Low-Frequency Cutoffs for the Dispersion Spectrum of Elastic Waves in a Thin-Walled Anisotropic Cylinder

A thin-walled cylinder of unrestricted anisotropy is considered. Low-frequency cutoffs corresponding to bending and extension-shear motions of the cylinder mid-surface are investigated. Their explicit approximations are found by two different methods: truncating the Peano series in the exact dispersion relation and using the Kirchhoff-Love theory of shells adapted to a generally anisotropic cylinder.     

On the Transparency of Alkali-Halide Crystal in the Terahertz Spectral Range

Optics and Spectroscopy - The transmission of THz (to 3000 μm) radiation by alkali halide single crystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr), and...     

A new class of electroluminescent metal complexes based on quinoline ligands containing the sulfanylamino group

The synthesis and properties of a new class of electroluminescent metal complexes based on quinoline ligands containing the sulfanylamino group in position 8 are described. These complexes contain C-N-M-N chains in the chelate cycles instead of the traditionally used C-O-M-N chains.     

Low-angle boundaries in germanium

Possible mechanisms of formation of dislocation defects—low-angle boundaries—in germanium single crystals used in optics are considered.     

Edge vibration of a pre-stressed semi-infinite strip with traction-free edge and mixed face boundary conditions

Edge-vibration, and associated resonance phenomena, is investigated in respect of a semi-infinite strip composed of pre-stressed incompressible elastic material. The strip is assumed to have a traction free outer edge, with the upper and lower edges subject to some simple mixed boundary conditions. The frequency of the modes of free edge-vibration are shown to depend on the surface wave speed. Moreover, when the normal pre-stress approaches one of two critical values, associated with the vanishing of the surface wave speed, the edge spectrum density of the boundary value problem increases significantly. This problem then provides an example for which the famous Weyls hypothesis, stating the edge spectrum is secondary in comparison with the whole bodys spectrum, is not true. However, the corresponding theorems statement is valid only with imposition of the Shapiro-Lopatinsky condition, which is not satisfied in this case. Variation of the pre-stress is also shown to greatly influence the resonance frequency arising in the forced vibration problem, to the extent that the phenomenon of resonance may be totally removed.     

A Refined Asymptotic Model of Fluid-Structure Interaction in Scattering by Elastic Shells

A refined asymptotic model of fluid-structure interaction in scattering by elastic shells is proposed. The model takes into consideration transverse compression of a shell by a fluid and some other phenomena. As an illustration, scattering of a plane acoustic wave by a circular cylindrical shell is considered. Comparison of numerical data corresponding various approximate approaches is provided. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of the dislocation structure in paratellurite single crystals using the piezo-optic effect

It is shown theoretically and experimentally that dislocations in paratellurite single crystals can be revealed using the piezo-optic effect. The mechanical-stress distribution near dislocations is calculated. Dislocations in the samples are observed using the photoelastic method and chemical etching. Data on the spatial distribution of dislocations in Czochralski-grown paratellurite crystals are reported.     

High frequency homogenization for structural mechanics

We consider a net created from elastic strings as a model structure to investigate the propagation of waves through semi-discrete media. We are particularly interested in the development of continuum models, valid at high frequencies, when the wavelength and each cell of the net are of similar order. Net structures are chosen as these form a general two-dimensional example, encapsulating the essential physics involved in the two-dimensional excitation of a lattice structure whilst retaining the simplicity of dealing with elastic strings.Homogenization techniques are developed here for wavelengths commensurate with the cellular scale. Unlike previous theories, these techniques are not limited to low frequency or static regimes, and lead to effective continuum equations valid on a macroscale with the details of the cellular structure encapsulated only through integrated quantities. The asymptotic procedure is based upon a two-scale approach and the physical observation that there are frequencies that give standing waves, periodic with the period or double-period of the cell. A specific example of a net created by a lattice of elastic strings is constructed, the theory is general and not reliant upon the net being infinite, none the less the infinite net is a useful special case for which Bloch theory can be applied. This special case is explored in detail allowing for verification of the theory, and highlights the importance of degenerate cases; the specific example of a square net is treated in detail. An additional illustration of the versatility of the method is the response to point forcing which provides a stringent test of the homogenized equations; an exact Green's function for the net is deduced and compared to the asymptotics.     

Formation of Germanium–Vacancy Color Centers in CVD Diamond

We study Ge-doped polycrystalline diamond films synthesized, using microwave plasma chemical vapor deposition (CVD) in CH₄-H₂ base mixtures. We compare two sources of the dopant – gaseous monogermane (GeH₄) and solid Ge plates. We investigate the structure and phase composition of the obtained films, using scanning electron microscopy, photoluminescence (PL), and Raman spectroscopy. We vary the precursor gas composition to maximize the intensity of the Germanium–vacancy (Ge-V) PL signal at 602 nm and discover that, using [C]-rich gas mixtures ([CH₄]=20%), we are able to increase the intensity of Ge-V signal by two orders of magnitude in comparison with Ge-doped high-quality microcrystalline films of the same thickness but grown at [CH₄]=4%. The attained results may be used for the fabrication of polycrystalline diamond films and plates with high concentrations of Ge-V centers, which may serve as source material for the fabrication of submicrometer-sized luminescent diamond particles for local optical thermometry.

     

Selective reduction of fullerene C60 by metals in neutral and alkaline media. Interaction of C60 with KOH

The reduction of fullerene C₆₀ by Zn and Mg in DMF was studied both in the presence and absence of KOH. Fullerene C₆₀ was reduced in these systems to form the C₆₀ ^n– (n = 1, 2, and 3) anions. The anions were detected by optical and ESR spectroscopies. It was found that Mg reduced C₆₀ to the monoanion, Mg/KOH and Zn reduced C₆₀ to the dianion, and Zn/KOH reduced C₆₀ to the trianion. Like KCN, potassium hydroxide adds to fullerene upon interaction with C₆₀ in DMF. The reaction of C₆₀ with KOH in benzonitrile was accompanied by the generation of the fullerene monoanion. A possible mechanism of the formation of fullerene monoanions in the presence of KOH is discussed. The degradation of the C₆₀ ^n– anions in air was studied.