Composition and structure of species along altitude gradient in Moghan-Sabalan rangelands,Iran     

Sahar Ghafari  Ardavan Ghorbani  Mehdi Moameri  Raoof Mostafazadeh  Mahmood Bidarlord 《山地科学学报》2018,15(6):1209-1228

This study provides a checklist of species distributed at the altitude gradient of Moghan-Sabalan rangelands in Ardabili province, Northwest Iran. We evaluated the changes in species composition, growth types of species, Raunkiaer’s life forms, geographical distribution, threat and endemicity status, and palatability of species along two altitudinal gradients in the sampling plots, which were conducted in eleven sites/habitats with 300 meters above sea level (masl) altitude intervals (from 100 to 3300 masl). We assessed the plant species composition with special reference to the gradient analysis, and identified overall 396 species, which was comprising 44 families and 194 genera. Results showed that Asteraceae family is by far the most species-rich family, followed by Poaceae, Fabaceae, Caryophyllaceae and Brassicaceae. Among the genera, Astragalus is the most diverse genus, followed by Allium, Veronica and Bromus, Galium, Silene and Ranunculus. Results indicated that the number of species increased as the altitude increased to 1200–1500 masl, but then starts to decline to 3300 masl. Family-to-genera ratio was 1:4.4, the family-tospecies ratio was 1:9, and the genera-to-species ratio was 1:2.04. Growth type of species analysis shows that the frequency of perennial plants was higher in the study area followed by annual species while the lower group was biennial species. The number of annuals showed a decreasing trend towards higher altitude. Hemicryptophytes and therophytes were the most frequent life forms constituted each with (41.9%). Hemicryptophytes showed an increasing trend with altitude, while therophytes showed a decreasing trend with altitude increase, followed by geophytes, chamaephytes, and phanerophytes. Results showed more than half of the species of the study area belonged to Iran-Turanian region and these species showed an increasing trend with altitude. In contrast, Sahara-Sindian species comprise a minor component of the spectrum, with decreasing trend with altitude. The rare and endangered species out of the surveyed taxonomic groups comprised 53 species in total which 29 of them are considered lower risk (LR), 13 data deficient (DD), 5 vulnerable (Vu) and with 3 rare (R) and identified endemic plants comprised 24 species. Some 56.6% species were identified as class III, 22.6% were class I and 20.8% were class II as the palatability variation. Moghan-Sabalan rangelands require strong conservation management policies in case of species loss and changing natural communities due to the occurrence of conversion into cropland, over-grazing and other anthropogenic effects.  相似文献   

Efficiency of carrier-phase integer ambiguity resolution for precise GPS positioning in noisy environments   总被引：1，自引：0，他引：1  

Liqiang Zhu  Ying-Cheng Lai  Mayur Shah  Sultan Mahmood 《Journal of Geodesy》2007,81(2):149-156

Precise GPS positioning relies on tracking the carrier-phase. The fractional part of carrier-phase can be measured directly using a standard phase-locked loop, but the integer part is ambiguous and the ambiguity must be resolved based on sequential carrier-phase measurements to ensure the required positioning precision. In the presence of large phase-measurement noise, as can be expected in a jamming environment for example, the amount of data required to resolve the integer ambiguity can be large, which requires a long time for any generic integer parameter estimation algorithm to converge. A key question of interest in significant applications of GPS where fast and accurate positioning is desired is then how the convergence time depends on the noise amplitude. Here we address this question by investigating integer least-sqaures estimation algorithms. Our theoretical derivation and numerical experiments indicate that the convergence time increases linearly with the noise variance, suggesting a less stringent requirement for the convergence time than intuitively expected, even in a jamming environment where the phase noise amplitude is large. This finding can be useful for practical design of GPS-based systems in a jamming environment, for which the ambiguity resolution time for precise positioning may be critical.  相似文献   

Influence of inherent anisotropy on mechanical behavior of granular materials based on DEM simulations     

Zafar Mahmood  Kazuyoshi Iwashita 《国际地质力学数值与分析法杂志》2010,34(8):795-819

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Fractal measures of drainage network to investigate surface deformation from remote sensing data: A paradigm from Hindukush (NE-Afghanistan)   总被引：1，自引：0，他引：1  

Syed Amer MAHMOOD  Richard GLOAGUEN 《山地科学学报》2011,8(5):641-654

This approach represents the relative susceptibility of the topography of the earth to active deformation by means of geometrical distinctiveness of the river networks. This investigation employs the fractal analysis of drainage system extracted from ASTER Global Digital Elevation Model (GDEM-30m resolution). The objective is to mark active structures and to pinpoint the areas robustly influenced by neotectonics. This approach was examined in the Hindukush, NE-Afghanistan. This region is frequently affected by deadly earthquakes and the modern fault activities and deformation are driven by the collision between the northward-moving Indian subcontinent and Eurasia. This attempt is based on the fact that drainage system is strained to linearize due to neotectonic deformation. Hence, the low fractal dimensions of the Kabul, Panjsher, Laghman, Andarab, Alingar and Kocha Rivers are credited to active tectonics. A comprehensive textural examination is conducted to probe the linearization, heterogeneity and connectivity of the drainage patterns. The aspects for these natural textures are computed by using the fractal dimension (FD), lacunarity (LA) and succolarity (SA) approach. All these methods are naturally interrelated, i.e. objects with similar FD can be further differentiated with LA and/or SA analysis. The maps of FD, LA and SA values are generated by using a sliding window of 50 arc seconds by 50 arc seconds (50" × 50"). Afterwards, the maps are interpreted in terms of regional susceptibility to neotectonics. This method is useful to pinpoint numerous zones where the drainage system is highly controlled by Hindukush active structures. In the North-Northeast of the Kabul block, we recognized active tectonic blocks. The region comprising, Kabul, Panjsher, Andrab, Alingar and Badakhshan is more susceptible to damaging events. This investigation concludes that the fractal analysis of the river networks is a bonus tool to localize areas vulnerable to deadly incidents influencing the Earth’s topography and consequently intimidate human lives.  相似文献   

Effect of anisotropic conductivity on suction and reliability index of unsaturated slope exposed to uniform antecedent rainfall     

Khalid Mahmood  Jeong Ho Ryu  Jin Man Kim 《Landslides》2013,10(1):15-22

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Ion acoustic solitary waves in electron-positron-ion magneto-rotating Lorentzian plasmas     

S. Hussain  N. Akhtar  S. Mahmood 《Astrophysics and Space Science》2013,348(2):475-481

Nonlinear ion acoustic solitary wave structures in electron-positron-ion (e-p-i) magnetized rotating plasmas is studied. The electron and positron species are assumed to be nonthermal and follow the kappa distribution function. The Korteweg de Vries (kdV) equation is derived by employing the reductive perturbation technique for solitary wave in the nonlinear regime. The variation in the amplitude and width of the solitary wave are discussed with the effects of positron concentration, temperature ratio of kappa distributed electrons to positrons, spectral index of the positrons, direction of propagation of the wave with magnetic field and effective gyrofrequency of the rotating nonthermal plasmas. The numerical results are also presented for illustration.  相似文献   

A semi-analytical model for estimating seismic behavior of buried steel pipes at bend point under propagating waves     

Miad Saberi  Farhad Behnamfar  Mahmood Vafaeian 《Bulletin of Earthquake Engineering》2013,11(5):1373-1402

A buried pipe extends over long distances and passes through soils with different properties. In the event of an earthquake, the same pipe experiences a variable ground motion along its length. At bends, geometrically a more complicated problem exists where seismic waves propagating in a certain direction affect pipe before and after bend differently. Studying these different effects is the subject of this paper. Two variants for modeling of pipe, a beam model and a beam-shell hybrid model are examined. The surrounding soil is modeled with the conventional springs in both models. A suitable boundary condition is introduced at the ends of the system to simulate the far field. Effects of angle of incidence in the horizontal and vertical planes, angle of pipe bend, soil type, diameter to thickness ratio, and burial depth ratio on pipe strains at bend are examined thoroughly. It is concluded that extensional strains are highest at bends and these strains increase with the angle of incidence with the vertical axis. The pipe strains attain their peaks when pipe bend is around $135^{\circ }$ and exceed the elastic limit in certain cases especially in stiffer soils, but remain below the rupture limit. Then equations for predicting the seismic response of the buried pipe at bend are developed using the analytical data calculated above and regression analysis. It is shown that these semi-analytical equations predict the response with very good accuracy saving much time and effort.  相似文献   

岩芯尺度的宽频介电常数频谱实验室测量设备的误差分析及其在物质测量中的应用(英文)     

张天华  AL-OFI Salah  Mahmood Akbar 《地球物理学进展》2012,27(2):582-595

宽频介电常数频谱测井技术最近被引进石油工业.这种新技术区别于传统介电常数测井技术在于多频率频谱的测定和利用.高频谱端包含介质油水饱和度信息,而低频谱端对介质中孔隙结构和水的分布形态很敏感.这种新技术可以有效地被应用于比如超淡水介质或者超黏度重油等对于常规测井来说是很困难的测量环境,而且受介质水中的含盐度影响很小.随着井下测井仪器的投入使用,相应的实验室岩芯测定设备和方法就变得重要起来.因为实验室环境相对较为稳定和可控,实验室岩芯测量结果是对井下测量的很好地验证和校订.文献中记载了许多非破坏性的实验室介电常数的测量设备,然而这些设备的共同局限性是它们对岩芯尺寸和岩芯样本的要求和限制,一般要求粉末状岩芯或者一厘米左右的小柱状岩芯.在碳酸盐介质中,非均匀性和各项异性非常普遍,小的岩芯样本能否涵盖井下设备测量尺度(1.5英寸)的特性很值得商榷.本文中介绍了一种最新设计的实验室大直径宽频介电常数测量设备.这个设备可以直接测量石油工业传统的1.5英寸岩芯样本,测量是非毁坏性的,也就是测量后的岩芯样本可以直接用于其它实验室测量设备,比如电阻率测量或核磁共振测量等.大量重复性试验测得的介电常数色散频谱的精确度对于低损耗介质在2%以内而对于高损耗介质在对孔隙度和含盐度校正以后精确度在3%.文中详细介绍了测量设备所使用的反演程序的算法模型,以及反演误差的算法.反演最后的误差可以用来做数据质量的评定.该测量装置被用于许多物质的测定.测定物质的数据库中合成石英(fused quartz),Teflon,合成陶瓷以及单晶硅的介电常数值可以在文献中找到.该设备的测量结果与文献参考值相符合,说明了该设备测量结果的可靠性.该设备还测量了矿物晶体碳酸钙,晶体白云石以及晶体硬石膏的介电常数,这是常见的碳酸盐介质的主要成分.这些测量给出了碳酸盐介质的边界成分区域值作为参考.该设备测量的两个单晶硅柱状样本的介电常数频谱特性发现退火会改变晶体的结构提高强度,同时会改变介质介电常数的特性.同时矿物晶体碳酸钙测量值高于粉末状测量结果也说明晶体结构可能会导致介电常数测量的不同.该设备具有1.5英寸的大尺度,因此具有和井下设备相仿的测量范围,因而不受介质水平各项异性的影响.但另一方面,该设备仍可以研究垂直各项异性.垂直各项异性的主要原因可能是化学成分不同,孔隙结构不对称或者温度对水分布的影响等等.在对岩石地面露头采样的研究中,宽频介电常数频谱实验室设备检测出了岩芯垂直各项异性,通过对比核磁共振一维孔隙度剖面结构发现总孔隙度不均衡以及分布不对称为该各项异性的主要来源,并且被CT图像所证实.  相似文献   

Scour Downstream of Grade Control Structures under the Influence of Upward Seepage     

Mahmood Shafai-Bejestan  Seyed Mojtaba Razavi Nabavi  Subhasish Dey 《Acta Geophysica》2016,64(3):694-710

The installation of free falling jet grade control structures has become a popular choice for river bed stabilization. However, the formation and development of scour downstream of the structure may lead to failure of the structure itself. The current approaches to scour depth prediction are generally based on studies conducted with the absence of upward seepage. In the present study, the effects of upward seepage on the scour depth were investigated. A total of 78 tests without and with the application of upward seepage were carried out using three different sediment sizes, three different tailwater depths, four different flow discharges, and four different upward seepage flow discharge rates. In some tests, the three-dimensional components of the flow velocity within the scour hole were measured for both the cases with and without upward seepage. The scour depth measured for the no-seepage results compared well with the most accurate relationship found in the literature. It was found that generally the upward seepage reduced the downward velocity components near the bed, which led to a decrease in the maximum scour depth. A maximum scour depth reduction of 49% was found for a minimum tailwater depth, small sediment size, and high flow discharge. A decay of the downward velocity vector within the jet impingement was found due to the upward seepage flow velocity. The well known equation of D’Agostino and Ferro was modified to account for the effect of upward seepage, which satisfactorily predicted the experimental scour depth, with a reasonable average error of 10.7%.  相似文献   

New data on the Indus Kohistan seismic zone and its extension into the Hazara–Kashmir Syntaxis, NW Himalayas of Pakistan     

MonaLisa  Azam A. Khwaja  M. Qasim Jan  Robert S. Yeats  Ahmad Hussain  Shahid A. Khan 《Journal of Seismology》2009,13(3):339-361

This paper deals with the data obtained from local networks in northern Pakistan for 251 earthquakes of magnitude ≥4.0 for October 8, 2005 to December 31, 2006 period. The study presents focal mechanism solutions (FMS) of 12 pre- (1904–2005) and 17 post- (October 8, 2005–December, 2005) Muzaffarabad Earthquake, their detailed tectonic interpretation, and correlation with surface evidence of co-seismic rupture with published synthetic aperture radar data. Distribution of landslides obtained from National Engineering Services of Pakistan and the earthquake damages are also discussed. Aftershock distribution, which is more prominent in the crystalline zone (northwest of Muzaffarabad), defines a 50-km-wide NW–SE trending zone that extends for 200 km from the main mantle thrust to the center of the Hazara–Kashmir Syntaxis. The FMS of the main shock and 16 aftershocks having magnitude ≥4.0 indicate thrusting to be the dominant mechanism with rupture planes having NW–SE trend and NE dip. In addition, 12 FMS of pre-Muzaffarabad Earthquake (1904–2004) from the same area have been determined and results are compared. This leads to the conclusion that the wedge-shaped NW–SE trending blind zone, referred to by earlier workers as the Indus Kohistan Seismic Zone (IKSZ), has been activated during the Muzaffarabad earthquake. The right-lateral component in all FMS, supported by the surface evidences, suggests the involvement of Balakot–Bagh Fault (BBF). We propose that the IKSZ is the source of the October 8, 2005 Muzaffarabad earthquake that reactivated the BBF. Furthermore, the IKSZ does not end at the nose of the syntaxis but extends further southeast of it. Tectonic complexity seems to be due to a variety of factors. Also, thrust and reverse solutions near the northern collisional boundary (main mantle thrust) have mostly NE/SW-directed P-axis orientations. From the detailed FMS analysis, three conclusions have been drawn: (1) Shallow events (depth ≤10 km) with prominent strike slip solutions (earlier earthquakes) are associated with the surface strike slip faults (e.g., Muzaffarabad Fault) and/or the Besham domal structure; (2) moderate depth events (depth 10–25 km) with thrust/reverse solutions but having minor right-lateral strike slip component (all Muzaffarabad earthquakes and two earlier) are associated with the IKSZ; (3) deeper earthquakes (depth below IKSZ) with pure thrust/reverse solutions may be related to the under-thrusting of the Indian plate beneath the IKSZ, which represents a major thrust zone. Imbricate thrusting and breaking and thickening of the crust are considered to be caused by steep bending of the under-thrusting plate at the collisional boundary. An erratum to this article can be found at  相似文献