2,026 research outputs found
Reliability of rank order in sampled networks
In complex scale-free networks, ranking the individual nodes based upon their
importance has useful applications, such as the identification of hubs for
epidemic control, or bottlenecks for controlling traffic congestion. However,
in most real situations, only limited sub-structures of entire networks are
available, and therefore the reliability of the order relationships in sampled
networks requires investigation. With a set of randomly sampled nodes from the
underlying original networks, we rank individual nodes by three centrality
measures: degree, betweenness, and closeness. The higher-ranking nodes from the
sampled networks provide a relatively better characterisation of their ranks in
the original networks than the lower-ranking nodes. A closeness-based order
relationship is more reliable than any other quantity, due to the global nature
of the closeness measure. In addition, we show that if access to hubs is
limited during the sampling process, an increase in the sampling fraction can
in fact decrease the sampling accuracy. Finally, an estimation method for
assessing sampling accuracy is suggested
Macroscopic Kinetic Effect of Cell-to-Cell Variation in Biochemical Reactions
Genetically identical cells under the same environmental conditions can show
strong variations in protein copy numbers due to inherently stochastic events
in individual cells. We here develop a theoretical framework to address how
variations in enzyme abundance affect the collective kinetics of metabolic
reactions observed within a population of cells. Kinetic parameters measured at
the cell population level are shown to be systematically deviated from those of
single cells, even within populations of homogeneous parameters. Because of
these considerations, Michaelis-Menten kinetics can even be inappropriate to
apply at the population level. Our findings elucidate a novel origin of
discrepancy between in vivo and in vitro kinetics, and offer potential utility
for analysis of single-cell metabolomic data
Anatomy of Scientific Evolution
The quest for historically impactful science and technology provides
invaluable insight into the innovation dynamics of human society, yet many
studies are limited to qualitative and small-scale approaches. Here, we
investigate scientific evolution through systematic analysis of a massive
corpus of digitized English texts between 1800 and 2008. Our analysis reveals
great predictability for long-prevailing scientific concepts based on the
levels of their prior usage. Interestingly, once a threshold of early adoption
rates is passed even slightly, scientific concepts can exhibit sudden leaps in
their eventual lifetimes. We developed a mechanistic model to account for such
results, indicating that slowly-but-commonly adopted science and technology
surprisingly tend to have higher innate strength than fast-and-commonly adopted
ones. The model prediction for disciplines other than science was also well
verified. Our approach sheds light on unbiased and quantitative analysis of
scientific evolution in society, and may provide a useful basis for
policy-making.Comment: Supplementary material attache
Energized soft tissue dissection in surgery simulation
With the development of virtual reality technology, surgery simulation has become an effective way to train the operation skills for surgeons. Soft tissue dissection, as one of the most frequently performed operations in surgery, is indispensable to an immersive and high-fidelity surgery simulator. Energized dissection tools are much more commonly used than the traditional sharp scalpels for patient safety. Unfortunately, the interaction of such tools with the soft tissues has been largely ignored in the research of surgical simulators. In this paper, we have proposed an energized soft tissue dissection model. We categorize the soft tissues into three types (fascia, membrane, and fat) and simulate their physical property accordingly. The dissection algorithm we propose employs an edge-based structure, which offers an effective mechanism for the generation of incisions dissected with energized tools. The mesh topology will not be changed when it is dissected by an energized tool, rather it is controlled by the heat transfer model. Our dissection method is highly compatible and efficient to the physically based simulation resolved by a pre-factorized linear system. We have proposed an energized soft tissue dissection model. We categorize the soft tissues into three types (fascia, membrane, and fat) and simulate their physical property accordingly. The dissection algorithm employs an edge-based structure, which offers an effective mechanism for the generation of incisions dissected with energized tools. Our dissection method is highly compatible and efficient to the physically based simulation resolved by a pre-factorized linear system
Pattern Formation in a Two-Dimensional Array of Oscillators with Phase-Shifted Coupling
We investigate the dynamics of a two-dimensional array of oscillators with
phase-shifted coupling. Each oscillator is allowed to interact with its
neighbors within a finite radius. The system exhibits various patterns
including squarelike pinwheels, (anti)spirals with phase-randomized cores, and
antiferro patterns embedded in (anti)spirals. We consider the symmetry
properties of the system to explain the observed behaviors, and estimate the
wavelengths of the patterns by linear analysis. Finally, we point out the
implications of our work for biological neural networks
Robust nodal superconductivity induced by isovalent doping in Ba(FeRu)As and BaFe(AsP)
We present the ultra-low-temperature heat transport study of iron-based
superconductors Ba(FeRu)As and
BaFe(AsP). For optimally doped
Ba(FeRu)As, a large residual linear term
at zero field and a dependence of are observed,
which provide strong evidences for nodes in the superconducting gap. This
result demonstrates that the isovalent Ru doping can also induce nodal
superconductivity, as P does in BaFe(AsP).
Furthermore, in underdoped Ba(FeRu)As and heavily
underdoped BaFe(AsP), manifests similar
nodal behavior, which shows the robustness of nodal superconductivity in the
underdoped regime and puts constraint on theoretical models.Comment: 5 pages, 4 figures - with two underdoped samples added, this paper
supersedes arXiv:1106.541
Cost-effective circadian mechanism: rhythmic degradation of circadian proteins spontaneously emerges without rhythmic post-translational regulation
Circadian protein oscillations are maintained by the lifelong repetition of protein production and degradation in daily balance. It comes at the cost of ever-replayed, futile protein synthesis each day. This biosynthetic cost with a given oscillatory protein profile is relievable by a rhythmic, not constant, degradation rate that selectively peaks at the right time of day but remains low elsewhere, saving much of the gross protein loss and of the replenishing protein synthesis. Here, our mathematical modeling reveals that the rhythmic degradation rate of proteins with circadian production spontaneously emerges under steady and limited activity of proteolytic mediators and does not necessarily require rhythmic post-translational regulation of previous focus. Additional (yet steady) post-translational modifications in a proteolytic pathway can further facilitate the degradation's rhythmicity in favor of the biosynthetic cost saving. Our work is supported by animal and plant circadian data, offering a generic mechanism for potentially widespread, time-dependent protein turnover
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