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Physics Faculty Research & Creative Works

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Articles 1021 - 1050 of 1762

Full-Text Articles in Physical Sciences and Mathematics

Extrapolation Of The Zα-Expansion And Two-Loop Bound-State Energy Shifts, Ulrich D. Jentschura Jul 2003

Extrapolation Of The Zα-Expansion And Two-Loop Bound-State Energy Shifts, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

Quantum electrodynamic (QED) effects that shift the binding energies of hydrogenic energy levels have been expressed in terms of a semi-analytic expansion in powers of Zα and ln[(Zα)-2], where Z is the nuclear charge number and α is the fine-structure constant. For many QED effects, numerical data are available in the domain of high Z where the Zα expansion fails. In this Letter, we demonstrate that it is possible, within certain limits of accuracy, to extrapolate the Zα-expansion from the low-Z to the high-Z domain. We also review two-loop self-energy effects and provide an estimate for the problematic …

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Charge Transfer In Slow Collisions Of H⁺ With Na, Anh-Thu Le, Chen-Nan Liu, C. D. Lin Jul 2003

Charge Transfer In Slow Collisions Of H⁺ With Na, Anh-Thu Le, Chen-Nan Liu, C. D. Lin

Physics Faculty Research & Creative Works

We reexamined charge-transfer cross sections for protons colliding with Na(3s) atoms for collision energies from the threshold at 1.7 eV to 40 eV using the recently developed hyperspherical close-coupling method. Our results disagree with the recent calculations by Dutta et al. [Phys. Rev. A 63, 022709 (2001)], but are in good agreement with the earlier calculations of Croft and Dickinson [J. Phys. B 29, 57 (1996)] except at energies below 3 eV. Our calculations support the doubt on the experimental data of Kushawaha.

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Laboratory Simulation Of Charge Exchange - Produced X-Ray Emission From Comets, P. Beiersdorfer, K. R. Boyce, G. V. Brown, H. Chen, S. M. Kahn, R. L. Kelley, M. May, Ronald E. Olson, F. S. Porter, C. K. Stahle, W. A. Tillotson Jun 2003

Laboratory Simulation Of Charge Exchange - Produced X-Ray Emission From Comets, P. Beiersdorfer, K. R. Boyce, G. V. Brown, H. Chen, S. M. Kahn, R. L. Kelley, M. May, Ronald E. Olson, F. S. Porter, C. K. Stahle, W. A. Tillotson

Physics Faculty Research & Creative Works

In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. the spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory.

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Projectile-Charge Sign Dependence Of Four-Particle Dynamics In Helium Double Ionization, Daniel Fischer, Robert Moshammer, Alexander Dorn, Jose R. Crespo Lopez-Urrutia, Bernold Feuerstein, C. Hohr, Claus Dieter Schroter, Siegbert Hagmann, Holger Kollmus, Rido Mann, Bhas Bapat, Joachim Hermann Ullrich, Holger Kollmus Jun 2003

Projectile-Charge Sign Dependence Of Four-Particle Dynamics In Helium Double Ionization, Daniel Fischer, Robert Moshammer, Alexander Dorn, Jose R. Crespo Lopez-Urrutia, Bernold Feuerstein, C. Hohr, Claus Dieter Schroter, Siegbert Hagmann, Holger Kollmus, Rido Mann, Bhas Bapat, Joachim Hermann Ullrich, Holger Kollmus

Physics Faculty Research & Creative Works

Double ionization of helium by 6 MeV proton impact has been explored in a kinematically complete experiment using a “reaction microscope.” For the first time, fully differential cross sections for positively charged projectiles have been obtained and compared with data from 2 keV electron impact. The significant differences observed in the angular distribution of the ejected electrons are attributed to the charge sign of the projectile, resulting in different dynamics of the four-particle Coulomb system, which is not considered in the first Born approximation.

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Giant Magnetoresistance Properties Of The La1-2xrxaxmno3 (R=Nd, A=Ca) Perovskites, Darshan C. Kundaliya, A. A. Tulapurkar, S. R. Shinde, R. Pinto, William B. Yelon, R. G. Kulkarni, S. K. Malik May 2003

Giant Magnetoresistance Properties Of The La1-2xrxaxmno3 (R=Nd, A=Ca) Perovskites, Darshan C. Kundaliya, A. A. Tulapurkar, S. R. Shinde, R. Pinto, William B. Yelon, R. G. Kulkarni, S. K. Malik

Physics Faculty Research & Creative Works

The giant magneto resistive behavior of an antiferromagnetic insulator, LaMnO3, was investigated by studying the effect of simultaneous substitution of Nd and Ca on the compound. the volume of unit cell decreased with increasing concentration of Nd/Ca. the changes in the temperature dependent resistivity, and ferromagnetic transition were observed with the increase in the compound series. the observing of metal-insulator transition at different temperatures, and magnetoresistance in the 2 T applied field were also recorded.

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Cation Intermixing And Ordering Phenomenon In M-O Layer Of Msr2ycu2oz(M-1212) Compounds With M=Fe, Co, Al, And Ga: A Neutron Powder Diffraction Study, V. P.S. Awana, E. Takayama-Muromachi, S. K. Malik, William B. Yelon, M. Karppinen, H. Yamauchi, V. V. Krishnamurthy May 2003

Cation Intermixing And Ordering Phenomenon In M-O Layer Of Msr2ycu2oz(M-1212) Compounds With M=Fe, Co, Al, And Ga: A Neutron Powder Diffraction Study, V. P.S. Awana, E. Takayama-Muromachi, S. K. Malik, William B. Yelon, M. Karppinen, H. Yamauchi, V. V. Krishnamurthy

Physics Faculty Research & Creative Works

M-1212 compounds with the composition MSr2YCu2Oz (with M = Fe, Co, Al and Ga) were studied. the phenomena of M-cation intermixing with Cu, and the ordering in the M-O layer of the M-1212 compounds when compared with the parent CuBa2YCu2O7-δ compound were investigated. Magnetization measurements and neutron powder diffraction results were presented.

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Hyperspherical Close-Coupling Calculations For Charge-Transfer Cross Sections In He²⁺ +H(1s) Collisions At Low Energies, Chen-Nan Liu, Anh-Thu Le, Toru Morishita, B. D. Esry, C. D. Lin May 2003

Hyperspherical Close-Coupling Calculations For Charge-Transfer Cross Sections In He²⁺ +H(1s) Collisions At Low Energies, Chen-Nan Liu, Anh-Thu Le, Toru Morishita, B. D. Esry, C. D. Lin

Physics Faculty Research & Creative Works

A theory for ion-atom collisions at low energies based on the hyperspherical close-coupling (HSCC) method is presented. In hyperspherical coordinates the wave function is expanded in analogy to the Born-Oppenheimer approximation where the adiabatic channel functions are calculated with B-spline basis functions while the coupled hyperradial equations are solved by a combination of R-matrix propagation and the slow/smooth variable discretization method. The HSCC method is applied to calculate charge-transfer cross sections for He²⁺ +H(1s)-->He⁺ (n=2) + H⁺ reactions at center-of-mass energies from 10 eV to 4 keV. The results are shown to be in general good agreement with calculations …

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Asymptotic Properties Of Self-Energy Coefficients, Ulrich D. Jentschura, Eric Olivier Le Bigot, Peter J. Mohr, Paul Indelicato, Gerhard Soff Apr 2003

Asymptotic Properties Of Self-Energy Coefficients, Ulrich D. Jentschura, Eric Olivier Le Bigot, Peter J. Mohr, Paul Indelicato, Gerhard Soff

Physics Faculty Research & Creative Works

We investigate the asymptotic properties of higher-order binding corrections to the one-loop self-energy of excited states in atomic hydrogen. We evaluate the historically problematic A60 coefficient for all P states with principal quantum numbers n ≤ 7 and D states with n ≤ 8 and find that a satisfactory representation of the n dependence of the coefficients requires a three-parameter fit. For the high-energy contribution to A60, we find exact formulas. The results obtained are relevant for the interpretation of high-precision laser spectroscopic measurements.

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Disorder-Induced Rounding Of Certain Quantum Phase Transitions, Thomas Vojta Mar 2003

Disorder-Induced Rounding Of Certain Quantum Phase Transitions, Thomas Vojta

Physics Faculty Research & Creative Works

We study the influence of quenched disorder on quantum phase transitions in systems with overdamped dynamics. For Ising order-parameter symmetry disorder destroys the sharp phase transition by rounding because a static order parameter can develop on rare spatial regions. This leads to an exponential dependence of the order parameter on the coupling constant. At finite temperatures the static order on the rare regions is destroyed. This restores the phase transition and leads to a double exponential relation between critical temperature and coupling strength. We discuss the behavior based on Lifshitz-tail arguments and illustrate the results by simulations of a model …

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Dynamical Electron-Electron Correlation In C²⁺ + He Simultaneous Target-Projectile Collisional Ionization, J. Fiol, Ronald E. Olson, R. Moshammer, J. Ullrich Feb 2003

Dynamical Electron-Electron Correlation In C²⁺ + He Simultaneous Target-Projectile Collisional Ionization, J. Fiol, Ronald E. Olson, R. Moshammer, J. Ullrich

Physics Faculty Research & Creative Works

Simultaneous target and projectile single ionization in 3.6 MeV u-1 C2++He collisions are considered, within a six-body classical trajectory Monte Carlo model. Analysis of the relative azimuthal angle between the two emitted electrons allows one to discriminate the ionization contribution produced by the two-centre dynamical electron-electron interaction from that due to nucleus-electron interactions. the present calculations agree well with cross section measurements recently performed in kinematically complete experiments.

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Temperature Dependence Of Droplet Nucleation In A Yukawa Fluid, Jinsong Li, Gerald Wilemski Feb 2003

Temperature Dependence Of Droplet Nucleation In A Yukawa Fluid, Jinsong Li, Gerald Wilemski

Physics Faculty Research & Creative Works

We have studied the temperature dependence of gas-to-liquid nucleation in Yukawa fluids with gradient theory and density functional theory. Each of these nonclassical theories exhibits a weaker (i.e., better) temperature dependence than classical nucleation theory. At fixed temperature, the reversible work to form a critical nucleus found from gradient theory approaches the value given by density functional theory as the supersaturation increases. At high temperatures, the two theories remain quite close over a wide range of vapor densities. As the temperature is reduced, the difference between the two theories increases with decreasing vapor density. Compared to the classical theory we …

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Neutron Diffraction, Structural And Magnetic Properties Of (La1-Ypry)0.9na0.1mno3, S. Megdiche, Mohamed Ellouze, A. Cheikh-Rouhou, Q. Cai, William B. Yelon Jan 2003

Neutron Diffraction, Structural And Magnetic Properties Of (La1-Ypry)0.9na0.1mno3, S. Megdiche, Mohamed Ellouze, A. Cheikh-Rouhou, Q. Cai, William B. Yelon

Physics Faculty Research & Creative Works

A systematic study of the structural and magnetic properties of the diluted perovskite manganite oxides (La1-yPry)0.9Na0.1MnO3 (0.2≤y≤0.8) had been carried on. in this study, the average ionic radius 〈rA〉 of a cation site was systematically varied while keeping fixed the carrier concentration (Mn3+/Mn4+ ratio). X-Ray diffraction investigations showed a structural transition from the rhombohedral to the orthorhombic system for 0.33≤y≤0.5. the unit cell volume decreases with increasing Pr3+ content. Magnetic measurements showed that our synthesized samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. Neutron diffraction …

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How To Establish Successful Cooperative Student Learning Centers For Stem Courses, Ronald James Bieniek, Douglas R. Carroll, Cesar Mendoza, Oran Allan Pringle, Ekkehard Sinn, Kai-Tak Wan, Donald C. Wunsch Jan 2003

How To Establish Successful Cooperative Student Learning Centers For Stem Courses, Ronald James Bieniek, Douglas R. Carroll, Cesar Mendoza, Oran Allan Pringle, Ekkehard Sinn, Kai-Tak Wan, Donald C. Wunsch

Physics Faculty Research & Creative Works

Students learn more if they are actively involved in the learning process, particularly in a cooperative manner. Several UMR faculty have operated course-based learning centers (LCs) as part of the campus-wide Learning Enhancement Across Disciplines (LEAD) Program of student learning assistance and enhancement. LCs are designed to assist large numbers of students in a cost- and time-efficient manner that promotes student engagement without requiring undue amounts of faculty time. Course instructors spend time in the open learning environment of the LC, in lieu of office hours, guiding students to master course material and skills in their evolution from novice to …

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Perturbative And Nonperturbative Calculations Of Electron-Hydrogen Ionization, Stephenie J. Jones, Don H. Madison, Mark D. Baertschy Jan 2003

Perturbative And Nonperturbative Calculations Of Electron-Hydrogen Ionization, Stephenie J. Jones, Don H. Madison, Mark D. Baertschy

Physics Faculty Research & Creative Works

We compare calculations of the fully differential cross section for ionization of atomic hydrogen by electron impact using two different theories-the perturbative CDW-EIS (continuum distorted wave with eikonal initial state) approximation and the nonperturbative ECS (exterior complex scaling) method. For this comparison, we chose an impact energy of 54.4 eV, since this is near the lowest energy that our perturbative approach would be applicable and near the highest energy that can be tackled by the ECS method with our present computational resources. For the case of equal-energy outgoing electrons investigated here, the two theories predict nearly identical results except that …

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Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto Jan 2003

Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto

Physics Faculty Research & Creative Works

We propose that higher-dimensional extended objects (p-branes) are created by super-Planckian scattering processes in theories with TeV scale gravity. As an example, we compute the cross section for p-brane creation in a (n + 4)-dimensional spacetime with asymmetric compactification. We find that the cross section for the formation of a brane which is wounded on a compact submanifold of size of the fundamental gravitational scale is larger than the cross section for the creation of a spherically symmetric black hole. Therefore, we predict that branes are more likely to be created than black holes in super-Planckian …

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Collision Cross Sections And The Size Of A Coin, Antonio C. Santos, A. Fröhlich Jan 2003

Collision Cross Sections And The Size Of A Coin, Antonio C. Santos, A. Fröhlich

Physics Faculty Research & Creative Works

An important question in education nowadays is how to convey some concepts of Modern Physics to students in high school, secondary education or the sixth form. This article presents an approach to atomic collisions suitable for intermediate level students. We describe an alternative way of measuring the area of a coin using a macroscopic analogy of the scattering of radiation by an atom or molecule—the collision cross section. We hope this article will help educators to illustrate such an important procedure and related concepts of Modern Physics. © 2003 IOP Publishing Ltd.

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Doubly Differential Measurements For Multiple Ionization Of Argon By Electron Impact: Comparison With Positron Impact And Photoionization, Antonio C. Santos, Ahmad Hasan, T. Yates, Robert D. Dubois Jan 2003

Doubly Differential Measurements For Multiple Ionization Of Argon By Electron Impact: Comparison With Positron Impact And Photoionization, Antonio C. Santos, Ahmad Hasan, T. Yates, Robert D. Dubois

Physics Faculty Research & Creative Works

Doubly differential cross sections for single and multiple ionization of Ar have been measured for 500, 750, and 1000 eV electron impact. the cross sections were measured as a function of projectile energy loss and scattering angle. the energy loss range was 0–85 % of the initial projectile energy and scattering angles were between [Formula Presented] the data were put on an absolute scale by normalizing to total ionization cross sections available in the literature and found to be in good agreement with the absolute electron impact cross sections from DuBois and Rudd. for 750 eV impact, a comparison was …

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High Precision Wavelength Measurements Of Qed-Sensitive Forbidden Transitions In Highly Charged Argon Ions, I. Draganić, J. R. Crespo López-Urrutia, Robert D. Dubois, S. Fritzsche, V. M. Shabaev, R. Soria Orts, I. I. Tupitsyn, Y. Zou, J. Ullrich Jan 2003

High Precision Wavelength Measurements Of Qed-Sensitive Forbidden Transitions In Highly Charged Argon Ions, I. Draganić, J. R. Crespo López-Urrutia, Robert D. Dubois, S. Fritzsche, V. M. Shabaev, R. Soria Orts, I. I. Tupitsyn, Y. Zou, J. Ullrich

Physics Faculty Research & Creative Works

We present the results of an experimental study of magnetic dipole ([Formula presented]) transitions in highly charged argon ions (ArX, ArXI, ArXIV, ArXV) in the visible spectral range using an electron beam ion trap. their wavelengths were determined with, for highly charged ions, unprecedented accuracy up to the sub-ppm level and compared with theoretical calculations. the QED contributions, calculated in this Letter, are found to be 4 orders of magnitude larger than the experimental error and are absolutely indispensable to bring theory and experiment to a good agreement. This method shows great potential for the study of QED effects in …

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Target Z Dependence And Additivity Of Cross Sections For Electron Loss By 6-Mev/Amu [Formula Presented] Projectiles, R. L. Watson, Yong Peng, V. Horvat, G. J. Kim, Ronald E. Olson Jan 2003

Target Z Dependence And Additivity Of Cross Sections For Electron Loss By 6-Mev/Amu [Formula Presented] Projectiles, R. L. Watson, Yong Peng, V. Horvat, G. J. Kim, Ronald E. Olson

Physics Faculty Research & Creative Works

The dependence of electron loss by 6-MeV/amu Xe18+ on target atomic number was investigated by measuring single-collision cross sections for loss of one to eight electrons in targets of the noble gases He, Ne, Ar, Kr, and Xe. the total-electron-loss cross sections were found to increase linearly with target atomic number, but an abrupt slope change was observed to occur between Ne and Kr. Calculated total-loss cross sections obtained using the n-body classical trajectory Monte Carlo method were in good agreement with the measurements. the dependence of the individual cross sections on the number of electrons lost was reasonably …

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Dynamic Nonlinear Effect On Lasing In Random Media, B. Liu, Alexey Yamilov, Y. Ling, J. Y. Xu, Hui Cao Jan 2003

Dynamic Nonlinear Effect On Lasing In Random Media, B. Liu, Alexey Yamilov, Y. Ling, J. Y. Xu, Hui Cao

Physics Faculty Research & Creative Works

We investigate the dynamic effect of nonlinearity on lasing in disordered medium. The third-order nonlinearity not only changes frequency and size of lasing mode, but also modifies laser emission intensity and laser pulse width.

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Postcollisional Decay In Ne Multiple Ionization By H2+ Ions In Breakup Collisions, M. M. Sant'anna, H. Luna, Antonio C. Santos, C. Mcgrath, M. B. Shah, E. G. Cavalcanti, G. M. Sigaud, E. C. Montenegro Jan 2003

Postcollisional Decay In Ne Multiple Ionization By H2+ Ions In Breakup Collisions, M. M. Sant'anna, H. Luna, Antonio C. Santos, C. Mcgrath, M. B. Shah, E. G. Cavalcanti, G. M. Sigaud, E. C. Montenegro

Physics Faculty Research & Creative Works

We measured the Neq+ charge-state yield distribution for Ne atoms multiply ionized by 1-MeV/amu H2+ in coincidence with the final state of the projectile, for both breakup and Non breakup channels. Measurements with 1-MeV H+ projectiles were also performed. While the H2+ Non breakup channel produces results similar to equal-velocity proton or electron projectiles, the breakup channels lead to a charge-state yield distribution very close to the known Ne 2s-1 post collisional decay distribution, measured through photoionization [T. A. Carlson, W. E. Hunt, and M. O. Krause, Phys. Rev. 151, 41 (1966)]. This …

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Electron Loss From 0.74- And 1.4-Mev/U Low-Charge-State Argon And Xenon Ions Colliding With Neon, Nitrogen, And Argon, Robert D. Dubois, Antonio C. Santos, Ronald E. Olson, Th Stöhlker, F. Bosch, A. Bräuning-Demian, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Mann, A. Oršić Muthig, U. Spillmann, S. Tachenov, W. Barth, L. Dahl Jan 2003

Electron Loss From 0.74- And 1.4-Mev/U Low-Charge-State Argon And Xenon Ions Colliding With Neon, Nitrogen, And Argon, Robert D. Dubois, Antonio C. Santos, Ronald E. Olson, Th Stöhlker, F. Bosch, A. Bräuning-Demian, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Mann, A. Oršić Muthig, U. Spillmann, S. Tachenov, W. Barth, L. Dahl

Physics Faculty Research & Creative Works

Absolute total-, single-, and multiple-electron-loss cross sections are measured for (Ar+-, Ar2+-, Xe3+)-~Ne, N2 Ar) collisions at 0.74 and 1.4 MeV/u. in addition, a many-body classical trajectory Monte Carlo model was used to calculate total- and multiple-electron-loss cross sections for Ar+ impact. for N2 and Ar targets, excellent agreement between the measured and calculated cross sections is found; for the Ne target the experimental data are approximately 40% smaller than the theoretical predictions. the experimental data are also used to examine cross-section scaling characteristics for electron loss from fast, low-charge-state, heavy …

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Magnetic Properties Of Er2mn3si5, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, A. V. Morozkin, Z. Chu, William B. Yelon, S. K. Malik, Y. Yamamoto, H. Hori Dec 2002

Magnetic Properties Of Er2mn3si5, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, A. V. Morozkin, Z. Chu, William B. Yelon, S. K. Malik, Y. Yamamoto, H. Hori

Physics Faculty Research & Creative Works

Magnetization measurements have been carried out on the Er2Mn3Si5 compound (tetragonal Sc2Fe3Si5-type, space group P4/mnc) in the temperature range 1.8-300 K. There is a crossover from a room temperature paramagnetic phase to a ferromagnetic phase at 75 K (TC1). A second magnetic transition is observed at 11.5 K (TC2). The magnetic susceptibility in the paramagnetic region, above 100 K, follows simple Curie-Weiss type behavior. The magnetization does not saturate at 2 K even in applied fields of 7 T. Neutron diffraction data collected at 300 …

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Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison Dec 2002

Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison

Physics Faculty Research & Creative Works

It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time …

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Intersubband Spin-Density Excitations In Quantum Wells With Rashba Spin Splitting, Carsten A. Ullrich, M. E. Flatté Nov 2002

Intersubband Spin-Density Excitations In Quantum Wells With Rashba Spin Splitting, Carsten A. Ullrich, M. E. Flatté

Physics Faculty Research & Creative Works

In inversion-asymmetric semiconductors, spin-orbit coupling induces a κ-dependent spin splitting of valence and conduction bands, which is a well-known cause for spin decoherence in bulk and heterostructures. Manipulating nonequilibrium spin coherence in device applications thus requires understanding how valence and conduction band spin splitting affects carrier spin dynamics. This paper studies the relevance of this decoherence mechanism for collective intersubband spin-density excitations (SDE's) in quantum wells. A density-functional formalism for the linear spin-density matrix response is presented that describes SDE's in the conduction band of quantum wells with subbands that may be nonparabolic and spin split due to bulk or …

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Degeneracy In Density Functional Theory: Topology In The V And N Spaces, Carsten A. Ullrich, W. Kohn Oct 2002

Degeneracy In Density Functional Theory: Topology In The V And N Spaces, Carsten A. Ullrich, W. Kohn

Physics Faculty Research & Creative Works

The problem of v-representability had cast a shadow of uncertainty over density functional theory (DFT). Building on CCR, the topology of the v(r)-n(r) mapping is clarified. The Be series and a lattice model are used for rl, to a continuous variable, r, does not appear to offer difficulties.

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Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi Sep 2002

Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

Physics Faculty Research & Creative Works

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk, boundary conformal correlators have a …

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Double-Logarithmic Two-Loop Self-Energy Corrections To The Lamb Shift, Ulrich D. Jentschura, I. Nandori Aug 2002

Double-Logarithmic Two-Loop Self-Energy Corrections To The Lamb Shift, Ulrich D. Jentschura, I. Nandori

Physics Faculty Research & Creative Works

Self-energy corrections involving logarithms of the parameter Z α can often be derived within a simplified approach, avoiding calculational difficulties typical of the problematic nonlogarithmic corrections (as customary in bound-state quantum electrodynamics, we denote by Z the nuclear charge number, and by α the fine-structure constant). For some logarithmic corrections, it is sufficient to consider internal properties of the electron characterized by form factors. We provide a detailed derivation of related self-energy “potentials” that give rise to the logarithmic corrections; these potentials are local in coordinate space. We focus on the double-logarithmic two-loop coefficient B62 for P states and …

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Nolan-Pollak Type Cn Counters In The Vienna Aerosol Workshop, J. L. Gras, Josef Podzimek, T. C. O'Connor, K. H. Enderle Jul 2002

Nolan-Pollak Type Cn Counters In The Vienna Aerosol Workshop, J. L. Gras, Josef Podzimek, T. C. O'Connor, K. H. Enderle

Physics Faculty Research & Creative Works

Three "standard" Nolan-Pollak (N-P) and modified N-P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N-P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N-P counters, typically better than ± 12% for a range of aerosol sizes and compositions from …

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Coincident Fragment Detection In Strong Field Photoionization And Dissociation Of H₂, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Alexander Dorn, Claus Dieter Schroter, Daniel Fischer, Jose R. Crespo Lopez-Urrutia, Paul B. Neumayer, J. Deipenwisch, C. Hohr, Bernold Feuerstein, Joachim Hermann Ullrich Jul 2002

Coincident Fragment Detection In Strong Field Photoionization And Dissociation Of H₂, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Alexander Dorn, Claus Dieter Schroter, Daniel Fischer, Jose R. Crespo Lopez-Urrutia, Paul B. Neumayer, J. Deipenwisch, C. Hohr, Bernold Feuerstein, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

An investigation of the correlated electronic and nuclear motion in fragmentation of H2 in 4 x 1014 W/cm2, fs laser pulses at 795 nm was presented using the electron-ion momentum spectroscopy. The channel selective electron energy distribution indicated assumption of a new H2 ionization mechanism to interpret the differences found in the fragmentation channels. The results showed that the momentum distribution of H+ ions in the dissociation channels H(1s) + H+ + e- and 2H+ + 2e- was independent of the kinetic energy of photoelectrons.

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