1,721,149 research outputs found
BeppoSAX view of the NS-LMXB GS 1826-238
No full textContext. The spectroscopic characteristics of GS 1826-238 a neutron star in a low-mass X-ray binary system, have already been studied by sensitive, wide band X-ray telescopes (e.g. BeppoSAX, RXTE, INTEGRAL). Up to now, the source has always been observed in a low-hard spectral state, with two spectral components typically detected. The persistent high-energy (>10 keV) emission is effectively explained by thermal Comptonisation by a hot electron cloud (kT e ∼ 20 keV); a further low energy component, modelled either by pure blackbody emission or by Compton-modified blackbody radiation by a few keV electron plasma, is generally needed to yield acceptable fits in the soft X-ray band. Aims. The aim of the present work is to investigate the origin and the nature of the low energy emission of GS 1826-238 further, along with its contribution to the bolometric output of the source, dominated by the high-temperature thermally Comptonised radiation. Methods. This kind of investigation needs sensitive data in the widest available energy band. Simultaneous covering of both the soft X-rays (below 1 keV) and the hard X-rays (up to hundreds of keV) is crucial for an unbiased characterisation of the two spectral components, so we searched the whole BeppoSAX-NFI archive for all the available GS 1826-238observations. We analysed a total of six data sets, collected from 1997 to 2000; data analysis of two of them was still unpublished. In this study we applied both a well-established (comptt) and a more recent, updated Comptonisation model (comptb), in order to get the widest quantitative information about the physical parameters at work. Results. Our results confirm that the 0.1-200 keV emission of GS 1826-238 needs two components to be explained. In particular, two populations of soft seed photons, with different colour temperatures, are observed. One population is Comptonised to high energies by a hot electron cloud (temperatures in the range 19-24 keV, anticorrelated with the source luminosity), while the other is directly observed and can be modelled by a pure blackbody. We also propose an alternative model in which both the seed photon populations are Compton-modified by the electron plasma. This model explains the observed emission of GS 1826-238 as accurately as the traditional one and, moreover, fits well in a wider evolutionary scenario able to describe the state transitions observed in neutron-star low-mass X-ray binaries. The use of comptb also indicates that, in the case of GS 1826-238, the seed photons populations are not distributed as a pure blackbody. © 2011 ESO
Flood prevention analyses in artificially drained basins : hydraulics and ecology.
No full textAn interdisciplinary study is presented dealing with the flood prevention techniques designed and applied to two artificially drained basins in Northern Italy (Lorno and Galasso, Parma Province). The analyses about lithology, land use and hydrology are described in Part I of the paper; Part II summarizes hydraulic and environmental aspects.
As previously mentioned, many subjects are coupled and a sharp distinction in the information and modelling flow cannot be traced. In particular lack of discharge time series entails a complex coupling of hydrological and hydrodynamic modelling in order to correctly estimate the discharge hydrographs as a function of probability which enter the artificial drainage network from each contributing sub-basin and which propagate along the main channels to build the shape and the volume of the flood wave flowing in the critical final reach of the system, where flooding threatens the populated town of Colorno.
The calibration of the rainfall-runoff hydrological model and the hydrodynamic model, based on the numerical integration of the classical Saint Venant equations, is performed by a trial-and-error procedure trying to match the records dates and effects of flooding, available for the last 60 years in the drainage network and in its downstream reach in particular. The procedure depends on the description of the channel geometry varying along the decades.The hydrological model is run for the rainfall events which caused some flooding and the corresponding hydrographs are routed through the hydrodynamic code: its results are compared with the local historical observations, in terms of time and place of water levels exceeding bank elevation. Model parameters (both hydrological and hydrodynamic) are adjusted deviating as little as possible from central value of their distributions.
After calibration, the following aspects are dealt with:
A) Hydrodynamic simulation of the behaviour of the critical reach of Lorno and Galasso main channels, under the probabilistic discharge hydrographs in the unmodified configuration, for various downstream boundary conditions (open and closed lock gates).
B) Evaluation of the effects on flood risk reduction when lateral reservoirs are introduced where in the next future three open quarries will make a large storage volume available.
C) Evaluation of the optimal design of the reservoirs in order to foster the ecological restoration of the site, where many birds are expected to find their natural dwelling; design of hydraulic structures to enhance the environmental function by minimizing the impact of periodical flooding.
The problem of uncertainty in the numerical estimates is also addressed, by conducting a sensitivity analysis over the most important parameters in the hydrological and hydrodynamic simulations
Flood prevention analyses in artificially drained basins: lithology, land use and hydrology.
No full textAn interdisciplinary study is presented dealing with the flood prevention techniques designed and applied to two artificially drained basins in Northern Italy (Parma Province). The analyses include lithological, land use, hydrological, hydrodynamic and environmental aspects, in addition to structural and economical computations.
This poster (Part 1) comprises lithology, land use and hydrology, while Part 2 describes hydraulic and ecological studies, although many subjects are coupled and a distinction in the information and modelling flow cannot be sharply traced.
The Lorno and Galasso Channels are the main outlets of two adjacent basins, whose areas are 20.8 and 91.3 km2 respectively. Their catchments are both very flat and are drained by a dense network of smaller artificial canals whose bed slope is often much less than 1m•km-1: during the flood events the driving energy is provided by the water surface slope. The main channels share the final reach of 0.5 km just before their common outlet in Parma River, which in its turn flows into Po River 8 km down-stream. High stages in both Rivers cause huge backwater effects in the final 8 km of Lorno and the final 4 km of Galasso main Channels: to prevent the flood risks to the densely populated and historical town of Colorno, a lock is operating at the con-fluence of the channels, whose movable gates close whenever water level down-stream gets higher than upstream, so disconnecting both artificial channels from the natural streams.
While floods in Parma River are comparatively short (hours), floods in Po River may last weeks: moreover they usually happen during the fall season when high flows in the Lorno e Galasso basins are most likely to occur, lasting days. So in the October-December period, the joint probability of high water stages downstream of the lock, causing the closure of the gates, and of high discharge from the upstream catchments is not negligible: the probability of upstream water levels exceeding the local levees is therefore higher than the usually accepted standards for hydraulic safety.
From the lithological point of view, the soil within the region around the channels outlet is mainly silt and clay: till the XIX century it was a marshy area, with a complex ecological system, where many species of birds found their dwelling.
In conjunction with the project of three clay open quarries for the local brick industry, the analyses aim at ascertaining if these structures, once exploited, might be trans-formed and operate both as qualified ecological sites where the original natural environment can be restored, and as hydraulic devices (lateral reservoirs) to reduce the local risk of flooding.
Part I of the paper describes the lithology and land use in Lorno and Galasso basins, together with hydrological evaluations and modelling. In particular the following aspects are presented:
A) Zonation of overall catchment area into smaller tributary sub-basins; check of topology, functioning and efficiency of the drainage network; evaluation of morphological, lithological and land use features of sub-basins sides in view of the overland processes; evaluation of morphological and hydraulic properties of each canal within the drainage system, in view of the channel processes.
B) Rainfall analysis, focussing on the statistics of extreme event likely to generate the flood waves relevant to the hydrodynamic modelling in the main channels, to the design of flood prevention devices and to the risk analysis of the system.
C) Through hydrological simulation, evaluation of probabilistic flood hydrographs as a function of return time likely to occur within the drainage system; evaluation of the joint probability distribution of downstream boundary water stages (Po and Parma Rivers) and discharge hydrographs in Lorno and Galasso basins
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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