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Full-Text Articles in Physics
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.
A New Formalism For Nonextensive Physical Systems: Tsallis Thermostatistics, Uğur Tirnakli, Fevzi Büyükkiliç, Doğan Demi̇rhan
A New Formalism For Nonextensive Physical Systems: Tsallis Thermostatistics, Uğur Tirnakli, Fevzi Büyükkiliç, Doğan Demi̇rhan
Turkish Journal of Physics
Although Boltzmann-Gibbs (BG) statistics provides a suitable tool which enables us to handle a large number of physical systems satisfactorily, it has some basic restrictions : (i) the range of the microscopic interactions must be small compared to the linear size of the macroscopic systems (short-range interactions) , (ii) the time range of the microscopic memory must be small compared to the observation time (Marcovian processes) and (iii) the system must evolve in an Euclidean-like space-time. In the case of a breakdown in one and/or the others of these restrictions, BG statistics fails. More precisely, the situation could be classified …
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.
Assessment Of The Degree Of Mix Of Powder Mixtures, Orhan Vai̇zoğlu
Assessment Of The Degree Of Mix Of Powder Mixtures, Orhan Vai̇zoğlu
Turkish Journal of Physics
The older methods for the determination of the degree of a random mix was solely based on the calculation of a simple standard deviation. Physical characteristics like, density, average particle weight and size of each component was not considered. Therefore, the evaluation, when the state of a random mix is reached, was somewhat superficial. Poole, Taylor, and Wall [1] have derived equations, where the physical characteristics of the components were taken into consideration. By this means, it is possible to calculate, in advance, the theoretical coefficient of variation and the corresponding confidence limits. One can then experimentally follow under which …
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 …
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.
Electron Liquid Beyond The Random Phase Approximation, Mehmet Tomak, Ceyhun Bulutay
Electron Liquid Beyond The Random Phase Approximation, Mehmet Tomak, Ceyhun Bulutay
Turkish Journal of Physics
A deeper understanding of low-dimensional and small-scale electronic systems requires an accurate characterization of the many-electron effects. Based on the electron liquid (EL) model, these many-body effects in the three-dimensional (3D) and two-dimensional (2D) electronic systems are dealt going beyond the random phase approximation within the zero-temperature framework. The dielectric formulation of the many-body problem is recapitulated and the longitudinal dielectric function of the EL is obtained using the self-consistent local-field correction scheme, known as STLS, under a general spin-valley degeneracy. Extensive explicit expressions are provided for the use of other researchers. The performance of this formalism is compared in …
Magnetic Excitations In Random Anisotropic Magnets, İbrahim Avgin
Magnetic Excitations In Random Anisotropic Magnets, İbrahim Avgin
Turkish Journal of Physics
A study is made for the magnetic excitations and their Anderson localization properties for a Heisenberg ferromagnet with random anisotropic fields. The system is assumed to be in a strong applied field so that complete spin alignment is established. The magnetic excitations, i.e., the harmonic spin waves, are computed using coherent-field-anisotropy approximation (a version of coherent potential approximation of the electronic problem). The spin wave shift and damping are calculated using the computed coherent field which is a complex function of energy approximating the random medium as a mean field level. The localizaton of the excitations are calculated by adopting …
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. …
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, …
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 …
Short-Period Rs Cvn And W Uma Binaries: How Are They Related?, Frans Van't Veer
Short-Period Rs Cvn And W Uma Binaries: How Are They Related?, Frans Van't Veer
Turkish Journal of Physics
Two groups of late-type very close main sequence binaries, the so-called short-period RS Canum Venaticorum (RS CVn) and W Ursae Majoris (W UMa) systems, are important for the understanding of the structure and evolutionary consequencies of angular momentum loss (AML) resulting from magnetic stellar winds of fast rotating solar type stars. The components of RS CVn stars are close to their Roche lobes, but still detached, whereas W UMa binaries are contact systems; both are rotating fast. One of the crucial problems is trying to answer the question if there is a dynamical relation between the two types of binaries …
Orbital Period Modulation In Chromospherically Active Close Binaries, Cafer İbanoğlu
Orbital Period Modulation In Chromospherically Active Close Binaries, Cafer İbanoğlu
Turkish Journal of Physics
The orbital period changes in some chromospherically active close binaries have been interpreted as a consequence of magnetic activity. At least in two active close binaries a possible relationship between the orbital period modulation and activity cycle was suggested. The existence of a third companion in these binaries has also been proposed. The light-time effect which arises from orbiting around a third-body has been subtracted from all the O-C values and a cyclic change of the orbital period has been obtained. These cyclic changes seem to be connected with the total brightness variations at least in two samples, namely, V471 …
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.
Three-Channel General-Purpose Astrophotometer, Romualdas Kalytis
Three-Channel General-Purpose Astrophotometer, Romualdas Kalytis
Turkish Journal of Physics
The high-speed three-channel photometer suitable for the time-series observations of the "Whole Earth Telescope" (WET) project as well as for multicolor photometry is described. The photometer, designed for the Capodimonte Astronomical Observatory, Italy, is the latest version of the WET photometers developed by the WET group of Vilnius University since 1992. The main optical and mechanical layouts of the optico-mechanical module as well as the block-diagram of electronics are presented. The main specifications of the photometer expected after its completion are given.
Photometric Imaging Of Starspots, Techniques And Reliability, Zeki̇ Eker
Photometric Imaging Of Starspots, Techniques And Reliability, Zeki̇ Eker
Turkish Journal of Physics
Historical development of the starspot hypothesis and the unsolved problems associated with it are presented. The "non{uniqueness" attributed to the spot solutions is a major problem which could still discredit current efforts of starspot modeling by photometric or spectroscopic data. The basics of the starspot photometry(direct and inverse photometric problem, and the error analysis of the inverse problem) are presented. Since an analytical formulation exists to compute synthetic light curves from the physical parameters of spots, and recomputing original parameters analytically from the synthetic curves are also possible, the starspot hypothesis is a consistent physical problem. According to the error …
Photometric Imaging With Distributive Solar Analogy, Zeki̇ Eker
Photometric Imaging With Distributive Solar Analogy, Zeki̇ Eker
Turkish Journal of Physics
The importance of DSA (Distributive Solar Analogy) when modeling starspots from a photometric data is discussed. It's advantage over the other modeling techniques to confine the solution parameters, especially the spot latitudes are described. Unlike the other photometric techniques which tries to locate limited number of cool surface spots, DSA aims to model global distribution of all virtually existing spots.
Facular Structures On Cool Stars, Serdar Evren
Facular Structures On Cool Stars, Serdar Evren
Turkish Journal of Physics
Activity has many manifestations, from dark spots to bright regions, to the presence of the heated chromosphere, to the superheated corona. Sunspots are extended, strongly magnetic regions on the Sun. Photospheric faculae are generally visible only at the limb. Polar faculae are smaller than the main-zone faculae. The contributions of the active region faculae and the facular network are at least as important as the solar spots in augmenting the solar emission.
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.
Solar Flares, E. Rennan Pekünlü
Solar Flares, E. Rennan Pekünlü
Turkish Journal of Physics
In this paper, the dynamics, the magnetohydrodynamics and the energetics of flaring magnetic loops are reviwed. It is also emphasized that the presented model is in no way a unique one. The most commonly occurring type is labelled as B type flares. This paper reviews the general features of a B type flare.
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 …
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 …
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.