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Wyświetlanie 1-15 z 1589
Tytuł:
Positron Annihilation Methods by Use of LSO Scintillators
Autorzy:
Hirade, T.
Oka, T.
Powiązania:
https://bibliotekanauki.pl/articles/1339992.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
$Lu_2SiO_5$:Ce (LSO) scintillator is one of the scintillators used for positron emission tomography because of its high efficiency of gamma-ray detection. We tried to use LSO for positron annihilation lifetime and age-momentum correlation measurements because the high efficiency is needed to reduce the positron irradiation effect during measurements. The high efficiency with reasonable time resolution was successfully obtained by use of the dynode signals from photomultiplier tubes.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 825-828
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bose-Hubbard Model in the Rotating Frame of Reference
Autorzy:
Polak, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1536643.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.30.Jp
03.75.Lm
03.75.Nt
Opis:
Following a novel experimental arrangement which can rotate a two-dimensional optical lattice at frequencies up to several kilohertz we discuss the ground state of the two-dimensional Bose-Hubbard Hamiltonian, relevant for rotating gaseous Bose-Einstein condensates, by employing U(1) quantum rotor approach and the topologically constrained path integral. Ultracold atoms in such a rotating lattice can be used for the direct quantum simulation of strongly correlated systems under large effective magnetic fields. We derive an effective quantum action for the Bose-Hubbard model, which enables a non-perturbative treatment of the zero-temperature phase transition in the rotating frame. We calculate the ground-state phase diagram, analytically deriving maximum repulsive energy for several rational values of the frustration rotation parameter f = 0, 1/2, 1/3, 1/4, and 1/6 for the square and triangular lattice. Performed calculations revealed strong non-monotonical dependence of the critical ratio of the kinetic energy to the repulsive on-site energy, that separates the global coherent from the insulating state, on topology of the lattice.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 279-282
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Neutral Bosonic Condensates in Layered 2D Structures under Artificial Magnetic Field
Autorzy:
Polak, T.
Zaleski, T.
Powiązania:
https://bibliotekanauki.pl/articles/1429105.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.30.Jp
03.75.Lm
03.75.Nt
Opis:
We show that the properties of the ideal Bose gas in three-dimensional optical lattice can be closely mimicked by finite two dimensional systems with only ten of layers. The match between critical properties strongly depends on the anisotropy of the hopping amplitudes in and between layers which we fully control. The theory we provided can be directly used in the experiments and results in less challenging requirements of the setups. We also present the phase diagram with its non-monotonic dependence of the ratio of tunneling to on-site repulsion when artificial magnetic field is applied to the system.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 1312-1314
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Energy Levels and Electrical Activity of Dislocation Electron States in GaAs
Autorzy:
Wosiński, T.
Figielski, T.
Powiązania:
https://bibliotekanauki.pl/articles/1924306.pdf
Data publikacji:
1993-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.70.-r
71.55.Eq
Opis:
Experimental results are presented confirming that the two energy levels in GaAs: E$\text{}_{c}$ - 0.68 eV and E$\text{}_{v}$ + 0.37 eV, discovered in plastically deformed crystals, belong actually to dislocations. In view of recent identification of the electron state of misfit dislocations at an InGaAs/GaAs interface, a correspondence between these levels and dislocation types has been reinterpreted. The first mentioned leve1 belongs likely to α while the second one to β dislocations of 60° (glide set) type. Such a correspondence is compatible with the observed effect of irradiation on dislocation glide motion in GaAs. It is also argued that these energy levels are involved in the phenomenon of unquenchability of the EL2 defects placed in high-stress regions near dislocations.
Źródło:
Acta Physica Polonica A; 1993, 83, 1; 51-58
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Anisotropy of NiMn/Ni and NiMn/Cu/Ni Thin Films
Autorzy:
Ogawa, T.
Sato, T.
Powiązania:
https://bibliotekanauki.pl/articles/2013074.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Gw
75.50.Lk
75.70.Ak
Opis:
The magnetic anisotropy of reentrant spin glass NiMn thin film, in the vicinity of the ferromagnetic Ni film, is investigated using NiMn/Ni, Cu/Ni/Cu (t=10 Å and 500 Å)/NiMn and NiMn/Ni/Cu (t=10 ÷ 5000 Å)/Ni films. The unidirectional anisotropy field of NiMn layer in NiMn/Ni film is smaller than that of bulk NiMn. In Cu/Ni/Cu (t=10 Å and 500 Å)/NiMn film, the unidirectional anisotropy field is almost independent of the Cu spacer thickness. These results can be explained in terms of magnetic coupling between the magnetic layers in addition to the film structure of NiMn layer.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 491-494
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Image Depth Profiling AES
Autorzy:
Sekine, T.
Sato, T.
Powiązania:
https://bibliotekanauki.pl/articles/1892328.pdf
Data publikacji:
1992-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
68.35.Dv
Opis:
Image depth profiling AES incorporating an image processing technique has been developed. This method reconstructs a cross-sectional image from acquired 2-dimensional and/or 3-dimensional data. A binary image produced from a secondary electron image through image processing can be used to cut the area of interest for selected area analysis. In a failure analysis of a relay contact, we found by cross-sectional image observation that Fe and Ni permeate from pin holes in an Au layer covering a Fe-Ni alloy. A VTR head made of a polycrystalline ferrite core covered with a Sendust (Si-Al-Fe alloy) layer at the gap has been analyzed. Depth distributions of Al, 0, and Fe on different grains, and Al and O distributions near grain boundaries have been successfully reassembled from the 3-dimensional data.
Źródło:
Acta Physica Polonica A; 1992, 81, 1; 145-157
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Disorder-Assisted Exciton Transport
Autorzy:
Scholak, T.
Zech, T.
Wellens, T.
Buchleitner, A.
Powiązania:
https://bibliotekanauki.pl/articles/1492761.pdf
Data publikacji:
2011-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
87.15.hj
05.60.Gg
03.65.Ud
03.65.Yz
Opis:
We discuss the possibly constructive role of disorder for the optimization of exciton transport in the FMO (Fenna-Matthews-Olson) light harvesting complex. Our analysis, which models the FMO as a 3D random graph, demonstrates the existence of a small fraction of optimal, though highly asymmetric, non-periodic conformations, which yield near-to-optimal coherent excitation transport. We argue that, on transient time scales, such quantum interference enhanced transport does always better than stochastic activation.
Źródło:
Acta Physica Polonica A; 2011, 120, 6A; A-089-A-094
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Anisotropy in Co/Nd Multilayers with Depth-Selectively Inserted $\text{}^{57}$Fe Probe Layer
Autorzy:
Baczewski, L. T.
Mibu, K.
Nagahama, T.
Shinjo, T.
Powiązania:
https://bibliotekanauki.pl/articles/2013044.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Gw
75.70.-i
76.80.+y
Opis:
Multilayers of Co/Nd with probe layer of 2 Å of $\text{}^{57}$Fe evaporated in UHV conditions were studied by means of vibrating sample magnetometry and Mössbauer spectroscopy at T = 4.2 K. Isomer shift, hyperfine field distribution and direction was obtained from the Mössbauer data computer fitting. Magnetic anisotropy was studied and discussed. The easy magnetization direction was close to the perpendicular direction for both samples but the tendency to perpendicular anisotropy was stronger when the Fe probe layer was placed in the vicinity of Co/Nd interface.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 439-442
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Spectral Functions in the Presence of the Antiferromagnetic Order in the Two-Dimensional Hubbard Model
Autorzy:
Zaleski, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1536615.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
71.10.-w
71.10.Pm
Opis:
We use a recently proposed quantum SU(2)×U(1) rotor approach for the Hubbard model to calculate electronic spectral functions in a presence of an antiferromagnetic state for any value of the Coulomb interaction. We isolate the collective variables for charge and spin in the form of the space-time fluctuating U(1) phase field and SU(2) rotating spin quantization axis, respectively. As a result, the fermion Green function in the space-time domain becomes a product of a $CP^1$ propagator resulting from the SU(2) gauge fields, U(1) phase propagator and the pseudo-fermion correlation function. In turn, the spectral lines are obtained by performing the convolution of spin, charge and pseudo-fermion Green's functions. We observe an emergence of a sharp peak in the electron spectral functions within the antiferromagnetic phase, whose spectral weight is equal to the antiferromagnetic order parameter.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 267-272
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dynamic Structure Factor of Ultracold Bosons in Optical Lattice
Autorzy:
Zaleski, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1398602.pdf
Data publikacji:
2016-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
03.75.Hh
05.30.Jp
67.85.Hj
Opis:
Ultracold atoms in optical lattices have been intensively investigated in recent years as they provide a very well controllable environment for observation of many-body quantum phenomena, closely mimicking physics of strongly interacting electronic systems. Here, we use the quantum rotor approach supplemented by the Bogolyubov method to investigate one- and two-particle excitations, which are a measure of inter-particle correlations. We calculate one-particle spectral function and dynamic structure factor, which can be observed using spectroscopy of cold atomic systems. Our calculations require a significant numerical effort to determine multidimensional convolutions of momentum and frequency dependent constituents functions, which we achieve using parallelised fast Fourier transform. We observe the appearance of sharp coherence peaks in the superfluid phase of the cold bosons, which closely resembles the formation of sharply defined quasiparticle excitations below $T_{c}$ in cuprates or smeared excitation spectra characteristic for strongly interacting systems.
Źródło:
Acta Physica Polonica A; 2016, 130, 2; 564-568
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultra-Cold Bosons in Optical Lattice: Time-of-Flight Imaging of Atom-Atom Correlations
Autorzy:
Zaleski, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1431254.pdf
Data publikacji:
2012-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
03.75.Kk
05.30.Jp
67.85.Hj
Opis:
In the present paper, we investigate a system of strongly interacting bosons confined in two-dimensional optical lattice. We propose a combination of the Bogoliubov method with the quantum rotor approach and determine the spatial atom-atom correlations. This allows us to calculate time-of-flight absorption images, which exhibit all the characteristic features present in experimental results, namely transition from superfluid peaks to Mott insulating blob.
Źródło:
Acta Physica Polonica A; 2012, 121, 4; 796-800
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Quantum Rotor Approach to the Mott-Insulator Transition in the Bose-Hubbard Model
Autorzy:
Polak, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1812265.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.30.Jp
03.75.Lm
03.75.Nt
Opis:
We present the novel approach to the Bose-Hubbard model using the U(1) quantum rotor description. We formulate a problem in the phase only action using an effective action formalism and obtain analytical formulae for the critical lines. We show that the nontrivial U(1) phase field configurations have an impact on the phase diagrams. The topological character of the quantum field is governed by terms of the integer charges -- winding numbers n. The comparison of the presented results with recently obtained quantum Monte Carlo numerical calculations suggests that the competition between quantum effects in strongly interacting boson systems is correctly captured by our model.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 29-34
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Antiferromagnetic Order in the Hubbard Model: Spin-Charge Rotating Reference Frame Approach
Autorzy:
Zaleski, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1812334.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.10.Jm
Opis:
We study the antiferromagnetic phase of three-dimensional Hubbard model with nearest neighbors hopping on a bipartite cubic lattice. We use the quantum SU(2)×U(1) rotor approach that yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties of the model and satisfies the Mermin-Wagner theorem. As our theory describes the evolution from a Slater (U ≪ t) to a Mott-Heisenberg (U ≫ t) antiferromagnet, we present the phase diagram of the antiferromagnetic Hubbard model as a function of the crossover parameter U/t.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 247-251
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Phase Transitions in Optical Lattices at Finite Temperatures
Autorzy:
Polak, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1810621.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.30.Jp
03.75.Lm
03.75.Nt
67.40.Kh
Opis:
We discuss the finite-temperature phase diagram in three-dimensional Bose-Hubbard model relevant for the Bose-Einstein condensates in optical lattices, by employing U(1) quantum rotor approach and the topologically constrained path integral, that includes a summation over U(1) topological charge. The effective action formalism allows us to formulate a problem in the phase only action and obtain analytical formulae for the critical lines beyond mean-field theory.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 418-420
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical Evaluation of Thermal Properties of TiO₂ Anatase and Rutile by using Einstein-Debye Approximation
Autorzy:
Mehmetoglu, T.
Powiązania:
https://bibliotekanauki.pl/articles/1030581.pdf
Data publikacji:
2018-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
specific heat capacities
Einstein-Debye model
Debye temperature
thermal properties
Opis:
In this work, we propose a new approach to accurate calculation of heat capacities at constant volume and pressure of TiO₂ anatase and rutile. The evaluation model is based on the Einstein-Debye approximation which has been extensively used in solid state physics. The application of proposed approach to anatase and rutile titanium dioxide computations results is shown to be well numerically satisfactory. This approach is valid in wide temperature ranges and can be suggested for accurate evaluation of thermal properties of solids. The calculation results are in well agreement with the literature values reported by other studies.
Źródło:
Acta Physica Polonica A; 2018, 133, 1; 126-128
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 1589

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