7,433 research outputs found
Orientation dependent current-induced motion of skyrmions with various topologies
We study the current-driven motion of metastable localized spin structures
with various topological charges in a (PtIr)/Fe bilayer on a
Pd(111) surface by combining atomistic spin model simulations with an approach
based on the generalized Thiele equation. We demonstrate that besides a
distinct dependence on the topological charge itself the dynamic response of
skyrmionic structures with topological charges and
to a spin-polarized current exhibits an orientation dependence.
We further show that such an orientation dependence can be induced by applying
an in-plane external field, possibly opening up a new pathway to the
manipulation of skyrmion dynamics
Inertia and delocalized twisted cohomology
We show that the inertia stack of a topological stack is again a topological
stack. We further observe that the inertia stack of an orbispace is again an
orbispace. We show how a U(1)-banded gerbe over an orbispace gives rise to a
flat line bundle over its inertia stack. Via sheaf theory over topological
stacks it gives rise to the twisted delocalized cohomology of the orbispace.
With these results and constructions we generalize concepts, which are
well-known in the smooth framework, to the topological case. In the smooth case
we show, that our sheaf-theoretic definition of twisted delocalized cohomology
of orbispaces coincides with former definitions using a twisted de Rham
complex.Comment: 42 page
Periodic twisted cohomology and T-duality
The initial motivation of this work was to give a topological interpretation
of two-periodic twisted de-Rham cohomology which is generalizable to arbitrary
coefficients. To this end we develop a sheaf theory in the context of locally
compact topological stacks with emphasis on the construction of the sheaf
theory operations in unbounded derived categories, elements of Verdier duality
and integration. The main result is the construction of a functorial
periodization functor associated to a U(1)-gerbe. As applications we verify the
-duality isomorphism in periodic twisted cohomology and in periodic twisted
orbispace cohomology.Comment: 128 pages; v2: small corrections (e.g. of typos), version to appear
in Asterisqu
Adaptive control in rollforward recovery for extreme scale multigrid
With the increasing number of compute components, failures in future
exa-scale computer systems are expected to become more frequent. This motivates
the study of novel resilience techniques. Here, we extend a recently proposed
algorithm-based recovery method for multigrid iterations by introducing an
adaptive control. After a fault, the healthy part of the system continues the
iterative solution process, while the solution in the faulty domain is
re-constructed by an asynchronous on-line recovery. The computations in both
the faulty and healthy subdomains must be coordinated in a sensitive way, in
particular, both under and over-solving must be avoided. Both of these waste
computational resources and will therefore increase the overall
time-to-solution. To control the local recovery and guarantee an optimal
re-coupling, we introduce a stopping criterion based on a mathematical error
estimator. It involves hierarchical weighted sums of residuals within the
context of uniformly refined meshes and is well-suited in the context of
parallel high-performance computing. The re-coupling process is steered by
local contributions of the error estimator. We propose and compare two criteria
which differ in their weights. Failure scenarios when solving up to
unknowns on more than 245\,766 parallel processes will be
reported on a state-of-the-art peta-scale supercomputer demonstrating the
robustness of the method
Transmission of Policy Shocks in a Monetary Asset-Pricing Model
In a framework of a two-country monetary asset-pricing model with production the effects of stochastic and structural fiscal and monetary policy shocks are investigated. The model is kept simple enough to allow the derivation of closed form solutions of the functional equation system for the equilibrium price functions. With money yielding liquidity services in the exchange process some correlation results are derived, especially for the impact of structural and stochastic policy shocks on stock prices, exchange rates etc. Furthermore it is investigated whether shares can provide protection against inflation resulting from monetary shocks.
Dilepton Production from Rho-Mesons in a Quark-Gluon Plasma
Assuming that rho-mesons exist in a quark-gluon plasma close to the QCD phase
transition, we calculate the dilepton production rate from quark-antiquark
annihilation via a rho-meson state using Vector Meson Dominance. The result is
compared to the rates from direct quark-antiquark annihilation and from pion
annihilation. Furthermore we discuss the suppression of low mass dileptons if
the quarks assume an effective mass in the quark-gluon plasma.Comment: 10 pages, REVTEX, 5 PostScript figure
Uncertainty-Aware Hand–Eye Calibration
We provide a generic framework for the hand–eye calibration of vision-guided industrial robots. In contrast to traditional methods, we explicitly model the uncertainty of the robot in a stochastically founded way. Albeit the repeatability of modern industrial robots is high, their absolute accuracy typically is much lower. This uncertainty—especially if not considered—deteriorates the result of the hand–eye calibration. Our proposed framework does not only result in a high accuracy of the computed hand–eye pose but also provides reliable information about the uncertainty of the robot. It further provides corrected robot poses for a convenient and inexpensive robot calibration. Our framework is computationally efficient and generic in several regards. It supports the use of a calibration target as well as self-calibration without the need for known 3-D points. It optionally enables the simultaneous calibration of the interior camera parameters. The framework is also generic with regard to the robot type and, hence, supports antropomorphic as well as selective compliance assembly robot arm (SCARA) robots, for example. Simulated and real experiments show the validity of the proposed methods. An extensive evaluation of our framework on a public dataset shows a considerably higher accuracy than 15 state-of-the-art methods
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