1,720,971 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Pacific Equatorial Transect
Get PDFIntegrated Ocean Drilling Program Expedition 320/321, "Pacific Equatorial Age Transect" (Sites U1331–U1338), was designed to recover a continuous Cenozoic record of the paleoequatorial Pacific by coring above the paleoposition of the Equator at successive crustal ages on the Pacific plate. These sediments record the evolution of the paleoequatorial climate system throughout the Cenozoic. As we gained more information about the past movement of plates and when in Earth's history "critical" climate events took place, it became possible to drill an age transect ("flow line") along the position of the paleoequator in the Pacific, targeting important time slices where the sedimentary archive allows us to reconstruct past climatic and tectonic conditions. The Pacific Equatorial Age Transect (PEAT) program cored eight sites from the sediment surface to at or near basement, with basalt aged between 53 and 16 Ma, covering the time period following maximum Cenozoic warmth, through initial major glaciations, to today. The PEAT program allows the reconstruction of extreme changes of the calcium carbonate compensation depth (CCD) across major geological boundaries during the last 53 m.y. A very shallow CCD during most of the Paleogene makes it difficult to obtain well-preserved carbonate sediments during these stratigraphic intervals, but we recovered a unique sedimentary biogenic sediment archive for time periods just after the Paleocene/Eocene boundary event, the Eocene cooling, the Eocene–Oligocene transition, the "one cold pole" Oligocene, the Oligocene–Miocene transition, and the middle Miocene cooling. Together with older Deep Sea Drilling Project and Ocean Drilling Program drilling in the equatorial Pacific, we can also delineate the position of the paleoequator and variations in sediment thickness from ~150°W to 110°W longitude
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
The Seismic Stratigraphy and Sedimentation along the Ninetyeast Ridge
Get PDFThe Ninetyeast Ridge (NER) is a ~5000 km-long aseismic volcanic ridge trending NS
in the eastern Indian Ocean basin. It is widely accepted that NER formed from the trace of
a single hotspot as the Indian plate moved northward during the Late Cretaceous and Early
Cenozoic due to the linear age progression from 43 Myo at the southern end to 77 Myo at the
northern end. What is not fully understood is the geologic history of the ridge since its
formation. This study examines the stratigraphy and sediment thickness on the ridge using
new seismic data to describe the sedimentary history of NER.
More than 3700 km of 2D multichannel seismic reflection profiles were collected
along NER at seven sites between 5.5 degrees N and 26.1 degrees S during cruise KNOX06RR of the R/V
Roger Revelle in 2007. Scientific objectives were to obtain site survey data for proposed
drilling and to understand the sedimentary layers, sediment distribution, and geologic history
of NER. Seismic survey sites were chosen primarily based on proximity to existing Deep
Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) drill holes (Sites 758, 216,
214, and 253) for interpretation and correlation with existing lithologic data.
Seismic data were processed (filtered, stacked, and time-migrated) and interpreted
using standard seismic stratigraphy principles. Three major horizons were interpreted, correlated with those previously recognized at the DSDP and ODP sites, and traced
throughout the seismic data. Seismic data were categorized into three units based on distinct
acoustic properties including changes in reflector amplitude, wavelength, continuity, and
geometry. Seismic Unit I comprises a succession of pelagic sediments and sedimentary rock
draped over Seismic Unit II, which consists of pelagic carbonates mixed with volcaniclastics.
Seismic Unit III is volcanic basement.
Sediment layer thicknesses and distribution were mapped at each site, and
bathymetric data were correlated with seismic data to interpret geologic features. Seismic
and core data indicate a common sedimentary history at each site: volcaniclastic-rich
sediments deposited during or shortly after ridge formation topped by a thick drape of pelagic
sediments. This history likely happened in three stages over the last ~77 My: 1) the initial
subaerial or submarine emplacement of the volcanic ridge, 2) the deposition of shallow water
sediments and volcaniclastics, and finally 3) the subsidence of the ridge followed by deep
water pelagic sediment deposition
Drilling Through Gas Hydrates Formations: Managing Wellbore Stability Risks
Get PDFAs hydrocarbon exploration and development moves into deeper water and
onshore arctic environments, it becomes increasingly important to quantify the drilling
hazards posed by gas hydrates.
To address these concerns, a 1D semi-analytical model for heat and fluid transport
in the reservoir was coupled with a numerical model for temperature distribution along
the wellbore. This combination allowed the estimation of the dimensions of the hydratebearing
layer where the initial pressure and temperature can dynamically change while
drilling. These dimensions were then used to build a numerical reservoir model for the
simulation of the dissociation of gas hydrate in the layer. The bottomhole pressure
(BHP) and formation properties used in this workflow were based on a real field case.
The results provide an understanding of the effects of drilling through hydratebearing
sediments and of the impact of drilling fluid temperature and BHP on changes in
temperature and pore pressure within the surrounding sediments. It was found that the
amount of gas hydrate that can dissociate will depend significantly on both initial
formation characteristics and bottomhole conditions, namely mud temperature and pressure. The procedure outlined suggested in this work can provide quantitative results
of the impact of hydrate dissociation on wellbore stability, which can help better design
drilling muds for ultra deep water operations
Erosion and Sedimentation on the Carnegie Ridge, Eastern Equatorial Pacific
Get PDFThe Carnegie Ridge is an aseismic ridge that bounds the south flank of the Panama Basin. Dynamic sedimentation around Carnegie Ridge is shown by evidence of erosion, dissolution and re-deposition of pelagic sediments where erosive episodes have carved out relict landscapes. I examine three aspects of these features: 1) What are the mechanisms involved in the erosive episodes; 2) Can the ages of the erosive events be constrained; and finally 3) Can the transport mechanism be identified?
The extent of erosion and re-deposition was studied during the R/V Melville cruise MV1014 from October to November 2010 to compare with geochemical estimates of sediment focusing. The MV1014 cruise acquired geochemical, geological and geophysical data to compare with earlier surveys and scientific drilling.
Large-scale erosion, presumably driven by massive, density-driven deepwater spillover events from the Peru Basin, created a prominent valley named Sand Dune Valley in the study area. A second, smaller valley, known as Western Valley, was likely formed by medium-scale erosion catalyzed by a ridge jump with subsequent normal faulting forming a fault scarp which has intensified near-bottom currents. Smaller-scale erosional events created small-scale surface sediment truncation. Utilizing a seismic stratigraphy developed by comparing seismic horizons to the sediment columns at DSDP Site 157 and ODP Site 846, and exposure of diagenetic chalk along the valley floors allowed a reconstruction of the timing of these highly erosive episodes.
Two major erosive episodes are proposed to have occurred at ~5 Ma and ~3Ma which removed as much as 75 km3 of sediment. The erosive episodes may be linked to a ridge jump of the Galapagos hotspot at ~5-4 Ma and the final closing of the Isthmus of Panama ~3Ma.
Sediment transport regimes for the Quaternary were determined using horizons dated at 2 Ma (PL-2), 1.7 Ma (PL-1) and 84 ka (Q-84). Isopachs created using the three horizons concluded that the dominant transport regime occurs to the NW of the study area with strong lateral transport to the sides of the valleys
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