26 research outputs found
Vibrational Signatures in the THz Spectrum of 1,3-DNB: A First-Principles and Experimental Study
Understanding the fundamental processes of light-matter interaction is
important for detection of explosives and other energetic materials, which are
active in the infrared and terahertz (THz) region. We report a comprehensive
study on electronic and vibrational lattice properties of structurally similar
1,3-dinitrobenzene (1,3- DNB) crystals through first-principles electronic
structure calculations and THz spectroscopy measurements on polycrystalline
samples. Starting from reported x-ray crystal structures, we use
density-functional theory (DFT) with periodic boundary conditions to optimize
the structures and perform linear response calculations of the vibrational
properties at zero phonon momentum. The theoretically identified normal modes
agree qualitatively with those obtained experimentally in a frequency range up
to 2.5 THz and quantitatively at much higher frequencies. The latter
frequencies are set by intra-molecular forces. Our results suggest that van der
Waals dispersion forces need to be included to improve the agreement between
theory and experiment in the THz region, which is dominated by intermolecular
modes and sensitive to details in the DFT calculation. An improved comparison
is needed to assess and distinguish between intra- and intermolecular
vibrational modes characteristic of energetic materials.Comment: 5 pages, 5 figure
trans-DiaquaÂbis(2,2′-bipyridine-Îş2 N,N′)ruthenium(II) bisÂ(trifluoroÂmethaneÂsulfonate)
The title compound, trans-[Ru(bpy)2(H2O)2](CF3SO3)2 (bpy = 2,2′-bipyridine, C10H8N2), crystallized from the decomposition of an aged aqueous solution of a dimeric complex of cis-Ru(bpy)2 in 0.1 M triflic acid. The RuII ion is located on a crystallographic inversion center and exhibits a distorted octaÂhedral coordination with equivalent ligands trans to each other. The Ru—O distance is 2.1053 (16) Å and the Ru—N distances are 2.0727 (17) and 2.0739 (17) Å. The bpy ligands are bent, due to inter-ligand steric interÂactions between H atoms of opposite pyridyl units across the Ru center. The crystal structure exhibits an extensive hydrogen-bonding network involving the water ligands and the trifluoromethaneÂsulfonate counter-ions within two-dimensional layers, although no close hydrogen-bond interÂactions exist between different layers
Ultrafast Radiographic Imaging and Tracking: An overview of instruments, methods, data, and applications
Ultrafast radiographic imaging and tracking (U-RadIT) use state-of-the-art
ionizing particle and light sources to experimentally study sub-nanosecond
dynamic processes in physics, chemistry, biology, geology, materials science
and other fields. These processes, fundamental to nuclear fusion energy,
advanced manufacturing, green transportation and others, often involve one mole
or more atoms, and thus are challenging to compute by using the first
principles of quantum physics or other forward models. One of the central
problems in U-RadIT is to optimize information yield through, e.g.
high-luminosity X-ray and particle sources, efficient imaging and tracking
detectors, novel methods to collect data, and large-bandwidth online and
offline data processing, regulated by the underlying physics, statistics, and
computing power. We review and highlight recent progress in: a.) Detectors; b.)
U-RadIT modalities; c.) Data and algorithms; and d.) Applications.
Hardware-centric approaches to U-RadIT optimization are constrained by detector
material properties, low signal-to-noise ratio, high cost and long development
cycles of critical hardware components such as ASICs. Interpretation of
experimental data, including comparisons with forward models, is frequently
hindered by sparse measurements, model and measurement uncertainties, and
noise. Alternatively, U-RadIT makes increasing use of data science and machine
learning algorithms, including experimental implementations of compressed
sensing. Machine learning and artificial intelligence approaches, refined by
physics and materials information, may also contribute significantly to data
interpretation, uncertainty quantification and U-RadIT optimization.Comment: 51 pages, 31 figures; Overview of ultrafast radiographic imaging and
tracking as a part of ULITIMA 2023 conference, Mar. 13-16,2023, Menlo Park,
CA, US