1,323 research outputs found
Goal conflicts in long-term cropping system trials - the example of carrots
Agricultural research on multiple cropping systems in parallel increases the potential for knowledge transfer between organic and conventional systems. This project aims to develop cropping systems towards greater sustainability through work in long-term trials that have a unique opportunity to contribute to a holistic research perspective. Data on the fourth crop rotation (2007-2012) are now being compiled. This paper presents preliminary results from cultivation of carrots as an example to demonstrate goal conflicts in organic and conventional systems between good nutrient management and good economy on one hand and nematode control and intensive cropping systems (good short-term economy) on the other. Good productivity and sustainable production levels are major overall goals in the project. The conclusion is that more research on nematode susceptibility and propagating at different crops and varieties is very important
Worldsheet boundary conditions in Poisson-Lie T-duality
We apply canonical Poisson-Lie T-duality transformations to bosonic open
string worldsheet boundary conditions, showing that the form of these
conditions is invariant at the classical level, and therefore they are
compatible with Poisson-Lie T-duality. In particular the conditions for
conformal invariance are automatically preserved, rendering also the dual model
conformal. The boundary conditions are defined in terms of a gluing matrix
which encodes the properties of D-branes, and we derive the duality map for
this matrix. We demonstrate explicitly the implications of this map for
D-branes in two non-Abelian Drinfel'd doubles.Comment: 20 pages, Latex; v2: typos and wording corrected, references added;
v3: three-dimensional example added, reference added, discussion clarified,
published versio
N=2 Boundary conditions for non-linear sigma models and Landau-Ginzburg models
We study N=2 nonlinear two dimensional sigma models with boundaries and their
massive generalizations (the Landau-Ginzburg models). These models are defined
over either Kahler or bihermitian target space manifolds. We determine the most
general local N=2 superconformal boundary conditions (D-branes) for these sigma
models. In the Kahler case we reproduce the known results in a systematic
fashion including interesting results concerning the coisotropic A-type branes.
We further analyse the N=2 superconformal boundary conditions for sigma models
defined over a bihermitian manifold with torsion. We interpret the boundary
conditions in terms of different types of submanifolds of the target space. We
point out how the open sigma models correspond to new types of target space
geometry. For the massive Landau-Ginzburg models (both Kahler and bihermitian)
we discuss an important class of supersymmetric boundary conditions which
admits a nice geometrical interpretation.Comment: 48 pages, latex, references and minor comments added, the version to
appear in JHE
Collodial particles at a range of fluid-fluid particles
The study of solid particles residing at fluid-fluid interfaces has become an established area in surface and colloid science recently experiencing a renaissance since around 2000. Particles at interfaces arise in many industrial products and processes like anti-foam formulations, crude oil emulsions, aerated foodstuffs and flotation. Although they act in many ways like traditional surfactant molecules, they offer distinct advantages also and the area is now multi-disciplinary involving research in the fundamental science and potential applications. In this Feature Article, a flavour of some of this interest is given based on recent work from our own group and includes the behaviour of particles at oil-water, air-water, oil-oil, air-oil and water-water interfaces. The materials capable of being prepared by assembling various kinds of particles at fluid interfaces include particle-stabilised emulsions, particle-stabilised aqueous and oil foams, dry liquids, liquid marbles and powdered emulsions
T-duality for the sigma model with boundaries
We derive the most general local boundary conditions necessary for T-duality
to be compatible with superconformal invariance of the two-dimensional N=1
supersymmetric nonlinear sigma model with boundaries. To this end, we construct
a consistent gauge invariant parent action by gauging a U(1) isometry, with and
without boundary interactions. We investigate the behaviour of the boundary
conditions under T-duality, and interpret the results in terms of D-branes.Comment: 48 pages, LaTeX, v2: typos corrected, references adde
D-branes and doubled geometry
We define the open string version of the nonlinear sigma model on doubled geometry introduced by Hull and Reid-Edwards, and derive its boundary conditions. These conditions include the restriction of D-branes to maximally isotropic submanifolds as well as a compatibility condition with the Lie algebra structure on the doubled space. We demonstrate a systematic method to derive and classify D-branes from the boundary conditions, in terms of embeddings both in the doubled geometry and in the physical target space. We apply it to the doubled three-torus with constant H-flux and find D0-, D1-, and D2-branes, which we verify transform consistently under T-dualities mapping the system to f-, Q- and R-flux backgrounds
T-duality and Generalized Complex Geometry
We find the explicit T-duality transformation in the phase space formulation
of the N=(1,1) sigma model. We also show that the T-duality transformation is a
symplectomorphism and it is an element of O(d,d). Further, we find the explicit
T-duality transformation of a generalized complex structure in this model. We
also show that the extended supersymmetry of the sigma model is preserved under
the T-duality.Comment: 18 pages; added references; published versio
Supersymmetric non-linear sigma-models with boundaries revisited
We study two-dimensional supersymmetric non-linear sigma-models with
boundaries. We derive the most general family of boundary conditions in the
non-supersymmetric case. Next we show that no further conditions arise when
passing to the N=1 model. We present a manifest N=1 off-shell formulation. The
analysis is greatly simplified compared to previous studies and there is no
need to introduce non-local superspaces nor to go (partially) on-shell. Whether
or not torsion is present does not modify the discussion. Subsequently, we
determine under which conditions a second supersymmetry exists. As for the case
without boundaries, two covariantly constant complex structures are needed.
However, because of the presence of the boundary, one gets expressed in terms
of the other one and the remainder of the geometric data. Finally we recast
some of our results in N=2 superspace and discuss applications.Comment: LaTeX, 23 page
Supersymmetric Boundaries and Junctions in Four Dimensions
We make a comprehensive study of (rigid) N=1 supersymmetric sigma-models with
general K\"ahler potentials K and superpotentials w on four-dimensional
space-times with boundaries. We determine the minimal (non-supersymmetric)
boundary terms one must add to the standard bulk action to make it off-shell
invariant under half the supersymmetries without imposing any boundary
conditions. Susy boundary conditions do arise from the variational principle
when studying the dynamics. Upon including an additional boundary action that
depends on an arbitrary real boundary potential B one can generate very general
susy boundary conditions. We show that for any set of susy boundary conditions
that define a Lagrangian submanifold of the K\"ahler manifold, an appropriate
boundary potential B can be found. Thus the non-linear sigma-model on a
manifold with boundary is characterised by the tripel (K,B,w). We also discuss
the susy coupling to new boundary superfields and generalize our results to
supersymmetric junctions between completely different susy sigma-models, living
on adjacent domains and interacting through a "permeable" wall. We obtain the
supersymmetric matching conditions that allow us to couple models with
different K\"ahler potentials and superpotentials on each side of the wall.Comment: 38 pages, 1 figur
Manifestly Supersymmetric RG Flows
Renormalisation group (RG) equations in two-dimensional N=1 supersymmetric
field theories with boundary are studied. It is explained how a manifestly N=1
supersymmetric scheme can be chosen, and within this scheme the RG equations
are determined to next-to-leading order. We also use these results to revisit
the question of how brane obstructions and lines of marginal stability appear
from a world-sheet perspective.Comment: 22 pages; references added, minor change
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