1,721,056 research outputs found
Simulation-Based Investigation of Wind Turbine Induced Shadow Flicker on IGBT Reliability and Energy Yield in Solar Converters in Hybrid Wind-Solar Systems
No full textWith the growing adoption of renewable energy, hybrid wind-solar plants are gaining interest because they allow the increase of energy yield per unit of surface area. However, the presence of wind turbines creates unique shading scenarios for the solar panels. This work presents a simulation-based approach to investigate the solar plant's energy yield and converter IGBT lifetime in the presence of dynamic and fast-moving shadows created by the wind turbine blades. First, the need for a dynamic simulation as opposed to a static one is examined. Next, the sensitivity of Photovoltaic (PV) string orientation, PV string location, wind direction, Maximum Power Point Tracker (MPPT) control speed, and turbine rotor speeds on energy yield and IGBT lifetime are investigated in a case study. Results show that dynamic and static simulations can show vastly different results. MPPT can have difficulty with shadow flicker, resulting in different string voltages depending on the MPPT update speed and wind turbine rotor speed. The shadow flicker introduces additional temperature swings in the IGBT, but these are too small to add any significant lifetime consumption (<1.2%). Thus, the observed changes in lifetime consumption are caused mainly by controller behavior and static shadows. Finally, it is concluded that PV strings are better placed south, east, or west of the wind turbine for optimal energy yield and lifetime consumption. A northern placement can be suitable if there is a significant distance (+50 m) between the PV string and the wind turbine.This work was supported by the Belgian Energy Transition Funds/Met de steun van het Energietransitiefonds
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
Netwerkgebaseerd modeleren van omics data
No full textUnderstanding the cellular behavior from a systems perspective requires the identification of functional and physical interactions among diverse molecular entities in a cell (i.e., DNA/RNA, proteins, metabolites,...). A network-based representation captures many of the essential characteristics of these various biological systems and can be exploited to study a molecular entity like a protein in a wider context than just in isolation and can provide valuable insights into the systems mode of action and functionalities. Unraveling these molecular networks is considered one of the foremost challenges in current bioinformatics research.Powerful and scalable technologies enabled the generation of genome-wide datasets that describe cellular systems by capturing the interactions of their building blocks or by characterizing the state of a system under different environmental stimuli. The distinct nature of these datasets often brings about complementary views on cellular behavior and integration of them holds the key to the successful reconstruction of the underlying networks. In a first part of the thesis we therefore aim to infer networks from diverse of omics datasets. We present ProBic, a method to identify modules of genes that show co-expression to a set of genes of interest (i.e., query or seed genes), and the conditions in which they are co-expressed. These modules are termed biclusters, and represent potentially co-regulated genes, highlighting part of the transcriptional network. We applied ProBic on a benchmark set in E. coli and showed that high quality biclusters with biological relevance could be obtained.Next, we integrated information from several functional datasets to predict protein-protein interactions from public experimental interaction data, using a naive Bayesian classifier. Clustering the obtained protein network illustrated the presence of functionally coherent modules, and showed the opportunity of assigning novel gene functions based on cluster functionality. Viewing a single entity or an experimental dataset in the light of an interaction network can reveal previous unknown insights in biological processes or functional behavior. Methodologies that identify and explore paths in networks between given input and output nodes have gained much interest. Such a path in a network can be seen as a mechanistic representation of the way information propagates through the network. Identifying biologically meaningful paths in the network between nodes of interest, nodes which can be defined from functional datasets that are independent from the network itself, can unveil previously uncovered signal flow mechanisms that are responsible for the observed functional behavior or define a measure for relatedness of two nodes in the network.In a second part of the thesis we present a novel network-based method to interpret eQTL data. One of the challenges in eQTL analysis, besides the identification of genetic loci that are associated to gene expression, is the exact identification of the true causal gene in an associated locus, causing the variation in gene expression. The method therefore aims to prioritize candidate genes in a locus based on their network-relatedness to a set of associated target genes. We show that the approach outperforms a state-of-the-art gene prioritization method in case a common causal factor is present for a set of targets, based on several performance criteria.Finally, we applied the methodology on a biological dataset in yeast that combined both genomic and expression variation of a pool of yeast segregants. We predicted several genes to be involved in ethanol production capacity, which is an important phenotype in the fermentation industry.status: Publishe
Een raamwerk voor het creëren en exploreren van cross-platform expressiecompendia
No full textWith the unprecedented ability to systematically probe gene expression at the genome scale, microarrays have become an indispensable technology adopted by most of the laboratories across the world, generating a wealth of data for a variety of species. Although comprehensive in the gene dimension, any microarray based study alone provides a limited scope at the level of condition. However combining expression data from different labs provides the opportunity to investigate gene expression of a particular species at a more global level, and to view a specific study from the perspective of existing knowledge. The goal of this research is developing a novel methodology and system to explore this opportunity.We first developed a methodology to create an organism-specific cross-platform compendium based on publicly available gene expression data. Special attention has been paid to facilitate automated data retrieval by resolving heterogeneities in the data representation and to improve data consistency and compatibility through systematic renormalization of the data. Compared with existing single platform compendia, our methodology provides a broader range of data (cross platform).Using this novel methodology, we constructed three comprehensive expression compendia for the bacterial model organisms: Escherichia coli, Bacillus subtilis, and Salmonella enterica serovar Typhimurium. Moreover, efforts have been taken to create a web portal with intuitive functionalities for data analysis and visualization, providing public access to these three compendia.One of the most important applications of compendia is to study the response of an organism to environmental changes by identifying condition dependent functional modules and studying the underlying regulatory mechanisms responsible for the observed expression variations. Different methods exist for this purpose. Each makes distinct assumptions to handle the under-deterministic nature of this complex problem, and consequently generates complementary results. Here, we demonstrated such complementarity between two methods, DISTILLER and COLOMBOS, in a case study, in which co-expression modules containing gene sodA are extracted from the E. coli compendium using each method, and compared against each other. Through this example, we stress the importance of choosing the right method based on the research purpose.At last, we extended the methodology to handle the increased complexity of the monocot Zea mays, specifically addressing the following two issues: inconsistencies in platform-probe annotation and having a more precise biological sample annotation which can reflect the different genetic repositories of maize (breeding lines), the complexity of the plants life style (development stage) and its more complex tissue structure. We also upgraded the web access portal accordingly with new functions adapted to queries specific for a higher organism like Zea mays.status: Publishe
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
Rol van structurele eigenschappen bij transcriptieregulatie
No full textTranscriptional regulation is an essential biological process as it is one of the main mechanisms available to all living organisms to control to the expression of their genes to their development and to adapt to the ever-changing conditions of the world that they live in. Research has suggested that the structure of the DNA molecule may impact transcription and its regulation in several different ways. The goal of this PhD is to investigate the role that the DNA structure plays in transcription and how this information can be used to the advantage of biological research.To achieve this goal, we created a general framework for representing structural DNA properties of functional genomic elements involved in transcription, which we have called CRoSSeD. The CRoSSeD framework was designed to use structural scales to derive the structural information and Conditional Random Fields to find relevant common characteristics in the DNA structure of the functional element. The advantages of this framework was demonstrated on the prediction of transcription factor binding sites. We found that CRoSSeD improved the accuracy of the classification of binding sites for given transcription factors and were able to make a set of novel target gene predictions for the model organism Escherichia coli. Further the model produced by the CRoSSeD framework could be directly linked to the binding mechanisms of the TF and this feature was used to construct the family-wide motif for the well-known LacI TF family.We also investigated the transcriptional behavior of the genes in several well characterized bacterial organisms with the eventual goal to link this analysis back to the influence of the DNA structure. To this end, we created comprehensive organism-specific cross-platform expression compendia for three bacterial model organisms (E. coli, Bacillus subtilis, and Salmonella enterica serovar Typhimurium). These compendia were made available to the general scientific community through an access portal, dubbed COLOMBOS, which provides a suite of tools for exploring, analyzing, and visualizing the data within these compendia. Additionally we developed a compendia management and creation system called COMMAND to support and expand the data contained within COLOMBOS. The expression compendia were then used to analyze the expression divergence of the orthologous genes of E. coli and S. Typhimurium. Here we found that the genes involved with essential cellular processes had conserved their expression domains while those associated with pathogenesis had diverged the most.status: Publishe
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
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