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2006

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Articles 661 - 690 of 738

Full-Text Articles in Physics

W-Boson Production With Large Transverse Momentum At The Lhc, Nikolaos Kidonakis, Richard J. Gonsalves, Agustin Sabio Vera Jan 2006

W-Boson Production With Large Transverse Momentum At The Lhc, Nikolaos Kidonakis, Richard J. Gonsalves, Agustin Sabio Vera

Faculty Articles

We study W-boson production with large transverse momentum, QT, in pp collisions at the LHC. We calculate the complete NLO corrections and the soft-gluon NNLO corrections to the differential cross section. The NLO corrections are large but they do not reduce the scale dependence relative to LO, while the NNLO soft-gluon corrections, although small, significantly reduce the scale dependence and thus provide a more stable result.

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Production Of Large Transverse Momentum W Bosons At The Tevatron, Nikolaos Kidonakis, Agustin Sabio Vera Jan 2006

Production Of Large Transverse Momentum W Bosons At The Tevatron, Nikolaos Kidonakis, Agustin Sabio Vera

Faculty Articles

We discuss the production of W bosons at large transverse momentum in p pbar collisions at the Tevatron Run I and II. W boson hadroproduction is a process of relevance in testing the Standard Model and in estimates of backgrounds to new physics. The next-to-leading order cross section in the region of large transverse momentum is dominated by threshold soft-gluon corrections which arise from incomplete cancellations near partonic threshold between graphs with real emission and virtual graphs due to the limited phase space available for real gluon emission. In this contribution it is shown how, by including next-to-next-to-leading-order (NNLO) soft-gluon …

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Soft-Gluon Corrections In Hard-Scattering Processes Through Nnnlo, Nikolaos Kidonakis Jan 2006

Soft-Gluon Corrections In Hard-Scattering Processes Through Nnnlo, Nikolaos Kidonakis

Faculty Articles

I discuss soft-gluon corrections in hard-scattering processes and their resummation. I present master formulas for the expansion of the resummed cross section through NNNLO and discuss the significance of these corrections in a number of processes.

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Helicity Dependence Of The \Vec\Gamma\Vec N \To \Pi N Reaction Channels In The \Delta-Resonance Region, Eed M. Darwish, Mohamed A. El-Zohry Jan 2006

Helicity Dependence Of The \Vec\Gamma\Vec N \To \Pi N Reaction Channels In The \Delta-Resonance Region, Eed M. Darwish, Mohamed A. El-Zohry

Turkish Journal of Physics

Based on a prior effective Lagrangian model on single pion photoproduction from the nucleon, successfully tested in total and differential cross sections, the helicity dependence from the interaction of circularly polarized photons and a longitudinally polarized nucleon target is studied in the energy range from \pi-threshold through the \Delta(1232)-resonance region. The doubly polarized total and differential cross section differences for parallel \sigma^{3/2} and antiparallel \sigma^{1/2} helicity states are predicted and compared with recent experimental data. We show that the results are sensitive to interferences among different contributions to the process and, thus, represent a complementary test of the theoretical model. …

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Pendant ^{13}C Nmr Spectroscopy Applied To Ch_N Groups, Azmi̇ Gençten, İrfan Şaka, Sedat Gümüş Jan 2006

Pendant ^{13}C Nmr Spectroscopy Applied To Ch_N Groups, Azmi̇ Gençten, İrfan Şaka, Sedat Gümüş

Turkish Journal of Physics

Polarization enhancement nurtured during attached nucleus testing (PENDANT) NMR spectroscopy gives signals of quaternary carbon atoms in addition to signals indicative of CH, CH_2 and CH_3 groups. In this study, using product operator theory, analytical description of PENDANT NMR spectroscopy for CH_n (IS_n, I = 1/2, S = 1/2, n = 0, 1, 2, 3) spin systems are presented. Simulation and experimental results of PENDANT NMR spectroscopy are also presented. Theoretical results are found to be in exact agreement with the simulation results and in good agreement with the experimental ones.

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Phase Distribution Of The Output Of Jaynes-Cummings Model With The Superposition Of Squeezed Displaced Fock States, Gamal Mohamed Abd Al-Kader Jan 2006

Phase Distribution Of The Output Of Jaynes-Cummings Model With The Superposition Of Squeezed Displaced Fock States, Gamal Mohamed Abd Al-Kader

Turkish Journal of Physics

The Wigner quasi-probability function for the superposition of squeezed displaced Fock states (SDFS's) is reviewed. The interaction of these states with a two-level atom in cavity with the presence of additional Kerr medium is studied. Exact general matrix elements of the time-dependent operators of a Jaynes-Cummings model (JCM), in the presence of a Kerr medium, with these states are derived. We have obtained the phase distribution by two different ways: one is by Pegg-Barnett formalism, the second is by integration of the Wigner function over the radial variable. Results of these two approaches are compared. The Wigner phase distributions for …

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Applications Of Genetic Algorithm To Quantum Mechanical Systems, Mehmet Şahi̇n, Ülfet Atav, Mehmet Tomak Jan 2006

Applications Of Genetic Algorithm To Quantum Mechanical Systems, Mehmet Şahi̇n, Ülfet Atav, Mehmet Tomak

Turkish Journal of Physics

Genetic algorithm (GA) inspired by the biological world is a general search and optimization method. It was first proposed by Holland in 1975. GA has been applied to many scientific areas especially in engineering optimization problems. It is also used in solving of quantum mechanical problems. In this study, we have applied this method to different realistic quantum mechanical problems of both self-consistent and non-self-consistent type. The results obtained are compared with the results of other methods and it is seen that the GA can be a very powerful alternative to some other traditional techniques such as variational method.

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First Principles Approach To Batio_3, Mustafa Uludoğan, Tahi̇r Çağin Jan 2006

First Principles Approach To Batio_3, Mustafa Uludoğan, Tahi̇r Çağin

Turkish Journal of Physics

We present state of art first-principles study on the static and dynamic properties of BaTiO_3, a typical ferroelectric material. Here, structure, equation of state, phase stability, and phase transformations of BaTiO_3 studied in Generalized Gradient Approximation. Furthermore, properties such as, Born effective charges, optical dielectric constant and phonon spectra are calculated from Density Functional Perturbation Theory.

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Molecular Dynamics Studies On Glass Formation Of Pd-Ni Alloys By Rapid Quenching, Sevgi̇ Özdemi̇r Kart, Mehmet Tomak, Mustafa Uludoğan, Tahi̇r Çağin Jan 2006

Molecular Dynamics Studies On Glass Formation Of Pd-Ni Alloys By Rapid Quenching, Sevgi̇ Özdemi̇r Kart, Mehmet Tomak, Mustafa Uludoğan, Tahi̇r Çağin

Turkish Journal of Physics

The rapid solidification of Pd-Ni alloys is studied with the constant-pressure and constant-temperature (TPN) and the constant-volume and constant-temperature (TVN) molecular dynamics technique to obtain an atomic description of glass formation in the alloy. Quantum Sutton-Chen potential for Pd-Ni binary system is applied in the simulations. We present some thermodynamic and structural results from simulations of such glasses over a range of compositions. The structural properties are analyzed by means of pair distribution function, volume, and enthalpy as a function of temperature and concentration at the cooling rates ranging from 5 K/ps to 0.05 K/ps to see whether the Pd-Ni …

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Effect Of A Finite Number Of Electrons On The Physical Properties Of Two Dimensional Parabolic Quantum Dot, Berna Gülveren, Ülfet Atav, Mehmet Tomak Jan 2006

Effect Of A Finite Number Of Electrons On The Physical Properties Of Two Dimensional Parabolic Quantum Dot, Berna Gülveren, Ülfet Atav, Mehmet Tomak

Turkish Journal of Physics

The effect of number of particles on the physical properties of a two dimensional parabolic quantum dot system is investigated numerically at finite temperature. The Thomas-Fermi equation is solved self consistently with Poisson equation. The changes induced by electron-electron interaction are also analyzed. It is shown that the numerical procedure that is applied to solve the problem is very efficient at all temperatures.

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Ramifications Of Lineland, Daniel Grumiller, Rene Meyer Jan 2006

Ramifications Of Lineland, Daniel Grumiller, Rene Meyer

Turkish Journal of Physics

A non-technical overview on gravity in two dimensions is provided. Applications discussed in this work comprise 2D type 0A/0B string theory, Black Hole evaporation/thermodynamics, toy models for quantum gravity, for numerical General Relativity in the context of critical collapse and for solid state analogues of Black Holes. Mathematical relations to integrable models, non-linear gauge theories, Poisson-sigma models, KdV surfaces and non-commutative geometry are presented.

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Equivariant Localization For Susy Quantum Mechanics, Levent Akant Jan 2006

Equivariant Localization For Susy Quantum Mechanics, Levent Akant

Turkish Journal of Physics

We apply equivariant localization to supersymmetric quantum mechanics and show that the partition function localizes on the instantons of the theory. Our construction of equivariant cohomology for SUSY quantum mechanics is different than the ones that already exist in the literature. A hidden bosonic symmetry is made explicit and the supersymmetry is extended. New bosonic symmetry is the square of the new fermionic symmetry. The D term is now the parameter of the bosonic symmetry. This construction provides us with an equivariant complex together with a Cartan differential and makes the use of localization principle possible.

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Plane Symmetric Solutions Of Gravitational Field Equations In Five Dimensions, A. N. Aliev, Hakan Cebeci̇, Teki̇n Dereli̇ Jan 2006

Plane Symmetric Solutions Of Gravitational Field Equations In Five Dimensions, A. N. Aliev, Hakan Cebeci̇, Teki̇n Dereli̇

Turkish Journal of Physics

We present the effective field equations obtained from a generalized gravity action with Euler-Poincaré term and a cosmological constant in a D dimensional bulk space-time. A class of plane-symmetric solutions that describe a 3-brane world embedded in a D=5 dimensional bulk space-time are given.

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Charges In Ads Spacetimes, İbrahi̇m Güllü, Bayram Teki̇n Jan 2006

Charges In Ads Spacetimes, İbrahi̇m Güllü, Bayram Teki̇n

Turkish Journal of Physics

We give a review of our recent work on conserved charges in cosmological spacetimes. We compute the mass and the angular momenta of various solutions in D dimensions. This is an extended version of a talk given by B. Tekin. The original material can be found in the related papers in our references.

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Coset Algebras Of The Maxwell-Einstein Supergravities, Nejat Tevfi̇k Yilmaz Jan 2006

Coset Algebras Of The Maxwell-Einstein Supergravities, Nejat Tevfi̇k Yilmaz

Turkish Journal of Physics

The general structure of the scalar cosets of the Maxwell-Einstein supergravities is given. Following an introduction of the non-linear coset formalism of the supergravity theories a comparison of the coset algebras of the Maxwell-Einstein supergravities in various dimensions is discussed.

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Pulsar Studies Of Tiny-Scale Structure In The Neutral Ism, Joel M. Weisberg, S. Stanimirovi´C Jan 2006

Pulsar Studies Of Tiny-Scale Structure In The Neutral Ism, Joel M. Weisberg, S. Stanimirovi´C

Physics and Astronomy Faculty Work

We describe the use of pulsars to study small-scale neutral structure in the interstellar medium (ISM). Because pulsars are high velocity objects, the pulsarEarth line of sight sweeps rapidly across the ISM. Multiepoch measurements of pulsar interstellar spectral line spectra therefore probe ISM structures on AU scales. We review pulsar measurements of small scale structure in HI and OH and compare these results with those obtained through other techniques.

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The Lazarus Project. Ii. Spacelike Extraction With The Quasi-Kinnersley Tetrad, Manuela Campanelli, Bernard Kelly, Carlos O. Lousto Jan 2006

The Lazarus Project. Ii. Spacelike Extraction With The Quasi-Kinnersley Tetrad, Manuela Campanelli, Bernard Kelly, Carlos O. Lousto

Physics & Astronomy Faculty Publications

The Lazarus project was designed to make the most of limited 3D binary black-hole simulations, through the identification of perturbations at late times, and subsequent evolution of the Weyl scalar Ψ4 via the Teukolsky formulation. Here we report on new developments, employing the concept of the “quasi-Kinnersley” (transverse) frame, valid in the full nonlinear regime, to analyze late-time numerical space-times that should differ only slightly from Kerr. This allows us to extract the essential information about the background Kerr solution, and through this, to identify the radiation present. We explicitly test this procedure with full-numerical evolutions of Bowen-York data for …

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Ultrashort, High Power, And Ultralow Noise Mode-Locked Optical Pulse Generation Using Quantum-Dot Semiconductor Lasers, Myoung-Taek Choi Jan 2006

Ultrashort, High Power, And Ultralow Noise Mode-Locked Optical Pulse Generation Using Quantum-Dot Semiconductor Lasers, Myoung-Taek Choi

Electronic Theses and Dissertations

This dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section devices. Short pulse generation from an external cavity mode-locked QD two-section diode laser is studied. High quality, sub-picosecond (960 fs), high peak power (1.2 W) pulse trains are obtained. The sign and magnitude of pulse …

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Dwba Of The Reaction ^0be(P, \Alpha )^6li At E_P = 18.6\Sim 50 Mev, S. E. Abdel-Kariem Jan 2006

Dwba Of The Reaction ^0be(P, \Alpha )^6li At E_P = 18.6\Sim 50 Mev, S. E. Abdel-Kariem

Turkish Journal of Physics

The compound nucleus produced in the reaction ^9Be(p, \alpha)^6Li in the incident energy range E_p = 18.6 \sim 50 MeV is mainly occurred when its excitation energy is greater than the \alpha -particle threshold separation energy by about 20 MeV, strongly suggesting the reaction mechanism is a direct one-step process. To understand this phenomenon, we employ semi-microscopic zero-range distorted-wave Born approximation (DWBA) theory to analyse experimental data obtained in this energy range for the lower three ^6Li-states: ground state (1^+; 0); 2.186 MeV (3^+; 0); and 3.563 MeV (0^+; 1). The Kurath-Millener spectroscopic-factor amplitudes for the triton-cluster transfer are used …

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Profiling Of Lithium And Potassium Into Silicon, Ali M. Mousa Jan 2006

Profiling Of Lithium And Potassium Into Silicon, Ali M. Mousa

Turkish Journal of Physics

The profiling of Lithium and Potassium into Silicon doped by electro deposition from molten salts (LiBr, KI) has been studied for various time periods and deposition currents. For the samples studied, changes in the deposition time and current have significant effects on the conductivity type and sheet resistance variation. This has been attributed to the high value of solid solubility of Lithium and Potassium in Silicon. Additionally, surface concentration variation with depth is affected significantly by variation in deposition time, particular for samples with a deposition time of 7 minutes. A junction was found 156 microns from the surface. For …

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Optical Pulse Distortion In Fibonacci-Class Multilayer Stacks, A Rostami, S. Matloub Jan 2006

Optical Pulse Distortion In Fibonacci-Class Multilayer Stacks, A Rostami, S. Matloub

Turkish Journal of Physics

Optical pulse distortion and propagation through quasi-periodic structures generally and especially for Fibonacci-class, is investigated analytically and simulated numerically. In this analysis, the transfer matrix method (TMM) for distortion evaluation is used. The simulated results for Fibonacci-class quasi-periodic structures and pure periodic multilayer stacks are compared. We show that the Fibonacci-class quasi-periodic structure has a large dispersion coefficient with respect to a similar case in the periodic structure. So, quasi-periodic structures will destroy the incident pulse shape for smaller stack length than a periodic case in a similar situation. Finally, using output power, the distortion limit can be estimated and …

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Inexpensive Near-Ir Photodetector, Omar A. Abdulrazaq, Evan T. Saleem Jan 2006

Inexpensive Near-Ir Photodetector, Omar A. Abdulrazaq, Evan T. Saleem

Turkish Journal of Physics

Fabrication and characterization of a CdS/Si heterojunction detector for 1.064 \mu m Nd:YAG laser detection has been carried out by pyrolytic spraying of CdS films onto single crystal n-type Si substrates. Response time has been determined in this study.

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Tensor Polarization And Quadrupole Form Factor Of The Deuteron, A. K. A. Azzam, M. A. Fawzy, E. M. Hassan, A. M. Yasser Jan 2006

Tensor Polarization And Quadrupole Form Factor Of The Deuteron, A. K. A. Azzam, M. A. Fawzy, E. M. Hassan, A. M. Yasser

Turkish Journal of Physics

A new experimental value, M = 0.06925 \pm 0.00281, of the peak of the quadrupole form factor F_Q(q) is obtained by fitting the straight line relation found between the peak values of both T_{21}(q) and F_Q(q).

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Transient Photoconductivity In Amorphous Se-Ge-Ag System, R. S. Sharma, D. Kumar, A. Kumar Jan 2006

Transient Photoconductivity In Amorphous Se-Ge-Ag System, R. S. Sharma, D. Kumar, A. Kumar

Turkish Journal of Physics

Transient Photoconductivity measurements have been made in vacuum evaporated thin films of Se_{0.80 - x}Ge_{0.20}Ag_x at different intensities, temperatures and illumination times. The films exhibit long-lived residual photoconductivity, called persistent photoconductivity, with an extremely slow decay rate. The persistent photoconductivity (PPC) increases with an increase in intensity and illumination time. However, this quantity decreases with increase in temperature. These results indicate that the decay of photoconductivity is not only governed by the carrier trapped in the intrinsic defects but also gets affected by the light induced defect creation through structural changes The persistent photoconductivity effect is found to be suppressed …

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Stagnation Point Flow And Heat Transfer Of A Micropolar Fluid In A Porous Medium, Hazem Ali Attia Jan 2006

Stagnation Point Flow And Heat Transfer Of A Micropolar Fluid In A Porous Medium, Hazem Ali Attia

Turkish Journal of Physics

The steady laminar flow in a porous medium of an incompressible non-Newtonian micropolar fluid impinging on a permeable flat plate with heat transfer is investigated. A numerical solution for the governing nonlinear momentum and energy equations is obtained. The effect of the porosity of the medium and the characteristics of the non-Newtonian fluid on both the flow and heat transfer is presented and discussed.

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Ensemble Teleportation, Thomas Krüger Jan 2006

Ensemble Teleportation, Thomas Krüger

Turkish Journal of Physics

The possibility of teleportation is by sure the most interesting consequence of quantum non-separability. So far, however, teleportation schemes have been formulated by use of state vectors and considering individual entities only. In the present article the feasibility of teleportation is examined on the basis of the rigorous ensemble interpretation of quantum mechanics (not to be confused with a mere treatment of noisy EPR pairs) leading to results which are unexpected from the usual point of view.

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The Calculations Of Oscillator Strengths And Transition Probabilities For Atomic Fluorine, Gülteki̇n Çeli̇k, H. Şükür Kiliç, Erhan Akin Jan 2006

The Calculations Of Oscillator Strengths And Transition Probabilities For Atomic Fluorine, Gülteki̇n Çeli̇k, H. Şükür Kiliç, Erhan Akin

Turkish Journal of Physics

Oscillator strengths for transitions between individual lines belonging to some doublet and quartet terms, and multiplet transition probabilities of atomic fluorine have been calculated using weakest bound electron potential model theory (WBEPMT). In the determination of relevant parameters, we employed numerical non-relativistic Hartree-Fock (NRHF) wave functions for expectation values of radii and the necessary energy values have been taken from experimental energy data in the literature. Oscillator strengths and transition probabilities obtained in this work have been compared to experimental and theoretical values given in the literature.

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Modulated Photoconductivity Studies Of A-As_2se_3 Thin Films, Ruhi̇ Kaplan Jan 2006

Modulated Photoconductivity Studies Of A-As_2se_3 Thin Films, Ruhi̇ Kaplan

Turkish Journal of Physics

Modulated photocurrent measurements in amorphous arsenic triselenide (a-As_2Se_3) is reported. Particular focus is paid towards photocarrier lifetimes as a function of temperature, and applied electric field (i.e. dc) were determined by using the quadrature frequency-resolved spectroscopy method. The activation energy from the photocurrent as a function of temperature was determined to be about 125 meV for a constant illumination intensity of 2.3 mW. Its value was found to be almost independent of the applied electric field. The exponent \nu in the power law relationship (I_{ph} \propto G^v) between generating flux and photocurrent was obtained under different electric fields. The electric …

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Electrical Switching Behaviour In Lead Phosphovanadate Glasses, B. Sujatha, C. Narayana Reddy Jan 2006

Electrical Switching Behaviour In Lead Phosphovanadate Glasses, B. Sujatha, C. Narayana Reddy

Turkish Journal of Physics

Electrical switching behaviour of lead phosphovanadate glasses were studied by determining the current-voltage characteristics. All the investigated glasses exhibit the dependence of threshold voltages on temperature, thickness and composition. Below holding current the I - V characteristics obey Ohms law followed by a negative resistance region where the bulk behaviour dominates and at higher values of current the samples goes to a low resistance state. The studied glasses exhibit memory type switching. It is suggested that the initial switching and channel formation are due to electronic, while thermal effects dominate in the formation of channels.

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Dimensional Crossover In Semiconductor Structures: From 3d Electron Transport To Ballistic Electrons In 1d, Karl-Fredrick Berggren Jan 2006

Dimensional Crossover In Semiconductor Structures: From 3d Electron Transport To Ballistic Electrons In 1d, Karl-Fredrick Berggren

Turkish Journal of Physics

Modern semiconductor technologies have made possible special devices in which a gradual dimensional crossover may be induced by means of applied electric fields. Two specific examples are described. The first one is a special GaAs field effect transistor in which the thickness of the active electron gas layer may be varied by external voltages. With decreasing layer thickness transverse states become quantized and by depopulating the corresponding subbands a tunable dimensional crossover from 3D to 2D is achieved. The second example describes how a 2D to 1D crossover may be obtained in high-mobility split-gate GaAs/AlGaAs heterostructures. Effects of interactions in …

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