4,463 research outputs found
Sobolev Metrics on Diffeomorphism Groups and the Derived Geometry of Spaces of Submanifolds
Given a finite dimensional manifold , the group
of diffeomorphism of which fall
suitably rapidly to the identity, acts on the manifold of submanifolds
on of diffeomorphism type where is a compact manifold with . For a right invariant weak Riemannian metric on
induced by a quite general operator
, we
consider the induced weak Riemannian metric on and we compute its
geodesics and sectional curvature. For that we derive a covariant formula for
curvature in finite and infinite dimensions, we show how it makes O'Neill's
formula very transparent, and we use it finally to compute sectional curvature
on .Comment: 28 pages. In this version some misprints correcte
Quantum-gravity-induced matter self-interactions in the asymptotic-safety scenario
We investigate the high-energy properties of matter theories coupled to
quantum gravity. Specifically, we show that quantum gravity fluctuations
generically induce matter self-interactions in a scalar theory. Our
calculations apply within asymptotically safe quantum gravity, where our
results indicate that the UV is dominated by an interacting fixed point, with
non-vanishing gravitational as well as matter couplings. In particular,
momentum-dependent scalar self-interactions are non-zero and induce a
non-vanishing momentum-independent scalar potential. Furthermore we point out
that terms of this type can have observable consequences in the context of
scalar-field driven inflation, where they can induce potentially observable
non-Gaussianities in the CMB.Comment: 15 + 8 pages, 8 figures, extended truncation, version to be published
in PR
Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy NiMnGa
Magnetic shape memory Heusler alloys are multiferroics stabilized by the
correlations between electronic, magnetic and structural order. To study these
correlations we use time resolved x-ray diffraction and magneto-optical Kerr
effect experiments to measure the laser induced dynamics in a Heusler alloy
NiMnGa film and reveal a set of timescales intrinsic to the system. We
observe a coherent phonon which we identify as the amplitudon of the modulated
structure and an ultrafast phase transition leading to a quenching of the
incommensurate modulation within 300~fs with a recovery time of a few ps. The
thermally driven martensitic transition to the high temperature cubic phase
proceeds via nucleation within a few ps and domain growth limited by the speed
of sound. The demagnetization time is 320~fs, which is comparable to the
quenching of the structural modulation.Comment: 5 pages, 3 figures. Supplementary materials 5 pages, 5 figure
The (Non-)Effect of Unemployment Benefits:Variations in the effect of unemployment on life-satisfaction between EU countries
Evolutionary multi-stage financial scenario tree generation
Multi-stage financial decision optimization under uncertainty depends on a
careful numerical approximation of the underlying stochastic process, which
describes the future returns of the selected assets or asset categories.
Various approaches towards an optimal generation of discrete-time,
discrete-state approximations (represented as scenario trees) have been
suggested in the literature. In this paper, a new evolutionary algorithm to
create scenario trees for multi-stage financial optimization models will be
presented. Numerical results and implementation details conclude the paper
Greater Expectations?
Physically Unclonable Functions (PUFs) are key tools in the construction of lightweight authentication and key exchange protocols. So far, all existing PUF-based authentication protocols follow the same paradigm: A resource-constrained prover, holding a PUF, wants to authenticate to a resource-rich verifier, who has access to a database of pre-measured PUF challenge-response pairs (CRPs). In this paper we consider application scenarios where all previous PUF-based authentication schemes fail to work: The verifier is resource-constrained (and holds a PUF), while the prover is resource-rich (and holds a CRP-database). We construct the first and efficient PUF-based authentication protocol for this setting, which we call converse PUF-based authentication. We provide an extensive security analysis against passive adversaries, show that a minor modification also allows for authenticated key exchange and propose a concrete instantiation using controlled Arbiter PUFs
Thermocurrents and their Role in high Q Cavity Performance
Over the past years it became evident that the quality factor of a
superconducting cavity is not only determined by its surface preparation
procedure, but is also influenced by the way the cavity is cooled down.
Moreover, different data sets exists, some of them indicate that a slow
cool-down through the critical temperature is favourable while other data
states the exact opposite. Even so there where speculations and some models
about the role of thermo-currents and flux-pinning, the difference in behaviour
remained a mystery. In this paper we will for the first time present a
consistent theoretical model which we confirmed by data that describes the role
of thermo-currents, driven by temperature gradients and material transitions.
We will clearly show how they impact the quality factor of a cavity, discuss
our findings, relate it to findings at other labs and develop mitigation
strategies which especially addresses the issue of achieving high quality
factors of so-called nitrogen doped cavities in horizontal test
A RNA Interference Screen Identifies the Protein Phosphatase 2A Subunit PR55γ as a Stress-Sensitive Inhibitor of c-SRC
Protein Phosphatase type 2A (PP2A) represents a family of holoenzyme complexes with diverse biological activities. Specific holoenzyme complexes are thought to be deregulated during oncogenic transformation and oncogene-induced signaling. Since most studies on the role of this phosphatase family have relied on the use of generic PP2A inhibitors, the contribution of individual PP2A holoenzyme complexes in PP2A-controlled signaling pathways is largely unclear. To gain insight into this, we have constructed a set of shRNA vectors targeting the individual PP2A regulatory subunits for suppression by RNA interference. Here, we identify PR55γ and PR55δ as inhibitors of c-Jun NH2-terminal kinase (JNK) activation by UV irradiation. We show that PR55γ binds c-SRC and modulates the phosphorylation of serine 12 of c-SRC, a residue we demonstrate to be required for JNK activation by c-SRC. We also find that the physical interaction between PR55γ and c-SRC is sensitive to UV irradiation. Our data reveal a novel mechanism of c-SRC regulation whereby in response to stress c-SRC activity is regulated, at least in part, through loss of the interaction with its inhibitor, PR55γ
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