1,721,008 research outputs found
Exact Results on the First Hitting via Conditional Strong Quasi-Stationary Times and Applications to Metastability
No full textIn the setting of non-reversible Markov chains on finite or countable state space, exact results on the distribution of the first hitting time to a given set G are obtained. A new notion of “conditional strong quasi stationary time” is introduced to describe the local relaxation time. This time is defined via a generalization of the strong stationary time. Rarity of the target set G is not required and the initial distribution can be completely general. The results clarify the the role played by the initial distribution on the exponential law; they are used to give a general notion of metastability and to discuss the relation between the exponential distribution of the first hitting time and metastability
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
On the essential features of metastability: tunnelling time and critical configurations
No full textWe consider Metropolis Markov chains with finite state space and transition probabilities of the form for given energy function H and symmetric Markov kernel q. We propose a simple approach to determine the asymptotic behavior, for large , of the first hitting time to the ground state starting from a particular class of local minima for H called metastable states. We separate the asymptotic behavior of the transition time from the determination of the tube of typical paths realizing the transition. This approach turns out to be useful when the determination of the tube of typical paths is too difficult, as for instance in the case of conservative dynamics. We analyze the structure of the saddles introducing the notion of essentiality and describing essential saddles in terms of gates. As an example we discuss the case of the 2D Ising Model in the degenerate case of integer
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
Implementation of SCADA systems for a real microgrid lab testbed
No full textConsidering the complexity of controller systems in and also managing a microgrid (MGs), using automation systems can be an effective step in increasing energy efficiency, high reliability, as well as economic and environmental issues. In order to achieve these goals, this paper presents a comprehensive testbed for control and energy management in MG lab project is called LAMBDA MG in Sapienza University of Rome. The MG is composed of several sources (Photovoltaic, Storage, Emergency Generator Set) a smart switchboard and loads (lights, HVAC, plugs). The control strategy consists of two different subnets: the first one is based on a distributed home and building electronic system (HBES) for the supervisory and control for energy and comfort goals and the second one based on a central PLC for the operation of the different sources in grid and island mode respect the grid. The two subnets are integrated in a common SCADA system able to provide a real time monitoring, alarm handling, human machine interfacing, event and data
``On the Essential Features of Metastability: Tunnelling Time and Critical Configurations''
No full textWe analyze metastability and nucleation in the context of a local version of
the Kawasaki dynamics for the two-dimensional anisotropic Ising lattice gas at
very low temperature. Let ⊂Z2 be a sufficiently large finite box. Particles perform
simple exclusion on , but when they occupy neighboring sites they feel
a binding energy −U1 <0 in the horizontal direction and −U2 <0 in the vertical
direction; we assume U1 U2. Along each bond touching the boundary of
from the outside, particles are created with rate ρ=e−β and are annihilated
with rate 1, where β is the inverse temperature and >0 is an activity parameter.
Thus, the boundary of plays the role of an infinite gas reservoir with
density ρ. We take ∈ (U1,U1 +U2) where the totally empty (full) configuration
can be naturally associated to metastability (stability). We investigate how
the transition from empty to full takes place under the dynamics. In particular,
we identify the size and some characteristics of the shape of the critical droplet
and the time of its creation in the limit as β→∞. We observe very different
behavior in the weakly or strongly anisotropic case. In both case we find that
Wulff shape is not relevant for the nucleation pattern
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