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Full-Text Articles in Physical Sciences and Mathematics

Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich Dec 2005

Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich

Physics Faculty Research & Creative Works

We studied mutual ionization in 200-keV H-+He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. Comparison of the data to our calculations, based on various theoretical models, show that mutual ionization proceeds predominantly through the interaction between both electrons. The post-collision interaction between the outgoing ejected electrons as well as higher order processes involving the interaction between the core of both collision partners are also important.


Nonrelativistic Qed Approach To The Lamb Shift, Ulrich D. Jentschura, Andrzej Czarnecki, Krzysztof Pachucki Dec 2005

Nonrelativistic Qed Approach To The Lamb Shift, Ulrich D. Jentschura, Andrzej Czarnecki, Krzysztof Pachucki

Physics Faculty Research & Creative Works

We calculate the one- and two-loop corrections of order α(Zα)6 and α2(Zα)6, respectively, to the Lamb shift in hydrogenlike systems using the formalism of nonrelativistic quantum electrodynamics. We obtain general results valid for all hydrogenic states with nonvanishing orbital angular momentum and for the normalized difference of S states. These results involve the expectation value of local effective operators and relativistic corrections to Bethe logarithms. The one-loop correction is in agreement with previous calculations for the particular cases of S, P, and D states. The two-loop correction in the order α2(Zα)6 includes ...


Extreme Sensitivity Of Differential Momentum Transfer Cross Sections To Target Atom Initial Conditions, Ronald E. Olson, J. Fiol Dec 2005

Extreme Sensitivity Of Differential Momentum Transfer Cross Sections To Target Atom Initial Conditions, Ronald E. Olson, J. Fiol

Physics Faculty Research & Creative Works

Heavy-particle cross sections differential in the momentum transferred to the target are investigated using the classical trajectory Monte Carlo method. with the 3.6  MeV/u Au53++He system as a test case, it is shown that these cross sections are extremely sensitive to the initial target temperature. In particular, when thermal motion is varied for one of the target's initial momentum components between 0 and 25 K the absolute cross sections vary by orders of magnitude and, in addition, their relative shapes undergo major changes. We find that by setting one of the target's transverse momenta to ...


Percolation Quantum Phase Transitions In Diluted Magnets, Thomas Vojta, Jörg Schmalian Nov 2005

Percolation Quantum Phase Transitions In Diluted Magnets, Thomas Vojta, Jörg Schmalian

Physics Faculty Research & Creative Works

We show that the interplay of geometric criticality and quantum fluctuations leads to a novel universality class for the percolation quantum phase transition in diluted magnets. All critical exponents involving dynamical correlations are different from the classical percolation values, but in two dimensions they can nonetheless be determined exactly. We develop a complete scaling theory of this transition, and we relate it to recent experiments in La2Cu1-p(Zn,Mg)pO4. Our results are also relevant for disordered interacting boson systems.


Erratum: Publisher's Note: Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States (Physical Review Letters (2005) 95 (180404)), Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki Nov 2005

Erratum: Publisher's Note: Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States (Physical Review Letters (2005) 95 (180404)), Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki

Physics Faculty Research & Creative Works

No abstract provided.


Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel Nov 2005

Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We investigate quantum electrodynamic effects under the influence of an external, time-dependent electromagnetic field, which mediates dynamic modifications of the radiative corrections. Specifically, we consider the quantum electrodynamic vacuum-polarization tensor under the influence of two external background fields: a strong laser field and a nuclear Coulomb field. We calculate the charge and current densities induced by a nuclear Coulomb field in the presence of a laser field. We find the corresponding induced scalar and vector potentials. The induced potential, in first-order perturbation theory, leads to a correction to atomic energy levels. The external laser field breaks the rotational symmetry of ...


Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States, Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki Oct 2005

Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States, Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki

Physics Faculty Research & Creative Works

General expressions for quantum electrodynamic corrections to the one-loop self-energy [of order α(Zα)6] and for the two-loop Lamb shift [of order α2(Zα)6] are derived. The latter includes all diagrams with closed fermion loops. The general results are valid for arbitrary excited non-S hydrogenic states and for the normalized Lamb shift difference of S states, defined as Δn=n3ΔE(nS)-ΔE(1S). We present numerical results for one-loop and two-loop corrections for excited S, P, and D states. In particular, the normalized Lamb shift difference of S states is calculated with an uncertainty ...


Sub-Femtosecond Correlated Dynamics Explored With Antiprotons, J. Ullrich, A. Dorn, Daniel Fischer, R. Moshammer, B. Najjari, Michael Schulz, A. B. Voitkiv, C. P. Welsch Oct 2005

Sub-Femtosecond Correlated Dynamics Explored With Antiprotons, J. Ullrich, A. Dorn, Daniel Fischer, R. Moshammer, B. Najjari, Michael Schulz, A. B. Voitkiv, C. P. Welsch

Physics Faculty Research & Creative Works

Ionizing collisions of antiprotons with atoms or molecules at energies between a few keV up to about one MeV provide a unique tool to explore correlated dynamics of electrons at large perturbations on a time scale between several femtoseconds (1 fs = 10-15 s) down to some tens of attoseconds (1 as = 10-18 s). Exploiting and developing many-particle imaging methods - Reaction-Microscopes - integrated into a novel ultra-low energy storage ring (USR) for slow antiprotons will enable to access for the first time fully differential cross sections for single and multiple ionization in such collisions. Moreover, the formation of antiprotonic atoms ...


Precise Calculation Of Transition Frequencies Of Hydrogen And Deuterium Based On A Least-Squares Analysis, Ulrich D. Jentschura, Svetlana A. Kotochigova, Eric Olivier Le Bigot, Peter J. Mohr, Barry N. Taylor Oct 2005

Precise Calculation Of Transition Frequencies Of Hydrogen And Deuterium Based On A Least-Squares Analysis, Ulrich D. Jentschura, Svetlana A. Kotochigova, Eric Olivier Le Bigot, Peter J. Mohr, Barry N. Taylor

Physics Faculty Research & Creative Works

We combine a limited number of accurately measured transition frequencies in hydrogen and deuterium, recent quantum electrodynamics (QED) calculations, and, as an essential additional ingredient, a generalized least-squares analysis, to obtain precise and optimal predictions for hydrogen and deuterium transition frequencies. Some of the predicted transition frequencies have relative uncertainties more than an order of magnitude smaller than that of the g factor of the electron, which was previously the most accurate prediction of QED.


Renormalization-Group Analysis Of Layered Sine-Gordon Type Models, I. Nandori, Sandor Alex Nagy, Kornel Sailer, Ulrich D. Jentschura Oct 2005

Renormalization-Group Analysis Of Layered Sine-Gordon Type Models, I. Nandori, Sandor Alex Nagy, Kornel Sailer, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

We analyze the phase structure and the renormalization group (RG) flow of the generalized sine-Gordon models with nonvanishing mass terms, using the Wegner-Houghton RG method in the local potential approximation. Particular emphasis is laid upon the layered sine-Gordon (LSG) model, which is the bosonized version of the multi-flavour Schwinger model and approaches the sum of two "normal", massless sine-Gordon (SG) models in the limit of a vanishing interlayer coupling J. Another model of interest is the massive sine-Gordon (MSG) model. The leading-order approximation to the UV (ultraviolet) RG flow predicts two phases for the LSG as well as for the ...


Relativistic Electron Correlation, Quantum Electrodynamics, And The Lifetime Of The 1s²2s²2p²PO3/2 Level In Boronlike Argon, Alain Lapierre, Ulrich D. Jentschura, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Daniel A. Fischer, Antonio J. Gonzalez, Zoltan Harman, Walter Johnson, Christoph H. Keitel, Vladimir Sergeyevich Mironov, C. J. Osborne, Guenther Sikler, R. Soria Orts, Vladimir M. Shabaev, Hiroyuki Tawara, I. I. Tupitsyn, Joachim Hermann Ullrich, Andrey V. Volotka Oct 2005

Relativistic Electron Correlation, Quantum Electrodynamics, And The Lifetime Of The 1s²2s²2p²PO3/2 Level In Boronlike Argon, Alain Lapierre, Ulrich D. Jentschura, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Daniel A. Fischer, Antonio J. Gonzalez, Zoltan Harman, Walter Johnson, Christoph H. Keitel, Vladimir Sergeyevich Mironov, C. J. Osborne, Guenther Sikler, R. Soria Orts, Vladimir M. Shabaev, Hiroyuki Tawara, I. I. Tupitsyn, Joachim Hermann Ullrich, Andrey V. Volotka

Physics Faculty Research & Creative Works

The lifetime of the Ar13+ 1s22s22p2Po3/2 metastable level was determined at the Heidelberg Electron Beam Ion Trap to be 9.573(4)(5)ms(stat)(syst). The accuracy level of one per thousand makes this measurement sensitive to quantum electrodynamic effects like the electron anomalous magnetic moment (EAMM) and to relativistic electron-electron correlation effects like the frequency-dependent Breit interaction. Theoretical predictions, adjusted for the EAMM, cluster about a lifetime that is approximately 3σ shorter than our experimental result.


Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin Sep 2005

Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin

Physics Faculty Research & Creative Works

We examined nearest-neighbor spacing (NNS) statistics in doubly excited states of helium near the double ionization threshold. Using the Brody parameter q to measure the NNS distribution between the regular Poisson distribution (q=0) and the chaotic Wigner distribution (q=1), we showed that for levels near the N=20 threshold of He⁺, or at about 0.13eV below the double ionization threshold, the NNS distribution has q=0.66. The result shows the slow approach of the NNS of helium energy levels towards the Wigner distribution vs the excitation energy. Using an s-wave model where the angular momentum of ...


Exchange Distortion And Postcollision Interaction For Intermediate-Energy Electron-Impact Ionization Of Argon, A. Prideaux, Don H. Madison, K. Bartschat Sep 2005

Exchange Distortion And Postcollision Interaction For Intermediate-Energy Electron-Impact Ionization Of Argon, A. Prideaux, Don H. Madison, K. Bartschat

Physics Faculty Research & Creative Works

Measurements of fully differential cross sections for electron impact ionization of atoms have been performed for over 30 years. However, only within the last ten years has agreement between experiment and theory been achieved for ionization of hydrogen and helium. For the heavier inert gases, reasonably good agreement between experiment and theory has only been achieved for high incident energies while serious discrepancies are common for intermediate and low incident energies. It is believed that a major source of the problem stems from an improper/inadequate treatment of exchange distortion (ED) and the effects of post-collision interactions (PCIs). In this ...


Channel Electron Multiplier And Channelplate Efficiencies For Detecting Positive Ions, M. Krems, J. Zirbel, Mark Allan Thomason, Robert D. Dubois Sep 2005

Channel Electron Multiplier And Channelplate Efficiencies For Detecting Positive Ions, M. Krems, J. Zirbel, Mark Allan Thomason, Robert D. Dubois

Physics Faculty Research & Creative Works

Absolute detection efficiencies for singly and multiply charged positive ions have been measured for a channelplate and for two different channel electron multipliers (CEM). The efficiencies were measured for impact energies between approximately 0.25 and 25 keV and for ion masses ranging from 14 to 132. The maximum efficiencies were found to be the same for all ions investigated and were approximately 58% for a channelplate and 89% for the CEMs. For a channelplate it is shown that the detection efficiencies for heavier ions scale to a single curve if plotted versus the impact energy divided by the square ...


Charge-Exchange-Produced K -Shell X-Ray Emission From Ar¹⁶⁺ In A Tokamak Plasma With Neutral-Beam Injection, P. Beiersdorfer, M. Bitter, M. Marion, Ronald E. Olson Sep 2005

Charge-Exchange-Produced K -Shell X-Ray Emission From Ar¹⁶⁺ In A Tokamak Plasma With Neutral-Beam Injection, P. Beiersdorfer, M. Bitter, M. Marion, Ronald E. Olson

Physics Faculty Research & Creative Works

High-resolution spectroscopy of a hot tokamak plasma seeded with argon ions and interacting with an energetic, short-pulse neutral hydrogen beam was used to obtain a high-resolution K -shell x-ray spectrum formed solely by charge exchange. The observed K -shell emission of Ar16+ is dominated by the intercombination and forbidden lines, providing clear signatures of charge exchange. Results from an ab initio atomic cascade model provide excellent agreement, validating a semiclassical approach for calculating charge-exchange cross sections.


Autoionization Of He Atoms By Partially Stripped Ion Impact, Sebastian Otranto, Ronald E. Olson Aug 2005

Autoionization Of He Atoms By Partially Stripped Ion Impact, Sebastian Otranto, Ronald E. Olson

Physics Faculty Research & Creative Works

A study of the autoionization process induced by partially stripped ion impact is performed. Electron spectra in momentum space are predicted within a classical model for partially stripped ions. The results are compared with those obtained for pure Coulomb-like projectiles. A quantum-mechanical extension of the Barrachina-Macek model is proposed for partially stripped projectiles. Structure on the electron angular distribution arising in quantum and classical treatments is identified and compared. The presence of rainbow scattering interference is observed in the binary ring profile of the outgoing autoionized electrons for positive-ion impact.


Complete Two-Loop Correction To The Bound-Electron Factor, Krzysztof Pachucki, Andrzej Czarnecki, Ulrich D. Jentschura, Vladimir A. Yerokhin Aug 2005

Complete Two-Loop Correction To The Bound-Electron Factor, Krzysztof Pachucki, Andrzej Czarnecki, Ulrich D. Jentschura, Vladimir A. Yerokhin

Physics Faculty Research & Creative Works

Within a systematic approach based on dimensionally regularized nonrelativistic quantum electrodynamics, we derive a complete result for the two-loop correction to order ( α/ π )2 ( Zα )4 for the g factor of an electron bound in an nS state of a hydrogenlike ion. The results obtained significantly improve the accuracy of the theoretical predictions for the hydrogenlike carbon and oxygen ions and influence the value of the electron mass inferred from g-factor measurements. D


Three-Coulomb-Wave Pluvinage Model For Compton Double Ionization Of Helium In The Region Of The Cross-Section Maximum, S. Jones, Joseph H. Macek, Don H. Madison Jul 2005

Three-Coulomb-Wave Pluvinage Model For Compton Double Ionization Of Helium In The Region Of The Cross-Section Maximum, S. Jones, Joseph H. Macek, Don H. Madison

Physics Faculty Research & Creative Works

Double ionization of ground-state helium by the Compton scattering of a photon is calculated using the well-known product of three Coulomb waves (3C) wave function for the final double-continuum state of the atom and the Pluvinage wave function for the initial ground state (also a product of three Coulomb waves). The theoretical model fails to predict both the shape and the overall magnitude of the observed integrated cross section vs. Incident-photon energy. However, when the monopole part of the electron-photon interaction is removed by an ad hoc procedure, qualitative agreement is obtained, although the absolute size of the cross section ...


Calculation Of Hydrogenic Bethe Logarithms For Rydberg States, Ulrich D. Jentschura, Peter J. Mohr Jul 2005

Calculation Of Hydrogenic Bethe Logarithms For Rydberg States, Ulrich D. Jentschura, Peter J. Mohr

Physics Faculty Research & Creative Works

We describe the calculation of hydrogenic (one-loop) Bethe logarithms for all states with principal quantum numbers 200. While, in principle, the calculation of the Bethe logarithm is a rather easy computational problem involving only the nonrelativistic (Schrdinger) theory of the hydrogen atom, certain calculational difficulties affect highly excited states, and in particular states for which the principal quantum number is much larger than the orbital angular momentum quantum number. Two evaluation methods are contrasted. One of these is based on the calculation of the principal value of a specific integral over a virtual photon energy. The other method relies directly ...


Charge Transfer In Slow Collisions Of C⁶⁺ With H Below 1 Kev / Amu, Chen-Nan Liu, Shu-Chun Cheng, Anh-Thu Le, C. D. Lin Jul 2005

Charge Transfer In Slow Collisions Of C⁶⁺ With H Below 1 Kev / Amu, Chen-Nan Liu, Shu-Chun Cheng, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We reexamine the charge transfer cross sections for C⁶⁺ + H collisions for energies below 1 keV / amu using a fully quantum mechanical approach, based on the hyperspherical close-coupling method. Whereas most previous theoretical and experimental data agree well for the dominant charge transfer to the C⁵⁺(n=4) states, there is significant disagreement among the theories for the transition to the weaker n=5 states. Using the present quantum mechanical calculations we analyze the origin of the discrepancy among these previous calculations. We further extend the calculations to collision energies down to about 1 eV and show that electron capture ...


Self-Energy Values For P States In Hydrogen And Low-Z Hydrogenlike Ions, Ulrich D. Jentschura, Peter J. Mohr Jul 2005

Self-Energy Values For P States In Hydrogen And Low-Z Hydrogenlike Ions, Ulrich D. Jentschura, Peter J. Mohr

Physics Faculty Research & Creative Works

We describe a nonperturbative (in Z α ) numerical evaluation of the one-photon electron self-energy for 3P1/2 , 3P3/2 , 4P1/2, and 4P3/2 states in hydrogenlike atomic systems with charge numbers Z = 1 to 5. The numerical results are found to be in agreement with known terms in the expansion of the self-energy in powers of Z α and lead to improved theoretical predictions for the self-energy shift of these states.


Erratum: Nonrelativistic Qed Approach To The Bound-Electron G Factor (Phys. Rev. Lett. (2004) 93 (150401)), Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin Jun 2005

Erratum: Nonrelativistic Qed Approach To The Bound-Electron G Factor (Phys. Rev. Lett. (2004) 93 (150401)), Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin

Physics Faculty Research & Creative Works

No abstract provided.


Temperature Dependence Of Homogeneous Nucleation Rates For Water: Near Equivalence Of The Empirical Fit Of Wölk And Strey, And The Scaled Nucleation Model, Barbara N. Hale May 2005

Temperature Dependence Of Homogeneous Nucleation Rates For Water: Near Equivalence Of The Empirical Fit Of Wölk And Strey, And The Scaled Nucleation Model, Barbara N. Hale

Physics Faculty Research & Creative Works

It is pointed out that the temperature fitting function of Wölk and Strey [J. Phys. Chem. 105, 11683 (2001)], recently shown to convert the Becker-Döring [Ann. Phys. (Leipzig) 24, 719 (1935)] nucleation rate into an expression in agreement with much of the experimental water nucleation rate data, also converts the Becker-Döring rate into a form nearly equivalent with the scaled nucleation rate model, Jscaled=Joc exp[-16πΩ3(Tc/T-1)3/3(ln S)2]. In the latter expression Joc is the inverse thermal wavelength cubed/sec, evaluated at Tc.


Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini Mar 2005

Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini

Physics Faculty Research & Creative Works

We discuss the cosmological amplification of tensor perturbations in a simple example of brane-world scenario, in which massless gravitons are localized on a higher-dimensional Kasner-like brane embedded in a bulk AdS background. Particular attention is paid to the canonical normalization of the quadratic action describing the massless and massive vacuum quantum fluctuations, and to the exact mass-dependence of the amplitude of massive fluctuations on the brane. The perturbation equations can be separated. In contrast to de Sitter models of brane inflation, we find no mass gap in the spectrum and no enhancement for massless modes at high curvature. The massive ...


Doubly Differential Cross Sections For Single And Multiple Ionization Of Ne By Electron Impact, Antonio C. Santos, Ahmad Hasan, Robert D. Dubois Mar 2005

Doubly Differential Cross Sections For Single And Multiple Ionization Of Ne By Electron Impact, Antonio C. Santos, Ahmad Hasan, Robert D. Dubois

Physics Faculty Research & Creative Works

We present doubly differential cross sections for single and multiple ionization of the outer shell of neon by 750 eV electron impact. The distinction between single and multiple ionization was achieved by performing a charge state analysis of the recoil ions in coincidence with forward scattered, energy analyzed electrons. By a comparison to photon impact data, the contribution of the second-order double ionization mechanism is estimated and found to be neglible at this impact energy. Following a similar procedure adopted by J. A. R. Samson [Phys. Rev. Lett. 65, 2861 (1990)], the importance of the first-order TS-1 double ionization mechanism ...


Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin Mar 2005

Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin

Physics Faculty Research & Creative Works

We present the positronium formation cross sections for a positron colliding with lithium and sodium for the collision energies from 0.01 eV up to 20 eV by the hyperspherical close-coupling method. For Li, our results agree with the experimental data and with other calculations. Our results for Na remain in agreement with previous close-coupling calculations, but do not support the latest experimental data for Na below 1 eV. To validate our model potentials and method in the low-energy regime, the binding energies of positronic lithium and positronic sodium as well as the s-wave scattering lengths for positronium scattering from ...


Muon Transfer From Muonic Hydrogen To Atomic Oxygen And Nitrogen, Anh-Thu Le, C. D. Lin Feb 2005

Muon Transfer From Muonic Hydrogen To Atomic Oxygen And Nitrogen, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

The results of diabatic hyperspherical close-coupling calculations are presented for the charge exchange of a negative muon from muonic hydrogen to oxygen and nitrogen for collision energies from 10-3 to 103 eV. It is shown that converged results can be obtained using a much smaller number of channels than in the traditional adiabatic approach. For the energy range below 10 eV our results for nitrogen are in good agreements with the available experimental data and the recent calculations within hyperspherical elliptic coordinates. However, discrepancies were found in the case of oxygen, where a p -wave shape resonance is ...


Tunable Conductivity And Conduction Mechanism In An Ultraviolet Light Activated Electronic Conductor, Mariana I. Bertoni, Thomas O. Mason, Julia E. Medvedeva, Arthur J. Freeman, Kenneth R. Poeppelmeier, B. Delley Jan 2005

Tunable Conductivity And Conduction Mechanism In An Ultraviolet Light Activated Electronic Conductor, Mariana I. Bertoni, Thomas O. Mason, Julia E. Medvedeva, Arthur J. Freeman, Kenneth R. Poeppelmeier, B. Delley

Physics Faculty Research & Creative Works

A tunable conductivity has been achieved by controllable substitution of an ultraviolet light activated electronic conductor. The transparent conducting oxide system H-doped Ca12-xMgxAl14O33 (x=0,0.1,0.3,0.5,0.8,1.0) presents a conductivity that is strongly dependent on the substitution level and temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x=0) to 0.106 S/cm (x=1) at room temperature. At each composition the conductivity increases (reversibly with temperature) until a decomposition temperature is reached; above this value, the conductivity drops dramatically due to hydrogen recombination and loss. The observed ...


Static Pairwise Annihilation In Complex Networks, M. F. Laguna, M. Aldana, H. Larralde, V. M. Kenkre, Paul Ernest Parris Jan 2005

Static Pairwise Annihilation In Complex Networks, M. F. Laguna, M. Aldana, H. Larralde, V. M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

We study static annihilation on complex networks, in which pairs of connected particles annihilate at a constant rate during time. Through a mean-field formalism, we compute the temporal evolution of the distribution of surviving sites with an arbitrary number of connections. This general formalism, which is exact for disordered networks, is applied to Kronecker, Erdös-Rényi (i.e., Poisson), and scale-free networks. We compare our theoretical results with extensive numerical simulations obtaining excellent agreement. Although the mean-field approach applies in an exact way neither to ordered lattices nor to small-world networks, it qualitatively describes the annihilation dynamics in such structures. Our ...


Projectile-Residual-Target-Ion Scattering After Single Ionization Of Helium By Slow Proton Impact, N. V. Maydanyuk, Ahmad Hasan, M. Foster, B. Tooke, Don H. Madison, Michael Schulz, Emilio Nanni Jan 2005

Projectile-Residual-Target-Ion Scattering After Single Ionization Of Helium By Slow Proton Impact, N. V. Maydanyuk, Ahmad Hasan, M. Foster, B. Tooke, Don H. Madison, Michael Schulz, Emilio Nanni

Physics Faculty Research & Creative Works

We have measured fully differential single ionization cross sections for 75 keV p+He collisions. At this relatively small projectile velocity, signatures of the projectile-residual-target-ion interaction, which are not observable for fast projectiles and for electron impact, are revealed rather sensitively. In fact, this interaction appears to be more important than the postcollision interaction, which so far was assumed to be the most important factor in higher-order effects for slow ion impact. These features are not well reproduced by our three-distorted-wave calculations.