Wyniki wyszukiwania - Biblioteka Nauki

1

The Efficiency of Transfer-matrix Simulations of Supramolecular Magnets in the Parallel Computing Environment

100%

Matysiak R. , Kamieniarz G.

Computational Methods in Science and Technology

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2006

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tom Vol. 12, nr 2

139-142

EN

The deterministic quantum transfer-matrix (QTM) technique and its mathematical background are presented. This important tool in computational physics can be applied to a class of the real physical low-dimensional magnetic systems described by the Heisenberg hamiltonian which includes the macroscopic molecular-based spin chains, small size magnetic clusters embedded in some supramolecules and other interesting compounds. In order to convert existing application for the susceptibility calculations to run on the grid, the speed-up and efficiency of parallelization are analyzed on the SGI Origin 3800 platform with p = 128 processor units. Using Message Parallel Interface (MPI) system libraries we find the efficiency of the code of 94% for p = 128 that makes our application suitable for the grid.

2

Visualization of Monte Carlo spin clusters for the ising model in 2 dimension

100%

Dębski L. , Kamieniarz G.

Computational Methods in Science and Technology

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1998

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tom Vol. 4

71-73

EN

The Monte Carlo algorithms and the Java applet designed for graphical presentation of spin cluster in the Ising model in two dimensions are presented. The procedure is available in the Division of Computational Physics under the address: http://pearl.amu.edu.pl/DSP.html

3

Optimization of Total Energy and Reduction of Computer Resources in Some Applications of the Ab-initio LMTO Package

100%

Kamieniarz G. , Sobczak P.

Computational Methods in Science and Technology

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2007

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tom Vol. 13, nr 1

13-22

EN

The computer resources needed to run the TB LMTO code have been reduced using a genetic algorithm in computations of the total energy requiring the interactive user-dependent mode. A computer program has been developed to search for the total energy minima and perform calculations in the background. The number of runs and output files is determined by the size of population and not by the number of scans of the configuration space.

4

Verification of the three-cluster molecular – field renormalization group approach for the ising model

100%

Kamieniarz G. , Musiał G.

Computational Methods in Science and Technology

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2002

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tom Vol. 8, nr 1

63-67

EN

A transfer matrix approach has been worked out to test the predictions of the three-step molecular-field renormalization group (MFRG) for square Ising clusters with linear size up t o L + 11. The convergence of the finite-size critical couplings and the critical exponents towards the exact values is shown.

5

Parallel Simulations of the Monte Carlo Type: 3D Ashkin-Teller Model

80%

Musiał G. , Dębski L. , Kamieniarz G.

Computational Methods in Science and Technology

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2007

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tom Vol. 13, nr 1

41-46

EN

The method of parallelization of processing in simulations of the Monte Carlo type is proposed and tested on the 3D Ashkin- -Teller model characterized by a rich phase diagram. The message passing is applied and the MPI library is exploited. It is demonstrated that the method works well in different regions of the phase diagram, where the phase transitions are first-order and continuous. The dependence of speedup and efficiency on the number of parallel processes is studied. The condition for the best speedup and efficiency in these simulations is formulated and discussed using the results obtained on symmetric NUMA multiprocessor and on symmetric multicomputer. The suggestion as to effective use of the method even in highly heterogeneous computer systems is also given.

6

Applicability of the DFT Augmented Symmetry Approach to Simulations of the Chromium-based Rings : Cross-validation Using the PBE Functional

80%

Wojciechowski M. , Brzostowski B. , Kamieniarz G.

Computational Methods in Science and Technology

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2016

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tom Vol. 22, No. 2

109--121

EN

We present comprehensive convergence and accuracy tests for predictions of the augmented symmetry approach suggested to reduce computational complexity of the DFT calculations for molecular rings. Using the PBE functional, we demonstrate the numerical stability of magnetic couplings, magnetic moments and the HOMO-LUMO gaps with respect to the size of the basic parameters RKM, the number of k-points and types of the unit cells as well as to the presence of full or absence of any point group symmetry. We show that both the performance and the final results are equal to those obtained for the standard approaches but the computing time is significantly lower. We conclude that the value RKM = 3:0 and a single k-point in the irreducible Brillouin zone are enough to reach the uncertainty of magnetic couplings of the order of 0:1 meV and a distortion resulting from the approach is irrelevant as far as the magnetic properties are concerned.

7

Time evolution of the haldane state after a quantum quench

80%

Woźniak D. , Drzewiński A. , Kamieniarz G.

Journal of Applied Mathematics and Computational Mechanics

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2014

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tom Vol. 13, nr 4

151--156

EN

In the framework of the Matrix Product States representation the effect of a sudden quench of the uniaxial anisotropy on the time evolution of the Haldane state has been investigated. The existence of the non-vanishing string correlations in the limit of a large distance in the Haldane phase has been verified. The overlap of the initial and time-evolved states, the so-called Loschmidt echo, has been investigated.

8

Highly Scalable Quantum Transfer Matrix Simulations of Molecule-Based Nanomagnets on a Parallel IBM BlueGene/P Architecture

80%

Antkowiak M. , Kucharski Ł. , Matysiak R. , Kamieniarz G.

Computational Methods in Science and Technology

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2016

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tom Vol. 22, No. 2

87--93

EN

In this work we present a very efficient scaling of our two applications based on the quantum transfer matrix method which we exploited to simulate the thermodynamic properties of Cr9 and Mn6 molecules as examples of the uniform and non-uniform molecular nanomagnets. The test runs were conducted on the IBM BlueGene/P supercomputer JUGENE of the Tier-0 performance class installed in the Jülich Supercomputing Centre.

9

Methods of computer simulations of phase transitions in the Ashkin - Teller model

80%

Musiał G. , Dębski L. , Kamieniarz G. , Rogiers J.

Computational Methods in Science and Technology

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2001

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tom Vol. 7, nr 1

67-82

EN

The complementary Monte Carlo and series expansions methods of computer simulations have been described to investigate the critical behaviour of the Ashkin-Teller model in three dimensions. In the first method the invariance of the ratio of the square of the second moment of the order parameter to its fourth moment in the critical region has been exploited and some critical points on the phase boundaries have been calculated in the regions where the continuous transitions are expected. The continuity of the order parameter on the critical lines is verified by a finite size scaling analysis. Large-scale simulations have been performed on SGI Power Challenge XL and L supercomputers using the 64-bit random number generator. The numerically generated series expansions method is described for which the effective algorithm for generation of graphs starting from polygons and based on collapsing the unlinked vertices, is introduced. The new feature of our algorithm is that for each graph we introduce new links between unlinked vertices and we decorate bonds with new vertices, so that more complex graphs in an early stage of the graph generation procedure are obtained. The resulting set of graphs enables the application of the series expansions method and achievement of the precision of allocation of points on the phase diagram comparable to the precision of the Monte Carlo method, i.e. at least 3 decimal digits.

10

Standardised computer tests for assessment of children manual dexterity

80%

Kamieniarz M. , Stryla W. , Haglauer P. , Kamieniarz G.

Computational Methods in Science and Technology

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1999

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tom Vol. 5

25-38

EN

The paper presents a computer program developed for the purpose of objectivisation of children hand dexterity. The program is composed of 6 subtests checking the control of the upper limb joints and the fine finger dexterity needed for mouse control. Measurements have been performed for a sample of 285 children aged from 7 to 15. Clinical standards for particular age groups have been proposed and statistical significance of differences among the corresponding mean values has been shown. A strong correlation of the hand control and age of the subjects has been found.

11

Algorithm for calculation of the partition function of frustrated s = 1/2 Heisenberg chains

80%

Szukowski G. , Bieliński M. , Kamieniarz G.

Computational Methods in Science and Technology

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2002

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tom Vol. 8, nr 1

97-101

EN

The paper presents the algorithm for calculation of the maximumeigenvalue of the transfer matrix for one-dimensional S = 1/2 Heisenberg model with nearest and next-nearest neighbours interactions. This value permits a calculation of the partition function and free energy of the quantum system. This algorithm is implemented in the mevnnn procedure written in FORTRAN 90. The procedure is available at the Poznan Supercomputing and Networking Center on Cray T3E supercomputer in the library /usr/local/lib/libms.a

12

Assessment of the children manual dexterity and hand grip strength : test - retest reliability study

80%

Kamieniarz M. , Stryla W. , Kowalska P. , Kamieniarz G.

Computational Methods in Science and Technology

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2002

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tom Vol. 8, nr 1

69-78

EN

A study was undertaken to verify reliability of both the new computer tests of manual dexterity and known dynamometric and Nine-Hole Peg tests in two groups of 84 (average age 10.5 plus or minus 2.4) and 61 (average age 11.02 plus or minus 2.45) children aged from 7 to 15, respectively. In these groups the series of measurements was twice repeated. A detailed statistical analysis of the results was made and indices describing reliability of the tests were determined. Correlation coefficients between the tests performance in the first and second series of measurements (at a week distance) by children from the same group were calculated proving a high and statistically significant correlation between the measurements.A comparison of the Pearson's coefficients calculated from our data with corresponding values for the tests known from literature proved a very good agreement. In addition, to check the computer tests stability, the statistical significance of differences between the average values of times of the tests completion in the two series, was analysed.

13

Computer-aided assessment of eye-hand coordination in children with mild mental retardation : a possible application as a screening test

70%

Kowalska P. , Krzywińska-Wiewiórowska M. , Kamieniarz M. , Krzyżaniak A. , Kamieniarz G.

Computational Methods in Science and Technology

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2002

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tom Vol. 8, nr 2

27--36

EN

Making use of the earlier designed computer tests assessing the hand dexterity, a study was performed in which the time of task completion was measured in a group of 88 mentally impaired children aged 7-15 and a group 86 of control children. All the children were also asked to take two types of psychological tests: Wechsler test subscales blocks and puzzles and Bender-Santucci test. Results of the computer tests discriminate these groups of children, indicating statistically significant differences between the corresponding mean values. The values of the Pearson coefficient (0.35 ≤ rp ≤ o.57) for the control group point to a relatively high correlation between the computer test results and those of psychological tests. The sensitivity and specificity analysis is also presented to show that the computer tests fulfil the criteria for a screening test.