289 research outputs found
Sidewall Buckling of Equal-width RHS Truss X-Joints
This paper presents a new design methodology for equal-width rectangular hollow section (RHS) X-joints failing by sidewall buckling. In the new approach, a slenderness parameter is defined based on the elastic local buckling stress of the sidewall, idealized as an infinitely long plate under patch loading. A Rayleigh-Ritz approximation is thereby used to obtain a closed-form solution. The proposed design equation is verified against experimental results over a wide range of wall slenderness values obtained from the literature and complemented by a brief experimental program carried out by the authors. It is demonstrated that the new design equation yields excellent results against the experimental data. Finally, a reliability analysis is performed within the framework of both the Eurocode and the AISI standards to ensure that the proposed design equation possesses the required level of safety. The newly proposed equation strongly outperforms the current Comité International pour le Développement et l’Etude de la Construction Tubulaire (CIDECT) design rule for sidewall buckling and also further extends the range of applicability to a wall slenderness ratio of up to 50
petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
We present the easy-to-use, publicly available, Python package petitRADTRANS,
built for the spectral characterization of exoplanet atmospheres. The code is
fast, accurate, and versatile; it can calculate both transmission and emission
spectra within a few seconds at low resolution ( = 1000;
correlated-k method) and high resolution (;
line-by-line method), using only a few lines of input instruction. The somewhat
slower correlated-k method is used at low resolution because it is more
accurate than methods such as opacity sampling. Clouds can be included and
treated using wavelength-dependent power law opacities, or by using optical
constants of real condensates, specifying either the cloud particle size, or
the atmospheric mixing and particle settling strength. Opacities of amorphous
or crystalline, spherical or irregularly-shaped cloud particles are available.
The line opacity database spans temperatures between 80 and 3000 K, allowing to
model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or
hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature
points and species will be added in the future, allowing to also model the
class of ultra hot-Jupiters, with equilibrium temperatures K. Radiative transfer results were tested by cross-verifying the low- and
high-resolution implementation of petitRADTRANS, and benchmarked with the
petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We
successfully carried out test retrievals of synthetic JWST emission and
transmission spectra (for the hot Jupiter TrES-4b, which has a of
1800 K). The code is publicly available at
http://gitlab.com/mauricemolli/petitRADTRANS, and its documentation can be
found at https://petitradtrans.readthedocs.io.Comment: 17 pages, 7 figures, published in A&
Koeien kiezen niet voor vreetstanden
Vreetstanden zijn afscheidingen die om de twee vreetplaatsen aan het voerhek gemonteerd zijn. De gedachte is dat koeien met vreetstanden meer rust hebben tijdens het vreten. Uit onderzoek bleek dat de dieren op het High-techbedrijf geen voorkeur hadden voor de gedeelten van het voerhek met vreetstanden
Spatially-resolved high-resolution retrievals of Ultra-hot Jupiters
Stars and planetary system
First light of a holographic aperture mask: observation at the Keck OSIRIS Imager
Instrumentatio
Behavior analysis of bar gaps in welded YT-joints for rolled-steel circular hollow sections
The Roasting Marshmallows Program with IGRINS on Gemini South I: Composition and Climate of the Ultra Hot Jupiter WASP-18 b
We present high-resolution dayside thermal emission observations of the
exoplanet WASP-18b using IGRINS on Gemini South. We remove stellar and telluric
signatures using standard algorithms, and we extract the planet signal via
cross correlation with model spectra. We detect the atmosphere of WASP-18b at a
signal-to-noise ratio (SNR) of 5.9 using a full chemistry model, measure H2O
(SNR=3.3), CO (SNR=4.0), and OH (SNR=4.8) individually, and confirm previous
claims of a thermal inversion layer. The three species are confidently detected
(>4) with a Bayesian inference framework, which we also use to retrieve
abundance, temperature, and velocity information. For this ultra-hot Jupiter
(UHJ), thermal dissociation processes likely play an important role. Retrieving
abundances constant with altitude and allowing the temperature-pressure profile
to freely adjust results in a moderately super-stellar carbon to oxygen ratio
(C/O=0.75^{+0.14}_{-0.17}) and metallicity ([M/H]=1.03^{+0.65}_{-1.01}).
Accounting for undetectable oxygen produced by thermal dissociation leads to
C/O=0.45^{+0.08}_{-0.10} and [M/H]=1.17^{+0.66}_{-1.01}. A retrieval that
assumes radiative-convective-thermochemical-equilibrium and naturally accounts
for thermal dissociation constrains C/O<0.34 (2) and
[M/H]=0.48^{+0.33}_{-0.29}, in line with the chemistry of the parent star.
Looking at the velocity information, we see a tantalising signature of
different Doppler shifts at the level of a few km/s for different molecules,
which might probe dynamics as a function of altitude and location on the planet
disk. Our results demonstrate that ground-based, high-resolution spectroscopy
at infrared wavelengths can provide meaningful constraints on the compositions
and climate of highly irradiated planets. This work also elucidates potential
pitfalls with commonly employed retrieval assumptions when applied to UHJ
spectra.Comment: 27 pages, 18 figures, submitted to AAS Journals. Community feedback
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Onderzoek op T-vormige vierkante buisverbindingen ter bepaling van de M-phi en F-delta karakteristieken, alsmede het vermoeiiingsgedrag
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