Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons

The stability of cosmological event and Cauchy horizons of spacetimes associated with plane symmetric domain walls are studied. It is found that both horizons are not stable against perturbations of null fluids and massless scalar fields; they are turned into curvature singularities. These singularities are light-like and strong in the sense that both the tidal forces and distortions acting on test particles become unbounded when theses singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques

Does covering of farm-associated Culicoides larval habitat reduce adult populations in the United Kingdom?

Culicoides biting midges (Diptera: Ceratopogonidae) are the biological vectors of a range of internationally important arboviruses of livestock, including bluetongue virus (BTV) and the recently emerging Schmallenberg virus (SBV). Culicoides species in the subgenus Avaritia (inthe UK: Culicoides obsoletus Meigen, Culicoides scoticus Downes & Kettle, Culicoides dewulfi Goetghebuer and Culicoides chiopterus Meigen) have been implicated in BTV transmissionin northern Europe and to a varying degree utilise cattle dung as a larval development substrate. The collection of cattle dung into heaps on farms provides a localised sourceof Culicoides emergence in close proximity to livestock. This study assesses the impact of covering dung heaps prior to the onset of adult Culicoides activity with the aim of reducing recruitment to the local adult populations at four livestock farms in England. Light suctiontrap catches of adult Culicoides from these farms were compared with those from four untreated control farms from a wide geographic range across the UK. It was demonstrated that implementing control of emergence from dung heaps did not have a significant impactupon the local adult subgenus Avaritia abundance at the treated farm holdings and thatthe onset of Culicoides activity was similarly unaffected. Use of this method in isolation isunlikely to have an effect in reducing the risk of BTV and SBV transmission. The implicationsof these results for control of farm-associated Culicoides in Europe are discussed

Canine Obesity: Do Owners See What You See?

No abstract available

Control techniques for Culicoides biting midges and their application in the U.K. and northwestern Palaearctic

The recent emergence of bluetongue virus (Reoviridae: Orbivirus ) (BTV)in northern Europe, for the first time in recorded history, has led to an urgent need for methods to control the disease caused by this virus and the midges that spread it. This paper reviews various methods of vector control that have been employed elsewhere and assesses their likely efficacy for controlling vectors of BTV in northern Europe. Methods of controlling Culicoides spp. (Diptera: Ceratopogonidae) have included: (a) application of insecticides and pathogens to habitats where larvae develop; (b) environmental interventions to remove larval breeding sites; (c) controlling adult midges by treating either resting sites, such as animal housing, or host animals with insecticides; (d) housing livestock in screened buildings, and (e) using repellents or host kairomones to lure and kill adult midges. The major vectors of BTV in northern Europe are species from the Culicoides obsoletus (Meigen) and Culicoides pulicaris (L.) groups, for which there are scant data on breeding habits, resting behaviour and host-oriented responses. Consequently, there is little information on which to base a rational strategy for controlling midges or for predicting the likely impact of interventions. However, data extrapolated from the results of vector control operations conducted elsewhere, combined with some assessment of how acceptable or not different methods may be within northern Europe, indicate that the treatment of livestock and animal housing with pyrethroids, the use of midge-proofed stabling for viraemic or high-value animals and the promotion of good farm practice to at least partially eliminate local breeding sites are the best options currently available. Research to assess and improve the efficacy of these methods is required and, in the longer term, efforts should be made to develop better bait systems for monitoring and, possibly, controlling midges. All these studies will need better methods of analysing the ecology and behaviour of midges in the field than are currently in use. The paucity of control options and basic knowledge serve to warn us that we must be better prepared for the possible emergence of other midge-borne diseases, particularly African horse sickness

Bluetongue in the Mediterranean: prediction of risk in space and time

Bluetongue virus (BTV) causes an infectious, non-contagious disease of ruminants and is transmitted by Culicoides biting midges. Currently an unprecedented epidemic of bluetongue (BT) is sweeping the Mediterranean Basin and a large number of countries are now involved in managing the disease. Therefore the development of new methods for accurate prediction of BT risk in space and time is essential. The life-history parameters of Culicoides and other parameters of the BTV transmission cycle are highly sensitive to climatic conditions. Thus the potential exists to define the limiting conditions and likelihood of spread of BTV, using geographical information systems (GIS) to combine vector, virus and environmental information. This paper reviews the progress and current status of GIS and remote sensing (RS) as applied to BTV in the Mediterranean Basin. These analytical tools have aided the determination of the relative roles of different Culicoides vectors in BTV transmission across the region and have facilitated prediction of the wide-scale distribution of the major field vector C. imicola from RS climate variables. On the basis of findings and lessons from statistical models of vector distribution, a strategy for development of dynamic biological or process-based models of BT risk is suggeste

Virus Akabane: enquête sérologique des anticorps chez les animaux d’élevage au Soudan

Cette étude porte sur une évaluation de la fréquence des anticorps antivirus Akabane chez les ruminants domestiques dans différentes zones écologiques au Soudan. Les anticorps neutralisants ont été détectés chez les moutons, les chèvres et les bovins. Les sérums de ces animaux ont été récoltés entre 1979 et 1980 à El Obeid, Nyala, Kassala, Sennar et Jonglei. C'est dans cette dernière région qu'ont été trouvés les plus forts taux de présence d'anticorps antivirus dans les sérums analysés : respectivement 27 %, 36 % et 47 % chez les moutons (6), les chèvres (11) et les bovins (90). Bien que les anticorps aient été détectés chez 8 % des 79 vaches et chez 15 % des 70 vaches dans deux troupeaux sentinelles au Centre du Soudan, respectivement à Shambat et Um Benein, aucun des veaux suivis dans ces élevages entre 1981 et 1983 ne s'est révélé positif. Par la suite, des sérums d'échantillons aléatoires prélevés en 1985 sur des animaux âgés de 1 à 3 ans ont montré la présence d'anticorps chez 8 veaux sur 57 (14 %) à Shambat et 5 veaux sur 40 (12 %) à Um Benein. Les implications de ces résultats sont discutées

The Usefulness of Classification Trees in Risk Factor Identification in Canine Obesity

No abstract available