Equilibrium and metastable states of classical systems

We formulate a characterization of equilibrium and metastable states of classical hard-core continuous systems in terms of certain global and local stability conditions. The equilibrium states are assumed to be those that are both locally and globally stable; the metastable states are assumed to be those that are locally, but not globally, stable, and that possess also a certain restricted global stability. It is found that a certain specified class of systems with appropriately weakly tempered, or long range forces, can support metastable states, possessing bona fide thermodynamic properties, whose pressure functions are real analytic continuations in the chemical potential of those of some equilibrium phases. This result is complementary to that of Lanford and Ruelle, concerning the absence of metastable states of systems with strongly tempered forces.     

A kinetic study of the initial oxidation of the Ni(001) surface by RHEED and x-ray emission

Nickel (001) surfaces were prepared by a combination of high temperature oxidation, argon ion bombardment and hydrogen reduction. The oxidation of this surface in pure C₂ to form NiO was studied by reflection high energy electron diffraction (RHEED) and X-ray emission. On exposure to oxygen the “clean” surface was found to chemisorb oxygen to produce a coverage of 0.014 $\text{micro}\text{g}\text{cm}{}^2$ in an ordered c(2 × 2) structure. Within this film there appears to exist a number of nucleation sites dependent on temperature and step density. Growth is by oxygen capture at the periphery of these sites to produce oxide islands approximately three oxygen planes thick which spread to cover the surface. At room temperature this film does not thicken with additional oxygen exposure.     

Applicability of scalar theory for analysis of mode reflection from an optical dielectric waveguide end

Scalar and vector theories are compared for weakly guided modes reflected from a planar optical dielectric waveguide end or laser facet. By utilizing the free space radiation mode method the range of validity of the scalar theory over a wide range of reflectivities is given explicitly for the first time.     

光子的帽子戏法

两个独立的研究组第一次通过实验展示了真正的三光子干涉。     

Optical waveguides in porous silicon pre-patterned by localised nitrogen implantation.

FIPOS technology forms islands of silicon isolated from a silicon substrate by (oxidised) porous silicon. The larger refractive index of the silicon islands suggests their use as optical waveguides. Sets of these silicon islands have been fabricated and the anticipated waveguiding has been observed at wavelengths of 1.15 and 1.3 μm in the silicon islands. However, the dominant waveguiding in these FIPOS structures is observed in the porous silicon between the silicon islands, close to the sample surface. A simple dynamic model of the anodisation process has been developed to explain the origin of this unexpected waveguiding.     

Modal Analysis of Holey Fibres with Convex and Non-Convex Polygon-Shaped Holes

The plane wave and localized function expansion methods are established for bandgap and modal calculations of holey fibres. The calculations rely on evaluating the Fourier transform coefficients of the dielectric constant profile. In this paper we derive a generalized formula for determining these coefficients for holey fibres with holes of arbitrary polygonal shape. The accuracy of the Fourier representation is studied for different hole shapes rotated at various angles to the lattice. We combine the approach with the localized function method to study the modal properties of some holey fibres, reporting new numerical results on the influence of the hole shape on the modal and group velocity dispersion of microstructured fibres with rhombic holes aligned along radial lines.     

The evolution of toxic gases from heated polymers—III. Isocyanate products

Attempts have been made to measure the amount of toluene di-isocyanate evolved from flexible polyurethane foam heated at temperatures in the range from 200° to 470°. This study involved heating a sample of about 2 g in a stream of air in a furnace followed by titration of the isocyanate fumes trapped in an absorber. Further investigation concerning the identity of the isocyanate species was also made using chromatographic and spectroscopic techniques. Most of the products which are isocyanate-active appear to be oligomeric ureas having isocyanate end groups. The amount of titratable isocyanate varied from 0·7 to 1·6% w/w calculated as toluene di-isocyanate, and the free toluene di-isocyanate is considered not to exceed 0·02–0·04% (w/w).     

Measurement of the ratio of total and differential cross sections on neutrons and protons for charged-current neutrino events

Charged-current neutrino interactions have been analysed in a sample of pictures from BEBC equipped with a TST. Using a method independent of both the neutrino flux and nuclear interaction corrections, the ratio R= σ_n/σ_p has been measured. The result is R=1.98±0.19 for the ratio of total cross sections. Bjorken x distributions for proton and neutron targets and for u and d quarks are compared.