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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Systematic study of spontaneous emission in a two-dimensional arbitrary inhomogeneous environment

The spontaneous emission (SE) of the excited atoms in a two-dimensional (2D) arbitrary inhomogeneous environment has been systematically studied. The local density of states, which determines the radiation dynamics of a point source (for 3D) or a line source (for 2D), in particular, the SE rate, is represented by the electric dyadic Green's function. The numerical solution of the electric Green's tensor has been accurately obtained with the finite-difference frequency-domain method with the proper approximations of the monopole and dipole sources. The SE of atoms in photonic crystal and plasmonic metal plates has been comprehensively and comparatively investigated. For both the photonic crystal and plasmonic plates systems, the SEs depend on their respective dispersion relations and could be modified by the finite-structure or finite-size effects. This work is important for SE engineering and the optimized design of optoelectronic devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Giant resonances in {sup 238}U within the quasiparticle random-phase approximation with the Gogny force

Fully consistent axially-symmetric deformed quasiparticle random-phase approximation (QRPA) calculations have been performed, using the same Gogny D1S effective force for both the Hartree-Fock-Bogolyubov mean field and QRPA matrix. New implementation of this approach leads to the applicability of QRPA to heavy deformed nuclei. Giant resonances and low-energy collective states for monopole, dipole, quadrupole, and octupole modes are predicted for the heavy deformed nucleus {sup 238}U and compared with experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Shell-model study for neutron-rich sd-shell nuclei

The microscopic structure of neutron-rich sd-shell nuclei is investigated by using the spherical-shell model in the sd-pf valence space with the extended pairing plus quadrupole-quadrupole forces accompanied by the monopole interaction (EPQQM). The calculation reproduces systematically the known energy levels for even-even and odd-mass nuclei including the recent data for {sup 43}S, {sup 46}S, and {sup 47}Ar. In particular, the erosion of the N=28 shell closure in {sup 42}Si can be explained. Our EPQQM results are compared with other shell-model calculations with the SDPF-NR and SDPF-U effective interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Pair-truncated shell-model analysis of nuclei around mass 130

Low-lying states for even-even, odd-mass, and doubly odd nuclei in the mass A{approx}130 region are systematically investigated using a pair-truncated shell model. In this model the collective nucleon pairs with angular momenta zero and two are the basic ingredients for even-even nuclei. Additional unpaired nucleons are added to the even-even core for a description of odd-mass and doubly odd nuclei. The effective interactions consist of single-particle energies and monopole and quadrupole pairing plus quadrupole-quadrupole interactions, whose strengths are assumed to be linearly changed as functions of the number of nucleons so as to describe the level schemes of the even-even and odd-mass nuclei. Energy levels of the low-lying collective states for even-even Xe, Ba, Ce, and Nd isotopes are reproduced very well along with intraband and interband B(E2) values, which simulate the typical features of the O(6) limit of the interacting boson model. For odd-mass and doubly odd nuclei, complicated level schemes and electromagnetic moments are in excellent agreement with the experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Toward an actual account for the angular dependence of the Brueckner-Bethe-Goldstone propagator in nuclear matter

Angular correlations arising from particle-particle (pp) propagation in symmetric nuclear matter are investigated. Their account follows a detailed treatment of the angular dependence of the energy denominator of the propagator in the Brueckner-Bethe-Goldstone (BBG) equation, in conjunction with the Pauli exclusion principle for intermediate states. As a result, taking a monopole approximation for the propagator, a correlation form factor emerges from the Cauchy principal-value integral of the pp propagator, while the imaginary part becomes structurally different from those in Lippmann-Schwinger-type equations. These features are investigated within the continuous choice of the single-particle potential considering the Argonne v{sub 18} and Paris two-nucleon potentials. We find that the behavior of the mass operator is affected, deepening slightly the saturation point of symmetric nuclear matter relative to those based on angle-averaged energy denominators. Implications of these angular correlations were also investigated in the context of proton-nucleus scattering, showing clear effects on scattering observables below 100 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Gas-like state of {alpha} clusters around a {sup 16}O core in {sup 24}Mg

We have studied gas-like states of {alpha} clusters around an {sup 16}O core in {sup 24}Mg based on a microscopic {alpha}-cluster model. The 0{sup +} states below the {sup 16}O+{alpha}+{alpha} threshold, which are candidates for the resonance solution judging from the energy convergence behavior, are strongly excited by an isoscalar monopole (E0) operator from the ground state, which could be observed as an experimental signature of well-developed {alpha} gas-like states in the excited states. These states have significant overlaps with the THSR (Tohsaki-Horiuchi-Schuck-Roepke) wave functions with large spatial extension.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Low-lying structure of neutron-rich Zn and Ga isotopes

Low-lying states of even-even Zn and odd-mass Ga nuclei with neutron numbers between 42 and 50 have been calculated within the framework of the SDG-pair approximation of the nuclear shell model. We employ a monopole and quadrupole pairing plus quadrupole-quadrupole interaction with optimized parameters, which are assumed to be constants for nuclei with the same proton number or neutron number. We calculate low-lying level schemes, electric quadrupole and magnetic dipole moments, and E2 and M1 transition rates. Reasonable agreement is achieved between the calculated results and experimental data. Dominant configurations in the ground states of odd-mass Ga nuclei are discussed in terms of pair correlations. The weak-coupling picture for some states of odd-mass Ga nuclei is studied.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Geodesics of electrically and magnetically charged test particles in the Reissner-Nordstroem space-time: Analytical solutions

We present the full set of analytical solutions of the geodesic equations of charged test particles in the Reissner-Nordstroem space-time in terms of the Weierstrass weierp, {sigma}, and {zeta} elliptic functions. Based on the study of the polynomials in the {theta} and r equations, we characterize the motion of test particles and discuss their properties. The motion of charged test particles in the Reissner-Nordstroem space-time is compared with the motion of neutral test particles in the field of a gravitomagnetic monopole. Electrically or magnetically charged particles in the Reissner-Nordstroem space-time with magnetic or electric charges, respectively, move on cones similar to neutral test particles in the Taub-NUT space-times.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Modified dispersion relations and the response of the rotating Unruh-DeWitt detector

We study the response of a rotating monopole detector that is coupled to a massless scalar field which is described by a nonlinear dispersion relation in flat spacetime. Since it does not seem to be possible to evaluate the response of the rotating detector analytically, we resort to numerical computations. Interestingly, unlike the case of the uniformly accelerated detector that has been considered recently, we find that defining the transition probability rate of the rotating detector poses no difficulties. Further, we show that the response of the rotating detector can be computed exactly (albeit, numerically) even when it is coupled to a field that is governed by a nonlinear dispersion relation. We also discuss the response of the rotating detector in the presence of a cylindrical boundary on which the scalar field is constrained to vanish. While superluminal dispersion relations hardly affect the standard results, we find that subluminal dispersion relations can lead to relatively large modifications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Tracing the redshift evolution of Hubble parameter with gravitational-wave standard sirens

Proposed space-based gravitational-wave detectors such as BBO and DECIGO can detect {approx}10{sup 6} neutron star (NS) binaries and determine the luminosity distance to the binaries with high precision. Combining the luminosity distance and electromagnetically derived redshift, one would be able to probe cosmological expansion out to high redshift. In this paper, we show that the Hubble parameter as a function of redshift can be directly measured with monopole and dipole components of the luminosity distance on the sky. As a result, the measurement accuracies of the Hubble parameter in each redshift bin up to z=1 are 3-14%, 1.5-8%, and 0.8-4% for the observation time 1 yr, 3 yr, and 10 yr, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Forecasting the cosmological constraints with anisotropic baryon acoustic oscillations from multipole expansion

Baryon acoustic oscillations imprinted in the galaxy power spectrum can be used as a standard ruler to determine the angular diameter distance and Hubble parameter from high-redshift galaxies. Combining redshift distortion effect which apparently distorts the galaxy clustering pattern, we can also constrain the growth rate of large-scale structure formation. Usually, future forecasts for constraining these parameters from galaxy redshift surveys are made with the full 2D power spectrum characterized as a function of wave number k and directional cosine {mu} between line-of-sight direction and wave vector, i.e., P(k,{mu}). Here, we apply the multipole expansion to the full 2D power spectrum, and discuss how much cosmological information can be extracted from the lower-multipole spectra, taking a proper account of the nonlinear effects on gravitational clustering and redshift distortion. Fisher matrix analysis reveals that compared to the analysis with the full 2D spectrum, using only the partial information from the monopole and quadrupole spectra generally degrades the constraints by a factor of {approx}1.3 for each parameter. The additional information from the hexadecapole spectrum helps to improve the constraints, leading to a result that is almost comparable to the one expected from the full 2D spectrum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Reducing orbital eccentricity of precessing black-hole binaries

Building initial conditions for generic binary black-hole evolutions which are not affected by initial spurious eccentricity remains a challenge for numerical-relativity simulations. This problem can be overcome by applying an eccentricity-removal procedure which consists of evolving the binary black hole for a couple of orbits, estimating the resulting eccentricity, and then restarting the simulation with corrected initial conditions. The presence of spins can complicate this procedure. As predicted by post-Newtonian theory, spin-spin interactions and precession prevent the binary from moving along an adiabatic sequence of spherical orbits, inducing oscillations in the radial separation and in the orbital frequency. For single-spin binary black holes these oscillations are a direct consequence of monopole-quadrupole interactions. However, spin-induced oscillations occur at approximately twice the orbital frequency, and therefore can be distinguished and disentangled from the initial spurious eccentricity which occurs at approximately the orbital frequency. Taking this into account, we develop a new eccentricity-removal procedure based on the derivative of the orbital frequency and find that it is rather successful in reducing the eccentricity measured in the orbital frequency to values less than 10{sup -4} when moderate spins are present. We test this new procedure using numerical-relativity simulations of binary black holes with mass ratios 1.5 and 3, spin magnitude 0.5, and various spin orientations. The numerical simulations exhibit spin-induced oscillations in the dynamics at approximately twice the orbital frequency. Oscillations of similar frequency are also visible in the gravitational-wave phase and frequency of the dominant l=2, m=2 mode.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Phase diagram of the lattice G{sub 2} Higgs model

We study the phases and phase transition lines of the finite temperature G{sub 2} Higgs model. Our work is based on an efficient local hybrid Monte-Carlo algorithm which allows for accurate measurements of expectation values, histograms, and susceptibilities. On smaller lattices we calculate the phase diagram in terms of the inverse gauge coupling {beta} and the hopping parameter {kappa}. For {kappa}{yields}0 the model reduces to G{sub 2} gluodynamics and for {kappa}{yields}{infinity} to SU(3) gluodynamics. In both limits the system shows a first order confinement-deconfinement transition. We show that the first order transitions at asymptotic values of the hopping parameter are almost joined by a line of first order transitions. A careful analysis reveals that there exists a small gap in the line where the first order transitions turn into continuous transitions or a crossover region. For {beta}{yields}{infinity} the gauge degrees of freedom are frozen and one finds a nonlinear O(7) sigma model which exhibits a second order transition from a massive O(7) symmetric to a massless O(6) symmetric phase. The corresponding second order line for large {beta} remains second order for intermediate {beta} until it comes close to the gap between the two first order lines. Besides this second order line and the first order confinement-deconfinement transitions we find a line of monopole-driven bulk transitions which do not interfere with the confinement-deconfinment transitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

BPS spectrum of supersymmetric CP(N-1) theory with Z{sub N} twisted masses

We revisit the Bogomol'nyi-Prasad-Sommerfeld (BPS) monopoles spectrum of the supersymmetric CP(N-1) two-dimensional model with Z{sub N}-symmetric twisted masses m{sub l} (l=0,1,...,N-1). A related issue we address is that of the curves of marginal stability (CMS) in this theory. Previous analyses were incomplete. We close the gap by exploiting a number of consistency conditions. In particular, we amend the Dorey formula for the BPS spectrum. Our analysis is based on the exact Veneziano--Yankielowicz-type superpotential and on the strong-coupling spectrum of the theory found from the mirror representation at small masses, |m{sub l}|<<{Lambda}. We show that at weak coupling the spectrum, with necessity, must include N-1 BPS towers of states, instead of just one, as was thought before. Only one of the towers is seen in the quasiclassical limit. We find the corresponding CMS for these towers, and argue that in the large-N limit they become circles, filling out a band on the plane of a single mass parameter of the model at hand. Inside the CMS, N-1 towers collapse into N stable states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Model Independence in Two Dimensions and Polarized Cold Dipolar Molecules

We calculate the energy and wave functions of two particles confined to two spatial dimensions interacting via arbitrary anisotropic potentials with negative or zero net volume. The general rigorous analytic expressions are given in the weak coupling limit where universality or model independence are approached. The monopole part of anisotropic potentials is crucial in the universal limit. We illustrate the universality with a system of two arbitrarily polarized cold dipolar molecules in a bilayer. We discuss the transition to universality as a function of polarization and binding energy and compare analytic and numerical results obtained by the stochastic variational method. The universal limit is essentially reached for experimentally accessible strengths.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu 2 OSeO 3

Topologically nontrivial spin textures such as vortices, skyrmions, and monopoles are promising candidates as information carriers for future quantum information science. Their controlled manipulation including creation and annihilation remains an important challenge toward practical applications and further exploration of their emergent phenomena. Here, we report controlled evolution of the helical and skyrmion phases in thin films of multiferroic Te-doped Cu 2 OSeO 3 as a function of material thickness, dopant, temperature, and magnetic field using in situ Lorentz phase microscopy. We report two previously unknown phenomena in chiral spin textures in multiferroic Cu 2 OSeO 3 : anisotropic scaling and channeling with a fixed-Q state. The skyrmion channeling effectively suppresses the recently reported second skyrmion phase formation at low temperature. Our study provides a viable way toward controlled manipulation of skyrmion lattices, envisaging chirality-controlled skyrmion flow circuits and enabling precise measurement of emergent electromagnetic induction and topological Hall effects in skyrmion lattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗