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FP-LAPW investigation of mechanical and thermodynamic properties of Na2X (X = S and Se) under pressure and temperature effects

Bidai K., Ameri M., Bensaid D, Moulay N. E., Al-Douri Y., Ameri I.

Materials Science Poland

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2015

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Vol. 33, No. 3

649--659

EN

Structural, elastic and thermodynamic properties of sodium chalcogenides (Na2X, X = S, Se) have been calculated using FP-APW+lo method. The ground state lattice parameter, bulk moduli have been obtained. The Zener anisotropy factor, Poisson’s ratio, shear modulus, Young’s modulus, have also been calculated. The calculated structural and elastic constants are in good agreement with the available data. We also determined the thermodynamic properties, such as heat capacities Cv and Cp, thermal expansion α, entropy S, and Debye temperature ΘD, at various pressures and temperatures for Na2X compounds. The elastic constants under high pressure and temperature are also calculated and elaborated.

2

Ab initio calculations of structural, elastic, electronic and thermodynamic properties of the cerium filled skutterudite CeRu4P12 under the effect of pressure

Berrahal M., Ameri M., Al-Douri Y., Hashim U., Varshney D., Ameri I., Boubchir M., Abderrahim B.

Materials Science Poland

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2015

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Vol. 33, No. 4

699--708

EN

The paper presents an investigation on crystalline, elastic and electronic structure in addition to the thermodynamic properties for a CeRu4P12 filled skutterudite device by using the full-potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximations (GGA) in the frame of density functional theory (DFT). For this purpose, the structural properties, such as the equilibrium lattice parameter, bulk modulus and pressure derivatives of the bulk modulus, were computed. By using the total energy variation as a function of strain we have determined the independent elastic constants and their pressure dependence. Additionally, the effect of pressure P and temperature T on the lattice parameters, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity for CeRu4P12 compound were investigated taking into consideration the quasi-harmonic Debye model.

3

Bonding xenon and krypton on the surface of uranium dioxide single crystal

Dąbrowski L., Szuta M.

Nukleonika

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2014

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Vol. 59, No. 3

83--89

EN

We present density functional theory (DFT) calculation results of krypton and xenon atoms interaction on the surface of uranium dioxide single crystal. A pseudo-potential approach in the generalised gradient approximation (GGA) was applied using the ABINIT program package. To compute the unit cell parameters, the 25 atom super-cell was chosen. It has been revealed that close to the surface of a potential well is formed for xenon and krypton atom due to its interaction with the atoms of oxygen and uranium. Depth and shape of the well is the subject of ab initio calculations in adiabatic approximation. The calculations were performed both for the case of oxygenic and metallic surfaces. It has been shown that the potential well for the oxygenic surface is deeper than for the metallic surface. The thermal stability of immobilising the atoms of krypton and xenon in the potential wells were evaluated. The results are shown in graphs.

4

Technologia pomiaru RTK czasu rzeczywistego ze zwiększoną częstotliwością pozycjonowania

Przestrzelski P., Bakuła M.

Elektronika : konstrukcje, technologie, zastosowania

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2013

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Vol. 54, nr 7

58-61

PL

W artykule zaprezentowano technologię rejestrowania dokładnych pomiarów RTK w czasie rzeczywistym z częstotliwością pozycjonowania większą niż 1 sekunda. Przedstawiono aplikację stworzoną specjalnie do tego celu, podstawowe algorytmy aplikacji oraz szereg rozwiązań, które umożliwiły zastosowanie opracowanej technologii do praktyki geodezyjnej. Poniższe opracowanie zawiera również syntetyczną charakterystykę środowiska programistycznego Delphi, opis urządzeń wykorzystanych w opracowanej technologii RTK oraz ich konfigurację. Na koniec poruszono również problematykę transmisji danych przy pomocy konwerterów RS232 - USB wraz z proponowanym jego rozwiązaniem.

EN

This paper presents the technology of accurate and reliable RTK positioning with more than one second recording interval. It contains description of an application created specifically for this purpose, the basic algorithms and a number of solutions, which enabled the use of the developed technology in geodetic practice. This paper also contains the synthetic characteristics of Delphi programming environment, and description of the equipment used within developed RTK technology and its configuration. At the end, data transmission by means of RS232-USB converters between a notebook and GNSS receivers was characterized together with the solution of the problem.

5

Local structure and cohesive properties of mixed thorium and uranium dioxides calculated by "ab initio" method

Dąbrowski L., Szuta M.

Nukleonika

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2012

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Vol. 57, No. 1

101-107

EN

Density functional theory (DFT) results of calculations of the mixed thorium and uranium dioxide Th1-xUxO2 for the following mole ratio x = 0, 0.25, 0.75 and 1 are presented and discussed. "Ab initio" calculations were performed using the Wien2k program package. To compute the unit cell parameters the 12 atom super-cell were chosen. The lattice parameters were calculated through minimization of the total energy by the change of lattice parameters and atom displacement within the unit cell. Calculations were performed for five different exchange energy approximations EXC with and without corrective orbital potential U, and obtained lattice constants are presented graphically and compared with experimental data. It is established that the initially assumed oxygen location within the unit cell plus or minus 0.25 of the mixed compounds are not their equilibrium positions. The oxygen atoms within the unit cell undergo dislocation in the (111) direction. So, the distances oxygen-uranium are smaller than the distances oxygen-thorium. The change of local structure is presented graphically and appropriate parameters values are given in Table. The bulk modulus and the cohesive properties are also counted and shown graphically.

6

„Ab initio” study of helium atoms immobilization in UO2 crystals

Dąbrowski L., Szuta M.

Nukleonika

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2012

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Vol. 57, No. 3

337-343

EN

We present density functional theory (DFT) calculation results concerning the uranium dioxide crystals with a helium atom incorporated in the octahedral interstitial position. "Ab initio" calculations were performed using the Wien2k program package. For comparison, a pseudo-potential approach in the generalized gradient approximation was applied using the ABINIT program package. To compute the unit cell parameters 13 atom super-cell was chosen. Parameters of the potential barrier, which the helium atom has to overcome while jumping to the next octahedral interstitial position, were calculated by the help of both the program packages. The results, obtained using two different program packages, are shown in the table and presented graphically. For the so described parameters, the quantum mechanical movement of the helium atom around the equilibrium position is considered. The parameters of Schrödinger's equation are collected in Table 2, while the results of mean square deviation and thermal occupation of energetic levels are presented in a graph. It is established that the helium atoms are located (with an accuracy of several percent of lattice constant) nearby the equilibrium position and form a local bound state. Applying a two site-model, we evaluated the time for an over-barrier jump. Graphically presented results show that the helium atom over-barrier jump is not possible even for temperatures as high as 1200 K. Influence of potential barrier height on the jump time was also considered.