658 research outputs found
Soil and water bioengineering: practice and research needs for reconciling natural hazard control and ecological restoration
Soil and water bioengineering is a technology that encourages scientists and practitioners to combine their knowledge and skills in the management of ecosystems with a common goal to maximize benefits to both man and the natural environment. It involves techniques that use plants as living building materials, for: (i) natural hazard control (e.g., soil erosion, torrential floods and landslides) and (ii) ecological restoration or nature-based re-introduction of species on degraded lands, river embankments, and disturbed environments. For a bioengineering project to be successful, engineers are required to highlight all the potential benefits and ecosystem services by documenting the technical, ecological, economic and social values. The novel approaches used by bioengineers raise questions for researchers and necessitate innovation from practitioners to design bioengineering concepts and techniques. Our objective in this paper, therefore, is to highlight the practice and research needs in soil and water bioengineering for reconciling natural hazard control and ecological restoration. Firstly, we review the definition and development of bioengineering technology, while stressing issues concerning the design, implementation, and monitoring of bioengineering actions. Secondly, we highlight the need to reconcile natural hazard control and ecological restoration by posing novel practice and research questions
On Low-Energy Effective Actions in N = 2, 4 Superconformal Theories in Four Dimensions
We study some aspects of low-energy effective actions in 4-d superconformal
gauge theories on the Coulomb branch. We describe superconformal invariants
constructed in terms of N=2 abelian vector multiplet which play the role of
building blocks for the N=2,4 supersymmetric low-energy effective actions. We
compute the one-loop effective actions in constant N=2 field strength
background in N=4 SYM theory and in N=2 SU(2) SYM theory with four
hypermultiplets in fundamental representation. Using the classification of
superconformal invariants we then find the manifestly N=2 superconformal form
of these effective actions. While our explicit computations are done in the
one-loop approximation, our conclusions about the structure of the effective
actions in N=2 superconformal theories are general. We comment on some
applications to supergravity - gauge theory duality in the description of
D-brane interactions.Comment: 18 pages, latex, comments/reference adde
1/4 Partial Breaking of Global Supersymmetry and New Superparticle Actions
We construct the worldline superfield massive superparticle actions which
preserve 1/4 portion of the underlying higher-dimensional supersymmetry. The
rest of supersymmetry is spontaneously broken and realized by nonlinear
transformations. We consider the cases of N=4 to N=1 and N=8 to N=2 partial
breaking. In the first case we present the corresponding Green-Schwarz type
target superspace action with one -supersymmetry. It is related to the
superfield action via a field redefinition. In the second case we find out two
possible models, one of which is a direct generalization of the N=4 to N=1
case, while another is essentially different. For the first model we formulate
Green-Schwarz type action with two kappa supersymmetries. We elaborate on the
bosonic part of the superfield action for the second model and find that only
in two special limits it takes the standard Nambu-Goto form. In the general
case it is determined by a fourth-order algebraic equation. The characteristic
common feature of these new superparticle models is that the algebras of their
spontaneously broken supersymmetries are non-trivial truncations of the general
extensions of N=1 and N=2 Poincare D=4 superalgebras by tensorial central
charges.Comment: 22 page
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