10,385 research outputs found
Reducing the Bias of Causality Measures
Measures of the direction and strength of the interdependence between two
time series are evaluated and modified in order to reduce the bias in the
estimation of the measures, so that they give zero values when there is no
causal effect. For this, point shuffling is employed as used in the frame of
surrogate data. This correction is not specific to a particular measure and it
is implemented here on measures based on state space reconstruction and
information measures. The performance of the causality measures and their
modifications is evaluated on simulated uncoupled and coupled dynamical systems
and for different settings of embedding dimension, time series length and noise
level. The corrected measures, and particularly the suggested corrected
transfer entropy, turn out to stabilize at the zero level in the absence of
causal effect and detect correctly the direction of information flow when it is
present. The measures are also evaluated on electroencephalograms (EEG) for the
detection of the information flow in the brain of an epileptic patient. The
performance of the measures on EEG is interpreted, in view of the results from
the simulation study.Comment: 30 pages, 12 figures, accepted to Physical Review
On the Origin of the Dark Gamma-Ray Bursts
The origin of dark bursts - i.e. that have no observed afterglows in X-ray,
optical/NIR and radio ranges - is unclear yet. Different possibilities -
instrumental biases, very high redshifts, extinction in the host galaxies - are
discussed and shown to be important. On the other hand, the dark bursts should
not form a new subgroup of long gamma-ray bursts themselves.Comment: published in Nuovo Ciment
Violation of local realism vs detection efficiency
We put bounds on the minimum detection efficiency necessary to violate local
realism in Bell experiments. These bounds depends of simple parameters like the
number of measurement settings or the dimensionality of the entangled quantum
state. We derive them by constructing explicit local-hidden variable models
which reproduce the quantum correlations for sufficiently small detectors
efficiency.Comment: 6 pages, revtex. Modifications in the discussion for many parties in
section 3, small erros and typos corrected, conclusions unchange
Tuning the electrically evaluated electron Lande g factor in GaAs quantum dots and quantum wells of different well widths
We evaluate the Lande g factor of electrons in quantum dots (QDs) fabricated
from GaAs quantum well (QW) structures of different well width. We first
determine the Lande electron g factor of the QWs through resistive detection of
electron spin resonance and compare it to the enhanced electron g factor
determined from analysis of the magneto-transport. Next, we form laterally
defined quantum dots using these quantum wells and extract the electron g
factor from analysis of the cotunneling and Kondo effect within the quantum
dots. We conclude that the Lande electron g factor of the quantum dot is
primarily governed by the electron g factor of the quantum well suggesting that
well width is an ideal design parameter for g-factor engineering QDs
From Theory to Practice: Plug and Play with Succinct Data Structures
Engineering efficient implementations of compact and succinct structures is a
time-consuming and challenging task, since there is no standard library of
easy-to- use, highly optimized, and composable components. One consequence is
that measuring the practical impact of new theoretical proposals is a difficult
task, since older base- line implementations may not rely on the same basic
components, and reimplementing from scratch can be very time-consuming. In this
paper we present a framework for experimentation with succinct data structures,
providing a large set of configurable components, together with tests,
benchmarks, and tools to analyze resource requirements. We demonstrate the
functionality of the framework by recomposing succinct solutions for document
retrieval.Comment: 10 pages, 4 figures, 3 table
Necessary and sufficient detection efficiency for the Mermin inequalities
We prove that the threshold detection efficiency for a loophole-free Bell
experiment using an -qubit Greenberger-Horne-Zeilinger state and the
correlations appearing in the -partite Mermin inequality is . If
the detection efficiency is equal to or lower than this value, there are local
hidden variable models that can simulate all the quantum predictions. If the
detection efficiency is above this value, there is no local hidden variable
model that can simulate all the quantum predictions.Comment: REVTeX4, 5 pages, 1 figur
Tree Compression with Top Trees Revisited
We revisit tree compression with top trees (Bille et al, ICALP'13) and
present several improvements to the compressor and its analysis. By
significantly reducing the amount of information stored and guiding the
compression step using a RePair-inspired heuristic, we obtain a fast compressor
achieving good compression ratios, addressing an open problem posed by Bille et
al. We show how, with relatively small overhead, the compressed file can be
converted into an in-memory representation that supports basic navigation
operations in worst-case logarithmic time without decompression. We also show a
much improved worst-case bound on the size of the output of top-tree
compression (answering an open question posed in a talk on this algorithm by
Weimann in 2012).Comment: SEA 201
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