1,721,017 research outputs found
Pattern formation and spatial correlation induced by the noise in two competing species
Full text linkWe analyze the spatio-temporal patterns of two competing species in the presence of two white noise sources: an additive noise acting on the interaction parameter and a multiplicative noise which aects directly the dynamics of the species densities. We use a coupled map lattice (CML) with uniform initial conditions. We nd a nonmonotonic behavior both of the pattern formation and the density correlation as a function of the multiplicative noise intensity
A Methodological Approach To Assess Seismic Resilience Of City Ecosystems Through The Complex Networks Theory
No full textEarthquakes have always been representing a sleeper risk affecting local and global communities, as they are low
-
probability
-high-
risk events. In addition, being contemporary urban societies threatened by increasing exposure along with
growing urbanization, resilience represents a key issue for modern societies, as the capability to withstand and recover from
disasters. Understanding resilience as an engineering issue in the sense of ecosystems, cities can be modelled as compl
ex
networks, made of coexisting and mutually interacting physical and social components.
The proposed methodology aims at quantifying seismic resilience of city ecosystems according to a multidisciplinary
approach. Resilience is evaluated while also ensu
ring an adequate level of sustainability, according to a social and human
-
centric perspective. A multi
-scale approach is then performed in order to measure urban efficiency and systemic structural
damage through the assessment of specific engineering measures.
Hence, to effectively do this, cities are modelled as hybrid social
-physical networks (HSPNs), merging the infrastructural
and human urban components. The efficiency of different hybrid network
typologies
is estimated, as nodes are modelled as
residen
tial buildings (citizen
-citizen efficiency)
or schools (
service-
citizen
efficiency).
A real case study for the inner city Naples, namely
the Quartieri Spagnoli area, is developed to validate the robustness of the
proposed metric
s. Synthetic HSPNs are also
modelled accounting for different geometric shapes, according to the most
common
topologies
in Europe and USA. Moreover, for each city shape, simulations are ran accounting for increasing city
size
, to study changes in resilience with the HSPN scale. As a point in matter, it is
fundamental to account for specific urban
dynamics in time and space. According to
diverse
studies in the literature,
urban dynamics grow proportionally with a city
size, becoming denser with the increasing scale, until a certain bou
ndary, out of which such dynamics become
unpredictable.
Seismic scenarios are simulated assuming for the earthquake’s intensity to be deterministic in terms of the attained peak
ground acceleration (PGA). The building portfolio for each modelled city is
assumed to be constituted by reinforced
concrete (RC)
frame building
s, non-
seismically designed and the vulnerability is quantified, by averaging fragility curves
selected from the literature.
Mathematical and engineering measures are performed before and af
ter
the seismic scenario and during the recovery phase
s
with a time
-discrete approach, enabling
to quantify the level of urban functionality and happiness of city inhabitants and
environmental sustainability
, as the urban resilience.
Hence, structural dama
ge is evaluated in a systemic manner over the entire urban territory soon after an earthquake occurs,
as a measure of the city efficiency drop.
Two diverse
recovery strategies
are
modelled
and simulated to study the efficien
cy
recovery and progress
with
a step
-by
-step procedure.
The proposed framework is a high
-potential means of seismic risk mitigation, which can help local communities and
support disaster managers to know the pre
-event urban capacity and to face the post
-event reconstruction. This can be even
more effective when arguing at the local level, where recovery actions and financial sources are more easily manageable
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
Hybrid recommendation methods in complex networks
Full text linkWe propose two recommendation methods, based on the appropriate normalization of already existing similarity measures, and on the convex combination of the recommendation scores derived from similarity between users and between objects. We validate the proposed measures on three data sets, and we compare the performance of our methods to other recommendation systems recently proposed in the literature. We show that the proposed similarity measures allow us to attain an improvement of performances of up to 20% with respect to existing nonparametric methods, and that the accuracy of a recommendation can vary widely from one specific bipartite network to another, which suggests that a careful choice of the most suitable method is highly relevant for an effective recommendation on a given system. Finally, we study how an increasing presence of random links in the network affects the recommendation scores, finding that one of the two recommendation algorithms introduced here can systematically outperform the others in noisy data sets
Asymptotic regime in N random interacting species
Full text linkThe asymptotic regime of a complex ecosystem with N random interacting species and in the presence of an external multiplicative noise is analyzed. We find the role of the external noise on the long time probability distribution of the ith density species, the extinction of species and the local field acting on the ith population. We analyze in detail the transient dynamics of this field and the cavity field, which is the field acting on the ith species when this is absent. We find that the presence or the absence of some population give different asymptotic distributions of these fields. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200605.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion, 05.45.-a Nonlinear dynamics and nonlinear dynamical systems, 87.23.Cc Population dynamics and ecological pattern formation, 89.75.-k Complex systems,
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
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