532 research outputs found
Instability of the shock wave/ sonic surface interaction
The work addresses 2D and 3D turbulent transonic flows past a wall with an
expansion corner. A curved shock wave is formed upstream of a cylinder located
above the corner. Numerical solutions of the Reynolds-averaged Navier-Stokes
equations are obtained on fine meshes with a finite-volume solver of the second
order accuracy. The solutions demonstrate the existence of adverse free-stream
Mach numbers which admit abrupt changes of the shock position at small
perturbations. This is explained by an instability of the closely spaced sonic
surface and shock wave on the wall
Bound states and resonances in the scalar sector of the MSSM
The trilinear couplings of squarks and sleptons to the Higgs bosons can give
rise to a spectrum of bound states with exotic quantum numbers, for example,
those of a leptoquark.Comment: 8 pages, 2 eps figures, latex, epsf; published version (minor changes
in wording and referencing
Архитектура, градостроительство, строительство – вызовы современности
The article gives a comprehensive review of the three contemporary town-planning problems: the formation of the settlement framework in the Russian Federation; the cohesion of all parts of the territory of the RF; organization of the living environment. The present-day situation in town planning is analyzed. The author is concerned about this situation and proposes the reasoned strategies for its solution.В статье всесторонне рассматриваются три основных проблемы современного градостроительства: формирование каркаса расселения Российской Федерации; связанность всех частей территории нашей страны; организация жилой среды. Проводится аналитика современной ситуации в градостроительстве и планировании. Автор высказывает тревогу сложившейся ситуацией и предлагает обоснованные стратегии для ее решения
Validation of moment tensor potentials for fcc and bcc metals using EXAFS spectra
Machine-learning potentials for materials, namely the moment tensor
potentials (MTPs), were validated using experimental EXAFS spectra for the
first time. The MTPs for four metals (bcc W and Mo, fcc Cu and Ni) were
obtained by the active learning algorithm of fitting to the results of the
calculations using density functional theory (DFT). The MTP accuracy was
assessed by comparing metal K-edge EXAFS spectra obtained experimentally and
computed from the results of molecular dynamics (MD) simulations. The
sensitivity of the method to various aspects of the MD and DFT models was
demonstrated using Ni as an example. Good agreement was found for W, Mo and Cu
using the recommended PAW pseudopotentials, whereas a more accurate
pseudopotential with 18 valence electrons was required for Ni to achieve a
similar agreement. The use of EXAFS spectra allows one to estimate the MTP
ability in reproducing both average and dynamic atomic structures
EVALUATION OF THE MINIMUM VELOCITY OF POLYDISPERSE BED FLUIDIZATION COMPOUNDED OF BIOMASS PELLETS AND THEIR MIXTURES WITH FINE PARTICLES OF COAL
It turned out that the change graphs of the absolute value of dimensionless amplitude of pressure fluctuations against air velocity can be used to evaluate values of the minimum fluidization velocity of polydisperse bed biomass pellets. An experimental verification is reported on the early predicting index of agglomeration in bubbling fluidized bed of biomass pellets and fine coal particles
A Frequency Selective Surface based focal plane receiver for the OLIMPO balloon-borne telescope
We describe here a focal plane array of Cold-Electron Bolometer (CEB)
detectors integrated in a Frequency Selective Surface (FSS) for the 350 GHz
detection band of the OLIMPO balloon-borne telescope. In our architecture, the
two terminal CEB has been integrated in the periodic unit cell of the FSS
structure and is impedance matched to the embedding impedance seen by it and
provides a resonant interaction with the incident sub-mm radiation. The
detector array has been designed to operate in background noise limited
condition for incident powers of 20 pW to 80 pW, making it possible to use the
same pixel in both photometric and spectrometric configurations. We present
high frequency and dc simulations of our system, together with fabrication
details. The frequency response of the FSS array, optical response measurements
with hot/cold load in front of optical window and with variable temperature
black body source inside cryostat are presented. A comparison of the optical
response to the CEB model and estimations of Noise Equivalent power (NEP) is
also presented
Interactions of ultrahigh-energy cosmic rays with photons in the galactic center
Ultrahigh-energy cosmic rays passing through the central region of the Galaxy
interact with starlight and the infrared photons. Both nuclei and protons
generate secondary fluxes of photons and neutrinos on their passage through the
central region. We compute the fluxes of these secondary particles, the
observations of which can be used to improve one's understanding of origin and
composition of ultrahigh-energy comic rays, especially if the violation of the
Greisen--Zatespin--Kuzmin cutoff is confirmed by the future data.Comment: 8 pages, 2 figure
A distributed terahertz metasurface with cold-electron bolometers for cosmology missions
We developed and tested a 2D periodic array of cold-electron bolometers arranged into a wideband frequency selective metasurface that absorbs more than 70% of the incident power in the frequency range 100–800 GHz. The array had 10
7 10 unit cells, each containing four bolometers incorporated into a ring. The chip with bolometers was mounted on the back side of the silicon lens without a back-reflector. Preliminary experiments demonstrated voltage responsivity as high as 10 V/W for the current-biased series array. Simulation of the noise performance shows realization of background noise-limited performance with NEP < NEP for the optical power load P > 15 pW. Results of numerical simulation made for the unit cell of the array are presented together with the equivalent diagram based on lumped network elements. The unit cell also was developed numerically to operate in two radiation modes
A flux-corrected RBF-FD method for convection dominated problems in domains and on manifolds
In this article we introduce a FCT stabilized Radial Basis Function (RBF)-Finite Difference (FD) method for the numerical solution of convection dominated problems. The proposed algorithm is designed to maintain mass conservation and to guarantee positivity of the solution for an almost random placement of scattered data nodes. The method can be applicable both for problems defined in a domain or if equipped with level set techniques, on a stationary manifold. We demonstrate the numerical behavior of the method by performing numerical tests for the solid-body rotation benchmark in a unit square and for a transport problem along a curve implicitly prescribed by a level set function. Extension of the proposed method to higher dimensions is straightforward and easily realizable
Fabrication of the Ni[3]Al-based alloy formed by spark plasma sintering of VKNA powders
The material based on Ni[3]Al intermetallic has been obtained from the industrial powder of a VKNA type by the method of spark plasma sintering. Materials sintering was conducted at the temperature of 1100 °С, compacting pressure of 20 MPa, and during soaking time equal to 5 minutes. The heating rate of samples amounted to 50 and 200 °С/min. It has been established that the material obtained by sintering at the rate of 50 °С/min possesses a maximum value of density (5.93 g/cm{3}) and a maximum level of bending strength (~ 400 MPa)
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