1,274 research outputs found
Detecting and Describing Dynamic Equilibria in Adaptive Networks
We review modeling attempts for the paradigmatic contact process (or SIS
model) on adaptive networks. Elaborating on one particular proposed mechanism
of topology change (rewiring) and its mean field analysis, we obtain a
coarse-grained view of coevolving network topology in the stationary active
phase of the system. Introducing an alternative framework applicable to a wide
class of adaptive networks, active stationary states are detected, and an
extended description of the resulting steady-state statistics is given for
three different rewiring schemes. We find that slight modifications of the
standard rewiring rule can result in either minuscule or drastic change of
steady-state network topologies.Comment: 14 pages, 10 figures; typo in the third of Eqs. (1) correcte
Dynamics and steady-state properties of adaptive networks
Tese de doutoramento, Física, Universidade de Lisboa, Faculdade de Ciências, 2013Collective phenomena often arise through structured interactions among a system's
constituents. In the subclass of adaptive networks, the interaction structure
coevolves with the dynamics it supports, yielding a feedback loop that is common
in a variety of complex systems. To understand and steer such systems, modeling
their asymptotic regimes is an essential prerequisite. In the particular case of a
dynamic equilibrium, each node in the adaptive network experiences a perpetual
change in connections and state, while a comprehensive set of measures characterizing
the node ensemble are stationary. Furthermore, the dynamic equilibria
of a wide class of adaptive networks appear to be unique, as their characteristic
measures are insensitive to initial conditions in both state and topology.
This work focuses on dynamic equilibria in adaptive networks, and while it does
so in the context of two paradigmatic coevolutionary processes, obtained results
easily generalize to other dynamics. In the rst part, a low-dimensional framework
is elaborated on using the adaptive contact process. A tentative description
of the phase diagram and the steady state is obtained, and a parameter region
identi ed where asymmetric microscopic dynamics yield a symmetry between node
subensembles. This symmetry is accounted for by novel recurrence relations, which
predict it for a wide range of adaptive networks. Furthermore, stationary nodeensemble
distributions are analytically generated by these relations from one free
parameter.
Secondly, another analytic framework is put forward that detects and describes
dynamic equilibria, while assigning to them general properties that must hold
for a variety of adaptive networks. Modeling a single node's evolution in state
and connections as a random walk, the ergodic properties of the network process
are used to extract node-ensemble statistics from the node's long-term behavior.
These statistical measures are composed of a variety of stationary distributions
that are related to one another through simple transformations. Applying this
fully self-su cient framework, the dynamic equilibria of three di erent
avors of
the adaptive contact process are subsequently described and compared.
Lastly, an asymmetric variant of the coevolutionary voter model is motivated and
proposed, and as for the adaptive contact process, a low-dimensional description
is given. In a parameter region where a dynamic equilibrium lets the in nite
system display perpetual dynamics, this description can be further reduced to a
one-dimensional random walk. For nite system sizes, this allows to analytically
characterize longevity of the dynamic equilibrium, with results being compared to
the symmetric variant of the process. A nontrivial parameter combination is identi
ed for which, in the low-dimensional description of the process, the asymmetric
coevolutionary model emulates symmetric voter dynamics without topological coevolution.
This emerging symmetry is partially con rmed for the full system and
subsequently elaborated on. Slightly varying the original asymmetric model, an
additional asymptotic regime is shown to occur that coexists with all others and
complicates system description.A estrutura das interacções entre os constituintes elementares de um sistema está
frequentemente na origem de comportamentos colectivos não triviais. Em redes
adaptativas, esta estrutura de interacção evolui a par com a dinâaica que nela
assenta, traduzindo uma retroacção que de comum encontrar em vários sistemas
complexos. Resultados analíticos sobre os estados assimptóticos destes sistemas
são uma peça essencial para a sua compreensão e controlo. O equilíbrio dinâmico
de um caso particular de estado assimptótico em que cada nodo da rede adaptativa
vai sempre mudando o seu estado e as suas ligações a outros nodos, enquanto que
um conjunto de medidas que caracterizam estatisticamente o ensemble dos nodos
mantêm valores fixos. Alémm disso, uma classe muito geral de redes adaptativas
apresenta equilíbrios dinâmicos que parecem ser únicos, no sentido em que aqueles
valores estacionários não dependem das condições iniciais, quer em termos do
estados dos nodos quer em termos da topologia da rede.Este trabalho incide no estudo do equilíbrio dinâmiico de redes adaptativas no contexto
particular de dois modelos paradigmáticos de coevolação, mas os principais
resultados podem ser facilmente generalizados a outros processos. Na primeira
parte, revisita-se e desenvolve-se uma abordagem da variante adaptativa do processo
de contacto baseada num modelo de baixa dimensão. Obtem-se uma descrição
aproximada do diagrama de fases do sistema e do equilíbrio dinâmico, e
identifica-se nessa fase uma combinação de parâmetros para a qual a dinâmica
microscópica, que de assimétrica nos estados dos nodos, da origem a uma simetria
entre os dois subconjuntos de nodos. Esta simetria é explicada através da
derivação de relações de recorrência para as distribuições de grau, que a preveêm
para uma ampla classe de redes adaptativas. Estas relações permitem também
gerar analiticamente as distribuições de grau estacionárias de cada subconjunto
de nodos a partir de um parâmetro livre.Na segunda parte, desenvolve-se uma outra abordagem analítica que permite detectar
e descrever o equilíbrio dinâmico, a partir de propriedades gerais que se
têm que verificar em muitas redes adaptativas. Na base desta abordagem está a
descrição do processo estocástico associado à evolução do estado e das ligações de
cada nó, e as propriedades ergódicas que permitem obter as estatísticas de ensemble
na rede a partir do comportamento a longo termo de um nó. Estas medidas
estatísticas podem ser calculadas a partir de várias distribuições estacionárias
que se relacionam umas com as outras através de transformações simples. Como
aplicação desta abordagem completa, os equilíbrios dinâmicos de três diferentes
variantes do processo de contacto adaptativo são descritos e comparados.
Finalmente, motiva-se e propõe-se uma variante assimétrica do voter model coevolutivo.
A fase activa metastável é tentativamente descrita como uma random
walk ao longo de uma variedade lenta, à semelhan ca do que foi feito na literatura
para o modelo simétrico, e os resultados para os dois casos são comparados.É
identicada uma combinação de parâmetros particular para a qual este modelo
assim etrico emula o modelo simétrico em rede fixa, o que é mais um exemplo da
simetria emergente prevista pelas relações de recorrência estabelecidas na primeira
parte. Considera-se ainda uma outra variante assimétrica, mais complexa, do voter
model co-evolutivo, que apresenta um diagrama de fases essencialmente diferente,
e cuja descrição se mostra requerer novas abordagens.Fundação para a Ciência e a Tecnologia (FCT, SFRH/BD/45179/2008
Die Krise der Männlichkeit: Oder: Die ewige Wiederkunft des Gleichen
Ebenso alt wie das Reden über Männlichkeit dürfte das Phänomen der medial ausgerufenen Krise der Männlichkeit sein, einer zutiefst nostalgischen Litanei, die von diversen Mitspielern produziert und regelmäßig wiederbelebt wird. Sie trägt verschiedene Gesichter in den Medien und reicht vom Entfesselungsaufruf, wie ihn Männerzeitschriften kultivieren, wenn sie ihre Verweichlichungshysterie mit Bildern bärtiger Großstädter am Holzkohlegrill oder am Steuer eines Geländewagens zu besänftigen suchen, bis hin zur rechten Polemik eines Akif Pirinçci, der in seinem Skandalbuch Deutschland von Sinnen (2014) dem „zur Memme transformierten deutschen Mann“ nachtrauert, der sich unter der vermeintlichen Knute von Feminismus, Political-Correctness-Zeitgeist und dem Diktat „abnormale[r] Sexualität“ selbst abhandengekommen sein soll.
Derlei kontroverse Einlassungen stehen durchaus symptomatisch (wenn auch besonders zugespitzt) für die andauernden publizistischen Erfolge von Titeln wie Männerbeben (2007), Was vom Manne übrigblieb (2008), So wird der Mann ein Mann! (2010), Das entehrte Geschlecht (2012) und Der ungezähmte Mann (2018) – Manifeste, die regelmäßig auf den Bestsellerlisten auftauchen und immer dann den ,Krisenmann‘ heraufbeschwören, wenn Debatten über Gewalt im großstädtischen Raum oder männliche ,Bildungsversager‘ geführt werden
Constructions of Masculinity in British Literature from the Middle Ages to the Present: Internationale Konferenz vom 17.–20. Juni 2009 in Dresden
"Anhand von vier theoretischen Beiträgen und 15 Analysen literarischer Texte vom Mittelalter bis zum 21. Jahrhundert leistete die Konferenz 'Constructions of Masculinity' eine theoretisch reflektierte und an die aktuelle Lebenswelt rückgebundene diachrone Untersuchung sowohl der Veränderungen männlicher Identitätskonstruktionen als auch der ihnen zugrunde liegenden Faktoren." (Autorenreferat)"Consisting of four theoretical contributions and 15 interpretations of key literary texts, ranging from the Middle Ages to the very present, the international conference 'Constructions of Masculinity' produced a sophisticated, theoretically founded analysis, not only of the diachronic changes of male identity constructions, but also of the underlying reasons for these changes." (author's abstract
Neuromelanin-Sensitive Magnetic Resonance Imaging in Schizophrenia: A Meta-Analysis of Case-Control Studies
Background: Psychiatry is in urgent need of reliable biomarkers. Novel neuromelanin-sensitive magnetic resonance imaging (NM-MRI) sequences provide a time-efficient and non-invasive way to investigate the human brain in-vivo. This gives insight into the metabolites of dopaminergic signaling and may provide further evidence for potential dopaminergic alterations in patients with schizophrenia (SCZ). The present systematic review provides a meta-analysis of case-control studies using neuromelanin-sensitive sequences in SCZ vs. healthy controls (HC).
Methods: According to predefined search terms and inclusion criteria studies were extracted on PubMed. Meta-analyses with a fixed and random-effects model with inverse variance method, DerSimonian-Laird estimator for tau(2), and Cohen's d were calculated. Bias was assessed using funnel plots. The primary study outcome was contrast-to-noise ratio (CNR) in the substantia nigra compared between HC and SCZ.
Results: The total sample of k = 6 studies included n = 183 cases and n = 162 controls. Across all studies we found a significant elevation of CNR in the substantia nigra (d = 0.42 [0.187; 0.655], z = 3.521, p < 0.001) in cases compared to controls. We found no significant difference in the control region of locus coeruleus (d = -0.07 [-0.446; 0.302], z = -0.192, p = 0.847), with CNR for the latter only reported in k = 3 studies.
Conclusion: CNR in the substantia nigra were significantly elevated in cases compared to controls. Our results support neuromelanin as a candidate biomarker for dopaminergic dysfunction in schizophrenia. Further studies need to assess this candidate marker in large, longitudinal cohorts and address potential effects of disease state, medication and correlations with symptoms
Spatially explicit assessment of water embodied in European trade: A product-level multi-regional input-output analysis
Responsible water management in an era of globalised supply chains needs to consider both local and regional water balances and international trade. In this paper, we assess the water footprints of total final demand in the EU-27 at a very detailed product level and spatial scale - an important step towards informed water policy. We apply the multi-regional input-output (MRIO) model EXIOBASE, including water data, to track the distribution of water use along product supply chains within and across countries. This enables the first spatially-explicit MRIO analysis of water embodied in Europe's external trade for almost 11,000 watersheds world-wide, tracing indirect ("virtual") water consumption in one country back to those watersheds where the water was actually extracted. We show that the EU-27 indirectly imports large quantities of blue and green water via international trade of products, most notably processed crop products, and these imports far exceed the water used from domestic sources. The Indus, Danube and Mississippi watersheds are the largest individual contributors to the EU-27's final water consumption, which causes large environmental impacts due to water scarcity in both the Indus and Mississippi watersheds. We conclude by sketching out policy options to ensure that sustainable water management within and outside European borders is not compromised by European consumption
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