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131.
Coupling the JNLT with the Keck telescope is of considerable interest. Further enhancement may be possible with auxiliary small telescopes, as planned for ESO's VLT. Current plans for installing the optical very large array at Mauna Kea provide opportunities for extra OVLA telescopes near the JNLT.A coudé field slicer is proposed for interferometric observing of a reference star together with the main object. Additions to the JNLT coudé spectrograph are also suggested for use as a speckle camera with multiple spectral channels.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
132.
A multi-period capacitated school location problem with modular equipment and closest assignment considerations 总被引:1,自引:0,他引:1
Eric M. Delmelle Jean-Claude Thill Dominique Peeters Isabelle Thomas 《Journal of Geographical Systems》2014,16(3):263-286
In rapidly growing urban areas, it is deemed vital to expand (or contract) an existing network of public facilities to meet anticipated changes in the level of demand. We present a multi-period capacitated median model for school network facility location planning that minimizes transportation costs, while functional costs are subject to a budget constraint. The proposed Vintage Flexible Capacitated Location Problem (ViFCLP) has the flexibility to account for a minimum school-age closing requirement, while the maximum capacity of each school can be adjusted by the addition of modular units. Non-closest assignments are controlled by the introduction of a parameter penalizing excess travel. The applicability of the ViFCLP is illustrated on a large US school system (Charlotte-Mecklenburg, North Carolina) where high school demand is expected to grow faster with distance to the city center. Higher school capacities and greater penalty on travel impedance parameter reduce the number of non-closest assignments. The proposed model is beneficial to policy makers seeking to improve the provision and efficiency of public services over a multi-period planning horizon. 相似文献
133.
Pierre Giresse Vincenzo Pascucci Gaël Lymer Virginie Gaullier Isabelle Thinon 《Geo-Marine Letters》2014,34(6):483-498
The narrow shelf and upper slope immediately above the Gonone canyon head off NE Sardinia represent areas of very low sedimentation rates. Along the sides of the canyon head (1,600 m water depth), the sediment deposits are homogeneous but show alternating light-grey intervals rich in carbonate and dark-grey ones rich in organic matter, possibly related to distal turbidite processes. Deposits older than 50,000 years are already encountered at core depths of 2.50 m, the sedimentation rates varying from 6–21 cm/103 years in the lower parts of two cores and from 1.5–3 cm/103 years in the upper parts. At about 35,000 years BP, both cores show a simultaneous drop in sedimentation rate by a factor of 3, probably in response to local mechanisms of channel avulsion. Lithological, mineralogical and geochemical properties reveal the environmental factors which are responsible for the extremely slow sediment accumulation. The southernmost sector of the coast, and partly also of the shelf, consists of Jurassic limestones which supply only small amounts of fine-grained material transported in suspension. During the last sea-level highstand, the accumulation of the Cedrino River pro-delta remained restricted to the coast, the low siliciclastic sediment yields resulting in poor shelf sediment trapping. The present morphology of the canyon head prevented the occurrence of gravity processes in the deeper part of the canyon system, including the coring sites. Accordingly, deposition was mainly fed by hemipelagic material of planktonic origin, together with only moderate terrigenous inputs. On a wider late Pleistocene timescale, seismic data indicate the occurrence of a coarse-grained, layered turbidite facies, implying a very different architecture of the canyon drainage system probably prior to 60,000 years BP. 相似文献
134.
Influence of the warm pool and cold tongue El Niños on the following Caribbean rainy season rainfall
Caribbean rainfall and associated regional-scale ocean–atmosphere anomalies are analyzed during and after warm pool (WP) and cold tongue (CT) El Niño (EN) events (i.e. from the usual peak of EN events in boreal winter to next summer from 1950 to 2011). During and after a CT event, a north–south dipolar pattern with positive (negative) rainfall anomalies over the northern (southern) Caribbean during the boreal winter tends to reverse in spring, and then to vanish in summer. On the contrary, during and after a WP event, weak rainfall anomalies during the boreal winter intensify themselves from spring, with anomalous wet conditions over most of the Caribbean basin observed during summer, except over the eastern coast of Nicaragua and Costa Rica. The Caribbean rainfall anomalies associated with WP and CT events are shaped by competition between at least four different, but interrelated, mechanisms; (1) the near-equatorial large-scale subsidence anomaly over the equatorial Atlantic linked to the zonal adjustment of the Walker circulation; (2) the extra-tropical wave-like train combining positive phase of the Pacific/North American mode and negative phase of the North Atlantic Oscillation; (3) the wind-evaporation-sea surface temperature (SST) positive feedback coupling warmer-than-normal SST with weaker-than-normal low level easterlies over the tropical North Atlantic; and (4) the air-sea coupling between the speed of low level easterlies, including the Caribbean low level jet, and the SST anomaly (SSTA) gradient between the Caribbean basin and the eastern equatorial Pacific. It seems that Caribbean rainfall anomalies are shaped mostly by mechanisms (1–3) during CT events from the boreal winter to spring. These mechanisms seem less efficient during WP events when the atmospheric response seems driven mostly by mechanism (4), coupling positive west-east SSTA gradient with weaker-than-normal low level easterlies, and secondary by mechanism (3), from the boreal spring to summer. 相似文献
135.
Résumé La variabilité du climat, une gestion non optimale de la ressource en eau et l'intensification des activités anthropiques pourraient être les trois facteurs majeurs menaçant les écoulements et l'état de la ressource en eau dans les sous-bassins algériens. C'est le cas du bassin de la Tafna dans la partie occidentale de l'Algérie. Ce bassin est situé dans une région au climat semi-aride. Outre l'influence des précipitations, nous examinerons dans cet article la contribution possible d'autres facteurs (géologiques, topographiques et anthropiques) à la variabilité des écoulements dans le bassin de la Tafna. Pour cela, en plus de l'analyse du régime pluviométrique et des débits, nous avons choisi d'analyser le baseflow index ou BFI et les débits de base. Cinq sous-bassins de la Tafna, où des données journalières de pluie et de débit étaient disponibles sur la période 1976–2006 ont été étudiés. L'analyse, qui a distingué deux sous-régions déterminées par la topographie: les bassins d'altitude et ceux de plaine, montre que, selon leur contexte géologique, les sous-bassins ont des comportements différents en terme d'écoulement. Les zones en altitude présentant un écoulement de base et un BFI plus importants que les bassins de plaine. Ceci peut être relié à la nature lithologique des formations, les bassins d'altitude présentant une composante karstique importante. Les analyses de tendance/rupture sur les précipitations annuelles ne montrent aucune tendance significative sur la période 1976–2006. On note une baisse des débits moyens annuels uniquement sur deux stations en altitude (significatives aux seuils 1 et 10% respectivement). Une tendance à une diminution significative des débits de base est obtenue sur deux bassins d'altitude et un bassin de plaine (au seuil 1 ou 5%). La baisse du BFI est significative au seuil 1% pour seulement une station d'altitude. Ceci serait le signe d'une baisse du stock dans les bassins d'altitude. La modification des écoulements de base sur certains sous-bassins de la Tafna serait donc imputable à des causes, notamment de nature anthropique, ne relevant pas d'une diminution de la pluviométrie. Editeur Z.W. Kundzewicz; Editeur associé M. Lang Citation Bakreti, A., Braud, I., Leblois, E., et Benali, A. 2013. Analyse conjointe des régimes pluviométriques et hydrologiques dans le bassin de la Tafna (Algérie Occidentale). Hydrological Sciences Journal, 58 (1), 1–19. 相似文献
136.
Haykel Sellami Sihem Benabdallah Isabelle La Jeunesse Marnik Vanclooster 《水文科学杂志》2013,58(8):1415-1429
ABSTRACTClimate models and hydrological parameter uncertainties were quantified and compared while assessing climate change impacts on monthly runoff and daily flow duration curve (FDC) in a Mediterranean catchment. Simulations of the Soil and Water Assessment Tool (SWAT) model using an ensemble of behavioural parameter sets derived from the Generalized Likelihood Uncertainty Estimation (GLUE) method were approximated by feed-forward artificial neural networks (FF-NN). Then, outputs of climate models were used as inputs to the FF-NN models. Subsequently, projected changes in runoff and FDC were calculated and their associated uncertainty was partitioned into climate model and hydrological parameter uncertainties. Runoff and daily discharge of the Chiba catchment were expected to decrease in response to drier and warmer climatic conditions in the 2050s. For both hydrological indicators, uncertainty magnitude increased when moving from dry to wet periods. The decomposition of uncertainty demonstrated that climate model uncertainty dominated hydrological parameter uncertainty in wet periods, whereas in dry periods hydrological parametric uncertainty became more important.
Editor M.C. Acreman; Associate editor S. Kanae 相似文献
137.
A.-L.?Auzende I.?DanielEmail author B.?Reynard C.?Lemaire F.?Guyot 《Physics and Chemistry of Minerals》2004,31(5):269-277
Four main serpentine varieties can be distinguished on the basis of their microstructures, i.e. lizardite, antigorite, chrysotile and polygonal serpentine. Among these, antigorite is the variety stable under high pressure. In order to understand the structural response of these varieties to pressure, we studied well-characterized serpentine samples by in situ Raman spectroscopy up to 10 GPa, in a diamond-anvil cell. All serpentine varieties can be metastably compressed up to 10 GPa at room temperature without the occurrence of phase transition or amorphization. All spectroscopic pressure-induced changes are fully reversible upon decompression. The vibrational frequencies of antigorite have a slightly larger pressure dependence than those of the other varieties. The O–H-stretching modes of the four varieties have a positive pressure dependence, which indicates that there is no enhancement of hydrogen bonding in serpentine minerals at high pressure. Serpentine minerals display two types of hydroxyl groups in the structure: inner OH groups lie at the centre of each six-fold ring while outer OH groups are considered to link the octahedral sheet of a given 1:1 layer to the tetrahedral sheet of the adjacent 1:1 layer. On the basis of the contrasting behaviour of the Raman bands as a function of pressure, we propose a new assignment of the OH-stretching bands. The strongly pressure-dependent modes are assigned to the vibrations of the outer hydroxyl groups, the less pressure-sensitive peaks to the inner ones. 相似文献
138.
Anne Alexandre Isabelle Basile-Doelsch Corinne Sonzogni Claude Parron Fabrice Colin 《Geochimica et cosmochimica acta》2006,70(11):2827-2835
The laser fluorination technique reported here for analyzing the oxygen isotope composition (δ18O) of fine quartz size fractions 50-20, 20-10, 10-5, 5-2, 2-1 and <1 μm has been validated by comparison with the ion microprobe technique. It yields accurate δ18O data with an external precision better than 0.15‰. This is a significant methodological improvement for isotopic studies dealing with materials such as soil or biogenic oxides and silicates: particles are often too small and recovered in insufficient amount to be easily handled for ion microprobe analysis. Both techniques were used to investigate δ18O composition of a Cretaceous quartzite and silcrete sequence from the South-East of France. Quartzite cements average 31.04 ± 1.93‰. They formed from Mid-Cretaceous seawater. Higher in the series, silcretes cements average 26.66 ± 1.36‰. They formed from Upper- or post-Upper-Cretaceous soil water and groundwater. Oxygen isotope data show that the silicification steps from one mineralogical phase to another and from one layer to another (including from an upper pedogenic silcrete to a lower groundwater silcrete) occurred in a closed or weakly evaporating hydrological system. 相似文献
139.
Fanny Lasry Isabelle Coll Sylvain Fayet Maxime Havre Robert Vautard 《Journal of Atmospheric Chemistry》2007,57(2):107-134
In Europe, in case of the observation or the forecast of a photochemical event, punctual and local reductions in anthropogenic
emissions can be triggered at the regional scale. Although the necessity for the establishment of such measures appears to
be justified by bad air quality records over large European cities, individual short-term action plans (STAPs) have been blindly
elaborated by regional authorities. Moreover, as they impose industrial and road traffic emission restrictions, these measures
have an elevated economical cost. It is consequently crucial to determine their efficiency and potential for ozone peak reduction.
The study presented in this paper aims to draw up an expertise on standard European STAPs, through the example of a French
Mediterranean city. The objective is to determine and investigate the impact of current STAPs on ozone peak formation and
to test ways to optimise their efficiency. In this frame, a set of emission scenarios has been elaborated and tested with
the chemistry-transport model CHIMERE on the Berre–Marseille area. Simulations have shown that the tested action plans are
not sufficient to eradicate severe ozone peaks and that more drastic restrictions on emissions are required to significantly
affect ozone plumes. However, results also showed that the potential for ozone reduction remains small, with a maximum impact
of only 5 ppbv for feasible STAPs. Finally, a temporal analysis of the ozone-emission relationship was engaged in order to
optimise their application. 相似文献