1,721,014 research outputs found
Chemical composition and antioxidant activity of Globularia alypum L. leaves essential oil from Ain-Defla (Algeria)
No full textpeer reviewedThe chemical composition of essential oil obtained by hydro-distillation with 2.10±0.09 % yield from dried Globularia alypum L. leaves was analyzed by GC-MS. It was determined 60 components representing 99.04 % of total oil. For the evaluation of the mentioned antioxidant activity, three different approaches were performed: the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging, β-carotene bleaching (BCB) test systems and ferric reducing/antioxidant power assay (FRAP).The antioxidant was compared with that of synthetic antioxidant ascorbic acid. These findings indicate that the G.alypum essential oil exhibited good antioxidant properties. © Amri H., Hamadouche M., Alsafra Z., Eppe G., El Abed D., 2018
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
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
Constraining quenching mechanisms at high redshift: the sizes, masses and star-formation histories of massive galaxies
No full textObservations of the local and high-redshift Universe have revealed a clear
bi-modality in the galaxy population. This is apparent in galaxy colours,
morphologies and star-formation rates, with galaxies being categorised into two
distinct populations; star-forming and quiescent. The existence of this bimodality
means that one or more mechanisms must be able to cease, or quench,
star-formation in galaxies. One of the key questions in extragalactic astronomy
is to identify which quenching mechanisms are most important and on what
timescales they operate.
In this thesis, I use a combination of photometry and spectroscopy to examine
the evolution of the quiescent galaxy population at high redshift in an attempt
to piece together a coherent picture of their evolution over the past ten billion
years of cosmic history. Some of the foundational results that have shaped our
understanding of galaxy evolution are the relationships between galaxy stellar
mass, size and age. In addition to the bi-modality observed up to z ∼ 2, it has also
been shown that galaxies which formed earlier in cosmic time are more massive
than their later counterparts, a phenomenon often referred to as “downsizing”.
In this thesis, ultra-deep spectroscopic data along with HST and JWST imaging
from large-scale surveys is used to study the sizes, masses and star-formation
histories of massive galaxies from z = 0.25 to z = 2.25.
Firstly, I present a study exploring the most massive galaxies at 0.6 < z < 1.3
using ultra-deep spectroscopy and photometry from the VANDELS and LEGA-C
ESO public spectroscopic surveys. I investigate the relationships between galaxy
stellar mass, physical size and age (using a well-known proxy for age predominant
in quiescent galaxy spectra; the Dn4000 index), and demonstrate for the first time
that downsizing is clearly evident in both our quiescent samples. I present a toy
model to explain the size evolution of massive quiescent galaxies from z = 1.3 to
z = 0.6 based on minor mergers.
Next, I present the results of full spectral fitting of the VANDELS quiescent
sample at 1.0 < z < 1.3, examining in further detail the relationship between
stellar mass and age, this time using galaxy formation and quenching times.
Upon further investigation into these trends, it becomes apparent that there is a
sample of quiescent galaxies which appear to have experienced very short periods
of star-formation, followed by abrupt quenching. These galaxies indicate higher
levels of α-enhancement compared to the rest of the quiescent galaxies in my
sample. This implies that there is an important mechanism at work which can
end star-formation on very short timescales. One galaxy in my sample formed
less than a billion years after the Big Bang, experiencing a short episode of
star-formation before quickly becoming quiescent, based on star-formation and
quenching timescales.
Building on these key results at z ∼ 1, I investigate whether these trends can be
seen at higher redshift using data obtained from the JWST PRIMER and JADES
surveys. Due to the improved sensitivity and spatial resolution of JWST imaging,
it is possible to examine the sizes and morphologies of star-forming and quiescent
galaxies to lower stellar masses than previously possible. Over the redshift range
0.25 < z < 2.25, I find that low-mass quiescent galaxies in my sample exhibit
Sérsic indices and sizes qualitatively consistent with these galaxies quenching by
infall into cluster environments. Contrastingly, the sizes and morphologies of
more massive quiescent galaxies are consistent with having quenched by internal
feedback mechanisms.
In summary, this thesis aims to provide a quantitative investigation of the
evolution of quiescent galaxies over cosmic time. The unprecedented size and
quality of the datasets used throughout this work have led to many important
findings, enabling a deeper understanding of the properties of quiescent galaxies,
and the overall formation and evolution of galaxies across time
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