A bivariate analysis of the volume and duration of low-flow events     

F. Ashkar  N. El Jabi  M. Issa 《Stochastic Hydrology and Hydraulics》1998,12(2):97-116

: The knowledge of the volume and duration of low-flow events in river channels is essential for water management and the design of hydraulics structures. In this study, both preceding characteristics, X ₁ and X ₂, are considered simultaneously via two types of bivariate distributions whose marginals are exponential. One of these bivariate distributions has been presented by Nagao and Kadoya (1971) and the other has been used by Singh and Singh (1991) to the study of rainfall intensity and rainfall depth. The results are applied to the low-flow series (“peaks-below-threshold”) of Lepreau River (station 01AQ001) in New Brunswick, Canada. These results show that the model that was successfully employed by Singh and Singh (1991) to study rainfall, presents certain difficulties when a very strong correlation, ρ, between the two random variables X ₁ and X ₂, exists. The model by Nagao and Kadoya (1971) seems to be more satisfactory for such situations, although this model seems also to be quite sensitive to variations in ρ.  相似文献   

A bivariate analysis of the volume and duration of low-flow events   总被引：2，自引：0，他引：2  

F. Ashkar  N. El Jabi  M. Issa 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(2):97-116

: The knowledge of the volume and duration of low-flow events in river channels is essential for water management and the design of hydraulics structures. In this study, both preceding characteristics, X ₁ and X ₂, are considered simultaneously via two types of bivariate distributions whose marginals are exponential. One of these bivariate distributions has been presented by Nagao and Kadoya (1971) and the other has been used by Singh and Singh (1991) to the study of rainfall intensity and rainfall depth. The results are applied to the low-flow series (“peaks-below-threshold”) of Lepreau River (station 01AQ001) in New Brunswick, Canada. These results show that the model that was successfully employed by Singh and Singh (1991) to study rainfall, presents certain difficulties when a very strong correlation, ρ, between the two random variables X ₁ and X ₂, exists. The model by Nagao and Kadoya (1971) seems to be more satisfactory for such situations, although this model seems also to be quite sensitive to variations in ρ.  相似文献   

Recent colluvial sedimentation in Jordan: fans evolving into sand ramps   总被引：1，自引：0，他引：1  

Brian R. Turner  Issa Makhlouf† 《Sedimentology》2002,49(6):1283-1298

Abstract High‐angle accumulations of sand and escarpment‐derived gravel along the outcrop walls of Plio‐Pleistocene sandstones, eastern Jordan, form small, coalesced colluvial fans, built by rockfalls, rockfall‐derived debris flows, dry sandfalls and sandy grainflows. These deposits are sourced through wind erosion of fault‐controlled outcrops of weakly cemented sandstone and a hard, gypsum‐cemented sandstone and fine conglomerate caprock exposed in sandpits. Eroded sediment is supplied to the fans directly as rockfalls and sandfalls, and indirectly as gully‐confined sandy grainflows. The preserved colluvium fans comprise sandy, matrix‐rich rockfall, rockfall‐derived, dry debris‐flow lenticular gravel deposits and minor lenticular sandy grainflow deposits. The fans develop initially against the footwall escarpment and, as erosion continues, the outcrop and the fans become covered by stable sand sheet ramps in a self‐regulatory geomorphic system. Preserved fan–sand ramp systems in eastern Jordan are characterized by a threefold hierarchy of genetically related bounding surfaces, which develop over short time scales. Rapid fault‐controlled uplift and/or rapid stream incision may produce non‐equilibrium scarp faces, identical to those in the sandpits, associated with the colluvial fan–sand ramp systems. Thus, such systems have the potential to identify fault‐related unconformities, rapid uplift events and episodes of rapid downcutting in the rock record. Colluvium deposits have good preservation potential, but are often associated with complex, coarse, basin‐margin facies, and are thus difficult to identify in the stratigraphic record; a problem exacerbated by the lack of adequate colluvium facies models and diagnostic sedimentary criteria.  相似文献   

Bacterial flora and antibiotic resistance from eggs of green turtles Chelonia mydas: An indication of polluted effluents     

Saif Al-Bahry  Ibrahim Mahmoud  Asila Al-Harthy  Issa Al-Amri 《Marine pollution bulletin》2009,58(5):720-725

Sea turtles migrate to various habitats where they can be exposed to different pollutants. Bacteria were collected from turtle eggs and their resistance to antibiotics was used as pollutant bio-indicators of contaminated effluents. Eggs were collected randomly from turtles when they were laying their eggs. A total of 90 eggs were collected and placed into sterile plastic bags (3 eggs/turtle) during June-December of 2003. The bacteria located in the eggshell, albumen and yolk were examined, and 42% of the eggs were contaminated with 10 genera of bacteria. Pseudomonas spp. were the most frequent isolates. The albumen was found to be the part of the egg to be the least contaminated by bacterial infection. Bacterial isolates tested with 14 antibiotics showed variations in resistance. Resistance to ampicillin was the highest. The presence of antibiotic resistant bacteria in eggs indicates that the green turtle populations were subjected to polluted effluents during some of their migratory routes and feeding habitats. Scanning electron microscopy revealed that Salmonella typhimurium penetrated all eggshell layers.  相似文献   

X-Ray Spectral Study of AGN Sources Content in Some Deep Extragalactic XMM-Newton Fields     

M. A. Hassan  B. A. Korany  R. Misra  I. A. M. Issa  M. K. Ahmed  F. A. Abdel-Salam 《Astrophysics and Space Science》2012,339(2):355-364

We undertake a spectral study of a sample of bright X-ray sources taken from six XMM-Newton fields at high galactic latitudes, where AGN are the most populous class. These six fields were chosen such that the observation had an exposure time more than 60 ksec, had data from the EPIC-pn detector in the full-Frame mode and lying at high galactic latitude |b|>25^∘. The analysis started by fitting the spectra of all sources with an absorbed power-law model, and then we fitted all the spectra with an absorbed power-law with a low energy black-body component model.The sources for which we added a black body gave an F-test probability of 0.01 or less (i.e. at 99% confidence level), were recognized as sources that display soft excess. We perform a comparative analysis of soft excess spectral parameters with respect to the underlying power-law one for sources that satisfy this criterion. Those sources, that do not show evidence for a soft excess, based on the F-test probability at a 99% confidence level, were also fitted with the absorbed power-law with a low energy black-body component model with the black-body temperature fixed at 0.1 and 0.2 keV. We establish upper limits on the soft excess flux for those sources at these two temperatures. Finally we have made use of Aladdin interactive sky atlas and matching with NASA/IPAC Extragalactic Database (NED) to identify the X-ray sources in our sample. For those sources which are identified in the NED catalogue, we make a comparative study of the soft excess phenomenon for different types of systems.  相似文献   

Probabilistic tsunami hazard assessment along Oman coast from submarine earthquakes in the Makran subduction zone     

Issa?El-HussainEmail author  Rachid?Omira  Ahmed?Deif  Zaid?Al-Habsi  Ghazi?Al-Rawas  Adel?Mohamad  Khalifa?Al-Jabri  Maria?Ana?Baptista 《Arabian Journal of Geosciences》2016,9(15):668

The Sultanate of Oman is among the Indian Ocean countries that were subjected to at least two confirmed tsunamis during the twentieth and twenty-first centuries: the 1945 tsunami due to an earthquake in the Makran subduction zone in the Sea of Oman (near-regional field tsunami) and the Indian Ocean tsunami in 2004, caused by an earthquake from the Andaman Sumatra subduction zone (far - field tsunami). In this paper, we present a probabilistic tsunami hazard assessment for the entire coast of Oman from tectonic sources generated along the Makran subduction zone. The tsunami hazard is assessed taking into account the contribution of small- and large-event magnitudes. Results of the earthquake recurrence rate studies and the tsunami numerical modeling for different magnitudes were used through a logic-tree to estimate the tsunami hazard probabilities. We derive probability hazard exceedance maps for the Omani coast considering the exposure times of 100, 250, 500, and 1000 years. The hazard maps consist of computing the likelihood that tsunami waves exceed a specific amplitude. We find that the probability that a maximum wave amplitude exceeds 1 m somewhere along the coast of Oman reaches, respectively, 0.7 and 0.85 for 100 and 250 exposure times, and it is up to 1 for 500 and 1000 years of exposure times. These probability values decrease significantly toward the southern coast of Oman where the tsunami impact, from the earthquakes generated at Makran subduction zone, is low.  相似文献   

Influence of size of granulated rubber on bearing capacity of fine-grained sand     

Seyed Mahmoud Anvari  Issa Shooshpasha 《Arabian Journal of Geosciences》2016,9(18):707

Nowadays, in most of the advanced and developing countries, waste tires have caused serious environmental problems such as fire and environmental contamination. For reusing them in an appropriate and beneficial way, waste tires have been utilized as a lightweight fill material in geotechnical engineering applications such as highway embankments. In this study, Babolsar fine-grained sand and granulated rubber with sizes in the ranges of 1 to 4, 1 to 9, and 4 to 9 mm were used. A series of model footing tests on reinforced sand with different sizes of granulated rubber were carried out. According to the results, 4- to 9-mm granulated rubber had the highest effect on enhancement of bearing capacity and reduction of fine-grained sand settlement. The results showed that sand-granulated rubber mixtures with granulated rubber in the range of 4 to 9 mm and content of 10% by weight of mixture can increase the bearing capacity of sand up to 50%. In addition, for this mixture, a series of laboratory tests were conducted to determine the optimum width and depth of the reinforcement layer consisting of sand-granulated rubber mixture. The results indicate that the optimum width and the most effective depth of this mixture are 5B and 1B, respectively (where B is the footing width).  相似文献