1,721,030 research outputs found
Modelling the Terrestrial Biosphere: Uncertainties and Constraints
No full textAnthropogenic activities such as the burning of fossil fuels and changes in land use have increased the presence of greenhouse gases in the atmosphere, altering the global climate system. The greenhouse gas concentration in the atmosphere is attenuated by the global biogeochemical cycles. To enhance our understanding of these complex cycles, and in effect the climate system, the expertise of a wide range of disciplines has to be brought together. State-of-the-art contemporary observations (e.g. remote sensing), long time archives (e.g. ice cores) and computer models all have a vital role to play.
This thesis focuses on the modelling of the terrestrial biosphere and how inherent model uncertainties can be reconciled with observational constraints. The first emphasis of the thesis is on the assimilation of observations in a Bayesian framework. The second focus is the simulation of the stable isotope of carbon (13C) and its use as a potential observational constraint.
In Chapter 1, an introduction to the thesis is given. The mechanisms behind the response of the climate system to changes in the radiation budget of the Earth are presented and set into context by discussing the contemporary anthropogenic perturbance of the carbon cycle. In a second part, more specific topics are discussed. The Dynamic Global Vegetation Model (DGVM) LPX-Bern and its development history are introduced. The chapter concludes with techniques for generating and evaluating perturbed model parameter ensembles, an introduction to land-use change and a section on the stable isotope of carbon, an important tracer in the climate system.
Chapter 2 contains a study published in Biogeosciences applying a probabilistic approach to the LPX-Bern model. By using observational constraints a new best-guess version of model parameters is formulated, termed LPX-Bern v1.4. The parameter ensemble is also used to quantify magnitude and uncertainty in historical land-use emissions of CO2. The spatial structure of the emissions are reported and compared to other independent estimates. Furthermore, mechanistic differences in the representation of land-use processes are investigated.
In Chapter 3 the implementation of carbon isotope discrimination of LPX-Bern and the land biosphere module (CLM4.5) of the Community Earth System Model (CESM) is compared to measurements in a Biogeosciences study. The models both show consistent results with a global compilation of C3 δ13C leaf measurements. Less agreement is found when comparing model results to tree-ring records. Intrinsic water use efficiency is related to carbon isotope discrimination and shows an increasing trend over the 20th century in the tree-ring measurements. This trend is captured by LPX-Bern but overestimated in CLM4.5, possibly explained by a too strong nitrogen limitation in the model. The study highlights the potential of 13C to evaluate global land carbon cycle models.
The importance of 13C is further explored in Chapter 4, where first steps toward fully coupled 13C simulations are taken. Two alternative formulations of terrestrial plant discrimination are presented and tested. The LPX-Bern model is modified to be able to prescribe C3 and C4 crop distribution, which has a strong impact on the global terrestrial 13C signature. Finally, a simulation of LPX-Bern is used in conjunction with a Bern3D ocean simulation to obtain global atmosphere-to-surface 13C fluxes. With the help of a model of atmospheric transport (TM2) those fluxes are translated to local concentration anomalies, allowing to compare the simulated seasonal cycle of 13C with measurements. The results are promising, indicating that it is in principle possible to accurately simulate the seasonal cycle of 13C in the atmosphere, but some further steps are needed for a successful coupled simulation of 13C.
Chapter 5 is a compilation of supplementary results of studies where simulations of LPX-Bern were featured. The Global Carbon Budget (GCB) is an annual publication aiming to improve our knowledge of the contemporary carbon cycle, featuring amongst other an ensemble of DGVMs. Different versions of LPX-Bern over the different iterations of the GCB are compared with each other and to the other DGVMs and GCB estimates. A similar project, focusing on the emissions of the important greenhouse gas N2O, is the N2O Model Intercomparison Project (NMIP). It is the first DGVM model intercomparison project focusing on the modelling of the terrestrial nitrogen cycle and associated emissions of N2O. The LPX-Bern simulation is set into the context of the ensemble and an additional factorial simulation on the effect of the timing of nitrogen fertilizer application is presented. Lastly, complementary results of a study investigating the sensitivity of European forests to climate variability are provided. The study features a novel tree-ring network allowing to quantify the interannual variations in biomass increment. Results from factorial simulations to investigate climate sensitivities in the interannual variability of net primary productivity in LPX-Bern are featured. Additionally, the relationship between mean production and interannual variability is examined in the model simulation.
The last Chapter 6 offers an outlook on potential future projects and model development. The thesis is accompanied by three appendices. In the first appendix daily in- and output capabilities of the model are discussed. Results from simulations focusing on specific sites are featured in the second appendix. The last appendix provides an overview of the implementation of the benchmarking framework featured in the probabilistic approach of chapter 2
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
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
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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