Flow spectra from spectral power density calculations for pulsed Doppler

Range gated pulsed Doppler can be used to make localized velocity measurements within a blood vessel. Both the transducer and the sample volume are of finite size, and this prohibits the measurement of velocity at a point. A spectral flow profile can be created by stepping a sufficiently small sample volume across the lumen of a vessel. However no such set of spectra will correspond directly to the true velocity profile. In this study we developed a systematic theoretical treatment which allows Doppler spectral power density (SPD) functions to be calculated under a very wide range of conditions. Simulated flow spectra were created from sets of these spectra. The model is based on the beam intensity weighted volume method and incorporates, through the idea of a spread function, Guidi's individual flow line spectrum. Our method can be applied for different spread functions; with beam profiles which are uniform, Gaussian or arbitrarily narrow (needle beam); with range gated sample volumes which can be maximal (CW-type) or minimal (PW-type); and for beams which intersect the flow tube axis, or are off centre. Under all conditions we find the spread function parameter k, equal to the ratio of the central Doppler shift to half the bandwidth, plays a key role. After formulating the model analytically, we sought simplifications to allow results to be obtained from simple, practical formulae. Spread and unspread SPD functions are in most cases given as single integrals which contain measurable physical parameters and can be easily evaluated numerically. Model results are presented for flow spectra of parabolic flow, illustrating the interplay between different factors in determining the appearance of spectral flow profiles.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Homoconjugation in the adamantane cage: DFT/IGLO studies of the 1, 3-dehydro-5-adamantyl cation, its isoelectronic boron analogue 1, 3-dehydro-5-boraadamantane, and related systems(1)(,)

The structure of 1,3-dehydro-5-adamantyl cation and its isoelectronic boron analogue 1,3-dehydro-5-boraadamantane as well as some related adamantane systems, hitherto unknown as persistent long-lived species, were investigated by using the density functional theory (DFT) method. (13)C and (11)B NMR chemical shifts of the compounds were also calculated using the IGLO method. Stabilization of the systems due to homoconjugation is discussed.     

Theoretical study of relative width of photonic band gap for the 3-D dielectric structure

Calculations for the relative width (Δω/ω₀) as a function of refractive index and relative radius of the photonic band gap for the fcc closed packed 3-D dielectric microstructure are reported and comparison of experimental observations and theoretical predictions are given. This work is useful for the understanding of photonic crystals and occurrence of the photonic band gap.     

离子液体作为溶剂/催化剂用于卤代烃对胺的选择性烷基化反应

在三乙胺存在下,在离子液体([bmim]I和[bmim]PF6)中进行了各种卤代烃对胺类化合物中氨基的选择性烷基化反应.反应在相对温和的条件下进行,转化率和选择性优异.离子液体可以回收并重复使用.     

High quality beam shaping by square soft-edge diaphragm combined with liquid crystal spatial light modulator

<正>The square soft-edge diaphragm with round angle is designed by Matlab,and is sent to a liquid crystal spatial light modulator by the computer.In order to obtain precompensation for the following laser system, local diaphragm transmission can be adjusted by feedback signals of surface-channel charge-coupled device (SCCD).This method can reduce the diffraction effect and realize no modulation,high stability,high homogeneity,and large scale laser beam.Several parameters of soft-edge diaphragms which affect the laser beam quality are studied systematically,and the optimized values are obtained.The method can avoid the serious modulation of hard edges and provide soft-edge diaphragms of different shapes in a fast and convenient way for the large scale laser beam system.     

Tuning surface tension and aggregate shape via a novel redox active fluorocarbon-hydrocarbon hybrid surfactant

This paper reports the surface and bulk properties of a newly designed redox active hybrid surfactant Fc(CH2)11N+(C2H5)2(CH2)2(CF2)5CF3 I- or FcFHUB, where Fc is ferrocene. This new surfactant displays strong surface tension lowering ability (31 mN/m) and low critical micelle concentration (0.03 mM in 100 mM Li2SO4). The minimum area per surfactant molecule at the interface is determined as 121 angstroms2/molecule. The electrochemical oxidation of ferrocene (Fc) to ferrocenium cationic (Fc+) leads to reversible changes in the surface and bulk properties of this surfactant. Following the oxidation, desorption of surfactant molecules from the surface of the solution takes place. This desorption of surfactant molecules gives rise to the oxidation-induced surface tension change up to 15 mN/m. Although this new molecule shows salt-insensitive behavior in its reduced form, the oxidized form of the surfactant shows slight sensitivity to the electrolyte concentration. The molecular structure of FcFHUB allows the formation of large aggregates in the form of coils at a temperature of 33 degrees C. When the temperature rises to 50 degrees C, the aggregates are determined to be in the vesicle structure. The oxidation of Fc to Fc+ disrupts large aggregates to the smaller aggregates at low temperatures. The oxidation of surfactant molecules at high temperature leads to disruption of the aggregates to monomers.     

Fluid flow over a thin deformable porous layer

The flow of a viscous fluid over a thin, deformable porous layer fixed to the solid wall of a channel is considered. The coupled equations for the fluid velocity and the infinitesimal deformation of the solid matrix within the porous layer are developed using binary mixture theory, Darcy's law and the assumption of linear elasticity. The case of pure shear is solved analytically for the displacement of the solid matrix, the fluid velocity both in the porous medium and the fluid above it. For a thin porous layer the boundary condition for the fluid velocity at the fluid-matrix interface is derived. This condition replaces the usual no slip condition and can be applied without solving for the flow in the porous layer.     

Distribution and fate of tributyltin in the united states marine environment

Tributyltin (TBT) has been measured in water in 12 of 15 harbors studied during US Navy baseline surveys. The highest concentrations of TBT (some exceeding laboratory toxicity limits) have been found in yacht harbors and near vessel repair facilities. Many sites (75%) in harbors and estuaries had no detectable (<5 ng dm^?3) TBT. TBT monitoring studies with increased detection limits (<1 ng dm^?3) have documented a high degree of TBT variability associated with tide, season and intermittent point source discharges. Although yacht harbors were shown to be the principal TBT source in most regions, dry-docks can be significant sources. Tributyltin degradation studies were conducted using unfiltered seawater from four geographic regions and incubated under natural conditions. Degradation half-lives were always in the range of 4–19 days, providing evidence that TBT is not highly persistent in the water column at environmental concentrations. Preliminary degradation experiments suggest that TBT has a longer residence time in sediment with a half-life of several months. Tributyltin is primarily in the dissolved form in unfiltered seawater, although the association with particulate fractions may increase in samples collected near yacht repair facilities, Partition coefficients for particulate TBT versus bulk water are frequently near 3000 and vary with the particulate concentration, salinity and presence of natural organics.