Influence of a vortex gas flow on an axial laser beam

An experimental investigation of the optical properties of a bilateral straight-through-flow small-scale (1.7410^–2 m) vortex tube has been carried out experimentally, and the influence of this tube on an axial small-section (310^–3 m) laser beam has been studied. Additional data confirming the reliability of the gas-dynamical model of formation of laser beams with an intensity dip at the center are obtained.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 58–62, January–February, 2005.     

Separated flow modelling and interfacial transport phenomena

A physical explanation of the different types of interfacial waves that appear in stratified and annular gas-liquid flows is presented. The role of waves in affecting process performance is discussed. Particular attention is paid to interfacial drag, gas absorption, the initiation of slug flow and atomization.This paper was presented at the Shell Conference on Computational Fluid Dynamics in Apeldoorn, December, 1989.     

Fluorescence Studies of the Acetylcholine Receptor: Structure and Dynamics in Membranes and Cells

The nicotinic acetylcholine receptor (AChR) is the archetype member of the superfamily of ligand-gated ion channels that mediate fast intercellular communication in response to endogenous neurotransmitters. Here I review a series of biophysical studies on the AChR protein, with particular focus on the interactions of the macromolecule with its lipid microenvironment. Fluorescence recovery after photobleaching and phosphorescence anisotropy studies of the membrane-embedded AChR have contributed to our understanding of the translational and rotational dynamics of this protein in synthetic lipid bilayers and in the native membrane. Electron spin resonance studies led to the discovery of a lipid fraction in direct contact with the AChR with rotational dynamics 50-fold slower than that of the bulk lipids. This lipid belt region around the AChR molecule has since been intensively studied with the aim to define its possible role in the modulation of receptor function. The polarity and molecular dynamics of solvent dipoles—mainly water—in the vicinity of the lipids in the AChR membrane have been studied exploiting the amphiphilic fluorescent probe Laurdan's exquisite sensitivity to the phase state of the membrane, and Förster-type resonance energy transfer (FRET) was introduced to characterize the receptor-associated lipid microenvironment. FRET was used to discriminate between the bulk lipid and the lipid belt region in the vicinity of the protein. Further refinement of this topographical information was provided by the parallax method using phospholipid spin labels. The AChR-vicinal lipid is in a liquid-ordered phase and exhibits a higher degree of order than the bulk bilayer lipid. Changes in FRET efficiency induced by fatty acids, phospholipid, and cholesterol also led to the identification of discrete sites for these lipids on the AChR protein. I also illustrate the extension of Laurdan fluorescence studies to intact living cells heterologously expressing AChR in a brief section devoted to recent studies using two-photon fluorescence microscopy. The spatial resolution afforded by the two-photon optical sectioning of the cell in combination with the advantageous spectroscopic properties of Laurdan are exploited to obtain information on the physical state of the lipid environment of the membrane. Finally, the application of site-specific labeling and steady-state fluorescence spectroscopy to probe the location of AChR membrane-embedded domains is illustrated. The topography of the pyrene-labeled Cys residues in transmembrane domains M1, M4, M1, and M4 with respect to the membrane was determined by differential fluorescence quenching with lipid-resident spin-labeled probes. Cys residues were found to lie in a shallow position. For M4 segments, this is compatible with a linear -helical structure, but not so for M1, for which classical models locate Cys residues at the center of the hydrophobic stretch. The transmembrane topography of M1 can be rationalized on the basis of the presence of a substantial amount of nonhelical structure and/or of kinks attributable to the occurrence of the evolutionarily conserved proline residues. The latter is a striking feature of M1 in the AChR and all members of the rapid ligand-gated ion channel superfamily.     

Quasi–Stationary Regime of Ring Laser Generation

An exact solution to the equations that describe the operation of a ring laser having nonstationary parameters is obtained. An iterative formula is derived and the conditions under which a quasi–stationary solution can be used are determined. Lasers with vibrating and reversing differences of the frequencies of opposite waves are considered. In the case of a reversing shift, it is always possible to isolate a quasi–stationary regime when transient processes are completed.     

Influences of phase shift on superresolution performances of annular filters

This paper investigates the influences of phase shift on superresolution performances of annular filters. Firstly, it investigates the influence of phase shift on axial superresolution. It proves theoretically that axial superresolution can not be obtained by two-zone phase filter with phase shift π, and it gets the phase shift with which axial superresolution can be brought by two-zone phase filter. Secondly, it studies the influence of phase shift on transverse superresolution. It finds that the three-zone phase filter with arbitrary phase shift has an almost equal optimal transverse gain to that of commonly used three-zone phase filter, but can produce a much higher axial superresolution gain. Thirdly, it investigates the influence of phase shift on three-dimensional superresolution. Three-dimensional superresolution capability and design margin of three-zone complex filter with arbitrary phase shift are obtained, which presents the theoretical basis for three-dimensional superresolution design. Finally, it investigates the influence of phase shift on focal shift. To obtain desired focal shifts, it designs a series of three-zone phase filters with different phase shifts. A spatial light modulator (SLM) is used to implement the designed filters. By regulating the voltage imposed on the SLM, an accurate focal shift control is obtained.     

复合载荷作用下带边缘大波纹膜片的非线性弯曲

采用轴对称旋转壳体的简化Reissuer方程,研究了在复合载荷作用下具有硬中心的带边缘大波纹膜片的非线性弯曲问题。应用格林函数方法,将波纹膜片的非线性边值问题化为非线性积分方程进行求解。为了求解积分方程并防止发散,引人一个插值参数到选代格式中。计算表明,当载荷很小时,任何插值参数值均能保证迭代的收敛性,取插值参数值接近或等于1获得较快的收敛速度;而当载荷较大时,插值参数值不能取得过大。绘出了不同载荷组合下波纹膜片的特征曲线,得到的特征曲线可供设计参考。由于均布压力和中心集中载荷的共同作用,将产生比均布压力单独作用更大的挠度。提出的解决方法适应于任意轴向截面的波纹壳体。     

Prediction of the interfacial shear-stress in vertical annular flow

Many improvements of the Wallis correlation for the interfacial friction in annular flow have been proposed in the literature. These improvements give in general a better fit to data, however, their physical basis is not always justified. In this work, we present a physical approach to predict the interfacial shear-stress, based on the theory on roughness in single-phase turbulent pipe flows. Using measured interfacial shear-stress data and measured data on roll waves, which provide most of the contribution to the liquid film roughness, we show that the interfacial shear-stress in vertical annular flow is in very close agreement with the theory. We show that the sand-grain roughness of the liquid film is not equal to four times the mean film thickness, as it is assumed in the Wallis correlation. Instead, the sand-grain roughness is proportional to the wave height, and the proportionality constant can be predicted accurately using the roughness density (or solidity). Furthermore, we show that our annular flow, which is in similar conditions to others in the literature, is fully rough. Hence, the bulk Reynolds number should not appear in the prediction of the interfacial friction coefficient, as is often done in the improvements of the Wallis correlation proposed in the literature.     

A mathematical approach to study fluid-coupled vibration of eccentric annular plates

A mathematical method is proposed to study fluid-coupled vibration of axisymmetric plate structures with asymmetries due to either imperfection or practical reasons, e.g. the weight reduction of structure, natural frequency shifting, and accessibility. The suggested approach makes use of the separation of variables to determine general solutions of the partial differential equation of the plate transverse displacement, whilst defining multiple polar coordinate systems, each of which offers its own formulation of the plate deformation with respect to its coordinate system. Moreover, closed-form geometric equations and the chain rule for determining derivatives are implemented to move from one coordinate system to the other in order to satisfy boundary conditions. The mode shapes of the vibrating plate in the dry condition are determined and in turn used in the Rayleigh–Ritz method to characterize vibrational properties of the fluid-coupled plate structure. While implementing such an energy method, the fluid motion is formulated employing the velocity potential and solved using the separation of variables. Fluid–structure interaction is also taken into account satisfying the compatibility condition on the fluid–plate​ interface. The developed methodology to predict natural frequencies has been validated by comparison with results obtained by a commercial finite element program. It is also found that the eccentricity tends to reduce natural frequencies of the fluid-coupled system for the lower serial mode, but increases them for the higher serial modes regardless of the presence of liquid.     

The existence of limit cycles for system\dot x=Q(x,y), Y=P(x)

In [1], by a transformation on the Lienard equation system