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Results for “STARK EFFECT”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

High-resolution spectra and photoabsorption coefficients for carbon monoxide absorption bands between 94.0 nm and 100.4 nm

Photoabsorption coefficients have been measured for the CO in interstellar clouds at a resolving power more than 20 times greater than previously obtainable. In order to facilitate comparisons, these data have been integrated over the same wavelength ranges as used in Letzelter et al. (1987). It is found that most of the results obtained for bands between 94.0 and 100.4 nm are larger than those of Letzelter; the discrepancy may be attributable to the difference between the resolving powers of the spectrometers used, because the saturation effects associated with low resolution can underestimate absorption coefficient values.

Yoshino, K.↗
NASA NTRS1995

NASA-UVA Light Aerospace Alloy and Structures Technology program (LA2ST)

The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light-weight aerospace alloys, composites, and thermal gradient structures in collaboration with NASA-Langley researchers. The general aim is to produce relevant data and basic understanding of material mechanical response, environment/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and a pool of educated students for aerospace technologies. Specific technical objectives are presented for each of the following research projects: time-temperature dependent fracture in advanced wrought ingot metallurgy, and spray deposited aluminum alloys; cryogenic temperature effects on the deformation and fracture of Al-Li-Cu-In alloys; effects of aging and temperature on the ductile fracture of AA2095 and AA2195; mechanisms of localized corrosion in alloys 2090 and 2095; hydrogen interactions in aluminum-lithium alloys 2090 and selected model alloys; mechanisms of deformation and fracture in high strength titanium alloys (effects of temperature and hydrogen and effects of temperature and microstructure); evaluations of wide-panel aluminum alloy extrusions; Al-Si-Ge alloy development; effects of texture and precipitates on mechanical property anisotropy of Al-Cu-Mg-X alloys; damage evolution in polymeric composites; and environmental effects in fatigue life prediction - modeling crack propagation in light aerospace alloys.

Starke, Edgar A., Jr.↗
DOE OSTI2025

Atomic Coherence of 2 Minutes and Instability of 1.5 × 10 −18 at 1 s in a Wannier-Stark Lattice Clock

We explore the limits of atomic coherence and measurement precision in a 87 Sr optical lattice clock. We perform a detailed characterization of key effects, including lattice Raman scattering and atomic collisions in a shallow lattice configuration, determining a 174(28) s 3 𝑃 0 clock state lifetime. Investigation of atomic coherence across a range of lattice depths and atomic densities reveals decoherence mechanisms related to photon scattering and atomic interaction. At a reduced density, we observe a coherence time of 118(9) s, approaching the fundamental limit set by spontaneous emission. Guided by this coherence understanding, we demonstrate a clock instability for an atomic ensemble of 1.5 × 10 −18 at 1 s in fractional frequency units. Our results are important for further advancing the state of the art of an optical lattice clock for fundamental physics applications.

atomic, optical, & lattice clocks↗
NASA NTRS1977

A shock tube study of line broadening in a temperature range of 6100 to 8300 K

Line widths of the Ca(II) 3968 A and Na(I) 5890 A resonance lines broadened by electric microfields in a plasma were measured. A pressure-driven shock tube was used as the light source. Radiation from the equilibrium region behind the reflected shock wave was studied using a rapid scanning Fabry-Perot interferometer. Electron and argon atom densities of about 8 x 10 to the 16th and 1 x 10 to the 19th/cu cm, respectively, were achieved at the relatively low temperature of around 7500 K by vaporizing a cesium powder that had been added to the shock tube as a solid aerosol in argon gas. The measured line widths were predominantly Stark broadened by the electrons and ions in the plasma, although Doppler, van der Waals, instrument function and optical depth effects had to be taken into account.

Baur, J. F.↗
NASA NTRS1991

A critical analysis of the ultraviolet temperature scale of the helium-dominated DB and DBV white dwarfs

The temperatures of the hottest of the DB and of some of the variable DBV white dwarfs have been reanalyzed, using a new helium-rich model atmosphere grid and archival IUE data. The grid covers variations in the effective temperature, surface gravity, and trace hydrogen abundance. Significantly lower temperatures than those found by earlier investigations are found. This has influence on the issue of which mixing-length theory is the best one for treatment of convection in DB white dwarfs. The prototype of the DBV stars, GD 358, is given particular attention in view of the recently reported HE II 1640-A line. The sensitivity of the new results to input physics is analyzed. It is found that uncertainties in Stark broadening parameters, convective efficiency, and equation of state and the assumptions of a fixed gravity (log g = 8) and a negligible abundance of hydrogen can at most give an error in the effective temperature of 400 K for a typical DB star. The uncertainty on the absolute calibration of the IUE cameras and the effect of small interstellar reddening dominate the error analysis.

Thejll, Peter↗
DOE OSTI2024

The Role of Side Chains and Hydration on Mixed Charge Transport in n ‐Type Polymer Films

Abstract Introducing ethylene glycol (EG) side chains to a conjugated polymer backbone is a well‐established synthetic strategy for designing organic mixed ion‐electron conductors (OMIECs). However, the impact that film swelling has on mixed conduction properties has yet to be scoped, particularly for electron‐transporting (n‐type) OMIECs. Here, the authors investigate the effect of the length of branched EG chains on mixed charge transport ofn‐type OMIECs based on a naphthalene‐1,4,5,8‐tetracarboxylic‐diimide‐bithiophene backbone. Atomic force microscopy (AFM), grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), and scanning tunneling microscopy (STM) are used to establish the similarities between the common‐backbone films in dry conditions. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM‐D) and in situ GIWAXS measurements reveal stark changes in film swelling properties and microstructure during electrochemical doping, depending on the side chain length. It is found that even in the loss of the crystallite content upon contact with the aqueous electrolyte, the films can effectively transport charges and that it is rather the high water content that harms the electronic interconnectivity within the OMIEC films. These results highlight the importance of controlling water uptake in the films to impede charge transport inn‐type electrochemical devices.

Chemistry↗
NASA NTRS2008

Uncertainty Analysis of Air Radiation for Lunar Return Shock Layers

By leveraging a new uncertainty markup technique, two risk analysis methods are used to compute the uncertainty of lunar-return shock layer radiation predicted by the High temperature Aerothermodynamic Radiation Algorithm (HARA). The effects of epistemic uncertainty, or uncertainty due to a lack of knowledge, is considered for the following modeling parameters: atomic line oscillator strengths, atomic line Stark broadening widths, atomic photoionization cross sections, negative ion photodetachment cross sections, molecular bands oscillator strengths, and electron impact excitation rates. First, a simplified shock layer problem consisting of two constant-property equilibrium layers is considered. The results of this simplified problem show that the atomic nitrogen oscillator strengths and Stark broadening widths in both the vacuum ultraviolet and infrared spectral regions, along with the negative ion continuum, are the dominant uncertainty contributors. Next, three variable property stagnation-line shock layer cases are analyzed: a typical lunar return case and two Fire II cases. For the near-equilibrium lunar return and Fire 1643-second cases, the resulting uncertainties are very similar to the simplified case. Conversely, the relatively nonequilibrium 1636-second case shows significantly larger influence from electron impact excitation rates of both atoms and molecules. For all cases, the total uncertainty in radiative heat flux to the wall due to epistemic uncertainty in modeling parameters is 30% as opposed to the erroneously-small uncertainty levels (plus or minus 6%) found when treating model parameter uncertainties as aleatory (due to chance) instead of epistemic (due to lack of knowledge).

Kleb, Bil↗
NASA NTRS1974

Birefringing arising from the reorientation of the polarizability anisotropy of molecules in collisionless gases

The refractive index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. For the limit of an extremely short-duration excitation, a multilevel coherent effect resulted in delayed refractive index bursts. Both stationary and transient responses of this birefringence to an optical field were considered for symmetric top molecules, with particular emphasis on the special case of linear molecules.

Lin, C. H.↗
NASA NTRS1976

Birefringence arising from the reorientation of the polarizability anisotropy of molecules in collisionless gases

The refractive-index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. In the limit of an extremely-short-duration excitation, a multilevel coherent effect results in delayed refractive-index bursts. Both stationary and transient responses of this birefringence to an optical field are considered for symmetric-top molecules, with particular emphasis on the special case of linear molecules.

Lin, C. H.↗
NASA NTRSDate not supplied

A Parametric Battery Model for the Conceptual Design of Electric Aircraft

Electric aircraft conceptual designs usually have an assumed specific power and specific energy for the aircraft’s energy storage system that dictates the total capacity and the peak power available. The specific energy and power are inherently linked to the state-of-charge and discharge rate from which they were derived; therefore, they will not directly correspond to the diverse circumstances encountered in various aircraft missions and flight segments. These parameters turn the battery system into a black box, disregard potential electrical restrictions, and disallow the aircraft and battery to be optimized as a system. Peering into this box, this study highlights the importance of incorporating a parametric battery model into the conceptual design workflow by splitting high-level terms such as power into voltage and current and investigating their variability during the discharge process. Through the modeling of these more detailed parameters, this methodology shows the feasibility of using low states-of-charge for contingency operations, including the end of the reserve mission, expanding the amount of usable capacity for electric aircraft. Stark differences in aircraft capabilities can arise between varying fidelity battery models due to late-mission, high-power flight operations. This parametric battery model effectively captures these differences by evaluating the limitations that arise within the individual battery cells and the aircraft powertrain. This paper shows that the unusable charge of a battery is set by the balked landing power requirement and can realistically range from 5% to 44% based on assumptions. This sets the analog to unusable fuel capacity in aircraft with liquid fuel systems. Needing only aircraft- and mission-level inputs and only seconds of run time, this model is a prime fit for the fast, accurate exploration of the electric aircraft conceptual design space.

Battery↗
DOE OSTI2025

Contrasting c -axis and in-plane uniaxial stress effects on superconductivity and stripe order in La 1.885 Ba 0.115 CuO 4

The cuprate superconductor La 2−x Ba x CuO 4 (LBCO) near x = 0.125 is a striking example of intertwined electronic orders, where 3D superconductivity is anomalously suppressed, allowing spin and charge stripe order to develop. Understanding this interplay remains a key challenge in cuprates, highlighting the necessity of external tuning for deeper insight. While in-plane uniaxial stress enhances superconductivity and suppresses stripe order, the effects of c -axis compression remains largely unexplored. Here, we use muon spin rotation ( μ SR) and AC susceptibility with an in situ piezoelectric stress device to investigate the spin-stripe order and superconductivity in LBCO-0.115 under c-axis compression. The measurements reveal a gradual suppression of the superconducting transition temperature ( T c ) with increasing c -axis stress, in stark contrast to the strong enhancement observed under in-plane stress. We further show that while in-plane stress rapidly reduces both the magnetic volume fraction ( V m ) and the spin-stripe ordering temperature ( T so ), c-axis compression has no effect, with V m and T so exhibiting an almost unchanged behavior up to the highest applied stress of 0.21 GPa. These findings demonstrate a strong anisotropy in stress response.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1975

Stark broadening tables for He I 4922 A

The Stark broadening of the He I 4922-A line and its forbidden components by both ions and electrons is calculated using a theory that includes ion dynamic effects. Tables are presented for temperatures from 5000 K to 40,000 K covering the density range 10 trillion to 10 quadrillion per cu cm for both helium and hydrogen ionic perturbers.-

Barnard, A. J.↗
NASA NTRS2005

Performance Analysis of Direct-Sequence Code-Division Multiple-Access Communications with Asymmetric Quadrature Phase-Shift-Keying Modulation

This article considers a quaternary direct-sequence code-division multiple-access (DS-CDMA) communication system with asymmetric quadrature phase-shift-keying (AQPSK) modulation for unequal error protection (UEP) capability. Both time synchronous and asynchronous cases are investigated. An expression for the probability distribution of the multiple-access interference is derived. The exact bit-error performance and the approximate performance using a Gaussian approximation and random signature sequences are evaluated by extending the techniques used for uniform quadrature phase-shift-keying (QPSK) and binary phase-shift-keying (BPSK) DS-CDMA systems. Finally, a general system model with unequal user power and the near-far problem is considered and analyzed. The results show that, for a system with UEP capability, the less protected data bits are more sensitive to the near-far effect that occurs in a multiple-access environment than are the more protected bits.

Wang, C.-W.↗
NASA NTRS1983

Pupillary escape intensified by large pupillary size

Pupil responses to light are greatly influenced by initial pupil size. Small pupils, operating under photopic conditions, show tonic responses to step increases of light and high gains; thus the pupil is a good regulator of light. Large pupils, operating under mesopic or scotopic conditions show phasic responses, 'pupillary escape', and smaller gains: the pupil only transiently influences retinal flux. By using accommodation level to set the size of the pupil, the mechanism of the 'pupil size effect' is shown to be dependent on retinal light level only so far as retinal activity sets pupil size.

Stark, L.↗