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2000

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Articles 421 - 450 of 470

Full-Text Articles in Physics

The Statistics Of Energy States Of A Hookean Model For Proteins, Ayşe Erzan, Erkan Tüzel Jan 2000

The Statistics Of Energy States Of A Hookean Model For Proteins, Ayşe Erzan, Erkan Tüzel

Turkish Journal of Physics

A generic model of a random polypeptide chain, with discrete torsional degrees of freedom and Hookean springs connecting pairs of hydrophobic residues, reproduces the energy probability distribution of real proteins over a very large range of energies. We show that this system with harmonic interactions, under dissipative dynamics driven by random noise, leads to a distribution of energy states obeying a modified one-dimensional Ornstein-Uhlenbeck process with reflecting boundary conditions, and giving rise to distributions of the Wigner or inverse Gaussian form. A continuum approximation leads to a path integral formulation of the problem. PACS 5.65+b,5.70Ln,87.17.Aa


Gauge Invariant Reduction And Integrability Of Sl(2 ,R)/ U(1) Wznw Theory, Chris Ford, George Jorjadze, Gerhard Weigt Jan 2000

Gauge Invariant Reduction And Integrability Of Sl(2 ,R)/ U(1) Wznw Theory, Chris Ford, George Jorjadze, Gerhard Weigt

Turkish Journal of Physics

The general solution of $SL(2,{\bf R})/U(1)$ WZNW theory is constructed by a gauge invariant reduction. This is done within both Lagrangian and Hamiltonian frameworks.


A Detour In De Sitter Space While Calculating Vacuum Fluctuatins, M. Hortaçsu Jan 2000

A Detour In De Sitter Space While Calculating Vacuum Fluctuatins, M. Hortaçsu

Turkish Journal of Physics

{We study vacuum fluctuations of different gravitational waves by taking a detour in de Sitter space in the intermediate steps. We find finite contributions when the coupling constant is dimensionless, whereas null result persists in the cases with dimensional coupling constants. We also test our method for exactly solvable cases, and show that no spurious perturbative effects are introduced through our method.


Multi-Species Asymmetric Exclusion Process In Ordered Sequential Update, M. Ebrahi̇m Fouladvand, Farhad Jafarpour Jan 2000

Multi-Species Asymmetric Exclusion Process In Ordered Sequential Update, M. Ebrahi̇m Fouladvand, Farhad Jafarpour

Turkish Journal of Physics

A multi-species generalization of the asymmetric simple exclusion process (ASEP) is studied in ordered sequential and sub-lattice parallel updating schemes. In this model, particles hop with their own specific probabilities to their rightmost empty site and fast particles overtake slow ones with a definite probability. Using Matrix Product Ansatz (MPA), we obtain the relevant algebra, and study the uncorrelated stationary state of the model both for an open system and on a ring. A complete comparison between the physical results in these updates and those of random sequential introduced in [20,21] is made.


Product Integral Representations Of Wilson Lines And Wilson Loops And Non-Abelian Stokes Theorem, Robert L. Karp, Freydoon Mansouri, Jung S. Rno Jan 2000

Product Integral Representations Of Wilson Lines And Wilson Loops And Non-Abelian Stokes Theorem, Robert L. Karp, Freydoon Mansouri, Jung S. Rno

Turkish Journal of Physics

We make use of product integrals to provide an unambiguous mathematical representation of Wilson line and Wilson loop operators. Then, drawing upon various properties of product integrals, we discuss such properties of Wilson lines and Wilson loops as approximating them with partial sums, their convergence, and their behavior under gauge transformations. We also obtain a surface product integral representation for the Wilson loop operator. The result can be interpreted as the non-abelian version of Stokes theorem.


On Integrable Systems Related To Semisimple Lie Groups, G. A. Keri̇mov Jan 2000

On Integrable Systems Related To Semisimple Lie Groups, G. A. Keri̇mov

Turkish Journal of Physics

Quantum scattering systems related to the noncompact semisimple Lie groups G in the sense that the Hamiltonian of the system can be written as a function of the Casimir operator of G are considered. The S-matrix for such systems are defined in terms of an interwining operator of underling symmetry group G.


Nonabelian Cosmic Strings From So(3) Gauge Symmetry, Mehmet Koca Jan 2000

Nonabelian Cosmic Strings From So(3) Gauge Symmetry, Mehmet Koca

Turkish Journal of Physics

The nature of $SO(3)$ breaking into its closed subgroups and the emergence of nonabelian cosmic strings are discussed. Relevance to GUT breaking and thereby to cosmology is pointed out. Classification of cosmic strings are associated with the affine ADE Lie algebras.


Cosmological Adiabatic Geometric Phase Of A Scalar Field In A Bianchi Spacetime, Ali̇ Mostafazadeh Jan 2000

Cosmological Adiabatic Geometric Phase Of A Scalar Field In A Bianchi Spacetime, Ali̇ Mostafazadeh

Turkish Journal of Physics

A two-component formulation of the Klein-Gordon equation is used to investigate the cyclic and noncyclic adiabatic geometric phases due to spatially homogeneous (Bianchi) cosmological models. It is shown that no adiabatic geometric phases arise for Bianchi type I models. For general Bianchi type IX models the problem of the adiabatic geometric phase is shown to be equivalent to the one for nuclear quadrupole interactions of a spin. For these models nontrivial non-Abelian adiabatic geometrical phases may occur in general.


From Antibracket To Equivariant Characteristic Classes, Armen Nersessian Jan 2000

From Antibracket To Equivariant Characteristic Classes, Armen Nersessian

Turkish Journal of Physics

We equip the exterior algebra of Riemann manifold by the odd symplectic structure. Then, by its use we construct the equivariant even (pre)symplectic structure, whose Poincare - Cartan invariants of the second structure define the equivariant Euler classes of the surfaces.


On The Duality Of Quantum Liouville Field Theory, L. O'Raifeartaigh, J. M. Pawlowski, V. V. Sreedhar Jan 2000

On The Duality Of Quantum Liouville Field Theory, L. O'Raifeartaigh, J. M. Pawlowski, V. V. Sreedhar

Turkish Journal of Physics

It has been found empirically that the Virasoro centre and 3-point functions of quantum Liouville field theory with potential $e^{2b\phi(x)}$ and external primary fields exp($\alpha\phi(x)$) are invariant with respect to the duality transformations $\hbar \alpha\rightarrow q-\alpha$ where $q=b^{-1}+b$. The steps leading to this result (via the Virasoro algebra and 3-point functions) are reviewed in the path-integral formalism. The duality stems from the fact that the quantum relationship between the $\alpha$ and the conformal weights $\Delta_\alpha$ is two-to-one. As a result the quantum Liouville potential may actually contain two exponentials (with related parameters). It is shown that in the two-exponential theory …


Chaos In Closed Isotropic Cosmological Models With Steep Scalar Field Potential, A. V. Toporensky Jan 2000

Chaos In Closed Isotropic Cosmological Models With Steep Scalar Field Potential, A. V. Toporensky

Turkish Journal of Physics

The dynamics of closed scalar field FRW cosmological models is studied for several types of exponentially and more than exponentially steep potentials. The parameters of scalar field potentials which allow a chaotic behaviour are found from numerical investigations. It is argued that analytical studies of equation of motion at the Euclidean boundary can provide an important information about the properties of chaotic dynamics. Several types of transition from chaotic to regular dynamics are described.


Coherent States For The Hydrogen Atom, Nuri̇ Ünal Jan 2000

Coherent States For The Hydrogen Atom, Nuri̇ Ünal

Turkish Journal of Physics

We obtained the coherent states for the hydrogen atom by transforming the problem onto the four oscillators in the parametric time at the classical level and quantizing these oscillators. We showed that for the coherent states the mean values of the physical position of the electron satisfy the Keplerian ellipsis and the dispersions of them oscillate in the parametric time.


Parameterized Absolute Parallelism: A Geometry For Physical Applications, Mamdouh Ishaac Wanas Jan 2000

Parameterized Absolute Parallelism: A Geometry For Physical Applications, Mamdouh Ishaac Wanas

Turkish Journal of Physics

Absolute parallelism (AP) geometry is frequently used for physical applications. Although it is wider than the Riemannian geometry, it has two main defects. The first is that its path equation does not represent physical trajectories of any test particle. The second is the identical vanishing of its curvature tensor. The present work shows that parameterizing this geometry would solve the two problems. Furthermore, the resulting parameterized (AP)-structure is more general than both the conventional (AP)-structure and the Riemannian structure. Also, it is shown that it can be reduced to one or the other, of these two geometric structures, in some …


Time Evolution Of Fast Particles During Decay Of Hadronic Systems, Mohamed Tarek Hussein, Nabila Mohamed Hassan, Nagla El-Harby Jan 2000

Time Evolution Of Fast Particles During Decay Of Hadronic Systems, Mohamed Tarek Hussein, Nabila Mohamed Hassan, Nagla El-Harby

Turkish Journal of Physics

A phenomenological model is presented based on the formation of a nuclear thermodynamic system during the collision of intermediate and high energy heavy ions. The formulation and the dynamic picture are determined by solving the Vlasov equation. The solution is dressed in the form of a power series the first term of which being the equilibrium distribution in phase space. The rest, are time dependent perturbation terms due to the multiple strong interactions inside the system. The temperature gradient and the derivatives of the phase function are calculated. The time dependence of the angular emission of the produced particles is …


Positron Annihilation And Xrd Studies On Deformed Al-Alloys With Low Concentration Of Mg, Emad A. Badawi, M. A. Abdel-Rahman, S. A. Mahmoud, A. A. Ramadan Jan 2000

Positron Annihilation And Xrd Studies On Deformed Al-Alloys With Low Concentration Of Mg, Emad A. Badawi, M. A. Abdel-Rahman, S. A. Mahmoud, A. A. Ramadan

Turkish Journal of Physics

Positron behaviour at grain boundaries is characterized by their bulk diffusibility D, their bulk free lifetime $\tau_f$ and their trapped lifetime $\tau_t$ ($\tau_t > \tau_f).$ Al-Mgx samples (x = 0-1.4 at \%) have been homogenized at 573 K for 12 hours. The mean lifetime, as (indirectly) measured at various concentrations, show a good fitting with Sigmodel giving $\tau_t$ = 180.664 ps and $\tau_{f}$ = 163.9 ps. The mean lifetime was found to vary exponentially with the degree of deformation. The XRD study showed that preferred orientation occurred at degrees of deformation $>$ 32 \%, whereas the peak intensity then increases …


A Glancing Incidence Exafs Study Of Evaporated Silver Films On Glass, Ahmet Bulut, Bünyami̇n Karabulut, Engi̇n Başaran, James Robinson Jan 2000

A Glancing Incidence Exafs Study Of Evaporated Silver Films On Glass, Ahmet Bulut, Bünyami̇n Karabulut, Engi̇n Başaran, James Robinson

Turkish Journal of Physics

A glancing incidence EXAFS experiment has been carried out with evaporated silver films on glass substrates. Prior to EXAFS data collection, a reflectivity curve was performed from which the critical angle for total external reflection of x-rays from surface were determined. The analysed EXAFS data revealed that there is a reduction in the coordination number and an increase in Debye-Waller factor compared to bulk values. These changes were explained in terms of grain size effect and the surface effects of the silver film.


Internal Photoemission Spectroscopy For A Ptsi/P-Si Schottky Junction, Bülent Aslan, Raşi̇t Turan Jan 2000

Internal Photoemission Spectroscopy For A Ptsi/P-Si Schottky Junction, Bülent Aslan, Raşi̇t Turan

Turkish Journal of Physics

Properties of internal photoemission in a PtSi-Si Schottky junction have been studied. The traditional Fowler plot of a detector's photoyield is found to be nonlinear for values close to the barrier height of the junction. It is shown that the model that takes all scattering mechanisms into account provides a successful description for the experimental results. It is also shown that the photoemission spectrum is independent of temperature in agreement with this model. The properties of detector's ambient influence the photoemission spectrum for wavelength of 3 $\mu$m or less. A strong loss in the detector's response is observed at around …


Consistency Of The Born Approximation For Aharonov-Bohm Scattering With Massless Spin-1/2 Particles, Müge Boz, Namik Kemal Pak Jan 2000

Consistency Of The Born Approximation For Aharonov-Bohm Scattering With Massless Spin-1/2 Particles, Müge Boz, Namik Kemal Pak

Turkish Journal of Physics

The second order contribution for the relativistic scattering of massless spin-$\frac{1}{2}$ particles from an infinitely long solenoid, in the context of covariant perturbation theory, is calculated and shown to vanish. Thus, Born approximation is consistent for this case as well.


Molecular Dynamics Simulations Of Super Heated Ni_4 Cluster, M. Haluk Güven Jan 2000

Molecular Dynamics Simulations Of Super Heated Ni_4 Cluster, M. Haluk Güven

Turkish Journal of Physics

The fragmentation mechanism of the super heated Ni4 cluster is studied by employing the microcanonical molecular dynamics simulations and an empirical model potential. Ni$_{4}$ cluster is heated up above the bulk Ni evaporation point temperature and then classical trajectory analysis as well as RRK theory are used to calculate survival probability, evaporation rate, average kinetic energy release and dissociation energy.


The Magnetic Super-Exchange Coupling In Copper(Ii) Acetate Monohydrate And A Redetermination Of The Crystal Structure, Ayhan Elmali Jan 2000

The Magnetic Super-Exchange Coupling In Copper(Ii) Acetate Monohydrate And A Redetermination Of The Crystal Structure, Ayhan Elmali

Turkish Journal of Physics

The magnetic properties and redetermination of crystal structure of copper(II) acetate monohydrate have been studied. The copper(II) centers are separated by 2.617(1) \AA \ and antiferromagnetically coupled (-2J = 292.2 cm$^{-1}$), which follows from temperature-dependent magnetic susceptibility measurements in the temperature range 4.2 to 300 K. The magnetic moment at 300 K is about 2.1 Bohr magnetons while 0.1 Bohr magnetons at 4.2 K. The magnetic susceptibility is at a maximum near 250 K and decreases rapidly as the temperature is lowered to liquid helium temperature.


Antiferromagnetic Transition In \Alpha-Mn-Fe System, R. K. Nkum, F. Boakye Jan 2000

Antiferromagnetic Transition In \Alpha-Mn-Fe System, R. K. Nkum, F. Boakye

Turkish Journal of Physics

Antiferromagnetic transition in $\alpha$-Mn-Fe alloys has been studied using resistivity-temperature measurements from 300 to 1.5 K. The results indicate that the transition temperature $T_N$ of the samples studied increases with increasing Fe concentration. This suggests that the N\'{e}el temperature is affected by Fe. Also, Fe plays a significant role in the local disorder on the magnetic moment of the ions in the complex manganese structure.


Determination Of Optical Constant Of Materials By Two Different Methods: An Application To Single Crystals Si, Hazi̇ret Durmuş, Haluk Şafak, Haldun Karabiyik Jan 2000

Determination Of Optical Constant Of Materials By Two Different Methods: An Application To Single Crystals Si, Hazi̇ret Durmuş, Haluk Şafak, Haldun Karabiyik

Turkish Journal of Physics

The normal reflectance of single crystal Si was measured at 0.5 ­5.6 eV range by unpolarized light. Optical parameters of Si were determined from this reflectance data by using two different methods: oscillator fit procedure and Kramers-Kronig analysis. The refractive index, extinction coefficient and the real and imaginary parts of complex dielectric constant obtained by these two methods were compared. A good agreement was found between two methods. Furthermore, the optical parameters so obtained seem to be in a satisfactory agreement with the literature.


Crystallographic Analysis Of Martensitic Transformation In Cusn Alloy, Ekrem Artunç, Seyfetti̇n Çakmak, Seval Çakmak Jan 2000

Crystallographic Analysis Of Martensitic Transformation In Cusn Alloy, Ekrem Artunç, Seyfetti̇n Çakmak, Seval Çakmak

Turkish Journal of Physics

In this study, the Kajiwara model has been applied to Cu-14.8at.\%Sn alloy with good agreement with experimental results. For this alloy, the austenite phase has a body centered cubic (bcc) lattice and the martensite phase has a monoclinic 9R superlattice. Using the lattice parameters of both phases, the calculated habit plane indices, magnitude of the lattice invariant shear and orientation relationships, have been compared with the observed results for this alloy.


Linac-Ring Type \Phi Factory Of Basic And Applied Research, A. Kenan Çi̇ftçi̇, Osman Gürkan, Turan Olgar, Erdal Recepoğlu, Saleh Sultansoy, Ömer Yavaş, Meti̇n Yilmaz Jan 2000

Linac-Ring Type \Phi Factory Of Basic And Applied Research, A. Kenan Çi̇ftçi̇, Osman Gürkan, Turan Olgar, Erdal Recepoğlu, Saleh Sultansoy, Ömer Yavaş, Meti̇n Yilmaz

Turkish Journal of Physics

In this paper, main parameters for linac-ring type collider designed for producing $\phi $ particles copiously are estimated and the potential of this machine in particle physics research is investigated. Moreover, parameters for free electron laser and synchrotron radiation obtained from electron linac and positron ring, respectively, are determined and applications of these radiations are summarized.


A Product Operator Formalism Of 3d J-Resolved Nmr Spectroscopy For Is_Nk_M(I = 1/2, S = 1/2, K = 1/2) Spin System, Özden Tezel, Azmi̇ Gençten Jan 2000

A Product Operator Formalism Of 3d J-Resolved Nmr Spectroscopy For Is_Nk_M(I = 1/2, S = 1/2, K = 1/2) Spin System, Özden Tezel, Azmi̇ Gençten

Turkish Journal of Physics

Product operator formalism is widely used for analytical description of multiple-pulse NMR experiments for weakly coupled spin systems. 3D J-resolved NMR spectroscopy is widely used in order to resolve the chemical shift along one axis and spin-spin coupling parameters along the two other axis. In this study, product operator theory is used for analytical description of heteronuclear 3D J-resolved NMR spectroscopy for the \( IS_nK_m (I=1/2, S=1/2, K=1/2; n=1,2, m=1,2,3) \) spin system.


Mass-Radius Relations For Helium White Dwarfs, Ri̇kkat Ci̇velek, Ni̇lgün Kiziloğlu Jan 2000

Mass-Radius Relations For Helium White Dwarfs, Ri̇kkat Ci̇velek, Ni̇lgün Kiziloğlu

Turkish Journal of Physics

We studied the static mass-radius relation of white dwarf stars with masses greater than 0.45 $M_\odot$. We assumed pure degenerate helium interiors at a finite temperature with luminosity-mass ratio due to neutrino energy loss. We compared the obtained M-R relation with those of other writers.


An Extended Adiabatic Approach For Nuclear Reactions, Mustafa Yilmaz, Bülent Gönül Jan 2000

An Extended Adiabatic Approach For Nuclear Reactions, Mustafa Yilmaz, Bülent Gönül

Turkish Journal of Physics

In this letter, an alternative approximation is developed for the treatment of breakup process in nuclear reactions, which presents a way of evaluating non-adiabatic corrections to the adiabatic model three-body wavefunction by introducing a more consistent prescription for the continuum n-p center of mass energy. Although the present formalism goes beyond the quasi-adiabatic approach, due to the use of exact continuum channel energies, its application to deuteron involving reactions at medium energies shows that such an approach can not be used in its present form. A possible reason behind this failure is discussed.


Microhardness Creep In Single Crystals Of Tin-Chalcogenides, S. M. Vyas, C. F. Desai, R. C. Shah, G. R. Pandya Jan 2000

Microhardness Creep In Single Crystals Of Tin-Chalcogenides, S. M. Vyas, C. F. Desai, R. C. Shah, G. R. Pandya

Turkish Journal of Physics

SnSe and SnS have been grown by Bridgman- Stockbarger method. Loading time as a function of vickers microhardness has been measured at different temperatures in the range 303 K to 388K. Al measurement of hardness have been carried out on the cleavage planes. The activation energy for creep has been evaluated to be 2.92 and 1.75 K Cal/mole, respectively, for SnSe and SnS crystals.


The Growth Of P-Type A^{Iii} B^{Iii} C_2^{V I} Single Crystals, Beki̇r Gürbulak, Cevdet Coşkun, Seydi̇ Doğan, Aytunç Ateş, Yahya Kemal Yoğurtçu Jan 2000

The Growth Of P-Type A^{Iii} B^{Iii} C_2^{V I} Single Crystals, Beki̇r Gürbulak, Cevdet Coşkun, Seydi̇ Doğan, Aytunç Ateş, Yahya Kemal Yoğurtçu

Turkish Journal of Physics

$A^{III}B^{III}C_2^{VI}$ single crystals were grown by the modified Bridgman-Stockbarger method, a procedure similar to direct freezing in our crystal growth laboratory. $A^{III}B^{III}C_2^{VI}$ compounds are collected into two groups (III. group: TI, Ga, In and VI. group: Se, S, Te): 1. TlGaSe$_2$, TlGaS$_2$ and TlInS$_2$ have layer structure. 2. TlInSe$_2$, TlInTe$_2$ and TlGaTe$_2$ have chained structure. The main reasons such crystals grown with this method is similar to the direct freezing method because 1) quality of crystals is the same as crystals grown by other methods, and 2) growth time of crystals is shorter by about 5-10 days. None of the …


Doping Of High-Temperature Superconductors, Sh. Meretliev, K. B. Sadykov, A. Berkeliev Jan 2000

Doping Of High-Temperature Superconductors, Sh. Meretliev, K. B. Sadykov, A. Berkeliev

Turkish Journal of Physics

High-temperature superconducting ceramics systems YBaCuO and BiSrCaCuO, both doped by Pb, Sb, Li, K, Na and non-doped, have been produced by the method of solid phase reaction synthesis. The principle of controlled valency by Vervey has been used to characterize high-temperature superconductors. High-temperature superconducting ceramics have been obtained with properties stable in time by single-purpose doping.