Data for figures in "Experimental study of Alfvén wave reflection from an Alfvén-speed gradient relevant to the solar coronal holes"
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Alfvén wave↗
Engineering topics
Hahn, Michael
Publications and source records attributed to Hahn, Michael.
Fundamental Studies in Basic Plasma Science: Experimental Investigations of Alfven Wave Damping Processes Relevant to the Solar Corona (Final Report)
Motivated by recent observations suggesting that the solar corona is heated by Alfvén wave damping at unexpectedly low heights, we performed experiments to study the basic plasma physics of Alfvén wave dissipation. Proposed coronal damping mechanisms rely on inhomogeneities in the plasma, but these theories have not been systematically studied in the laboratory. We performed experiments using the Large Plasma Device (LAPD) to test these theories.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Ion energy distribution in an electron beam ion trap inferred from simulations of the trapped ion cloud
For this work, we have inferred the energy distribution of trapped ions in an electron beam ion trap (EBIT) from simulations of the spatial distribution of Fe 13+ ions and a comparison with measured visible light images of the ion cloud. We simulated the cloud of Fe 13+ ions by computing ion trajectories in the EBIT for different ion energy distributions used to initialize the trajectories. We then performed a least-squares fit to infer the ion energy distribution that best reproduced the measured ion cloud. These best-fit distributions were typically non-Maxwellian. For electron beam energies of 395–475 eV and electron beam currents of 1–9 mA, we find that the average ion energy is in the range of 10–300 eV. We also find that the average ion energy increases with increasing beam current approximately as $\langle$E$\rangle$ ≈ 25 I e eV, where I e is the electron beam current in mA. We have also compared our results to Maxwell-Boltzmann-distribution ion clouds. We find that our best-fit non-thermal distributions have an $\langle$E$\rangle$ that is less than half that of the T from the best-fit Maxwell-Boltzmann distributions ($\langle$E$\rangle$/q)/T=0.41 ± 0.05.
74 ATOMIC AND MOLECULAR PHYSICS↗
International Meeting on Fuel Cell and Electrolyzer Quality Control: Summary Report
Quality control (QC) for both polymer electrolyte membrane fuel cell and electrolysis membrane electrode assembly (MEA) materials is a key challenge for scale-up and cost reduction. Developing methods for detecting defects, as well as measuring critical material properties and understanding the impact of as-manufactured variations in these materials on cell performance and lifetime, are critical barriers. To help address these needs, the National Research Council Canada (NRC), Fraunhofer Institute for Solar Energy Systems (ISE), and the National Renewable Energy Laboratory (NREL) have organized and facilitated a series of workshops on the topic, bringing together industry, academia, and research institutions from North America and Europe. Prior workshops in Canada and Germany have focused on the status of quality tool capabilities and identification of needed developments for fuel cells. These meetings have garnered an excellent response and follow-on attendance, with over 100 unique attendees.
30 DIRECT ENERGY CONVERSION↗
Roadmap on cosmic EUV and x-ray spectroscopy
Cosmic EUV/x-ray spectroscopists, including both solar and astrophysical analysts, have a wide range of high-resolution and high-sensitivity tools in use and a number of new facilities in development for launch. As this bandpass requires placing the spectrometer beyond the Earth’s atmosphere, each mission represents a major investment by a national space agency such as NASA, ESA, or JAXA, and more typically a collaboration between two or three. In general justifying new mission requires an improvement in capabilities of at least an order of magnitude, but the sensitivity of these existing missions are already taxing existing atomic data quantity and accuracy. This roadmap reviews the existing missions, showing how in a number of areas atomic data limits the science that can be performed. The missions that will be launched in the coming Decade will without doubt require both more and improved measurements of wavelengths and rates, along with theoretical calculations of collisional and radiative cross sections for a wide range of processes.
79 ASTRONOMY AND ASTROPHYSICS↗
Laboratory Calibrations of Fe xii–xiv Line-Intensity Ratios for Electron Density Diagnostics
In this work, we have used an electron beam ion trap to measure electron-density-diagnostic line-intensity ratios for extreme ultraviolet lines from Fe xii, xiii, and xiv at wavelengths of ≈185–205 and 255–276 Å. These ratios can be used as density diagnostics for astrophysical spectra and are especially relevant to solar physics. We found that density diagnostics using the Fe xiii 196.53/202.04 and the Fe xiv 264.79/274.21 and 270.52A/274.21 line ratios are reliable using the atomic data calculated with the Flexible Atomic Code (FAC). On the other hand, we found a large discrepancy between the FAC theory and experiment for the commonly used Fe xii (186.85 + 186.88)/195.12 line ratio. These FAC theory calculations give results similar to the data tabulated in CHIANTI, which are commonly used to analyze solar observations. Our results suggest that the discrepancies seen between solar coronal density measurements using the Fe xii (186.85 + 186.88)/195.12 and Fe xiii 196.54/202.04 line ratios are likely due to issues with the atomic calculations for Fe xii.
74 ATOMIC AND MOLECULAR PHYSICS↗
The Effect of Different Annealing Conditions on the Anisotropy of the Fracture Toughness of Ti-6Al-4V
The room-temperature tensile and fracture toughness properties of Ti-6Al-4V plate were tested to characterize the effect of rolling direction on the fracture toughness in two different heat treatment conditions. Optical and scanning electron microscopy was used to characterize the microstructure and fracture surfaces. It was found that beta annealing increased the fracture toughness compared to a mill annealed product in all three orientations relative to the rolling direction; however, it had minimal effects on strength and modulus. Ti-6Al-4V was found to be isotropic in fracture toughness, varying 0.48% in the beta annealed condition and 6.4% in the mill annealed condition.
36 MATERIALS SCIENCE↗
Measured Reduction in Alfvén Wave Energy Propagating through Longitudinal Gradients Scaled to Match Solar Coronal Holes
We have explored the effectiveness of a longitudinal gradient in Alfvén speed in reducing the energy of propagating Alfvén waves under conditions scaled to match solar coronal holes. The experiments were conducted in the Large Plasma Device at the University of California, Los Angeles. Our results show that the energy of the transmitted Alfvén wave decreases as the inhomogeneity parameter, λ/L A, increases. Here, λ is the wavelength of the Alfvén wave and L A is the scale length of the gradient in Alfvén speed. For gradients similar to those in coronal holes, the waves are observed to lose a factor of ≈5 more energy than they do when propagating through a uniform plasma without a gradient. Furthermore, we have carried out experiments and analyses to constrain the cause of wave energy reduction in the gradient. The loss of Alfvén wave energy from mode coupling is unlikely, as we have not detected any other modes. Contrary to theoretical expectations, the reduction in the energy of the transmitted wave is not accompanied by a detectable reflected wave. Nonlinear effects are ruled out because the amplitude of the initial wave is too small and the wave frequency well below the ion cyclotron frequency. Since the total energy must be conserved, it is possible that the lost wave energy is being deposited in the plasma. Further studies are needed to explore where the energy is going.
79 ASTRONOMY AND ASTROPHYSICS↗
The dual effect of tubulin manipulation on Populus wood formation and drought tolerance
The main objectives were to generate transgenic Populus with altered alpha- (TUA) and beta-tubulin (TUB) expression and/or post-translational modifications (PTMs) in a plant-wide, guard cell-specific or xylem-specific manner, and then to characterize the effects of the modifications on tree growth and wood properties. In short, strong effects on cell wall composition were noted in leaves where transgene expression was strong (Harding et al. 2017; Hu et al. in review). Subtle, but noteworthy effects were observed in wood (developing xylem) where transgene expression was weak (Swamy et al. 2015). Any effect of PTM manipulation was functionally recessive and/or confounded by tubulin overexpression. It was anticipated that PTM manipulation would affect tubulin half-life, and this is the question that was being addressed, but overall tubulin protein levels correlated with transgene expression levels. We also demonstrated that a dynamic C-terminal PTM known as the tyrosination/detyrosination cycle, so common in animal systems, and purportedly operational in plants, does not occur in wood-forming tissues of Populus (Hu et al. 2016). Contrary to the commonly hypothesized role of microtubules in directing microfibril deposition, cellulose content and microfibril angle were not changed in tubulin-overexpressing plants, nor were hemicellulose and lignin contents, in either wood or leaves. Instead, this project demonstrated that the extractability of pectin and xylan polysaccharides was sensitive to tubulin perturbations, with consequences in stomatal stress response and lignocellulosic biomass utilization. The work also revealed a complex interplay by multi-compartmental (cell wall and cytoskeleton) signaling that impinged upon the control of phenylpropanoid metabolic flux to modulate stomatal response to environmental stimuli.
59 BASIC BIOLOGICAL SCIENCES↗
High Doping of ZnO Varistor Powder and Manganese pH Speciation Experiments.
Abstract not provided.
Hahn, Michael↗
Mn Speciation and High Doping of ZnO Varistor Powder Experiments.
Abstract not provided.
Hahn, Michael↗
Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions
Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. We find the significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.
59 BASIC BIOLOGICAL SCIENCES↗
Modifications to Nano- and Microstructural Quality and the Effects on Mechanical Integrity in Paget's Disease of Bone
ABSTRACT Paget's disease of bone (PDB) is the second most common bone disease mostly developing after 50 years of age at one or more localized skeletal sites; it is associated with severely high bone turnover, bone enlargement, bowing/deformity, cracking, and pain. Here, to specifically address the origins of the deteriorated mechanical integrity, we use a cohort of control and PDB human biopsies to investigate multiscale architectural and compositional modifications to the bone structure (ie, bone quality) and relate these changes to mechanical property measurements to provide further insight into the clinical manifestations (ie, deformities and bowing) and fracture risk caused by PDB. Here, at the level of the collagen and mineral (ie, nanometer-length scale), we find a 19% lower mineral content and lower carbonate-to-phosphate ratio in PDB, which accounts for the 14% lower stiffness and 19% lower hardness promoting plastic deformation in pathological bone. At the microstructural scale, trabecular regions are known to become densified, whereas cortical bone loses its characteristic parallel-aligned osteonal pattern, which is replaced with a mosaic of lamellar and woven bone. Although we find this loss of anisotropic alignment produces a straighter crack path in mechanically-loaded PDB cases, cortical fracture toughness appears to be maintained due to increased plastic deformation. Clearly, the altered quality of the bone structure in PDB affects the mechanical integrity leading to complications such as bowing, deformities, and stable cracks called fissure fractures associated with this disease. Although the lower mineralization and loss of aligned Haversian structures do produce a lower modulus tissue, which is susceptible to deformities, our results indicate that the higher levels of plasticity may compensate for the lost microstructural features and maintain the resistance to crack growth. © 2014 American Society for Bone and Mineral Research
Zimmermann, Elizabeth A.↗
Trabecular Reorganization in Consecutive Iliac Crest Biopsies when Switching from Bisphosphonate to Strontium Ranelate Treatment
Background: Several agents are available to treat osteoporosis while addressing patient-specific medical needs. Individuals’ residual risk to severe fracture may require changes in treatment strategy. Data at osseous cellular and microstructural levels due to a therapy switch between agents with different modes of action are rare. Our study on a series of five consecutively taken bone biopsies from an osteoporotic individual over a six-year period analyzes changes in cellular characteristics, bone microstructure and mineralization caused by a therapy switch from an antiresorptive (bisphosphonate) to a dual action bone agent (strontium ranelate). Methodology/Principal Findings: Biopsies were progressively taken from the iliac crest of a female patient. Four biopsies were taken during bisphosphonate therapy and one biopsy was taken after one year of strontium ranelate (SR) treatment. Furthermore, serum bone markers and dual x-ray absorptiometry measurements were acquired. Undecalcified histology was used to assess osteoid parameters and bone turnover. Structural indices and degree of mineralization were determined using microcomputed tomography, quantitative backscattered electron imaging, and combined energy dispersive x-ray/mx-ray-fluorescence microanalysis. Conclusions/Significance: Microstructural data revealed a notable increase in bone volume fraction after one year of SR treatment compared to the bisphosphonate treatment period. Indices of connectivity density, structure model index and trabecular bone pattern factor were predominantly enhanced indicating that the architectural transformation from trabecular rods to plates was responsible for the bone volume increase and less due to changes in trabecular thickness and number. Administration of SR following bisphosphonates led to a maintained mineralization profile with an uptake of strontium on the bone surface level. Reactivated osteoclasts designed tunneling, hook-like intratrabecular resorption sites. The appearance of tunneling resorption lacunae and the formation of both mini-modeling units and osteon-like structures within increased plate-like cancellous bone mass provides additional information on the mechanisms of strontium ranelate following bisphosphonate treatment, which may deserve special attention when monitoring a treatment switch.
59 BASIC BIOLOGICAL SCIENCES↗
A National Offshore Wind Strategy: Creating an Offshore Wind Energy Industry in the United States
This document outlines the Department of Energy's strategy for accelerating the responsible development of offshore wind energy in the United States.
17 WIND ENERGY↗