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1998

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Articles 481 - 502 of 502

Full-Text Articles in Physics

Analysis Of Atmospheric Concentrations Of Radon And Thoron Using Beta Counting Technique, G. S. Islam, S. M. Basunia Jan 1998

Analysis Of Atmospheric Concentrations Of Radon And Thoron Using Beta Counting Technique, G. S. Islam, S. M. Basunia

Turkish Journal of Physics

This paper presents a detailed theory and experimental procedure for measurement and analysis of mixed radon and thoron in the environment. The technique has been successfully applied to the study of seasonal variations of radon and thoron in the atmosphere around Rajshahi, Banladesh, during the years 1989-1991. The maximum radon concentration in outdoor air was observed in the winter from December to January while the indoor radon concentration was found to be maximum during the monsoon months of July and August. The implication of the results is briefly discussed in the paper.

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Isotope Effect And Phonon Softening In Superconducting Borocarbides And Boronitrides, Tuğrul Haki̇oğlu, Valery A. Ivanov Jan 1998

Isotope Effect And Phonon Softening In Superconducting Borocarbides And Boronitrides, Tuğrul Haki̇oğlu, Valery A. Ivanov

Turkish Journal of Physics

The isotope effect in the recently disvovered class o superconductors LuNi_2B_2C and La_3Ni_2B_2N_3 is investigated in the context of electron-squezed phonon interaction renormalizing the Ni-d electron-electron correlations. Squeezed phonon mode originates from the anharmonic character of the tetragonal Ni-B structure and is polarized in the vortical direction to the Ni layers. The isotope effect arises as a result of the zero point motion of the Ni-Ni d-electron hopping amplitude dominantly due to this vertical phonon mode. Within this model the isotope exponent is calculated to be \alpha_B \leq 0.20 as compared to the recently found experimental value \alpha_B^{exp} = 0.27 …

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Photoconductivity Studies Of Crystalline Si:H P-I-N, Ruhi Kaplan, Bengü Kaplan Jan 1998

Photoconductivity Studies Of Crystalline Si:H P-I-N, Ruhi Kaplan, Bengü Kaplan

Turkish Journal of Physics

Optically modulated photoconductivity (PC) properties of hydrogenated crystalline silicon (c-Si:H) with p-i-n junctions were investigated by frequency-resolved spectroscopy in the temperature range 20-290 K. The PC lifetime measurements of c-Si:H p-i-n show a second lifetime distribution which only dominates at low temperature under low illumination levels of excitation. Unlike the room temperature single lifetime distribution seen in c-Si:H p-i-n, the maximum of this second lifetime distribution shifts to longer times when the excitation intensity decreases, which reconciles with non-geminate pair recombination and thus the distant-pair model. In addition to lifetime measurements, the direct current-voltage (I-V) characteristics, the excitation light intensity- …

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A Study Of Heavy-Ion Elastic Scattering Reactions Using A Semimicroscopic Model, A. A. Farra Jan 1998

A Study Of Heavy-Ion Elastic Scattering Reactions Using A Semimicroscopic Model, A. A. Farra

Turkish Journal of Physics

The differential cross sections for elastic scattering of ^{16}O from ^{20}Ne have been calculated using an optical potential and distorted wave Born approximation (DWBA) calculations. In the present calculations several prescriptions were tried in the ion-ion potential. The DWBA calculations were performed employing folded real and Woods-Saxon optical potentials for the distorted waves. Inclusion of the exchange process explains the large back-angle cross sections. The elastic scattering differential cross sections are successfully described by calculations in which elastic alpha-transfer amplitudes are coherently added to direct elastic scattering amplitudes.

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Effect Of Deposition Conditions On Composition Of Rf-Sputtered Bi-Sr-Ca-Cu-O Thin Films, Ayhan Güldeste Jan 1998

Effect Of Deposition Conditions On Composition Of Rf-Sputtered Bi-Sr-Ca-Cu-O Thin Films, Ayhan Güldeste

Turkish Journal of Physics

The effect of rf-magnetron sputtering conditions on as-deposited film composition using a stoichiometric Bi_2Sr_2CaCu_2O_y (Bi-2212) target was investigated in an on-axis configuration, as the stoichiometrical control of the film is the most important parameter for the proper study of film characteristics. It was found that substrate target distance up to 55-60 mm may provide a film composition close to the target composition. The sputtering chamber pressure effecting film composition, especially in respect of Bi, is an important parameter which needs very pracise control. Bi ratio in the deposited films increases with increasing Ar pressure while Sr and Ca are not …

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Flavour Violating \Tau-Decays In Magnetic Interaction And E_6 Models, A.T. Alan, Z.Z. Aydin And S. Sultansoy Jan 1998

Flavour Violating \Tau-Decays In Magnetic Interaction And E_6 Models, A.T. Alan, Z.Z. Aydin And S. Sultansoy

Turkish Journal of Physics

In the view of future c-\tau-factories, we report an analysis of the rare decays of the \tau lepton via \tau \to \mu e \overline{e}, \tau \to e \mu \overline{\mu}, \tau \to \mu \mu \overline{\mu} and \tau \to ee \overline{e} in the two models, i.e., in Barut's magnetic interaction model (MIM) and in an E_6 model proposed by Gürsey and his collaborators. The energy distributions of one of the final leptons are given for both models. Numerical estimates reveal that these decays can be as large as 10^{-6}, which may be observed in LEP experiments or at other c-\tau factories.

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Quantum Integrable Systems Of The Group Su(1, 1), Mehmet Sezgi̇n, Yılmaz Asad Verdi̇yev Jan 1998

Quantum Integrable Systems Of The Group Su(1, 1), Mehmet Sezgi̇n, Yılmaz Asad Verdi̇yev

Turkish Journal of Physics

Quantum integrable systems related with SU(1, 1) group manifold or hyperboloid [x, x] = x^2_1 + x^2_2 - x^2_3 - x^2_4 = 1 in spherical, hyperbolic and parabolic coordinates systems are considered. The explicit expressions for waves functions, spectra and S-matrices are given.

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The Image Reconstruction By Photocounts Triple Correlations, R. R. Vildanov, M. S. Ismatov, N. Z. Kodirov, A. T. Mirzaev, A. N. Yakubov Jan 1998

The Image Reconstruction By Photocounts Triple Correlations, R. R. Vildanov, M. S. Ismatov, N. Z. Kodirov, A. T. Mirzaev, A. N. Yakubov

Turkish Journal of Physics

An optoelectronic system is constructed for the recording of the triple correlation function for radiation intensity being detected in a photon counting operation. The results of the investigation show the possibility an image reconstruction for faint objects from the derivation of comprehensive information related to the coherence function.

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Optical Anisotropy Of Iron Garnets With Growing Anisotropy, Odil Ochilov Jan 1998

Optical Anisotropy Of Iron Garnets With Growing Anisotropy, Odil Ochilov

Turkish Journal of Physics

The theoretical analysis of the position of principal diachronic directions at magnetization rotation in (100) and (110) planes for the case of growing dichroism axes in random directions was made. The calculations of angular dependencies of dichroic axes (DA) position for different values of the magneto-optical anisotropy parameter, a, have been done. The relations between the growing and magneto-optical dichroism, K/M, and the angle \delta characterizing the direction of principal growing dichroism axes were given. The angular dependences of DA position in epitaxial iron garnet films have been investigated experimentally. The measurements at the different light wavelengths permitted one to …

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Infrared Absorption Study Of Potassium-Boro-Vanadate-Iron Glasses, Dinesh K. Kanchan, Harshvadan R. Panchal Jan 1998

Infrared Absorption Study Of Potassium-Boro-Vanadate-Iron Glasses, Dinesh K. Kanchan, Harshvadan R. Panchal

Turkish Journal of Physics

The IR studies have been made in the K_2O-B_2O_3-V_2O_5-Fe_2O_3 glass system. The increase in intensity and shifting of vibrational bands towards lower wave number at 1400-1350 cm^{-1}, 1200 cm^{-1} and 100-940 cm^{-1} in IR spectra have been ascribed to the formation of BO_3 to BO_4 and VO_5 to VO_4 tetrahedra along with the formation of non-bridging oxygens attached to boron and vanadium. In heat-treated glass samples, many new vibrational bands have been observed which were however, absent in the untreated samples. The preservation of the 1020 cm^{-1} band assigned to V=O bond suggests that K_2O shows the preference for borate …

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Domain Structures Of Epitaxial Perovskite Ferroelectric Films: Part Ii. Applications, S. Pamir Alpay, Alexander L. Roytburd Jan 1998

Domain Structures Of Epitaxial Perovskite Ferroelectric Films: Part Ii. Applications, S. Pamir Alpay, Alexander L. Roytburd

Turkish Journal of Physics

The use of domain stability maps for epitaxial perovskite ferroelectric films is illustrated with some examples. The equilibrium domain structure and domain fractions as a function of temperature are predicted for PbTiO_3(001) films grown epitaxially on three different substrates: MgO(001), KTaO_3(001), and SrTiO_3(001). Misfit dislocation formation at the growth temperature is found to have a profound effect on both the domain selection and relative domain populations. Theoretical predictions are compared with available experimental data.

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Low-Temperature Phase Transition In Tl In Se_{2} Crystals, Oktay Zeynelabidin O Alekperov, Mazahir Amirjan Oglu Aljanov, Elmira M. Ali Gizi Keri̇mova Jan 1998

Low-Temperature Phase Transition In Tl In Se_{2} Crystals, Oktay Zeynelabidin O Alekperov, Mazahir Amirjan Oglu Aljanov, Elmira M. Ali Gizi Keri̇mova

Turkish Journal of Physics

Heat capacity, lattice parameter, spectral and temperature dependences of photoconductivity of chained crystal Tl In Se_{2} have been investigated in this work. For the first time, it has been found that the phase transtion takes plase at temperatures 135 and 184 K in this crystal. The changes of heat capacity, photoconductivity and lattice parameter of Tl In Se_{2} in the region of phase transition is supposed to be connected with the presence of an incommensurate phase in this crystal.

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Coulomb Breakup Of Nucleus ^6 Li On Ion ^{208}Pb, B. F. Irgaziev, H. T. Ergashbaev Jan 1998

Coulomb Breakup Of Nucleus ^6 Li On Ion ^{208}Pb, B. F. Irgaziev, H. T. Ergashbaev

Turkish Journal of Physics

In the framework of the three-body approach the A(a,bc)A Coulomb breakup has been investigated. The three-body Coulomb dynamic is taken into account to derive the expression for the reaction matrix element. The mechanism of the breakup includes the direct process and the excitation of resonance state of the particle a. The calculation of the triple differential cross section of the ^{208}Pb(^6Li, \alpha d)^{208}Pb Coulomb dissociation have been performed in the energy region E_{\alpha d} < 1MeV. Calculations for the Coulomb dissociation ^{208}Pb(^6Li, \alpha d)^{208}Pb, including consideration of the triple cross section going through the first resonance of ^6Li have been performed. The results of the calculations are compared with experimental data.

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Formation Of Hot Zone By The Application Of An Electric Field To Superconducting Bi_{1.6}Pb_{0.4}Sr_2ca_3cu_4o_X (2234) Rod, E. Yanmaz Jan 1998

Formation Of Hot Zone By The Application Of An Electric Field To Superconducting Bi_{1.6}Pb_{0.4}Sr_2ca_3cu_4o_X (2234) Rod, E. Yanmaz

Turkish Journal of Physics

The formation of hot zone by electric field on superconducting Bi-Pb-Sr-Ca-Cu-O (BSCCO) rods is described. Bulk samples with a nominal composition of Bi_{1.6}Pb_{0.4}Sr_2Ca_3Cu_4O_x (2234) were prepared as rods by a melt casting process. An electrical field was applied to the BSCCO rods and this current caused the resistance of the rod to fall and after a few minutes the initial voltage fell while the current was increased to 2.5A. Under certain conditions, a well-defined hot zone formed at the positive electrode, travelled along the rod and eventually disappeared on reaching the negative electrode. A small increase in the applied current …

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Diode Lasers And Their Application For Raman Spectroscopy, Richard Bandell Homard Jan 1998

Diode Lasers And Their Application For Raman Spectroscopy, Richard Bandell Homard

Theses and Dissertations

Diode lasers are semiconductor devices and as such are small, relatively inexpensive, and modest in power requirements. They are being used more and more in a variety of spectroscopic measurement systems. Diodes can be configured to provide a single wavelength for Raman measurement or be tuned over a 10-20 nm range for absorption studies. Most commercial diode-based Raman systems currently employ lasers with output powers in the 100-1000 mW range. There are obvious strategic and economic advantages associated with low power diode chemical analyzers, especially those being developed for on-line industrial and environmental monitoring. A diode-based Raman measurement system which …

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Hierarchical Search Strategy For The Detection Of Gravitational Waves From Coalescing Binaries: Extension To Post-Newtonian Waveforms, Soumya Mohanty Jan 1998

Hierarchical Search Strategy For The Detection Of Gravitational Waves From Coalescing Binaries: Extension To Post-Newtonian Waveforms, Soumya Mohanty

Physics & Astronomy Faculty Publications

The detection of gravitational waves from coalescing compact binaries would be a computationally intensive process if a single bank of template wave forms (one step search) is used. In an earlier paper we presented a detection strategy, called a two step search, that utilizes a hierarchy of template banks. It was shown that in the simple case of a family of Newtonian signals, an on-line two step search was ≃8 times faster than an on-line one step search (for the initial LIGO). In this paper we extend the two step search to the more realistic case of …

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Measurement Of The He Ground State Lamb Shift Via The Two-Photon 1 1S-2 1S Transition, Scott D. Bergeson, A. Balakrishnan, K. G. H. Baldwin, T. B. Lucatorto, J. P. Marangos, T. J. Mcilrath, T. T. O'Brian, S. L. Rolston, C. J. Sansonetti, Jesse Wen, N. Westbrook, C. H. Cheng, E. E. Eyler Jan 1998

Measurement Of The He Ground State Lamb Shift Via The Two-Photon 1 1S-2 1S Transition, Scott D. Bergeson, A. Balakrishnan, K. G. H. Baldwin, T. B. Lucatorto, J. P. Marangos, T. J. Mcilrath, T. T. O'Brian, S. L. Rolston, C. J. Sansonetti, Jesse Wen, N. Westbrook, C. H. Cheng, E. E. Eyler

Faculty Publications

We have extended two-photon Doppler-free spectroscopy to the vacuum ultraviolet spectral region, to accurately measure the He 11S-21S transition at 120 nm. Our result is 4984872315(48) MHz. This yields a ground state Lamb shift of 41104(48) MHz, in fair agreement with theory and other experiments. This approach has the potential for significantly better accuracy once improvements in the laser and the wavelength metrology are implemented.

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Surface Studies Of Metals After Interaction With Hydrogen Isotopes, David Samuel Silver Jan 1998

Surface Studies Of Metals After Interaction With Hydrogen Isotopes, David Samuel Silver

Dissertations and Theses

The objective of this research is to characterize surfaces of metals after interaction with hydrogen isotopes. Iron, which does not readily bond with hydrogen, and palladium, which strongly bonds with hydrogen, were studied. Observations of surfaces are used to determine the nature of their metamorphosis due to such exposures. An experimental study of pure iron foil (99.99%) exposed to a hot, dense hydrogen and argon gas mixture in a ballistic compressor yielded evidence for new structural and compositional changes of the metal due to the exposure. Atomic force microscope (AFM) studies demonstrated surfaces to be highly uneven, where height variations …

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Temperature Dependence Of Step Density On Vicinal Pb(111), Z. H. Zhang, H. E. Elsayed-Ali Jan 1998

Temperature Dependence Of Step Density On Vicinal Pb(111), Z. H. Zhang, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The temperature dependence of step density on the vicinal Pb(111) surface is investigated using reflection high-energy electron diffraction. When the temperature is increased from 323 to 590 K. the average terrace width and the average string length at the step edge decrease from 85±25 to 37±16 Å and from 220±33 to 25±8 Å, respectively. Thermal step collapse on the Pb(111) surface near its bulk melting temperature is not observed. Above 530±7 K, the change in the string length at the step edge with temperature becomes small, and the intensity of the (00) beam is significantly decreased. We conclude that partial …

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Femtosecond Photoemission Study Of Ultrafast Electron Dynamics In Single-Crystal Au(111) Films, J. Cao, Y. Gao, H. E. Elsayed-Ali, R. J. D. Miller, D. A. Mantell Jan 1998

Femtosecond Photoemission Study Of Ultrafast Electron Dynamics In Single-Crystal Au(111) Films, J. Cao, Y. Gao, H. E. Elsayed-Ali, R. J. D. Miller, D. A. Mantell

Electrical & Computer Engineering Faculty Publications

The energy-dependent relaxation of photoexcited electrons has been measured by time-resolved two-photon photoemission spectroscopy on single-crystal Au(111) films with thickness ranging from 150 to 3000 Å. It is found that the energy-dependent relaxation does not show any significant thickness dependence, which indicates that electron transport is a much slower dynamical process in the near-surface region than expected from bulk properties. Furthermore, lifetimes of the photoexcited electrons can be fitted well by the Fermi-liquid theory with a scaling factor plus an effective upper lifetime. This observation enables separation of electron-electron scattering, and to a lesser extent electron-phonon scattering, processes from electron-transport …

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Atomic Hydrogen Cleaning Of Inp(100) For Preparation Of A Negative Electron Affinity Photocathode, K. A. Elamrawi, M. A. Hafez, H. E. Elsayed-Ali Jan 1998

Atomic Hydrogen Cleaning Of Inp(100) For Preparation Of A Negative Electron Affinity Photocathode, K. A. Elamrawi, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Atomic hydrogen cleaning is used to clean InP(100) negative electron affinity photocathodes. Reflection high-energy electron diffraction patterns of reconstructed, phosphorus-stabilized, InP(100) surfaces are obtained after cleaning at ∼400 °C. These surfaces produce high quantum efficiency photocathodes (∼8.5%), in response to 632.8 nm light. Without atomic hydrogen cleaning, activation of InP to negative electron affinity requires heating to ∼530 °C. At this high temperature, phosphorus evaporates preferentially and a rough surface is obtained. These surfaces produce low quantum efficiency photocathodes (∼0.1%). The use of reflection high-energy electron diffraction to measure the thickness of the deposited cesium layer during activation by correlating …

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Review Of The Future Of U.S. Nuclear Weapons Policy, David W. Hafemeister Jan 1998

Review Of The Future Of U.S. Nuclear Weapons Policy, David W. Hafemeister

Physics

No abstract provided.

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