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2000

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Articles 451 - 470 of 470

Full-Text Articles in Physics

The Absorption Properties Of P-Type Tlin_X Ga_{(1-X)} Se_2 And Tlgase_2, Beki̇r Gürbulak, Muhammet Yildirim, Aytunç Ateş, Sebahatti̇n Tüzemen, Yahya Kemal Yoğurtçu Jan 2000

The Absorption Properties Of P-Type Tlin_X Ga_{(1-X)} Se_2 And Tlgase_2, Beki̇r Gürbulak, Muhammet Yildirim, Aytunç Ateş, Sebahatti̇n Tüzemen, Yahya Kemal Yoğurtçu

Turkish Journal of Physics

$p-TlGaSe_2$, $p-TlIn_{0.3}Ga_{0.7}Se_2$ and $p-TlIn_{0.5}Ga_{0.5}Se_2$ single crystals were grown by the modified Bridgman-Stockbarger method in our crystal growth laboratory. The absorption measurements were carried out on $p-TlIn_xGa_{(1-x)}Se_2$ samples in temperature range 10-300 K in steps of 10 K. The binding energies of $p-TlGaSe_2$, $p-TlIn_{0.3}Ga_{0.7}Se_2$ and $p-TlIn_{0.5} Ga_{0.5}$ $Se_2$ were obtained as \\ 35.0 meV, 16.5 meV and 14.5 meV, respectively. THe direct band gaps were calculated as 2.244 eV, 2.195 eV, 2.164 eV in $p-TlGaSe_2$, 2.158 eV, 2.131 eV, 2.098 eV in $p-TlIn_{0.3}Ga_{0.7}Se_2$, and 2.107 eV, 2.075 eV, 2.019 eV in $p-TlIn_{0.5}Ga_{0.5}Se_2$ respectively, at sample temperatures of 10 K, 140 K …


Chemically Synthesised Cd_{(1-X)}Zn_Xse Thin Films: Spectro-Structural And Microscopic Studies, D. S. Sutrave, G. S. Shahane, V. B. Patil, L. P. Deshmukh Jan 2000

Chemically Synthesised Cd_{(1-X)}Zn_Xse Thin Films: Spectro-Structural And Microscopic Studies, D. S. Sutrave, G. S. Shahane, V. B. Patil, L. P. Deshmukh

Turkish Journal of Physics

This paper presents information pertaining to the chemo-mechanical synthesis of (Cd,Zn) Se thin films with a variable composition which has been brought about with the objective to study deposition history and growth kinetics, as well as structural changes and the optical properties. The effect of various process parameters, such as deposition time and temperature, concentration of species, speed of the substrate rotation, pH etc., on the growth and quality of the films is studied experimentally. At first sight, mechanistic interpretation of the reaction mechanism is given based on the influence of the process parameters on the film growth and the …


A Local-Pair Mechanism For High-Temperature Superconductivity At The Di- And Trivalent Sites, John A. Wilson, Ali̇ İhsan Demi̇rel Jan 2000

A Local-Pair Mechanism For High-Temperature Superconductivity At The Di- And Trivalent Sites, John A. Wilson, Ali̇ İhsan Demi̇rel

Turkish Journal of Physics

The \( p/d \) hybridization that primarily characterizes copper leads to local moments, lacking of the pair-breaking variety, both at di- and trivalent sites. Support for the negative-U model is extracted from the author's earlier work on the metal-insulator transition. A more magnetically oriented model, like the resonant valence band model which we have recently associated with our observations in d1 TiOCl etc., does not really seem suited to the geometry and electronic conditions in the copper oxides present. However it is suggested that TiB$_2$, La$_3$S$_4$ and the Chevrel phases might be open to treatment by such a model. Comment …


Switching Process In A Surface-Stabilized Ferroelectric Liquid Crystal Film, Ridvan Karapinar Jan 2000

Switching Process In A Surface-Stabilized Ferroelectric Liquid Crystal Film, Ridvan Karapinar

Turkish Journal of Physics

In this paper we first discuss the operating principle of a ferroelectric liquid crystal film in the surface stabilized configuration, and then examine the switching characteristics using optical measurements performed with a polarizing microscope.


Effects Of Disorder On The Drag Rate In Double Quantum-Wire Systems, B. Tanatar Jan 2000

Effects Of Disorder On The Drag Rate In Double Quantum-Wire Systems, B. Tanatar

Turkish Journal of Physics

We study the Coulomb drag rate for electrons in a double quantum-wire structure in the presence of disorder. We use the particle number-conserving relaxation-time approximation to phenomenologically broaden the response functions entering the drag rate expression to account for the disorder effects. In contrast to the usual low-temperature regime investigated by various researchers, we focus our attention on the high-temperature drag rate to which plasmon modes are known to make substantial contribution. The full wave vector and frequency dependent random-phase approximation (RPA) at finite temperature and disorder strength is employed to describe the effective interlayer Coulomb interaction. The interplay between …


Optimisation Of Transverse Arc Array Laser, Albert Kok Foo Ng Jan 2000

Optimisation Of Transverse Arc Array Laser, Albert Kok Foo Ng

Student Works (2000-2009)

A novel discharge scheme is proposed for the pumping of short wavelen,gth lasers. This scheme had been tested to produce fast current pulse and a 5 kA current in 60 nsec is obtained. Lasing action has been observed by using nitrogen gas. The laser line is 337 nm from the strong transitions of nitrogen molecules. The new discharge scheme is based on the concept of an arc array amplifier. It essentially consists of 48 pairs of electrodes which are lined up to form an array of arc discharge. Its electrical circuitry allows each pair of the electrodes to be decoupled …


Infrared Spectoscopy And Electrical Conductivity Of Copper(Ii) 4-Aminobenzoate And Iondine-Doped Copper(Ii) 4-Aminobenzoate, Chang Fu Dee Jan 2000

Infrared Spectoscopy And Electrical Conductivity Of Copper(Ii) 4-Aminobenzoate And Iondine-Doped Copper(Ii) 4-Aminobenzoate, Chang Fu Dee

Student Works (2000-2009)

Copper(II) 4-aminobenzoate (CAB), prepared from copper(II) acetate monohydrate and 4-aminobenzoic acid, was a dark green powder. Fourier Transfonn lnfrared (FTIR) spectrum of CAB, recorded as KBr disc, indicated the presence of all bonds and functional groups expected of it, and the absence of hydrogen bonding. Its conductivity at room temperature was 4.2 x 10^-11 Scm^·1. The value increased as temperature decreased indicating metallic behaviour. Density of states at Fenni level, hopping distance, hopping energy and density of charge carriers calculated based on Mon's Variable Range Hopping model (VRH) are 2.65x 10^-22 (eV)^-1 cm^-3, 7.47 x 10^-8 cm, 0.02 eV and …


Investigations Of Transverse Arc Array Laser Action In Nitrogen Gas, Kee Siang Goh Jan 2000

Investigations Of Transverse Arc Array Laser Action In Nitrogen Gas, Kee Siang Goh

Student Works (2000-2009)

In almost all pulsed gas lasers, transverse electrical discharge is employed in the excitation of the atoms or molecules. These lasers normally employ discharge across a pair of common electrodes to provide large volume and uniform glow discharge. The scaling of output power in such lasers is obtained by increasing the volume of the discharge and also the pressure of the discharge gas. For this reason. the energy coupled into the discharge channel is kept low enough to avoid arcing. Under these circumstances, the electron temperature of such uniform glow discharge is not sufficient to produce excitation of VUV or …


Investigations On The Conductivity Of Organotin-Doped Polyethyleneoxide Polymer System, Lekshmi Sarojiniamma Jan 2000

Investigations On The Conductivity Of Organotin-Doped Polyethyleneoxide Polymer System, Lekshmi Sarojiniamma

Student Works (2000-2009)

Poly(ethylene oxide) (PEO) has been doped with selected organotin compounds. The organotin dopants used were triphenyltin thiocyanate (Ph3SnSCN) and tetramethylammonium dichlorotriphenylstannate [Ph3SnClr[Me4N)•. Tin incorporation in the polymers was established by several physical techniques. The infrared spectroscopic analysis of the Pb3SnSCN - doped electrolyte film showed bands at 2080-2050 cm.·' which are also given by pure Ph3SnSCN. Different concentrations of organotin doped electrolytes were prepared and conductivity studies on these were perfonned using impedance spectroscopy. From the measurements it was found that the best conductivity of 7.6xJ0.g Siem was obtained for the composition with PEO :dopant ratio of90:10 at room temperature. …


A Study Of Traffic Noise From Selected Urban And Suburban Areas, Savitri Ramiah Jan 2000

A Study Of Traffic Noise From Selected Urban And Suburban Areas, Savitri Ramiah

Student Works (2000-2009)

The main aim of this study is to determine the noise levels in selected urban and suburban roads and to compare the difference in traffic noise levels between these areas. 1be noise attenuated by noise barrier was also surveyed as a small portion of this study. Analysis of traffic noise was surveyed at five locations. Two locations were surveyed for the urban area and two locations for the suburban area and one location for noise barrier. The traffic volume for the duration of the survey was also recorded. Both day time and night time noise levels were studied. The survey …


Distribution Of Petrogenic Hydrocarbons In Water, Sediment And Cockles (Anadara Granosa) From Kuala Sungai Sepetang And Kuala Sungai Selangor, Mohd Hilmi Jaafar Jan 2000

Distribution Of Petrogenic Hydrocarbons In Water, Sediment And Cockles (Anadara Granosa) From Kuala Sungai Sepetang And Kuala Sungai Selangor, Mohd Hilmi Jaafar

Student Works (2000-2009)

In order to assess the level of oil pollution in the cockle culture areas along the Straits of Malacca, water, sediment and cockle samples were collected from the culture beds of Kuala Sepetang and Kuala Selangor, two of the largest cockle producing areas of Malaysia. The samples were analysed for petrogenic hydrocarbons by employing a spectrofluorometric technique which measures the content of polycyclic aromatic hydrocarbons (PAH) in oil. The content of aliphatic straight chain hydrocarbons were measured by using gas chromatography􀀐mass spectrometry (GCMS) which also allowed for the estimation of carbon preference indices and hence providing a means of estimating …


Development Of Multiple Channels Edf Lasers, Muhammad Zamzuri Abdul Kadir Jan 2000

Development Of Multiple Channels Edf Lasers, Muhammad Zamzuri Abdul Kadir

Student Works (2000-2009)

This thesis presents the research work carried out on the development and analysis of single wavelength EDFL and multiple wavelength EDFL. Two types of single wavelength EDF ring laser were studied namely a fixed signal wavelength system and a tuneable signal wavelength system. However, emphasis was given to the first case. The analyses made, were based on the following parameters: pump and signal stability, pump power, reflectivity, EDF length and cavity loss. The influence of each cavity component such as isolator, polarisation controller, attenuator and tuneable filter were also investigated and reported here. Only one type of multiple wavelength EDFL …


Digital Holography And Application In Laser Metrology, Thian Khok Yong Jan 2000

Digital Holography And Application In Laser Metrology, Thian Khok Yong

Student Works (2000-2009)

A digital holography system has been developed in this study. The object is recorded and the hologram is stored electronically with a charged-couple-device (CCD) camera without any focusing optics. The reconstruction of the digitally sampled hologram is done numerically with a computer. The algorithm and software for numerical reconstruction, which consists in a numerical realization of the Fresnel-Kirchhoff diffraction integral, are designed and implemented with two­dimensional and three-dimensional simple objects. The characteristics of the system have been studied. For the CCD camera (768x494 pixels) been used with spatial resolution of about I 00 lines/mm, the angle between reference and object …


Erbium-Ytterbium Codoped Fiber Amplifiers, Wai Yee Chan Jan 2000

Erbium-Ytterbium Codoped Fiber Amplifiers, Wai Yee Chan

Student Works (2000-2009)

The amplification characteristics of an Erbium/Ytterbium codoped fiber amplifier(EYDFA) pumped in both the 800nm and 980nm pump bands is reported. With -3m long Er-Yb fiber, the 813nm pumped-EYDFA shows small-signal gain exceeding 20dB over a 20nm bandwidth in the l.Sµm region where the peak gain of 38.4dB is achieved at 1535nm. A low noise figure of ~3.6d8 is also achieved at 1550nm. However, it is found that 980nm pumped­EYDF A suffers lower gain due to the effect of nonsaturable absorption by Yb³⁺ ions which causes high pump poWer loss, thus degrades the signal amplification in Er³⁺ system. Compared to the …


Thickness Variation Of Self-Processing Acrylamide-Based Photopolymer And Reflection Holography, F. O'Neill, Justin Lawrence, J. Sheridan Jan 2000

Thickness Variation Of Self-Processing Acrylamide-Based Photopolymer And Reflection Holography, F. O'Neill, Justin Lawrence, J. Sheridan

Articles

There are many types of holographic recording material. The acrylamide-based recording material examined here has one significant advantage: it is self-processing. This simplifies the recording process and enables holographic interferometry to be carried out without the need for complex realignment procedures. However, the effect that the polymerization process has on the grating thickness must be examined. This question is fundamental to the material's use in holographic optical elements, as thickness variations affect the replay conditions of the produced elements. This paper presents a study of this thickness variation and reports for the first time the production of reflection holographic gratings …


Production Of A Signal By Irradiated Cells Which Leads To A Response In Unirradiated Cells Characteristic Of Initiation Of Apoptosis, Fiona Lyng, C. Seymour, C. Mothersill Jan 2000

Production Of A Signal By Irradiated Cells Which Leads To A Response In Unirradiated Cells Characteristic Of Initiation Of Apoptosis, Fiona Lyng, C. Seymour, C. Mothersill

Articles

This study investigated the ability of medium from irradiated cells to induce early events in the apoptotic cascade, such as mobilization of intracellular calcium, loss of mitochondrial membrane potential and increase in reactive oxygen species, in cells which were never exposed to radiation. Medium from irradiated human keratinocytes was harvested and transferred to unirradiated keratinocytes. Endpoints characteristic of the initiation of apoptosis were monitored for a period of 24 h following medium transfer. Clonogenic survival was also measured. Rapid calcium fluxes (within 30 s), loss of mitochondrial membrane potential, increases in reactive oxygen species (from 6 h after medium transfer), …


Beyond The Dipole Approximation: Angular-Distribution Effects In The 1s Photoemission From Small Molecules, Dennis W. Lindle, Oliver Hemmers, H. Wang, P. Focke, I. A. Sellin, J. D. Mills, J. A. Sheehy, P. W. Langhoff Jan 2000

Beyond The Dipole Approximation: Angular-Distribution Effects In The 1s Photoemission From Small Molecules, Dennis W. Lindle, Oliver Hemmers, H. Wang, P. Focke, I. A. Sellin, J. D. Mills, J. A. Sheehy, P. W. Langhoff

Environmental Studies Faculty Publications

Over the past two decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Recent experiments on the 1s inner shells of small molecules at relatively low photon energies (⩽ 1000 eV) show strong nondipole effects. They are significant and measurable at energies close to threshold, in conflict with a common assumption that the dipole approximation is valid for photon energies below 1 keV.


Measurement Of The Spin-Density Matrix Elements In Exclusive Electroproduction Of Ρ0 Mesons At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti Jan 2000

Measurement Of The Spin-Density Matrix Elements In Exclusive Electroproduction Of Ρ0 Mesons At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

Exclusive electroproduction of ρ0 mesons has been measured using the ZEUS detector at HERA in two Q2 ranges, 0.25 < Q2 < 0.85 GeV2 and 3 < Q2 < 30 GeV2. The low-Q2 data span the range 20 < W < 90 GeV; the high-Q2 data cover the 40 < W < 120 GeV interval. Both samples extend up to four-momentum transfers of |t| = 0.6 GeV2. The distribution in the azimuthal angle between the positron scattering plane and the ρ0 production plane shows a small but significant violation of s-channel helicity conservation, corresponding to the production of longitudinally polarised (i.e. helicity zero) ρ0 mesons from transverse photons. Measurements of the 15 combinations of spin-density matrix elements which completely define the angular distributions are presented and discussed.


Textured Mos 2 Thin Films Obtained On Tungsten: Electrical Properties Of The W/Mos 2 Contact, E. Gourmelon, J. C. Bernède, J. Pouzet, S. Marsillac Jan 2000

Textured Mos 2 Thin Films Obtained On Tungsten: Electrical Properties Of The W/Mos 2 Contact, E. Gourmelon, J. C. Bernède, J. Pouzet, S. Marsillac

Electrical & Computer Engineering Faculty Publications

Textured films of molybdenum disulfide have been obtained by solid state reaction between the constituents in thin films form when a (200) oriented tungsten sheet is used as substrate. The crystallites have their c axis perpendicular to the plane of the substrate. The annealing conditions are T=1073K and t=30 min. The films are stoichoimetric and p type. Such highly textured films are achieved without foreign atom addition (Ni, Co...). It appears, as shown by x-ray photoelectron spectroscopy, that a thin WS2 layer is present at the interface W/MoS2. The crystallization process is discussed by a …


Time Step Truncation Error In Direct Simulation Monte Carlo, Alejandro Garcia, W. Wagner Jan 2000

Time Step Truncation Error In Direct Simulation Monte Carlo, Alejandro Garcia, W. Wagner

Faculty Publications

No abstract provided.