124,666 research outputs found
Coccolithophorid biogeography in the Gulf of Manfredonia (South Adriatic Sea): preliminary results from water samples and surface sediments.
No full textA generalization of Gompertz law compatible with the Gyllenberg–Webb theory for tumour growth
No full textGeneral scores for accessibility and inequality measures in urban areas
No full textIn the last decades, the acceleration of urban growth has led to an unprecedented level of urban interactions and interdependence. This situation calls for a significant effort among the scientific community to come up with engaging and meaningful visualizations and accessible scenario simulation engines. The present paper gives a contribution in this direction by providing general methods to evaluate accessibility in cities based on public transportation data. Through the notion of isochrones, the accessibility quantities proposed measure the performance of transport systems at connecting places and people in urban systems. Then we introduce scores ranking cities according to their overall accessibility. We highlight significant inequalities in the distribution of these measures across the population, which are found to be strikingly similar across various urban environments. Our results are released through the interactive platform: www.citychrone.org, aimed at providing the community at large with a useful tool for awareness and decision-making
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Coccolithophore communities in the Gulf of Manfredonia (Southern Adriatic Sea): data from water and surface sediments
No full textLiving coccolithophore distributions from the Gulf of Manfredonia (Southern Adriatic Sea) were investigated and comparedwith
the coccolith assemblages in the underlying surface sediments. In total, 55 samples from 13 stations in four transects collected
at the end of October 2000 were analyzed to determine spatial and vertical distribution of individual taxa in the coastal environment. At
all stations, the maximum coccosphere densities were between 10m and 30m of water depth (maximum values were ~4x104
coccospheres per litre of seawater). Coccolithophore absolute abundances show a vertical stratification and spatial variation, as well as
variable species diversity, increasing from the coast to the open sea and decreasing with depth. Different coccolithophore communities
are recorded in the shallow and deep photic zone. Emiliania huxleyi, Syracosphaera spp., Rhabdosphaera spp., Coronosphaera spp.,
Umbellosphaera tenuis and holococcolithophores are present mainly in the surface waters, above the thermocline between 25-30m
depth. In the deeper water samples, there is a significant increase in coccospheres of Florisphaera profunda. The coccolithophore cell
density variability is compared with in situ measurements of environmental parameters (temperature, salinity, nitrates and phosphates).
Cell densities of all dominant taxa are most highly correlated with temperature variability. The low correlations of cell densities with nitrates
and phosphates may be caused by insufficient sampling resolution, nutrient levels close to detection limits, or both. The comparison
of the living assemblage with surface sediment records shows significant differences in the presence and abundance of some species.
The recognised fossil record in the surface sediments ismainly represented by Cretaceous-Pleistocene reworked species, showing stronger
dynamic processes at the bottom, such as terrigenous input and resuspension, than phytoplankton growth. Most marked correspondence
between living and fossil assemblages has been found in the deeper and open sea sediment
Cretaceous flysch deposits of the Northern Apennines, Italy: age of inception of orogenesis-controlled sedimentation
No full textCretaceous flysch deposits of the Northern Apennines, Italy: age of inception of orogenesis-controlled sedimentation
No full textCalcareous nannofossils have proved to be very effective in determining the age of Cretaceous flysch sequences of the Northern Apennines. Here, we focus on the beginning of flysch sedimentation, which replaced previous pelagic deposition during the Late Cretaceous convergence stage. In all the examined sequences an early to late Campanian age has been determined for the bases of the flysch formations, implying an essentially synchronous start of orogenesis-controlled sedimentation within the Ligurian Apenninic (Ligurian) Ocean Basin. Data obtained from the siliciclastic turbidite sequence (Vat Lavagna/Mt. Gottero Sandstones) overlying Jurassic ophiolites and sedimentary cover, indicate continuous sedimentation from earliest Campanian to early Paleocene. Thus, either a forearc or 'dormant trench' tectonic setting seems to be required for this sequence. Regarding the calcareous Helminthoid Flysch, a minor diachrony in the basal ages suggest a general younging from south to north. The onset ages of flysch sedimentation range from early Campanian (Southern Tuscany Flysch), to early-middle Campanian (Mt. Caio/Ottone Flysch), to latest Campanian (S. Remo, Mt. Antola, Mt. Cassio, Mt. Caio/Orocco Flysch). This diachrony could be the consequence of Late Cretaceous-early Tertiary transcurrent tectonics in the Apenninic Basin and/or of multiple source areas (from both the European/Iberian and Adriatic margins). These tectonic implications are in agreement with the kinematic evidence of a transpressional regime along the Iberian/Adriatic plate boundary (Apenninic sector) during the Late Cretaceous
Waves of novelties in the expansion into the adjacent possible
No full textThe emergence of novelties and their rise and fall in popularity is an ubiquitous phenomenon in human activities. The coexistence of popular evergreens with novel and sometimes ephemeral trends pervades technological, scientific and artistic production. Though this phenomenon is very intuitively captured by our common sense, a comprehensive explanation of how waves of novelties are not hampered by well established old-comers is still lacking. Here we first quantify this phenomenology by empirically looking at different systems that display innovation at very different levels: the creation of hashtags in Twitter, the evolution of online code repositories, the creation of texts and the listening of songs on online platforms. In all these systems surprisingly similar patterns emerge as the non-trivial outcome of two contrasting forces: the tendency of retracing already explored avenues (exploit) and the inclination to explore new possibilities. These findings are naturally explained in the framework of the expansion of the adjacent possible, a recently introduced theoretical framework that postulates the restructuring of the space of possibilities conditional to the occurrence of innovations. The predictions of our theoretical framework are borne out in all the phenomenologies investigated, paving the way to a better understanding and control of innovation processes
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