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Articles 30661 - 30690 of 36659

Full-Text Articles in Physical Sciences and Mathematics

Population Trapping In Extremely Highly Excited States In Microwave Ionization, Michael W. Noel, W. M. Griffith, T. F. Gallagher Jan 1999

Population Trapping In Extremely Highly Excited States In Microwave Ionization, Michael W. Noel, W. M. Griffith, T. F. Gallagher

Physics Faculty Research and Scholarship

When a lithium atom in a Rydberg state (n 􏰟 80) is exposed to a short, intense microwave pulse we find that substantial population is left in extremely highly excited states (n . 120), in spite of the fact that the microwave field amplitude is more than 40 times larger than required to classically ionize these states.

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Orbital Period Modulation In Chromospherically Active Close Binaries, Cafer İbanoğlu Jan 1999

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 …

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Photon Counting In Astrophotometry. Fundamentals And Some Advices For Beginners, Romualdas Kalytis Jan 1999

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.

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Solar Flares, E. Rennan Pekünlü Jan 1999

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.

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Kinematics Of Rs Cvn And W Uma Binaries In The Hipparcos Catalogue, Zeki̇ Aslan, Tuncay Özdemi̇r, Cahi̇t Yeşi̇lyaprak, Ahmet İskender Jan 1999

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.

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Ordering Due To Disorder In Frustrated Quantum Magnetic Systems, Taner Yildirim Jan 1999

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 …

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Experimental Determination Of \Beta And \Gamma Critical Exponents In The Sol-Gel Phase Transition By Using Steady-State Fluorescence Technique, Y. Yilmaz, Ö. Pekcan Jan 1999

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.

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Magnetic Excitations In Random Anisotropic Magnets, İbrahim Avgin Jan 1999

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 …

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The Structure Of Liquid Alkali Metals Calculated By The Thermodynamic Perturbation Theory, H. Bi̇rtan Kavanoz, İdri̇s Gümüş Jan 1999

The Structure Of Liquid Alkali Metals Calculated By The Thermodynamic Perturbation Theory, H. Bi̇rtan Kavanoz, İdri̇s Gümüş

Turkish Journal of Physics

The structure of a hard sphere fluid has been calculated numerically via the Percus-Yevick (PY) and hypernetted-chain (HNC) closure relations and used as a reference system to calculate the structure of liquid alkali metals under the optimized random-phase approximation (ORPA) using the effective ion-ion pair potential formed by the Heine-Abarenkov (HA), and the empty-core (EC) pseudopotentials. The results are compared with experimental results. The calculations made by the reference system under the HNC closure relation are in better agreement with experimental results than those found under the PY closure relation.

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Determination Of Partial Coordinate Number Of Atoms In Amorphous Yb-As-S(Se, Te) Systems, Rasi̇m Ali̇-Zade, Eldar Efendi̇yev, Elman Haji̇yev Jan 1999

Determination Of Partial Coordinate Number Of Atoms In Amorphous Yb-As-S(Se, Te) Systems, Rasi̇m Ali̇-Zade, Eldar Efendi̇yev, Elman Haji̇yev

Turkish Journal of Physics

Partial coordinate number for amorphous compounds, consisting three type of atoms has been determined by way of calculation of the radial distribution curve maximum. The equation solution method has been used as algorithm in programme, which writed in FORTRAN language for working in IBM compatible computers. The programme is compact and integable. The programme has been used for determination partial coordinate number of ytterbium atom in amorphous compounds- YbAs_2S_4, Yb_3As_4S_9, YbAs_4Te_7, Yb_3As_4Se_9 YbAs_4Se_7. Real value of partial coordinate number of ytterbium in this compunds is 2 or 3.

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Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts Jan 1999

Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts

Turkish Journal of Physics

Hot Electron Light emission and Lasing In Semiconductor Heterostructures (HEL-LISH-1) is a novel hot electron surface emitter consisting of a GaAs QW on the n side of an Ga_{1-x}Al_xAs p-n junction. It utilises hot electron transport parallel to the junction plane. The injection of hot electron hole pairs into the QW is achieved via tunnelling and thermionic emission processes. Recently this structure has been modified by the incorporation of an upper and lower DBR defining a VCSEL (HELLISH-VCSEL). This has been shown to lase at room temperature with a Full Width at Half Maximum (FWHM) of 1.5 nm. In this …

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Wigner Crystalization In Semiconductor Quantum Wires, I. Al-Hayek, B. Tanatar, M. Tomak Jan 1999

Wigner Crystalization In Semiconductor Quantum Wires, I. Al-Hayek, B. Tanatar, M. Tomak

Turkish Journal of Physics

We study the Wigner crystallization in semiconductor quantum wires within the density functional approach. As the density of electrons in quasi-one-dimensional structures is lowered, we find that the system favors the crystalline phase as envisioned by Wigner.

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Optimisation Of The Tunable Wavelength Hot Electron Light Emitter, Ali̇ Teke, Naci̇ Balkan Jan 1999

Optimisation Of The Tunable Wavelength Hot Electron Light Emitter, Ali̇ Teke, Naci̇ Balkan

Turkish Journal of Physics

We report on the optimization of the hot electron tunable wavelength surface light emitting device developed by us. The device consists of a p-GaAs, and n-Ga_{1-x}Al_xAs heterojunction containing an inversion layer on the p- side, and GaAs quantum wells on the n- side, and is referred to as HELLISH-2 (Hot Electron Light Emitting and Lasing in Semiconductor Heterojunction). The device utilises hot electron longitudinal transport and, therefore, light emission is independent of the polarity of the applied voltage. In order to optimise the operation of the device a theoretical model that calculates the tunnelling and the thermionic components of the …

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Interference Of Charged Particles In A Vector Potential With Vanishing Magnetic Field, İsmai̇l Hakki Duru Jan 1999

Interference Of Charged Particles In A Vector Potential With Vanishing Magnetic Field, İsmai̇l Hakki Duru

Turkish Journal of Physics

An interference experiment in a magnetic field free region with non vanishing vector potential created by two perpendicularly intersecting planes carrying uniform currents is discussed. The relation of this configuration to the Aharonov-Bohm potential is examined. An experimental set up which is finite in the direction of electronic motion is studied.

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On The Concept Of Spin In Electrodynamics, Ivangoe Pestov Jan 1999

On The Concept Of Spin In Electrodynamics, Ivangoe Pestov

Turkish Journal of Physics

It is substantiated that spin is a notion associated with the group of internal symmetry that is tightly connected with the geometrical structure of spacetime. The wave equation for the description of a particle with spin one half is proposed. On this ground it is shown that the spin of electron is exhibited through the quantum number and accordingly the Dirac equation describes properties of particles with the projection of spin \pm \hbar/2. On the contrary, we put forward the conjecture that the spin of the quark cannot be considered as a quantum number, but only as an origin of …

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The Gauge Freedoms Of Enlarged Helmholtz Theorem And Debye Potentials; Their Use In The Multipole Expansion Of Conserved Current, Elena N. Bukina, Vladimir M. Dubovik Jan 1999

The Gauge Freedoms Of Enlarged Helmholtz Theorem And Debye Potentials; Their Use In The Multipole Expansion Of Conserved Current, Elena N. Bukina, Vladimir M. Dubovik

Turkish Journal of Physics

We discuss gauge freedom within the scope of the enlarged Helmholtz theorem and Neumann-Debye decomposition and then demonstrate its realization for the multipole expansion of a conserved electromagnetic current. The exact solution to the latter problem was obtained in 1974, but answers to some purely mathematical questions raised by I.B. French and Y. Shimamoto [1] about 40 years ago are given in this paper for the first time.

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Electronic And Lattice Thermal Conductivity Of Bi_{1-X} Sb_X And Ag-Sb-Te Systems, Sabi̇r Ali̇yev, Agami̇rza Movsum-Zadeh, Sadiyar Ragimov, Eldar Zulfigarov Jan 1999

Electronic And Lattice Thermal Conductivity Of Bi_{1-X} Sb_X And Ag-Sb-Te Systems, Sabi̇r Ali̇yev, Agami̇rza Movsum-Zadeh, Sadiyar Ragimov, Eldar Zulfigarov

Turkish Journal of Physics

An investigation of the electronic (\aleph_e) and lattice (\aleph_L) parts of the thermal conductivity for samples of Bi_{1-x} Sb_x (0,02 < X < 0,12) and system of Ag-Sb-Te was carried out in the temperature interval 6-300K. Separation of \aleph_L and \aleph_e has been made by suppressing \aleph_e in magnetic field. The experimental data of \aleph_L and \aleph_e have been compared, respectively, with Gallaway's theory and with a theory which takes into account the inelastic character of scattering. It is observed that the Lorentz number L calculated by using the experimental values of \aleph_e and thermomagnetic coefficients is smaller than its Zommerfeld's value L_0 in high doping Bi_{0.88}Sb_{0.12}. A satisfactory agreement between the theory and the experiment allows to conclude that besides the normal and U-processes in Bi_{1-x}Sb_x the defects of mass also plays a considerable role in scattering. It is observed that \aleph_L of single phase samples Ag_{0.82}Sb_{1.18}Te_{2.18} is smaller than AgSbTe_2 samples. It is shown that this is due to the presence of p-Ag_2 Te in AgSbTe_2. It is established that the high concentration of intrinsic defects plays a considerable role in scattering for Ag-Sb-Te as well.

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Supersymmetric Electroweak Radiative Corrections To E^+ E^- -> W^+W^-, S. Alam Jan 1999

Supersymmetric Electroweak Radiative Corrections To E^+ E^- -> W^+W^-, S. Alam

Turkish Journal of Physics

In this short note we summarize some of the work of our thesis, which is also reported elsewhere in detail. We have examined the one loop quantum corrections to the W pair production in the electron positron annihilation in the context of supersymmetric electroweak theory. We have adopted the On Mass Shell Renormalization scheme of Sakakibara and previously demonstrated the consistency of this scheme. The relevant analytic results are written out. A complete computer program for these corrections has been developed. This program has been checked in several ways to ensure against errors over the life of the calculation where …

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Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira Jan 1999

Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira

Publications

A multispecies kinetic model of the thermal plasma in the plasmasphere is used to predict the spatial dependence of the hydrogen ion and helium ion density and temperature for different levels of geomagnetic and solar activity. The particular convection electric field model chosen is intended for the time intervals between substorms. The plasma density and temperature in the equatorial plane are found to exhibit a local-time variation that is sensitive to the details of the convection electric field. In particular, the parallel temperature increases with altitude and the perpendicular temperature decreases with altitude, except in the postmidnight sector, features that …

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Nonextensivity And Quantum Groups, Metin Arik Jan 1999

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.

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Statistical Physics, Neural Networks, Brain Studies, Gerard Toulouse Jan 1999

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, …

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Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya Jan 1999

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. …

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The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov Jan 1999

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 …

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Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley Jan 1999

Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley

Turkish Journal of Physics

Electrons and polar optical phonons and their interactions are considered in the context of semiconductor quantum well devices, with particular reference to real quantum well laser structures. Distinction is made between wide-barrier and narrow-barrier structures and we explore the implications of these regimes for the description of the electron capture process. Special emphasis is made on the significant effects arising from the large effective mass ratio in AlN/GaN structures.

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Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves Jan 1999

Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves

Turkish Journal of Physics

No abstract provided.

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Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen Jan 1999

Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen

Turkish Journal of Physics

The numerical results of the study of a novel wavelength converter which can be tuned with the application of an external field are presented. For this device, exciton binding energies, radiuses and the absorption coefficient are numerically analysed as a function of electric field. We showed that the interband transition energy and the overlap function between electron and hole changes abruptly when an electric field is applied. This phenomenon can be used the increase the change in the absorption coefficient and reduce the on-state transmission loss in electroabsorption modulators.

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Electromagnetic Waves In Disordered Dielectric Media: Coupled-Dipole Model, Arkadiusz Orlowski, Marian Rusek Jan 1999

Electromagnetic Waves In Disordered Dielectric Media: Coupled-Dipole Model, Arkadiusz Orlowski, Marian Rusek

Turkish Journal of Physics

An effective approach to multiple scattering of electromagnetic waves by disordered dielectric media is developed. A self-consistent energy-conserving coupled-dipole model is used. Applications to the Anderson localization of electromagnetic waves are presented. A complete set of Maxwell's equations is used to describe the propagation of waves and the vector character of the electromagnetic field is fully taken into account.

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Electrodynamics With Toroid Polarization, V. M. Dubovik, B. H. Saha Jan 1999

Electrodynamics With Toroid Polarization, V. M. Dubovik, B. H. Saha

Turkish Journal of Physics

A modified system of equations of electrodynamics of continuous media has been obtained. Beside the Lagrangian system an alternative gauge-like formalism has been developed to introduce the toroid moment contributions in the obtained equations. The two potential formalism that was worked out by us earlier has been developed further where along with the two vector potentials we introduce two scalar potentials thus taking into account all four basic equations of electromagnetism.

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Measuring The Diameter Of Your Blind Spot, Jeff Sanny Jan 1999

Measuring The Diameter Of Your Blind Spot, Jeff Sanny

Physics Faculty Works

A simple experiment to determine the diameter of the blind spot is described. Students are divided into groups of three and work together to perform the experiment. The procedure takes about 15 minutes and seems to be quite enjoyable to the class.

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Mach’S Principle In A Mixed Newton-Einstein Context, Evert Jan Post, Michael Berg Jan 1999

Mach’S Principle In A Mixed Newton-Einstein Context, Evert Jan Post, Michael Berg

Mathematics, Statistics and Data Science Faculty Works

A closed physical space, in conjunction with scalar versus pseudo scalar distinctions, and an accordingly adapted Gauss theorem, reveal unexpected perspectives on Mach's principle, the mass-energy theorem, and a bonus insight into the nature of the solutions of the Einstein field equations of gravity.

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