Ad Hoc Basis (ad + hoc_basis)

Distribution by Scientific Domains

Selected Abstracts

Optimal eradication: when to stop looking for an invasive plant

Tracey J. Regan
Abstract The notion of being sure that you have completely eradicated an invasive species is fanciful because of imperfect detection and persistent seed banks. Eradication is commonly declared either on an ad hoc basis, on notions of seed bank longevity, or on setting arbitrary thresholds of 1% or 5% confidence that the species is not present. Rather than declaring eradication at some arbitrary level of confidence, we take an economic approach in which we stop looking when the expected costs outweigh the expected benefits. We develop theory that determines the number of years of absent surveys required to minimize the net expected cost. Given detection of a species is imperfect, the optimal stopping time is a trade-off between the cost of continued surveying and the cost of escape and damage if eradication is declared too soon. A simple rule of thumb compares well to the exact optimal solution using stochastic dynamic programming. Application of the approach to the eradication programme of Helenium amarum reveals that the actual stopping time was a precautionary one given the ranges for each parameter. [source]

Functional reconstitution of the HIV receptors CCR5 and CD4 in liposomes

FEBS JOURNAL, Issue 21 2002
François Devesa
Reconstitution of membrane proteins allows their study in a membrane environment that can be manipulated at will. Because membrane proteins have diverse biophysical properties, reconstitution methods have so far been developed for individual proteins on an ad hoc basis. We developed a postinsertion reconstitution method for CCR5, a G protein coupled receptor, with seven transmembrane ,,helices and small ecto- and endodomains. A His6 -tagged version of CCR5 was expressed in mammalian cells, purified using the detergent N -dodecyl-,- d -maltoside (DDM) and reconstituted into preformed liposomal membranes saturated with DDM, removing the detergent with hydrophobic polystyrene beads. We then attempted to incorporate CD4, a protein with a single transmembrane helix and a large hydrophilic ectodomain into liposomal membranes, together with CCR5. Surprisingly, reconstitution of this protein was also achieved by the method. Both proteins were found to be present together in individual liposomes. The reconstituted CCR5 was recognized by several monoclonal antibodies, recognized its natural ligand, and CD4 bound a soluble form of gp120, a subunit of the HIV fusion protein that uses CD4 as a receptor. Moreover, cells expressing the entire fusion protein of HIV bound to the liposomes, indicating that the proteins were intact and that most of them were oriented right side out. Thus, functional coreconstitution of two widely different proteins can be achieved by this method, suggesting that it might be useful for other proteins. [source]

Crime and Punishment on the Margins of the Postapartheid State

Lars Buur
This article examines how communities on the margin of the new postapartheid state reclaim "stolen goods" and deal with "criminals" in ways that inflict physical punishment and are often profoundly brutal or violent. It explores how the use of corporal punishment in the form of beatings and other forms of inflicting pain comes to be seen as both necessary and legitimate by the affected communities. Crime is often articulated by township communities as their biggest obstacle to accessing development funding, investments, and employment initiatives. By drawing on past forms of organization from the struggle against apartheid, township residents, believing that the police are unable to preserve law and order, take the law into their own hands. These residents have created a range of local security structures to deal with crime,some well organized, others working on a more ad hoc basis. The kind of "justice" these emerging structures stand for is often the only kind of justice that large numbers of citizens in the South African townships can afford. The particular manner in which criminals are dealt with in the township is intimately related to the socioeconomic marginalization that most township residents encounter on a daily basis. [source]

Striking a balance between retaining populations of protected seahorses and maintaining swimming nets

David Harasti
Abstract 1.The fish family Syngnathidae (seahorses, pipefish, pipehorses and seadragons) is fully protected in New South Wales, Australia, but in some countries certain species are threatened by unsustainable collecting, capture as incidental bycatch, and habitat degradation. 2.Within Sydney Harbour, two species of seahorses (Hippocampus abdominalis and Hippocampus whitei) have been found to colonize artificial structures such as jetty pylons and protective netted swimming enclosures. These protective nets are subject to fouling from epibiotic growth (algae, ascidians, bryozoans, etc.) and rubbish, which causes the nets to collapse from the additional weight. Local authorities employ diving contractors on an ad hoc basis to remove the epibiota from nets. 3.Surveys showed a significant decline in the numbers of both seahorse species at one site following the replacement of a net, and recovery of the H. whitei population took more than 15 months. 4.A manipulative experiment tested the importance of epibiotic growth for seahorses. H. whitei, tagged with individual marks, were allocated to sections of a net that had undergone different cleaning procedures. Seahorse size, position on the net and total population abundance were recorded every 2 weeks over a 3 month period. It was demonstrated that seahorses have a significant positive association with epibiotic growth and proximity to the sea floor. Seahorse populations also showed seasonal variation in abundance with increased numbers on the net during the breeding season (spring,summer). 5.This project has led to the development of best practice net cleaning procedures for local authorities in Sydney Harbour to manage growth on the nets while minimizing impacts on seahorse populations. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Managing the "hollow state": procedural policy instruments and modern governance

Michael Howlett
Recent works by Canadian, Dutch, American, British and French scholars have begun to describe a common set of policy instruments contemporary governments now use to indirectly steer social actors towards their preferred policy options. Unlike traditional "substantive" instruments, which directly affect the delivery of goods and services in society, these "procedural" policy instruments are intended to manage state-societal interactions in order to assure general support for government aims and initiatives. Used on an ad hoc basis in the past, these tools have become an essential feature of modern governance. This article advances the study of these procedural policy instruments by developing a taxonomy and outlining the rationale for choosing between particular instrument types. Sommaire: Les gouvernements se trouvent aujourd'hui face à un paradoxe: d'une part, leur pouvoir d'intervention est en principe important au niveau des connais-sances, de I'expertise, des budgets et du personnel; d'autre part, les phénomènes tels que la mondialisation et la démocratisation ont fortement sapé leur capacité d'influer directement sur les résultats sociaux. Des travaux récents d'auteurs canadiens, néer-landais, américains, britanniques et français amorcent la description d'un ensemble commun d'instruments directifs dont se servent actuellement les gouvernements pour orienter indirectement les intervenants sociaux vers les options politiques que les gouvernements préfèrent. À I'encontre des instruments classiques « substantifs » influant directement sur la prestation de biens et services au sein de la société, ces instruments « procéduraux » visent é gkrer l'interaction État-société de manière à ce que les initiatives et objectifs gouvernementaux reçoivent l'appui de tous. Utilisés de manière ponctuelle dans le passé, ces outils sont devenus un éléments essentiel de la gouvemance moderne. Cet article fait progresser l'étude de ces instruments de procédure pour l'élaboration des politiques, en définissant une taxonomie et en pré-cisant les raisons pour lesquelles un type d'instrument particulier serait préférable à un autre. [source]