Physics Commons^™

Electric-Field Generated By The Combustion Of Titanium In Nitrogen, Karen S. Martirosyan, Mona Setoodeh, Dan Luss

Physics & Astronomy Faculty Publications

A short temporal electrical impulse (duration of 30–150ms) was generated during the nitridation of mixtures of titanium and titanium nitride by a high temperature moving reaction front. The maximum voltage and current were generated in the combustion front region, in which the conversion of Ti to TiN was incomplete. The electric field (voltage up to 2V and current up to 60mA) decayed and vanished before the maximum combustion temperature was attained. The generation of an electric field during a rapid high-temperature nitridation is most probably due to the different diffusion velocities of charge carriers through the growing titanium nitride shell …

Some Physical Properties Of \Gamma Irradiated Ge_X(As_2te_3)_{100 - X} Chalcogenide System, Afaf Abdel-Aal, Bahiga Abdel-Hameed Mansour, Hoda Mohamed Eissa

Turkish Journal of Physics

The effect of \gamma -radiation on the electrical conductivity, switching, and optical properties of the chalcogenide amorphous system Ge_x(As_2Te_3)_{100 - x} (where x = 0,1,5,10 atm %) have been studied. The results show that the radiation causes a shift of the optical gap,as well as a change in the electrical activation energy and the threshold voltage. As the \gamma -doses increase, the values of the allowed indirect optical energy gap E_{opt} for the different compositions decreases and the tail energy width increases.

Standard Ubv Observations At The Çanakkale University Observatory (Çuo), Hi̇cran Bakiş, Volkan Bakiş, Osman Demi̇rcan, Edwin Budding

Turkish Journal of Physics

By using standard and comparison star observations carried out at different times of the year, at Çanakkale Onsekiz Mart University Observatory, we obtained the atmospheric extinction coefficients at the observatory. We also obtained transformation coefficients and zero-point constants for the transformation to the standard Johnson UBV system, of observations in the local system carried out with the SSP5A photometer and T40 telescope. The transmission curves and the mean wavelengths of the UBV filters as measured in the laboratory appear not much different from those of the standard Johnson system and found inside the transmission curve of the standard mean atmosphere.

Photoconductivity Of Selenium And Sulphur Doped A-Si:H Thin Films, Sanjeev Kumar Sharma, Himanshu Gupta, Rajendra Kumar, Ram Mohan Mehra

Turkish Journal of Physics

This paper presents a study of photoconductivity of S- and Se-doped a-Si:H as a function of composition and temperature. Temperature dependence of photoconductivity of the films was measured under the illumination of white light at 100~mW/cm^2. The room temperature photoconductivity for the same doping concentration of 10^{-4} (to develop H_2Se/SiH_4 and H_2S/SiH_4) is found to be higher in Se-doped -- than S-doped -- a-Si:H film due to a low defect density. From the measurement of intensity dependence of photoconductivity, it is found that the addition of Se and S changes the recombination mechanism from monomolecular, for low-doped films, to bimolecular …

Features Of Daily Variation In Cosmic Ray Intensity During High/Low Amplitude Events, Rajesh K. Mishra, Rekha Agarwal Mishra

Turkish Journal of Physics

A detailed study has been conducted on the long-term changes in the diurnal, semi-diurnal and tri-diurnal anisotropy of cosmic rays in terms of the high/low amplitude anisotropic wave train events (HAE/LAE) during the period 1981--94 using the neutron monitor data from the Deep River neutron monitoring station. In all, 38 HAE and 28 LAE cases have been studied. An inter-comparison of the first three harmonics during these events has been made so as to understand the basic reason causing the occurrence of these types of events. It has been observed that the phase of diurnal anisotropy shifts towards earlier hours …

Dirac Sextic Oscillator In The Constant Magnetic Field, Ramazan Koç, Mehmet Koca

Turkish Journal of Physics

We introduce a Dirac equation which reproduces the usual radial sextic oscillator potential in the non-relativistic limit. We determine its energy spectrum in the presence of the magnetic field. It is shown that the equation is solved in the context of quasi-exactly-solvable problems. The equation possesses hidden sl_2-algebra and the destroyed symmetry of the equation can be recovered for specific values of the magnetic field which leads to exact determination of the eigenvalues.

Unsteady Flow Of A Dusty Conducting Fluid Between Parallel Porous Plates With Temperature Dependent Viscosity, Hazem Ali Attia

Turkish Journal of Physics

This paper studies unsteady laminar flow of dusty conducting fluid between parallel porous plates with temperature dependent viscosity. The fluid is acted upon by a constant pressure gradient and an external uniform magnetic field is applied perpendicular to the plates. The parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below. The viscosity of the fluid is assumed to vary exponentially with temperature. The governing nonlinear partial differential equations are solved numerically and some important effects for the variable viscosity and the uniform magnetic field on the transient flow and heat …

Magic Gold Nanotubes, R. Tuğrul Senger, Sefa Dağ, Sali̇m Çiraci

Turkish Journal of Physics

In recent ultra-high-vacuum transmission-electron-microscopy experiments evidence is found for the formation of suspended gold single-wall nanotubes (SWNTs) composed of five helical strands. Similar to carbon nanotubes, the (n,m) notation defines the structure of the gold SWNTs. Experimentally, only the (5,3) tube has been observed to form among several other possible alternatives. Using first-principles calculations we demonstrate that gold atoms can form both freestanding and tip-suspended, chiral, single-wall nanotubes. Although freestanding, infinite (5,5) tube is found to be energetically the most favorable, the experimentally observed (5,3) tube, suspended between two tips, corresponds to a local minimum in the variation of string-tension …

Synthesis And Characterization Of Co-Pb/Sba-15 Mesoporous Catalysts, Mukaddes Can, Burcu Akça, Ayşen Yilmaz, Deni̇z Üner

Turkish Journal of Physics

Pure SBA-15 and Co and/or Pb incorporated SBA-15 have been prepared by direct synthesis. The synthesized samples were characterized by powder X-ray diffraction and N_2 adsorption isotherms. It is observed that the surface area of pure SBA-15 mesoporous structure slowly decreases by the addition of metal oxides. By the loading of 5, 10, 15 wt % Pb into SBA-15, no characteristic peaks of metal oxide observed in the large angle XRD pattern. But loading of 20 wt % Pb in SBA-15 shows more appreciable characteristic peaks, indicating small quantity of crystallites of metal oxide existing on the surface of silica. …

A Theoretical Study On Silicon And Iii-V Compound Nanotubes, Engi̇n Durgun, Sali̇m Çiraci

Turkish Journal of Physics

In this paper we present a theoretical study on single-wall silicon and III-V compound nanotubes. First principles plane wave calculations within density functional theory are used to predict energetics and electronic structures of armchair and zigzag nanotubes. The stability of tubular structures is further investigated at finite temperature by ab initio molecular dynamics calculations. Our results indicate that (n,0) zigzag and (n,n) armchair single-wall Si nanotubes are stable for n >= 6. Mechanically, the Si nanotubes are radially soft, however they are strong against axial deformations. Electronic analysis showed that zigzag nanotubes are metallic for n Keywords: silicon, nanotube, first …

Electrical Properites Of Superconducting Cross - (Nano) Whiskers Junction, Serdar Altin, Eyüphan Yakinci, Yakup Balci, M. Ali̇ Aksan

Turkish Journal of Physics

Bi-2212 superconducting single crystal (nano) whiskers have been fabricated by annealing a melt-quenched (glass) Bi_3Sr_2Ca_2Cu_3O_x precursor. A couple of (nano) Whiskers obtained were placed crosswise on a YSZ single crystal substrate and then heat treated at 830 C for 25 minute to form nano-scale junction. The T_c of each nano-whisker was found to be 85 K and the critical current density, J_c, of the whiskers was calculated to be 1177 Acm^{-2} at zero field. The I-V characteristics of the nano-junction at 30 K were found to show a multiple-branch structure, which is the main behavior of the Josephson junction.

Physical Properties Of Holmium Promoted Superconductivity In Nd-Doped Ybco Ht_C-Superconductors, Morsy Abou Sekkina, Abdul Raouf Tawfik, Osama Hemeda, Mohamad Ahmad Taher Dawoud, Samy El-Attar

Turkish Journal of Physics

Samples of the nominal composition (Y_{0.5}Nd_{0.5-x}Ho_x) Ba_2Cu_3O_{7- \delta} , 0 \le x \le 0.5, have been prepared using the conventional solid state reaction. The effect of holmium and neodymium substitution on electrical resistivity, transition temperature T_c, lattice parameters, size of crystallite and grain size has been investigated. X-ray diffraction, electron micro-probe, scanning electron microscope and IR spectra, have been used in our investigation. The results show that the transition temperature T_c, electron-hole jump rate and lattice parameters (a, b) have minimum values at x = 0.2, while c increases to maximum at x = 0.2. The size of crystallite, the …

Study Of Density Of Localized States In A-Se_{100 - X}Sb_X Films By Space Charge Limited Conduction Measurements, V. S. Kushwaha, Santosh Kumar, A. Kumar

Turkish Journal of Physics

The present paper reports dc conductivity measurements at high electric fields in vacuum evaporated a-Se_{1 - x}Sb_x (x = 0, 0.02, 0.04, 0.06) thin films. At high fields (~ 10^4 V .cm^{-1}), current can be modelled by the theory of space charge-limited conduction in the case of uniform distribution of localised states in the mobility gap of these materials. The addition of Sb in Se results in an increase in the density of localised states.

Dielectric Properties Of Industrial Polymer Composite Materials, Muhammad Akram, Athar Javed, Tasneem Zahra Rizvi

Turkish Journal of Physics

Frequency and temperature dependence of dielectric constant \varepsilon' and dielectric loss \varepsilon" in pure polyester resin and polymer composites with various types of glass fiber are studied in the frequency range 330 Hz-3 MHz and in the temperature range 25-150 °C. The experimental results show that \varepsilon' and \varepsilon'' increased with the addition of glass fiber in polyester resin. The value of \varepsilon' decreased with increasing frequency, which indicates that the major contribution to the polarization comes from orientation polarization. Dielectric loss peaks were also observed in the composite materials at high temperature due to T_g of polyester. The value …

Origins Of Reverse Bias Currents In A Typical Bpw34 Photodiode, Habi̇be Bayhan, Şadan Özden

Turkish Journal of Physics

Measurements of the dark reverse current in a typical BPW34 silicon photodiode have been made in the temperature range 100-300 K at various reverse bias voltages ranging from 0 to 60 V. Various transport models have been applied to analyze the temperature dependence of the reverse current-voltage data. We suggest that Bardeen's model for a modified Schottky-like interfacial junction, that takes into account the effect of interfacial localized states, can be satisfactorily applied to describe the reverse current-voltage characteristics at bias voltages below 50 V.

Technical Risk Information: Decision Tool Or Rhetorical Ammunition? Undisputed Facts In The Yucca Mountain Debate, David M. Hassenzahl, Denise Tillery, Paulette Laidler

Public Policy and Leadership Faculty Research

This paper examines how both opponents and proponents of the proposed high-level nuclear waste repository at Yucca mountain Nevada claim that uncontroversial information supports their conflicting positions. Four pieces of information in particular are claimed by both sides: the distance of the proposed site from Las Vegas, the volume of waste that has been produced, the threat of terrorism since 9/11/01, and the occurrence of an earthquake in early 2002. Possible explanations for the difference include naive positivism, social constructionism, persistent beliefs and implicit warrants. The latter two models better explain observed knowledge/preference states. If so, more or better information …

Radiation Transport Modeling Using Parallel Computational Techniques, William Culbreth, Denis Beller

Reactor Campaign (TRP)

One of the most significant tools available for the design and analysis of accelerator-driven systems, such as the systems proposed for transmutation, is the high-energy particle transport code MCNPX. The MCNPX code suite, developed by the national laboratories, allows researchers and engineers to model the complex interactions of high-energy particles with the target and related systems, including the spallation reaction and subsequent neutron multiplication expected in the accelerator targets.

The next stage in the development of the MCNPX code suite is to validate the code by comparing the theoretical predictions from the models with experimental observations. Additionally, the nuclear database, …

University Of Nevada, Las Vegas Transmutation Research Program: Annual Report Academic Year 2004-2005, Anthony Hechanova, Kathy Lauckner

Transmutation Research Program Reports (TRP)

It is my pleasure to present the UNLV Transmutation Research Program’s fourth annual report that highlights the academic year 2004 – 2005. Supporting this document are the many technical reports and scientific papers that have been generated over the past three years.

In the fourth year of our program, we added 11 new research tasks and saw the conclusion of 8 of the initial 16 independent student research tasks started in 2001 and 2002. In all, the program has sponsored to their conclusion 28 M.S. and 2 Ph.D. degrees. The program supported 58 graduate students and 13 undergraduates in 6 …

Corrosion Of Steel By Lead Bismuth Eutectic, John Farley, Allen L. Johnson, Dale L. Perry

Transmutation Sciences Materials (TRP)

There is an active international interest in lead-bismuth eutectic and similar liquid lead systems because of the relevance to the transmutation of nuclear waste, fast reactors, and spallation neutron sources.

Materials in these systems must be able to tolerate high neutron fluxes, high temperatures, and chemical corrosion. For lead bismuth eutectic (LBE) systems, there is an additional challenge because the corrosive behaviors of materials in LBE are not well understood. Most of the available information on LBE systems has come from the Russians, who have over 80 reactor-years experience with LBE coolant in their Alpha-class submarine reactors. The Russians found …

Neutron Multiplicity Measurements Of Target/Blanket Materials, Denis Beller

Transmutation Sciences Physics (TRP)

To optimize the performance of accelerator-driven sub-critical (ADS) transmutation systems, engineers will need to design the system to operate with a neutron multiplication factor just less than that of a critical, or self-sustaining, system. This design criterion requires particle transport codes that instill the highest level of confidence with minimal uncertainty, because larger uncertainties in the codes require larger safety margins in the design and result in a lower efficiency of the ADS transmuter. For current design efforts in the U.S., a Monte Carlo particle transport code MCNPX is used to model neutron production and transport for spallation neutron systems. …

Development Of Dose Coefficients For Radionuclides Produced In Spallation Targets, Phillip W. Patton, Mark Rudin

Transmutation Sciences Physics (TRP)

Dose coefficients permit simple determination of radiation dose associated with various exposure scenarios, and ultimately permit radiation safety personnel to assess the health risks to workers in a nuclear facility. Specifically, radiation safety personnel use dose coefficients to determine the radiation dose incurred to a tissue or organ system from a given exposure. These parameters are often expressed in terms of Annual Limits on Intake (ALIs) and Derived Air Concentrations (DACs).

The research consortium comprised of representatives from several universities and national laboratories has successfully generated internal and external dose conversion coefficients for twenty radionuclides produced in spallation neutron sources. …

Reactor Physics Studies For The Afci Reactor-Accelerator Coupling Experiments (Race) Project, Denis Beller

Transmutation Sciences Physics (TRP)

The specific research objective of this three-year project is to design and conduct an accelerator driven experiment at one of the Texas universities. This experiment will help demonstrate in the U.S. the ability to design, compute, and conduct ADSS experiments; and to predict and measure source importance, coupling efficiency, sub-critical reactor kinetics and source-driven transients. In addition, both steady state and transient ADSS benchmarks will be created for the nuclear community to develop and test new computational codes and methods, and the importance of a driving neutron source in various regions of different subcritical assemblies will be mapped. Experiments will …

Nuclear Criticality, Shielding, And Thermal Analyses Of Separations Processes For The Transmutation Fuel Cycle, William Culbreth, Denis Beller

Separations Campaign (TRP)

The first step in any transmutation strategy is the separation of radionuclides in used nuclear fuel. The current separation strategy supporting the Advanced Fuel Cycle Initiative (AFCI) program is based on the use of a solvent extraction separation process to separate the actinides, fission products, and uranium from used commercial nuclear fuel, and on the use of pyrochemical separation technologies to process used transmuter fuels. To separate the fission products and transuranic elements from the uranium in used fuel, the national program is developing a new solvent extraction process, the Uranium Extraction Plus, or UREX+, process based on the traditional …

Anion And Cation-Yield Spectroscopy Of Core-Excited Sf6, Maria Novella Piancastelli, Wayne C. Stolte, Renaud Guillemin, A. Wolska, M. M. Sant'anna, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We report an extensive study on total and partial-ion-yield spectroscopy around both the S 2p and F 1s thresholds in SF₆. All positive and negative single-ion channels have been measured. Below the F 1s threshold we detect a large variation in relative intensity of the resonant structures according to the specific channel monitored, indicating selective fragmentation. Above threshold, at variance with previous cases described by us, we detect high-intensity structures related to shape resonances not only in the cation channels but also for the anions. We discuss the applicability and limits of a model we …

Fragmentation Dynamics Of H2s Following S 2p Photoexcitation, Renaud Guillemin, S-W Yu, Wayne C. Stolte, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

The fragmentation dynamics of core-excited H₂S has been studied by means of partial anion and cation yield measurements around the S L_2,3-subshell ionization thresholds. All detectable ionic fragments are reported, and significant differences between partial ion yields are observed. Possible dissociation pathways are discussed by comparison to previous studies of electron spectra.

Near-Edge X-Ray Absorption Fine Structure Study Of Ion-Beam-Induced Phase Transformation In Gd2(Ti1-Yzry)2o7, Ponnusamy Nachimuthu, S. Thevuthasan, V. Shutthanandan, E. M. Adams, W. J. Weber, B. D. Begg, D. K. Shuh, Dennis W. Lindle, Eric M. Gullikson, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

The structural and electronic properties of Gd₂(Ti_1−yZr_y)₂O₇ (y=0–1) pyrochlores following a 2.0-MeV Au²⁺ ion-beam irradiation (~5.0 X 10¹⁴ Au²⁺/cm²) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd₂(Ti_1−yZr_y)₂O₇ leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd₂(Ti_{1−y …}

Design And Analysis Of A Process For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides, Yitung Chen, Darrell Pepper, Randy Clarksean

Fuels Campaign (TRP)

The goal of this project is to investigate the casting processes for metallic fuels to help design a process that minimizes the loss of the volatile actinide elements from the fuel. The research effort centers on the development of advanced numerical models to assess conditions that significantly impact the transport of volatile actinides during the melt casting process and represents a joint effort between researchers at UNLV and Argonne National Laboratory (ANL). Assessing critical equipment and process variables is required to build a successful system that will operate efficiently.

Interaction Between Metal Fission Products And Triso Coating Materials: A Study Of Chemical Bonding And Interdiffusion: 1st Quarter Report, 2005, Clemens Heske

Fuels Campaign (TRP)

In this project we utilize a combination of state-of-the-art soft X-ray spectroscopies to understand the chemical bonding between metal fission products (Pd and Ag) with coating layers in TRISO fuel particles (SiC and pyrocarbon). We are primarily focusing on an analysis of intermediate chemical phases at the interface, the intermixing/diffusion behavior, and the electronic interface structure as a function of material choice (metal and coating materials), temperature, and external stress. In the current first project year, we are beginning these investigations with the Pd/SiC interface, as discussed in the previous two quarterly reports. Our first experiments (both using our lab …

Investigation Of The Effect Of Subcutaneous Fat On Image Quality Performance Of 2d Conventional Imaging And Tissue Harmonic Imaging, Jacinta Browne, Amanda Watson, Peter Hoskins, Alex Elliott

Articles

Tissue harmonic imaging (THI) has been reported to improve contrast resolution, tissue differentiation and overall image quality in clinical examinations. However, a study carried out previously by the authors (Browne et al. 2004) found improvements only in spatial resolution and not in contrast resolution or anechoic target detection. This result may have been due to the homogeneity of the phantom. Biologic tissues are generally inhomogeneous and THI has been reported to improve image quality in the presence of large amounts of subcutaneous fat. The aims of the study were to simulate the distortion caused by subcutaneous fat to image quality …

Structure-Property Relationships For Electron-Vibrational Coupling In Conjugated Organic Oligomeric Systems, Luke O'Neill, Hugh Byrne

Articles

A series of ð-conjugated oligomers containing one to six monomer units were studied by absorption and photoluminescence spectroscopy. As is common for these systems, a linear relationship between the positioning of the lowest-energy absorption and the highest-energy photoluminescence maxima plotted versus inverse conjugation length is observed, in good agreement with a simple nearly free electron model, one of the earliest descriptions of the properties of one-dimensional organic molecules. It was observed that the Stokes shift and therefore Huang-Rhys factor also exhibit a well-defined relationship with increasing conjugation length, implying a correlation between the electron-vibrational coupling and chain length. This correlation …