8,824 research outputs found
Dispersive Fourier Transformation for Versatile Microwave Photonics Applications
Abstract: Dispersive Fourier transformation (DFT) maps the broadband spectrum of an ultrashort optical pulse into a time stretched waveform with its intensity profile mirroring the spectrum using chromatic dispersion. Owing to its capability of continuous pulse-by-pulse spectroscopic measurement and manipulation, DFT has become an emerging technique for ultrafast signal generation and processing, and high-throughput real-time measurements, where the speed of traditional optical instruments falls short. In this paper, the principle and implementation methods of DFT are first introduced and the recent development in employing DFT technique for widespread microwave photonics applications are presented, with emphasis on real-time spectroscopy, microwave arbitrary waveform generation, and microwave spectrum sensing. Finally, possible future research directions for DFT-based microwave photonics techniques are discussed as well
Soft Methodology for Cost-and-error Sensitive Classification
Many real-world data mining applications need varying cost for different
types of classification errors and thus call for cost-sensitive classification
algorithms. Existing algorithms for cost-sensitive classification are
successful in terms of minimizing the cost, but can result in a high error rate
as the trade-off. The high error rate holds back the practical use of those
algorithms. In this paper, we propose a novel cost-sensitive classification
methodology that takes both the cost and the error rate into account. The
methodology, called soft cost-sensitive classification, is established from a
multicriteria optimization problem of the cost and the error rate, and can be
viewed as regularizing cost-sensitive classification with the error rate. The
simple methodology allows immediate improvements of existing cost-sensitive
classification algorithms. Experiments on the benchmark and the real-world data
sets show that our proposed methodology indeed achieves lower test error rates
and similar (sometimes lower) test costs than existing cost-sensitive
classification algorithms. We also demonstrate that the methodology can be
extended for considering the weighted error rate instead of the original error
rate. This extension is useful for tackling unbalanced classification problems.Comment: A shorter version appeared in KDD '1
Global Spatio-temporal Patterns of Influenza in the Post-pandemic Era
We study the global spatio-temporal patterns of influenza dynamics. This is
achieved by analysing and modelling weekly laboratory confirmed cases of
influenza A and B from 138 countries between January 2006 and May 2014. The
data were obtained from FluNet, the surveillance network compiled by the the
World Health Organization. We report a pattern of {\it skip-and-resurgence}
behavior between the years 2011 and 2013 for influenza H1N1/09, the strain
responsible for the 2009 pandemic, in Europe and Eastern Asia. In particular,
the expected H1N1/09 epidemic outbreak in 2011 failed to occur (or"skipped") in
many countries across the globe, although an outbreak occurred in the following
year. We also report a pattern of {\it well-synchronized} 2010 winter wave of
H1N1/09 in the Northern Hemisphere countries, and a pattern of replacement of
strain H1N1/77 by H1N1/09 between the 2009 and 2012 influenza seasons. Using
both a statistical and a mechanistic mathematical model, and through fitting
the data of 108 countries (108 countries in a statistical model and 10 large
populations with a mechanistic model), we discuss the mechanisms that are
likely to generate these events taking into account the role of multi-strain
dynamics. A basic understanding of these patterns has important public health
implications and scientific significance
Romans Supergravity from Five-Dimensional Holograms
We study five-dimensional superconformal field theories and their holographic
dual, matter-coupled Romans supergravity. On the one hand, some recently
derived formulae allow us to extract the central charges from deformations of
the supersymmetric five-sphere partition function, whose large N expansion can
be computed using matrix model techniques. On the other hand, the conformal and
flavor central charges can be extracted from the six-dimensional supergravity
action, by carefully analyzing its embedding into type I' string theory. The
results match on the two sides of the holographic duality. Our results also
provide analytic evidence for the symmetry enhancement in five-dimensional
superconformal field theories.Comment: 57 pages, 4 figures, 6 tables; v2: references adde
Diffusion Dynamics, Moments, and Distribution of First Passage Time on the Protein-Folding Energy Landscape, with Applications to Single Molecules
We study the dynamics of protein folding via statistical energy-landscape
theory. In particular, we concentrate on the local-connectivity case with the
folding progress described by the fraction of native conformations. We obtain
information for the first passage-time (FPT) distribution and its moments. The
results show a dynamic transition temperature below which the FPT distribution
develops a power-law tail, a signature of the intermittency phenomena of the
folding dynamics. We also discuss the possible application of the results to
single-molecule dynamics experiments
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