4,422 research outputs found
Subcellular optogenetic activation of Cdc42 controls local and distal signaling to drive immune cell migration
Migratory immune cells use intracellular signaling networks to generate and orient spatially polarized responses to extracellular cues. The monomeric G protein Cdc42 is believed to play an important role in controlling the polarized responses, but it has been difficult to determine directly the consequences of localized Cdc42 activation within an immune cell. Here we used subcellular optogenetics to determine how Cdc42 activation at one side of a cell affects both cell behavior and dynamic molecular responses throughout the cell. We found that localized Cdc42 activation is sufficient to generate polarized signaling and directional cell migration. The optically activated region becomes the leading edge of the cell, with Cdc42 activating Rac and generating membrane protrusions driven by the actin cytoskeleton. Cdc42 also exerts long-range effects that cause myosin accumulation at the opposite side of the cell and actomyosin-mediated retraction of the cell rear. This process requires the RhoA-activated kinase ROCK, suggesting that Cdc42 activation at one side of a cell triggers increased RhoA signaling at the opposite side. Our results demonstrate how dynamic, subcellular perturbation of an individual signaling protein can help to determine its role in controlling polarized cellular responses
A Conformational Switch Regulates Receptor-G Protein Interaction
AbstractA peptide specific to a G protein γ subunit C terminus undergoes a conformational shift concordant with receptor activation, providing direct support for a long-standing proposal that a conformational switch in the γ subunit tail mediates G protein activation by a receptor
Neutrinos from Stellar Collapse: Comparison of signatures in water and heavy water detectors
Signatures of neutrino and antineutrino signals from stellar collapse in
heavy water detectors are contrasted with those in water detectors. The effects
of mixing, especially due to the highly dense matter in the supernova core, are
studied. The mixing parameters used are those sets allowed by current
understanding of available neutrino data: from solar, atmospheric and
laboratory neutrino experiments. Signals at a heavy water detector, especially
the dominant charged current reactions on deuteron, are very sensitive to some
of these sets of allowed mixing parameters. Theoretical uncertainties on
supernova neutrino spectra notwithstanding, a combination of supernova
measurements with water and heavy water detectors may be able to distinguish
many of these mixing possibilities and thus help in ruling out many of them.Comment: 36 pages Latex file, with 13 postscript figures; important
improvements in the analysis and more detailed presentation of results. To
appear in Phys. Rev.
Scalar sector properties of two-Higgs-doublet models with a global U(1) symmetry
We analyze the scalar sector properties of a general class of
two-Higgs-doublet models which has a global U(1) symmetry in the quartic terms.
We find constraints on the parameters of the potential from the considerations
of unitarity of scattering amplitudes, the global stability of the potential
and the -parameter. We concentrate on the spectrum of the non-standard
scalar masses in the decoupling limit which is preferred by the Higgs data at
the LHC. We exhibit charged-Higgs induced contributions to the diphoton decay
width of the 125\,GeV Higgs boson and its correlation with the corresponding
width.Comment: 12 pages, 15 eps figure files; minor modifications made and a few
references adde
Optical waveguide arrays: quantum effects and PT symmetry breaking
Over the last two decades, advances in fabrication have led to significant
progress in creating patterned heterostructures that support either carriers,
such as electrons or holes, with specific band structure or electromagnetic
waves with a given mode structure and dispersion. In this article, we review
the properties of light in coupled optical waveguides that support specific
energy spectra, with or without the effects of disorder, that are
well-described by a Hermitian tight-binding model. We show that with a
judicious choice of the initial wave packet, this system displays the
characteristics of a quantum particle, including transverse photonic transport
and localization, and that of a classical particle. We extend the analysis to
non-Hermitian, parity and time-reversal () symmetric Hamiltonians
which physically represent waveguide arrays with spatially separated, balanced
absorption or amplification. We show that coupled waveguides are an ideal
candidate to simulate -symmetric Hamiltonians and the transition
from a purely real energy spectrum to a spectrum with complex conjugate
eigenvalues that occurs in them.Comment: 16 pages, 12 figures, Invited Review for European Physics Journal -
Applied Physic
Tunable waveguide lattices with non-uniform parity-symmetric tunneling
We investigate the single-particle time evolution and two-particle quantum
correlations in a one-dimensional -site lattice with a site-dependent
nearest neighbor tunneling function . Since
the bandwidth and the energy levels spacings for such a lattice both depend
upon , we show that the observable properties of a wavepacket, such as
its spread and the relative phases of its constitutents, vary dramatically as
is varied from positive to negative values. We also find that the
quantum correlations are exquisitely sensitive to the form of the tunneling
function. Our results suggest that arrays of waveguides with position-dependent
evanascent couplings will show rich dynamics with no counterpart in
present-day, traditional systems.Comment: 5 pages, 4 figure
Exact Persistence Exponent for One-dimensional Potts Models with Parallel Dynamics
We obtain \theta_p(q) = 2\theta_s(q) for one-dimensional q-state
ferromagnetic Potts models evolving under parallel dynamics at zero temperature
from an initially disordered state, where \theta_p(q) is the persistence
exponent for parallel dynamics and \theta_s(q) = -{1/8}+
\frac{2}{\pi^2}[cos^{-1}{(2-q)/q\sqrt{2}}]^2 [PRL, {\bf 75}, 751, (1995)], the
persistence exponent under serial dynamics. This result is a consequence of an
exact, albeit non-trivial, mapping of the evolution of configurations of Potts
spins under parallel dynamics to the dynamics of two decoupled reaction
diffusion systems.Comment: 13 pages Latex file, 5 postscript figure
The logic and linguistic model for automatic extraction of collocation similarity
The article discusses the process of automatic identification of collocation similarity. The semantic analysis is one of the most advanced as well as the most difficult NLP task. The main problem of semantic processing is the determination of polysemy and synonymy of linguistic units. In addition, the task becomes complicated in case of word collocations. The paper suggests a logical and linguistic model for automatic determining semantic similarity between colocations in Ukraine and English languages. The proposed model formalizes semantic equivalence of collocations by means of semantic and grammatical characteristics of collocates. The basic idea of this approach is that morphological, syntactic and semantic characteristics of lexical units are to be taken into account for the identification of collocation similarity. Basic mathematical means of our model are logical-algebraic equations of the finite predicates algebra. Verb-noun and noun-adjective collocations in Ukrainian and English languages consist of words belonged to main parts of speech. These collocations are examined in the model. The model allows extracting semantically equivalent collocations from semi-structured and non-structured texts. Implementations of the model will allow to automatically recognize semantically equivalent collocations. Usage of the model allows increasing the effectiveness of natural language processing tasks such as information extraction, ontology generation, sentiment analysis and some others
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