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Prototyping Large-Sized Objects Using Freeform Thick Layers of Plastic Foam
Current Rapid Prototyping systems are primarily aimed at small-sized objects containing many
shape details. In this paper a Rapid Prototyping technology is presented that is aimed at largesized objects having a complex, freeform outer shape. This new technology builds the model out
ofthick layers, each having freeform outside faces. The paper will present: an overview of current
methods to produce large prototypes, the basics of the new method, the technology used to
produce the layers, the toolpath planning and finally the overall system design.Mechanical Engineerin
Remarks on the realization of the Atiyah-Singer index theorem in lattice gauge theory
We discuss the interplay between topologically non-trivial gauge field
configurations and the spectrum of the Wilson-Dirac operator in lattice gauge
theory. Our analysis is based on analytic arguments and numerical results from
a lattice simulation of QED_2.Comment: Talk given at LATTICE97, 3 pages, 1 figur
Spin resolved Hall effect driven by spin-orbit coupling
Spin and electric Hall currents are calculated numerically in a
two-dimensional mesoscopic system with Rashba and Dresselhaus spin-orbit
coupling by means of the Landauer-Buttiker formalism. It is found that both
electric and spin Hall currents circulate when two spin-orbit couplings
coexist, while the electric Hall conductance vanishes if either one is absent.
The electric and spin Hall conductances are suppressed in strong disorder, but
survive in weak disorder. Physically it can be understood that the spinomotive
transverse "force" generated by spin-orbit coupling is responsible for the
formation of the spin Hall current and the lack of transverse reflection
symmetry is the origin of the electric Hall current.Comment: 4 pages, 5 figure
Simulations of Cold Electroweak Baryogenesis: Finite time quenches
The electroweak symmetry breaking transition may supply the appropriate
out-of-equilibrium conditions for baryogenesis if it is triggered sufficiently
fast. This can happen at the end of low-scale inflation, prompting baryogenesis
to occur during tachyonic preheating of the Universe, when the potential energy
of the inflaton is transfered into Standard Model particles. With the proper
amount of CP-violation present, the observed baryon number asymmetry can be
reproduced. Within this framework of Cold Electroweak Baryogenesis, we study
the dependence of the generated baryon asymmetry on the speed of the quenching
transition. We find that there is a separation between ``fast'' and ``slow''
quenches, which can be used to put bounds on the allowed Higgs-inflaton
coupling. We also clarify the strong Higgs mass dependence of the asymmetry
reported in a companion paper (hep-ph/0604263).Comment: 18 pages, 20 figure
Spin Hall effect of conserved current: Conditions for a nonzero spin Hall current
We study the spin Hall effect taking into account the impurity scattering
effect as general as possible with the focus on the definition of the spin
current. The conserved bulk spin current (Shi et al. [Phys. Rev. Lett. 96,
076604 (2006)]) satisfying the continuity equation of spin is considered in
addition to the conventional one defined by the symmetric product of the spin
and velocity operators. Conditions for non-zero spin Hall current are
clarified. In particular, it is found that (i) the spin Hall current is
non-zero in the Rashba model with a finite-range impurity potential, and (ii)
the spin Hall current vanishes in the cubic Rashba model with a
-function impurity potential.Comment: 5 pages, minor change from the previous versio
Numerical Simulation of an Electroweak Oscillon
Numerical simulations of the bosonic sector of the
electroweak Standard Model in 3+1 dimensions have demonstrated the existence of
an oscillon -- an extremely long-lived, localized, oscillatory solution to the
equations of motion -- when the Higgs mass is equal to twice the boson
mass. It contains total energy roughly 30 TeV localized in a region of radius
0.05 fm. A detailed description of these numerical results is presented.Comment: 12 pages, 8 figures, uses RevTeX4; v2: expanded results section,
fixed typo
Instanton dominance of topological charge fluctuations in QCD?
We consider the local chirality of near-zero eigenvectors from Wilson-Dirac
and clover improved Wilson-Dirac lattice operators as proposed recently by
Horv\'ath et al. We studied finer lattices and repaired for the loss of
orthogonality due to the non-normality of the Wilson-Dirac matrix. As a result
we do see a clear double peak structure on lattices with resolutions higher
than 0.1 fm. We found that the lattice artifacts can be considerably reduced by
exploiting the biorthogonal system of left and right eigenvectors. We conclude
that the dominance of instantons on topological charge fluctuations is not
ruled out by local chirality measurements.Comment: 10 pages, 6 figure
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