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The flow induced by a disk rotating at the bottom of a cylindrical tank is characterised using numerical techniques – computation of steady solutions or time-averaged two-dimensional and three-dimensional direct simulations – as well as laser-Doppler velocimetry measurements. Axisymmetric steady solutions reveal the structure of the toroidal flow located at the periphery of the central solid body rotation region. When viewed in a meridional plane, this flow cell is found to be bordered by four layers, two at the solid boundaries, one at the free surface and one located at the edge of the central region, which possesses a sinuous shape. The cell intensity and geometry are determined for several fluid-layer aspect ratios; the flow is shown to depend very weakly on Froude number (associated with surface deformation) or on Reynolds number if sufficiently large. The paper then focuses on the high Reynolds number regime for which the flow has become unsteady and three-dimensional while the surface is still almost flat. Direct numerical simulations show that the averaged flow shares many similarities with the above steady axisymmetric solutions. Experimental measurements corroborate most of the numerical results and also allow for the spatio-temporal characterisation of the fluctuations, in particular the azimuthal structure and frequency spectrum. Mean azimuthal velocity profiles obtained in this transitional regime are eventually compared to existing theoretical models.
The aim of this study was to compare the effects of various activating factors on feline oocytes. The study included activation within the ovary (natural), activation during in vitro maturation (spontaneous activation), chemical activation (ionomycin + 6-DMAP), activation by spermatozoa and injection (ICSI) and mechanical activation (sham ICSI). According to our results, parthenogenetic embryos could emerge at every step of in vitro embryo production (IVP) procedures. After oocyte collection, 6% of parthenogenetic embryos were observed, mainly at the 2–4-blastomere stages. After 24 h of in vitro maturation, parthenogenetic activation was observed in 7% of oocytes. Using ionomycin and 6-DMAP to artificially activate oocytes, 53% of cleaved embryos were obtained. The results after ICSI (54% cleaved embryos) were not significantly different from the results in Group III using chemical activation (53% cleaved embryos). But only after ICSI were blastocysts obtained (5/73.7%) as a result of in vitro culture. Moreover, embryos after ICSI were of the best morphological quality with minor levels of fragmentation evident in the embryos. After sham mechanical activation, ‘sham ICSI’, 8% of cleaved embryos were noted. Therefore, it is advised to maintain a negative control in parallel with each step of IVP techniques, to avoid misleading results. Chemical methods for artificial activation of feline oocytes are the most promising for application to the cloning and production of parthenogenetic embryos for experimental studies.
As multi-use conservation landscapes, biosphere reserves (BRs) exemplify the landscape mosaic approach to environmental decision-making. In this study, time-series remotely-sensed data (1993–2006–2012) were used to monitor vegetation transformation in the Kruger to Canyons Biosphere Reserve (K2C) of South Africa, updating previous land-cover research. We identified changes in spatial extent, rate and intensity of land-cover change and extrapolated observed trends to 2018. The increased rate of change in the recent observation period (2.3 vs. 5.7%) was driven by more intensive gains in impacted vegetation and settlement since 2006 (>210 km2 and >120 km2), with resultant transformation of intact habitat undermining regional connectivity. By 2012, intact vegetation had suffered losses of 6.3% (>350 km2) since 2006 and >14% (>750 km2) since 1993. A further 9.5% loss of intact habitat may represent a critical threshold, establishing K2C above the 50% threshold of landscape transformation, whereafter a rapid decline in landscape resilience is likely. Given the BR's spatial zonation, such a loss across the full extent of K2C is unlikely, at least in the short-term (i.e., by 2018). Yet, based on past trends of transformation in the unprotected transition zone, anticipating such losses in the longer term, is not unfounded (i.e., 2024).
Trois résolutions ont été adoptées par la 4e Assemblée générale de l’Union astronomique internationale, à Cambridge (Mass.) en 1932.
Elles se rapportaient à l’opération internationale des longitudes (réalisée en 1933) et avaient pour objet:
(1)L’émission d’un trait d’une durée de 10 secondes après tout envoi de signaux horaires.
(2)La mission confiée au Bureau international de l’Heure (B.I.H.) de centraliser, discuter et publier les résultats de l’opération.
(3)L’approbation du programme des opérations, exposé dans le Rapport présenté à Cambridge par le Président et le Secrétaire de la Commission.
Le Président est heureux de constater que les propositions de ce Rapport ont pu être réalisées dans une très large part. Il remercie tous les Observatoires et organismes participants de leur collaboration et les félicite vivement de l’activité qu’ils ont déployée pendant la campagne scientifique de 1933.
La centralisation au Bureau international de l’Heure des résultats d’observations de l’Opération internationale de 1933 a été très lente, puisque les dernières données attendues ont été reçues vers la fin de 1937.
Le nombre des stations ayant coopéré à l’Opération internationale et ayant transmis leurs observations à l’organisme centralisateur s’élève à soixante et onze. Ainsi qu’il a été expliqué à notre Commission mixte, lors du Congrès de l’Union géodésique et géophysique internationale tenu à Édimbourg en 1936, ces stations ont été réparties en trois groupes:
Le Ier comprenant vingt Observatoires, disposant chacun de plusieurs horloges de première classe (soit à poids sous pression et à température constantes, soit à quartz piézoélectrique);
In agricultural settings, environment shapes patterns of settlement and land use. Using the Great Plains of the United States during the period of its initial Euro-American settlement (1880–1940) as an analytic lens, this article explores whether the same environmental factors that determine settlement timing and land use—those that indicate suitability for crop-based agriculture—also shape initial family formation, resulting in fewer and smaller families in areas that are more conducive to livestock raising than to cropping. The connection between family size and agricultural land availability is now well known, but the role of the environment has not previously been explicitly tested. Descriptive analysis offers initial support for a distinctive pattern of family formation in the western Great Plains, where precipitation is too low to support intensive cropping. However, multivariate analysis using county-level data at 10-year intervals offers only partial support to the hypothesis that environmental characteristics produce these differences. Rather, this analysis has found that the region was also subject to the same long-term social and demographic changes sweeping the rest of the country during this period.
The various hypotheses on the origin of comets are surveyed, with particular reference to the phenomenon of comet-streaming, as revealed by statistical analysis of the directions of the perihelia of cometary orbits. The difficulties of reconciling comet-streaming with any of the hypotheses of cometary origin is pointed out. It is shown that in the case of the interstellar hypothesis these difficulties may be overcome by supposing that the velocities of incoming comets are decreased through the accretion of material from an Oort cloud of solar-system comets. An estimate is made of the total number of interstellar comets in the Galaxy.
We present results of cathodoluminescence (CL) investigations of high-quality zinc oxide (ZnO) nanorods obtained by an extremely fast hydrothermal method on a silicon substrate. A scanning electron microscopy (SEM) system equipped with CL allows direct comparison of SEM images and CL maps, taken from exactly the same areas of samples. Investigations are performed at a temperature of 5 K. An interlink between sample microstructure and emission properties is investigated. CL confirms a very high quality of ZnO nanorods produced by our method. In addition, the presence of super radiation effects in ZnO nanorod arrays is suggested.
In the following communication an account is given of some experiments made in the Physical Laboratory of the Glasgow University, whose object was the measurement of the change of conductivity produced by strain in a metal conductor.
Two constants are required in order to determine this alteration in the most general case of a homogeneous isotropic conductor, strained in any way, as may be easily inferred from the analogy with elastic strains and stresses, constants expressing the change produced by uniform cubical compression and by simple distortion. The determination of the latter for brass is the object of the present paper.
Despite electrification, over 90% of rural households in certain areas of South Africa continue to depend on fuelwood, and this affects woody vegetation structure, with associated cascading effects on biodiversity within adjacent lands. To promote sustainable use, the interactions between anthropogenic and environmental factors affecting vegetation structure in savannahs need to be understood. Airborne light detection and ranging (LiDAR) data collected over 4758 ha were used to examine woody vegetation structure in five communal rangelands around 12 settlements in Bushbuckridge, a municipality in the Kruger to Canyons Biosphere Reserve (South Africa). The importance of underlying abiotic factors was evaluated by measuring size class distributions across catenas and using canonical correspondence analysis. Landscape position was significant in determining structure, indicating the importance of underlying biophysical factors. Differences in structure were settlement-specific, related to mean annual precipitation at one site, and human population density and intensity of use at the other four sites. Size class distributions of woody vegetation revealed human disturbance gradients around settlements. Intensity of use affected the amplitude, not the shape, of the size class distribution, suggesting the same height classes were being harvested across settlements, but amount harvested varied between settlements. Highly used rangelands result in a disappearance of disturbance gradients, leading to homogeneous patches of low woody cover around settlements with limited rehabilitation options. Reductions in disturbance gradients can serve as early warning indicators of woodland degradation, a useful tool in planning for conservation and sustainable development.
We investigate theoretically and experimentally the temperature-dependent linear optical properties of the clean c(4×2) reconstructed Si(100) surface for a wide range of temperatures. We combine two theoretical formalisms: the first one incorporates the contribution of temperature-dependent atomic motion to the surface optical response and, the second uses a dielectric function layer-by-layer separation method. Using these formalisms, we model temperature-dependent reflectance anisotropy (RA) of this surface for the first time: finite temperature ab-initio Car-Parrinello Molecular Dynamics (CPMD) at different temperatures up to 1000 K provide temperature-dependent atomic structural inputs for optical calculations and subsequent average of dielectric functions. Experimentally, one-domain c(4x2) Si(100) surface was prepared and characterised by Reflectance Anisotropy Spectroscopy (RAS) in a temperature range between 300 K and 800 K. Good agreement between experiment and theory is demonstrated, including a temperature-induced red shift of both the surface and bulk optical peaks. Theoretical results indicate that the temperature-induced modification of the optical response is substantially more pronounced for the surface than for the bulk.
Par une étude de stabilité linéaire nous nous proposons d’analyser un écoulement dans une
cavité cylindrique remplie de fluide, dont le fond tourne. Le rayon de la cavité est grand
devant la hauteur de fluide. Une étude expérimentale récente [S. Poncet, M.P. Chauve, J.
Flow Vis. Image Process 14 (2007) 85–105] a mis en évidence une instabilité aux motifs
particulièrement intéressants. Dans ce travail, nous considérons une modélisation de la
surface libre plane (conditions de symétrie) afin de comparer les résultats expérimentaux
et notre étude de stabilité linéaire. Nous discuterons de la pertinence de cette
modélisation, c’est-à-dire de la nécessité de prendre en compte la déformation de la