8,991 research outputs found
The 'black box' problem in the study of participation
Research on citizen participation has been guided by two core issues: first, the observation of a widening repertory of modes of participation, and second, the argument that participation is not an undifferentiated phenomenon, but must be conceived as an inherently multidimensional reality. In this article, we argue that conventional participation research has focused too one-sidedly on quantitatively expanding the range of types of activities, while the complex dimensionality is not reflected in the measures used. We formulate a methodological critique by using the metaphor of the 'black box', which refers to the implicit and unquestioned assumption that distinct types of activities and associations represent homogeneous and consistent realities that do not warrant further analytical decomposition. Surveys of participation allocate individuals to different 'participation boxes' by means of a binary logic, leaving a void of what is actually happening inside the boxes. To conclude, we reflect upon the fundamental dilemmas the black box of participation raises for theory and research, and offer conceptual and methodological keys to unlock the participation box
An elliptic boundary problem acting on generalized Sobolev spaces
We consider an elliptic boundary problem over a bounded region in
and acting on the generalized Sobolev space
for . We note that similar problems for
either a bounded region in or a closed manifold acting
on , called H\"{o}rmander space, have been the subject of
investigation by various authors. Then in this paper we will, under the
assumption of parameter-ellipticity, establish results pertaining to the
existence and uniqueness of solutions of the boundary problem. Furthermore,
under the further assumption that the boundary conditions are null, we will
establish results pertaining to the spectral properties of the Banach space
operator induced by the boundary problem, and in particular, to the angular and
asymptotic distribution of its eigenvalues
Time ordered perturbation theory for non-local interactions; applications to NCQFT
In the past decades, time ordered perturbation theory was very successful in
describing relativistic scattering processes. It was developed for local
quantum field theories. However, there are field theories which are governed by
non-local interactions, for example non-commutative quantum field theory
(NCQFT). Filk (Phys. Lett. B 376 (1996) 53) first studied NCQFT perturbatively
obtaining the usual Feynman propagator and additional phase factors as the
basic elements of perturbation theory. However, this treatment is only
applicable for cases, where the deformation of space-time does not involve
time. Thus, we generalize Filk's approach in two ways: First, we study
non-local interactions of a very general type able to embed NCQFT. And second,
we also include the case, where non-locality involves time. A few applications
of the obtained formalism will also be discussed.Comment: 21 pages, 2 figure
R-boundedness, pseudodifferential operators, and maximal regularity for some classes of partial differential operators
It is shown that an elliptic scattering operator on a compact manifold
with boundary with coefficients in the bounded operators of a bundle of Banach
spaces of class (HT) and Pisier's property has maximal regularity
(up to a spectral shift), provided that the spectrum of the principal symbol of
on the scattering cotangent bundle of the manifold avoids the right
half-plane.
This is deduced directly from a Seeley theorem, i.e. the resolvent is
represented in terms of pseudodifferential operators with R-bounded symbols,
thus showing by an iteration argument the R-boundedness of
for .
To this end, elements of a symbolic and operator calculus of
pseudodifferential operators with R-bounded symbols are introduced. The
significance of this method for proving maximal regularity results for partial
differential operators is underscored by considering also a more elementary
situation of anisotropic elliptic operators on with operator valued
coefficients.Comment: 21 page
Consistent Construction of Perturbation Theory on Noncommutative Spaces
We examine the effect of non-local deformations on the applicability of
interaction point time ordered perturbation theory (IPTOPT) based on the free
Hamiltonian of local theories. The usual argument for the case of quantum field
theory (QFT) on a noncommutative (NC) space (based on the fact that the
introduction of star products in bilinear terms does not alter the action) is
not applicable to IPTOPT due to several discrepancies compared to the naive
path integral approach when noncommutativity involves time. These discrepancies
are explained in detail. Besides scalar models, gauge fields are also studied.
For both cases, we discuss the free Hamiltonian with respect to non-local
deformations.Comment: 22 pages; major changes in Section 3; minor changes in the
Introduction and Conclusio
Twin-Photon Confocal Microscopy
A recently introduced two-channel confocal microscope with correlated
detection promises up to 50% improvement in transverse spatial resolution
[Simon, Sergienko, Optics Express {\bf 18}, 9765 (2010)] via the use of photon
correlations. Here we achieve similar results in a different manner,
introducing a triple-confocal correlated microscope which exploits the
correlations present in optical parametric amplifiers. It is based on tight
focusing of pump radiation onto a thin sample positioned in front of a
nonlinear crystal, followed by coincidence detection of signal and idler
photons, each focused onto a pinhole. This approach offers further resolution
enhancement in confocal microscopy
- …