Simulation of Counter-Current Spontaneous Imbibition Based on Momentum Equations with Viscous Coupling,Brinkman Terms and Compressible Fluids

Transport in Porous Media - A numerical model is investigated representing counter-current spontaneous imbibition of water to displace oil or gas from a core plug. The model is based on mass and...     

Caminoside A,an antimicrobial glycolipid isolated from the marine sponge Caminus sphaeroconia

Extracts of the marine sponge Caminus sphaeroconia showed potent activity in a screen for bacterial type III secretion inhibitors. Bioassay guided fractionation of the extract led to the isolation of the novel antimicrobial glycolipid caminoside A (1). The structure of caminoside A was elucidated by analysis of spectroscopic data and chemical degradation.[structure: see text]     

Changes in orcine muscle water characteristics during growth--an in vitro low-field NMR relaxation study

This study investigates the effects of developmental stage and muscle type on the mobility and distribution of water within skeletal muscles, using low-field (1)H-NMR transverse relaxation measurements in vitro on four different porcine muscles (M. longissimus dorsi, M. semitendinosus, M. biceps femoris, M. vastus intermedius) from a total of 48 pigs slaughtered at various weight classes between 25 kg and 150 kg. Principal component analysis (PCA) revealed effects of both slaughter weight and muscle type on the transverse relaxation decay. Independent of developmental stage and muscle type, distributed exponential analysis of the NMR T(2) relaxation data imparted the existence of three distinct water populations, T(2b), T(21), and T(22), with relaxation times of approximately 1-10, 45-120, and 200-500 ms, respectively. The most profound change during muscle growth was a shift toward faster relaxation in the intermediate time constant, T(21). It decreased by approx. 24% in all four muscle types during the period from 25 to 150 kg live weight. Determination of dry matter, fat, and protein content in the muscles showed that the changes in relaxation time of the intermediate time constant, T(21), during growth should be ascribed mainly to a change in protein content, as the protein content explained 77% of the variation in the T(21) time constant. Partial least squares (PLS) regression revealed validated correlations in the region of 0.58 to 0.77 between NMR transverse relaxation data and muscle development for all the four muscle types, which indicates that NMR relaxation measurements may be used in the prediction of muscle developmental stage.     

The Formation of Porous Membranes by Filtration of Aerosol Nanoparticles

Flame-generated aerosol particles of Al₂O₃ were deposited by gas filtration on two types of porous and ceramic tubes of -Al₂O₃ with mean pore diameters of 450 and 2700nm, respectively. The particles were aggregates with average mobility diameters in the range of 30–100nm and primary particle diameters of 4–8nm. The particles are characterized by differential mobility analysis, transmission electron microscopy, and by their specific surface area. The deposited membranes are characterized by gas permeability measurements, scanning electron microscopy, and by their pore size distribution from nitrogen capillary condensation. The particles form a distinct, homogeneous membrane layer with a porosity of 90% on top of the substrate surface and only penetrate slightly into the substrate structure. The mean pore sizes of the deposited membranes determined by nitrogen condensation agree approximately with those determined by gas permeation and the specific surface area. The mean pore diameter varies in the range of 30–70nm. The gas permeability of the deposited membranes is related to the specific surface area but influenced by the high porosity. The mean pore size and the permeability of the membranes are almost independent of the substrate structure.The development of a membrane with uniform properties is preceded by a short initial period in which the deposited particles, with an equivalent membrane thickness of roughly 2m, have a significantly lower permeability than the ultimately developed uniform membrane layer. This effect is particularly significant for the aerosol particles with the lowest mean size, probably due to particles deposited in the pore mouths of the substrate.The particles and the deposited membranes are X-ray amorphous but retain their specific surface area on heating to even high temperatures. When the membranes are heated to 1473K for 10h, X-ray diffraction shows a mixture of - and -alumina, accompanied by a partial disintegration of the membrane and a considerable loss of surface area.     

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5 dB by use of 550 m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24 turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel-and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5 dB for nontwisted fiber to 0.5 dB for fiber that is twisted at a rate of 8 turns/m, and the twist rate should be more than 4 turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8 turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4 pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.     

Fibre-optic beam delivery systems for particle image velocimetry

The role of fibre-optics in the formation of light sheets for particle image velocimetry is reviewed, concentrating on the power handling capacities of fibres and their effect on laser beam quality. It is shown that when continuous wave lasers are used, chopped to form a pulsed light sheet, then it is feasible to use a single multimode optical fibre to deliver the beam. Conversely, with Q-switched lasers, the peak power densities are so high that to achieve an adequate compromise between pulse energy and beam quality, delivery systems based on bundles of multimode fibres have been developed.     

Lower bounds on the cover-index of a graph

In this paper we give some new lower bounds for the cover-index of graphs with multiple edges permitted. The results are analogous to upper bounds for the chromatic index. We show that a simple graph with cover-index different from the minimum degree has at least three vertices of minimum degree. This implies that almost all simple graphs have cover-index equal to the minimum degree.     

Radiative lifetimes in Zn(II), Cd(II) and Hg(II) measured by fast-beam zero-field level-crossing technique

The zero-field level-crossing technique has been used to determine radiative lifetimes of excited states in singly ionized zinc, cadmium, and mercury. The excited levels in Zn(II), Cd(II) and Hg(II) were populated by collisions between fast ions and helium gas. Particular attention has been paid to the systematic errors occurring in radiative lifetimes by this technique. The results are compared with the lifetimes obtained by beam-foil, phase-shift, delayed-coincidence techniques and theoretical calculations.