2,028 research outputs found
Molecular-Kinetic Simulations of Escape from the Ex-planet and Exoplanets: Criterion for Transonic Flow
The equations of gas dynamics are extensively used to describe atmospheric
loss from solar system bodies and exoplanets even though the boundary
conditions at infinity are not uniquely defined. Using molecular-kinetic
simulations that correctly treat the transition from the continuum to the
rarefied region, we confirm that the energy-limited escape approximation is
valid when adiabatic expansion is the dominant cooling process. However, this
does not imply that the outflow goes sonic. In fact in the sonic regime, the
energy limited approximation can significantly under estimate the escape rate.
Rather large escape rates and concomitant adiabatic cooling can produce
atmospheres with subsonic flow that are highly extended. Since this affects the
heating rate of the upper atmosphere and the interaction with external fields
and plasmas, we give a criterion for estimating when the outflow goes transonic
in the continuum region. This is applied to early terrestrial atmospheres,
exoplanet atmospheres, and the atmosphere of the ex-planet, Pluto, all of which
have large escape rates. The paper and its erratum, combined here, are
published: ApJL 768, L4 (2013); ApJ, 779, L30 (2013).Comment: 11 pages, 3 figure
One model to rule them all: unified classification model for geotagging websites
The paper presents a novel approach to finding regional scopes (geotagging) of websites. It relies on a single binary classification model per region type to perform the multi-label classification and uses a variety of different features that have not been yet used together for machine-learning based regional classification of websites. The evaluation demonstrates the advantage of our one model per region type method versus the traditional one model per region approach
An Universal Image Attractiveness Ranking Framework
We propose a new framework to rank image attractiveness using a novel
pairwise deep network trained with a large set of side-by-side multi-labeled
image pairs from a web image index. The judges only provide relative ranking
between two images without the need to directly assign an absolute score, or
rate any predefined image attribute, thus making the rating more intuitive and
accurate. We investigate a deep attractiveness rank net (DARN), a combination
of deep convolutional neural network and rank net, to directly learn an
attractiveness score mean and variance for each image and the underlying
criteria the judges use to label each pair. The extension of this model
(DARN-V2) is able to adapt to individual judge's personal preference. We also
show the attractiveness of search results are significantly improved by using
this attractiveness information in a real commercial search engine. We evaluate
our model against other state-of-the-art models on our side-by-side web test
data and another public aesthetic data set. With much less judgments (1M vs
50M), our model outperforms on side-by-side labeled data, and is comparable on
data labeled by absolute score.Comment: Accepted by 2019 Winter Conference on Application of Computer Vision
(WACV
Study of Transient Interaction in a System with Transformer Supplied from Network through a Cable: Assessment of Interaction Frequencies and Resonance Evolvement
Transformer together with its windings is a complex oscillatory system. The interaction between
the transformer and an electric network during transients can cause the development of resonance
phenomenon in the windings leading to overvoltages and the risk of transformer fault.
This report presents the results of studies of resonance phenomena in transformer windings,
caused by interaction with an electric network containing the feeder cable. The approach to a simple
assessment of dominant oscillation frequency of a voltage in the system “feeder cable – transformer” and
estimation of the resonant frequencies of transformer winding is considered. The report also describes
the technique for measurement of winding resonance voltages. The resonance phenomenon evolvement
in transformer windings is considered and the impact of decaying oscillating applied voltage on maximum
ratio of resonance overvoltages is estimated
Smooth gauge for topological insulators
We develop a technique for constructing Bloch-like functions for 2D
Z_2-insulators (i.e., quantum spin-Hall insulators) that are smooth functions
of k on the entire Brillouin-zone torus. As the initial step, the occupied
subspace of the insulator is decomposed into a direct sum of two "Chern bands,"
i.e., topologically nontrivial subspaces with opposite Chern numbers. This
decomposition remains robust independent of underlying symmetries or specific
model features. Starting with the Chern bands obtained in this way, we
construct a topologically nontrivial unitary transformation that rotates the
occupied subspace into a direct sum of topologically trivial subspaces, thus
facilitating a Wannier construction. The procedure is validated and illustrated
by applying it to the Kane-Mele model
Reclaiming of Monoethanolamine (MEA) Used in Post-Combustion CO2-capture with Electrodialysis
AbstractHeat-stable salts (HSS) in amine-based solvents may lead to a long-term performance impairment of post-combustion CO2- capture process system. They can cause a loss of solvent capacity, corrosion, heat exchanger fouling, increased foaming or flooding, etc. The application of electrodialysis (ED) can be a possible cost effective technique for removal of HSS from degraded amine solutions. The paper presents the results of lab-scale ED experiments on HSS removal from synthetic degraded MEA solutions with different HSS content and CO2-loadings. The efficiency of ED-process for reclaiming of MEA solvent is shown. The influence of solvent CO2-loading on the specific energy consumption of ED-process is presented. The lab-scale data have been used for design and manufacturing of a pilot ED plant. Within the OCTAVIUS project it has been planned to test the ED-pilot plant at the EnBW post-combustion CO2 capture pilot plant
Study of the machinability of an Inconel 625 composite with added NiTi-TiB2 fabricated by direct laser deposition
This work studies the process feasibility of milling a metal-matrix composite based on Inconel 625 with added NiTi-TiB2 fabricated by direct laser deposition. The composite is intended for manufacturing turbine blades and it has strength characteristics on par with those of Inconel 625. However, the addition of TiB2 has improved its heat and wear resistance. This material is new, and its machinability has not been studied. The new composite was milled with end mill cutters, and recommendations were worked out on the cutting speed, feed per tooth, cutter flank angle, as well as depth and width of milling. The wear of cutter teeth flank was more intense. After the flank wear land on the back surface of a tooth had reached 0.11–0.15 mm, there was a sharp increase in the forces applied which was followed by brittle fracture of the tooth. Milling at a speed of 25 m/min ensured 28 min of stable operation. However, afterwards the critical wear value of 0.11 mm was quickly approached at a cutting speed of 50 m/min, and critical wear followed after 14 min.я Dependencies of the cutting forces vs. time for all the selected cutting speeds and throughout the entire testing time period have a tendency to increase, which indicates the influence of cutter wear on the cutting forces. It was found that the durability of the cutters increases with an increase in the milling width and a decrease in the milling depth
Size effects in near-ultraviolet Raman spectra of few-nanometer-thick silicon-oninsulator nanofilms
We have fabricated Si-on-insulator (SOI) layers with a thickness h1 of a few nanometers and
examined them by Raman spectroscopy with 363.8 nm excitation. We have found that phonon and
electron confinement play important roles in SOI with h1<10 nm. We have confirmed that the
first-order longitudinal optical phonon Raman band displays size-induced major homogeneous
broadening due to phonon lifetime reduction as well as minor inhomogeneous broadening due to
wave vector relaxation (WVR), both kinds of broadening being independent of temperature. Due to
WVR, transverse acoustic (TA) phonons become Raman-active and give rise to a broad band in the
range of 100–200 cm 1. Another broad band appeared at 200–400 cm 1 in the spectrum of SOI is
attributed to the superposition of 1st order Raman scattering on longitudinal acoustic phonons and
2nd order scattering on TA phonons. Suppression of resonance-assisted 2-nd order Raman bands in
SOI spectra is explained by the electron-confinement-induced direct band gap enlargement compared
to bulk Si, which is confirmed by SOI reflection spectra. Published by AIP Publishing.
[http://dx.doi.org/10.1063/1.4947021
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