137 research outputs found
The International Trade Network: weighted network analysis and modelling
Tools of the theory of critical phenomena, namely the scaling analysis and
universality, are argued to be applicable to large complex web-like network
structures. Using a detailed analysis of the real data of the International
Trade Network we argue that the scaled link weight distribution has an
approximate log-normal distribution which remains robust over a period of 53
years. Another universal feature is observed in the power-law growth of the
trade strength with gross domestic product, the exponent being similar for all
countries. Using the 'rich-club' coefficient measure of the weighted networks
it has been shown that the size of the rich-club controlling half of the
world's trade is actually shrinking. While the gravity law is known to describe
well the social interactions in the static networks of population migration,
international trade, etc, here for the first time we studied a non-conservative
dynamical model based on the gravity law which excellently reproduced many
empirical features of the ITN.Comment: 5 pages, 5 figure
Anomalous lifetime distributions and topological traps in ordering dynamics
We address the role of community structure of an interaction network in
ordering dynamics, as well as associated forms of metastability. We consider
the voter and AB model dynamics in a network model which mimics social
interactions. The AB model includes an intermediate state between the two
excluding options of the voter model. For the voter model we find dynamical
metastable disordered states with a characteristic mean lifetime. However, for
the AB dynamics we find a power law distribution of the lifetime of metastable
states, so that the mean lifetime is not representative of the dynamics. These
trapped metastable states, which can order at all time scales, originate in the
mesoscopic network structure.Comment: 7 pages; 6 figure
Small But Slow World: How Network Topology and Burstiness Slow Down Spreading
Communication networks show the small-world property of short paths, but the
spreading dynamics in them turns out slow. We follow the time evolution of
information propagation through communication networks by using the SI model
with empirical data on contact sequences. We introduce null models where the
sequences are randomly shuffled in different ways, enabling us to distinguish
between the contributions of different impeding effects. The slowing down of
spreading is found to be caused mostly by weight-topology correlations and the
bursty activity patterns of individuals
Observation of a New Surface State on 4He Crystal Interfaces
The equilibrium shape of hcp 4He crystals has been studied at temperatures 0.05≤T≤0.7 K by means of a high-precision optical interferometer. We find that the profile of the interfacial boundary, close to an almost horizontal c-facet, has a well-defined slope discontinuity separating two angular regions with different behavior of the surface stiffness α̃. For surfaces tilted by an angle φ≲100 μrad with respect to the c-facet, we obtain α̃=κ/φ, contrary to the linear angular dependence predicted by current theories. Our results on four large crystals yield κ=(11±3)×10 exp −4T erg/ cm exp 2 K.Peer reviewe
Analysis of a large-scale weighted network of one-to-one human communication
We construct a connected network of 3.9 million nodes from mobile phone call
records, which can be regarded as a proxy for the underlying human
communication network at the societal level. We assign two weights on each edge
to reflect the strength of social interaction, which are the aggregate call
duration and the cumulative number of calls placed between the individuals over
a period of 18 weeks. We present a detailed analysis of this weighted network
by examining its degree, strength, and weight distributions, as well as its
topological assortativity and weighted assortativity, clustering and weighted
clustering, together with correlations between these quantities. We give an
account of motif intensity and coherence distributions and compare them to a
randomized reference system. We also use the concept of link overlap to measure
the number of common neighbors any two adjacent nodes have, which serves as a
useful local measure for identifying the interconnectedness of communities. We
report a positive correlation between the overlap and weight of a link, thus
providing strong quantitative evidence for the weak ties hypothesis, a central
concept in social network analysis. The percolation properties of the network
are found to depend on the type and order of removed links, and they can help
understand how the local structure of the network manifests itself at the
global level. We hope that our results will contribute to modeling weighted
large-scale social networks, and believe that the systematic approach followed
here can be adopted to study other weighted networks.Comment: 25 pages, 17 figures, 2 table
Evidence of 4He Crystallization via Quantum Tunneling at mK Temperatures
We have investigated creation of 4He crystals from the superfluid phase at the temperature range 2 mK–1.0 K. Statistical nucleation-event distributions in overpressure were found to be broad, asymmetric, and temperature independent below 100 mK. Our statistical analysis agrees with a theoretical model suggesting that solid formation is driven by macroscopical quantum-mechanical fluctuations from a seed preexisting in a cavity on the wall.Peer reviewe
Human thymic T cell repertoire is imprinted with strong convergence to shared sequences
A highly diverse repertoire of T cell antigen receptors (TCR) is created in the thymus by recombination of gene segments and the insertion or deletion of nucleotides at the junctions. Using next-generation TCR sequencing we define here the features of recombination and selection in the human TCR alpha and TCR beta locus, and show that a strikingly high proportion of the repertoire is shared by unrelated individuals. The thymic TCRa nucleotide repertoire was more diverse than TCR beta, with 4.1 x 10(6) vs. 0.81 x 10(6) unique clonotypes, and contained nonproductive clonotypes at a higher frequency (69.2% vs. 21.2%). The convergence of distinct nucleotide clonotypes to the same amino acid sequences was higher in TCRa than in TCR beta repertoire (1.45 vs. 1.06 nucleotide sequences per amino acid sequence in thymus). The gene segment usage was biased, and generally all individuals favored the same genes in both TCR alpha and TCR beta loci. Despite the high diversity, a large fraction of the repertoire was found in more than one donor. The shared fraction was bigger in TCR alpha than TCR beta repertoire, and more common in in-frame sequences than in nonproductive sequences. Thus, both biases in rearrangement and thymic selection are likely to contribute to the generation of shared repertoire in humans.Peer reviewe
Facet Growth of 4He Crystals at mK Temperatures
We have investigated growth of c facets in good quality helium crystals with screw dislocation densities 0–20 cm exp −2 along the c axis. Three distinct regimes of growth were observed. One of them can be explained by spiral growth provided that kinetic energy of moving steps and their tendency to localization at large driving forces are taken into account. In the absence of screw dislocations we find burstlike growth unless the speed is less than 0.5 nm/s, in which case anomalous, intrinsic growth of facets is detected.Peer reviewe
Characterization of human T cell receptor repertoire data in eight thymus samples and four related blood samples
T cell receptor (TCR) is a heterodimer consisting of TCR alpha and TCR beta chains that are generated by somatic recombination of multiple gene segments. Nascent TCR repertoire undergoes thymic selections where non-functional and potentially autoreactive receptors are removed. During the last years, the development of high-throughput sequencing technology has allowed a large scale assessment of TCR repertoire and multiple analysis tools are now also available. In our recent manuscript, Human thymic T cell repertoire is imprinted with strong convergence to shared sequences [1], we show highly overlapping thymic TCR repertoires in unrelated individuals. In the current Data in Brief article, we provide a more detailed characterization of the basic features of these thymic and related peripheral blood TCR repertoires. The thymus samples were collected from eight infants undergoing corrective cardiac surgery, two of whom were monozygous twins [2]. In parallel with the surgery, a small aliquot of peripheral blood was drawn from four of the donors. Genomic DNA was extracted from mechanically released thymocytes and circulating leukocytes. The sequencing of TCR alpha and TCR beta repertoires was performed at ImmunoSEQ platform (Adaptive Biotechnologies). The obtained repertoire data were analysed applying relevant features from immunoSEQ (R) 3.0 Analyzer (Adaptive Biotechnologies) and a freely available VDJTools software package for programming language R [3]. The current data analysis displays the basic features of the sequenced repertoires including observed TCR diversity, various descriptive TCR diversity measures, and V and J gene usage. In addition, multiple methods to calculate repertoire overlap between two individuals are applied. The raw sequence data provide a large database of reference TCRs in healthy individuals at an early developmental stage. The data can be exploited to improve existing computational models on TCR repertoire behaviour as well as in the generation of new models. (C) 2021 The Authors. Published by Elsevier Inc.Peer reviewe
New approaches to model and study social networks
We describe and develop three recent novelties in network research which are
particularly useful for studying social systems. The first one concerns the
discovery of some basic dynamical laws that enable the emergence of the
fundamental features observed in social networks, namely the nontrivial
clustering properties, the existence of positive degree correlations and the
subdivision into communities. To reproduce all these features we describe a
simple model of mobile colliding agents, whose collisions define the
connections between the agents which are the nodes in the underlying network,
and develop some analytical considerations. The second point addresses the
particular feature of clustering and its relationship with global network
measures, namely with the distribution of the size of cycles in the network.
Since in social bipartite networks it is not possible to measure the clustering
from standard procedures, we propose an alternative clustering coefficient that
can be used to extract an improved normalized cycle distribution in any
network. Finally, the third point addresses dynamical processes occurring on
networks, namely when studying the propagation of information in them. In
particular, we focus on the particular features of gossip propagation which
impose some restrictions in the propagation rules. To this end we introduce a
quantity, the spread factor, which measures the average maximal fraction of
nearest neighbors which get in contact with the gossip, and find the striking
result that there is an optimal non-trivial number of friends for which the
spread factor is minimized, decreasing the danger of being gossiped.Comment: 16 Pages, 9 figure
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