242 research outputs found
Modelling of chemical reactions in metallurgical processes
Since the last three decades, the study of reduction of iron-ore has gained much attention as it is considered a core process for the steel industry. Fluidized bed and moving bed reactors are utilized to reduce the iron-ore efficiently. As reducing agents coal, coke or natural gases are used, which are released as CO2 gas, or sometimes in small amounts as H2O to the environment. The conditions in these reactors are harsh and provide limited accessibility, therefore computational tools are used to investigate them. One such tool is the CFD-DEM method, where the reacting gas species and the governing equations for the gas flow are calculated in the Eulerian (CFD) side, whereas the particle reactions and equation of motion are calculated in the Lagrangian (DEM) side.
In the current work, the CFD-DEM method is extended to cover the most dominant types of models for heterogeneous reactions between submerged solids and fluids. One of these models is the Shrinking Particle Model (SPM), which is used to verify the commu- nication framework between the CFD and DEM
sides by running preliminary test cases. Another model is the Unreacted Shrinking Core Model (USCM), which is considered as a good model for a reality like iron-ore reduction modelling
Nonperturbative contributions to the QCD pressure
We summarize the most important arguments why a perturbative description of
finite-temperature QCD is unlikely to be possible and review various
well-established approaches to deal with this problem. Then, using a recently
proposed method, we investigate nonperturbative contributions to the QCD
pressure and other observables (like energy, anomaly and bulk viscosity)
obtained by imposing a functional cutoff at the Gribov horizon. Finally, we
discuss how such contributions fit into the picture of consecutive effective
theories, as proposed by Braaten and Nieto, and give an outline of the next
steps necessary to improve this type of calculation.Comment: 15 pages, 13 figures, uses xcolor.sty; in v2 quality of some figures
has been improved, discussion of other approaches has been extende
Superfluid 4He dynamics beyond quasiparticle excitations
The dynamics of superfluid 4He at and above the Landau quasiparticle regime
is investigated by high precision inelastic neutron scattering measurements of
the dynamic structure factor. A highly structured response is observed above
the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for
phonon-phonon, maxon-roton and roton-roton coupling processes. The experimental
dynamic structure factor is compared to the calculation of the same physical
quantity by a Dynamic Many-body theory including three-phonon processes
self-consistently. The theory is found to provide a quantitative description of
the dynamics of the correlated bosons for energies up to about three times that
of the Landau quasiparticles.Comment: 5 pages, 3 figure
Gravitomagnetism, clocks and geometry
New techniques to evaluate the clock effect using light are described. These
are based on the flatness of the cylindrical surface containing the world lines
of the rays constrained to move on circular trajectories about a spinning mass.
The effect of the angular momentum of the source is manifested in the fact that
inertial observers must be replaced by local non rotating observers. Starting
from this an exact formula for circular trajectories is found. Numerical
estimates for the Earth environment show that light would be a better probe
than actual clocks to evidence the angular momentum influence. The advantages
of light in connection with some principle experiments are shortly reviewed.Comment: TCI Latex, 12 pages, 2 figures. To appear in European Journal of
Physic
Detection of the gravitomagnetic clock effect
The essence of the gravitomagnetic clock effect is properly defined showing
that its origin is in the topology of world lines with closed space
projections. It is shown that, in weak field approximation and for a
spherically symmetric central body, the loss of synchrony between two clocks
counter-rotating along a circular geodesic is proportional to the angular
momentum of the source of the gravitational field. Numerical estimates are
presented for objects within the solar system. The less unfavorable situation
is found around Jupiter.Comment: 14 pages; Latex. To be published on Classical and Quantum Gravit
On the Possibility of Measuring the Gravitomagnetic Clock Effect in an Earth Space-Based Experiment
In this paper the effect of the post-Newtonian gravitomagnetic force on the
mean longitudes of a pair of counter-rotating Earth artificial satellites
following almost identical circular equatorial orbits is investigated. The
possibility of measuring it is examined. The observable is the difference of
the times required to in passing from 0 to 2 for both senses of
motion. Such gravitomagnetic time shift, which is independent of the orbital
parameters of the satellites, amounts to 5 s for Earth; it is
cumulative and should be measured after a sufficiently high number of
revolutions. The major limiting factors are the unavoidable imperfect
cancellation of the Keplerian periods, which yields a constraint of 10
cm in knowing the difference between the semimajor axes of the satellites,
and the difference of the inclinations of the orbital planes which, for
, should be less than . A pair of spacecrafts
endowed with a sophisticated intersatellite tracking apparatus and drag-free
control down to 10 cm s Hz level might allow to meet
the stringent requirements posed by such a mission.Comment: LaTex2e, 22 pages, no tables, 1 figure, 38 references. Final version
accepted for publication in Classical and Quantum Gravit
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