54 research outputs found
A skeleton approximate solution of the Einstein field equations for multiple black-hole systems
An approximate analytical and non-linear solution of the Einstein field
equations is derived for a system of multiple non-rotating black holes. The
associated space-time has the same asymptotic structure as the Brill-Lindquist
initial data solution for multiple black holes. The system admits an
Arnowitt-Deser-Misner (ADM) Hamiltonian that can particularly evolve the
Brill-Lindquist solution over finite time intervals. The gravitational field of
this model may properly be referred to as a skeleton approximate solution of
the Einstein field equations. The approximation is based on a conformally flat
truncation, which excludes gravitational radiation, as well as a removal of
some additional gravitational field energy. After these two simplifications,
only source terms proportional to Dirac delta distributions remain in the
constraint equations. The skeleton Hamiltonian is exact in the test-body limit,
it leads to the Einsteinian dynamics up to the first post-Newtonian
approximation, and in the time-symmetric limit it gives the energy of the
Brill-Lindquist solution exactly. The skeleton model for binary systems may be
regarded as a kind of analytical counterpart to the numerical treatment of
orbiting Misner-Lindquist binary black holes proposed by Gourgoulhon,
Grandclement, and Bonazzola, even if they actually treat the corotating case.
Along circular orbits, the two-black-hole skeleton solution is quasi-stationary
and it fulfills the important property of equality of Komar and ADM masses.
Explicit calculations for the determination of the last stable circular orbit
of the binary system are performed up to the tenth post-Newtonian order within
the skeleton model.Comment: 15 pages, 1 figure, submitted to Phys. Rev. D, 3 references added,
minor correction
COMBINING ABILITY AND HETEROTIC PATTERN IN WEST AFRICAN SORGHUM LANDRACES
Heterotic grouping based on combining ability for traits of interest,
in addition to plant performance and genetic relationship among
germplasm, would be useful in planning crosses in breeding programmes.
This study aimed at determining the combining abilities of selected
landraces for morphological and physiological traits under contrasted
environments and identifying the suitable heterotic grouping method for
superior hybrid production. For this purpose, nineteen accessions
representing different origins and population structure among West
African Sorghum Accessions Panel (WASAP) and two female lines, were
used in \uab\ua0Line x tester\ua0\ubb mating design to produce
thirty-eight (38) hybrids. Analysis of variance showed significant
general combining ability and specific combining ability effects for
grain weight, plant height, days to flowering, panicle length and
chlorophyll content implying existence of heterotic responses for these
traits. Both additive and non-additive gene effects were important in
controlling the inheritance of the traits. Parents K31.3, K37 and Ni331
were the best combiners for grain weight, providing the opportunity for
breeders to improve grain yield under diverse environments. AVG-1 x
K31.3 and AVG-1 x Tg148 were the superior hybrids. Combining ability
based heterotic grouping methods classified sorghum accessions into
four groups. The heterotic group\u2019s specific and general combining
ability (HSGCA) method was the suitable in predicting hybrid
superiority. This combining abilities based heterotic grouping study is
an additional tool that breeders could use to identify the best parents
for superior hybrids development in West Africa.La d\ue9termination des groupes h\ue9t\ue9rotiques bas\ue9e sur
les aptitudes \ue0 la combinaison des traits
d\u2019int\ue9r\ueat en plus des performances et des relations
g\ue9n\ue9tiques dans une collection est importante pour planifier
les croisements en s\ue9lection. Cette visait la d\ue9termination
des aptitudes \ue0 la combinaison des accessions locales pour
certains traits morphologiques sous environnements contrast\ue9s et
l\u2019identification de la meilleure m\ue9thode dans la
pr\ue9diction de la vigueur hybride. Dans cette perspective, dix-neuf
accessions repr\ue9sentant diff\ue9rentes origines et la structure
de la population d\u2019un panel ouest africain de sorgho (WASAP) et
deux m\ue2les st\ue9riles ont \ue9t\ue9 utilis\ue9s dans un
croisement \uab\ua0Line x tester\ua0\ubb pour produire
trente-huit hybrides F1, objet de cette \ue9tude. L\u2019analyse de
variance a indiqu\ue9 des effets significatifs de l\u2019aptitude
g\ue9n\ue9rale et sp\ue9cifique \ue0 la combinaison pour le
poids grain, la hauteur plante, la dur\ue9e semis floraison et la
concentration en chlorophylle traduisant l\u2019existence des
r\ue9ponses h\ue9t\ue9rotiques pour ces traits. Les effets
g\ue9niques additif et non-additif ont \ue9t\ue9 importants dans
le contr\uf4le de ces caract\ue8res. K31.3, K37 et Ni331
pr\ue9sentent les meilleures aptitudes g\ue9n\ue9rales \ue0 la
combinaison puis AVG-1 x K31.3 et AVG-1 x Tg148 ont \ue9t\ue9 les
meilleurs hybrides pour le poids grains. Ils constituent une
opportunit\ue9 pour l\u2019am\ue9lioration dans divers
environnements. Les diff\ue9rentes m\ue9thodes ont class\ue9 les
accessions de sorgho en quatre groupes. Le groupage bas\ue9 sur la
m\ue9thode HSGCA accroit l\u2019efficience en s\ue9lection de 15
%. Cette \ue9tude offre un outil d\u2019aide pour les
s\ue9lectionneurs dans le choix des meilleurs parents \ue0 croiser
pour la production des hybrides sup\ue9rieurs en Afrique de
l\u2019Ouest
Surveillance des sols dans l'environnement par télédétection et systèmes d'information géographiques = Monitoring soils in the environment with remote sensing and GIS
Le potentiel d'infiltration des sols constitue un des paramètres essentiels intervenant dans les modèles hydrodynamiques décrivant le comportement des nappes. Classiquement, l'estimation de ce potentiel d'infiltration est basée sur la paramétrisation d'une cartographie pédologique des sols, mais celle-ci est souvent non disponible et serait beaucoup trop lourde à mettre en oeuvre en sus des campagnes de prospection hydrogéologique. Dans ces circonstances, le BRGM a jugé essentiel de tester les possibilités offertes par la télédétection satellitaire. L'objectif est d'aboutir à une cartographie des états de surface des sols fondée sur des relations entre états de surfaces et potentiels d'infiltration. Le résultat est alors directement intégrable dans les processus de modélisation hydrogéologiques. La zone test choisie est située à 100 km au nord de Gaborone, où le BRGM était intervenu, à l'aide d'une campagne hydrogéologique complète, pour contribuer à l'approvisionnement en eau de la capitale du Botswana. Cette zone où l'archive hydrogéologique est importante (géophysique, géochimie, géologie structurale et nombreux forages) offre en outre l'avantage de présenter une couverture végétale faible et donc de montrer assez directement l'état minéral des sols. L'approche par télédétection s'appuie sur une classification supervisée des images Landsat. Les résultats des classifications ont permis de préciser les interprétations des spatiocartes en terme d'états de surface ; les interprétations sont étalonnées sur le terrain afin d'établir une cartographie de leur potentiel d'infiltration (202 points de contrôle). Les résultats cartographiques sont intégrés au modèle hydrodynamique MARTHE. Pour estimer le potentiel de la cartographie par télédétection, la comparaison est faite avec un produit cartographique de référence établi par le modèle MARTHE. (Résumé d'auteur
Characterization of beta-fructosidase, an extracellular glycoprotein of carrot cells
International audienc
Oviposition responses of Anopheles gambiae s.s. (Diptera: Culicidae) and identification of volatiles from bacteria-containing solutions
In this study, a dual-choice oviposition bioassay was used to screen responses of gravid An. gambiae toward 17 bacterial species, previously isolated from Anopheles gambiae s.l. (Diptera: Culicidae) midguts or oviposition sites. The 10 isolates from oviposition sites have been identified by phylogenetic analyses of their 16S rRNA genes. Eight of the 10 isolates were gram-positive, out of which six belonged to the Bacilli class. Solid phase microextraction and gas chromatography coupled to mass spectrometry (GC-MS) were used to identify the volatiles emitted from the bacterial isolates. Aromatic and aliphatic alcohols, aliphatic ketones, alkylpyrazines, dimethyl oligosulfides, and indole were among the chemical compounds identified from the headspace above bacteria-containing saline. The mosquitoes laid significantly more eggs in six of the bacteria-containing solutions compared with the sterile solution. These six bacteria did not emit any compounds in common that could explain the positive oviposition response. Instead, the bacteria were grouped according to principal component analysis (PCA) based on the relative amounts of volatiles emitted. The PCA-plots facilitated the identification of 13 putative oviposition attractants for An. gambiae mosquitoe
Re-introducing bacteria in mosquitoes - A method for determination of mosquito feeding preferences based on coloured sugar solutions
In this study, sugar-feeding was investigated as a possible means of re-introducing bacteria into mosquito midguts with the aim of identifying bacteria that are suitable for creating paratransgenic mosquitoes. In a paratransgenic approach, bacteria are utilised to deliver effector molecules capable of inhibiting pathogen development in the midgut of the vector. To determine if mosquitoes discriminate between sterile sugar solutions and sugar solutions with bacteria, a method for screening mosquito feeding preferences was developed. This method was tested for Aedes aegypti, Anopheles arabiensis and An. gambiae s.s. mosquitoes and is based on a dual-choice test of solutions labelled with food dyes. Three different tests (dye/colour detection, sugar detection and sugar-concentration detection) were performed to evaluate the method, after which bacteria previously isolated from mosquitoes were used in the experiments. It was shown that mosquitoes do not discriminate between sugar solutions with or without these bacteria indicating that sugar-feeding is a possible means to introduce bacteria into mosquitoes. Furthermore, two different setups of the method were used, enabling us to differentiate between tactile/taste and olfactory responses. The method described in this paper is easy to use, cost-effective and allows broad screening of mosquito sugar-feeding preference
Systematics and biogeography of the genus Pseudocodium (Bryopsidales, Chlorophyta), including the description of P. natalense sp. nov. from South Africa
This study examines the diversity of Pseudocodium, a small green algal genus assigned to its own family in the order Bryopsidales. The included species are characterized by uncalcified thalli with a medulla composed of a limited number of interwoven siphons that form a cortex of distinctive utricles toward the periphery. Detailed morphological descriptions are provided for all known species. A combination of characters relating to general habit, morphology of the axes, apices and utricles distinguishes all species easily. Re-examination of Indonesian and Papua New Guinean specimens, previously reported as Pseudocodium floridanum, reveals that they belong to the recently described Pseudocodium okinawense. South African specimens formerly attributed to P. floridanum are described as a new species, Pseudocodium. natalense. Pseudocodium australasicum, a species endemic to southern Australia, does not fit the generic concept of Pseudocodium in that it does not possess a cortex composed of utricles. Putative reproductive structures have thus far only been reported for P. floridanum. Observations on Pseudocodium devriesii and P. natalense reveal very similar spherical to irregular structures formed laterally on medullary siphons in the axils of peripheral utricles. Interestingly, and confirming the earlier observations of Dawes & Mathieson, no basal cross wall is formed at the base of the reproductive structures. Instead, a translucent plug at the base of the reproductive structures prevents the cytoplasm from leaking. This suggests that Pseudocodium is not holocarpic, unlike most Halimedineae. DNA sequences of rbcL and tufA are presented for all species and the resulting phylogenies are used as a framework to study the evolution of morphological features as well as the biogeography of the genus, both at the global scale and within the Indian Ocean
Systematics and biogeography of the genus <i>Pseudocodium</i> (Bryopsidales, Chlorophyta), including the description of <i>P. natalense</i> sp. nov. from South Africa
This study examines the diversity of Pseudocodium, a small green algal genus assigned to its own family in the order Bryopsidales. The included species are characterized by uncalcified thalli with a medulla composed of a limited number of interwoven siphons that form a cortex of distinctive utricles toward the periphery. Detailed morphological descriptions are provided for all known species. A combination of characters relating to general habit, morphology of the axes, apices and utricles distinguishes all species easily. Re-examination of Indonesian and Papua New Guinean specimens, previously reported as Pseudocodium floridanum, reveals that they belong to the recently described Pseudocodium okinawense. South African specimens formerly attributed to P. floridanum are described as a new species, Pseudocodium. natalense. Pseudocodium australasicum, a species endemic to southern Australia, does not fit the generic concept of Pseudocodium in that it does not possess a cortex composed of utricles. Putative reproductive structures have thus far only been reported for P. floridanum. Observations on Pseudocodium devriesii and P. natalense reveal very similar spherical to irregular structures formed laterally on medullary siphons in the axils of peripheral utricles. Interestingly, and confirming the earlier observations of Dawes & Mathieson, no basal cross wall is formed at the base of the reproductive structures. Instead, a translucent plug at the base of the reproductive structures prevents the cytoplasm from leaking. This suggests that Pseudocodium is not holocarpic, unlike most Halimedineae. DNA sequences of rbcL and tufA are presented for all species and the resulting phylogenies are used as a framework to study the evolution of morphological features as well as the biogeography of the genus, both at the global scale and within the Indian Ocean
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