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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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At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Microsecond Carrier Lifetimes in Polycrystalline CdSeTe Heterostructures and in CdSeTe Thin Film Solar Cells

We report significant advances in understanding and reducing nonradiative Shockley-Read-Hall recombination in polycrystalline CdSe x Te 1-x , leading to microsecond charge carrier lifetimes. In undoped Al 2 O 3 -passivated heterostructures we find external radiative efficiency 0.2%, quasi-Fermi level splitting 950 mV, mobility 100 cm 2 /(Vs), and diffusion length 14 µm. In solar cells measured lifetimes can exceed 1 µs. We interpret this data to indicate MgZnO/CdSeTe interface recombination velocity <; 100 cm/s. Based on our results, it appears CdTe PV technology has potentially overcome longstanding “recombination lifetime” limitation and in the near future will transition to improving other aspects of device design.

41 EE - Solar Energy Technologies Office (EE-4S)↗
NASA NTRS1999

Preparing for Mars: the physiologic and medical challenges

As the twentieth century closes, retrospectives cite the Apollo moon missions as one of the important events of the past 100 years. A trip to Mars, however, would be even more challenging and significant. A round-trip Mars journey would require nearly three years away from Earth, a significant leap in complexity compared to the two week long Moon trips or the record-breaking fourteen-month flight on Mir. What would be the physiologic and medical challenges of a Mars flight? Two key areas of physiology present the greatest potential problems--calcium metabolism and radiation exposure. Data from Mir missions show that bone loss continues in space despite an aggressive countermeasure program. Average losses were 0.35% per month, but some load bearing areas lost >1% per month. A 1% loss rate, if it continued unabated for 30 months, could produce osteoporosis. Smaller losses could still increase fracture risk. Some bone loss can be well tolerated, particularly if the bone can be regained after the mission. But the effectiveness of post-flight rehabilitation to restore the density and quality of bone after spaceflight is not well known. Bone loss estimates are based on continuous weightlessness exposure, but this is not a requirement for a Mars trip. Most of the time on a Mars trip will be spent in the 1/3 Earth's gravity environment on Mars, and either intermittent or continuous artificial gravity can be provided for the transit between planets (although at an engineering cost). The dosing of the gravity exposure (e.g. the level and duration), however, has not been established. Radiation protection also requires a balance between engineering cost and human health. Excessive shielding could add billions of dollars to the cost of a mission. Trips in interplanetary space, however, expose the crew to heavy high-energy particles from cosmic rays (HZE particles), which have a high linear energy transfer. This high energy leads to significant biological damage (e.g. chromosomal aberrations, cancer induction). A recent report from the Committee on Space Biology and Medicine notes that only one systematic study of cancer induction from high-energy particles has been conducted (using the mouse Harderian gland). Predictions of cancer risk and acceptable radiation exposure in space are extrapolated from minimal data. Other areas of physiology also present problems, such as muscle loss, cardiovascular deconditioning, and vestibular adaptation. Despite all the issues, however, a focussed, aggressive research program that uses the resources of the International Space Station should pave the way for mankind's greatest adventure--a trip to Mars.

STS-90 Shuttle Project↗
NASA NTRS2020

Preparing for Human Missions to Mars: The role of ISS and Artemis as Analogs for Research and Technology Testing

The hazards of spaceflight to the human system are present in in varying degrees on different spaceflight platforms: altered gravity, isolation and confinement, distance from Earth, radiation, and hostile closed environments. A strategic view of the fidelity of hazards experienced on different platforms can shape the testing plans for human research and technology demonstration related to crew health and performance. Working across the international partnership, the International Space Station (ISS) is planning periods of modified operations to improve the fidelity of Mars simulations. To understand transit durations as an independent variable, a series of 1-year, 6-month and 30-45 day missions are being planned on ISS. Standard measurements across ISS missions of different durations, lunar missions and ground analogs offers the opportunity to distinguish different hazards and their effects in the context of the relevance to future mission concepts. The ISS partnership is planning for additional test cases that are aligned with Mars mission plans. (1) Evaluating crew performance capabilities when transitioning to gravity after long durations in microgravity representative of a Mars transit. (2) Simulating crew medical care under Mars-like autonomous operations. (3) Identification and testing of operations under communications delay and autonomy expected for Mars missions and the linked effects on behavioral health and performance of the crew. Artemis missions serve as a valuable analogs for Mars surface operations, with partial gravity and deep space radiation hazards, but with crewmembers that are probably more physically capable than their counterparts would be after a Mars transit. Getting unobtrusive data from early Artemis missions, and knowledge gained from operational experience as Artemis operations develop can improve engineering design, medical requirements and countermeasures, and ultimately ensure mission success on Mars. Linking Mars architectures with the plans and capabilities for ISS and Artemis allows us to plan to most operationally relevant tests of crew health and performance on current spaceflight missions to inform planning for future missions to Mars. By using human spaceflight platforms as well as ground simulation in an integrated way, the international community can improve exploration readiness, develop countermeasures and reduce risks of future human space missions.

International Space Station↗
NASA NTRS2003

Fan Beam Emission Tomography for Laminar Fires

Obtaining information on the instantaneous structure of turbulent and transient flames is important in a wide variety of applications such as fire safety, pollution reduction, flame spread studies, and model validation. Durao et al. has reviewed the different methods of obtaining structure information in reacting flows. These include Tunable Laser Absorption Spectroscopy, Fourier Transform Infrared Spectroscopy, and Emission Spectroscopy to mention a few. Most flames emit significant radiation signatures that are used in various applications such as fire detection, light-off detection, flame diagnostics, etc. Radiation signatures can be utilized to maximum advantage for determining structural information in turbulent flows. Emission spectroscopy is most advantageous in the infrared regions of the spectra, principally because these emission lines arise from transitions in the fundamental bands of stable species such as CO2 and H2O. Based on the above, the objective of this work was to develop a fan beam emission tomography system to obtain the local scalar properties such as temperature and mole fractions of major gas species from path integrated multi-wavelength infrared radiation measurements.

Sivathanu, Yudaya↗
DOE OSTI2022

Frozen storage of proteins: Use of mannitol to generate a homogenous freeze-concentrate

Therapeutic proteins may be subjected to several freeze–thaw cycles throughout manufacturing and storage. The protein solution composition and the freezing conditions may lead to incomplete ice crystallization in the frozen state. This can also result in freeze-concentrate heterogeneity characterized by multiple glass transition temperatures and protein destabilization. The overall objective was to investigate the potential advantages of including a crystallizing excipient (mannitol) along with a sugar (sucrose or trehalose) for frozen storage. Here, this study showed that the addition of mannitol, a readily crystallizing excipient, facilitated ice crystallization. Inclusion of an isothermal hold during cooling (annealing) maximized the mannitol crystallization and resulted in a homogenous freeze-concentrate of a constant composition characterized by a single glass transition temperature. The role of freezing rate and annealing on both mannitol and ice crystallization were discerned using high intensity synchrotron radiation. The addition of sucrose or trehalose, at an appropriate concentration, stabilized the protein. The mannitol to sugar ratio (3:1 or 1:1, 5 % w/v) was optimized to selectively cause maximal crystallization of mannitol while retaining the sugar amorphous. Human serum albumin (1 mg/mL) in these optimized and annealed compositions did not show any meaningful aggregation, even after multiple freeze–thaw cycles. Thus, in addition to a sugar as a stabilizer, the use of a crystallizing excipient coupled with an annealing step can provide an avenue for frozen storage of proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Physical Properties of Candidate X-ray Detector Material Rb 4 Ag 2 BiBr 9

Recently, metal halide perovskites have emerged as promising semiconductor candidates for sensitive X-ray photon detection due to their suitable band gap energies, excellent charge transport properties, and low material cost afforded by their low-temperature solution-processing preparation. Furthermore, we report an improved methodology for single crystal growth and thermal and electrical properties of a two-dimensional (2D) layered halide material Rb 4 Ag 2 BiBr 9 , which has been identified as a potential candidate for X-ray radiation detection applications. The measured heat capacity for Rb 4 Ag 2 BiBr 9 implies that there are no structural phase transitions upon cooling. Temperature dependence of thermal transport measurements further suggests remarkably low thermal conductivities of Rb 4 Ag 2 BiBr 9 that are comparable to the lowest reported in literature. The bulk crystal resistivity is determined to be 2.59 × 10 9 Ω·cm from the current–voltage (I–V) curve. Density of trap states is estimated to be ~10 10 cm –3 using the space-charge-limited-current measurements. The fabricated Rb 4 Ag 2 BiBr 9 -based X-ray detector shows good operational stability with no apparent current drift, which may be ascribed to the 2D crystal structure of Rb 4 Ag 2 BiBr 9 . Finally, by varying the X-ray tube current to change the corresponding dose rate, the Rb4Ag2BiBr9 X-ray detector sensitivity is determined to be 222.03 μC Gy –1 cm –2 (at an electric field of E = 24 V/mm).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Modeling the energetic tail of a dusty plasma's electron energy distribution and its effect on dust grain charge and behavior

A model for a weakly ionized dusty plasma is proposed in which UV or x-ray radiation continuously creates free electrons at high energy, which then cool through collisions with a cold neutral gas before recombining. The transition of a free electron from high energy at birth to low energy at demise implies that the electron energy distribution is not the simple Maxwellian of an isolated system in thermal equilibrium, but instead has a high-energy tail that depends on the recombination time. This tail can have a major effect on dust grain charging because the flux of tail electrons can be substantial even if the density of tail electrons is small. Detailed analytic and numerical calculations of dust grain charging show that situations exist in which a small high-energy tail dominates charge behavior. This implies that dust grain charge in terrestrial and space dusty plasmas may be significantly underestimated if a Maxwellian distribution is assumed and the non-thermal dynamics are neglected.

Physics↗
DOE OSTI2024

Extracting the electronic structure of light elements in bulk materials through a Compton scattering method in the readily accessible hard x-ray regime

Here, our Compton profile measurements of Ti and TiH 2 using readily available hard X-ray radiation at 27.5 keV, detected by both a Hitachi Vortex silicon-drift detector and a high-resolution superconducting transition-edge sensor array, are found to be in excellent accord with state-of-the-art density functional theory based calculations. The spherically averaged difference between the Compton profiles of TiH 2 and Ti is well described by an inverted parabola, supporting an itinerant behavior of the electron gas screening the protons in the Ti matrix. Our experimental approach, validated by two different detectors, extends the applicability of Compton scattering technique to the readily accessible hard x-ray regime (below 30 keV). Our study suggests possibilities for experiments at low-flux bending magnet synchrotron beamlines and paves the way for the development of tabletop Compton experiments with x-ray tubes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Laser spectroscopy of metastable palladium at 340 and 363 nm

Here we report measurements of the isotope shift of the mass 104, 105, 106, 108, and 110 stable palladium isotopes for transitions from the metastable state $4d^9(^2D_{5/2})5s$, $^2[5/2]_3 → 4d^9(^2D_{5/2})5p, ^2[7/2]^o_4$ at 340 nm, and $4d^9(^2D_{5/2})5_s, ^2[5/2]_3 → 4d^9(^2D_{5/2})5p, ^2[3/2]^o_2$ at 363 nm. For 105 Pd , we determine the hyperfine structure of both transitions. The measurements were performed by saturation absorption spectroscopy in a custom-built hollow cathode lamp and will serve as a reference for collinear laser spectroscopy of short-lived neutron-rich palladium isotopes. We also report on the observation of a population inversion for the 363-nm transition under certain discharge conditions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

𝜂 and 𝜂′ Production in 𝐽/𝜓 Radiative Decays from Quantum Chromodynamics

We present a first principles calculation within quantum chromodynamics (QCD) of the radiative decays of the 𝐽/𝜓 into the light pseudoscalar mesons 𝜂 and 𝜂′. Within a lattice computation we obtain the transition form factors as a function of photon virtuality from the timelike region, accessible experimentally via the “Dalitz” decay 𝐽/𝜓 →𝑒 + ⁢𝑒 − ⁢𝜂 (′) , through to the real photon point corresponding to 𝐽/𝜓 →𝛾⁢𝜂 (′) . This is the first calculation in lattice QCD with two (heavier than physical) degenerate flavors of light quark and a heavier strange quark, in which the 𝜂′ appears as the first excited state with pseudoscalar isoscalar quantum numbers. We access it reliably by using variationally optimized operators , the use of which also improves the purity of the 𝐽/𝜓 and 𝜂 signals, reducing systematic uncertainties. High quality results at a large number of kinematic points are obtained in a typically noisy disconnected process by using a novel correlator averaging procedure. Our results show the expected enhanced production of the 𝜂′ over the 𝜂 in this process, and suggest that the demonstrated lattice technology is suitable for future calculations considering processes in which light meson resonances are produced.

form factors↗
NASA NTRS1971

Infrared Absorption of Carbon Dioxide at High Densities With Application to the Atmosphere of Venus

Several new infrared absorptions were found in carbon dioxide. All are normally forbidden, and were collision-induced in an absorbing cell whose combination of pressure and path length has a unique sensitivity for induced absorptions. The new absorptions in the 2.3 micron region are attributed to transitions from ground to the 3(1)1 Fermi pair at 4248 and 4391/cm. Other absorptions are attributed to simultaneous CO2-N2 transitions and to the 00(0)0-00(0)2 transition in CO2 polarizability derivatives and regular progressions in strength versus increasing quantum number. The spectra were used to predict the radiative transfer in a dry CO2 model of the lower Venus atmosphere. The results indicate that the radiation balance in the lower atmosphere is adequately explained by a dry massive atmosphere of CO2 with a layer of infrared-opaque clouds. The absorptions in the 2.3 micron region are significant in accounting for the opacity to sustain Venus' 768 K surface temperature.

John Fitzallen Moore↗
NASA NTRS1977

The angular dependence of partially redistributed resonance radiation

Explicit expressions for the angular distribution and frequency dependence of radiation scattered by a spatially degenerate atom undergoing collisions are derived using a previously developed formalism of the quantum theory of line broadening for an atom in its rest frame. Results valid in the impact regime for resonant scattering are presented for the cases of linear incident and scattered polarization circular incident and linear scattered polarization, and unpolarized incident radiation with no monitoring of the scattered polarization. These results relate to scattering involving a j - j + or - 1 - j atomic transition, with lower-state interactions neglected; the expressions obtained take a relatively simple form involving atomic multipolar relaxation rates of the order of k = 0 and k = 2. The angular distributions for each case are combined with the frequency dependences to yield a three-component frequency redistribution function for an s-p-s transition, the components being a coherent term, a frequency-redistributed term with the same angular dependence as the coherent term, and an isotropic frequency-redistributed term.

Ballagh, R. J.↗
NASA NTRS1983

Conductive flux in the chromosphere derived from line linear polarization observation

It is shown that quantitative information on the mechanisms of energy transport which take place in solar flares can be obtained by measurement of impact line polarization. Linear polarization in two chromospheric lines (H-alpha and SI 1437 A) observed in the gradual phase of solar flares was investigated. The polarized electric vector is shown to be directed towards the center of the disk. The relationship between conductive heat flux and linear line polarization is determined using a function which represents the velocity distribution of electrons carrying heat flux. The relationship between linear polarization and heat flux is applied to the observed degree of polarization, which yields the conductive heat flux in the high chromosphere. It is determined that this conductive flux is of the order of magnitude of the total radiation loss in the chromosphere and below, which is also of the order of magnitude of the conductive flux in the transition zone.

Henoux, J.-C.↗
NASA NTRS1986

The lower atmosphere of solar flares; Proceedings of the Solar Maximum Mission Symposium, Sunspot, NM, Aug. 20-24, 1985

The topics discussed by the present conference encompass the chromospheric flare phenomenon, white light flares, UV emission and the flare transition region, the flare corona and high energy emissions, stellar flares, and flare energy release and transport. Attention is given to radiative shocks and condensation in flares, impulsive brightening of H-alpha flare points, the structure and response of the chromosphere to radiation backwarming during solar flares, the interpretation of continuum emissions in white light flares, and the radiation properties of solar plasmas. Also discussed are EUV images of a solar flare and C III intensity, an active region survey in H-alpha and X-rays, dynamic thermal plasma conditions in large flares, the evolution of the flare mechanism in dwarf stars, the evidence concerning electron beams in solar flares, the energetics of the nonlinear tearing mode, macroscopic electric fields during two-ribbon flares, and the low temperature signatures of energetic particles.

Neidig, Donald F.↗
NASA NTRS1989

IR line emission from dense photodissociation regions

The results of the study on the molecular and fine structure line emission, from dense photodissociation regions, are discussed. The work is focused on the prediction of the line emission from CO and H2 molecules. It is found that, when the gas density is sufficiently high, self-shielding of the molecules can move the C(+)/CO and H/H2 transitions close to the surfaces of the molecular cloud where they can feel the full effect of heating by the ultraviolet radiation field. Collisional de-excitation of the H2 can move the lower levels towards low temperature emission producing an apparently shocked line ratio for two low-J levels, while the high-J levels retain a fluorescent value. Appreciable emission in high-J CO molecules originates in this warm molecular gas. Comparison with observation suggests that high density clumps are a common phenomena in photodissociation regions.

Burton, M.↗
NASA NTRS1995

The neutral oxygen spectrum. 1: Collisionally excited level populations and line intensities under optically thin conditions

This is the first paper in a projected program to produce quantitative information on the spectrum of the neutral oxygen atom under a variety of excitation conditions. Radiative rates and effective collision strengths are assembled from the recent literature where available, or are calculated for as yet untreated transitions using the University College superstructure/distorted-wave computer package, to produce a complete set of atomic data for a 13 hybrid level model of neutral oxygen. Level populations and relative intensities for 28 allowed, inter-combination, and forbidden oxygen lines are computed, under optically thin conditions, for the electron density range 4.0 less than log N(sub e) less than 12.0 and the electron temperature values T(sub e) = 5000, 10,000, 20,000, 50,000, and 100,000 K. Preliminary applications to observed intercombination/allowed and forbidden/allowed line ratios are discussed.

Bhatia, A. K.↗
NASA NTRS2001

Kinetic Inductance Photodetectors Based on Nonequilibrium Response in Superconducting Thin-Film Structures

While experimental studies of kinetic-inductance sensors have been limited so far by the temperature range near the superconducting transition, these detectors can be very sensitivity at temperatures well below the transition, where the number of equilibrium quasiparticles is exponentially small. In this regime, a shift of the quasiparticle chemical potential under radiation results in the change of the kinetic inductance, which can be measured by a sensitive SQUID readout. We modeled the kinetic inductance response of detectors made from disordered superconducting Nb, NbC, and MoRe films. Low phonon transparency of the interface between the superconductor and the substrate causes substantial re-trapping of phonons providing high quantum efficiency and the operating time of approximately 1 ms at 1 K. Due to the small number of quasiparticles, the noise equivalent power of the detector determined by the quasiparticle generation-recombination noise can be as small as approximately 10(exp -19) W/Hz(exp 1/2) at He4 temperatures.

Sergeev, A. V.↗