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Climate Code Foundation
Poster presented at the VSMF Symposium held in the Unilever Centre on 2011-01-17Climate Code Foundation - who are we? A non-profit organisation founded in August 2010; our goal is to promote the public understanding of climate science, by increasing the visibility and clarity of the software used in climate science and by encouraging climate scientists to do the same, by encouraging good software development and management practices among climate scientists and by encouraging the publication of climate science software as Open Source. [http://www.climatecode.org/
Key Distillation and the Secret-Bit Fraction
We consider distillation of secret bits from partially secret noisy
correlations P_ABE, shared between two honest parties and an eavesdropper. The
most studied distillation scenario consists of joint operations on a large
number of copies of the distribution (P_ABE)^N, assisted with public
communication. Here we consider distillation with only one copy of the
distribution, and instead of rates, the 'quality' of the distilled secret bits
is optimized, where the 'quality' is quantified by the secret-bit fraction of
the result. The secret-bit fraction of a binary distribution is the proportion
which constitutes a secret bit between Alice and Bob. With local operations and
public communication the maximal extractable secret-bit fraction from a
distribution P_ABE is found, and is denoted by Lambda[P_ABE]. This quantity is
shown to be nonincreasing under local operations and public communication, and
nondecreasing under eavesdropper's local operations: it is a secrecy monotone.
It is shown that if Lambda[P_ABE]>1/2 then P_ABE is distillable, thus providing
a sufficient condition for distillability. A simple expression for
Lambda[P_ABE] is found when the eavesdropper is decoupled, and when the honest
parties' information is binary and the local operations are reversible.
Intriguingly, for general distributions the (optimal) operation requires local
degradation of the data.Comment: 12 page
Asymptotic Correlations in Gapped and Critical Topological Phases of 1D Quantum Systems
Topological phases protected by symmetry can occur in gapped
and---surprisingly---in critical systems. We consider non-interacting fermions
in one dimension with spinless time-reversal symmetry. It is known that the
phases are classified by a topological invariant and a central charge
. We investigate the correlations of string operators, giving insight into
the interplay between topology and criticality. In the gapped phases, these
non-local string order parameters allow us to extract . Remarkably,
ratios of correlation lengths are universal. In the critical phases, the
scaling dimensions of these operators serve as an order parameter, encoding
and . We derive exact asymptotics of these correlation functions
using Toeplitz determinant theory. We include physical discussion, e.g.,
relating lattice operators to the conformal field theory. Moreover, we discuss
the dual spin chains. Using the aforementioned universality, the topological
invariant of the spin chain can be obtained from correlations of local
observables.Comment: 35 pages, 5 page appendi
Evolutionary Inference for Function-valued Traits: Gaussian Process Regression on Phylogenies
Biological data objects often have both of the following features: (i) they
are functions rather than single numbers or vectors, and (ii) they are
correlated due to phylogenetic relationships. In this paper we give a flexible
statistical model for such data, by combining assumptions from phylogenetics
with Gaussian processes. We describe its use as a nonparametric Bayesian prior
distribution, both for prediction (placing posterior distributions on ancestral
functions) and model selection (comparing rates of evolution across a
phylogeny, or identifying the most likely phylogenies consistent with the
observed data). Our work is integrative, extending the popular phylogenetic
Brownian Motion and Ornstein-Uhlenbeck models to functional data and Bayesian
inference, and extending Gaussian Process regression to phylogenies. We provide
a brief illustration of the application of our method.Comment: 7 pages, 1 figur
Holographic graphene in a cavity
The effective strength of EM interactions can be controlled by confining the fields to a cavity and these effects might be used to push graphene into a strongly coupled regime. We study the similar D3/probe D5 system on a compact space and discuss the gravity dual for a cavity between two mirrors. We show that the introduction of a conformal symmetry breaking length scale introduces a mass gap on a single D5 sheet. Bilayer configurations display exciton condensation between the sheets. There is a first order phase transition away from the exciton condensate if a strong enough magnetic field is applied. We finally map out the phase structure of these systems in a cavity with the presence of mirror reflections of the probes - a mass gap may form through exciton condensation with the mirror image
Highly comparative feature-based time-series classification
A highly comparative, feature-based approach to time series classification is
introduced that uses an extensive database of algorithms to extract thousands
of interpretable features from time series. These features are derived from
across the scientific time-series analysis literature, and include summaries of
time series in terms of their correlation structure, distribution, entropy,
stationarity, scaling properties, and fits to a range of time-series models.
After computing thousands of features for each time series in a training set,
those that are most informative of the class structure are selected using
greedy forward feature selection with a linear classifier. The resulting
feature-based classifiers automatically learn the differences between classes
using a reduced number of time-series properties, and circumvent the need to
calculate distances between time series. Representing time series in this way
results in orders of magnitude of dimensionality reduction, allowing the method
to perform well on very large datasets containing long time series or time
series of different lengths. For many of the datasets studied, classification
performance exceeded that of conventional instance-based classifiers, including
one nearest neighbor classifiers using Euclidean distances and dynamic time
warping and, most importantly, the features selected provide an understanding
of the properties of the dataset, insight that can guide further scientific
investigation
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