Towards gravitationally assisted negative refraction of light by vacuum

Propagation of electromagnetic plane waves in some directions in gravitationally affected vacuum over limited ranges of spacetime can be such that the phase velocity vector casts a negative projection on the time-averaged Poynting vector. This conclusion suggests, inter alia, gravitationally assisted negative refraction by vacuum.Comment: 6 page

The full set of cnc_n-invariant factorized SS-matrices

We use the method of the tensor product graph to construct rational (Yangian invariant) solutions of the Yang-Baxter equation in fundamental representations of $c_n$ and thence the full set of $c_n$-invariant factorized $S$-matrices. Brief comments are made on their bootstrap structure and on Belavin's scalar Yangian conserved charges.Comment: 10p

On the Bergman-Milton bounds for the homogenization of dielectric composite materials

The Bergman-Milton bounds provide limits on the effective permittivity of a composite material comprising two isotropic dielectric materials. These provide tight bounds for composites arising from many conventional materials. We reconsider the Bergman-Milton bounds in light of the recent emergence of metamaterials, in which unconventional parameter ranges for relative permittivities are encountered. Specifically, it is demonstrated that: (a) for nondissipative materials the bounds may be unlimited if the constituent materials have relative permittivities of opposite signs; (b) for weakly dissipative materials characterized by relative permittivities with real parts of opposite signs, the bounds may be exceedingly large

Diffraction-limited CCD imaging with faint reference stars

By selecting short exposure images taken using a CCD with negligible readout noise we obtained essentially diffraction-limited 810 nm images of faint objects using nearby reference stars brighter than I=16 at a 2.56 m telescope. The FWHM of the isoplanatic patch for the technique is found to be 50 arcseconds, providing ~20% sky coverage around suitable reference stars.Comment: 4 page letter accepted for publication in Astronomy and Astrophysic

Local control of Hamiltonian chaos

We review a method of control for Hamiltonian systems which is able to create smooth invariant tori. This method of control is based on an apt modification of the perturbation which is small and localized in phase space

The Influence of Drying Conditions and Other Factors on Twist and Torque in Pinus Radiata Studs

Pinus radiata studs of cross section 4 X 1 1/2 inch, sawn to enclose the pith, were dried in conditions of high and low temperatures, high and low air velocities, with and without presteaming, and with and without mechanical restraint. The resultant twist and torque values were measured and it was found that torque developed during drying was negatively correlated with drying rate. The results are interpreted in terms of the elastic-plastic properties of wood during drying. Torque values were used to calculate the equivalent loads required to restrain packs of this timber from twisting during drying and these compared well with optimum loads derived empirically in commercial trials

Properties of Northern Aspen Discolored Wood Related to Drying Problems

Discolored wood isolated from the inner sapwood area of trembling aspen and balsam poplar shrinks more and is weaker in compression perpendicular-to-the-grain, than adjacent normal sapwood. When the green moisture content is higher than that of adjacent normal wood, then the drying rate (E-value) is slower. Excessive shrinkage and wet pockets may be anticipated during kiln-drying; therefore drying practices must be adapted to allow for these difficulties

Inhibition of intra-Golgi transport in mitotic extracts

Many stages of vesicle-mediated exocytic and endocytic membrane traffic are inhibited in mitotic mammalian cells. The fact that transport between the ER and the Golgi is inhibited in mitosis made it technically very difficult to monitor mitotic intra-Golgi protein transport in vivo. Therefore, a cell-free assay was supplemented with heterologous cytosols to study transport inhibition in vitro. A high-speed supernatant ('cytosol') with high histone kinase activity was prepared from mitotic cells and markedly inhibited intra-Golgi transport. The inhibition was mimicked by treatment of interphase cytosol with the p34cdc-2-associated protein cyclin A, and was reversed by the kinase inhibitor staurosporine, strongly linking a mitotic kinase-phosphatase cycle with control of the assay. The histone kinase activity of the S-phase kinase p33cdc-2 did not promote transport inhibition, and destruction of p34cdc-2 a temperature sensitive cell line prevented the cyclin effect. These results supported the hypothesis that the mitotic kinase p34cdc-2 was responsible for transport inhibition, though probably not directly. Pharmacological and biochemical experiments suggested that the fusion of transport vesicles with their target was the site of the inhibition. The proteins involved are not known at present. These data support a model which links inhibition of vesicle fusion with the observed vesiculation of the Golgi during mitosis