118 research outputs found
The 3D MHD code GOEMHD3 for large-Reynolds-number astrophysical plasmas
The numerical simulation of turbulence and flows in almost ideal,
large-Reynolds-number astrophysical plasmas motivates the implementation of
almost conservative MHD computer codes. They should efficiently calculate, use
highly parallelized schemes scaling well with large numbers of CPU cores,
allows to obtain a high grid resolution over large simulation domains and which
can easily be adapted to new computer architectures as well as to new initial
and boundary conditions, allow modular extensions. The new massively parallel
simulation code GOEMHD3 enables efficient and fast simulations of almost ideal,
large-Reynolds-number astrophysical plasma flows, well resolved and on huge
grids covering large domains. Its abilities are validated by major tests of
ideal and weakly dissipative plasma phenomena. The high resolution (
grid points) simulation of a large part of the solar corona above an observed
active region proved the excellent parallel scalability of the code using more
than 30.000 processor cores.Comment: The revised versio
Eigenvalue bounds for polynomial central potentials in d dimensions
If a single particle obeys non-relativistic QM in R^d and has the Hamiltonian
H = - Delta + f(r), where f(r)=sum_{i = 1}^{k}a_ir^{q_i}, 2\leq q_i < q_{i+1},
a_i \geq 0P_i =
P_{n\ell}^{(d)}(q_k) and a general approximation formula if P_i =
P_{n\ell}^{(d)}(q_i). For the quantum anharmonic oscillator f(r)=r^2+\lambda
r^{2m},m=2,3,... in d dimension, for example, E = E_{n\ell}^{(d)}(\lambda) is
determined by the algebraic expression
\lambda={1\over \beta}({2\alpha(m-1)\over mE-\delta})^m({4\alpha \over
(mE-\delta)}-{E\over (m-1)}) where \delta={\sqrt{E^2m^2-4\alpha(m^2-1)}} and
\alpha, \beta are constants. An improved lower bound to the lowest eigenvalue
in each angular-momentum subspace is also provided. A comparison with the
recent results of Bhattacharya et al (Phys. Lett. A, 244 (1998) 9) and Dasgupta
et al (J. Phys. A: Math. Theor., 40 (2007) 773) is discussed.Comment: 13 pages, no figure
Operator Method for Nonperturbative Calculation of the Thermodynamic Values in Quantum Statistics. Diatomic Molecular Gas
Operator method and cumulant expansion are used for nonperturbative
calculation of the partition function and the free energy in quantum
statistics. It is shown for Boltzmann diatomic molecular gas with some model
intermolecular potentials that the zeroth order approximation of the proposed
method interpolates the thermodynamic values with rather good accuracy in the
entire range of both the Hamiltonian parameters and temperature. The systematic
procedure for calculation of the corrections to the zeroth order approximation
is also considered.Comment: 22 pages, 7 Postscript figures, accepted for publication in Journal
of Physics
Multiply charged ions from iodine laser-produced plasma of medium- and high-Z targets
Maximum charge states of ions registered in the far expansion zone from laser-produced plasma of Al, Co, Ni, Cu, Ta, W, Pt, Au, Pb, and Bi are presented. The Thomson parabola spectrometer was used to display a general view of the ion species of an expanding plasma while detailed ion charge-energy spectra were determined by the cylindrical electrostatic ion energy analyzer. The current densities of highly charged ion groups above 20 mA/cm2 were measured by use of an ion collector at a distance of 1 m from the target. The photodissociation iodine laser system PERUN (λ = 1.315 μm, power density up to 1015 W cm−2) was employed as a drive
Ion production by lasers using high-power densities in a near infrared region
Results are presented of experiments on ion production from Ta targets using a short pulse (350-600 ps in focus) illumination with focal power densities exceeding 1014 Wcm-2 at the wavelength of an iodine photodissociation laser (1.315 μm) and its harmonics. Strong evidence of the existence of tantalum ions with the charge state +45 near the target surface was obtained by X-ray spectroscopy methods. The particle diagnostics point to the existence of frozen high charge states (4 MeV) for the highest observed charge states. A tentative theoretical explanation of the observed anomalous charge state freezing phenomenon in the expanding plasma produced by a subnanosecond laser pulse is give
Contribution to understanding the mathematical structure of quantum mechanics
Probabilistic description of results of measurements and its consequences for
understanding quantum mechanics are discussed. It is shown that the basic
mathematical structure of quantum mechanics like the probability amplitudes,
Born rule, commutation and uncertainty relations, probability density current,
momentum operator, rules for including the scalar and vector potentials and
antiparticles can be obtained from the probabilistic description of results of
measurement of the space coordinates and time. Equations of motion of quantum
mechanics, the Klein-Gordon equation, Schrodinger equation and Dirac equation
are obtained from the requirement of the relativistic invariance of the
space-time Fisher information. The limit case of the delta-like probability
densities leads to the Hamilton-Jacobi equation of classical mechanics. Many
particle systems and the postulates of quantum mechanics are also discussed.Comment: 21 page
Metal-support interaction and charge distribution in ceria-supported Au particles exposed to CO
Understanding how reaction conditions affect metal-support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure-activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal-support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au+ atoms in contact with the ceria substrate and neutral Au0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Auδ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy
Space weathering simulations through controlled growth of iron nanoparticles on olivine
Airless planetary bodies are directly exposed to space weathering. The main spectral effects of space weathering are darkening, reduction in intensity of silicate mineral absorption bands, and an increase in the spectral slope towards longer wavelengths (reddening). Production of nanophase metallic iron (npFe0) during space weathering plays major role in these spectral changes. A laboratory procedure for the controlled production of npFe0 in silicate mineral powders has been developed. The method is based on a two-step thermal treatment of low-iron olivine, first in ambient air and then in hydrogen atmosphere. Through this process, a series of olivine powder samples was prepared with varying amounts of npFe0 in the 7-20 nm size range. A logarithmic trend is observed between amount of npFe0 and darkening, reduction of 1 µm olivine absorption band, reddening, and 1 µm band width. Olivine with a population of physically larger npFe0 particles follows spectral trends similar to other samples, except for the reddening trend. This is interpreted as the larger, ~40-50 nm sized, npFe0 particles do not contribute to the spectral slope change as efficiently as the smaller npFe0 fraction. A linear trend is observed between the amount of npFe0 and 1 µm band center position, most likely caused by Fe2+ disassociation from olivine structure into npFe0 particles.Peer reviewe
Predicting discharge location of hip fracture patients; the new discharge of hip fracture patients score
Purpose This paper reports on the development and validity of a new instrument, called the discharge of hip fracture patients score (DHP), that predicts at admission the discharge location in patients living in their own home prior to hip fracture surgery. Methods A total of 310 patients aged 50 years and above were included. Risk factors for discharge to an alternative location (DAL) were analysed with a multivariable regression analysis taking the admission variables into account with different weights based on the estimates. The score ranged from 0-100 points. The cut-off point for DAL was calculated using a ROC analysis. Reliability of the DHP was evaluated. Results Risk factors for DAL were higher age, female gender, dementia, absence of a partner and a limited level of mobility. The cut-off point was set at 30 points, with a sensitivity of 83.8%, a specificity of 64.7% and positive predictive value of 79.2%. Conclusion The DHP is a valid, simple and short instrument to be used at admission to predict discharge location of hip fracture patients
Phosphorus poisoning during wet oxidation of methane over Pd@CeO2/graphite model catalysts
10siThe influence of phosphorus and water on methane catalytic combustion was studied over Pd@CeO2 model catalysts supported on graphite, designed to be suitable for X-ray Photoelectron Spectroscopy/Synchrotron Radiation Photoelectron Spectroscopy (XPS/SRPES) analysis. In the absence of P, the catalyst was active for the methane oxidation reaction, although introduction of 15% H2O to the reaction mixture did cause reversible deactivation. In the presence of P, both thermal and chemical aging treatments resulted in partial loss of activity due to morphological transformation of the catalyst, as revealed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis. At 600 °C the combined presence of PO43− and water vapor caused a rapid, irreversible deactivation of the catalyst. XPS/SRPES analysis, combined with operando X-ray Absorption Near Edge Structure (XANES) and AFM measurements, indicated that water induces severe aggregation of CeO2 nanoparticles, exposure of CePO4 on the outer layer of the aggregates and incorporation of the catalytic-active Pd nanoparticles into the bulk. This demonstrates a temperature-activated process for P-poisoning of oxidation catalysts in which water vapor plays a crucial role.partially_openembargoed_20171009Monai, Matteo; Montini, Tiziano; Melchionna, Michele; Duchoň, Tomáš; Kúš, Peter; Tsud, Nataliya; Prince, Kevin C.; Matolin, Vladimir; Gorte, Raymond J.; Fornasiero, PaoloMonai, Matteo; Montini, Tiziano; Melchionna, Michele; Duchoň, Tomáš; Kúš, Peter; Tsud, Nataliya; Prince, Kevin C.; Matolin, Vladimir; Gorte, Raymond J.; Fornasiero, Paol
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