1,025 research outputs found
Geographical Coarsegraining of Complex Networks
We perform the renormalization-group-like numerical analysis of
geographically embedded complex networks on the two-dimensional square lattice.
At each step of coarsegraining procedure, the four vertices on each square box are merged to a single vertex, resulting in the coarsegrained
system of the smaller sizes. Repetition of the process leads to the observation
that the coarsegraining procedure does not alter the qualitative
characteristics of the original scale-free network, which opens the possibility
of subtracting a smaller network from the original network without destroying
the important structural properties. The implication of the result is also
suggested in the context of the recent study of the human brain functional
network.Comment: To appear in Phys. Rev. Let
Comment on ``Loss of Superconducting Phase Coherence in YBa_2Cu_3O_7 Films: Vortex-Loop Unbinding and Kosterlitz-Thouless Phenomena''
Recently, Kotzler et al. measured the frequency-dependent conductance for
YBa_2Cu_3O_7 and interpreted their results as evidences that the decay of the
superfluid density is caused by a 3D vortex loop proliferation mechanism and a
dimensional crossover when the correlation length along the c axis
becomes comparable to the sample thickness [PRL 87, 127005(2001)]. In this
Comment, we show that the complex conductance data presented by Kotzler et al.
have characteristic key features not compatible with their analysis, which are
instead described by the existing phenomenology of 2D vortex fluctuation
associated with a partial decoupling of CuO_2-planes.Comment: 2 pages, 1 figure, accepted in PR
Instability of defensive alliances in the predator-prey model on complex networks
A model of six-species food web is studied in the viewpoint of spatial
interaction structures. Each species has two predators and two preys, and it
was previously known that the defensive alliances of three cyclically predating
species self-organize in two-dimensions. The alliance-breaking transition
occurs as either the mutation rate is increased or interaction topology is
randomized in the scheme of the Watts-Strogatz model. In the former case of
temporal disorder, via the finite-size scaling analysis the transition is
clearly shown to belong to the two-dimensional Ising universality class. In
contrast, the geometric or spatial randomness for the latter case yields a
discontinuous phase transition. The mean-field limit of the model is
analytically solved and then compared with numerical results. The dynamic
universality and the temporally periodic behaviors are also discussed.Comment: 5 page
Critical currents for vortex defect motion in superconducting arrays
We study numerically the motion of vortices in two-dimensional arrays of
resistively shunted Josephson junctions. An extra vortex is created in the
ground states by introducing novel boundary conditions and made mobile by
applying external currents. We then measure critical currents and the
corresponding pinning energy barriers to vortex motion, which in the
unfrustrated case agree well with previous theoretical and experimental
findings. In the fully frustrated case our results also give good agreement
with experimental ones, in sharp contrast with the existing theoretical
prediction. A physical explanation is provided in relation with the vortex
motion observed in simulations.Comment: To appear in Physical Review
Spatiotemporal Stochastic Resonance in Fully Frustrated Josephson Ladders
We consider a Josephson-junction ladder in an external magnetic field with
half flux quantum per plaquette. When driven by external currents, periodic in
time and staggered in space, such a fully frustrated system is found to display
spatiotemporal stochastic resonance under the influence of thermal noise. Such
resonance behavior is investigated both numerically and analytically, which
reveals significant effects of anisotropy and yields rich physics.Comment: 8 pages in two columns, 8 figures, to appear in Phys. Rev.
Dynamic transition and Shapiro-step melting in a frustrated Josephson-junction array
We consider a two-dimensional fully frustrated Josephson-junction array
driven by combined direct and alternating currents. Interplay between the mode
locking phenomenon, manifested by giant Shapiro steps in the current-voltage
characteristics, and the dynamic phase transition is investigated at finite
temperatures. Melting of Shapiro steps due to thermal fluctuations is shown to
be accompanied by the dynamic phase transition, the universality class of which
is also discussed
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Tracing diagnosis trajectories over millions of patients reveal an unexpected risk in schizophrenia.
The identification of novel disease associations using big-data for patient care has had limited success. In this study, we created a longitudinal disease network of traced readmissions (disease trajectories), merging data from over 10.4 million inpatients through the Healthcare Cost and Utilization Project, which allowed the representation of disease progression mapping over 300 diseases. From these disease trajectories, we discovered an interesting association between schizophrenia and rhabdomyolysis, a rare muscle disease (incidence < 1E-04) (relative risk, 2.21 [1.80-2.71, confidence interval = 0.95], P-value 9.54E-15). We validated this association by using independent electronic medical records from over 830,000 patients at the University of California, San Francisco (UCSF) medical center. A case review of 29 rhabdomyolysis incidents in schizophrenia patients at UCSF demonstrated that 62% are idiopathic, without the use of any drug known to lead to this adverse event, suggesting a warning to physicians to watch for this unexpected risk of schizophrenia. Large-scale analysis of disease trajectories can help physicians understand potential sequential events in their patients
Netons: Vibrations of Complex Networks
We consider atoms interacting each other through the topological structure of
a complex network and investigate lattice vibrations of the system, the quanta
of which we call {\em netons} for convenience. The density of neton levels,
obtained numerically, reveals that unlike a local regular lattice, the system
develops a gap of a finite width, manifesting extreme rigidity of the network
structure at low energies. Two different network models, the small-world
network and the scale-free network, are compared: The characteristic structure
of the former is described by an additional peak in the level density whereas a
power-law tail is observed in the latter, indicating excitability of netons at
arbitrarily high energies. The gap width is also found to vanish in the
small-world network when the connection range .Comment: 9 pages, 6 figures, to appear in JP
Hydrogen Cyanide Produced by Pseudomonas chlororaphis O6 Exhibits Nematicidal Activity against Meloidogyne hapla
Root-knot nematodes (Meloidogyne spp.) are parasites that attack many field crops and orchard trees, and affect both the quantity and quality of the products. A root-colonizing bacterium, Pseudomonas chlororaphis O6, possesses beneficial traits including strong nematicidal activity. To determine the molecular mechanisms involved in the nematicidal activity of P. chlororaphis O6, we constructed two mutants; one lacking hydrogen cyanide production, and a second lacking an insecticidal toxin, FitD. Root drenching with wild-type P. chlororaphis O6 cells caused juvenile mortality in vitro and in planta. Efficacy was not altered in the fitD mutant compared to the wild-type but was reduced in both bioassays for the mutant lacking hydrogen cyanide production. The reduced number of galls on tomato plants caused by the wild-type strain was comparable to that of a standard chemical nematicide. These findings suggest that hydrogen cyanide-producing root colonizers, such as P. chlororaphis O6, could be formulated as “green” nematicides that are compatible with many crops and offer agricultural sustainability
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