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1.
Maedo Michael Sánchez Marcelo Aljeznawi Duaa Manzoli Osvaldo Guimarães Leonardo J. N. Cleto Pedro Rogério 《Acta Geotechnica》2020,15(9):2619-2635
This paper focuses on the shrinkage behavior of soil specimens involving sand, kaolinite, and kaolinite/sand mixtures subjected to desiccation under controlled conditions. Both, free and restrained shrinkage conditions are studied. The experiments show that pure soils do not curl upon unrestrained shrinkage; however, (under the same conditions) kaolinite/sand mixtures exhibited a marked curling. Furthermore, the mixture with the higher sand content broke through the middle of the sample after displaying a significant curling. Soils subjected to restricted shrinkage developed cracks with slight curling. To simulate the observed behavior, a mechanical model able to reproduce the detachment of the soil sample from the mold is proposed in this work and implemented in a fully coupled hydro-mechanical finite-element code. It is concluded that suction and differential shrinkage are key factors influencing the curling behavior of soils. The proposed framework was able to satisfactorily explain and reproduce the different stages and features of soil behavior observed in the experiments.
相似文献2.
Osvaldo Manzoli Marcelo Sánchez Michael Maedo Jumanah Hajjat Leonardo J. N. Guimarães 《Acta Geotechnica》2018,13(5):1171-1186
The study of drying process in soils has received an increased attention in the last few years. This is very complex phenomenon that generally leads to the formation and propagation of desiccation cracks in the soil mass. In recent engineering applications, high aspect ratio elements have proved to be well suited to tackle this type of problem using finite elements. However, the modeling of interfaces between materials with orthotropic properties that generally exist in this type of problem using standard (isotropic) constitutive model is very complex and challenging in terms of the mesh generation, leading to very fine meshes that are intensive CPU demanding. A novel orthotropic interface mechanical model based on damage mechanics and capable of dealing with interfaces between materials in which the strength depends on the direction of analysis is proposed in this paper. The complete mathematical formulation is presented together with the algorithm suggested for its numerical implementation. Some simple yet challenging synthetic benchmarks are analyzed to explore the model capabilities. Laboratory tests using different textures at the contact surface between materials were conducted to evaluate the strengths of the interface in different directions. These experiments were then used to validate the proposed model. Finally, the approach is applied to simulate an actual desiccation test involving an orthotropic contact surface. In all the application cases the performance of the model was very satisfactory. 相似文献
3.
Juan Pablo Isacch Daniel Augusto Cardoni Oscar Osvaldo Iribarne 《Estuaries and Coasts》2014,37(1):229-239
We studied variation in bird assemblages with plant associations for three different coastal marshes from Southeastern South America (SESA) and assessed how marsh bird assemblages related to nearby upland bird assemblages. We surveyed bird species and plant structure along the tidal gradient of each locality from the low tide level to the upper habitats bordering coastal marshes. Twenty species frequently used coastal marshes, including relatively few migratory species. We found that birds occurring in SESA coastal marshes do not have distributions constrained to coastal marshes. Nonetheless, four bird assemblages were recognized in association with vegetation types and/or sites. Among the recorded coastal marsh species, the bay-capped wren-spinetail (Spartonoica maluroides) is both the most frequent and the most habitat constrained. Bird richness increases steadily along the tidal gradient associated with the increase in vegetation structure, suggesting that bird richness is directly explained by vegetation and indirectly by the physical conditions influencing vegetation structure. Results highlight the importance of SESA middle marshes as habitat for conservation of some threatened SESA grassland birds. 相似文献
4.
Polycyclic aromatic hydrocarbons in water, seston and copepods in a harbour area in the Western Mediterranean (Ligurian Sea) 总被引：2，自引：0，他引：2
Luigi Pane Simona Boccardo Fabio Bonfiglioli Gian Luigi Mariottini Francesca Priano & Osvaldo Conio 《Marine Ecology》2005,26(2):89-99
Polycyclic aromatic hydrocarbons (PAHs) are widespread carcinogenic, mutagenic and teratogenic pollutants that can significantly affect ecosystems and exert an influence on marine planktonic and benthic communities as well as on higher organisms such as fish and mammals, including humans. In this paper the concentrations of six PAHs in water, seston and copepods were examined in a harbour zone of the Genova Gulf (Ligurian Sea) from November 1997 to June 1998. The importance of freshwater inputs coming from a polluted stream and the influence of seasonal and atmospheric factors were also considered. Highest PAH values were recorded during spring. Fluoranthene, Benzo[b]fluoranthene and Benzo[k]fluoranthene were the most abundant PAHs either in water, seston or copepods. The concentration of total PAHs in seawater was often lower than the detection limit: recorded values ranged between 0.001 and 0.06 ppb. In seston, total PAHs ranged between 0.033 and 6.26 ng·g?1 and in copepods between 0.01 and 2.34 ng·g?1. With this study, PAH contamination in the harbour zone of Genova Sestri‐Ponente and the importance of inputs of organic pollutants coming from land and freshwaters have been emphasized. 相似文献
5.
Faggioni Osvaldo Beverini Nicolò Carmisciano Cosmo Giori Italiano 《Marine Geophysical Researches》2001,22(2):63-79
We show the results obtained by means of a seabed reduction technique on the intensity of geomagnetic anomaly fields applied
to a synthetic case and then to the real case of a geomagnetic survey of eastern Ligurian Sea (Italy). The eastern Ligurian
Sea has very intense short waves anomaly fields and a sea bed that varies greatly in depth. As a result the geomagnetic space
signal is characterized by a very large spectral content; in these conditions it is not possible to obtain a full sampled
marine survey and vertical continuation analytic procedures and standard numerical bottom reduction based on a single vertical
incremental parameter, whichever is applicable, fails to give accurate results. The present technique, which has been fine-tuned
over 4 years of experimentation in environmental researchs, aims to provide a simple and efficient means to reduce the distortion
of geomagnetic anomalies field caused by the variation of distance between survey plane and magnetic outcrop source position.
The compensation procedure is based on evaluation, by comparison of two measurements carried out at different altitudes, of
the mean vertical increment typical of each anomaly field principal frequency component bands. The component anomaly fields
are then corrected by application of the corresponding vertical increments and lastly, the anomaly geomagnetic field reduced
to the sea-bed is computed as Inverse Fourier Transform of a spectrum built as synthesis of the component anomaly fields'
spectra. The results obtained have shown a notable increase in definition of anomaly field intensity without the production
of appreciable distortions or false geomagnetic echoes.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
6.
7.
Osvaldo M. Rabbia Laura B. Hernández David H. French Robert W. King John C. Ayers 《Mineralium Deposita》2009,44(8):849-866
Mineralogical, textural, and chemical analyses (EPMA and PIXE) of hydrothermal rutile in the El Teniente porphyry Cu–Mo deposit
help to better constrain ore formation processes. Rutile formed from igneous Ti-rich phases (sphene, biotite, Ti-magnetite,
and ilmenite) by re-equilibration and/or breakdown under hydrothermal conditions at temperatures ranging between 400°C and
700°C. Most rutile nucleate and grow at the original textural position of its Ti-rich igneous parent mineral phase. The distribution
of Mo content in rutile indicates that low-temperature (∼400–550°C), Mo-poor rutile (5.4 ± 1.1 ppm) is dominantly in the Mo-rich
mafic wallrocks (high-grade ore), while high-temperature (∼550-700°C), Mo-rich rutile (186 ± 20 ppm) is found in the Mo-poor
felsic porphyries (low-grade ore). Rutile from late dacite ring dikes is a notable exception to this distribution pattern.
The Sb content in rutile from the high-temperature potassic core of the deposit to its low-temperature propylitic fringe remains
relatively constant (35 ± 3 ppm). Temperature and Mo content of the hydrothermal fluids in addition to Mo/Ti ratio, modal
abundance and stability of Ti-rich parental phases are key factors constraining Mo content and provenance in high-temperature
(≥550°C) rutile. The initial Mo content of parent mineral phases is controlled by melt composition and oxygen fugacity as
well as timing and efficiency of fluid–melt separation. Enhanced reduction of SO2-rich fluids and sulfide deposition in the Fe-rich mafic wallrocks influences the low-temperature (≤550°C) rutile chemistry.
The data are consistent with a model of fluid circulation of hot (>550°C), oxidized (ƒO2 ≥ NNO + 1.3), SO2-rich and Mo-bearing fluids, likely exsolved from deeper crystallizing parts of the porphyry system and fluxed through the
upper dacite porphyries and related structures, with metal deposition dominantly in the Fe-rich mafic wallrocks. 相似文献
8.
Nadiane Smaha Kruk Íria Fernades Vendrame Humberto Ribeiro da Rocha Sin Chan Chou Osvaldo Cabral 《Theoretical and Applied Climatology》2010,99(1-2):115-123
The accurate estimate of the surface longwave fluxes contribution is important for the calculation of the surface radiation budget, which in turn controls all the components of the surface energy budget, such as evaporation and the sensible heat fluxes. This study evaluates the performance of the various downward longwave radiation parameterizations for clear and all-sky days applied to the Sertãozinho region in São Paulo, Brazil. Equations have been adjusted to the observations of longwave radiation. The adjusted equations were evaluated for every hour throughout the day and the results showed good fits for most of the day, except near dawn and sunset, followed by nighttime. The seasonal variation was studied by comparing the dry period against the rainy period in the dataset. The least square linear regressions resulted in coefficients equal to the coefficients found for the complete period, both in the dry period and in the rainy period. It is expected that the best fit equation to the observed data for this site be used to produce estimates in other regions of the State of São Paulo, where such information is not available. 相似文献
9.
Osvaldo F. Canziani 《Global Change & Human Health》2001,2(1):5-5
There has been increasing recognition of the link between human activity and natural and man-made systems. Policies and programs
designed to achieve sustainable development and human health, as one of the main components for sustainability, require understanding
of global environmental issues and their regional and local implications.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
10.
Osvaldo L. L. Moraes 《Boundary-Layer Meteorology》1988,43(3):223-230
A model for the logarithmic spectra of velocity in the stable boundary layer is developed using the concept of local scaling. The resulting expressions for peak wavelength are in agreement with empirical data from Minnesota 1973.Partially financed by CAPES and FINEP.On leave from Faculdade de Engenharia de Joinville, SC, Brasil. 相似文献