50,363 research outputs found
Compression for Smooth Shape Analysis
Most 3D shape analysis methods use triangular meshes to discretize both the
shape and functions on it as piecewise linear functions. With this
representation, shape analysis requires fine meshes to represent smooth shapes
and geometric operators like normals, curvatures, or Laplace-Beltrami
eigenfunctions at large computational and memory costs.
We avoid this bottleneck with a compression technique that represents a
smooth shape as subdivision surfaces and exploits the subdivision scheme to
parametrize smooth functions on that shape with a few control parameters. This
compression does not affect the accuracy of the Laplace-Beltrami operator and
its eigenfunctions and allow us to compute shape descriptors and shape
matchings at an accuracy comparable to triangular meshes but a fraction of the
computational cost.
Our framework can also compress surfaces represented by point clouds to do
shape analysis of 3D scanning data
Summary of working group g: beam material interaction
For the first time, the workshop on High-Intensity and High-Brightness Hadron
Beams (HB2010), held at Morschach, Switzerland and organized by the Paul
Scherrer Institute, included a Working group dealing with the interaction
between beam and material. Due to the high power beams of existing and future
facilities, this topic is already of great relevance for such machines and is
expected to become even more important in the future. While more specialized
workshops related to topics of radiation damage, activation or thermo -
mechanical calculations, already exist, HB2010 provided the occasion to discuss
the interplay of these topics, focusing on components like targets, beam dumps
and collimators, whose reliability are crucial for a user facility. In
addition, a broader community of people working on a variety of issues related
to the operation of accelerators could be informed and their interest sparked.Comment: 3 pp. 46th ICFA Advanced Beam Dynamics Workshop HB2010, Sep 27 - Oct
1 2010: Morschach, Switzerlan
Spherically Symmetric solutions in Multidimensional Gravity with the SU(2) Gauge Group as the Extra Dimensions
The multidimensional gravity on the principal bundle with the SU(2) gauge
group is considered. The numerical investigation of the spherically symmetric
metrics with the center of symmetry is made. The solution of the gravitational
equations depends on the boundary conditions of the ``SU(2) gauge potential''
(off-diagonal metric components) at the symmetry center and on the type of
symmetry (symmetrical or antisymmetrical) of these potentials. In the chosen
range of the boundary conditions it is shown that there are two types of
solutions: wormhole-like and flux tube. The physical application of such kind
of solutions as quantum handles in a spacetime foam is discussed.Comment: misprints are correcte
Renormalization group flows in one-dimensional lattice models: impurity scaling, umklapp scattering and the orthogonality catastrophe
We show that to understand the orthogonality catastrophe in the half-filled
lattice model of spinless fermions with repulsive nearest neighbor interaction
and a local impurity in its Luttinger liquid phase one has to take into account
(i) the impurity scaling, (ii) unusual finite size corrections of the form
, as well as (iii) the renormalization group flow of the umklapp
scattering. The latter defines a length scale which becomes exceedingly
large the closer the system is to its transition into the charge-density wave
phase. Beyond this transition umklapp scattering is relevant in the
renormalization group sense. Field theory can only be employed for length
scales larger than . For small to intermediate two-particle interactions,
for which the regime can be accessed, and taking into account the
finite size corrections resulting from (i) and (ii) we provide strong evidence
that the impurity backscattering contribution to the orthogonality exponent is
asymptotically given by . While further increasing the two-particle
interaction leads to a faster renormalization group flow of the impurity
towards the cut chain fixed point, the increased bare amplitude of the umklapp
scattering renders it virtually impossible to confirm the expected asymptotic
value of given the accessible system sizes. We employ the density matrix
renormalization group.Comment: 12 pages, 9 figure
Quantum effects with an X-ray free electron laser
A quantum kinetic equation coupled with Maxwell's equation is used to
estimate the laser power required at an XFEL facility to expose intrinsically
quantum effects in the process of QED vacuum decay via spontaneous pair
production. A 9 TW-peak XFEL laser with photon energy 8.3 keV could be
sufficient to initiate particle accumulation and the consequent formation of a
plasma of spontaneously produced pairs. The evolution of the particle number in
the plasma will exhibit non-Markovian aspects of the strong-field pair
production process and the plasma's internal currents will generate an electric
field whose interference with that of the laser leads to plasma oscillations.Comment: 4 pages, LaTeX2
Pair creation and plasma oscillations
We describe aspects of particle creation in strong fields using a quantum
kinetic equation with a relaxation-time approximation to the collision term.
The strong electric background field is determined by solving Maxwell's
equation in tandem with the Vlasov equation. Plasma oscillations appear as a
result of feedback between the background field and the field generated by the
particles produced. The plasma frequency depends on the strength of the initial
background field and the collision frequency, and is sensitive to the necessary
momentum-dependence of dressed-parton masses.Comment: 11 pages, revteX, epsfig.sty, 5 figures; Proceedings of 'Quark Matter
in Astro- and Particlephysics', a workshop at the University of Rostock,
Germany, November 27 - 29, 2000. Eds. D. Blaschke, G. Burau, S.M. Schmid
On a Possibility to Measure Thermoelectric Power in SNS Structures
Two dissimilar Josephson junctions, which are connected to a heater can act
as precise batteries. Because of the difference in thermoelectric power of
these batteries, circuit with two dissimilar batteries, under heat flow would have a net EMF around the zero-resistance
loop leading to a loop's magnetic flux oscillating in time. It is shown its
theoretical value is proportional to both the temperature difference as well as
the disparity in the thermoelectric powers of the two junctions.Comment: 5 page
- …