Mapping and initial dilution estimation of an ocean outfall plume using an autonomous underwater vehicle     

P.A. Ramos  M.V. Neves  F.L. Pereira 《Continental Shelf Research》2007

A monitoring mission to study the shape and estimate initial dilution of the S. Jacinto outfall plume using an autonomous underwater vehicle (AUV) was performed on July 30, 2002. In order to reduce the uncertainty about plume location and to concentrate the vehicle mission only in the hydrodynamic mixing zone, outputs of a near-field prediction model, based on effective real-time in situ measurements of current speed and direction and density stratification, were opportunistically used to specify in real time the mission transects. The surface characteristics of the outfall plume were found to be influenced strongly by the relatively weak stratification and low current velocities. Dilution was estimated using a temperature–salinity (TS-) diagram with initial mixing lines between wastewater and ambient waters. Effluent dilutions were at least 30:1 in this study. In order to efficiently map the plume dispersion we applied the least-squares collocation method technique. Our results demonstrate that AUVs can provide high-quality measurements of physical properties of effluent plumes in a quite effective manner and valuable considerations about the initial mixing processes under real oceanic conditions can be further investigated.  相似文献   

Structural control of Au–Pd mineralization (Jacutinga): An example from the Cauê Mine, Quadrilátero Ferrífero, Brazil     

H.F. Galbiatti  M.A. Fonseca  M.C. Pereira  J.C. Polnia 《Ore Geology Reviews》2007,32(3-4):614

Precambrian banded iron formations (BIFs) in the Quadrilátero Ferrífero host a special kind of Au–Pd mineralization known as Jacutinga. The main orebodies are hosted within the Cauê Syncline, a SW-verging fold that involves Paleoproterozoic metasedimentary rocks in the Itabira District, a regional synclinorium with BIFs in the core of synclinal folds in the northeastern part of Quadrilatéro Ferrífero, Minas Gerais. Structural analysis reveals two important features of the district: the polydeformed character of the rocks and the importance of brittle structures in the control of the orebodies. Two deformational events are recognized in this area. The first event developed the main foliation, S1, that is the enveloping surface of the Cauê Syncline. The second event is better defined in the northern boundary of the structure where it is represented by a right-lateral wrench fault zone that has developed a foliation, S2, that truncates S1. This wrench fault was also responsible for the development of a system of fractures (Frm) that host the Au–Pd mineralization. The auriferous bodies of Cauê Syncline (Y, X, Área Central, Aba Norte, Noroeste and Aba Leste/Aba Leste Inferior) were generated during this second event. Shear fractures (R, R′ and P) and tension fractures (T) developed in response to the wrench fault system under brittle conditions. The best-developed, and most commonly mineralized fractures are R and T in all auriferous bodies. Elsewhere, the best mineralization occurs in the contacts of hematite bodies (soft/hard) and intrusive rocks with fractured itabirites. Other mineralization (Aba Norte, Área Central and X) is hosted on the contacts of other units.A system of fractures, as well as their intersections, thus represents the structural control on Jacutinga bodies and is responsible for the geometry of the orebodies. Of importance, there is no control by mineral/stretching lineations, fold axes and other ductile structure on the geometry and plunge of the orebodies.  相似文献   

Book reviews     

S. I. Rasool  Charles Pereira F.R.S.  Stephen H. Schneider 《Climatic change》1980,3(1):105-110

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Plate Tectonics and mineralization in the Tethyan region   总被引：1，自引：0，他引：1  

C. J. Dixon  J. Pereira 《Mineralium Deposita》1974,9(3):185-198

The association between mineralization and plate movements is becoming evident in the American Cordillera and the Pacific Island Arcs. This paper attempts to show how these ideas apply to the zone along which the Eurasian and Afro-Arabia plates collided during the late Mesozoic, between the Alps and the Himalayas. The study highlights some of the outstanding problems concerned with plate collision and the important question of the origin of ophiolite complexes. Some of the major mineralized districts in Greece, Turkey and Iran can be related to active plate edges, to island arc development and to related tectonism around pre-Mesozoic crystalline massifs. The study reinforces the view that the younger tectonic zones traversing the Middle East will become major mineral-producing areas in the future.  相似文献   

Solar Spectral Irradiance at 782 nm as Measured by the SES Sensor Onboard Picard     

M. Meftah  A. Hauchecorne  A. Irbah  G. Cessateur  S. Bekki  L. Damé  D. Bolsée  N. Pereira 《Solar physics》2016,291(4):1043-1057

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Changes in extremes and hydroclimatic regimes in the CREMA ensemble projections   总被引：2，自引：0，他引：2  

Filippo Giorgi  Erika Coppola  Francesca Raffaele  Gulilat Tefera Diro  Ramon Fuentes-Franco  Graziano Giuliani  Ashu Mamgain  Marta Pereira Llopart  Laura Mariotti  Csaba Torma 《Climatic change》2014,125(1):39-51

We analyze changes of four extreme hydroclimatic indices in the RCP8.5 projections of the Phase I CREMA experiment, which includes 21st century projections over 5 CORDEX domains (Africa, Central America, South America, South Asia, Mediterranean) with the ICTP regional model RegCM4 driven by three CMIP5 global models. The indices are: Heat Wave Day Index (HWD), Maximum Consecutive Dry Day index (CDD), fraction of precipitation above the 95th intensity percentile (R95) and Hydroclimatic Intensity index (HY-INT). Comparison with coarse (GPCP) and high (TRMM) resolution daily precipitation data for the present day conditions shows that the precipitation intensity distributions from the GCMs are close to the GPCP data, while the RegCM4 ones are closer to TRMM, illustrating the added value of the increased resolution of the regional model. All global and regional model simulations project predominant increases in HWD, CDD, R95 and HY-INT, implying a regime shift towards more intense, less frequent rain events and increasing risk of heat wave, drought and flood with global warming. However, the magnitudes of the changes are generally larger in the global than the regional models, likely because of the relatively low “climate sensitivity” of the RegCM4, especially when using the CLM land surface scheme. In addition, pronounced regional differences in the change signals are found. The data from these simulations are available for use in impact assessment studies.  相似文献   

Variability over time in the sources of South Portuguese Zone turbidites: evidence of denudation of different crustal blocks during the assembly of Pangaea     

M. F. Pereira  C. Ribeiro  F. Vilallonga  M. Chichorro  K. Drost  J. B. Silva  L. Albardeiro  M. Hofmann  U. Linnemann 《International Journal of Earth Sciences》2014,103(5):1453-1470

This study combines geochemical and geochronological data in order to decipher the provenance of Carboniferous turbidites from the South Portuguese Zone (SW Iberia). Major and trace elements of 25 samples of graywackes and mudstones from the Mértola (Visean), Mira (Serpukhovian), and Brejeira (Moscovian) Formations were analyzed, and 363 U-Pb ages were obtained on detrital zircons from five samples of graywackes from the Mira and Brejeira Formations using LA-ICPMS. The results indicate that turbiditic sedimentation during the Carboniferous was marked by variability in the sources, involving the denudation of different crustal blocks and a break in synorogenic volcanism. The Visean is characterized by the accumulation of immature turbidites (Mértola Formation and the base of the Mira Formation) inherited from a terrane with intermediate to mafic source rocks. These source rocks were probably formed in relation to Devonian magmatic arcs poorly influenced by sedimentary recycling, as indicated by the almost total absence of pre-Devonian zircons typical of the Gondwana and/or Laurussia basements. The presence of Carboniferous grains in Visean turbidites indicates that volcanism was active at this time. Later, Serpukhovian to Moscovian turbiditic sedimentation (Mira and Brejeira Formations) included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism. The abundance of Precambrian and Paleozoic zircons reveals strong recycling of the Gondwana and/or Laurussia basements. A peri-Gondwanan provenance is indicated by zircon populations with Neoproterozoic (Cadomian-Avalonian and Pan-African zircon-forming events), Paleoproterozoic, and Archean ages. The presence of late Ordovician and Silurian detrital zircons in Brejeira turbidites, which have no correspondence in the Gondwana basement of SW Iberia, indicates Laurussia as their most probable source.  相似文献   

Experimental study on the mechanical behaviour of a heat exchanger pile using physical modelling     

Neda Yavari  Anh Minh Tang  Jean-Michel Pereira  Ghazi Hassen 《Acta Geotechnica》2014,9(3):385-398

This study aims to provide knowledge on the thermo-mechanical behaviour of heat exchanger piles, through a laboratory scale model. The model pile (20 mm in external diameter) was embedded in dry sand. The behaviour of the axially loaded pile under thermal cycles was investigated. After applying the axial load on the pile head, the pile temperature was varied between 5 and 30 °C. Seven tests, corresponding to various axial loads ranging from 0 to 70 % of the pile estimated bearing capacity, were performed. The results on pile head displacement show that heating under low axial load induced heave and cooling induced settlement; the pile temperature-displacement curve was found to be reversible and compatible with the thermal expansion curve of the pile. However, at higher axial loads, irreversible settlement of the pile head was observed after a few thermal cycles. The axial load profile measured by the strain gauges evidenced that the pile head load was mainly transferred to the pile toe. Nevertheless, thermal cycles modified significantly the mobilised skin friction along the pile. The total pressure measured at various locations in the soil mass was also slightly influenced by the thermal cycles.  相似文献   

Natural Variability of Shear Strength in a Granite Residual Soil from Porto     

Luís Pinheiro Branco  António Topa Gomes  António Silva Cardoso  Carla Santos Pereira 《Geotechnical and Geological Engineering》2014,32(4):911-922

The renewal imposed by the Eurocodes regarding the methodologies of safety evaluation requires a statistical analysis of the variability of ground geotechnical parameters. However, the studies published in the reviewed literature do not cover the typical materials from the northeast region of Portugal—residual soils from granite—to which a strong heterogeneity is associated. Hence, a statistical characterization of the natural variability of a granite residual soil from Porto has been made through a significant amount of experimental tests, focusing on its geomechanical properties. In order to provide a database for probabilistic analysis of problems involving this type of soils, an appropriate statistical law has been used to model its variability, which has been quantified by means of coefficients of variation and scales of fluctuation.  相似文献   

The Ushnus in the astronomy of the Inca culture     

Milton Rojas Gamarra  Mônica Baptista Pereira Estrázulas  Steven R. Gullberg  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230181

Inferences are made about the relationship that existed between the Ushnus, pyramid-shaped, terraced structures used by the Incas in the most important ceremonies of the Tawantinsuyo, and Inka Astronomy. We draw attention to Ayni, Kawsaypacha, Duality, and Tinkuy principles, multidimensional codes of conduct and wisdom that are at the root of the Andean cosmovision and on their perception of the world and the Cosmos. These principles, examined as postulates, allow to elaborate axiomatic propositions to identify the Ushnus with ancient Astronomy practices. In a complementary statement, starting from a bi-conditional proposition, we may infer through reciprocal corollaries that the Inka earliest roots to a holistic learning and educational ambient in the Tawantinsuyo was not elitist, instead it was based on a epistemological construct that differs from the corresponding Western educational ambients. An epistemological and cognitive approach allows to identify an ancient elaborate process of knowledge construction, based on the four fundamental principles, corresponding to different levels of assimilation and comprehension. As a complementary aspect, we identify some of the most preserved Ushnus of the Inka “Empire.” Then we complement this contribution with a broader interpretation for the Ushnus.  相似文献