Criteria of geographic relevance: an experimental study     

Stefano De Sabbata  Tumasch Reichenbacher 《International journal of geographical information science》2013,27(8):1495-1520

The relevance of geographic information has become an emerging problem in geographic information science due to an enormous increase in volumes of data at high spatial, temporal, and semantic resolution, because of ever faster rates of new data capturing. At the same time, it is not clear whether the concept of relevance developed in information science and implemented for document-based information retrieval can be directly applied to this new, highly dynamic setting. In this study, we analyze the criteria users apply when judging the relevance of geographic entities in a given mobile usage context. Two different experiments have been set up in order to gather users' opinions on a set of possible criteria, and their relevance judgements in a given scenario. The importance ascribed to the criteria in both experiments clearly implies that a new concept of relevance is required when dealing with geographic entities instead of digital documents. This new concept of ‘Geographic Relevance’ is highly dependent on personal mobility and user's activity, whose understanding may in turn be refined by the assimilation of ‘Geographic Relevance’ itself.  相似文献   

Shifts in isotopic signatures of animals with complex life-cycles can complicate conclusions on cross-boundary trophic links     

Maria Alp  Barbara L. Peckarsky  Stefano M. Bernasconi  Christopher T. Robinson 《Aquatic Sciences - Research Across Boundaries》2013,75(4):595-606

Stable isotopes (¹³C and ¹⁵N) are widely applied in studies of trophic links. We used this method to investigate the contribution of aquatic and terrestrial prey to the diet of riparian predatory arthropods in two mountain headwater streams in Colorado, USA. Aquatic and terrestrial prey and riparian predators were collected during summer 2009. To evaluate the reliability of conclusions based on stable isotope ratios, we compared the isotopic signatures of aquatic larval and terrestrial adult stages of three abundant stream insect species and assessed variation in mixing model estimates for spider diet composition under varying assumptions for trophic fractionation. Adult isotopic signatures of some aquatic prey species were indistinguishable from those of prey species with exclusively terrestrial life histories (stoneflies: ¹³C and ¹⁵N, chironomids: ¹³C). Other prey had distinctly aquatic isotopic signatures as both larvae and adults (a mayfly and a caddisfly). There was no evidence that prey with aquatic isotopic signatures contributed to the diet of the spiders near one stream. For the other stream, mixing model analysis suggested that chironomids were included in the diets of lycosid, linyphiid and liocranid spiders. Reliable estimates of the contributions of prey sources were compromised by the sensitivity of mixing models to assumptions on trophic fractionation and the presence of “isotopically cryptic” prey. This study emphasizes the importance of supporting isotope-based studies on cross-boundary trophic links with data on isotopic shifts in prey with complex life cycles and assessment of fractionation rates specific to the study system.  相似文献   

On the propagation of topographically trapped waves     

Stefano Pierini 《地球物理与天体物理流体动力学》2013,107(1-4):97-108

Abstract

In the context of ageostrophic theory in a homogeneous ocean, a nondimensional number is determined which corresponds to the Ursell number for long gravity waves. It is defined as Q = NL ²/h ³, where N is the amplitude of the wave travelling along the long length-scale direction, L is its length and h (which for gravity waves is the water depth) is given by h=(l ⁴ f ²/g)^1/3. where l is the short length-scale, f the Coriolis parameter and g the acceleration due to gravity. The physical meaning of Q is as follows: if Q? O(1) the free evolution of the wave is linear and weakly dispersive, if Q = O(1) nonlinear and dispersive effects balance out and finally if Q ?O(1) the evolution is nonlinear and non-dispersive. Expressions for the time scales for the development of dispersive and nonlinear effects are also determined. These results apply to topographically trapped waves, namely barotropic continental shelf and double Kelvin waves travelling along a rectilinear topographic variation.  相似文献   

Angular and Frequency-Dependent Wave Velocity and Attenuation in Fractured Porous Media   总被引：1，自引：0，他引：1  

José M. Carcione  Boris Gurevich  Juan E. Santos  Stefano Picotti 《Pure and Applied Geophysics》2013,170(11):1673-1683

Wave-induced fluid flow generates a dominant attenuation mechanism in porous media. It consists of energy loss due to P-wave conversion to Biot (diffusive) modes at mesoscopic-scale inhomogeneities. Fractured poroelastic media show significant attenuation and velocity dispersion due to this mechanism. The theory has first been developed for the symmetry axis of the equivalent transversely isotropic (TI) medium corresponding to a poroelastic medium containing planar fractures. In this work, we consider the theory for all propagation angles by obtaining the five complex and frequency-dependent stiffnesses of the equivalent TI medium as a function of frequency. We assume that the flow direction is perpendicular to the layering plane and is independent of the loading direction. As a consequence, the behaviour of the medium can be described by a single relaxation function. We first consider the limiting case of an open (highly permeable) fracture of negligible thickness. We then compute the associated wave velocities and quality factors as a function of the propagation direction (phase and ray angles) and frequency. The location of the relaxation peak depends on the distance between fractures (the mesoscopic distance), viscosity, permeability and fractures compliances. The flow induced by wave propagation affects the quasi-shear (qS) wave with levels of attenuation similar to those of the quasi-compressional (qP) wave. On the other hand, a general fracture can be modeled as a sequence of poroelastic layers, where one of the layers is very thin. Modeling fractures of different thickness filled with CO₂ embedded in a background medium saturated with a stiffer fluid also shows considerable attenuation and velocity dispersion. If the fracture and background frames are the same, the equivalent medium is isotropic, but strong wave anisotropy occurs in the case of a frameless and highly permeable fracture material, for instance a suspension of solid particles in the fluid.  相似文献   

Rock grade control structures and stepped gabion weirs: Scour analysis and flow features     

Stefano Pagliara  Michele Palermo 《Acta Geophysica》2013,61(1):126-150

Rock and stepped gabion weirs are peculiar hydraulic structures that received relatively little attention in technical literature. Nevertheless, they can be successfully used for river restoration instead of traditional hydraulic structures. They have the advantage of being elastic structures and to preserve the natural environment. They can easily adapt to the in situ conditions and can be effortlessly modified according to the different hydraulic or geometric conditions which can occur in a natural river. The present study aims to analyze the effects of their presence on flow pattern and on the scour hole occurring downstream. The analysis involved scour processes, hydraulic jump types, stilling basin morphology and flow patterns. Two different hydraulic jump types were distinguished and classified. It was shown that the flow regime deeply influences the scour process, which evolves much more rapidly when a Skimming Flow regime takes place. Empirical relationships are proposed to evaluate maximum scour depth, maximum axial length, and non dimensional axial profiles.  相似文献   

All-sky Data Assimilation of MWTS-2 and MWHS-2 in the Met Office Global NWP System.     

Fabien CARMINATI  Stefano MIGLIORINI 《大气科学进展》2021,38(10):1682-1694

Microwave radiances from passive polar-orbiting radiometers have been, until recently, assimilated in the Met Office global numerical weather prediction system after the scenes significantly affected by atmospheric scattering are discarded.Recent system upgrades have seen the introduction of a scattering-permitting observation operator and the development of a variable observation error using both liquid and ice water paths as proxies of scattering-induced bias. Applied to the Fengyun 3 Microwave Temperature Sounder 2(MWTS-2) and the Microwave Humidity Sounder 2(MWHS-2), this methodology increases the data usage by up to 8% at 183 GHz. It also allows for the investigation into the assimilation of MWHS-2 118 GHz channels, sensitive to temperature and lower tropospheric humidity, but whose large sensitivity to ice cloud have prevented their use thus far. While the impact on the forecast is mostly neutral with small but significant shortrange improvements, 0.3% in terms of root mean square error, for southern winds and low-level temperature, balanced by 0.2% degradations of short-range northern and tropical low-level temperature, benefits are observed in the background fit of independent instruments used in the system. The lower tropospheric temperature sounding Infrared Atmospheric Sounding Interferometer(IASI) channels see a reduction of the standard deviation in the background departure of up to 1.2%. The Advanced Microwave Sounding Unit A(AMSU-A) stratospheric sounding channels improve by up to 0.5% and the Microwave Humidity Sounder(MHS) humidity sounding channels improve by up to 0.4%.  相似文献   

Magnetic behavior of trioctahedral micas with different octahedral Fe ordering     

Stefano Pini  Maria Franca Brigatti  Marco Affronte  Daniele Malferrari  Augusto Marcelli 《Physics and Chemistry of Minerals》2012,39(8):665-674

This contribution is finalized at the discussion of the magnetic structure of two samples, belonging to phlogopite–annite [sample TK, chemical composition ^IV(Si_2.76Al_1.24) ^VI(Al_0.64Mg_0.72 $ {\text{Fe}}_{1.45}^{2 + } $ Mn_0.03Ti_0.15) (K_0.96Na_0.05) O_10.67 (OH)_1.31 Cl_0.02] and polylithionite–siderophyllite joints [sample PPB, chemical composition ^IV(Si_3.14Al_0.86)^VI(Al_0.75Mg_0.01 $ {\text{Fe}}_{1.03}^{2 + } $ $ {\text{Fe}}_{1.03}^{3 + } $ Mn_0.01Ti_0.01Li_1.09) (K_0.99Na_0.01) O_10.00 (OH)_0.65F_1.35]. Samples differ for Fe ordering in octahedral sites, Fe²⁺/(Fe²⁺?+?Fe³⁺) ratio, octahedral composition, defining a different environment around Fe cations, and layer symmetry. Spin-glass behavior was detected for both samples, as evidenced by the dependency of the temperature giving the peak in the susceptibility curve from the frequency of the applied alternating current magnetic field. The crystal chemical features are associated to the different temperature at which the maximum in magnetic susceptibility is observed: 6?K in TK, where Fe is disordered in all octahedral sites, and 8?K in PPB sample, showing a smaller and more regular coordination polyhedron for Fe, which is ordered in the trans-site and in one of the two cis-sites.  相似文献   

Syn-thrust deformation across a transverse zone: the Grem–Vedra fault system (central Southern Alps, N Italy)     

Andrea Zanchi  Paolo D’Adda  Stefano Zanchetta  Fabrizio Berra 《Swiss Journal of Geoscience》2012,105(1):19-38

The lateral continuity of the E?CW trending thrust sheets developed within the Lower to Middle Triassic cover of the central Southern Alps (Orobic belt) is disturbed by the occurrence of several N?CS trending transverse zones, such as the poorly known Grem?CVedra Transverse Zone (GVTZ). The GVTZ developed during the emplacement of the up to six S-verging thrust sheets consisting of Lower to Middle Triassic units, occurring immediately south of the Orobic Anticlines. The transverse zone, active during thrust emplacement related to the early Alpine compressions which pre-date the Adamello intrusion, includes three major vertical shear zones, the Grem, Pezzel and Zuccone faults. The major structure of the transverse zone is the dextral Grem fault, forming a deep lateral ramp between thrust sheets 3 and 5. A similar evolution also occurred along the Zuccone and Pezzel faults, which show a left-lateral displacement of syn-thrust folds. The Grem fault was later reactivated as an oblique tear fault during the emplacement of the Orobic Anticlines, due to back-thrusting along out-of-sequence thrust surfaces (Clusone fault). Transpressional deformations along the fault zone are recorded by the rotation of major syn-thrust folds, which also suggest a horizontal offset close to 0.5?km. Records of the first stage of evolution of the Grem fault are better preserved along its northern segment, and structural relationships suggest that it propagated southward and downward in the growing thrust stack. The study of the meso and megascopic structures developed along the GVTZ constrains the evolution of the transverse zone, illustrating the complex deformational phenomena occurring in a transpressional regime. The GVTZ probably reflects the existence of pre-existing tectonic lineaments with a similar orientation. Evidence of pre-existing structures are not preserved in the exposed units, nevertheless the N?CS extensional fault systems that characterize the Norian to Jurassic rifting history of the Lombardian basin are valid candidates.  相似文献   

In Situ Determination of Au and Cu in Natural Pyrite by Near‐Infrared Femtosecond Laser Ablation‐Inductively Coupled Plasma‐Quadrupole Mass Spectrometry: No Evidence for Matrix Effects     

German Velásquez  Anastassia Y. Borisova  Stefano Salvi  Didier Béziat 《Geostandards and Geoanalytical Research》2012,36(3):315-324

Gold and copper concentrations were determined in natural pyrite by near‐infrared femtosecond LA‐ICP‐QMS, using both sulfide reference materials (pyrrhotite Po‐726 and in‐house natural chalcopyrite Cpy‐RM) and NIST SRM 610 as external calibrators. Firstly, using NIST SRM 610 as the external calibrator, we calculated the Au concentration in Po‐726 and the Cu concentration in Cpy‐RM. The calculated concentration averages for Au and Cu were similar to the values published for Po‐726 and Cpy‐RM, respectively. Secondly, we calculated Au and Cu concentrations taking NIST SRM 610 as an unknown sample and using Po‐726 and Cpy‐RM as external calibrators. Again, the average values obtained closely reflected the preferred concentrations for NIST SRM 610. Finally, we calculated Au and Cu concentrations in natural pyrite using sulfide and silicate reference materials as external calibrators. In both cases, calculated concentrations were very similar, independent of the external calibrator used. The aforementioned data, plus the fact that we obtained very small differences in relative sensitivity values (percentage differences are between 5% and 17% for ⁵⁷Fe, ⁶³Cu and ¹⁹⁷Au) on analyses of silicate and sulfide RMs, indicate that there were no matrix effects related to the differences in material composition. Thus, it is possible to determine Au and Cu in natural sulfides using NIST silicate glasses as an external calibrator.  相似文献   

Modelling hydrostratigraphy and groundwater flow of a fractured and karst aquifer in a Mediterranean basin (Salento peninsula, southeastern Italy)   总被引：2，自引：0，他引：2  

Mauro Giudici  Stefano Margiotta  Fiorella Mazzone  Sergio Negri  Chiara Vassena 《Environmental Earth Sciences》2012,67(7):1891-1907

The control exerted by the hydrostratigraphic structure on aquifer recharge, groundwater flow and discharge along the coastal areas of a Mediterranean basin (Salento peninsula, about 5,000?km² wide, southern Italy) is assessed through the development and application of a groundwater flow model based on the reconstruction of the hydrostratigraphic architecture at the regional scale. The hydrostratigraphic model, obtained by processing surface and subsurface data, is applied to map the top of the main aquifer, which is hosted in the deep hydrostratigraphic unit corresponding to Cretaceous and Oligocene limestones with complex geometrical relationships with the sea. It is also used to estimate the aquifer recharge, which occurs by percolation through overlying younger sediments with low permeability. These data are completed with information about the soil use to estimate water abstraction for irrigation and with literature data to estimate the water abstraction for drinking and industrial purposes. The above-sketched conceptual model is the basis for a finite difference groundwater 2D pseudo-stationary flow model, which assumes the following fundamental approximations: the fractured and karst limestone hydrostratigraphic unit can be approximated, at the model scale, as a continuous medium for which the discrete Darcy??s law is valid; the transition zone between salt and fresh water is so small with respect to the grid spacing that the Ghyben?CHerzberg??s approximation for a sharp interface can be applied. Along the coastline different boundary conditions are assigned if the top of the limestone hydrostratigraphic unit lies either above the sea level (the aquifer has a free surface and fresh water is drained), or below the sea level (the aquifer is under pressure and the contact with sea occurs off-shore). The groundwater flow model correctly predicts the areas where the aquifer is fully saturated with salt water.  相似文献