Add a filter

Of all publications in the section: 17

Sort:

by name

by year

Working paper

We consider a general continuous mean-variance problem where the cost functional has an integral and a terminal-time component. We transform the problem into a superposition of a static and a dynamic optimization problem. The value function of the latter can be considered as the solution to a degenerate HJB equation either in viscosity or in Sobolev sense (after regularization) under suitable assumptions a nd with implications with regards to the optimality of strategies.

Added: Oct 15, 2015

Working paper

In recent paper of Falkovich and Levitov it was shown, that geometry of separatrixes for viscous electronic flow in graphene is sensitive to boundary conditions. Here we discover theis relation in details. Also we propose, how boundary conditions could be probed experimentally, using weak magnetic field and observed features of separatrixes.

Added: Apr 4, 2018

Working paper

We study a lattice model of a magnetic elastomer, where Ising spins are located on the sites of a lattice self-avoiding walk in d=2. We consider the regime where both conformations and magnetic degrees of freedom are dynamic, thus the Ising model is defined on a dynamic lattice and conformations generate an annealed disorder. We perform Monte Carlo simulations across the theta-point and find the joint ferromagnet-to-paramagnet and globule-coil transition, which is continuous -- in contrast to d=3 where it is first-order. At the transition, the metric exponent takes the theta-polymer value, but the crossover exponent is different.

Added: Jul 27, 2021

Working paper

Sobral T. A., de Holanda V. H., Leal F. C. et al. arxiv.org. cond-mat. Cornell University, 2020. No. 2012.06944.

The injection of a long piece of flexible rod into a two-dimensional domain yields a complex pattern commonly studied through elasticity theory, packing analysis, and fractal geometries. "Loop" is an one-vertex entity which which is naturally formed in this system. The role of the elastic features of each individual loop in 2D packing has not yet been discussed. In this work we point out how the shape of a given loop in the complex structure allows to estimate local deformations and forces. First, we build sets of symmetric free loops and performed compression experiments. Then, tight packing configurations are analyzed by using image processing. We found that the dimensions of the loops, confined or not, obey the same dependence on the deformation. The result is consistent with a simple model based on 2D elastic theory for filaments, where the rod adopts the shape of Euler's elasticas between its contact points. The force and the stored energy are obtained from numerical integration of the analytic expressions. In an additional experiment, we obtain that the compression force for deformed loops corroborates the theoretical findings. The importance of the shape of the loop is discussed and we hope that the theoretical curves may allow statistical considerations in future investigations.

Added: Feb 11, 2021

Working paper

Drovosekov A. B., Kreines N. M., Savitsky A. O. et al. arxiv.org. cond-mat. Cornell University, 2015

A set of thin film Mn<sub>x</sub>Si<sub>1-x</sub> alloy samples with different manganese concentration x = 0.44 - 0.63 grown by the pulsed laser deposition (PLD) method onto the Al<sub>2</sub>O<sub>3</sub> (0001) substrate was investigated in the temperature range 4 - 300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies (f = 7 - 60 GHz) and magnetic fields (H = 0 - 30 kOe). For samples with x = 0.52 - 0.55, FMR data show clear evidence of ferromagnetism with high Curie temperatures T<sub>c</sub> ~ 300 K. These samples demonstrate complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second order easy plane anisotropy contribution and the additional forth order uniaxial anisotropy contribution with easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. The existence of extra strains at the crystallite boundaries leads to an essential inhomogeneous magnetic anisotropy in the film plane.

Added: Jun 17, 2016

Working paper

Recent chain-like structured materials have shown a robust superconducting phase. These materials exhibit the presence of quasi-one-dimensional bands (q1D) coupled to conventional higher-dimensional bands. On the mean-field level such systems have a high critical temperature when the chemical potential is close to the edge of a q1D band and the related Lifshitz transition is approached. However, the impact of the pair fluctuations compromises the mean-field results. Recently it has been demonstrated that these fluctuations can be suppressed (screened) by a specific multiband mechanism based on the pair-exchange coupling of the q1D condensate to a stable higher-dimensional one. In the present work we demonstrate that strikingly enough, this mechanism is not very sensitive to the basic parameters of the stable condensate such as its strength and dimensionality. For example, even the presence of a passive higher-dimensional band, which does not exhibit any superconducting correlations when taken as a separate superconductor, results in suppression of the pair fluctuations.

Added: Feb 11, 2021

Working paper

Polynomial convergence rate to stationarity is shown for extended Erlang -- Sevastyanov's model.

Added: Dec 16, 2014

Working paper

Conditions for positive and polynomial recurrence have been proposed for a class of reliability models of two elements with transitions from working state to failure and back. As a consequence, uniqueness of stationary distribution of the model is proved; the rate of convergence towards this distribution may be theoretically evaluated on the basis of the established recurrence.

Added: Nov 1, 2019

Working paper

Polynomial convergence rates in total variation are established in Erlang-Sevastyanov's type problem with an infinite number of servers and a general distribution of service under assumptions on the intensity of serving.

Added: Oct 23, 2014

Working paper

We study a model of a spatial evolutionary game, based on the Prisoner's dilemma for two regular arrangements of players, on a square lattice and on a triangular lattice. We analyze steady state distributions of players which evolve from irregular, random initial configurations. We find significant differences between the square and triangular lattice, and we characterize the geometric structures which emerge on the triangular lattice.

Added: Nov 21, 2018

Working paper

In this letter the phenomenon of macroscopic quantization is investigated using the particle on the ring interacting with the dissipative environment as an example. It is shown that the phenomenon of macroscopic quantization has the clear physical origin in that case. It follows from the angular momentum conservation combined with momentum quantization for bare particle on the ring . The existence an observable which can take only integer values in the zero temperature limit is rigorously proved. With the aid of the mapping between particle on the ring and Ambegaokar-Eckern-Schon model, which can be used to describe single-electron devices, it is demonstrated that this observable is analogous to the "effective charge" introduced by Burmistrov and Pruisken for the single-electron box problem. Different consequences of the revealed physics are discussed, as well as a generalization of the obtained results to the case of more complicated systems.

Added: Feb 9, 2015

Working paper

Bakurskiy S. V., Klenov N. V., Soloviev I. I. et al. arxiv.org. cond-mat. Cornell University, 2018. No. 1808.07090.

We study the peculiarities in current-phase relations (CPR) of the SIsFS junction in the region of 0 to p
transition. These CPR consist of two independent branches corresponding to 0− and p− states of the contact.
We have found that depending on the transparency of the SIs tunnel barrier the decrease of the s-layer thickness
leads to transformation of the CPR shape going in the two possible ways: either one of the branches exists only
in discrete intervals of the phase difference j or both branches are sinusoidal but differ in the magnitude of their
critical currents. We demonstrate that the difference can be as large as 10% under maintaining superconductivity
in the s layer. An applicability of these phenomena for memory and logic application is discussed.

Added: Oct 28, 2018

Working paper

We prove pathwise uniqueness for a class of stochastic differential equations (SDE) on a Hilbert space with cylindrical Wiener noise, whose non-linear drift parts are sums of the subdifferential of a convex function and a bounded part. This generalizes a classical result by one of the authors (Veretennikov) to infinite dimensions.

Added: Oct 22, 2014

Working paper

We propose a superconducting spin-triplet valve of a new type. This spin valve consists of a bilayer
that involves a superconductor and an itinerant magnetic material, with the magnet showing an
intrinsic non-collinear magnetic order characterized by a wave vector Q that may be aligned in a
few equivalent preferred directions under control of a weak external magnetic field. Re-orienting the
direction of Q allows one to controllably modify long-range spin-triplet superconducting correlations
in the magnetic material, leading to spin-valve switching behavior. This new type of superconducting
spin valve may be used as a magnetic memory element for cryogenic nanoelectronics. It has the
following advantages in comparison with superconducting spin valves proposed earlier: (i) it contains
only one magnetic layer, which may be more easily fabricated and controlled; (ii) its ground states
are separated by a potential barrier, which solves the “half-select” problem of the addressed switch
of such memory elements.

Added: Sep 30, 2017

Working paper

Weyl semimetal is a three-dimensional material with a conical spectrum near an even number of point nodes, where two bands touch each other. Here we study spectral properties of surface electron states in such a system. We show that the density of surface states possesses a logarithmic singularity for the energy to 0. It decreases linearly at the intermediate energy of surface electron states and approaches zero. This universal behavior is a hallmark of the topological order that offers a new wide range of applications.

Added: Mar 8, 2016

Working paper

Tomi M.,

, et al. arxiv.org. cond-mat. Cornell University, 2021. No. 2106.07503.
We study, both theoretically and experimentally, the features on the current-voltage characteristic of a highly transparent Josephson junction caused by transition of the superconducting leads to the normal state. These features appear due to the suppression of the Andreev excess current. We show that by tracing the dependence of the voltages, at which the transition occurs, on the bath temperature one can obtain valuable information about the cooling mechanisms in the junction. We verify theory predictions by fabricating two highly transparent superconductor-graphene-superconductor (SGS) Josephson junctions with suspended and non-suspended graphene as an interlayer between Al leads. Applying the above mentioned technique we show that the cooling power of the suspended junction depends on the bath temperature as ∝T^3 close to the superconducting critical temperature.

Added: Jun 21, 2021

Working paper

Weigel M., Barash L. Y.,

et al. arxiv.org. cond-mat. Cornell University, 2021. No. 2102.06611.
Population annealing is a recent addition to the arsenal of the practitioner in computer simulations in statistical physics and beyond that is found to deal well with systems with complex free-energy landscapes. Above all else, it promises to deliver unrivaled parallel scaling qualities, being suitable for parallel machines of the biggest caliber. Here we study population annealing using as the main example the two-dimensional Ising model which allows for particularly clean comparisons due to the available exact results and the wealth of published simulational studies employing other approaches. We analyze in depth the accuracy and precision of the method, highlighting its relation to older techniques such as simulated annealing and thermodynamic integration. We introduce intrinsic approaches for the analysis of statistical and systematic errors and provide a detailed picture of the dependence of such errors on the simulation parameters. The results are benchmarked against canonical and parallel tempering simulations.

Added: Feb 15, 2021