arXiv subjects

Yu. Holovatch

Publications and source records attributed to Yu. Holovatch.

At least 55 records · Page 3Linked to original sources

arXiv2011

Field theory of bicritical and tetracritical points. IV. Critical dynamics including reversible terms

This article concludes a series of papers (R. Folk, Yu. Holovatch, and G. Moser, Phys. Rev. E 78, 041124 (2008); 78, 041125 (2008); 79, 031109 (2009)) where the tools of the field theoretical renormalization group were employed to explain and quantitatively describe different types of static and dynamic behavior in the vicinity of multicritical points. Here, we give the complete two loop calculation and analysis of the dynamic renormalization-group flow equations at the multicritical point in anisotropic antiferromagnets in an external magnetic field. We find that the time scales of the order parameters characterizing the parallel and perpendicular ordering with respect to the external field scale in the same way. This holds independent whether the Heisenberg fixed point or the biconical fixed point in statics is the stable one. The non-asymptotic analysis of the dynamic flow equations shows that due to cancelation effects the critical behavior is described - in distances from the critical point accessible to experiments - by the critical behavior qualitatively found in one loop order. Although one may conclude from the effective dynamic exponents (taking almost their one loop values) that weak scaling for the order parameter components is valid, the flow of the time scale ratios is quite different and they do not reach their asymptotic values.

cond-mat.stat-mech↗

arXiv2011

Editorial process in scientific journals: analysis and modeling

The editorial handling of papers in scientific journals as a human activity process is considered. Using recently proposed approaches of human dynamics theory we examine the probability distributions of random variables reflecting the temporal characteristics of studied processes. The first part of this paper contains our results of analysis of the real data about papers published in scientific journals. The second part is devoted to modeling of time-series connected with editorial work. The purpose of our work is to present new object that can be studied in terms of human dynamics theory and to corroborate the scientometrical application of the results obtained.

physics.data-an↗

arXiv2011

Proportionate vs disproportionate distribution of wealth of two individuals in a tempered Paretian ensemble

We study the distribution P(ω) of the random variable ω= x_1/(x_1 + x_2), where x_1 and x_2 are the wealths of two individuals selected at random from the same tempered Paretian ensemble characterized by the distribution Ψ(x) \sim ϕ(x)/x^{1 + α}, where α> 0 is the Pareto index and $ϕ(x)$ is the cut-off function. We consider two forms of ϕ(x): a bounded function ϕ(x) = 1 for L \leq x \leq H, and zero otherwise, and a smooth exponential function ϕ(x) = \exp(-L/x - x/H). In both cases Ψ(x) has moments of arbitrary order. We show that, for α> 1, P(ω) always has a unimodal form and is peaked at ω= 1/2, so that most probably x_1 \approx x_2. For 0 < α< 1 we observe a more complicated behavior which depends on the value of δ= L/H. In particular, for δ< δ_c - a certain threshold value - P(ω) has a three-modal (for a bounded ϕ(x)) and a bimodal M-shape (for an exponential ϕ(x)) form which signifies that in such ensembles the wealths x_1 and x_2 are disproportionately different.

q-fin.GN↗

arXiv2011

Entropic equation of state and scaling functions near the critical point in scale-free networks

We analyze the entropic equation of state for a many-particle interacting system in a scale-free network. The analysis is performed in terms of scaling functions which are of fundamental interest in the theory of critical phenomena and have previously been theoretically and experimentally explored in the context of various magnetic, fluid, and superconducting systems in two and three dimensions. Here, we obtain general scaling functions for the entropy, the constant-field heat capacity, and the isothermal magnetocaloric coefficient near the critical point in scale-free networks, where the node-degree distribution exponent $λ$ appears to be a global variable and plays a crucial role, similar to the dimensionality $d$ for systems on lattices. This extends the principle of universality to systems on scale-free networks and allows quantification of the impact of fluctuations in the network structure on critical behavior.

cond-mat.stat-mech↗

arXiv2010

About the relevance of the fixed dimension perturbative approach to frustrated magnets in two and three dimensions

We show that the critical behaviour of two- and three-dimensional frustrated magnets cannot reliably be described from the known five- and six-loops perturbative renormalization group results. Our conclusions are based on a careful re-analysis of the resummed perturbative series obtained within the zero momentum massive scheme. In three dimensions, the critical exponents for XY and Heisenberg spins display strong dependences on the parameters of the resummation procedure and on the loop order. This behaviour strongly suggests that the fixed points found are in fact spurious. In two dimensions, we find, as in the O(N) case, that there is apparent convergence of the critical exponents but towards erroneous values. As a consequence, the interesting question of the description of the crossover/transition induced by Z2 topological defects in two-dimensional frustrated Heisenberg spins remains open.

cond-mat.stat-mech↗

arXiv2010

Biconical critical dynamics

A complete two loop renormalization group calculation of the multicritical dynamics at a tetracritical or bicritical point in anisotropic antiferromagnets in an external magnetic field is performed. Although strong scaling for the two order parameters (OPs) perpendicular and parallel to the field is restored as found earlier, in the experimentally accessible region the effective dynamical exponents for the relaxation of the OPs remain different since their equal asymptotic values are not reached.

cond-mat.stat-mech↗

arXiv2010

Intelligent data analysis based on the complex network theory methods: a case study

The development of modern information technologies permits to collect and to analyze huge amounts of statistical data in different spheres of life. The main problem is not to only to collect but to process all relevant information. The purpose of our work is to show the example of intelligent data analysis in such complex and non-formalized field as science. Using the statistical data about scientific periodical it is possible to perform its comprehensive analysis and to solve different practical problems. The combination of various approaches including the statistical analysis, methods of the complex network theory and different techniques that can be used for the concept mapping permits to perform an intelligent data analysis in order to obtain underlying patterns and hidden connections. Results of such analysis can be used for particular practical problems like information retrieval within journal.

cs.IR↗

arXiv2010

Human activity as the decision-based queueing process: statistical data analysis of waiting times in scientific journals

We consider the editorial processing of papers in scientific journals as a human activity process based on the decision making. A functional form of the probability distributions of random variables describing a human dynamics is studied using classical approaches of mass service systems theory, physics of critical phenomena and statistical methods of data analysis. Our additional goal is to corroborate the scientometrical application of the results obtained. Keywords: data analysis, statistics, mass service systems, human activity, scientometrics

physics.data-an↗

arXiv2010

Critical phenomena on scale-free networks: logarithmic corrections and scaling functions

In this paper, we address the logarithmic corrections to the leading power laws that govern thermodynamic quantities as a second-order phase transition point is approached. For phase transitions of spin systems on d-dimensional lattices, such corrections appear at some marginal values of the order parameter or space dimension. We present new scaling relations for these exponents. We also consider a spin system on a scale-free network which exhibits logarithmic corrections due to the specific network properties. To this end, we analyze the phase behavior of a model with coupled order parameters on a scale-free network and extract leading and logarithmic correction-to-scaling exponents that determine its field- and temperature behavior. Although both non-trivial sets of exponents emerge from the correlations in the network structure rather than from the spin fluctuations they fulfil the respective thermodynamic scaling relations. For the scale-free networks the logarithmic corrections appear at marginal values of the node degree distribution exponent. In addition we calculate scaling functions, which also exhibit nontrivial dependence on intrinsic network properties.

cond-mat.stat-mech↗

arXiv2009

On the universality class of the 3d Ising model with long-range-correlated disorder

We analyze a controversial question about the universality class of the three-dimensional Ising model with long-range-correlated disorder. Whereas both analytical and numerical studies performed so far support an extended Harris criterion (A. Weinrib, B. I. Halperin, Phys. Rev. B 27 (1983) 413) and bring about the new universality class, the numerical values of the critical exponents found so far differ essentially. To resolve this discrepancy we perform extensive Monte Carlo simulations of a 3d Ising magnet with non-magnetic impurities arranged as lines with random orientation. We apply Wolff cluster algorithm accompanied by a histogram reweighting technique and make use of the finite-size scaling to extract the values of critical exponents governing the magnetic phase transition. Our estimates for the exponents differ from the results of the two numerical simulations performed so far and are in favour of a non-trivial dependency of the critical exponents on the peculiarities of long-range correlations decay.

cond-mat.dis-nn↗

arXiv2009

Field Theoretical Approach to Bicritical and Tetracritical Behavior: Static and Dynamics

We discuss the static and dynamic multicritical behavior of three-dimensional systems of $O(n_\|)\oplus O(n_\perp)$ symmetry as it is explained by the field theoretical renormalization group method. Whereas the static renormalization group functions are currently know within high order expansions, we show that an account of two loop contributions refined by an appropriate resummation technique gives an accurate quantitative description of the multicritical behavior. One of the essential features of the static multicritical behavior obtained already in two loop order for the interesting case of an antiferromagnet in a magnetic field ($n_\|=1$, $n_\perp=2$) are the stability of the biconical fixed point and the neighborhood of the stability border lines to the other fixed points leading to very small transient exponents. We further pursue an analysis of dynamical multicritical behavior choosing different forms of critical dynamics and calculating asymptotic and effective dynamical exponents within the minimal subtraction scheme.

cond-mat.stat-mech↗

arXiv2009

Resilience of public transport networks against attacks

The behavior of complex networks under failure or attack depends strongly on the specific scenario. Of special interest are scale-free networks, which are usually seen as robust under random failure but appear to be especially vulnerable to targeted attacks. In recent studies of public transport networks of fourteen major cities of the world it was shown that these systems when represented by appropriate graphs may exhibit scale-free behavior [C. von Ferber et al., Physica A 380, 585 (2007), Eur. Phys. J. B 68, 261 (2009)]. Our present analysis, focuses on the effects that defunct or removed nodes have on the properties of public transport networks. Simulating different directed attack strategies, we derive vulnerability criteria that result in minimal strategies with high impact on these systems.

physics.soc-ph↗

arXiv2009

A coupled order parameter system on a scale-free network

The system of two scalar order parameters on a complex scale-free network is analyzed in the spirit of Landau theory. To add a microscopic background to the phenomenological approach we also study a particular spin Hamiltonian that leads to coupled scalar order behavior using the mean field approximation. Our results show that the system is characterized by either of two types of ordering: either one of the two order parameters is zero or both are non-zero but have the same value. While the critical exponents do not differ from those of a model with a single order parameter on a scale free network there are notable differences for the amplitude ratios and susceptibilities. Another peculiarity of the model is that the transverse susceptibility is divergent at all T<T_c, when O(n) symmetry is present. This behavior is related to the appearance of Goldstone modes.

cond-mat.stat-mech↗

arXiv2008

Field theory of bicritical and tetracritical points. III. Relaxational dynamics including conservation of magnetization (Model C)

We calculate the relaxational dynamical critical behavior of systems of $O(n_\|)\oplus O(n_\perp)$ symmetry including conservation of magnetization by renormalization group (RG) theory within the minimal subtraction scheme in two loop order. Within the stability region of the Heisenberg fixed point and the biconical fixed point strong dynamical scaling holds with the asymptotic dynamical critical exponent $z=2ϕ/ν-1$ where $ϕ$ is the crossover exponent and $ν$ the exponent of the correlation length. The critical dynamics at $n_\|=1$ and $n_\perp=2$ is governed by a small dynamical transient exponent leading to nonuniversal nonasymptotic dynamical behavior. This may be seen e.g. in the temperature dependence of the magnetic transport coefficients.

cond-mat.stat-mech↗

arXiv2008

Field theory of bi- and tetracritical points: Relaxational dynamics

We calculate the relaxational dynamical critical behavior of systems of $O(n_\|)\oplus O(n_\perp)$ symmetry by renormalization group method within the minimal subtraction scheme in two loop order. The three different bicritical static universality classes previously found for such systems correspond to three different dynamical universality classes within the static borderlines. The Heisenberg and the biconical fixed point lead to strong dynamic scaling whereas in the region of stability of the decoupled fixed point weak dynamic scaling holds. Due to the neighborhood of the stability border between the strong and the weak scaling dynamic fixed point corresponding to the static biconical and the decoupled fixed point a very small dynamic transient exponent, of $ω_v^{\cal B}=0.0044$, is present in the dynamics for the physically important case $n_\|=1$ and $n_\perp=2$ in $d=3$.

cond-mat.stat-mech↗

arXiv2008

Field theory of bi- and tetracritical points: Statics

We calculate the static critical behavior of systems of $O(n_\|)\oplus O(n_\perp)$ symmetry by renormalization group method within the minimal subtraction scheme in two loop order. Summation methods lead to fixed points describing multicritical behavior. Their stability boarder lines in the space of order parameter components $n_\|$ and $n_\perp$ and spatial dimension $d$ are calculated. The essential features obtained already in two loop order for the interesting case of an antiferromagnet in a magnetic field ($n_\|=1$, $n_\perp=2$) are the stability of the biconical fixed point and the neighborhood of the stability border lines to the other fixed points leading to very small transient exponents. We are also able to calculate the flow of static couplings, which allows to consider the attraction region. Depending on the nonuniversal background parameters the existence of different multicritical behavior (bicritical or tetracritical) is possible including a triple point.

cond-mat.stat-mech↗

arXiv2008

Scaling of complex polymers: new universality classes and beyond

We analyse scaling laws that govern macromolecules of different topology: polymer chains, homogeneous and miktoarm star polymers in a good solvent possibly constrained by a porous medium. The latter is modelled by long-range-correlated disorder with a pair correlation function g(r) that decays with a power law g(r) r^{-a} at large distances r. We show that this type of disorder changes the universality class of the system. Within the frames of the field-theoretical renormalization group approach we obtain the corresponding new universal critical exponents for systems of homogeneous and star copolymers and discuss different consequences of the architecture dependent change of the scaling behaviour.

cond-mat.soft↗

arXiv2008

Fixed points in frustrated magnets revisited

We analyze the validity of perturbative renormalization group estimates obtained within the fixed dimension approach of frustrated magnets. We reconsider the resummed five-loop beta-functions obtained within the minimal subtraction scheme without epsilon-expansion for both frustrated magnets and the well-controlled ferromagnetic systems with a cubic anisotropy. Analyzing the convergence properties of the critical exponents in these two cases we find that the fixed point supposed to control the second order phase transition of frustrated magnets is very likely an unphysical one. This is supported by its non-Gaussian character at the upper critical dimension d=4. Our work confirms the weak first order nature of the phase transition occuring at three dimensions and provides elements towards a unified picture of all existing theoretical approaches to frustrated magnets.

cond-mat.stat-mech↗