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1
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Monte Carlo Study of Chain Entanglements in Polymer Melt

100%
Sikorski A., Romiszowski P.
Acta Physica Polonica A
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2001
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vol. 100
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issue 4
477-484
EN
The new multibond algorithm for the Monte Carlo simulations of polymers developed for an isolated chain was extended for the case of dense polymer melts. Polymer chains were confined to a simple cubic lattice with excluded volume and no attractive interactions (good solvent conditions). The simulations were carried out by the means of the classical Metropolis scheme. The algorithm was verified by the analysis of static and dynamic properties of polymer melts. The dependence of the longest relaxation time and the self-diffusion coefficient on the chain length and the polymer concentration was discussed and the proper scaling laws were formulated. The number of entanglements, their distribution, and lifetimes were determined for different chain lengths and melt concentrations using the new algorithm.
2
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Scale-Free Properties of Board and Director Networks Quantities

100%
Siudak D., Sankowska A.
Acta Physica Polonica A
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2016
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vol. 130
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issue 6
1261-1264
EN
It is often claimed that corporate and board networks display a scale-free nature, but there is no robust support for this nature. Based on data concerning the corporate board and director networks from companies listed on the Warsaw Stock Exchange Market, we applied a rigorous approach to determine whether quantities of these networks, such as degree, board size, and directorship number, exhibit power-law distribution.
3
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New Multi-Bond Algorithm for Monte Carlo Simulation of Lattice Chains

100%
Romiszowski P., Sikorski A.
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vol. 96
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issue 6
691-697
EN
The new algorithm for the Monte Carlo simulations of polymer lattice chains was developed. The model chains were constructed on a simple cubic lattice. The simulations were carried out on chains with and without excluded volume effect using the Metropolis scheme. The basic concept of the new algorithm is the multi-bond modification of the chain conformation instead of applying the classical set of elementary micromodifications. The correctness of the algorithm was verified by studying both static and dynamic properties of the chains. The new algorithm was found to be 3 to 8 times faster than the classical one.
4
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Properties of Confined Polymer Melts

80%
Sikorski A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 3
443-450
EN
Properties of simple models of confined linear polymer chains were studied by means of the Monte Carlo method. Model chains were built of united atoms (statistical segments) and embedded to a simple cubic lattice. Then polymers were put into a slit formed by two parallel impenetrable surfaces. Chain lengths were varied up to 800 segments and the density of the polymer melt was changed up to 0.5. A Metropolis-like sampling Monte Carlo algorithm was used to determine the static properties of this model. The influence of the size of the confinement, the polymer melt concentration and the chain length on the chain's size and the structure was studied. The universal behavior of all confined polymer linear chains under consideration was found and discussed.
5
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Thickness Dependence of Effective Critical Exponents in Three-Dimensional Ising Plates

80%
Marqués M., Gonzalo J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 6
1033-1037
EN
Phase transitions in Ising plates of equal area and different thicknesses have been studied by the Monte Carlo approach. The evolution of the critical temperature and of the effective critical exponents with the thickness of the lattice has been numerically determined. The thickness dependence of the maximum value of the effective critical exponents is well described by an exponential decay towards the respective three-dimensional value.
6
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Debugging of ORNL Series of Mathematical Phantoms of Human Body

80%
Krstic D., Nikezic D.
Acta Physica Polonica A
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2011
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vol. 119
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issue 3
279-281
EN
Series of mathematical phantoms of human body, given by Oak Ridge National Laboratory (ORNL), was programmed as input files for MCNP-4B code. Detailed check of geometry of these phantoms performed by MCNP-4B, discovered some minor errors, that resulted in overlapping of some organs. Three types of errors were found and described here: (a) colon overlaps with pelvis bone; (b) facial skeleton penetrate the head skin, and (c) esophagus overlaps with stomach. These errors prevent correct execution of program. Proposal for correction of these errors are given in this paper.
7
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Comprehensive Analyses of Gaussian Graphical Model under Different Biological Networks

80%
Dokuzoğlu D., Purutçuoğlu V.
Acta Physica Polonica A
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2017
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vol. 132
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issue 3
1106-1111
EN
Naturally, genes interact with each other by forming a complicated network and the relationship between groups of genes can be shown by different functions as gene networks. Recently, there has been a growing concern in uncovering these complex structures from gene expression data by modeling them mathematically. The Gaussian graphical model is one of the very popular parametric approaches for modelling the underlying types of biochemical systems. In this study, we evaluate the performance of this probabilistic model via different criteria, from the change in dimension of the systems to the change in the distribution of the data. Hereby, we generate high dimensional simulated datasets via copulas and apply them in Gaussian graphical model to compare sensitivity, specificity, F-measure and various other accuracy measures. We also assess its performance under real datasets. We consider that such comprehensive analyses can be helpful for assessing the limitation of this common model and for developing alternative approaches, to overcome its disadvantages.
8
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Structure of Dense Polymer Systems Confined to a Slit

80%
Sikorski A.
Acta Physica Polonica A
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2006
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vol. 109
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issue 2
133-141
EN
The linear polymer chains were approximated as series of identical segments on a simple cubic lattice. The excluded volume was included into the model with no attractive interactions which corresponded to the good solvent conditions. The polymer chains were put into a slit formed by a pair of parallel surfaces. These walls were impenetrable for polymer segments and no other interactions between walls and chains were assumed. The models chains were studied by the means of the Monte Carlo method. The sampling algorithm was Metropolis-type and employing micromodifications of chain's conformation to sample efficiently the conformational space. The influence of the chain length, density of the polymer system, and the distance between the surfaces on the shape of macromolecules was studied. It was found that the decrease in the size of the slit and the decrease in the polymer density led to the formation of more spherical macromolecules. This is partially caused by the interpenetration of polymer chains.
9
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Evaluation of Multiple Backscattering and Saturation Thickness of Gamma Rays

80%
Akar Tarim U.
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EN
A Monte Carlo code was written to determine the saturation thickness for multiply scattered gamma rays from aluminium targets. Interactions of incident gamma rays with the energies of 123, 279, 360, 511, 662, 1115, and 1250 keV were simulated. This work aims to design a convenient code which can be used in investigations on gamma backscattering. Obtained results for saturation thickness values have been compared with experimental ones and the Monte Carlo N-particle (MCNP) code results, and showed good agreement. Also, based on the similar behavior of number of multiple scattered photons between these three methods, the expected spectrum of singly or multiply scattered photons which is not possible to observe with experiment has been presented.
10
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The Shape of Confined Polymer Chains

80%
Sikorski A.
Acta Physica Polonica A
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2003
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vol. 103
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issue 4
339-347
EN
The linear polymer chains were modeled on a simple cubic lattice. The excluded volume was included into the model while the system remained athermal (no attractive interactions) which simulated the good solvent conditions. The polymer chain was located between two parallel impenetrable walls and the distance between the walls was changing. No interaction between walls and polymer segments was assumed. These models of polymer chains were simulated by the means of the Monte Carlo method. In the sampling algorithm we used the micromodifications of chain's conformations to sample efficiently the conformational space. The size of the chain did not change monotonically for all lengths under consideration (up to 800 statistical segments). For distances between the plates close to the double value of chain's radius of gyration the size of the chain approached its minimum value. It was shown that scaling of chain dimensions with its length changed from N^{1.18} to N^{1.5} while the distance between the walls was decreasing. The behavior of the asymmetry of the chain was found to be analogous to that of the radius of gyration.
11
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Relation of Gutzwiller Variational State with Matrix Model

70%
Koper A., Mucha M.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
391-394
EN
It is shown that mean values of electron operators in variational Gutzwiller state are equal to mean values of corresponding classical quantities calculated by means of a hermitian matrix model. In cases with small number of electrons in the system this property enables exact calculation of the mean values. In case of large number of electrons a simple and effective Monte Carlo method is formulated (within matrix model).
12
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On Stability of Frustrated Quantum Magnetic States in Fullerenes

61%
Koper A., Mucha M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
395-398
EN
Gutzwiller variational ground states |Φ^{G}⟩ of π electrons, described by single-band half-filling Hubbard model, were determined for the molecules C_{60} and C_{70} and their energies and magnetic properties investigated. To construct these states two types of trial functions were used: generalized spin-density wave |Φ_{SD}⟩ and tight-binding wave |Φ_{ΤΒ}⟩. Our results evidently show that the Gutzwiller state |Φ^{G}_{TΒ}⟩ determined by means of function |Φ_{ΤΒ}⟩ has lower energy than the other investigated variational states |Φ^{G}_{SD}⟩. Mean values of the operators in the Gutzwiller states were calculated using Monte Carlo method.
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