Capture of molybdenum in pyrite-forming sediments: role of ligand-induced reduction by polysulfides     

Trent P. Vorlicek  Mani D. Kahn  George R. Helz 《Geochimica et cosmochimica acta》2004,68(3):547-556

Capture of Mo by FeS₂ is an important sink for marine Mo. X-ray spectroscopy has shown that Mo forms Mo-Fe-S cuboidal clusters on pyrite. Reduction of Mo^VI must occur to stabilize these structures. Sulfide alone is a poor reductant for Mo, producing instead a series of Mo^VI thioanions (MoO_xS_4−x²⁻, x = 0-3). In solutions that contain both H₂S and S⁰-donors (i.e. polysulfides; dissolved S₈), Mo is transformed to Mo^IV or Mo^V₂ polysulfide/sulfide anions. This intramolecular reduction requires no external reducing agent. Remarkably, an oxidizing agent (S⁰ donor), rather than a reducing agent, stabilizes the reducible Mo^VI complex. Thiomolybdates and their reduction products do not precipitate spontaneously; solutions supersaturated by 10⁹ with respect to molybdenite, MoS₂, produce no precipitate in 40 days. In 10-minute exposures, pyrite can scavenge MoOS₃²⁻ and MoS₄²⁻ weakly at mildly alkaline pH but can scavenge an unidentified product of the S⁰-induced reduction of MoOS₃²⁻ very strongly. On the basis of these observations, a reaction pathway for Mo capture by pyrite is proposed. Conditions that favor Mo capture by this pathway also favor pyrite growth. Ascribing Mo capture simply to low redox potential is too simplistic and neglects the likely role of oxidizing S⁰-donors. The aqueous speciation of Mo in anoxic environments will be a function of the activity of zero-valent sulfur as well as the activity of H₂S(aq).  相似文献   

Vertical vibration of an embedded rigid foundation in a poroelastic soil   总被引：4，自引：0，他引：4  

T. Senjuntichai  S. Mani  R.K.N.D. Rajapakse 《Soil Dynamics and Earthquake Engineering》2006,26(6-7):626-636

This paper considers time-harmonic vertical vibration of an axisymmetric rigid foundation embedded in a homogeneous poroelastic soil. The soil domain is represented by a homogeneous poroelastic half space that is governed by Biot's theory of poroelastodynamics. The foundation is subjected to a time-harmonic vertical load and is perfectly bonded to the surrounding half space. The contact surface can be either fully permeable or impermeable. The dynamic interaction problem is solved by employing an indirect boundary integral equation method. The kernel functions of the integral equation are the influence functions corresponding to vertical and radial ring loads, and a ring fluid source applied in the interior of a homogeneous poroelastic half space. Analytical techniques are used to derive the solution for influence functions. The indirect boundary integral equation is solved by using numerical quadrature. Selected numerical results for vertical impedance of rigid foundations are presented to demonstrate the influence of poroelastic effect, foundation geometry, hydraulic boundary condition along the contact surface and frequency of excitation.  相似文献   

Numerical modelling of flow around coastal structures and scour prediction     

K. Jyothi  J. S. Mani  M. R. Pranesh 《Ocean Engineering》2002,29(4):417-444

The nearshore circulation and the wave characteristics are important parameters, which control coastline morphology. The interaction of nearshore circulation with coastal structures, modify the wave characteristics and seabed topography, often resulting in scour near the foundation of the structures. This paper deals with the numerical prediction of nearshore circulation induced due to wave setup in the nearshore region with and without the structure [(i) structure resting on seabed (ii) structure raised above the seabed]. It is also helps understand the deficiencies in studying the coastal characteristics by describing the flow field due to the wave velocity potential alone. Comparison of the results of both nearshore circulation and the wave potential model are discussed and the importance of the study and its prototype applications are highlighted.  相似文献   

Spatial distribution,sources and risk assessment of potentially toxic trace elements and rare earth elements in soils of the Langtang Himalaya,Nepal     

Lekhendra Tripathee  Shichang Kang  Dipesh Rupakheti  Qianggong Zhang  Roshan Man Bajracharya  Chhatra Mani Sharma  Jie Huang  Ayush Gyawali  Rukumesh Paudyal  Mika Sillanpää 《Environmental Earth Sciences》2016,75(19):1332

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Experimental and numerical investigations on zigzag porous screen breakwater     

J. S. Mani 《Natural Hazards》2009,49(2):401-409

Pile supported porous breakwaters are commonly adopted for shielding small-scale harbors, such as marinas, fishing harbors, and recreational harbors from external waves. To improve efficiency of such breakwaters, attempts have been made to provide a filter screen containing porous material. Possible alternative to the existing pile supported screen breakwaters is the zigzag breakwater. This article details on the numerical and experimental investigations carried out on the performance of zigzag porous screen breakwater. Results related to the wave amplification in front of the structure, wave reflection, and transmission, forces exerted by the waves on the structure are discussed. The studies clearly indicate that the transmission coefficient of the order of 0.5 can be achieved for H _i/gT ² > 0.008 for 50% submergence, whereas the reflection coefficient can be effectively reduced to 0.2. Reduction in wave force is of the order of 50% which is primarily due to reduction in reflection coefficient. Substantial reduction in wave force contributes directly to reduction in the cost of construction of the breakwater, a definite advantage over other similar breakwaters.  相似文献   

Fusion of remote sensing images     

V. R. S. Mani  S. Arivazhagan 《Journal of the Geological Society of India》2015,86(6):726-732

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Biotechnological advances in bioremediation of heavy metals contaminated ecosystems: an overview with special reference to phytoremediation   总被引：2，自引：0，他引：2  

D. Mani  Chitranjan Kumar 《International Journal of Environmental Science and Technology》2014,11(3):843-872

The ability of heavy metals bioaccumulation to cause toxicity in biological systems—human, animals, microorganisms and plants—is an important issue for environmental health and safety. Recent biotechnological approaches for bioremediation include biomineralization (mineral synthesis by living organisms or biomaterials), biosorption (dead microbial and renewable agricultural biomass), phytostabilization (immobilization in plant roots), hyperaccumulation (exceptional metal concentration in plant shoots), dendroremediation (growing trees in polluted soils), biostimulation (stimulating living microbial population), rhizoremediation (plant and microbe), mycoremediation (stimulating living fungi/mycelial ultrafiltration), cyanoremediation (stimulating algal mass for remediation) and genoremediation (stimulating gene for remediation process). The adequate restoration of the environment requires cooperation, integration and assimilation of such biotechnological advances along with traditional and ethical wisdom to unravel the mystery of nature in the emerging field of bioremediation. This review highlights better understanding of the problems associated with the toxicity of heavy metals to the contaminated ecosystems and their viable, sustainable and eco-friendly bioremediation technologies, especially the mechanisms of phytoremediation of heavy metals along with some case studies in India and abroad. However, the challenges (biosafety assessment and genetic pollution) involved in adopting the new initiatives for cleaning-up the heavy metals-contaminated ecosystems from both ecological and greener point of view must not be ignored.  相似文献   

Groundwater resources development in hard rock terrain - an approach using remote sensing and GIS techniques     

Jagannathan Krishnamurthy  Arul Mani  Venkatakrishnan Jayaraman  M Manivel 《International Journal of Applied Earth Observation and Geoinformation》2000,2(3-4)

To demonstrate the capabilities of remote sensing and Geographic Information System (GIS) techniques for groundwater resources development in hard rock terrains, specifically for the demarcation of suitable sites for artificial recharge of groundwater aquifers, a study was carried out in the Kallar Basin, which is located in parts of the Salem and Tiruchirapalli districts, Tamil Nadu, India. Thematic maps defining lithology, lineaments, landforms, landuse, drainage density, thickness of weathered zone, thickness of fractured zone, hydrological soils, and well yield were prepared from data collected by the Indian Remote Sensing Satellite (IRS) -1C and by conventional methods. All the thematic layers were integrated using a GIS-based model developed specifically for this purpose, enabling a map showing artificial recharge zones to be generated. The exact type of artificial recharge structure, eg, check dam, nallabund, gully plugging and percolation pond, suitable for replenishing groundwater was identified by superposing a drainage network map over an artificial recharge zones map. The GIS-based demarcation of artificial zones developed in the study was based on logical conditions and reasoning, so that the same techniques (with appropriate modifications) could be adopted elsewhere, especially in hard rock terrain, where the occurrence of groundwater is restricted and subject to greater complexity.  相似文献   

Infrared photometry and spectrophotometry of Comet Halley     

Chen Pei-sheng  Gao Heng  Zhang Yun  Chen Yan-kang  Yang Jing  Mei Mani 《Chinese Astronomy and Astrophysics》1987,11(4):309-311

We report on our photometric and spectrophotmetric measurement of Comet Halley in near infrared. The observations confirmed the explosion found in the preceding article and showed the post-explosion behaviour of the comet was different in the visible and the infrared. Water emission lines at 1.4 cm and 1.9 cm were found.  相似文献   

Effects of shallow and deep geology on seismic hazard estimates: a case study of pseudo-acceleration response spectra for the northwestern Balkans     

Borko Ð. Bulajić  Miodrag I. Manić  Đorđe Lađinović 《Natural Hazards》2013,69(1):573-588

Northwestern Balkans represents one of the rare regions where data on both the shallow geology (i.e., local soil conditions) and the deep geology exist for stations that recorded hundreds of strong motion records. The strong motion database used in this study consists of 203 strong motion accelerograms (each with three orthogonal translational components), recorded in former Yugoslavia in the period 1976–1983, from 108 contributing earthquakes. In this paper, the results of a series of regression analyses are presented where empirical equations for scaling pseudo-acceleration response spectra were developed on the basis of 5 subsets of data and using three prediction models. Results of the regression analyses show that for ground motion in the horizontal direction, both the shallow and deep geology site conditions have to be taken into account or else the spectral estimates might be considerably biased. Results show that the shallow geology influences spectral amplitudes the most in the short period range and has much lesser effects for larger periods, while the influence of the deep geology is expressed in a wider range of intermediate to long periods. Results also show that if the prediction model that considers solely the shallow geology effects is used, the spectral peaks that have been related to the deep geology effects will completely vanish for larger source-to-site distances, while in the case when solely the deep geology is considered, the peaks related to the shallow geology will not be visible for any distance. As for the amplitudes in the vertical direction, although both the shallow and the deep geology effects are less expressed than in the horizontal one, they still cannot be neglected—the deep geology effects are visible for a wider range of vibration periods, while the shallow geology has some effects only for periods smaller than ~0.3 s.  相似文献