1,021 research outputs found
Curvature Fields, Topology, and the Dynamics of Spatiotemporal Chaos
The curvature field is measured from tracer particle trajectories in a
two-dimensional fluid flow that exhibits spatiotemporal chaos, and is used to
extract the hyperbolic and elliptic points of the flow. These special points
are pinned to the forcing when the driving is weak, but wander over the domain
and interact in pairs at stronger driving, changing the local topology of the
flow. Their behavior reveals a two-stage transition to spatiotemporal chaos: a
gradual loss of spatial and temporal order followed by an abrupt onset of
topological changes.Comment: 5 pages, 5 figure
Superconducting Diamagnetic Fluctuations in MgB2
The fluctuating diamagnetic magnetization Mfl at constant field H as a
function of temperature and the isothermal magnetization Mfl vs H are measured
in MgB2, above the superconducting transition temperature. The expressions for
Mfl in randomly oriented powders are derived in the Gaussian approximation of
local Ginzburg-Landau theory and used for the analysis of the data. The scaled
magnetization Mfl/H^{1/2}*T is found to be field dependent. In the limit of
evanescent field the behaviour for Gaussian fluctuations is obeyed while for
H>~ 100 Oe the field tends to suppress the fluctuating pairs, with a field
dependence of Mfl close to the one expected when short wavelength fluctuations
and non-local electrodynamic effects are taken into account. Our data, besides
providing the isothermal magnetization curves for T>Tc(0) in a BCS-type
superconductor such as MgB2, evidence an enhancement of the fluctuating
diamagnetism which is related to the occurrence in this new superconductor of
an anisotropic spectrum of the superconducting fluctuations.Comment: Tex file, 4 pages, 3 ps figures, submitted to Phys. Rev. Let
Dynamic Topology in Spatiotemporal Chaos
By measuring the tracks of tracer particles in a quasi-two-dimensional spatiotemporally chaotic laboratory flow, we determine the instantaneous curvature along each trajectory and use it to construct the instantaneous curvature field. We show that this field can be used to extract the time-dependent hyperbolic and elliptic points of the flow. These important topological features are created and annihilated in pairs only above a critical Reynolds number that is largest for highly symmetric flows. We also study the statistics of curvature for different driving patterns and show that the curvature probability distribution is insensitive to the details of the flow
Temporal Modulation of the Control Parameter in Electroconvection in the Nematic Liquid Crystal I52
I report on the effects of a periodic modulation of the control parameter on
electroconvection in the nematic liquid crystal I52. Without modulation, the
primary bifurcation from the uniform state is a direct transition to a state of
spatiotemporal chaos. This state is the result of the interaction of four,
degenerate traveling modes: right and left zig and zag rolls. Periodic
modulations of the driving voltage at approximately twice the traveling
frequency are used. For a large enough modulation amplitude, standing waves
that consist of only zig or zag rolls are stabilized. The standing waves
exhibit regular behavior in space and time. Therefore, modulation of the
control parameter represents a method of eliminating spatiotemporal chaos. As
the modulation frequency is varied away from twice the traveling frequency,
standing waves that are a superposition of zig and zag rolls, i.e. standing
rectangles, are observed. These results are compared with existing predictions
based on coupled complex Ginzburg-Landau equations
Discovery potential for a charged Higgs boson decaying in the chargino-neutralino channel of the ATLAS detector at the LHC
We have investigated charged Higgs boson production via the gluon-bottom
quark mode, gb -> tH+, followed by its decay into a chargino and a neutralino.
The calculations are based on masses and couplings given by the Minimal
Supersymmetric Standard Model (MSSM) for a specific choice of MSSM parameters.
The signature of the signal is characterized by three hard leptons, a
substantial missing transverse energy due to the decay of the neutralino and
the chargino and three hard jets from the hadronic decay of the top quark. The
possibility of detecting the signal over the Standard Model (SM) and non-SM
backgrounds was studied for a set of tanBeta and mA. The existence of 5-sigma
confidence level regions for H+ discovery at integrated luminosities of 100
fb-1 and 300 fb-1 is demonstrated, which cover also the intermediate region 4 <
tanBeta < 10 where H+ decays to SM particles cannot be used for H+ discovery
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