10,535 research outputs found
Pyrotechnic device provides one-shot heat source
Pyrotechnic heater provides a one-shot heat source capable of creating a predetermined temperature around sealed packages. It is composed of a blend of an active chemical element and another compound which reacts exothermically when ignited and produces fixed quantities of heat
Efficacy and Residue Comparisons between Two Slow-release Formulations of Fluridone
Residue profiles and efficacy of Avast and Sonar, two slow
release pellet formulations of fluridone {1-methyl-3-phenyl-5-
[3-(trifluoromethyl)phenly]-4(1H)-pyridinone}, were compared
in outdoor tanks. Hydrilla (Hydrilla verticillata (L.f.)
Royle) and southern naiad (Najas guadalupensis (Sprengel)
Magnus) were treated with a split application of 6, 12, 18 and
24 μg/l a.i. fluridone and the concentrations of both formulations
compared over a 134-day period. Both pellet formulations
exhibited very similar residues over time for each
respective treatment, resulted in peak concentrations of fluridone
40 to 50 days after application, and effectively and
similarly controlled southern naiad and hydrilla at all rates
tested by 92 days after initial application. (PDF contains 3 pages.
A case study of random field models applied to thin-walled composite cylinders in finite element analysis
Reduced-order Description of Transient Instabilities and Computation of Finite-Time Lyapunov Exponents
High-dimensional chaotic dynamical systems can exhibit strongly transient
features. These are often associated with instabilities that have finite-time
duration. Because of the finite-time character of these transient events, their
detection through infinite-time methods, e.g. long term averages, Lyapunov
exponents or information about the statistical steady-state, is not possible.
Here we utilize a recently developed framework, the Optimally Time-Dependent
(OTD) modes, to extract a time-dependent subspace that spans the modes
associated with transient features associated with finite-time instabilities.
As the main result, we prove that the OTD modes, under appropriate conditions,
converge exponentially fast to the eigendirections of the Cauchy--Green tensor
associated with the most intense finite-time instabilities. Based on this
observation, we develop a reduced-order method for the computation of
finite-time Lyapunov exponents (FTLE) and vectors. In high-dimensional systems,
the computational cost of the reduced-order method is orders of magnitude lower
than the full FTLE computation. We demonstrate the validity of the theoretical
findings on two numerical examples
Precision Measurements of Stretching and Compression in Fluid Mixing
The mixing of an impurity into a flowing fluid is an important process in
many areas of science, including geophysical processes, chemical reactors, and
microfluidic devices. In some cases, for example periodic flows, the concepts
of nonlinear dynamics provide a deep theoretical basis for understanding
mixing. Unfortunately, the building blocks of this theory, i.e. the fixed
points and invariant manifolds of the associated Poincare map, have remained
inaccessible to direct experimental study, thus limiting the insight that could
be obtained. Using precision measurements of tracer particle trajectories in a
two-dimensional fluid flow producing chaotic mixing, we directly measure the
time-dependent stretching and compression fields. These quantities, previously
available only numerically, attain local maxima along lines coinciding with the
stable and unstable manifolds, thus revealing the dynamical structures that
control mixing. Contours or level sets of a passive impurity field are found to
be aligned parallel to the lines of large compression (unstable manifolds) at
each instant. This connection appears to persist as the onset of turbulence is
approached.Comment: 5 pages, 5 figure
Excitonic Aharonov-Bohm Effect in Isotopically Pure 70Ge/Si Type-II Quantum Dots
We report on a magneto-photoluminescence study of isotopically pure 70Ge/Si
self-assembled type-II quantum dots. Oscillatory behaviors attributed to the
Aharonov-Bohm effect are simultaneously observed for the emission energy and
intensity of excitons subject to an increasing magnetic field. When the
magnetic flux penetrates through the ring-like trajectory of an electron moving
around each quantum dot, the ground state of an exciton experiences a change in
its angular momentum. Our results provide the experimental evidence for the
phase coherence of a localized electron wave function in group-IV Ge/Si
self-assembled quantum structures.Comment: 4 pages, 4 figure
Spin Susceptibility of Noncentrosymmetric Heavy-fermion Superconductor CeIrSi3 under Pressure: 29Si-Knight Shift Study on Single Crystal
We report 29Si-NMR study on a single crystal of the heavy-fermion
superconductor CeIrSi3 without an inversion symmetry along the c-axis. The
29Si-Knight shift measurements under pressure have revealed that the spin
susceptibility for the ab-plane decreases slightly below Tc, whereas along the
c-axis it does not change at all. The result can be accounted for by the spin
susceptibility in the superconducting state being dominated by the strong
antisymmetric (Rashba-type) spin-orbit interaction that originates from the
absence of an inversion center along the c-axis and it being much larger than
superconducting condensation energy. This is the first observation which
exhibits an anisotropy of the spin susceptibility below Tc in the
noncentrosymmetric superconductor dominated by strong Rashba-type spin-orbit
interaction.Comment: 4 pages, 4 figures, Accepted for publication in Phys. Rev. Let
Parabolic resonances and instabilities in near-integrable two degrees of freedom Hamiltonian flows
When an integrable two-degrees-of-freedom Hamiltonian system possessing a
circle of parabolic fixed points is perturbed, a parabolic resonance occurs. It
is proved that its occurrence is generic for one parameter families
(co-dimension one phenomenon) of near-integrable, t.d.o. systems. Numerical
experiments indicate that the motion near a parabolic resonance exhibits new
type of chaotic behavior which includes instabilities in some directions and
long trapping times in others. Moreover, in a degenerate case, near a {\it flat
parabolic resonance}, large scale instabilities appear. A model arising from an
atmospherical study is shown to exhibit flat parabolic resonance. This supplies
a simple mechanism for the transport of particles with {\it small} (i.e.
atmospherically relevant) initial velocities from the vicinity of the equator
to high latitudes. A modification of the model which allows the development of
atmospherical jets unfolds the degeneracy, yet traces of the flat instabilities
are clearly observed
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