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81.
Owing to the mathematical similarities between heat and mass transport, the multi-species transport model MT3DMS should be able to simulate heat transport if the effects of buoyancy and changes in viscosity are small. Although in several studies solute models have been successfully applied to simulate heat transport, these studies failed to provide any rigorous test of this approach. In the current study, we carefully evaluate simulations of a single borehole ground source heat pump (GSHP) system in three scenarios: a pure conduction situation, an intermediate case, and a convection-dominated case. Two evaluation approaches are employed: first, MT3DMS heat transport results are compared with analytical solutions. Second, simulations by MT3DMS, which is finite difference, are compared with those by the finite element code FEFLOW and the finite difference code SEAWAT. Both FEFLOW and SEAWAT are designed to simulate heat flow. For each comparison, the computed results are examined based on residual errors. MT3DMS and the analytical solutions compare satisfactorily. MT3DMS and SEAWAT results show very good agreement for all cases. MT3DMS and FEFLOW two-dimensional (2D) and three-dimensional (3D) results show good to very good agreement, except that in 3D there is somewhat deteriorated agreement close to the heat source where the difference in numerical methods is thought to influence the solution. The results suggest that MT3DMS can be successfully applied to simulate GSHP systems, and likely other systems with similar temperature ranges and gradients in saturated porous media. 相似文献
82.
83.
Fishes present on small artificial reefs located 2 km off the central east coast of Florida (USA) were surveyed to determine the acceptability of using stabilized oil and coal ash residue as a component material in construction of artificial fishing reefs. Species richness was not significantly different over 2.5 yr on stabilized oil and coal ash reefs compared to concrete control reefs. Of 19 species tested for significant differences in mean abundance, lane snapper was observed at significantly higher mean abundances on fossil-fuel ash reefs (stabilized oil ash/coal fly ash), while three reef species (hairy blenny, porkfish and gray snapper) were significantly more common on concrete control reefs. Further study is needed to determine whether contaminants (Cu, V, Ni and Zn) from stabilized ash blocks can cause abundance differences for some fishes. Plausible alternate explanations for the differences in mean abundance include both interspecific interactions (competition and predation) and differences in the attraction or retention of fish among reef replicates due to slight variations in reef dimensions. 相似文献
84.
Juliet G. Crider David Frank Stephen D. Malone Michael P. Poland Cynthia Werner Jacqueline Caplan-Auerbach 《Bulletin of Volcanology》2011,73(2):175-189
Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic
gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned
to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative
microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements
suggest slight deflation of the edifice between 1981–83 and 2006–07. The volcano remains seismically quiet with regard to
impulsive volcano-tectonic events, but experiences shallow (<3 km) low-frequency events likely related to glacier activity,
as well as deep (>10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical
and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker
in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening
of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential
to this assessment of magmatic activity. 相似文献
85.
Till Czypionka Cristian A. Vargas Nelson Silva Giovanni Daneri Humberto E. González José Luis Iriarte 《Continental Shelf Research》2011,31(3-4):216-224
Mixotrophy, the combination of autotrophic and heterotrophic nutrition in the same organism, is widespread in planktonic algae. Several reports from temperate and high-latitude fjords in Scandinavia suggest the occurrence of a niche in late summer and autumn during post-bloom conditions in which mixotrophic algae can become important grazers in pelagic ecosystems, accessing the nutrients bound in their prey to overcome nutrient limitation. Here, we experimentally determined the trophic modes and bacterivory rates for the nanoplankton community (2–20 μm) in Aysén Fjord located in the Chilean Northern Patagonia during two contrasting seasons: winter and spring. While mixotrophic nanoplankton was virtually absent from the system in spring, in winter at occasions it even constituted the dominant trophic group of the nanoplankton with abundances of >900 cells mL?1. This indicates a second niche for mixotrophs in winter, when mixotrophy allows overcoming light limitation. 相似文献
86.
Willard S. Moore Kenneth W. Bruland Jacqueline Michel 《Earth and Planetary Science Letters》1981,53(3):391-399
Samples from the MANOP Santa Barbara Basin sediment trap intercomparison were analyzed for the isotopes of uranium, thorium, radium, lead, and polonium. All of the traps showed approximately the same compositions and isotopic ratios, indicating that they trapped similar materials. The234Th flux via falling particles was very close to the flux predicted from the production and scavenging rates of234Th from the water column. The210Pb content of the trapped particles and the surface sediments were the same, however, the measured flux of210Pb was seven times greater than the predicted flux. Predicted and measured fluxes of228Th and210Po were similarly out of balance. To explain this apparent inconsistency, we suggest (as others have done) that the Santa Barbara Basin is an area where scavenging from the water column is intensified and where sediments deposited initially on the margins may be physically remobilized on a short time scale. These two effects increase the apparent area from which the basin derives the longer-lived isotopes but does not increase significantly the supply of the short-lived234Th. 相似文献
87.
Shear effects on hollow section piers under seismic actions: experimental and numerical analysis 总被引:1,自引:0,他引:1
Raimundo Delgado Pedro Delgado Nelson Vila Pouca António Arêde Patrício Rocha Aníbal Costa 《Bulletin of Earthquake Engineering》2009,7(2):377-389
Shear effects are often a very important issue on the seismic behaviour of piers, particularly for hollow section bridge piers.
In fact, for this type of piers the cyclic response is similar to that of a structural wall in which both the transverse reinforcement
ratio and the detailing can play an important role on its performance, even likely to be determinant in terms of the failure
mechanism. On the other hand, codes and design guidelines are usually very conservative concerning shear capacity in order
to avoid any shear failure mechanism likely to trigger well known catastrophic consequences. Therefore, research studies on
this topic are still needed for a better understanding of pier cyclic shear response and also for improvement of the performance
under seismic actions. Pursuing this general objective, this paper partially reports on an experimental/numerical campaign
carried out on 1:4 reduced scale bridge piers in order to highlight and investigate shear-type problems. Within the scope
of this paper, two specimens types were selected having equal rectangular hollow section (900 × 450 mm2, 75 mm thick) but different transverse reinforcement detailing, namely one with a single stirrup per wall (representative
of typical bridge construction without seismic design requirements) and another with multiple stirrups, according to Eurocode
8 provisions. Numerical simulations of the experimental results were also conducted aiming at contributing for complete and
consistent interpretations of experimental results. Detailed modelling was performed allowing for realistic simulations of
the non linear behaviour, particularly suitable when a significant shear component is involved. Therefore, the numerical strategy
was based on a detailed 3D FEM discretization using a two-scalar variable damage model for the concrete constitutive law and
a suitable cyclic behaviour law for steel bars represented by truss elements. Results have shown that shear deformation and
failure modes are well simulated, while providing detailed insight concerning concrete damage pattern and distribution of
yielding on the transverse and longitudinal reinforcement. 相似文献
88.
Post-earthquake investigation on several geosynthetic-reinforced soil retaining walls and slopes during the Ji-Ji earthquake of Taiwan 总被引:1,自引:0,他引:1
Hoe I. Ling Dov Leshchinsky Nelson N. S. Chou 《Soil Dynamics and Earthquake Engineering》2001,21(4):3087
This paper gives an overview on the application of geosynthetic-reinforced soil structures in Taiwan. Taiwan has an unique topography and geotechnical conditions that rendered a less conservative and more challenging design compared to that of North America, Europe and Japan. The Ji-Ji (Chi-Chi) earthquake of 1999 gave an opportunity to examine the behavior of reinforced soil structures. The performance of several modular-block reinforced soil retaining walls and reinforced slopes at the vicinity of the fault was evaluated. Reinforced structures performed better than unreinforced soil retaining walls. The failure cases were highlighted and the cause of failure was identified. The lack of seismic design consideration could be a major cause of failure. The compound failure mode, the inertia force of the blocks, and the connection stiffness and strength relative to the large dynamic earth pressure, were among major items that would warrant further design consideration. 相似文献
89.
90.
Macarena Bravo Mª de los ngeles Gallardo Guillermo Luna-Jorquera Paloma Núez Nelson Vsquez Martin Thiel 《Marine pollution bulletin》2009,58(11):1718-1726
Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m−2 and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation. 相似文献