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Articles 31 - 46 of 46
Full-Text Articles in Physics
Scaling Laws For Single And Multiple Electron Loss From Projectiles In Collisions With A Many-Electron Target, Antonio C. Santos, Robert D. Dubois
Scaling Laws For Single And Multiple Electron Loss From Projectiles In Collisions With A Many-Electron Target, Antonio C. Santos, Robert D. Dubois
Physics Faculty Research & Creative Works
Using measured cross sections, empirical scaling laws are extracted for projectile stripping induced by collisions with a many-electron target. by scaling both the cross sections and the impact velocities, it is shown that a single universal curve can be used to fit data for single and multiple electron loss from negative ions, neutral particles, and singly or multiply charged positive ions. The scaling applies to projectiles ranging from hydrogen to uranium and collision energies ranging from below keV∕u to hundreds of MeV∕u . At high energies, existing data are consistent with a v−1 impact velocity dependence for scaled velocities less …
Comment On "Role Of The Ground State In Electron-Atom Double Ionization" [1] (Multiple Letters), Jamal Berakdar, Stephenie J. Jones, Don H. Madison
Comment On "Role Of The Ground State In Electron-Atom Double Ionization" [1] (Multiple Letters), Jamal Berakdar, Stephenie J. Jones, Don H. Madison
Physics Faculty Research & Creative Works
No abstract provided.
Doubly Differential Multiple Ionization Of Krypton By Positron And Electron Impact, Kay Dubois, Antonio C. Santos, Ahmad Hasan
Doubly Differential Multiple Ionization Of Krypton By Positron And Electron Impact, Kay Dubois, Antonio C. Santos, Ahmad Hasan
Physics Faculty Research & Creative Works
Measurements of doubly differential single and multiple ionization of krypton atoms have been performed for 750 eV positron and electron impact. Data were measured as a function of projectile energy-loss and scattering angle. For electrons, the energy-loss range was 0-85% of the initial projectile energy and scattering angles were between ±22°. Following the procedure adopted previously for argon, the electron impact data were placed on an absolute scale by normalizing to total ionization cross sections available in the literature. The present results for krypton show differences between positron and electron impact that are less pronounced than was found for argon. …
Effects Of Localization And Amplification On Intensity Distribution Of Light Transmitted Through Random Media, Alexey Yamilov, Hui Cao
Effects Of Localization And Amplification On Intensity Distribution Of Light Transmitted Through Random Media, Alexey Yamilov, Hui Cao
Physics Faculty Research & Creative Works
We numerically study the statistical distribution of intensity of light transmitted through quasi-one-dimensional random media by varying the dimensionless conductance g and the amount of absorption or gain. A markedly non-Rayleigh distribution is found to be well fitted by the analytical formula of Nieuwenhuizen et al. [Phys. Rev. Lett. 74, 2674 (1995)] with a single parameter g′ . We show that in the passive random system g′ is uniquely related to g , while in amplifying or absorbing random media g′ also depends on the gain or absorption coefficient.
Highest-Quality Modes In Disordered Photonic Crystals, Alexey Yamilov, Hui Cao
Highest-Quality Modes In Disordered Photonic Crystals, Alexey Yamilov, Hui Cao
Physics Faculty Research & Creative Works
We studied the modes of the highest-quality factor Qm in disordered photonic crystals. by varying the strength of disorder, we identified five different scaling regimes of the ensemble averaged (Qm) with the system size. For sufficiently large systems, (Qm) reaches the maximum at some finite degree of disorder, where its value is comparable to the quality factor of an intentionally introduced single defect at the center of a photonic band gap. Near this optimal degree of disorder, we predict a superexponential increase of (Qm) with the system size, due to migration of the frequencies of the highest-quality modes toward the …
Laser Writing Of Semiconductor Nanoparticles And Quantum Dots, Massimo F. Bertino, Raghuveer Reddy Gadipalli, J. Greg Story, C. G. Williams, Guo-Hui Zhang, Chariklia Sotiriou-Leventis, Akira Tokuhiro, Suchi Guha, Nicholas Leventis
Laser Writing Of Semiconductor Nanoparticles And Quantum Dots, Massimo F. Bertino, Raghuveer Reddy Gadipalli, J. Greg Story, C. G. Williams, Guo-Hui Zhang, Chariklia Sotiriou-Leventis, Akira Tokuhiro, Suchi Guha, Nicholas Leventis
Physics Faculty Research & Creative Works
Silica aerogels were patterned with CdS using a photolithographic technique based on local heating with infrared (IR) light. The solvent of silica hydrogels was exchanged with an aqueous solution of the precursors CdNO3 and NH4 OH, all precooled to a temperature of 5°C. Half of the bathing solution was then replaced by a thiourea solution. After thiourea diffused into the hydrogels, the samples were exposed to a focused IR beam from a continuous wave, Nd-YAG laser. The precursors reacted in the spots heated by the IR beam to form CdS nanoparticles. We lithographed features with a diameter of …
Smeared Phase Transition In A Three-Dimensional Ising Model With Planar Defects: Monte Carlo Simulations, Rastko Sknepnek, Thomas Vojta
Smeared Phase Transition In A Three-Dimensional Ising Model With Planar Defects: Monte Carlo Simulations, Rastko Sknepnek, Thomas Vojta
Physics Faculty Research & Creative Works
We present results of large-scale Monte Carlo simulations for a three-dimensional Ising model with short-range interactions and planar defects, i.e., disorder perfectly correlated in two dimensions. We show that the phase transition in this system is smeared, i.e., there is no single critical temperature, but different parts of the system order at different temperatures. This is caused by effects similar to but stronger than Griffiths phenomena. In an infinite-size sample there is an exponentially small but finite probability to find an arbitrary large region devoid of impurities. Such a rare region can develop true long-range order while the bulk system …
Ultraviolet Photonic Crystal Laser, Alexey Yamilov, Hui Cao, Robert P. H. Chang, Xiaohua Wu, Xang Liu, Shuyou Li, Vinayak P. Dravid
Ultraviolet Photonic Crystal Laser, Alexey Yamilov, Hui Cao, Robert P. H. Chang, Xiaohua Wu, Xang Liu, Shuyou Li, Vinayak P. Dravid
Physics Faculty Research & Creative Works
We fabricated two-dimensional photonic crystal structures in zinc oxide films with focused-ion-beam etching. Lasing is realized in the near-ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process. ©2004 American Institute of Physics
Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan
Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan
Physics Faculty Research & Creative Works
We derive an order-parameter field theory for a quantum phase transition between a disordered metal and an exotic (non- s -wave) superconductor. Mode coupling effects between the order parameter and other fermionic soft modes lead to an effective long-range interaction between the anomalous density fluctuations which is reflected in singularities in the free energy functional. However, this long-range interaction is not strong enough to suppress disorder fluctuations. The asymptotic critical region is characterized by run-away flow to large disorder. For weak coupling, this asymptotic region is very narrow. It is preempted by a wide crossover regime with mean-field critical behavior …
Asymmetry Of Above-Threshold Ionization Of Metal Clusters In Two-Color Laser Fields: A Time-Dependent Density-Functional Study, H. S. Nguyen, A. D. Bandrauk, Carsten A. Ullrich
Asymmetry Of Above-Threshold Ionization Of Metal Clusters In Two-Color Laser Fields: A Time-Dependent Density-Functional Study, H. S. Nguyen, A. D. Bandrauk, Carsten A. Ullrich
Physics Faculty Research & Creative Works
A spherical jellium model and time-dependent density functional theory for two-color ultrashort laser pulses as a function of phase difference between two fields were used to calculate the above threshold ionization (ATI) spectra of small metal clusters. ATI spectra and the ionized electrons fluxes were obtained in the two opposite directions of the linearly polarized laser fields. It is found that ATI spectra has long energy plateaus, with cutoffs up to 30-40 times the ponderomotive energy Up. However, no extended plateaus were observed in high-harmonic generation spectra.
Variational Considerations In The Study Of Carrier Transport In Organic Crystals, V. M. Kenkre, Paul Ernest Parris
Variational Considerations In The Study Of Carrier Transport In Organic Crystals, V. M. Kenkre, Paul Ernest Parris
Physics Faculty Research & Creative Works
A variational approach is used to investigate consequences of electron-phonon interactions between a charge carrier and multiple (specifically two) phonon branches. Phase diagrams are obtained and the nature of the transition from undressed to dressed phases of the carrier is studied with their help. No sharp transition between singly dressed and doubly dressed phases occurs. The effective carrier bandwidth, reduced by strong coupling to the high-frequency branch is found to be stable with respect to small to intermediate values of additional coupling to the low-frequency branch. This finding lends support to transport calculations based on the idea that carriers in …
Renormalization-Group Analysis Of The Generalized Sine-Gordon Model And Of The Coulomb Gas For D > 3 Dimensions, I. Nandori, Ulrich D. Jentschura, Kornel Sailer, Gerhard Soff
Renormalization-Group Analysis Of The Generalized Sine-Gordon Model And Of The Coulomb Gas For D > 3 Dimensions, I. Nandori, Ulrich D. Jentschura, Kornel Sailer, Gerhard Soff
Physics Faculty Research & Creative Works
Renormalization-group (RG) flow equations have been derived for the generalized sine-Gordon model (GSGM) and the Coulomb gas (CG) in d ≥ 3 of dimensions by means of the Wegner-Houghton method, and by way of the real-space RG approach. The UV scaling laws determined by the leading-order terms of the flow equations are in qualitative agreement for all dimensions d ≥ 3, independent of the dimensionality, and in sharp contrast to the special case d=2. For the 4-dimensional GSGM it is demonstrated explicitly (by numerical calculations) that the blocked potential tends to a constant effective potential in the infrared limit, satisfying …
Kinetics Of Binary Nucleation Of Vapors In Size And Composition Space, Sergey P. Fisenko, Gerald Wilemski
Kinetics Of Binary Nucleation Of Vapors In Size And Composition Space, Sergey P. Fisenko, Gerald Wilemski
Physics Faculty Research & Creative Works
We reformulate the kinetic description of binary nucleation in the gas phase using two natural independent variables: the total number of molecules g and the molar composition x of the cluster. The resulting kinetic equation can be viewed as a two-dimensional Fokker-Planck equation describing the simultaneous Brownian motion of the clusters in size and composition space. Explicit expressions for the Brownian diffusion coefficients in cluster size and composition space are obtained. For characterization of binary nucleation in gases three criteria are established. These criteria establish the relative importance of the rate processes in cluster size and composition space for different …
Study Of Structural And Magnetic Properties Of Iron-Rich Mixed Rare-Earth Nddyfe (17-Y-X)Coxsiy Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, M. S. Kim, Qingsheng Cai, William Joseph James
Study Of Structural And Magnetic Properties Of Iron-Rich Mixed Rare-Earth Nddyfe (17-Y-X)Coxsiy Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, M. S. Kim, Qingsheng Cai, William Joseph James
Physics Faculty Research & Creative Works
A series of NdDyFe(17-y-x)CoxSiy solid solutions with = 2 and 3 and = 0.5 1.0 and 1.5 were prepared by induction melting stoichiometric amounts of high-purity elements. The postannealed samples consist of two phases belonging to the space groups R3 m and P63 mmc . The lattice parameters and the unit cell volumes were calculated from the refinements of the magnetic and structural unit cells using the FULLPROF version of the Rietveld program. For a fixed content of Co, the maximum Curie temperatures (305 C to 405 C) were observed in samples with = 1 and having two phases, a …
Traversal Times For Random Walks On Small-World Networks, V. M. Kenkre, Paul Ernest Parris
Traversal Times For Random Walks On Small-World Networks, V. M. Kenkre, Paul Ernest Parris
Physics Faculty Research & Creative Works
We study the mean traversal time tau for a class of random walks on Newman-Watts small-world networks, in which steps around the edge of the network occur with a transition rate F that is different from the rate f for steps across small-world connections. when f>>F, the mean time tau to traverse the network exhibits a transition associated with percolation of the random graph (i.e., small-world) part of the network, and a collapse of the data onto a universal curve. This transition was not observed in earlier studies in which equal transition rates were assumed for all allowed steps. …
Progress At The Heidelberg Ebit, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Christina Dimopoulou, I. N. Draganic, Daniel Fischer, Antonio J. Gonzalez, A. Lapierre, V. Mironov, Robert Moshammer, R. Soria Orts, Hiroyuki Tawara, M. Trinczek, Joachim Hermann Ullrich
Progress At The Heidelberg Ebit, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Christina Dimopoulou, I. N. Draganic, Daniel Fischer, Antonio J. Gonzalez, A. Lapierre, V. Mironov, Robert Moshammer, R. Soria Orts, Hiroyuki Tawara, M. Trinczek, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
Two years after the relocation of the Heidelberg EBIT, several experiments are already in operation. Spectroscopic measurements in the optical region have delivered the most precise reported wavelengths for highly charged ions, in the case of the forbidden transitions of Ar XIV and Ar XV. The lifetimes of the metastable levels involved in those transitions has been determined with an error of less than 0.2%. A new, fully automatized x-ray crystal spectrometer allows systematic measurements with very high precision and reproducibility. Absolute measurements of the Lyman series of H-like ions are currently underway. Dielectronic recombination studies have yielded information on …