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Efficient Simulation of Tracer Transport in Fractured Porous Media and Data-Driven Aperture Estimation
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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
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
Genesis of intrusive-related hydrothermal gold deposits
Get PDFThe nature of gold transport and deposition in deep, intrusive-related hydrothermal
systems has been the topic of this PhD-research. Specifically, the role of I-type
granites in the formation of gold deposits that occur in contact metamorphic aureoles
has been addressed by an integrated field study of gold deposits in the aureole of
the Cullen Batholith in the Proterozoic Pine Creek Inlier, northern Australia.
This investigation shows that gold was deposited in quartz vein which formed
near the thermal peak of contact metamorphism at 550 ≤ T ≤ 620°C at a pressure
around 200 MPa. Gold is localized within quartz veins that occupy fracture arrays
in a variety of structural types of major antiforms. The gold veins formed in two
distinct structural settings. In the first, the veins indicate fluid flow focusing while
the host structure was actively deforming. In the second, predominantly bedding-conformable
vein systems and randomly oriented stockworks indicate the focusing
of fluids into anticlines in the absence of deformation.
On a regional scale, gold mineralization occurs where the vein systems intersect
carbonaceous units in the metapelitic host-rock sequence or where veins formed near
carbonaceous units (≤100 m to contacts). Although abundant, veins further from
carbonaceous beds are usually barren. This association prompted the question of
what unique chemical conditions existed within or near the carbonaceous slates and
what was their effect on gold solubility.
The chemical conditions of gold transport and deposition have been inferred
by interpretation of paragenetic relationships, a detailed study on the host-rock
sequence (Matthiii and Henley, in prep.), and predictions about the nature of magmatic
hydrothermal fluid. Throughout the central Pine Creek Inlier gold-quartz
veins are associated with pyrrhotite, arsenopyrite and potassium silicate alteration
(K-feldspar + biotite in paragenesis with andalusite and cordierite). Potassium
metasomatism accompanied gold mineralization while N a, Ca was leached from the
hydrothermally altered rocks. In the absence of evaporites in the metasedimentary
sequence, high fluorine contents in biotite from the alteration selvages of the goldquartz
veins ( 4,300≤F≤49,000 ppm) indicate that a magmatic fluid was involved in
ore genesis. This involvement is consistent also with ( 1) mutual cross-cutting relations of
gold-quartz veins, pegmatites, and aplite dykes in many of the deposits, (2) the
location of the deposits in the roof of the I-type granites at a vertical distance less
than 2 km (typically ≤1 km) from the sub-horizontal intrusive contact, and (3) the
high salinity of the mineralizing fluid as estimated from the Cl-content of biotite
in most of the deposits. A magmatic derivation of the sulphur in the epigenetic
sulphides is consistent with sulphur isotopic data from the Cosmo Howley deposit
(-0.3 to +7.2 per mil 8348). Here an early-magmatic, oxidizing fluid could explain
the heavy sulphur isotopic signatures of sulphides in structurally early gold-quartz
veins which constitute the high grade stage of mineralization ( 834S arsenopyrite:
+3. 7 to + 7.2 per mil).
The I-type granitoids have I-SC characteristics (Ague and Brimhall, 1988): hornblende,
pink-K-feldspar, accessory shene, and fluorite; whole rock Fe⁺³ /Fe⁺² ≥ 0.24
which indicate that the redox state of the magmatic fluid was at or above the NNO
buffer at the temperature of crystallization. But the pyrrhotite-arsenopyrite assemblage
in the veins and the association of ore with carbonaceous units indicates that
gold was deposited under fairly reducing conditions {10⁻²²·⁵ ≤ fO₂ ≤ 10⁻²⁰ ). Thus,
local reduction of initially more oxidized fluid passing in the vicinity of carbonaceous
metasediments appears to have been responsible for localized gold deposition in the
deposits in the Pine Creek Inlier. That this mechanism is highly efficient, and may
explain the concentration of gold in many gold deposits globally, has been confirmed
by speciation and reaction-progress calculations. These calculations indicate that
AuCl₂⁻ was more important than Au(HS)₂⁻ and AuHS⁰ at the high temperature of
gold precipitation in the Pine Creek Deposits. However, even at lower temperatures
(400-500°C), total gold solubility has a minimum near the maximum stability of
graphite, so that reaction with carbonaceous matter could be an important precipitation
mechanism. Fluid-phase immiscibility consequent upon fluid contamination
by hydrocarbons could also have occurred in the gold deposits, but its effects on
gold solubility at high temperatures have yet to be determined. In the Cosmo Howley gold deposit, most of the vein-hosted ore is located in
hornfels and biotitic slate within 50 meters of the footwall of carbonaceous slates.
For this zone, it was inferred (from the field evidence of near-lithostatic fluid pressure
and the nature of chemical alteration) that fluid flow was upward and down
a temperature gradient. Flow focusing into the vein-fault conduits should have entailed
mixing of mineralizing fluid rising from greater depth with hydrocarbon-rich
fluid which ascended along the steeply-dipping beds of carbonaceous slate prior to
being focused laterally in the subvertical vein-fault conduits. This mixing hypothesis has been corroborated by results from steady-state modelling
of pressure-driven fluid flow for a cross-sectional geometry of the Cosmo Howley
deposit with the writer's Monte Carlo method for modelling flow processes in
complex geometries with order-of-magnitude variations in permeability. Another
numerical method has been designed to track fluid batches on their migration paths
through the flow models. This tool has been applied in a simplistic flow model of
the Cosmo Howley deposit. Using boundary conditions determined from the field
study and from chemical calculations, preliminary results indicate that hydrocarbon
concentrations in the vein-fluid in the footwall of the slate can exceed the threshold
value for fluid immiscibility upon fluid mixing which occurs within the vein conduits
near the carbonaceous slate units. Flow patterns which could lead to this type of
mixing have also been identified for a range of steady-state models based on other
structural geometries which typify many gold deposits in a metamorphic setting.
Dynamic patterns of fluid flow near actively-deforming faults have been simulated
in laboratory experiments using a newly-designed electric analog apparatus
that models fluid flow in metamorphic environments using analogs between charge
transport and fluid flux, storativity and capacity, and permeability and impedance.
The electric analog experiments model the field evidence of ( 1) episodic faulting in
the deposits and (2) the common presence of crack-seal textures in the gold-bearing
veins which suggest that fluid flow was intermittent and that the permeability magnitude
and distribution changed incrementally with time.
The boundary conditions for the electric analog model experiments comprise
measurements of permeabilities, porosities and storativities of appropriate finegrained
rock at relevant PT-conditions of metamorphism. The electric analog simulations
show that the steady-state models provide upper bounds on the dynamic
focusing of fluids by fault/vein conduits, because the hydraulic conductivity of the
faults has to be increased for years to thousands of years before fluid is drawn into
the fault from a wider region upstream. This applies under the proviso that the
permeability of the metamorphic rocks is in the micro to nano-darcy range. Electric analog experiments also show that after short-lived events of fault dilation
(months to tens of years) during which the hydraulic conductivity of the fault
was increased by up to eight orders of magnitude, the fluid pressure upstream in
the fault recovers instantaneously to nearly the pre-failure pressure as soon as fault
compaction and sealing is simulated. This indicates that equilibrium between the
fluid pressure in the fault and the fluid pressure in the wallrock is not attained. Furthermore,
although decompression upon fault dilation is complete, extremely little
inflow occurs in the subsequent tens to hundreds of years, because the rate of inflow
is determined by the hydraulic conductivity of the wallrock. These electric analog experimental results represent a range of manifestations of
the slow diffusivity of fluid pressure which is inferred to describe metamorphic lowpermeability
environments. This diffusivity decreases proportional to the hydraulic
conductivity and the storativity of the rock. Small diffusivity values (e.g., tens of
meters per year) imply that single fault-slip events cannot decrease fluid pressure
in the host rocks significantly if the fault-slip-induced increase in the hydraulic
conductivity of the fault is sustained for less than tens to hundreds of years. For the
case in which the fault undergoes dilation during failure, the decompression within
the fault is complete, so that the effective stress on the faulted rock is very high.
Under those conditions and temperatures above 400°C, healing and sealing of the
fault should occur within months to hundreds of years, as will be shown on the basis
of experimental data from the literature.
Summarizing these results, a sustained or frequently regenerated high hydraulic
conductivity seems to be the pre-requisite for substantial focusing of fluid flow by
faults. Alternatively, the escape of overpressured fluids by hydrofracturing can be
focused by the regional permeability distribution. This has occurred in those gold
deposits in the Pine Creek Inlier which were not actively deformed during oregenesis
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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