DNS and LES of turbulent channel flow with hydrophobic surface

Hydrophobic surface benefits for drag reduction. Min and Kim[1] do the first Direct Numerical Simulation on drag reduction in turbulent channel flow. And Fukagata and Kasagi[2] make some theoretical analysis based on Dean[3]'s formula and some observations in the DNS results. Using their theory, they conclude that drag reduction is possible in large Reynolds number. Both Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) are performed in our research. How the LES behaving in the turbulent channel flow with hydrophobic surface is examined. Original Smagorinsky model and its Dynamical model are used in LES. The slip velocities predicted by LES using Dynamical model are in good agreement with DNS as shown in the Figure. Although the percentage of drag reduction predicted by LES shows some discrepancies, it is in the error limit for industrial flow. First order and second order moments of LES are also examined and compared with DNS's results. The first-order moments is calculated well by LES. But there are some discrepancies of second-order moments between LES and DNS. [GRAPHICS]

Influence of recording conditions on crossed-beam photorefractive gratings in doubly doped LiNbO3 crystals

The influence of the recording conditions, including the widths of the recording beams, the width ratio of the recording beams, and the recording angles, on the properties of crossed-beam photorefractive gratings in doubly doped LiNbO3 crystals is studied. A theoretical model that combines the band transport model with two-dimensional coupled-wave theory is proposed. The numerical calculations of the space-charge field, the intensity profiles of the diffracted beam, and the diffraction efficiency are presented. (C) 2006 Optical Society of America.

Pulse shaping properties of volume holographic gratings in anisotropic media

Based on a modified coupled wave theory, the pulse shaping properties of volume holographic gratings (VHGs) in anisotropic media VHGs are studied systematically. Taking photorefractive LiNbO3 crystals as an example, the combined effect that the grating parameters, the dispersion and optical anisotropy of the crystal, the pulse width, and the polarization state of the input ultrashort pulsed beam (UPB) have on the pulse shaping properties are considered when the input UPB with arbitrary polarization state propagates through the VHG. Under the combined effect, the diffraction bandwidth, pulse profiles of the diffracted and transmitted pulsed beams, and the total diffraction efficiency are shown. The studies indicate that the properties of the shaping of the o and e components of the input UPB in the crystal are greatly different; this difference can be used for pulse shaping applications. (c) 2006 Optical Society of America.

Research on a scanner for tilting orthogonal double prisms

The original scanner for tilting orthogonal double prisms is studied to test the tracking performance in intersatellite laser communications. With a reduction ratio of more than 100 times from the change rate of the angle of beam deviation to that of the tilting angle of each prism, the theoretical analysis performed, as well as the verification experiment, indicates that the scanner can meet the requirements of the scanning accuracy superior to 0.5 mu rad with the scanning range greater than 500 mu rad and can facilitate the mechanical structure design. (c) 2006 Optical Society of America.

Anisotropic diffraction of stratified volume holographic grating in photorefractive media

We have studied the anisotropic diffraction properties of the stratified volume holographic gratings recorded in photorefractive media using the anisotropic coupled wave theory. It is shown that the diffraction efficiency of such system exhibit the uniform periodic Bragg selectivity properties. In addition the dependence of the stratified volume holographic optical elements (SVHOEs) diffraction properties on the buffer-layer thickness, grating-layer thickness, number of modulation layers, and total thickness of system are discussed in detail. (c) 2005 Elsevier GrnbH. All rights reserved.

Diffraction properties of volume holographic gratings for an ultrashort pulsed beam with different polarization states readout

The diffraction properties of volume holographic gratings are studied when the gratings are illuminated by an ultrashort pulsed beam with different polarization states. The developed coupled wave theory of Kogelnik is used. Considering the dispersion effect of the grating media, solutions for the diffracted and transmitted intensities, diffraction efficiencies and the bandwidths of the gratings are given in transmission volume holographic gratings and reflection volume holographic gratings. The bandwidths of the gratings are reduced by the dispersion effect of the grating media. They also have different influences on the diffraction of an ultrashort pulsed beam with different polarization states. For different values of the ratio of the spectral bandwidth of the input pulse to that of the grating, the changes of the spectral and temporal distributions of the diffracted intensities, as well as the diffraction efficiencies of the gratings are shown.

Application of the compatibility relationship(1) in seeking a functional relationship among species' equilibrium quantities in complex systems

A new algorithm, representing an important advance in determination of the functional relationship, is first reported here. The algorithm is very useful and convenient for analyzing the incorporation of impurities. To show how the algorithm works, two early and well-known vapor phase epitaxy (VPE) experiments-Ashen's (Ashen, D. J.; Dean, P. J.; Hurle, D. T. J.; Mullin, J. B.; Royle, A.; White, A. M. Gallium Arsenide and Related Compounds, Institute of Physics Conference Series 24, 1974; Institute of Physics: London, 1975; p 229.), involving the doping of silicon and DiLorenzo's (DiLorenzo, J. V. J. Cryst. Growth 1972, 17, 189.), involving the mole fraction effect-are calculated to find the functional relationship between the Si contamination and the partial pressure of HCl. The calculated curves agree with the experimental results. A conclusion that the calculated values are greater than the true values has been drawn.

Second-order solutions for random interfacial waves under steady uniform currents

In the present research, the study of Song (2004) for random interfacial waves in two-layer fluid is extended to the case of fluids moving at different steady uniform speeds. The equations describing the random displacements of the density interface and the associated velocity potentials in two-layer fluid are solved to the second order, and the wave-wave interactions of the wave components and the interactions between the waves and currents are described. As expected, the extended solutions include those obtained by Song (2004) as one special case where the steady uniform currents of the two fluids are taken as zero, and the solutions reduce to those derived by Sharma and Dean (1979) for random surface waves if the density of the upper fluid and the current of the lower fluid are both taken as zero.

香鼬的活动节律和巢区

本文采用无线电遥测技术对栖息在自然环境中香鼬（Musteal altaica）的活动节律及其巢区进行了较为系统的研究。结果表明，香鼬多营独居生活．除繁殖期外，无论雌雄个体均无长期稳定的巢穴，经常更换活动的位置。香鼬的每日活动主要为玩耍、自身的修饰、光浴、探视和取食，在繁殖期还有育幼及对幼鼬的保护。在不同时期香鼬日活动高峰和巢区大小均有不同。幼鼬出洞活动前，其亲体雌性成鼬活动呈现两个明显的高峰，11:00～13:00和16:00～17:00，雄性成鼬则只有一个活动高峰在11:00左右；在这一时期，成体香鼬的地面活动高峰与其食物──高原鼠兔的地面活动高峰不相吻合，雌性成鼬的巢区面积为7.21ｈａ，雄性成鼬的巢区面积为11.7ha。幼鼬出洞活动后，雌性成鼬的活动高峰为8:00～9:00和17:00～19:00，巢区面积平均为82.72ha。幼鼬扩散期间，雌性成鼬的活动高峰期分别为8:00～9:00和15:00～20:00。在这两个时期，成体香鼬的地面活动高峰与高原鼠兔的地面活动高峰趋于一致。影响香鼬活动和巢区大小的主要因素是食物的丰富度、猎物的活动性和繁殖行为，同时种群密度也是主要因素之一。

赤狐的活动节律与产仔洞穴的选择

本文对赤狐（Ｖｕｌｐｅｓｖｕｌｐｅｓ）的产仔洞穴、活动节律和巢区大小进行了研究。赤狐产仔洞穴全部为喜马拉雅旱獭（Ｍａｒｍｏｔａｈｕｍａｌａｙａｎａ）的居住洞，一般洞口数较多（平均４．８个），分布于高寒灌丛（７１％），距干扰因素较远（大于１．５ｋｍ），常位于坡中部（７１％）．影响其选择的主要因素是隐蔽性和安全性。赤狐的产仔洞穴相对稳定，平均利用时间为３．３年，利用时间的长短与环境条件的稳定性有关。赤狐通常在夜间活动，主要是觅食，而白天有时成体携幼体在洞穴附近进行短时间的非觅食活动，活动的高峰期为１８００一０８００时。雌雄成体共同哺育幼体，活动范围相同而多单独活动。成体赤狐的巢区面积平均为７．９ｋｍ２。

香鼬的栖息地选择、觅食和育幼行为

香鼬（Ｍｕｓｔｅｌａａｌｔａｉｃａ）喜栖于人类居住区附近的高寒草甸草场，主要以高原鼠兔（Ｏｃｈｏｔｏｎａｃｕｒｚｏｎｉａｅ）为食，其数量分布与高原鼠兔的密度分布成正相关。在高原鼠兔的繁殖盛期，香鼬主要捕食鼠兔幼体，每只成体平均每天捕获鼠兔６．２只，相当于每１００克体重日获取食物重量２７３．５克，在高原鼠兔的繁殖后期和非繁殖期，每只成体平均每天捕获鼠兔２．７５只，相当于每１００克体重日获取食物重量２９６．３克。繁殖期育幼任务全部由雌性成鼬承担，幼鼬从７月初开始地面活动，８月初开始扩散。