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21.
Shkuratov Y Petrov D Videen G 《Journal of the Optical Society of America. A, Optics, image science, and vision》2003,20(11):2081-2092
Using the scale invariance of classical photometry, we develop an approach to finding the photometric function of prefractal structures that form a random topography. The photometric function of the prefractal surfaces is found as the general solution of the resulting differential equation in partial derivatives. The function depends on two parameters: the number of hierarchical levels of the prefractal structures and the roughness parameter of the single-level generation. As a limiting case, the approach includes our previous theory that considered fractoids. 相似文献
22.
Numerical method for modeling the E-polarized wave scattering by electrically large quasioptical two-dimensional (2-D) reflectors is presented. Reflectors are assumed zero-thickness and perfectly electrically conducting. Efficient numerical solution is obtained from the coupled singular integral equations discretized using new quadrature formulas of interpolation type. It has controlled accuracy and deals with small-size matrices. To simulate a small-horn feeding, the incident field is taken as a beam generated by a complex-source-point (CSP) current. Presented numerical results validate empirical rule of -10 dB edge illumination needed to provide the best electromagnetic performance of reflector 相似文献
23.
Ivan Gavrilyuk Martin Hermann Volodymyr Trotsenko Yuriy Trotsenko Alexander Timokha 《Journal of Engineering Mathematics》2010,68(2):165-178
A spectral boundary problem on axisymmetric eigenoscillations of a cupola-shaped shell is considered with emphasis on small
shell thickness. The problem deals with a singularly perturbed system of ordinary differential equations. The paper examines
analytical properties of the solution and, based on that, constructs an appropriate functional basis for Ritz’ method. Employing
this basis provides fast convergence in the C
3-metrics. 相似文献
24.
Irina V. Ovsienko Lyudmila Yu. Matzuy Nykolai I. Zakharenko Nykolai G. Babich Tetyana A. Len Yuriy I. Prylutskyy David Hui Yuri M. Strzhemechny Peter C. Eklund 《Nanoscale research letters》2008,3(2):60-64
It is shown that magnetometry can be employed as an effective tool to control the content of a ferromagnetic constituent in
nanocarbon materials. We propose a thermochemical treatment protocol to achieve extensive cleaning of the source nanocarbon
materials from ferromagnetic refuses. 相似文献
25.
The possibility of Bose-Einstein condensation of excitations has been discussed for a long time. The phenomenon of the phase-coherent
precession of magnetization in superfluid 3He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different
states of coherent precession has been observed in 3He-B: homogeneously precessing domain (HPD); persistent signal formed by Q-balls at very low temperatures; coherent precession with fractional magnetization; and a mode of the coherent precession
in compressed aerogel. The coherent precession has been also found in 3He-A in compressed aerogel. Here we demonstrate that all these cases are examples of a Bose-Einstein condensation of magnons,
with the magnon interaction term in the Gross-Pitaevskii equation being provided by different types of spin-orbit coupling
in the background of the coherent precession.
相似文献
26.
Evgeny M. Garanin Marta S. Towers Patrick W. Toothaker Kenneth Laali Yuriy V. Tolmachev 《Polymer Bulletin》2010,64(6):595-605
Block-copolymers with highly sulfonated ionomer blocks are considered as leading candidates for low-humidity high-temperature
Polymer Electrolyte Fuel Cell membranes. We present a new approach that allows for faster measurement of conductivity of powdered
ionomers in a wide range of temperature and humidity with a single 10–30 mg sample. Our method is exemplified by a case study
of polyphenylenesufide with a degree of sulfonation 0.70. This material shows 0.12 S/cm conductivity at 127 °C and 50% relative
humidity. At higher temperatures and lower humidities, this polymer undergoes irreversible cross-linking. Further routes to
improving conductivity, chemical and mechanical properties of the polymer are discussed. 相似文献
27.
28.
Eddy Collin Laure Filleau Thierry Fournier Yuriy M. Bunkov Henri Godfrin 《Journal of Low Temperature Physics》2008,150(5-6):739-790
Nowadays microfabrication techniques originating from micro-electro nics enable to create mechanical objects of micron-size.
The field of Micro-Electro-Mechanical devices (MEMs) is continuously expanding, with an amazingly broad range of applications
at room temperature.
Vibrating objects (torsional oscillators, vibrating wires) widely used at low temperatures to study quantum fluids, can be
replaced advantageously by Silicon MEMs. In this letter we report on the study of Silicon vibrating wire devices. A goal-post
structure covered with a metal layer is driven at resonance by the Laplace force acting on a current in a magnetic field,
while the induced voltage arising from the cut magnetic flux allows to detect the motion. The characteristics of the resonance
have been studied from 10 mK to 30 K, in vacuum and in 4He gas. In this article, we focus on the results obtained above 1.5 K, in vacuum and gas, and introduce some features observed
at lower temperatures.
The resonant properties can be quantitatively understood by means of simple models, from the linear regime to a highly non-linear
response at strong drives. We demonstrate that the non-linearity is mostly due to the geometry of the vibrators. We also show
that in our device the friction mechanisms originate in the metallic layers, and can be fully characterized. The interaction
with 4He gas is fit to theory without adjustable parameters.
相似文献
29.
Vladimir D Blank Boris A Kulnitskiy Igor A Perezhogin Yuriy L Alshevskiy Nikita V Kazennov 《Science and Technology of Advanced Materials》2009,10(1)
The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe3C). However, for Hägg carbide nanoparticles (χ-Fe5C2), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber. 相似文献
30.
This paper discusses ongoing research to formulate, develop and test a reliability assessment model (GenRel) based on genetic algorithms (GAs). GAs are powerful and broadly applicable stochastic search techniques based on the principles of natural selection, heredity and genetics. The reason for selecting GAs is the fact that the reliability of mining equipment changes over time due to its dependence upon several covariates/factors (e.g. equipment age, operating environment, number and quality of repairs). These factors combine to create a complex impact on a piece of equipment's reliability function. This impact encapsulates and inherits to some degree the individual characteristics of the factors as they evolve over time. Theoretical probability distributions are commonly used to fit equipment failure data. GenRel uses the exponential probability distribution as its engine to generate predictive patterns based upon historical failure data. Overall, this paper suggests a methodology for applying GAs for reliability assessment of mining equipment. An example is given to demonstrate the effectiveness of using GAs in reliability studies. The research discussed in this paper was carried out by the Laurentian University Mining Automation Laboratory (LUMAL). 相似文献