnetism in both transition-metals doped and undoped semiconductor thin films and nanostructures challenges our understanding of the magnetism in solids. In this report, we performed the magnetic measurement and Andreev reflection spectroscopy study on undoped Indium-Tin oxide (ITO) thin films and bulk samples. The magnetic measurement results of thin films show that the total magnetization/cm² is thickness independent. Prominent ferromagnetism signal was also discovered in bulk samples. Spin polarized electron transports were probed on ITO thin film/superconductor interface and bulk samples surface/superconductor interface. Based on the magnetic measurement results and spin polarization measurement data, we propose that the ferromagnetism in this material originates from the surface spin polarization and this surface polarization may also explain the room temperature ferromagnetism discovered in other undoped oxide semiconductor thin films and nanostructures.     

NMR and spin-lattice relaxation rate of89Y,63Cu in radiation disordered YBa2Cu3O6.9

NMR line shifts and spin-lattice relaxation rates of⁸⁹Y and⁶³Cu in YBa₂Cu₃O_6.9 were measured in disordered samples irradiated by fast neutrons with a fluence of: ?=5·10¹⁸ cm^?2 (T _c ^ons =70 K), ?=1.2·10¹⁹ cm^?2 (T _c ^ons =20 K), in order to investigate the evolution of spin susceptibility χ_S under irradiation. According to the data obtained, χ_S decreases markedly as structural disorder accumulates in the samples. The variation of χ_S is related closely to that observed in oxygen-depleted YBa₂Cu₃O_7?δ compounds with nearly the sameT _c value. The data for yttrium display some features that are absent in oxygen-depleted samples. The different temperature dependence of the⁸⁹Y and⁶³Cu Knight shifts and the increase of the⁸⁹Y spin-lattice relaxation rate in irradiated samples are discussed in terms of the electron localization effects arising in the CuO₂ planes due to the radiation-induced structural disorder.     

Characterization of free radicals from vitamin K1 and menadione by 2 mm-band EPR,ENDOR and ESEEM

The anion and cation radicals of vitamin K₁ and its analog menadione were characterized using the magnetic resonance techniques of Electron Nuclear Double Resonance (ENDOR), Electron Spin Echo Envelope Modulation (ESEEM), and Electron Paramagnetic Resonance (EPR) at X-band and 2 mm-band. Theg-factor anisotropy of the radicals at 2 mm-band allow them to be distinguished from each other in the solid state. Theg-factor matrix of the radical anion of vitamin K₁ is virtually identical with that reported for the reduced A₁ acceptor in green plant photosystem I thus demonstrating that reduced A₁ is the anion radical of vitamin K₁.     

一种电流型超导储能脉冲变压器的放电模式

本文针对高温超导电感储能脉冲变压器(HTSPPT)提出了一种振荡放电模式.该模式中HTSPPT的原边绕组电感与电容器组成振荡回路,放电时原边电流通过该振荡回路使电流变化量增加,使得副边绕组感应出更大的电流脉冲.在放电过程中,电容器作为能量转换器件可实现开关的零电压关断,避免了断路开关出现过电压的问题.本文对振荡放电模式的工作原理进行了理论分析,利用一个小型HTSPPT搭建了小型实验系统,成功实现了从电流100A到3.78kA的放大,证明了的该放电模式的可行性.