Nanostructure Formation in Superior Quality Rails

Using transmission electron microscopy methods the layer by layer analysis of the bulk hardened superior quality rails is carried out and the quantitative parameters of structure, phase state and defect substructure gradients are established. The gradient character of changing of structure-phase states and dislocation substructure along the cross section of rail head is revealed. The oil bulk hardening of superior quality rails is accompanied by the formation of morphologically different structure, being produced according to the shear and diffusion of γ-α transformation. The base structure volume is formed by the diffusion mechanism and is consisted of plate pearlite grains, free ferrite grains and grains of ferrite-carbide mixture. The presence of the bend extinction contours testifying to curvature-torsion of crystal lattice is revealed on electron microscope images. The analysis of far acting internal field stresses created by interfaces of cementite plates of pearlite grains and interfaces of pearlite and ferrite grains is carried out. It is shown that the interface boundaries globular cementite particles-matrix are the possible places of microcracks initiation

Nanostructure Formation in Superior Quality Rails

Using transmission electron microscopy methods the layer by layer analysis of the bulk hardened superior quality rails is carried out and the quantitative parameters of structure, phase state and defect substructure gradients are established. The gradient character of changing of structure-phase states and dislocation substructure along the cross section of rail head is revealed. The oil bulk hardening of superior quality rails is accompanied by the formation of morphologically different structure, being produced according to the shear and diffusion of γ-α transformation. The base structure volume is formed by the diffusion mechanism and is consisted of plate pearlite grains, free ferrite grains and grains of ferrite-carbide mixture. The presence of the bend extinction contours testifying to curvature-torsion of crystal lattice is revealed on electron microscope images. The analysis of far acting internal field stresses created by interfaces of cementite plates of pearlite grains and interfaces of pearlite and ferrite grains is carried out. It is shown that the interface boundaries globular cementite particles-matrix are the possible places of microcracks initiation

Project of deuteron accelerator based neutron source for rib production

The project of a high-intense neutron source for the SPES project in LNL, Legnaro, Italy [1] is developed. The source is based on the rotating carbon target. The target is bombarded by the deuteron beam with energy 20 MeV, diameter 1 cm, average power 100 kW. The target is cooled by its thermal radiation, and its temperature can reach 1800ºC. It is shown that high density graphite can be used as a material for neutron production. The source can produce up to 10¹⁴ neutrons per second with energy within few MeV - few dozens MeV range, its lifetime is around few thousand hours

Project of a fast neutron target based on a 10 MeV 300 kW proton accelerator

Project of targets for high intense neutron source is proposed. The source is based on a proton continuous accelerator with the 10 MeV particle energy and up to 300 kW mean beam power. Problems of fabrication of these targets are discussed. Hot solid state and liquid target designs are considered. Maximum admissible target parameters are presented. Advantages and disadvantages of various types of target for neutron production are discussed

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017

A millimeter-submillimeter phonon-cooled hot-electron bolometer mixer based on two-dimensional electron gas in an AlGaAs/GaAs heterostructure

Experimental results obtained by studying the main characteristics of a millimeter–submillimeterwave mixer based on the hot-electron effect in a two-dimensional electron gas in a AlGaAs/GaAs heterostructure with a phonon-scattering cooling mechanism for charge carriers are reported. The gain bandwidth of the mixer is 4 GHz, the internal conversion losses are 13 dB, and the optimum local-oscillator power is 0.5 µW (for a mixer area of 1 µm2 ). It is shown that a millimeter–submillimeter-wave receiver with a noise temperature of 1900 K can be developed on the basis of a AlGaAs/GaAs mixer. This mixer also appears to be promising for use in array receiver elements. Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 39, No. 9, 2005, pp. 1117–1121. Original Russian Text Copyright © 2005 by Morozov, K. Smirnov, A. Smirnov, Lyakhov, Goltsman

Frequency bandwidth and conversion loss of a semiconductor heterodyne receiver with phonon cooling of two-dimensional electrons

The temperature and concentration dependences of the frequency bandwidth of terahertz heterodyne AlGaAs/GaAs detectors based on hot electron phenomena with phonon cooling of two-dimensional electrons have been measured by submillimeter spectroscopy with a high time resolution. At a temperature of 4.2 K, the frequency bandwidth at a level of 3 dB (f3 dB) is varied from 150 to 250 MHz with a change in the concentration ns according to the power law f3dB ∝ ns−0.5 due to the dominant contribution of piezoelectric phonon scattering. The minimum conversion loss of the semiconductor heterodyne detector is obtained in structures with a high carrier mobility (μ > 3 × 105 cm2 V−1 s−1 at 4.2 K). Original Russian Text © E.L. Shangina, K.V. Smirnov, D.V. Morozov, V.V. Kovalyuk, G.N. Gol’tsman, A.A. Verevkin, A.I. Toropov, 2010, published in Fizika i Tekhnika Poluprovodnikov, 2010, Vol. 44, No. 11, pp. 1475–1477

Concentration dependence of the intermediate frequency bandwidth of submillimeter heterodyne AlGaAs/GaAs nanostructures

The concentration dependence of the intermediate frequency bandwidth of heterodyne AlGaAs/GaAs detectors with 2D electron gas is measured using submillimeter spectroscopy with high time resolution at T= 4.2 K. The intermediate frequency bandwidth f3dBfalls from 245 to 145 MHz with increasing concentration of 2D electrons n s = (1.6-6.6) × 10[su11] cm-2. The dependence f3dB ≈ n s - 0.04±is observed in the studied concentration range; this dependence is determined by electron scattering by the deformation potential of acoustic phonons and piezoelectric scattering