1,720,982 research outputs found
The MAP/MSP/1/r Queueing System With Background Customers
No full textA single server queueing system with Markov flow of principal customers and background
customers arriving from infinite reserve source is studied. The Markov service processes of customers
of both types are considered. The system has a finite buffer for principal customers. The
service discipline is characterized by non-preemptive priority of principal customers respect to
background customers. An effective matrix-recurrent algorithm for the calculation of the stationary
state probabilities of the underlying Markov process is derived
Integrating TPNs and performance bound techniques in ITPN-PerfBound: a new import functionality
No full text
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
Effiziente Systemevaluation mit stochastischen Modellen
No full textEfficient and accurate methods are indispensible in the evaluation of complex
systems. Methods of various abstraction levels may be applied, ranging from
measurements in test-beds over simulation to analytical approaches. These
methods vary in their efficiency and accuracy. In order to obtain realistic
results, methods from all abstraction levels should be applied. Furthermore,
real-world phenomena must be represented in a suitable way at all abstraction
levels. This approach requires the use of stochastic models for the faults
that may affect a system. This thesis explores several important issues of
system evaluation using stochastic fault models. The first part of the thesis
provides a survey of stochastic fault-models for system evaluation. We survey
a broad range of existing fault-models and provide a new classification scheme
for fault models in service-oriented systems. In the second part of the thesis
we address the use of phase-type (PH) distributions as fault models in system
evaluation. We study algorithms for random-variate generation and discuss
their computational costs. An optimisation method for reducing the cost of
random-variate generation by transformation of the representation is presented
and an optimality result for the sub-class of acyclic phase-type distributions
is derived. We then develop a new algorithm for efficient and user-friendly
fitting of PH distributions to data sets using clustering. The algorithm is
implemented as part of the HyperStar tool. We additionally illustrate
application of HyperStar as a graphical user interface for prototype
algorithms using a new algorithm for fitting general PH distributions. The
third part illustrates application of the results from the first and second
parts. We first study the application of stochastic fault models for IP packet
loss in fault-injection and investigate the interaction between fault models
and traffic arrival streams and its impact on evaluation results. We then
describe a library for random-variate generation from phase-type distributions
and show its use in two case-studies.Die Evaluation komplexer Systeme erfordert effiziente und genaue
Untersuchungsmethoden. Abhängig vom Abstraktionsniveau existieren
unterschiedliche Verfahren, die Messungen in Testbetten ebenso umfassen wie
Simulationen und analytische Ansätze. Die Verfahren unterscheiden sich
hinsichlich ihrer Effizienz und der Genauigkeit der erzielbaren Ergebnisse.
Für realistische Aussagen sollten in einer Evaluation immer Methoden ̈ aller
Abstraktionsebenen kombiniert werden. Überdies sollten auf allen Ebenen
Phänomene der echten Welt in die Untersuchung einfließen. Dies erfordert den
Einsatz stochastischer Modelle für die Fehler, die das System beeinträchtigen
können. In dieser Arbeit werden wichtige Aspekte der Systemevaluation mit
stochastischen Fehlermodellen untersucht. ̈ Im ersten Teil der Arbeit wird
eine Übersicht uber stochastische Fehlermodelle erarbeitet und ein neues
Klassifikationsschema für Fehler in Service-Orientierten Systemen vorgestellt.
Der zweite Teil der Arbeit konzentriert sich auf den Einsatz von
Phasentypverteilungen als Fehlermodelle. Es werden Algorithmen zur
Zufallszahlenerzeugung aus Phasentypverteilungen und ihre Kosten untersucht.
Anschließend wird ein Verfahren vorgestellt, das Phasentypverteilungen so
umformt, daß die Kosten der Zufallszahlenerzeugung minimiert werden. Für
diesen Ansatz wird ein Optimalitätsresultat für die Unterklasse der
azyklischen Phasentypverteilungen hergeleitet. Des weiteren wird ein auf
Clustering basierender Algorithmus zur effizienten und nutzerfreundlichen
Anpassung von Phasentypverteilungen an Datensätze entwickelt. Der Algorithmus
wurde im Programm HyperStar implementiert. HyperStar kann überdies als
graphische Benutzeroberfläche für dieEntwicklung von Fitting-Algorithmen
dienen. Diese Verwendungsweise wird anhand eines neuen Algorithmus’ zur
Anpassung allgemeiner Phasentypverteilungen demonstriert. Im dritten Teil
werden die Ergebnisse des ersten und zweiten Teils in der Anwendung
illustriert. Es wird zunächst die Anwendung stochastischer Fehlermodelle für
IP-Paketverluste in der Fehlerinjektion untersucht. Der Schwerpunkt liegt
hierbei auf der Wechselwirkung zwischen Fehlermodellen und
Verkehrsankunftsströmen und ihrem Einfluß auf die Evaluationsergebnisse.
Anschließend wird eine Bibliothek zur effizienten Zufallszahlenerzeugung in
Simulationen vorgestellt und in einer Fallstudie evaluiert. Eine zweite
Fallstudie demonstriert die mögliche Effizienzsteigerung durch den Einsatz von
Phasentypverteilungen in Simulationen
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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