Los Angeles as a digital place: The geographies of user‐generated content     

Andrea Ballatore  Stefano De Sabbata 《Transactions in GIS》2020,24(4):880-902

Online representations of places are becoming pivotal in informing our understanding of urban life. Content production on online platforms is grounded in the geography of their users and their digital infrastructure. These constraints shape place representation, that is, the amount, quality, and type of digital information available in a geographic area. In this article we study the place representation of user‐generated content (UGC) in Los Angeles County, relating the spatial distribution of the data to its geo‐demographic context. Adopting a comparative and multi‐platform approach, this quantitative analysis investigates the spatial relationship between four diverse UGC datasets and their context at the census tract level (about 685,000 geo‐located tweets, 9,700 Wikipedia pages, 4 million OpenStreetMap objects, and 180,000 Foursquare venues). The context includes the ethnicity, age, income, education, and deprivation of residents, as well as public infrastructure. An exploratory spatial analysis and regression‐based models indicate that the four UGC platforms possess distinct geographies of place representation. To a moderate extent, the presence of Twitter, OpenStreetMap, and Foursquare data is influenced by population density, ethnicity, education, and income. However, each platform responds to different socio‐economic factors and clusters emerge in disparate hotspots. Unexpectedly, Twitter data tend to be located in denser, more deprived areas, and the geography of Wikipedia appears peculiar and harder to explain. These trends are compared with previous findings for the area of Greater London.  相似文献   

Geant4 simulations of soft proton scattering in X-ray optics     

Valentina?Fioretti  Teresa?Mineo  Andrea?Bulgarelli  Paolo?Dondero  Vladimir?Ivanchenko  Fan?Lei  Simone?Lotti  Claudio?Macculi  Alfonso?Mantero 《Experimental Astronomy》2017,44(3):413-435

Low energy protons (< 300 keV) can enter the field of view of X-ray telescopes, scatter on their mirror surfaces at small incident angles, and deposit energy on the detector. This phenomenon can cause intense background flares at the focal plane decreasing the mission observing time (e.g. the XMM-Newton mission) or in the most extreme cases, damaging the X-ray detector. A correct modelization of the physics process responsible for the grazing angle scattering processes is mandatory to evaluate the impact of such events on the performance (e.g. observation time, sensitivity) of future X-ray telescopes as the ESA ATHENA mission. The Remizovich model describes particles reflected by solids at glancing angles in terms of the Boltzmann transport equation using the diffuse approximation and the model of continuous slowing down in energy. For the first time this solution, in the approximation of no energy losses, is implemented, verified, and qualitatively validated on top of the Geant4 release 10.2, with the possibility to add a constant energy loss to each interaction. This implementation is verified by comparing the simulated proton distribution to both the theoretical probability distribution and with independent ray-tracing simulations. Both the new scattering physics and the Coulomb scattering already built in the official Geant4 distribution are used to reproduce the latest experimental results on grazing angle proton scattering. At 250 keV multiple scattering delivers large proton angles and it is not consistent with the observation. Among the tested models, the single scattering seems to better reproduce the scattering efficiency at the three energies but energy loss obtained at small scattering angles is significantly lower than the experimental values. In general, the energy losses obtained in the experiment are higher than what obtained by the simulation. The experimental data are not completely representative of the soft proton scattering experienced by current X-ray telescopes because of the lack of measurements at low energies (< 200 keV) and small reflection angles, so we are not able to address any of the tested models as the one that can certainly reproduce the scattering behavior of low energy protons expected for the ATHENA mission. We can, however, discard multiple scattering as the model able to reproduce soft proton funnelling, and affirm that Coulomb single scattering can represent, until further measurements at lower energies are available, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.  相似文献   

Drainage reorganization and Laramide tectonics in north-central New Mexico and downstream effects in the Gulf of Mexico     

Tyson M. Smith  Kurt E. Sundell  Shelby N. Johnston  Carlos N. Guilherme Andrade  Ross A. Andrea  Jordan N. Dickinson  Yiduo A. Liu  Michael Andrew Murphy  Tom J. Lapen  Joel E. Saylor 《Basin Research》2020,32(3):419-452

The El Rito and Galisteo depocenters in north-central New Mexico archive tectonically-driven Paleogene drainage reorganization, the effects of which influenced sedimentation along the northwestern margin of the Gulf of Mexico. Although separated by ~100 km and lacking depositional chronology for the El Rito Formation, the two aforementioned New Mexican depocenters are commonly considered remnants of a single basin with coeval deposition and shared accommodation mechanism. Detrital zircon U-Pb maximum depositional ages indicate that the El Rito and Galisteo formations are not coeval. Moreover, stratigraphic thickness trends and mapping relationships indicate different accommodation mechanisms for the Galisteo and El Rito depocenters; tectonically-induced subsidence versus infilling of incised topography, respectively. The regional unconformity that bounds the base of both the El Rito and Galisteo formations is a correlative surface induced by local tectonic activity and associated drainage reorganization in the early Eocene, and was diachronously buried by northward onlap of fluvial sediments. Detrital zircon distributions in both depocenters indicate increased recycling of Mesozoic strata above the unconformity, but diverge upsection as topographic prominence of local basement-involved uplifts waned. Sediment capture in these depocenters is coeval with deposition in other externally-drained Laramide basins. Further, it corresponds to a period of low Laramide province-derived sediment input and replacement by Appalachian-sourced sediment along the northwestern margin of the Gulf of Mexico during a basin-wide transgression. This illustrates the potential effect that pockets of sediment storage within the catchment of a transcontinental drainage system can have over the sedimentary record in the receiving marine basin.  相似文献   

From cylindrical to non‐cylindrical foreland basin: Pliocene–Pleistocene evolution of the Po Plain–Northern Adriatic basin (Italy)     

Chiara Amadori  Giovanni Toscani  Andrea Di Giulio  Francesco Emanuele Maesano  Chiara D&#x;Ambrogi  Manlio Ghielmi  Roberto Fantoni 《Basin Research》2019,31(5):991-1015

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Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments     

Andrea Saage  Olav Vadstein  Ulrich Sommer 《Journal of Sea Research》2009,62(1):16-21

The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response, with close to zero ingestion rates at concentrations below 5 µg C l^− 1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 µg C l^− 1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C. hamatus can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available.  相似文献   

Characteristics of Thermal and Geopotential Height Differences Between Continent and Ocean and Its Role in the Strength of the Asian Summer Monsoon     

Andrea Silverman SUN Jilin 《中国海洋大学学报(英文版)》2005,4(4):366-376

The interdecadal factors affecting the summer monsoon winds over Somalia and the South China Sea were studied. Global geopotential heights and wind velocity fields of the 850-hPa and 200-hPa pressure levels, as well as sea surface temperature anomaly data and correlation coefficients were analyzed. The monsoons over Somalia and the South China Sea were found to be two different monsoon systems, operating on different mechanisms and being affected by different ocean-atmosphere interactions. The intensity of the Asian subtropical summer monsoon is influenced by the intensity of the summer monsoon over Somalia in the month of June and by the intensity of the summer monsoon over the South China Sea in the months of June and July. The summer monsoon wind strength over Somalia is affected by regional factors, such as the heating of the Tibetan plateau, and by global mechanisms, such as the subtropical heat exchange with Antarctica. The summer monsoon over the South China Sea is affected by different ocean-atmosphere interactions. The Somalia and subtropical summer monsoons have wind blowing down the pressure gradient from area over ocean to that over land, like typical summer monsoons. The South China Sea summer monsoon has winds that blow down the pressure gradient from area over land to that over ocean. The South China Sea summer monsoon is affected by the Kuroshio Current off the east coast of Japan.  相似文献   

New noble gas data of primitive and differentiated achondrites including Northwest Africa 011 and Tafassasset     

Andrea PATZER  Ludolf SCHULTZ  Luitgard FRANKE 《Meteoritics & planetary science》2003,38(10):1485-1497

Abstract— This work reports on the noble gas inventory of 3 new acapulcoites, 3 brachinites, 2 new eucrites from the Dar al Gani region in Libya, the unique achondrite Dar al Gani (DaG) 896 from the same locality, the new eucrite‐like achondrite Northwest Africa (NWA) 011, and the controversial sample Tafassasset. We determined cosmic ray exposure and gas retention ages, evaluated shielding conditions, and discuss the trapped noble gas component of the specimens. All exposure ages are within the known range of stony meteorites and partly confirm previously established age clusters. Shielding conditions vary, suggesting substantial shielding for all 3 brachinites and Tafassasset. We cannot exclude, however, that the Mg‐rich composition of brachinites simply simulates heavy shielding. Regarding the trapped component, we found Q‐like compositions only for the acapulcoite Thiel Mountains (TIL) 99002. The brachinite Elephant Moraine (EET) 99402 yields a high, subsolar ³⁶Ar/¹³²Xe ratio of ?400 along with a slightly elevated ⁸⁴Kr/¹³²atio, indicating minor atmospheric contamination. All the other samples, particularly the eucrite DaG 983, are characterized by clearly elevated Ar/Kr/Xe ratios due to significant terrestrial alteration. Tafassasset exhibits noble gas parameters that are different from those of CR chondrites, including a relatively high cosmic ray exposure age, the absence of a solar component, low ¹³²Xe concentrations, a low trapped ³⁶Ar/¹³²Xe ratio of ?30, and a noticeable amount of radiogenic ¹²⁹Xe. Similar attributes have been observed for some primitive achondrites. These attributes are also consistent with the metamorphic character of the sample. We, therefore, consider Tafassasset's noble gas record to be inconclusive as to its classification (primitive achondrite versus metamorphosed CR chondrite).  相似文献   

A finite element method for localized erosion in porous media with applications to backward piping in levees     

Andrea Francesco Rotunno  Carlo Callari  Francesco Froiio 《国际地质力学数值与分析法杂志》2019,43(1):293-316

This paper presents a computational method able to effectively model both the simultaneous processes typically observed in backward erosion piping, ie, the pipe tip propagation and the conduit cross-section enlargement. The numerical method is based on the novel formulation of a problem of localized erosion along a line propagating in a multidimensional porous medium. In this line, a conduit with evolving transverse size is embedded, which conveys a multiphase flow. The two systems, porous medium and pipe, are bridged by exchange terms of multiphase fluid mass and by a shared fluid pressure field. On the contrary, different fields are considered to describe flows, which are assumed as Darcian in the porous medium and turbulent in the conduit. These two flows drive pipe propagation and enlargement, respectively, as modeled by means of proper erosion kinetic laws. The corresponding numerical formulation is based on the combination between one- and multidimensional finite elements, to model the erosion conduit and the porous medium, respectively. Several simulations are proposed to demonstrate the ability of the proposed approach in reproducing available experimental data of real-scale tests on levees. Our results point out the crucial role played by the combined influence of pipe propagation and enlargement, as well as of three-dimensional (3D) effects. We also assess the mesh independence of the proposed numerical solution, particularly as concerns the calculated pipe propagation history.  相似文献   

Seismological constraints on the 2018 Mt. Etna (Italy) flank eruption and implications for the flank dynamics of the volcano     

Salvatore Alparone  Graziella Barberi  Elisabetta Giampiccolo  Vincenza Maiolino  Antonino Mostaccio  Carla Musumeci  Antonio Scaltrito  Luciano Scarfì  Tiziana Tuv  Andrea Ursino 《地学学报》2020,32(5):334-344

3D earthquake locations, focal mechanisms and stress tensor distribution in a 16‐month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post‐eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ₁, NE‐SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano.  相似文献   

Flow dynamics at the continental scale: Streamflow correlation and hydrological similarity     

Andrea Betterle  Mario Schirmer  Gianluca Botter 《水文研究》2019,33(4):627-646

Streamflow variability in space and time critically affects anthropic water uses and ecosystem services. Unfortunately, spatiotemporal patterns of flow regimes are often unknown, as discharge measurements are usually recorded at a limited number of hydrometric stations unevenly distributed along river networks. Advances in understanding the physical processes that control the spatial patterns of river flows are therefore necessary to predict water availability at ungauged locations or to extrapolate pointwise streamflow observations. This work explores the use of the spatial correlation of river flows as a metric to quantify the similarity between hydrological responses of two catchments. Following a stochastic framework, 340,000 cross‐correlations between pairs of daily streamflows time series are predicted at a seasonal timescale across the contiguous United States using 413 catchments of the MOPEX dataset. Model predictions of streamflow correlation obtained in absence of run‐off information are successfully used to identify catchment outlets sharing similar discharge dynamics and flow regimes across a broad range of geomorphoclimatic conditions, without relying on calibration. The selection of reference streamgauges based on predicted streamflow correlation generally outperforms the selection based on spatial proximity, especially as the density of available gauged sections decreases. Interestingly, correlated outlets share a broad spectrum of hydrological signatures (mean discharge, flow variability, and recession properties), suggesting that catchments forced by analogous frequency and intensity of effective rainfall events might exhibit common geomorphoecological traits leading to similar hydrological responses. The proposed framework provides a physical basis to assist the regionalization of flow dynamics and to interpret the spatial variability of flow regimes along stream networks.  相似文献