On non-adiabatic oscillations of gaseous systems in hydromagnetics     

Serge Pineault  S. P. S. Anand 《Astrophysics and Space Science》1973,24(1):105-115

The general variational principle obtained by Unno for the study of stellar stability is extended to include the effects of magnetic fields in the general case where the perturbations are nonadiabatic. The unperturbed configuration is non-rotating, but internal motions are possible.A general stability equation is derived, using the modified variational principle. In the simplest case, this equation is identical to the one derived by Unno except for the appearance of magnetic terms in one of the coefficients (through the Lorentz force). If dissipation is neglected, the characteristic equation reduces to the one derived by Frieman and Rotenberg in the stationary case and by Kovetz in the static case.The stability of magnetic stars against homologous oscillations is examined and the usual result for the dynamical mode is obtained.  相似文献   

Influence of injection conditions on field tracer experiments   总被引：2，自引：0，他引：2  

Brouyère S  Carabin G  Dassargues A 《Ground water》2005,43(3):389-400

Calibration of ground water transport models is often performed using results of field tracer experiments. However, little attention is usually paid to the influence, on resulting breakthrough curves, of injection conditions and well-aquifer interactions, more particularly of the influence of the possible trapping of the tracer in the injection wellbore. Recently, a new mathematical and numerical approach has been developed to model injection conditions and well-aquifer interactions in a very accurate way. Using an analytical solution derived from this model, a detailed analysis is made of the evolution of the tracer input function in the aquifer. By varying injection conditions from one simulation to another, synthetic breakthrough curves are generated with the SUFT3D ground water flow and transport finite-element simulator. These tests show clearly that the shape of the breakthrough curves can be dramatically affected by injection conditions. Using generated breakthrough curves as "actual" field results, a calibration of hydrodispersive parameters is performed, neglecting the influence of injection conditions. This shows that neglecting the influence of actual injection conditions can lead to (1) errors on fitted parameters and (2) misleading identification of the active transport processes. Conclusions and guidelines are drawn in terms of proposed methodologies for better controlling the tracer injection in the field, in order to minimize risk of misinterpretation of results.  相似文献   

B.S. Daya Sagar: Mathematical Morphology in Geomorphology and GISci     

Serge Beucher 《Mathematical Geosciences》2015,47(2):247-248

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A fast flux tube-based method for solute-transport simulation     

Olivier Atteia  Serge Huberson  Alain Dupuy 《Hydrogeology Journal》2011,19(2):317-328

A new method to calculate the transport of dissolved species in aquifers is presented. This approach is an extension of the stream tubes which are used for flow computation. The flux tubes defined here are conservative for solutes, but not for water mass. The flux tubes are first defined in a general domain and then calculated in a two-dimensional uniform flow field. The tubes?? computation is based on a parametric solution. The method is extended further in order to deal with heterogeneous media. A particle-tracking algorithm is used where the deviation of the flux-tube boundaries due to dispersion is accounted for. The approximate solution obtained by this approach is compared to classical numerical solutions given by a finite difference code (RT3D) and a finite element code (FEFLOW). This comparison was performed for several test cases with increasing complexity. The differences between the flux-tube approach and the other methods always remain small, even regarding mass conservation. The major advantage of the flux-tube approach is the ability to reach a solution quickly, as the method is hundreds to thousands of times faster than classical finite difference or finite element models.  相似文献   

Review of the causes of the rise of the illegal South African abalone fishery and consequent closure of the rights-based fishery     

Serge Raemaekers  Maria HauckMarkus Bürgener  Angus MackenzieGenevieve Maharaj  Éva E. Plagányi  Peter J. Britz 《Ocean & Coastal Management》2011,54(6):433-445

The rise of organised illegal fishing and trade in abalone from the late 1990s destabilised South Africa’s historically stable, quota-managed fishery, culminating in its closure in 2008. The development of the fishery is described in a historical context, including the evolution of South Africa’s science-based abalone fishery management system. The diverse suite of responses deployed to combat illegal fishing and the black market trade in abalone are reviewed, including;- fishery reform to expand rights to a greater number of previously disadvantaged fishers, a territorial user rights fishery (TURF) system, special compliance operations and courts, the CITES listing of abalone, and the serial reduction in the TAC, culminating in the controversial and legally contested closure of the fishery. The main causes of the rise of the illegal fishery are diagnosed as 1) the massive increase in the abalone price that occurred in the 1990s triggering an abalone fishing “gold-rush” and 2) the failure of the post-Apartheid fishery reform process to accommodate many traditional fishers in a legal fishing rights framework resulting in them operating outside the formal fishery management system. By contextualising the abalone fishery as a complex system, embedded in South Africa’s socio-political setting, we show how the resource focussed fishery management system did not have the capacity to incorporate the powerful social, political and economic drivers determining fisher behaviour. We conclude with the need to revisit South Africa’s abalone fishery management paradigm, and argue that a more integrated governance approach is required that takes into account the biological, socio-political and economic factors determining the fishery activities.  相似文献   

Differential regional responses in drought length, intensity and timing to recent climate changes in a Mediterranean forested ecosystem     

Julien Ruffault  Nicolas K. Martin-StPaul  Serge Rambal  Florent Mouillot 《Climatic change》2013,117(1-2):103-117

The Mediterranean area is one of the regions of the world where GCMs agree the most on precipitation changes due to climate change. In this study we aim to assess the impact of recent climate change on drought features of Mediterranean ecosystems in Southern France. Regional climatic trends for the 1971–2006 period are compared to drought trends based on a water balance model accounting for soil properties, vegetation structure and functioning. Drought, defined here as periods when soil water potentials drop below ??0.5 MPa, is described in terms of intensity, duration and timing, which are integrative of both climate variability and site conditions. Temporal trends in precipitation, temperature and solar radiation lead altogether to drier and warmer conditions over the region but with a high spatial heterogeneity; for similar climatic trends, a significant increase in drought intensity was detected in the wettest areas of the region, whereas drought intensity in the driest areas did not change. Indeed, in the wettest areas, we observed an earlier onset of drought by about 1 month, but a constant end of drought. In the driest areas of the region, we observed the same earlier onset of drought but combined with an earlier end of drought, thus leading to a shift of the dry season without increasing its duration. The definition of drought features both in terms of intensity but also of seasonal timing appears relevant to capture historical or forecasted changes in ecosystem functioning. Studies concerning climate change impacts on forested ecosystems should be interpreted with caution when using climate proxies alone.  相似文献   

Une methode d'etude experimentale “in situ” de la zone d'echange entre les nuages convectifs et leur environnement     

Serge Chauzy  Antoine Elefterion  Philippe Sarthou 《大气与海洋》2013,51(2):49-61

Le développement d'un projet de recherche consacré à l'étude des nuages convectifs a amené les auteurs à concevoir et à élaborer un système complet de mesures adapté à cette étude. Les grandeurs thermodynamiques classiques (Température, Pression, Humidité) ainsi que les vitesses d'ascendance autour et à l'intérieur des nuages sont mesurées grâce à l'utilisation d'un avion Cessna 206 équipé de ce système. Une première étape consiste à mettre en évidence les phénomènes relatifs aux échanges entre le nuage et le milieu environnant.  相似文献   

The finest white-light coronal features     

Serge Koutchmy  Olivier Bouchard  Jean Mouette  Olga Koutchmy 《Solar physics》1993,148(1):169-172

An attempt to detect the finest white-light coronal features observed with a large optical telescope was made at the July 11, 1991 Solar Total Eclipse. A few selected results taken from the video-CCD high speed observations obtained at the prime focus of the Canada-France-Hawaï-Telescope (CFHT) with a red coronal interference filter are presented. The smallest (sub-arsec) detected and/or resolved coronal features are shown. The methods that were used to extract them from the noisy and seeing-limited images taken from video frames are described.  相似文献   

The United Nations system responds to Agenda 21.17: Oceans     

Heiner Naeve  Serge M. Garcia 《Ocean & Coastal Management》1995,29(1-3)

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Photometry of the unlit face of Saturn's rings     

Audouin Dollfus  Serge Brunier 《Icarus》1982,52(3):516-525

From our telescopic observations of Saturn's rings in 1966, 1979, and 1980, the luminance of the unlit face at λ = 0.58 μm is derived as a function of the height B′ of the Sun above the lit face. A maximum is reached at B′ = 1.9° and a decrease is observed for larger values of B′. Ring B is 1.8 time less bright than ring A and Cassini division. The unlit/lit luminances ratios for the two rings merged together is 8% at B′ = 1.0° and 3% at B′ = 2.8°. The larger value at more grazing incidence is related to the photometric “opposition effect” which reflects more of the incident light backward into the ring plane when the height of the sun is small; the light so reflected is again reflected and scattered and a certain flux reaches the unlit face to escape toward the observer. The unlit face luminances for blue and for yellow light indicate a contribution by micron size particles. The Saturn globe produces a ring illumination which, observed from the Earth, amounts to 1.8 × 10^?3 of the disk center reflectance. The rings observed exactly edge-on do not disappear but a faint lineament remains, which produces a flux of (0.30 ± 0.15) 10^?3 times the brightness of a segment of 1 arcsec width at Saturn disk center; illuminations of rings' borders or particles outside the exact ring plane are indicated.  相似文献