602 research outputs found
Coarse grained force field for the molecular simulation of natural gases and condensates
AbstractThe atomistically-detailed molecular modelling of petroleum fluids is challenging, amongst other aspects, due to the very diverse multicomponent and asymmetric nature of the mixtures in question. Complicating matters further, the time scales for many important processes can be much larger than the current and foreseeable capacity of modern computers running fully-atomistic models. To overcome these limitations, a coarse grained (CG) model is proposed where some of the less-important degrees of freedom are safely integrated out, leaving as key parameters the average energy levels, the molecular conformations and the range of the Mie intermolecular potentials employed as the basis of the model. The parametrization is performed by using an analytical equation of state of the statistical associating fluid theory (SAFT) family to link the potential parameters to macroscopically observed thermophysical properties. The parameters found through this top-down approach are used directly in molecular dynamics simulations of multi-component multi-phase systems. The procedure is exemplified by calculating the phase envelope of the methane–decane binary and of two synthetic light condensate mixtures. A methodology based on the discrete expansion of a mixture is used to determine the bubble points of these latter mixtures, with an excellent agreement to experimental data. The model presented is entirely predictive and an abridged table of parameters for some fluids of interest is provided
Implications of atmospheric non-detections for Trappist-1 inner planets on atmospheric retention prospects for outer planets
JWST secondary eclipse observations of Trappist-1b seemingly disfavor
atmospheres >~1 bar since heat redistribution is expected to yield dayside
emission temperature below the ~500 K observed. Given the similar densities of
Trappist-1 planets, and the theoretical potential for atmospheric erosion
around late M-dwarfs, this observation might be assumed to imply substantial
atmospheres are also unlikely for the outer planets. However, the processes
governing atmosphere erosion and replenishment are fundamentally different for
inner and outer planets. Here, an atmosphere-interior evolution model is used
to show that an airless Trappist-1b (and c) only weakly constrains stellar
evolution, and that the odds of outer planets e and f retaining substantial
atmospheres remain largely unchanged. This is true even if the initial volatile
inventories of planets in the Trappist-1 system are highly correlated. The
reason for this result is that b and c sit unambiguously interior to the
runaway greenhouse limit, and so have potentially experienced ~8 Gyr of
XUV-driven hydrodynamic escape; complete atmospheric erosion in this
environment only weakly constrains stellar evolution and escape
parameterizations. In contrast, e and f reside within the habitable zone, and
likely experienced a comparatively short steam atmosphere during Trappist-1's
pre-main sequence, and consequently complete atmospheric erosion remains
unlikely across a broad swath of parameter space (e and f retain atmospheres in
~98% of model runs). Naturally, it is still possible that all Trappist-1
planets formed volatile-poor and are all airless today. But the airlessness of
b (and c) does not require this, and as such, JWST transit spectroscopy of e
and f remains the best near-term opportunity to characterize the atmospheres of
habitable zone terrestrial planets.Comment: Accepted for publication in ApJL (June 7th 2023). First submitted May
3rd, 2023. 15 pages, 6 figures, 1 tabl
CONTEMPORARY ASIAN ART: INDONESIA
Conducted fieldwork and research in preparation for a book on Indonesian art
Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components
Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels
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Computational methodology for solubility prediction: Application to sparingly soluble organic/inorganic materials.
The solubility of a crystalline material can be estimated from the absolute free energy of the solid and the excess solvation free energy. In the earlier work, we presented a general-purpose molecular-dynamics-based methodology enabling solubility predictions of crystalline compounds, yielding accurate estimates of the aqueous solubilities of naphthalene at various pressures and temperatures. In the present work, we investigate a number of prototypical complex materials, including phenanthrene, calcite, and aragonite over a range of temperatures and pressures. Our results provide stronger evidence for the power of the methodology for universal solubility predictions.BP International Centre for Advanced Materials (BP-ICAM
Is the Pale Blue Dot unique? Optimized photometric bands for identifying Earth-like exoplanets
The next generation of ground and space-based telescopes will image habitable
planets around nearby stars. A growing literature describes how to characterize
such planets with spectroscopy, but less consideration has been given to the
usefulness of planet colors. Here, we investigate whether potentially
Earth-like exoplanets could be identified using UV-visible-to-NIR wavelength
broadband photometry (350-1000 nm). Specifically, we calculate optimal
photometric bins for identifying an exo-Earth and distinguishing it from
uninhabitable planets including both Solar System objects and model exoplanets.
The color of some hypothetical exoplanets - particularly icy terrestrial worlds
with thick atmospheres - is similar to Earth's because of Rayleigh scattering
in the blue region of the spectrum. Nevertheless, subtle features in Earth's
reflectance spectrum appear to be unique. In particular, Earth's reflectance
spectrum has a 'U-shape' unlike all our hypothetical, uninhabitable planets.
This shape is partly biogenic because O2-rich, oxidizing air is transparent to
sunlight, allowing prominent Rayleigh scattering, while ozone absorbs visible
light, creating the bottom of the 'U'. Whether such uniqueness has practical
utility depends on observational noise. If observations are photon limited or
dominated by astrophysical sources (zodiacal light or imperfect starlight
suppression), then the use of broadband visible wavelength photometry to
identify Earth twins has little practical advantage over obtaining detailed
spectra. However, if observations are dominated by dark current then optimized
photometry could greatly assist preliminary characterization. We also calculate
the optimal photometric bins for identifying extrasolar Archean Earths, and
find that the Archean Earth is more difficult to unambiguously identify than a
modern Earth twin.Comment: 10 figures, 38 page
Robert Burns Woodward
This poster for the Natural Sciences Poster Session at Parkland College features chemist Robert Burns Woodward (1917-1979). Woodward was awarded the Nobel Prize in Chemistry in 1965 for his work on organic synthesis. His work on total synthesis includes cholesterol, chlorophyll, colchicine, erythromycin, reserpine, and vitamin B12
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