Reaction of dicarbomethoxycarbene with quadricyclane

Dicarbomethoxycarbene reacts with quadricyclane to give mainly 3,3-dicarbomethoxy-$\text{exo}$-tricyclo[3.2.1.0^2,4]oct-6-ene. Although this is the same major product as formed by reaction of the carbene with norbornadiene, it is shown that reaction with quadricyclane is direct and does not involve prior isomerization to the diene.     

Flow properties of freshly prepared ettringite suspensions in water at 25 degrees C

The rheology of a complex, heterogeneous mineral colloid was rationalised using models devised for model rod systems. Mixing a calcium hydroxide slurry with an aluminium sulphate solution produces a suspension of rod-shaped ettringite particles. Ettringite rod suspensions exhibit non-Newtonian flow behaviour, which depends on the shape of the particles, their size distribution, concentration and surface properties as well as the suspension medium characteristics. We have measured the shear viscosity of suspensions of ettringite rods with a median aspect ratio, r(i) approximately 8, at 25 degrees C as a function of particle volume fraction, phi, in the range 0.0001-0.08. It was found that the viscosity of the suspensions increased with phi, and showed a marked change of slope at phi approximately 0.01, which we identified as the minimum overlap concentration phi(*). Above phi(*), the system is in the semi-dilute regime. At phi>phi(*), when Pe(rot)>1, hydrodynamic interactions between rods become increasingly significant, and we observe shear-thinning behaviour. The high effective hydrodynamic volume of rotating rods, resulting in much lower values of the maximum packing fraction, phi(c), than for spheres, dominates the rheological behaviour of ettringite suspensions.     

Ideals of factors

Every primitive C*-algebra is prime. An old theorem of Dixmier shows that the converse is true if the algebra is separable. Recently Weaver has shown that without separability this is false. AW* -factors are easily seen to be prime. Are all their ideals primitive? A number of partial results have appeared recently. It turns out that the answer is always positive and that this follows immediately from a theorem of FB Wright proved nearly 50 years ago. His proof was hard and complicated. He works in a more general setting but when his result is specialised to the class of operator algebras investigated here, we are able to give a new, easy proof that the ideals of an AW* -factor form a well-ordered set; from this, it follows swiftly that every proper ideal of an AW*-factor is primitive.     

Exact solution of Maxwell's equations for optical interactions with a macroscopic random medium: addendum

This Addendum provides a revised set of figures containing converged numerical data for total scattering cross section (TSCS), replacing the figures in our recent publication [Opt. Lett. 29, 1393 (2004)]. Due to the use of an overly large time step, our original TSCS data exhibited a systematic, nonphysical diminution above 150 THz for all cases studied. We have determined that numerical convergence in the temporal sense for the pseudospectral time-domain (PSTD) algorithm employed previously requires limiting the time step to no more than 1/60th of the sinusoidal period at the maximum frequency of interest, which in the previous case was 300 THz. This is an important point that we hereby report to future users of PSTD simulations in electrodynamics and optics. Note that all our original conclusions remain valid.     

Control of density fluctuations and electron transport in the reversed-field pinch

Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He (2) in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.     

Momentum transport from nonlinear mode coupling of magnetic fluctuations

A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets of tearing modes produce internal torques that redistribute momentum. Evidence for the nonlinear torque is acquired by detecting the correlation of momentum redistribution with the mode triplets, with the elimination of one of the modes in the triplet, and with the external driving of one of the modes.     

Polarized light propagation through tissue phantoms containing densely packed scatterers

We demonstrate that polarized light is maintained differently in densely packed versus dilute suspensions of polystyrene microspheres. The degrees of linear and circular polarization were measured versus scatterer concentration in aqueous suspensions of 0.48-, 0.99-, 2.092-, and 9.14-mum-diameter polystyrene microspheres. The results indicate that, for dilute suspensions of microspheres where independent scattering is assumed, the degrees of linear and circular polarization decrease as the scatterer concentration increases. For dense suspensions, however, the degree of polarization begins to increase as the scatterer concentration increases. The preferential propagation of linear over circular polarization states in dense suspensions is similar to results seen in biological tissue.