Real-time phase-resolved functional optical coherence tomography by use of optical Hilbert transformation

We have developed a novel real-time phase-resolved functional optical coherence tomography system that uses optical Hilbert transformation. When we use a resonant scanner in the reference arm of the interferometer, with an axial scanning speed of 4 kHz, the frame rate of both structural and Doppler blood-flow imaging with a size of 100 by 100 pixels is 10 Hz. The system has high sensitivity and a larger dynamic range for measuring the Doppler frequency shift that is due to moving red blood cells. Real-time images of in vivo blood flow in human skin obtained with this interferometer are presented.     

Imaging and quantifying transverse flow velocity with the Doppler bandwidth in a phase-resolved functional optical coherence tomography

The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved functional optical coherence tomography (F-OCT) was used to image the velocity component that is transverse to the optical probing beam. It was found that above a certain threshold level the Doppler bandwidth is a linear function of flow velocity and that the effective numerical aperture of the optical objective in the sample arm determines the slope of this dependence. The Doppler bandwidth permits accurate measurement of flow velocity without the need for precise determination of flow direction when the Doppler flow angle is within +/-15 degrees perpendicular to the probing beam. Such an approach extends the dynamic range of flow velocity measurements obtained with the phase-resolved F-OCT.     

The alkylation of an α,α'-dianion in a β-ketosulphone leading to the preparation of axial 2-substituted thiane-1,1-dioxides

The 1,3-dianion formed across the sulphone of a β- ketosulphone may be selectively dialkylated in a controlled way with an α, ω-difunctional electrophile to give a 2-ketothiane- 1,1-dioxide. Polar groups in the 2-position of thiane-1,1-dioxides preferentially adopt an axial orientation as shown by detailed nmr studies. In cyclic sulphones such conformational preferences, arising from polar rather than steric effects are rare.     

High resolution high field rodent cardiac imaging with flow enhancement suppression

A method that incorporates cardiorespiratory-gated 2DFT spin-echo imaging with blood flow enhancement suppression is described which enables high resolution microimaging of the rodent heart. This methodology was applied to obtain in vivo cardiac mouse and rat images with in-plane resolutions of 100–200 μm using high field vertical bore magnet systems. Suppression of intraventricular blood flow enhancement was achieved using a combined spin-echo/gradient-refocussed sequence to dephase magnetization from flowing spins prior to imaging.     

Gravity flow of coarse cohesionless granular materials in conical hoppers

This paper is concerned with the flow of cohesionless granular materials in conical hoppers. The granules are considered to be coarse such that the effects of interstitial fluid can be neglected. Two analytical approaches based upon the method of integral relations are presented. In the first the detailed variations of shear and normal stresses over the cross-section of the hopper are considered. The second is a very simple analysis which makes use of a mean normal stress averaged over the cross-section. The two analyses yield predictions for the flow rate which are almost identical. After the inclusion of an empirical correction factor to account for non-uniform exit velocity profiles and bulk density reductions near the outlet, the flow rate predictions and their variations with internal and wall friction angles and with hopper wall slope are found to agree well with experimental measurements.

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Résumé Cet article traite de l'écoulement de matières granuleuses sans cohésion dans des trémies coniques. On admet que les granules sont assez gros pour que les effets dûs au fluide intersistiel restent négligeables. 2 méthodes d'approche analytiques basées sur la méthode des relations intégrales sont présentées. La première considère en détail la distribution des contraintes normales et de cisaillement sur la section de la trémie. La seconde méthode est une simple analyse basée sur la moyenne des contraintes normales sur cette section. Les 2 analyses fournissent des prédictions presque identiques sur le taux d'écoulement. En introduisant un facteur de correction empirique pour tenir compte de la non-uniformité de profils de vitesses d'écoulement ainsi que de la réduction de densité à la sortie, l'analyse fournit des taux d'écoulement et leurs variations avec la friction interne, les angles de friction aux parois et l'inclinaison des parois de la trémie. Les résultants obtenus sont en accord avec des mesures expérimentales.

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On leave at the Department of Applied Mathematics and Theoretical Physics, University of Cambridge.