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61.
F. A. Lopes G. Michard M. Poulin A. Roué F. Prévot D. Jézéquel E. Viollier 《Aquatic Geochemistry》2010,16(4):587-610
A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake
Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into
the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described
in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis
and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various
kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate
depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical
pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing. 相似文献
62.
João Magalhães Neto Heliana Teixeira Joana Patrício Alexandra Baeta Helena Veríssimo Rute Pinto João Carlos Marques 《Estuaries and Coasts》2010,33(6):1327-1339
Anthropogenic activities are a disturbance factor of coastal systems and can be widely recognized as a major threat to the
health of coastal systems. However, natural events cannot be disregarded from management issues because of their significant
influence on the communities living in these areas. Based on long-term subtidal data from the Mondego Estuary (Portugal),
the effects of natural events (e.g., floods and droughts) on macrobenthic communities were compared with the anthropogenic
events. Sampling stations were grouped into characteristic zones (mouth, north arm, south arm) so the community dynamics of
each of these estuarine areas could be followed over time. Environmental assessment was performed for stations using the Benthic
Assessment Tool (BAT), and compared with the existing pressures. Human impacts persist over a number of years and gradually
reduce ecosystem health, as discussed in the European Water Framework Directive. Paradoxically, natural events cause stronger
impacts but are of a shorter duration, which allows for a faster recovery of macrobenthic communities. The study showed that
caution should be taken when developing and implementing water policies so as not to disregard the importance of the different
events (natural and human-caused) on the ecosystem health (e.g., community degradation and water quality and ecological quality
status assessment). 相似文献
63.
64.
Alireza Talebinejad Hamid Chakeri Mahdi Moosavi Yılmaz Özçelik Bahtiyar Ünver Mehmet Ali Hindistan 《Arabian Journal of Geosciences》2014,7(9):3913-3923
Underground structures are currently widely used and are built as urbanism develops. The interactions between perpendicularly crossing and parallel tunnels in the Tehran region are investigated by using a full three-dimensional (3D) finite difference analysis with elastic-plastic material models. Special attention is paid to the effect of subsequent tunneling on the support system, i.e., the shotcrete lining and rock bolts of the existing tunnel. Eventually, as the tunnels are excavated at certain levels, the interaction between the tunnels will certainly have a significant influence on both stress distribution and consequently deformations. Since multilayer tunneling is a three-dimensional phenomenon in nature, 3D numerical solutions must be utilized for analyzing effect of perpendicularly crossing tunnels at various levels. As Tohid twin tunnels and Line 7 pass beneath the Line 4 metro tunnel, changes in stress distribution, deformations, and surface settlements are studied for various conditions and the results are presented in this paper. Consequently, it is shown that there is a significant interaction between tunnels that necessitate certain preventive measures to maintain a stable tunneling operation. 相似文献
65.
Filipe Rafael Ceia Joana Patrício João Carlos Marques João Alveirinho Dias 《Ocean & Coastal Management》2010,53(8):478-486
Coastal vulnerability in barrier island systems is extremely high. The barrier island shoreline is exposed to many threats, such as storm erosion, reductions in sediment longshore drift and sea level rise. Many of these threats to coastal areas, such as Ria Formosa, are likely to increase in the near future. The main objectives of the present study are to identify the areas in the system that are at most risk by assessing the evolution of the Ria Formosa barrier island system since the 1940s, and determine which interventions would be necessary to protect these areas.The coastal vulnerability of the system was assessed based on current literature, data available from official institutions, and aerial and terrestrial in situ examination. The results obtained for the evolution of the Ria Formosa coastal system reveal that there are several vulnerable areas that have very dynamic processes, such as extremely high evolution rates of islands and inlets. Human actions that affect the whole system, namely the construction of many physical structures, are the main cause of the instability. Moreover, as several stakeholders are involved, efficient management of the coastal system is imperative. Extensive and careful interventions are urgently needed to avoid irreversible negative impacts on the barrier island system. Three types of techniques could be adopted to deal with the threats to barrier islands: hard stabilization, soft techniques, and non-structural alternatives. However, using hard techniques has many negative effects compared to soft techniques, and as a result it is necessary to remove existing structures from the areas at most risk. 相似文献
66.
Interface damage and delamination is usually accompanied by frictional slip at contacting interfaces under compressive normal stress. The present work is concerned with an analysis of progressive interface failure using the cohesive crack model with the critical stress softening and frictional traction present at the contact. Both monotonic and cyclic loadings are considered for anti‐plane shear of an elastic plate bonded to a rigid substrate by means of cohesive interface. An analytical solution can be obtained by neglecting the effect of minor shear stress component. The analysis of progressive delamination process revealed three solution types, namely: short, medium and long plate solutions. The long plate solution was obtained under an assumption of quasistatic progressive growth of the delamination zone. In view of snap back response, the quasistatic deformation process cannot be executed by either traction or displacement control. The states of frictional slip accompanied by shake down or incremental failure are distinguished in the case of cyclic loading, related to load amplitude and structural dimensions. The analysis provides a reference solution for numerical treatment of more complex cases. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
67.
de Rezende Igor Marasini Prietto Pedro Domingos Marques Thomé Antônio Dalla Rosa Francisco 《Geotechnical and Geological Engineering》2022,40(4):1997-2008
Geotechnical and Geological Engineering - New sustainable ground improvement techniques have been recently required for applications in onshore and offshore geotechnical structures. The... 相似文献
68.
Sedimentology,three‐dimensional geobody reconstruction and carbon dioxide origin of Pleistocene travertine deposits in the Ballık area (south‐west Turkey)
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69.
70.
P. Hily-Blant E. Falgarone G. Pineau des Forêts T. G. Phillips 《Astrophysics and Space Science》2004,292(1-4):285-289
We present a multitransition study in the 13CO(1-0), 12CO(2-1), 12CO(3-2) and 12CO(4-3) lines of a parsec scale elongated structure connected to a low-mass dense core. Densities larger than n H 2 = 104 cm?3 are inferred in the central regions of this structure, supporting the proposition that it is a genuine filament denser than its environment. The sharp observed drop of the 12CO and 13CO emissions requires a power law density fall-off steeper than r ?1 although a single density law cannot reproduce the spatial shift of 0.1 pc between the 13CO and 12CO drops. Our results support the previous proposition that this elongated structure is a filament threaded by helical magnetic fields, channeling the gas inflow onto the dense core. 相似文献