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Search Results: 1 - 10 of 2558 matches for " Dmitry Bocharov "
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A Low-Power 9-bit Pipelined CMOS ADC with Amplifier and Comparator Sharing Technique
Yuri Bocharov,Vladimir Butuzov,Dmitry Osipov
Computer Science , 2012,
Abstract: This paper describes a pipelined analog-to-digital converter (ADC) employing a power and area efficient architecture. The adjacent stages of a pipeline share operational amplifiers. In order to keep accuracy of the amplifiers in the first stages, they use a partially sharing technique. The feature of the proposed scheme is that it also shares the comparators. The capacitors of the first stages of a pipeline are scaled down along a pipeline for a further reducing the chip area and its power consumption. A 9-bit 20-MSamples/s ADC, intended for use in multi-channel mixed-signal chips, has been fabricated via Europractice in a 180-nm CMOS process from UMC. The prototype ADC shows a spurious-free dynamic range of 58.5 dB at a sample rate of 20 MSamples/s, when a 400 kHz input signal with a swing of 1 dB below full scale is applied. The effective number of bits is 8.0 at the same conditions. ADC occupies an active area of 0.4 mm2 and dissipates 8.6 mW at a 1.8 V supply.
Quantum chemistry studies of the O K-edge X-ray absorption in WO3 and AWO3
Dmitry Bocharov,Alexei Kuzmin,Juris Purans,Yuri Zhukovskii
Physics , 2010, DOI: 10.1117/12.815297
Abstract: In this work we present an interpretation of experimental O K-edge x-ray absorption near edge structure (XANES) in perovskite-type WO3 and AWO3 compounds (A = H and Na) using three different first principles approaches: (i) full-multiple-scattering (FMS) formalism (the real-space FEFF code), (ii) hybrid density functional theory (DFT) method with partial incorporation of exact Hartree-Fock exchange using formalism of the linear combination of atomic orbitals (LCAO) as implemented in the CRYSTAL code; (iii) plane-wave DFT method using formalism of the projector-augmented waves (PAW) as implemented in the VASP code.
Ab initio modeling of oxygen impurity atom incorporation into uranium mononitride surface and subsurface vacancies
Dmitry Bocharov,Denis Gryaznov,Yuri F. Zhukovskii,Eugene A. Kotomin
Physics , 2010, DOI: 10.1016/j.jnucmat.2010.11.090
Abstract: The incorporation of oxygen atoms has been simulated into either nitrogen or uranium vacancy at the UN(001) surface, sub-surface or central layers. For calculations on the corresponding slab models both the relativistic pseudopotentials and the method of projector augmented-waves (PAW) as implemented in the VASP computer code have been used. The energies of O atom incorporation and solution within the defective UN surface have been calculated and discussed. For different configurations of oxygen ions at vacancies within the UN(001) slab, the calculated density of states and electronic charge re-distribution was analyzed. Considerable energetic preference of O atom incorporation into the N-vacancy as compared to U-vacancy indicates that the observed oxidation of UN is determined mainly by the interaction of oxygen atoms with the surface and sub-surface N vacancies resulting in their capture by the vacancies and formation of O-U bonds with the nearest uranium atoms. Keywords: Density functional calculations, uranium mononitride, surface, defects, N and U vacancies
Chemisorption of a molecular oxygen on the UN (001) surface: ab initio calculations
Yuri F. Zhukovskii,Dmitry Bocharov,Eugene A. Kotomin
Physics , 2010, DOI: 10.1016/j.jnucmat.2009.07.010
Abstract: The results of DFT GGA calculations on oxygen molecules adsorbed upon the (001) surface of uranium mononitride (UN) are presented and discussed. We demonstrate that O2 molecules oriented parallel to the substrate can dissociate either (i) spontaneously when the molecular center lies above the surface hollow site or atop N ion, (ii) with the activation barrier when a molecule sits atop the surface U ion. This explains fast UN oxidation in air.
DFT calculations of point defects on UN(001) surface
Dmitry Bocharov,Denis Gryaznov,Yuri F. Zhukovskii,Eugene A. Kotomin
Physics , 2010, DOI: 10.1016/j.susc.2010.11.007
Abstract: The density functional theory (DFT) is used in a study of point defects on both UN (001) surface and sub-surface layers. We compare results for slabs of different thicknesses (both perfect and containing nitrogen or uranium vacancies) with a full geometry, electronic and spin density optimization. The electronic charge density re-distribution, density of states, magnetic moments of atoms as well as local atomic displacements around defects are carefully analyzed. It is predicted that the vacancies are formed easier on the surface whereas the sub-surface layer does not differ signifincantly from the central one in the slab.
Electronic charge redistribution in LaAlO$_3$(001) thin films deposited at SrTiO$_3$(001) substrate: First principles analysis and the role of stoichiometry
Alexandre Sorokine,Dmitry Bocharov,Sergei Piskunov,Vyacheslavs Kashcheyevs
Physics , 2012, DOI: 10.1103/PhysRevB.86.155410
Abstract: We present a comprehensive first-principles study of the electronic charge redistribution in atomically sharp LaAlO$_3$/SrTiO$_3$(001) heterointerfaces of both n- and p-types allowing for non-stoichiometric composition. Using two different computational methods within the framework of the density functional theory (linear combination of atomic orbitals and plane waves) we demonstrate that conducting properties of LaAlO$_3$/SrTiO$_3$(001) heterointerfaces strongly depend on termination of LaAlO$_3$ (001) surface. We argue that both the polar "catastrophe" and the polar distortion scenarios may be realized depending on the interface stoichiometry. Our calculations predict that heterointerfaces with a non-stoichiometrc film---either LaO-terminated n-type or AlO$_2$-terminated p-type---may exhibit the conductivity of n- or p-type, respectively, independently of LaAlO$_3$(001) film thickness.
Ab initio modelling of UN grain boundary interfaces
Eugene A. Kotomin,Yuri F. Zhukovkii,Dmitry Bocharov,Denis Gryaznov
Physics , 2012, DOI: 10.1088/1757-899X/38/1/012058
Abstract: The uranium mononitride (UN) is a material considered as a promising candidate for Generation-IV nuclear reactor fuels. Unfortunately, oxygen in air affects UN fuel performance and stability. Therefore, it is necessary to understand the mechanism of oxygen adsorption and further UN oxidation in the bulk and at surface. Recently, we performed a detailed study on oxygen interaction with UN surface using density functional theory (DFT) calculations. We were able to identify an atomistic mechanism of UN surface oxidation consisting of several important steps, starting with the oxygen molecule dissociation and finishing with oxygen atom incorporation into vacancies on the surface. However, in reality most of processes occur at the interfaces and on UN grain boundaries. In this study, we present the results of first DFT calculations on O behaviour inside UN grain boundaries performed using GGA exchange-correlation functional PW91 as implemented into the VASP computer code. We consider a simple interface (310)[001](36.8{\deg}) tilt grain boundary. The N vacancy formation energies and energies of O incorporation into pre-existing vacancies in the grain boundaries as well as O solution energies were compared with those obtained for the UN (001) and (110) surfaces.
First principles calculations of oxygen adsorption on the UN (001) surface
Yuri F. Zhukovskii,Dmitry Bocharov,Eugene Kotomin,Robert Evarestov,Andrey V. Bandura
Physics , 2010, DOI: 10.1016/j.susc.2008.10.019
Abstract: Fabrication, handling and disposal of nuclear fuel materials require comprehensive knowledge of their surface morphology and reactivity. Due to unavoidable contact with air components (even at low partial pressures), UN samples contain considerable amount of oxygen impurities affecting fuel properties. The basic properties of O atoms adsorbed on the UN(001) surface are simulated here combining the two first principles calculation methods based on the plane wave basis set and that of the localized atomic orbitals.
A note on the polynomial moments of the partition function in the SK model
Sergey Bocharov
Mathematics , 2015,
Abstract: We prove a simple identity relating the $k$th moment of the partition function $Z_N(\cdot)$ in the SK model to the $N$th moment of the partition function $Z_k(\cdot)$. As a corollary we find a characterisation of the limit $\lim_{N \to \infty} \frac{1}{N} \log \mathbb{E} Z_N(\beta)^k$ alternative to the one found previously by Michel Talagrand in \cite{4}.
Application of Kullback-Leibler Metric to Speech Recognition
Igor Bocharov,Pavel Lukin
Computer Science , 2003,
Abstract: Article discusses the application of Kullback-Leibler divergence to the recognition of speech signals and suggests three algorithms implementing this divergence criterion: correlation algorithm, spectral algorithm and filter algorithm. Discussion covers an approach to the problem of speech variability and is illustrated with the results of experimental modeling of speech signals. The article gives a number of recommendations on the choice of appropriate model parameters and provides a comparison to some other methods of speech recognition.
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