Elasticity of an Air Cavity in a Magnetic Fluid on an Annular Magnet Segment with Changing Magnetic Field Sign

Russian Physics Journal - The paper discusses the results of experimental research on air cavity capture by magnetic fluid and elasticity of the produced oscillatory system on an annular magnet...     

Structural parameters of synthetic opals: Statistical analysis of electron microscopy images

The paper reports on a comprehensive study of the statistical characteristics of an ensemble of a-SiO₂ particles in synthetic opals. The results of processing of the electron microscopy images obtained in the investigation of the (111) growth layer are presented. To calculate the statistical parameters, an algorithm is developed which permits determination of the diameters of a-SiO₂ particles and coordinates of their centers. The algorithm is based on the pattern recognition procedure of objects with radially symmetric boundaries by means of a transformation of the original image similar to the Hough transformation. Our image processing study yields structural parameters of the (111) growth layer, more specifically, the average particle diameter, ～316 nm, the distribution profile half-width, ～7%, and the average distance between the centers of neighboring particles, ～315 nm. The results of the opal image processing are compared with data of optical experiments.     

Amplification of noise in the quantum theory of parametric processes

A quantum mechanical treatment is given of the acousto-optical parametric amplification processes in dielectric crystals when the signal acoustical and idler light waves are amplified in the presence of intensive optical pumping. The approximate Heisenberg equations of motion are found and solved for the creation and annihilation operators of signal and idler modes with due regard for the interaction of these modes with other light and vibratory modes of the crystal (“the thermostat”). It is shown that the thermostat influence results in noise and attenuation effects. These persistent noises are also amplified. If the pumping is not far above the threshold the persistent noises are more important than the initial ones.     

Intramolekulare Cycloadditionen in der Reihe der Binaphthyle

Intramolecular cyloadditions of binaphtyl compounds Three new bridged ketones, 7,8 and 9 , have been isolated in 44%, 3% and 19% yields respectively (Scheme 2) by heating 2,2′-bis-allyloxy-1,1′-binaphthyl ( 5 ) at 215° for 16 hours. These compounds could be epimerized about C(16) by bases, and in particular 9 yielded the new epimer 10 . The structures of the alcohols obtained by reduction of the keto group are also given (Scheme 2). The constitution of all compounds was derived from spectroscopic data, chiefly from their ¹H-NMR, spectra (tab. 2, 3 and fig. 1). The assignments were based on the observed long-range coupling constant between H(endo)-C(16) and H(endo)-C(5) in 7 and 10 and on the analysis of chemical shifts and coupling constants in both the ketones and their derivatives. Moreover, the structures of the compounds investigated have been proved by x-ray analysis of ketone 8 (chap. 3, fig. 2). The thermal conversion of binaphthylether 5 to the bridged ketones proceeds via an intramolecular Diels-Alder reaction, followed by Claisen rearrangement (Scheme 8). On heating, the bis-beta-methylallyl ether 20 yielded the ketone 21 and a small amount of the ether 23 (Schemes 5 and 7). Ether 23 and binaphthyl monoallyl ether 26 were converted thermally to the bridged ketones 31 (Scheme 7) and 27 (Scheme 6) respectively. In addition, 26 underwent an intramolecular ene-reaction to give the spiroketone 28 (Schemes 6 and 9). The structures of these compounds were also established, mainly by analysis of their ¹H-NMR. spectra.     

Resonant behavior and selective switching of stop bands in three-dimensional photonic crystals with inhomogeneous components

We demonstrate that, in contrast with the well-studied photonic crystals consisting of two homogeneous components, photonic crystals comprised of inhomogeneous or multiple (three or more) components may bring new opportunities to photonics due to the discovered quasiperiodic resonant behavior of their (hkl) stop bands as a function of the reciprocal lattice vector. A resonant stop band cannot be switched off for any permittivity of structural components. Tuning the permittivity or structural parameters allows the selective on-off switching of nonresonant (hkl) stop bands. This independent manipulation of light at different Bragg wavelengths provides a new degree of freedom to design selective optical switches and waveguides. Transmission experiments performed on synthetic opals confirmed the theoretical predictions.     

High‐Capacity Anode Materials for Lithium‐Ion Batteries: Choice of Elements and Structures for Active Particles

Growing market demand for portable energy storage has triggered significant research on high‐capacity lithium‐ion (Li‐ion) battery anodes. Various elements have been utilized in innovative structures to enable these anodes, which can potentially increase the energy density and decrease the cost of Li‐ion batteries. In this review, electrode and material parameters are considered in anode fabrication. The periodic table is then used to explore how the choice of anode material affects rate performance, cycle stability, Li‐ion insertion/extraction potentials, voltage hysteresis, volumetric and specific capacities, and other critical parameters. Silicon (Si), germanium (Ge), and tin (Sn) anodes receive more attention in literature and in this review, but other elements, such as antimony (Sb), lead (Pb), magnesium (Mg), aluminum (Al), gallium (Ga), phosphorus (P), arsenic (As), bismuth (Bi), and zinc (Zn) are also discussed. Among conversion anodes focus is placed on oxides, nitrides, phosphides, and hydrides. Nanostructured carbon (C) receives separate consideration. Issues in high‐ capacity research, such as volume change, insufficient coulombic efficiency, and solid electrolyte interphase (SEI) layer stability are elucidated. Finally, advanced carbon composites utilizing carbon nanotubes (CNT), graphene, and size preserving external shells are discussed, including high mass loading (thick) electrodes and electrodes capable of providing load‐bearing properties.     

Effect of the shape of the blunt leading edges of a delta wing on the distribution of the heat transfer coefficient over its surface

The results of an experimental investigation of the effect on heat transfer of the shape of the blunt leading edges of a delta wing are presented for a Mach number M=5 and angles of attack =10 and 15. The shape of the bluntness is observed to have a strong influence on the heat transfer to the edges and upper surface of the wing.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 180–183, September–October, 1990.     

Thermodynamic characteristics of a nonrelativistic electron in constant parallel electric and magnetic fields

The large statistical sum of a noninteracting nonrelativistic electron gas in constant parallel electric and magnetic fields is calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 64–67, September, 1979.