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81.
J. Quiñones J. Arzúa L. R. Alejano F. García-Bastante D. Mas Ivars G. Walton 《Acta Geotechnica》2017,12(6):1229-1242
A total of 28 uniaxial compressive strength tests were performed on cylindrical Blanco Mera granite samples with diameters ranging between 14 and 100 mm, with results indicating that this granite undergoes a significant reverse size effect: the UCS increases as sample diameter increases up to 54 mm, but thereafter decreases. It was also found that the results tend to be more scattered for smaller sample diameters. We also found an apparent correlation between Young’s modulus and sample diameter. It was not possible to draw any clear conclusions regarding the variability in Poisson’s ratio with sample size. With respect to crack initiation and crack damage stresses, the behaviour of the tested samples also indicates a reverse effect. This research would suggest that the traditionally assumed decrease in strength as sample size increases does not hold for granite samples with diameters below 54 mm. 相似文献
82.
Influence of transient storage on stream nutrient uptake based on substrata manipulation 总被引:3,自引:0,他引:3
Alba Argerich Eugènia Martí Francesc Sabater Roy Haggerty Miquel Ribot 《Aquatic Sciences - Research Across Boundaries》2011,73(3):365-376
Quantification of the transient storage zone (As) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected
that higher As may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature
are controversial. We hypothesized that besides of the size of As, the intrinsic physical and biological characteristics of stream structures that generate As are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of
a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify
As. We estimated ammonium and phosphate uptake coefficients in both the main channel and As using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction
of substrata packs decreased water velocity and increased As similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type
substrata packs; however, nutrient uptake coefficients measured in As differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in As, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest
that the contribution of As in nutrient uptake not only depends on the size of As but on the type of materials used to increase As, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology. 相似文献
83.
J. Alonso‐Azcrate M. Rodas L. Fernndez‐Díaz S.H. Bottrell J. R. Mas S. Lpez‐Andrs 《Geological Journal》2001,36(2):159-170
The low‐grade metasediments of the Cameros Basin, northern Spain, host a number of deposits of spectacular quality pyrite mineralization. These formed during regional metamorphism and the pyrite crystals exhibit a wide range of morphologies. On the basis of pyrite crystal habit, the deposits can be classified into two groups: Group I comprises deposits with cubic, elongated or platy crystals; Group II comprises deposits characterized by pyritohedra and cubo‐pyritohedra with striated faces, along with blocky crystals and fine‐grained aggregates. Group I deposits are formed in sequences dominated by meandriform fluviatile sediments, while Group II is hosted by deltaic plain and lacustrine metasediments. Temperature differences between deposits and As content are possible causes of the different pyrite morphologies in the deposits, but no significant variation exists between the two groups for either factor. Comparison with experimentally grown pyrite crystals suggests that Group I deposits have morphologies indicative of lower degrees of pyrite supersaturation than pyrite crystals in Group II deposits. The sedimentary facies hosting Group II deposits provides a greater availability of sedimentary sulphur (pyrite and sulphates). Moreover, reactions involving sulphate during metamorphism may have modified fluid chemistry, which would also act to produce higher degrees of pyrite saturation in fluids derived from the sulphate‐rich deltaic plain and lacustrine metasediments hosting the Group II deposits. This hypothesis is confirmed by sulphur isotope data on the pyrites, which show a larger component of34S‐enriched sulphate‐derived sulphur in these deposits. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献