7,490 research outputs found
Classification of extremal elliptic K3 surfaces and fundamental groups of open K3 surfaces
We present a complete list of extremal elliptic K3 surfaces. There are
altogether 325 of them. The first 112 coincides with Miranda-Persson's list for
semi-stable ones. The data include the transcendental lattice which determines
uniquely the K3 surface by a result of Shioda and Inose, the singular fibre
type and the Mordell Weil group. As an application, we give a sufficient
condition for the topological fundamental group of complement to an
ADE-configuration of smooth rational curves on a K3 surface to be trivial.Comment: 25 pages, Nagoya Math. J. to appea
The Alternating Groups and K3 Surfaces
In this note, we consider all possible extensions G of a non-trivial perfect
group H acting faithfully on a K3 surface X. The pair (X, G) is proved to be
uniquely determined by G if the transcendental value of G is maximum. In
particular, we have G/H < Z/(2) + Z/(2), if H is the alternating group A_5 and
normal in G.Comment: Journal of Pure and Applied Algebra (21 pages) to appea
Time-reversal focusing of an expanding soliton gas in disordered replicas
We investigate the properties of time reversibility of a soliton gas,
originating from a dispersive regularization of a shock wave, as it propagates
in a strongly disordered environment. An original approach combining
information measures and spin glass theory shows that time reversal focusing
occurs for different replicas of the disorder in forward and backward
propagation, provided the disorder varies on a length scale much shorter than
the width of the soliton constituents. The analysis is performed by starting
from a new class of reflectionless potentials, which describe the most general
form of an expanding soliton gas of the defocusing nonlinear Schroedinger
equation.Comment: 7 Pages, 6 Figure
Computing Lyapunov spectra with continuous Gram-Schmidt orthonormalization
We present a straightforward and reliable continuous method for computing the
full or a partial Lyapunov spectrum associated with a dynamical system
specified by a set of differential equations. We do this by introducing a
stability parameter beta>0 and augmenting the dynamical system with an
orthonormal k-dimensional frame and a Lyapunov vector such that the frame is
continuously Gram-Schmidt orthonormalized and at most linear growth of the
dynamical variables is involved. We prove that the method is strongly stable
when beta > -lambda_k where lambda_k is the k'th Lyapunov exponent in
descending order and we show through examples how the method is implemented. It
extends many previous results.Comment: 14 pages, 10 PS figures, ioplppt.sty, iopl12.sty, epsfig.sty 44 k
Interminiband Rabi oscillations in biased semiconductor superlattices
Carrier dynamics at energy level anticrossings in biased semiconductor
superlattices, was studied in the time domain by solving the time-dependent
Schroedinger equation. The resonant nature of interminiband Rabi oscillations
has been explicitly demonstrated to arise from interference of intrawell and
Bloch oscillations. We also report a simulation of direct Rabi oscillations
across three minibands, in the high field regime, due to interaction between
three strongly coupled minibands.Comment: 13 pages, 16 figure
Effects of demographic stochasticity on biological community assembly on evolutionary time scales
We study the effects of demographic stochasticity on the long-term dynamics
of biological coevolution models of community assembly. The noise is induced in
order to check the validity of deterministic population dynamics. While
mutualistic communities show little dependence on the stochastic population
fluctuations, predator-prey models show strong dependence on the stochasticity,
indicating the relevance of the finiteness of the populations. For a
predator-prey model, the noise causes drastic decreases in diversity and total
population size. The communities that emerge under influence of the noise
consist of species strongly coupled with each other and have stronger linear
stability around the fixed-point populations than the corresponding noiseless
model. The dynamics on evolutionary time scales for the predator-prey model are
also altered by the noise. Approximate fluctuations are observed with
noise, while fluctuations are found for the model without demographic
noise
Transport Properties of Carbon Nanotube C Peapods
We measure the conductance of carbon nanotube peapods from room temperature
down to 250mK. Our devices show both metallic and semiconducting behavior at
room temperature. At the lowest temperatures, we observe single electron
effects. Our results suggest that the encapsulated C molecules do not
introduce substantial backscattering for electrons near the Fermi level. This
is remarkable given that previous tunneling spectroscopy measurements show that
encapsulated C strongly modifies the electronic structure of a nanotube
away from the Fermi level.Comment: 9 pages, 4 figures. This is one of two manuscripts replacing the one
orginally submitted as arXiv:cond-mat/0606258. The other one is
arXiv:0704.3641 [cond-mat
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