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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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An R-matrix analysis of the old high energy resolution experimental data [4, 5] in the excitation region of 11.7–13.78 MeV of 22 Ne was performed.
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Image plates (IPs) are a quickly recoverable and reusable radiation detector often used to measure proton and x-ray fluence in laser-driven experiments. Recently, IPs have been used in a proton radiography detector stack on the OMEGA laser, a diagnostic historically implemented with CR-39, or radiochromic film. The IPs used in this and other diagnostics detect charged particles, neutrons, and x-rays indiscriminately. IPs detect radiation using a photo-stimulated luminescence (PSL) material, often phosphor, in which electrons are excited to metastable states by ionizing radiation. Protons at MeV energies deposit energy deeper into the IP compared with x rays below ∼20 keV due to the Bragg peak present for protons. This property is exploited to discriminate between radiation types. Doses of mono-energetic protons between 1.7 and 14 MeV are applied to IPs using the MIT linear electrostatic ion accelerator. This paper presents the results from consecutive scans of IPs irradiated with different proton energies. The PSL ratios between subsequent scans are shown to depend on proton energy, with higher energy protons having lower PSL ratios for each scan. This finding is separate from the known energy dependence in the absolute sensitivity of IPs. The results can be compared to complimentary work on x rays, showing a difference between protons and x rays, forging a path to discriminate between proton and x-ray fluence in mixed radiation environments.
Magnetic tunnel junctions (MTJs) can integrate novel single molecular device elements to overcome long-standing fabrication challenges, thus unlocking their novel potential. This study employs magnetic force microscopy (MFM) to demonstrate that organometallic molecules, when placed between two ferromagnetic electrodes along cross-junction shaped MTJ edges, dramatically altered the magnetic properties of the electrodes, affecting areas several hundred microns in size around the molecular junction vicinity at room temperature. These findings are supported by magnetic resonance and magnetometer studies on ∼7000 MTJ pillars. MFM on the pillar sample showed an almost complete disappearance of the magnetic contrast. The spatial magnetic image suggests that molecular channels significantly impacted the spin density of states in the ferromagnetic electrodes. This advancement in MTJ-based molecular devices paves the way for a new generation of commercially viable logic and memory devices controlled by molecular quantum states at near-room temperatures.
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Thin membrane-delimited fluid cells supporting up to 1 at (0.1 MPa) of pressure are well known and commercially available for use in vacuum chambers of electron, photon, or various particle beam microscopies or spectroscopies. Hereby, we report on the development of fluid cells capable of working at 1–10 MPa, extending the analysis domain for investigating chemical, biochemical, or physical processes at pressures of interest in chemical synthesis, underwater biochemistry studies or underground geology. We explored ways to optimize cell membranes to better resist pressure beyond simply increasing the thickness or decreasing the size of the membranes, using finite element analysis and experimental validation via membrane bulging experiments and failure statistics. Fluid cell prototypes were fabricated using ∼75 nm-thick SiN x membranes, engineered to withstand 4.7 MPa (average value), compared to regular (un-engineered) membranes withstanding only 3.4 MPa (average value). The fluid cell prototypes include eight microchannels for feeding/evacuating the fluids and applying pressure into micro-reaction chambers, two electrodes for electrochemical or conduction measurements in the sample, and a possible pressure or temperature sensor, customizable for specific experiments.
Ion cyclotron emission (ICE) driven by fast ions has the potential to be a reactor relevant diagnostic of confined and escaping fast ions; moreover, controlled experiments in magnetic fusion devices can shed light on similar magnetospheric instabilities below and above the ion cyclotron frequency f ci . Dedicated DIII-D experiments studied instabilities below f ci and at cyclotron harmonics l f ci by injecting thirteen different neutral beam populations into plasmas with different thermal compositions of H, D, and 3He at five different values of toroidal field. High-frequency magnetic loops diagnose mode properties. Each beam type is individually injected for an approximate slowing-down time (~100 ms), resulting in a database of 2529 conditions that are analyzed in frequency bands corresponding to ICE harmonics and < f ci global Alfvén eigenmodes. The sub-cyclotron modes are more unstable at low field and in plasmas with large H concentration. For D injection, first harmonic ICE at f cD is more unstable in hydrogen plasmas but, for H injection, the converse is true (ICE at f cH is more unstable in D), suggesting that thermal same-species ions damp fundamental ICE. ICE stability also depends upon the pitch-angle anisotropy gradient and upon the ‘bump-on-tail’ gradient ∂f/∂v. Although the frequency of unstable ICE in these plasmas always occurs near the central cyclotron frequency, the precise value also depends on the Alfvén speed and beam direction, consistent with the idea that instability occurs for modes that simultaneously satisfy ω ≃ 2πlf ci , the magnetosonic dispersion relation, and the Doppler-shifted resonance condition.
Dedicated DIII-D experiments studied instabilities below the ion cyclotron frequency f ci and at cyclotron harmonics by injecting thirteen different neutral beam populations into plasmas with different thermal compositions of H and D at five different values of toroidal field. The resulting database of 2529 conditions is described in Part 1: Stability. This paper focuses on the temporal evolution. For some beam geometries, the ion cyclotron emission (ICE) is much stronger at the beginning of injection, suggesting the importance of ‘bump-on-tail’ energy drive. Sawtooth crashes cause the emission to cease for some beam types and emission bands, but the opposite effect occurs for others. When unstable, for virtually all conditions and frequency bands, the emission bursts in a cycle reminiscent of predator-prey oscillations. Evidence for nonlinear interaction between ICE harmonics is observed. Strongly unstable modes typically appear within 1 ms from the start of beam injection and often decay within 0.1 ms when the beam turns off, but both the initial rise and final decay of the mode power exhibit a wide variety of behavior.
Dedicated DIII-D experiments studied instabilities above and below the ion cyclotron frequency by injecting thirteen different neutral beam populations into L-mode plasmas with different thermal compositions of H, D, and 3 He at five different values of toroidal field. Two companion papers describe the results of these experiments in detail. This paper focuses on data and analysis of two instabilities that occur at ${\sim}0.6$ of the deuterium and hydrogen cyclotron frequencies $f_\mathrm {cD}$ and $f_\mathrm {cH}$ in mixed hydrogen and deuterium plasmas. The modes below $f_\mathrm {cD}$ are often driven unstable by deuterium beams but are rarely destabilized by hydrogen beams. The modes below $f_\mathrm {CD}$ are reported here for the first time in a fusion plasma. These $\mathrm{sub-}f_\mathrm {cH}$ modes are only driven by deuterium beams but, unlike the $\mathrm{sub-}f_\mathrm {cD}$ modes, they are only unstable in plasmas with deuterium concentrations that are ${\lesssim}20\%$; they also have a smaller amplitude than the sub-deuterium modes. Addition of fully-ionized 3 He to the plasma has little effect on the sub-cyclotron deuterium modes but is stabilizing for the sub-cyclotron hydrogen modes. The modes are excited in the core and have toroidal mode numbers around 20. These trends are compared with calculations of the growth rate in a simplified model. The theory successfully predicts global Alfvén eigenmode instability with frequencies and mode numbers close to experimental values, the stronger amplitude of the sub-deuterium modes, and the species-mix dependence of the sub-hydrogen modes. Increased damping associated with the ion-ion hybrid, cutoff, and crossover frequencies plausibly accounts for the stabilization of the $\mathrm{sub-}f_\mathrm {cH}$ modes when 3 He is puffed. However, the relative stability of $\mathrm{sub-}f_\mathrm {cH}$ modes during hydrogen injection remains unexplained.
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Red leaf blotch of soybean, caused by the fungus Coniothyrium glycines, is a foliar disease characterized by blotching, necrosis, and defoliation that has only been reported from Africa. The species is listed as a Select Agent by the Federal Select Agent Program due to its potentially devastating impacts to soybean production should it spread to the United States. Despite its potential import, very few isolates are available for study. Herein, we obtained 96 new C. glycines isolates from six soybean-producing countries throughout sub-Saharan Africa. Along with 12 previously collected ones, we sequenced each at the internal transcribed spacer (ITS) region. Between all isolates, we identified a total of 28 single-nucleotide polymorphisms and 23 haplotypes. One hypothesis to explain the tremendous diversity uncovered at the ITS—which is generally conserved within a species—is that our current species concept of C. glycines is too broad and that there may be multiple species that cause red leaf blotch. Zambia contained the highest haplotype diversity, a significant fraction of which remains unsampled. Most haplotypes were specific to a single country, except for two, which were found in Zambia and either neighboring Mozambique or Zimbabwe. This geographic specificity indicates that the ITS region may be useful for identifying source populations or routes of transmission should this pathogen spread beyond Africa. The observed geographic partitioning of this pathogen is likely the result of millions of years of replication on little-studied native hosts, given that soybean has only been cultivated in Africa since the early 1900s.
We use muon spin rotation/relaxation/resonance ( μ SR ) to investigate the magnetic properties of niobium pentoxide ( Nb 2 O 5 ) and tantalum pentoxide ( Ta 2 O 5 ) thin films. In both oxides, we observe a magnetic response at the lowest available temperature of 2.8 K. This response appears to be structurally dependent: thermally oxidized Ta 2 O 5 with low crystallinity demonstrates suppressed magnetism, while fully amorphous Ta 2 O 5 demonstrates local static magnetism. In contrast, amorphous Nb 2 O 5 is dominated by magnetic fluctuations and is strongly magnetically disordered compared to Ta 2 O 5 . Our results suggest that these fundamental differences in the magnetism of Ta and Nb oxides could explain the performance limitations in superconducting qubits and resonators.
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The recent discovery of unconventional surface-state pairs, which give rise to Fermi arcs and spin textures, in antiferromagnetically ordered rare-earth monopnictides attracted the interest in these materials. Here, we use angle-resolved photoemission spectroscopy measurements in conjunction with density functional theory calculations to investigate the evolution of the electronic structure of GdBi and DyBi. We find that new surface states, including a Dirac cone, emerge in the antiferromagnetic (AFM) state. However, they are located along a direction in momentum space that is different than what was found in NdSb, NdBi, and CeBi. The observed changes in the electronic structure are consistent with the presence of AFM-II-A type order.
Here, we present a comprehensive investigation of the intricate spin dynamics in the noncentrosymmetric compound Sm 7 Pd 3 , revealing the coexistence of spin-glass, domain-glass, and ferromagnetic (FM) behaviors. Magnetic field-dependent measurements indicate large coercivity, suggesting ferromagnetic domain formation below the Curie temperature (𝑇 C ≈ 173 K), while temperature-dependent magnetization data point to antiferromagnetic (AFM) coupling, highlighting the competition between FM and AFM interactions. Detailed ac susceptibility, isothermal remanent magnetization, and aging effect measurements demonstrate the presence of two distinct types of glassiness in the sample, and their possible origins are discussed extensively. Magnetization measurements reveal the mixing of the 𝐽 = 5/2 ground state of Sm 3+ with the excited 𝐽 = 7/2 multiplet, lying 965 K above. The specific heat data show further crystalline electric field splitting of the 𝐽 = 5/2 state into a ground-state doublet and a fourfold-degenerate excited state.
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