2,084 research outputs found
Enhance synchronizability by structural perturbations
In this paper, we investigate the collective synchronization of system of
coupled oscillators on Barab\'{a}si-Albert scale-free network. We propose an
approach of structural perturbations aiming at those nodes with maximal
betweenness. This method can markedly enhance the network synchronizability,
and is easy to be realized. The simulation results show that the eigenratio
will sharply decrease to its half when only 0.6% of those hub nodes are under
3-division processes when network size N=2000. In addition, the present study
also provides a theoretical evidence that the maximal betweenness plays a main
role in network synchronization.Comment: 4 pages, 3 eps figure
High Energy Neutrinos from Astrophysical Sources: An Upper Bound
We show that cosmic-ray observations set a model-independent upper bound to
the flux of high-energy, > 10^14 eV, neutrinos produced by photo-meson (or p-p)
interactions in sources of size not much larger than the proton photo-meson (or
pp) mean-free-path. The bound applies, in particular, to neutrino production by
either AGN jets or GRBs. This upper limit is two orders of magnitude below the
flux predicted in some popular AGN jet models, but is consistent with our
predictions from GRB models. We discuss the implications of these results for
future km^2 high-energy neutrino detectors.Comment: Added discussion showing bound cannot be evaded by invoking magnetic
fields. Accepted Phys Rev
Well-posedness of Hydrodynamics on the Moving Elastic Surface
The dynamics of a membrane is a coupled system comprising a moving elastic
surface and an incompressible membrane fluid. We will consider a reduced
elastic surface model, which involves the evolution equations of the moving
surface, the dynamic equations of the two-dimensional fluid, and the
incompressible equation, all of which operate within a curved geometry. In this
paper, we prove the local existence and uniqueness of the solution to the
reduced elastic surface model by reformulating the model into a new system in
the isothermal coordinates. One major difficulty is that of constructing an
appropriate iterative scheme such that the limit system is consistent with the
original system.Comment: The introduction is rewritte
Neutrino signatures of the supernova - gamma ray burst relationship
We calculate the TeV-PeV neutrino fluxes of gamma-ray bursts associated with
supernovae, based on the observed association between GRB 030329 and supernova
SN 2003dh. The neutrino spectral flux distributions can test for possible
delays between the supernova and the gamma-ray burst events down to much
shorter timescales than what can be resolved with photons. As an illustrative
example, we calculate the probability of neutrino induced muon and electron
cascade events in a km scale under-ice detector at the South Pole, from the GRB
030329. Our calculations demonstrate that km scale neutrino telescopes are
expected to detect signals that will allow to constrain supernova-GRB models.Comment: 7 pages, 2 figures. Accepted for publication in Phys. Rev.
CRISPR-mediated reactivation of DKK3 expression attenuates TGF-beta signaling in prostate cancer
The DKK3 gene encodes a secreted protein, Dkk-3, that inhibits prostate tumor growth and metastasis. DKK3 is downregulated by promoter methylation in many types of cancer, including prostate cancer. Gene silencing studies have shown that Dkk-3 maintains normal prostate epithelial cell homeostasis by limiting TGF-β/Smad signaling. While ectopic expression of Dkk-3 leads to prostate cancer cell apoptosis, it is unclear if Dkk-3 has a physiological role in cancer cells. Here, we show that treatment of PC3 prostate cancer cells with the DNA methyltransferase (DNMT) inhibitor decitabine demethylates the DKK3 promoter, induces DKK3 expression, and inhibits TGF-β/Smad-dependent transcriptional activity. Direct induction of DKK3 expression using CRISPR-dCas9-VPR also inhibited TGF-β/Smad-dependent transcription and attenuated PC3 cell migration and proliferation. These effects were not observed in C4-2B cells, which do not respond to TGF-β. TGF-β signals can regulate gene expression directly via SMAD proteins and indirectly by increasing DNMT expression, leading to promoter methylation. Analysis of genes downregulated by promoter methylation and predicted to be regulated by TGF-β found that DKK3 induction increased expression of PTGS2, which encodes cyclooxygenase-2. Together, these observations provide support for using CRISPR-mediated induction of DKK3 as a potential therapeutic approach for prostate cancer and highlight complexities in Dkk-3 regulation of TGF-β signaling
The optical depth of the Universe to ultrahigh energy cosmic ray scattering in the magnetized large scale structure
This paper provides an analytical description of the transport of ultrahigh
energy cosmic rays in an inhomogeneously magnetized intergalactic medium. This
latter is modeled as a collection of magnetized scattering centers such as
radio cocoons, magnetized galactic winds, clusters or magnetized filaments of
large scale structure, with negligible magnetic fields in between. Magnetic
deflection is no longer a continuous process, it is rather dominated by
scattering events. We study the interaction between high energy cosmic rays and
the scattering agents. We then compute the optical depth of the Universe to
cosmic ray scattering and discuss the phenomological consequences for various
source scenarios. For typical parameters of the scattering centers, the optical
depth is greater than unity at 5x10^{19}eV, but the total angular deflection is
smaller than unity. One important consequence of this scenario is the
possibility that the last scattering center encountered by a cosmic ray be
mistaken with the source of this cosmic ray. In particular, we suggest that
part of the correlation recently reported by the Pierre Auger Observatory may
be affected by such delusion: this experiment may be observing in part the last
scattering surface of ultrahigh energy cosmic rays rather than their source
population. Since the optical depth falls rapidly with increasing energy, one
should probe the arrival directions of the highest energy events beyond
10^{20}eV on an event by event basis to circumvent this effect.Comment: version to appear in PRD; substantial improvements: extended
introduction, sections added on angular images and on direction dependent
effects with sky maps of optical depth, enlarged discussion of Auger results
(conclusions unchanged); 27 pages, 9 figure
Maximum Likelihood Analysis of Clusters of Ultra-High Energy Cosmic Rays
We present a numerical code designed to conduct a likelihood analysis for
clusters of nucleons above 10**19 eV originating from discrete astrophysical
sources such as powerful radio galaxies, gamma-ray bursts or topological
defects. The code simulates the propagation of nucleons in a large-scale
magnetic field and constructs the likelihood of a given observed event cluster
as a function of the average time delay due to deflection in the magnetic
field, the source activity time scale, the total fluence of the source, and the
power law index of the particle injection spectrum. Other parameters such as
the coherence length and the power spectrum of the magnetic field are also
considered. We apply it to the three pairs of events above 4X10**19 eV recently
reported by the Akeno Giant Air Shower Array (AGASA) experiment, assuming that
these pairs were caused by nucleon primaries which originated from a common
source. Although current data are too sparse to fully constrain each of the
parameters considered, and/or to discriminate models of the origin of
ultra-high energy cosmic rays, several tendencies are indicated. If the
clustering suggested by AGASA is real, next generation experiments with their
increased exposure should detect more than 10 particles per source over a few
years and our method will put strong constraints on both the large-scale
magnetic field parameters and the nature of these sources.Comment: 11 latex pages, 8 postscript figures included, uses revtex.sty in
two-column format and epsf.sty. Submitted to Physical Review
High Energy Neutrino Signals of Four Neutrino Mixing
We evaluate the upward shower and muon event rates for two characteristic
four neutrino mixing models for extragalactic neutrinos, as well as for the
atmospheric neutrinos, with energy thresholds of 1 TeV, 10 TeV and 100 TeV. We
show that by comparing the shower to muon event rates, one can distinguish
between oscillation and no-oscillation models. By measuring shower and muon
event rates for energy thresholds of 10 TeV and 100 TeV, and by considering
their ratio, it is possible to use extragalactic neutrino sources to determine
the type of four-flavor mixing pattern. We find that one to ten years of data
taking with kilometer-size detector has a very good chance of providing
valuable information about the physics beyond the Standard Model.Comment: version accepted for publication in Phys. Rev.
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