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Full-Text Articles in Physics

Observation Of The Plasma Channel Dynamics And Coulomb Explosion In The Interaction Of A High-Intensity Laser Pulse With A He Gas Jet, G.S. Sarkisov, V. Yu. Bychenkov, V.T. Tikhonchuk, Anatoly Maksimchuk, Shouyuan Chen, R. Wagner, G. Mourou, Donald P. Umstadter Dec 1997

Observation Of The Plasma Channel Dynamics And Coulomb Explosion In The Interaction Of A High-Intensity Laser Pulse With A He Gas Jet, G.S. Sarkisov, V. Yu. Bychenkov, V.T. Tikhonchuk, Anatoly Maksimchuk, Shouyuan Chen, R. Wagner, G. Mourou, Donald P. Umstadter

Donald Umstadter Publications

We report the first interferometric observations of the dynamics of electron–ion cavitation of relativistically self-focused intense 4 TW, 400 fs laser pulse in a He gas jet. The electron density in a channel 1 mm long and 30 mm in diameter drops by a factor of approximately 10 from the maximum value of ~8x1019 cm23. A high radial velocity of the plasma expansion, ~3.8x108 cm/s, corresponding to an ion energy of about 300 keV, is observed. The total energy of fast ions is estimated to be 6% of the laser pulse energy. The high-velocity ...


Nanoscale Imaging Of Domain Dynamics And Retention In Ferroelectric Thin Films, Alexei Gruverman, H. Tokumoto, A. S. Prakash, S. Aggarwal, B. Yang, M. Wuttig, R. Ramesh, O. Auciello, T. Venkatesan Dec 1997

Nanoscale Imaging Of Domain Dynamics And Retention In Ferroelectric Thin Films, Alexei Gruverman, H. Tokumoto, A. S. Prakash, S. Aggarwal, B. Yang, M. Wuttig, R. Ramesh, O. Auciello, T. Venkatesan

Alexei Gruverman Publications

We report results on the direct observation of the microscopic origins of backswitching in ferroelectric thin films. The piezoelectric response generated in the film by a biased atomic force microscope tip was used to obtain static and dynamic piezoelectric images of individual grains in a polycrystalline material. We demonstrate that polarization reversal occurs under no external field (i.e., loss of remanent polarization) via a dispersive continuous-time random walk process, identified by a stretched exponential decay of the remanent polarization.


Measurement Of The Decay Amplitudes And Branching Fractions Of BJK* And BJK Decays, C.P. Jessop, Kenneth A. Bloom, Cleo Collaboration Dec 1997

Measurement Of The Decay Amplitudes And Branching Fractions Of B → J/Ψ K* And B → J/Ψ K Decays, C.P. Jessop, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using data taken with the CLEO II detector at the Cornell Electron Storage Ring, we present the first full angular analysis in the color-suppressed modes B0JK *0and B0JK*+. This leads to a complete determination of the decay amplitudes of these modes including the longitudinal polarization ΓL/Γ= 0.52 ± 0.07 ± 0.04 and the P wave component │P2= 0.16 ± 0.08 ± 0.04. In addition, we update the branching fractions for BJK and BJK*.


Stern-Gerlach Effect For Electron Beams, Herman Batelaan, Timothy J. Gay, J. J. Schwendiman Dec 1997

Stern-Gerlach Effect For Electron Beams, Herman Batelaan, Timothy J. Gay, J. J. Schwendiman

Timothy J. Gay Publications

The conflict between Bohr’s assertion that the magnetic moment of the electron cannot be measured with experiments based on the concept of classical trajectories, and the measurement of the magnetic moment of electrons in a modified Penning trap by Dehmelt et al. has led us to reevaluate other implications of Bohr’s assertion. We show that, contrary to the analysis of Bohr and Pauli, the assumption of classical trajectories in a Stern-Gerlach–like device can result in a high degree of spin separation for an electron beam. This effect may persist within a fully quantum-mechanical analysis. The magnetic fields ...


Electron-Impact Total Ionization Cross Sections Of Ch And C2H2, Yong-Ki Kim, M. Asgar Ali, M. Eugene Rudd Dec 1997

Electron-Impact Total Ionization Cross Sections Of Ch And C2H2, Yong-Ki Kim, M. Asgar Ali, M. Eugene Rudd

M. Eugene Rudd Publications

Electron-impact total ionization cross sections for the CH radical and C2H2 (acetylene) have been calculated using the Binary-Encounter-Bethe (BEB) model. The BEB model combines the Mott cross section and the asymptotic form of the Bethe theory, and has been shown to generate reliable ionization cross sections for a large variety of molecules. The BEB cross sections for CH and C2H2 are in good agreement with the available experimental data from ionization thresholds to hundreds of eV in incident energies.


Shielding Strategies For Human Space Exploration Chapter 9: Hze Interactions In Biological Materials, M. Eugene Rudd Dec 1997

Shielding Strategies For Human Space Exploration Chapter 9: Hze Interactions In Biological Materials, M. Eugene Rudd

M. Eugene Rudd Publications

It is shown that most of the energy deposited by fast charged particles traversing matter occurs through ionization, i.e., the ejection of electrons during the atomic collision. The important mechanisms of ionization are identified and several methods of calculating the relevant differential and total cross sections are described. These include both classical and quantum theoretical methods and two semi-empirical models. The calculational methods were intended only for light, bare-ion projectiles, and care must be exercised in extending them to heavy, dressed projectiles.


Low-Field Hole Mobility In A Photorefractive Polymer, Arosha Goonesekera, Stephen Ducharme, James M. Takacs, Lei Zhang Nov 1997

Low-Field Hole Mobility In A Photorefractive Polymer, Arosha Goonesekera, Stephen Ducharme, James M. Takacs, Lei Zhang

Stephen Ducharme Publications

We present the time-of-flight measurements of hole mobility in a photorefractive polymer composite as a function of temperature and applied electric field. The analysis shows that the temperature dependence of the low-field mobility is in apparent disagreement with the predictions of the Gaussian disorder model and also with polaron models.


Study Of The Decay Τ-→2Π-Π+0ΝΤ, S. Anderson, Kenneth A. Bloom, Cleo Collaboration Nov 1997

Study Of The Decay Τ-→2Π-Π+3Π0ΝΤ, S. Anderson, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

The decay τ-→2π-π+0ντ has been studied with the CLEO II detector at the Cornell Electron Storage Ring. The branching fraction is measured to be (2.85 ± 0.56 ± 0.51) X 10-4. The result is in good agreement with the isospin expectation but somewhat below the conserved-vectorcurrent prediction. We have searched for resonance substructure in the decay. Within the statistical precision, the decay is saturated by the channels τ-→π-0ωντ, 2π-π+ωντ, and π-0ωντ This is the first observation of this ω decay ...


Limit On The Two-Photon Production Of The Glueball Candidate FJ(2220) At The Cornell Electron Storage Ring, R. Godang, Kenneth A. Bloom, Cleo Collaboration Nov 1997

Limit On The Two-Photon Production Of The Glueball Candidate FJ(2220) At The Cornell Electron Storage Ring, R. Godang, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We use the CLEO detector at the Cornell e+e- storage ring, CESR, to search for the two-photon production of the glueball candidate fJ (2220) in its decay to KsKs. We present a restrictive upper limit on the product of the two-photon partial width and the KsKs branching fraction, (Γγγ BKsKs)fJ(2220). We use this limit to calculate a lower limit on the stickiness, which is a measure of the two-gluon coupling relative to the two-photon coupling. This limit on stickiness indicates that the fJ ...


New Upper Limit On The Decay Η→E+E-, T.E. Browder, Kenneth A. Bloom, Cleo Collaboration Nov 1997

New Upper Limit On The Decay Η→E+E-, T.E. Browder, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for the rare decay of the η meson η→e+e- using the CLEO II detector. The η’s were produced in e+e- collisions with 10 GeV center-of-mass energy at the Cornell Electron Storage Ring (CESR). We find with 90% confidence the upper limit on the branching fraction B (η→e+e-)<7.7×10-5. The application of conventional elementary particle theory to this decay predicts a branching fraction of about 10-9.


Dispersion Coefficients For Highly Excited Molecular States Of K2, Mircea Marinescu, Anthony F. Starace Nov 1997

Dispersion Coefficients For Highly Excited Molecular States Of K2, Mircea Marinescu, Anthony F. Starace

Anthony F. Starace Publications

We report results of theoretical calculations for the dispersion coefficients associated with the long-range interaction of two 39K atoms in the states 39K(4s)- 39K(5d,6d,7s). These results have been found by Wang et al. [Phys. Rev. Lett. 78, 4173 (1997)] to be in a good agreement with their measurements.


Search For The Decay Τ-→4Π-+0Τ, K.W. Edwards, Kenneth A. Bloom, Cleo Collaboration Nov 1997

Search For The Decay Τ-→4Π-3Π+(Π0)ΝΤ, K.W. Edwards, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for the decay of the τ lepton into seven charged particles and zero or one π0. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.61 fb-. No evidence for a signal is found. Assuming all the charged particles are pions, we set an upper limit on the branching fraction B-→4π-+0) ντ) < 2.4X10-6 at the 90% confidence level. This limit represents a significant improvement over the previous limit.


Determination Of The Michel Parameters And The Τ Neutrino Helicity In Τ Decay, J.P. Alexander, Kenneth A. Bloom, Cleo Collaboration Nov 1997

Determination Of The Michel Parameters And The Τ Neutrino Helicity In Τ Decay, J.P. Alexander, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using the CLEO II detector at the Cornell Electron Storage Ring operated at √s =10.6 GeV, we have determined the Michel parameters ρ, ξ, and δ in τ±→l±νν̅ decay as well as the τ neutrino helicity parameter h in τ±→π±π0ν decay. From a data sample of 3.02×106 produced τ pairs we analyzed events of the topologies e+e-→τ+τ-→(l±νν̅)(π±π0ν) and e+e-→τ+τ-→(π±π0ν̅)(π±π0ν). We obtain ρ=0.747ρ=0.747±0.010±0.006 ...


Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xi. Intensive Monitoring Of The Ultraviolet Spectrum Of Ngc 7469, I. Wanders, Bradley M. Peterson, D. Alloin, T.R. Ayres, J. Clavel, D. Michael Crenshaw, K. Horne, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Paul T. O'Brien, G.A. Reichert, P.M. Rodriguez-Pascual, W. Wamsteker, T. Alexander, K. S.J. Anderson, E. Benitez, N.G. Bochkarev, A.N. Burenkov, F.-Z. Cheng, S.J. Collier, A. Comastri, M. Dietrich, D. Dultzin-Hacyan, B.R. Espey, A. V. Filippenko, C. Martin Gaskell, I.M. George, M.R. Goad, L.C. Ho, Shai Kaspi, W. Kollatschny, Kirk T. Korista, Ari Laor, G.M. Macalpine, M. Mignoli, S.L. Morris, K. Nandra, S. Penton, Richard William Pogge, R.L. Ptak, J.M. Rodriguez-Espinoza, M. Santos-Lleo, A.I. Shapovalova, J.M. Shull, Stephanie A. Snedden, L.S. Sparke, G.M. Stirpe, W.-H. Sun, T.J. Turner, M.-H. Ulrich, T.-G. Wang, C. Wei, W.F. Welsh, S.-J. Xue, Z.-L. Zhou Nov 1997

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xi. Intensive Monitoring Of The Ultraviolet Spectrum Of Ngc 7469, I. Wanders, Bradley M. Peterson, D. Alloin, T.R. Ayres, J. Clavel, D. Michael Crenshaw, K. Horne, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Paul T. O'Brien, G.A. Reichert, P.M. Rodriguez-Pascual, W. Wamsteker, T. Alexander, K. S.J. Anderson, E. Benitez, N.G. Bochkarev, A.N. Burenkov, F.-Z. Cheng, S.J. Collier, A. Comastri, M. Dietrich, D. Dultzin-Hacyan, B.R. Espey, A. V. Filippenko, C. Martin Gaskell, I.M. George, M.R. Goad, L.C. Ho, Shai Kaspi, W. Kollatschny, Kirk T. Korista, Ari Laor, G.M. Macalpine, M. Mignoli, S.L. Morris, K. Nandra, S. Penton, Richard William Pogge, R.L. Ptak, J.M. Rodriguez-Espinoza, M. Santos-Lleo, A.I. Shapovalova, J.M. Shull, Stephanie A. Snedden, L.S. Sparke, G.M. Stirpe, W.-H. Sun, T.J. Turner, M.-H. Ulrich, T.-G. Wang, C. Wei, W.F. Welsh, S.-J. Xue, Z.-L. Zhou

Martin Gaskell Publications

From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 2.d3-3.d1 for Lyα, 2.d7 for C IV λ1549, 1.d9-2.d4 for N IV λ 1240, 1.d7-1.d ...


Controlled Formation Of Weakly Bound Atomic Negative Ions By Electron Transfer From State-Selected Rydberg Atoms, M. Reicherts, T. Roth, A. Gopalan, M.-W. Ruf, Harmut Hotop, C. Desfrançuois, Ilya I. Fabrikant Oct 1997

Controlled Formation Of Weakly Bound Atomic Negative Ions By Electron Transfer From State-Selected Rydberg Atoms, M. Reicherts, T. Roth, A. Gopalan, M.-W. Ruf, Harmut Hotop, C. Desfrançuois, Ilya I. Fabrikant

Faculty Publications, Department of Physics and Astronomy

Using crossed atomic beams and mass spectrometric ion detection we have studied the formation of negative Ca ions in slow collisions between laser-excited state-selected Ne**(ns; J = 2) and Ne** (nd; J = 4) Rydberg atoms and ground state Ca atoms. The rate coefficients exhibit resonant behavior with maxima at an effective principal quantum number n* of about 11.5 and an estimated peak value of about 10-8 cm3 s-1. Two different theoretical calculations, based on a curve-crossing model and on a modified adiabatic theory, respectively, yield n*-dependences of the rate coefficients in good agreement with the ...


Observation Of Laser Satellites In A Plasma Produced By A Femtosecond Laser Pulse, S.A. Pikuz, Anatoly Maksimchuk, Donald Umstadter, M. Nantel, I. Yu. Skobelev, A. Ya. Faenov, A. Osterheld Oct 1997

Observation Of Laser Satellites In A Plasma Produced By A Femtosecond Laser Pulse, S.A. Pikuz, Anatoly Maksimchuk, Donald Umstadter, M. Nantel, I. Yu. Skobelev, A. Ya. Faenov, A. Osterheld

Donald Umstadter Publications

Laser satellites are detected in the emission spectra of magnesium and aluminum plasmas produced by femtosecond laser pulses. This is made possible by the realization of picosecond time resolution in a highluminosity x-ray spectrograph with a spherically curved mica crystal. The temporal characteristics of these newly recorded spectral lines show unequivocally that they are formed as a result of nonlinear processes.


Inclusive Decays BDx And BD*X, L. Gibbons, Kenneth A. Bloom, Cleo Collaboration Oct 1997

Inclusive Decays B→Dx And B→D*X, L. Gibbons, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We report new measurements of the differential and total branching ratios for inclusive B decay to D0, D+, and D*+ and the first measurement of the same quantities for inclusive B decay to D*0. Here B is the mixture of Bd and Bu from Υ(4S) decay. Furthermore, since more than one charm particle (or antiparticle) of the same kind can be produced in B decay, here ‘‘inclusive B branching ratio’’ is used to mean the average number of charm particles and their antiparticles of a certain species produced in B decay. We obtain the ...


First Observation Of Τ→3ΠηνΤ And Τ→ F1ΠνΤ Decays, T. Bergfeld, Kenneth A. Bloom, Cleo Collaboration Sep 1997

First Observation Of Τ→3ΠηνΤ And Τ→ F1ΠνΤ Decays, T. Bergfeld, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have observed new channels for τ decays with an η in the final state. We study 3-prong tau decays, using the η →γγ and η → 3π 0 decay modes and 1-prong decays with two π 0’s using the η →γγ channel. The measured branching fractions are B- → π-π-π+ηντ) = (3. -0.5+0.6 ± 0.6) X 10-4 and B- → π-0ηντ) = (1.4 ± 0.6 ± 0.3) X 10-4. We observe clear evidence for f1 → ηππ substructure and measure B- → f1 π-ντ ...


Electron-Collision-Induced Alignment Of Rare Gases Near Threshold, V. Zeman, K. Bartschat, Timothy J. Gay, K. W. Trantham Sep 1997

Electron-Collision-Induced Alignment Of Rare Gases Near Threshold, V. Zeman, K. Bartschat, Timothy J. Gay, K. W. Trantham

Timothy J. Gay Publications

Results of a semirelativistic R-matrix calculation are compared with experimental values for light polarizations and alignment parameters of the second excited-state manifolds of neon and krypton following electron impact excitation. The calculations focus on the near-threshold regime, where negative-ion resonances have a significant effect on the atomic alignment. A grouping of the alignment values according to the electronic angular momentum J of the excited state is observed and qualitatively explained by angular momentum coupling considerations.


Remanence Enhancement And Exchange Coupling In Prco/Co Films, J. Ping Liu, Yi Liu, Z.S. Shan, David J. Sellmyer Sep 1997

Remanence Enhancement And Exchange Coupling In Prco/Co Films, J. Ping Liu, Yi Liu, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

PrCo/Co multilayer thin films have been prepared by sputtering. After heat treatment, high coercivity is developed and the remanence is enhanced for the insertion of the CO layers and the exchange coupling between the hard phase and the soft phase, which leads to high energy products of the composite magnets. The nanostructure of the films has been studied by TEM. It is found that the grain size of the films with high energy products is in the range from 10 to 25 nanometers.


“Atomic Processes In High Energy Density Plasmas," Summaries Of Fy 1997 Research In The Chemical Sciences, Donald P. Umstadter Sep 1997

“Atomic Processes In High Energy Density Plasmas," Summaries Of Fy 1997 Research In The Chemical Sciences, Donald P. Umstadter

Donald Umstadter Publications

Several important plasma atomic processes are studied in a controlled manner. These studies are enabled by the recent invention of ultrashortpulse- duration lasers, which produce plasmas with independently controllable parameters.


High Coercivity Smfealc Thin Films Fabricated By Multilayer Sputtering, M.L. Yan, Z.S. Shan, Yi Liu, David J. Sellmyer Sep 1997

High Coercivity Smfealc Thin Films Fabricated By Multilayer Sputtering, M.L. Yan, Z.S. Shan, Yi Liu, David J. Sellmyer

David Sellmyer Publications

Multilayer sputtering of SmFe/C(Al) plus appropriate thermal processing has been used to fabricate SmFeC thin films with A1 substitution for Fe. It was found that the SmFeAlC thin films exhibited exceptionally high Coercivities. A coercivity of 28 kOe was realized for the thin film with structure of Ta(l000 Å)/|SmFe(40Å)/ C(Al)(5Å)]x50/Ta(200Å) with subsequent annealing at 650°C.


Magnetic And Structural Properties Of Sm2Fe10Co7/MXCY Thin Films, I.A. Al-Omari, N. J. Cunningham, David J. Sellmyer Sep 1997

Magnetic And Structural Properties Of Sm2Fe10Co7/MXCY Thin Films, I.A. Al-Omari, N. J. Cunningham, David J. Sellmyer

David Sellmyer Publications

The structural and magnetic properties of Sm2Fe10Co7/MxCy (M=A1 and Si; x≥0 and y≥0) multilayer films with Ta underlayers and overlayers before and after annealing at 700 °C for 5-12 min have been fabricated and studied. Structural studies show evidence of layer diffusion upon annealing. X-ray diffraction shows that the samples after annealing consist of a soft phase, α -Fe, and a hard phase with the 2-17-type structure. The samples studied have in-plane anisotropy with single hysteresis loops indicating that the two phases are strongly exchange coupled. After annealing ...


A Football Chase On Video, Norman F. Derby, Robert Fuller, Thomas A. Summers Sep 1997

A Football Chase On Video, Norman F. Derby, Robert Fuller, Thomas A. Summers

Robert G. Fuller Publications and Presentations

At some universities, football examples are used to motivate students in physics courses to study the law of kinematics and collisions. (In fact, it has been rumored that the number of such examples is inversely related the national ranking of the local football team.) In addition, pursuit-and-evasion strategies are often introduced in beginning calculus courses as a device for teaching mathematical modeling and problem solving. Some recent papers describe theoretical strategies for pursuit-and-evasion that are appropriate for a one-on-one situation in a football game. But what do players actually do in a real football game? We decided to look into ...


Absolute Triply Differential (E,2E) Cross Section Measurements For H With Comparison To Theory, J. Roder, H. Erhardt, Cheng Pan, Anthony F. Starace, Igor Bray, Dmitry V. Fursa Sep 1997

Absolute Triply Differential (E,2E) Cross Section Measurements For H With Comparison To Theory, J. Roder, H. Erhardt, Cheng Pan, Anthony F. Starace, Igor Bray, Dmitry V. Fursa

Anthony F. Starace Publications

Absolute triply differential (e,2e) cross section measurements are presented for H (for incident energies, E0, of 15.6 and 17.6 eV) for equal energy sharing and the θ12 = π configuration. Results of distorted partial wave calculations agree with the measurements; those of convergent close coupling calculations agree with the relative angular distributions, but are lower than experiment by factors of from 2 to 7. Relative experimental results for H for E0 = 14.6 eV show a qualitative change in shape, which agrees with theory. Implications of the absolute experimental results for the range of ...


High Temperature Superconducting Josephson Junctions In A Stacked Bicrystal Geometry, H.Q. Li, R.H. Ono, L.R. Vale, D.A. Rudman, Sy_Hwang Liou Aug 1997

High Temperature Superconducting Josephson Junctions In A Stacked Bicrystal Geometry, H.Q. Li, R.H. Ono, L.R. Vale, D.A. Rudman, Sy_Hwang Liou

Si-Hwang Liou Publications

Bicrystal grain boundary Josephson junctions were fabricated in a stack of two layers of YBa2Cu3Oχ separated by epitaxial SrTiO3. Weak link behavior was observed in the bridges formed in both layers that had similar shunted-junction characteristics but significantly different critical currents. Characteristic voltages up to 1.9 mV were measured at 4.5 K. The resonant structure was seen in the current–voltage characteristics of the upper-layer junctions, and interactions between junctions in the two layers were evident.


Observation Of The Decay DS+ → Ωπ+, R. Balest, Kenneth A. Bloom, Cleo Collaboration Aug 1997

Observation Of The Decay DS+ → Ωπ+, R. Balest, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using e+e- annihilation data collected by the CLEO II detector at CESR, we have observed the decay Ds+ → ωπ+. This final state may be produced through the annihilation decay of the i>Ds+, or through final state interactions. We find a branching ratio of γ(Ds+ → ωπ+)/γ(Ds+ →ηπ+) = 0.16±0.04±0.03, where the first error is statistical and the second is systematic.


Forming B1-XCX Semiconductor Layers By Chemical Vapor Deposition, Peter A. Dowben Aug 1997

Forming B1-XCX Semiconductor Layers By Chemical Vapor Deposition, Peter A. Dowben

Peter Dowben Publications

Active semiconductor devices including heterojunction diodes and thin film transistors are formed by PECVD deposition of a boron carbide thin film on an N-type substrate. The boron to carbon ratio of the deposited material is controlled so that the film has a suitable band gap energy. Boron carbides such as B4.7C, B7.2C and B19C have suitable band gap energies between 0.8 and 1.7 eV. The stoichiometry of the film can be selected by varying the partial pressure of precursor gases, such as nido pentaborane and methane. The precursor gas or ...


Search For Neutrinoless Τ Decays Involving Π0 Or Η Mesons, G. Bonvicini, Kenneth A. Bloom, Cleo Collaboration Aug 1997

Search For Neutrinoless Τ Decays Involving Π0 Or Η Mesons, G. Bonvicini, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for lepton flavor violating decays of the τ lepton using final states with an electron or a muon and one or two π0 or η mesons but no neutrinos. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.68 fb-1. No evidence for signals was found, resulting in much improved limits on the branching fractions for the one-meson modes and the first upper limits for the two-meson modes.


Search For The Decays B0D (*)+D (*)-, D.M. Asner, Kenneth A. Bloom, Cleo Collaboration Aug 1997

Search For The Decays B0 → D (*)+D (*)-, D.M. Asner, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using the CLEO-II data set we have searched for the decays B0D(*)+D(*)-. We observe one candidate signal event for the decay B0D*+D*- with an expected background of 0.022 ± 0.011 events. This yield corresponds to a branching fraction of B(B0D*+D*-) = [5.317-3.7+7.1(stat) ± 1.0(syst)] x 10-4 and an upper limit of B(B0D*+D*-) < 2.2 X 10-3 at the 90% C.L. We see no significant excess of signal above the expected background level in the other modes, and we calculate the ...