25,576 research outputs found
Emission FTIR analyses of thin microscopic patches of jet fuel residues deposited on heated metal surfaces
The relationship of fuel stability to fuel composition and the development of mechanisms for deposit formation were investigated. Fuel deposits reduce heat transfer efficiency and increase resistance to fuel flow and are highly detrimental to aircraft performance. Infrared emission Fourier transform spectroscopy was chosen as the primary method of analysis because it was sensitive enough to be used in-situ on tiny patches of monolayers or of only a few molecular layers of deposits which generally proved completely insoluble in any nondestructive solvents. Deposits of four base fuels were compared; dodecane, a dodecane/tetralin blend, commercial Jet A fuel, and a broadened-properties jet fuel particularly rich in polynuclear aromatics. Every fuel in turn was provided with and without small additions of such additives as thiophene, furan, pyrrole, and copper and iron naphthenates
Emission FTIR analyses of thin microscopic patches of jet fuel residue deposited on heated metal surface
Deposits laid down in patches on metal strips in a high pressure/high temperature fuel system simulator operated with aerated fuel at varying flow rates were analyzed by emission FTIR in terms of functional groups. Significant differences were found in the spectra and amounts of deposits derived from fuels to which small concentrations of oxygen-, nitrogen-, or sulfur-containing heterocyclics or metal naphthenates were added. The spectra of deposits generated on strips by heating fuels and air in a closed container were very different from those of the flowing fluid deposits. One such closed-container dodecane deposit on silver gave a strong surface-enhanced Raman spectrum
On continuum modeling of sputter erosion under normal incidence: interplay between nonlocality and nonlinearity
Under specific experimental circumstances, sputter erosion on semiconductor
materials exhibits highly ordered hexagonal dot-like nanostructures. In a
recent attempt to theoretically understand this pattern forming process, Facsko
et al. [Phys. Rev. B 69, 153412 (2004)] suggested a nonlocal, damped
Kuramoto-Sivashinsky equation as a potential candidate for an adequate
continuum model of this self-organizing process. In this study we theoretically
investigate this proposal by (i) formally deriving such a nonlocal equation as
minimal model from balance considerations, (ii) showing that it can be exactly
mapped to a local, damped Kuramoto-Sivashinsky equation, and (iii) inspecting
the consequences of the resulting non-stationary erosion dynamics.Comment: 7 pages, 2 Postscript figures, accepted by Phys. Rev. B corrected
typos, few minor change
Computer program developed for flowsheet calculations and process data reduction
Computer program PACER-65, is used for flowsheet calculations and easily adapted to process data reduction. Each unit, vessel, meter, and processing operation in the overall flowsheet is represented by a separate subroutine, which the program calls in the order required to complete an overall flowsheet calculation
True photo-counting statistics of multiple on-off detectors
We derive a closed photo-counting formula, including noise counts and a
finite quantum efficiency, for photon number resolving detectors based on
on-off detectors. It applies to detection schemes such as array detectors and
multiplexing setups. The result renders it possible to compare the
corresponding measured counting statistics with the true photon number
statistics of arbitrary quantum states. The photo-counting formula is applied
to the discrimination of photon numbers of Fock states, squeezed states, and
odd coherent states. It is illustrated for coherent states that our formula is
indispensable for the correct interpretation of quantum effects observed with
such devices.Comment: 7 pages, 4 figure
System Size and Energy Dependence of Dilepton Production in Heavy-Ion Collisions at SIS Energies
We study the dilepton production in heavy-ion collisions at energies of 1-2
AGeV as well as in proton induced pp, pn, pd and p+A reactions from 1 GeV up to
3.5 GeV. For the analysis we employ three different transport models - the
microscopic off-shell Hadron-String-Dynamics (HSD) transport approach, the
Isospin Quantum Molecular Dynamics (IQMD) approach as well as the
Ultra-relativistic Quantum Molecular Dynamics (UrQMD) approach. We confirm the
experimentally observed enhancement of the dilepton yield (normalized to the
multiplicity of neutral pions ) in heavy-ion collisions with respect
to that measured in collisions. We identify two contributions
to this enhancement: a) the bremsstrahlung which scales with the number of
collisions and not with the number of participants, i.e. pions; b) the dilepton
emission from intermediate 's which are part of the reaction cycles
and . With
increasing system size more generations of intermediate 's are created.
If such decays into a pion, the pion can be reabsorbed, however, if it
decays into a dilepton, the dilepton escapes from the system. Thus,
experimentally one observes only one pion (from the last produced )
whereas the dilepton yield accumulates the contributions from all 's of
the cycle. We show as well that the Fermi motion enhances the production of
pions and dileptons in the same way. Furthermore, employing the off-shell HSD
approach, we explore the influence of in-medium effects like the modification
of self-energies and spectral functions of the vector mesons due to their
interactions with the hadronic environment.Comment: 46 pages, 48 figures, version to be published in Phys. Rev.
Quaternions, octonions and Bell-type inequalities
Multipartite Bell-type inequalities are derived for general systems. They
involve up to eight observables with arbitrary spectra on each site. These
inequalities are closely related to the algebras of quaternions and octonions.Comment: 4 pages, no figure
Hot entanglement in a simple dynamical model
How mixed can one component of a bi-partite system be initially and still
become entangled through interaction with a thermalized partner? We address
this question here. In particular, we consider the question of how mixed a
two-level system and a field mode may be such that free entanglement arises in
the course of the time evolution according to a Jaynes-Cummings type
interaction. We investigate the situation for which the two-level system is
initially in mixed state taken from a one-parameter set, whereas the field has
been prepared in an arbitrary thermal state. Depending on the particular choice
for the initial state and the initial temperature of the quantised field mode,
three cases can be distinguished: (i) free entanglement will be created
immediately, (ii) free entanglement will be generated, but only at a later time
different from zero, (iii) the partial transpose of the joint state remains
positive at all times. It will be demonstrated that increasing the initial
temperature of the field mode may cause the joint state to become distillable
during the time evolution, in contrast to a non-distillable state at lower
initial temperatures. We further assess the generated entanglement
quantitatively, by evaluating the logarithmic negativity numerically, and by
providing an analytical upper bound.Comment: 5 pages, 2 figures. Contribution to the proceedings of the
'International Conference on Quantum Information', Oviedo, July 13-18, 2002.
Discusses sudden changes of entanglement properties in a dynamical quantum
mode
Spatial properties of entangled photon pairs generated in nonlinear layered structures
A spatial quantum model of spontaneous parametric down-conversion in
nonlinear layered structures is developed expanding the interacting vectorial
fields into monochromatic plane waves. A two-photon spectral amplitude
depending on the signal- and idler-field frequencies and propagation directions
is used to derive transverse profiles of the emitted fields as well as their
spatial correlations. Intensity spatial profiles and their spatial correlations
are mainly determined by the positions of transmission peaks formed in these
structures with photonic bands. A method for geometry optimization of the
structures with respect to efficiency of the nonlinear process is suggested.
Several structures composed of GaN/AlN layers are analyzed as typical examples.
They allow the generation of photon pairs correlated in several emission
directions. Photon-pair generation rates increasing better than the second
power of the number of layers can be reached. Also structures efficiently
generated photon pairs showing anti-bunching and anti-coalescence can be
obtained. Three reasons for splitting the correlated area in photonic-band-gap
structures are revealed: zig-zag movement of photons inside the structure,
spatial symmetry and polarization-dependent properties. Also spectral splitting
can be observed in these structures.Comment: 13 pages, 17 figure
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