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The Gueydan, a new middle Tertiary formation from the southwestern coastal plain of Texas
Accompanied by 1 foldout plate -- Plate 1 : Geologic map of part of southern Texas showing outcrops of Gueydan and adjacent formations. University of Texas bulletin ; no. 2645 : Dec. 1, 1926UT Librarie
Influence of turbulence on the dynamo threshold
We use direct and stochastic numerical simulations of the magnetohydrodynamic
equations to explore the influence of turbulence on the dynamo threshold. In
the spirit of the Kraichnan-Kazantsev model, we model the turbulence by a
noise, with given amplitude, injection scale and correlation time. The addition
of a stochastic noise to the mean velocity significantly alters the dynamo
threshold. When the noise is at small (resp. large) scale, the dynamo threshold
is decreased (resp. increased). For a large scale noise, a finite correlation
time reinforces this effect
A turbulent model of torque in von Karman swirling flow
A stochastic model is derived to predict the turbulent torque produced by a
swirling flow. It is a simple Langevin process, with a colored noise. Using the
unified colored noise approximation, we derive analytically the PDF of the
fluctuations of injected power in two forcing regimes: constant angular
velocity or constant applied torque. In the limit of small velocity
fluctuations and vanishing inertia, we predict that the injected power
fluctuates twice less in the case of constant torque than in the case of
constant angular velocity forcing. The model is further tested against
experimental data in a von Karman device filled with water. It is shown to
allow for a parameter-free prediction of the PDF of power fluctuations in the
case where the forcing is made at constant torque. A physical interpretation of
our model is finally given, using a quasi-linear model of turbulence
Ătude expĂ©rimentale des transferts d'eau provoquĂ©s par l'irrigation sur une parcelle en moyenne vallĂ©e du fleuve SĂ©nĂ©gal
Alors que l'irrigation paraĂźt ĂȘtre le recours essentiel face aux besoins croissants de la population mondiale en cĂ©rĂ©ales, la dĂ©gradation des sols et des eaux annihile presque totalement les efforts d'amĂ©nagement. Aussi l'Ă©tude de la dĂ©gradation des sols dans la moyenne vallĂ©e du fleuve SĂ©nĂ©gal constitue l'un des quatre objectifs du pĂŽle de recherches sur les systĂšmes irriguĂ©s sahĂ©liens qui regroupe quatre pays dont le Mali, la Mauritanie, le Niger et le SĂ©nĂ©gal. Le suivi de l'Ă©volution des eaux et des sols sous culture apparaĂźt indispensable pour garantir une agriculture irriguĂ©e rentable et durable dans la zone. Dans cette rĂ©gion, les risques de dĂ©gradation des sols font suite Ă l'effet de deux processus de dĂ©gradation que sont l'alcalinisation et la salinisation des sols. Ces types de dĂ©gradation sont fortement corrĂ©lĂ©s Ă la remontĂ©e des nappes d'eaux souterraines. Dans cet article, l'Ă©tude des transferts d'eau dans les parcelles irriguĂ©es par le biais d'un suivi expĂ©rimental " in situ " met en Ă©vidence les relations existantes entre les eaux d'irrigation et les mouvements de la nappe. L'Ă©tude a permis une meilleure comprĂ©hension de la dynamique hydrique au sein de la parcelle : saturation du profil et processus de recharge de la nappe. Elle a Ă©galement permis de montrer que les Ă©changes avec la nappe pendant la pĂ©riode d'irrigation sont nĂ©gligeables. Cette pratique de la riziculture inondĂ©e, entraĂźne une variation de stock importante qui reprĂ©sente plus de 40% des apports et qui se traduit par une remontĂ©e de nappe de prĂšs de 2 mĂštres.Whereas irrigation appears to be the main approach to satisfy the growing worldwide demand for cereal, soil and water degradation continues to be an on-going problem in agriculture development. One of the main four concerns of the regional group for research on Sahelian irrigated systems (including Mali, Mauritania, Niger and Senegal) is soil degradation in the middle Senegal River valley. These soils are subject to various forms of degradation, mainly from salinisation and/or alkalinisation. These degradation processes are strongly correlated with water table dynamics, with water level fluctuations being significant. Therefore, to guarantee sustainable development of irrigated agriculture in the area, irrigation must be coupled with complete and permanent monitoring of soil and water quality.In this paper, we present a complete study concerning water transfer in irrigated plots and its effects on the groundwater table. The experimental site is located in the Podor region, at 16°.37'N, 14°.52'W in the Donaye irrigated area. The surface area is about 50 ha. Water supply is assured by filling a main channel using a group of pumps on the DouĂ© River. Irrigation of the parcels is performed with siphons from this channel. The experimental plot of 0.33 ha is used for an underwater rice crop. One or two rice crop production harvests are made every year, with the decision been taken by the farmers. There is no drainage system in the area.The experimental plot was equipped with 8 piezometers located along a stream line. One is situated between the plot and the river in order to study the water movements caused by the exchange between the groundwater and the water in the river. Three are situated in the plot, one close to the DouĂ© River, one in the middle of the plot and one near a dam, which is the opposite boundary compared to the river. Four other piezometers are located beyond the dam to estimate groundwater input and output at this boundary. Five tensiometers at 20, 40, 60, 95 and 135 cm depth are placed close to the piezometers located in the plot. Four water content profiles were measured during the irrigation period at depths 20, 40, 60 95 and 135 cm and the irrigation was performed over 84 days.The water table level variations at 2 meters were recorded. The groundwater inflow decreased during the first part of the irrigation period due to infiltration below the irrigated experimental plot. This inflow increased during a second period due to water level variations in the river close to this site. At the output, the head gradient did not vary appreciably and the outflow was assumed to be constant during the observation period. Moreover, this gradient is quite low and the flow rate is very low. The water content and pressure profiles clearly show the infiltration of water in the soil during irrigation. The head gradients show the water movement in the unsaturated soil during infiltration and evaporation. Upward flow due to evaporation is observed at about 10 days after irrigation. The last measured water profile (76 days after the end of irrigation) shows that evaporation modifies the water content profile until at least a depth of 120 cm.The water balance during the irrigation period showed that the input due to irrigation and precipitation was equal to 4150 m3. The evapotranspiration output was estimated to be 2370 m3. Groundwater exchange at the downstream boundary can be neglected during the duration of irrigation (84 days), since the average hydraulic gradient remained low (less than 0.8 %) and the hydraulic conductivity of the aquifer was not important (about 250 cm/day). It was assumed that the water storage quantified with the rise of the groundwater level was equal to the difference between surface input and evapotranspiration (more than 40 % of the contributions), leading to a 27 % change in water content, which is quite reasonable for this type of soil (clay).The stored water was then recovered by evapotranspiration and groundwater outflow at the plot boundaries. We are away from a reasonable irrigation that would reduce the used water quantity and decrease the risk of soil degradation. This study allows a better understanding of the water dynamics in the experimental plot, which includes soil saturation, recharge processes, and exchanges between the aquifer and the river
Effect of antimicrobial use on the resistance of Escherichia coli in faecal flora of pigs
The antimicrobial use in veterinary medicine is of concern because of possible transmisston of resistant bacteria to humans. However the relation between use and occurrence of resistance is poorly documented in the field. Sixteen farrow-to-fimsh herds were selected and classified on the frequency of antimicrobial administrations (low (LU), medium (MU) and high (HU) users). lndtcative Eschenchia coli strains were tsolated from faeces of sows (5 per herd) and young pigs (3 per sow) at several ttmes during animals\u27 hfe and tested for reststance to amoxicillin, gentamicin, trimethoprim-sulfamids and tetracyclin. The percentages of resistant strams were compared between herd groups
Characterization of microbulk detectors in argon- and neon-based mixtures
A recent Micromegas manufacturing technique, so called Microbulk, has been
developed, improving the uniformity and stability of this kind of detectors.
Excellent energy resolutions have been obtained, reaching values as low as 11%
FWHM at 5.9 keV in Ar+5%iC4H10. This detector has other advantages like its
flexible structure, low material budget and high radio-purity. Two microbulk
detectors with gaps of 50 and 25 um have been characterized in argon- and
neon-based mixtures with ethane, isobutane and cyclohexane. The results will be
presented and discussed. The gain curves have been fitted to the Rose-Korff
gain model and dependences of the electron mean free path and the threshold
energy for ionization have been obtained. The possible relation between these
two parameters and the energy resolution will be also discussed.Comment: Submitted to the Journal of Instrumentatio
Gap, a mycobacterial specific integral membrane protein, is required for glycolipid transport to the cell surface
The cell envelope of mycobacteria is a complex multilaminar structure that protects the cell from stresses encountered in the environment, and plays an important role against the bactericidal activity of immune system cells. The outermost layer of the mycobacterial envelope typically contains species-specific glycolipids. Depending on the mycobacterial species, the major glycolipid localized at the surface can be either a phenolglycolipid or a peptidoglycolipid (GPL). Currently, the mechanism of how these glycolipids are addressed to the cell surface is not understood. In this study, by using a transposon library of Mycobacterium smegmatis and a simple dye assay, six genes involved in GPLs synthesis have been characterized. All of these genes are clustered in a single genomic region of approximately 60 kb. We show by biochemical analyses that two non-ribosomal peptide synthetases, a polyketide synthase, a methyltransferase and a member of the MmpL family are required for the biosynthesis of the GPLs backbone. Furthermore, we demonstrate that a small integral membrane protein of 272 amino acids named Gap (gap: GPL addressing protein) is specifically required for the transport of the GPLs to the cell surface. This protein is predicted to contain six transmembrane segments and possesses homologues across the mycobacterial genus, thus delineating a new protein family. This Gap family represents a new paradigm for the transport of small molecules across the mycobacterial envelope, a critical determinant of mycobacterial virulence
Perpendicular momentum injection by lower hybrid wave in a tokamak
The injection of lower hybrid waves for current drive into a tokamak affects
the profile of intrinsic rotation. In this article, the momentum deposition by
the lower hybrid wave on the electrons is studied. Due to the increase in the
poloidal momentum of the wave as it propagates into the tokamak, the parallel
momentum of the wave increases considerably. The change of the perpendicular
momentum of the wave is such that the toroidal angular momentum of the wave is
conserved. If the perpendicular momentum transfer via electron Landau damping
is ignored, the transfer of the toroidal angular momentum to the plasma will be
larger than the injected toroidal angular momentum. A proper quasilinear
treatment proves that both perpendicular and parallel momentum are transferred
to the electrons. The toroidal angular momentum of the electrons is then
transferred to the ions via different mechanisms for the parallel and
perpendicular momentum. The perpendicular momentum is transferred to ions
through an outward radial electron pinch, while the parallel momentum is
transferred through collisions.Comment: 22 pages, 4 figure
Supernova Remnants in the Magellanic Clouds III: An X-ray Atlas of LMC Supernova Remnants
We have used archival ROSAT data to present X-ray images of thirty-one
supernova remnants (SNRs) in the Large Magellanic Cloud (LMC). We have
classified these remnants according to their X-ray morphologies, into the
categories of Shell-Type, Diffuse Face, Centrally Brightened, Point-Source
Dominated, and Irregular. We suggest possible causes of the X-ray emission for
each category, and for individual features of some of the SNRs.Comment: 27 pages, 6 figures (9 figure files). To appear in the Supplement
Series of the Astrophysical Journal, August 1999 Vol. 123 #
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