Al hematites prepared by homogeneous precipitation of oxinates: material characterization and determination of the Morin transition     

G. M. da Costa  E. Van San  E. De Grave  R. E. Vandenberghe  V. Barrón  L. Datas 《Physics and Chemistry of Minerals》2002,29(2):122-131

A novel method for synthesis of aluminium hematites, based upon the homogeneous precipitation of Fe and Al oxinates in various proportions, is presented. The precursor precipitates are heated in air at 700?°C. X-ray diffraction, thermal analyses, BET, FTIR, optical reflection analysis, TEM and Mössbauer spectroscopy at room temperature and 80?K of the resulting products indicate that single-phase hematites are formed with structural Al substitution of up to 10 at%. Interestingly, the particle size (>100?nm) is not substantially reduced by the Al content. Although it remains difficult to obtain a homogeneously distributed Al substitution in the final hematite, this processing line offers a unique opportunity to separate the effects of grain size and Al substitution on the Morin transition temperature (T _M) of Al hematite. From the comparison between the present hematites and a series of Al-substituted hematites with lepidocrocite as precursor, it could be shown that the effect on T _M, associated with a change of a factor 10 in grain size, is about 1/3 of the effect caused by a change of 10 in the degree of substitution. Finally, it is suggested that proper thermal treatments under different conditions of the same precursors are likely to produce spinel phases.  相似文献   

Mixing, sediment accumulation and focusing using 210Pb and 137Cs     

San Miguel  J.P. Bolívar  R. García-Tenorio 《Journal of Paleolimnology》2003,29(1):1-11

The Portil lagoon is a natural freshwater reservoir located at the southwest of Spain, near the coast. In its surroundings an important tourist complex has been developed since the earlier 1970s. This has resulted in increased loads of nutrients, specially during summer months. In order to evaluate the impact from humans on the lagoon caused by anthropogenic activities, we have determined vertical profiles of excess ²¹⁰Pb and ¹³⁷Cs in a sediment core taken from its bottom. Vertical profile of excess ²¹⁰Pb seems to indicate that the sediment core was affected by large-scale mixing processes. Nevertheless this possibility was ruled out based on the shape of the ¹³⁷Cs vertical distribution after modelling the ¹³⁷Cs profile considering large-scale mixing. The chronology developed from ²¹⁰Pb and ¹³⁷Cs has allowed us to calculate the temporal evolution of the mass sedimentation rate during the last century. This mass sedimentation rate increased in 1973: from 0.08(2) g cm^-2 a^-1 in the period 1900-1973 to 0.17(5) g cm^-2 a^-1 in the period 1973-1995. This increase could be related to land-movements in the drainage area and to permitted sewage inputs into the lagoon, both with its origin in the growing/running of the surrounding tourist complex.  相似文献   

“地球动力学”的研究现状与展望——第32届国际地质大会研究成果综述     

刘少峰  程三友  张会平  苏三 《现代地质》2004,18(4):404-414

第32届国际地质大会通过按地域和构造作用过程等形式划分11个专题会场,展示了地球动力学的研究成果。其成果主要包括特提斯域构造演化及其不同阶段的块体裂解、拼合及后期改造的细节过程,地质历史中的超大陆分布和成因,俯冲—碰撞带深部构造和变质机制,安第斯山(Andes)缓倾角平坦式俯冲过程及其地壳变形和岩浆作用的响应,显微构造对动力作用过程的影响和控制,地壳和上地幔熔融、流变学和动力学意义,大洋岩石圈构造与演化,大陆地盾区构造和再活动,稳定大陆区地震,空间大地测量学和现代板块运动等方面。这些研究成果充分显示了地球动力学研究具有多学科、多手段(如古地磁、超深钻、地球物理、大地测量和GPS等)、多尺度(宏观、微观)和多时期、全面、综合、并逐步接近定时、定位和定量地探索和研究的特点,它从地球(主要为上地幔和地壳)的组成、结构构造入手,逐步认识地球(主要为地球岩石圈)的演化和动力学。  相似文献   

Projected rainfall and temperature changes over Malaysia at the end of the 21st century based on PRECIS modelling system     

Jui Le Loh  Fredolin Tangang  Liew Juneng  David Hein  Dong-In Lee 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(2):191-208

This study investigates projected changes in rainfall and temperature over Malaysia by the end of the 21st century based on the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2, A1B and B2 emission scenarios using the Providing Regional Climates for Impacts Studies (PRECIS). The PRECIS regional climate model (HadRM3P) is configured in 0.22° × 0.22° horizontal grid resolution and is forced at the lateral boundaries by the UKMO-HadAM3P and UKMOHadCM3Q0 global models. The model performance in simulating the present-day climate was assessed by comparing the modelsimulated results to the Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation (APHRODITE) dataset. Generally, the HadAM3P/PRECIS and HadCM3Q0/PRECIS simulated the spatio-temporal variability structure of both temperature and rainfall reasonably well, albeit with the presence of cold biases. The cold biases appear to be associated with the systematic error in the HadRM3P. The future projection of temperature indicates widespread warming over the entire country by the end of the 21st century. The projected temperature increment ranges from 2.5 to 3.9°C, 2.7 to 4.2°C and 1.7 to 3.1°C for A2, A1B and B2 scenarios, respectively. However, the projection of rainfall at the end of the 21st century indicates substantial spatio-temporal variation with a tendency for drier condition in boreal winter and spring seasons while wetter condition in summer and fall seasons. During the months of December to May, ~20-40% decrease of rainfall is projected over Peninsular Malaysia and Borneo, particularly for the A2 and B2 emission scenarios. During the summer months, rainfall is projected to increase by ~20-40% across most regions in Malaysia, especially for A2 and A1B scenarios. The spatio-temporal variations in the projected rainfall can be related to the changes in the weakening monsoon circulations, which in turn alter the patterns of regional moisture convergences in the region.  相似文献   

Bioaccumulation of heavy metals in <Emphasis Type="Italic">Limnobium laevigatum</Emphasis> and <Emphasis Type="Italic">Ludwigia peploides</Emphasis>: their phytoremediation potential in water contaminated with heavy metals     

M. Rocío Fernández San Juan  Carolina B. Albornoz  Karen Larsen  Roberto Najle 《Environmental Earth Sciences》2018,77(11):404

Contamination with heavy metals in surface and groundwater is a threat to human health and ecosystems. Due to this, the need arises to remediate water polluted through ecological and profitable technologies, such as phytoremediation. The objective of the work was to evaluate the concentration of lead (Pb) and zinc (Zn) in the floating macrophytes Limnobium laevigatum and Ludwigia peploides, after being exposed to contaminated water experimentally. In this way to be able to determine if these plants have mechanisms that allow them to accumulate the metals in the roots and to perform the translocation of these to different vegetative organs, L. laevigatum and L. peploides were placed in solutions contaminated with Pb ([Pb]?=?5 mg/l) and Zn ([Zn]?=?20 mg/l). The concentrations of metals in water, root and leaf samples were evaluated as a function of time (0, 1, 2 and 4 days). The determination of the metals was performed by the atomic absorption spectrophotometry technique. After 4 days of exposure to Pb and Zn, the plants showed high metal removal efficiencies of water, more to 70% in all cases. Pb was accumulated fundamentally by roots, while Zn was accumulated more in the leaves. In addition, the bioconcentration and translocation factors for each metal were calculated.  相似文献   

Development of groundwater favourability map using GIS-based driven data mining models: an approach for effective groundwater resource management     

Kehinde Anthony Mogaji  Hwee San Lim 《国际地球制图》2018,33(4):397-422

The development of groundwater favourability map is an effective tool for the sustainability management of groundwater resources in typical agricultural regions, such as southern Perak Province, Malaysia. Assessing the potentiality and pollution vulnerability of groundwater is a fundamental phase of favourability mapping. A geographic information system (GIS)-based Boolean operator of a spatial analyst module was applied to combine a groundwater potentiality map (GPM) model and a groundwater vulnerability to pollution index (GVPI) map, thereby establishing the favourable zones for drinking water exploration in the investigated area. The area GPM model was evaluated by applying a GIS-based Dempster–Shafer–evidential belief function model. In the evaluation, six geoelectrically determined groundwater potential conditioning factors (i.e. overburden resistivity, overburden thickness, aquifer resistivity, aquifer thickness, aquifer transmissivity and hydraulic conductivity) were synthesized by employing the probability-based algorithms of the model. The generated thematic maps of the seven hydrogeological parameters of the DRASTIC model were considered as pollution potential conditioning factors and were analysed with the developed ordered weighted average–DRASTIC index model algorithms to construct the GVPI map. Approximately 88.8 and 85.71% prediction accuracies for the Groundwater Potentiality and GVPI maps were established using the reacting operating characteristic curve method and water quality status–vulnerability zone relationship scheme, respectively. Finally, the area groundwater favourability map (GFM) model was produced by applying a GIS-based Boolean operator on the Groundwater Potentiality and GVPI maps. The GFM model reveals three distinct zones: ‘not suitable’, ‘less suitable’ and ‘very suitable’ zones. The area analysis of the GFM model indicates that more than 50% of the study area is covered by the ‘very suitable’ zones. Results produce a suitability map that can be used by local authorities for the exploitation and management of drinking water in the area. The study findings can also be applied as a tool to help increase public awareness of groundwater issues in developing countries.  相似文献   

Precambrian crustal components,plutonic associations,plate environment of the Hercynian Fold Belt of central Europe: Indications from a Nd and Sr isotopic study   总被引：8，自引：0，他引：8  

T. C. Liew  A. W. Hofmann 《Contributions to Mineralogy and Petrology》1988,98(2):129-138

Chichi-jima, Bonin Islands, consists of dominant Eocene submarine volcanic rocks, comprising boninites, andesites and dacites, and subordinate sedimentary rocks. The dacites occur frequently in breccias and pillows overlying a boninite pillow lava sequence. The boninite pillows are intruded by a multiple dike, in which a core boninite is chilled against outer dacites. A density-stratified chamber may have been capped by a dacite magma. The dacites, which can be divided into quartz dacite and quartz-free dacite, are differentiates from the boninite-forming magmas, because they vary continuously in composition from boninites through andesites. The quartz dacites, corresponding to rhyolite in SiO₂, are lower in Na₂O and K₂O than most orogenic dacites. Some of the dacites are characterized by ferropigeonite (Wo_7–16En_23–39Fs_68-54) phenocrysts and are clearly ferrodacite, producing variable amounts of Fs-rich normative pyroxenes. The relation of SiO₂ to total FeO/MgO ratio indicates that many of both types of dacites, with glasses in boninites, are enriched in total FeO despite the strong calc-alkalic affinity of boninites. The crystallization temperature of ferropigeonite with Mg value 30 in a quartz dacite is estimated to be 900° C and that in a quartz-free dacite to be 1050° C, which are unusually high for differentiated silicic rocks. Some Chichi-jima rocks are fresh, having a low ratio of Fe₂O₃ to FeO. On the basis of the experimental study of magmatic ferric-ferrous equilibria at 1 bar, the oxygen fugacities are calculated as 10^–13.6 bars at 900° C for a ferropigeonite quartz dacite and 10^–8.9 bars at 1200° C for a boninite with the lowest Fe³⁺/Fe²⁺. Both values lie below the quartz-fayalite-magnetite buffer line. The boninite series volcanic rocks have preserved low oxygen fugacities as well as high temperatures until the latest differentiation stage. The ferropigeonite phenocrysts have crystallized from the dacite magmas under the conditions of moderately high temperatures, very low oxygen fugacities and high total FeO and SiO₂ concentrations.  相似文献   

Genesis of granitoid batholiths of Peninsular Malaysia and implications for models of crustal evolution: Evidence from a NdSr isotopic and UPb zircon study     

T.C Liew  M.T McCulloch 《Geochimica et cosmochimica acta》1985,49(2):587-600

Nd, Sr and U-Pb isotopic data for the late Triassic West Coast Province batholiths and Permian to Triassic East Coast Province batholiths of Peninsular Malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made. Initial ?_Nd and ?_Sr values for granitoids from the West Coast Province range from ?6 to ?10 and +160(0.716) to +660(0.751) respectively. Nd model ages calculated based on a depleted mantle evolution model (T_DM^Nd) range from 1300 Ma to 1800 Ma and are in general agreement with the mid-Proterozoic upper intersection ages of U-Pb zircon reverse discordia (1500–1700 Ma). Initial ?_Nd and ?_Sr values for granitoids from the East Coast Province range from ?0.8 to ?6 and +10(0.705) to +130(0.714) respectively. Calculated T_DM^Nd ages of 900–1400 Ma for these granitoids are comparable to two U-Pb zircon reverse discordia intercepts that yield 800 Ma and 1350 Ma. The general agreement of U-Pb zircon inheritance ages and T_DM^Nd ages are interpreted to correspond to the Proterozoic ‘crust formation’ ages of the continental fragments represented by the West Coast and East Coast batholithic provinces. Mid-Proterozoic (~ 1300–1900 Ma) ‘crust formation’ ages are commonly shown by other Phanerozoic continental margin plutonic and volcanic belts. The ubiquitous mid-Proterozoic ‘crust formation’ ages and the absence of Archaean signatures suggest voluminous juvenile additions to the continental crust in the mid-Proterozoic. Such ages at continental margins would imply that many continental blocks had achieved very much their present-day extent by the mid-Proterozoic.  相似文献   

Diabatic wind and temperature profiles obtained from a 100 m tower: A statistical comparison of model performances     

R. San José  J. Regueroa  J. Casanova 《Boundary-Layer Meteorology》1986,37(1-2):1-15

More than 8000 10-min profiles of wind and temperature obtained during an extensive field experiment have been analyzed. The study was carried out in the environs of Valladolid (Spain) where a 100-m and a 6-m meteorological tower are located. Less than 20% of data were discarded due to equipment failure. Because of its exceptional flatness, the site is almost ideal for model performance comparisons.Predicted profiles of wind speed and potential temperature at 12, 26, 51, and 100 m heights were obtained using the methods proposed by Berkowicz and Prahm (1982) and San José (1983) based on values observed on a 6 m tower. Statistical t, F, and R tests were used to determine bias, scatter and correlation. The data were classified according to atmospheric stratification and height above ground. Finally, a determination was made of the predicted wind speeds and potential temperatures that fell within the 1 and 20% confidence ranges centered at the measured value. San José's method performed better than did that of Berkowicz and Prahm for the temperature profiles in both unstable and stable conditions. However, no significant differences were found for the wind speed profiles.  相似文献   

Nutrient mediated stress on the marine communities of a coastal lagoon (Puerto Galera, Philippines)     

M. L. San Diego-McGlone  C. L. Villanoy  P. M. Alio 《Marine pollution bulletin》1995,31(4-12):355-366

Puerto Galera Bay is a coastal lagoon with a variety of marine habitats and high species diversity. It is an area in the Phillippines where the growing influence of human activities is affecting the quality of its marine resources. This study examined the distribution and behaviour of nutrients and the physical hydrography of Puerto Galera Bay and determined how its physico-chemical nature affected the condition of biotic components in the bay. The relative importance of the nitrogen and phosphorus signals were used as indicators to implicate the influence of sewage and run-off into the bay. A nutrient pool accumulated in the bay as a result of low flushing rates. The interaction of hydrodynamic forcing with the biota have implications on the phytoplankton production and coral communities in the area.  相似文献