9,051 research outputs found
Robustness of the avalanche dynamics in data packet transport on scale-free networks
We study the avalanche dynamics in the data packet transport on scale-free
networks through a simple model. In the model, each vertex is assigned a
capacity proportional to the load with a proportionality constant . When
the system is perturbed by a single vertex removal, the load of each vertex is
redistributed, followed by subsequent failures of overloaded vertices. The
avalanche size depends on the parameter as well as which vertex triggers
it. We find that there exists a critical value at which the avalanche
size distribution follows a power law. The critical exponent associated with it
appears to be robust as long as the degree exponent is between 2 and 3, and is
close in value to that of the distribution of the diameter changes by single
vertex removal.Comment: 5 pages, 7 figures, final version published in PR
Sandpiles on multiplex networks
We introduce the sandpile model on multiplex networks with more than one type
of edge and investigate its scaling and dynamical behaviors. We find that the
introduction of multiplexity does not alter the scaling behavior of avalanche
dynamics; the system is critical with an asymptotic power-law avalanche size
distribution with an exponent on duplex random networks. The
detailed cascade dynamics, however, is affected by the multiplex coupling. For
example, higher-degree nodes such as hubs in scale-free networks fail more
often in the multiplex dynamics than in the simplex network counterpart in
which different types of edges are simply aggregated. Our results suggest that
multiplex modeling would be necessary in order to gain a better understanding
of cascading failure phenomena of real-world multiplex complex systems, such as
the global economic crisis.Comment: 7 pages, 7 figure
A system to enrich for primitive streak-derivatives, definitive endoderm and mesoderm, from pluripotent cells in culture
Two lineages of endoderm develop during mammalian embryogenesis, the primitive endoderm in the pre-implantation blastocyst and the definitive endoderm at gastrulation. This complexity of endoderm cell populations is mirrored during pluripotent cell differentiation in vitro and has hindered the identification and purification of the definitive endoderm for use as a substrate for further differentiation. The aggregation and differentiation of early primitive ectoderm-like (EPL) cells, resulting in the formation of EPL-cell derived embryoid bodies (EPLEBs), is a model of gastrulation that progresses through the sequential formation of primitive streak-like intermediates to nascent mesoderm and more differentiated mesoderm populations. EPL cell-derived EBs have been further analysed for the formation of definitive endoderm by detailed morphological studies, gene expression and a protein uptake assay. In comparison to embryoid bodies derived from ES cells, which form primitive and definitive endoderm, the endoderm compartment of embryoid bodies formed from EPL cells was comprised almost exclusively of definitive endoderm. Definitive endoderm was defined as a population of squamous cells that expressed Sox17, CXCR4 and Trh, which formed without the prior formation of primitive endoderm and was unable to endocytose horseradish peroxidase from the medium. Definitive endoderm formed in EPLEBs provides a substrate for further differentiation into specific endoderm lineages; these lineages can be used as research tools for understanding the mechanisms controlling lineage establishment and the nature of the transient intermediates formed. The similarity between mouse EPL cells and human ES cells suggests EPLEBs can be used as a model system for the development of technologies to enrich for the formation of human ES cell-derived definitive endoderm in the future.Sveltana Vassilieva, Hweee Ngee Goh, Kevin X. Lau, James N. Hughes, Mary Familari, Peter D. Rathjen and Joy Rathje
Validation of the English and Chinese versions of the Quick-FLIC quality of life questionnaire.
A useful measure of quality of life should be easy and quick to complete. Recently, we reported the development and validation of a shortened Chinese version of the Functional Living Index-Cancer (FLIC), which we called the Quick-FLIC. In the present study of 327 English-speaking and 221 Chinese-speaking cancer patients, we validated the English version of the Quick-FLIC and further assessed the Chinese version. The 11 Quick-FLIC items were administered alongside the 11 remaining items of the full FLIC, but there appeared to be little context effect. Validity of the English version of the Quick-FLIC was attested by its strong correlation with two other measures of quality of life, and its ability to detect differences between patients with different performance status and treatment status (each P<0.001). Its internal consistency (alpha=0.86) and test-retest reliability (intraclass correlation=0.76) were also satisfactory. The measure was responsive to changes in performance status (P<0.001). The Chinese version showed similar characteristics. The Quick-FLIC behaved in ways that are highly comparable with the FLIC, even though the Quick-FLIC comprised only 11 items whereas the FLIC comprised 22. Further research is required to see whether the use of shorter instruments can improve data quality and response rates, but the fact that shorter instruments place less burden on the patients is itself inherently important
A box-covering algorithm for fractal scaling in scale-free networks
A random sequential box-covering algorithm recently introduced to measure the
fractal dimension in scale-free networks is investigated. The algorithm
contains Monte Carlo sequential steps of choosing the position of the center of
each box, and thereby, vertices in preassigned boxes can divide subsequent
boxes into more than one pieces, but divided boxes are counted once. We find
that such box-split allowance in the algorithm is a crucial ingredient
necessary to obtain the fractal scaling for fractal networks; however, it is
inessential for regular lattice and conventional fractal objects embedded in
the Euclidean space. Next the algorithm is viewed from the cluster-growing
perspective that boxes are allowed to overlap and thereby, vertices can belong
to more than one box. Then, the number of distinct boxes a vertex belongs to is
distributed in a heterogeneous manner for SF fractal networks, while it is of
Poisson-type for the conventional fractal objects.Comment: 12 pages, 11 figures, a proceedings of the conference, "Optimization
in complex networks." held in Los Alamo
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