Additive coloration of crystals of calcium and cadmium fluorides

The particular features of additive coloration—formation of color centers as a result of annealing in a reducing atmosphere—have been considered for two crystals with fluorite structure, calcium and cadmium fluorides. The significant differences in the processes of coloration of these crystals are related to both the chemical reactions on their surface and the interaction (or absence of such) between the two components diffusing into the crystal bulk: anion vacancies and electrons.     

Exact solutions for network rewiring models

Evolving networks with a constant number of edges may be modelled using a rewiring process. These models are used to describe many real-world processes including the evolution of cultural artifacts such as family names, the evolution of gene variations, and the popularity of strategies in simple econophysics models such as the minority game. The model is closely related to Urn models used for glasses, quantum gravity and wealth distributions. The full mean field equation for the degree distribution is found and its exact solution and generating solution are given.     

90 W average power 100 microJ energy femtosecond fiber chirped-pulse amplification system

We report on an ytterbium-doped fiber based chirped-pulse amplification system delivering 100 microJ pulse energy at a repetition rate of 900 kHz, corresponding to an average power of 90 W. The emitted pulses are as short as 500 fs. To the best of our knowledge, this is the highest average power ever reported for high-energy femtosecond solid-state laser systems.     

Pressure-Sensitive Paint measurement of the flow around a simplified car model

In applying Pressure-Sensitive Paint (PSP) to low-speed flow wind tunnel testing, it is important to minimize any measurement uncertainties. There are various error sources such as camera noise, misalignment of images due to model displacement and temperature distribution over the model. Among these factors, the effects of temperature distribution change during tests on pressure measurement accuracies were studied in the present paper. Pressure and temperature distributions over a simplified car model (1/10 scale Ahmed model) were measured using PSP and Temperature-Sensitive Paint (TSP). Sequential images were acquired at the same intervals over the entire test period, including for the conditions before and after the tunnel run. As a result, it was found that the measurement error caused by temperature distribution over the model could be reduced using a single-point temperature measurement. In addition, by measuring surface temperature distributions on the model using TSP, it was proved that the most accurate pressure measurement could be made by rationing the wind-off image acquired immediately after shutting down the tunnel to the wind-on image acquired immediately before shutting down the tunnel. Using the present measurement technique, complicated pressure fields over the Ahmed model were successfully visualized.     

Features of the electronic spectrum and optical absorption of ultrathin Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> films

The electronic spectra and relative permittivity of ultrathin (1–3 QL) films of Bi₂Se₃ topological insulator have been calculated by the density functional theory. The calculated spectra exhibit a characteristic feature: the range of 0.0–0.9 eV below the Fermi level contains two doubly degenerate valence bands (“U-bands”), which are geometrically congruent to low-lying spectral branches in the conduction band. It has been shown that the saturation of optical absorption can result in a significant rearrangement of the electronic structure and properties in the near infrared spectral range in the considered film. In particular, the semiconductor (in the absence of interaction with light) type of conductivity of the film can be changed to the metallic type of conductivity strongly nonlinear in the intensity of light.     

Application of Crystal Elements for Charged Particle Beam Steering and Radiation Beam Generation on the U-70 Synchrotron

Dependences of the tunnel magnetoresistance and in-plane component of the spin transfer torque on the applied voltage in a magnetic tunnel junction have been calculated in the approximation of ballistic transport of conduction electrons through an insulating layer with embedded magnetic or nonmagnetic nanoparticles. A single-barrier magnetic tunnel junction with a nanoparticle embedded in an insulator forms a double-barrier magnetic tunnel junction. It has been shown that the in-plane component of the spin transfer torque in the double-barrier magnetic tunnel junction can be higher than that in the single-barrier one at the same thickness of the insulating layer. The calculations show that nanoparticles embedded in the tunnel junction increase the probability of tunneling of electrons, create resonance conditions, and ensure the quantization of the conductance in contrast to the tunnel junction without nanoparticles. The calculated dependences of the tunnel magnetoresistance correspond to experimental data demonstrating peak anomalies and suppression of the maximum magnetoresistances at low voltages.     

An assessment of the high frequency boundary element and Rayleigh integral approximations

This paper revisits the popular Rayleigh integral approximation and also considers a second approximation, the high frequency boundary element method, which is similar to the Rayleigh integral. The Rayleigh integral approximation under consideration is enhanced so that only the elements visible to a particular point in the field are used to calculate the sound pressure at that point. It is demonstrated how both the Rayleigh integral and high frequency boundary element method are approximations to the boundary integral equation so that similarities between the two methods are recognized. Several test cases were conducted in order to assess and compare both methods. The first set of test cases was the pulsating and oscillating sphere. Both methods were then compared on more applied examples including a running engine, construction cab, and transmission housing. It was concluded that though both methods can reliably predict the sound power for some problems, the high frequency boundary element method is the more robust.     

Long Pulse Operation of the THz Gyrotron with a Pulse Magnet

Long pulse operation up to 1 msec of a high frequency gyrotron with a pulse magnet has been successfully carried out in a frequency range including 1 THz. In the experiments, the timing of an electron beam pulse injection is adjusted at the top of the magnetic field pulse, where the variation of field intensity is negligible. The operation cavity modes seem to be TE_{1, 12} and TE_4,12 at the second harmonics. The corresponding frequencies are 903 GHz and 1,013 GHz, respectively. Additionally several features of radiation measurement results of the gyrotron are described and brief considerations are presented.     

Coaxial ZnO/SiO<Subscript>2</Subscript> nanocables fabricated by thermal evaporation/oxidation

ZnO/SiO₂ coaxial nanocables have been synthesized on silicon substrates by simply evaporating zinc powder under an argon and argon/oxygen mixed atmosphere sequentially. The diameters of these nanocables vary from 50 to 100 nm and the lengths up to several millimeters. Electron microscopy and chemical composition investigations reveal that the nanocable consists of a crystalline ZnO core surrounded by an amorphous silica sheath. The electron diffraction pattern proves that the long-axis direction of ZnO cores grows along the [0001] direction. Silica nanotubes with wall structures have been obtained by the selective dissolution of the cores with hydrochloric acid. PACS 81.10.Bk; 81.05.Hd