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21.
Iman Mallakpour 《水文科学杂志》2013,58(2):245-254
AbstractThe Pettitt test is a non-parametric test that has been used in a number of hydroclimatological studies to detect abrupt changes in the mean of the distribution of the variable of interest. This test is based on the Mann-Whitney two-sample test (rank-based test), and allows the detection of a single shift at an unknown point in time. This test is often used to detect shifts in extremes because of the lack of distributional assumptions. However, the downside of not specifying a distribution is that the Pettitt test may be inefficient in detecting breaks when dealing with extremes. Here we adopt a Monte Carlo approach to examine the sensitivity of the Pettitt test in detecting shifts in the mean under different conditions (location of the break within the series, magnitude of the shift, record length, level of variability in the data, extreme vs non-extreme records, and pre-assigned significance level). These simulation results show that the sensitivity of this test in detecting abrupt changes increases with the increase in the magnitude of the shift and record length. The number of detections is higher when the time series represents the central part of the distribution (e.g. changes in the time series of medians), while the skill decreases as we move toward either low or high extremes (e.g. changes in the time series of maxima). Furthermore, the number of detections decreases as the variability in the data increases. Finally, abrupt changes are more easily detected when they occur toward the center of the time series.
Editor D. Koutsoyiannis Associate editor K. Hamed 相似文献
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Iman ROUSTA Mehdi DOOSTKAMIAN Esmaeil HAGHIGHI Hamid Reza GHAFARIAN MALAMIRI Parvane YARAHMADI 《大气科学进展》2017,34(9):1069-1081
Rainfall is a highly variable climatic element, and rainfall-related changes occur in spatial and temporal dimensions within a regional climate. The purpose of this study is to investigate the spatial autocorrelation changes of Iran's heavy and super-heavy rainfall over the past 40 years. For this purpose, the daily rainfall data of 664 meteorological stations between 1971 and 2011 are used. To analyze the changes in rainfall within a decade, geostatistical techniques like spatial autocorrelation analysis of hot spots, based on the Getis-Ord Gistatistic, are employed. Furthermore, programming features in MATLAB, Surfer, and GIS are used. The results indicate that the Caspian coast, the northwest and west of the western foothills of the Zagros Mountains of Iran, the inner regions of Iran, and southern parts of Southeast and Northeast Iran,have the highest likelihood of heavy and super-heavy rainfall. The spatial pattern of heavy rainfall shows that, despite its oscillation in different periods, the maximum positive spatial autocorrelation pattern of heavy rainfall includes areas of the west, northwest and west coast of the Caspian Sea. On the other hand, a negative spatial autocorrelation pattern of heavy rainfall is observed in central Iran and parts of the east, particularly in Zabul. Finally, it is found that patterns of super-heavy rainfall are similar to those of heavy rainfall. 相似文献
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Iman Malekmohamadi Mohammad Reza Bazargan-Lari Reza Kerachian Mohammad Reza Nikoo Mahsa Fallahnia 《Ocean Engineering》2011,38(2-3):487-497
Wave Height (WH) is one of the most important factors in design and operation of maritime projects. Different methods such as semi-empirical, numerical and soft computing-based approaches have been developed for WH forecasting. The soft computing-based methods have the ability to approximate nonlinear wind–wave and wave–wave interactions without a prior knowledge about them. In the present study, several soft computing-based models, namely Support Vector Machines (SVMs), Bayesian Networks (BNs), Artificial Neural Networks (ANNs) and Adaptive Neuro-Fuzzy Inference System (ANFIS) are used for mapping wind data to wave height. The data set used for training and testing the simulation models comprises the WH and wind data gathered by National Data Buoy Center (NDBC) in Lake Superior, USA. Several statistical indices are used to evaluate the efficacy of the aforementioned methods. The results show that the ANN, ANFIS and SVM can provide acceptable predictions for wave heights, while the BNs results are unreliable. 相似文献
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Iman Attar Morteza Ahmadi Majid Nikkhah Ali Attar 《Arabian Journal of Geosciences》2014,7(4):1479-1489
Knowledge of the magnitude and orientation of the initial in situ stress of rock mass in underground spaces in mining, construction, and oil projects are so vital; hence, putting it aside could not only cost a lot rather incur some irrecoverable damage. Various methods are available to estimate in situ stress in rock mass. However, the most commonly used one, i.e., hydraulic fracturing (HF) method is considered expensive and time consuming. As a matter of fact, laboratory methods based on drilled “core” have become prevalent these days considering them simple, cheap, and quick. Taking into account one such procedure, i.e., deformation rate analysis (DRA), the current research tries to review the DRA capability in determining the magnitude of initial in situ stress is in different parts of stress–strain curve. Further, an investigation was made about the usage of DRA method for both brittle and ductile rocks. To compare the DRA and hydraulic fracturing methods in in situ stress measurement, the water conveyance tunnel of Gotvand Dam was selected as a case study. The DRA tests were conducted on core samples prepared from blocks of tuff (as brittle) and soft sandstones (as ductile) from shallow quarry. The results show that the DRA method is suitable for all types of intact rock and that this could easily estimate in situ stress values. A comparison between in situ stress values obtained by DRA and those of HF method show the feasibility of geotechnical project, simplicity, speed, and low cost. 相似文献
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Nalivan Omid Asadi Badehian Ziaedin Sadeghinia Majid Soltani Adel Islami Iman Boustan Ali 《Natural Hazards》2022,111(2):1661-1684
Natural Hazards - In an effort to improve the previous gully susceptibility assessments in Iran, we attempted to conglomerate the notions of susceptibility, vulnerability, and exposure associated... 相似文献
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Moghadam Seyed Iman Taheri Ehsan Ahmadi Morteza Ghoreishian Amiri Seyed Ali 《Acta Geotechnica》2022,17(10):4359-4375
Acta Geotechnica - This paper presents a constitutive model enabled to simulate monotonic and cyclic behaviour of clay and sand in a unified framework. The bounding surface concept has been... 相似文献
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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
28.
Iman Khosravi Majid Mohammad-Beigi 《Journal of the Indian Society of Remote Sensing》2014,42(2):423-428
One of the most widely used outputs of remote sensing technology is Hyperspectral image. This large amount of information can increase classification accuracy. But at the same time, conventional classification techniques are facing the problem of statistical estimation in high-dimensional space. Recently in remote sensing, support vector machines (SVMs) have shown very suitable performance in classifying high dimensionality problem. Another strategy that has recently been used in remote sensing is multiple classifier system (MCS). It can also improve classification accuracy by combining different classifier methods or by a diversity of the same classifier. This paper aims to classify a Hyperspectral data using the most common methods of multiple classifier systems i.e. adaboost and bagging and a MCS based on SVM. The data used in the paper is an AVIRIS data with 224 spectral bands. The final results show the high capability of SVMs and MCSs in classifying high dimensionality data. 相似文献
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