41,051 research outputs found
Comments on the Links between su(3) Modular Invariants, Simple Factors in the Jacobian of Fermat Curves, and Rational Triangular Billiards
We examine the proposal made recently that the su(3) modular invariant
partition functions could be related to the geometry of the complex Fermat
curves. Although a number of coincidences and similarities emerge between them
and certain algebraic curves related to triangular billiards, their meaning
remains obscure. In an attempt to go beyond the su(3) case, we show that any
rational conformal field theory determines canonically a Riemann surface.Comment: 56 pages, 4 eps figures, LaTeX, uses eps
Nonlinear dielectric response of Debye, alpha, and beta relaxation in 1-propanol
We present nonlinear dielectric measurements of glass-forming 1-propanol, a
prototypical example for the monohydroxy alcohols that are known to exhibit
unusual relaxation dynamics, namely an additional Debye relaxation, slower than
the structural alpha relaxation. Applying high ac fields of 468 kV/cm allows
for a detailed investigation of the nonlinear properties of all three
relaxation processes occurring in 1-propanol, namely the Debye, alpha, and beta
relaxation. Both the field-induced variations of dielectric constant and loss
are reported. Polarization saturation and the absorption of field energy govern
the findings in the Debye-relaxation regime, well consistent with the suggested
cluster-like nature of the relaxing entities. The behavior of the alpha
relaxation is in good accord with the expectations for a heterogeneous
relaxation scenario. Finally, the Johari-Goldstein beta-relaxation in
1-propanol seems to exhibit no or only weak field dependence, in agreement with
recent findings for the excess wing of canonical glass formers.Comment: 8 pages, 4 figure
Cooperativity and Heterogeneity in Plastic Crystals Studied by Nonlinear Dielectric Spectroscopy
The glassy dynamics of plastic-crystalline cyclo-octanol and ortho-carborane,
where only the molecular reorientational degrees of freedom freeze without
long-range order, is investigated by nonlinear dielectric spectroscopy. Marked
differences to canonical glass formers show up: While molecular cooperativity
governs the glassy freezing, it leads to a much weaker slowing down of
molecular dynamics than in supercooled liquids. Moreover, the observed
nonlinear effects cannot be explained with the same heterogeneity scenario
recently applied to canonical glass formers. This supports ideas that molecular
relaxation in plastic crystals may be intrinsically non-exponential. Finally,
no nonlinear effects were detected for the secondary processes in
cyclo-octanol.Comment: Final version as accepted for publication in Phys. Rev. Lett. 6
pages, 5 figures (including 1 page and figure in Supplemental Material
Nonlinear dielectric response at the excess wing of glass-forming liquids
We present nonlinear dielectric measurements of glass-forming glycerol and
propylene carbonate applying electrical fields up to 671 kV/cm. The
measurements extend to sufficiently high frequencies to allow for the
investigation of the nonlinear behavior in the regime of the so-far mysterious
excess wing, showing up in the loss spectra of many glass formers as a second
power law at high frequencies. Surprisingly, we find a complete lack of
nonlinear behavior in the excess wing, in marked contrast to the
alpha-relaxation where, in agreement with previous reports, a strong increase
of dielectric constant and loss is found.Comment: 8 pages (including 3 pages Supplementary Information), 4 + 1 figures.
Revised according to suggestions of referee
Runtime Verification of Temporal Properties over Out-of-order Data Streams
We present a monitoring approach for verifying systems at runtime. Our
approach targets systems whose components communicate with the monitors over
unreliable channels, where messages can be delayed or lost. In contrast to
prior works, whose property specification languages are limited to
propositional temporal logics, our approach handles an extension of the
real-time logic MTL with freeze quantifiers for reasoning about data values. We
present its underlying theory based on a new three-valued semantics that is
well suited to soundly and completely reason online about event streams in the
presence of message delay or loss. We also evaluate our approach
experimentally. Our prototype implementation processes hundreds of events per
second in settings where messages are received out of order.Comment: long version of the CAV 2017 pape
Shape analysis on homogeneous spaces: a generalised SRVT framework
Shape analysis is ubiquitous in problems of pattern and object recognition
and has developed considerably in the last decade. The use of shapes is natural
in applications where one wants to compare curves independently of their
parametrisation. One computationally efficient approach to shape analysis is
based on the Square Root Velocity Transform (SRVT). In this paper we propose a
generalised SRVT framework for shapes on homogeneous manifolds. The method
opens up for a variety of possibilities based on different choices of Lie group
action and giving rise to different Riemannian metrics.Comment: 28 pages; 4 figures, 30 subfigures; notes for proceedings of the Abel
Symposium 2016: "Computation and Combinatorics in Dynamics, Stochastics and
Control". v3: amended the text to improve readability and clarify some
points; updated and added some references; added pseudocode for the dynamic
programming algorithm used. The main results remain unchange
Repeated Evolution of Digital Adhesion in Geckos: A Reply to Harrington and Reeder
We published a phylogenetic comparative analysis that found geckos had gained and lost adhesive toepads multiple times over their long evolutionary history (Gamble et al., PLoS One, 7, 2012, e39429). This was consistent with decades of morphological studies showing geckos had evolved adhesive toepads on multiple occasions and that the morphology of geckos with ancestrally padless digits can be distinguished from secondarily padless forms. Recently, Harrington & Reeder (J. Evol. Biol., 30, 2017, 313) reanalysed data from Gamble et al. (PLoS One, 7, 2012, e39429) and found little support for the multiple origins hypothesis. Here, we argue that Harrington and Reeder failed to take morphological evidence into account when devising ancestral state reconstruction models and that these biologically unrealistic models led to erroneous conclusions about the evolution of adhesive toepads in geckos
Phase Transitions in a Two-Component Site-Bond Percolation Model
A method to treat a N-component percolation model as effective one component
model is presented by introducing a scaled control variable . In Monte
Carlo simulations on , , and simple cubic
lattices the percolation threshold in terms of is determined for N=2.
Phase transitions are reported in two limits for the bond existence
probabilities and . In the same limits, empirical formulas
for the percolation threshold as function of one
component-concentration, , are proposed. In the limit a new
site percolation threshold, , is reported.Comment: RevTeX, 5 pages, 5 eps-figure
First-principles study of magnetization relaxation enhancement and spin-transfer in thin magnetic films
The interface-induced magnetization damping of thin ferromagnetic films in
contact with normal-metal layers is calculated from first principles for clean
and disordered Fe/Au and Co/Cu interfaces. Interference effects arising from
coherent scattering turn out to be very small, consistent with a very small
magnetic coherence length. Because the mixing conductances which govern the
spin transfer are to a good approximation real valued, the spin pumping can be
described by an increased Gilbert damping factor but an unmodified gyromagnetic
ratio. The results also confirm that the spin-current induced magnetization
torque is an interface effect.Comment: 10 pages, 8 figures, RevTeX; modified according to Referees' request
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