401 research outputs found
Paper Session III-A - Electrolytic Oxygen Enrichment Using Supernoxide Ion in a Solid Polymer Membrane Electrolyte
Electrochemical cells are among the technologies under consideration for gaseous oxygen concentration or enrichment in both aerospace and civilian applications. Current electrochemical technology involves the electro-reduction of molecular oxygen, O2, to water at one electrode, and the electro-oxidation of water to oxygen at the other. In terms of the overall chemical mechanism, this is a 4-electron, 4-proton process.
From an economic point of view, one would like to use as little energy as possible to effect oxygen transport. The simplest possible mechanistic scenario would be if the O-, reduction product is the superoxide ion, O2~, involving only a single electron exchange: O2 + e = O 2
Superoxide anion can be produced electrochemically via reduction of O 2 in an organic aprotic solvent, such as dimethyl formamide or acetonitrile. Moreover, production of superoxide via electrolysis is electrochemically reversible (i.e., the forward and reverse reaction is so rapid that it proceeds under diffusion control near the thermodynamic potential). Considerable energy savings may be realized if electrochemical O, transport could be performed using superoxide ion
Learning the Tangent Space of Dynamical Instabilities from Data
For a large class of dynamical systems, the optimally time-dependent (OTD)
modes, a set of deformable orthonormal tangent vectors that track directions of
instabilities along any trajectory, are known to depend "pointwise" on the
state of the system on the attractor, and not on the history of the trajectory.
We leverage the power of neural networks to learn this "pointwise" mapping from
phase space to OTD space directly from data. The result of the learning process
is a cartography of directions associated with strongest instabilities in phase
space. Implications for data-driven prediction and control of dynamical
instabilities are discussed
Optimal neural network feature selection for spatial-temporal forecasting
In this paper, we show empirical evidence on how to construct the optimal
feature selection or input representation used by the input layer of a
feedforward neural network for the propose of forecasting spatial-temporal
signals. The approach is based on results from dynamical systems theory, namely
the non-linear embedding theorems. We demonstrate it for a variety of
spatial-temporal signals, with one spatial and one temporal dimensions, and
show that the optimal input layer representation consists of a grid, with
spatial/temporal lags determined by the minimum of the mutual information of
the spatial/temporal signals and the number of points taken in space/time
decided by the embedding dimension of the signal. We present evidence of this
proposal by running a Monte Carlo simulation of several combinations of input
layer feature designs and show that the one predicted by the non-linear
embedding theorems seems to be optimal or close of optimal. In total we show
evidence in four unrelated systems: a series of coupled Henon maps; a series of
couple Ordinary Differential Equations (Lorenz-96) phenomenologically modelling
atmospheric dynamics; the Kuramoto-Sivashinsky equation, a partial differential
equation used in studies of instabilities in laminar flame fronts and finally
real physical data from sunspot areas in the Sun (in latitude and time) from
1874 to 2015.Comment: 11 page
Towards a hybrid computational strategy based on Deep Learning for incompressible flows
The Poisson equation is present in very different domains of physics and engineering. In most cases, this equation can not be solved directly and iterative solvers are used. For many solvers, this step is computationally intensive. In this study, an alternative resolution method based on neural networks is evaluated for incompressible flows. A fluid solver coupled with a Convolutional Neural Network is developed and trained on random cases with constant density to predict the pressure field. Its performance is tested in a plume configuration, with different buoyancy forces, parametrized by the Richardson number. The neural network is compared to a traditional Jacobi solver. The performance improvement is considerable, although the accuracy of the network is found to depend on the flow operating point: low errors are obtained at low Richardson numbers, whereas the fluid solver becomes unstable with large errors for large Richardson number. Finally, a hybrid strategy is proposed in order to benefit from the calculation acceleration while ensuring a user-defined accuracy level. In particular, this hybrid CFD-NN strategy, by maintaining the desired accuracy whatever the flow condition, makes the code stable and reliable even at large Richardson numbers for which the network was not trained for. This study demonstrates the capability of the hybrid approach to tackle new flow physics, unseen during the network training
Magnetic field sensitivity of variable thickness microbridges in tbcco, bscco and ybco.
We describe results of a study comparing the magnetic field sensitivities of variable thickness bridge (VTB) arrays fabricated in TBCCO, BSCCO, and YBCO thin films. Identical structures were patterned in a variety of films, and the bridges were thinned by four different methods. Analysis of the data yields experimental evidence as to the suitability of these types of films for devices such as the superconducting flux flow transistor (SFFT) which is based on this geometry. The volt-ampere characteristics of the arrays were measured in low uniform magnetic fields (⩽130 G) and in nonuniform fields (⩽5 G) produced by a nearby control line. For these films in this geometry, no measurable effect of the control line magnetic field was observed. Large values of transresistance and current gain could only be attained through a thermal mechanism when the control line was driven normal. Upper bounds for (magnetically generated) transresistance (⩽5 mΩ) and current gains (⩽0.005) have been inferred from the uniform field data assuming a standard best-case device geometry. All volt-ampere curves followed closely a power law relationship (V~I n), with exponent n ~1.2-10. We suggest materials considerations that may yield improved device performancePeer Reviewe
Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1
In order to identify the sources of the observed diffuse high-energy neutrino
flux, it is crucial to discover their electromagnetic counterparts. IceCube
began releasing alerts for single high-energy ( TeV) neutrino
detections with sky localisation regions of order 1 deg radius in 2016. We used
Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for
any optical transients that may be related to the neutrinos. Typically 10-20
faint ( mag) extragalactic transients are found within the
Pan-STARRS1 footprints and are generally consistent with being unrelated field
supernovae (SNe) and AGN. We looked for unusual properties of the detected
transients, such as temporal coincidence of explosion epoch with the IceCube
timestamp. We found only one transient that had properties worthy of a specific
follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of
astrophysical origin of 50 %), we found a SN PS16cgx, located at 10.0'
from the nominal IceCube direction. Spectroscopic observations of PS16cgx
showed that it was an H-poor SN at z = 0.2895. The spectra and light curve
resemble some high-energy Type Ic SNe, raising the possibility of a jet driven
SN with an explosion epoch temporally coincident with the neutrino detection.
However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously
difficult. Based on all available data we conclude that the transient is more
likely to be a Type Ia with relatively weak SiII absorption and a fairly normal
rest-frame r-band light curve. If, as predicted, there is no high-energy
neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence,
and unrelated to the IceCube-160427A. We find no other plausible optical
transient for any of the five IceCube events observed down to a 5
limiting magnitude of mag, between 1 day and 25 days after
detection.Comment: 20 pages, 6 figures, accepted to A&
Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected
to produce neutrinos with a typical energy cutoff well below 100 TeV. For the
IceCube Neutrino Observatory located at the South Pole, the southern sky,
containing the inner part of the Galactic plane and the Galactic Center, is a
particularly challenging region at these energies, because of the large
background of atmospheric muons. In this paper, we present recent advancements
in data selection strategies for track-like muon neutrino events with energies
below 100 TeV from the southern sky. The strategies utilize the outer detector
regions as veto and features of the signal pattern to reduce the background of
atmospheric muons to a level which, for the first time, allows IceCube
searching for point-like sources of neutrinos in the southern sky at energies
between 100 GeV and several TeV in the muon neutrino charged current channel.
No significant clustering of neutrinos above background expectation was
observed in four years of data recorded with the completed IceCube detector.
Upper limits on the neutrino flux for a number of spectral hypotheses are
reported for a list of astrophysical objects in the southern hemisphere.Comment: 19 pages, 17 figures, 2 table
Magnetic field sensitivity of variable thickness microbridges in tbcco, bscco and ybco
We describe results of a study comparing the magnetic field sensitivities of variable thickness bridge (VTB) arrays fabricated in TBCCO, BSCCO, and YBCO thin films. Identical structures were patterned in a variety of films, and the bridges were thinned by four different methods. Analysis of the data yields experimental evidence as to the suitability of these types of films for devices such as the superconducting flux flow transistor (SFFT) which is based on this geometry. The volt-ampere characteristics of the arrays were measured in low uniform magnetic fields (⩽130 G) and in nonuniform fields (⩽5 G) produced by a nearby control line. For these films in this geometry, no measurable effect of the control line magnetic field was observed. Large values of transresistance and current gain could only be attained through a thermal mechanism when the control line was driven normal. Upper bounds for (magnetically generated) transresistance (⩽5 mO) and current gains (⩽0.005) have been inferred from the uniform field data assuming a standard best-case device geometry. All volt-ampere curves followed closely a power law relationship (V~I n), with exponent n ~1.2-10. We suggest materials considerations that may yield improved device performance [-]Peer ReviewedPostprint (published version
Condensation of an ideal gas with intermediate statistics on the horizon
We consider a boson gas on the stretched horizon of the Schwartzschild and
Kerr black holes. It is shown that the gas is in a Bose-Einstein condensed
state with the Hawking temperature if the particle number of the
system be equal to the number of quantum bits of space-time N \simeq
{A}/{{\l_{p}}^{2}}. Entropy of the gas is proportional to the area of the
horizon by construction. For a more realistic model of quantum degrees of
freedom on the horizon, we should presumably consider interacting bosons
(gravitons). An ideal gas with intermediate statistics could be considered as
an effective theory for interacting bosons. This analysis shows that we may
obtain a correct entropy just by a suitable choice of parameter in the
intermediate statistics.Comment: 12 pages, added new sections related to an ideal gas with
intermediate statistic
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