1,148 research outputs found
Trapped modes in finite quantum waveguides
The Laplace operator in infinite quantum waveguides (e.g., a bent strip or a
twisted tube) often has a point-like eigenvalue below the essential spectrum
that corresponds to a trapped eigenmode of finite L2 norm. We revisit this
statement for resonators with long but finite branches that we call "finite
waveguides". Although now there is no essential spectrum and all eigenfunctions
have finite L2 norm, the trapping can be understood as an exponential decay of
the eigenfunction inside the branches. We describe a general variational
formalism for detecting trapped modes in such resonators. For finite waveguides
with general cylindrical branches, we obtain a sufficient condition which
determines the minimal length of branches for getting a trapped eigenmode.
Varying the branch lengths may switch certain eigenmodes from non-trapped to
trapped states. These concepts are illustrated for several typical waveguides
(L-shape, bent strip, crossing of two stripes, etc.). We conclude that the
well-established theory of trapping in infinite waveguides may be incomplete
and require further development for being applied to microscopic quantum
devices
1-D Convolutional Graph Convolutional Networks for Fault Detection in Distributed Energy Systems
This paper presents a 1-D convolutional graph neural network for fault
detection in microgrids. The combination of 1-D convolutional neural networks
(1D-CNN) and graph convolutional networks (GCN) helps extract both
spatial-temporal correlations from the voltage measurements in microgrids. The
fault detection scheme includes fault event detection, fault type and phase
classification, and fault location. There are five neural network model
training to handle these tasks. Transfer learning and fine-tuning are applied
to reduce training efforts. The combined recurrent graph convolutional neural
networks (1D-CGCN) is compared with the traditional ANN structure on the
Potsdam 13-bus microgrid dataset. The achievable accuracy of 99.27%, 98.1%,
98.75%, and 95.6% for fault detection, fault type classification, fault phase
identification, and fault location respectively.Comment: arXiv admin note: text overlap with arXiv:2210.1517
Direct measurements of DOCO isomers in the kinetics of OD+CO
Quantitative and mechanistically-detailed kinetics of the reaction of
hydroxyl radical (OH) with carbon monoxide (CO) have been a longstanding goal
of contemporary chemical kinetics. This fundamental prototype reaction plays an
important role in atmospheric and combustion chemistry, motivating studies for
accurate determination of the reaction rate coefficient and its pressure and
temperature dependence at thermal reaction conditions. This intricate
dependence can be traced directly to details of the underlying dynamics
(formation, isomerization, and dissociation) involving the reactive
intermediates cis- and trans-HOCO, which can only be observed transiently.
Using time-resolved frequency comb spectroscopy, comprehensive mechanistic
elucidation of the kinetics of the isotopic analogue deuteroxyl radical (OD)
with CO has been realized. By monitoring the concentrations of reactants,
intermediates, and products in real-time, the branching and isomerization
kinetics and absolute yields of all species in the OD+CO reaction are
quantified as a function of pressure and collision partner.Comment: 19 pages, 4 figure
When can we reconstruct the ancestral state? Beyond Brownian motion
Reconstructing the ancestral state of a group of species helps answer many
important questions in evolutionary biology. Therefore, it is crucial to
understand when we can estimate the ancestral state accurately. Previous works
provide a necessary and sufficient condition, called the big bang condition,
for the existence of an accurate reconstruction method under discrete trait
evolution models and the Brownian motion model. In this paper, we extend this
result to a wide range of continuous trait evolution models. In particular, we
consider a general setting where continuous traits evolve along the tree
according to stochastic processes that satisfy some regularity conditions. We
verify these conditions for popular continuous trait evolution models including
Ornstein-Uhlenbeck, reflected Brownian Motion, and Cox-Ingersoll-Ross
Detection of lithium in nearby young late-M dwarfs
Late M-type dwarfs in the solar neighborhood include a mixture of very
low-mass stars and brown dwarfs which is difficult to disentangle due to the
lack of constraints on their age such as trigonometric parallax, lithium
detection and space velocity.
We search for young brown dwarf candidates among a sample of 28 nearby late-M
dwarfs with spectral types between M5.0 and M9.0, and we also search for debris
disks around three of them.
Based on theoretical models, we used the color , the -band absolute
magnitude and the detection of the Li I 6708 doublet line as a strong
constraint to estimate masses and ages of our targets. For the search of debris
disks, we observed three targets at submillimeter wavelength of 850 m.
We report here the first clear detections of lithium absorption in four
targets and a marginal detection in one target. Our mass estimates indicate
that two of them are young brown dwarfs, two are young brown dwarf candidates
and one is a young very low-mass star. The closest young field brown dwarf in
our sample at only 15 pc is an excellent benchmark for further studying
physical properties of brown dwarfs in the range 100150 Myr. We did not
detect any debris disks around three late-M dwarfs, and we estimated upper
limits to the dust mass of debris disks around them.Comment: 10 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Maize in Vietnam: Production Systems, Constraints, and Research Priorities
Crop Production/Industries,
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