960 research outputs found
Generation and structural characterization of Ge carbides GeCn ( n = 4, 5, 6) by laser ablation, broadband rotational spectroscopy, and quantum chemistry
International audienc
The Open MatSci ML Toolkit: A Flexible Framework for Machine Learning in Materials Science
We present the Open MatSci ML Toolkit: a flexible, self-contained, and
scalable Python-based framework to apply deep learning models and methods on
scientific data with a specific focus on materials science and the OpenCatalyst
Dataset. Our toolkit provides: 1. A scalable machine learning workflow for
materials science leveraging PyTorch Lightning, which enables seamless scaling
across different computation capabilities (laptop, server, cluster) and
hardware platforms (CPU, GPU, XPU). 2. Deep Graph Library (DGL) support for
rapid graph neural network prototyping and development. By publishing and
sharing this toolkit with the research community via open-source release, we
hope to: 1. Lower the entry barrier for new machine learning researchers and
practitioners that want to get started with the OpenCatalyst dataset, which
presently comprises the largest computational materials science dataset. 2.
Enable the scientific community to apply advanced machine learning tools to
high-impact scientific challenges, such as modeling of materials behavior for
clean energy applications. We demonstrate the capabilities of our framework by
enabling three new equivariant neural network models for multiple OpenCatalyst
tasks and arrive at promising results for compute scaling and model
performance.Comment: Paper accompanying Open-Source Software from
https://github.com/IntelLabs/matscim
Vibrational Satellites of CS, CS, and CS: Microwave Spectral Taxonomy as a Stepping Stone to the Millimeter-Wave Band
We present a microwave spectral taxonomy study of several hydrocarbon/CS
discharge mixtures in which more than 60 distinct chemical species, their more
abundant isotopic species, and/or their vibrationally excited states were
detected using chirped-pulse and cavity Fourier-transform microwave
spectroscopies. Taken together, in excess of 85 unique variants were detected,
including several new isotopic species and more than 25 new vibrationally
excited states of CS, CS, and CS, which have been assigned on the
basis of published vibration-rotation interaction constants for CS, or
newly calculated ones for CS and CS. On the basis of these precise,
low-frequency measurements, several vibrationally exited states of CS and
CS were subsequently identified in archival millimeter-wave data in the
253--280 GHz frequency range, ultimately providing highly accurate catalogs for
astronomical searches. As part of this work, formation pathways of the two
smaller carbon-sulfur chains were investigated using C isotopic
spectroscopy, as was their vibrational excitation. The present study
illustrates the utility of microwave spectral taxonomy as a tool for complex
mixture analysis, and as a powerful and convenient `stepping stone' to higher
frequency measurements in the millimeter and submillimeter bands.Comment: Accepted in PCC
Implementation of Rare Isotopologues into Machine Learning of the Chemical Inventory of the Solar-Type Protostellar Source IRAS 16293-2422
Machine learning techniques have been previously used to model and predict
column densities in the TMC-1 dark molecular cloud. In interstellar sources
further along the path of star formation, such as those where a protostar
itself has been formed, the chemistry is known to be drastically different from
that of largely quiescent dark clouds. To that end, we have tested the ability
of various machine learning models to fit the column densities of the molecules
detected in source B of the Class 0 protostellar binary IRAS 16293-2422. By
including a simple encoding of isotopic composition in our molecular feature
vectors, we also examine for the first time how well these models can replicate
the isotopic ratios. Finally, we report the predicted column densities of the
chemically relevant molecules that may be excellent targets for
radioastronomical detection in IRAS 16293-2422B.Comment: Accepted for publication in Digital Discovery. 18 pages, 8 figures, 5
table
HSCO and DSCO: a multi-technique approach in the laboratory for the spectroscopy of interstellar ions
Protonated molecular species have been proven to be abundant in the
interstellar gas. This class of molecules is also pivotal for the determination
of important physical parameters for the ISM evolution (e.g. gas ionisation
fraction) or as tracers of non-polar, hence not directly observable, species.
The identification of these molecular species through radioastronomical
observations is directly linked to a precise laboratory spectral
characterisation. The goal of the present work is to extend the laboratory
measurements of the pure rotational spectrum of the ground electronic state of
protonated carbonyl sulfide (HSCO) and its deuterium substituted isotopomer
(DSCO). At the same time, we show how implementing different laboratory
techniques allows the determination of different spectroscopical properties of
asymmetric-top protonated species. Three different high-resolution experiments
were involved to detected for the first time the type rotational spectrum
of HSCO, and to extend, well into the sub-millimeter region, the type
spectrum of the same molecular species and DSCO. The electronic
ground-state of both ions have been investigated in the 273-405 GHz frequency
range, allowing the detection of 60 and 50 new rotational transitions for
HSCO and DSCO, respectively. The combination of our new measurements
with the three rotational transitions previously observed in the microwave
region permits the rest frequencies of the astronomically most relevant
transitions to be predicted to better than 100 kHz for both HSCO and
DSCO up to 500 GHz, equivalent to better than 60 m/s in terms of equivalent
radial velocity. The present work illustrates the importance of using different
laboratory techniques to spectroscopically characterise a protonated species at
high frequency, and how a similar approach can be adopted when dealing with
reactive species.Comment: 7 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
Explaining the Chemical Inventory of Orion KL through Machine Learning
The interplay of the chemistry and physics that exists within astrochemically
relevant sources can only be fully appreciated if we can gain a holistic
understanding of their chemical inventories. Previous work by Lee et al. (2021)
demonstrated the capabilities of simple regression models to reproduce the
abundances of the chemical inventory of the Taurus Molecular Cloud 1 (TMC-1),
as well as provide abundance predictions for new candidate molecules. It
remains to be seen, however, to what degree TMC-1 is a ``unicorn'' in
astrochemistry, where the simplicity of its chemistry and physics readily
facilitates characterization with simple machine learning models. Here we
present an extension in chemical complexity to a heavily studied high-mass star
forming region: the Orion Kleinmann-Low (Orion KL) nebula. Unlike TMC-1, Orion
KL is composed of several structurally distinct environments that differ
chemically and kinematically, wherein the column densities of molecules between
these components can have non-linear correlations that cause the unexpected
appearance or even lack of likely species in various environments. This
proof-of-concept study used similar regression models sampled by Lee et al.
(2021) to accurately reproduce the column densities from the XCLASS fitting
program presented in Crockett et al. (2014).Comment: 14 pages; 6 figures, 1 table in the main text. 0 figures, 1 table in
the appendix. Accepted for publication in The Astrophysical Journal.
Molecular dataset for machine learning can be found in the Zenodo repository
here: https://zenodo.org/record/767560
A rotational and vibrational investigation of phenylpropiolonitrile (CHCN)
The evidence for benzonitrile (CHCN}) in the starless cloud core
TMC-1 makes high-resolution studies of other aromatic nitriles and their
ring-chain derivatives especially timely. One such species is
phenylpropiolonitrile (3-phenyl-2-propynenitrile, CHCN), whose
spectroscopic characterization is reported here for the first time. The low
resolution (0.5 cm) vibrational spectrum of CHCN} has been
recorded at far- and mid-infrared wavelengths (50 - 3500 cm) using a
Fourier Transform interferometer, allowing for the assignment of band centers
of 14 fundamental vibrational bands. The pure rotational spectrum of the
species has been investigated using a chirped-pulse Fourier transform microwave
(FTMW) spectrometer (6 - 18 GHz), a cavity enhanced FTMW instrument (6 - 20
GHz), and a millimeter-wave one (75 - 100 GHz, 140 - 214 GHz). Through the
assignment of more than 6200 lines, accurate ground state spectroscopic
constants (rotational, centrifugal distortion up to octics, and nuclear
quadrupole hyperfine constants) have been derived from our measurements, with a
plausible prediction of the weaker bands through calculations. Interstellar
searches for this highly polar species can now be undertaken with confidence
since the astronomically most interesting radio lines have either been measured
or can be calculated to very high accuracy below 300 GHz.Comment: 7 figures, 4 tables. Accepted for publication in J. Mol. Spe
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