4,398 research outputs found
Writeshop ASSP/ASDP-L in Zanzibar - Writing stories on Managing for impact
From 7th – 11th October 2009 a writeshop was held in Zanzibar. This workshop was organised on request of the IFAD funded programme ASSP/ASDP-L in Zanzibar. The idea was to enhance the writing skills of participants and to write stories that reflect some experiences in relation to the managing for impact (M4I) approach that was introduced to the programme 2 years ago. The regional programme to strengthen managing for impact (SMIP) in East and Southern Africa is working with ASSP/ASDP-L as one of their action learning sites. A series of inputs have been provided to assist the programme in their efforts to manage for impact. This writeshop aimed to document some of the lessons learned in the form of written stories. The output of the writeshop is a booklet that contains all the stories from writeshop participants. These stories will be shared during a policy event that is planned to take place by the end of this year in Zanzibar. Also the stories will be used in writing a booklet on managing for impact, which is supported by Wageningen UR under the KB7 programme. Furthermore, ASSP-ASDP-L wishes to share their stories through existing websites and through other communication with the ‘outside world’
The Complexity of Simultaneous Geometric Graph Embedding
Given a collection of planar graphs on the same set of
vertices, the simultaneous geometric embedding (with mapping) problem, or
simply -SGE, is to find a set of points in the plane and a bijection
such that the induced straight-line drawings of
under are all plane.
This problem is polynomial-time equivalent to weak rectilinear realizability
of abstract topological graphs, which Kyn\v{c}l (doi:10.1007/s00454-010-9320-x)
proved to be complete for , the existential theory of the
reals. Hence the problem -SGE is polynomial-time equivalent to several other
problems in computational geometry, such as recognizing intersection graphs of
line segments or finding the rectilinear crossing number of a graph.
We give an elementary reduction from the pseudoline stretchability problem to
-SGE, with the property that both numbers and are linear in the
number of pseudolines. This implies not only the -hardness
result, but also a lower bound on the minimum size of a
grid on which any such simultaneous embedding can be drawn. This bound is
tight. Hence there exists such collections of graphs that can be simultaneously
embedded, but every simultaneous drawing requires an exponential number of bits
per coordinates. The best value that can be extracted from Kyn\v{c}l's proof is
only
A method for molecular dynamics on curved surfaces
Dynamics simulations of constrained particles can greatly aid in
understanding the temporal and spatial evolution of biological processes such
as lateral transport along membranes and self-assembly of viruses. Most
theoretical efforts in the field of diffusive transport have focussed on
solving the diffusion equation on curved surfaces, for which it is not
tractable to incorporate particle interactions even though these play a crucial
role in crowded systems. We show here that it is possible to combine standard
constraint algorithms with the classical velocity Verlet scheme to perform
molecular dynamics simulations of particles constrained to an arbitrarily
curved surface, in which such interactions can be taken into account.
Furthermore, unlike Brownian dynamics schemes in local coordinates, our method
is based on Cartesian coordinates allowing for the reuse of many other standard
tools without modifications, including parallelisation through domain
decomposition. We show that by applying the schemes to the Langevin equation
for various surfaces, confined Brownian motion is obtained, which has direct
applications to many biological and physical problems. Finally we present two
practical examples that highlight the applicability of the method: (i) the
influence of crowding and shape on the lateral diffusion of proteins in curved
membranes and (ii) the self-assembly of a coarse-grained virus capsid protein
model.Comment: 30 pages, 5 figure
A temperature overshoot on a catalyst pellet
An unexpected temperature overshoot was found for a Pd on alumina catalyst pellet in its course towards a new steady state, after a change in concentration of one of the reactants. The reaction mixture consisted of ethylene, hydrogen and nitrogen as inert. A speculative model is introduced, which can explain these overshoots by a slow adsorption of one of the reactants on the active sites of the catalyst
Confinement without boundaries: Anisotropic diffusion on the surface of a cylinder
Densely packed systems of thermal particles in curved geometries are
frequently encountered in biological and microfluidic systems. In 2D systems,
at sufficiently high surface coverage, diffusive motion is widely known to be
strongly affected by physical confinement, e.g., by the walls. In this Letter,
we explore the effects of confinement by shape, not rigid boundaries, on the
diffusion of particles by confining them to the surface of a cylinder. We find
that both the magnitude and the directionality of lateral diffusion is strongly
influenced by the radius of the cylinder. An anisotropy between diffusion in
the longitudinal and circumferential direction of the cylinder develops. We
demonstrate that the origin of this effect lies in the fact that screw-like
packings of mono- and oligodisperse discs on the surface of a cylinder induce
preferential collective motions in the circumferential direction, but also show
that even in polydisperse systems lacking such order an intrinsic finite size
confinement effect increases diffusivity in the circumferential direction
On Universal Point Sets for Planar Graphs
A set P of points in R^2 is n-universal, if every planar graph on n vertices
admits a plane straight-line embedding on P. Answering a question by Kobourov,
we show that there is no n-universal point set of size n, for any n>=15.
Conversely, we use a computer program to show that there exist universal point
sets for all n<=10 and to enumerate all corresponding order types. Finally, we
describe a collection G of 7'393 planar graphs on 35 vertices that do not admit
a simultaneous geometric embedding without mapping, that is, no set of 35
points in the plane supports a plane straight-line embedding of all graphs in
G.Comment: Fixed incorrect numbers of universal point sets in the last par
Strengthening Managing for Impact in Eastern and Southern Africa : Grant Completion Report
The Strengthening Managing for Impact Programme (SMIP) was a pilot initiative established to test the extent to which the use of the Managing for Impact (M4I) approach could enhance the impact of pro-poor interventions for greater development effectiveness. This programme was implemented in the Eastern and Southern Africa region (including French speaking countries) from 2006 till the end of 2009 and was largely funded by IFAD. A partnership was developed between Wageningen UR Centre for Development Innovation (formerly part of Wageningen International), Khanya6aicdd, IFPRI6IKCD (formerly IFPRI/ISNAR) and Haramaya University (in a joint partnership ‘Carmpolea’); and the Impact Alliance
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