3,283 research outputs found
Effect of electron irradiation on superconductivity in single crystals of Ba(FeRu)As (0.24)
A single crystal of isovalently substituted Ba(FeRu)As
() was sequentially irradiated with 2.5 MeV electrons up to a maximum
dose of electrons/cm^2. The electrical resistivity was
measured \textit{in - situ} at 22 K during the irradiation and \textit{ex -
situ} as a function of temperature between subsequent irradiation runs. Upon
irradiation, the superconducting transition temperature, , decreases and
the residual resistivity, , increases. We find that electron
irradiation leads to the fastest suppression of compared to other types
of artificially introduced disorder, probably due to the strong short-range
potential of the point-like irradiation defects. A more detailed analysis
within a multiband scenario with variable scattering potential strength shows
that the observed vs. is fully compatible with pairing,
in contrast to earlier claims that this model leads to a too rapid a
suppression of with scattering
Quantification of Cell Movement Reveals Distinct Edge Motility Types During Cell Spreading
Actin-based motility is central to cellular processes such as migration, bacterial engulfment, and cancer metastasis, and requires precise spatial and temporal regulation of the cytoskeleton. We studied one such process, fibroblast spreading, which involves three temporal phases: early, middle, and late spreading, distinguished by differences in cell area growth. In these studies, aided by improved algorithms for analyzing edge movement, we observed that each phase was dominated by a single, kinematically and biochemically distinct cytoskeletal organization, or motility type. Specifically, early spreading was dominated by periodic blebbing; continuous protrusion occurred predominantly during middle spreading; and periodic contractions were prevalent in late spreading. Further characterization revealed that each motility type exhibited a distinct distribution of the actin-related protein VASP, while inhibition of actin polymerization by cytochalasin D treatment revealed different dependences on barbed-end polymerization. Through this detailed characterization and graded perturbation of the system, we observed that although each temporal phase of spreading was dominated by a single motility type, in general cells exhibited a variety of motility types in neighboring spatial domains of the plasma membrane edge. These observations support a model in which global signals bias local cytoskeletal biochemistry in favor of a particular motility type
Separation of trajectories and its Relation to Entropy for Intermittent Systems with a Zero Lyapunov exponent
One dimensional intermittent maps with stretched exponential separation of
nearby trajectories are considered. When time goes infinity the standard
Lyapunov exponent is zero. We investigate the distribution of
,
where is determined by the nonlinearity of the map in the vicinity of
marginally unstable fixed points. The mean of is determined
by the infinite invariant density. Using semi analytical arguments we calculate
the infinite invariant density for the Pomeau-Manneville map, and with it
obtain excellent agreement between numerical simulation and theory. We show
that \alpha \left is equal to Krengel's entropy and
to the complexity calculated by the Lempel-Ziv compression algorithm. This
generalized Pesin's identity shows that \left and
Krengel's entropy are the natural generalizations of usual Lyapunov exponent
and entropy for these systems.Comment: 12 pages, 10 figure
Stochastic stability at the boundary of expanding maps
We consider endomorphisms of a compact manifold which are expanding except
for a finite number of points and prove the existence and uniqueness of a
physical measure and its stochastical stability. We also characterize the
zero-noise limit measures for a model of the intermittent map and obtain
stochastic stability for some values of the parameter. The physical measures
are obtained as zero-noise limits which are shown to satisfy Pesin?s Entropy
Formula
Pesin-type relation for subexponential instability
We address here the problem of extending the Pesin relation among positive
Lyapunov exponents and the Kolmogorov-Sinai entropy to the case of dynamical
systems exhibiting subexponential instabilities. By using a recent rigorous
result due to Zweim\"uller, we show that the usual Pesin relation can be
extended straightforwardly for weakly chaotic one-dimensional systems of the
Pomeau-Manneville type, provided one introduces a convenient subexponential
generalization of the Kolmogorov-Sinai entropy. We show, furthermore, that
Zweim\"uller's result provides an efficient prescription for the evaluation of
the algorithm complexity for such systems. Our results are confirmed by
exhaustive numerical simulations. We also point out and correct a misleading
extension of the Pesin relation based on the Krengel entropy that has appeared
recently in the literature.Comment: 10 pages, 4 figures. Final version to appear in Journal of
Statistical Mechanics (JSTAT
Effect of Electron Irradiation on Superconductivity in Single Crystals of Ba(Fe1−xRux)2As2 (x=0.24)
A single crystal of isovalently substituted Ba(Fe1−xRux)2As2 (x=0.24) is sequentially irradiated with 2.5 MeV electrons up to a maximum dose of 2.1×1019 e−/cm2. The electrical resistivity is measuredin situ at T=22 K during the irradiation and ex situ as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature Tc decreases and the residual resistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of Tccompared to other types of artificially introduced disorder, probably due to the strong short-range potential of the pointlike irradiation defects. A more detailed analysis within a multiband scenario with variable scattering potential strength shows that the observed Tc versus ρ0 is fully compatible with s±pairing, in contrast to earlier claims that this model leads to a too rapid suppression of Tc with scattering
Constraints on new interactions from neutron scattering experiments
Constraints for the constants of hypothetical Yukawa-type corrections to the
Newtonian gravitational potential are obtained from analysis of neutron
scattering experiments. Restrictions are obtained for the interaction range
between 10^{-12} and 10^{-7} cm, where Casimir force experiments and atomic
force microscopy are not sensitive. Experimental limits are obtained also for
non-electromagnetic inverse power law neutron-nucleus potential. Some
possibilities are discussed to strengthen these constraints.Comment: 18 pages, 3 figure
Diboson-Jets and the Search for Resonant Zh Production
New particles at the TeV-scale may have sizeable decay rates into boosted
Higgs bosons or other heavy scalars. Here, we investigate the possibility of
identifying such processes when the Higgs/scalar subsequently decays into a
pair of W bosons, constituting a highly distinctive "diboson-jet." These can
appear as a simple dilepton (plus MET) configuration, as a two-prong jet with
an embedded lepton, or as a four-prong jet. We study jet substructure methods
to discriminate these objects from their dominant backgrounds. We then
demonstrate the use of these techniques in the search for a heavy spin-one Z'
boson, such as may arise from strong dynamics or an extended gauge sector,
utilizing the decay chain Z' -> Zh -> Z(WW^(*)). We find that modes with
multiple boosted hadronic Zs and Ws tend to offer the best prospects for the
highest accessible masses. For 100/fb luminosity at the 14 TeV LHC, Z' decays
into a standard 125 GeV Higgs can be observed with 5-sigma significance for
masses of 1.5-2.5 TeV for a range of models. For a 200 GeV Higgs (requiring
nonstandard couplings, such as fermiophobic), the reach may improve to up to
2.5-3.0 TeV.Comment: 23 pages plus appendices, 9 figure
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