arXiv subjects

A. Ustinov

Publications and source records attributed to A. Ustinov.

6 recordsLinked to original sources

arXiv2022

Feynman checkers: towards algorithmic quantum theory

We survey and develop the most elementary model of electron motion introduced by R$.$Feynman. In this game, a checker moves on a checkerboard by simple rules, and we count the turns. Feynman checkers are also known as a one-dimensional quantum walk or an Ising model at imaginary temperature. We solve mathematically a problem by R$.$Feynman from 1965, which was to prove that the discrete model (for large time, small average velocity, and small lattice step) is consistent with the continuum one. We study asymptotic properties of the model (for small lattice step and large time) improving the results by J$.$Narlikar from 1972 and by T$.$Sunada-T$.$Tate from 2012. For the first time we observe and prove concentration of measure in the small-lattice-step limit. We perform the second quantization of the model.

math-ph↗

arXiv2019

National Report to the International Association of Geodesy of the International Union of Geodesy and Geophysics 2015-2019

In this National Report are given major results of researches conducted by Russian geodesists in 2015-2018 on the topics of the International Association of Geodesy (IAG) of the International Union of Geodesy and Geophysics (IUGG). This report is prepared by the Section of Geodesy of the National Geophysical Committee of Russia. In the report prepared for the XXVII General Assembly of IUGG (Canada, Montreal, 8-18 July 2019), the results of principal researches in geodesy, geodynamics, gravimetry, in the studies of geodetic reference frame creation and development, Earth's shape and gravity field, Earth's rotation, geodetic theory, its application and some other directions are briefly described. For some objective reasons not all results obtained by Russian scientists on the problems of geodesy are included in the report.

physics.geo-ph↗

arXiv2018

Investigation of the thermal and hydraulic properties of a novel heat exchanger for smart heat supply systems

In this study, analysis of shell and tube heat exchanger (HE) is performed. Theory part on heat transfer, calculation of heat exchanger and general thermal and hydrological properties are described. Several models are developed and computed in different cases: plain tubes and twisted tubes; common and separated inlet and outlet; heat exchanger with different baffles and geometry inside a shell; changed gas matter, tube's material, tube's thickness; modification of inlet and outlet. Twisted tubes shows better heat transfer efficiency than plain tubes. Baffles increase intensity of water mixing but dead zones can be formed in some cases. Length of air inlet and outlet influence on temperature distribution that is important for location of measuring systems. Experimental setup for a gas-liquid case is being created to verify the modelling and test new heat exchanger.

physics.flu-dyn↗

arXiv2015

National Report for the International Association of Geodesy of the International Union of Geodesy and Geophysics 2011-2014

In this National Report are given major results of researches conducted by Russian geodesists in 2011-2014 on the topics of the International Association of Geodesy (IAG) of the International Union of Geodesy and Geophysics (IUGG). This report is prepared by the Section of Geodesy of the National Geophysical Committee of Russia. In the report prepared for the XXVI General Assembly of IUGG (Czhech Republic, Prague, 22 June - 2 July 2015), the results of principal researches in geodesy, geodynamics, gravimetry, in the studies of geodetic reference frame creation and development, Earth's shape and gravity field, Earth's rotation, geodetic theory, its application and some other directions are briefly described. For some objective reasons not all results obtained by Russian scientists on the problems of geodesy are included in the report.

physics.geo-ph↗

arXiv2014

Wide-Range Bolometer with RF Readout TES

To improve both scalability and noise-filtering capability of a Transition-Edge Sensor (TES), a new concept of a thin-film detector is suggested, which is based on embedding a microbridge TES into a high-Q planar GHz range resonator weakly coupled to a 50 Ohm-readout transmission line. Such a TES element is designed as a hot-electron microbolometer coupled to a THz range antenna and as a load of the resonator at the same time. A weak THz signal coupled to the antenna heats the microbridge TES, thus reducing the quality factor of the resonator and leading to a power increment in the readout line. The power-to-power conversion gain, an essential figure of merit, is estimated to be above 10. To demonstrate the basic concept, we fabricated and tested a few submicron sized devices from Nb thin films for operation temperature about 5 K. The dc and rf characterization of the new device is made at a resonator frequency about 5.8 GHz. A low-noise HEMT amplifier is used in our TES experiments without the need for a SQUID readout. The optical sensitivity to blackbody radiation within the frequency band 600-700 GHz is measured as $\sim3\times 10^{-14} \textrm W/\sqrt{\textrm Hz}$ at Tc {\approx} 5 K at bath temperature ~ 1.5 K.

physics.ins-det↗

arXiv2008

Limiting Distribution of Frobenius Numbers for $n=3$

The purpose of this paper is to give a complete derivation of the limiting distribution of large Frobenius numbers outlined in earlier work of J. Bourgain and Ya. Sinai and fill some gaps formulated there as hypotheses.

math.NT↗