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2004

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Articles 481 - 510 of 516

Full-Text Articles in Physics

Hyperon Photoproduction In The Nucleon Resonance Region, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration Jan 2004

Hyperon Photoproduction In The Nucleon Resonance Region, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

High-statistics cross sections and recoil polarizations for the reactions γ+p → K++ Λ and γ+p→K++ Σ0 have been measured at CLAS for center-of-mass energies between 1.6 and 2.3 GeV. In the K+Λ channel we confirm a resonance-like structure near W = 1.9 GeV at backward kaon angles. Our data show more complex s- and u- channel behavior than previously seen, since structure is also present at forward angles, but not at central angles. The position and width change with angle, indicating that more than one resonance is playing a role. Large positive Λ polarization at …

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Unique Electron Polarimeter Analyzing Power Comparison And Precision Spin-Based Energy Measurement, J. M. Grames, C. K. Sinclair, J. Mitchell, E. Chudakov, H. Fenker, A. Freyberger, D. W. Higinbotham, M. Poelker, M. Steigerwald, M. Tiefenback, Vipuli Dharmawardane Jan 2004

Unique Electron Polarimeter Analyzing Power Comparison And Precision Spin-Based Energy Measurement, J. M. Grames, C. K. Sinclair, J. Mitchell, E. Chudakov, H. Fenker, A. Freyberger, D. W. Higinbotham, M. Poelker, M. Steigerwald, M. Tiefenback, Vipuli Dharmawardane

Physics Faculty Publications

Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of …

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First Upper Limits From Ligo On Gravitational Wave Bursts, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres Jan 2004

First Upper Limits From Ligo On Gravitational Wave Bursts, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres

Physics and Astronomy Faculty Publications and Presentations

We report on a search for gravitational wave bursts using data from the first science run of the Laser Interferometer Gravitational Wave Observatory (LIGO) detectors. Our search focuses on bursts with durations ranging from 4 to 100 ms, and with significant power in the LIGO sensitivity band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than 1.6 events per day at a 90% confidence level. This result is interpreted in terms of the detection efficiency for ad hoc waveforms (Gaussians and sine Gaussians) as a function of their root-sum-square strain hrss; typical sensitivities …

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Speed-Up Collisions In Strong-Field Double Ionization, Stanley L. Haan, J. C. Cully, K. Hoekema Jan 2004

Speed-Up Collisions In Strong-Field Double Ionization, Stanley L. Haan, J. C. Cully, K. Hoekema

University Faculty Publications and Creative Works

We compare quantum and classical models of double ionization (DI) for aligned-electron helium in strong laser fields, considering specifically the role of recollision processes in which the returning electron travels in the direction of the laser force. Quantum studies show that for the knee region in our model a small but persistent portion of the total DI occurs through these speed-up collisions. We show that classical modeling displays similar collisions and reveals that with-the-force doubly ionizing collisions typically involve two-particle trajectories in which both electrons can be said to have been bound or very nearly bound at the zero of …

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Uranium Oxide As A Highly Reflective Coating From 100-400 Ev, Richard L. Sandberg, David D. Allred, Luke J. Bissell, Jed E. Johnson, R. Steven Turley Jan 2004

Uranium Oxide As A Highly Reflective Coating From 100-400 Ev, Richard L. Sandberg, David D. Allred, Luke J. Bissell, Jed E. Johnson, R. Steven Turley

Faculty Publications

We present the measured reflectances (Beamline 6.3.2, ALS and LBNL) of naturally oxidized uranium and naturally oxidized nickel thin films from 100-460 eV (2.7 to 11.6 nm) at 5 and 15 degrees grazing incidence. These show that uranium as UO2, can fulfill its promise as the highest known single surface reflector for this portion of the soft x-ray region, being nearly twice as reflective as nickel in the 124-250 eV (5-10 nm) region. This is due to its large index of refraction coupled with low absorption. Nickel is commonly used in soft x-ray applications in astronomy and synchrotrons. (Its reflectance …

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Setting Upper Limits On The Strength Of Periodic Gravitational Waves From Psr J1939+2134 Using The First Science Data From The Geo 600 And Ligo Detectors, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres Jan 2004

Setting Upper Limits On The Strength Of Periodic Gravitational Waves From Psr J1939+2134 Using The First Science Data From The Geo 600 And Ligo Detectors, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres

Physics and Astronomy Faculty Publications and Presentations

Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar’s gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar’s equatorial ellipticity.

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Analysis Of First Ligo Science Data For Stochastic Gravitational Waves, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano Jan 2004

Analysis Of First Ligo Science Data For Stochastic Gravitational Waves, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano

Physics and Astronomy Faculty Publications and Presentations

We present the analysis of between 50 and 100 h of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a f−3 power spectrum of …

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High-Q2 Neutral Current Cross Sections In E+ P Deep Inelastic Scattering At √S = 318 Gev, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, S. Miglioranzi, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, A. Montanari, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli Jan 2004

High-Q2 Neutral Current Cross Sections In E+ P Deep Inelastic Scattering At √S = 318 Gev, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, S. Miglioranzi, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, A. Montanari, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

Cross sections for e+ p neutral current deep inelastic scattering have been measured at a center-of-mass energy of √s = 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 63.2 pb -1. The double-differential cross section, d2σ/ dxdQ2, is presented for 200 GeV2 < Q2 < 30 000 GeV2 and for 0.005 < x < 0.65. The single-differential cross sections dσ/dQ2, dσ/dx and dσ/dy are presented for Q2 > 200 GeV2. The effect of Z-boson-exchange is seen in dσ/dx measured for Q2 > 10 000 GeV2. The data presented here were combined with ZEUS e+ p neutral current data taken at √s = 300 GeV and the structure function F2em was extracted. All results agree well with the predictions of the Standard Model.

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Environmental Swap Energy And Role Of Configurational Entropy In Transfer Of Small Molecules From Water Into Alkanes, Pavel Smejtek, Robert Campbell Word Jan 2004

Environmental Swap Energy And Role Of Configurational Entropy In Transfer Of Small Molecules From Water Into Alkanes, Pavel Smejtek, Robert Campbell Word

Physics Faculty Publications and Presentations

We studied the effect of segmented solvent molecules on the free energy of transfer of small molecules from water into alkanes (hexane, heptane, octane, decane, dodecane, tetradecane, and hexadecane). For these alkanes we measured partition coefficients of benzene, 3-methylindole (3MI), 2,3,4,6-tetrachlorophenol (TeCP), and 2,4,6-tribromophenol (TriBP) at 3, 11, 20, 3, and 47 °C. For 3MI, TeCP, and TriBP the dependence of free energy of transfer on length of alkane chains was found to be very different from that for benzene. In contrast to benzene, the energy of transfer for 3MI, TeCP, and TriBP was independent of the number of carbons …

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Effects Of Localization And Amplification On Intensity Distribution Of Light Transmitted Through Random Media, Alexey Yamilov, Hui Cao Jan 2004

Effects Of Localization And Amplification On Intensity Distribution Of Light Transmitted Through Random Media, Alexey Yamilov, Hui Cao

Physics Faculty Research & Creative Works

We numerically study the statistical distribution of intensity of light transmitted through quasi-one-dimensional random media by varying the dimensionless conductance g and the amount of absorption or gain. A markedly non-Rayleigh distribution is found to be well fitted by the analytical formula of Nieuwenhuizen et al. [Phys. Rev. Lett. 74, 2674 (1995)] with a single parameter g′ . We show that in the passive random system g′ is uniquely related to g , while in amplifying or absorbing random media g′ also depends on the gain or absorption coefficient.

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Kinetics Of Binary Nucleation Of Vapors In Size And Composition Space, Sergey P. Fisenko, Gerald Wilemski Jan 2004

Kinetics Of Binary Nucleation Of Vapors In Size And Composition Space, Sergey P. Fisenko, Gerald Wilemski

Physics Faculty Research & Creative Works

We reformulate the kinetic description of binary nucleation in the gas phase using two natural independent variables: the total number of molecules g and the molar composition x of the cluster. The resulting kinetic equation can be viewed as a two-dimensional Fokker-Planck equation describing the simultaneous Brownian motion of the clusters in size and composition space. Explicit expressions for the Brownian diffusion coefficients in cluster size and composition space are obtained. For characterization of binary nucleation in gases three criteria are established. These criteria establish the relative importance of the rate processes in cluster size and composition space for different …

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Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan Jan 2004

Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan

Physics Faculty Research & Creative Works

We derive an order-parameter field theory for a quantum phase transition between a disordered metal and an exotic (non- s -wave) superconductor. Mode coupling effects between the order parameter and other fermionic soft modes lead to an effective long-range interaction between the anomalous density fluctuations which is reflected in singularities in the free energy functional. However, this long-range interaction is not strong enough to suppress disorder fluctuations. The asymptotic critical region is characterized by run-away flow to large disorder. For weak coupling, this asymptotic region is very narrow. It is preempted by a wide crossover regime with mean-field critical behavior …

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Smeared Phase Transition In A Three-Dimensional Ising Model With Planar Defects: Monte Carlo Simulations, Rastko Sknepnek, Thomas Vojta Jan 2004

Smeared Phase Transition In A Three-Dimensional Ising Model With Planar Defects: Monte Carlo Simulations, Rastko Sknepnek, Thomas Vojta

Physics Faculty Research & Creative Works

We present results of large-scale Monte Carlo simulations for a three-dimensional Ising model with short-range interactions and planar defects, i.e., disorder perfectly correlated in two dimensions. We show that the phase transition in this system is smeared, i.e., there is no single critical temperature, but different parts of the system order at different temperatures. This is caused by effects similar to but stronger than Griffiths phenomena. In an infinite-size sample there is an exponentially small but finite probability to find an arbitrary large region devoid of impurities. Such a rare region can develop true long-range order while the bulk system …

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Ultraviolet Photonic Crystal Laser, Alexey Yamilov, Hui Cao, Robert P. H. Chang, Xiaohua Wu, Xang Liu, Shuyou Li, Vinayak P. Dravid Jan 2004

Ultraviolet Photonic Crystal Laser, Alexey Yamilov, Hui Cao, Robert P. H. Chang, Xiaohua Wu, Xang Liu, Shuyou Li, Vinayak P. Dravid

Physics Faculty Research & Creative Works

We fabricated two-dimensional photonic crystal structures in zinc oxide films with focused-ion-beam etching. Lasing is realized in the near-ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process. ©2004 American Institute of Physics

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Renormalization-Group Analysis Of The Generalized Sine-Gordon Model And Of The Coulomb Gas For D > 3 Dimensions, I. Nandori, Ulrich D. Jentschura, Kornel Sailer, Gerhard Soff Jan 2004

Renormalization-Group Analysis Of The Generalized Sine-Gordon Model And Of The Coulomb Gas For D > 3 Dimensions, I. Nandori, Ulrich D. Jentschura, Kornel Sailer, Gerhard Soff

Physics Faculty Research & Creative Works

Renormalization-group (RG) flow equations have been derived for the generalized sine-Gordon model (GSGM) and the Coulomb gas (CG) in d ≥ 3 of dimensions by means of the Wegner-Houghton method, and by way of the real-space RG approach. The UV scaling laws determined by the leading-order terms of the flow equations are in qualitative agreement for all dimensions d ≥ 3, independent of the dimensionality, and in sharp contrast to the special case d=2. For the 4-dimensional GSGM it is demonstrated explicitly (by numerical calculations) that the blocked potential tends to a constant effective potential in the infrared limit, satisfying …

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The Changing Role Of Non-Co2 Greenhouse Gases, M. A. K. Khalil Jan 2004

The Changing Role Of Non-Co2 Greenhouse Gases, M. A. K. Khalil

Physics Faculty Publications and Presentations

During the last century, the concentrations of several greenhouse gases have increased considerably - most notably carbon dioxide, methane and nitrous oxide. In addition, new, entirely man-made gases have been put into the atmosphere that also cause the greenhouse effect; these include the chlorofluorocarbons. Calculations have shown that during the last century the non-CO₂ greenhouse gases could together be almost as effective as the increase of carbon dioxide in causing global warming. These and similar gases were therefore included in the Kyoto Protocol to develop a comprehensive plan for controlling potentially unfavorable climatic change. Studies show however that the other …

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Observation Of KS0KS0 Resonances In Deep Inelastic Scattering At Hera, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, A. Montanari, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi Jan 2004

Observation Of KS0KS0 Resonances In Deep Inelastic Scattering At Hera, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, A. Montanari, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi

Faculty Publications

Inclusive Ks0Ks0 production in deep inelastic ep scattering at HERA has been studied with the ZEUS detector using an integrated luminosity of 120 pb-1. Two states are observed at masses of 1537-8-9 MeV and 1726 ± 7 MeV, as well as an enhancement around 1300 MeV. The state at 1537 MeV is consistent with the well established f′2(1525). The state at 1726 MeV may be the glueball candidate f0(1710). However, it's width of 38 -14-20 MeV is narrower than 125 ± 10 MeV observed by previous experiments for the f0(1710). © 2003 Elsevier B.V. All rights reserved.

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Excimer Emission From Cathode Boundary Layer Discharges, Mohamed Moselhy, Karl H. Schoenbach Jan 2004

Excimer Emission From Cathode Boundary Layer Discharges, Mohamed Moselhy, Karl H. Schoenbach

Bioelectrics Publications

The excimer emission from direct current glow discharges between a planar cathode and a ring-shaped anode of 0.75 and 1.5 mm diameter, respectively, separated by a gap of 250 μm, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the “cathode boundary layer” plasma, in the 100 μm range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. The radiant excimer emittance at 172 nm increases with pressure and reaches a value of 4 W/cm2 for …

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Microscopic Analysis For Water Stressed By High Electric Fields In The Prebreakdown Regime, R. P. Joshi, J. Qian, K. H. Schoenbach, E. Schamiloglu Jan 2004

Microscopic Analysis For Water Stressed By High Electric Fields In The Prebreakdown Regime, R. P. Joshi, J. Qian, K. H. Schoenbach, E. Schamiloglu

Bioelectrics Publications

Analysis of the electrical double layer at the electrode-water interface for voltages close to the breakdown point has been carried out based on a static, Monte Carlo approach. It is shown that strong dipole realignment, ion-ion correlation, and finite-size effects can greatly modify the electric fields and local permittivity (hence, leading to optical structure) at the electrode interface. Dramatic enhancements of Schottky injection, providing a source for electronic controlled breakdown, are possible. It is also shown that large pressures associated with the Maxwell stress tensor would be created at the electrode boundaries. Our results depend on the ionic density, and …

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Laser Writing Of Semiconductor Nanoparticles And Quantum Dots, Massimo F. Bertino, Raghuveer Reddy Gadipalli, J. Greg Story, C. G. Williams, Guo-Hui Zhang, Chariklia Sotiriou-Leventis, Akira Tokuhiro, Suchi Guha, Nicholas Leventis Jan 2004

Laser Writing Of Semiconductor Nanoparticles And Quantum Dots, Massimo F. Bertino, Raghuveer Reddy Gadipalli, J. Greg Story, C. G. Williams, Guo-Hui Zhang, Chariklia Sotiriou-Leventis, Akira Tokuhiro, Suchi Guha, Nicholas Leventis

Physics Faculty Research & Creative Works

Silica aerogels were patterned with CdS using a photolithographic technique based on local heating with infrared (IR) light. The solvent of silica hydrogels was exchanged with an aqueous solution of the precursors CdNO3 and NH4 OH, all precooled to a temperature of 5°C. Half of the bathing solution was then replaced by a thiourea solution. After thiourea diffused into the hydrogels, the samples were exposed to a focused IR beam from a continuous wave, Nd-YAG laser. The precursors reacted in the spots heated by the IR beam to form CdS nanoparticles. We lithographed features with a diameter of …

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Highest-Quality Modes In Disordered Photonic Crystals, Alexey Yamilov, Hui Cao Jan 2004

Highest-Quality Modes In Disordered Photonic Crystals, Alexey Yamilov, Hui Cao

Physics Faculty Research & Creative Works

We studied the modes of the highest-quality factor Qm in disordered photonic crystals. by varying the strength of disorder, we identified five different scaling regimes of the ensemble averaged (Qm) with the system size. For sufficiently large systems, (Qm) reaches the maximum at some finite degree of disorder, where its value is comparable to the quality factor of an intentionally introduced single defect at the center of a photonic band gap. Near this optimal degree of disorder, we predict a superexponential increase of (Qm) with the system size, due to migration of the frequencies of the highest-quality modes toward the …

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Study Of Structural And Magnetic Properties Of Iron-Rich Mixed Rare-Earth Nddyfe (17-Y-X)Coxsiy Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, M. S. Kim, Qingsheng Cai, William Joseph James Jan 2004

Study Of Structural And Magnetic Properties Of Iron-Rich Mixed Rare-Earth Nddyfe (17-Y-X)Coxsiy Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, M. S. Kim, Qingsheng Cai, William Joseph James

Physics Faculty Research & Creative Works

A series of NdDyFe(17-y-x)CoxSiy solid solutions with = 2 and 3 and = 0.5 1.0 and 1.5 were prepared by induction melting stoichiometric amounts of high-purity elements. The postannealed samples consist of two phases belonging to the space groups R3 m and P63 mmc . The lattice parameters and the unit cell volumes were calculated from the refinements of the magnetic and structural unit cells using the FULLPROF version of the Rietveld program. For a fixed content of Co, the maximum Curie temperatures (305 C to 405 C) were observed in samples with = 1 and having two phases, a …

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Traversal Times For Random Walks On Small-World Networks, V. M. Kenkre, Paul Ernest Parris Jan 2004

Traversal Times For Random Walks On Small-World Networks, V. M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

We study the mean traversal time tau for a class of random walks on Newman-Watts small-world networks, in which steps around the edge of the network occur with a transition rate F that is different from the rate f for steps across small-world connections. when f>>F, the mean time tau to traverse the network exhibits a transition associated with percolation of the random graph (i.e., small-world) part of the network, and a collapse of the data onto a universal curve. This transition was not observed in earlier studies in which equal transition rates were assumed for all allowed steps. …

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Variational Considerations In The Study Of Carrier Transport In Organic Crystals, V. M. Kenkre, Paul Ernest Parris Jan 2004

Variational Considerations In The Study Of Carrier Transport In Organic Crystals, V. M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

A variational approach is used to investigate consequences of electron-phonon interactions between a charge carrier and multiple (specifically two) phonon branches. Phase diagrams are obtained and the nature of the transition from undressed to dressed phases of the carrier is studied with their help. No sharp transition between singly dressed and doubly dressed phases occurs. The effective carrier bandwidth, reduced by strong coupling to the high-frequency branch is found to be stable with respect to small to intermediate values of additional coupling to the low-frequency branch. This finding lends support to transport calculations based on the idea that carriers in …

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Progress At The Heidelberg Ebit, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Christina Dimopoulou, I. N. Draganic, Daniel Fischer, Antonio J. Gonzalez, A. Lapierre, V. Mironov, Robert Moshammer, R. Soria Orts, Hiroyuki Tawara, M. Trinczek, Joachim Hermann Ullrich Jan 2004

Progress At The Heidelberg Ebit, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Christina Dimopoulou, I. N. Draganic, Daniel Fischer, Antonio J. Gonzalez, A. Lapierre, V. Mironov, Robert Moshammer, R. Soria Orts, Hiroyuki Tawara, M. Trinczek, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Two years after the relocation of the Heidelberg EBIT, several experiments are already in operation. Spectroscopic measurements in the optical region have delivered the most precise reported wavelengths for highly charged ions, in the case of the forbidden transitions of Ar XIV and Ar XV. The lifetimes of the metastable levels involved in those transitions has been determined with an error of less than 0.2%. A new, fully automatized x-ray crystal spectrometer allows systematic measurements with very high precision and reproducibility. Absolute measurements of the Lyman series of H-like ions are currently underway. Dielectronic recombination studies have yielded information on …

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Power Consideration In The Pulsed Dielectric Barrier Discharge At Atmospheric Pressure, M. Laroussi, X. Lu, V. Kolobov, R. Arslanbekov Jan 2004

Power Consideration In The Pulsed Dielectric Barrier Discharge At Atmospheric Pressure, M. Laroussi, X. Lu, V. Kolobov, R. Arslanbekov

Electrical & Computer Engineering Faculty Publications

Nonequilibrium, atmospheric pressure discharges are rapidly becoming an important technological component in material processing applications. Amongst their attractive features is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. To further enhance the plasma chemistry, pulsed operation with pulse widths in the nanoseconds range has been suggested. We report on a specially designed, dielectric barrier discharge based diffuse pulsed discharge and its electrical characteristics. Two current pulses corresponding to two consecutive discharges are generated per voltage pulse. The second discharge, which occurs at the falling edge of the voltage pulse, is induced by the …

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Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala Jan 2004

Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

The effect of the direction of the detected beam on the intensity of ECE is studied. It is found that the combined effects of the strong dependence of the conversion efficiencey of O mode at the plasma resonance on the direction of the incident wave and the partial screening of the beam waist by the MAST vessel wall, can be responsible for the weakening of ECE emission for some frequencies. The theoretical model for ECE data interpretation on MAST has been significantly improved. New features of the model are as follows: the quasioptical treatment of the receiving antenna, interference, polarization …

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Photonic Band Gap Analysis Using Finite-Difference Frequency-Domain Method, Shangping Guo, Feng Wu, Sacharia Albin Jan 2004

Photonic Band Gap Analysis Using Finite-Difference Frequency-Domain Method, Shangping Guo, Feng Wu, Sacharia Albin

Electrical & Computer Engineering Faculty Publications

A finite-difference frequency-domain (FDFD) method is applied for photonic band gap calculations. The Maxwell’s equations under generalized coordinates are solved for both orthogonal and non-orthogonal lattice geometries. Complete and accurate band gap information is obtained by using this FDFD approach. Numerical results for 2D TE/TM modes in square and triangular lattices are in excellent agreements with results from plane wave method (PWM). The accuracy, convergence and computation time of this method are also discussed.

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Quantum Lattice Representation Of Dark Solitons, George Vahala, Linda L. Vahala, Jeffrey Yepez Jan 2004

Quantum Lattice Representation Of Dark Solitons, George Vahala, Linda L. Vahala, Jeffrey Yepez

Electrical & Computer Engineering Faculty Publications

The nonlinear Schrodinger (NLS) equation in a self-defocusing Kerr medium supports dark solitons. Moreover the mean field description of a dilute Bose-Einstein condensate (BEC) is described by the Gross-Pitaevskii equation, which for a highly anisotropic (cigar-shaped) magnetic trap reduces to a one-dimensional (1D) cubic NLS in an external potential. A quantum lattice algorithm is developed for the dark solitons. Simulations are presented for both black (stationary) solitons as well as (moving) dark solitons. Collisions of dark solitons are compared with the exact analytic solutions and coupled dark-bright vector solitons are examined. The quantum algorithm requires 2 qubits per scalar field …

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Comparative Analysis Of Bragg Fibers, Shangping Guo, Sacharia Albin, Robert S. Rogowski Jan 2004

Comparative Analysis Of Bragg Fibers, Shangping Guo, Sacharia Albin, Robert S. Rogowski

Electrical & Computer Engineering Faculty Publications

In this paper, we compare three analysis methods for Bragg fibers, viz. the transfer matrix method, the asymptotic method and the Galerkin method. We also show that with minor modifications, the transfer matrix method is able to calculate exactly the leakage loss of Bragg fibers due to a finite number of H/L layers. This approach is more straightforward than the commonly used Chew’s method. It is shown that the asymptotic approximation condition should be satisfied in order to get accurate results. The TE and TM modes, and the band gap structures are analyzed using Galerkin method.

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