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Wyświetlanie 1-15 z 28
Tytuł:
In the Search of Electron Correlation Effects in DNA
Autorzy:
Wróbel, A.
Wróbel, P.
Powiązania:
https://bibliotekanauki.pl/articles/1537235.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
87.14.gk
75.20.-g
71.10.Fd
Opis:
We discuss the energy scale separation induced in DNA by gaps between molecular orbital states of individual bases and by electron correlations. We also demonstrate how this separation gives rise to effective low energy models of electron transport in DNA.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 409-412
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Modification of commercial activated carbons for CO₂ adsorption
Autorzy:
Sreńscek-Nazzal, J.
Narkiewicz, U.
Morawski, A.
Wróbel,A. Gęsikiewicz-Puchalska, R.
Michalkiewicz, B.
Powiązania:
https://bibliotekanauki.pl/articles/1070602.pdf
Data publikacji:
2016-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.05.U-
68.43.-h
Opis:
The aim of the investigations was a modification of DTO, a commercial activated carbon (AC), to improve CO₂ adsorption capacity. The adsorption of CO₂ up to 40 bar at 40°C temperature was investigated. The volumetric method was applied for CO₂ adsorption isotherm measurements. The starting material - DTO - was modified using chemical activation (KOH, ZnCl₂, K₂CO₃). The textural parameters of all the ACs were determined by nitrogen adsorption at the liquid nitrogen temperature of -196°C on Quadrasorb SI. Results showed that the AC modified with KOH had the highest S_{BET}, V_{tot}, V_{mic} values of 2063 m²/g, 1.13 cm³/g, and 0.67 cm³/g, respectively. ACs with a wider pore size distribution (from micropores to mesopores) were obtained. The maximum CO₂ adsorption was equal to 14.44 mmol/g for DTO/KOH - modified carbon whereas 8.07 mmol/g of CO₂ was adsorbed at DTO. The CO₂ adsorption capacities of the ACs were found to be closely correlated with the BET surface areas of the materials tested. The experimental data was fitted to the Freundlich, Langmuir, Sips and Toth equations to determine the model isotherm. The Sips model was found to be the best for fitting the adsorption of CO₂.
Źródło:
Acta Physica Polonica A; 2016, 129, 3; 394-401
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymmetric Tunneling Conductance in Doped Antiferromagnets
Autorzy:
Maciąg, A.
Wróbel, P.
Powiązania:
https://bibliotekanauki.pl/articles/2046776.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
74.20.Mn
74.25.Fy
Opis:
We calculate the tunneling conductance in the framework of the spin polaron model, which is an effective model for the t-J model, in the limit where at least short-range antiferromagnetic correlations exist. We show that both in the normal state and in the superconducting state the asymmetry of tunneling conductance is present. This fact is the implication of the particle-hole asymmetry of the spin polaron Hamiltonian in the limit of low density of spin polarons which are quasiparticles emerging in a hole doped antiferromagnet. Experimental evidence of analogous asymmetric tunneling conductance was found in the tunneling spectroscopy measurements of high T$\text{}_{c}$ superconductors.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 607-610
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Electronic Structure on the Phase Diagram of Weakly Doped Superconducting Cuprates
Autorzy:
Maciąg, A. M.
Wróbel, P.
Powiązania:
https://bibliotekanauki.pl/articles/2047334.pdf
Data publikacji:
2007-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
74.20.Mn
74.25.Dw
Opis:
Motivated by the difference between the experimental phase diagram of cuprates and expectations of the t-J model, we analyze the influence of the electronic structure on superconducting state generation for small levels of doping. Following some theoretical studies of the Fermi surface for hole doped superconducting cuprates we base our calculations on the t-t'-t''-J model. We construct the spin polaron model, which is an effective model for the t-J model, and we expand it by adding the new terms related to the next neighbor hopping integrals t' and t''. In the framework of this model we study evolutions of superconducting correlation functions with doping. As a result of numerical calculations we find out that superconducting state vanishes for small levels of doping and finite values of t' and t''. This is in qualitative agreement with experimental results.
Źródło:
Acta Physica Polonica A; 2007, 111, 5; 721-725
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of asymmetric cold rolling on texture of a commercially pure copper
Autorzy:
Uniwersał, A.
Wróbel, M.
Wierzbanowski, K.
Wroński, M.
Powiązania:
https://bibliotekanauki.pl/articles/1112983.pdf
Data publikacji:
2016-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.40.Ef
Opis:
This study deals with the influence of the rolling asymmetry and applied strain on the crystallographic texture of polycrystalline copper. It was shown that textures of asymmetrically rolled materials are rotated with respect to those rolled symmetrically and the rotation angle increases both with the rolling asymmetry and strain. The asymmetric rolling leads also to a decrease of intensity of texture components forming skeleton lines in the orientation space. However, individual texture components exhibit different sensitivity to the effect of asymmetric rolling.
Źródło:
Acta Physica Polonica A; 2016, 130, 4; 1049-1052
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Unconventional Superconductivity, Spontaneous Time-Reversal Symmetry Breaking and Lowering of Kinetic Energy in Doped, Short-Range Antiferromagnets
Autorzy:
Wróbel, P.
Maciąg, A.
Eder, R.
Fulde, P.
Micnas, R.
Powiązania:
https://bibliotekanauki.pl/articles/2038385.pdf
Data publikacji:
2004-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Mn
71.10.Fd
Opis:
In this paper we focus on the anomalous temperature dependence of the in-plane conductivity and symmetry mixing of the superconducting order parameter observed in various experiments on cuprates. We show that the one-band Hubbard model is not capable of describing the physics of cuprates because the kinetic energy is lowered in this model in the superconducting state, which contradicts experimental observations. The proper model to investigate doped, short-range antiferromagnets is the t-J model, for which our results agree with experiments. We analyze a spin polaron model, that is an effective model for a doped antiferromagnet. In the framework of this model we also study the superconducting order-parameter symmetry-mixing phenomenon. We show that the expected mixing of d-wave symmetry with p-wave symmetry takes place in the superconducting order-parameter at a finite value of the doping parameter. This symmetry mixing brakes the time-reversal symmetry.
Źródło:
Acta Physica Polonica A; 2004, 106, 5; 575-581
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin Polaron-Bipolaron Scenario of Three Gap-Like Energy Scales in Superconducting Cuprates
Autorzy:
Wróbel, P.
Maciąg, A.
Suleja, W.
Eder, R.
Micnas, R.
Powiązania:
https://bibliotekanauki.pl/articles/1536806.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Mn
74.72.Kf
Opis:
We argue that three gaps observed in underdoped cuprates can be attributed to the formation of antiferromagnetic spin polarons and bipolarons. Within the spin polaron scenario the antinodal pseudogap at he high energy scale originates from the change of the Fermi surface topology, induced by antiferromagnetic correlations. That change gives rise to the diminishing of the spectral weight at the antinodal region near the Brillouin zone boundary. We demonstrate that effect by analyzing effective models of doped antiferromagnets. The second type of pseudogap appearing at the intermediate energy scale originates from the phenomena which are precursory to superconductivity and predominantly concern the portion of the Fermi surface near the nodal region. In order to analyze the latter phenomenon we use the negative U Hubbard model, in which many details typical to spin polaron physics are neglected, but which contains the essential ingredient of it, that is the strong short range attraction. The lowest energy scale is related to the true superconducting gap which develops with doping, although both types of pseudogap diminish with doping. This behavior can be explained by the fact that the spin polaron band is empty in the undoped system and therefore the formation of the superconducting state in the system is forbidden. Due to a pedagogical character of this report, we present in the introduction a short overview of mostly recent experimental results which are related to the gap-pseudogap physics.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 292-298
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin Reorientation Studies in Nd$\text{}_{2}$Fe$\text{}_{14-x}$Si$\text{}_{x}$B (0
Autorzy:
Gargula, R.
Pędziwiatr, A.
Bogacz, B.
Wróbel, S.
Bartolomé, J.
Stankiewicz, J.
Powiązania:
https://bibliotekanauki.pl/articles/2030427.pdf
Data publikacji:
2002-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.50.Ww
76.80.+y
64.60.-i
Opis:
Nd$\text{}_{2}$Fe$\text{}_{14-x}$Si$\text{}_{x}$B (x=0.25, 0.5, 0.75, 1.0, 1.5, 2.0) intermetallic compounds were investigated by magnetometry, $\text{}^{57}$Fe Mössbauer effect, electric resistivity, and differential scanning calorimetry mainly in the vicinity of the spin reorientation temperature, T$\text{}_{SR}$. The Curie temperature, T$\text{}_{C}$, and T$\text{}_{SR}$ were determined for different compositions and the spin phase diagram was constructed. $\text{}^{57}$Fe Mössbauer spectra showed noticeable changes in the reorientation region. For temperatures above the transition, the spectra were analysed using 6 Zeeman patterns associated with 6 inequivalent crystal sites in Nd$\text{}_{2}$Fe$\text{}_{14}$B according to site occupations (16k$\text{}_{1}$:16k$\text{}_{2}$:8j$\text{}_{1}$:8j$\text{}_{2}$:4c:4e). In the transition region, 12 subspectra had to be incorporated in the analysis. Electric resistivity measurements showed a typical metallic behaviour with no anomalies in the magnetic transition region. Differential scanning calorimetry measurements revealed broad endothermic two stage peaks around T$\text{}_{SR}$.
Źródło:
Acta Physica Polonica A; 2002, 101, 2; 289-294
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bistability of (Ga,Mn)As Ferromagnetic Nanostructures Due to the Domain Walls Switching
Autorzy:
Andrearczyk, T.
Wosiński, T.
Mąkosa, A.
Figielski, T.
Wróbel, J.
Sadowski, J.
Powiązania:
https://bibliotekanauki.pl/articles/1791342.pdf
Data publikacji:
2009-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.50.Jt
75.50.Pp
75.30.Gw
75.60.Ch
85.75.-d
Opis:
We designed and investigated four-arm nanostructures, composed of two perpendicularly crossed stripes, fabricated from ferromagnetic (Ga,Mn)As layer by means of electron-beam lithography patterning and chemical etching. The nanostructures exhibit a bistable resistance behavior resulting from two configurations of magnetic domain walls in the central part of the structures. We demonstrate a possibility of switching between two stable resistance states in zero magnetic field by applying a pulse of either weak magnetic field or electric current through the structure.
Źródło:
Acta Physica Polonica A; 2009, 116, 5; 901-903
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Activated carbons from molasses as CO₂ sorbents
Autorzy:
Młodzik, J.
Sreńscek-Nazzal, J.
Narkiewicz, U.
Morawski, A.
Wróbel, R.
Michalkiewicz, B.
Powiązania:
https://bibliotekanauki.pl/articles/1070546.pdf
Data publikacji:
2016-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.05.U-
68.43.-h
Opis:
Aim of this research is to obtain effective, molasses based activated carbon, which would adsorb big amounts of CO₂. Molasses was mixed with KOH. Weight ratio of dry materials was 1:1 (AC1, AC3) and 1:2 (only AC2). Homogeneous mixture was obtained. Material was left for 3 h at 25°C. Drying lasted for 12 h at 200°C, and the material was grounded. The mixture was pyrolysed at 750°C, under constant flow (18 dm³/min) of nitrogen. The material was grounded again. Then, powder was washed with water, until filtrate was neutral, which took about 5 dm³ of water. AC3 was washed with 1 dm³ of water. After drying, materials were soaked in HCl (0.1 mol/dm³) for 19 h, and washed with water, until filtrate was neutral. CO₂ adsorption was performed under high pressure up to 40 atm, at 40°C. Specific surface area (according to the Brunauer-Emmett-Teller equation) was calculated for AC1, AC2 and AC3 and it is respectively 1985, 1967, and 2026 m²/g, micropore volume - 0.714, 0.707, and 0.728 cm³/g and it was between 75% and 89% of total pore volume. The excess uptake at 40 atm pressure was as follows: AC1 - 14.02 mmol/g, AC2 - 12.75 mmol/g, and AC3 - 15.79 mmol/g.
Źródło:
Acta Physica Polonica A; 2016, 129, 3; 402-404
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Preparation of activated carbon from beet molasses and TiO₂ as the adsorption of CO₂
Autorzy:
Glonek, K.
Sreńscek-Nazzal, J.
Narkiewicz, U.
Morawski, A.
Wróbel, R.
Michalkiewicz, B.
Powiązania:
https://bibliotekanauki.pl/articles/1075525.pdf
Data publikacji:
2016-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.05.U-
68.43.-h
Opis:
The objective of this work is to produce activated carbon from sugar beet molasses containing TiO₂ for CO₂ adsorption and reduction. Textural properties of activated carbons were obtained based on the adsorption-desorption isotherms of nitrogen at 77 K. The specific surface areas of activated carbons were calculated by the Brunauer-Emmett-Teller method. The volumes of micropores were obtained by density functional theory method. The adsorption isotherms of CO₂ were measured up to the pressure of 1 atm at a temperature of 40°C. The best activated carbon adsorbed 1.9 mmol/g of CO₂.
Źródło:
Acta Physica Polonica A; 2016, 129, 1; 158-161
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dielectric and Conductivity Anisotropy in Liquid Crystalline Phases of Strongly Polar Thioesters
Autorzy:
Mikułko, A.
Fraś, M.
Marzec, M.
Wróbel, S.
Ossowska-Chruściel, M.
Chruściel, J.
Powiązania:
https://bibliotekanauki.pl/articles/1813171.pdf
Data publikacji:
2008-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.30.-v
61.30.Eb
77.22.-d
66.10.Ed
Opis:
The main objective of this paper is to study dielectric properties of two compounds of acronyms 5OSCl and 6OSCl having strongly polar bond (C-Cl) at para position. Dielectric measurements were done in the frequency range from 40 Hz to 15 MHz. The dielectric spectra were measured for two principal alignments. For homeotropic alignment, the reorientation of molecule around the short molecular axis was observed. Both substances studied exhibit large positive dielectric anisotropy and the anisotropy of conductivity was obtained in smectic A as well as nematic phase.
Źródło:
Acta Physica Polonica A; 2008, 113, 4; 1155-1160
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetotransport through Nanoconstriction in Ferromagnetic Semiconductor (Ga,Mn)As
Autorzy:
Figielski, T.
Wosiński, T.
Pelya, O.
Sadowski, J.
Morawski, A.
Mąkosa, A.
Dobrowolski, W.
Jagielski, J.
Wróbel, J.
Powiązania:
https://bibliotekanauki.pl/articles/2035752.pdf
Data publikacji:
2003-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.63.-b
75.60.-d
73.20.Fz
Opis:
We studied narrow (submicron) constrictions in the layers of ferromagnetic semiconductor (Ga,Mn)As. We have demonstrated a contribution of the quantum localization effects to the magnetoresistance of the constricted samples. We have also found a negative contribution of a domain wall trapped in the constriction to the resistance, due presumably to the erasing of the localization effects by the domain wall.
Źródło:
Acta Physica Polonica A; 2003, 103, 6; 525-531
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Surface Chemistry of Zirconia Nanopowders Doped with $Pr_2O_3$: an XPS Study
Autorzy:
Suchorski, Y.
Wrobel, R.
Becker, S.
Opalińska, A.
Narkiewicz, U.
Podsiadly, M.
Weiss, H.
Powiązania:
https://bibliotekanauki.pl/articles/1811498.pdf
Data publikacji:
2008-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
79.60.-i
61.46.-w
61.46.Hk
Opis:
Zirconia nanopowders of tetragonal crystallographic structure doped with $Pr_2O_3$ were prepared by the microwave-assisted hydrothermal synthesis and coprecipitation method. The surface compositions were studied by X-ray photoelectron spectroscopy. The nanopowder particles appear to be inhomogeneous in their structure: for the surface region an enrichment with praseodymium is detected by X-ray photoelectron spectroscopy measurements. This allows the assumption of a core-shell-like structure of single nanopowders particles. The X-ray photoelectron spectroscopy studies confirm also $Zr^{4+}$ and $Pr^{3+}$ as main oxidation states of zirconium and praseodymium in the studied compounds.
Źródło:
Acta Physica Polonica A; 2008, 114, S; S-125-S-134
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Anomalous Dielectric Spectra of Ferro- and Ferrielectric Liquid Crystalline Phase in MHPNBC
Autorzy:
Dubois, F.
Douali, R.
Wawrzyniak, A.
Legrand, Ch.
Ropa, P.
Wróbel, S.
Dąbrowski, R.
Powiązania:
https://bibliotekanauki.pl/articles/1399013.pdf
Data publikacji:
2013-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
77.22.Gm
77.84.Nh
64.70.M
Opis:
MHPOBC analogue with long achiral alkyl chain has been investigated by dielectric spectroscopy studies in the wide temperature range. Low frequency dielectric spectroscopy revealed the existence of normal ferroelectric phase (in a narrow gap), two ferri- and three antiferroelectric phases in addition to paraelectric phase and alpha sub-phase. The compound studied shows exceptionally strong dependence of the dielectric permittivities on measuring electric field in the temperature range of ferro- and ferrielectric phases.
Źródło:
Acta Physica Polonica A; 2013, 124, 6; 937-939
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 28

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