Consecutive retrieval with redundancy: an optimal linear and an optimal cyclic arrangement and their storage space requirements

Information retrieval, file organization, consecutive retrieval property, consecutive retrieval with redundancy, storage space requirements 1

Sterilization of heparinized Cuprophan hemodialysis membranes

The effects of sterilization of dry heparinized Cuprophan hemodialysis membranes by means of ethylene oxide (EtO) exposure, gamma irradiation, or steam on the anticoagulant activity and chemical characteristics of immobilized heparin and the permeability of the membrane were investigated. Sterilization did not result in a release of heparin or heparin fragments from heparinized Cuprophan. Sterilization of heparinized Cuprophan by means of EtO exposure and gamma irradiation induced a slight, insignificant decrease of the anticoagulant activity. In contrast, steam-sterilized heparinized Cuprophan showed a higher anticoagulant activity than unsterilized heparinized Cuprophan, which was most likely caused by cleavage of some of the covalent bonds between heparin and Cupropha. The effects of sterilization on the permeability of unmodified Cuprophan and heparinized Cuprophan were compared. The permeability of unmodified Cuprophan for vitamin B12 (Vit B12) and sulfobromophthalein (SBP) was reduced by 20–35% after EtO exposure and gamma irradiation and was reduced by 90–95% after steam sterilization. The water permeability of unmodified Cuprophan remained the same after EtO exposure and gamma irradiation but also dramatically reduced after steam sterilization. These reductions were ascribed to the collapse of pores of the membrane. The permeability of heparinized Cuprophan was not affected by EtO exposure and gamma irradiation but dramatically reduced after steam sterilization, although to a lesser extent than in the case of unmodified Cuprophan. Apparently, the presence of immobilized heparin (partially) prevented the collapse of pores during sterilization. Gamma irradiation was recommended as the preferred method of sterilization for heparinized Cuprophan.\u

Aspects of average response computation by aperiodic stimulation

A mathematical analysis of the variance of the average evoked-response computation as a function of the numberN of stimuli presented is made for the case when the response is disturbed by additive stationary noise. A comparison is made between the variance for purely periodic stimuli and that for stimuli of which the interstimulus durations are Gaussian distributed. In the latter situation, the interval durations may be correlated with each other, e.g. according to a Gaussian Markov process. It is deduced that, in general, the introduction of aperiodic stimulation tends to make the functional relationship between the variance andN behave as though it holds for noise with a very broad frequency spectrum; the variance is proportional to 1/N

Preventing the spread and mitigating the impact of cocoa diseases in the Caribbean

With the arrival of frosty pod rot (FPR, caused by Moniliophthora roreri) in Jamaica, the insular Caribbean is now home to three of the “big five” of cocoa (Theobroma cacao) diseases. Black pod disease of cocoa (caused by Phytophthora spp.) is ubiquitous in the region whereas witches' broom (WB, caused by M. perniciosa) and FPR are still restricted to a few countries. The recent arrival of FPR however, is particularly worrying since it is considered to be the most destructive of all cocoa diseases. Even though the Caribbean contributes little to global cocoa production, it ranks second when it comes to fine flavor cocoa. Moreover, cocoa remains an important source of revenue for a large number of people in the Caribbean. Unfortunately, much of the varieties grown, known for their fine flavor qualities, have little resistance to diseases, especially FPR and/or WB. On top of that, most cocoa producing countries in the region are poorly equipped to prevent the arrival of FPR or WB or eradicate them once they do arrive. Thus, continual spread of these diseases in the Caribbean will have a severe impact on the fine flavor cocoa sector and the livelihoods of those depending on cocoa. In order to prevent further disease spread within the Caribbean, it is necessary to implement a major programme integrating awareness raising, capacity building, and development of early detection and rapid response measures for eradication. Additionally, countries will have to prepare for when these diseases do become established. The introduction of elite, highly productive cocoa germplasm combining resistance to WB and FPR and good quality attributes is urgently needed. Good agricultural practices that enable maximal expression of these attributes should be developed with and communicated to farmers and other relevant stakeholders. Such an undertaking will have the added benefit of revitalizing the sector and increasing productivity. This can only be successfully realized however, through a concerted effort among all cocoa producing countries bordering or in the Caribbean. There is an urgent need to make this financially and politically feasible. Only through such a concerted effort will cocoa remain a driver for the sustainable development of the Caribbean. (Texte intégral

Le taux de wilt est-il un facteur limitant de la production des cacaoyers ?

La production des cacaoyers dépend de nombreux facteurs: le nombre de fleurs produites par arbre, la pollinisation des fleurs, la tenue des jeunes fruits, les dégâts occasionnés par les maladies et les ravageurs. Parmi ces facteurs, nous nous sommes intéressés à la tenue des jeunes fruits, et donc aux pertes dues au cherelle wilt. Le wilt affecte tous les cacaoyers en production et nous avons voulu répondre à la question : le taux de wilt est il un facteur de régulation de la production des arbres, c'est-à-dire, le taux de wilt augmente t'il avec la charge en fruits des arbres ? ou bien, ce taux est il indépendant de la production ? Pour répondre à ces questions, nous avons suivi le chérelle wilt durant 2 années consécutives sur une parcelle de cacaoyers hybrides : les chérelles wiltées, les cabosses malades et les cabosses mures saines ont été répertoriées chaque semaine et sur chaque arbre. Il apparaît que le wilt affecte l'ensemble des arbres même ceux ayant des niveaux de production très faibles et la moyenne du taux de wilt est supérieur à 50 %. Le taux de wilt est relativement constant en fonction de la charge en fruits des arbres jusqu'à une charge totale en fruits d'environ 100 cabosses adultes par arbre. Le wilt intervient donc comme facteur de régulation au delà d'une production par arbre dépassant les 100 cabosses adultes par arbre, soit une production d'environ 4 tonnes de cacao marchand à l'hectare, rendement très rarement atteint en parcelle de production. Le taux wilt est apparu très héritable dans un essai comparatif de clones au Cameroun et il est donc possible de réduire les pertes dues à ce problème par amélioration génétique. Il parait toutefois important d'étudier plus finement les processus physiologiques intervenant dans le wilt pour tenter de diminuer ce phénomène qui touche plus de 50% des jeunes fruits. (Résumé d'auteur

Probando el control biológico en cacao. CIBB-SIMP-CA-003

Tres enfermedades de mazorcas del cacao (Theobroma cacao) ocasionan grandes pérdidas en las Américas: moniliasis, escoba de bruja (EB) y mazorca negra (MN). Los patógenos responsables son los basidiomicetes Moniliophthora roreri y Moniliophthora perniciosa, así como oomicetes del género Phytophthora, respectivamente. Su control es difícil y costoso, con desafíos comunes: (1) La infección concurrente por Phytophthora spp., M. roreri y/o M. perniciosa requiere biocontrol simultáneo de dos a tres patógenos muy diferentes; (2) La infección latente interna de mazorcas por Moniliophthora spp. restringe la ventana de oportunidad para controlarla; (3) Existe una gran diversidad de esos patógenos, con un rango de susceptibilidades hacía sus controladores potenciales; (4) La altura de los árboles de cacao muchas veces no se presta al manejo fitosanitario. Nuestros objetivos son: (1) compartir lecciones aprendidas con el control biológico de esas enfermedades en el Perú y en Costa Rica y (2) presentar metodologías sencillas para desarrollar exitosamente biocontroladores contra esos patógenos del cacao en otros países del continente. Nuestro enfoque es en agentes fungosos (micoparásitos y hongos endofíticos) para la aplicación inundativa y para el control biológico clásico con biocontroladores co-evolucionados. Recomendamos buscar biocontroladores donde es probable que trabajen naturalmente, en nichos similares a los sitios de aplicación prevista Presentamos la técnica de placas precolonizadas como método de cebo para micoparásitos. La selección de candidatos promisorios a partir de la colección inicial debe usar bioensayos (en vivo) para el pretamizado. Debe ser una eliminación estricta de cualquier organismo que no cumple con todos los requisitos consistentemente aunque sea confrontado con un patógeno pre-establecido así como otra microflora natural. Indicamos varias técnicas sencillas de pretamizado, trabajando con distintas cepas del patógeno en el proceso. Con el fin de controlar patógenos diversos (especies y cepas), proponemos el uso de mezclas de biocontroladores. Las mismas además tiene la ventaja que se pueden diseñar en forma que cubren un rango amplio de condiciones agroecológicos. Pruebas preliminares de campo contra Moniliophthora spp. deben ejecutarse durante un periodo mínimo de 4 meses. Los ensayos de campo se llevan a cabo para un mínimo de dos ciclos de producción. La optimización iterativa de tratamientos eficaces implica no replicar tratamientos que fallaron una vez. Eso invariablemente resulta en diseños experimentales no balanceados y datos faltantes. Paquetes estadísticas modernas pueden analizar estos datos; se recomienda consultar un biometrista ya durante la fase de planificación del estudio para aprovechas al máximo herramientas existentes y datos costosos de ensay del campo. (Résumé d'auteur

Field optimization of pheromone traps for monitoring and controlling cocoa mirids, Sahlbergella singularis

In Cameroon, pheromone traps appear interesting to monitor or even control Sahlbergella singularis populations on cocoa farms. The efficiency of traps baited with pheromones relies on a good knowledge of both visual and olfactory stimuli that attract cocoa mirids and on appropriate trap deployment in cocoa plantations. The aim of this preliminary study is first to compare the attractiveness of traps of different colors and baited with different pheromone blends. To achieve this purpose, we monitored a total of 90 traps of 3 different colors (30 red, 30 yellow and 30 white) and baited with 2 different pheromone blends, deployed in ten 1-ha plots (100 x 100m) PVC tubular traps were monitored from March on a weekly basis. Simultaneously, experiments in flight tunnel were conducted in the laboratory to confirm trends observed in the field. Secondly, to better understand how trap deployment influences mirid capture rate, we tested 3 trap densities in a total of twenty one 1-ha plots (100 x 100m) which received different treatments: 7 plots with a high trap density (16 traps ha-1), 7 plots with a medium trap density (9 traps ha-1) and 7 plots with a low trap density (4 traps ha-1). Traps were monitored on a weekly basis. Also, mirid populations and damage were assessed in each plot twice a year. Seven plantations with no trap were sprayed with insecticide according to spraying recommendations and were also monitored to evaluate the productivity gain or loss between the two control methods. Understanding the factors involved in oriented movements of mirids in the field, will help to formulate relevant recommendations to improve integrated management of S. singularis and potentially to reduce the economical cost of control strategies. (Résumé d'auteur

Spatial relationships between dominant ants and the cocoa mirid Sahlbergella singularis in traditional cocoa-based agroforestry systems

Manipulating ant communities to control pests of cocoa has proven to be a promising strategy, especially in Asia. However, concerning African cocoa mirids, the main pests of cocoa in Africa, basic knowledge on mirid-ant relationships is still incomplete. Our study aimed to characterize the spatial relationships between dominant ant species and the mirid Sahlbergella singularis (Hemiptera: Miridae) in traditional cocoa-based agroforestry systems of Cameroon. Over two consecutive years, mirid and ant populations were assessed by a chemical knock-down sampling method in four plots of 100 cocoa trees, located in three different agroecological zones in the Centre region of Cameroon. Mapping procedures were used to display spatial distribution of mirid and ant populations. Also, we adapted spatial statistics methodologies of point pattern analysis to consider the regular tree position effects on insect positions. These techniques allow testing the statistical significance of Poisson null models, leading to the classification of the spatial patterns of insects into association vs. segregation. Our results clearly demonstrated spatial segregation between mirid and the dominant weaver ant Oecophylla longinoda, known as a key-predator in natural ecosystems. Weaver ant trumps, especially its dominant status in ant communities of cocoa ecosystems and its ecological preferences for open habitats, make it a promising candidate for conservation biocontrol against cocoa mirids in Africa. (Résumé d'auteur

Impact of barriers on the onset of a Phytophthora megakarya epidemic in cocoa

Black pod rot of cocoa caused by Phytophthora megakarya causes significant losses in Cameroon. Normally (chemical) control efforts only begin when the first diseased pods appear. In theory, preventive control, focusing on reducing primary inoculum or barring it from infecting cocoa pods could alter the spatial and temporal development of a P. megakarya epidemic and reduce its impact. The principal source of primary inoculum is thought to originate from the soil. Therefore, the objective of this study was to study the effect of barriers between the soil and the cocoa tree, physical as well as chemical, on the onset of a P. megakarya epidemic. A completely randomized plot design was used, including five treatments with three replicate plots per treatment. Each plot consisted of 16 cocoa trees. Treatments were i) Control, no intervention, ii) Bare Soil, removal of the litter layer surrounding the cocoa trees, iii) Double Litter Layer, the removed organic matter (OM) from the bare soil treatment was added to this third treatment, iv) Ridomil, Ridomil was applied in three week intervals unto the OM surrounding the cocoa trees and v) Plastic Barrier, a plastic sheet was spread on top of the litter layer surrounding the cocoa trees. Data, the number of healthy and diseased pods below or above 3 meters above ground level, were recorded weekly. The cumulative number of diseased pods (CDP) as well as the pod rot rate (PRR) were calculated and plotted over time. The results showed that the bare soil treatment had the highest number of diseased pods as well as PRR, followed by the control, double litter layer and Ridomil treatments. The plastic barrier treatment had the lowest CDP and PRR, moreover, the first diseased pods appeared later in time compared with the other treatments. Pod rot rate and number of diseased pods was higher up to 3 meters than above 3 meters. The results of this study clearly demonstrate the importance of soil-born primary inoculum. Moreover, it demonstrates that it should be possible to delay the onset and subsequently reduce the severity of a P. megakarya epidemic, which could lead to less fungicide applications and higher yields. More attention should be given to the development of preventive control measures for P. megakarya pod rot. (Texte intégral