BEPCⅡ正电子环真空度随流强的非线性变化

 观察发现负电子环的真空度随流强呈线性变化,正电子环的真空度随流强呈非线性变化,在正电子环的弧区,真空度的非线性变化很明显。讨论了非线性变化的原因,可能是同步光电子在正电子束流横向作用下加速碰壁,发生了二次电子发射,并在一定条件下形成了束流引起的多次碰壁效应,造成了大量放气。改变正电子束流的束团填充方式来观察真空度的非线性变化,得到了与KEK-B低能环一致的实验结果,该非线性变化呈现一定的阈值性,发生非线性的条件是有足够大的单束团流强和每列足够多的连续束团。     

Search for invisible decays of eta and eta' in J/psi --> phi eta and phi eta'

Using a data sample of 58 x 10(6) J/psi decays collected with the Beijing Spectrometer II detector at the Beijing Electron Positron Collider, searches for invisible decays of eta and eta' in J/psi to phi eta and phi eta' are performed. The phi signals, which are reconstructed in K+K- final states, are used to tag the eta and eta' decays. No signals are found for the invisible decays of either eta or eta', and upper limits at the 90% confidence level are determined to be 1.65 x 10(-3) for the ratio B(eta-->invisible)/B(eta --> gamma gamma) and 6.69 x 10(-2) for B(eta' --> invisible)/B(eta' --> gammagamma). These are the first searches for eta and eta' decays into invisible final states.     

Estimation of the acceleration ability for electrons in SiO2 and the tunneling effect

Silicon dioxide (SiO₂) plays an important role in layered optimization scheme and solid-state cathodoluminescence (SSCL). Initially, it was believed that the SiO₂ layer would (i) generate extra interface states contributing to a number of primary electrons available for exciting the luminescent centers, and/or (ii) act as acceleration layer resulted in gaining high energy for those electrons that would tunnel into the luminescent layer to excite luminescent centers. Based on the brightness vs. voltage (B-V) measurements, we deem that the latter case, i.e. acceleration and tunneling, is the dominant mechanism. A detailed discussion in terms of electrons acceleration and tunneling as the main contributions to the enhancement of brightness is presented.     

有中心缺陷孔的椭圆孔光子晶体光纤传输特性研究

基于超格子构造法,采用全矢量模型研究了具有中心缺陷孔的椭圆光子晶体光纤的传输特性。着重讨论了中心缺陷孔对光纤中基模的模场分布、双折射特性和色散特性的影响。研究表明：与椭圆孔光子晶体光纤相比。由于中心椭圆缺陷孔的引入,使该光纤具有更高的模式双折射。光纤的传输特性对光纤的结构参量和波长具有较强的依赖关系。随着波长和中心缺陷孔的增加。双折射将增大,其模式双折射在10^-3量级。改变光纤的结构参量,可以获得超宽带的色散平坦或异常的色散特性。分析结果显示,当中心孔的尺寸de／D=0．4时。在波长1．55μm附近,可获得近400nm的色散平坦区。     

Annealing effect on microstructure and mechanical properties of amorphous Al-C-N films

Al-C-N thin films with different Al contents were deposited on Si (1 0 0) substrates by closed-field unbalanced reactive magnetron sputtering in the mixture of argon and nitrogen gases. These films were subsequently vacuum-annealed at 700 °C and 1000 °C, respectively. The microstructures of as-deposited and annealed films were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM); while the hardness and elastic modulus values were measured by nano-indention method. The results indicated that the microstructure of both as-deposited and annealed Al-C-N films strongly depended on Al content. For thin films at low Al content, film delamination rather than crystallization occurred after the sample was annealed at 1000 °C. For thin films at high Al content, annealing led to the formation of AlN nanocrystallites, which produced nanocomposites of AlN embedded into amorphous matrices. Both the density and size of AlN nanocrystallites were found to decrease with increasing depth from the film surface. With increasing of annealing temperature, both hardness and elastic modulus values were decreased; this trend was decreased at high Al content. Annealing did not change elastic recovery property of Al-C-N thin films.     

Study of the synthesis and Cl2 gas-sensing properties of nanometer HNO3-doped SnO2

We focused on the effects of the inorganic acid HNO₃ on the gas-sensing properties of nanometer SnO₂ and prepared the powders via a dissolution-pyrolysis method. Furthermore, the powders were characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectra (EDS). Several aspects were surveyed, including the calcining temperature, concentration of nitric acid and the working temperature. The results showed that the gas response of 3 wt% HNO₃-doped SnO₂ powders (calcined at 500 °C) to 10 ppm Cl₂ reached 316.5, at the working temperature 175 °C. Compared with pure SnO₂, appropriate HNO₃ could increase the gas sensitivity to Cl₂ gas more significantly.     

喷管直径对微尺度扩散火焰特性的影响

对均匀空气流中微尺度甲烷扩散燃烧进行了数值模拟,重点考察微喷管内的流动和传热传质对微尺度燃烧特性的影响.研究结果表明,在保持燃料喷出速度一定的条件下,随着喷管直径的减小,喷管内与甲烷喷出速度相反方向上发生热量和质量的传递,燃料与空气的混合在喷管内已经发生,火焰的一部分热量回流到喷管内顶热了未燃混合气,同时也增加了火焰的热损失.当管径为0.15 mm时,甲烷在微喷管内就开始发生化学反应,在进行微尺度解析计算时,必须包含一定的喷管区域.     

组氨酸电离能与红外光谱的密度泛涵理论计算研究

采用混合密度泛涵理论中的B3LYP方法,结合4种基组6-31G(d),6-31G(df, p),6-31+G(d)和6-311+G(2d, 2p),系统计算了光合反应中心叶绿素的配位体-组氨酸在空气、四碌化碳、四氢呋喃、水和蛋白质模拟环境中的几何结构、电离能、红外光谱及同位素标记谱。计算及分析结果表明：组氨酸分子的几何参数在不同计算基组和介质中略有不同,且C₂—N₃,N₃—C₄的键长在空气中最大;同一介质中,增大计算基组和采用扩散函数,均使计算的单点势能和振动频率降低,电离能增加,对应光谱强度增高;而同一计算方法下,介质的电介常数越高,分子的单点势能越低,电离能越小,对应的振动频率减小强度增加;另外,电离能和主要特征峰位及其15N和13C标记谱的计算结果与文献中的实验结果相吻合。所有计算均显示,高基组和施加扩散函数的计算结果与实验更接近。该研究为深入探索叶绿素与组氨酸配位后在光合反应中心的功能与振动光谱特性提供理论参考依据。     

Linearly polarized operation of Yb-doped fiber laser by Brewster's angle-polished fiber end

<正>A new method to obtain linear polarization operation by Brewster's angle-polished fiber end is demonstrated. By using the special polarization operation technique together with introducing a narrow-linewidth fiber grating into the laser cavity,a cladding-pumped linear polarization and single-transverse-mode (M~21.1) Yb-doped fiber laser with narrow linewidth whose full-width at half-maximm(FWHM) is less than 0.2 nm,is obtained in a simple configuration.The output power is up to 10 W which is continuouswave output at 1085 nm,and the slope efficiency is 63%with respect to the coupled pump power and 75%with respect to the absorbed pump power,respectively.The measured 21-dB polarization extinction ratio does not degrade with the output power.The simplicity of such an approach is highly beneficial for a number of applications,including the use of a fiber laser for the nonlinear wavelength conversion (especially for the intracavity frequency doubling) and for the coherent and spectral beam combination.     

Effects of space duty cycle on the characteristics of fiber laser coherent beam combination

<正>The characteristics of fiber laser coherent beam combination are investigated by using a 2×2 fiber laser array with a self-Fourier cavity.The experimental results show that with a certain output width the power ratio of the center spot is increased with the increase of space duty cycle,meanwhile the number of secondary spots is decreased correspondingly.The results are in agreement with theoretic analysis.