Papers by Elka Korutcheva
On the quantum finite-size sealing
Physica A: Statistical Mechanics and its Applications, 1993
The finite-size scaling hypothesis, in the presence of quantum fluctuations, is verified by means... more The finite-size scaling hypothesis, in the presence of quantum fluctuations, is verified by means of the ε-expansion. The analysis is performed within the framework of three models commonly used in the theory of structural phase transitions, superconducting phase transitions and Bose systems.
Statistical mechanics of the knapsak problem
Journal of Physics a Mathematical and General, 1994
The knapsack problem is an NP-complete combinatorial optimization problem with inequality constra... more The knapsack problem is an NP-complete combinatorial optimization problem with inequality constraints. Using the replica method of statistical physics, we study the space of its solutions for a large problem size. It turns out that this problem is closely related to the theory of the binary perception
Stability of the Mutual Information of a Noisy Perceptron. Analysis of the Optimal Solution
9.09> = x j + j , is then processed by the channel. The output ~ V j fV i g i=1;:::;p is a bin... more 9.09> = x j + j , is then processed by the channel. The output ~ V j fV i g i=1;:::;p is a binary variable taking values 0 or 1. The couplings between inputs and outputs are given by a general coupling matrix J with elements f ~ J i g , i = 1; : : : ; P as independent, random vectors with components distributed according to the distribution ae(fJ i;j g). In the large-N limit it is enough to take into account only its first two moments. We will assume : hhJ i;j ii = 0 (3) hh J i;j J i 0 ;k ii = ffi i;i 0 Gamma jk : (4) where the symbol<F3
Effect of colored noise on the critical dynamics of the time-dependent Landau-Ginzburg model A
On the quantum finite-size scaling
Berichte der Bunsengesellschaft für physikalische Chemie, 1994
ABSTRACT We verify the finite-size scaling hypothesis in the presence of quantum fluctuations up ... more ABSTRACT We verify the finite-size scaling hypothesis in the presence of quantum fluctuations up to one-loop order in the ϵ-expansion, using the formalism of Brézin [1], Brézin and Zinn-Justin [2] and Rudnick et al. [3]. The analysis is performed within the framework of three models commonly used in the theory of structural phase transitions, superconducting phase transitions and Bose systems.
Physics Letters A, 1992
The domains of attraction in neural network models with correlations between the patterns are ana... more The domains of attraction in neural network models with correlations between the patterns are analytically investigated for different asymptotic regimes. A similar behavioras in the uncorrelated case is present with limitingvalues ofthe storage capacity and basins of attraction dependent on the existing correlations.
On the Quantum Critical Behaviour of Systems with Extended Impurities
physica status solidi (b), 1985
Mean‐Field Theory of an Extended Hubbard Model
physica status solidi (b), 1989
Information processing by a noisy binary channel
Network: Computation in Neural Systems, 1997
Fluctuation Effects and Anisotropy in Unconventional Superconductors
Modern Physics Letters B, 1989
The renormalization group procedure is used to study the interacting-fluctuations regime of an m-... more The renormalization group procedure is used to study the interacting-fluctuations regime of an m-component complex order-parameter field with a cubic anisotropy of the type recently discussed group-theoretically in search for an explanation of superconductivity in heavy-fermion systems as well as in high-T c superconductors. The intrinsic magnetic fluctuations are also taken into consideration. The main scaling and the corrections to the scaling laws are completely elucidated. The cross-coupling between the real and the imaginary parts in the cubic term modifies significantly the renormalization-group flow equations in comparison with the real φ4-model with a cubic anisotropy. We find that anisotropy acts to 'stiffen' the first-order character of the transition (the Halperin-Lubensky-Ma effect).
Journal of Statistical Physics, 1993
Prompted by a recent article of Chakravarty, we reexamine the O(N) vector model with twisted boun... more Prompted by a recent article of Chakravarty, we reexamine the O(N) vector model with twisted boundary conditions in d dimensions in the various frameworks of the e = d-2 expansion, the ~ = 4-d expansion, and the large-N expansion. These continuum models describe the physics below the critical temperature Tc and near T c of a lattice O(N) spin model. We determine the effect of the twisting on finite-size scaling functions, for various geometries.
Journal of Statistical Physics, 1991
We present a systematic approach to the calculation of finite-size (FS) effects for an O(n) field... more We present a systematic approach to the calculation of finite-size (FS) effects for an O(n) field-theoretic model with both short-range (SR) and long-range (LR) exchange interactions. The LR exchange interaction decays at large distances as 1/r a+2-2~, ~t-~0 +. Renormalization group calculations in d=d,-e are performed for a system with a fully finite (block) geometry under periodic boundary conditions. We calculate the FS shift of the critical temperature and the FS renormalized coupling constant of the model to one-loop order. The universal scaling variable is obtained and the FS scaling hypothesis is verified.
The number of metastable states of a simple perceptron with gradient descent learning algorithm
Journal of Physics A: Mathematical and General, 1993
Journal of Physics A: Mathematical and General, 1994
The hapsack problem is an NP-complete mmbinatorial optimization problem with inequality constnint... more The hapsack problem is an NP-complete mmbinatorial optimization problem with inequality constnints. Using the replica method of statistical physics, we study the space of its solutions for a large problem sire. It turns out that this problem is closely related to the theory of the binary percepkon.
Influence of long-range correlated impurities upon the phase transition in model superconductors
Journal of Physics A: Mathematical and General, 1984
Computer Physics Communications, 1999
We investigated the information processing of a signal which is a N-dimensional linear mixture of... more We investigated the information processing of a signal which is a N-dimensional linear mixture of N-independent sources:
Arxiv preprint cond-mat/0404673, 2004
Quantum dots have promising properties for optoelectronic applications. They can be grown free of... more Quantum dots have promising properties for optoelectronic applications. They can be grown free of dislocations in highly mismatched epitaxy in the coherent Stranski-Krastanov mode. In this chapter, some thermodynamic aspects related to the wetting in the growth and self-assembly of three-dimensional (3D) coherent islands are studied using an energy minimization scheme in a 1+1-dimensional atomic model with anharmonic interactions. The conditions for equilibrium between the different phases are discussed. It is found that the thermodynamic driving force for 3D-cluster formation is the reduced adhesion of the islands to the wetting layer at their edges. In agreement with experimental observations, for values of the lattice mismatch larger than a critical misfit, a critical island size for the 2D-3D transition is found. Beyond it, monolayer islands become unstable against bilayer ones. Compressed coherent overlayers show a greater tendency to clustering than expanded ones. The transition to 3D islands takes place through a series of intermediate stable states with thicknesses discretely increasing in monolayer steps. Special emphasis is made on the analysis of the critical misfit. Additionally, the effect of neighbouring islands mediated through a deformable wetting layer is considered. The degree of wetting of the substrate by a given island depends on the size and shape distributions of the neighbouring islands. Implications for the self-assembled growth of quantum dots are discussed.
Physica A: Statistical Mechanics and its Applications
Half of the world population resides in cities and urban segregation is becoming a global issue. ... more Half of the world population resides in cities and urban segregation is becoming a global issue. One of the best known attempts to understand it is the Schelling model, which considers two types of agents that relocate whenever a transfer rule depending on the neighbor distribution is verified. The main aim of the present study is to broaden our understanding of segregated neighborhoods in the city, i.e. ghettos, extending the Schelling model to consider economic aspects and their spatial distribution. To this end we have considered a monetary gap between the two social groups and five types of urban structures, defined by the house pricing city map. The results show that ghetto sizes tend to follow a power law distribution in all the considered cases. For each city framework the interplay between economical aspects and the geometrical features determine the location where ghettos reach their maximum size. The system first steps shape greatly the city's final appearance. Moreover, the segregated population ratios depends largely on the monetary gap and not on the city type, implying that ghettos are able to adapt to different urban frameworks.
Improved Storage Capacity of Hebbian Learning Attractors
1 Introduction Recently, the bump formations in recurrent neural networks have been analyzedin se... more 1 Introduction Recently, the bump formations in recurrent neural networks have been analyzedin several investigations concerning linear-threshold units [1, 2], binary units [3] and Small-World networks of Integrate and Fire neurons [4]. These bump for-mations represent geometrically localized patterns of activity and have a size proportional to the number of connections per neuron.
Coupled Ising models are studied in a discrete choice theory framework, where they can be underst... more Coupled Ising models are studied in a discrete choice theory framework, where they can be understood to represent interdependent choice making processes for homogeneous populations under social influence. Two different coupling schemes are considered. The nonlocal or group interdependence model is used to study two interrelated groups making the same binary choice. The local or individual interdependence model represents a single group where agents make two binary choices which depend on each other. For both models, phase diagrams, and their implications in socioeconomic contexts, are described and compared in the absence of private deterministic utilities (zero opinion fields).
Uploads
Papers by Elka Korutcheva