23,959 research outputs found
Finished Genome Sequences of Xanthomonas fragariae, the Cause of Bacterial Angular Leaf Spot of Strawberry.
Xanthomonas fragariae is a foliar pathogen of strawberry that is of significant concern to nursery production of strawberry transplants and field production of strawberry fruit. Long-read sequencing was employed to generate finished genomes for two isolates (each with one chromosome and two plasmids) from symptomatic plants in northern California
Modified Frank-Wolfe Algorithm for Enhanced Sparsity in Support Vector Machine Classifiers
This work proposes a new algorithm for training a re-weighted L2 Support
Vector Machine (SVM), inspired on the re-weighted Lasso algorithm of Cand\`es
et al. and on the equivalence between Lasso and SVM shown recently by Jaggi. In
particular, the margin required for each training vector is set independently,
defining a new weighted SVM model. These weights are selected to be binary, and
they are automatically adapted during the training of the model, resulting in a
variation of the Frank-Wolfe optimization algorithm with essentially the same
computational complexity as the original algorithm. As shown experimentally,
this algorithm is computationally cheaper to apply since it requires less
iterations to converge, and it produces models with a sparser representation in
terms of support vectors and which are more stable with respect to the
selection of the regularization hyper-parameter
Destroyed quantum Hall effect in graphene with [0001] tilt grain boundaries
The reason why the half-integer quantum Hall effect (QHE) is suppressed in
graphene grown by chemical vapor deposition (CVD) is unclear. We propose that
it might be connected to extended defects in the material and present results
for the quantum Hall effect in graphene with [0001] tilt grain boundaries
connecting opposite sides of Hall bar devices. Such grain boundaries contain
5-7 ring complexes that host defect states that hybridize to form bands with
varying degree of metallicity depending on grain boundary defect density. In a
magnetic field, edge states on opposite sides of the Hall bar can be connected
by the defect states along the grain boundary. This destroys Hall resistance
quantization and leads to non-zero longitudinal resistance. Anderson disorder
can partly recover quantization, where current instead flows along returning
paths along the grain boundary depending on defect density in the grain
boundary and on disorder strength. Since grain sizes in graphene made by
chemical vapor deposition are usually small, this may help explain why the
quantum Hall effect is usually poorly developed in devices made of this
material.Comment: 5 pages, 4 figure
Efficient method for measuring the parameters encoded in a gravitational-wave signal
Once upon a time, predictions for the accuracy of inference on
gravitational-wave signals relied on computationally inexpensive but often
inaccurate techniques. Recently, the approach has shifted to actual inference
on noisy signals with complex stochastic Bayesian methods, at the expense of
significant computational cost. Here, we argue that it is often possible to
have the best of both worlds: a Bayesian approach that incorporates prior
information and correctly marginalizes over uninteresting parameters, providing
accurate posterior probability distribution functions, but carried out on a
simple grid at a low computational cost, comparable to the inexpensive
predictive techniques.Comment: 17 pages, 5 figure
CHANGES IN AGRICULTURAL MARKETS IN TRANSITION ECONOMIES
Economic reform in the transition economies of the former Soviet bloc has transformed the volume and mix of these economies' agricultural production, consumption, and trade. Output drops in most countries have ranged from 25 to 50 percent. The livestock sector has been hit particularly hard, all but eliminating U.S. grain exports to the region. This report concludes that the output decline has been an inevitable part of market reform and that the main goal of agricultural policy in the transition economies should not be to return output to pre-reform levels but to increase the productivity of input use. Although reform has created a food security problem in some countries, the cause of the problem is not insufficient food supplies, but rather inadequate access to food by segments of the population and regions within countries.Russia, Ukraine, former Soviet Union, Central and Eastern European countries, transition economies, agricultural production, livestock sector, food consumption, trade, policy reform, productivity, International Relations/Trade,
On the Capacity of the Wiener Phase-Noise Channel: Bounds and Capacity Achieving Distributions
In this paper, the capacity of the additive white Gaussian noise (AWGN)
channel, affected by time-varying Wiener phase noise is investigated. Tight
upper and lower bounds on the capacity of this channel are developed. The upper
bound is obtained by using the duality approach, and considering a specific
distribution over the output of the channel. In order to lower-bound the
capacity, first a family of capacity-achieving input distributions is found by
solving a functional optimization of the channel mutual information. Then,
lower bounds on the capacity are obtained by drawing samples from the proposed
distributions through Monte-Carlo simulations. The proposed capacity-achieving
input distributions are circularly symmetric, non-Gaussian, and the input
amplitudes are correlated over time. The evaluated capacity bounds are tight
for a wide range of signal-to-noise-ratio (SNR) values, and thus they can be
used to quantify the capacity. Specifically, the bounds follow the well-known
AWGN capacity curve at low SNR, while at high SNR, they coincide with the
high-SNR capacity result available in the literature for the phase-noise
channel.Comment: IEEE Transactions on Communications, 201
Operations and single particle interferometry
Interferometry of single particles with internal degrees of freedom is
investigated. We discuss the interference patterns obtained when an internal
state evolution device is inserted into one or both the paths of the
interferometer. The interference pattern obtained is not uniquely determined by
the completely positive maps (CPMs) that describe how the devices evolve the
internal state of a particle. By using the concept of gluing of CPMs, we
investigate the structure of all possible interference patterns obtainable for
given trace preserving internal state CPMs. We discuss what can be inferred
about the gluing, given a sufficiently rich set of interference experiments. It
is shown that the standard interferometric setup is limited in its abilities to
distinguish different gluings. A generalized interferometric setup is
introduced with the capacity to distinguish all gluings. We also connect to
another approach using the well known fact that channels can be realized using
a joint unitary evolution of the system and an ancillary system. We deduce the
set of all such unitary `representations' and relate the structure of this set
to gluings and interference phenomena.Comment: Journal reference added. Material adde
The Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment: Where do we stand?
We review the status of the hadronic light-by-light contribution to the muon
anomalous magnetic moment and critically compare recent calculations. We also
study in detail which momentum regions the pi^0 exchange main contribution
originates. We also argue that a_\mu^{light-by-light} = (11 \pm 4) \times
10^{-10} encompasses the present understanding of this contribution and comment
on some directions to improve on that.Comment: 16 pages, 9 figure
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