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Wyświetlanie 1-15 z 22
Tytuł:
Bonding xenon and krypton on the surface of uranium dioxide single crystal
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147310.pdf
Data publikacji:
2014
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
noble gases
uranium dioxide
chemical bond
DFT
GGA
Opis:
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.
Źródło:
Nukleonika; 2014, 59, 3; 83-89
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Local structure and cohesive properties of mixed thorium and uranium dioxides calculated by "ab initio" method
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147874.pdf
Data publikacji:
2012
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
uranium
thorium dioxide
DFT+U
LDA
GGA
local structure
cohesive properties
bulk modulus
Opis:
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.
Źródło:
Nukleonika; 2012, 57, 1; 101-107
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Xe and Kr bonding abilities in the single crystal oxygen vacancies of the uranium based fuel
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147880.pdf
Data publikacji:
2012
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
noble gases
chemical bond
UO2 single crystal
valence electron density distribution
atomic force constants
bond energy
crystal lattice
Opis:
The valence electron density distribution of krypton and xenon located in the oxygen vacancy and in its nearest neighbourhood was performed by application of the method “ab initio”. The results are presented on the graphs. The bonding energies of krypton and xenon in the uranium dioxide crystal lattice were calculated. It was found also that krypton and xenon cause a local increase of UO1.75Xe0.25 and UO1.75Kr0.25 unit cell and cause its deformation what is presented in tables. The force constants of krypton and xenon were also assigned what gives evidence about the strong bond of krypton and xenon with the UO1.75Xe0.25 and UO1.75Kr0.25 single crystal lattice. Obtained results are compared with the analogical studies of He atom incorporation into UO2 single crystal lattice.
Źródło:
Nukleonika; 2012, 57, 1; 95-100
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bonding xenon on the surface of uranium dioxide single crystal
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147186.pdf
Data publikacji:
2013
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
noble gases
uranium dioxide
chemical bond
density functional theory (DFT)
generalized gradient approximation (GGA)
Opis:
We present density functional theory (DFT) calculation results of xenon atom interaction with the surface of uranium dioxide single crystal. A pseudo-potential approach in the generalized gradient approximation (GGA) was applied using the ABINIT program package. It has been revealed that close to the surface a potential well is formed for xenon 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. 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.
Źródło:
Nukleonika; 2013, 58, 4; 453-458
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
„Ab initio” study of helium atoms immobilization in UO2 crystals
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/146654.pdf
Data publikacji:
2012
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
uranium
dioxide
DFT+U
LDA
GGA
ABINIT
over-barrier jumps
incorporated helium
harmonic oscillator
Opis:
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.
Źródło:
Nukleonika; 2012, 57, 3; 337-343
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Diffusion of helium in the perfect uranium and thorium dioxide single crystals
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147700.pdf
Data publikacji:
2013
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
uranium
thorium dioxide
diffusion
tunneling
DFT+U
generalized gradient approximation (GGA)
potential barrier
incorporated helium
Opis:
We present quantum-mechanical evaluation of helium diffusion coefficient in the crystalline UO2 and ThO2. Parameters assignment of Schrödinger’s equation were done using the crystal field potentials which were obtained applying the density functional theory (DFT). “Ab initio” calculations were performed using the Wien2k program package. To compute the unit cell parameters the 13 atom super-cell was chosen. Applying two-site model we evaluated the time for an over-barrier jump and diffusion of interstitial He. The obtained values for diffusion coefficient are compared with the experimentally obtained values and with the theoretical values of other authors. In addition, it is simultaneously shown that helium diffusion in these materials is a quantum diffusion.
Źródło:
Nukleonika; 2013, 58, 2; 295-300
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The quantum diffusion of carbon in alfa-iron in low temperature
Autorzy:
Dąbrowski, L.
Andreev, A.
Georgiev, M.
Powiązania:
https://bibliotekanauki.pl/articles/147484.pdf
Data publikacji:
2006
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
carbon
diffusion
tunneling
adiabatic
polaron
Opis:
Recent experimental data on the diffusion coefficient of carbon in á-iron below liquid nitrogen temperature (LNT) question the classical approach to the observed temperature dependence. As the temperature is lowered below LNT, the diffusion constant tends to a nearly temperature-independent value rather than continuing its activated trend. The low temperature branch is apparently characteristic of a quantum mechanical process dominated by tunneling in ground state. Concomitantly we apply an occurrence-probability approach to describing the overall temperature dependence as a single continuous rate. Within the adiabatic approximation the electronic eigenvalue depending parametrically on the nuclear coordinates is taken to be the potential energy to control the motion of the nuclei. The resulting rate involves all horizontal-tunneling energy-conserving elastic transitions at the quantized energy levels of the migrating atom. A small though not negligible slope in the temperature dependence as the temperature is raised below 100 K is dealt with by complementing for the rate of a parallel one-phonon inelastic-tunneling process in excess to the basic elastic-tunneling rate. Our combined approach agrees well with the experimental data. In particular, the frequency of the coupled vibration is obtained virtually identical to the carbon vibrational frequency from inelastic neutron scattering data. The migrational barrier is also found to be within the limits expected for alfa-iron.
Źródło:
Nukleonika; 2006, 51, 2; 93-99
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electrical discharge machining of difficult to cut materials
Autorzy:
Świercz, R.
Oniszczuk-Świercz, D.
Dąbrowski, L.
Powiązania:
https://bibliotekanauki.pl/articles/139553.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
EDM
Inconel 718
surface roughness
material removal rate
response surface methodology (RSM)
chropowatość powierzchni
szybkość usuwania materiału
metodologia powierzchni odpowiedzi (RSM)
Opis:
The development of industry is determined by the use of modern materials in the production of parts and equipment. In recent years, there has been a significant increase in the use of nickel-based superalloys in the aerospace, energy and space industries. Due to their properties, these alloys belong to the group of materials hard-to-machine with conventional methods. One of the non-conventional manufacturing technologies that allow the machining of geometrically complex parts from nickel-based superalloys is electrical discharge machining. The article presents the results of experimental investigations of the impact of EDM parameters on the surfaces roughness and the material removal rate. Based on the results of empirical research, mathematical models of the EDM process were developed, which allow for the selection of the most favourable processing parameters for the expected values of the surface roughness Sa and the material removal rate.
Źródło:
Archive of Mechanical Engineering; 2018, LXV, 4; 461-476
0004-0738
Pojawia się w:
Archive of Mechanical Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Behaviour of steel with the metastable austenite during segmental grinding
Autorzy:
Dąbrowski, L.
Jeleńkowski, J.
Marciniak, M.
Szczęśniak, D.
Powiązania:
https://bibliotekanauki.pl/articles/132144.pdf
Data publikacji:
2014
Wydawca:
Stowarzyszenie Inżynierów i Techników Mechaników Polskich
Tematy:
segmental grinding
temperature registration
metastable austenite
deformation martensite
phase transformation
Opis:
The methods of the grinding process efficiency evaluation have been presented in this paper basing upon the temperature in the workpiece tool contact area. The technique of determining this temperature has also been given as a combination of analytical and experimental process. These are especially useful by properties and phase transformation investigations in the metastable austenite steels.
Źródło:
Advanced Technologies in Mechanics; 2014, 1, no. 1 (1); 32-40
2392-0327
Pojawia się w:
Advanced Technologies in Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Investigation of low temperature diffusion of carbon in martensite by Mössbauer spectroscopy and X-ray diffraction
Autorzy:
Jabłońska, A.
Dąbrowski, L.
Suwalski, J.
Neov, S.
Powiązania:
https://bibliotekanauki.pl/articles/147492.pdf
Data publikacji:
2006
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
martensite
diffusion coefficients
Mössbauer specroscopy
X-ray studies
Opis:
Martensite containing 0.87 wt.% carbon was studied by Mössbauer spectroscopy at temperatures, T = 10, 15, 25, 40 and 78 K and by X-ray diffraction at T = 78 K in the course of 35 days. Samples in the form of 30 mm thick foil of pure carbon martensite with enhanced tetragonality were synthesized applying non-standard technology. The measured by X-rays (c/a - 1) ratio varies within the limits 0.044-0.055 by pulsations with a period of few hours. According to Kurdimov’s model any changes in tetragonality of martensite are fully related to the passage of carbon atoms from Oc to Oa and Ob octahedral sites or vice versa. Pulsations of the central and satellite sextets were observed by Mössbauer spectroscopy. In accordance with the conventional interpretation of satellites, these pulsations result from different spatial distribution of carbon around the Fe atoms in the diffusion process. The data of (c/a - 1) pulsations were used to determine the diffusion coefficient below 78 K. The measured diffusion coefficient of carbon in a-iron below 78 K contradicts the classical approach to the observed temperature dependence. As the temperature is lowered below 78 K, the diffusion constant approaches the nearly temperature-independent value. The low temperature branch is apparently characteristic of a quantum mechanical process dominated by tunnelling in the ground state.
Źródło:
Nukleonika; 2006, 51, 2; 101-104
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Mössbauer effect studies of Dy(Mn0.4-xAlxFe0.6)2 intermetallics
Autorzy:
Stoch, P.
Pszczoła, J.
Guzdek, P.
Jabłońska, A.
Suwalski, J.
Dąbrowski, L.
Pańta, A.
Powiązania:
https://bibliotekanauki.pl/articles/147206.pdf
Data publikacji:
2004
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
intermetallics
crystal structure
57Fe Mössbauer effect
hyperfine interactions
Slater-Pauling curve
Opis:
Both 3d subbands in the Dy(Mn0.4Fe0.6)2 compound are filled up only partially with 3d electrons. So, it was interesting to study the consequence of Mn/Al substitution in the Dy(Mn0.4 xAlxFe0.6)2 series. The cubic, MgCu2-type, Fd3m crystal structure was observed across the series. However, for x = 0.35 and 0.40 a stoichiometric admixture of the hexagonal, MgZn2-type, P63/mmc structure was evidenced. Mössbauer effect measurements at 57Fe nuclei were performed at 77 K. The magnetic hyperfine field decreases vs. the aluminium content x. This dependence is related to the possible 3d-electron band structure.
Źródło:
Nukleonika; 2004, 49,suppl.3; 23-25
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Novel Properties of Atomically Arranged Perovskites
Autorzy:
Dabrowski, B.
Kolesnik, S.
Chmaissem, O.
Suescun, L.
Mais, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047207.pdf
Data publikacji:
2007-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.47.Lx
75.47.Gk
61.12.Ld
Opis:
Perovskites AMO$\text{}_{3-δ}$ attain unique electronic, magnetic, ferroelectric, thermoelectric, mixed-conducting, and other functional properties through selection of the A- and M-site ions, their fractions, ionic sizes and valences, spin states, and orbital orderings, as well as the oxygen content and vacancy ordering. We illustrate here our systematic exploration of the effects of composition, temperature, pressure, and oxygen content on the thermodynamic stability and magnetic properties for La$\text{}_{1-x-y}$Sr$\text{}_{x}$Ba$\text{}_{y}$MnO$\text{}_{3}$ manganites. Parameters controlling magnetic transitions are identified through examples of single-valent compounds of RMnO$\text{}_{3}$ (the Mn-O-Mn bond angles that can be equivalently described in terms of the tolerance factor) and Sr$\text{}_{1-x}$Ca$\text{}_{x}$MnO$\text{}_{3}$ (the tolerance factor and disorder described in terms of the variance of A-site ion sizes), and the mixed-valent La$\text{}_{0.5}$Sr$\text{}_{0.5-y}$Ba$\text{}_{y}$MnO$\text{}_{3}$ (the tolerance factor, variance of sizes, and the local strains described in terms of the elongated Mn-O bonds). By using an example of kinetically stable, atomically-ordered layered-perovskites we show that improved useful properties, such as the increase in the Curie temperature T$\text{}_{C}$ and enhancement of colossal magneto-resistive effect at room temperature, can be achieved through decreases in structural distortions such as variance of sizes and local strains.
Źródło:
Acta Physica Polonica A; 2007, 111, 1; 15-25
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Barriers and factors supporting agritourism and eco-agritourism activities in the Bug Valley municipalities in the opinion of farm owners
Autorzy:
Radwanska, K.
Dabrowski, D.
Sokol, J.L.
Powiązania:
https://bibliotekanauki.pl/articles/38266.pdf
Data publikacji:
2019
Wydawca:
Szkoła Główna Gospodarstwa Wiejskiego w Warszawie. Wydawnictwo Szkoły Głównej Gospodarstwa Wiejskiego w Warszawie
Opis:
Bariery i czynniki sprzyjające agroturystycznej oraz ekoagroturystycznej działalności w gminach nadbużańskich w opiniach właścicieli gospodarstw
Źródło:
Acta Scientiarum Polonorum. Oeconomia; 2019, 18, 1
1644-0757
Pojawia się w:
Acta Scientiarum Polonorum. Oeconomia
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Use of regression analysis for comparative evaluation of accident hazard in Poland, by regions
Autorzy:
Prochowski, L.
Gidlewski, M.
Dąbrowski, F.
Powiązania:
https://bibliotekanauki.pl/articles/246586.pdf
Data publikacji:
2017
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
regression analysis
road accidents
accident hazard by regions
Opis:
Calculations carried out made it possible to characterize changes in the accident hazard, in numerical terms, based on the course of the regression line. An analysis of the distribution, by regions, of the accident hazard and, above all, the showing of changes in this hazard is an important contribution to the actions taken to improve the road transport system. The rate of decrease in the number of accidents undergoes changes, which are particularly conspicuous in some voivodships (provinces) against the background of the general process of decline in the nationwide number of accidents. A graph to characterize this hazard has been presented, plotted with taking into account the changes in the number of accidents, recorded in monthly steps for a period of 7 years. The rate of these changes was also evaluated, in medium-term and short-term intervals. The calculation results were used to ascertain whether a decline in the total number of accidents in Poland is accompanied by similar changes taking place in individual regions. The symptoms of increasing share of the number of accidents that occur in a few regions in the total number of accidents taking place in Poland may be a cause for alarm.
Źródło:
Journal of KONES; 2017, 24, 4; 255-264
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Role of Microstructure in High Temperature Tribology of Iron Alloys
Autorzy:
Krawczyk, J.
Rożniata, E.
Zimowski, S.
Kot, M.
Dąbrowski, R.
Dziurka, R.
Frocisz, Ł.
Powiązania:
https://bibliotekanauki.pl/articles/355366.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
microstructure
tribology
iron alloys
cast steel
wear
cementite
Opis:
The present paper describe the issue of tool materials wear in a high temperature conditions. The investigations were performed at the cast steel tool material at the tribological contact to the structural steel. The investigations aim was to determine the role of microstructure in a tribological properties between the structural steel and tool material. The results of such investigation could be referenced to the industry conditions and could answer about the problems of tool materials wear. The observations of the wear mechanisms were referred to the microstructure of the mill rolls. The laboratory tests ware aimed at evaluating the thermal treatment modification effect on the cast steels properties. A significant role of the morphology of ledeburitic cementite and secondary cementite on the tribological properties was exhibited. The investigations assumed the presence of an austenitic matrix with primary and secondary cementite. Influence of varying morphology carbides was described. in the cast steel microstructure. The investigation results make possible to point to a direction of carbide morphology change with the purpose of obtaining the assumed properties of hot operation tools.
Źródło:
Archives of Metallurgy and Materials; 2018, 63, 2; 915-920
1733-3490
Pojawia się w:
Archives of Metallurgy and Materials
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 22

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