1,094 research outputs found
Selective Laser Melting of Porous Structures
Within the Center of Smart Interfaces âUnderstanding and Designing Fluid Boundariesâ,
a German Excellence Initiative, the Institute of Production Management, Technology and
Machine Tools examines the manufacturing of porous structures by using selective laser melting
(SLM). In this paper two different strategies are presented in order to obtain porosity: One
strategy is to manufacture geometrically defined lattice structures. SLM allows here complex
geometries that cannot be manufactured by conventional technologies to be built. The second
approach is to manufacture geometrically undefined porosity by a specific modification of
exposure parameters. The SLM generated porous structures are investigated with respect to the
heat and mass transfer. The research focus is to increase the efficiency of spraycooling effects
and the manipulation of the Leidenfrost point.Mechanical Engineerin
Characterisation of HTSC ceramics from their resistive transition
The resistivity vs. temperature relation in bulk ceramic HTSC under
self-field conditions as well as in weak external magnetic fields is modelled
by local Lorentz force induced fluxon motion with temperature dependent
pinning. A pinning force density and two viscous drag coefficients in
intergrain and intragrain regions, respectively, can be used as characteristic
parameters describing the temperature, current, and external field dependences
of the sample resistance.Comment: 12 pages, LaTeX2e, 6 figures (epsfig), to be published in Supercond.
Sci. and Techno
On the Mixing of the Scalar Mesons , and
Based on a mass matrix describing the mixing of the scalar states
, and , the hadronic decays of the three
states are investigated. Taking into account the two possible assumptions
concerning the mass level order of the bare states
, and in the
scalar sector, and , we obtain the
glueball-quarkonia content of the three states by solving the unlinear
equations. Some predictions about the decays of the three states in two cases
are presented, which can provide a stringent consistency check of the two
assumptions.Comment: revtex 10 pages, 1 eps figur
Testing the Unitarity of the CKM Matrix with a Space-Based Neutron Decay Experiment
If the Standard Model is correct, and fundamental fermions exist only in the
three generations, then the CKM matrix should be unitary. However, there
remains a question over a deviation from unitarity from the value of the
neutron lifetime. We discuss a simple space-based experiment that, at an orbit
height of 500 km above Earth, would measure the kinetic-energy, solid-angle,
flux spectrum of gravitationally bound neutrons (kinetic energy K<0.606 eV at
this altitude). The difference between the energy spectrum of neutrons that
come up from the Earth's atmosphere and that of the undecayed neutrons that
return back down to the Earth would yield a measurement of the neutron
lifetime. This measurement would be free of the systematics of laboratory
experiments. A package of mass kg could provide a 10^{-3} precision in
two years.Comment: 10 pages, 4 figures. Revised and updated for publicatio
Scalar Quarkonium Masses and Mixing with the Lightest Scalar Glueball
We evaluate the continuum limit of the valence (quenched) approximation to
the mass of the lightest scalar quarkonium state, for a range of different
quark masses, and to the mixing energy between these states and the lightest
scalar glueball. Our results support the interpretation of as
composed mainly of the lightest scalar glueball.Comment: 14 pages of Latex, 5 PostScript figure
Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling
We report a detailed study of the vortex dynamics and vortex phase diagrams
of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar
defects, but different interlayer coupling. A pinned Bose-glass phase in the
more weakly coupled sample exists only below a cross-over field H* in striking
contrast to the strongly coupled film. Above H* the flux lines are thought to
break up into pancake vortices and the cross-over field is significantly
increased when the field is aligned along the extended defects. The two films
show different vortex creep excitations in the Bose-glass phase.Comment: zip file: 1 RevTex, 5 figures (png
A quantum mechanical description of the experiment on the observation of gravitationally bound states
Quantum states in the Earth's gravitational field were observed, when
ultra-cold neutrons fall under gravity. The experimental results can be
described by the quantum mechanical scattering model as it is presented here.
We also discuss other geometries of the experimental setup which correspond to
the absence or the reversion of gravity. Since our quantum mechanical model
describes, particularly, the experimentally realized situation of reversed
gravity quantitatively, we can practically rule out alternative explanations of
the quantum states in terms of pure confinement effects.Comment: LaTeX, 10 pages, 4 figures, v2: references adde
A window to quantum gravity phenomena in the emergence of the seeds of cosmic structure
Inflationary cosmology has, in the last few years,received a strong dose of
support from observations. The fact that the fluctuation spectrum can be
extracted from the inflationary scenario through an analysis that involves
quantum field theory in curved space-time, and that it coincides with the
observational data has lead to a certain complacency in the community, which
prevents the critical analysis of the obscure spots in the derivation. We argue
here briefly, as we have discussed in more detail elsewhere, that there is
something important missing in our understanding of the origin of the seeds of
Cosmic Structure, as is evidenced by the fact that in the standard accounts the
inhomogeneity and anisotropy of our universe seems to emerge from an exactly
homogeneous andisotropic initial state through processes that do not break
those symmetries. This article gives a very brief recount of the problems faced
by the arguments based on established physics. The conclusion is that we need
some new physics to be able to fully address the problem. The article then
exposes one avenue that has been used to address the central issue and
elaborates on the degree to which, the new approach makes different predictions
from the standard analyses. The approach is inspired on Penrose's proposals
that Quantum Gravity might lead to a real, dynamical collapse of the wave
function, a process that we argued has the properties needed to extract us from
the theoretical impasse described above.Comment: 13 pages, 3 figures. To appear in DICE 2008 conference proceeding
Lattice calculation of hybrid mesons with improved Kogut-Susskind fermions
We report on a lattice determination of the mass of the exotic
hybrid meson using an improved Kogut-Susskind action. Results from both
quenched and dynamical quark simulations are presented. We also compare with
earlier results using Wilson quarks at heavier quark masses. The results on
lattices with three flavors of dynamical quarks show effects of sea quarks on
the hybrid propagators which probably result from coupling to two meson states.
We extrapolate the quenched results to the physical light quark mass to allow
comparison with experimental candidates for the hybrid meson. The
lattice result remains somewhat heavier than the experimental result, although
it may be consistent with the .Comment: 24 pages, 12 figures. Replaced to match published versio
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