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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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Real-time laser holographic interferometry technique has been applied successfully in the detection of 1mm x 1mm x 0.025mm duct tapes hidden beneath a 150mm x 150mm x 16mm ceramic-epoxy-fiberglass sandwiched structure. The experimental results clearly demonstrate future applicability of this technique in the optical nondestructive detection of debonds and flaws in such composite structures.
An investigation is conducted concerning the resonance model for the rings of Uranus proposed by Dermott and Gold (1977). Dermott and Gold had dismissed resonances involving Miranda as insignificant. The reported investigation shows, however, that the strongest resonances are all associated with Miranda. It is also found that the hypothesis that the rings are made up of librating particles is incorrect. If the ring positions are determined by resonances, the control is more subtle than previously suggested. One possibility is that the rings are the crests of nonlinear density waves in an optically thin disk of particles.
I will discuss two types of one-dimensional photonic bandgap (PBG) effects that can arise in systems of coupled spherical resonators: (1) nearly-free-photon Fabry-Perot photonic bands that arise in quarter-wave concentrically stratified spheres and, (2) tight- binding photonic bands that arise in weakly-coupled mutually-resonant spheres as a result of whispering-gallery mode splitting. These effects can be derived directly from Mie theory, in a more straightforward manner, by exploiting an analogy with stratified planar systems. For odd numbers of mutually-resonant lossless coupled ring resonators, the circulating intensity can increase exponentially with the number of resonators, which can potentially be exploited for the development of advanced sensors. For even numbers of resonators, mode splitting and classical destructive interference lead to a cancellation of absorption and slow light on-resonance, reminiscent of electromagnetic induced transparency. The analogy between these coherent photon trapping effects and population trapping in an atomic system will be explored.
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This paper provides the compilations of properties of the quasars newly obtained by the Sloan Digital Sky Survey (SDSS) during the fourth stage (SDSS-IV). The catalog is available on the journal's website. We have measured the main properties of emission lines around C $\tiny{IV}$ Mg $\tiny{II}$, Hβ, and Hα spectral regions. We estimate the quasar redshifts from our fits of narrow [O $\tiny{III}$], broad Mg $\tiny{II}$, and broad C $\tiny{IV}$ emission lines and find that the best redshifts included in DR16Q are robust with respect to our measurements. Based on the broad C $\tiny{IV}$, Mg $\tiny{II}$, Hβ, and/or Hα emission lines, we calculate the virial black hole mass with empirical relationships provided by previous works. Systematic biases are found among the different line-based mass estimators.
Bulk shape memory alloys, such as Nitinol or CuAlZn, display strong recovery forces undergoing a phase transformation after being strained in their martensitic state. These recovery forces are used for actuation. As the phase transformation is thermally driven, the response time of the actuation can be slow, as the heat must be passively inserted or removed from the alloy. Shape memory alloy TiNi torque tubes have been investigated for at least 20 years and have demonstrated high actuation forces [3,000 in.-lb (approximately equal to 340 N-m) torques] and are very lightweight. However, they are not easy to attach to existing structures. Adhesives will fail in shear at low-torque loads and the TiNi is not weldable, so that mechanical crimp fits have been generally used. These are not reliable, especially in vibratory environments. The TiNi is also slow to heat up, as it can only be heated indirectly using heater and cooling must be done passively. This has restricted their use to on-off actuators where cycle times of approximately one minute is acceptable. Self-propagating high-temperature synthesis (SHS) has been used in the past to make porous TiNi metal foams. Shape Change Technologies has been able to train SHS derived TiNi to exhibit the shape memory effect. As it is an open-celled material, fast response times were observed when the material was heated using hot and cold fluids. A methodology was developed to make the open-celled porous TiNi foams as a tube with integrated hexagonal ends, which then becomes a torsional actuator with fast response times. Under processing developed independently, researchers were able to verify torques of 84 in.-lb (approximately equal to 9.5 Nm) using an actuator weighing 1.3 oz (approximately equal to 37 g) with very fast (less than 1/16th of a second) initial response times when hot and cold fluids were used to facilitate heat transfer. Integrated structural connections were added as part of the net shape process, eliminating the need for welding, adhesives, or mechanical crimping. Inexpensive net-shape processing was used, which reduces the cost of the actuator by over a factor of 10 over nonporous TiNi made by hot drawing of tube or electrical discharge machining. By forming the alloy as an open-celled foam, the surface area for heat transfer is dramatically increased, allowing for much faster response times. The technology also allows for netshape fabrication of the actuator, which allows for structural connections to be integrated into the actuator material, making these actuators significantly less expensive. Commercial applications include actuators for concepts such as the variable area chevron and nozzle in jet aircraft. Lightweight tube or rod components can be supplied to interested parties.
Galaxy formation and evolution are regulated by the feedback from galactic winds. Absorption lines provide the most widely available probe of winds. However, since most data only provide information integrated along the line of sight, they do not directly constrain the radial structure of the outflows. In this paper, we present a method to directly measure the gas electron density in outflows (n e ), which in turn yields estimates of outflow cloud properties (e.g., density, volume filling factor, and sizes/masses). We also estimate the distance (r n ) from the starburst at which the observed densities are found. We focus on 22 local star-forming galaxies primarily from the COS Legacy Archive Spectroscopic SurveY (CLASSY). In half of them, we detect absorption lines from fine-structure excited transitions of Si $\tiny{II}$ (i.e., Si $\tiny{II}$ * ). We determine n e from relative column densities of Si $\tiny{II}$ and Si $\tiny{II}$ * , given Si $\tiny{II}$ * originates from collisional excitation by free electrons. We find that the derived n e correlates well with the galaxy's star formation rate per unit area. From photoionization models or assuming the outflow is in pressure equilibrium with the wind fluid, we get r n ~ 1–2r * or ~5r * , respectively, where r * is the starburst radius. Based on comparisons to theoretical models of multiphase outflows, nearly all of the outflows have cloud sizes large enough for the clouds to survive their interaction with the hot wind fluid. Most of these measurements are the first ever for galactic winds detected in absorption lines and, thus, will provide important constraints for future models of galactic winds.
Filamentary structures in neutral hydrogen (H$\tiny{I}$) emission are well aligned with the interstellar magnetic field, so H$\tiny{I}$ emission morphology can be used to construct templates that strongly correlate with measurements of polarized thermal dust emission. We explore how the quantification of filament morphology affects this correlation. We introduce a new implementation of the Rolling Hough Transform (RHT) using spherical harmonic convolutions, which enables efficient quantification of filamentary structure on the sphere. We use this Spherical RHT algorithm along with a Hessian-based method to construct H$\tiny{I}$-based polarization templates. We discuss improvements to each algorithm relative to similar implementations in the literature and compare their outputs. By exploring the parameter space of filament morphologies with the Spherical RHT, we find that the most informative H$\tiny{I}$ structures for modeling the magnetic field structure are the thinnest resolved filaments. For this reason, we find a ~10% enhancement in the B-mode correlation with polarized dust emission with higher-resolution H$\tiny{I}$ observations. We demonstrate that certain interstellar morphologies can produce parity-violating signatures, i.e., nonzero TB and EB, even under the assumption that filaments are locally aligned with the magnetic field. Finally, we demonstrate that B modes from interstellar dust filaments are mostly affected by the topology of the filaments with respect to one another and their relative polarized intensities, whereas E modes are mostly sensitive to the shapes of individual filaments.
Given the anisotropic emission from quasar accretion discs, their viewing angle affects estimates of the quasar luminosity, black hole mass, and Eddington ratio. Discs appear overluminous when viewed pole-on and underluminous when viewed at high inclination. In radio-quiet quasars, the viewing angle is usually unknown, although spectroscopic indicators have been proposed. Here, we use a recently discovered universality in the variability structure function (SF) of quasar light curves (LCs), where all quasars show the same SF when clocks run in units of orbital time-scale. As an offset from the mean relation can be caused by incorrect orbital time-scales and thus incorrect luminosities, we correlate these offsets with suggested inclination indicators. We derive SFs from NASA/Asteroid Terrestrial-impact Last Alert System (ATLAS) LCs spanning ~6 yr of observation, using a sample of 183 luminous quasars with measured H β lines as well as 753 quasars with C $\tiny{IV}$ and Mg $\tiny{II}$ lines. Starting from the proposed orientation indicators, we expect quasars with narrower H β lines and with more blueshifted C $\tiny{IV}$ lines to be viewed more pole-on and thus appear overluminous. In contrast, our SF analysis finds that presumed pole-on discs appear underluminous, consistently for both line indicators. We discuss possible explanations for the behaviour of quasars with highly blueshifted C $\tiny{IV}$ lines irrespective of inclination angle, including dusty outflows that might render the accretion disc underluminous and flatter disc temperature profiles with longer orbital time-scales than in thin-disc models but reach no satisfying conclusion.
The efficiency of thermionic energy converters is improved by internal distribution of tiny sorted cesium diodes driven by the thermal gradient between the primary emitter and the collector. The tiny, sorted diode distribution comprises protrusions of the emitter material from the main emitter face which contact the main collector face thermally but not electrically. The main collector ends of the protrusions are separated from the main collector by a thin layer of insulation, such as aluminum oxide. The shorted tiny diode distribution augments cesium ionization through internal thermal effects only within the main diode. No electrical inputs are required. This ionization enhancement by the distribution of the tiny shorted diodes not only reduces the plasma voltage drop but also increases the power output and efficiency of the overall thermionic energy converter.
The NASA HRP’s Space Radiation Element funds research to characterize and mitigate adverse health outcomes from space radiation including cardiovascular risks to astronauts to enable deep space exploration and sustained human presence in space. Non-cancer effects such as damage to the cardiovascular system have been observed at clinically relevant high doses of ionizing radiation. However, an association between lower doses and risk of cardiovascular disease (CVD) remains somewhat controversial, especially in relation to the existence of low dose thresholds, radiation quality, and dose-rate effects, as well as gaps in characterizing the mechanisms and major pathways of disease. To facilitate, accelerate, and incubate new ideas to characterize and mitigate this risk, the Element is planning to organize a series of miniature technical interchange meetings (Tiny-TIMs) to provide a venue for HRP-funded investigators and thought leaders to present ongoing work and engage in open discussion on presented results, limitations of current approaches, incorporating better experimental strategies, model systems, etc. The initial Tiny-TIM held during the NASA HRP Investigators’ Workshop earlier this year – Upping the ante on characterizing and mitigating cardiovascular disease risk from space radiation exposure – aimed to stimulate discussion on the current state of scientific knowledge of CVD risk from space-like radiation exposure. The Tiny-TIM consisted of two 90-minute sessions; the first session concentrated on current knowledge of CVD risk from space radiation and the second session focused on innovative ideas, newer approaches, and techniques to accelerate research. The second session was followed by an open spirited discussion amongst peers on the current issues impeding the characterization of CVD risk from space radiation. The Element facilitated the discussion using a set of pressing open questions/gaps in knowledge that need to be addressed by the scientific community. The outcomes of the Tiny-TIM will be presented along with a plan of proposed future workshops and other initiatives of the Space Radiation Element.
Here, we use updated Type Ia Pantheon+ supernova, baryon acoustic oscillation, and Hubble parameter (now also accounting for correlations) data, as well as new reverberation-measured C $\tiny{IV}$ quasar data, and quasar angular size, H $\tiny{II}$ starburst galaxy, reverberation-measured Mg $\tiny{II}$ quasar, and Amati correlated gamma-ray burst data to constrain cosmological parameters. We show that these data sets result in mutually consistent constraints and jointly use them to constrain cosmological parameters in six different spatially-flat and non-flat cosmological models. Our analysis provides summary model independent determinations of two key cosmological parameters: the Hubble constant, H 0 = 69.8 ± 1.3 km s -1 Mpc -1 , and the current non-relativistic matter density parameter, Ω m0 = 0.288 ± 0.017. Our summary error bars are 2.4 and 2.3 times those obtained using the flat ΛCDM model and Planck TT,TE,EE + lowE + lensing cosmic microwave background (CMB) anisotropy data. Our H 0 value is very consistent with that from the local expansion rate based on the Tip of the Red Giant Branch and Type Ia supernova (SN Ia) data, is 2σ lower than that from the local expansion rate based on Cepheid and SN Ia data, and is 2σ higher than that in the flat ΛCDM model based on Planck TT,TE,EE + lowE + lensing CMB data. Our data compilation shows at most mild evidence for non-flat spatial hypersurfaces, but more significant evidence for dark energy dynamics, 2σ or larger in the spatially-flat dynamical dark energy models we study.
Dense Z-pinch plasmas produced from current-carrying exploding wires frequently produce very brief (less than 0.1 nanosecond), intense, bursts of soft X-rays from tiny (about 1 micrometer), very hot (10-30 million K) regions of the plasma. This project addresses the physical processes that lead to those tiny, high-energy density plasmas and develops means to measure the conditions just before and during the X-ray bursts. One possible relevant process is radiative collapse, which starts if the power radiated by a dense Z-pinch, proportional to the density-squared, exceeds the resistive heating rate from the current flow, thereby cooling the plasma and enabling the magnetic pinching force to exceed the outward plasma thermal pressure. As the resulting radius reduction further increases the radiation rate, this process produces a runaway magnetic implosion. A competing mechanism is a sausage-like instability that can develop in a Z-pinch plasma at a lower current than is needed to induce radiative collapse. This mechanism can also produce tiny hot spots in the neck regions of the sausage-shaped plasma column. It is also possible that these two mechanisms work together to produce the X-ray emitting hot spots. If radiative collapse does contribute to hot spot formation, it would be terminated when the plasma becomes so dense that the radiation cannot escape, enabling the plasma kinetic pressure to build up and stop the current-driven implosion. This project aims to study the development of the hot spots by means of high temporal and spatial resolution X-ray spectroscopy to determine if there is evidence for the presence of the radiative collapse mechanism. Progress toward this goal is presented. To summarize, during the four-year period 09/15/2017 - 9/14/2021, we have collected necessary spectroscopic data to determine the plasma conditions and continue to do so. We are also now in the process of calibrating diagnostic systems (especially the x-ray streak camera system) and analyzing data to determine plasma conditions as a function of time before, during and after the X-ray burst.
This paper is intended to illustrate the considerable effect that small in-service undetectable multi-site-damage (MSD) can have on the residual strength capability of aging aircraft structures. In general, very few people in the industry believe that tiny cracks of undetectable size are a problem because they know that many aircraft have been able to survive much larger damage. In fact they have been certified for this large damage capability. However, this is not the issue. The real issue is the effect the tiny cracks, at multiple sites, have on the large damage capability which the industry has become accustomed to expect and which the aircraft have been certified to sustain. The concern is that this message does not appear to be fully understood by many people outside the fracture community. The prime purpose of this paper, therefore, has been to convey this message by describing in simple terms the net section yielding phenomenon in ductile materials which causes loss in lead crack residual strength in the presence of MSD. The explanation continues with a number of examples on complex stiffened structures, using the results of previous finite element analyses, which illustrate that the effect of MSD is extremely sensitive to structural configuration. It is hoped that those members of the aviation community who believe that tiny cracks are not a problem will read this paper very carefully.