Dynamic Behavior in Piezoresponse Force Microscopy

Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM) implemented on a beam-deflection atomic force microscope (AFM) is analyzed using a combination of modeling and experimental measurements. The PFM signal comprises contributions from local electrostatic forces acting on the tip, distributed forces acting on the cantilever, and three components of the electromechanical response vector. These interactions result in the bending and torsion of the cantilever, detected as vertical and lateral PFM signals. The relative magnitudes of these contributions depend on geometric parameters of the system, the stiffness and frictional forces of tip-surface junction, and operation frequencies. The dynamic signal formation mechanism in PFM is analyzed and conditions for optimal PFM imaging are formulated. The experimental approach for probing cantilever dynamics using frequency-bias spectroscopy and deconvolution of electromechanical and electrostatic contrast is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques

On completeness of description of an equilibrium canonical ensemble by reduced s-particle distribution function

In this article it is shown that in a classical equilibrium canonical ensemble of molecules with $s$-body interaction full Gibbs distribution can be uniquely expressed in terms of a reduced s-particle distribution function. This means that whenever a number of particles $N$ and a volume $V$ are fixed the reduced $s$-particle distribution function contains as much information about the equilibrium system as the whole canonical Gibbs distribution. The latter is represented as an absolutely convergent power series relative to the reduced $s$-particle distribution function. As an example a linear term of this expansion is calculated. It is also shown that reduced distribution functions of order less than $s$ don't possess such property and, to all appearance, contain not all information about the system under consideration.Comment: This work was reported on the International conference on statistical physics "SigmaPhi2008", Crete, Greece, 14-19 July 200

Experimental and Theoretical Investigation into the Effect of the Electron Velocity Distribution on Chaotic Oscillations in an Electron Beam under Virtual Cathode Formation Conditions

The effect of the electron transverse and longitudinal velocity spread at the entrance to the interaction space on wide-band chaotic oscillations in intense multiple-velocity beams is studied theoretically and numerically under the conditions of formation of a virtual cathode. It is found that an increase in the electron velocity spread causes chaotization of virtual cathode oscillations. An insight into physical processes taking place in a virtual cathode multiple velocity beam is gained by numerical simulation. The chaotization of the oscillations is shown to be associated with additional electron structures, which were separated out by constructing charged particle distribution functions.Comment: 9 pages, 8 figure

OPERATIONAL REGIMES OF MOLDAVIAN POWER SYSTEM UNDER DEVELOPMENT OF NETWORK INTERCONNECTIONS

The paper discusses and analyzes the basic steady state regimes in accordance with various strategies Moldova's accession to ENTSO-E. The four strategies have been analyzed for the accession of Moldova to the ENTSO-E: 1-without Ukraine and Transnistria; 2-without Ukraine; 3-together with Ukraine and 4- currently existing schemes. Evaluation of the proposed options: the following parameters were considered as criteria for active losses in the power system as a whole, and also in the network elements by voltage grades, coefficients of static stability of active power and voltage, the assessment of import / export of electrical power. As a result of the comparative analysis have been selected the most effective strategies for the accession of Moldova to the ENTSO-E

Crab cavities for linear colliders

Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favour a 3.9 GHz superconducting, multi-cell cavity as the solution for ILC, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are fundamental issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders.Comment: 3 pages. To be published in proceedings of LINAC 2008, Victoria, Canad

Асимптотический метод минимизации интегрального квадратичного функционала на траекториях квазилинейной динамической системы

The problem of minimizing the integral quadratic functional on the trajectories of a quasilinear dynamical system with linear terminal constraints is under consideration. Asymptotic approximations to the optimal open-loop and optimal feedback controls for this problem are constructed. Communicated by Corresponding Member Valentine V. GorokhovikРассматривается задача минимизации интегрального квадратичного функционала на траекториях квазилинейной динамической системы с линейными терминальными ограничениями. Строятся асимптотические приближения к оптимальному программному управлению и оптимальной обратной связи в этой задаче.Представлено членом-корреспондентом В. В. Гороховико

Применение метода возмущений к задаче оптимизации переходного процесса в квазилинейной динамической системе

The problem of optimizing the transient process in a quasi-linear dynamic system with a performance index, being a linear combination of the energy costs and the process duration, is considered. Asymptotic approximations of a given order to the solution of this problem are constructed.Рассматривается задача оптимизации переходного процесса в квазилинейной динамической системе с критерием качества, который представляет собой линейную комбинацию энергетических затрат и длительности процесса. Строятся асимптотические приближения заданного порядка к решению этой задачи

СИНГУЛЯРНЫЕ ВОЗМУЩЕНИЯ В ЛИНЕЙНО-КВАДРАТИЧНОЙ ЗАДАЧЕ ОПТИМАЛЬНОГО УПРАВЛЕНИЯ

The control problem for a linear singularly perturbed system with minimum energy is under consideration. The final state of the system and the transition time are assumed to be given. Asymptotic approximations to the optimal open-loop and optimal feedback controls for this problem are constructed. The main advantage of the proposed algorithms is that the original optimal control problem is split into two unperturbed problem of smaller dimension.Рассматривается задача об управлении с минимальной энергией линейной сингулярно возмущенной системой. Конечное состояние системы и время перехода считаются заданными. Строятся асимптотические приближения к оптимальному программному управлению и оптимальной обратной связи в этой задаче. Основное достоинство предлагаемых алгоритмов состоит в том, что при их применении исходная задача оптимального управления распадается на две невозмущенные задачи меньшей размерности

Conductivity of twin walls - surface junctions in ferroelastics: interplay of deformation potential, octahedral rotations, improper ferroelectricity and flexoelectric coupling

Electronic and structural phenomena at the twin domain wall-surface junctions in the ferroelastic materials are analyzed. Carriers accumulation caused by the strain-induced band structure changes originated via the deformation potential mechanism, structural order parameter gradient, rotostriction and flexoelectric coupling is explored. Approximate analytical results show that inhomogeneous elastic strains, which exist in the vicinity of the twin walls - surface junctions due to the rotostriction coupling, decrease the local band gap via the deformation potential and flexoelectric coupling mechanisms. This is the direct mechanism of the twin walls static conductivity in ferroelastics and, by extension, in multiferroics and ferroelectrics. On the other hand, flexoelectric and rotostriction coupling leads to the appearance of the improper polarization and electric fields proportional to the structural order parameter gradient in the vicinity of the twin walls - surface junctions. The "flexo-roto" fields leading to the carrier accumulation are considered as indirect mechanism of the twin walls conductivity. Comparison of the direct and indirect mechanisms illustrates complex range of phenomena directly responsible for domain walls static conductivity in materials with multiple order parameters.Comment: 35 pages, 11 figures, 3 table, 3 appendices Improved set of rotostriction coefficients are used in calculation