35,466 research outputs found
Sedimentology of a pseudomeandering river: the Cecina R. (central Italy)
No full textThe study reports about the result of a field investigation on the geomorphology and sedeimntology of a pseudomeandering river. A five phases model of bar evolution is proposed and discussed
Rio Quequén Grande basin (Argentina): impact of geological, environmental and human activities on water quality
No full textIn spite of the low urbanization and industrialization density of the Rio Quequén Grande basin, the socio-economical development of the last decades has produced a high environmental impact with a degradation of the water resources. This degradation is progressively increasing in intensity and expanding towards more internal zones of the basin. In the present research, we carried out a geochemical characterization of the superficial and underground water of Rio Quequén Grande basin. The Rio Quequén Grande drainage area is about 10.000 km2, located in the south-eastern sector of the Buenos Aires Province. It mainly consists of a flat environment of Quaternary aeolian
sediments and it flows into the Atlantic Ocean close to Necochea, the principal city within the area. The superficial waters of the principal fluvial branches and the groundwater of the Rio Quequén Grande basin have been sampled during the end of the 2001
and the beginning of the 2002. For the determination of the geochemical composition of the water resources samples from the superficial hydrographic network and wells
were collected and analysed in the laboratory. In particularly, a) electrical conductivity, temperature and pH have been measured in situ; b) Mg++, Ca++, Cl-, SO4- -and NO3-
anions and cations have been measured using spectrophotometer methods and c) Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Ag, Cd, Pb, and U have been measured using a ICP-MS standard procedure. The integrated analysis of the obtained geochemical results allows us to infer the following: a) The geological setting has a strong influence on the water geochemical composition. b) The intense anthropogenic activity (predominantly
farming) heavily contribute to the environmental resource quality. c) The high-risk pollution zones have been recognised. In particular the water analyses show high variations of the physico-chemical characteristics. Also, near the river outlet, Cl
values of about 700 mg/l can be observed due to the intrusion of oceanic salty water.
d) In some of these locations a remarkably high concentration of toxic elements was found. Among those, the arsenic content reaches a concentration higher than 100 μg/l in the north-eastern sector of the hydrographic basin principally due to the lithological
composition of the Quaternary deposits locally rich in grains of volcanic origin
Sedimentology of a pseudomeandering river (Cecina R., central Italy)
No full textPseudomeandering rivers (Wolman & Brush, 1961; Hickin, 1969) or wandering rivers (Church, 1983; Ferguson & Werrity, 1983; Desloges & Church, 1987) have not been studied in as much detail as other river morphologies and hence they are not well known. In recent decades, only a few studies have been carried out on them (Wolman & Brush, 1961; Church, 1983; Ferguson & Werrity, 1983; Desloges & Church, 1987). CANCELLARE LA FRASE 2 LASCIARE LA BIBLIOGRAFIA CHE SOSTIENE LA FRASE 3. Some authors considered pseudomeandering rivers as an unstable stage of transition between braided and meandering morphologies. By this assumption, even a very small variation in the hydraulics, sediment supply or structural setting would determine a change in the channel pattern. According to this hypothesis, pseudomeandering morphology should be just an exceptional, rare case. However, modern examples of pseudomeandering rivers are very common in the Northern Apennines (Orcia R., Ombrone R., Cornia R., Albegna R., Sieve R., Arno R., Cecina R.) as they were in the Pleistocene Valdarno basin (Billi et al., 1987)
Geochemical characterization of the bed sediments of the Rio Quequen catchment, Argentina
No full textThe aim of this study was to conduct geochemical analyses of mud bed sediments and the superficial waters of the Rio Quequén Grande catchment, located in the southeast section of the province of Buenos
Aires. The Rio Quequén Grande outflow into the Atlantic Ocean, near the city of Necochea. The river has cut its
channel into aeolian deposits (loess and reworked loess). Most of the catchment consists of a flat plain.
Bed sediments and superficial water were sampled along the drainage network of the Rio Quequén Grande
catchment.
The mud bottom sediments were analyzed to determine the major and trace elements, using the Ray-X fluorescence (X RF) method and loss on ignition (LOI). Together with the analyzed samples, the composition of other
samples of Argentinian loess and the composition of the Upper Continental Crust (UCC) were also plotted. They
revealed considerable compositional variation.
The sample analysis also showed compositional differences as regards grain size. The samples from the Rio
Quequén Grande are of sedimentary origin, as are the majority of loess deposits in the world.
The main cations and anions of the superficial water were analyzed. In some samples a remarkably high concentration of toxic elements was found. Of these, the concentration of the arsenic content is higher than 100 μg/l
in the northeastern sector of the hydrographic basin, principally due to the lithological composition of the
Quaternary deposits, which are locally rich in grains of volcanic origin.
The integrated analysis of the geochemical results allows us to conclude that the geological setting has a strong
influence on the geochemical composition of the sediment and water. The major zones with a pollution risk were
identifie
Monitoring and numerical modelling of riverbank erosion processes: a case study along the Cecina River (central Italy)
No full textRiverbank retreat along a bend of the Cecina River, Tuscany (central Italy) was monitored across a near annual cycle (autumn 2003 to summer 2004) with the aim of better understanding the factors influencing bank changes and processes at a seasonal scale. Seven flow events occurred during the period of investigation, with the largest having an estimated return period of about 1·5 years. Bank simulations were performed by linking hydrodynamic, fluvial erosion, groundwater flow and bank stability models, for the seven flow events, which are representative of the typical range of hydrographs that normally occur during an annual cycle. The simulations allowed identification of (i) the time of onset and cessation of mass failure and fluvial erosion episodes, (ii) the contributions to total bank retreat made by specific fluvial erosion and mass-wasting processes, and (iii) the causes of retreat. The results show that the occurrence of bank erosion processes (fluvial erosion, slide failure, cantilever failure) and their relative dominance differ significantly for each event, depending on seasonal hydrological conditions and initial bank geometry. Due to the specific planimetric configuration of the study bend, which steers the core of high velocity fluid away from the bank at higher flow discharges, fluvial erosion tends to occur during particular phases of the hydrograph. As a result fluvial erosion is ineffective at higher peak discharges, and depends more on the duration of more moderate discharges. Slide failures appear to be closely related to the magnitude of peak river stages, typically occurring in close proximity to the peak phase (preferentially during the falling limb, but in some cases even before the peak), while cantilever failures more typically occur in the late phase of the flow hydrograph, when they may be induced by the cumulative effects of any fluvial erosion
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
Geochemical characterization of sediment quality in the river basin of the Rio Grande Quequén (Argentina)
No full textThe hydrographic basin of Rio Quequén Grande (Argentine) occupies 10.000 Km2 of the south-east area of the Buenos Aires province, in the area "pampeana bonaerense", located in the bigger area of Argentine loess, between latitude 20° and 40°South. The area of the basin is for the 97,5 % flat and, thanks to the abundance of water resources and the fertility of the soil, it has been interested by the intensification of agriculture which made of it, in the last decades, one of the greater areas of food supplying on worldwide scale.
Through sedimentological, chemical and petrographic analysis, this study provides informations on the quality of river sediments, from source to mouth of Rio Quequén Grande. A comparison of the results with those obtained in the 2002 campaign, has allowed an assessment, after somthe e time, about problems of pollution due to storage of heavy metals such as Pb, V and Zn, and salinity phenomena
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
Measurement of the ratio of branching fractions B(B0→K∗0γ )/B(B0s→φγ ) and the directCP asymmetry inB 0→K∗0γ
No full textThe ratio of branching fractions of the radiative B decays B0→K⁎0γ and B0s→ϕγ has been measured using an integrated luminosity of 1.0 fb−1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of s√=7TeV. The value obtained is
B(B0→K⁎0γ)B(B0s→ϕγ)=1.23±0.06(stat.)±0.04(syst.)±0.10(fs/fd),
where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for B(B0→K⁎0γ), the branching fraction B(B0s→ϕγ) is measured to be (3.5±0.4)×10−5.
The direct CP asymmetry in B0→K⁎0γ decays has also been measured with the same data and found to be
ACP(B0→K⁎0γ)=(0.8±1.7(stat.)±0.9(syst.))%.
Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations
Letter from Carl Hayden to L. B. Williams
No full textLetter from Carl Hayden to L. B. Williams concerning the proposed township in the Grand Canyon
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