Exploratory experiments to determine the effect of alternative operations on the efficiency of subsurface arsenic removal in rural Bangladesh     

M. M. Rahman  M. Bakker  S. C. Borges Freitas  D. van Halem  B. M. van Breukelen  K. M. Ahmed  A. B. M. Badruzzaman 《Hydrogeology Journal》2015,23(1):19-34

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Investigation of seasonal droughts and related large-scale atmospheric dynamics over the Potwar Plateau of Pakistan     

N. U. Ain  M. Latif  K. Ullah  S. Adnan  R. Ahmed  M. Umar  M. Azam 《Theoretical and Applied Climatology》2020,140(1):69-89

As a result of climate change and unsustainable land use management in the recent past, droughts have become one of the most devastating climatic hazards whose impacts may prolong from months to years. This study presents analysis of droughts for two major cropping seasons, i.e., Kharif (May–September) and Rabi (October–April), over the Potwar Plateau of Pakistan. The analysis is performed using various datasets viz. observational, reanalysis, and Regional Climate Models (RCMs), for the past (1981–2010) and future (2011–2100) time periods. The following two methods for the identification of dry and wet years, also referred to as drought and wetness, are applied: (1) the percentile rank approach and (2) the drought indices, Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI). Future projections of droughts are investigated using RCM (RegCM4.4 and RCA4) outputs from CORDEX South Asia domain under two Representative Concentration Pathway (RCP) scenarios, RCP4.5 and RCP8.5. Generally, the indices show non-significant decreasing trends of drought severity in the recent past for all cases; however, significant increasing trends are observed for annual (0.006) and Kharif (0.007) cases under RCP4.5 scenario. The analysis of large-scale atmospheric dynamics suggests the significant role of low-level geopotential height anomalies over Tibetan Plateau (northwest of Pakistan) during Kharif (Rabi) season in controlling drought occurrence by transporting moisture from the Bay of Bengal (Arabian Sea). Moreover, composites of vertically integrated moisture transport, moisture flux convergence/divergence, and precipitable water anomalies show their marked contribution in maintaining the drought/wetness conditions over the Potwar region.  相似文献   

An evaluation of the CORDEX regional climate models in simulating future rainfall and extreme events over Mzingwane catchment,Zimbabwe     

S. Sibanda  S. W. Grab  F. Ahmed 《Theoretical and Applied Climatology》2020,140(1):91-100

The study evaluated CORDEX RCMs’ ability to project future rainfall and extreme events in the Mzingwane catchment using an ensemble average of three RCMs (RCA4, REMO2009 and CRCM5). Model validation employed the statistical mean and Pearson correlation, while trends in projected rainfall and number of rainy days were computed using the Mann-Kendall trend test and the magnitudes of trends were determined by Sen’s slope estimator. Temporal and spatial distribution of future extreme dryness and wetness was established by using the Standard Precipitation Index (SPI). The results show that RCMs adequately represented annual and inter-annual rainfall variability and the ensemble average outperformed individual models. Trend results for the projected rainfall suggest a significant decreasing trend in future rainfall (2016–2100) for all stations at p < 0.05. In addition, a general decreasing trend in the number of rainy days is projected for future climate, although the significance and magnitude varied with station location. Model results suggest an increased occurrence of future extreme events, particularly towards the end of the century. The findings are important for developing proactive sustainable strategies for future climate change adaption and mitigation.  相似文献   

Anticipated economic costs and benefits of ratification of the Kyoto Protocol by the State of Qatar     

Azhari F.M. Ahmed  M. J. Al Maslamani 《Climate Policy》2013,13(1):75-80

Abstract

Further ratification of the Kyoto Protocol by non-Annex 1 countries such as the State of Qatar will not affect the entrance into force of the Treaty; however, ratification remains an important decision due to other considerations, primarily the economic costs and benefits associated with ratification. As a member of the Organization of Petroleum Exporting Countries (OPEC), Qatar's economic position is closely allied with revenue generated from its oil and natural gas resources. Qatar expects adverse impacts from implementing the Kyoto Protocol, though the estimated magnitude varies enormously with different models. Also, the impacts depend significantly on how the implementation is done; for example, the kind of policies that other countries use. Qatar is able to counter adverse impacts by exploiting its greater share of natural gas and developing energy-intensive industries that produce nonenergy goods such as steel, petrochemicals, and chemicals. Furthermore, it is clear that clauses in the Protocol can be developed to protect OPEC interests, and if Qatar does not ratify the Protocol, it will be excluded from the subsequent rule-making processes. On balance, there are benefits to ratifying the Treaty, and there is also a strong need for extensive further research.  相似文献   

Effect of ion temperature on arbitrary amplitude Kinetic Alfvén solitons in a plasma with a q-nonextensive electron velocity distribution     

M. K. Ahmed  O. P. Sah 《Astrophysics and Space Science》2014,353(1):145-150

Taking into account of ion temperature effect, existence conditions of arbitrary amplitude solitary Kinetic Alfvén Waves (KAWs) in a plasma with q-nonextensive electrons are investigated by the conventional Sagdeev pseudo potential method. It is found that only solitons with density hump can exist, the amplitude of which depends sensitively on the parameter q, ion temperature ( \(\sigma= \frac{T_{i}}{T_{e}}\) ) and plasma β. There is an upper limit of solitary wave amplitude which decreases with increase of q, σ and β. The amplitude of solitary KAWs is found to increase with increase in ion temperature. The results obtained in the framework of Maxwellian distribution are reproduced when q→1.  相似文献   

NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic‐bearing fluids on Mars     

Yangting Lin  Ahmed El Goresy  Sen Hu  Jianchao Zhang  Philippe Gillet  Yuchen Xu  Jialong Hao  Masaaki Miyahara  Ziyuan Ouyang  Eiji Ohtani  Lin Xu  Wei Yang  Lu Feng  Xuchao Zhao  Jing Yang  Shin Ozawa 《Meteoritics & planetary science》2014,49(12):2201-2218

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ¹³C = ?12.8 to ?33.1‰) are significantly lighter than Martian atmospheric CO₂ and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic‐rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.  相似文献   

Pan African layered diorite-tonalite-granodiorite from Sinai massif: an open system fractionation at a subduction zone     

Ahmed A. El-Metwally  Mohmed E. Ibrahim 《地学学报》1995,7(3):367-374

This paper reports on the occurrence of layered Pan African dioritetonalite-granodiorite (DTG) rocks. The layering is marked by alternation of melanocratic (M) layers (diorites and tonalites) and leucocratic (L) layers (tonalites and granodiorites). M-samples have cumulus biotite+hornblende+relict pyroxene+plagioclase+K-feldspars+magnetite+apatite, and have transitional calc-alkaline and metaluminous affinities. They were derived from subduction-related magma enriched in Rb, Ba, K and LREE and depleted in Sr and Nb. L-samples have cumulus plagioclase+hornblende. They are enriched in Sr and depleted in Rb, Ba, K, Nb and LREE. They have calc-alkaline and peraluminous affinites.
The formation of the rhythmic layers of DTG composition can be attributed to periodical replenishment of pulses of basic magma into a more evolved acidic magma chamber under open system conditions. Field relations, mineralogy and element concentration among the M- and L-layers indicate that at the subduction zone, the ascending magma was contaminated with lower crustal materials (marginal basin metasediments) which led to LILE-enrichment, Nb-depletion and transition from calc-alkaline to alkaline and from metaluminous to peraluminous affinities as well.  相似文献   

Hook whistlers observed at low latitude ground station Varanasi     

P. N. Khosa  Lalmani  M. M. Ahmed  B. D. Singh 《Earth, Moon, and Planets》1983,28(1):29-35

Employing the Haselgrove ray tracing equations and a diffusive equilibrium model of the ionosphere, the propagation characteristics of hook whistlers recorded at low-latitude ground station Varanasi (geomag. lat., 16°6′.N) are discussed. It is shown that the two traces of the hook whistlers are caused by the VLF waves radiated from the return stroke of a lightning discharge which after penetrating the ionosphere at two different entry points, propagated to the opposite hemisphere in the whistler mode and were received at 16 geomagnetic latitude. Further the crossing of ray paths for the same frequency leads to the explanation of the hook whistler. The lower and higher cut-off frequencies are explained in terms of their deviating away from the bunch of the recorded whistler waves and crossing of ray paths for the same frequency.  相似文献   

Instability of a streaming jet under the influence of vacuum magnetic fields     

Ahmed E. Radwan  Samia S. Elazab 《Astrophysics and Space Science》1989,158(2):281-295

The magnetohydrodynamic stability of a streaming liquid cylinder subject to surface tension and pervaded by a magnetic vacuum field has been elaborated for all axisymmetric and non-axisymmetric disturbances. The dispersion relation is obtained and studied analytically and numerically. the streaming has always a destabilizing effect. The axial magnetic fields inside and outside the jet have always stabilizing effects for all perturbations. The transverse magnetic field has a destabilizing effect. However, if the axial field intensity is so high and paramount over that the transverse field, the destabilizing character of the model is suppressed. The latter is satisfied if the Alfvén wave velocity is greater than the equilibrium liquid velocity.  相似文献   

Lie transforms and the Hamiltonization of non-Hamiltonian systems   总被引：1，自引：0，他引：1  

Ahmed Aly Kamel 《Celestial Mechanics and Dynamical Astronomy》1971,4(3-4):397-405

To develop the perturbation solution of the non-Hamiltonian system of differential equationsy=g(y, t; ), it is sufficient to obtain the perturbation solution of a Hamiltonian system represented by the HamiltonianK=Y·g(y, t; ) which is linear in the adjoint vectorY. This Hamiltonization allows the direct use of the perturbation methods already established for Hamiltonian systems. To demonstrate this fact, a Hamiltonian algorithm developed by this author and based on the Lie-Deprit transform is applied to the Hamiltonized system and is shown to be equivalent to the application of the non-Hamiltonian form of this same algorithm to the original non-Hamiltonian system.  相似文献