1,720,986 research outputs found
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
Photonic Structures in Nature: Through Order, Quasi-order and Disorder
Full text linkThe majority of colours in the natural world are produced via the wavelength selective absorption of light by pigmentation. Some species of both flora and
fauna, however, are particularly eye-catching and visually remarkable as a result
of the sub-micron, light-manipulating architecture of their outer-integument material. This thesis describes detailed investigations of a range of previously unstudied photonic structures that underpin the creation of the interesting visual appearances of several such species of flora and fauna.
These structures were examined using a variety of methods, including optical
microscopy, scanning and transmission electron microscopy, focused ion-beam
milling and atomic force microscopy. This enabled detailed characterisation of the
species’ photonic systems. The degree of order discerned in the species’ photonic
structures ranged from: ‘ordered’ systems, where multiple layers of two materials produces metallic and often mirror-like reflections; to ‘quasi-ordered’ systems,
where an average periodicity of the structure in all directions gives rise to diffuse, coloured scatter; to disordered systems, where no discernible order is observed, which results in a diffuse, broad-band, white appearance. In addition to this, the range of systems also encompassed: periodicities in one-dimension in the form of multilayering; ‘quasi-two-dimensional’ structures in the form of aligned fibres; and three-dimensional structures formed from arrangements of spherical particles.
Alongside this experimental characterisation, an in-depth series of supporting theoretical analyses were undertaken. For the one-dimensional systems studied here,
the models’ theoretical reflectance was calculated using analytical methods. For
other systems, with more complex structural-geometries, theoretical simulations
of their electromagnetic response to incident radiation were carried out using finite-difference-time-domain and finite-element-method numerical modelling approaches.
Theoretical modelling results were compared to experimental measurements of
each sample's optical properties. These were primarily reflectance measurements,
which were taken using a range of techniques appropriate for each specific investigation. In addition to this, a synthetic sample, mimicking the white-appearance and remarkable polarisation-dependant reflectance of one insect’s photonic structure, was created using polymer electrospinning.
Using these experimental measurements and theoretical simulation predictions,
the structural colour production mechanisms adopted by several species of flora
and fauna were elucidated
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
Investigating Naturally Occurring 3-Dimensional Photonic Crystals
No full textThis thesis describes my research into the highly tuned naturally occurring
3D photonic structures that are present on a selection of insects. The experimental
and theoretical work presented in this thesis was performed in
both the optical and microwave regimes.
The work performed in the optical regime included both the geometric and
optical characterisation of the native photonic structures present on the
beetle Eupholus magni cus and the butter
y Parides sesostris. The native
photonic structures of these organisms were probed in order to determine
their photonic responses and also to ascertain their geometries and structural
classes. In cases where the geometry of a photonic crystal system has
been determined, I have performed additional theoretical analysis of the
structure to establish how it might be optimised for a particular optical
function. The overall aim of the work performed in the optical regime is to
further the understanding of the photonic structural designs present on a
selection of beetles and butter
ies, by both identifying and characterising
their underlying structural geometries and consequent photonic responses.
Eupholus magni cus is a species of weevil that produces its coloured appearance
from photonic structures that are present on its outer wing casing,
producing a striped coloured pattern. The photonic structures that I discovered
were present on this weevil were found to be contrasting in structural
order. I used a wide-ranging variety of experimental and theoretical
techniques in order to perform an extensive electromagnetic and structural
characterisation of these contrasting structures. The two contrasting photonic
mechanisms employed by E. magni cus were found to produce a similar
optical response in terms of angle-independent colour whilst re
ecting
di erent coloured hues.
Parides sesostris is a species of butter
y that uses a gyroid photonic crystal
structure, contained within scales, to produce green coloured patches
on the dorsal side of its wings. In addition to this, P. sesostris uses embellishments
to its scale morphology in order to produce a highly tuned
angle-independent optical response. The optical e ects brought about by
these structural embellishments were investigated with optical experimental
techniques and they were found to di usely scatter light and aid iridescence
suppression. In addition to this, theoretical modelling was performed on a
variety of gyroid geometries. The gyroid photonic structure found in the
wing scales of P. sesostris was determined to be highly optimised to re
ect
the largest range of frequencies possible from this geometry, also aiding iridescence
suppression. In addition to this, the arrangement of gyroid arrays
within each scale was determined to produce the highest intensity possible
by using the smallest possible number of unit cells.
In addition to the optical characterisations of the organic naturally occurring
photonic structures found on these organisms, I also synthetically
replicated the three fundamental naturally occurring triply periodic bicontinuous
cubic photonic crystal structures for experimental and theoretical
electromagnetic characterisation in the microwave regime. The microwave
regime was selected to perform the characterisation as a high-resolution
fabrication method can be employed in order to produce millimetre-scale
structures, suitable for probing in this wavelength regime. A high resolution
fabrication method is an absolute requirement for accurately replicating
the complex geometries of constant mean curvature structures and retaining
a high level of detail. I have electromagnetically characterised these
three structures with the aim of gaining a better understanding of their
polarisation-dependent photonic stop-band responses. Speci cally, I have
identi ed the origin of, and the dispersion of, photonic stop-bands produced
by each unique structural geometry. I have principally focused on the characterisation
of the electromagnetic responses of these structures, how they
di er from each other and also why a linear polarisation dependence arises
from these 3D photonic structures. In addition to this I have related the
electromagnetic responses of these structures to analogous optical structures
that naturally occur on the wings of the butter
y P. sesostris and elytra of
the weevil E. magni cus. With this I aimed to gain a better understanding
of the origin of the optical e ects they provide the host biological system.
This includes the characterisation of the gyroid photonic crystal structures,
chosen to mimic that found in P. sesostris wing scales. The results from
this were also subsequently used in the optical optimisation examination
performed on the P. sesostris gyroid.
Finally, I have investigated a dynamic aspect of the 3D gyroid photonic crystal,
formed from a constant mean curvature surface. A compliant gyroid
structure was fabricated for analysis in the microwave regime and a systematic
compression force applied to it. I have measured the electromagnetic
response of this compliant gyroid at each compression distance. Alongside
this, I used theoretical modelling to electromagnetically characterise
an analogous system under compression. In doing this I have identi ed the
origin of the novel and complex photonic band-shifting behaviour produced
by this 3D geometry.University of Exeter, EPSR
Bio-Inspired Optical Systems
No full textThis thesis presents an investigation into some of the structural colours that are produced in nature. There are many animals and plants that produce structural colour, with a particularly high structural colour diversity in insects. Of the species that exhibit structural colours, three species are the subjects for investigation of this thesis. Those comprise a group of beetles from South-East Asia, Torynorrhina flammea, a buttery, Parides sesostris and a fruit, Margaritaria nobilis, both from South American rainforests. The structures that produce the vivid colours of these species were analysed using electron microscopy. This information aided the design and creation of three inorganic, synthetic replicas of the natural structures.
The fruit of Margaritaria nobilis was structurally analysed, yielding the discovery of a novel multilayer fibre. These fibres were cylindrical in design and were found to be layered together producing the epidermis of the fruit. The multilayer structure produced a vivid blue colour appearance, which is believed to offer a selective advantage because the colour deceives birds into thinking that the fruit contains nutritious flesh. This selective advantage earns M. nobilis the label of mimetic fruit.
The structure found within the M. nobilis fruit epidermis inspired the synthesis of a structure which comprises single cylindrical multilayer fibres. The synthetic fibres were manufactured from elastic materials which allow the structure to be deformed under strain and, therefore, a change in colour can be observed. As the structure was stretched, this made the layers get thinner and, therefore, the colour of the fibre blue-shifted. The fibre was able to be stretched to over twice its original length which yields a shift in peak reflected wavelength of over 200 nm.
Four beetles from the Torynorrhina flammea species were investigated with the aim of replicating the nanostructures responsible for their colour appearance. The initial interest in the beetles came from their strikingly vivid colour appearances. The structure responsible for the vivid colours in all four of the subspecies is a multilayer with high structural order and over 100 laminae. Both of these attributes contribute to the saturation of the colours exhibited. The multilayer was found to be intersected by an array of rods, the long axis of which is orthogonal to the surface. The rods are believed to be the cause of an interesting diffraction phenomenon exhibited by the beetles. Using imaging scatterometry, the structure was found to diffract the colour produced by the multilayers into an annulus around a specularly reflected white spot.
This inspired the synthesis of a multilayer permeated with an array of holes with the aim of replicating a system that could reproduce the annular pattern of colour reflection. The initial synthesised system comprised a quarter-wave stack with a perfectly ordered hexagonal array of holes permeating the surface orthogonally. The sample displayed the scattering characteristics of a hexagonal array, and the reflection spectra of the multilayer stack. When disordered hexagonal arrays were milled into the structure with a focussed ion beam, the scattering pattern started to show more of the green colour from the multilayer and less of the ordered scattering pattern. The highly disordered, synthesised structure displayed no hexagonal scattering pattern, but instead it showed a highly scattered bluish-green colouration. One sample was created by directly mapping out the array of holes using an image of the original array from one of the beetle samples. This sample was expected the same annular diffraction pattern as the beetles, however, the sample instead exhibited the same scattering pattern as the highly disordered array.
Some structurally coloured systems in nature have more than one light scattering structure, all of which contribute to the overall colour of the system. For complicated systems such as this, it is necessary to devise a technique to characterise the individual scattering structures separately. One such species that displays a complex, multicomponent system is Parides sesostris. The male of the species displays bright green patches on the dorsal side of the forewings which are made up of thousands of green wing scales. These green scales contain a 3D gyroid poly-crystal at centre with a membrane layer surrounding the underside of each scale and a scattering structure on top. Using focussed ion beam milling techniques allowed the individual characterisation of each of these structures. The gyroid poly-crystal was found to reflect not green but blue wavelengths. This led to the discovery by another group [1] that the scales contain at least one type of fluorophore. The removal of the membrane structure and some of the gyroid poly-crystal from the base of the scale resulted in the change of the overall scale structure from green to cyan. This suggests that the membrane maybe a significant source of fluorescence. Computational modelling, without fluorescence, suggests that the addition of the membrane layer to the gyroid does not shift the band-gap wavelengths; however, the overall reflection intensity does increase.
The scattering structure on the top side of each scale is comprised a bi-grating which sits on top of the 3D gyroid structure. The long periodicity of the bi-grating protrudes above the surface, resulting in the very top layer of the scale to be a mono-grating. This whole structure decreases the angular-dependence of the colour by efficiently scattering the incident light into the gyroid and also scattering the reflected light from the gyroid, resulting in a double-scattering. FIB-milling was used to isolate the scattering part of the structure. Analysis of this component of the structure revealed that it was not a source of the green colour itself; however, it did show the characteristic scattering pattern of a mono-grating. The small periodicity of the bi-grating did not produce a scattering pattern since the periodicity is too small to produce optical diffraction at normal incidence.
To characterise the effect of the fluorophores, the whole scale structure was photo-bleached using ultra-violet radiation for two months with the aim of destroying the fluorophores contained within the structure. The expected result occurred which was the blue-shifting of the peak reflected wavelengths. However, it could not be confirmed whether or not the photo-bleaching reduced the physical size of the light scattering structures which would, in theory, result in a blue-shift of the peak reflected wavelengths.
The male P. sesostris green wing scales were also the subject for investigation for trying to make inorganic replicas of the gyroid-polycrystal. A surface sol-gel coating process was utilised to coat the green wing scales with titania. This coating process was performed using a few different methods. Half of the samples were coated with TiO2 and the other half with tin-doped TiO2. Half of each of these samples had their surfaces dendritically amplified before the coating processes and the other half were left untreated. The samples were coated with 25 surface sol-gel (SSG) cycles of each treatment at a time. After each 25 cycle treatment the samples were optically characterised. The total number of cycles applied to the samples at the end was 150. The addition of layers of titania resulted in a general red-shift that was higher for the tin-doped titania samples than for the titania samples. Another general trend found was that the samples that had their surfaces dendritically amplified, produced a lower red-shift in peak wavelength. This was contrary to the hypothesis that the amplification process was supposed to aid the SSG coating process and, therefore, increases the red-shift in peak wavelength.
The unamplified, tin-doped titania coated samples exhibited the highest red-shift in peak reflected wavelengths and were, therefore, chosen for pyrolysis. This process essentially heated the coated scale structures until the organic chitin material vapourised. This left a gyroid structure that comprised of only inorganic tin-doped titania. The pyrolysis process also caused some shrinkage to the structure therefore a blue-shift from the coated samples to the pyrolised samples was observed. Another observation made was that the more cycles of SSG coating that each sample underwent meant a reduction in the amount of structural shrinkage. This meant that the replicas that were produced with a higher number of SSG cycles had a higher peak reflected wavelength. The parameters involved in producing the inorganic replicas mean that the structures could be tuned to specific colours.AFOS
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
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