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Articles 1141 - 1170 of 1374
Full-Text Articles in Physical Sciences and Mathematics
Electronic Energy Spectrum In A Dqws Within A Tilted Magnetic Field, S. Elagöz, H. Sari, Y. Ergün, P. Karasu, İ. Sökmen
Electronic Energy Spectrum In A Dqws Within A Tilted Magnetic Field, S. Elagöz, H. Sari, Y. Ergün, P. Karasu, İ. Sökmen
Turkish Journal of Physics
The analytical solution of the Schrödinger equation for a DQWS subjected to an externally applied tilted magnetic field are obtained and the results are discussed. The dependency of energy spectrum of the system on the applied magnetic field direction is also given.
Studies On Extremal Segments In Random Sequences, Deniz Ertaş, Yacov Kantor
Studies On Extremal Segments In Random Sequences, Deniz Ertaş, Yacov Kantor
Turkish Journal of Physics
We review our main findings on the size distribution of the largest neutral segments in a sequence of N randomly charged monomers. Upon mapping to one--dimensional random walks (RWs), this corresponds to finding the probability distribution for the size L of the largest segment that returns to its starting position in an N--step RW. Using analytical, exact enumeration, and Monte Carlo methods, we reveal the complex structure of the probability distribution in the large N limit. In particular, the size of the longest neutral segment has a distribution with a square-root singularity at \ell\equiv L/N = 1, an essential singularity …
Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya
Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya
Turkish Journal of Physics
Effect of subtitutional impurities on electron localization in two dimensional (2D) lattice near the middle of the band is studied. Calculation of density of the electronic states, \rho (\varepsilon ), increases logaritmically in the middle of the band. This singularity in the density of states of noninteracting electron gas on lattice gives rise to anomalous dependencies of thermodynamic quantities on the temperature. The quantum correction to the conductivity of a nonintreracting electron gas due to Umklapp electron--impurity scattering is calculated. This correction to the conductivity is shown to compete with that from the localization corrrection for a Normal scattering process. …
Cyclic Nature Of The Orbital Period Variations Of Some Algol-Type Binaries, Seli̇m O. Selam, Osman Demi̇rcan
Cyclic Nature Of The Orbital Period Variations Of Some Algol-Type Binaries, Seli̇m O. Selam, Osman Demi̇rcan
Turkish Journal of Physics
The long-term period variations of the classical algol-type binaries XZ And, U Cep, \beta Per, RT Per, ST Per and TX UMa were studied by using all available observed times of eclipse minima. The (O-C) diagrams formed by the times of eclipse minima were found to be representable by one or more cyclic variations superimposed on a secular parabolic variation. The secular variations in the orbital periods should be caused by the mass transfer between the component stars and the mass loss from the systems. For our sample of Algol systems, none of the cyclic variations were found caused by …
On The Coronal Activity Of The Rs Cvn-Type Binaries, Osman Demi̇rcan, Hasan Ak
On The Coronal Activity Of The Rs Cvn-Type Binaries, Osman Demi̇rcan, Hasan Ak
Turkish Journal of Physics
We re-analysed the behaviour of coronal activity of the RS CVn-type binaries as a function of stellar and orbital parameters. Highly significant correlations were found between the x-ray luminosity L_x and the stellar radius R, the Roche lobe filling fraction \Gamma, and the Alfven radius RA. The correlations of L_x with the mass M, the absolute magnitude M_V, the surface gravity g, the Roche lobe filling fraction \Gamma, and the Alfven radius RA are likely to be due to correlations of these quantities with the stellar radius R. Surprisingly, no correlation of L_x on the color (B-V), the rotation velocity …
Fundamental Research And Device Technology, B. K. Ridley
Fundamental Research And Device Technology, B. K. Ridley
Turkish Journal of Physics
Highlights of the interaction between fundamental research and semiconductor device technology are summarized.
Electrons In Large-Bandgap Bulk Semiconductors And Quantum Wells, N. A. Zakhleniuk, M. Babiker, C. R. Bennett, B. K. Ridley
Electrons In Large-Bandgap Bulk Semiconductors And Quantum Wells, N. A. Zakhleniuk, M. Babiker, C. R. Bennett, B. K. Ridley
Turkish Journal of Physics
The analytical theory of hot electrons interacting with lattice vibrations, impurities, and interface roughness in quantum wells is developed. We have obtained new distribution functions which describe all the kinetic properties of the non-equilibrium electron gas. As a specific example we present the electric field dependence of the electron mobility in GaN-based quantum wells and in bulk GaN. The relative importance of the different scattering mechanisms is analysed in detail.
Nonextensivity And Quantum Groups, Metin Arik
Nonextensivity And Quantum Groups, Metin Arik
Turkish Journal of Physics
Classical set theory is nonextensive since the mathematical definition of a set excludes the possibility that more than one copy of the same element can be in a set. We show that the description of random sets in terms of an algebra of creation operators and their hermitean conjugates yields an interpretation of the unitary quantum group SU_q(d) as the symmetry associated with the construction of d random sets from a given source set of M=(1-q)^{-1} elements.
Q-Calculus And Irreversible Dynamics On A Hierarchical Lattice, Ayşe Erzan, Ayşe Gorbon
Q-Calculus And Irreversible Dynamics On A Hierarchical Lattice, Ayşe Erzan, Ayşe Gorbon
Turkish Journal of Physics
On a lattice with equal spacing on the logarithmic scale, a momentum operator that respects the asymmetry of this nonlinear lattice yields a kinetics that can be understood in terms of diffusion on an underlying ultrametric space, if one also identifies the cannonical commutator with the time dilation operator. The motion to which this non-conventional kinetics corresponds is irreversible, with an explicit violation of time reversal symmetry resulting from the spreading with time of a probability distribution over a larger and larger volume of the phase space.
Statistical Physics, Neural Networks, Brain Studies, Gerard Toulouse
Statistical Physics, Neural Networks, Brain Studies, Gerard Toulouse
Turkish Journal of Physics
An overview of some aspects of a vast domain, located at the crossroads of physics, biology and computer science is presented: 1) During the last fifteen years, physicists advancing along various pathways have come into contact with biology (computational neurosciences) and engineering (formal neural nets). 2) This move may actually be viewed as one component in a larger picture. A prominent trend of recent years, observable over many countries, has been the establishment of interdisciplinary centers devoted to the study of: cognitive sciences; natural and artificial intelligence; brain, mind and behaviour; perception and action; learning and memory; robotics; man-machine communication, …
Neural Classifiers For Learning Higher-Order Correlations, Marifi Güler
Neural Classifiers For Learning Higher-Order Correlations, Marifi Güler
Turkish Journal of Physics
Studies by various authors suggest that higher-order networks can be more powerful and are biologically more plausible with respect to the more traditional multilayer networks. These architectures make explicit use of nonlinear interactions between input variables in the form of higher-order units or product units. If it is known a priori that the problem to be implemented possesses a given set of invariances like in the translation, rotation, and scale invariant pattern recognition problems, those invariances can be encoded, thus eliminating all higher-order terms which are incompatible with the invariances. In general, however, it is a serious set-back that the …
Ordering Due To Disorder In Frustrated Quantum Magnetic Systems, Taner Yildirim
Ordering Due To Disorder In Frustrated Quantum Magnetic Systems, Taner Yildirim
Turkish Journal of Physics
The phenomenon of order by disorder in frustrated magnetic systems is reviewed. Disorder (thermal or quantum fluctuations) may sometimes give rise to long range ordering in systems with frustration, where one must often consider the selection among classically degenerate ground states which are not equivalent by any symmetry. The lowest order effects of quantum fluctuations in such frustrated systems usually resolves the continues degeneracy of the ground state manifold into discrete Ising--type degeneracy. A unique ground state selection out of this Ising degenerate manifold then occurs due to higher order effects of quantum fluctuations. For systems such as face-centered cubic …
The Renormalization-Group Microscope: The Local Statistical Mechanics Of Heterogeneous Systems, Dicle Yeşi̇lleten, A. Nihat Berker
The Renormalization-Group Microscope: The Local Statistical Mechanics Of Heterogeneous Systems, Dicle Yeşi̇lleten, A. Nihat Berker
Turkish Journal of Physics
Renormalization-group theory is developed to yield all local microscopic thermodynamic densities in heterogeneous systems. Local energy densities and local magnetizations are thus obtained for random-bond systems, random-field systems, and spin-glasses, in two and three dimensions. Different order-disorder mechanisms in these diverse systems, such as chaotic ordering and domain-wall melting, become quantitatively evident.
Experimental Determination Of \Beta And \Gamma Critical Exponents In The Sol-Gel Phase Transition By Using Steady-State Fluorescence Technique, Y. Yilmaz, Ö. Pekcan
Experimental Determination Of \Beta And \Gamma Critical Exponents In The Sol-Gel Phase Transition By Using Steady-State Fluorescence Technique, Y. Yilmaz, Ö. Pekcan
Turkish Journal of Physics
The gelation of methyl methacrylate and ethylene glycol dimethacrylate was studied using the steady-state fluorescence technique. Samples with various crosslinker densities were prepared and sol-gel phase transitions were observed at various temperatures. Percolation theory was employed to interpret the results. For all samples the gel fraction and the average cluster size exponents, \beta and \gamma, were measured and found to be around 0.42 and 1.7 respectively. These values show excellent agreement with theoretical and simulation results.
Diverging Strains Near Threshold: Breakdown Of The Elastic Description Of A Charge Density Wave Model, Muhittin Mungan, Susan N. Coppersmith, Valeri M. Vinokur
Diverging Strains Near Threshold: Breakdown Of The Elastic Description Of A Charge Density Wave Model, Muhittin Mungan, Susan N. Coppersmith, Valeri M. Vinokur
Turkish Journal of Physics
We analyze the strains near threshold in 1-d charge density wave models at zero temperature and strong pinning. We show that in these models local strains diverge near the depinning threshold and characterize the scaling behavior of the phenomenon. This helps quantify when the underlying elastic description breaks down and plastic effects have to be included.
Spectral Broadening Functions, Slavek Rucinski
Spectral Broadening Functions, Slavek Rucinski
Turkish Journal of Physics
Many astrophysical phenomena involving velocity fields produce broadening of spectral lines. Frequently, the cross-correlation function (CCF) is used to extract information about this broadening from segments of high resolution spectra. CCF has become the standard tool for handing extraction of radial-velocity and broadening information from high resolution spectra as it permits integration of information which is common to many spectral lines into one function which is easy to calculate, visualize and interpret. However, it can be argued that this is not the best tool for applications such as determinations of metallicities ([Fe/H]), for finding locations of star spots on active …
Angular Momentum Evolution In Close Late-Type Binaries, Carla Maceroni
Angular Momentum Evolution In Close Late-Type Binaries, Carla Maceroni
Turkish Journal of Physics
Accurate monitoring of the orbital period of late-type close binaries can provide important information on their secular evolution and on the structural changes of their components on very short timescales (i.e. decades). The orbital period turns out to be a powerful tool of investigation: it can be measured to great accuracy even with simple equipments and its change produces an easily detectable cumulative effect over time. This paper focuses on two physical mechanisms that cause orbital periods changes in late type binaries with negligible mass loss from the system: the dynamical evolution due to magnetic braking in tidally locked systems, …
Photon Counting In Astrophotometry. Fundamentals And Some Advices For Beginners, Romualdas Kalytis
Photon Counting In Astrophotometry. Fundamentals And Some Advices For Beginners, Romualdas Kalytis
Turkish Journal of Physics
The beginners in astrophotometry are reminded of fundamentals of photon counting. Several advices for new users of electrophotometric technics are given.
The Light And Colour Variations Of Mm Her, Günay Taş
The Light And Colour Variations Of Mm Her, Günay Taş
Turkish Journal of Physics
RS CVn type eclipsing binary MM Herculis have been observed using B, V, R filters in 1997 and obtained light and colour curves were examined together with the earlier 12 light and colour curves obtained between 1976 and 1997. It was seen that the system is bluer, while it is fainter. Such finding probably reveals the evolutionary effect of the photospheric bright facular structures surrounding starspots.
Magnetic Activity In The Extreme Ultraviolet, Mihalis Mathioudakis
Magnetic Activity In The Extreme Ultraviolet, Mihalis Mathioudakis
Turkish Journal of Physics
The wealth of astronomical observations obtained in the extreme ultraviolet in recent years, have allowed comprehensive studies of the stellar transition regions and coronae to be carried out. For the first time we have been able to resolve individual coronal lines of various elements formed over a large temperature range (10^{5} - 10^{7.2} K). The temperature, densities, abundances and magnetic field strengths of the stellar coronae can now be determined. Here we review some of the observations in the field of cool stars and discuss the implications on atmospheric heating requirements.
Dynamical Evolution Of The Rs Cvn-Type Binaries, Osman Demi̇rcan
Dynamical Evolution Of The Rs Cvn-Type Binaries, Osman Demi̇rcan
Turkish Journal of Physics
The orbital angular momentum (orbital AM) of a sample of forty RS CVn-type binaries with the orbital periods P \leq 10 days were estimated and the orbital AM distribution with respect to P was critically interpreted as the orbital AM evolution of these systems caused by the magnetic breaking process with the existence of spin-orbit coupling. The empirical relations (between the orbital AM loss, mass loss and period variation) derived from the diagram of the orbital AM distribution were used in deriving a semi-empirical formula for the dynamical evolution of the RS CVn-type binaries. The magnetic breaking induced dynamical evolution …
Kinematics Of Rs Cvn And W Uma Binaries In The Hipparcos Catalogue, Zeki̇ Aslan, Tuncay Özdemi̇r, Cahi̇t Yeşi̇lyaprak, Ahmet İskender
Kinematics Of Rs Cvn And W Uma Binaries In The Hipparcos Catalogue, Zeki̇ Aslan, Tuncay Özdemi̇r, Cahi̇t Yeşi̇lyaprak, Ahmet İskender
Turkish Journal of Physics
Space motions of RS CVn and W UMa binaries have been calculated using parallaxes and proper motions from Hipparcos catalogue and radial velocities from the literature. We have calculating the mean motions and velocity dispersions. We have excluded those binaries with relative parallax errors \geq 0.5. The comparison of the asymmetric drift, velocity ellipsoids and vertex deviation with those of main sequence stars given by Dehnen and Binney indicates that both RS CVn and W UMa binaries have kinematics similar to main sequence stars slightly bluer than the Parenago's discontinuity and B-V \simeq 0.62. Implication of this has been discussed.
Co-Ordinated Multi-Wavelength Observations Of The Rs Cvn System Cf Tuc, Edwin Budding, K. L. Jones, O. B. Slee, L. Watson
Co-Ordinated Multi-Wavelength Observations Of The Rs Cvn System Cf Tuc, Edwin Budding, K. L. Jones, O. B. Slee, L. Watson
Turkish Journal of Physics
A `multi-site, multi-wavelength' campaign on the eclipsing RS CVn binary CF Tuc was carried out in 1996 over both optical (photometry and spectroscopy) and radio (microwave) ranges. The microwave data was taken with the Australia Telescope Compact Array (ATCA). It covered slightly more than one complete orbital cycle at 4.8 and 8.64 GHz in one continuous run. There was also coverage of about 25% of the light curve at 1.38 and 2.38 GHz. High dispersion spectroscopy was obtained using the McLellan 1m telescope and échelle spectrograph at Mt John University Observatory (New Zealand). Supporting photometry came from various smaller-scale facilities …
The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov
The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov
Turkish Journal of Physics
Photoelectron spectra (PES) taken from crystalline Zr at 8.4 eV and 10 eV have been studied by a high resolution photoelectron analyzer, with \Delta E = 0.1 eV, and the results were compared to the results calculated for electron density of states in the valence band. Photoelectron work function (WF) measured from the atomically clean Zr surface by Fowler isothermal curves was found to be 3.95 eV \pm 0.02 eV. It was shown that a small dose of residual gas, namely CO, absorbed on the Zr surface, resulted in a decrease of the WF by 0.15-0.25 eV as well as …
Magnetodielectrical Polymer Compositional Materials, Sh. V. Mamedov, Y. Lenger, Sevi̇l Bolcal, Vilayet A. Alekperov, M. A. Ramazanov, R. Z. Sadikhov
Magnetodielectrical Polymer Compositional Materials, Sh. V. Mamedov, Y. Lenger, Sevi̇l Bolcal, Vilayet A. Alekperov, M. A. Ramazanov, R. Z. Sadikhov
Turkish Journal of Physics
Magnetodielectrical polymer compositional materials containing carbonyl iron (CI) were obtained. The changes of permittivity and permeability, loss angle tangent, resistivity, mechanical and electrical properties, depending on the content of carbonyl iron have been investigated. It is shown that the magnetodielectrical materials with 20-40% mass content of carbonyl iron have possible practical use.
Heat Pulse Studies Of The Emission And Absorption Of Acoustic Phonons In Gaas Quantum Wells And Wires, A. J. Kent
Heat Pulse Studies Of The Emission And Absorption Of Acoustic Phonons In Gaas Quantum Wells And Wires, A. J. Kent
Turkish Journal of Physics
This paper reviews some recent experiments in which heat pulse techniques have been used to study the interaction of acoustic phonons with electrons in semiconductor quantum wells and wires. Heat pulse experiments provide temporal and spatial resolution of the phonons that are emitted or absorbed by the electrons and so give more detailed information about the electron-phonon interaction than can be obtained by other methods (e.g. transport measurements). Phonon experiments demonstrate clearly the effect of the electron confinement on the carrier-phonon interaction and the overall energy loss rate due to acoustic phonon emission. A qualitative explanation of the results is …
Electron Transport In Gaas Quantum Wells: Effect Of Interface Roughness Scatterin, Rita Gupta
Electron Transport In Gaas Quantum Wells: Effect Of Interface Roughness Scatterin, Rita Gupta
Turkish Journal of Physics
The importance of interface roughness (IFR) scattering of electrons and LO-phonons for electron transport in semiconductor quantum wells is discussed. Modulation doping of quantum wells minimizes the effect of impurity scattering on the low-field electron mobility so that IFR scattering of electrons in the well becomes the major limiting factor. A model calculation of IFR scattering of electrons in quantum wells is presented and it is shown that (both)\Lambda and \Delta, the parameters defining IFR, can be estimated by comparing the theoretical and experimental electron mobilities. The application of high electric field leads to a distribution of hot electrons which …
Exchange-Correlation Effects In The Impurity-Limited Mobility Of Gaas Quantum Wires, B. Tanatar
Exchange-Correlation Effects In The Impurity-Limited Mobility Of Gaas Quantum Wires, B. Tanatar
Turkish Journal of Physics
We study the many-body effects described by the local-field corrections on the mobility of quasi-one dimensional electron systems. The low temperature mobility due to remote-impurity doping and interface-roughness scattering is calculated within the relaxation time approximation. We find that correlation effects significantly reduce the mobility at low density.
Well-Width Dependence Of Warm Electron Relaxation And Interface Roughness Scattering In Gaas/Ga_{1-X}Al_Xas Multiple Quantum Wells, M. Cankurtaran, H. Çeli̇k, E. Tiraş, A. Bayrakli, N. Balkan
Well-Width Dependence Of Warm Electron Relaxation And Interface Roughness Scattering In Gaas/Ga_{1-X}Al_Xas Multiple Quantum Wells, M. Cankurtaran, H. Çeli̇k, E. Tiraş, A. Bayrakli, N. Balkan
Turkish Journal of Physics
We review our recent results concerning the well-width dependence of the acoustic-phonon-assisted energy relaxation of two-dimensional (2D) warm electrons in modulation-doped GaAs/Ga_{1-x}Al_xAs multiple quantum wells. Electron energy-loss rates via the emission of acoustic phonons are determined from the amplitude of Shubnikov-de Haas (SdH) oscillations, measured as a function of lattice temperature and applied electric field. Experimental results are compared with the existing theoretical models that involve deformation-potential and screened and unscreened piezoelectric scattering. Well-width dependence of the quantum and transport mobilities of 2D electrons in the same samples have also been determined by measuring the quantum oscillations in both the …
Large-Bandgap Semiconductors, B. K. Ridley
Large-Bandgap Semiconductors, B. K. Ridley
Turkish Journal of Physics
The general features of large-bandgap semiconductors that make them interesting for electronic and optoelectronic applications are briefly reviewed. The nitrides AIN, GaN and InN are singled out for a more focused treatment.