Study of Aerosol Direct and Indirect Effects and Auto-conversion Processes over the West African Monsoon Region Using a Regional Climate Model     

Zeinab SALAH  Ahmed SHALABY  Allison L.STEINER  Ashraf S.ZAKEY  Ritesh GAUTAM  Mohamed M.ABDEL WAHAB 《大气科学进展》2018,35(2):182-194

This study assesses the direct and indirect effects of natural and anthropogenic aerosols(e.g., black carbon and sulfate)over West and Central Africa during the West African monsoon(WAM) period(June–July–August). We investigate the impacts of aerosols on the amount of cloudiness, the influences on the precipitation efficiency of clouds, and the associated radiative forcing(direct and indirect). Our study includes the implementation of three new formulations of auto-conversion parameterization [namely, the Beheng(BH), Tripoli and Cotton(TC) and Liu and Daum(R6) schemes] in Reg CM4.4.1,besides the default model's auto-conversion scheme(Kessler). Among the new schemes, BH reduces the precipitation wet bias by more than 50% over West Africa and achieves a bias reduction of around 25% over Central Africa. Results from detailed sensitivity experiments suggest a significant path forward in terms of addressing the long-standing issue of the characteristic wet bias in Reg CM. In terms of aerosol-induced radiative forcing, the impact of the various schemes is found to vary considerably(ranging from-5 to-25 W m~(-2)).  相似文献   

黄土孢粉分析的新途径——筛滤分析法   总被引：7，自引：0，他引：7  

李小强  周杰  A.R. Ashraf  Eva Wacker 《中国沙漠》1999,19(4):399-402

黄土-古土壤序列在全球古气候、古环境研究中占有不可替代的重要地位,而其中的孢粉是黄土高原生态环境演化过程中保存的直接生物学证据,它对建立黄土高原降水或湿度状况的时空变化特征,认识季风变迁的过程、规律以及未来发展趋势等具有重要的意义。随着黄土研究工作的不断深入,作为直接生物学证据的孢粉研究相对薄弱。其中最困扰的因素是从黄土中提取孢粉极其困难,分析技术上始终未能找到一个突破口,因此需要一种分析效果好、快捷、成本低的分析方法以获得大量高精度的孢粉数据。筛滤分析法正是为了适应黄土研究的需要而设计的一种新型的黄土孢粉分析方法。筛滤分析法利用真空状态下的气压差使样品在水中完全悬浮跳动,样品得到充分的冲洗并促使孢粉与其它无机质与有机质分离。相对真空的状态减少了微细颗粒对极为细小的网眼的阻塞,重力作用促使水及各类颗粒不断冲击筛网,使粒径小于10μm的物质较容易被过滤到聚水容器中,而孢粉与较少的大颗粒物质则被隔离在筛网之上,这使我们很容易用重液浮选出干净、清晰的孢粉底样。筛滤分析法与常规的黄土孢粉分析相比,具有以下特点:①大大降低了分析样品的重量及药品的消耗,一般仅需样品30 g左右,是常规分析法用量的1/6~1/8。②整个分析流程短, 12个样品一个流程仅需3~4 d。③筛滤分析法使孢粉几乎全部被隔离在筛网上而丢失极少,提高了黄土孢粉研究精度。④筛滤分析法几乎不破坏孢粉的结构,孢粉底样干净、清晰。使用筛滤分析法共分析耀县全新世黄土剖面69块孢粉样品,均发现数量不等的孢粉。孢粉底样干净、杂质少,结构清楚。共统计孢粉14978粒,分属27个科属,这些科属包括了黄土高原主要的孢粉类型。从孢粉结果可以初步确定,在全新世时期,位于黄土高原南缘的耀县地区,草本植物占全部孢粉总量的93.6%,而乔木植物仅占孢粉总量的4.7%。在整个剖面中没有出现乔木植物含量超过30%,可以认为在黄土高原的全新世时期是以草原植被为主,并无森林生长。  相似文献   

AGN Lifetimes in UV-selected Galaxies:A Clue to Supermassive Black Hole-galaxy Coevolution     

Xiaozhi Lin  Yongquan Xue  Guanwen Fang  Lulu Fan  Huynh Anh N Le  Ashraf Ayubinia 《天文和天体物理学研究(英文版)》2022,(1):104-113

The coevolution between supermassive black holes(SMBHs)and their host galaxies has been proposed for more than a decade,albeit with little direct evidence about...  相似文献   

Isolation and characterization of alkane degrading bacteria from petroleum reservoir waste water in Iran (Kerman and Tehran provenances)     

Mehdi Hassanshahian  Mohammad Ahmadinejad  Hamid Tebyanian  Ashraf Kariminik 《Marine pollution bulletin》2013

Petroleum products spill and leakage have become two major environmental challenges in Iran. Sampling was performed in the petroleum reservoir waste water of Tehran and Kerman Provinces of Iran. Alkane degrading bacteria were isolated by enrichment in a Bushnel–Hass medium, with hexadecane as sole source of carbon and energy. The isolated strains were identified by amplification of 16S rDNA gene and sequencing. Specific primers were used for identification of alkane hydroxylase gene. Fifteen alkane degrading bacteria were isolated and 8 strains were selected as powerful degradative bacteria. These 8 strains relate to Rhodococcus jostii, Stenotrophomonas maltophilia, Achromobacter piechaudii, Tsukamurella tyrosinosolvens, Pseudomonas fluorescens, Rhodococcus erythropolis, Stenotrophomonas maltophilia, Pseudomonas aeruginosa genera. The optimum concentration of hexadecane that allowed high growth was 2.5%. Gas chromatography results show that all strains can degrade approximately half of hexadecane in one week of incubation. All of the strains have alkane hydroxylase gene which are important for biodegradation. As a result, this study indicates that there is a high diversity of degradative bacteria in petroleum reservoir waste water in Iran.  相似文献   

A novel hybrid approach of Bayesian Logistic Regression and its ensembles for landslide susceptibility assessment     

Mousa Abedini  Bahareh Ghasemian  Ataollah Shirzadi  Himan Shahabi  Kamran Chapi  Binh Thai Pham 《国际地球制图》2013,28(13):1427-1457

Abstract

A novel artificial intelligence approach of Bayesian Logistic Regression (BLR) and its ensembles [Random Subspace (RS), Adaboost (AB), Multiboost (MB) and Bagging] was introduced for landslide susceptibility mapping in a part of Kamyaran city in Kurdistan Province, Iran. A spatial database was generated which includes a total of 60 landslide locations and a set of conditioning factors tested by the Information Gain Ratio technique. Performance of these models was evaluated using the area under the ROC curve (AUROC) and statistical index-based methods. Results showed that the hybrid ensemble models could significantly improve the performance of the base classifier of BLR (AUROC?=?0.930). However, RS model (AUROC?=?0.975) had the highest performance in comparison to other landslide ensemble models, followed by Bagging (AUROC?=?0.972), MB (AUROC?=?0.970) and AB (AUROC?=?0.957) models, respectively.  相似文献   

Geochemistry, petrogenesis and radioactivity of El Hudi I-type younger granites, South Eastern Desert, Egypt     

Ashraf Emam  Nasser M. Moghazy  Anas M. El-Sherif 《Arabian Journal of Geosciences》2011,4(5-6):863-878

The present study deals with geochemical characteristics and petrogenesis of three younger granite varieties (coarse-grained biotite-muscovite granites (CBG), garnetiferous muscovite granites (GMG) and Abu Aggag biotite granites (AAG)) in El-Hudi area, east of Aswan, southeastern desert of Egypt. Mineral chemistry and whole rock chemistry data revealed that all granites have high SiO₂ (70.8-74.7 wt.%), Al₂O₃ (12.8-14.3 wt.%), Na₂O and K₂O (>3.2 wt.%) contents with high Na₂O/K₂O ratios (～>1). Plagioclase feldspars range in composition from albite to oligoclase (An_9-27) in CBG, oligoclase (An_13-18) in GMG and albite (An_2-6) in AAG. Potash feldspars are mainly perthitic microcline and exhibit chemical formulae as (Or_93-96 Ab_7-4 An₀) in CBG, (Or_95-98 Ab_5-2 An₀) in GMG and (Or_82-98 Ab_18-2 An₀) in AAG. Biotites from CBG and GMG are enriched in (Mg and Ti) and depleted in (Al, Fe, Mn and K) compared with those of AAG. Biotites from CBG and GMG had been derived from calc-alkaline magma, whereas those from AAG had been derived from peraluminous magma. Chlorites from CBG and GMG are Mg-Fe bearing, while that from AAG is Fe-rich chlorite (chamosite). The CBG and GMG are Mg-rich monzogranites originated from high-K calc-alkaline magma with metaluminous to mildly peraluminous nature. The AAG are Fe-rich monzogranites to syenogranites generated from high-K calc-alkaline peraluminous magma. Both CBG and GMG are late- to post-orogenic granites, while the AAG are post-orogenic granites. All three granite varieties are considered as evolved I-type granites, formed under low to moderate water pressures (～ 0.5-7 kbars) and relatively high ranges of crystallization temperatures (～700-890°C). They were generated from partial melting of crustal materials at lower (CBG >30 km depth) and intermediate (GMG & AAG ～20-30 km depth) levels. The crystal fractionation was the predominant process during differentiation of parent magmas of these granites. Geochemical characteristics manifest that AAG represent the highly fractionated member of magma cycle differs from that produced CBG and GMG. The CBG are relatively enriched in both U and Th existing only within the accessory minerals such as zircon, sphene, and allanite.  相似文献   

Sorption of lead by chemically modified rice bran     

T. Fatima  R. Nadeem  A. Masood  R. Saeed  M. Ashraf 《International Journal of Environmental Science and Technology》2013,10(6):1255-1264

In this work, the effectiveness of native and chemically modified rice bran to remove heavy metal Pb(II) ions from aqueous solution was examined. Chemical modifications with some simple and low-cost chemicals resulted in enhancement of the adsorption capacities and had faster kinetics than native rice bran. Experiments were conducted in shake flasks to monitor the upshot of parameters over a range of pH, initial Pb(II) concentrations and contact times using a batch model study. The sorption capacities q (mg g^?1) increased in the following order: NaOH (147.78), Ca(OH)₂ (139.08), Al(OH)₃ (127.24), esterification (124.28), NaHCO₃ (118.08), methylation (118.88), Na₂CO₃ (117.12) and native (80.24). The utmost uptake capacity q (mg g^?1) was shown by NaOH-pretreated rice bran. The results showed that, using NaOH-modified rice bran, the chief removal of Pb(II) was 74.54 % at pH 5, primary Pb(II) concentration 100 mg L^?1 and contact time 240 min. Equilibrium isotherms for the Pb(II) adsorption were analyzed by Langmuir and Freundlich isotherm models. The Langmuir isotherm model, showing Pb(II) sorption as accessible through the high value of the correlation coefficient (R ² = 0.993), showed a q _max value of 416.61 mg g^?1. The kinetic model illustrated adsorption rates well, depicted by a second order, which gives an indication concerning the rate-limiting step. Thermodynamic evaluation of the metal ion ?G ^o was carried out and led to the observation that the adsorption reaction is spontaneous and endothermic in nature. NaOH chemically modified rice bran was a superb biosorbent for exclusion of Pb(II) and proved to be excellent for industrial applications.  相似文献   

Mineralogy and microchemistry of the Egat gold deposit, South Eastern Desert of Egypt     

Ashraf Emam 《Arabian Journal of Geosciences》2013,6(12):4619-4634

Gold-bearing quartz lodes from the Egat gold mine, South Eastern Desert of Egypt, are associated with pervasively silicified, highly sheared ophiolitic metagabbro and island-arc metavolcanic rocks. The mineralized quartz veins and related alteration haloes are controlled by NNW-trending shear/fault zones. Microscopic and electron probe microanalyses (EPMA) data of the ore and gangue minerals reveal that fine-grained auriferous sulfarsenides represent early high-temperature (355–382 °C) phases, with formation conditions as (fS₂?=??10, and fO₂ around ?31). A late, low-temperature (302–333 °C) assemblage includes coarse pyrite, arsenopyrite, and free-milling gold grains (88–91 wt.% Au), with formation conditions as (fS₂?=??8 and fO₂ around ?30). Gold was impounded within early sulfarsenides, while free-milling gold blebs occur along microfractures in quartz veins and as inclusions in late sulfides. Infiltration of hydrothermal fluids under brittle–ductile shear conditions led to mobilization of refractory Au from early sulfarsenide phases and reprecipitated free gold, simultaneous with silicification of the host rocks. The positive correlation between Au and As favors and verifies the use of As as the best pathfinder for gold targets, along the NNW-trending shear zones.  相似文献   

Evidences of Holocene transgression on Domingos Petrolini Swamp, southern coastal plain, Rio Grande do Sul, Brazil     

Soraia G.Bauermann  Paulo C.P.Neves  Marleni Marques-Toigo  Abdul R.Ashraf 《东北亚地学研究》2005,(Z1)

The Domingos Petrolini Swamp, located on the Southern Coastal Plain of Rio Grande do Sul, near the town of Rio Grande, constitutes an ample holocene lagoonal deposit. Events related to the holocene transgression and their diverse phases of glacial-eustatic ocillations were found through palynological analysis. Bases on these palynological data, four distinct phases to the paleoenvironmental evolution of the ecosystem were identified. It has also shown a transgressive restricted marine sequence on the base , which suggests the existence of a coastal brackish lagoon or a marisme type of environment. Later, there was a gradation for continentality conditions along with a scarce pollinical record. The third phase is characterized by the presence of marine components and halophyte vegetation, showing another transgressive event in that place. Lastly, the end of direct marine influence over the swamp was recorded and also the vegetation development as it appears these days.  相似文献   

Hydrological and geochemical constraints on the mechanism of formation of arsenic contaminated groundwater in Sonargaon,Bangladesh     

Takaaki Itai  Harue Masuda  Ashraf A. Seddique  Muneki Mitamura  Teruyuki Maruoka  Xiaodong Li  Minoru Kusakabe  Biswas K. Dipak  Abida Farooqi  Toshiro Yamanaka  Shinji Nakaya  Jun-ichi Matsuda  Kazi Matin Ahmed 《Applied Geochemistry》2008

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