Modelling of the pressure-velocity correlation in turbulence diffusion

Most current computations of trubulent flows with second-moment closure adopt the diffusion models which neglect the effect of pressure-velocity correlation. In the present paper the importance of this correlation effect is elucidated the neglect of this effect accounts for some major defects in the wide application of the second-moment closures. Through the relation between and , established by Lumley, we propose here a new turbulence diffusion model which takes into consideration the pressure effect. Applications of this new model in the computation of shearless turbulence mixing layer and plane and round-jet flows show that the spreading rate of these flows can be satisfactorily captured.     

Influence of the position of the nitro group on the structural and spectroscopic characteristics of N"-(nitrobenzylidene)isonicotinic hydrazides in the crystalline state

N"-Substituted isonicotinic hydrazides of the general formula Py—C(=O)—N(H)-N"=C(H)—R, where R is o- (1), m- (2), or p-nitrophenyl (3), were studied by IR spectroscopy and X-ray diffraction analysis. The position of the nitro group in these compounds has no effect on the type of the crystal structure. The crystal packings are based on stacks consisting of antiparallel planar molecules. The molecules from the adjacent stacks are linked to each other via the N—H...N_Py hydrogen bonds. Depending on the position of the nitro group, the N...N_Py distance increases in the series 3 > 1 > 2 and the energy of the hydrogen bonds decreases (according to the IR spectroscopic data) from 3.9 to 3.1 kcal mol^–1. Analysis of the IR spectra demonstrated that the intensity of absorption in the (C—H) stretching region of the pyridine ring increases substantially as the the N—H...N_Py hydrogen bond is strengthened. Some regularities of the changes, which are observed for the (NO₂) bands in the spectra of the nitrophenyl-containing conjugated molecules in solutions, persist in the crystalline state.     

Must thermodynamic functions be piecewise analytic?

There seems to be no general theoretical argument to support the idea that thermodynamic functions are piecewise analytic. We suggest that nonanalyticity may be associated with Gibbs states which are quasiperiodic under space translations, or have a more general nonperiodic (turbulent) behavior.     

电极结构对等离子体显示单元放电效率的影响

利用实验和数值模拟方法研究等离子体显示屏放电单元中的电极间隙、长度、壁障高度等不同参数对放电特性的影响.结果表明,放电效率随电极长度、间隙大小的增大而增大,壁障的存在也使效率略有增加并导致单元有效电容减小,但对放电电压影响很小.单元高度对放电效率影响不大,但可以降低同样间隙下的放电电压.合理选择电极结构可以在较低的维持电压下获得较高的放电效率.     

高校图书馆数字化建设中的特色服务

数字化时代，高校图书馆要利用自身优势，在数字化建设中做出自己的特色，即服务内容上突出学术性，大力发展多媒体型信息；服务方式上依托校园网，拓展数字化信息服务；服务形象上体现高素质，做好信息导航服务。     

一种高分子电阻型湿度传感器的制备及研究

以苯乙烯-马来酸酐共聚物钠盐(Na-SMA)为湿敏材料,采用浸涂的方法,在小型叉指金电极上成膜,制备了高分子电阻型湿度传感器.研究了浸涂液组成对传感器响应特性的影响.研究表明,随着浸涂液中Na-SMA浓度的提高,元件的电阻、湿滞降低;而随着浸涂液中聚乙烯醇(PVA)浓度的提高,元件的电阻降低,湿滞增加.     

北京-郑州运输通道内旅客出行的特征

为研究运输通道内客流变化规律,结合北京郑州铁路客运专线建设,运用简单抽样方法确定样本抽样率和样本容量,对通道内不同运输方式旅客出行调查数据进行统计分析。结果表明:出行旅客中企管人员最多;月收入小于1 000元的旅客主要选择公路出行,高于2 000元的旅客主要选择民航出行,介于二者之间的旅客多选择铁路出行;旅客多以出差、经商和探亲为出行目的;在小于300 km的出行距离内,公路占绝对优势;在300~1 500 km内,铁路优势明显;服务属性中,旅客最为关心的是安全,最不满意的是运行速度。     

数字光栅测振传感器性能分析与测试

为完善光栅测振传感器的性能,将光栅莫尔条纹技术应用到振动测量,在完成光栅测振传感器原理性实验的基础上,进行了理论分析,并就其特性进行了实验研究.通过构建高精度光栅传感器测试系统,对传感器的静动态特性进行深入研究,并建立了动态模型.实验证明,光栅测振传感器分辨力可达0.025μm,动态频率误差小于1.5%,振幅误差小于3.8%.     

动力学系统状态演化特征的Lyapunov指数

论述了确定性动力学系统运动状态长时间演化的普遍规律,同时指出Lyapunov指数是反映系统相轨变化特征的重要宏观量.并且,分析研究了Lyapunov指数的定义和计算方法.     

几种农作物对垃圾污水中N、P、Cl吸收特性

用阜阳市区中、西清河垃圾污水培养几种农作物种子,探讨污水培养下幼苗对污水中N、P、Cl等营养盐的吸 收特性．结果表明:菜豆和玉米在萌芽阶段的抗污水胁迫能力要高于上海青和荆荠种子,荆荠和上海青种子虽能萌 芽但不能长成幼苗．从同一种种子萌苗也可以看出两条河流水质的污染状况:西清河水质污染状况比中清河严重．N 和Cl在菜豆和玉米幼苗内都是随着污水浓度升高而增加;但玉米幼苗在自来水、2种污水培养中P的含量却呈现负 增加．菜豆对N、P、Cl元素的吸收率均高于玉米,这表明菜豆对N、P、Cl元素的吸收效果要比玉米好．