7,643 research outputs found
The Fubini-Furlan-Rossetti Sum Rule Revisited
The Fubini-Furlan-Rossetti sum rule for pion photoproduction on the nucleon
is evaluated by dispersion relations at constant t, and the corrections to the
sum rule due to the finite pion mass are calculated. Near threshold these
corrections turn out to be large due to pion-loop effects, whereas the sum rule
value is closely approached if the dispersion integrals are evaluated for
sub-threshold kinematics. This extension to the unphysical region provides a
unique framework to determine the low-energy constants of chiral perturbation
theory by global properties of the excitation spectrum.Comment: 12 pages, 7 postscript figures, EPJ style files include
Threshold Two-Pion Photo- and Electroproduction: More neutrals than expected
We present an exploratory study of two pion photo-- and electroproduction off
the nucleon in the threshold region. To calculate the pertinent amplitudes, we
make use of heavy baryon chiral perturbation theory. We show that due to finite
chiral loops the production cross section for final states with two neutral
pions is considerably enhanced. The experimental implications are briefly
discussed.Comment: 23pp, plain TeX, 11 figures available upon request, CRN 94/1
Explaining the Conversion to Organic Farming of Farmers of the Obwalden Canton, Switzerland - Extension of the Theory of Planned Behavior within a Structural Equation Modeling Approach
Farmers' decisions about conversion to organic farming are analyzed with a structural equation model. The Theory of Planned Behavior (ToPB), one of the prominent theories in the social psychology, is used as the theoretical basis of this study. Though ToPB is a well-defined theory, it is static rather than procedural and cannot model the individual decision-making as a process. Therefore, we first examine the general applicability of ToPB in an agricultural context and explain the variance in intentions of farmers to convert to organic farming. Second, we extend the ToPB to make it more procedural. For this purpose, research findings from the Diffusion Theory are included as part of the behavioral model. The empirical results indicate that, overall, the model has an acceptable fit to the data. The effects of the additional variables "Goal" and "Communication" are highly significant. This illustrates the importance of forming personal goals in the behavior domain and that people act in a goal-directed, rational way. Moreover, it gives empirical evidence that communication through personal channels has a great impact on individual decision-making. Altogether, this study shows that the extended ToPB provides an appropriate approach to investigate individual decision-making processes in agriculture.behavior research, conversion to particularly animal friendly stabling system, theory of planned behavior, diffusion theory, structural equation modelling, Farm Management, C8, D1, Q12, Z13,
A Combinatorial Solution to Non-Rigid 3D Shape-to-Image Matching
We propose a combinatorial solution for the problem of non-rigidly matching a
3D shape to 3D image data. To this end, we model the shape as a triangular mesh
and allow each triangle of this mesh to be rigidly transformed to achieve a
suitable matching to the image. By penalising the distance and the relative
rotation between neighbouring triangles our matching compromises between image
and shape information. In this paper, we resolve two major challenges: Firstly,
we address the resulting large and NP-hard combinatorial problem with a
suitable graph-theoretic approach. Secondly, we propose an efficient
discretisation of the unbounded 6-dimensional Lie group SE(3). To our knowledge
this is the first combinatorial formulation for non-rigid 3D shape-to-image
matching. In contrast to existing local (gradient descent) optimisation
methods, we obtain solutions that do not require a good initialisation and that
are within a bound of the optimal solution. We evaluate the proposed method on
the two problems of non-rigid 3D shape-to-shape and non-rigid 3D shape-to-image
registration and demonstrate that it provides promising results.Comment: 10 pages, 7 figure
Whitman and American Personalistic Philosophy
Traces Whitman\u27s influence on the late-nineteenth and early-twentieth-century philosophical movement known as "Personalism"--"a nonempirical philosophy in which the self obtains knowledge from a mighty power of reason, which is creative and can fashion reality from its own ideas"--and argues that "the American writer who first formally used the term \u27Personalism\u27 was Walt Whitman" and that "wherever the Personalistic path leads, it should not be forgotten that there was a distinct philosophical school that formally began with Whitman\u27s article \u27Personalism.\u27
Consistent Calculation of the Nucleon Electromagnetic Polarizabilities in Chiral Perturbation Theory Beyond Next-to-Leading Order
We calculate the nucleons' electromagnetic polarizabilities in heavy baryon
chiral perturbation theory including all terms to order . The
chiral prediction of the electric polarizabilities for the neutron and the
proton are in good agreement with the data. In the case of the magnetic
polarizabilities the big positive contribution from the
resonance is largely cancelled by a non--analytic loop contribution of the type. This novel effect helps to understand the rather small empirical
value of the nucleons' magnetic polarizability.Comment: 10 pp, TeX, BUTP-93/22 and CRN-93-3
Linear spin-2 fields in most general backgrounds
We derive the full perturbative equations of motion for the most general
background solutions in ghost-free bimetric theory in its metric formulation.
Clever field redefinitions at the level of fluctuations enable us to circumvent
the problem of varying a square-root matrix appearing in the theory. This
greatly simplifies the expressions for the linear variation of the bimetric
interaction terms. We show that these field redefinitions exist and are
uniquely invertible if and only if the variation of the square-root matrix
itself has a unique solution, which is a requirement for the linearised theory
to be well-defined. As an application of our results we examine the constraint
structure of ghost-free bimetric theory at the level of linear equations of
motion for the first time. We identify a scalar combination of equations which
is responsible for the absence of the Boulware-Deser ghost mode in the theory.
The bimetric scalar constraint is in general not manifestly covariant in its
nature. However, in the massive gravity limit the constraint assumes a
covariant form when one of the interaction parameters is set to zero. For that
case our analysis provides an alternative and almost trivial proof of the
absence of the Boulware-Deser ghost. Our findings generalise previous results
in the metric formulation of massive gravity and also agree with studies of its
vielbein version.Comment: Latex, 20 pages. Matches published versio
Conditions for Posterior Contraction in the Sparse Normal Means Problem
The first Bayesian results for the sparse normal means problem were proven
for spike-and-slab priors. However, these priors are less convenient from a
computational point of view. In the meanwhile, a large number of continuous
shrinkage priors has been proposed. Many of these shrinkage priors can be
written as a scale mixture of normals, which makes them particularly easy to
implement. We propose general conditions on the prior on the local variance in
scale mixtures of normals, such that posterior contraction at the minimax rate
is assured. The conditions require tails at least as heavy as Laplace, but not
too heavy, and a large amount of mass around zero relative to the tails, more
so as the sparsity increases. These conditions give some general guidelines for
choosing a shrinkage prior for estimation under a nearly black sparsity
assumption. We verify these conditions for the class of priors considered by
Ghosh and Chakrabarti (2015), which includes the horseshoe and the
normal-exponential gamma priors, and for the horseshoe+, the inverse-Gaussian
prior, the normal-gamma prior, and the spike-and-slab Lasso, and thus extend
the number of shrinkage priors which are known to lead to posterior contraction
at the minimax estimation rate
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