Assessing climate-relevant vulnerability of the Indian Himalayan Region (IHR): a district-level analysis     

Alam  Mir Khursheed  Dasgupta  Shyamasree  Barua  Anamika  Ravindranath  N. H. 《Natural Hazards》2022,112(2):1395-1421

Natural Hazards - Indian Himalayan Region (IHR) is highly vulnerable to climate change and its variability. The present study employs an indicator-based approach to assess...  相似文献   

Influence of drainage and root biomass on soil mechanical behavior in triaxial tests     

Alam  Mehtab  Jiang  Yuan-Jun  Umar  Muhammad  Su  Li-jun  Rahman  Mahfuzur  Ullah  Faheem 《Acta Geotechnica》2022,17(7):2875-2893

Acta Geotechnica - This paper presents a study in which triaxial tests were performed on loess soil reinforced with natural roots. Triaxial compression tests were performed on soil specimens with...  相似文献   

Cylindrical and spherical positron-acoustic Gardner solitons in electron-positron-ion plasmas with nonthermal electrons and positrons     

M. M. Rahman  M. S. Alam  A. A. Mamun 《Astrophysics and Space Science》2014,352(1):193-200

A theoretical investigation has been performed on the nonlinear propagation of nonplanar (cylindrical and spherical) Gardner solitons (GSs) associated with the positron-acoustic (PA) waves in a four component plasma system consisting of nonthermal distributed electrons and hot positrons, mobile cold positrons, and immobile positive ions. The well-known reductive perturbation method has been employed to derive the modified Gardner (MG) equation. The basic features (viz. amplitude, polarity, speed, etc.) of nonplanar PA Gardner solitons (GSs) have been examined by the numerical analysis of the MG equation. It has been observed that the properties of the PA GSs in a nonplanar geometry differ from those in a planar geometry. It has been also investigated that the presence of nonthermal (Cairns distributed) electrons and hot positrons significantly modify the amplitude, polarity, speed, and thickness of such PA GSs. The results of our investigation should play an important role in understanding various interstellar space plasma environments as well as laboratory plasmas.  相似文献   

Role of the gaunt factor in the derivation of dielectronic recombination coefficient     

Badré Alam  S. M. Razaullah Ansari 《Solar physics》1985,96(2):219-227

A new formula for the coefficient of dielectronic recombination has been derived by substituting excitation cross-section extrapolated below threshold for capture cross-section in Equation (7) of Burgess (1964). In this case the excitation cross-section modified by Mewe (1972b) through a fitted gaunt factor has been used. The dielectronic recombination coefficients calculated by the new formula are found to be about an order of magnitude smaller than those obtained by Burgess simplified formula. The results for coronal ions of silicon and iron are presented here as our sample calculations. A comparative study of the dielectronic recombination with radiative recombination is also made.  相似文献   

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation     

Tariq Masood Ali Khan  Dewan Abdul Quadir  T. S. Murty  Anwarul Kabir  Fahmida Aktar  Majajul Alam Sarker 《Marine Geodesy》2002,25(1):133-143

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.  相似文献   

Enhancement of the solar X-ray line intensities due to dielectronic recombination as an excitation process     

S. M. Razaullah Ansari  Badré Alam 《Solar physics》1975,41(1):97-107

Intensities of resonance lines in X-ray region for Si ix–Si xiv ions are calculated by considering total excitation, i.e., excitation due to electron impact and dielectronic recombination. It is found that the contribution of the latter is quite significant. For consistency, the electron density effect in our calculations is not only accounted for in the ionization equilibrium but also in the total rate of excitation. It is also found that the contribution of electron density effect is pronounced with the inclusion of dielectronic recombination as an excitation mechanism. The computed average line intensities are compared with the available observations and a table of line flux for various wavelengths of the above-mentioned ions at different temperatures is also given.  相似文献   

Petrology of the prehistoric lavas and dyke of the Barren Island,Andaman Sea,Indian Ocean     

M. A. Alam  D. Chandrasekharam  O. Vaselli  B. Capaccioni  P. Manetti  P. B. Santo 《Journal of Earth System Science》2004,113(4):715-721

Although Barren Island (Andaman Sea, Indian Ocean) witnessed several volcanic eruptions during historic times, the eruptions that led to the formation of this volcanic island occurred mainly during prehistoric times. It is still active and currently in the fumarolic stage. Its volcanic evolution appears to be characterized by a constructive phase with the piling up of lava flows and scoria deposits and Strombolian activities, followed by a sudden collapse of the main cone. Deposits of a possible caldera-forming eruption were not recognized earlier. After a period of peri-calderic hydromagmatic activity, whose deposits presently mantle inner and outer caldera walls, a new phase of intracalderic Vulcanian activities took place. A prominent dyke in the SE inner side of the caldera wall was recognized. Petrographically the lava flows and dyke are similar but they differ in their chemical composition (viz., SiO₂, MgO, Ni, Cr) significantly. Similarity in major, minor and trace element composition (viz., K/La, K/Nb, K/Rb, K/Ti ratios) of these rocks together with Chondrite normalized trace element (Rb, Ba, Sr, P, Zr, Ti and Nb) and REE (La, Ce, Nd and Y) patterns of the Barren Island prehistoric lava flows and dyke and low-K lavas of Sunda Arc indicates that Barren Island must have evolved from a source similar to that of Sunda Arc lavas during the Quaternary Period.  相似文献   

重庆老龙洞地下河不同部位水体、表层沉积物有机氯农药含量及组成研究   总被引：2，自引：0，他引：2  

师阳  孙玉川  徐昕  任坤  Md.Jahangir Alam 《中国岩溶》2014,33(2):238-247

为研究重庆老龙洞地下河不同部位水体、表层沉积物有机氯农药分布特征,用气相色谱-微池电子捕获检测器(GC-μECD)分析了样品中OCPs含量。结果表明:研究区水样、表层沉积物中OCPs检出率均为100 %,其浓度在时间上存在季节差异,水体中OCPs、DDTs、HCHs含量丰水期小于枯水期,而在表层沉积物中则表现为OCPs、HCHs丰水期大于枯水期,DDTs丰水期小于枯水期;在空间上则表现为水体中有机氯农药总体下游大于上游,而沉积物中则与之相反。通过对比可知,岩溶洞穴环境由于缺乏光照,空气流动缓慢,生物活动不频繁,使水体中的HCHs不易降解,沉积物中的HCHs不易重新释放而浓度高于洞外。枯水期由于洞内流速较小且变幅不大,水体中的DDTs大量沉积因而其浓度低于洞口,而丰水期洞口因受大量雨水的稀释作用DDTs反而低于洞内的含量;洞内沉积物中的DDTs则因洞内环境恒定不易重新释放和枯水期水体中的大量沉积而一直高于洞外。洞穴环境、不同污水汇入对水体中DDTs和表层沉积物中DDTs、HCHs的组成结构均有不同程度的影响,而对水体中HCHs的组成结构影响不大。此外,地下河不同部位污染源的输入对有机氯污染物的组成结构也有影响。与国内外水体及表层沉积物中HCHs、DDTs相比较,研究区水体、表层沉积物中HCHs、DDTs浓度分别处于中等和偏高水平。   相似文献   

Determination of aquifer geometry through geophysical methods: A case study from Quetta Valley, Pakistan     

Khurshaid Alam  Nasir Ahmad 《Acta Geophysica》2014,62(1):142-163

Due to increase in population and agricultural activities, the aquifer of Quetta Valley is under tremendous stress and the water table is declining at an increasing rate. This situation necessitates evaluation of the aquifer system, for which information about geometry of the aquifer is a prerequisite. However, there are no drilling-to-bedrock data available; therefore, electrical resistivity, seismic reflection and gravity methods were employed to determine geometry of the aquifer. Interpretation of vertical electrical soundings provided information about the depth-tobedrock at some specific points, whereas seismic reflection delineated bedrock topography along two lines. The depths to bedrock inferred from electrical resistivity and seismic reflection data were used as constraints in the modeling of gravity data. 2.75D gravity models were constructed along lines with a regular spacing. Map of depth-to-bedrock was prepared by contouring the depth given by the gravity models. Combination of these geophysical methods depicted the geometry of the aquifer. This example shows that in a similar geological setting proper integration of geophysical exploration methods can determine the aquifer geometry with an acceptable reliability and at an appropriate cost.  相似文献   

Biomonitoring of Heavy Metals Using the Bivalve Molluscs in Sunderban Mangrove Wetland,Northeast Coast of Bay of Bengal (India): Possible Risks to Human Health   总被引：2，自引：0，他引：2  

Santosh Kumar Sarkar  Henrique Cabral  Mousumi Chatterjee  Ines Cardoso  Asok Kumar Bhattacharya  Kamala Kanta Satpathy  Mohammad Aftab Alam 《洁净——土壤、空气、水》2008,36(2):187-194

The suitability of using four bivalve molluscs (Sanguinolaria acuminata, Anadara granosa, Meretrix meretrix, and Pelecyora trigona) in biomonitoring of heavy metals (Cu, Pb, Cd, Zn, and Hg) collected from intertidal regions of the Sunderban mangrove wetland, northeastern part of the Bay of Bengal, were evaluated. Both speciesdependent variability and temporal variations were pronounced. A high degree of organ specificity was evident in the bivalves where gill and mantle exhibited higher metal accumulation due to ion exchange property of the mucous layer covering these organs while shells represent very poor accumulation. Elevated values of Zn and Cu reflect high potential for biomagnification through marine food chain. Metal concentrations in different body size groups of the bivalves do not follow uniform trend. Correlation coefficient between different metal couplings as tested statistically revealed significant coupling for Pb–Zn, Pb–Cu, Zn–Cu, and Hg–Cu. Concentrations of all the metals in specific organs (visceral mass, mantle and gill) of the bivalves exceeded the safe levels according to the international standards for metals compiled by Food and Agricultural Organization of the United Nations and would be of great risk for human consumption. It is concluded that the mussel and clam are suitable biomonitors to employ in programs designed to assess changes in metal pollution in the Sunderban mangrove wetland.  相似文献