37,235 research outputs found
Electron-Phonon Interactions for Optical Phonon Modes in Few-Layer Graphene
We present a first-principles study of the electron-phonon (e-ph)
interactions and their contributions to the linewidths for the optical phonon
modes at and K in one to three-layer graphene. It is found that due to
the interlayer coupling and the stacking geometry, the high-frequency optical
phonon modes in few-layer graphene couple with different valence and conduction
bands, giving rise to different e-ph interaction strengths for these modes.
Some of the multilayer optical modes derived from the - mode of
monolayer graphene exhibit slightly higher frequencies and much reduced
linewidths. In addition, the linewidths of K- related modes in
multilayers depend on the stacking pattern and decrease with increasing layer
numbers.Comment: 6 pages,5 figures, submitted to PR
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The polymeric conformational effect on capacitive deionization performance of graphene oxide/polypyrrole composite electrode
Exploitation of novel faradic materials is an alternative implementation for solving the problem of poor specific electrosorption capacity that conventional carbon materials are encountered in capacitive deionization. Particularly, composite electrode is just a suitable choice because of its potentially high ion-storage ability. Herein, a cyclic voltammetric treatment method with different low limit of potential window was used to manipulate the polymeric conformation and doping level of graphene oxide/polypyrrole (GO/PPy) composite electrode. Based on it, the effect of polymeric structure on the electrosorption performance was systematically studied. When the low limit of potential window is shifted negatively enough, the irreversible polymeric conformational shrinks of GO/PPy are promoted, which not only hinders the insertion process of ions, but also decreases the doping level of polymer due to the intensive interchain-action produced by more entangled polymeric chain. Thus, the number of intercalated ions should decrease, which is expressed by electrochemical impedance spectroscopy (EIS) results and is proportional to the electrosorption capacity of GO/PPy composite electrode in membrane capacitive deionization (MCDI) process. Our work suggests that the less packing density, higher doping level and more charge delocalization on PPy backbone in electrode are beneficial to enhance its capacitive deionization performance
Towards Analyzing Semantic Robustness of Deep Neural Networks
Despite the impressive performance of Deep Neural Networks (DNNs) on various
vision tasks, they still exhibit erroneous high sensitivity toward semantic
primitives (e.g. object pose). We propose a theoretically grounded analysis for
DNN robustness in the semantic space. We qualitatively analyze different DNNs'
semantic robustness by visualizing the DNN global behavior as semantic maps and
observe interesting behavior of some DNNs. Since generating these semantic maps
does not scale well with the dimensionality of the semantic space, we develop a
bottom-up approach to detect robust regions of DNNs. To achieve this, we
formalize the problem of finding robust semantic regions of the network as
optimizing integral bounds and we develop expressions for update directions of
the region bounds. We use our developed formulations to quantitatively evaluate
the semantic robustness of different popular network architectures. We show
through extensive experimentation that several networks, while trained on the
same dataset and enjoying comparable accuracy, do not necessarily perform
similarly in semantic robustness. For example, InceptionV3 is more accurate
despite being less semantically robust than ResNet50. We hope that this tool
will serve as a milestone towards understanding the semantic robustness of
DNNs.Comment: Presented at European conference on computer vision (ECCV 2020)
Workshop on Adversarial Robustness in the Real World (
https://eccv20-adv-workshop.github.io/ ) [best paper award]. The code is
available at https://github.com/ajhamdi/semantic-robustnes
Methods for The Testing of Nanopowder
Methods for the testing of nanopowders produced by wires electric explosion
were considered. The following characteristics were proposed for the testing of
nanopowders : main substance content, characteristic sizes of particles,
specific surface area etc..Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
The Absolute Magnitudes of Red Horizontal Branch Stars in the ugriz System
Based on photometric data of the central parts of eight globular clusters and
one open cluster presented by An and his collaborators, we select red
horizontal branch (RHB) stars in the (g-r)0-g0 diagram and make a statistical
study of the distributions of their colors and absolute magnitudes in the SDSS
ugriz system. Meanwhile, absolute magnitudes in the Johnson VRI system are
calculated through the translation formulae between gri and VRI in the
literature. The calibrations of absolute magnitude as functions of metallicity
and age are established by linear regressions of the data.
It is found that metallicity coefficients in these calibrations decrease,
while age coefficients increase, from the blue filter to the red
filter. The calibration of Mi= 0.06[Fe/H]+0.040t+0.03 has the smallest scatter
of 0.04 mag, and thus i is the best filter in the system when RHB stars
are used for distance indicators. The comparison of the MI calibration from our
data with that from red clump stars indicates that the previous suggestion that
the filter is better than the V filter in distance determination may not be
true because of its significant dependence on age.Comment: 19 pages, 7 figures, accepted by Ap
Sign reversal of field-angle resolved heat capacity oscillations in a heavy fermion superconductor CeCoIn and pairing symmetry
To identify the superconducting gap symmetry in CeCoIn5 (Tc=2.3 K), we
performed angle-resolved specific heat (C_\phi) measurements in a field rotated
around the c-axis down to very low temperatures 0.05Tc and detailed theoretical
calculations. In a field of 1 T, a sign reversal of the fourfold angular
oscillation in C_\phi has been observed at T ~ 0.1Tc on entering a
quasiclassical regime where the maximum of C_\phi corresponds to the antinodal
direction, coinciding with the angle-resolved density of states (ADOS)
calculation. The C_\phi behavior, which exhibits minima along [110] directions,
unambiguously allows us to conclude d_{x^2-y^2} symmetry of this system. The
ADOS-quasiclassical region is confined to a narrow T and H domain within T/Tc ~
0.1 and 1.5 T (0.13Hc2).Comment: 4 pages, 4 figure
Earliest Holocene south Greenland ice sheet retreat within its late Holocene extent
Early Holocene summer warmth drove dramatic Greenland ice sheet (GIS) retreat. Subsequent insolation-driven cooling caused GIS margin readvance to late Holocene maxima, from which ice margins are now retreating. We use 10Be surface exposure ages from four locations between 69.4°N and 61.2°N to date when in the early Holocene south to west GIS margins retreated to within these late Holocene maximum extents. We find that this occurred at 11.1 ± 0.2 ka to 10.6 ± 0.5 ka in south Greenland, significantly earlier than previous estimates, and 6.8 ± 0.1 ka to 7.9 ± 0.1 ka in southwest to west Greenland, consistent with existing 10Be ages. At least in south Greenland, these 10Be ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late Holocene temperatures in the early Holocene. Current south Greenland ice margin retreat suggests that south Greenland may have now warmed to or above earliest Holocene summer temperatures
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