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941.
The production and transportation of fluorescent light produced in wavelength-shifting fibers (WSFs) coupled to YAP scintillation crystal is simulated using the GEANT4 codes.An advantage of the wavelength-shifting fiber readout technique over a direct readout with a position-sensitive photo-sensor is the reduced requirement for position sensitive photomultiplier tube photocathode area.With this gamma-ray detector,the gamma camera is small and flexible and has larger effective field of view and low cost.Simulation results show that a) a mean 12 of photons per 59.5 keV gamma ray interaction is produced in the WSF located nearest to the incident gamma ray,and a spatial resolution of 3.6 mm FWHM is obtained,b)a mean 27 of photons per 140 keV gamma ray interaction is produced and a spatial resolution of 3.1 mm FWHM is obtained.Results demonstrate the feasibility of this concept of a compact gamma-ray detector based on wavelength-shifting fibers readout.However,since the very low photoelectron levels,it is very important to use a photon counting device with good single photo-electron response to readout the WSFs. 相似文献
942.
943.
The delayed damper (DD) is a new active vibration absorption technique that uses time-delayed partial state feedback to generate ideal resonance on a passive vibration absorber. It has many attractive features such as real-time adjustability, ease of implementation, and total suppression of vibration for tonal frequency disturbances. In this paper, a major advantage of engineering structures analysis is the reduction of characteristic roots from infinite to finite numbers and the consequent simplicity in the dynamic analysis of the controller. The dynamic model principle is employed to design controllers for the structure. The system is examined by simulation. It is shown that engineering structures control application for DD yields better vibration suppression considering the sampled control structure in implementations. 相似文献
944.
945.
Sn-doped Ge2Sb2Te5 thin films deposited on Si(100)/SiO2 substrates by rf magnetron sputtering are investigated by a differential scanning calorimeter, x-ray diffraction and sheet resistance measurement. The crystallization temperatures of the 3.58 at.%, 6.92 at.% and 10.04 at.% Sn-doped Ge2Sb2Te5 thin films have decreases of 5.3, 6.1 and 0.9℃, respectively, which is beneficial to reduce the switching current for the amorphous-to-crystalline phase transition. Due to Sn-doping, the sheet resistance of crystalline Ge2Sb2Te5 thin films increases about 2-10 times, which may be useful to reduce the switching current for the amorphous-to-crystalline phase change. In addition, an obvious decreasing dispersibility for the sheet resistance of Sn-doped Ge2Sb2Te5 thin films in the crystalline state has been observed, which can play an important role in minimizing resistance difference for the phase-change memory cell element arrays. 相似文献
946.
Dielectric Properties of Multilayered Ba0.5Sr0.5TiO3 Thin Films Deposited on ITO-Coated Corning 1737 Glass by rf Magnetron Sputtering 总被引:1,自引:0,他引:1
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A new stacking method via variation ofsubstrate temperature in rfmagnetron sputter is used to fabricate polycrystalline/polycrystalline Ba0.5Sr0.5TiO3 thin films with higher dielectric constant, higher breakdown strength and lower leakage current densities than those prepared by a conventionM deposition method. The improved figure of merit G (ε0εrEb) of the Ba0.5Sr0.5TiO3 thin films implies that they are a feasible insulation layer for thin film electroluminescent devices. 相似文献
947.
指出了景深、可见光衍射、辐射输运是CCD图像接收系统模糊效应的3个影响因素。用MCNP方法研究了转换屏内的辐射输运,给出了不同入射光子能谱和转换屏厚度下转换屏内能量沉积随半径的变化关系。结果表明:能量沉积随转换屏厚度的增加而线性增加;辐射输运引起的模糊与光子能谱有关,但硬化谱引起的模糊随转换屏厚度的变化小于非硬化谱;转换屏内的辐射输运是CCD图像接收系统模糊效应的主要影响因素;辐射输运引起的模糊和高斯模糊是不同的。 相似文献
948.
Generation of 2.1 W Continuous Wave Blue Light by Intracavity Doubling of a Diode-End-Pumped Nd:YAG Laser in a 30 mm LBO 总被引:2,自引:0,他引:2
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A folded four-mirror cavity with a composite Nd:YAG rod is optimized to obtain high efficient cw 473nm blue output. The laser could operate stably in the region of the thermal-lens focal length from 20mm to 70mm. LBO is used for intracavity frequency doubling of the 946nm transition of Nd:YAG and the optimum LBO length is investigated. A maximum output power of 2.1 Win the blue spectral range at 473nm is achieved with 30-mm-long LBO, corresponding to an optical conversion efficiency of 9.1%. 相似文献
949.
制备了含多芳氨基甲烷类化合物的高分子变色薄膜,经紫外线辐照后,这种薄膜随吸收剂量的不同由无色透明逐渐变为绿色,在可见光区主要吸收峰位于626 nm附近,光密度响应与辐照时间近似成线性关系。研究表明:该辐射变色薄膜变色响应随紫外线能量密度增加而增加;分次辐照能略微提高光密度响应;辐射变色薄膜响应受温度和湿度影响较大,在20~50 ℃温度范围、40%~60%相对湿度范围,响应基本稳定;卤代物添加剂可以大大提高辐射变色薄膜的响应灵敏度;受后辐照效应影响,辐照结束最初2 h内响应迅速增加,2 h后响应才基本稳定。 相似文献
950.
采用直流磁控溅射方法制备了纯Ti膜,研究了不同功率下Ti膜的沉积速率、表面形貌及晶型结构,并对其应力进行了研究。研究表明:薄膜的沉积速率随溅射功率的增加而增加,当溅射功率为20 W时,原子力显微镜(AFM)图像显示Ti膜光洁、致密,均方根粗糙度最小可达0.9 nm。X射线衍射(XRD)分析表明薄膜的晶体结构为六方晶型,Ti膜应力先随溅射功率增大而增大,在60 W时达到最大值(为945.1 MPa),之后随溅射功率的增大有所减小。 相似文献