arXiv subjects

Yurij Holovatch

Publications and source records attributed to Yurij Holovatch.

At least 55 records · Page 3Linked to original sources

arXiv2016

Universal shape characteristics for the mesoscopic polymer chain via dissipative particle dynamics

In this paper we study the shape characteristics of a polymer chain in a good solvent using a mesoscopic level of modelling. The dissipative particle dynamics simulations are performed in the $3D$ space at a range of chain lengths $N$. The scaling laws for the end-to-end distance and gyration radius are examined first and found to hold for $N\geq 10$ yielding reasonably accurate value for the Flory exponent $ν$. Within the same interval of chain lengths, the asphericity, prolateness, size ratio and other shape characteristics of the chain are found to become independent of $N$. Their mean values are found to agree reasonably well with the respective theoretical results and lattice Monte Carlo simulations. Broad probability distributions for the shape characteristics are found resembling in form the results of lattice Monte Carlo simulations. By means of analytic fitting of these distributions the most probable values for the shape characteristics are found to supplement their mean values.

cond-mat.soft↗

arXiv2016

Critical behavior of the 2D Ising model with long-range correlated disorder

We study critical behavior of the diluted 2D Ising model in the presence of disorder correlations which decay algebraically with distance as $\sim r^{-a}$. Mapping the problem onto 2D Dirac fermions with correlated disorder we calculate the critical properties using renormalization group up to two-loop order. We show that beside the Gaussian fixed point the flow equations have a non trivial fixed point which is stable for $0.995<a<2$ and is characterized by the correlation length exponent $ν= 2/a + O((2-a)^3)$. Using bosonization, we also calculate the averaged square of the spin-spin correlation function and find the corresponding critical exponent $η_2=1/2-(2-a)/4+O((2-a)^2)$.

cond-mat.dis-nn↗

arXiv2016

Complex Networks of Words in Fables

In this chapter we give an overview of the application of complex network theory to quantify some properties of language. Our study is based on two fables in Ukrainian, Mykyta the Fox and Abu-Kasym's slippers. It consists of two parts: the analysis of frequency-rank distributions of words and the application of complex-network theory. The first part shows that the text sizes are sufficiently large to observe statistical properties. This supports their selection for the analysis of typical properties of the language networks in the second part of the chapter. In describing language as a complex network, while words are usually associated with nodes, there is more variability in the choice of links and different representations result in different networks. Here, we examine a number of such representations of the language network and perform a comparative analysis of their characteristics. Our results suggest that, irrespective of link representation, the Ukrainian language network used in the selected fables is a strongly correlated, scale-free, small world. We discuss how such empirical approaches may help form a useful basis for a theoretical description of language evolution and how they may be used in analyses of other textual narratives.

physics.soc-ph↗

arXiv2016

Analyses of a Virtual World

We present an overview of a series of results obtained from the analysis of human behavior in a virtual environment. We focus on the massive multiplayer online game (MMOG) Pardus which has a worldwide participant base of more than 400,000 registered players. We provide evidence for striking statistical similarities between social structures and human-action dynamics in the real and virtual worlds. In this sense MMOGs provide an extraordinary way for accurate and falsifiable studies of social phenomena. We further discuss possibilities to apply methods and concepts developed in the course of these studies to analyse oral and written narratives.

physics.soc-ph↗

arXiv2015

Academic research groups: evaluation of their quality and quality of their evaluation

In recent years, evaluation of the quality of academic research has become an increasingly important and influential business. It determines, often to a large extent, the amount of research funding flowing into universities and similar institutes from governmental agencies and it impacts upon academic careers. Policy makers are becoming increasingly reliant upon, and influenced by, the outcomes of such evaluations. In response, university managers are increasingly attracted to simple indicators as guides to the dynamics of the positions of their various institutions in league tables. However, these league tables are frequently drawn up by inexpert bodies such as newspapers and magazines, using rather arbitrary measures and criteria. Terms such as "critical mass' and "metrics" are often bandied about without proper understanding of what they actually mean. Rather than accepting the rise and fall of universities, departments and individuals on a turbulent sea of arbitrary measures, we suggest it is incumbent upon the scientific community itself to clarify their nature. Here we report on recent attempts to do that by properly defining critical mass and showing how group size influences research quality. We also examine currently predominant metrics and show that these fail as reliable indicators of group research quality.

physics.soc-ph↗

arXiv2015

Quantifying the evolution of a scientific topic: reaction of the academic community to the Chornobyl disaster

We analyze the reaction of academic communities to a particular urgent topic which abruptly arises as a scientific problem. To this end, we have chosen the disaster that occurred in 1986 in Chornobyl (Chernobyl), Ukraine, considered as one of the most devastating nuclear power plant accidents in history. The academic response is evaluated using scientific-publication data concerning the disaster using the Scopus database to present the picture on an international scale and the bibliographic database "Ukrainika naukova" to consider it on a national level. We measured distributions of papers in different scientific fields, their growth rates and properties of co-authorship networks. {The elements of descriptive statistics and the tools of the complex network theory are used to highlight the interdisciplinary as well as international effects.} Our analysis allows to compare contributions of the international community to Chornobyl-related research as well as integration of Ukraine in the international research on this subject. Furthermore, the content analysis of titles and abstracts of the publications allowed to detect the most important terms used for description of Chornobyl-related problems.

cs.DL↗

arXiv2015

Monte-Carlo study of anisotropic scaling generated by disorder

We analyze the critical properties of the three-dimensional Ising model with linear parallel extended defects. Such a form of disorder produces two distinct correlation lengths, a parallel correlation length $ξ_\parallel$ in the direction along defects, and a perpendicular correlation length $ξ_\perp$ in the direction perpendicular to the lines. Both $ξ_\parallel$ and $ξ_\perp$ diverge algebraically in the vicinity of the critical point, but the corresponding critical exponents $ν_\parallel$ and $ν_\perp$ take different values. This property is specific for anisotropic scaling and the ratio $ν_\parallel/ν_\perp$ defines the anisotropy exponent $θ$. Estimates of quantitative characteristics of the critical behaviour for such systems were only obtained up to now within the renormalization group approach. We report a study of the anisotropic scaling in this system via Monte Carlo simulation of the three-dimensional system with Ising spins and non-magnetic impurities arranged into randomly distributed parallel lines. Several independent estimates for the anisotropy exponent $θ$ of the system are obtained, as well as an estimate of the susceptibility exponent $γ$. Our results corroborate the renormalization group predictions obtained earlier.

cond-mat.stat-mech↗

arXiv2014

Predicting results of the Research Excellence Framework using departmental $h$-Index

We compare estimates for past institutional research performances coming from two bibliometric indicators to the results of the UK's Research Assessment Exercise which last took place in 2008. We demonstrate that a version of the departmental h-index is better correlated with the actual results of that peer-review exercise than a competing metric known as the normalised citation-based indicator. We then determine the corresponding h-indices for 2008-2013, the period examined in the UK's Research Excellence Framework (REF) 2014. We place herewith the resulting predictions on the arXiv in advance of the REF results being published (December 2014). These may be considered as unbiased predictions of relative performances in that exercise. We will revisit this paper after the REF results are available and comment on the reliability or otherwise of these bibliometrics as compared with peer review.

cs.DL↗

arXiv2014

Is your EPL attractive? Classification of publications through download statistics

Here we consider the download statistics of EPL publications. We find that papers in the journal are characterised by fast accumulations of downloads during the first couple of months after publication, followed by slower rates thereafter, behaviour which can be represented by a model with predictive power. We also find that individual papers can be classified in various ways, allowing us to compare categories for open-access and non-open-access papers. For example, for the latter publications, which comprise the bulk of EPL papers, a small proportion (2%) display intense bursts of download activity, possibly following an extended period of less remarkable behaviour. About 18% have an especially high degree of attractiveness over and above what is typical for the journal. One can also classify the ageing of attractiveness by examining download half-lives. Approximately 18% have strong interest initially, waning in time. A further 20% exhibit "delayed recognition" with relatively late spurs in download activity. Although open-access papers enjoy more downloads on average, the proportions falling into each category are similar.

cs.DL↗

arXiv2014

Interevent time distributions of human multi-level activity in a virtual world

Studying human behaviour in virtual environments provides extraordinary opportunities for a quantitative analysis of social phenomena with levels of accuracy that approach those of the natural sciences. In this paper we use records of player activities in the massive multiplayer online game Pardus over 1,238 consecutive days, and analyze dynamical features of sequences of actions of players. We build on previous work were temporal structures of human actions of the same type were quantified, and extend provide an empirical understanding of human actions of different types. This study of multi-level human activity can be seen as a dynamic counterpart of static multiplex network analysis. We show that the interevent time distributions of actions in the Pardus universe follow highly non-trivial distribution functions, from which we extract action-type specific characteristic "decay constants". We discuss characteristic features of interevent time distributions, including periodic patterns on different time scales, bursty dynamics, and various functional forms on different time scales. We comment on gender differences of players in emotional actions, and find that while male and female act similarly when performing some positive actions, females are slightly faster for negative actions. We also observe effects on the age of players: more experienced players are generally faster in making decisions about engaging and terminating in enmity and friendship, respectively.

physics.soc-ph↗

arXiv2010

Analysis of temporal characteristics of the editorial processing in scientific periodicals

The first part of our work is connected with the analysis of typical random variables for the specific human-initiated process. We study the data characterizing editorial work with received manuscripts in several scientific journals. In such a way we found the waiting time distributions that could be called the typical for an ordinary peer-review scientific journal. In the second part of this study a model of editorial processing of received manuscripts is developed. Within the model, different scenarios of the manuscript editorial processing are examined. Combining the results of the quantitative experiment and model simulations we arrive to the set of conclusions about time characteristics of editorial process in scientific journals and a peer-review contribution.

cs.DL↗

arXiv2010

Star copolymers in porous environments: scaling and its manifestations

We consider star polymers, consisting of two different polymer species, in a solvent subject to quenched correlated structural obstacles. We assume that the disorder is correlated with a power-law decay of the pair correlation function g(x)\sim x^{-a}. Applying the field-theoretical renormalization group approach in d dimensions, we analyze different scenarios of scaling behavior working to first order of a double ε=4-d, δ=4-a expansion. We discuss the influence of the correlated disorder on the resulting scaling laws and possible manifestations such as diffusion controlled reactions in the vicinity of absorbing traps placed on polymers as well as the effective short-distance interaction between star copolymers.

cond-mat.soft↗

arXiv2010

Spin vortices and vacancies: interactions and pinning on a square lattice

The study gives a decisive answer to the recently risen question about the type and origin of interaction between spin vortices and spin vacancies in 2D spin models. The approach is based on the low-temperature approximation of the 2D XY model known as the Villain model and does not involve any additional approximations, thus preserving the lattice structure. The exact form of the Hamiltonian describing a system of topological charges and a vacant site supports the attractive type of interaction between the vacancy and the charges. The quantitative difference between the characteristics of the vortex behavior in the 2D XY and Villain models due to the different energy of the vortex "cores" in the two models is pointed out. This leads to a conclusion that the interaction between a vortex and a spin vacancy and between a vortex and the antivortex differs quantitatively for small separations in the two mentioned models.

cond-mat.stat-mech↗

arXiv2010

Universal features of polymer shapes in crowded environment

We study the universal characteristics of the shape of a polymer chain in an environment with correlated structural obstacles, applying the field-theoretical renormalization group approach. Our results qualitatively indicate an increase of the asymmetry of the polymer shape in crowded environment comparing with the pure solution case.

cond-mat.soft↗

arXiv2010

Public Transport Networks under Random Failure and Directed Attack

The behaviour 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 a recent study of public transport networks of 14 major cities of the world we have shown that these systems when represented by appropriate graphs may exhibit scale-free behaviour. In this paper we briefly review some of the recent results about 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↗

arXiv2008

Interplay of topological and structural defects in the 2D XY model

The present work is devoted to the investigation of the interaction between vortices (topological defects) and site-impurities (structural defects) in the 2D XY model and its influence on the well-known properties of the pure system. The main goal is a theoretical description of the Berezinskii-Kosterlitz-Thouless (BKT) temperature reduction by quenched non-magnetic impurities, based on the vacancy-vortex interactions and the vortex-pair dissociation mechanism of the transition. The non-magnetic impurity interaction with a system of vortices can be found either from the phenomenological theory of topological defects or from the Villain model. We take both paths and compare the results obtained. Our prediction for the BKT temperature reduction is confirmed by the available Monte Carlo data.

cond-mat.stat-mech↗

arXiv2006

The 2D XY model on a finite lattice with structural disorder: quasi-long-range ordering under realistic conditions

We present an analytic approach to study concurrent influence of quenched non-magnetic site-dilution and finiteness of the lattice on the 2D XY model. Two significant deeply connected features of this spin model are: a special type of ordering (quasi-long-range order) below a certain temperature and a size-dependent mean value of magnetisation in the low-temperature phase that goes to zero (according to the Mermin-Wagner-Hohenberg theorem) in the thermodynamic limit. We focus our attention on the asymptotic behaviour of the spin-spin correlation function and the probability distribution of magnetisation. The analytic approach is based on the spin-wave approximation valid for the low-temperature regime and an expansion in the parameters which characterise the deviation from completely homogeneous configuration of impurities. We further support the analytic considerations by Monte Carlo simulations performed for different concentrations of impurities and compare analytic and MC results. We present as the main quantitative result of the work the exponent of the spin-spin correlation function power law decay. It is non universal depending not only on temperature as in the pure model but also on concentration of magnetic sites. This exponent characterises also the vanishing of magnetisation with increasing lattice size.

cond-mat.stat-mech↗

arXiv2006

Perturbation expansion for the diluted two-dimensional XY model

We study the quasi-long-range ordered phase of a 2D XY model with quenched site-dilution using the spin-wave approximation and expansion in the parameter which characterizes the deviation from completely homogeneous dilution. The results, obtained by keeping the terms up to the third order in the expansion, show good accordance with Monte Carlo data in a wide range of dilution concentrations far enough from the percolation threshold. We discuss different types of expansion.

cond-mat.stat-mech↗