New Albian macro- and palynoflora from the Negev (Israel) with description of a new gymnosperm morphotaxon     

Valentin Krassilov  Eckart Schrank 《Cretaceous Research》2011,32(1):13-29

New plant macrofossil localities are found in the middle-upper part of the Albian Upper Hatira Formation of Makhtesh Qatan, an erosion crater in the northern Negev. These are so far the only outcrop localities in the Negev containing plant compressions and well-preserved sporomorphs. Their age assignments are controlled by the ammonite Knemiceras records below and above the plant-bearing sequence in the adjacent Makhtesh Hatira. The macrofossil assemblages are strikingly different in the sandy fluvial and shaly lacustrine facies, the former being dominated by Araucaria, Athrotaxopsis, Brachyphyllum and pinnatifid Sapindopsis, comparable at the plant assemblage and leaf morphological levels to the early to early late Albian assemblage of the North American Potomac flora. The lacustrine shale macrofossil assemblages appear archaic on account of their diverse pteridophyte component and sparse angiosperm remains. A new supposedly gnetophytic genus and species Qataniaria noae Krassilov, gen. et sp. nov. is dominant in the shale horizon. The sporomorph assemblages are strongly dominated by psilate trilete spores (87-93%). In the absence of elaterate forms, the angiosperm pollen Afropollis jardinus, Pennipollis, Tricolpites spp. and Walkeripollis sp. is consistent with the early Albian age. The abundance and diversity of conifers and the prominence of the fern bog assemblage suggest a relatively humid phase of the regional Albian climates.  相似文献   

Experimental Study of the Brittle Behavior of Clay shale in Rapid Unconfined Compression   总被引：6，自引：3，他引：3  

Florian Amann  Edward Alan Button  Keith Frederick Evans  Valentin Samuel Gischig  Manfred Blümel 《Rock Mechanics and Rock Engineering》2011,44(4):415-430

The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal, underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France) in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress–strain behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress.  相似文献   

A laboratory-numerical approach for modelling scale effects in dry granular slides     

Matthew Kesseler  Valentin Heller  Barbara Turnbull 《Landslides》2018,15(11):2145-2159

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as flow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25 and 1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 10²???10³. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter et al. (Acta Mech 109:127–165, 1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as flow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects.  相似文献   

Erosion feature reclamation in urban areas: typical unsuccessful examples from Brazil   总被引：1，自引：0，他引：1  

Cláudia Marisse dos Santos Rotta  Lázaro Valentin Zuquette 《Environmental Earth Sciences》2014,72(2):535-555

Erosion is responsible for environmental degradation in continental and coastal areas with varying degrees of intensity and spatial range. In continental areas, rills and gullies affect urban and non-urban areas and may occur isolated or in groups. In urban areas, many forms of degradation occur, ranging from relief modifications (with runoff and other hydrological changes) to channel and reservoir silting. Other forms of degradation include the destruction of infrastructure items, such as streets, power lines and pipelines. Many mechanical, structural, agricultural, ecological and bioengineering measures can be adopted to control and restore these areas, with various results. In many cases, the applied techniques are unsuccessful and worsen the environmental problems. To illustrate such cases in Brazil, this study examines the adoption of different techniques to restore gullies in the cities of São Pedro, Franca, São Carlos, Casa Branca and Cajuru, in the state of São Paulo. These areas are characterized by sandy geology in a variety of landscapes, and the erosion processes result from natural and anthropogenic conditions. Additionally, Brazil’s coastal area has been affected by erosion, as in Fortaleza (in the state of Ceará). This study demonstrates that the primary factor associated with erosion in coastal and continental urban areas is the lack of territorial planning that considers the geological, hydrological and geotechnical limitations. In some of the studied areas, positive results have been achieved. However, unsatisfactory results predominate primarily because appropriate geological, environmental and geotechnical studies were not performed before the interventions were selected and implemented.  相似文献   

Effects of climate change on bioclimatic indices in vineyards along Lake Neuchatel,Switzerland     

Comte  Valentin  Schneider  Léonard  Calanca  Pierluigi  Rebetez  Martine 《Theoretical and Applied Climatology》2022,147(1-2):423-436

Theoretical and Applied Climatology - In this study, we investigated the consequences of climate change on bioclimatic indices in vineyards along the edge of Lake Neuchatel in Switzerland. Like in...  相似文献   

Unstructured-mesh modeling of the Congo river-to-sea continuum     

Yoann Le Bars  Valentin Vallaeys  Éric Deleersnijder  Emmanuel Hanert  Loren Carrere  Claire Channelière 《Ocean Dynamics》2016,66(4):589-603

With the second largest outflow in the world and one of the widest hydrological basins, the Congo River is of a major importance both locally and globally. However, relatively few studies have been conducted on its hydrology, as compared to other great rivers such as the Amazon, Nile, Yangtze, or Mississippi. The goal of this study is therefore to help fill this gap and provide the first high-resolution simulation of the Congo river-estuary-coastal sea continuum. To this end, we are using a discontinuous-Galerkin finite element marine model that solves the two-dimensional depth-averaged shallow water equations on an unstructured mesh. To ensure a smooth transition from river to coastal sea, we have considered a model that encompasses both hydrological and coastal ocean processes. An important difficulty in setting up this model was to find data to parameterize and validate it, as it is a rather remote and understudied area. Therefore, an important effort in this study has been to establish a methodology to take advantage of all the data sources available including nautical charts that had to be digitalized. The model surface elevation has then been validated with respect to an altimetric database. Model results suggest the existence of gyres in the vicinity of the river mouth that have never been documented before. The effect of those gyres on the Congo River dynamics has been further investigated by simulating the transport of Lagrangian particles and computing the water age.  相似文献   

The Effect of Scale on the Applicability of Taylor’s Frozen Turbulence Hypothesis in the Atmospheric Boundary Layer     

Chad W. Higgins  Martin Froidevaux  Valentin Simeonov  Nikki Vercauteren  Caitlin Barry  Marc B. Parlange 《Boundary-Layer Meteorology》2012,143(2):379-391

Taylor’s frozen turbulence hypothesis is the central assumption invoked in most experiments designed to investigate turbulence physics with time resolving sensors. It is also frequently used in theoretical discussions when linking Lagrangian to Eulerian flow formalisms. In this work we seek to quantify the effectiveness of Taylor’s hypothesis on the field scale using water vapour as a passive tracer. A horizontally orientated Raman lidar is used to capture the humidity field in space and time above an agricultural region in Switzerland. High resolution wind speed and direction measurements are conducted simultaneously allowing for a direct test of Taylor’s hypothesis at the field scale. Through a wavelet decomposition of the lidar humidity measurements we show that the scale of turbulent motions has a strong influence on the applicability of Taylor’s hypothesis. This dependency on scale is explained through the use of dimensional analysis. We identify a ‘persistency scale’ that can be used to quantify the effectiveness of Taylor’s hypothesis, and present the accuracy of the hypothesis as a function of this non-dimensional length scale. These results are further investigated and verified through the use of large-eddy simulations.  相似文献   

Hydrophysical aspects of oxygen regime formation in a shallow ice-covered lake     

A. Yu. Terzhevik  N. I. Pal’shin  S. D. Golosov  R. E. Zdorovennov  G. E. Zdorovennova  A. V. Mitrokhov  M. S. Potakhin  E. A. Shipunova  I. S. Zverev 《Water Resources》2010,37(5):662-673

Long-term observational data on a small, shallow Lake Vendyurskoe (Karelia) were used to analyze the space and time dissolved-oxygen dynamics in winter. Biochemical consumption was found to play a leading role in the reduction of dissolved-oxygen concentration in lake water in winter. The total decrease in the amount of dissolved oxygen since the beginning of under-ice period until mid-April was shown to amount to one third of the initial value. The year-to-year variations in winter oxygen consumption are ~10%, suggesting the process to be stable in the years of observations. The rate of oxygen consumption and variations in dissolved oxygen content of lake water in winter were evaluated. The analysis and literary data allow us to conclude that the hydrophysical processes taking place in shallow lakes in winter have a considerable effect on their oxygen regime.  相似文献   

Low-temperature hydrothermal alteration of intra-caldera tuffs,Miocene Tejeda caldera,Gran Canaria,Canary Islands     

Eleanor Donoghue  Valentin R. Troll  Chris Harris  Aoife O'Halloran  Thomas R. Walter  Francisco J. Pérez Torrado 《Journal of Volcanology and Geothermal Research》2008

The Miocene Tejeda caldera on Gran Canaria erupted ~ 20 rhyolite–trachyte ignimbrites (Mogán Group 14–13.3 Ma), followed by ~ 20 phonolitic lava flows and ignimbrites (Fataga Group 13–8.5 Ma). Upper-Mogán tuffs have been severely altered immediately within the caldera margin, whereas extra-caldera Mogán ignimbrites, and overlying Fataga units, are apparently unaltered. The altered intra-caldera samples contain minerals characteristic of secondary fluid–rock interaction (clays, zeolites, adularia), and relics of the primary mineral assemblage identified in unaltered ignimbrites (K-feldspar, plagioclase, pyroxene, amphibole, and groundmass quartz). Major and trace-element data indicate that Si, Na, K, Pb, Sr, and Rb, were strongly mobilized during fluid–rock interaction, whereas Ti, Zr, and Nb behaved in a more refractory manner, experiencing only minor mobilization. The δ¹⁸O values of the altered intra-caldera tuffs are significantly higher than in unaltered extra-caldera ignimbrites, consistent with an overall low-temperature alteration environment. Unaltered extra-caldera ignimbrites have δD values between − 110‰ and − 173‰, which may reflect Rayleigh-type magma degassing and/or post-depositional vapour release. The δD values of the altered intra-caldera tuffs range from − 52‰ to − 131‰, with ambient meteoric water at the alteration site estimated at ca. − 15‰. Interaction and equilibration of the intra-caldera tuffs with ambient meteoric water at low temperature can only account for whole-rock δD values of around − 45‰, given that ?D_clay–water is ca. − 30‰ at 100 °C, and decreases in magnitude at higher temperatures. All altered tuff samples have δD values that are substantially lower than − 45‰, indicating interaction with a meteoric water source with a δD value more negative than − 15‰, which may have been produced in low-temperature steam fumaroles. Supported by numerical modeling, our Gran Canaria data reflect the near-surface, epithermal part of a larger, fault-controlled hydrothermal system associated with the emplacement of the high-level Fataga magma chamber system. In this near-surface environment, fluid temperatures probably did not exceed 200–250 °C.  相似文献   

The effective stiffness of modern unreinforced masonry walls          下载免费PDF全文

Bastian Valentin Wilding  Katrin Beyer 《地震工程与结构动力学》2018,47(8):1683-1705

Code design of unreinforced masonry (URM) buildings is based on elastic analysis, which requires as input parameter the effective stiffness of URM walls. Eurocode estimates the effective stiffness as 50% of the gross sectional elastic stiffness, but comparisons with experimental results have shown that this may not yield accurate predictions. In this paper, 79 shear‐compression tests of modern URM walls of different masonry typologies from the literature are investigated. It shows that both the initial and the effective stiffness increase with increasing axial load ratio and that the effective‐to‐initial stiffness ratios are approximately 75% rather than the stipulated 50%. An empirical relationship that estimates the E‐modulus as a function of the axial load and the masonry compressive strength is proposed, yielding better estimates of the elastic modulus than the provision in Eurocode 6, which calculates the E‐modulus as a multiple of the compressive strength. For computing the ratio of the effective to initial stiffness, a mechanics‐based formulation is built on a recently developed analytical model for the force‐displacement response of URM walls. The model attributes the loss in stiffness to diagonal cracking and brick crushing, both of which are taken into account using mechanical considerations. The obtained results of the effective‐to‐initial stiffness ratio agree well with the test data. A sensitivity analysis using the validated model shows that the ratio of effective‐to‐initial stiffness is for most axial load ratios and wall geometries around 75%. Therefore, a modification of the fixed ratio of effective‐to‐initial stiffness from 50% to 75% is suggested.  相似文献