不同叶轮形式下离心泵噪声特性对比研究

针对具有无短叶片和有短叶片两种叶轮形式的离心泵,对设计状态下离心泵内部流场进行了全三维、非定常数值模拟,对比分析了其非定常流场特性和噪声辐射特性。流场分析表明:叶轮叶片和蜗舌的相互作用造成了叶片表面强烈的压力脉动,对长短叶片的叶轮形式,在局部增加长叶片表面压力脉动的同时,短叶片表面的压力脉动保持较低水平;同时能够有效降低泵体进口压力脉动,但出口压力脉动有所增强。以叶轮叶片表面作为声源辐射面,对比分析了两种叶轮的偶极子噪声辐射特性,结果表明:长短叶片结构通过改变声能在频域上的分布,从而能有效降低总声压级。     

一种基于声相似律的旋转流体机械噪声声源分离方法

针对管道系统中的流体机械发声问题,提出了一种声源函数与声响应函数的频谱分离方法。该方法以声相似律为基础,分别采用最小均方值多重线性回归方法和高斯滤波获得声源函数和声响应函数。通过算例验证了该方法的有效性,辨识得到的声源函数和声响应函数的相对误差均远小于现有方法。利用该方法分析了自由空间和带管道两种安装条件下轴流风扇的辐射噪声,辨识得到了相应的声源函数、声响应函数和叶尖速度律指数,并对风扇的主要噪声成分进行了分析。     

Study on autonomous navigation based on pulsar timing model

The basic principle of pulsar timing model was introduced, and the general relativistic corrections were analyzed when pulse time of arrival (TOA) was transferred to coordinate TOA at the Solar System Barycentre. Based on the shifting, an iterative method of autonomous position determination for spacecraft was developed. Accordingly, the linear form of the position offset equation was evolved. Using the initial estimated value of spacecraft’s position as the input of pulsar timing equation, through calculation of the offset between measured or transferred and predicted TOA, the position offset can be solved by Least Squares. At last, the main error sources including modeling error and parameters error were discussed. Supported by the National Defence Laboratory Foundation of China (Grant No. 9140C3601010901) and Science Foundation of Shaanxi Province (Grant No. 2007F12) and the Technology Specialism Foundation of Shaanxi Education Department of Shaanxi Province (Grant No. 07JK332), and the Innovative Research Plan of Xi’an University of Technology (Grant No. 105-210714)     

铝丝阵Z箍缩辐射产生机理初步研究

利用一维非平衡辐射磁流体力学程序研究了铝丝阵内爆过程中的能量转化规律和辐射产生机理.细致讨论了Z箍缩过程中脉冲功率驱动器电磁能馈入等离子体,等离子体动能转化为内能以及通过一系列原子过程电子内能转化为X射线辐射的能量转化机理.结合离子布居信息深入分析了Z箍缩过程中的辐射产生机理.结果表明,在内爆压缩阶段,电离和激发过程占优,线辐射占据总辐射的绝大部分.在滞止时,离子大都处于裸核离化度,连续谱辐射达到峰值.在滞止附近,线辐射出现两个峰值.在膨胀过程中,光电复合过程优于三体复合,线辐射占总辐射的份额逐渐下降.     

Microstructure and strain films using in-plane grazing analysis of GaN epitaxial incidence x-ray diffraction

This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.     

XPS and ionic conductivity studies on Li1.3Al0.15Y0.15Ti1.7(PO4)3 ceramics

Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃ compound was synthesized by solid-state reaction, and ceramics were sintered. The surfaces of the ceramics were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃ samples were tested in solid galvanic cells Ag|O₂+CO₂|Li₂CO₃|Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃|LiMnO₂+Mn₂O₃|O₂|Ag. The electromotive force measurements of this cell indicated that investigated samples are practically pure Li-ion conductors. Impedance spectroscopy studies have been performed in the frequency range 10^?2–3·10⁹ Hz and temperatures from ?57 °C to 334 °C. Three dispersion regions related to Li⁺ ionic transport in bulk, grain boundaries of the ceramics and to polarization of electrodes have been found. Total conductivity changes according to Arrhenius law in the studied temperature range, but an anomalous behavior was observed for the bulk conductivity of the ceramics.     

番茄碰伤和可溶性固形物近红外光谱同时在线检测

可溶性固形物和碰伤是影响番茄品质的两个主要因素。研究的目的是探索可见近红外漫透射光谱同时在线检测番茄碰伤和可溶性固形物的可行性。在单通道送果速度5个每秒条件下,采集番茄近红外漫透射光谱。对比分析碰伤与正常番茄样品的近红外漫透射光谱特性,结果表明,碰伤与正常番茄样品的近红外漫透射光谱在光强上存在明显差异,碰伤果光强要强于正常果,其原因可能是碰伤后果肉变软,透光性变强;在650和675 nm处碰伤果比正常果要多两个吸收峰,可能是碰伤后,番茄表皮颜色发生变化所致。选取贡献率占比最多的前三个主成数,对正常果与碰伤果近红外漫透射光谱主成分定性分析,正常果与碰伤果不能有效聚类,故近红外漫透射光谱主成分定性分析效果不明显,需选择建立高维近红外漫透射光谱定性判别模型。故建立了碰伤番茄样品的近红外漫透射光谱偏最小二乘定性判别模型,误判率为0%,能正确判别碰伤果,故选用碰伤番茄样品的近红外漫透射光谱偏最小二乘定性判别模型作为番茄碰伤果在线剔除分选模型。通过对未参与建模的样品进行验证,能正确识别出碰伤果。经近红外漫透射光谱偏最小二乘定性判别模型剔除碰伤果后,按照可溶性固形物指标进行分级。分别使用全部波段和606～850 nm的波段进行建模预处理,且对全部波段和606～850 nm波段光谱进行2阶导数预处理,前后平滑设为9,利用连续投影算法与遗传算法优选可溶性固形物的光谱建模变量,对比发现,利用未经算法筛选过的606～850 nm波段光谱变量进行建模,效果最好,建立了可溶性固形物在线检测模型,预测集均方根误差为0.43 Brix°。采用未参与建模的样品进行碰伤和可溶性固形物同时在线检测验证,碰伤样品的分选准确率达96%,可溶性固形物样品的分选准确率达91%。表明：番茄碰伤和可溶性固形物近红外漫透射光谱同时在线检测是可行的。     

The dielectric behaviour of doped near-stoichiometric lithium niobate in the terahertz range

The dielectric properties of near-stoichiometric LiNbO₃:Fe and LiNbO₃:Ce single crystals have been investigated using terahertz time domain spectroscopy in a frequency range of 0.7-1.6 THz at room temperature. When coupled with an applied external optical field, obvious photorefractive effects were observed, resulting in a modulation of the complex dielectric constant for the crystals. The variation in refractive index, |Δn|, had a linear relationship with the applied light intensity, accompanied by a step-like decrease at high intensity. The findings were attributed to the internal space charge field of the photorefraction and the light-induced domain reversal in the crystals.     

Enhanced robustness of zero-line modes in graphene via magnetic field

We systematically studied the influence of magnetic field on zero-line modes (ZLMs) in graphene and demonstrated the physical origin of their enhanced robustness by employing nonequilibrium Green’s functions and the Landauer–Büttiker formula. We found that a perpendicular magnetic field can separate the wavefunctions of the counter-propagating kink states into opposite directions. Specifically, the separation vanishes at the charge neutrality point and increases as the Fermi level deviates from the charge neutrality point and can reach a magnitude comparable to the wavefunction spread at a moderate field strength. Such spatial separation of oppositely propagating ZLMs effectively suppresses backscattering and is more significant under zigzag boundary condition than under armchair boundary condition. Moreover, the presence of magnetic field enlarges the bulk gap and suppresses the bound states, thereby further reducing the scattering. These mechanisms effectively increase the mean free paths of the ZLMs to approximately 1 μm in the presence of a disorder.     

全局耦合网络上的两种类集团的聚集-湮没反应动力学

利用Monte-Carlo模拟研究了全局耦合网络上扩散限制的不可逆聚集-湮没过程的动力学行为. 在系统中, 同种类集团相遇, 将发生聚集反应; 不同种类的集团相遇, 则发生部分湮没反应. 模拟结果表明:1) 当两种粒子初始浓度相等时, 系统长时间演化后, 集团浓度c(t)和粒子浓度g(t)呈现幂律形式, c(t)～t^{- α}和g(t)～t^-β, 其中幂指数α 和β 满足α=2β 的关系, 且α=2/(2 + q); 集团大小分布随时间的演化满足标度律, a_kt)=k^-τt^-ω\varPhi (k/t^z), 其中τ≈-1.27q, ω≈(3 + 1.27q)/(2 + q), z=α/2=1/(2 + q); 2) 当两种粒子初始浓度不相等时, 系统经长时间演化后, 初始浓度较小的种类完全湮没, 而初始浓度较大的那个种类的集团浓度c_A(t)仍具有幂律形式, c_A(t)～t^-α, 其中α=1/(1+q), 其集团大小分布随时间的演化也满足标度律, 标度指数为τ≈-1.27q, ω≈(2 + 1.27q)/(1 + q)和z=α=1/(1 + q). 模拟结果与已报道的理论分析结果相符得很好.