oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 1 )

2019 ( 169 )

2018 ( 195 )

2017 ( 219 )

Custom range...

Search Results: 1 - 10 of 200751 matches for " P. Zawadzki "
All listed articles are free for downloading (OA Articles)
Page 1 /200751
Display every page Item
Recording of bioelectrical activity changes in sheep cerebral cortex
Cwynar,P; Zawadzki,W;
Archivos de medicina veterinaria , 2010, DOI: 10.4067/S0301-732X2010000200006
Abstract: the aim of the study was to present a practical application of electroencephalographic techniques. the essential aspects of eeg in sheep and its usefulness in the analysis of changes in the cns, are demonstrated in the paper. the experiments were conducted on 10 ewes, hybrids of the polish merino, selected especially for laboratory purposes. there is no standard pattern in encephalographic methods in animals, that?s why the authors made a registration of the induced biopotentials in sheep from the experimentally chosen points of the animals head. it was presented during the experiment that the cerebral cortex is characterized by a high dynamism index, which was proved during the experiments on cns reactions to the factors such as hunger, sonic emission or control xylazine influence. the cerebral cortex of sheep in a vesting conditions reveals a bioelectric activity of a mean amplitude of 30 μv and a frequency of 25 hz, which confirms existence of a beta [β] rhythm. an application of a sonic stimulus enables the stimulation of the central nervous system of sheep, which is confirmed by an increased mean amplitude (of 23%) and a frequency (of 21%) of the cerebral cortex activity, and also by the electroencephalogram. results obtained prove that the region of the mesencephalon is characterised by the shortest time of reaction to the introduced stimulus, and the mean time of response is 0.56 seconds (± 0.005 s). the ways of the most suitable practices as well as the chances for unification of eeg method were discussed.
Recording of bioelectrical activity changes in sheep cerebral cortex Registro de cambios en la actividad bioeléctrica de la corteza cerebral de ovejas
P Cwynar,W Zawadzki
Archivos de medicina veterinaria , 2010,
Abstract: The aim of the study was to present a practical application of electroencephalographic techniques. The essential aspects of EEG in sheep and its usefulness in the analysis of changes in the CNS, are demonstrated in the paper. The experiments were conducted on 10 ewes, hybrids of the Polish Merino, selected especially for laboratory purposes. There is no standard pattern in encephalographic methods in animals, that’s why the authors made a registration of the induced biopotentials in sheep from the experimentally chosen points of the animals head. It was presented during the experiment that the cerebral cortex is characterized by a high dynamism index, which was proved during the experiments on CNS reactions to the factors such as hunger, sonic emission or control xylazine influence. The cerebral cortex of sheep in a vesting conditions reveals a bioelectric activity of a mean amplitude of 30 μV and a frequency of 25 Hz, which confirms existence of a beta [β] rhythm. An application of a sonic stimulus enables the stimulation of the central nervous system of sheep, which is confirmed by an increased mean amplitude (of 23%) and a frequency (of 21%) of the cerebral cortex activity, and also by the electroencephalogram. Results obtained prove that the region of the mesencephalon is characterised by the shortest time of reaction to the introduced stimulus, and the mean time of response is 0.56 seconds (± 0.005 s). The ways of the most suitable practices as well as the chances for unification of EEG method were discussed. El objetivo de este estudio es presentar el uso práctico de la electroencefalografía (EEG), demostrando el aspecto básico de EEG en ovejas, así como su utilidad en el análisis de las alteraciones provenientes del sistema nervioso central. Se examinaron 10 hembras híbridas de Oveja Merino Polaca, seleccionadas especialmente con fines experimentales. Debido a la falta de una fórmula unificada en el método de EEG en animales, se realizó un registro de potenciales provenientes de algunos puntos escogidos tras el experimento en cabezas de animales. Durante los experimentos realizados se demostró que la corteza cerebral de ovejas se caracteriza por una dinámica muy alta, hecho que fue demostrado al examinar las reacciones del sistema nervioso central a los factores tales como: el hambre, la estimulación auditiva o la inyección de xylazyna. La corteza cerebral de ovejas en el estado de reposo muestra una actividad bioeléctrica de una amplitud media de 30 μV y una frecuencia de 25 Hz, con lo cual se confirma la existencia del ritmo beta [β]. La aplica
Electrons in finite superlattices: the birth of crystal momentum
P. Pfeffer,W. Zawadzki
Physics , 2008,
Abstract: Properties of electrons in superlattices (SLs) of a finite length are described using standing waves resulting from the fixed boundary conditions (FBCs) at both ends. These electron properties are compared with those predicted by the standard treatments using running waves (Bloch states) resulting from the cyclic boundary conditions (CBCs). It is shown that, while the total number of eigenenergies in a miniband is the same according to both treatments, the number of different energies is twice higher according to the FBCs. It is also shown that the wave vector values corresponding to the eigenenergies are spaced twice as densely for the FBCs as for the CBCs. The reason is that a running wave is characterized by a single value of wave vector k, while a standing wave in a finite SL is characterized by a pair of wavevectors +/- q. Using numerical solutions of the Schroedinger equation for an electron in an increasing number N of periodic quantum wells (beginning with N = 2) we investigate the "birth" of an energy miniband and of a Brillouin zone according to the two approaches. Using the Fourier transforms of the computed wave functions for a few quantum wells we follow the "birth" of electron's momentum. It turns out that the latter can be discerned already for a system of two wells. We show that the number of higher values of the wave vector q involved in an eigenenergy state is twice higher for a standing wave with FBCs than for a corresponding Bloch state. Experiments using photons and phonons are proposed to observe the described properties of electrons in finite superlattices.
Spin and cyclotron energies of electrons in GaAs/Ga$_{1-x}$Al$_x$As quantum wells
P. Pfeffer,W. Zawadzki
Physics , 2006, DOI: 10.1103/PhysRevB.74.115309
Abstract: A five-level {\Pp} model of the band structure for GaAs-type semiconductors is used to describe the spin $g^*$-factor and the cyclotron mass $m^*_c$ of conduction electrons in GaAs/Ga$_{1-x}$Al$_x$As quantum wells in an external magnetic field parallel to the growth direction. It is demonstrated that the previous theory of the $g^*$-factor in heterostructures is inadequate. Our approach is based on an iteration procedure of solving 14 coupled differential {\Pp} equations. The applicability of the iteration procedure is verified. The final eigenenergy problem for the conduction subbands is reduced to two differential equations for the spin-up and spin-down states of consecutive Landau levels. It is shown that the bulk inversion asymmetry of III-V compounds is of importance for the spin $g^*$-factor. Our theory with no adjustable parameters gives an excellent description of experimental data on the electron spin $g^*$-factor in GaAs/Ga$_{0.67}$Al$_{0.33}$As rectangular quantum wells for different well widths between 3 and 12 nm. The same theory describes very well experimental cyclotron masses in GaAs/Ga$_{0.74}$Al$_{0.26}$As quantum wells for the well widths between 6 and 37 nm.
On the thermal broadening of a quantum critical phase transition
P. T. Coleridge,P. Zawadzki
Physics , 1999, DOI: 10.1016/S0038-1098(99)00346-4
Abstract: The temperature dependence of an integer Quantum Hall effect transition is studied in a sample where the disorder is dominated by short-ranged potential scattering. At low temperatures the results are consistent with a $(T/T_0)^{\kappa}$ scaling behaviour and at higher temperatures by a linear dependence similar to that reported in other material systems. It is shown that the linear behaviour results from thermal broadening produced by the Fermi-Dirac distribution function and that the temperature dependence over the whole range depends only on the scaling parameter T$_0^{\kappa}$.
Improvement of quality of a gravity die casting made from aluminum bronze be application of numerical simulation
A. Fajkiel,P. Dudek,W. Walczak,P. Zawadzki
Archives of Foundry Engineering , 2007,
Abstract: The paper describes the possibility of improving the quality of gravity die cast connectors for overhead power transmission lines. The castings were made from aluminum bronze, grade CuAl9Fe1Ni1. A MAGMAsoft computer programme was used for simulation of the process of die filling and casting solidification to avoid defects, like shrinkage depression and gas porosities. The results of the simulation have finally led to redesigning of the metal feeding and cooling system and to reduced level of defects in castings.
Metal Insulator transition at B=0 in p-SiGe
P. T. Coleridge,R. L. Williams,Y. Feng,P. Zawadzki
Physics , 1997, DOI: 10.1103/PhysRevB.56.R12764
Abstract: Observations are reported of a metal-insulator transition in a 2D hole gas in asymmetrically doped strained SiGe quantum wells. The metallic phase, which appears at low temperatures in these high mobility samples, is characterised by a resistivity that decreases exponentially with decreasing temperature. This behaviour, and the duality between resistivity and conductivity on the two sides of the transition, are very similar to that recently reported for high mobility Si-MOSFETs.
Metallic and Insulating behaviour in p-SiGe at nu = 3/2
P. T. Coleridge,R. L. Williams,J. Lapointe,P. Zawadzki
Physics , 2002,
Abstract: Shubnikov-de Haas data is presented for a p-SiGe sample exhibiting strongly insulating behaviour at nu = 3/2. In addition to the fixed points defining a high field metal- insulator transition into this phase separate fixed points can also be identified for the nu = 3 --> 2 and 2 --> 1 Integer quantum Hall transitions. Another feature of the data, that the Hall resistivity approaches zero in the insulating phase, indicates it is not a re-entrant Hall insulator. The behaviour is explained in terms of the strong exchange interactions. At integer filling factors these cause the 0 uparrow and 1 downarrow Landau levels to cross and be well separated but at non-integer values of nu screening reduces exchange effects and causes the levels to stick together. It is suggested the insulating behaviour, and high field metal/insulator transition, is a consequence of the strong exchange interactions.
Weak localisation, interaction effects and the metallic phase in p-SiGe
P. T. Coleridge,A. S. Sachrajda,P. Zawadzki
Physics , 1999,
Abstract: Magnetoresistance results are presented for p-SiGe samples on the metallic side of the B=0 metal-insulator transition. It was possible to separate the weak localisation and Zeeman interaction effects but the results could not be explained quantitatively within the framework of standard theories for quantum corrections of a weakly interacting 2-dimensional system. Analysis using a theory for interaction corrections at intermediate temperatures, recently proposed by Zala, Narozhny and Aleiner, provided values of the Fermi liquid parameter $F_0^{\sigma}$ of order -0.5. Similar values also explain the linear increase of resistance with temperature characteristic of the metallic phase. e
Interaction effects and the metallic phase in p-SiGe
P. T. Coleridge,A. S. Sachrajda,P. Zawadzki
Physics , 2000,
Abstract: Magnetoresistance results are presented for p-SiGe samples on the metallic side of the B=0 metal-insulator transition. The results cannot be understood within the framework of standard theories for quantum corrections of a weakly interacting 2- dimensional system. In particular no logarithmic dependence on temperature is observed, at low fields, in either the longitudinal or Hall resistivities despite evidence in the magnetoresistance of weak localisation effects. Further, the Hall coefficient shows a strong logarithmic dependence on field. The results are better explain by renormalisation group theories and by an anomalous Hall effect associated with strong spin-orbit coupling in the presence of a background spin texture.
Page 1 /200751
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.