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Tytuł:
Use of Energy Summing for Selection of Coincidence Events in Positron-Lifetime Spectroscopy
Autorzy:
Bec̆vár̆, F.
C̆iz̆ek, J.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/2007883.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
A BaF$\text{}_{2}$ positron-lifetime spectrometer equipped with a coincidence system that represents a compromise between the traditional fast-fast and fast-slow arrangements is described. The main difference of the present configuration from both the fast-slow and fast-fast ones consists in use of a sum of the energy signals from the start and stop detectors to select the coincidence events. Quality of the spectrometer response function (≈ 150 ps FWHM for $\text{}^{22}$Na) is very close to that observed for our fast-slow configuration with the equivalent detectors but throughput of the present apparatus is increased almost by a factor of two. Moreover, the electronic scheme becomes less complicated, which has also a positive impact on its cost.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 448-454
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spatially Modulated Bragg Gratings
Autorzy:
Procházka, I.
Kotac̆ka, L.
Petrás̆, F.
Powiązania:
https://bibliotekanauki.pl/articles/2008273.pdf
Data publikacji:
1999-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
42.70.Dj
Opis:
A set of coupled mode differential equations which describe the light propagation in an optical fiber containing a photoinduced Bragg grating is derived. Reflection spectra based on numerical solution to these equations are presented when basic grating parameters are varied. In addition, the influence of these parameters on the maximum reflectivity and 3 dB bandwidth is examined. Finally, reflection spectra of the chirped grating and the grating with spatially modulated refractive index changes are discussed.
Źródło:
Acta Physica Polonica A; 1999, 95, 5; 821-835
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hydrogen-Induced Defects in Palladium
Autorzy:
Melikhova, O.
Čížek, J.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/1338026.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.-y
Opis:
In the present work positron annihilation spectroscopy was employed for investigation of hydrogen-induced defects in Pd. Well annealed Pd samples were electrochemically charged with hydrogen and development of defects with increasing hydrogen concentration $x_{H}$ was investigated. At low concentrations (α-phase, $x_{H}$ < 0.017 H/Pd) hydrogen loading introduced vacancies, since absorbed hydrogen segregating at vacancies lowers remarkably the vacancy formation energy. When hydrogen concentration exceeds 0.017 H/Pd, particles of palladium hydride (PdH) are formed. Stress induced by growing PdH particles leads to plastic deformation which generates dislocations and vacancies in the sample.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 752-755
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Performance of a High-Resolution Digital Positron-Lifetime Spectrometer
Autorzy:
Bečvář, F.
Čížek, J.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/1812465.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
This work describes a digital positron-lifetime spectrometer based on two ultrafast digitizers. Performance of the digital spectrometer in conditions of a routine measurement is compared with an analogue setup connected to the same detectors. It was found that engagement of the digital setup leads to an improvement of timing resolution (FWHM for $\text{}^{22}Na$) from 169 ps for the traditional analogue setup to 146 ps for the digital setup. The coincidence count rate for 1.2 MBq $\text{}^{22}Na$ source is 75-80 coinc./s for both configurations. These results clearly demonstrate the advantages of the digital timing over the traditional analogue setup.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1279-1284
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Defects in Zirconia Nanomaterials Doped with Rare-Earth Oxides
Autorzy:
Prochazka, I.
Cizek, J.
Melikhova, O.
Konstantinova, T.
Danilenko, I.
Powiązania:
https://bibliotekanauki.pl/articles/1338541.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.07.Wx
61.46.Hk
78.70.Bj
Opis:
Positron lifetime and coincidence Doppler broadening measurements on $ZrO_2$+3 mol.% $RE_2O_3$ (RE = Eu, Gd, Lu) nanopowders and ceramics obtained by sintering these nanopowders are reported. The initial nanopowders were prepared by a co-precipitation technique and exhibited a mean particle size of ≈ 15 nm. The nanopowders were calcined and pressure-compacted. All compacted nanopowders exhibited the prevailing tetragonal phase with at most 15% of the monoclinic admixture. Positrons in compacted nanopowders were found to annihilate almost exclusively at grain boundaries: (i) vacancy-like misfit defects along grain boundaries and (ii) larger defects situated at intersections of grain boundaries (triple points). In nanopowders, a small portion of positrons formed positronium in pores between crystallites. Sintering of nanopowders at 1500C caused a substantial grain growth and formation of ceramics. Sintering-induced grain growth led to a disappearance of the triple points and pores. The ceramics containing Eu and Gd dopants consist of mixture of the monoclinic and the tetragonal phase, while the ceramics with Lu dopant exhibits almost exclusively the tetragonal phase.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 760-763
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Precipitation Effects in Mg-Zn Alloys Studied by Positron Annihilation and Hardness Testing
Autorzy:
Hruška, P.
Čížek, J.
Vlček, M.
Melikhova, O.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/1196079.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.J-
Opis:
In the present work positron annihilation spectroscopy combined with Vickers hardness testing were employed in order to investigate precipitation effects in Mg-Zn alloys. It was found that incoherent precipitates of a metastable Zn-rich phase formed in the samples isochronally annealed above 200C cause hardening of the alloy.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 718-721
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Investigation of Precipitation Effects in Mg-Tb and Mg-Tb-Nd Alloys
Autorzy:
Vlček, M.
Čížek, J.
Melikhova, O.
Hruška, P.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/1196115.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.J-
Opis:
Investigation of precipitation effects in solution treated Mg-Tb and Mg-Tb-Nd alloy was performed. Solution treated alloys were compared with samples deformed by high pressure torsion to examine influence of deformation on precipitation effects. Dislocations present in samples processed by high pressure torsion can serve as diffusion channels for atoms and also as nucleation sites for precipitates. Therefore precipitation of some phases in high pressure torsion deformed samples was observed at lower temperatures than in solution treated ones.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 744-747
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Ceramic Nanoparticles on Thermal Stability of Ultra Fine Grained Copper
Autorzy:
Čížek, J.
Procházka, I.
Cieslar, M.
Islamgaliev, R.
Kulyasova, O.
Powiązania:
https://bibliotekanauki.pl/articles/1812477.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
79.60.Jv
Opis:
A detailed study of the bulk ultra fine grained pure copper and copper with $Al_2O_3$ particles was carried out in the present work. The specimens were prepared by the high-pressure torsion and their microstructure was investigated by positron lifetime spectroscopy combined with transmission electron microscopy and microhardness tests. Defects in the as-deformed materials were characterized and the thermal stability of the ultra fine grained microstructure was subsequently examined in annealing experiments. An addition of $Al_2O_3$ nanoparticles was found to improve significantly the thermal stability of the ultra fine grained structure, the optimum content of $Al_2O_3$ being ≈0.5 wt.%.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1285-1292
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Lifetime Spectroscopy of Nanocrystalline Copper
Autorzy:
C̆ížek, J.
Procházka, I.
Vostrý, P.
Chmelík, F.
Islamgaliev, R. K.
Powiązania:
https://bibliotekanauki.pl/articles/2007957.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
79.60.Jv
Opis:
Positron lifetime spectroscopy was applied to investigate the thermal stability of nanocrystalline copper prepared by severe plastic torsion deformation. Positrons annihilating in as prepared specimens exhibited free positron component τ$\text{}_{1}$ and two defect components τ$\text{}_{2}$=164 ps and τ$\text{}_{3}$=255 ps. Evolution of the lifetimes and relative intensities of all the three components with increasing annealing temperature during step-by-step isochronal annealing up to 630°C was studied. Behaviour of positrons in nanocrystalline copper could not be interpreted in the frame of conventional 3-state trapping model due to highly inhomogeneous defect distribution. Therefore a modified trapping model was developed and applied to explain the experimental results.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 487-495
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Defects Studies of ZnO Single Crystals Prepared by Various Techniques
Autorzy:
Lukáč, F.
Čížek, J.
Procházka, I.
Melikhova, O.
Anwand, W.
Brauer, G.
Powiązania:
https://bibliotekanauki.pl/articles/1196118.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.J-
Opis:
The aim of the present work was a comparison of defects in ZnO crystals grown by various techniques available nowadays, namely hydrothermal growth, pressurized melt, Bridgman method growth and vapor phase growth. Positron annihilation spectroscopy was employed as a principal tool for characterization of defects in ZnO crystals grown by above mentioned various techniques. ZnO crystals can be divided into two groups: (i) hydrothermal grown crystals, which exhibit positron lifetime of 179-182 ps and (ii) ZnO crystals grown by the other techniques (pressurized melt, Bridgman method, vapor phase growth) which are characterized by the lower lifetimes falling in the range of 160-173 ps. Comparison of experimental data with ab initio theoretical calculations revealed that HT grown ZnO crystals contains Zn vacancies associated with hydrogen atom in a bond-centered site. On the other hand, ZnO crystals prepared by other techniques contain most probably stacking faults created by stresses induced by temperature gradients in the melt.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 748-751
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Lifetimes in Zirconia-Based Nanomaterials
Autorzy:
Procházka, I.
Čížek, J.
Kuriplach, J.
Melikhova, O.
Konstantinova, T.
Danilenko, I.
Powiązania:
https://bibliotekanauki.pl/articles/1812546.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.46.Hk
81.05.Je
81.07.Wx
Opis:
Positron lifetime spectroscopy is employed in a comparative study of several zirconia-based materials: (i) the pressure-compacted nanopowders of the three zirconia polymorphs - pure $ZrO_2$ (monoclinic), yttria-stabilized $ZrO_2$+3 mol.% $Y_2O_3$ (tetragonal) and yttria-stabilized $ZrO_2$+8 mol.% $Y_2O_3$ (cubic), (ii) ceramic materials obtained by sintering of the above two yttria-stabilized zirconia nanopowders and (iii) the tetragonal and cubic yttria-stabilized zirconia monocrystals. Positron lifetime data observed on the nanopowders suggest that the two shortest components, exhibiting lifetimes of ≈180 and ≈370 ps, arise from the annihilation of positrons trapped in defects associated with grain boundaries, presumably the vacancy-like defects and tripple points, respectively. Positron lifetime spectra observed on the ceramic materials resemble those found for the corresponding monocrystals, giving thus an additional support to the above interpretation of the nanopowders results.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1495-1499
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu-Based Alloys
Autorzy:
Melichova, O.
Vostrý, P.
Procházka, I.
Cieslar, M.
Stulíková, I.
Faltus, J.
Powiązania:
https://bibliotekanauki.pl/articles/2008146.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.Hh
81.30.Mh
Opis:
The improved workability of the commercial automatic machine designed alloy Al-Cu-Bi-Pb is guaranteed by the presence of Pb. Nevertheless, the toxic element Pb reduces some of the alloy properties. Therefore new Pb-free machinable Al-based alloys are developed. The Al-Cu-Bi-Sn alloy belongs to these non-traditional materials. The contribution deals with the investigation of precipitation effects in Al-Cu-Bi-Sn alloy during step-by-step isochronal annealing up to 500°C after previous solution heat treatment by means of positron annihilation spectroscopy completed with electrical resistivity measurements and results of independent transmission electron microscopy studies. The used combination of experimental methods gives the possibility to detect separately the redistribution of Sn and Cu atoms in the matrix and to study the influence of vacancies on this process.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 627-631
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy
Autorzy:
Αda, P.
Cieslar, M.
Vostrý, P.
Bečvář, F.
Νovotný, I.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/1933483.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.72.-y
78.70.-g
81.40.-z
Opis:
Decomposition of the supersaturated solid solution of 2 at.% Cu in Al was investigated by means of electrical resistivity and high-resolution positron lifetime measurements. The phase composition of this alloy was determined by transmission electron microscopy. Electrical resistivity measurements were performed by a classical four-point method. Positron lifetime spectra were measured by means of a spectrometer consisting of two BaF$\text{}_{2}$ detectors and a standard fast-slow coincidence system. The specimens were first exposed to the solution heat treatment at 783 K for 19 hours with a subsequent quenching. Then the specimens were isochronally annealed in the temperature range 293 ÷ 573 K. Annealing responses of electrical resistivity and positron annihilation were studied. Resistivity measurements as well as transmission electron microscopy observations confirmed the well-known decomposition sequence of the Al-Cu alloy. The decomposition of the alloy was manifested by the decrease in the intensity of positron lifetime component τ$\text{}_{2}$ = (207 ±2 ) ps correlated with simultaneous appearance and increase in the intensity of τ$\text{}_{3}$ = (180 ± 5) ps component. Component τ$\text{}_{2}$ originates from positron annihilation in vacancies trapped at the Guinier-Preston zones while τ$\text{}_{3}$ comes from annihilation of the positrons localized in the misfit dislocations at coherent precipitates of the Al$\text{}_{2}$Cu phase. The shortest observed component τ$\text{}_{1}$ apparently belongs to annihilation of untrapped positrons.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 111-117
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analytical method for determining antropometric parameters in body mass reduction process in the aspect of health safety
Analityczna metoda określania parametrów antropometrycznych w procesie redukcji masy ciała w aspekcie bezpieczeństwa zdrowia
Autorzy:
Ślęzak, A.
Ślęzak-Prochazka, I.
Batko, K. M.
Zyska, A.
Gawrys, W.
Jóźwiak, J.
Powiązania:
https://bibliotekanauki.pl/articles/103598.pdf
Data publikacji:
2017
Wydawca:
Uniwersytet Humanistyczno-Przyrodniczy im. Jana Długosza w Częstochowie. Wydawnictwo Uczelniane
Tematy:
overweight reduction
mathematical model
bioelectric impendance method
overweight reduction coefficient
low-sugar diet
health security
redukcja nadwagi
model matematyczny
metoda impedancji bioelektrycznej
współczynniki redukcji nadwagi
dieta niskocukrowa
bezpieczeństwo zdrowotne
Opis:
In this study, for the first time we developed a mathematical model showing that the reduction in parameters such as total body mass, total fat mass, visceral fat mass, waist circumference, hip circumference and body mass index (BMI) can be described using exponential equations. Constants kt, kf, kfv, kBMI, kp, kb that occur in particular equations characterize individual features related to these anthropometric parameters. The presented model was verified using experimental data obtained by analysis of body composition. These individuals were overweight in the initial moment of the experiment and eliminated or limited easily digestible products containing sugar from their diet. We showed that there is a critical time, when each individual achieved normal values of body mass index, fat mass, visceral fat mass, waist circumference, hip circumference, and waist-hip ratio. This critical time ranged between 35 and 46 weeks.
W tym badaniu jako pierwsi opracowaliśmy model matematyczny pokazujący, że zmniejszenie parametrów, takich jak całkowita masa ciała, całkowita masa tłuszczu, trzewna masa tłuszczowa, obwód talii, obwód bioder i wskaźnik masy ciała (BMI), można opisać za pomocą równania wykładniczego. Stałe kt, kf, kfv, kBMI, kp, kb występujące w poszczególnych równaniach charakteryzują poszczególne cechy związane z tymi parametrami antropometrycznymi. Przedstawiony model zweryfikowano za pomocą danych eksperymentalnych uzyskanych poprzez analizę składu ciała. Osoby badane miały nadwagę w początkowym momencie eksperymentu i wyeliminowały lub ograniczyły z diety łatwo przyswajalne produkty zawierające cukier. Pokazaliśmy krytyczny czas, kiedy każdy człowiek osiąga normalne wartości wskaźnika masy ciała, masy tłuszczu, masy trzewnej, obwodu talii, obwodu bioder i stosunku talii do bioder. Ten krytyczny czas waha się od 35 do 46 tygodni.
Źródło:
Prace Naukowe Akademii im. Jana Długosza w Częstochowie. Technika, Informatyka, Inżynieria Bezpieczeństwa; 2017, T. 5; 191-208
2300-5343
Pojawia się w:
Prace Naukowe Akademii im. Jana Długosza w Częstochowie. Technika, Informatyka, Inżynieria Bezpieczeństwa
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Simulation of Positron Annihilation Response to Mechanical Deformation of Nanostructured AgCo
Autorzy:
Melikhova, O.
Kuriplach, J.
Čížek, J.
Procházka, I.
Hou, M.
Pisov, S.
Zhurkin, E.
Powiązania:
https://bibliotekanauki.pl/articles/1812541.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.15.Pd
61.46.Hk
Opis:
Nanostructured materials attract nowadays a broad attention due to their specific properties. Defects play an essential role in material properties so their characterisation is very important. The evolution of the various open volume defects in AgCo nanowire modelled samples obtained using molecular dynamics was studied. Isothermal and isoenergetic deformation mechanisms are considered. General analyses of open volume defects concerning their size and their chemical environment were performed. Positron lifetimes, binding energies, and high momentum parts of the momentum distribution of annihilationγ-quanta were calculated for selected defects.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1455-1464
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 19

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