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1999

Physics

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Articles 31 - 60 of 456

Full-Text Articles in Physical Sciences and Mathematics

Laser Light In, 50-Mev Protons Out, Phillip F. Schewe, Ben Stein, Donald P. Umstadter Nov 1999

Laser Light In, 50-Mev Protons Out, Phillip F. Schewe, Ben Stein, Donald P. Umstadter

Donald Umstadter Publications

At next week's meeting of the American Physical Society Division of Plasma Physics in Seattle, three groups will independently announce their ability to generate powerful, intense streams of ions by shining ultrashort laser pulses on tiny spots of solid material. Potentially, this approach offers an alternative to bulky, expensive ion accelerators for producing high-velocity ions useful for cancer therapy and electronics manufacturing. Using a single pulse of light from Livermore's Petawatt laser, the most powerful in the world, researchers at that laboratory (Scott Wilks, 925-422-2974, wilks@icf.llnl.gov) have reported generating 30 trillion protons with energies up to 50 MeV, from a …

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Coherence Properties Of An Atom Laser, Marek Trippenbach, Y. B. Bland, Mark Edwards, Marya Doery, P. S. Julienne, E. W. Hagley, L. Deng, M. Kozuma, K. Helmerson, S. L. Rolston, W. D. Phillips Nov 1999

Coherence Properties Of An Atom Laser, Marek Trippenbach, Y. B. Bland, Mark Edwards, Marya Doery, P. S. Julienne, E. W. Hagley, L. Deng, M. Kozuma, K. Helmerson, S. L. Rolston, W. D. Phillips

Department of Physics and Astronomy Faculty Publications

We study the coherence properties of an atom laser, which operates by extracting atoms from a gaseous Bose-Einstein condensate via a two-photon Raman process, by analysing a recent experiment (Hagley et al1999 Phys. Rev. Lett.833112). We obtain good agreement with the experimental data by solving the time-dependent Gross-Pitaevskii equation in three dimensions both numerically and with a Thomas-Fermi model. The coherence is strongly affected by the space-dependent phase developed by the condensate when the trapping potential is turned off.

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Light Backscatter Of Milk Products For Transition Sensing Using Optical Fibers, Frederick A. Payne, Czarena L. Crofcheck, Sue E. Nokes, Klat C. Kang Nov 1999

Light Backscatter Of Milk Products For Transition Sensing Using Optical Fibers, Frederick A. Payne, Czarena L. Crofcheck, Sue E. Nokes, Klat C. Kang

Biosystems and Agricultural Engineering Faculty Publications

Transition sensors are needed, particularly in the dairy industry, for detecting transitions in pipe flow systems from product-to-water or product-to-product (such as from chocolate to vanilla ice cream mix). Transition information is used to automatically sequence valves to minimize product waste. Optical fibers were used to measure light backscatter between 400 and 950 nm as a function of milk concentration in water and milkfat concentration in milk. The normalized response (100% for product and 0% for water) as a function of product concentration in water was approximately logarithmic for skim milk between 400 and 900 nm and approximately linear for …

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Shock-Like Dynamics Of Inelastic Gases, E. Ben-Naim, S.Y. Chen, G.D. Doolen Nov 1999

Shock-Like Dynamics Of Inelastic Gases, E. Ben-Naim, S.Y. Chen, G.D. Doolen

Eli Ben-Naim

No abstract provided.

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Intercomparison Of Retrospective Radon Detectors, R. William Field, Daniel J. Steck, Mary Ann Parkhurst, Judy A. Mahaffey, Michael C.R. Alavanja Nov 1999

Intercomparison Of Retrospective Radon Detectors, R. William Field, Daniel J. Steck, Mary Ann Parkhurst, Judy A. Mahaffey, Michael C.R. Alavanja

Physics Faculty Publications

We performed both a laboratory and a field intercomparison of two novel glass-based retrospective radon detectors previously used in major radon case-control studies performed in Missouri and Iowa. The new detectors estimate retrospective residential radon exposure from the accumulation of a long-lived radon decay product, 210Pb, in glass. The detectors use track registration material in direct contact with glass surfaces to measure the α-emission of a 210Pb-decay product, 210Po. The detector's track density generation rate (tracks per square centimeter per hour) is proportional to the surface α-activity. In the absence of other strong sources of α-emission in …

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Crossover Photonic Switching Network With Cmos/Seed Smart Pixel Device And 2d Optical Fiber Bundle Array, Fengguang Luo, Mingcui Cao, Qiaoyan Hu, Anjun Wan, Jun Xu, Cong Deng, Deming Liu Nov 1999

Crossover Photonic Switching Network With Cmos/Seed Smart Pixel Device And 2d Optical Fiber Bundle Array, Fengguang Luo, Mingcui Cao, Qiaoyan Hu, Anjun Wan, Jun Xu, Cong Deng, Deming Liu

Electro-Optics and Photonics Faculty Publications

A 16 X 16 Crossover photonic switching network with hybrid integrated CMOS/SEED smart pixel device and 2D optical fiber bundle array I/O access device is reported in this paper. SEEd array devices ar used as light receivers and transmitters, while CMOS devices make efficient logical processing. 4 X 40 2D multilayer optical fiber bundle arrays are fabricated and are used as I/O access devices in the crossover photonic switching network. The center to center spacing between adjacent optical fibers in the same layer of the fiber array is 125micrometers , and the spacing between adjacent layers is 250micrometers . Displacing …

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Low-Frequency Noise In N-Gan With High Electron Mobility, M. E. Levinshtein, S. L. Rumyantsev, David C. Look, Richard J. Molnar, M. A. Khan, G. Simin, V. Adivarahan, M. S. Shur Nov 1999

Low-Frequency Noise In N-Gan With High Electron Mobility, M. E. Levinshtein, S. L. Rumyantsev, David C. Look, Richard J. Molnar, M. A. Khan, G. Simin, V. Adivarahan, M. S. Shur

Physics Faculty Publications

We report on the results of measurements of low frequency noise in n-type gallium nitride (GaN) grown on sapphire with 300 K electron mobility of 790 cm2/V s. The noise spectra have the form of 1/f noise with a Hooge parameter α of approximately 5×10−2. This value of α is two orders of magnitude smaller than that observed before in n-GaN. The obtained results show that the level of flicker noise in GaN, just like that in GaAs and Si, strongly depends on the structural perfection of the material (the amplitude of the …

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Slow-Binding Inhibition Of The Aminopeptidase From Aeromonas Proteolytica By Peptide Thiols: Synthesis And Spectroscopic Characterization, Kristi M. Huntington, David L. Bienvenue, Yaoming Wei, Brian Bennett, Richard C. Holz, Dehua Pei Nov 1999

Slow-Binding Inhibition Of The Aminopeptidase From Aeromonas Proteolytica By Peptide Thiols: Synthesis And Spectroscopic Characterization, Kristi M. Huntington, David L. Bienvenue, Yaoming Wei, Brian Bennett, Richard C. Holz, Dehua Pei

Physics Faculty Research and Publications

Peptide-derived thiols of the general structure N-mercaptoacyl-leucyl-p-nitroanilide (1a−c) were synthesized and found to be potent, slow-binding inhibitors of the aminopeptidase from Aeromonas proteolytica (AAP). The overall potencies (KI*) of these inhibitors against AAP range from 2.5 to 57 nM exceeding that of the natural product bestatin and approaching that of amastatin. The corresponding alcohols (2a−b) are simple competitive inhibitors of much lower potencies (KI = 23 and 360 μM). These data suggest that the free thiols are involved in the formation of the E·I …

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Strain Splitting Of The Gamma(5) And Gamma(6) Free Excitons In Zno, D. C. Reynolds, David C. Look, B. Jogai, C. W. Litton, T. C. Collins, M T. Harris, M. J. Callahan, J. S. Bailey Nov 1999

Strain Splitting Of The Gamma(5) And Gamma(6) Free Excitons In Zno, D. C. Reynolds, David C. Look, B. Jogai, C. W. Litton, T. C. Collins, M T. Harris, M. J. Callahan, J. S. Bailey

Physics Faculty Publications

High-quality ZnO crystals have been grown by vapor-phase techniques and by the hydrothermal method. Depending on the surface preparation technique, some hydrothermally grown crystals contain strain. These strains result in energy shifts of the free excitons as well as relaxation of the selection rules. The Γ6 unallowed exciton is observed in these samples without the application of a magnetic field. The Γ6 exciton is also observed to split in a strain field, consistent with the Γ9 symmetry for the top valence band in ZnO. The Γ5 and Γ6 excitons have been observed to split in …

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Velocity Distributions Of C Atoms In Co+ Dissociative Recombination: Implications For Photochemical Escape Of C From Mars, Jane L. Fox, Aleksander Hać Nov 1999

Velocity Distributions Of C Atoms In Co+ Dissociative Recombination: Implications For Photochemical Escape Of C From Mars, Jane L. Fox, Aleksander Hać

Physics Faculty Publications

We have carried out Monte Carlo calculations to determine the velocity distributions of C atoms produced by dissociative recombination of CO+ using recent data for the branching ratios of various allowed channels and ion and electron temperatures appropriate to the Martian thermosphere. We find that the fractions of 12C atoms with velocities greater than the escape velocity are ∼ 0.66 and ∼ 0.62, and those for 13C are ∼ 0.47 and ∼ 0.48 at the plasma temperatures characteristic of the exobases at low and high solar activities, respectively. The ratio of the escape fractions of 13C …

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Measurement Of B Quark Fragmentation Fractions In The Production Of Strange And Light B Mesons In Pp̅ Collisions At √S =1.8 Tev, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Nov 1999

Measurement Of B Quark Fragmentation Fractions In The Production Of Strange And Light B Mesons In Pp̅ Collisions At √S =1.8 Tev, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

A new technique to measure the ratio of b quark fragmentation fractions in pp̅ collisions is described. Using a 70-pb-1 sample of low-mass dimuon trigger data recorded with the Collider Detector at Fermilab, we identify B mesons by observing the double semileptonic decays b→cμX with c→sμ X. By counting the numbers of K*(892) 0, K*(892) 1, and Φ (1020) mesons produced in association with these muon pairs, we measure the ratio of strange to nonstrange B meson production to be fs /( fu+ i>fd)=[21.0±3.6(stat) -3.0 …

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A Spin Network Primer, Seth Major Nov 1999

A Spin Network Primer, Seth Major

Articles

Spin networks, essentially labeled graphs, are “good quantum numbers” for the quantum theory of geometry. These structures encompass a diverse range of techniques which may be used in the quantum mechanics of finite dimensional systems, gauge theory, and knot theory. Though accessible to undergraduates,spin network techniques are buried in more complicated formulations. In this paper a diagrammatic method, simple but rich, is introduced through an association of 2×2" role="presentation" style="display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; …

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Coordinate Realizations Of Deformed Lie Algebras With Three Generator, Ranabir Dutt, Asim Gangopadhyaya, C. Rasinariu, Uday P. Sukhatne Nov 1999

Coordinate Realizations Of Deformed Lie Algebras With Three Generator, Ranabir Dutt, Asim Gangopadhyaya, C. Rasinariu, Uday P. Sukhatne

Physics: Faculty Publications and Other Works

Differential realizations in coordinate space for deformed Lie algebras with three generators are obtained using bosonic creation and annihilation operators satisfying Heisenberg commutation relations. The unified treatment presented here contains as special cases all previously given coordinate realizations of so(2,1), so(3), and their deformations. Applications to physical problems involving eigenvalue determination in nonrelativistic quantum mechanics are discussed.

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Intensity Dependence Of Plateau Structures In Laser-Assisted X-Ray–Atom Scattering Processes, Dejan B. Miloševic, Anthony F. Starace Nov 1999

Intensity Dependence Of Plateau Structures In Laser-Assisted X-Ray–Atom Scattering Processes, Dejan B. Miloševic, Anthony F. Starace

Anthony F. Starace Publications

The dependence on laser intensity of recently discovered plateau structures in laser-assisted x-ray–atom scattering, both with and without a static electric field present, is analyzed. Using the “three-step” model and the strong-field approximation we demonstrate a connection between laser-assisted, x-ray–atom scattering and high-order harmonic generation: For high laser-field intensities without a static field present, both processes have plateaus whose energies extend to the cutoff value 3.17Up, where Up is the ponderomotive potential energy. For x-ray–atom scattering in the presence of a static electric field we show that at high laser-field intensities two plateaus appear: One is …

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Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story Nov 1999

Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

Stabilization of autoionizing states of barium by laser-induced, stimulated emission of light is demonstrated. Relative to purely flourescent stabilization, the data clearly show an enhancement of the stabilization process for laser pulses short compared to the flourescent lifetime of the autoionizing states. Shakeup spectra in which the principal quantum number of both electrons changes during the stimulated emission process are also clearly demonstrated.

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Resonant Enhancement Of Relativistic Electron Fluxes During Geomagnetically Active Periods, I Roth, M Temerin, M K. Hudson Oct 1999

Resonant Enhancement Of Relativistic Electron Fluxes During Geomagnetically Active Periods, I Roth, M Temerin, M K. Hudson

Dartmouth Scholarship

The strong increase in the ̄ux of relativistic electrons during the recovery phase of magnetic storms and during other active periods is investigated with the help of Hamiltonian formalism and simulations of test electrons which interact with whistler waves. The intensity of the whistler waves is enhanced signi®cantly due to injection of 10±100 keV electrons during the substorm. Electrons which drift in the gradient and curvature of the magnetic ®eld generate the rising tones of VLF whistler chorus. The seed population of relativ- istic electrons which bounce along the inhomogeneous magnetic ®eld, interacts resonantly with the whistler waves. Whistler wave …

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Comment On "Ideal Capacitor Circuits And Energy Conservation" By K. Mita And M. Boufaida [Am. J. Phys. 67 (8), 737-739 (1999)], Asim Gangopadhyaya, Jeffrey Mallow Oct 1999

Comment On "Ideal Capacitor Circuits And Energy Conservation" By K. Mita And M. Boufaida [Am. J. Phys. 67 (8), 737-739 (1999)], Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

No abstract provided.

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Performance Of The Cleo Iii Lif-Tea Ring Imaging Cherenkov Detector In A High Energy Muon Beam, Raymond Mountain, Marina Artuso, R. Ayad, F. Azfar Oct 1999

Performance Of The Cleo Iii Lif-Tea Ring Imaging Cherenkov Detector In A High Energy Muon Beam, Raymond Mountain, Marina Artuso, R. Ayad, F. Azfar

Physics - All Scholarship

The CLEO III Ring Imaging Cherenkov detector uses LiF radiators to generate Cherenkov photons which are then detected by proportional wire chambers using a mixture of CH$_4$ and TEA gases. The first two photon detector modules which were constructed, were taken to Fermilab and tested in a beam dump that provided high momentum muons. We report on results using both plane and "sawtooth" shaped radiators. Specifically, we discuss the number of photoelectrons observed per ring and the angular resolution. The particle separation ability is shown to be sufficient for the physics of CLEO III.

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Search For The Flavor-Changing Neutral Current Decays B+→ Μ+Μ-K+ And B0→ Μ+Μ-K*0, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Oct 1999

Search For The Flavor-Changing Neutral Current Decays B+→ Μ+Μ-K+ And B0→ Μ+Μ-K*0, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on a search for the flavor-changing neutral current decays B+→ μ+μ-K+ and i>B0→ μ+μ-K*0 using 88 pb-1 of data from p̅p collisions at √s =1.8 TeV, collected with the Collider Detector at Fermilab. Finding no evidence for these decays, we set upper limits on the branching fractions Ɓ(B+→ μ+μ-K+) < 5.2 X 10-6 and Ɓ(B+→ μ+μ-K*0) -6 at the 90% confidence level.

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Phase Imaging: Deep Or Superficial?, Nancy Burnham, O Behrend, L Odoni, J Loubet Oct 1999

Phase Imaging: Deep Or Superficial?, Nancy Burnham, O Behrend, L Odoni, J Loubet

Nancy A. Burnham

Phase images acquired while intermittently contacting a sample surface with the tip of an atomic force microscope cantilever are not easy to relate to material properties. We have simulated dynamic force curves and compared simulated with experimental results. For some cantilever–sample combinations, the interaction remains a surface effect, whereas for others, the tip penetrates the sample significantly. Height artifacts in the “topography” images, and the role of the sample stiffness, work of adhesion, damping, and topography in the cantilever response manifest themselves to different extents depending on the indentation depth.

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Computational Study Of Molecular Hydrogen In Zeolite Na-A. I. Potential Energy Surfaces And Thermodynamic Separation Factors For Ortho And Para Hydrogen, Cherry-Rose K. Anderson , '95, D. F. Coker, J. Eckert, Amy Lisa Graves Oct 1999

Computational Study Of Molecular Hydrogen In Zeolite Na-A. I. Potential Energy Surfaces And Thermodynamic Separation Factors For Ortho And Para Hydrogen, Cherry-Rose K. Anderson , '95, D. F. Coker, J. Eckert, Amy Lisa Graves

Physics & Astronomy Faculty Works

We simulate H-2 adsorbed within zeolite Na-A. We use a block Lanczos procedure to generate the first several (9) rotational eigenstates of the molecule, which is modeled as a rigid, quantum rotor with an anisotropic polarizability and quadrupole moment. The rotor interacts with Na cations and O anions; interaction parameters are chosen semiempirically and the truncation of electrostatic fields is handled with a switching function. A Monte Carlo proceedure is used to sample a set of states based on the canonical distribution. Potential energy surfaces, favorable adsorbtion sites, and distributions of barriers to rotation are analyzed. Separation factors for ortho-parahydrogen …

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Inflation And Preheating In Nonoscillatory Models, Gary Felder, Lev Kofman, Andrei Linde Oct 1999

Inflation And Preheating In Nonoscillatory Models, Gary Felder, Lev Kofman, Andrei Linde

Physics: Faculty Publications

We study inflationary models in which the effective potential of the inflaton field does not have a minimum, but rather gradually decreases at large φ. In such models the inflaton field does not oscillate after inflation, and its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not apply. For a long time the only mechanism of reheating in such non-oscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems …

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Search For A Technicolor ΩT Particle In Events With A Photon And A B-Quark Jet At Fermilab, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Oct 1999

Search For A Technicolor ΩT Particle In Events With A Photon And A B-Quark Jet At Fermilab, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

If the technicolor ωT particle exists, a likely decay mode is ωT→ γπT , followed by πT → bb̅, yielding the signature γbb̅. We have searched 85 pb-1 of data collected by the CDF experiment at the Fermilab Tevatron for events with a photon and two jets, where one of the jets must contain a secondary vertex implying the presence of a b quark. We find no excess of events above standard model expectations. We express the result as an exclusion region in the MωT -MπT …

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Chiral Lagrangian Treatment Of Pi Eta Scattering, Joseph Schechter, Deirdre Black, Amir H. Fariborz Oct 1999

Chiral Lagrangian Treatment Of Pi Eta Scattering, Joseph Schechter, Deirdre Black, Amir H. Fariborz

Physics - All Scholarship

We study pi eta scattering in a model which starts from the tree diagrams of a non-linear chiral Lagrangian including appropriate resonances. Previously, models of this type were applied to pi pi and pi K scattering and were seen to require the existence of light scalar sigma(560) and kappa(900) mesons and to be consistent with the f0(980). The present calculation extends this to include the a0(980), thereby completing a possible nonet of light scalars, all ``seen'' in the same manner. We note that, at the initial level, the pi eta channel is considerably cleaner than the pi pi and pi …

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Differential Photometry Of Suspected Cataclysmic Variables, N. Bennert, I. König, E. Manthey, H. Bleul, K. Fieger, M. Hess, A. Hovest, W. Hovest, T. Jürges, J. Kleimann, C. Kriegeskorte, E. Krusch, D. Münstermann, D. Reymann, K. Rösler, M. Nielbock, M. Pohlen, L. Schmidtobreick, C. Tappert, R. Vanscheidt Oct 1999

Differential Photometry Of Suspected Cataclysmic Variables, N. Bennert, I. König, E. Manthey, H. Bleul, K. Fieger, M. Hess, A. Hovest, W. Hovest, T. Jürges, J. Kleimann, C. Kriegeskorte, E. Krusch, D. Münstermann, D. Reymann, K. Rösler, M. Nielbock, M. Pohlen, L. Schmidtobreick, C. Tappert, R. Vanscheidt

Physics

No abstract provided.

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Transparent Stacked Organic Light Emitting Devices. I. Design Principles And Transparent Compound Electrodes, G. Gu, G. Parthasarathy, P. E. Burrows, Peifang Tian, I. G. Hill, A. Kahn, S. R. Forrest Oct 1999

Transparent Stacked Organic Light Emitting Devices. I. Design Principles And Transparent Compound Electrodes, G. Gu, G. Parthasarathy, P. E. Burrows, Peifang Tian, I. G. Hill, A. Kahn, S. R. Forrest

Peifang Tian

Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is a means for achieving full-color flat panel displays. The physics, performance, and applications of stacked OLEDs (SOLEDs) are discussed in this and the following paper (Papers I and II, respectively). In Paper I, we analyze optical microcavity effects that can distort the emission colors of SOLEDs if not properly controlled, and describe design principles to minimize these parasitic effects. We also describe the fabrication and operating characteristics of transparent contacts that are an integral part of SOLEDs. We demonstrate that both metal-containing and metal-free transparent …

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Transparent Stacked Organic Light Emitting Devices. Ii. Device Performance And Applications To Displays, G. Gu, G. Parthasarathy, Peifang Tian Oct 1999

Transparent Stacked Organic Light Emitting Devices. Ii. Device Performance And Applications To Displays, G. Gu, G. Parthasarathy, Peifang Tian

Peifang Tian

Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, …

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State-To-State Rotational Excitation Of Co By H2 Near 1000 Cm-1 Collision Energy, Stiliana Antonova, Antonis P. Tsakotellis, Ao Lin, George C. Mcbane Oct 1999

State-To-State Rotational Excitation Of Co By H2 Near 1000 Cm-1 Collision Energy, Stiliana Antonova, Antonis P. Tsakotellis, Ao Lin, George C. Mcbane

Peer Reviewed Articles

Relative state-to-state rotationally inelastic cross sections for excitation of carbon monoxide by hydrogen were measured in a crossed molecular beam experiment at collision energies 795, 860, and 991 cm-1. The results are compared to predictions of a recent ab initio potential energy surface [J. Chem. Phys. 108, 3554 (1998)]. The agreement is very good. A comparison with older data on thermally averaged total depopulation cross sections [Chem. Phys. 53, 165 (1980)] indicates that the absolute magnitudes of the cross sections predicted by the surface are too high. The CO excitation is dominated by collisions that are …

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Phonon And Elastic Instabilities In Moc And Mon, Gus L. W. Hart, Barry M. Klein Oct 1999

Phonon And Elastic Instabilities In Moc And Mon, Gus L. W. Hart, Barry M. Klein

Faculty Publications

We present several results related to the instability of MoC and MoN in the B1 (sodium chloride) structure. These compounds were proposed as potential superconductors with moderately high transition temperatures. We show that the elastic instability in B1-structure MoN, demonstrated several years ago, persists at elevated pressures, thus offering little hope of stabilizing this material without chemical doping. For MoC, another material for which stoichiometric fabrication in the B1 structure has not proven possible, we find that all of the cubic elastic constants are positive, indicating elastic stability. Instead, we find X-point phonon instabilities in MoC (and in MoN as …

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Bacterial Magnetosomes: Microbiology, Biomineralization And Biotechnological Applications, Dirk Schlϋer, Richard B. Frankel Oct 1999

Bacterial Magnetosomes: Microbiology, Biomineralization And Biotechnological Applications, Dirk Schlϋer, Richard B. Frankel

Physics

Magnetotactic bacteria orient and migrate along geomagnetic field lines. This ability is based on intracellular magnetic structures, the magnetosomes, which comprise nanometer-sized, membrane-bound crystals of the magnetic iron minerals magnetite (Fe3O4) or greigite (Fe3O4). Magnetosome formation is achieved by a mineralization process with biological control over the accumulation of iron and the deposition of the mineral particle with specific size and orientation within a membrane vesicle at specific locations in the cell. This review focuses on the current knowledge about magnetotactic bacteria and will outline aspects of the physiology and molecular biology …

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