117,973 research outputs found
From First Lyapunov Coefficients to Maximal Canards
Hopf bifurcations in fast-slow systems of ordinary differential equations can
be associated with surprising rapid growth of periodic orbits. This process is
referred to as canard explosion. The key step in locating a canard explosion is
to calculate the location of a special trajectory, called a maximal canard, in
parameter space. A first-order asymptotic expansion of this location was found
by Krupa and Szmolyan in the framework of a "canard point"-normal-form for
systems with one fast and one slow variable. We show how to compute the
coefficient in this expansion using the first Lyapunov coefficient at the Hopf
bifurcation thereby avoiding use of this normal form. Our results connect the
theory of canard explosions with existing numerical software, enabling easier
calculations of where canard explosions occur.Comment: preprint version - for final version see journal referenc
First measurement of interference fragmentation on a transversely polarized hydrogen target
The HERMES experiment has measured for the first time single target-spin
asymmetries in semi-inclusive two-pion production using a transversely
polarized hydrogen target. These asymmetries are related to the product of two
unknowns, the transversity distribution function and the interference
fragmentation function. In the invariant mass range 0.51 GeV < M_inv < 0.97 GeV
the measured asymmetry deviates significantly from zero, indicating that
two-pion semi-inclusive deep-inelastic scattering can be used to probe
transversity.Comment: 6 pages, 6 figures, contribution to the proceedings of the
International Workshop on Transverse Polarisation Phenomena in Hard Processes
(Transversity 2005), Como, Italy, Sep 7 - 10, 200
WASH coalition building guidelines
The Water Supply and Sanitation Collaborative Council (WSSCC) is an international membership organisation that has worked, since 1990, to achieve sustainable water
supply and sanitation for all people, through enhancing collaboration among sector agencies and professionals.
As part of its activities within two of its programme areas – Networking & Knowledge Management, and Advocacy & Communications – WSSCC encourages the development of national water supply, sanitation and hygiene (WASH) Coalitions.
The role of WASH Coalitions ranges from information sharing to the advocacy of specific policy changes, but they universally address a felt need for improved
systematic communication, collaboration and joint action among the sector players in a certain country. As a vehicle for awareness raising and advocacy, most national
WASH Coalitions have developed national WASH Campaigns. A special role is given to the National Coordinators, who are expected to maintain the links with the WSSCC Secretariat, exercise quality control and practise a degree of coordination and facilitation of the coalition.
However, coalitions, like partnerships, are complicated organisms and some of the existing WASH Coalitions have had only limited impact and varying degrees of success. This is partly due to the complexity of building a successful coalition that responds to the specific needs of the country in which it is created, and partly due to
the undefined or open mandate of the WASH Coalitions, resulting in a lack of clarity about what they are intended to do
The Horseshoe Estimator: Posterior Concentration around Nearly Black Vectors
We consider the horseshoe estimator due to Carvalho, Polson and Scott (2010)
for the multivariate normal mean model in the situation that the mean vector is
sparse in the nearly black sense. We assume the frequentist framework where the
data is generated according to a fixed mean vector. We show that if the number
of nonzero parameters of the mean vector is known, the horseshoe estimator
attains the minimax risk, possibly up to a multiplicative constant. We
provide conditions under which the horseshoe estimator combined with an
empirical Bayes estimate of the number of nonzero means still yields the
minimax risk. We furthermore prove an upper bound on the rate of contraction of
the posterior distribution around the horseshoe estimator, and a lower bound on
the posterior variance. These bounds indicate that the posterior distribution
of the horseshoe prior may be more informative than that of other one-component
priors, including the Lasso.Comment: This version differs from the final published version in pagination
and typographical detail; Available at
http://projecteuclid.org/euclid.ejs/141813426
Updates in metabolomics tools and resources: 2014-2015
Data processing and interpretation represent the most challenging and time-consuming steps in high-throughput metabolomic experiments, regardless of the analytical platforms (MS or NMR spectroscopy based) used for data acquisition. Improved machinery in metabolomics generates increasingly complex datasets that create the need for more and better processing and analysis software and in silico approaches to understand the resulting data. However, a comprehensive source of information describing the utility of the most recently developed and released metabolomics resources—in the form of tools, software, and databases—is currently lacking. Thus, here we provide an overview of freely-available, and open-source, tools, algorithms, and frameworks to make both upcoming and established metabolomics researchers aware of the recent developments in an attempt to advance and facilitate data processing workflows in their metabolomics research. The major topics include tools and researches for data processing, data annotation, and data visualization in MS and NMR-based metabolomics. Most in this review described tools are dedicated to untargeted metabolomics workflows; however, some more specialist tools are described as well. All tools and resources described including their analytical and computational platform dependencies are summarized in an overview Table
Comment on "Creating in-plane pseudomagnetic fields in excess of 1000 T by misoriented stacking in a graphene bilayer"
In a recent paper [Phys. Rev. B 89, 125418 (2014)], the authors argue that it
is possible to map the electronic properties of twisted bilayer graphene to
those of bilayer graphene in an in-plane magnetic field. However, their
description of the low-energy dynamics of twisted bilayer graphene is
restricted to the extended zone scheme and therefore neglects the effects of
the superperiodic structure. If the energy spectrum is studied in the supercell
Brillouin zone, we find that the comparison with an in-plane magnetic field
fails because (i) the energy spectra of the two situations exhibit different
symmetries and (ii) the low-energy spectra are very different.Comment: 3 pages, 2 figure
Two-hadron single target-spin asymmetries: first measurement by HERMES
Single target-spin asymmetries in semi-inclusive two-pion production were
measured for the first time by the HERMES experiment, using a longitudinally
polarized deuterium target. These asymmetries relate to the unknown
transversity distribution function through, also unknown, interference
fragmentation functions. The presented results are compared with a model for
the dependence of one of these interference fragmentation functions on the
invariant mass of the pion pair.Comment: 4 pages, 4 figures, contribution to the proceedings for the 16th
international spin physics symposium (SPIN'2004
Tuplix Calculus
We introduce a calculus for tuplices, which are expressions that generalize
matrices and vectors. Tuplices have an underlying data type for quantities that
are taken from a zero-totalized field. We start with the core tuplix calculus
CTC for entries and tests, which are combined using conjunctive composition. We
define a standard model and prove that CTC is relatively complete with respect
to it. The core calculus is extended with operators for choice, information
hiding, scalar multiplication, clearing and encapsulation. We provide two
examples of applications; one on incremental financial budgeting, and one on
modular financial budget design.Comment: 22 page
Structure and Strategy, How Do They Match in the Netherlands?
Farm organization, and the balance between the household and the farm have changed. This paper explores the relation between the organizational form and strategy of Dutch farmers and shows that strategy and structure are related. Legal persons and partnerships with multiple households can be especially found among the farmers focusing on economies of scale. One-man businesses and the one household partnerships more often show diversification strategies. One-man businesses are relatively more encountered amongst the life style farmers, whilst one household partnerships are stronger present amongst rural entrepreneurs.family farm, household, legal form, strategy, typology, Farm Management,
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