124 research outputs found
Detection of Jovian seismic waves: a new probe of its interior structure
Knowledge of Jupiter's deep interior would provide unique constraints on the
formation of the Solar System. Measurement of its core mass and global
composition would shed light on whether the planet formed by accretion or by
direct gravitational collapse. At present, the inner structure of Jupiter is
poorly constrained and seismology, which consists of identifying acoustic
eigenmodes, offers a way to directly measure its deep sound speed profile, and
thus its physical properties. Seismology of Jupiter has been considered since
the mid 1970s, but hitherto the various attempts to detect global modes led, at
best, to ambiguous results. We report the detection of global modes of Jupiter,
based on radial velocity measurements performed with the SYMPA Fourier
spectro-imager. The global seismic parameters that we measure include the
frequency of maximum amplitude 1213+/-50 \mu Hz, the mean large frequency
spacing between radial harmonics 155.3+/-2.2 \mu Hz and the mode maximum
amplitude 49 (-10/+8) cm/s, all values that are consistent with current models
of Jupiter. This result opens the way to the investigation of the inner
structure of the Solar System's giant planets based on seismology techniques.Comment: Accepted in Astronomy & Astrophysics (8 pages, 9 figures
Force-induced acoustic phonon transport across single-digit nanometre vacuum gaps
Heat transfer between bodies separated by nanoscale vacuum gap distances has
been extensively studied for potential applications in thermal management,
energy conversion and data storage. For vacuum gap distances down to 20 nm,
state-of-the-art experiments demonstrated that heat transport is mediated by
near-field thermal radiation, which can exceed Planck's blackbody limit due to
the tunneling of evanescent electromagnetic waves. However, at sub-10-nm vacuum
gap distances, current measurements are in disagreement on the mechanisms
driving thermal transport. While it has been hypothesized that acoustic phonon
transport across single-digit nanometre vacuum gaps (or acoustic phonon
tunneling) can dominate heat transfer, the underlying physics of this
phenomenon and its experimental demonstration are still unexplored. Here, we
use a custom-built high-vacuum shear force microscope (HV-SFM) to measure heat
transfer between a silicon (Si) tip and a feedback-controlled platinum (Pt)
nanoheater in the near-contact, asperity-contact, and bulk-contact regimes. We
demonstrate that in the near-contact regime (i.e., single-digit nanometre or
smaller vacuum gaps before making asperity contact), heat transfer between Si
and Pt surfaces is dominated by force-induced acoustic phonon transport that
exceeds near-field thermal radiation predictions by up to three orders of
magnitude. The measured thermal conductance shows a gap dependence of
in the near-contact regime, which is consistent with acoustic
phonon transport modelling based on the atomistic Green's function (AGF)
framework. Our work suggests the possibility of engineering heat transfer
across single-digit nanometre vacuum gaps with external force stimuli, which
can make transformative impacts to the development of emerging thermal
management technologies.Comment: 9 pages with 4 figures (Main text), 13 pages with 7 figures
(Methods), and 13 pages with 6 figures and 1 table (Supplementary
Information
Raman spectroscopy investigation of the H content of heated hard amorphous carbon layers
We revisit here how Raman spectroscopy can be used to estimate the H content
in hard hydrogenated amorphous carbon layers. The H content was varied from 2
at.% to 30 at.%, using heat treatments of a a-C:H, from room temperature to
1300 K and was determined independently using ion beam analysis. We examine the
correlation of various Raman parameters and the consistency of their thermal
evolution with thermo-desorption results. We identify a weak band at 860 cm-1
attributed to H bonded to C(sp2). We show that the HD/HG parameter (Height
ratio between the D and G bands) is quasi-linear in the full range of H content
and can thus be used to estimate the H content. Conversely, we show that the
m/HG parameter (ratio between the photoluminescence background, m, and the
height of the G band), often used to estimate the H content, should be used
with care, first because it is sensitive to various photoluminescence quenching
processes and second because it is not sensitive to H bonded to C(sp2)
Raman micro-spectroscopy as a tool to measure the absorption coefficient and the erosion rate of hydrogenated amorphous carbon films heat-treated under hydrogen bombardment
We present a fast and simple way to determine the erosion rate and absorption
coefficient of hydrogenated amorphous carbon films exposed to a hydrogen atomic
source based on ex-situ Raman micro-spectroscopy. Results are compared to
ellipsometry measurement. The method is applied to films eroded at different
temperatures. A maximum of the erosion rate is found at ~ 450 {\degree}C in
agreement with previous results. This technique is suitable for future
quantitative studies on the erosion of thin carbonaceous films, especially of
interest for plasma wall interactions occurring in thermonuclear fusion
devices
Evolution-Based Online Automated Machine Learning
International audienceAutomated Machine Learning (AutoML) deals with finding well-performing machine learning models and their corresponding configurations without the need of machine learning experts. However, if one assumes an online learning scenario, where an AutoML instance executes on evolving data streams, the question for the best model and its configuration with respect to occurring changes in the data distribution remains open. Algorithms developed for online learning settings rely on few and homogeneous models and do not consider data mining pipelines or the adaption of their configuration. We, therefore, introduce EvoAu-toML, an evolution-based online learning framework consisting of heterogeneous and connectable models that supports large and diverse configuration spaces and adapts to the online learning scenario. We present experiments with an implementation of EvoAutoML on a diverse set of synthetic and real datasets, and show that our proposed approach outperforms state-of-the-art online algorithms as well as strong ensemble baselines in a traditional test-then-train evaluation
Long Term H-Release from Amorphous Carbon Evidenced by in Situ Raman Microscopy under Isothermal Heating
We study the kinetics of the H release from plasma-deposited hydrogenated
amorphous carbon films under isothermal heating at 450, 500 and 600 {\degree}C
for long times up to several days using in situ Raman microscopy. Four Raman
parameters are analyzed. They allow the identification of different processes
such as the carbon network reorganization and the H release from sp3 or sp2
carbon atoms and the corresponding timescales. Carbon reorganization with
aromatization and loss of sp3 hybridization occurs first in 100 minutes at 500
{\degree}C. The final organization is similar at all investigated temperatures.
Full H release from sp3 carbon occurs on a longer timescale of about 10 hours
while H release from sp2 carbon atoms is only partial, even after several days.
All these processes occur more rapidly with higher initial H content, in
agreement with what is known about the stability of these types of films. A
quantitative analysis of these kinetics studies gives valuable information
about the microscopic processes at the origin of the H release through the
determination of activation energies
Raman study of CFC tiles extracted from the toroidal pump limiter of Tore Supra
International audienceThe structure of six tiles extracted from the erosion and deposition zones (thin and thick deposition) of the Tore Supra toroidal pump limiter (TPL) have been analysed in the framework of the DITS campaign using micro-Raman spectroscopy. This post-mortem analysis gives information on both carbon structure and D content. We have found that the carbon structure is most often similar to that of plasma-deposited hard amorphous carbon layers. The role of the surface temperature during the discharge in the D content is investigated: in all locations where the temperature does not reach more than 500°C the D content seems to be roughly uniform with D/D+C ≈ 20%
Concert recording 2022-10-12
[Track 1]. Sonata for four trombones / Georg Daniel Speer -- [Track 2]. Scarborough fair / traditional ; arr. Bill Reichenbach -- [Track 3]. Quartet for trombones / Leslie Bassett -- [Track 4]. You made me love you / James Monaco ; arr. Bill Holcombe -- [Track 5]. Fanfare for 8 trombones / Michael P. Terry -- [Track 6]. Andante cantabile from Symphony no. 5, Mtv. II / Pyort IIlich Tchaikovsky ; arr. Nolan Miller -- [Track 7]. Rising tide / Jack Wilds
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