577 research outputs found
Amorphous interface layer in thin graphite films grown on the carbon face of SiC
Cross-sectional transmission electron microscopy (TEM) is used to
characterize an amorphous layer observed at the interface in graphite and
graphene films grown via thermal decomposition of C-face 4H-SiC. The amorphous
layer does not to cover the entire interface, but uniform contiguous regions
span microns of cross-sectional interface. Annular dark field scanning
transmission electron microscopy (ADF-STEM) images and electron energy loss
spectroscopy (EELS) demonstrate that the amorphous layer is a carbon-rich
composition of Si/C. The amorphous layer is clearly observed in samples grown
at 1600{\deg}C for a range of growth pressures in argon, but not at
1500{\deg}C, suggesting a temperature-dependent formation mechanism
Dealing with the challenges of legitimacy, values, and politics in policy advice
Policy advice has been the subject of ongoing research in the policy sciences as it raises fundamental
issues about what constitutes policy knowledge, expertise, and their effects on policymaking. This
introduction reviews the existing literature on the subject and introduces the themes motivating the
articles in the issue. It highlights the need to consider several key subjects in the topic in the contemporary
era: namely the challenge of legitimacy, that of values, and the challenge of politics. The
papers in the issue shed light on the ongoing delegitimization of conventional knowledge providers,
the problem of the normative basis of experts’ advice, the increasing politicization of expertise in policymaking,
and the relevance of political context in influencing not only the role of experts but also
whether or not their advice is accepted and implemented. It is argued that these modern challenges,
when not addressed, reinforce trends toward the inclusion of antidemocratic values and uninformed
ideas in contemporary policymaking
Observation of quantum-Hall effect in gated epitaxial graphene grown on SiC (0001)
Epitaxial graphene films were formed on the Si-face of semi-insulating 4H-SiC
substrates by a high temperature sublimation process. A high-k gate stack on
epitaxial graphene is realized by inserting a fully oxidized nanometer thin
aluminum film as a seeding layer followed by an atomic-layer deposition
process. The electrical properties of epitaxial graphene films are sustained
after gate stack formation without significant degradation. At low
temperatures, the quantum-Hall effect in Hall resistance is observed along with
pronounced Shubnikov-de Hass oscillations in diagonal magneto-resistance of
gated epitaxial graphene on SiC (0001).Comment: 2 new references adde
Ab initio Study of Misfit Dislocations at the SiC/Si(001) Interface
The high lattice mismatched SiC/Si(001) interface was investigated by means
of combined classical and ab initio molecular dynamics. Among the several
configurations analyzed, a dislocation network pinned at the interface was
found to be the most efficient mechanism for strain relief. A detailed
description of the dislocation core is given, and the related electronic
properties are discussed for the most stable geometry: we found interface
states localized in the gap that may be a source of failure of electronic
devices
Model systematics in time domain tests of binary black hole evolution
We perform several consistency tests between different phases of binary black hole dynamics; the inspiral, the merger, and the ringdown on the gravitational wave events GW150914 and GW170814. These tests are performed explicitly in the time domain, without any spectral leakage between the different phases. We compute posterior distributions on the mass and spin of the initial black holes and the final black hole. We also compute the initial areas of the two individual black holes and the final area from the parameters describing the remnant black hole. This facilitates a test of Hawking's black hole area theorem. We use different waveform models to quantify systematic waveform uncertainties for the area increase law with the two events. We find that these errors may lead to overstating the confidence with which the area theorem is confirmed. For example, we find agreement with the area theorem for GW150914 if a damped sinusoid consisting of a single-mode is used at merger to estimate the final area. This is because this model overestimates the final mass. Including an overtone of the dominant mode decreases the confidence to ; using a full merger-ringdown model further decreases the confidence to . We find that comparing the measured change in the area to the expected change in area yields a more robust test, as it also captures over estimates in the change of area. We find good agreement with GR when applying this test to GW150914 and GW170814
A comparative DFT study of electronic properties of 2H-, 4H- and 6H-SiC(0001) and SiC(000-1) clean surfaces: Significance of the surface Stark effect
Electric field, uniform within the slab, emerging due to Fermi level pinning
at its both sides is analyzed using DFT simulations of the SiC surface slabs of
different thickness. It is shown that for thicker slab the field is nonuniform
and this fact is related to the surface state charge. Using the electron
density and potential profiles it is proved that for high precision simulations
it is necessary to take into account enough number of the Si-C layers. We show
that using 12 diatomic layers leads to satisfactory results. It is also
demonstrated that the change of the opposite side slab termination, both by
different type of atoms or by their location, can be used to adjust electric
field within the slab, creating a tool for simulation of surface properties,
depending on the doping in the bulk of semiconductor. Using these simulations
it was found that, depending on the electric field, the energy of the surface
states changes in a different way than energy of the bulk states. This
criterion can be used to distinguish Shockley and Tamm surface states. The
electronic properties, i.e. energy and type of surface states of the three
clean surfaces: 2H-, 4H-, 6H-SiC(0001), and SiC() are analyzed and
compared using field dependent DFT simulations.Comment: 18 pages, 10 figures, 4 table
The effects of the ketogenic diet in refractory partial seizures with reference to tuberous sclerosis.
Posterior samples of the parameters of binary black holes from Advanced LIGO, Virgo's second observing run
This paper presents a parameter estimation analysis of the seven binary black hole mergers-GW170104, GW170608, GW170729, GW170809, GW170814, GW170818, and GW170823-detected during the second observing run of the Advanced LIGO and Virgo observatories using the gravitational-wave open data. We describe the methodology for parameter estimation of compact binaries using gravitational-wave data, and we present the posterior distributions of the inferred astrophysical parameters. We release our samples of the posterior probability density function with tutorials on using and replicating our results presented in this paper
3-OGC: Catalog of gravitational waves from compact-binary mergers
We present the third Open Gravitational-wave Catalog (3-OGC) of compact-binary coalescences, based on the analysis of the public LIGO and Virgo data from 2015 through 2019 (O1, O2, O3a). Our updated catalog includes a population of 57 observations, including four binary black hole mergers that had not previously been reported. This consists of 55 binary black hole mergers and the two binary neutron star mergers GW170817 and GW190425. We find no additional significant binary neutron star or neutron star--black hole merger events. The most confident new detection is the binary black hole merger GW190925\_232845 which was observed by the LIGO Hanford and Virgo observatories with ; its primary and secondary component masses are and , respectively. We estimate the parameters of all binary black hole events using an up-to-date waveform model that includes both sub-dominant harmonics and precession effects. To enable deep follow-up as our understanding of the underlying populations evolves, we make available our comprehensive catalog of events, including the sub-threshold population of candidates, and the posterior samples of our source parameter estimates
Self-Organized Criticality model for Brain Plasticity
Networks of living neurons exhibit an avalanche mode of activity,
experimentally found in organotypic cultures. Here we present a model based on
self-organized criticality and taking into account brain plasticity, which is
able to reproduce the spectrum of electroencephalograms (EEG). The model
consists in an electrical network with threshold firing and activity-dependent
synapse strenghts. The system exhibits an avalanche activity power law
distributed. The analysis of the power spectra of the electrical signal
reproduces very robustly the power law behaviour with the exponent 0.8,
experimentally measured in EEG spectra. The same value of the exponent is found
on small-world lattices and for leaky neurons, indicating that universality
holds for a wide class of brain models.Comment: 4 pages, 3 figure
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