EFFECTIVE TEMPERATURE COMFORT INDICES FOR SOME MALAYSIAN TOWNS     

Mohammed Ilyas  MSc.  Ph.D.    Pang Chong Yen  BSc.  Chan Ah Wah  BSc. 《Singapore journal of tropical geography》1981,2(1):27-31

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World conference on natural disaster reduction     

Mohammed I. El-Sabh 《Natural Hazards》1994,9(3):333-352

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Seasonal variation of carbon fluxes in a sparse savanna in semi arid Sudan     

Jonas Ardö  Meelis Mölder  Bashir Awad El-Tahir  Hatim Abdalla Mohammed Elkhidir 《Carbon balance and management》2008,3(1):1-18

Background

Large spatial, seasonal and annual variability of major drivers of the carbon cycle (precipitation, temperature, fire regime and nutrient availability) are common in the Sahel region. This causes large variability in net ecosystem exchange and in vegetation productivity, the subsistence basis for a major part of the rural population in Sahel. This study compares the 2005 dry and wet season fluxes of CO₂ for a grass land/sparse savanna site in semi arid Sudan and relates these fluxes to water availability and incoming photosynthetic photon flux density (PPFD). Data from this site could complement the current sparse observation network in Africa, a continent where climatic change could significantly impact the future and which constitute a weak link in our understanding of the global carbon cycle.

Results

The dry season (represented by Julian day 35–46, February 2005) was characterized by low soil moisture availability, low evapotranspiration and a high vapor pressure deficit. The mean daily NEE (net ecosystem exchange, Eq. 1) was -14.7 mmol d^-1 for the 12 day period (negative numbers denote sinks, i.e. flux from the atmosphere to the biosphere). The water use efficiency (WUE) was 1.6 mmol CO₂ mol H₂O^-1 and the light use efficiency (LUE) was 0.95 mmol CO₂ mol PPFD^-1. Photosynthesis is a weak, but linear function of PPFD. The wet season (represented by Julian day 266–273, September 2005) was, compared to the dry season, characterized by slightly higher soil moisture availability, higher evapotranspiration and a slightly lower vapor pressure deficit. The mean daily NEE was -152 mmol d^-1 for the 8 day period. The WUE was lower, 0.97 mmol CO₂ mol H₂O^-1 and the LUE was higher, 7.2 μmol CO₂ mmol PPFD^-1 during the wet season compared to the dry season. During the wet season photosynthesis increases with PPFD to about 1600 μmol m^-2s^-1 and then levels off.

Conclusion

Based on data collected during two short periods, the studied ecosystem was a sink of carbon both during the dry and wet season 2005. The small sink during the dry season is surprising and similar dry season sinks have not to our knowledge been reported from other similar savanna ecosystems and could have potential management implications for agroforestry. A strong response of NEE versus small changes in plant available soil water content was found. Collection and analysis of flux data for several consecutive years including variations in precipitation, available soil moisture and labile soil carbon are needed for understanding the year to year variation of the carbon budget of this grass land/sparse savanna site in semi arid Sudan.  相似文献   

Compressibility and shear strength of a residual soil     

Yahia E.-A. Mohamedzein  Mohammed H. Aboud 《Geotechnical and Geological Engineering》2006,24(5):1385-1401

A detailed study was performed to investigate the compressibility and the shear strength of a residual soil in Omdurman, Sudan. The soil resulted from weathering of sandstone and mudstone. The soil is classified as sandy clayey silt (MH-CH) and is generally partially saturated. Consolidation tests were performed to study the compressibility of the soil and UU, CIU and insitu tests (CPT and SPT) were performed to study the shear strength characteristics of the soil. The characteristics of this residual soil can generally be predicted using correlations proposed in the literature for transported soils. The soil is of low to medium compressibility and exhibits slight apparent overconsolidation behavior. The soil dilates during shear and shows no long term effective cohesion. Problems associated with open cuts in this soil are attributed to loss of strength upon saturation.  相似文献   

Origin and Formational Environment of Noda-Tamagawa Manganese Ore, Northeast Japan: Constraints from Isotopic Studies     

Mohammed El Rhazi  Ken-ichiro Hayashi 《Chemie der Erde / Geochemistry》2003,63(2):149-162

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Assessment of contaminants in Dubai coastal region, United Arab Emirates     

H. A. Al-Darwish  E. A. Abd El-Gawad  F. H. Mohammed  M. M. Lotfy 《Environmental Geology》2005,49(2):240-250

Coastal uses and other human activities have inevitably impinged on the Gulf environment; therefore, these regions require continuous monitoring. The investigated area covered the maximum fragments of Dubai coastal region in the Arabian Gulf. The determination of major oxides and trace metal concentrations in Dubai sediments revealed three heavily and moderately contaminated regions. One is in the far northeastern part at Al-Hamriya Sts 1–3 and contaminated by Fe, Cu, Pb, and Zn; the second is in the mid-northeastern part at Dry Docks and contaminated by Cu, Ni, Pb, and Zn; and finally, the third is in the near southwestern part at Dubal and contaminated by Fe, Mg, Cr, Ni, and Zn. Al-Hamriya St 3 represented the highest values of Cu, Pb, and Zn, whereas Dubal exhibited the maximum values of Fe, Mg, Ba, Cr, Mn, Ni, and V. The anthropogenic discharge and natural deposits are the main sources of contamination. In general, all trace and major elements showed the minimal levels at Jebel Ali Sanctuary (Sts 11, 12, 13) except for Sr and Ca, which showed their maximum values. The highest concentrations of Ca and Sr are mainly attributed to carbonate gravel sands and sands, which cover most stations. Each of V and Ni showed negative correlation with TPH, which may be indicated that the source of oil contamination in the region is not related to crude oil but mostly attributable to anthropogenic sources. The significant positive correlation, which was found between trace metals and TOC indicates that organic matter plays an important role in the accumulation of trace metals in case of Cu, Zn, and Pb.  相似文献   

Application of a revised hydrostratigraphical classification and nomenclature to the Mesozoic and Cenozoic succession of Saudi Arabia   总被引：1，自引：0，他引：1  

Abdulaziz M. Al-Bassam  Mohammed E. Al-Dabbagh  Mohammed Tahir Hussein 《Journal of African Earth Sciences》2000,30(4):917

At the dawn of the 21st century many parts of the world are suffering a shortage of water resources. Arid and semi-arid areas in particular are facing challenges and increasing pressure is being put on their groundwater management plans. Such a situation created an urgent need to put forward a design for classification and nomenclature that can help to differentiate highly productive zones from small locally exploited productive zones. A previously proposed hydrostratigraphical classification and nomenclature scheme is revised, modified, and applied to the Mesozoic-Cenozoic sedimentary succession of Saudi Arabia. The scheme utilised in the present paper is modified to include, in addition, productivity, water quality criteria, usability, and recharge as criteria reflecting the hydrogeological importance of the productive zones.The Triassic Sudair Mega-aquitard forms the lower hydrostratigraphic boundary for the Ad-Dahna'a Aquasystem. The Ad-Dahna'a Aquasystem comprises two aquagroups: the Riyadh and Rub'Al-Khali Aquagroups. Each aquagroup is in turn subdivided into superaquifers, aquifers and possibly subaquifers, separated by aquitards of different ranks. The physical and hydrogeological characteristics of each unit are also discussed.  相似文献   

Stratigraphy of multiple piston-core sediments for the last 30,000 years from Lake Biwa, Japan     

Keiji Takemura  Akira Hayashida  Makoto Okamura  Hiromi Matsuoka  Mohammed Ali  Mohammed Ali  Yoshiki Kuniko  Masayuki Torii  Masayuki Torii 《Journal of Paleolimnology》2000,23(2):185-199

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Origin of peraluminous granites and granodiorites, Iberian massif, Spain: an experimental test of granite petrogenesis   总被引：27，自引：0，他引：27  

Antonio Castro  Alberto E. Patiño Douce  L. Guillermo Corretgé  Jesús D. de la Rosa  Mohammed El-Biad  Hassan El-Hmidi 《Contributions to Mineralogy and Petrology》1999,135(2-3):255-276

The discrimination between potential source materials involved in the genesis of Iberian granites and granodiorites, as well as the role of mantle-crust interactions, are examined using constraints imposed by melting experiments, melting-assimilation experiments and Sr-Nd isotope systematics. The Sr-Nd isotope relationships indicate the existence of different genetic trends in which juvenile mantle materials are involved by different mechanisms: (1) a source trend, traced by a particular evolution of the pre-Hercynian basement and indicating mantle participation at the time of sedimentation; (2) a set of magmatic trends traced by gabbro-tonalite-enclave-granodiorite associations, implying the incorporation of new mantle material at the time of granite generation. These relationships strongly support a pure crustal origin for the peraluminous leucogranites, derived from partial melting of crustal protoliths, and a hybrid origin for the peraluminous granodiorites. These granodiorites are the most abundant granitic rocks of the Central Iberian zone (CIZ) of the Iberian massif, implying that processes of hybridisation by assimilation and/or magma mixing played an important role in granitoid production during the Hercynian orogeny. These hypotheses have been tested by means of melting and assimilation experiments. Melting experiments in the range 800–900 °C and at pressures of 3, 6, 10 and 15 kbar indicate that: (1) several potential source materials such as Bt-Ms gneisses and metagreywackes are suitable for the production of peraluminous leucogranite melts; (2) the melt compositions are always leucogranitic, regardless of pressure; (3) pressure exerts a strong influence on the fertility of the source: experiments at 3 kbar produce more than 20 vol% of melt, compared with less than 5 vol% of melt produced at 10 and 15 kbar and at the same temperature. The melting-assimilation experiments carried out at 1000 °C and 4, 7 and 10 kbar and using a proportion of 50% gabbro and 50% gneiss give high melt proportions (more than 50 vol.%) and noritic residues. These melts have the composition of leucogranodiorites, and overlap with part of the compositional range of peraluminous granodiorites of the Iberian massif. The generation of more mafic granodiorites may be explained by the incorporation of some residual orthopyroxene to the granodiorite magmas. The low solubility of Fe + Mg prevents the generation of granodiorite melts with more than 3 wt% of MgO + FeO at all crustal pressures. The large volumes of peraluminous, hybrid granodiorites, produced by assimilation of crustal rocks by mantle magmas, imply that an important episode of crustal growth took place during the Late-Palaeozoic Hercynian orogeny in the Iberian massif. Received: 30 June 1998 / Accepted: 27 November 1998  相似文献   

Identification of palaeochannels around Cauvery river near Talakad, Karnataka using remote sensing data     

M A Mohammed Aslam  A Balasubramanian 《Journal of the Indian Society of Remote Sensing》2001,29(4):237-242

Visual interpretation of satellite images could help in the identification of present and past landforms. An attempt has been made to identify the palaeochannels of the Cauvery river in Karnataka state through visual interpretation of IRS-1C, LISS III False Colour Composites (FCC). In order to assess their inter-relationship with other hydrogeomorphic elements, various geomorphic units have been mapped. Major geomorphic units like alluvial plain, pediplain, valley fill. residual hill, ridges, meander scar, channel bars and water bodies have been demarcated. Considering the hydrogeomorphic setup of the palaeochannels. it is inferred that the disposition of palaeochannels of the area are controlled by the geology and structure and the prevailing geomorphic process.  相似文献