37 research outputs found
Negative magnetic eddy diffusivities from test-field method and multiscale stability theory
The generation of large-scale magnetic field in the kinematic regime in the
absence of an alpha-effect is investigated by following two different
approaches, namely the test-field method and multiscale stability theory
relying on the homogenisation technique. We show analytically that the former,
applied for the evaluation of magnetic eddy diffusivities, yields results that
fully agree with the latter. Our computations of the magnetic eddy diffusivity
tensor for the specific instances of the parity-invariant flow-IV of G.O.
Roberts and the modified Taylor-Green flow in a suitable range of parameter
values confirm the findings of previous studies, and also explain some of their
apparent contradictions. The two flows have large symmetry groups; this is used
to considerably simplify the eddy diffusivity tensor. Finally, a new analytic
result is presented: upon expressing the eddy diffusivity tensor in terms of
solutions to auxiliary problems for the adjoint operator, we derive relations
between magnetic eddy diffusivity tensors that arise for opposite small-scale
flows v(x) and -v(x).Comment: 29 pp., 19 figures, 42 reference
Fluorescent silica manoparticles with well-separated intensity distributions from batch reactions
Silica chemistry provides pathways to uniquely tunable nanoparticle platforms for biological imaging. It has been a long-standing problem to synthesize fluorescent silica nanoparticles (SNPs) in batch reactions with high and low fluorescence intensity levels for reliable use as an intensity barcode, which would greatly increase the number of molecular species that could be tagged intracellularly and simultaneously observed in conventional fluorescence microscopy. Here, employing an amino-acid catalyzed growth, highly fluorescent SNP probes were synthesized with sizes <40 nm and well-separated intensity distributions, as mapped by single-particle imaging techniques. A seeded growth approach was used to minimize the rate of secondary particle formation. Organic fluorescent dye affinity for the SNP during shell growth was tuned using specifics of the organosilane linker chemistry. This work highlights design considerations in the development of fluorescent probes with well-separated intensity distributions synthesized in batch reactions for single-particle imaging and sensing applications, where heterogeneities across the nanoparticle ensemble are critical factors in probe performance
Fluorescent silica manoparticles with well-separated intensity distributions from batch reactions
Silica chemistry provides pathways to uniquely tunable nanoparticle platforms for biological imaging. It has been a long-standing problem to synthesize fluorescent silica nanoparticles (SNPs) in batch reactions with high and low fluorescence intensity levels for reliable use as an intensity barcode, which would greatly increase the number of molecular species that could be tagged intracellularly and simultaneously observed in conventional fluorescence microscopy. Here, employing an amino-acid catalyzed growth, highly fluorescent SNP probes were synthesized with sizes <40 nm and well-separated intensity distributions, as mapped by single-particle imaging techniques. A seeded growth approach was used to minimize the rate of secondary particle formation. Organic fluorescent dye affinity for the SNP during shell growth was tuned using specifics of the organosilane linker chemistry. This work highlights design considerations in the development of fluorescent probes with well-separated intensity distributions synthesized in batch reactions for single-particle imaging and sensing applications, where heterogeneities across the nanoparticle ensemble are critical factors in probe performance
Controlled Synchronization of One Class of Nonlinear Systems under Information Constraints
Output feedback controlled synchronization problems for a class of nonlinear
unstable systems under information constraints imposed by limited capacity of
the communication channel are analyzed. A binary time-varying coder-decoder
scheme is described and a theoretical analysis for multi-dimensional
master-slave systems represented in Lurie form (linear part plus nonlinearity
depending only on measurable outputs) is provided. An output feedback control
law is proposed based on the Passification Theorem. It is shown that the
synchronization error exponentially tends to zero for sufficiantly high
transmission rate (channel capacity). The results obtained for synchronization
problem can be extended to tracking problems in a straightforward manner, if
the reference signal is described by an {external} ({exogenious}) state space
model. The results are applied to controlled synchronization of two chaotic
Chua systems via a communication channel with limited capacity.Comment: 8 pages, 2 figure
Chaotic Observer-based Synchronization Under Information Constraints
Limit possibilities of observer-based synchronization systems under
information constraints (limited information capacity of the coupling channel)
are evaluated. We give theoretical analysis for multi-dimensional
drive-response systems represented in the Lurie form (linear part plus
nonlinearity depending only on measurable outputs). It is shown that the upper
bound of the limit synchronization error (LSE) is proportional to the upper
bound of the transmission error. As a consequence, the upper and lower bounds
of LSE are proportional to the maximum rate of the coupling signal and
inversely proportional to the information transmission rate (channel capacity).
Optimality of the binary coding for coders with one-step memory is established.
The results are applied to synchronization of two chaotic Chua systems coupled
via a channel with limited capacity.Comment: 7 pages, 6 figures, 27 reference
Controlled Synchronization Under Information Constraints
The class of controlled synchronization systems under information constraints
imposed by limited information capacity of the coupling channel is analyzed. It
is shown that the framework proposed in A. L. Fradkov, B. Andrievsky, R. J.
Evans, Physical Review E 73, 066209 (2006) is suitable not only for
observer-based synchronization but also for controlled master-slave
synchronization via communication channel with limited information capacity. A
simple first order coder-decoder scheme is proposed and a theoretical analysis
for multi-dimensional master-slave systems represented in the Lurie form
(linear part plus nonlinearity depending only on measurable outputs) is
provided. An output feedback control law is proposed based on the Passification
theorem. It is shown that the upper bound of the limit synchronization error is
proportional to the upper bound of the transmission error. As a consequence,
both upper and lower bounds of limit synchronization error are proportional to
the maximum rate of the coupling signal and inversely proportional to the
information transmission rate (channel capacity). The results are applied to
controlled synchronization of two chaotic Chua systems coupled via a controller
and a channel with limited capacity.Comment: 7 pages, 8 figure
The Chemical Composition of HD47536: A Planetary Host Halo Giant with Possible 位 Bootis Features and Signs of Interstellar Matter Accretion
We investigated the chemical composition of the planetary host halo star HD47536 via high-resolution spectral observations
recorded using a 1.5 meter Cerro Tololo Inter-American Observatory (CTIO) telescope (Chile). Furthermore, we determined
the abundances of 38 chemical elements. Both light and heavy elements were overabundant compared to the iron group
elements. The abundance pattern of HD47536 was similar to that of halo-type stars, with an enrichment of heavy elements.
We analyzed the relationships between the relative abundances of chemical elements and their second ionization potentials
and condensation temperatures. We demonstrated that the interplay of charge-exchange reactions owing to the accretion
of interstellar matter and the gas-dust separation mechanism can influence the initial abundances and can be used to
qualitatively explain the abundance patterns in the atmosphere of HD47536