Boundary layer characteristics and turbulent exchange mechanisms in highly complex terrain   总被引：2，自引：0，他引：2  

Mathias W. Rotach  Marco Andretta  Pierluigi Calanca  Andreas P. Weigel  Alexandra Weiss 《Acta Geophysica》2008,56(1):194-219

The Mesoscale Alpine Programme’s Riviera project investigated the turbulence structure and related exchange processes in an Alpine valley by combining a detailed experimental campaign with high-resolution numerical modelling. The present contribution reviews published material on the Riviera Valley’s boundary layer structure and discusses new material on the near-surface turbulence structure. The general conclusion of the project is that despite the large spatial variability of turbulence characteristics and the crucial influence of topography at all scales, the physical processes can accurately be understood and modelled. Nevertheless, many of the “text book characteristics” like the interaction between the valley and slope wind systems or the erosion of the nocturnal valley inversion need reconsideration, at least for small non-ideal valleys like the Riviera Valley. The project has identified new areas of research such as post-processing methods for turbulence variables in complex terrain and new approaches for the surface energy balance when advection is non-negligible. The exchange of moisture and heat between the valley atmosphere and the free troposphere is dominated by local “secondary” circulations due to the curvature of the valley axis. Because many curved valleys exist, and operational models still have rather poor resolution, parameterization of these processes may be required.  相似文献   

Modification of stochastic ground motion models for matching target intensity measures   总被引：1，自引：0，他引：1       下载免费PDF全文

Alexandra Tsioulou  Alexandros A. Taflanidis  Carmine Galasso 《地震工程与结构动力学》2018,47(1):3-24

Stochastic ground motion models produce synthetic time‐histories by modulating a white noise sequence through functions that address spectral and temporal properties of the excitation. The resultant ground motions can be then used in simulation‐based seismic risk assessment applications. This is established by relating the parameters of the aforementioned functions to earthquake and site characteristics through predictive relationships. An important concern related to the use of these models is the fact that through current approaches in selecting these predictive relationships, compatibility to the seismic hazard is not guaranteed. This work offers a computationally efficient framework for the modification of stochastic ground motion models to match target intensity measures (IMs) for a specific site and structure of interest. This is set as an optimization problem with a dual objective. The first objective minimizes the discrepancy between the target IMs and the predictions established through the stochastic ground motion model for a chosen earthquake scenario. The second objective constraints the deviation from the model characteristics suggested by existing predictive relationships, guaranteeing that the resultant ground motions not only match the target IMs but are also compatible with regional trends. A framework leveraging kriging surrogate modeling is formulated for performing the resultant multi‐objective optimization, and different computational aspects related to this optimization are discussed in detail. The illustrative implementation shows that the proposed framework can provide ground motions with high compatibility to target IMs with small only deviation from existing predictive relationships and discusses approaches for selecting a final compromise between these two competing objectives.  相似文献   

A conceptual model of the copper–porphyry ore formation based on joint analysis of deep 3D geophysical models: Sorskoe complex (Russia) case study     

Viacheslav V. Spichak  Alexandra G. Goidina 《Acta Geophysica》2017,65(6):1133-1144

Joint analysis of deep three-dimensional models of the electrical resistivity, seismic velocity, and density of the complex hosting the Sorskoe Cu–Mo deposit (Russia) is carried out aimed at finding geophysical markers characterizing the areas of ore generation, transportation and deposition. The three-dimensional lithology model of the study area is built based on the empirical relationship between the silica content of the rocks and seismic velocities. It is in agreement with geological and geochemical studies provided in this area earlier and could be used as a basis for forecasting locations of the copper–molybdenum ore deposits at depth. A conceptual model of the copper–porphyry complex explaining the mechanisms of ore generation, transportation from the lower to the upper crust and deposition in the upper crust is suggested. In particular, it is supposed that post-magmatic supercritical gas–water ore-bearing fluids are upwelling through the plastic crust due to the sliding of the fluid films along the cleavage planes of the foliated rocks while at the depths of the brittle upper crust this mechanism could be changed by volumetric fluid transportation along the network of large pores and cracks.  相似文献   

Analysis of the incommensurately modulated OS phase of SiO2 tridymite     

Alexandra K. A. Pryde  Volker Heine 《Physics and Chemistry of Minerals》1998,25(8):603-610

The structure, symmetry and origin of the incommensurately modulated OS phase of tridymite (SiO₂) and its lock-in to the OP three-fold superlattice structure are discussed in a computational study. The structure of the OS phase (which has not been determined experimentally) is deduced as the only geometrically possible structure derived from the parent OC phase by rotation and translation of the SiO₄ tetrahedra without significant distortion of these units. It can be visualised conveniently in terms of the McConnell formalism of two component difference structures C₁ and C₂ whose space group symmetries are derived. The results are in accordance with the known lock-in structure at wave vector Q= a ^*. In the latter, the ±C₁ regions expand and the structure can square up in a very general way to take advantage of the lost symmetries (lost compared with the OC phase). Received: 4 August 1997 / Revised, accepted 24 November 1997  相似文献   

Thermodynamics of element partitioning: (1) Systematics of transition metals in crystalline and molten silicates and (2) Defect chemistry and “the Henry's law problem”     

Alexandra Navrotsky 《Geochimica et cosmochimica acta》1978,42(6):887-902

The distribution of Mg, Mn, Fe, Co and Ni among olivine, orthopyroxene, calcic clinopyroxene and liquid can be described by exchange reactions of the form: M (phase A) + Mg (phase B) = M (phase B) + Mg (phase A). The thermochemical data predict the observed partitioning within the limits of error of both sets of data when assumptions of ideal solid solution are used, except for Mn-Mg exchange. Because ΔS and ΔV for these exchange reactions are generally small, K_D varies relatively little with temperature and pressure, although individual ion distribution coefficients (D values) are more sensitive to these variables and to changing liquid composition.Trace elements present at the ppm level can enter crystals in normal lattice sites, can participate in point defect equilibria and can enter various defect sites present metastably in the crystal as a result of its P,T history. Metastable defect equilibria, in which the number of sites (grain boundaries, surfaces, intergrowths, etc.) is fixed, can lead to enhanced trace element solubility in the crystal at very low concentrations and thus to apparent deviations from Henry's law.  相似文献   

Capitalising the farm family entrepreneur: negotiating private equity partnerships in Australia     

Alexandra Langford 《The Australian geographer》2019,50(4):473-491

ABSTRACT

Research on the financialisation of land and agribusiness has highlighted major shifts in agri-food systems globally. Yet these accounts tend to focus on the activities of financial actors, and few take seriously the role of farmers in negotiating investments in land and agribusiness. Farmers in the global North may be well placed to benefit from partnerships with financial investors, although little is known about the way that such partnerships are formed. Australian studies of farmer agency have been productive in examining farm family entrepreneurs and globally engaged farmers who work beyond the farm gate to organise supply chains. This paper adds to these studies by providing insights about a capitalising farm family entrepreneur, who successfully negotiated and entered into a direct equity partnership with a large foreign pension fund. Several observations are significant: the exceptional skill, time and expense required to negotiate these partnerships; the role of consultants and non-human actors in structuring them; and the spatially- and temporally divergent farm development practices that are enabled by a shift from debt to equity financing. These observations are indicative of a new adaptive strategy of family farmers to shifting financial landscapes and of emergent family, corporate, and financial farm hybridity.  相似文献   

Slow growth and early sexual maturity: Bane and boon for the red coral Corallium rubrum     

Ivo Gallmetzer  Alexandra Haselmair  Branko Velimirov 《Estuarine, Coastal and Shelf Science》2010

This study investigates the size, age and growth of Corallium rubrum which is a key species of the only large reef-like structure in the Mediterranean Sea, the coralligéne. Two populations were studied in the Ligurian Sea at a depth between 36 and 42 m. Basal diameter, colony height and numbers of branches of 230 colonies were measured, and age and growth rates were assessed from 25 colonies. Mean growth rate was 0.2 mm yr⁻¹ of basal diameter growth, corresponding to a mean annual total branch length increase of 5 mm. These results point to a coral growth much slower than assumed in many earlier studies. Additionally, age and size at first reproduction were analysed. Male colonies were shown to become sexually mature at a minimum age of six years (1.2 mm of basal diameter), while female colonies reached maturity when at least 10 years old (2 mm of basal diameter). We further discuss the implications of slow growth and early sexual maturity for red coral management and conservation.  相似文献   

Diamond precipitation from ascending reduced fluids in the Kaapvaal lithosphere: Thermodynamic constraints     

Jan Marten Huizenga  Alexandra Crossingham  Fanus Viljoen 《Comptes Rendus Geoscience》2012,344(2):67-76

Previous research has shown that the Kaapvaal lithospheric mantle is generally reduced and characterised by a decreasing redox state with increasing depth. As a consequence, C-O-H fluids in the Kaapvaal lithospheric mantle are dominated by H₂O, CH₄, and C₂H₆. Thermodynamic calculations demonstrate that diamond precipitation from such a fluid during ascend is possible as it is exposed to a more oxidised environment and both CH₄ and C₂H₆ are oxidised. However, the calculations also demonstrate that the diamond precipitation potential from such a fluid decreases when: (1) the mantle is either more reduced or oxidised compared to the Kaapvaal mantle, or (2) the change in temperature with pressure is smaller compared to that of the Kaapvaal mantle. Therefore, the presence of reduced mantle fluid species and a generally decreasing oxygen fugacity with increasing depth do not necessarily warrant diamond precipitation from a rising reduced fluid.  相似文献   

The Filter Imager SuFI and the Image Stabilization and?Light Distribution System ISLiD of the Sunrise Balloon-Borne Observatory: Instrument Description     

A. Gandorfer  B. Grauf  P. Barthol  T. L. Riethm��ller  S. K. Solanki  B. Chares  W. Deutsch  S. Ebert  A. Feller  D. Germerott  K. Heerlein  J. Heinrichs  D. Hirche  J. Hirzberger  M. Kolleck  R. Meller  R. M��ller  R. Sch?fer  G. Tomasch  M. Kn?lker  V. Mart��nez?Pillet  J. A. Bonet  W. Schmidt  T. Berkefeld  B. Feger  F. Heidecke  D. Soltau  A. Tischenberg  A. Fischer  A. Title  H. Anwand  E. Schmidt 《Solar physics》2011,268(1):35-55

We describe the design of the Sunrise Filter Imager (SuFI) and the Image Stabilization and Light Distribution (ISLiD) unit onboard the Sunrise balloon borne solar observatory. This contribution provides the necessary information which is relevant to understand the instruments?? working principles, the relevant technical data, and the necessary information about calibration issues directly related to the science data.  相似文献   

Paleoproterozoic mafic dyke swarms of the Belomorian Province,eastern Fennoscandian Shield     

Alexandra Stepanova  Vladimir Stepanov 《Precambrian Research》2010

Paleoproterozoic mafic igneous rocks (2450–1970 Ma) are exposed in the form of layered intrusions, dykes, and volcanic rocks in the Karelian, Kola and Murmansk provinces and in the form of dykes and small intrusions in the Belomorian Province, Eastern Fennoscandian Shield. The age and sequence of mafic dyke emplacement during the Paleoproterozoic are very similar in these regions. Further comparisons of geochemical characteristics of mafic dyke swarms in the Belomorian Province and neighboring cratons show considerable similarities.  相似文献