Adsorption of fibrinogen and heparin on insulator surfaces — an electrokinetic study

The adsorption of fibrinogen, a plasma protein, and heparin, an anticoagulant on insulator materials, glass and polymethyl methacrylate was investigated. The technique of streaming potential determination was employed. The protein and the drug were dissolved in a dilute Krebs solution (containing CaCl₂, NaCl, NaHCO₃, KH₂PO₄, MgSO₄ and KCl) and the streaming potentials developed when the solutions were flowed at pressures up to 40 cm of mercury were recorded. The results show that even at a very low concentration (10 μg ml^?1) fibrinogen reduced significantly the zeta potential of glass and polymethyl methacrylate. Subsequent addition of heparin to the solution had little effect on glass but slightly enhanced the zeta potential of the acrylic polymer. The effect due to fibrinogen persists even after pre-treatment of the surface with heparin.     

Passive control of discrete-frequency tones generated by coupled detuned cascades

Discrete-frequency tones generated by rotor-stator interactions are of particular concern in the design of fans and compressors. Classical theory considers an isolated flat-plate cascade of identical uniformly spaced airfoils. The current analysis extends this tuned isolated cascade theory to consider coupled aerodynamically detuned cascades where aerodynamic detuning is accomplished by changing the chord of alternate rotor blades and stator vanes. In a coupled cascade analysis, the configuration of the rotor influences the downstream acoustic response of the stator, and the stator configuration influences the upstream acoustic response of the rotor. This coupled detuned cascade unsteady aerodynamic model is first applied to a baseline tuned stage. This baseline stage is then aerodynamically detuned by replacing alternate rotor blades and stator vanes with decreased chord airfoils. The nominal aerodynamically detuned stage configuration is then optimized, with the stage acoustic response decreased 13 dB upstream and 1 dB downstream at the design operating condition. A reduction in the acoustic response of the optimized aerodynamically detuned stage is then demonstrated over a range of operating conditions.     

Mesonic wakes in nuclear matter,with application to meson production in nuclear collisions

The process of meson production by a source moving uniformly through infinite nuclear matter is studied in field theoretic models in which a source-meson coupling is assumed, and in which the only effect of the nuclear medium is to modify the propagator of the mesons. If the meson dispersion relation, ω(k), in the medium becomes space-like in some region of k, k > ω(k), there is, for relativistic source velocities, energy loss to the mesonic excitations. Models of the pion propagator in nuclear matter lead to such a space-like region. Rates of pion production are calculated in the lowest order of the pion-source coupling. Consideration of higher order terms leads to an interesting class of problems which we designate as those of “non-Abelian Cherenkov radiation.” Brief consideration is given to the excitation of nuclear collective modes and to the problems of treating meson production in finite nuclei.     

Observations on the structure of first generation polybenzimidazole reverse osmosis membranes

The structure-property relationships of polybenzimidazole (PBI) reverse osmosis (RO) membranes are important in process optimization. The membrane transport properties are influenced by the morphology which, in turn, is established by the process variables. Microscopical observation of the in situ porous textures of experimental membranes required development of special sample preparation methods. The preparation involves gradual replacement of water, and infiltration by an embedding resin, which permits thin sectioning for microscopical observation without collapse of the structure. p]Optical microscopy observations using the newly developed method provide an excellent overview useful for screening process variables. Scanning electron microscopy (SEM) was used to obtain useful three-dimensional fracture views of samples, although the membrane structure is somewhat collapsed during specimen preparation. Pore size and distribution, particularly in the region of the dense surface layer critical for effective separation properties (the active layer), were analyzed using transmission electron microscopy (TEM). Membrane surfaces were characterized using SEM and high resolution scanning electron imaging (SEI). Preliminary study revealed major morphological variation as flux levels varied. A study of high-flux as-cast and annealed first generation membranes revealed finger-like macrovoids below the top 500 nm layer. The top 20 nm has no resolvable pores (resolution limit about 10 nm, limited by sample thickness), whereas the bulk membrane exhibits pores about 100 nm across. The annealing process appears to shrink the membrane and reduce the pores to half the as-cast size.     

Competitive reactions among three monomers over a catalytic surface

We studied in this work a three-monomer reaction model on one- and two-dimensional lattices. We have taken different reactivity rates among pairs of monomers and the reaction between two selected monomers was forbidden. We have employed the mean field and the pair approximation to decouple the equations of motion for the densities of single and pairs of monomers. We found the stationary states and the phase diagram of the model. We have shown that, in two dimensions and within the pair approximation, there is a first-order transition line between active and poisoned steady states.     

Large reaction rate enhancement in formation of ultrathin AuSi eutectic layers

Metal-semiconductor eutectic liquids play a key role in both the fundamental understanding of atomic interactions and nanoscale synthesis and catalysis. At reduced sizes they exhibit properties distinct from the bulk. In this work we show an unusual effect that the formation of AuSi eutectic liquid layers is much easier for smaller thicknesses. The alloying reaction rate is enhanced by over 20 times when the thickness is reduced from 300 to 20 nm. The strong enhancement is attributed to a strain-induced increase in the chemical potential of the solid layer prior to the alloying reaction.     

Laser based accelerator for ultracold atoms

We present our first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams, and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F=2, m(F)=2] state, but the scheme is not restricted to atoms in any particular magnetic substates and can readily be extended to other atomic species as well.