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21.
Atmospheric stability conditions over the water surface can affect the evaporative and convective heat fluxes from the water surface. Atmospheric instability occurred 72.5% of the time and resulted in 44.7 and 89.2% increases in the average and maximum estimated evaporation, respectively, when compared to the neutral condition for a small shallow lake (Binaba) in Ghana. The proposed approach is based on the bulk-aerodynamic transfer method and the Monin-Obukhov similarity theory (MOST) using standard meteorological parameters measured over the surrounding land. For water surface temperature, a crucial parameter in heat flux estimation from water surfaces, an applicable method is proposed. This method was used to compute heat fluxes and compare them with observed heat fluxes. The heat flux model was validated using sensible heat fluxes measured with a 3-D sonic anemometer. The results show that an unstable atmospheric condition has a significant effect in enhancing evaporation alongside the sensible heat flux from water surfaces. 相似文献
22.
Alireza Abbasi 《Natural Hazards》2014,71(3):1957-1969
This study aims to understand the mechanisms of emergency response network evolution by quantitatively examining the link formation pattern among participants involved in a real emergency collaboration network. This is achieved by identifying the participants’ characteristics which can affect forming new links over time. The result indicates the existence of cumulative advantage process, where highly connected participants gain more new links over time. It also reveals the structural position of participants involved in a response network, i.e. brokering position, affects their number of future links. Understanding the link formation pattern is important for understanding the mechanisms of network evolution which help predict more precisely the behavior of actors and dynamics of network structure over time. This can assist researchers, decision makers and practitioners to manage and support the collaboration of actors in their systems in order to reach their organizational goals. The overall findings can contribute further to the development of network organizational theory in different contexts especially disaster and emergency response management. 相似文献
23.
The study of human mobility has gained much attention in recent years. To date, various models have been developed to predict human mobility patterns for intra- and/or inter-city cases. These models incorporate the populations as proxy variables in the place of real variables which cannot be observed easily. However, inaccuracies in predicting human mobility within cities are usually encountered. One source of inaccuracies in intra-city scenarios arises from the fact that cities’ populations are influenced by people from other areas. Therefore, population cannot be regarded as a good proxy variable for movement modeling. The objectives of this article are to introduce new proxy variables for use in current models for predicting human mobility patterns within cities, and to evaluate the accuracy of the predictions. In this study, we have introduced new proxy variables, namely, venues and check-ins, extracted from location-based social networks (LBSNs). In order to evaluate the models, we have compared our results with empirical data obtained from taxi vehicles, based on trip distances and destination population distributions. The Sørensen similarity index (SSI) and R-squared measures were also used to compare the performances of models using each variable. The results show that all models with LBSN variables can capture real human movements better within Manhattan, New York City. Our analytical results indicated that the predicted trips using LBSN data are more similar to the real trips, on average, by about 20% based on the SSI. Moreover, the R-squared measures obtained from regression analyses were enhanced significantly. 相似文献
24.
Iftikhar Ahmed Abbasi Osman Salad Hersi Abdulrahman Al-Harthy Iman Al-Rashdi 《Arabian Journal of Geosciences》2013,6(12):4931-4945
Over 70 m thick interbedded sandstone, siltstone and claystone of the upper member of the Gharif Formation are exposed in western Huqf area in Oman Interior Sedimentary Basin. The Gharif Formation, particularly its upper member hosts major hydrocarbon reservoir in the subsurface of the Oman Interior Sedimentary Basin. The upper member of the Gharif Formation is comprised of interbedded thick sandstone, siltstone, carbonaceous clays and intraformational conglomerates. The sandstone lithofacies, on average, constitute 10 m thick multistoreyed sequences, which are composed internally of 2–3 m thick and 100 s of metres across vertically and laterally amalgamated sandstone bodies. Two major types of sandstones (types 1 and 2) are identified on the basis of their lithofacies association and internal architecture. The type 1 sandstone constitutes the lower part of the member and is comprised of pebbly to coarse-grained, planar and trough cross-bedded sandstone, plane bedded sandstone and pebble lags at the base of major sandstone bodies. The cross-beds are, on average, 30 cm thick exhibiting a dominant paleoflow direction towards NW (280–300° N). It is interpreted to be deposited by low sinuosity braided streams. The type 2 sandstone constitutes the upper part of the member and is comprised of medium-grained sandstone, trough to low angle plane bedding associated with lateral accretion surfaces. It is commonly interbedded with carbonaceous clays. Silicified plant fragments are commonly distributed in the upper part of the sandstone. Interbedded clays and siltstones are red, mottled and extensively bioturbated due to root burrows. It is interpreted to be deposited by high sinuosity meandering streams. In the uppermost part of the section, several dark grey to black carbonaceous clay/coal beds with plant matter are interbedded with sandstone and red clay indicating development of swampy conditions during onset of the coastal setting in the uppermost part of the formation. About 30 cm thick bioclastic sandstone deposited by the marine coastal bars mark transition from the Gharif Formation to carbonate dominated Khuff Formation. The sandstone of the Gharif Formation is arkosic in composition. Very small amount of cement and negligible compaction of constituent grains in sandstone indicates shallow burial before uplift. 相似文献
25.
Assessment and Modification of Sherard Chemical Method for Evaluation of Dispersion Potential of Soils 总被引：1，自引：1，他引：0
Soil dispersion is a phenomenon in which soil particles become afloat when they are exposed to water, and are carried away by the force of seepage. In spite of that soil dispersion is due to its chemical composition, the results obtained from the chemical methods, especially from the most widely used, Sherard method does not match with the results of well-known Pinhole test. This study tries to evaluate and modify the Sherard diagram for determination of dispersion potential of clayey soils. For this purpose, several natural soil samples were collected from different regions of Iran and some artificial soil samples were made by adding different percentages of four chemical agents, including sodium chloride, sodium carbonate, sodium sulfate, and sodium polyphosphate to a natural soil. The physical, chemical and index properties of all samples were determined and for determination of dispersion potential, the commonly used chemical test (Sherard method) and Pinhole test were employed. The results obtained from the tests showed that the Sherard chemical method which is solely based on the amount and type of the existing cations, is not able to determine soil dispersion correctly since the role of some anions, especially chloride is neglected. It was also found that among the existing anions in the soil, the chloride on the contrary to sodium acts as a flocculating factor. The results showed that by converting the vertical axis of the Sherard chart from sodium% to (sodium chloride)%, its conformity to the results of Pinhole tests increases considerably. 相似文献
26.
Summary. Gumbel's theory of extreme value has been employed in the statistical forecasting of maximum-magnitude earthquake occurrence. The basic working hypothesis behind this method assumes that observations follow either Gumbel type I or type III asymptotic distributions. In certain cases, however, it is found that neither type of distribution fits the data well enough to produce accurate parameter-estimates, particularly in the larger earthquake range. This article proposes an alternative approach based on finite-mixture distributions whereby a more realistic prediction of upper earthquake magnitudes (at given return periods) is expected using a combined analysis of both Gumbel types I and III extremal distributions. 相似文献
27.
Airborne LaCoste &; Romberg gravimetry: a space domain approach 总被引：1，自引：0，他引：1
This paper introduces a new approach to reduce the airborne gravity data acquired by a LaCoste &; Romberg (L&;R) air/sea gravimeter, or other similar gravimeters. The acceleration exerted on the gravimeter is the sum of gravity and the vertical and Eötvös accelerations of the aircraft. The L&;R gravimeter outputs are: (1) the beam position, (2) the spring tension and (3) the cross coupling. Vertical and Eötvös accelerations are computed from GPS-derived aircraft positions. However, the vertical perturbing acceleration sensed by the gravimeter is not the same as the one sensed by the aircraft (via GPS). A determination of the aircraft-to-sensor transfer function is necessary. The second-order differential equation of the motion of the gravimeter’s beam mixes all the input and output parameters of the gravimeter. Conventionally, low-pass filtering in the frequency domain is used to extract the gravity signal, the filter being applied to each flight-line individually. By transforming the differential equation into an integral equation and by introducing related covariance matrices, we develop a new filtering method based on a least-squares approach that is able to take into account, in one stage, the data corresponding to all flight-lines. The a posteriori covariance matrix of the estimated gravity signal is an internal criterion of the precision of the method. As an example, we estimate the gravity values along the flight-lines from an airborne gravity survey over the Alps and introduce an a priori covariance matrix of the gravity disturbances from a global geopotential model. This matrix is used to regularize the ill-posed Fredholm integral equation introduced in this paper. 相似文献
28.
Omid?Hamidi Leili?Tapak Hamed?Abbasi Zohreh?MaryanajiEmail author 《Theoretical and Applied Climatology》2018,134(3-4):769-776
We have conducted a case study to investigate the performance of support vector machine, multivariate adaptive regression splines, and random forest time series methods in snowfall modeling. These models were applied to a data set of monthly snowfall collected during six cold months at Hamadan Airport sample station located in the Zagros Mountain Range in Iran. We considered monthly data of snowfall from 1981 to 2008 during the period from October/November to April/May as the training set and the data from 2009 to 2015 as the testing set. The root mean square errors (RMSE), mean absolute errors (MAE), determination coefficient (R 2), coefficient of efficiency (E%), and intra-class correlation coefficient (ICC) statistics were used as evaluation criteria. Our results indicated that the random forest time series model outperformed the support vector machine and multivariate adaptive regression splines models in predicting monthly snowfall in terms of several criteria. The RMSE, MAE, R 2, E, and ICC for the testing set were 7.84, 5.52, 0.92, 0.89, and 0.93, respectively. The overall results indicated that the random forest time series model could be successfully used to estimate monthly snowfall values. Moreover, the support vector machine model showed substantial performance as well, suggesting it may also be applied to forecast snowfall in this area. 相似文献
29.
Ercan Özcan İftikhar Ahmed Abbasi Katica Drobne Abiraman Govindan Luigi Jovane Kamel Boukhalfa 《Geodinamica Acta》2016,28(3):160-184
The upper member of the Jafnayn Formation in Wadi Rusayl and Al Khoud, Seeb Area in north Oman contains Nemkovella stockari Less & Özcan, 2007, an Early Eocene orthophragminid recorded here for the first time from the Arabian Peninsula. N. stockari, the only orthophragminid identified in Jafnayn Formation, is quite distinct from any other species from Tethys in having spiral and orbitoidiform chambers around the isolepidine embryon developed before the onset of annular chambers. The Oman specimens exhibit equal-sized principal auxiliary chambers and symmetrical spirals and are assigned to N. stockari bejaensis Özcan, Boukhalfa & Scheibner, 2014, an advanced form of the N. stockari lineage. The associated alveolinids, revised in this study, rotaliids and other age-diagnostic foraminiferal taxa in the transgressive basal part of the upper member have enabled us to revise the age as middle Ilerdian (Early Eocene), assignable to SBZ 7/8 and 8; OZ 3/4. Integrating a new record of this species from Arabian Plate margin in Belen, S Turkey, and previous records from north Africa, N. stockari appears to be a diagnostic marker for the Early Eocene along the southern peri-Tethys platforms, facilitating the Tethyan correlation by orthophragminids. The palaeobiogeographic distribution of N. stockari is discussed. 相似文献
30.
Sajjad Abbasi Behnam Keshavarzi Farid Moore Hossein Delshab Naghmeh Soltani Armin Sorooshian 《Environmental Earth Sciences》2017,76(23):798
This study aimed to (1) investigate microrubbers (MRs) for the first time and identify microplastics (MPs) in street dust, (2) determine the physicochemical and mineralogical characteristics and morphology of dust particles, (3) understand the concentration and the possible source(s) of heavy metals/metalloids, (4) identify the chemical speciation and mobility potential of trace metals in urban street dusts, and (5) determine adverse health effects of street dust on children and adults living in the city of Bushehr in southwestern Iran. Generally, twenty four street dust samples were collected and analyzed. Calculated enrichment factors indicate high levels of contamination. Statistical analysis reveals that the two main sources of trace elements include road traffic emissions (Cu, Zn, Sb, Hg, Pb, Mo) and re-suspended soil particles (Al, Mn, Ni, Ti, Cd, Co). BCR sequential extraction results indicated that As, Zn, Cu, and Pb mainly occur in the exchangeable fraction and hence are highly bioavailable. X-ray powder diffraction analysis revealed the presence of calcite, dolomite, quartz, and magnetite. The size distribution of dust particles was also investigated using a scanning electron microscope (SEM), while elemental distribution was analyzed using an attached energy dispersive X-ray spectrometer (SEM–EDS) unit. Dust particles from heavy traffic areas are much finer compared with other investigated areas. MPs and MRs, mostly fibers and fragments, were detected in all samples [ranging from 210 to 1658 (MPs) and 44 to 782 (MRs) items/10 g dust] using fluorescence microscopy. The hazard index for As is higher than 10?4 for children and adults indicative of high risk. According to the calculated potential ecological risk index, Hg indicated moderate ecological risk in the street dust of the study area. 相似文献