73 research outputs found
Robustness and Closeness Centrality for Self-Organized and Planned Cities
Street networks are important infrastructural transportation systems that
cover a great part of the planet. It is now widely accepted that transportation
properties of street networks are better understood in the interplay between
the street network itself and the so called \textit{information} or
\textit{dual network}, which embeds the topology of the street network
navigation system. In this work, we present a novel robustness analysis, based
on the interaction between the primal and the dual transportation layer for two
large metropolis, London and Chicago, thus considering the structural
differences to intentional attacks for \textit{self-organized} and planned
cities. We elaborate the results through an accurate closeness centrality
analysis in the Euclidean space and in the relationship between primal and dual
space. Interestingly enough, we find that even if the considered planar graphs
display very distinct properties, the information space induce them to converge
toward systems which are similar in terms of transportation properties
On the problem of boundaries and scaling for urban street networks
Urban morphology has presented significant intellectual challenges to
mathematicians and physicists ever since the eighteenth century, when Euler
first explored the famous Konigsberg bridges problem. Many important
regularities and scaling laws have been observed in urban studies, including
Zipf's law and Gibrat's law, rendering cities attractive systems for analysis
within statistical physics. Nevertheless, a broad consensus on how cities and
their boundaries are defined is still lacking. Applying an elementary
clustering technique to the street intersection space, we show that growth
curves for the maximum cluster size of the largest cities in the UK and in
California collapse to a single curve, namely the logistic. Subsequently, by
introducing the concept of the condensation threshold, we show that natural
boundaries of cities can be well defined in a universal way. This allows us to
study and discuss systematically some of the regularities that are present in
cities. We show that some scaling laws present consistent behaviour in space
and time, thus suggesting the presence of common principles at the basis of the
evolution of urban systems
Gravity vs radiation model: on the importance of scale and heterogeneity in commuting flows
We test the recently introduced radiation model against the gravity model for
the system composed of England and Wales, both for commuting patterns and for
public transportation flows. The analysis is performed both at macroscopic
scales, i.e. at the national scale, and at microscopic scales, i.e. at the city
level. It is shown that the thermodynamic limit assumption for the original
radiation model significantly underestimates the commuting flows for large
cities. We then generalize the radiation model, introducing the correct
normalisation factor for finite systems. We show that even if the gravity model
has a better overall performance the parameter-free radiation model gives
competitive results, especially for large scales.Comment: in press Phys. Rev. E, 201
Genetic flow directionality and geographical segregation in a Cymodocea nodosa genetic diversity network
We analyse a large data set of genetic markers obtained from populations of
Cymodocea nodosa, a marine plant occurring from the East Mediterranean to the
Iberian-African coasts in the Atlantic Ocean. We fully develop and test a
recently introduced methodology to infer the directionality of gene flow based
on the concept of geographical segregation. Using the Jensen-Shannon
divergence, we are able to extract a directed network of gene flow describing
the evolutionary patterns of Cymodocea nodosa. In particular we recover the
genetic segregation that the marine plant underwent during its evolution. The
results are confirmed by natural evidence and are consistent with an
independent cross analysis
The need for a network to establish and validate predictive biomarkers in cancer immunotherapy.
Immunotherapies have emerged as one of the most promising approaches to treat patients with cancer. Recently, the entire medical oncology field has been revolutionized by the introduction of immune checkpoints inhibitors. Despite success in a variety of malignancies, responses typically only occur in a small percentage of patients for any given histology or treatment regimen. There are also concerns that immunotherapies are associated with immune-related toxicity as well as high costs. As such, identifying biomarkers to determine which patients are likely to derive clinical benefit from which immunotherapy and/or be susceptible to adverse side effects is a compelling clinical and social need. In addition, with several new immunotherapy agents in different phases of development, and approved therapeutics being tested in combination with a variety of different standard of care treatments, there is a requirement to stratify patients and select the most appropriate population in which to assess clinical efficacy. The opportunity to design parallel biomarkers studies that are integrated within key randomized clinical trials could be the ideal solution. Sample collection (fresh and/or archival tissue, PBMC, serum, plasma, stool, etc.) at specific points of treatment is important for evaluating possible biomarkers and studying the mechanisms of responsiveness, resistance, toxicity and relapse. This white paper proposes the creation of a network to facilitate the sharing and coordinating of samples from clinical trials to enable more in-depth analyses of correlative biomarkers than is currently possible and to assess the feasibilities, logistics, and collated interests. We propose a high standard of sample collection and storage as well as exchange of samples and knowledge through collaboration, and envisage how this could move forward using banked samples from completed studies together with prospective planning for ongoing and future clinical trials
Wikipedia Information Flow Analysis Reveals the Scale-Free Architecture of the Semantic Space
In this paper we extract the topology of the semantic space in its encyclopedic acception, measuring the semantic flow between the different entries of the largest modern encyclopedia, Wikipedia, and thus creating a directed complex network of semantic flows. Notably at the percolation threshold the semantic space is characterised by scale-free behaviour at different levels of complexity and this relates the semantic space to a wide range of biological, social and linguistics phenomena. In particular we find that the cluster size distribution, representing the size of different semantic areas, is scale-free. Moreover the topology of the resulting semantic space is scale-free in the connectivity distribution and displays small-world properties. However its statistical properties do not allow a classical interpretation via a generative model based on a simple multiplicative process. After giving a detailed description and interpretation of the topological properties of the semantic space, we introduce a stochastic model of content-based network, based on a copy and mutation algorithm and on the Heaps' law, that is able to capture the main statistical properties of the analysed semantic space, including the Zipf's law for the word frequency distribution
Limited Urban Growth: London's Street Network Dynamics since the 18th Century
We investigate the growth dynamics of Greater London defined by the
administrative boundary of the Greater London Authority, based on the evolution
of its street network during the last two centuries. This is done by employing
a unique dataset, consisting of the planar graph representation of nine time
slices of Greater London's road network spanning 224 years, from 1786 to 2010.
Within this time-frame, we address the concept of the metropolitan area or city
in physical terms, in that urban evolution reveals observable transitions in
the distribution of relevant geometrical properties. Given that London has a
hard boundary enforced by its long-standing green belt, we show that its street
network dynamics can be described as a fractal space-filling phenomena up to a
capacitated limit, whence its growth can be predicted with a striking level of
accuracy. This observation is confirmed by the analytical calculation of key
topological properties of the planar graph, such as the topological growth of
the network and its average connectivity. This study thus represents an example
of a strong violation of Gibrat's law. In particular, we are able to show
analytically how London evolves from a more loop-like structure, typical of
planned cities, toward a more tree-like structure, typical of self-organized
cities. These observations are relevant to the discourse on sustainable urban
planning with respect to the control of urban sprawl in many large cities,
which have developed under the conditions of spatial constraints imposed by
green belts and hard urban boundaries.Comment: PlosOne, in publicatio
Ideas in the Hispanic Caribbean in the nineteenth century: The antillanismo as emancipatory and integration ideal
En la compleja y conflictiva realidad del Caribe hispano del siglo XIX, emerge un conjunto de ideas que se organizan en torno de la voluntad de independencia, de libertad y autoafirmación polÃtica y cultural, de integración antillana y nuestroamericana. Ideas que pueden ser sintetizadas en el término antillanismo. Fueron esgrimidas en oposición al colonialismo y al imperialismo y fundamentadas desde posiciones filosóficas que abarcaron un amplio espectro, desde la ilustración al positivismo y el krausismo. Su originalidad radica en haber constituido una trama discursiva ligada dialécticamente a los acontecimientos de la situación social e histórica que buscaba comprender y transformar.In the Spanish Caribbean complex and conflicting realities of nineteenth–century,
grows a set of ideas that are organized around the desire for independence, freedom, political and cultural self–assertion and integration. These ideas can be summarized in the term antillanismo. They were put forward in opposition to colonialism and imperialism and reasoned from philosophical positions that covered a wide spectrum, from illustration to positivism and krausism. Its originality lies in having formed a discursive frame dialectically linked to the events of the socio–historical situation that sought to understand and transform.Fil: Arpini, Adriana Maria. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Mendoza. Instituto de Ciencias Humanas, Sociales y Ambientales; Argentin
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