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Partha Sarathi Roi Gurka Paul J. Sullivan Gregory A. Kopp 《Boundary-Layer Meteorology》2010,137(2):167-185
The sudden release of a quantity of gas into the atmospheric boundary layer produces a contaminant cloud. The expected mass
fraction function provides a relatively simple measure of the contaminant concentration values found within the cloud and
represents the ensemble-averaged fraction of the conserved release mass found at the different contaminant concentration intervals
as the cloud evolves. The plume generated by a line source in grid turbulence is used to investigate the expected mass fraction
function as it applies to scalar concentration values found on a typical line normal to the plume axis. Simultaneous particle
image velocimetry and planar laser induced fluorescence are used to measure velocity and concentration fields, respectively.
The measured expected mass fraction functions are observed to be approximately self-similar when concentration values are
normalized by the centreline mean concentration. The moments of the expected mass fraction function are observed to be simply
related to the centreline moments of the probability density function of scalar concentration. Arguments based on a source
fluid, non-source fluid decomposition of the scalar probability density function are used to explain these observations. The
results are compared with the theoretical and experimental results established for a line source of scalar in grid turbulence. 相似文献
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Surface moisture area during rainfall–run‐off events to understand the hydrological dynamics of a basin in a plain region 
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下载免费PDF全文 María Guadalupe Ares Mauro Holzman Ilda Entraigas Marcelo Varni Luisa Fajardo Natalia Vercelli 《水文研究》2018,32(10):1351-1362
The understanding of the hydrology of plain basins may be improved by the combined analysis of rainfall–run‐off records and remote sensed surface moisture data. Our work evaluates the surface moisture area (SMA) produced during rainfall–run‐off events in a plain watershed of the Argentine Pampas Region, and studies which hydrological variables are related to the generated SMA. The study area is located in the upper and middle basins of the Del Azul stream, characterized by the presence of small gently hilly areas surrounded by flat landscapes. Data from 9 rainfall–run‐off events were analysed. MODIS surface reflectance data were processed to calculate SMA subsequent to the peak discharge (post‐SMA), and previous to the rainfall events (prev‐SMA), to consider the antecedent wetness. Rainfall–run‐off data included total precipitation depth (P), maximum intensity of rainfall over 6 hr (I6max), surface run‐off registered between the beginning of the event and the day previous to the analysed MODIS scene (R), peak flow (Qp), and flood intensity (IF). In contrast with other works, post‐SMA showed a negative relationship with the R. Three groups of cases were identified: (a) Events of low I6max, high prev‐SMA, and low R were associated with slow and weakly channelized flow over plain areas, leading to saturated overland flow (SOF), with large SMA; (b) events of high I6max, low prev‐SMA, and medium to high R were rapidly transported along the gentle slopes of the basin, related to Hortonian overland flow (HOF) and low post‐SMA; and (c) events of medium to high I6max and prev‐SMA with medium R were related to heterogeneous input‐antecedent‐run‐off conditions combined: Local spatial conditions may have produced HOF or SOF, leading to an averaged response with medium SMA. The interactions between the geomorphology of the basin, the characteristics of the events, and the antecedent conditions may explain the obtained results. This analysis is relevant for the general knowledge of the hydrology of large plains, whose functioning studies are still in their early stages. 相似文献
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Sorin Lisker Anton Vaks Miryam Bar-Matthews Roi Porat Amos Frumkin 《Quaternary Science Reviews》2009,28(1-2):80-92
A varied assemblage of algal stromatolites was encountered in caves along the northern section of the Dead Sea Fault Escarpment. The caves are situated at the lower part of the escarpment at altitudes ?310 to ?188 m relative to mean sea level (m.s.l.), i.e. ca 110–230 m above the present Dead Sea level. The cave stromatolites are mainly composed of aragonite yielding U–Th ages of ～75–17 ka. The altitude, mineralogy and ages, as well as comparison with previously documented stromatolite outcrops in the area, ascribe the cave stromatolites to the aragonite-precipitating hypersaline Lake Lisan—the Late Pleistocene predecessor of the Dead Sea.The stromatolites are used as a lake level gauge, based on the algae being reliant upon the light of the upper water layer. Preservation of the original structure and aragonite mineralogy of the stromatolites, suggests a closed system regarding the radioactive elements, enabling reliable U–Th dating. A curve of Lake Lisan levels is constructed based on the stromatolite ages and cave elevations. The following points are noted: (1) Lake levels of ?247 m relative to m.s.l., are recorded at ～75–72.5 ka; (2) relatively high lake levels above ?220 m relative to m.s.l., are achieved at ～41.5 ka, and are still recorded at ～17 ka; (3) the peak level is ?188 m relative to m.s.l., at ～35.5–29.5 ka. These results indicate lake stands up to 80 m higher than previously accepted, for large parts of the Lake Lisan time span. This difference is explained by tectonic subsidence of up to 2.2 m/ka within the Dead Sea depression since the latest Pleistocene. This subsidence rate is in the same order of magnitude with previously calculated subsidence rates for the Dead Sea depression [Begin, Z.B., Zilberman, E., 1997. Main Stages and Rate of the Relief Development in Israel. Geological Survey of Israel report, Jerusalem]. Unlike previous Lake Lisan level estimations, the new curve is measured at the relatively stable shoulders of the Dead Sea depression. 相似文献
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Saša Vranić Hrvoje Matijević Miodrag Roić 《International journal of geographical information science》2013,27(3):454-474
Modern land administration systems must fulfil the emerging need for a faster and more efficient processing of real estate transactions. In order to achieve such a goal, one way to go can be to outsource a larger segment of the cadastral geometry updating process to the actors external to the organisation maintaining the data. In case the spatial component of the combined legal–spatial transactions is to be outsourced, the underlying transaction processing system must be able to autonomously handle all possible cases in a safe and consistent manner. In this paper we developed a framework that can be used to design a system that is based on standard database transaction concepts and guarantees the safe processing of externally prepared transactions on polygon-based cadastral parcels. In order to be able to detach the process of editing from the consistency control, we adjusted our basic concepts to only consider the net effect of a transaction. In creating the framework we first detect all possible types of transactions. We do that by observing the cardinalities of the transaction’s affected and the resulting sets of parcels and the identities of each set’s members. Following the detection, we attach the basic integrity constraints to each of the transaction types. Finally we classify the detected transaction types into two subtypes with the primary criteria being the strict or relaxed requirements regarding the planar partition correctness. A strict definition of what can be done within each such transaction type provides a reference that can be used for linking the legal and the spatial component of a combined legal–spatial transaction. In order to substantiate the developed framework, we describe the implementation of a proof of the concept system. 相似文献
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Jonah V. Steinbuck Amatzia Genin Stephen G. Monismith Jeffrey R. Koseff Roi Holzman Rochelle G. Labiosa 《Continental Shelf Research》2010
Turbulence measurements in fine-scale phytoplankton layers (∼1 to ∼10 m) in the Gulf of Aqaba (Red Sea) were used to evaluate mechanisms of layer formation, maintenance, and breakdown. Simultaneous profiles of chlorophyll a (Chl a) fluorescence and temperature microstructure were measured in the upper 40 m of a 430 m water column over a 16-d period, using a Self Contained Autonomous MicroProfiler (SCAMP). Layers of concentrated phytoplankton were identified in 95 of the 456 profiles. The layers were situated in density stratified regions between 15 and 38 m depth and were characterized by intensities of 0.1 to 0.35 μg Chl a L−1 (as much as two times background concentrations) and an average thickness of 10 m. We show that turbulent mixing and isopycnal displacements associated with internal waves modulated the thickness of the layers. Variations in mixing rates within layers were connected to the vertical structure of the stratified turbulence and the stage of layer development. The breakdown of a persistent phytoplankton layer was tied to strong turbulent mixing at the base of the surface mixed layer, which encroached on the layer from above. Hydrographic observations and scaling analysis suggest that the layers most likely formed in horizontal intrusions from the adjacent coastal region. The cross-shore propagation of phytoplankton-rich intrusions may have important implications for the trophic state of offshore planktonic communities. 相似文献
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The Moringa Cave within Pleistocene sediments in the En Gedi area of the Dead Sea Fault Escarpment contains a sequence of various Pleistocene lacustrine deposits associated with higher-than-today lake levels at the Dead Sea basin. In addition it contains Chalcolithic remains and 5th century BC burials attributed to the Persian period, cemented and covered by Late Holocene travertine flowstone. These deposits represent a chain of Late Pleistocene and Holocene interconnected environmental and human events, echoing broader scale regional and global climate events. A major shift between depositional environments is associated with the rapid fall of Lake Lisan level during the latest Pleistocene. This exposed the sediments, providing for cave formation processes sometime between the latest Pleistocene (ca. 15 ka) and the Middle Holocene (ca. 4500 BC), eventually leading to human use of the cave. The Chalcolithic use of the cave can be related to a relatively moist desert environment, probably related to a shift in the location of the northern boundary of the Saharo-Arabian desert belt. The travertine layer was U-Th dated 2.46 ± 0.10 to 2.10 ± 0.04 ka, in agreement with the archaeological finds from the Persian period. Together with the inner consistency of the dating results, this strongly supports the reliability of the radiometric ages. The 2.46-2.10 ka travertine deposition within the presently dry cave suggests a higher recharge of the Judean Desert aquifer, correlative to a rising Dead Sea towards the end of the 1st millennium BC. This suggests a relatively moist local and regional climate facilitating human habitation of the desert. 相似文献
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We present preliminary results on variable stars of aSTARE's three month observational run centered at the Cygnus constellation.A total amount of aprox. 14000 stars with 9^2 FOV, have been analyzed to obtainlightcurves for each of these stars.The data spans for 90 nights.In this single field, we detect more that 40 stars withpulsation modes between 5 and 40 c/d, the vast mayoritypreviously unknown to be variables. 相似文献
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P. Rafanelli S. Roi A. Tegon H. Schulz S. Di Serego-Alighieri S. Komossa G. Richter J. Vennik 《Astronomische Nachrichten》1997,318(6):319-327
[OIII] images and blue spectra of the emission-line dwarf galaxy F348 are presented. In [OIII] light, the object contains two knots about 9” NE of the nucleus and one large extended knot 11” to the SW. The nuclear region is hundred times less luminous in emission-line light than the knots. Despite the presence of line intensity ratios [OIII]λ5007/Hβ > 3 the prior classification as a Seyfert-2 object cannot be upheld. This clinches an earlier suggestion by Veron-Cetty & Veron (1986). In particular, we show that the line spectra can be modeled with photoionization models employing stellar input continua. Also, the line luminosities of the extranuclear knots are typical for giant HII regions. There is neither evidence for tidal tails nor for high velocity differences between the knots. In addition, the linear arrangement of the knots does not support interaction. It rather suggests self-propagating star formation In this picture, the faintness of the nuclear region can be understood by an edge-on view. In addition, the nuclear starburst appears to be fading in contrast to the young extranuclear star formation regions. Within the scheme of Melnick (1987), F348 has to be classified as a multiple-system HII galaxy. 相似文献
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