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Search Results: 1 - 10 of 198140 matches for " N. Abrosimov "
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Mathematical modelling deflected mode of flexible shells anchored along the contour
V. N. Filatov,A. A. Abrosimov
Magazine of Civil Engineering , 2011,
Abstract: Thin walled cold-formed steel structures became popular solution for low-rise buildings, mansards, walling of multistorey buildings. The modeling of perforated thin-walled cold-formed profile is rather difficult, especially for profiles with irregular shape apertures used in racking systems.The main aim of this work is creating the methods of finite element modeling such profiles.The result of work is a method of construction of profile with given section, aperture formation and construction of final calculation model. The software package SCAD Soft was used for modeling.
The infimum of the volumes of convex polytopes of any given facet areas is 0
N. V. Abrosimov,E. Makai, Jr.,A. D. Mednykh,Yu. G. Nikonorov,G. Rote
Mathematics , 2013, DOI: 10.1556/SSc.Math.2014.1292
Abstract: We prove the theorem mentioned in the title, for ${\mathbb{R}}^n$, where $n \ge 3$. The case of the simplex was known previously. Also, the case $n=2$ was settled, but there the infimum was some well-defined function of the side lengths. We also consider the cases of spherical and hyperbolic $n$-spaces. There we give some necessary conditions for the existence of a convex polytope with given facet areas, and some partial results about sufficient conditions for the existence of (convex) tetrahedra.
Electron spin coherence and electron nuclear double resonance of Bi donors in natural Si
Richard E. George,Wayne Witzel,H. Riemann,N. V. Abrosimov,N. Notzel,Mike L. W. Thewalt,John J. L. Morton
Physics , 2010, DOI: 10.1103/PhysRevLett.105.067601
Abstract: Donors in silicon hold considerable promise for emerging quantum technologies, due to the their uniquely long electron spin coherence times. Bi donors in silicon differ from P and other Group V donors in several significant respects: they have the strongest binding energy (70.98 meV), a large nuclear spin (I = 9/2) and strong hyperfine coupling constant (A = 1475.4 MHz). These larger energy scales allow a detailed test of theoretical models describing the spectral diffusion mechanism that is known to govern the electron spin coherence time (T2e) of P-donors in natural silicon. We report the electron nuclear double resonance spectra of the Bi donor, across the range 200 MHz to 1.4 GHz, and confirm that coherence transfer is possible between electron and nuclear spin degrees of freedom at these higher frequencies.
Hyperfine structure and nuclear hyperpolarization observed in the bound exciton luminescence of Bi donors in natural Si
T. Sekiguchi,M. Steger,K. Saeedi,M. L. W. Thewalt,H. Riemann,N. V. Abrosimov,N. Noetzel
Physics , 2009, DOI: 10.1103/PhysRevLett.104.137402
Abstract: As the deepest group V donor in Si, Bi has by far the largest hyperfine interaction, and also a large I=9/2 nuclear spin. At zero field this splits the donor ground state into states having total spin 5 and 4, which are fully resolved in the photoluminescence spectrum of Bi donor bound excitons. Under a magnetic field, the 60 expected allowed transitions cannot be individually resolved, but the effects of the nuclear spin distribution, -9/2 <= I_z <= 9/2, are clearly observed. A strong hyperpolarization of the nuclear spin, with sign opposite to the expected equilibrium polarization, is observed to result from the nonresonant optical excitation. This is very similar to the recently reported optical hyperpolarization of P donors observed by EPR at higher magnetic fields. We introduce a new model to explain this effect, and predict that it may be very fast.
Volumes of polytopes in spaces of constant curvature
Nikolay Abrosimov,Alexander Mednykh
Mathematics , 2013,
Abstract: We overview the volume calculations for polyhedra in Euclidean, spherical and hyperbolic spaces. We prove the Sforza formula for the volume of an arbitrary tetrahedron in $H^3$ and $S^3$. We also present some results, which provide a solution for Seidel problem on the volume of non-Euclidean tetrahedron. Finally, we consider a convex hyperbolic quadrilateral inscribed in a circle, horocycle or one branch of equidistant curve. This is a natural hyperbolic analog of the cyclic quadrilateral in the Euclidean plane. We find a few versions of the Brahmagupta formula for the area of such quadrilateral. We also present a formula for the area of a hyperbolic trapezoid.
On the Macroscopic Limit of Nuclear Dissipation
Valery I. Abrosimov,Helmut Hofmann
Physics , 1994, DOI: 10.1016/0375-9474(94)90982-2
Abstract: The Landau-Vlasov equation is applied to a slab of width $L$. This geometry is introduced to simulate somehow the finiteness of real nuclei but to allow for analytical solutions, nevertheless. We focus on the damping of low frequency surface modes and discuss their friction coefficient. For this quantity we study the macroscopic limit as defined by $L\to \infty$. We demonstrate that the same result can be obtained for finite $L$ by applying an appropriate frequency smoothing, if only the smearing interval is sufficiently large. The apparent, but important consequences are discussed which this result will have for the understanding of the nature of dissipation in real nuclei.
Soft gamma-ray optics: new Laue lens design and performance estimates
N. Barriere,L. Natalucci,N. Abrosimov,P. von Ballmoos,P. Bastie,P. Courtois,M. Jentschel,J. Knodlseder,J. Rousselle,P. Ubertini
Physics , 2009, DOI: 10.1117/12.826138
Abstract: Laue lenses are an emerging technology based on diffraction in crystals that allows the concentration of soft gamma rays. This kind of optics that works in the 100 keV - 1.5 MeV band can be used to realize an high-sensitivity and high-angular resolution telescope (in a narrow field of view). This paper reviews the recent progresses that have been done in the development of efficient crystals, in the design study and in the modelisation of the answer of Laue lenses. Through the example of a new concept of 20 m focal length lens focusing in the 100 keV - 600 keV band, the performance of a telescope based on a Laue lens is presented. This lens uses the most efficient mosaic crystals in each sub-energy range in order to yield the maximum reflectivity. Imaging capabilities are investigated and shows promising results.
Optically detected NMR of optically hyperpolarized 31P neutral donors in 28Si
M. Steger,T. Sekiguchi,A. Yang,K. Saeedi,M. E. Hayden,M. L. W. Thewalt,K. M. Itoh,H. Riemann,N. V. Abrosimov,P. Becker,H. -J. Pohl
Physics , 2010, DOI: 10.1063/1.3577614
Abstract: The electron and nuclear spins of the shallow donor 31P are promising qubit candidates invoked in many proposed Si-based quantum computing schemes. We have recently shown that the near-elimination of inhomogeneous broadening in highly isotopically enriched 28Si enables an optical readout of both the donor electron and nuclear spins by resolving the donor hyperfine splitting in the near-gap donor bound exciton transitions. We have also shown that pumping these same transitions can very quickly produce large electron and nuclear hyperpolarizations at low magnetic fields, where the equilibrium electron and nuclear polarizations are very small. Here we show preliminary results of the measurement of 31P neutral donor NMR parameters using this optical nuclear hyperpolarization mechanism for preparation of the 31P nuclear spin system, followed by optical readout of the resulting nuclear spin population after manipulation with NMR pulse sequences. This allows for the observation of single-shot NMR signals with very high signal to noise ratio under conditions where conventional NMR is not possible, due to the low concentration of 31P and the small equilibrium polarization.
Simultaneous sub-second hyperpolarization of the nuclear and electron spins of phosphorus in silicon
A. Yang,M. Steger,T. Sekiguchi,M. L. W. Thewalt,T. D. Ladd,K. M. Itoh,H. Riemann,N. V. Abrosimov,P. Becker,H. -J. Pohl
Physics , 2009, DOI: 10.1103/PhysRevLett.102.257401
Abstract: We demonstrate a method which can hyperpolarize both the electron and nuclear spins of 31P donors in Si at low field, where both would be essentially unpolarized in equilibrium. It is based on the selective ionization of donors in a specific hyperfine state by optically pumping donor bound exciton hyperfine transitions, which can be spectrally resolved in 28Si. Electron and nuclear polarizations of 90% and 76%, respectively, are obtained in less than a second, providing an initialization mechanism for qubits based on these spins, and enabling further ESR and NMR studies on dilute 31P in 28Si.
The Relationship of Synthesis Intensity, Accumulation and Secretion of Natriuretic Peptide of Atrial Myocytes with Cardiac Rhythm Regulation in Rats in Early Postperfusion Period
М.L. Bugrova,Е.I. Yakovleva,D.А. Abrosimov
Sovremennye Tehnologii v Medicine , 2012,
Abstract: The aim of the investigation is to assess the relationship of the intensity of synthesis processes, accumulation and secretion of atrial natriuretic peptide (ANP) of atrial myocytes with cardiac rhythm regulation in rats in early postperfusion period. Materials and methods. The experiments were carried out on 25 white nonlinear male rats of 200–250 g. Total ischemia (10 min) was simulated by the compression of cardiovascular bunch according to V.G. Korpachev technique. The cardiac regulation level in post-perfusion period was determined by the cardiac rhythm variability indices. The intensity of synthesis processes, accumulation and secretion of ANP was estimated using morphometric analysis of immunoreactive labelled granules of atrial myocytes. Conclusion. Short-term increase of arterial pressure and the activation of sympathoadrenal, pituitary-adrenal and rennin-angiotensin systems have no effect on ANP synthesis and secretion in right atrial myocytes in the first moments of postperfusion period. On the 60th minute of cardiac functioning on intracardial level, there was found high intensity of synthesis processes, accumulation and secretion of ANP in atrial myocytes due to stimulating effect of hypoxic and ischemic factors in this period.
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