6,043 research outputs found
On the Closing Lemma problem for vector fields of bounded type on the torus
We investigate the open Closing Lemma problem for vector fields on the
2-dimensional torus. Under the assumption of bounded type rotation number, the
Closing Lemma is verified for smooth vector fields that are
area-preserving at all saddle points. Namely, given such a vector field
, , with a non-trivially recurrent point , there exists a vector
field arbitrarily near to in the topology and obtained from
by a twist perturbation, such that is a periodic point of .
The proof relies on a new result in 1-dimensional dynamics on the
non-existence of semi-wandering intervals of smooth maps of the circle.Comment: 11 pages, 1 figur
A semi-invertible Oseledets Theorem with applications to transfer operator cocycles
Oseledets' celebrated Multiplicative Ergodic Theorem (MET) is concerned with
the exponential growth rates of vectors under the action of a linear cocycle on
R^d. When the linear actions are invertible, the MET guarantees an
almost-everywhere pointwise splitting of R^d into subspaces of distinct
exponential growth rates (called Lyapunov exponents). When the linear actions
are non-invertible, Oseledets' MET only yields the existence of a filtration of
subspaces, the elements of which contain all vectors that grow no faster than
exponential rates given by the Lyapunov exponents. The authors recently
demonstrated that a splitting over R^d is guaranteed even without the
invertibility assumption on the linear actions. Motivated by applications of
the MET to cocycles of (non-invertible) transfer operators arising from random
dynamical systems, we demonstrate the existence of an Oseledets splitting for
cocycles of quasi-compact non-invertible linear operators on Banach spaces.Comment: 26 page
Coherent sets for nonautonomous dynamical systems
We describe a mathematical formalism and numerical algorithms for identifying
and tracking slowly mixing objects in nonautonomous dynamical systems. In the
autonomous setting, such objects are variously known as almost-invariant sets,
metastable sets, persistent patterns, or strange eigenmodes, and have proved to
be important in a variety of applications. In this current work, we explain how
to extend existing autonomous approaches to the nonautonomous setting. We call
the new time-dependent slowly mixing objects coherent sets as they represent
regions of phase space that disperse very slowly and remain coherent. The new
methods are illustrated via detailed examples in both discrete and continuous
time
‘Not Just Another Anonymous Spot’: Government Support for Memory Institutions in Prince Edward Island and Wales
In view of the important role that libraries, archives and museums – collectively referred to here as memory institutions – can play in regenerating communities that have faced economic and social difficulties, this essay examines government support for this sector in Prince Edward Island (PEI) through a comparative study with Wales. A historical sketch of the development of government administrative and planning capacity in this field in both Wales and PEI is offered, followed by a comparison of current funding commitments by each government. The study finds that relative funding levels are about the same in both jurisdictions, but that the Welsh government can offer an instructive
example to the government of PEI through the former’s commitment to planning for museums, archives and libraries, and for cultural and heritage activity as whole
Complete spatial characterization of an optical wavefront using a variable-separation pinhole pair
We present a technique for measuring the transverse spatial properties of an
optical wavefront. Intensity and phase profiles are recovered by analysis of a
series of interference patterns produced by the combination of a scanning
X-shaped slit and a static horizontal slit; the spatial coherence may be found
from the same data. We demonstrate the technique by characterizing high
harmonic radiation generated in a gas cell, however the method could be
extended to a wide variety of light sources.Comment: 4 pages, 3 figures, 1 tabl
Mapping PAMP Responses and Disease Resistance in Brassicas
The first layer of active defence in plants is based on the perception of pathogen-associated molecular patterns (PAMPs) leading to PAMP-triggered immunity (PTI). PTI is increasingly being investigated in crop plants, where it may have potential to provide durable disease resistance in the field. Limiting this work, however, is an absence of reliable bioassays to investigate PAMP responses in some species. Presented here is a series of methods to investigate PTI in Brassica napus. The assays allow measuring early cell signalling responses, gene expression changes, cell wall reinforcement, metabolome changes and scoring PAMP-Induced resistance. Illumina-based RNA sequencing analysis produced a genome-wide survey of transcriptional changes upon PAMP treatment seen in both the A and C genomes of the allotetraploid B. napus.
Using these assays substantial variation in PAMP-responsiveness was observed amongst elite varieties of B. napus. Taking this further, a genome wide association study (GWAS) of the flg22 and elf18 triggered oxidative bursts, resistance to Pseudomonas syringae and Botrytis cinerea was carried out in a population of B. napus. A substantial number of molecular markers, covering both sequence and expression variation, have been identified as having significant association with these four traits.
QTL mapping of the flg22 triggered oxidative burst in the ADxGD double haploid cross identified a major quantitative trait loci (QTL) on C9 of B. oleracea. mRNA-seq of the parents led to a non-synonymous single nucleotide polymorphism (SNP) list and enabled fine mapping through the addition of KASPar markers to the original map. This produced a relatively small list of candidate genes including CYLIC NUCLEOTIDE GATED ION CHANNEL 4 (CNGC4) also known as DEFENCE NO DEATH 2 (DND2). An insertion in Arabidopsis thaliana DND2 showed phenotypic difference in the oxidative burst between the insertion line and Col-0, potentially indicating a role for the gene in regulating early PTI
Quantum Computing with an 'Always On' Heisenberg Interaction
Many promising ideas for quantum computing demand the experimental ability to
directly switch 'on' and 'off' a physical coupling between the component
qubits. This is typically the key difficulty in implementation, and precludes
quantum computation in generic solid state systems, where interactions between
the constituents are 'always on'. Here we show that quantum computation is
possible in strongly coupled (Heisenberg) systems even when the interaction
cannot be controlled. The modest ability of 'tuning' the transition energies of
individual qubits proves to be sufficient, with a suitable encoding of the
logical qubits, to generate universal quantum gates. Furthermore, by tuning the
qubits collectively we provide a scheme with exceptional experimental
simplicity: computations are controlled via a single 'switch' of only six
settings. Our schemes are applicable to a wide range of physical
implementations, from excitons and spins in quantum dots through to bulk
magnets.Comment: 4 pages, 3 figs, 2 column format. To appear in PR
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