Browsing by Subject "physics, applied"

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Acceleration Of Protons To Above 6 MeV Using H2O >Snow> Nanowire Targets
(2012-11) Pomerantz, I.; Schleifer, E.; Nahum, E.; Eisenmann, S.; Botton, M.; Gordon, D.; Sprangel, P.; Zigler, A.; Pomerantz, I.
A scheme is presented for using H2O >snow> nanowire targets for the generation of fast protons. This novel method may relax the requirements for very high laser intensities, thus reducing the size and cost of laser based ion acceleration system.
Air-Coupled Surface Wave Transmission Measurement Across A Partially Closed Surface-Breaking Crack In Concrete
(2011-06) Kee, S. H.; Zhu, J. Y.; Kee, S. H.; Zhu, J. Y.
Previous researchers have demonstrated that the transmission of surface waves is effective to estimate the depth of a surface-breaking crack in solids. However, most of the results were obtained using a well-defined crack (or notch) in laboratory. In fact, there is a critical gap to apply the theory to surface-breaking cracks in concrete structures subjected to external loadings where the cracks are generally ill-defined, and partially closed. In this study, the authors investigated transmission coefficients of surface waves across a partially closed surface-breaking crack in concrete subjected to monotonically increasing compressive loadings. First, a concrete beam (0.5 X 0.154 X 2.1 m(3)) having two surface-breaking cracks with various crack widths was prepared in laboratory. Second, transmission coefficients of impact-induced surface waves were measured across a surface-breaking crack in the concrete beam with increasing compressive loadings from 0 to 140kN (10% of the ultimate compressive strength of the concrete beam). External post-tensioning was used to apply the compression. For comparison purpose, sensitivity of surface wave velocity to compressive loading was also investigated. As a result, observations in this study reveal that transmission coefficient is a more sensitive acoustic parameter than phase velocity to evaluate a surface-breaking cracking in concrete subjected to compressive loadings.
Alfven-Wave Studies On Pretext
(1985) Valanju, P. M.; Bengtson, R. D.; Booth, W. D.; Cook, R. W.; Evans, T. E.; Mahajan, S. M.; Oakes, M. E.; Ross, D. W.; Surko, C. M.; Valanju, P. M.; Bengtson, R. D.; Booth, W. D.; Cook, R. W.; Evans, T. E.; Mahajan, S. M.; Oakes, M. E.; Ross, D. W.
Analytic Model Of Electron Self-Injection In A Plasma Wakefield Accelerator In The Strongly Nonlinear Bubble Regime
(2012-06) Yi, S. A.; Khudik, V.; Siemon, C.; Shvets, G.; Yi, S. A.; Khudik, V.; Siemon, C.; Shvets, G.
Self-injection of background electrons in plasma wakefield accelerators in the highly nonlinear bubble regime is analyzed using particle-in-cell and semi-analytic modeling. It is shown that the return current in the bubble sheath layer is crucial for accurate determination of the trapped particle trajectories.
Anisotropic Small-Polaron Hopping In W:Bivo4 Single Crystals
(2015-01) Rettie, Alexander J. E.; Chemelewski, William D.; Lindemuth, Jeffrey; McCloy, John S.; Marshall, Luke G.; Zhou, Jianshi S.; Emin, David; Mullins, C. Buddie; Rettie, Alexander J. E.; Chemelewski, William D.; Marshall, Luke G.; Zhou, Jianshi S.; Mullins, C. Buddie
DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO4). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10(-1) cm(2) V-1 s(-1) at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 x 10(-5) cm(2) V-1 s(-1) at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (approximate to 5 angstrom) transfers in addition to the somewhat shorter (approximate to 4 angstrom), nearly isotropic nearest-neighbor transfers. (C) 2015 AIP Publishing LLC.
Assembly Of The First Dwarf Galaxies
(2010-11) Pawlik, A.; Milosavljevic, M.; Bromm, V.; Pawlik, Andreas; Milosavljević, Miloš; Bromm, Volker
Understanding the formation and evolution of the first stars and galaxies is crucial to understanding reionization, a key epoch in the history of the Universe. Detailed theoretical studies of the galaxies before and during reionization are now particularly urgent because of the wealth of observational data that will soon be provided by the next generation of telescopes, such as JWST, ALMA, LOFAR, MWA, and others. We simulate the formation of the first galaxies using cosmological smoothed particle hydrodynamics simulations. Zooming in on individual galaxies, we explore how various physical processes affect their assembly and further evolution. A highlight of our study will be the simulation of the radiation-hydrodynamics of galaxy assembly, which we will perform using our multi-frequency radiative transfer method TRAPHIC. Feedback from radiation has long been suspected to play a decisive role in galaxy formation and we will investigate its implications for observable properties of the first galaxies.
Asymmetric Time Evolution And Indistinguishable Events
(2010-11) Bryant, P. W.; Bryant, P. W.
With a time asymmetric theory, in which quantum mechanical time evolution is given by a semigroup of operators rather than by a group, the states of open systems are represented by density operators exhibiting a branching behavior. To treat the indistinguishably of the members of experimental ensembles, we hypothesize that environmental interference occurs during events that are themselves fundamentally indistinguishable.
Attraction And Repulsion Of Multi-Color Laser Beams In Plasmas: A Computational Study
(2009-01) Yi, S. A.; Kalmykov, S.; Shvets, G.; Yi, S. A.; Kalmykov, S.; Shvets, G.
The nonlinear interaction of high-power multi-color laser beams in plasmas is investigated numerically. Both the relativistic mass increase and the driven plasma wave contribute to the mutual beam-beam interaction and to the development of the electromagnetic cascade. The propagation of the individual cascade sidebands is modelled in the paraxial approximation. The resulting set of coupled nonlinear envelope equations is solved numerically using a newly developed pseudospectral method. We predict that two beams intersecting in the plasma can either attract or deflect each other depending on whether their frequency detuning is slightly below or above the electron Langmuir frequency.
Bayesian Analysis Of RR Lyrae Luminosities And Kinematics
(2007-11) Jefferys, T. R.; Barnes, T. G.; Dambis, A.; Jefferys, W. H.; Jefferys, Thomas R.
We are using a hierarchical Bayes model to analyze the distances, luminosities, and kinematics of RR Lyrae stars. Our model relates these characteristics to the raw data of proper motions, radial velocities, apparent luminosities and metallicities of each star. A combination of Gibbs and Metropolis-Hastings sampling, using latent variables for the actual velocity and luminosity of each star, is used to draw a sample from the full posterior distribution of these variables, with consideration to identifiability and the properness of the hierarchical model, and draw inferences on the quantities of interest in the usual way. We have applied our model to the large HIPPARCOS database, and we have attempted to include metallicity and period in our model, which has not been done previously.
Bayesians Can Learn From Old Data
(2007-11) Jefferys, W. H.; Jefferys, William H.
In a widely-cited paper, Glymour (Theory and Evidence, Princeton, N. J.: Princeton University Press, 1980, pp. 63-93) claims to show that Bayesians cannot team from old data. His argument contains an elementary error. I explain exactly where Glymour went wrong, and how the problem should be handled correctly. When the problem is fixed, it is seen that Bayesians, just like logicians, can indeed learn from old data.
Characterization Of Thermal Stresses And Plasticity In Through-Silicon Via Structures For Three-Dimensional Integration
(2014) Jiang, T. F.; Ryu, S. K.; Im, J.; Huang, R.; Ho, P. S.; Jiang, Tengfei; Ryu, Suk-Kyu; Im, Jay; Huang, Rui; Ho, Paul S.
Through-silicon via (TSV) is a critical element connecting stacked dies in three-dimensional (3D) integration. The mismatch of thermal expansion coefficients between the Cu via and Si can generate significant stresses in the TSV structure to cause reliability problems. In this study, the thermal stress in the TSV structure was measured by the wafer curvature method and its unique stress characteristics were compared to that of a Cu thin film structure. The thermo-mechanical characteristics of the Cu TSV structure were correlated to microstructure evolution during thermal cycling and the local plasticity in Cu in a triaxial stress state. These findings were confirmed by microstructure analysis of the Cu vias and finite element analysis (FEA) of the stress characteristics. In addition, the local plasticity and deformation in and around individual TSVs were measured by synchrotron x-ray microdiffraction to supplement the wafer curvature measurements. The importance and implication of the local plasticity and residual stress on TSV reliabilities are discussed for TSV extrusion and device keep-out zone (KOZ).
Cold Atom Ballistics By Coherent Control
(2008-04) Reichl, L. E.; Holder, B. P.; Reichl, Linda E.; Holder, Benjamin P.
We use the technique of Stimulated Raman adiabatic passage (STIRAP) to affect transport of ultracold atoms between two optical lattices in relative motion. We show, using Floquet analysis and degenerate perturbation theory, that the dynamics of atoms in a particular time-dependent optical lattice system can be reduced to the 3-level STIRAP model, allowing for a simple description of their coherent acceleration.
Collision-Induced Absorption At Temperatures Of Thousands Of Kelvin, From First Principles, For Astrophysical Applications
(2010-06) Frommhold, L.; Abel, M.; Wang, F.; Li, X. P.; Hunt, K. L. C.; Frommhold, Lothar; Abel, Martin
New ab initio surfaces of the potential energies and the induced electric dipole moments of H-2-H-2 and H-2-He collisional complexes are obtained with H-2 bond distances from 0.942 to 2.801 bohr. These data permit the calculation of collision-induced absorption (CIA) spectra of dense hydrogen-helium gas mixtures at temperatures up to thousands of kelvin, i.e., under conditions where strong rotovibrational excitations of the H-2 molecules exist. First results of CIA spectra are obtained over an extended range of frequencies and temperatures. The work is an extension of our previous work on the opacities of the (low-temperature) atmospheres of the outer planets.
Collision-Induced Absorption By Supermolecular Complexes From A New Potential Energy And Induced Dipole Surface, Suited For Calculations Up To Thousands Of Kelvin
(2010-06) Abel, M.; Frommhold, L.; Wang, F.; Gustafsson, M.; Li, X. P.; Hunt, K. L. C.; Abel, Martin; Frommhold, Lothar
Absorption by pairs of H-2 molecules is an important opacity source in the atmospheres of the outer planets, and thus of special astronomical interest. The emission spectra of cool white dwarf stars differ significantly from the expected blackbody spectra, amongst other reasons due to absorption by H-2 H-2, H-2 He, and H-2-H collisional complexes in the stellar atmospheres. To model the radiative processes in these atmospheres, which have temperatures of several thousand kelvin, one needs accurate knowledge of the induced dipole (ID) and potential energy surfaces (PES) of such collisional complexes. These come from quantum-chemical calculations with the H-2 bonds stretched or compressed far from equilibrium. Laboratory measurements of collision-induced (CI) absorption exist only at much lower temperature. For H-2 pairs at room temperature, the calculated spectra of the rototranslational band, the fundamental band, and the first overtone match the experimental data very well. In addition, with the newly obtained IDS it became possible to reproduce the measurements in the far blue wing of the rototranslational spectrum of H-2 at 77.5 K, as well as at 300 K. Similarly good agreement between theory and measurement is seen in the fundamental band of molecular deuterium at room temperature. Furthermore, we also show the calculated absorption spectra of H-2-He at 600 K and of H-2-H-2 at 2,000 K, for which there are no experimental data for comparison.
Comment On >Assessment Of Field-Induced Quantum Confinement In Heterogate Germanium Electron-Hole Bilayer Tunnel Field-Effect Transistor> Appl. Phys. Lett. 105, 082108 (2014)
(2015-01) Hsu, William; Mantey, Jason; Register, Leonard F.; Banerjee, Sanjay K.; Hsu, William; Mantey, Jason; Register, Leonard F.; Banerjee, Sanjay K.
Not Available
A Conservative Discontinuous Galerkin Scheme With O(N-2) Operations In Computing Boltzmann Collision Weight Matrix
(2014-07) Gamba, I. M.; Zhang, C. L.; Gamba, Irene M.; Zhang, Chenglong
In the present work, we propose a deterministic numerical solver for the homogeneous Boltzmann equation based on Discontinuous Galerkin (DG) methods. The weak form of the collision operator is approximated by a quadratic form in linear algebra setting. We employ the property of >shifting symmetry> in the weight matrix to reduce the computing complexity from theoretical O(N-3) down to O(N-2), with N the total number of freedom for d-dimensional velocity space. In addition, the sparsity is also explored to further reduce the storage complexity. To apply lower order polynomials and resolve loss of conserved quantities, we invoke the conservation routine at every time step to enforce the conservation of desired moments (mass, momentum and/or energy), with only linear complexity. Due to the locality of the DG schemes, the whole computing process is well parallelized using hybrid OpetiMP and MPI. The current work only considers integrable angular cross-sections under elastic and/or inelastic interaction laws. Numerical results on 2-D and 3-D problems are shown.
Crystallographic Changes In Lead Zirconate Titanate Due To Neutron Irradiation
(2014-11) Henriques, A.; Graham, J. T.; Landsberger, S.; Ihlefeld, J. F.; Brennecka, G. L.; Brown, D. W.; Forrester, J. S.; Jones, J. L.; Landsberger, Sheldon
Piezoelectric and ferroelectric materials are useful as the active element in non-destructive monitoring devices for high-radiation areas. Here, crystallographic structural refinement (i. e., the Rietveld method) is used to quantify the type and extent of structural changes in PbZr0.5Ti0.5O3 after exposure to a 1 MeV equivalent neutron fluence of 1.7x10(15) neutrons/cm(2). The results showa measurable decrease in the occupancy of Pb and O due to irradiation, with O vacancies in the tetragonal phase being created preferentially on one of the two O sites. The results demonstrate a method by which the effects of radiation on crystallographic structure may be investigated. (C) 2014 Author(s).
Deceleration Of Projectiles In Sand
(2012-03) Bless, S.; Cooper, W.; Watanabe, K.; Peden, R.; Bless, S
Penetration of projectiles was measured for hemispherical and conical nose shapes penetrating granular media. Targets were beds of Ottawa sand and Eglin sand. Projectiles were rigid metals. Experimental parameters that were varied included velocity (from 300 to 600 m/s), nose shape, sand density, and scale (from 5 mm to 20 mm). Strong evidence for scale effects is found: 5 mm diameter projectiles are less effective penetrators than 12.5, 15, or 20 mm diameter penetrators.
Detecting Dark Matter In The MSSM With Non-Universal Higgs Masses
(2009-02) Sandick, P.; Sandick, Pearl
We discuss the direct detection prospects for neutralino dark matter via elastic scattering in variations of the MSSM with non-universal supersymmetry-breaking contributions to the Higgs masses Taking as our starting point the CMSSM, in which supersymmetry-breaking contributions to all scalar masses are universal, we examine scenarios in which both Higgs scalar masses are non-universal by the same amount (NUHM1) and scenarios in which the Higgs scalar masses are independently non-universal (NUHM2)
Detection Of Gravitational Collapse
(1983) Wheeler, J. C.; Wheeler, J. A.; Wheeler, J. Craig; Wheeler, John A.