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Scale-free Properties (scale-free + property)
Selected AbstractsApplying Network Analysis to the Conservation of Habitat Trees in Urban Environments: a Case Study from Brisbane, AustraliaCONSERVATION BIOLOGY, Issue 3 2006MONIKA RHODES conectividad de perchas; fauna que utiliza oquedades; planificación de la conservación; red sin escala; Tadarida australis Abstract:,In Australia more than 300 vertebrates, including 43 insectivorous bat species, depend on hollows in habitat trees for shelter, with many species using a network of multiple trees as roosts. We used roost-switching data on white-striped freetail bats (Tadarida australis; Microchiroptera: Molossidae) to construct a network representation of day roosts in suburban Brisbane, Australia. Bats were caught from a communal roost tree with a roosting group of several hundred individuals and released with transmitters. Each roost used by the bats represented a node in the network, and the movements of bats between roosts formed the links between nodes. Despite differences in gender and reproductive stages, the bats exhibited the same behavior throughout three radiotelemetry periods and over 500 bat days of radio tracking: each roosted in separate roosts, switched roosts very infrequently, and associated with other bats only at the communal roost. This network resembled a scale-free network in which the distribution of the number of links from each roost followed a power law. Despite being spread over a large geographic area (>200 km2), each roost was connected to others by less than three links. One roost (the hub or communal roost) defined the architecture of the network because it had the most links. That the network showed scale-free properties has profound implications for the management of the habitat trees of this roosting group. Scale-free networks provide high tolerance against stochastic events such as random roost removals but are susceptible to the selective removal of hub nodes. Network analysis is a useful tool for understanding the structural organization of habitat tree usage and allows the informed judgment of the relative importance of individual trees and hence the derivation of appropriate management decisions. Conservation planners and managers should emphasize the differential importance of habitat trees and think of them as being analogous to vital service centers in human societies. Resumen:,En Australia, más de 300 vertebrados, incluyendo 43 especies de murciélagos insectívoros, dependen de oquedades en árboles para refugiarse; muchas de ellas perchan en una red de múltiples árboles. Utilizamos datos de cambio de perchas en Tadarida australis (Microchiroptera: Molossidae) para construir una representación reticular de las perchas diurnas en los suburbios de Brisbane, Australia. Los murciélagos fueron capturados en un árbol con un grupo de varios cientos de individuos y liberados con transmisores. Cada percha utilizada por los murciélagos representó un nodo individual en la red, y los movimientos de murciélagos entre perchas constituyeron los eslabones entre los nodos. A pesar de las diferencias de género y etapas reproductivas, los murciélagos mostraron el mismo comportamiento en tres períodos de radiotelemetría y en más de 500 días de seguimiento de murciélagos: cada uno utilizó perchas separadas, cambiaban de percha poco frecuentemente, y se asociaron con otros murciélagos sólo en las perchas comunales. Esta red fue semejante a una red sin escala en la que la distribución del número de eslabones de cada percha cumplió una ley potencial. A pesar de estar dispersas en un área geográfica extensa (>200 km2), cada percha estaba conectada con otras por menos de tres eslabones. Una percha (el centro o percha comunal) definió la arquitectura de la red porque tenía a la mayoría de los eslabones. El hecho de que la red mostrara propiedades libres de escala tiene implicaciones profundas para la gestión de árboles que funcionan como perchas. Las redes libres de escala proporcionan alta tolerancia a eventos estocásticos como la remoción aleatoria de perchas, pero son susceptibles a la remoción selectiva de nodos centrales. El análisis de redes es una herramienta útil para el entendimiento de la organización estructural del uso de de árboles y permite el juicio informado de la importancia relativa de árboles individuales y por lo tanto la derivación de decisiones administrativas apropiadas Los planificadores y gestores de la conservación deberían enfatizar la importancia diferencial de árboles y considerarlos análogos a los centros de servicio vitales en las sociedades humanas. [source] Theoretical framework for the histone modification network: modifications in the unstructured histone tails form a robust scale-free networkGENES TO CELLS, Issue 7 2009Yohei Hayashi A rapid increase in research on the relationship between histone modifications and their subsequent reactions in the nucleus has revealed that the histone modification system is complex, and robust against point mutations. The prevailing theoretical framework (the histone code hypothesis) is inadequate to explain either the complexity or robustness, making the formulation of a new theoretical framework both necessary and desirable. Here, we develop a model of the regulatory network of histone modifications in which we encode histone modifications as nodes and regulatory interactions between histone modifications as links. This network has scale-free properties and subnetworks with a pseudo,mirror symmetry structure, which supports the robustness of the histone modification network. In addition, we show that the unstructured tail regions of histones are suitable for the acquisition of this scale-free property. Our model and related insights provide the first framework for an overall architecture of a histone modification network system, particularly with regard to the structural and functional roles of the unstructured histone tail region. In general, the post-translational "modification webs" of natively unfolded regions (proteins) may function as signal routers for the robust processing of the large amounts of signaling information. [source] Scale-free networks in biology: new insights into the fundamentals of evolution?,BIOESSAYS, Issue 2 2002Yuri I. Wolf Scale-free network models describe many natural and social phenomena. In particular, networks of interacting components of a living cell were shown to possess scale-free properties. A recent study(1) compares the system-level properties of metabolic and information networks in 43 archaeal, bacterial and eukaryal species and claims that the scale-free organization of these networks is more conserved during evolution than their content. BioEssays 24:105,109, 2002. Published 2002 Wiley Periodicals, Inc. [source] The Small World of Canadian Capital Markets: Statistical Mechanics of Investment Bank Syndicate Networks, 1952,1989CANADIAN JOURNAL OF ADMINISTRATIVE SCIENCES, Issue 4 2004Joel A.C. Baum We investigate the structure of investment bank syndicate networks in Canada. We consider two banks to be connected if they have participated in an underwriting syndicate together, and construct networks of such connections using data drawn from the Record of New Issues (Financial Data Group). We show that these interfirm networks form "small worlds", in which banks are both locally clustered and globally connected by short paths of intermediate banks, and are "scale free", in which the connectivity of the network is highly skewed and with most banks tied to a small set of prominent banks. We examine changes over time in the network's small-world and scale-free properties, and demonstrate their theoretical and practical implications for the structure and operation of Canadian capital markets by linking these properties to the network's cliquey-ness, resilience, and speed of information transmission. Résumé Cette étude porte sur la structure des réseaux que for-ment les syndicats d'émission des banques d'investissement au Canada. Nous posons que deux banques sont liées si elles ont participé ensemble à un syndicat d'émission, et nous retraçons les réseaux de liens en utilisant des données extraites du Record of New Issues (Financial Data Group). Nous montrons que ces réseaux interorganisationnels (RIO)forment des petits mondes dans lesquels les banques sont à la fois localement regroupées et mondialement reliées par des courts chemins de banques intermédiaires. Les RIO sont également sans échelle (scale free): la connectivité dans le réseau est fortement inégale et la plupart des banques sont liées à un petit nombre de banques dominantes. Nous examinons l'évolution des propriétés de petit monde et d'absence d'échelle du réseau et mettons en Evidence leurs implications théoriques et pratiques pour la structure et le fonctionnement du marché canadien des capitaux en reliant ces propriétés aux caractères de clique, de résilience et de vitesse de transmission de l'information du réseau. [source] Theoretical framework for the histone modification network: modifications in the unstructured histone tails form a robust scale-free networkGENES TO CELLS, Issue 7 2009Yohei Hayashi A rapid increase in research on the relationship between histone modifications and their subsequent reactions in the nucleus has revealed that the histone modification system is complex, and robust against point mutations. The prevailing theoretical framework (the histone code hypothesis) is inadequate to explain either the complexity or robustness, making the formulation of a new theoretical framework both necessary and desirable. Here, we develop a model of the regulatory network of histone modifications in which we encode histone modifications as nodes and regulatory interactions between histone modifications as links. This network has scale-free properties and subnetworks with a pseudo,mirror symmetry structure, which supports the robustness of the histone modification network. In addition, we show that the unstructured tail regions of histones are suitable for the acquisition of this scale-free property. Our model and related insights provide the first framework for an overall architecture of a histone modification network system, particularly with regard to the structural and functional roles of the unstructured histone tail region. In general, the post-translational "modification webs" of natively unfolded regions (proteins) may function as signal routers for the robust processing of the large amounts of signaling information. [source] Understanding on the residue contact network using the log-normal cluster model and the multilevel wheel diagram,BIOPOLYMERS, Issue 10 2010Weitao Sun Abstract Residue clusters play essential role in stabilizing protein structures in the form of complex networks. We show that the cluster sizes in a native protein follow the log-normal distribution for a dataset consisting of 424 proteins. To our knowledge, this is the first time of such fitting for the native structures. Based on log-normal model, the asymptotically increasing mean cluster sizes produce a critical protein chain length of about 200 amino acids, beyond which length most globular proteins have nearly the same mean cluster sizes. This suggests that the larger proteins use a different packing mechanism than the smaller proteins. We confirmed the scale-free property of the residue contact network for most of the protein structures in the dataset, although the violations were observed for the tightly packed proteins. Residue cluster network wheel (RCNW) is proposed to visualize the relationship between the multiple properties of the residue network such as the cluster size, the residue types and contacts, and the flexibility of the residue. We noticed that the residues with large cluster size have smaller C, displacement measured using the normal mode analysis. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 904,916, 2010. [source] | ||||||||||