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At least 1,171 records · Page 65

Muon Creation in Supernova Matter Facilitates Neutrino-Driven Explosions

Muons can be created in nascent neutron stars (NSs) due to the high electron chemical potentials and the high temperatures. Because of their relatively lower abundance compared to electrons, their role has so far been ignored in numerical simulations of stellar core collapse and NS formation. However, the appearance of muons softens the NS equation of state, triggers faster NS contraction, and thus leads to higher luminosities and mean energies of the emitted neutrinos. This strengthens the postshock heating by neutrinos and can facilitate explosions by the neutrino-driven mechanism.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Tensorized Feature Spaces for Feature Explosion

In this paper 1 1 This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-000R22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan) This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-000R22725., we present a novel framework that uses tensor factorization to generate richer feature spaces for pixel classification in hyperspectral images. In particular, we assess the performance of different tensor rank decomposition methods as compared to the traditional kernel-based approaches for the hyperspectral image classification problem. We propose Orion, which takes as input a hyperspectral image tensor and a rank and outputs an enhanced feature space from the factor matrices of the decomposed tensor. Our method is a feature explosion technique that inherently maps low dimensional input space in $\mathbb{R}^{K}$ to high dimensional space in $\mathbb{R}^{R}$ , where $R\gg K$ , say in the order of 1000x, like a kernel. We show how the proposed method exploits the multi-linear structure of hyperspectral three dimensional tensor. We demonstrate the effectiveness of our method with experiments on three publicly available hyperspectral datasets with labeled pixels and compare their classification performance against traditional linear and non-linear supervised learning methods such as SVM with Linear, Polynomial, RBF kernels, and the Multi-Layer Perceptron model. Finally, we explore the relationship between the rank of the tensor decomposition and the classification accuracy using several hyperspectral datasets with ground truth.

Pasricha, Ravdeep Singh↗

Deep Koopman Neural Network for Analyzing High-Energy-Density Simulations of Electrical Wire Explosions

Megaampere-scale electrical wire experiments (EWEs) provide a platform for studying magnetohydrodynamic (MHD) instability growth in magneto-inertial fusion (MIF) devices. Even when nonlinear simulations of these experiments can digitally reproduce much of the experimentally observed instability growth, interpreting the results and understanding mode growth and evolution can be non-trivial. As a first step toward providing better interpretation of these simulation features, this work investigates the use of a deep neural network that uses Koopman operator theory to analyze the dynamics of pulsed-power-driven explosions of EWEs. This deep neural network is trained on 1-D resistive MHD simulations of EWEs. This neural network learns to transform the nonlinear data into a lower-dimensional representation where the time dynamics are linear. Layers of this neural network are shown to learn features of the simulations, including the locations of shock waves and different physical regimes of the simulation. Using the learned features, the network can compress a time state of the simulation consisting of 5120 data point into a 36-parameter lower-dimensional latent space embedding. Furthermore, these embeddings are shown to be clustered in the latent space by initial radius and time state.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Characterization and differentiation of aluminum powders used in improvised explosive devices. Part 2: Micromorphometric method refinement and preliminary statistical analysis

Abstract Aluminum (Al) powder is commonly encountered in improvised explosive devices (IEDs) as a metallic fuel due to its availability and low cost. Although available commercially in powder form, amateur bomb‐makers also produce their own Al powder via simple methods found online. In order to provide investigative leads and forensic intelligence, it is important to evaluate not only the composition of homemade devices, but also to distinguish between the various forms of Al powder they contain. To achieve this goal, a method using automated microscopy in combination with statistical techniques has been demonstrated to have the potential to provide source discrimination and investigative leads in source attribution of Al powders in IEDs. The present research refined this method and investigated 59 industrially and amateurly produced Al powder sources with seven subsamples per source using two traditional linear discriminant analyses (LDA), one with a standard data split for training and testing, and another using leave‐one‐out cross‐validation. Averaging the classification accuracies for the two LDA‐based analyses, LDA has the ability to correctly classify 59.26%, 83.35%, and 80.69% of the samples based on their powder source, type, and production method, respectively. This classification accuracy represents a 3407%, 317%, and 61.38% increase in accuracy from random class assignment, respectively. Further, in most instances of incorrect data attribution to a particular source, the subsample has been misidentified with another sample of the same powder type or production method.

Ommen, Danica M.↗

Early Time Evolution of Circumferential Perturbation of Initial Particle Volume Fraction in Explosive Cylindrical Multiphase Dispersion

When an annular bed of solid particles that surrounds a cylindrical high-energy explosive core gets radially dispersed after detonation, the expanding front of particles undergoes instabilities. One of the possible causes of the instabilities is an inhomogeneous initial distribution of particles. This study explores this possibility by introducing two-dimensional perturbations to the initial distribution of particles within the annular bed and quantifying the growth of these perturbations over time using two-dimensional simulations. The initial perturbations are in the form of superposition of up to three sinusoidal azimuthal modal variations in the initial particle volume fraction (PVF, ratio of particle to cell volume). These are observed to impact the particle distribution at later times through a channeling instability whose effects are: (i) to decrease the velocity in regions of larger particle volume (PV) and (ii) to facilitate circumferential particle migration into the slow moving high PV sectors. These departures from axisymmetry are quantified by introducing two metrics. The effect of varying the number of azimuthal modes contained in the initial PVF perturbation, along with their amplitudes, wavelengths, and relative phases is investigated. The proposed metrics do not vary substantially with the relative phases; however, there is a strong variation in the metrics due to changes in the wavenumber. Unimodal perturbations were found to amplify both metrics the most.

Engineering↗

Infrared Scattering Scanning Near-Field Optical Microscopy Using An External Cavity Quantum Cascade Laser For Nanoscale Chemical Imaging And Spectroscopy of Explosive Residues

Infrared scattering scanning near-field optical microscopy (s-SNOM) is an apertureless superfocusing technique that uses the antenna properties of a conducting atomic force microscope (AFM) tip to achieve infrared spatial resolution below the diffraction limit. The instrument can be used either in imaging mode, where a fixed wavelength light source is tuned to a molecular resonance and the AFM raster scans an image, or in spectroscopy mode where the AFM is held stationary over a feature of interest and the light frequency is varied to obtain a spectrum. In either case, a strong, stable, coherent infrared source is required. Here we demonstrate the integration of a broadly tunable external cavity quantum cascade laser (ECQCL) into an s-SNOM and use it to obtain infrared spectra of microcrystals of chemicals adsorbed onto gold substrates. Residues of the explosive compound tetryl was deposited onto gold substrates. s-SNOM experiments were performed in the 1260-1400 cm-1 tuning range of the ECQCL, corresponding to the NO2 symmetric stretch vibrational fingerprint region. Vibrational infrared spectra were collected on individual chemical domains with a collection area of *500nm2 and compared to ensemble averaged far-field reflection-absorption infrared spectroscopy (RAIRS) results.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Simulations of the Stable Expansion of a Monoelement Three-Component Explosive-Emission Plasma

The results of numerical simulations of the stable expansion stage of a micro explosive plasma plume are presented. A three-liquid hydrodynamic model was used with corrections allowing its application to the consistent description of the transfer of particles in a monoelement plasma with ions with two different charges and of the electron transfer in a changing plasma–collector vacuum gap. The evolution of concentration profiles, the drift velocity, and electron and ion temperatures in plasma are analyzed depending on conditions of a collector. It is shown in the model that the velocity separation of ions with different charges occurs efficiently in the absence of an external electric field, whereas in a current-carrying plasma, the ions with different charges move with almost identical velocities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Magic ultramagnetized nuclei in explosive nucleosynthesis

Direct evidence of the presence of {sup 44}Ti and content of the isotope in the supernova remnant Cassiopeia A are obtained from the analysis of gamma-ray spectrum of the remnant. A significant excess of observational {sup 44}Ti volume on predictions of supernova models can be explained as the magnetization effect in the process of explosive nucleosynthesis. The formation of chemical elements is considered accounting for superstrong magnetic fields predicted for supernovae and neutron stars. Using the arguments of nuclear statistical equilibrium, a significant effect of magnetic field on the nuclear shell energy is demonstrated. The magnetic shift of the most tightly 'bound' nuclei from the transition metals of iron series to titanium leads to an exponential increase in the portion of {sup 44}Ti and, accordingly to a significant excess of the yield of these products of nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Supernova-Explosion Mechanism Involving Neutrinos

A major part of the energy released upon the gravitational collapse of massive-star cores is carried away by neutrinos. Neutrinos play a crucial role in collapsing supernovae (SNe). At the present time, mathematical models of core-collapse SNe are based on multidimensional gas dynamics and thermonuclear reactions, whereas the neutrino transport is frequently treated in simplified way. An accurate analysis of neutrinos in a spherically symmetric gravitational collapse is performed on the basis of Boltzmann kinetic equations including all weak-interaction reactions with exact quantum-mechanical matrix elements. The role of multidimensional effects is studied bymeans of multidimensional gas dynamics allowing for the neutrino transport via diffusion treated by employing flux limiters. The possibility of largescale convection, which is of interest both from the point of view of explaining a type II supernova (SN) and from the point of view of implementing an experiment aimed at detecting possible energetic (≳10 MeV) neutrinos from an SN, is discussed. Thermonuclear burning leads to the explosion of a type I SN. A hot central region and the subsequent large-scale convection may also play an important role in the SN mechanism. If neutrinos and convection play a key role for a type II SN, then, in order to explain gamma radiation from product radioactive elements, convection is of importance in the case of SNe belonging to both types. In addition, convection may be important for bright type I SNe. Original methods are presented for multidimensional gas dynamics involving thermonuclear burning and for multitemperature gas dynamics involving radiative transfer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Experimental Detection of the Signs of a Coulomb Explosion in Micropinch Plasma

A flow of ions with energies of about 3 MeV propagating in the direction perpendicular to the symmetry axis of discharge has been detected in high-current low inductance vacuum spark. Estimations show that the measured ion energies quite well correspond to the value that can be achieved as a result of “Coulomb explosion” of the waist of a plasma channel of discharge current at the stage preceding its radiation compression.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Explosive Ice Multiplication Induced by Multiplicative-Noise Fluctuation of Mechanical Breakup in Ice–Ice Collisions

The number of ice fragments generated by breakup of large graupel in collisions with small graupel fluctuates randomly owing to fluctuations in relative sizes and densities of colliding graupel particles and the stochastic nature of fracture propagation. This paper investigates the impact of the stochasticity of breakup on ice multiplication. When both the rate of generation of primary ice and the initial number concentration of ice crystals are low, the system most likely loses all the initial ice and graupel owing to a lack of sustaining sources. Even randomness does not change this mean evolution of the system in its phase space. However, a fluctuation of ice breakup number gives a small but finite chance that substantial ice crystal fragments are generated by breakup of large graupel. That, in turn, generates more large graupel. This multiplicative process due to fluctuations potentially leads to a small but finite chance of explosive growth of ice number.A rigorous stochastic analysis demonstrates this point quantitatively. The randomness considered here belongs to a particular category called ‘‘multiplicative’’ noise, because the noise amplitude is proportional to a given physical state. To contrast the multiplicative-noise nature of ice breakup with a standard ‘‘additive’’ noise process, fluctuation of the primary ice generation rate is also considered as an example of the latter. These processes are examined by taking the Fokker–Planck equation that explicitly describes the evolution of the probability distribution with time. As an important conclusion, stability in the phase space of the cloud microphysical system of breakup in ice–ice collisions is substantially altered by the multiplicative noise.

54 ENVIRONMENTAL SCIENCES↗

Growing Pacific Linkage with Western North Atlantic Explosive Cyclogenesis

Abstract Explosive cyclones (ECs), defined as extratropical cyclones that experience normalized pressure drops of at least 24 hPa in 24 h, are impactful weather events in the North Atlantic sector, but year-to-year changes in the frequency and impacts of these storms are sizeable. To analyze the sources of this interannual variability, we track cases of ECs and dissect them into two spatial groups: those that formed near the east coast of North America (coastal) and those in the north central Atlantic (high latitude). The frequency of high-latitude ECs is strongly correlated with the North Atlantic Oscillation, a well-known feature, whereas coastal EC frequency is statistically linked with an atmospheric wave train emanating from the North Pacific in the last 30 years. This wave train pattern of alternating high and low pressure is associated with heightened upper-level divergence and Eady growth rates along the east coast of North America, likely resulting in a stronger correspondence between the atmospheric wave train and coastal EC frequency. Using coupled model experiments, we show that the tropical and North Pacific oceans are an important factor for this atmospheric wave train and the subsequent enhancement of seasonal baroclinicity in the North Atlantic.

58 GEOSCIENCES↗

Polymorphic Phase Control of RDX-Based Explosives

The polymorphic phase of 1,3,5-trinitro-1,3,5-triazine (RDX) was examined as a function of mass loading, solvent, and sample deposition technique. When RDX was deposited at a high mass loading, the vibrational modes in the obtained Raman spectra were indicative of concomitant polymorphism as both the α-RDX and β-RDX phases were present. At low mass loadings, only β-RDX was observed regardless of solvent when using the drop cast crystallization method. However, α-RDX (the thermodynamically stable polymorphic phase observed with visible quantities of the explosive) was observed when RDX deposits were dry transferred. Observation of α-RDX was independent of the initial mass loading or the initial deposition solvent when using the dry transfer methodology. These data indicate that the use of the dry transfer preparation method can be used to successfully prepare RDX-based test articles with the α-RDX phase regardless of the solvent used to initially dissolve the RDX, the initial deposition technique, or the mass loading.

Brady, John J.↗

Exascale models of stellar explosions: Quintessential multi-physics simulation

The ExaStar project aims to deliver an efficient, versatile, and portable software ecosystem for multi-physics astrophysics simulations run on exascale machines. The code suite is a component-based multi-physics toolkit, built on the capabilities of current simulation codes (in particular Flash-X and Castro), and based on the massively parallel adaptive mesh refinement framework AMReX. It includes modules for hydrodynamics, advanced radiation transport, thermonuclear kinetics, and nuclear microphysics. The code will reach exascale efficiency by building upon current multi- and many-core packages integrated into an orchestration system that uses a combination of configuration tools, code translators, and a domain-specific asynchronous runtime to manage performance across a range of platform architectures. The target science includes multi-physics simulations of astrophysical explosions (such as supernovae and neutron star mergers) to understand the cosmic origin of the elements and the fundamental physics of matter and neutrinos under extreme conditions.

79 ASTRONOMY AND ASTROPHYSICS↗

Infrared near-field spectroscopy of trace explosives using an external cavity quantum cascade laser

Utilizing a broadly-tunable external cavity quantum cascade laser for scattering-type scanning near-field optical microscopy (s-SNOM), we measure infrared spectra of explosives particles by probing characteristic nitro-group resonances in the 7.1-7.9 µm wavelength range. Measurements are presented with spectral resolution of 0.25 cm-1, spatial resolution of 25 nm, <100 attomolar sensitivity, and at a rapid acquisition time of 90 s per spectrum. We demonstrate high reproducibility of the acquired s-SNOM spectra with very high signal-to-noise ratios and relative noise of <0.02 in self-homodyne detection.

(140.5965) Semiconductor lasers, quantum cascade↗

PoroTomo: Horizontal Distributed Acoustic Sensing (DAS) Measurements During an M 2.3 Explosion

Included here are Distributed Acoustic Sensing (DAS) data collected by the horizontal DAS array at Brady's Hot Springs Geothermal Field. The system recorded this data during an M 2.3 explosion at the Nevada Test Site (NTS), which is located approximately 400km southeast of the field. On December 19, 2018, a Silixa iDAS interrogator continuously acquired data on single-mode fibers, starting approximately two hours prior to the detonation and extending until 15 minutes after the event. This dataset comprises separate SEG-Y files that span the entire recording interval. The measurement fiber was part of the PoroTomo experiment and is horizontally emplaced in alluvial fan gravels at a depth of approximately one meter for a distance of more than 2.5 km in a zig-zag pattern. Exact coordinates of this DAS surface array are provided in the attached GDR dataset below. The iDAS interrogator channel spacing is 1.021 m and gauge length is 10 m. Concurrent Distributed Temperature Sensing (DTS) measurements made with a Silixa XT on the multi-mode fibers aided in calibrating the DAS measurements.

15 GEOTHERMAL ENERGY↗