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Articles 31201 - 31230 of 36659

Full-Text Articles in Physical Sciences and Mathematics

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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Correlation Function Formulation For The State Selected Total Reaction Probability, Sophya V. Garashchuk, D. J. Tannor Jan 1998

Correlation Function Formulation For The State Selected Total Reaction Probability, Sophya V. Garashchuk, D. J. Tannor

Faculty Publications

A correlation function formulation for the state-selected total reaction probability, Nα(E), is suggested. A wave packet, correlating with a specific set of internal reactant quantum numbers, α, is propagated forward in time until bifurcation is complete at which time the nonreactive portion of the amplitude is discarded. The autocorrelation function of the remaining amplitude is then computed and Fourier transformed to obtain a reactivity spectrum. Dividing by the corresponding spectrum of the original, unfiltered, wave packet normalizes the reactivity spectrum, yielding the total reaction probability from the internal state, α. The procedure requires negligible storage and just one time-energy Fourier …

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Factorization For High-Energy Scattering, Ian Balitsky Jan 1998

Factorization For High-Energy Scattering, Ian Balitsky

Physics Faculty Publications

I demonstrate that the amplitude for the high-energy scattering can be factorized into a product of two independent functional integrals over “fast” and “slow” fields which interact by means of Wilson-line operators—gauge factors ordered along the straight lines.

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First Observation Of The Very Rare Decay Neutral Kaon(Long) Going To Electron Positron, Robert David Martin Iii Jan 1998

First Observation Of The Very Rare Decay Neutral Kaon(Long) Going To Electron Positron, Robert David Martin Iii

Dissertations, Theses, and Masters Projects

Brookhaven National Laboratory AGS Experiment 871 (E871) has carried out a search for the very rare, GIM and helicity suppressed decay of the long-lived neutral kaon into an electron-positron pair. This decay is predicted within the Standard Model to occur with a branching ratio of {dollar}(9.0 \pm 0.4)\times 10\sp{lcub}-12{rcub}.{dollar} Data were taken during the 1995 and 1996 AGS HEP running periods on the B5 beamline. A signal of (4 {dollar}\pm{dollar} 2) {dollar}K\sbsp{lcub}L{rcub}{lcub}0{rcub} \to e\sp+e\sp-{dollar} events is seen with a physics background expectation of 0.2 events. The ratio of the partial decay widths {dollar}\Gamma(K\sbsp{lcub}L{rcub}{lcub}0{rcub} \to e\sp+e\sp-)/\Gamma(K\sbsp{lcub}L{rcub}{lcub}0{rcub}\to\mu\sp+\mu\sp-){dollar} is determined to be {dollar}(1.3\sbsp{lcub}-0.6{rcub}{lcub}+0.8{rcub} …

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Frequency Modulated Excitation Of A Two-Level Atom, Michael W. Noel, W. M. Griffith, T. F. Gallagher Jan 1998

Frequency Modulated Excitation Of A Two-Level Atom, Michael W. Noel, W. M. Griffith, T. F. Gallagher

Physics Faculty Research and Scholarship

We present a detailed experimental study of the frequency-modulated excitation of a two-level atom, using a microwave field to drive transitions between two Rydberg Stark states of potassium. In the absence of a modulation the interaction is the standard model of the Rabi problem, producing sinusoidal oscillations of the population between the two states. In the presence of a frequency modulation of the interacting field, however, the time evolution of the system is significantly modified, producing square wave oscillations of the popula- tion, sinusoidal oscillations at a different frequency, or even sinusoidal oscillations built up in a series of stair …

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A Time-Dependent Quantum Study Of Li+Hf(\Nu=1) -> Lif(\Nu')+H, Fahrettin Gögtaş, Gabriel G. Balint-Kurti Jan 1998

A Time-Dependent Quantum Study Of Li+Hf(\Nu=1) -> Lif(\Nu')+H, Fahrettin Gögtaş, Gabriel G. Balint-Kurti

Turkish Journal of Physics

Time-dependent quantum wave packet calculations are performed for a model based (two-dimensional) $Li+HF(\nu=1)\ra LiF(\nu^{\prime})+H$ reaction. The reaction probabilities for a broad range of collison energies are calculated by a single solution of the time-dependent Schr\\"{o}dinger equation. The calculated reaction probabilities show many sharp features as a function of energy which are ascribed to scattering resonances.

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Alpha Particle Fragments Produced From Multifragmentation Of ^{16}O+^{16}O, M.Y.H. Farag Jan 1998

Alpha Particle Fragments Produced From Multifragmentation Of ^{16}O+^{16}O, M.Y.H. Farag

Turkish Journal of Physics

Angular distribution for alpha particles produced from multifragmentation of ^{16}O + ^{16}O reactions are calculated using the statistical scission model. The alpha particles are sequentially emitted from long lived states of primary fragments populated in these reactions. Eight alpha particles are produced in these reactions. The calculations are carried out for different energies and for different nuclear temperatures. The variances of this multifragmentation process have been numerically calculated. The obtained results are in good agreement with previous calculations.

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Characterization Of Sb Doped Y Bacuo Superconducting Ceramics, K. Kocabaş, N. Kazanci, M. Tepe Jan 1998

Characterization Of Sb Doped Y Bacuo Superconducting Ceramics, K. Kocabaş, N. Kazanci, M. Tepe

Turkish Journal of Physics

In this study the structural characteristics of $Sb_2O_3$ doped $YBa_2Cu_3O_{7-x}$ superconductive ceramics are investigated by electrical and XRD analyses. It is determined that, while in undoped specimens the value of $T_c$ is equal to 92 K, this value is negatively influenced by the addition of $Sb$. Structural phase results obtained from XRD analysis confirm the result obtained from the electrical measurements.

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Microscopic Calculations Of The Nucleus-Nucleus Optical Potential, M. M. Osman Jan 1998

Microscopic Calculations Of The Nucleus-Nucleus Optical Potential, M. M. Osman

Turkish Journal of Physics

In present work, a density dependent nucleon-nucleon interactions based on the $G$-matrix elements of the Paris nucleon-nucleon potential have been used to calculate the real part of the nucleus-nucleus optical potential. We have compared our results with those deduced from experiment. We found that our results, obtained using a suitable approximation of the kinetic energy density, agree satisfactory with those extracted from experiment at the strong absorption radius. Moreover, the higher values of the compressibility, $K$, agree better with experiment than the lower values.

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Deformation Methods For Investigation Of The Deep Level Parameters In Semiconductors, S. Z. Zainabidinov, A. Abduraimov, O. O. Mamatkarimov, I.G. Tursunov, R.Kh. Khamidov Jan 1998

Deformation Methods For Investigation Of The Deep Level Parameters In Semiconductors, S. Z. Zainabidinov, A. Abduraimov, O. O. Mamatkarimov, I.G. Tursunov, R.Kh. Khamidov

Turkish Journal of Physics

In this paper deformation methods are offered to investigate deep level parameters in semiconductors. It is based on strain parameters measurements of compensated and overcompensated semiconductors. The dynamic changes of current flow in compensated and overcompensated samples of $p$-type $Si: Ni$ and $n$-type $Si: Mn$ under uniform pulse hydrostatic compression (UHC) was investigated. It was observed that in $p$-type $Si: Ni$ samples ionization energy levels $Ni$ at UHC increases, on the contrary in samples $n$-type $Si: Mn$ it decreases. The ionization energy and baric coefficient of the shift of $Ni$ and $Mn$ levels were bounded.

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Interrelation Of Magnetic Properties With The Crystal Structures Of Mefese (Me = Ti; V; Cr; Fe; Co; Ni) Compounds, R. Sadikhov, A. Namazov, J. Guseinov Jan 1998

Interrelation Of Magnetic Properties With The Crystal Structures Of Mefese (Me = Ti; V; Cr; Fe; Co; Ni) Compounds, R. Sadikhov, A. Namazov, J. Guseinov

Turkish Journal of Physics

Magnetization of MeFe$_2$Se$_4$ (Me = Ti; V; Cr; Fe; Co; Ni) compounds at low temperatures has been investigated. It is shown that these compounds are ferrimagnetics with low values of specific magnetization. It is established that along the crystal axis $c$ of a given compound, there have been carried out two types of exchange interactions; cation-cation and cation-anion-cation with different dependence of their quantity on interatomic distance.

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Studies Of Structure Of Ceramic Materials Containing Molibdenum Particles Within The Framework Of Theory Of Non-Homogeneous Systems, Sh. Kami̇lov, M. Karabaeva, U. Abdurahmanov Jan 1998

Studies Of Structure Of Ceramic Materials Containing Molibdenum Particles Within The Framework Of Theory Of Non-Homogeneous Systems, Sh. Kami̇lov, M. Karabaeva, U. Abdurahmanov

Turkish Journal of Physics

The structure of ceramic materials containing molibdenum powder is considered within the framework of leakage theory. Determined are the density of the endless cluster, volumetric parts of the skeleton and dead ends, as well as their dependence on the component concentration. Volumetric part of the skeleton near the threshold of leakage makes a negligible part of the full volume.

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A New Probe Head Design For The Weak Field Double Resonance Spectrometer, A. Oral Salman, M. Maral Sünnetçi̇oğlu, Rıza Sungur, Gökçe Bi̇ngöl Jan 1998

A New Probe Head Design For The Weak Field Double Resonance Spectrometer, A. Oral Salman, M. Maral Sünnetçi̇oğlu, Rıza Sungur, Gökçe Bi̇ngöl

Turkish Journal of Physics

In order to observe low field $\sigma$ EPR spectra of free radicals a new probe head was designed to work at 1.53 mT. As a double resonance spectrometer, at 1.53 mT the probe head includes both NMR and EPR rf coils. To induce the $\sigma$ transitions EPR rf coil must produce an rf field parallel to the main static field. Various coil designs were examined for this aim and the best results was obtained with a solenoid NMR coil and saddle shaped single turn EPR coil design combination.

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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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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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The Effect Of Spatially Dependent Screening On The Donor Ionization Energy In A Quantum Wire, B.N. Onwuagba Jan 1998

The Effect Of Spatially Dependent Screening On The Donor Ionization Energy In A Quantum Wire, B.N. Onwuagba

Turkish Journal of Physics

The effect of the spatially dependent screening on the ionization energy of a shallow donor in a 1D quantum well wire made of Ga_{1-x}Al_x/GaAs superlattice is presented. A variational approach is used to obtain ionization energy of the on-centre impurity at the origin of the well and the results obtained are compared with the existing values.

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Inversion Of Plasmaspheric Euv Remote Sensing Data From The Stp 72-1 Satellite, R.R. Meier, A.C. Nicholas, J.M. Picone, D.J. Melendez-Alvira, G. Ganguli, Mark Anthony Reynolds, E.C. Roelof Jan 1998

Inversion Of Plasmaspheric Euv Remote Sensing Data From The Stp 72-1 Satellite, R.R. Meier, A.C. Nicholas, J.M. Picone, D.J. Melendez-Alvira, G. Ganguli, Mark Anthony Reynolds, E.C. Roelof

Publications

Observations of the extreme ultraviolet emission of helium ions at 30.4 nm can be used to study the global shape of the plasmasphere and its dynamical response to geomagnetic forcing. In order to retrieve number densities of plasmaspheric He+ from such observations, we have developed a new inversion technique based on discrete inverse theory, which uses the optical data to optimize a parameterized model of the He+ distribution. We apply this inversion technique to several orbits of data obtained from the Naval Research Laboratory extreme ultraviolet photometric experiment launched on the STP 72-1 satellite in October 1972. The inversion is …

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The Influence Of The Dispersion Of Boron Silicate On The Migration Of Non-Equilibrium Charge Carriers Generated By Eect Of An Electric Discharge, A.M. Hasanov Jan 1998

The Influence Of The Dispersion Of Boron Silicate On The Migration Of Non-Equilibrium Charge Carriers Generated By Eect Of An Electric Discharge, A.M. Hasanov

Turkish Journal of Physics

ESR was used in an investigation of the influence of Boron Silicate dispersion on the accumulation of paramagnetic centers (PC). It was observed that the rate of accumulation of PC increase by increasing of the grain size (r). At $r < 0.08$ mm the electrons ($F^+$-centers) are localized on the surface and with increasing grain size up to $0.08 < r < 0.22$ mm charge stratification takes place, the electrons are distributed in near-surface layer and the holes ($V$-centers) are localized in the bulk of the insulator. It was established that the transport of non-equilibrium charge carriers (NCC) from the bulk to the surface of Boron Silicate was due to a drift from the depth $(d \sim 10 \mu m)$ to a bulk-charge field generated by an electric discharge. The value of the surface field $E_s \sim 10^5 V/cm$ is determined by experimental results of the data. The kinetics of the isothermal annealing (300 K) are used to establish the influence of the surface field on the annihilation of NCC in the ''dead'' layer of separated charges.

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Analytical Expressions Of Matrix Elements For Saxon-Woods Potential And Pad'{E} Approximations, Valentin L. R. Niculescu, Dumitru Catana Jan 1998

Analytical Expressions Of Matrix Elements For Saxon-Woods Potential And Pad'{E} Approximations, Valentin L. R. Niculescu, Dumitru Catana

Turkish Journal of Physics

The paper presents the analytical matrix elements of the kinetic hamiltonian in the oscillator base. The Pad'{e} approximations for the potential part (Saxon - Woods and alike) was used. From residue calculus the potential matrix elements are analytical. Many parts of these expressions can be computed once for ever. In this way the evaluation time can be reduced and the relations obtained are well suited for parallel computation.

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^{19}F Nmr Study Of Flux-Line Dynamics In Fluorinated Yba_2cu_4o_8, Figen Tabak, Mavrizio Corti̇ Jan 1998

^{19}F Nmr Study Of Flux-Line Dynamics In Fluorinated Yba_2cu_4o_8, Figen Tabak, Mavrizio Corti̇

Turkish Journal of Physics

Measurements of the ^{19}F NMR linewidth \Delta \nu and spin-lattice relaxation rate 1/T_1 have been performed in an oriented powder sample of fluorinated YBa_2Cu_4O_8 at temperatures 4 < T < 300 K and static magnetic fields 0.3 < H_0 < 9.4 T for Hollc. Thermal motion of flux lines was evidenced from the effect on NMR linewidth while 1/T_1 showed the effects due to interaction with Fermi liquid.

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Searches For Exotic Matter, David Lee Morgan Jan 1998

Searches For Exotic Matter, David Lee Morgan

Dissertations, Theses, and Masters Projects

This research encompasses two quite distinct searches for exotic matter. The first half concerns exotic matter on the scale of elementary particles. In this chapter, I consider the production of gluinos, the supersymmetric partner of the gluon, in models where the gluino is very light. Cross sections are calculated for electroproduction and hadroproduction of gluinos and the results indicate that existing accelerators are capable of probing the region of gluino masses between 1.0 and 2.0GeV with lifetimes between 10{dollar}\sp{lcub}-10{rcub}{dollar} and 10{dollar}\sp{lcub}-6{rcub}{dollar} seconds. Such experiments could find a light gluino if it exists, or to close this unexplored mass-lifetime window. The …

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Measurement Of The Diffractive Structure Function FD(4)2 At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, M. Chiarini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, I. Gialas, P. Giusti, G. Iacobucci Jan 1998

Measurement Of The Diffractive Structure Function FD(4)2 At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, M. Chiarini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, I. Gialas, P. Giusti, G. Iacobucci

Faculty Publications

This paper presents the first analysis of diffractive photon dissociation events in deep inelastic positron-proton scattering at HERA in which the proton in the final state is detected and its momentum measured. The events are selected by requiring a scattered proton in the ZEUS leading proton spectrometer (LPS) with xL > 0.97, where xL is the fraction of the incoming proton beam momentum carried by the scattered proton. The use of the LPS significantly reduces the contamination from events with diffractive dissociation of the proton into low mass states and allows a direct measurement of t, the square of the four-momentum …

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High-ET Inclusive Jet Cross Sections In Photoproduction At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, 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 1998

High-ET Inclusive Jet Cross Sections In Photoproduction At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, 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

Inclusive jet differential cross sections for the reaction e+p → e+ + jet + X with quasi-real photons have been measured with the ZEUS detector at HERA. These cross sections are given for the photon-proton centre-of-mass energy interval 134 < W < 277 GeV and jet pseudorapidity in the range -1 < ηjet < 2 in the laboratory frame. The results are presented for three cone radii in the η - φ plane, R = 1.0, 0.7 and 0.5. Measurements of dσ/dηjet above various jet-transverse-energy thresholds up to 25 GeV and in three ranges of W are presented and compared to next-to-leading order (NLO) QCD calculations. For jets defined with R = 1.0 differences between data and NLO calculations are seen at high ηjet and low EjetT. The measured cross sections for jets defined with R = 0.7 are well described by the calculations in the entire measured range ηjet and EjetT. The inclusive jet cross section for EjetT > 21 GeV is consistent with an approximately linear variation with the cone radius R in the range between 0.5 and 1.0, and with NLO calculations.

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Higher Order Isotropic Velocity Grids In Lattice Methods, Pavol Pavlo, George Vahala, Linda L. Vahala Jan 1998

Higher Order Isotropic Velocity Grids In Lattice Methods, Pavol Pavlo, George Vahala, Linda L. Vahala

Electrical & Computer Engineering Faculty Publications

Kinetic lattice methods are a very attractive representation of nonlinear macroscopic systems because of their inherent parallelizability on multiple processors and their avoidance of the nonlinear convective terms. By uncoupling the velocity lattice from the spatial grid, one can employ higher order (non-space-filling) isotropic lattices-lattices which greatly enhance the stable parameter regions, particularly in thermal problems. In particular, the superiority of the octagonal lattice over previous models used in 2D (hexagonal or square) and 3D (projected face-centered hypercube) is shown.

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Integrable Unsteady Motion With An Application To Ocean Eddies, A. D. Kirwan Jr., Bruce L. Lipphardt Jan 1998

Integrable Unsteady Motion With An Application To Ocean Eddies, A. D. Kirwan Jr., Bruce L. Lipphardt

CCPO Publications

Application of the Brown-Samelson theorem, which shows that particle motion is integrable in a class of vorticity-conserving, two-dimensional incompressible hows, is extended here to a class of explicit time dependent dynamically balanced flows in multilayered systems. Particle motion for nonsteady two-dimensional flows with discontinuities in the vorticity or potential vorticity fields (modon solutions) is shown to be integrable. An example of a two-layer modon solution constrained by observations of a Gulf Stream ring system is discussed.

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A Search For Lepton Flavor Violation In The Neutral Kaon System, Christopher Henry Hoff Jan 1998

A Search For Lepton Flavor Violation In The Neutral Kaon System, Christopher Henry Hoff

Dissertations, Theses, and Masters Projects

The conservation of separate lepton number is an ad hoc conservation principle in the Standard Model but several non-Standard Model theories allow violation of separate lepton number conservation. A very sensitive search for lepton flavor violation in the neutral kaon system, via the decay K0L→me , was undertaken by Brookhaven National Laboratory Experiment 871 (E871) during the 1995 and 1996 AGS HEP running periods. No K0L→me decays were observed and a single event sensitivity (SES) of 1.97x10-12 was achieved. This single event sensitivity corresponds to an upper limit on the branching fraction of BK0L→m e<4.53+/-0.21+/-0.46x 10-12 at a 90% confidence level.

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The Role Of Adsorbed Oxygen In Secondary Emission From Metallic Substrates, Scott Gregory Walton Jan 1998

The Role Of Adsorbed Oxygen In Secondary Emission From Metallic Substrates, Scott Gregory Walton

Dissertations, Theses, and Masters Projects

Low energy, ion- and photon-induced secondary electron and anion emission from metallic substrates has been investigated as a function of adsorbate coverage. Sodium positive ions (Na+), with kinetic energies up to 500 eV, and photons, with energies up to 23 eV, are utilized to initiate secondary emission. The principal adsorbate is oxygen with coverages ranging from none to a few monolayers.;For ion-induced emission, the secondary electron and negative ion absolute and relative yields from 302 stainless steel and polycrystalline tungsten (W) have been measured as a function of both impact energy and oxygen coverage. Additionally, the yields from a "technical" …

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Steady Incompressible Magnetohydrodynamic Flow Near A Point Of Reattachment, J. M. Dorrepaal, S. Moosavizadeh Jan 1998

Steady Incompressible Magnetohydrodynamic Flow Near A Point Of Reattachment, J. M. Dorrepaal, S. Moosavizadeh

Mathematics & Statistics Faculty Publications

The oblique stagnation-point flow of an electrically conducting fluid in the presence of a magnetic field is a highly nonlinear problem whose solution is of interest even in the simplest of geometries. The problem models the flow of a viscous conducting fluid near a point where a separation vortex reattaches itself to a rigid boundary. A similarity solution exists which reduces the problem to a coupled system of four ordinary differential equations which can be integrated numerically. The problem has two independent parameters, the conductivity of the fluid and the strength of the magnetic field. Solutions are tabulated for a …

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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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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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