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All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Interstellar Extinction, Polarization, and Grain Alignment in High-Latitude Clouds

From new near-infrared photometry and optical and near-infrared polarimetry, we determine the ratio of total-to-selective extinction and the wavelength of maximum polarization for a sample of stars behind molecular clouds at high Galactic latitude. In general, we find that at high latitude, these parameters have values comparable to those observed closer to the Galactic plane. One notable exception is the line of sight towards HD 210121, where unusually small values of these parameters suggest an abundance of small grains in the foreground cloud.

Larson, K. A.↗
NASA NTRS2006

Mission Architecture Comparison for Human Lunar Exploration

The Vision for Space Exploration outlines a bold new national space exploration policy that holds as one of its primary objectives the extension of human presence outward into the Solar System, starting with a return to the Moon in preparation for the future exploration of Mars and beyond. The National Aeronautics and Space Administration is currently engaged in several preliminary analysis efforts in order to develop the requirements necessary for implementing this objective in a manner that is both sustainable and affordable. Such analyses investigate various operational concepts, or mission architectures , by which humans can best travel to the lunar surface, live and work there for increasing lengths of time, and then return to Earth. This paper reports on a trade study conducted in support of NASA s Exploration Systems Mission Directorate investigating the relative merits of three alternative lunar mission architecture strategies. The three architectures use for reference a lunar exploration campaign consisting of multiple 90-day expeditions to the Moon s polar regions, a strategy which was selected for its high perceived scientific and operational value. The first architecture discussed incorporates the lunar orbit rendezvous approach employed by the Apollo lunar exploration program. This concept has been adapted from Apollo to meet the particular demands of a long-stay polar exploration campaign while assuring the safe return of crew to Earth. Lunar orbit rendezvous is also used as the baseline against which the other alternate concepts are measured. The first such alternative, libration point rendezvous, utilizes the unique characteristics of the cislunar libration point instead of a low altitude lunar parking orbit as a rendezvous and staging node. Finally, a mission strategy which does not incorporate rendezvous after the crew ascends from the Moon is also studied. In this mission strategy, the crew returns directly to Earth from the lunar surface, and is thus referred to as direct return. Figures of merit in the areas of safety and mission success, mission effectiveness, extensibility, and affordability are used to evaluate and compare the lunar orbit rendezvous, libration point rendezvous, and direct return architectures, and this paper summarizes the results of those assessments.

Geffre, Jim↗
NASA NTRS2008

VHF Wide-Band, Dual-Polarization Microstrip-Patch Antenna

The figure depicts selected aspects of a very-high-frequency (VHF) microstrip patch antenna designed and built to satisfy requirements specific to an airborne synthetic-aperture radar system for measuring the thickness of sea ice. One of the requirements is that the antenna be capable of functioning over the relatively wide frequency band of 127 to 172 MHz corresponding to a fractional bandwidth of about 30 percent relative to a nominal mid-band frequency of 149.5 MHz. Another requirement is that the antenna be capable of functioning in either or both of two orthogonal linear polarizations. In addition, the antenna is required to be as compact and lightweight as possible. In a basic design according to generally accepted microstrip-patch-antenna engineering practice, one would ordinarily use a relatively thick dielectric substrate and multiple feed probes to obtain the desired combination of wide-band and dual-polarization capabilities. However, the combination of a thick substrate and multiple feeds would give rise to higher-order electromagnetic nodes, thereby undesirably contributing to cross polarization and to reduction of the isolation between feed probes. To counter these adverse effects while satisfying the requirements stated above, the design of this antenna incorporates several improvements over the basic design.

Huang, John↗
DOE OSTI2026

Quantum critical collapse abhors a naked singularity

Classical critical collapse yields naked singularities from smooth initial data, challenging cosmic censorship, and shaping the spectrum of primordial black holes. We show that one-loop vacuum polarization near the threshold qualitatively changes this outcome by dressing the singularity with a horizon within a controlled semiclassical regime. In analytically tractable Einstein-scalar critical spacetimes, a one-loop $s$-wave treatment linearized around self-similar backgrounds shows that regularity uniquely selects an asymptotically Minkowskian, vacuum-polarization state. Its renormalized stress tensor carries a universal quantum growing mode that competes with the classical unstable mode, shifts the critical point, and generates a trapped surface along with a finite mass gap at the new threshold, thereby enforcing horizon formation even under arbitrary fine-tuning. In primordial collapse, the threshold shift enters exponentially into the formation fraction, while the mass gap truncates the low-mass tail, suggesting potentially important consequences for the predicted mass spectrum. Furthermore, these results provide a self-consistent semiclassical treatment of critical collapse and yield sharp predictions within the one-loop, near-critical, linearized regime.

Anomalies↗
NASA NTRS1977

Symmetry and selection rules for wave-wave interactions

Selection rules for nonlinear three-wave interactions are derived on the basis of the symmetry of the background medium and the waves themselves. The process described bypasses the formal derivation of the coupling coefficient itself. The primary concern is with the effect of the polarization of the waves on the selection rules. Although consideration is limited to three-wave interactions, the method is easily generalized to more waves. Results are derived for these examples: three waves with parallel propagation vectors in an unmagnetized medium, and three waves propagating parallel, and then perpendicular, to a static magnetic field.

Harker, K. J.↗
NASA NTRS1987

Earth Observing System (EOS)/NOAA candidate propulsion system assessment and instrument contamination requirements

The instrumentation payloads of the Space Station polar platforms consist primarily of Earth Observing System (EOS) instruments and National Oceanic and Atmospheric Administration (NOAA) instruments. The accuracy, lifetime, and mission effectiveness of the instrumentation is adversely affected by the degradation of contamination sensitive surfaces. This paper describes the analysis and results of a study undertaken to select a propellant system for the polar platforms from a contamination standpoint, by evaluation of the potential contamination to three platforms, from three candidate propellant systems. In addition, this paper reports the results of a study which determined both the molecular and particulate contamination requirements for 37 EOS/NOAA instruments. These requirements provide an upper bound for acceptable levels of contamination.

Millard, Jerry M.↗
DOE OSTI2020

Selective and Efficient Production of Biomass-Derived Vinylfurans

We describe a two-step catalytic process for the selective and rapid conversion of biomass-derived acetylfurans into vinylfurans. This is accomplished by nearly quantitatively reducing acetylfurans into furyl alcohols using a copper chromite catalyst and exploiting the promoter-like properties of ethanol, the solvent. Subsequently, furyl alcohol is dehydrated using solid-acid catalysts. Catalyst deactivation due to oligomeric species is a major issue, but the activity can be partially recovered by calcination. Optimization of reaction conditions showed that the selectivity could be increased by using nitrobenzene, a polar aprotic solvent. Here, the high-boiling point solvent allows the formation of vinylfurans with a selectivity of up to 85%; the product can be isolated in high purity by distillation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1984

Crop moisture estimation over the southern Great Plains with dual polarization 1.66 centimeter passive microwave data from Nimbus 7

Moisture content of snow-free, unfrozen soil is inferred using passive microwave brightness temperatures from the scanning multichannel microwave radiometer (SMMR) on Nimbus-7. Investigation is restricted to the two polarizations of the 1.66 cm wavelength sensor. Passive microwave estimates of soil moisture are of two basic categories; those based upon soil emissivity and those based upon the polarization of soil emission. The two methods are compared and contrasted through the investigation of 54 potential functions of polarized brightness temperatures and, in some cases, ground-based temperature measurements. Of these indices, three are selected for the estimated emissivity, the difference between polarized brightness temperatures, and the normalized polarization difference. Each of these indices is about equally effective for monitoring soil moisture. Using an antecedent precipitation index (API) as ground control data, temporal and spatial analyses show that emissivity data consistently give slightly better soil moisture estimates than depolarization data. The difference, however, is not statistically significant. It is concluded that polarization data alone can provide estimates of soil moisture in areas where the emissivity cannot be inferred due to nonavailability of surface temperature data.

Mcfarland, M. J.↗
DOE OSTI2020

Relativistic Effects in Magnetic Circular Dichroism: Restricted Magnetic Balance and Temperature Dependence

Magnetic circular dichroism of transition metal complexes and open-shell systems are challenging to simulate and analyze, mainly due to the interplay of spin–orbit couplings and finite-magnetic-field induced Zeeman effects with the complex selection rules dictated by the circularly polarized light. In this study, we introduce an ab initio relativistic two-component formalism based on the restricted magnetic-balanced Hamiltonian for simulating MCD spectra. Both homogeneous finite magnetic field and relativistic effects are included variationally in the ground state reference. Finite-field London orbitals are used to enforce the constrained gauge-origin independence in the calculation using localized atomic orbitals. Through benchmark studies of AuCl 4 – , Pt(CN) 4 2– , and Mo(CN) 8 3– , we discuss how relativistic effects are manifested in MCD for both closed-shell and open-shell molecular complexes and how the interplay between spin–orbit coupling and magnetic field modulates the MCD selection rules. Finally, an investigation on temperature-dependent MCD is carried out and compared to experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Pentavalent Uranium Enriched Mineral Surface under Electrochemically Controlled Reducing Environments

Redox reactions of uranium (U) in aqueous environments have important impacts on the mobility and isotopic fractionation of U in the geosphere. Pentavalent U as the cationic uranyl ion, UO 2 +, is rarely observed in naturally occurring samples because of its limited lifetime, but it may be an important intermediate state controlling the redox kinetics between hexavalent and tetravalent U. Increasing evidence has indicated that U(V) can be stabilized under laboratory conditions. Here, we showed that U(V) is the dominant species on the magnetite (Fe 3 O 4 ) surface under reducing conditions controlled by electrochemical methods. Cyclic voltammetry reveals coupled redox peaks corresponding to the U(VI)O 2 2+ /U(V)O 2+ one-electron redox reaction. Magnetite electrodes polarized at a series of potentials to reduce U(VI)O 2 2+ were characterized by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and Auger electron mapping. Overall, the results showed that up to twice the amount of U(V) to U(VI) was present on the magnetite surface. U(V) adopted a typical uranyl-type structure, and the U coverage on the magnetite surface increased with decreasing potentials. The formation of mixed-valence U(V)/U(VI) species on the surface of magnetite may hinder the U(V) disproportionation reaction, thereby eliminating the presence of tetravalent U. These results show that U(V) can exist over short time scales as the dominant U species on mineral surfaces under selected reducing conditions by the controlled polarization of a mineral electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Plant Responses to Increased UV-B Radiation: A Research Project

Ozone decrease implies more ultraviolet-B (UV-B) radiation reaching the surface of the Earth. Increased UV-B radiation triggers responses by living organisms. Despite the large potential impacts on vegetation, little is known about UV-B effects on terrestrial ecosystems. Long-term ecological studies are needed to quantify the effects of increased UV radiation on terrestrial ecosystems, asses the risks, and produce reliable data for prediction. Screening pigments are part of one of the protective mechanism in plants. Higher concentrations of screening pigments in leaves may be interpreted as a response to increased UV radiation. If the screening effect is not sufficient, important molecules will be disturbed by incoming radiation. Thus, genetics, photosynthesis, growth, plant and leaf shape and size, and pollen grains may be affected. This will have an impact on ecosystem dynamics, structure and productivity. It is necessary to monitor selected terrestrial ecosystems to permit detection and interpretation of changes attributable to global climate change and depleted ozone shield. The objectives of this project are: (1) To identify and measure indicators of the effects of increased solar UV-B radiation on terrestrial plants; (2) to select indicators with the greatest responses to UV-B exposure; (3) to test, adapt or create ecosystem models that use the information gathered by this project for prediction and to enhance our understanding of the effects of increased UV-B radiation on terrestrial ecosystems. As a first step to achieve these objectives we propose a three-year study of forest and steppe vegetation on the North slope of the Brooks Range (within the Arctic circle, in Alaska), in the Saguaro National Monument (near Tucson, Arizona) and in the forests and steppes of Patagonia (Argentina). We selected (1) vegetation north of the Polar Circle because at 70N there is 8% risk of plant damage due to increased UV-B radiation; (2) the foothills of Catalina Mountains because there is anecdotal evidence of plant damage on the saguaros that has been linked to increased UV radiation, and (3) the forests of Nothofagus spp. and the steppe of Patagonia where the risk of plant damage at 35S is 5% and increases to as much as 15% at 55S due to increased UV-B radiation. Measurements of UV-B radiation impinging on the surface at 55S largely exceed the predicted UV-B radiation values at 50 latitude and 0% ozone depletion. Preliminary HPLC analyses of UV-B absorbing compounds in Nothofagus antartica, N. pumilio, N. betuloides and Rumex sp. in natural conditions show species-specific patterns. The spectrum of N. antartica grown at 38S differs significantly from that of N. antartica in natural conditions in Ushuaia (55S). These results suggest that the selected main area (Patagonia) is appropriate for assessing the problem and its magnitude and that Nothofagus is appropriate for our study.

DAntoni, H. L.↗
DOE OSTI2025

Attosecond Optical Orientation

Circularly polarized light offers opportunities to probe symmetry-dependent properties of matter such as chirality and spin. Circular-dichroic measurements typically require further intrinsic or extrinsic breaking of symmetry by, e.g., enantiomeric excess, orientation, magnetic fields, or direction-sensitive detectors. Here we introduce circular-dichroic attosecond transient absorption spectroscopy by leveraging the angular momentum of two circularly polarized pulses, both pump and probe, in an isotropic medium, optically orienting the angular momentum of excited states on an attosecond timescale. We investigate a circular-dichroic measurement of the attosecond transient absorption of He Rydberg states. By limiting the allowed pathways via dipole selection rules for co- and counterrotating circularly polarized near-infrared and extreme ultraviolet (XUV) pulses, different spectral reshapings of the XUV transient absorption due to the AC Stark effect are observed. Furthermore, paired with time-dependent Schrödinger equation calculations, the results show the role of selection and propensity rules and open up new opportunities to study coupling pathways of excited states as well as spin-dependent dynamics in atoms and beyond via attosecond optical orientation.

Angular momentum of light↗
NASA NTRS1996

The Clementine Bistatic Radar Experiment

During the Clementine 1 mission, a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle, beta, for selected lunar areas. Observations of the lunar south pole yield a same-sense polarization enhancement around beta = 0. Analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole. Radar observations of periodically solar-illuminated lunar surfaces, including the north pole, yielded no such enhancement. A probable explanation for these differences is the presence of low-loss volume scatterers, such as water ice, in the permanently shadowed region at the south pole.

Nozette, S.↗
DOE OSTI2021

Valley-selective optical Stark effect of exciton-polaritons in a monolayer semiconductor

Selective breaking of degenerate energy levels is a well-known tool for coherent manipulation of spin states. Though most simply achieved with magnetic fields, polarization-sensitive optical methods provide high-speed alternatives. Exploiting the optical selection rules of transition metal dichalcogenide monolayers, the optical Stark effect allows for ultrafast manipulation of valley-coherent excitons. Compared to excitons in these materials, microcavity exciton-polaritons offer a promising alternative for valley manipulation, with longer lifetimes, enhanced valley coherence, and operation across wider temperature ranges. Here, we show valley-selective control of polariton energies in WS 2 using the optical Stark effect, extending coherent valley manipulation to the hybrid light-matter regime. Ultrafast pump-probe measurements reveal polariton spectra with strong polarization contrast originating from valley-selective energy shifts. This demonstration of valley degeneracy breaking at picosecond timescales establishes a method for coherent control of valley phenomena in exciton-polaritons.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ionic Control over Ferroelectricity in 2D Layered van der Waals Capacitors

The van der Waals layered material CuInP 2 S 6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneous polarization. Therefore, Cu migration across the lattice results in unusual ferroelectric behavior. Here, we demonstrate how the interplay of polar and ionic properties provides a path to ionically controlled ferroelectric behavior, achieved by applying selected DC voltage pulses and subsequently probing ferroelectric switching during fast triangular voltage sweeps. Using current measurements and theoretical calculations, we observe that increasing DC pulse duration results in higher ionic currents, the buildup of an internal electric field that shifts polarization loops, and an increase in total switchable polarization by ~50% due to the existence of a high polarization phase which is stabilized by the internal electric field. Apart from tuning ferroelectric behavior by selected square pulses, hysteretic polarization switching can even be entirely deactivated and reactivated, resulting in three-state systems where polarization switching is either inhibited or can be performed in two different directions.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Observations of the Earth in polarized light from the US Space Shuttle

During the four American Space Shuttle missions of year 1985, the crewmembers took pictures of the Earth in polarized light. Different problems were encountered in the quantitative use of the data: induced polarization by the shuttle window, lack of calibration correction of the window polarization and enveloped in flight calibration methods. The analysis of the selected data first confirmed the previous observation over snow and sand. A low polarization on these surfaces was observed. On the other hand, the measurements show the potentiability of the polarization for agricultural inventory. Contamination of the atmosphere is well characterized.

Roger, Jean-Claude↗
DOE OSTI2025

Enhancing the Optically Detected Magnetic Resonance Signal of Organic Molecular Qubits

In quantum information science and sensing, electron spins are often purified into a specific polarization through an optical-spin interface, a process known as optically detected magnetic resonance (ODMR). Diamond-NV centers and transition metals are both excellent platforms for these so-called color centers, while metal-free molecular analogues are also gaining popularity for their extended polarization lifetimes, milder environmental impacts, and reduced costs. In our earlier attempt at designing such organic high-spin π-diradicals, we proposed to spin-polarize by shelving triplet M S = ±1 populations as singlets. This was recently verified by experiments albeit with low ODMR contrasts of <1% at temperatures above 5 K. In this work, we propose to improve the ODMR signal by moving singlet populations back into the triplet M S = 0 sublevel, designing a true carbon-based molecular analogue to the NV center. Our proposal is based upon transition-orbital and group-theoretical analyses of beyond-nearest-neighbor spin–orbit couplings, which are further confirmed by ab initio calculations of a realistic trityl-based radical dimer. Microkinetic analyses point toward high ODMR contrasts of around 30% under experimentally feasible conditions, a stark improvement from previous works. Finally, in our quest toward ground-state optically addressable molecular spin qubits, we exemplify how our symmetry-based design avoids Zeeman-induced singlet–triplet mixings, setting the scene for realizing electron spin qubit gates.

Group theory↗