5,410 research outputs found
The impact of space and space-related activities on a local economy. a case study of boulder, colorado. part ii- the income-product accounts
Total impact of space and space related activities on local economy of Boulder, Colorado - income-product account
The susceptibility and excitation spectrum of (VO)PO in ladder and dimer chain models
We present numerical results for the magnetic susceptibility of a Heisenberg
antiferromagnetic spin ladder, as a function of temperature and the spin-spin
interaction strengths and . These are contrasted with new
bulk limit results for the dimer chain. A fit to the experimental
susceptibility of the candidate spin-ladder compound vanadyl pyrophosphate,
(VO)PO, gives the parameters meV and meV. With these values we predict a singlet-triplet energy gap of
meV, and give a numerical estimate of the ladder triplet
dispersion relation . In contrast, a fit to the dimer chain model
leads to meV and meV, which predicts a gap of meV.Comment: 16 pages, 6 figures available upon request, RevTex 3.0, preprint
ORNL-CCIP-94-04 / RAL-94-02
Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12
The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.Comment: To be published in PR
Linear Magnetic Chains with Anisotropic Coupling
Linear chains (and rings) of S=12 spins with the anisotropic (Ising-Heisenberg) Hamiltonian ℋ=−2JΣi=1N{SizSi+1z+γ(SixSi+1x+SiySi+1y)}−gβΣi=1NH·Si have been studied by exact machine calculations for N=2 to 11, γ=0 to 1 and for ferro- and antiferro-magnetic coupling. The results reveal the dependence on finite size and anisotropy of the spectrum and dispersion laws, of the energy, entropy, and specific heat, of the magnetization and susceptibilities, and of the pair correlations. The limiting N→∞ behavior is accurately indicated, for all γ, in the region kT∣∣J∣∣\u3e~0.5 which includes the maxima in the specific heat and susceptibility. The behavior of thermal and magnetic properties of infinite chains at lower temperatures is estimated by extrapolation. For infinite antiferromagnetic chains the ground-state degeneracy, the anisotropy gap, and the magnetization, perpendicular susceptibility, and pair correlations at T=0 are similarly studied. Estimates of the long-range order suggest that it vanishes only at the Heisenberg limit γ=1 and confirm the accuracy of Walker\u27s perturbation series in γ
Different time scales in plasmonically enhanced high-order harmonic generation
We investigate high-order-harmonic generation in inhomogeneous media for reduced dimensionality models. We perform a phase-space analysis, in which we identify specific features caused by the field inhomogeneity. We compute high-order-harmonic spectra using the numerical solution of the time-dependent Schrödinger equation, and provide an interpretation in terms of classical electron trajectories. We show that the dynamics of the system can be described by the interplay of high-frequency and slow-frequency oscillations, which are given by Mathieu's equations. The latter oscillations lead to an increase in the cutoff energy, and, for small values of the inhomogeneity parameter, take place over many driving-field cycles. In this case, the two processes can be decoupled and the oscillations can be described analytically
Microscopic Electron Models with Exact SO(5) Symmetry
We construct a class of microscopic electron models with exact SO(5) symmetry
between antiferromagnetic and d-wave superconducting ground states. There is an
exact one-to-one correspondence between both single-particle and collective
excitations in both phases. SO(5) symmetry breaking terms can be introduced and
classified according to irreducible representations of the exact SO(5) algebra.
The resulting phase diagram and collective modes are identical to that of the
SO(5) nonlinear sigma model.Comment: 5 pages, LATEX, 4 eps fig
Comprehensive Uncertainty Quantification in Nuclear Safeguards
Nuclear safeguards aim to confirm that nuclear materials and activities are used for peaceful purposes. To ensure that States are honoring their safeguards obligations, quantitative conclusions regarding nuclear material inventories and transfers are needed. Statistical analyses used to support these conclusions require uncertainty quantification (UQ), usually by estimating the relative standard deviation (RSD) in random and systematic errors associated with each measurement method. This paper has two main components. First, it reviews why UQ is needed in nuclear safeguards and examines recent efforts to improve both top-down (empirical) UQ and bottom-up (first-principles) UQ for calibration data. Second, simulation is used to evaluate the impact of uncertainty in measurement error RSDs on estimated nuclear material loss detection probabilities in sequences of measured material balances
Study of the magnetic susceptibility in the spin-Peierls system CuGeO
We study numerically, using a one-dimensional Heisenberg model, the
spin-Peierls transition in the linear Cu spin-1/2 chains in the
inorganic compound CuGeO which has been recently observed experimentally.
We suggest that the magnetic susceptibility, the temperature dependence of the
spin gap and the spin-Peierls transition temperature of this material can be
reasonably described by including nearest and next nearest neighbor
antiferromagnetic interactions along the chain. We estimate that the nearest
neighbor exchange parameter J is approximately , and that the next
nearest neighbor exchange parameter is approximately .Comment: 14 pages, Revtex v2.0, 4 figures available upon reques
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