11,709 research outputs found
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 -invariant factorized -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 and thence the full set of -invariant factorized -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
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