1,721,016 research outputs found
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
Analysen zur Bedeutung der genomischen Prägung für genetische Variabilität beim Nutztier
Get PDFIn a series of analyses the importance of genomic imprinting for the genetic variation in livestock was investigated. A problem solving model, allowing for both paternal and maternal imprinting simultaneously as well as for full and partial imprinting, was applied to a set of 105 traits from slaughter animals (pigs and fattening bulls). A significant genetic imprinting variance was found for 33 traits, mostly related to carcass composition and growth. Between 5% and 25% of the total additive genetic variance was attributed to imprinted loci. Preliminary results for traits known to be maternally affected were obtained from gametic models, indicating proportions of 12% and 20% of the direct additive genetic variance for gestation length and birth weight in Holstein dairy cattle due to genomic imprinting.Mit Hilfe mehrerer Analysen wurde die Bedeutung der genomischen Prägung für die genetische Variation beim Nutztier untersucht. Ein problemorientiertes Modell, das paternale und maternale Prägung gleichzeitig berücksichtigt, ebenso wie vollständige und partielle Prägung, wurde auf insgesamt 105 Merkmale von Schlachttieren (Schweine und Mastbullen) angewandt. Signifikante genetische Imprintingvarianzen wurde für 33 dieser Merkmale gefunden, die meisten bei Merkmalen der Schlachtkörperzusammensetzung und des Wachstums. Zwischen 5% und 25% der gesamten additiv genetischen Varianz konnte geprägten Loci
zugeschrieben werden. Erste Ergebnisse für Merkmale mit bekannter maternaler genetischer Variation wurden mittels gametischer Modelle erzielt und zeigten auf, dass 12% der Trächtigkeitsdauer und 20% des Geburtsgewichtes der direkten genetischern Varianz bei Holstein Milchrindern durch genomische Prägung beeinflusst werden
A similarity matrix and its application in genomic selection for hedging haplotype diversity
Get PDFMendelian sampling variance (MSV) has many breeding applications. However, its computationally intensive nature limits its widespread use. Recently proposed selection indices for long-term genetic gain combine genomic estimated breeding value and MSV. However, these indices tend to select similar parents with high MSV potential under high selection intensity, resulting in favorable haplotypes losses. Therefore, this thesis aimed to develop a faster approach for computing MSV and derive a similarity matrix for hedging haplotype diversity. The thesis first develops an efficient approach for computing MSV using marker effects, a genetic map, and phased genotypes. Then, using the same information as MSV, it derives a similarity matrix. The off-diagonal elements of this matrix represent the similarities between parental haplotypes, and diagonal elements represent the similarity of a parent to itself, which equals its MSV. A high similarity indicates that the parents share many heterozygous markers, with large effects on a trait in the same linkage phase. Similar to how covariance matrices of asset prices are used in finance to create diversified portfolios, the similarity matrix can help avoid repeated matings of similar parents and achieve expected genetic gain while hedging haplotype diversity in the next generation. The thesis then develops the Python package PyMSQ for computing MSV and similarity matrix to facilitate their use in breeding programs. Compared to gamevar (a recently published Fortran program), PyMSQ was up to 240 times faster at computing MSV in the analyzed data sets. Finally, similarity matrices for milk production and longevity traits were calculated using PyMSQ for a large German Holstein population to assess their applicability, relevance, and influencing factors. The similarity matrix presented in this thesis introduces new criteria for genomic selection, allowing for increased genetic gain while hedging haplotype diversity in breeding programs
Modifizierte zufällige Modelle für die QTL-Identifizierung in F2-Populationen
Get PDFA variance component method (VCM) considering quantitative trait loci (QTL) effects as random in a linear model may be computational expensive, especially with multiple QTL and interactions, because of a large number of genetic effects. This thesis deals with possibilities to reduce this computational burden by modifying elements of the underlying random model for inbred line-derived F2 populations, considering additive genetic, dominance and epistatic interaction effects.
A reduced random model (RRM), as suggested in Chapter One, considers average genetic effects for all possible marker genotypes instead of genetic effects for each individual as the traditional individual random model (IRM) does. It could be shown that the genetic covariance structure of the RRM is asymptotically equivalent to the genetic covariance in the IRM. Because the number of parameters to be estimated is essentially decreased in the RRM it clearly outperforms the IRM with respect to computational speed.
Comprehensive comparisons as done in Chapter Two show that the RRM is competitive to the IRM in terms of the precision of the estimated QTL positions and the observed power. Both VCM were also compared to fixed models like regression interval mapping (RIM) and multiple interval mapping (MIM). No major differences between RRM compared to IRM, RIM and MIM in terms of the QTL detection power and the accuracy of the estimated QTL positions and their effects occurred. Hence, the RRM is a computationally tractable method and is recommended for QTL analyses instead of the IRM, especially in experiments with multiple families.
Chapter Three revisits additive and additive-by-additive genetic relationship matrices. Alternative covariance matrices are proposed, capitalizing on the prior knowledge of only two different QTL alleles in the considered type of experiments. The resulting covariance matrices and their inverses have a considerable amount of zero elements, leading to a remarkable gain in computational speed if this sparse structure is exploited in the estimation of genetic variance components. Thereby the restricted log-likelihood function remains unaltered. Moreover, more realistic standard errors for genetic effects are obtained.
In conclusion QTL analyses in inbred line-derived F2 families can be speeded up by applying the RRM and, in case of only additive genetic effects and their interactions, by applying a sparse type of genetic covariance matrices.Varianzkomponentenmethoden mit als zufällig betrachteten QTL-Effekten (quantitative trait loci, QTL) können wegen einer großen Anzahl an genetischen Effekten sehr rechenintensiv sein, insbesondere wenn multiple QTL mit additiven, dominanten und epistatischen Effekten berücksichtigt werden. Diese Arbeit untersucht Möglichkeiten, den Rechenaufwand durch geeignete Anpassungen des zufälligen Modells zu reduzieren. Hierbei werden aus Inzuchtlinien abgeleitete F2-Populationen betrachtet.
Im ersten Kapitel wird ein reduziertes zufälliges Modell (RRM) mit durchschnittlichen genetischen Effekten für alle auftretenden Markergenotypen vorgeschlagen, anstelle von individuellen genetischen Effekten, wie im bekannten individuellen zufälligen Modell (IRM). Die asymptotische Äquivalenz der genetischen Kovarianz von RRM und IRM wurde gezeigt. Durch die geringere Anzahl von Parametern im RRM ergibt sich eine deutliche Verringerung der Rechenzeiten im Vergleich zu IRM.
Umfangreiche Simulationen im zweiten Kapitel demonstrieren die Gleichwertigkeit von RRM und IRM hinsichtlich der Leistungsfähigkeit (Güte) der Kartierung und der Genauigkeit der geschätzten QTL-Positionen, sowie deren Effekte. Auch zu fixen Modellen, namentlich der Regressionsmethode und der multiple Intervallkartierung, traten keine nennenswerten Unterschiede auf. Wegen der rechentechnischen Vorteile kann deshalb das RRM für QTL-Analysen empfohlen werden, wobei Experimente mit multiplen Familien das Hauptanwendungsgebiet darstellen.
Im dritten Kapitel werden alternative additive und additiv-mal-additive Kovarianzmatrizen vorgeschlagen, welche die Vorkenntnis nutzen, dass nur zwei QTL-Allele im untersuchten F2-Versuchsdesign vorliegen. Diese neuen Kovarianzmatrizen und ihre Inversen haben einen beachtlichen Anteil an Nullelementen, was zu einer höheren Rechengeschwindigkeit führt, wenn diese dünn besetzten Strukturen für die Schätzung der Varianzkomponenten genutzt werden. Dabei bleibt die restringierte log-Likelihoodfunktion unverändert, allerdings werden realistischere Standardfehler für die geschätzten genetischen Effekte erhalten.
Somit können QTL-Analysen in aus Inzuchtlinien abgeleiteten F2-Populationen unter Verwendung von RRM beschleunigt werden, außerdem durch die Anwendung der vorgeschlagenen dünn besetzten Verwandtschaftsmatrizen für additive Effekte und deren Interaktionen
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
Über Random Regression Modelle einschließlich elterlicher Herkunftseffekte
Get PDFThis work addresses the modeling of genetic variation in quantitative traits in livestock using random regression models. Thereby, emphasis was placed on the inclusion of parent-of-origin effects, which include both genomic imprinting and maternal effects. First, genetic variation in milk urea content and its genetic correlations with other milk traits were examined. An analysis of 4.16 million milk samples of German Holsteins resulted in moderate heritabilities. Genetic correlations with other milk traits were close to zero. Thus, selection against high milk urea levels without undesirable side effects on other milk traits seems possible. However, it remains unclear whether this can achieve the hoped-for reduction in nitrogen output. In more in-depth analyses, significant parent-of-origin effects were found for yield traits as well as milk composition. When averaged over all lactation stages, between 9.8 % and 27.3 % of the total additive genetic variance could be explained by parent-of-origin effects. During lactation the estimated genetic variance of maternal gametes predominantly exceeded that of paternal gametes. A novel random regression model was developed for the trait total litter weight in mice that refrained from distinguishing between the two types of parent-of-origin effects and was able to cover both maternal and imprinting effects. In total, weights of 6 934 litters from two mouse lines were analyzed. Paternal genetic effects were found to be significant in both lines. Averaged over all litter sizes, heritabilities were 0.42 and 0.43. In contrast to known evaluation approaches, the model reflects the changing heritability of total litter weight with increasing litter size. Applications in livestock are in the selection on birth weight in all types of multiparous animals, for which only total litter weight has to be recorded.Diese Arbeit befasst sich mit der Modellierung der genetischen Variation quantitativer Merkmale bei Nutztieren mit Hilfe von Random Regression Modellen (RRM). Schwerpunkt war die Einbeziehung elterlicher Herkunftseffekte (POEs), wozu genomische Prägung und maternale Effekte zählen. Zunächst wurde die genetische Variation des Milchharnstoffgehaltes (MU) und dessen genetische Korrelationen mit anderen Milchmerkmalen (MM) untersucht. Eine Auswertung von 4,16 Mio. Probegemelken Deutscher Holsteins ergab moderate Heritabilitäten. Genetische Korrelationen zu anderen MM waren nahe Null. Eine Selektion gegen hohe MU ohne unerwünschte Nebeneffekte auf andere MM erscheint also möglich. Es bleibt jedoch offen, ob damit die erhoffte Senkung des Stickstoffausstoßes erreicht werden kann. In vertiefenden Analysen konnten signifikante POEs für MM gefunden werden. Im Laktationsdurchschnitt konnten zwischen 9,8% und 27,3% der gesamten additiven genetischen Varianz durch POEs erklärt werden. Während des größten Teils der Laktation übertraf die geschätzte genetische Varianz der mütterlichen Gameten diejenige der väterlichen Gameten. Für das Merkmal Gesamtwurfgewicht (GWG) von Mäusen wurde ein neuartiges RRM entwickelt, dass auf eine Unterscheidung beider Arten von POEs verzichtet und sowohl maternale als auch Imprintingeffekte abzudecken vermag. Insgesamt wurden GWG von 6934 Würfen aus zwei Mauslinien analysiert. Väterliche genetische Effekte erwiesen sich in beiden Linien als signifikant. Im Mittel über alle Wurfgrößen ergaben sich Heritabilitäten von 0,42 und 0,43. Im Unterschied zu bekannten Auswertungsansätzen spiegelt das RRM die sich mit steigender Wurfgrößen ändernde Heritabilität des GWG wieder. Anwedungen liegen in der züchterischen Beeinflussung des GWG bei allen Arten von multiparen Tieren, wozu nur GWG erfasst werden muss
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