Nanoparticle composites: FePt with wide-band-gap semiconductor

We present a simple way to synthesize FePt and ZnO (wide-band-gap semiconductor) nanoparticle composites. The FePt nanoparticles were fabricated using the method reported by Sun et al. By controlling the heating rate, 3 nm FePt nanoparticles were synthesized. Well-dispersed FePt and ZnO nanoparticle composites were prepared by further adding zinc acetate and oleyl amine into the 3 nm FePt nanoparticle dispersion. By controlling the molar ratio of the FePt and zinc acetate, FePt and ZnO nanoparticle composites with different FePt particle fractions were obtained. The intensity of photo luminescence spectra of the nanoparticle composites increases very much with decreasing FePt particle fraction, whereas the peak position shifts a little. After annealing at 550 °C for half an hour, the nanoparticle composites become magnetically hard or semi-hard with coercivity much dependent on the FePt particle volume fraction. The coercivity of the composites increases with annealing temperature. The composites hold the promise of applications in new generation recording and/or optical devices.     

Generalization of Einstein relation for doped organic semiconductors

Under the assumption of Gaussian energy distributions of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), analytical expressions of generalized Einstein relation for electron and hole transport in doped organic semiconductor thin films are developed. Numerical calculations show that, although traditional Einstein relation still holds for low carrier concentrations, that is, the diffusion-coefficient-to-mobility ratio in units of k_BT/q, with k_B the Boltzmann’s constant, T the temperature and q the elementary charge, equals 1. But when the electron (hole) concentration is high, the diffusion-coefficient-to-mobility ratio for electrons (holes) changes strongly with the electron (hole) concentration, the doping level, the mean energy of LUMOs (HOMOs) of the dopant E_Ld (E_Hd) and the host E_L (E_H), as well as their variances. Dopants with E_Ld<E_L (E_Hd>E_H) affect the diffusion-coefficient-to-mobility ratio mainly in the range of low and middle carrier concentrations, while those with E_Ld>E_L (E_Hd<E_H) have significant effect only in the range of high carrier concentrations. It was found that there can be a maximum in the dependence of the diffusion-coefficient-to-mobility ratio on the quasi-Fermi energy or carrier concentration exist, for appropriate values of the doping level, the mean energy and variance of LUMO or HOMO states of the dopant. PACS 71.20.Rv; 72.90.+y; 73.50.-h     

Optical characteristics of semiconductor saturable absorber mirrors investigated by the reflection Z-scan technique

Recently, the semiconductor saturable absorber mirror (SESAM) has become a key component of passive mode-locked solid-state lasers. Here we present a simple method based on the reflection Z-scan technique to measure the key optical parameters of SESAM such as saturation fluence and modulation depth. The experimental results demonstrate that our method is able to perform with a high accuracy of 10⁻⁴ and a dynamic range of over four orders of magnitude.     

DIELECTRIC EFFECT ON THE RADIO-FREQUENCY CHARACTERISTICS OF A RECTANGULAR WAVEGUIDE GRATING TRAVELING WAVE TUBE

A new type of partial-dielectric-loaded rectangular waveguide grating slow-wave structure (SWS) for millimeter wave traveling wave tube (TWT) is presented in this paper. The radio-frequency characteristics including the dispersion properties, the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analyzed. The results show that the dispersion of the rectangular waveguide grating circuit is weakened, the phase velocity is reduced and the position of the maximum E _z is basically invariant after partially filling the dielectric materials in the rectangular waveguide grating SWS. Although the coupling impedance decreases a little, it still keeps above 40 Ω.     

Dispersion Compensation in Externally Modulated Transmission System Using Chirped Fiber Grating

We present an externally modulated NTSC AM-VSB erbium-doped fiber amplifier (EDFA)-repeated system in the 1550 nm region which uses a chirped fiber grating (CFG) as a dispersion compensation device. In contrast to the conventional externally modulated fiber optical CATV systems, either with or without dispersion compensation fiber (DCF), good performances of carrier-to-noise ratio (CNR) ≥50 dB, composite second order (CSO) ≥74 dB, and composite triple beat (CTB) ≥65 dB were achieved for the full channel band after a 100-km single-mode fiber (SMF) transmission.     

神经网络在工程爆破应力波规律探讨中的应用

采用BP（Back Propagation)前馈人工神经网络模型，对工程爆破中柱状震源的自由场应力波传播规律进行了探讨。结果表明：利用人神经网络模型的非线性映射功能，可以较好地给出工程爆破引起的近区自由场力学规律，对于同类型问题的研究，也有着很重要的意义。     

关于Asgeirsson均值等式的反问题

对于常系数线性偏微分算子(?),方程L_xu(x,y)=L_yu(x,y)的所有C^m解满足Asgcirsson均值等式的充分必要条件是L_x=c+a△_x,这里a(≠0),c为常数,△_x为Laplace算子.     

水雾化制备Fe74Al4Sn2P10C2B4Si4非晶合金粉末及其磁粉芯性能研究

采用水雾化方法制备Fe7Al4Sn2P10C2B4Si4合金粉末,研究发现该合金具有强的非晶形成能力和高热稳定性,在粉末粒度小于400目时可以形成非晶态合金.采用该非晶粉末制备的磁粉芯在高频下品质因数显著高于MPP粉芯,说明该磁粉芯高频损耗较低.分析表明,非晶合金磁粉芯高频下损耗低的主要原因是电阻率较高.     

B—模糊集合代数和广义互信息公式

基于两种概率的区分，推导出了一个广义Shannon熵公式和一个广义互信息公式。后者和模糊性有关，并且柯用于语言和感觉中的信息度量。为了由原子语句为真的条件概率求出合语句为真的条件概率，提出了一个遵循存尔运算的模糊集合代数。所谓的模糊信息被还原为概率信息。新的理论在经典理论－概率论，集合论及Shannon信息论－的基础上容易理解。     

Quantitative and high mass ToF-SIMS studies of siloxane segregation in hydrogel polymers using cryogenic sample handling techniques

This paper examines the capabilities of cryogenic sample handling to examine composition and structure of hydrogel materials where siloxane components are central to the analysis. XPS analysis of multicomponent polymers with cryogenic sample handling following exposure to aqueous environments has revealed the composition and kinetics of near surface reorganization for siloxane and fluorocarbon containing polymers. In this study we report results from a ToF-SIMS protocol for cryogenic sample handling applied to the analysis of surface changes upon hydration/dehydration of hydrogel polymers. Comparison of results from angle dependent XPS and ToF-SIMS are discussed for a range of commercial soft contact lens materials. Both methods detected changes in surface chemistry between the hydrated (frozen) and dehydrated surfaces. Analysis of the hydrated surfaces detected polymer components indicative of the commercial formulation as well as ice clusters. Analysis of the dehydrated materials detected changes in surface chemistry relative to the hydrated surface in addition to loss of water due to sample dehydration. A quantitative standard additions method for ToF-SIMS data was used to determine submonolayer amounts of PDMS impurities at the surface of the hydrogels. ToF-SIMS analysis of a series of seven poly (allyl methacrylate-g-dimethylsiloxane), AMA-g-DMS, graft copolymers in the hydrated state revealed high mass oligomeric ion distributions for systems with bulk PDMS content greater than 25 wt.%. This marks the first time that detection of high mass oligomeric ion distributions from hydrated (frozen) surfaces has been reported. Analysis of the dehydrated surface detected formation of high mass oligomeric ion distributions for systems with PDMS bulk content greater than 15 wt.%, but only detected these ion distributions in wet (frozen) samples when the bulk concentration was greater than 25 wt.%.