X-ray spectra produced by a hot plasma containing cold clouds     

Julien Malzac  Annalisa Celotti 《Monthly notices of the Royal Astronomical Society》2002,335(1):23-29

We compute the hard X-ray spectra from a hot plasma pervaded by small cold dense clouds. The main cooling mechanism of the plasma is Compton cooling by the soft thermal emission from the clouds. We compute numerically the equilibrium temperature of the plasma together with the escaping spectrum. The spectrum depends mainly on the amount of cold clouds filling the hot phase. The clouds covering factor is constrained to be low in order to produce spectra similar to those observed in Seyfert galaxies and X-ray binaries, implying that an external reflector is required in order to reproduce the full range of observed reflection amplitudes. We also derive analytical estimates for the X-ray spectral slope and reflection amplitude using an escape probability formalism.  相似文献   

Wave run-up on cylindrical and cone shaped foundations for offshore wind turbines     

Leen De Vos  Peter Frigaard  Julien De Rouck 《Coastal Engineering》2007

During the last decade, several offshore wind-farms were built and offshore wind energy promises to be a suitable alternative to provide green energy. However, there are still some engineering challenges in placing the foundations of offshore wind turbines. For example, wave run-up and wave impacts cause unexpected damage to boat landing facilities and platforms. To assess the forces due to wave run-up, the distribution of run-up around the pile and the maximum run-up height need to be known. This article describes a physical model study of the run-up heights and run-up distribution on two shapes of foundations for offshore wind turbines, including both regular and irregular waves. The influence of wave steepness, wave height and water depth on run-up is investigated. The measured run-up values are compared with applicable theories and previous experimental studies predicting run-up on a circular pile.  相似文献   

Dynamics of a wave-dominated tidal inlet and influence on adjacent beaches,Currumbin Creek,Gold Coast,Australia     

Bruno Castelle  Julien Bourget  Nathalie Molnar  Darrell Strauss  Sophie Deschamps  Rodger Tomlinson 《Coastal Engineering》2007

Currumbin Creek on the Australian Gold Coast is a wave-dominated tidal inlet which exhibits a particularly active morphology. The recent history of Currumbin Creek entrance has seen rapid growth of the entrance for access to the ocean by fishermen, as a world class surfing site, and as a recreational area. Before the construction of two groynes in the 70's, Currumbin Creek entrance was highly variable in terms of inlet location and sand bar characteristics due to a cyclical behaviour of spit migration. Nowadays, the entrance is stabilised. However, natural processes continue with the entrance infilling causing flood and navigation issues, resulting in a regular dredging program to maintain an open entrance and for regular beach nourishment plans.  相似文献   

Field measurements of wave overtopping at the rubble mound breakwater of Rome–Ostia yacht harbour     

Riccardo Briganti  Giorgio Bellotti  Leopoldo Franco  Julien De Rouck  Jimmy Geeraerts 《Coastal Engineering》2005,52(12):351-1174

This paper describes a new station for full-scale measurement of wave overtopping at the Rome yacht harbour rubble mound breakwater in Ostia (Italy) and the results of the successful first measurement campaign carried out during the winter season 2003–2004. The equipment and the research activities were supported by the EU project CLASH, focusing on scale effects for wave overtopping at coastal structures. The site is characterized by a very small tidal range, a long shallow foreshore and depth-limited breaking waves which interact with a shallow sloping porous rock structure. Overtopping water is collected by a steel tank installed on the crown slab behind the parapet wall. The measurement of water level variation inside the tank by means of two pressure transducers allows the calculation of individual overtopping volumes. Incident waves, sea levels and wind are also measured. During seven independent storms, more than 400 individual overtopping events were recorded and about 86 h of valid data are available. This extensive dataset is presented, discussed and then used for comparison with two commonly used overtopping prediction formulae based on small-scale model tests showing their tendency to underestimate the prototype results. A strong correlation between the hourly mean overtopping discharge and corresponding maximum volume is also presented. The paper generally confirms the validity of the approach used in Troch et al. (2004) [Troch, P., Geeraets, J., Van de Walle, B., De Rouck, J., Van Damme, L., Allsop, W., Franco, L., 2004. Full-scale wave overtopping measurements on the Zeebrugge rubble mound breakwater. Coastal Engineering 51, 609–628] for field measurement of wave overtopping.  相似文献   

Ending groundwater overdraft in hydrologic-economic systems   总被引：1，自引：1，他引：0  

Julien J. Harou  Jay R. Lund 《Hydrogeology Journal》2008,16(6):1039-1055

Groundwater overdraft occurs when extraction exceeds both natural and induced aquifer recharge over long periods. While ultimately unsustainable and invariably having detrimental effects, overdrafting aquifers is common and may be temporarily beneficial within a long-term water management strategy. Once a region chooses to end overdrafting, water management must change if increased water scarcity is to be avoided. Integrated water-management models allow aquifers and overdraft to be analyzed as part of a regional water-supply system. Incorporating economics into the model establishes a framework for evaluating the costs and effects of groundwater management actions on the entire system. This economic-engineering approach is applied in a case study of the Tulare Basin in California, USA, where previous economic studies showed optimal pumping depths have been reached. A hydro-economic optimization model is used to study the economic effects and water management actions that accompany ending overdraft. Results show that when overdraft is prohibited, groundwater banking using conjunctive-use infrastructure built between 1990 and 2005 largely annuls the cost of not overdrafting. The integrated economic-engineering approach quantifies effects of groundwater policies on complex regional water-resource systems and suggests promising strategies for reducing the economic costs of ending aquifer overexploitation.  相似文献   

Control of shortwave radiation parameterization on tropical climate SST-forced simulation     

Julien Crétat  Sébastien Masson  Sarah Berthet  Guillaume Samson  Pascal Terray  Jimy Dudhia  Françoise Pinsard  Christophe Hourdin 《Climate Dynamics》2016,47(5-6):1807-1826

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Devonian lacustrine shore zone architecture: Giving perspective to cliff exposures with ground penetrating radar          下载免费PDF全文

Steven D. Andrews  Julien Moreau  Stuart Archer 《Sedimentology》2016,63(7):2087-2105

Lake margin sedimentary systems have been the subject of only limited study. The cyclic Middle Devonian lacustrine succession of Northern Scotland contains repeated developments of shore zone sandstones and thus provides an ideal location for the study of these units. The cycles comprise deep lake, shallow lake, playa and shore zone facies. Detailed field observations are presented alongside ground penetrating radar data which has aided large‐scale and three‐dimensional characterization of the shore zone sand bodies. Loading and discrete channel forms are recognized in thin‐bedded sandstones within the lower portion of the lake shore zone successions. Up‐section, the sandstone beds appear to become amalgamated, forming subtle low angle accretionary bar complexes. Where imaged on the radar profiles, the repeated development of shoreward migrating features succeeded by more shallow angled lakeward accreting surfaces is recognized; these are ascribed to washover and swash–backwash processes, respectively. The orientation of these features is similar to palaeocurrent measurements from oscillation ripples, suggesting an alignment of the shore zone bars perpendicular to the prevailing wind direction. Further loaded sandstone beds and sand‐filled shallow channel features overlie the bar forms. The context of the shore zone facies allows the controls on its formation to be examined. The shore zone sandstones overlie playa facies which contain abundant desiccation horizons, reflecting the most arid phase in the climatically controlled lacustrine cycle. As climatic conditions ameliorated, the rejuvenation of fluvial systems resulted in the transport of sand out into the basin. Initial deposition was limited to intermittent events where sediment was laid down on a water‐saturated substrate. High resolution fluctuations in lake level resulted in periodic short‐lived reworking events along the lake margins which produced amalgamated sands, forming low relief bars. Shore zone reworking is likely to have occurred over a wide  area as the lake margin migrated back and forth, and gradually transgressed.  相似文献   

Can metric-based approaches really improve multi-model climate projections? The case of summer temperature change in France     

Julien Boé  Laurent Terray 《Climate Dynamics》2015,45(7-8):1913-1928

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Würmian deglaciation of western Lake Geneva (Switzerland) based on seismic stratigraphy     

Julien Fiore  Stéphanie Girardclos  André Pugin  Georges Gorin  Walter Wildi 《Quaternary Science Reviews》2011,30(3-4):377-393

Western Lake Geneva (le Petit-Lac) was filled during the Quaternary over a major erosion surface truncating the cemented, folded and thrusted Tertiary sediments of the foreland Alpine basin. The carving of the lake occurred during Quaternary glaciations with ice originating from the Rhone valley catchment basin flowing in two branches oriented SW and NE over the Swiss Plateau. Lake Geneva is situated on the South-Western branch of this paleo ice-cap.For the first time, a dense grid of high-resolution seismic profiles (airgun 5-inch³, airgun 1-inch³ and echosounder) has imaged the whole Quaternary sequence, providing a paleoenvironmental interpretation and a detailed reconstruction of the Rhone glacier retreat stages during glacial events that led to the formation of western Lake Geneva.The Quaternary sequence filling up the bedrock valley is exceptionally thick with up to 220 m of deposits and consists of glacial, glacio-lacustrine and lacustrine sediments. Fourteen seismic units have been defined (units U1–U14). Unit U1 represents the remnants of glacial deposits older than the last glacial cycle, preserved in the deepest part of the lake and in secondary bedrock valleys. Unit U2 represents gravel and sands deposited by meltwater circulation at the bottom of the glacial valley. Unit U3 is a thick, stratified unit marking the beginning of the deglaciation, when the Rhone glacier became thinner and buoyant and allowed the formation of a subglacial lake. Younger glacial units (units U4, U5, U7, U9, U11) are acoustically chaotic sediments deposited subglacially under the water table (undermelt tills), while the glacier was thinning. These glacial units are bounded by synform erosion surfaces corresponding to readvances of the glacier.The transition from a glacial to a glacio-lacustrine environment started with the appearance of a marginal esker-fan system (unit U6). Esker formation was followed by a small advance–retreat cycle leading to the deposition of unit U7. Then, the ice front receded and stratified sediments were deposited in a glacio-lacustrine environment (units U8, U10 and U12). This retreat was punctuated by two readvances – Coppet (unit U9) and Nyon (unit U11) – producing large push moraines and proglacial debris flows. Finally, a lacustrine environment with a characteristic lake current pattern and mass movement deposits took place (units U13 and U14).Except for unit U1, the sedimentary sequence records the Würmian deglaciation in a fjord-like environment occupied by a tidewater glacier with a steep, calving ice front. The presence of an esker-fan system reveals the importance of subglacial meltwater flow in continental deglaciation. Push-moraines and erosion surfaces below the glacier indicate at least 5 readvances during the deglaciation thus revealing that oscillations of ice front are the key process in deglaciation of perialpine fjord-lakes. The dating of these continental glacier fluctuations would allow correlation with oceanic and ice records and help to understand the climatic mechanisms between oceans and continents.  相似文献   

Tectono‐stratigraphic history of the southern Junggar basin: seismic profiling evidences     

Sheng‐Li Wang  Yan Chen  Julien Charreau  Dong‐Tao Wei  Dong Jia 《地学学报》2013,25(6):490-495

The modern Tianshan is an active intracontinental range in central Asia. Its initial timing is poorly known and still hotly debated. As the subsidence of foreland basins is intrinsically coupled with the uplift of orogenic wedges, the foreland sedimentary records may accurately constrain the Tianshan uplifting history. To better address the question, we analyse a seismic profile across the southern Junggar foreland basin to decipher its tectonic and stratigraphic history. Four structural layers can be identified in an ascending order: the Permian – Lower Jurassic transtension‐related layer, the Jurassic – Cretaceous thermal‐subsistence layer, the Palaeogene layer and the Miocene – Quaternary foreland sedimentary layer. The oldest sedimentary sequence in the foreland succession is of the Shawan Formation deposited at ~24 Ma based on magnetostratigraphic constraints. This indicates that foreland deformation in the northern Tianshan and uplifting of the modern Tianshan probably initiated at the beginning of the Miocene.  相似文献