1,720,964 research outputs found
Non-growing season CH4 fluxes over arctic and boreal environments
No full textNon-growing season CH4 fluxes over boreal and arctic environments using the snowpack diffusion gradient method. This dataset consists of 802 snowpack diffusion gradient measurements made over five different boreal and arctic ecosystems in Canada and Finland: closed-crown coniferous boreal forest, open-crown coniferous boreal forest, erect tundra shrubs, prostrate tundra shrubs and boreal wetlands. Snow and soil data are incorporated into the dataset as environmental variables
Non-growing season CO2 fluxes over arctic and boreal environments
No full textNon-growing season CO2 fluxes over boreal and arctic environments using the snowpack diffusion gradient method. This dataset consists of 558 snowpack diffusion gradient measurements made over a latitudinal gradient of four different boreal and arctic ecosystems in Canada: closed-crown coniferous boreal forest, open-crown coniferous boreal forest, erect tundra shrubs and prostrate tundra shrubs. Snow and soil data are incorporated into the dataset as environmental variables
Caractérisation diélectrique micro-onde (1,4 GHz) des arbres et des sols
No full textLe découplage du signal d’émission micro-onde entre la végétation et le sol demeure
une difficulté omniprésente pour toutes applications en télédétection. Pour améliorer les
produits micro-ondes globaux (e.g. humidité du sol, état de gel/dégel du sol) en milieu
forestier, une meilleure estimation de la permittivité électrique de la végétation et du
sol est requise. Dans le cadre de ce projet, un nouveau prototype de sonde coaxiale à
terminaison ouverte adaptée aux mesures sur le terrain a été développé. Nous montrons
dans ce travail que la sonde est apte à mesurer la permittivité électrique en bande L (1.4
GHz) de la végétation et du sol.
La sonde affiche des incertitudes maximales de 3,3% pour une large plage de valeurs
de permittivité. La permittivité complexe de sept espèces d’arbres différentes a été caractérisée
dans des conditions de gel et de dégel. Les résultats montrent que la permittivité
électrique du tronc des arbres est fortement corrélée avec l’état de gel/dégel de la végétation
et que cet état de gel/dégel de la végétation est sensible aux courts événements
de dégel hivernal. Il a aussi été démontré que les différences de permittivité électrique
interespèces sont importantes. La sonde coaxiale à terminaison ouverte s’est également
révélée suffisamment précise pour capturer le cycle diurne de teneur en eau à l’intérieur
du tronc des arbres.
Les mesures de permittivité électrique de sols organiques en chambre froide mettent
en évidence une hystérésis importante entre le cycle de gel et de dégel du sol. Un tel phénomène
n’est pas considéré dans les modèles de permittivité du sol actuel ni dans les
algorithmes de détection du gel/dégel des sols. La sonde devrait permettre d’améliorer
la modélisation du transfert radiatif en milieu forestier et ainsi permettre d’améliorer les
produits satellitaires en bande L.The decoupling of the signal between vegetation and soil remains an omnipresent
difficulty for all remote sensing applications in the microwave spectrum. To improve global
microwave products (e.g. soil moisture, freeze/thaw soil state) in the forest environment,
a better estimate of the permittivity of vegetation and soil is required. As part of this
project, a new prototype of open-ended coaxial probe adapted for field measurements has
been developed.
The probe is designed to measure the L-band permittivity (1.4 GHz) of vegetation
and soil. The probe displays maximum uncertainties of 3.3% for a wide range of
permittivity values. The complex permittivity of seven different tree species was characterized
under freezing and thawing conditions. The results show that the permittivity
of tree trunks is strongly correlated with the freeze/thaw state of vegetation, the tree
freeze/thaw state is sensitive to short winter thawing events and the inter species differences
in permittivity are important. The open-ended coaxial probe is also precise enough
to capture the diurnal cycle of water content within the tree trunks.
The permittivity measurements of organic soils in cold chamber show a significant
hysteresis between the freezing and thawing cycles. Such phenomenon is not considered
in current soil permittivity models or in soil freeze/thaw detection algorithms. The probe
will allow to improve radiative transfer models in forest environment and thus improve
L-band satellite products
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
Caractérisation diélectrique micro-onde (1,4 GHz) des arbres et des sols
No full textLe découplage du signal d’émission micro-onde entre la végétation et le sol demeure
une difficulté omniprésente pour toutes applications en télédétection. Pour améliorer les
produits micro-ondes globaux (e.g. humidité du sol, état de gel/dégel du sol) en milieu
forestier, une meilleure estimation de la permittivité électrique de la végétation et du
sol est requise. Dans le cadre de ce projet, un nouveau prototype de sonde coaxiale à
terminaison ouverte adaptée aux mesures sur le terrain a été développé. Nous montrons
dans ce travail que la sonde est apte à mesurer la permittivité électrique en bande L (1.4
GHz) de la végétation et du sol.
La sonde affiche des incertitudes maximales de 3,3% pour une large plage de valeurs
de permittivité. La permittivité complexe de sept espèces d’arbres différentes a été caractérisée
dans des conditions de gel et de dégel. Les résultats montrent que la permittivité
électrique du tronc des arbres est fortement corrélée avec l’état de gel/dégel de la végétation
et que cet état de gel/dégel de la végétation est sensible aux courts événements
de dégel hivernal. Il a aussi été démontré que les différences de permittivité électrique
interespèces sont importantes. La sonde coaxiale à terminaison ouverte s’est également
révélée suffisamment précise pour capturer le cycle diurne de teneur en eau à l’intérieur
du tronc des arbres.
Les mesures de permittivité électrique de sols organiques en chambre froide mettent
en évidence une hystérésis importante entre le cycle de gel et de dégel du sol. Un tel phénomène
n’est pas considéré dans les modèles de permittivité du sol actuel ni dans les
algorithmes de détection du gel/dégel des sols. La sonde devrait permettre d’améliorer
la modélisation du transfert radiatif en milieu forestier et ainsi permettre d’améliorer les
produits satellitaires en bande L.The decoupling of the signal between vegetation and soil remains an omnipresent
difficulty for all remote sensing applications in the microwave spectrum. To improve global
microwave products (e.g. soil moisture, freeze/thaw soil state) in the forest environment,
a better estimate of the permittivity of vegetation and soil is required. As part of this
project, a new prototype of open-ended coaxial probe adapted for field measurements has
been developed.
The probe is designed to measure the L-band permittivity (1.4 GHz) of vegetation
and soil. The probe displays maximum uncertainties of 3.3% for a wide range of
permittivity values. The complex permittivity of seven different tree species was characterized
under freezing and thawing conditions. The results show that the permittivity
of tree trunks is strongly correlated with the freeze/thaw state of vegetation, the tree
freeze/thaw state is sensitive to short winter thawing events and the inter species differences
in permittivity are important. The open-ended coaxial probe is also precise enough
to capture the diurnal cycle of water content within the tree trunks.
The permittivity measurements of organic soils in cold chamber show a significant
hysteresis between the freezing and thawing cycles. Such phenomenon is not considered
in current soil permittivity models or in soil freeze/thaw detection algorithms. The probe
will allow to improve radiative transfer models in forest environment and thus improve
L-band satellite products
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
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