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At least 487 records · Page 27

All sources NASA NTRS DOE OSTI

NASA NTRS2012

Agile Science Operations: A New Approach for Primitive Exploration Bodies

Primitive body exploration missions such as potential Comet Surface Sample Return or Trojan Tour and Rendezvous would challenge traditional operations practices. Earth-based observations would provide only basic understanding before arrival and many science goals would be defined during the initial rendezvous. It could be necessary to revise trajectories and observation plans to quickly characterize the target for safe, effective observations. Detection of outgassing activity and monitoring of comet surface activity are even more time constrained, with events occurring faster than round-trip light time. "Agile science operations" address these challenges with contingency plans that recognize the intrinsic uncertainty in the operating environment and science objectives. Planning for multiple alternatives can significantly improve the time required to repair and validate spacecraft command sequences. When appropriate, time-critical decisions can be automated and shifted to the spacecraft for immediate access to instrument data. Mirrored planning systems on both sides of the light-time gap permit transfer of authority back and forth as needed. We survey relevant science objectives, identifying time bottlenecks and the techniques that could be used to speed missions' reaction to new science data. Finally, we discuss the results of a trade study simulating agile observations during flyby and comet rendezvous scenarios. These experiments quantify instrument coverage of key surface features as a function of planning turnaround time. Careful application of agile operations techniques can play a significant role in realizing the Decadal Survey plan for primitive body exploration

Agile science↗

NASA NTRS2002

Ocular input for human melatonin regulation: relevance to breast cancer

The impact of breast cancer on women across the world has been extensive and severe. As prevalence of breast cancer is greatest in industrialized regions, exposure to light at night has been proposed as a potential risk factor. This theory is supported by the epidemiological observations of decreased breast cancer in blind women and increased breast cancer in women who do shift-work. In addition, human, animal and in vitro studies which have investigated the melatonin-cancer dynamic indicate an apparent relationship between light, melatonin and cancer, albeit complex. Recent developments in understanding melatonin regulation by light in humans are examined, with particular attention to factors that contribute to the sensitivity of the light-induced melatonin suppression response. Specifically, the role of spectral characteristics of light is addressed, and recent relevant action spectrum studies in humans and other mammalian species are discussed. Across five action spectra for circadian and other non-visual responses, a peak sensitivity between 446-484 nm was identified. Under highly controlled exposure circumstances, less than 1 lux of monochromatic light elicited a significant suppression of nocturnal melatonin. In view of the possible link between light exposure, melatonin suppression and cancer risk, it is important to continue to identify the basic related ocular physiology. Visual performance, rather than circadian function, has been the primary focus of architectural lighting systems. It is now necessary to reevaluate lighting strategies, with consideration of circadian influences, in an effort to maximize physiological homeostasis and health.

Review↗

DOE OSTI2019

Neutron-star mergers and new opportunities in rare isotope experimental research

The recent observation of the first neutron-star merger event GW170817 had major impact on our understanding of stellar nucleosynthesis. It was identified for the first time as one of the sites for the astrophysical r process, a process that is responsible for the synthesis of roughly half of the isotopes of the heavy elements. The observed kilonova afterglow from the neutronstar merger event was interpreted as the result of the radioactive decays of r-process isotopes as they decay back to the valley of stability. The observed kilonova light curve is however broad due to its complex composition and the Doppler-shift due to fast moving matter, and is therefore impossible to interpret without accurate knowledge of the nuclear properties of the nuclei involved. This work focuses on the current experimental efforts to measure the relevant nuclear properties, together with plans for the next generation radioactive beam facilities, and in particular the Facility for Rare Isotope Beams (FRIB).

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Optimization of a short-pulse-driven Si He-α soft x-ray backlighter

High backlighter brightness is important to maximize the number of detected photons in radiography experiments and to minimize the background while backlighting high-energy density plasmas with strong self-emission. Here, several different configurations were tested to improve the brightness of the Si He-α x-ray line emission at a photon energy of 1865 eV from high-energy (>1 kJ), short-pulse (~20-ps), laser-driven backlighter targets. The emission from low-density SiO 2 foam targets, the effects of a laser prepulse, and Si targets with a CH “shield” that form a small cavity were compared to solid-density, flat Si targets. The CH “shield” targets showed the best performance with a >5× improvement in time integrated emission and an x-ray pulse duration of ~25 ps with no measurable spectral shift of the Si He-α emission line. A conversion efficiency from laser light into Si He-α photons of the order of 1 × 10 –5 was inferred from the data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Crystal growth and characterization of high performance KSr 2 Br x I 5-x :Eu scintillators

In this work we investigated the effects of replacing some of the matrix iodine atoms in KSr 2 I 5 :Eu with bromine, forming new solid solutions of KSr 2 Br x I (5-x) :Eu (where 0.05 ≤ x ≤ 1). Transparent 15 and 22mm diameter single crystals of KSr 2 Br x I (5-x) :Eu were grown via the vertical Bridgman technique using a two-zone transparent furnace. The scintillation properties of the mixed compounds were investigated and compared to the non-mixed parent compound, KSr 2 I 5 :Eu. The addition of bromine blue-shifted the x-ray excited emission from 450 to 446 nm, increased the light yield by ~11% and decreased the scintillation decay time by suppressing its secondary component (≥3 μs), while maintaining energy resolutions comparable to the reference crystal. Thermoluminescence glow curves showed that the addition of bromine modified the shallow traps located between 25 and 55 K, suggesting that these traps are responsible for lengthening KSI’s decay time. In large sizes (10.3 cm 3 ), KSr 2 Br 0.10 I 4.90 :Eu 2% had light yields up to 79,000 ph/MeV and energy resolutions as low as 3.2% at 662 keV.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Xenon Doping of Liquid Argon

Doping liquid argon with xenon will shift the peak scintillation wavelength towards longer wavelengths. Tests were performed on photon detectors, light absorbing materials, and other equipment in preparation for an experiment on the scintillation of liquid argon doped with xenon.

43 PARTICLE ACCELERATORS↗

DOE OSTI2025

Design of a High-Pressure Fuel System for Use with Dimethyl Ether

The paper documents the modeling and experimental work on a common rail fuel injection system for Dimethyl Ether, a potential diesel substitute with a low carbon intensity signature. The DME fuel system is deployed on a light duty 2.2L compression ignition engine. The paper describes the injector optimization to shift to higher flows to account for the lower heating value and density of the DME when compared to diesel. The type of the injection system used for the DME application is an advanced rendering of the Common rail noted for a one-piece piston-needle injector construction and a solenoid driven spill valve featuring a pressure balanced poppet. A dedicated high-pressure fuel pump designed to pressurize DME is used. The design results in a fast acting open and close injection event, reduced leakage, with reduced cavitation in the fuel injector volume. Design parameters for system optimization included fill and spill orifices, needle lift, bias spring, and injector hole size. The design model provides good correlation of the instantaneous rates of injection with experiments across a wide range of pressure and injection timings. Proposed performance milestones for the design included similar DME injection duration to the diesel counterpart for same fuel energy injected into the cylinder to retain high engine cycle efficiency. Here, the dedicated DME design provided reduced hydraulic delays of 50%. Tests demonstrated sustained operation at pressures of 1000 bar, with capability to reach 1500bar. Durability tests showed no cavitation-deterioration over a 200-hour test cycle by means of spray imaging and hardware inspection.

De Ojeda, William [WM International Engineering, L↗

NASA NTRS1975

Interpretation of the pulsed gamma ray emission from Vela

A model is proposed for the Vela pulsar in which the radio emission originates near the surface of the neutron star while the pulsed gamma ray emission is produced by synchrotron radiation near the speed of light cylinder. This model can explain the energy flux, double pulse structure, and phase shift with respect to the radio of the gamma ray emission and offers approximate quantitative predictions for other X-ray and gamma-ray fluxes.

Thompson, D. J.↗

NASA NTRS1975

Interpretation of the pulsed gamma-ray emission from Vela

A model is proposed for the Vela pulsar in which the radio emission originates near the surface of the neutron star while the pulsed gamma-ray emission is produced by synchrotron radiation near the speed-of-light cylinder. This model can explain the energy flux, double pulse structure, and phase shift (with respect to the radio) of the gamma-ray emission, and offers approximate quantitative predictions for other X- and gamma-ray fluxes.

Thompson, D. J.↗

NASA NTRS1977

Optical scanning system for laser velocimeter

An optical system was developed to provide fast incremental scanning of a backscattered laser velocimeter focus point over a 36-cm distance. The system is used to measure flow velocities at 16 positions along its optical axis and to scan these 16 positions up to 30 times a second. Dwell time at each location is approximately 2 milliseconds. Sample volumes typically are 0.2 mm in diameter by 1.4 cm in length. The optical scanning system consists of a wheel containing plane parallel quartz windows of various thicknesses. The laser velocimeter beams are imaged to a primary focus within the dead airspace of an optical cell. The beams emerging from the cell pass through the windows of the scanning wheel. The refraction of the beams passing through the windows causes an apparent shift of the focus within the optical cell and hence in the test zone. Light scattered from the secondary focus within the test zone is concurrently collected and reimaged through the same optical path which originally projected the primary focus. The reimaged backscattered light containing the velocity information is then collected and focused onto a photomultiplier detector system to complete the scanned laser velocimeter optical system.

Rhodes, D. B.↗

NASA NTRS1985

New Techniques for Studying Calcium Gradients

Improved techniques for detecting and manipulating spatial gradients of cytosolic free Ca(2+) concentrations (Ca(2)) sub i and intracellular stores are discussed. Three areas of progress are: (1) development of new fluorescent indicators for Ca(2+) that are the first to be suitable for measuring Ca(2+)) sub i and its inhomogeneities in individual cells; (2) invention of photolabile chelators which shift irreversibly from high to low affinity for Ca(2+) upon illumination, permitting light-controlled jumps in (Ca(2+)) sub i; and (3) fixation methods to trap dynamic intraorganellar Ca stores in a form readily visible by electron microscopy.

Tsien, R. Y.↗

NASA NTRS1990

The spectra of relativistic accretion disks - Application to A0620-00

The X-ray flux emitted from a geometrically thin, relativistic accretion disk in the steady state approximation is investigated in order to place limits on the quiescent state mass flow rate in the soft X-ray transient black hole candidate source A0620-00. Specific attention is focused on the effects associated with gravitational redshifts, Doppler shifts, and on the enhancement of the apparent accretion disk area due to gravitational light bending on the continuum spectrum. It is found that the upper limit to the mass flow rate within the inner regions of the disk, constrained by the lack of soft X-rays in the quiescent state, is about 2.8 x 10 to the -11th solar mass/yr for black hole masses greater than about 5.4 solar mass. The optical data are consistent with these upper limits provided that the inclination angle of the binary system is less than about 65 deg. The upper limits and the lack of a hard X-ray flux, together, suggest that the soft X-ray transient model based upon a mass transfer instability situated in the stellar envelope of the companion is inapplicable to A0620-00.

Fu, Albert↗

NASA NTRS1990

A tentative explanation of cosmological red shift

The authors suggest a possible alternative explanation of cosmological red shift. They consider that there exists a background field in the universe, and that light (the photon) has an extremely weak interaction with this background, and as result, experiences an energy loss. By analogy with damped oscillations, the authors introduce a dumping term with the first derivative with respect to time in the wave equation. The solution yields a linearly reduced frequency of the light with travel distance. The purpose of this exercise is to demonstrate how a simple alternative interpretation of the Hubble relation can be generated.

Chang, T.↗

NASA NTRS1995

Very Light Aircraft: Revitalization through Certification

As the future of the general aviation industry seems to be improving, a cultural paradigm shift may be imminent with the implementation of an advanced, revolutionary transportation system within the United States. By observing the support of government and industry for this idea, near and long term effects must be addressed if this change is going to occur. The high certification costs associated with general aviation aircraft must be reduced without compromising safety if a new transportation system is to be developed in the future. With the advent of new, streamlined rules recently issued for the certification of small aircraft, it seems as though new opportunities are now available to the general aviation industry. Not only will immediate benefits be realized with increased sales of certified small aircraft, but there would now be a way of introducing the advanced concepts of future aircraft at varying degrees of technology and cost as options to the customer.

Zyskowski, Michael K.↗

NASA NTRS2007

An Adaptive Cross-Correlation Algorithm for Extended-Scene Shack-Hartmann Wavefront Sensing

This viewgraph presentation reviews the Adaptive Cross-Correlation (ACC) Algorithm for extended scene-Shack Hartmann wavefront (WF) sensing. A Shack-Hartmann sensor places a lenslet array at a plane conjugate to the WF error source. Each sub-aperture lenslet samples the WF in the corresponding patch of the WF. A description of the ACC algorithm is included. The ACC has several benefits; amongst them are: ACC requires only about 4 image-shifting iterations to achieve 0.01 pixel accuracy and ACC is insensitive to both background light and noise much more robust than centroiding,

Terrestrial Planet Finder (TPF)↗

DOE OSTI2021

Strong Purcell enhancement at telecom wavelengths afforded by spinel Fe 3 O 4 nanocrystals with size-tunable plasmonic properties

Developments in the field of nanoplasmonics have the potential to advance applications from information processing and telecommunications to light-based sensing. Traditionally, nanoscale noble metals such as gold and silver have been used to achieve the targeted enhancements in light-matter interactions that result from the presence of localized surface plasmons (LSPs). However, interest has recently shifted to intrinsically doped semiconductor nanocrystals (NCs) for their ability to display LSP resonances (LSPRs) over a much broader spectral range, including the infrared (IR). Among semiconducting plasmonic NCs, spinel metal oxides (sp-MOs) are an emerging class of materials with distinct advantages in accessing the telecommunications bands in the IR and affording useful environmental stability. In this work, we report the plasmonic properties of Fe 3 O 4 sp-MO NCs, known previously only for their magnetic functionality, and demonstrate their ability to modify the light-emission properties of telecom-emitting quantum dots (QDs). We establish the synthetic conditions for tuning sp-MO NC size, composition and doping characteristics, resulting in unprecedented tunability of electronic behavior and plasmonic response over 450 nm. In particular, with diameter-dependent variations in free-electron concentration across the Fe 3 O 4 NC series, we introduce a strong NC size dependency onto the optical response. In addition, our observation of plasmonics-enhanced decay rates from telecom-emitting QDs reveals Purcell enhancement factors for simple plasmonic-spacer-emitter sandwich structures up to 51-fold, which are comparable to values achieved previously only for emitters in the visible range coupled with conventional noble metal NCs.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Biomimetic Light Harvesting Complexes Based on Self-Assembled Dye-DNA Nanostructures (Final Technical Report)

A fundamental limitation in the development of artificial molecular light harvesting structures is that generally if one places pigment molecules close enough to achieve very high energy transfer efficiency and absorbance cross section, the dyes interact in such a way that self-quenching occurs. This limits both the optical cross section and the overall efficiency of light capture in such systems. Nature overcomes this problem and achieves efficient energy transfer without self-quenching by controlling the environment, vibration characteristics, orientation and dynamics of the pigments involved in light harvesting. Natural light harvesting systems have evolved highly intricate chromophore architectures of protein-bound organic molecules that absorb and funnel solar energy with high efficiency and fast transfer rates using elegant excitonic circuitries. Nature achieves this precise control over the properties of pigment complexes by using specific proteins as templates to guide the formation of very well-defined pigment aggregates, groups of pigment molecules that are in close enough contact to undergo excitonic interactions resulting in new electronic properties that were not present in the monomer. In synthetic systems, pigment aggregates are well known, and J-aggregates and H-aggregates have been long studied for their unique properties. In Nature, the chlorosomes of green bacteria form what appear to be classical J-aggregates and the light harvesting complexes of purple nonsulfur bacteria form ring structures that have many of the properties of J-aggregates such as a red-shifted absorbance spectrum and excited states that are delocalized over multiple pigment molecules. These photosynthetic systems leverage the spectral and enhanced transport properties of J-like aggregates to achieve fast exciton transport within the antenna and thus high light-harvesting efficiency. The close interaction of the pigments results in substantial electronic coupling that lifts the degeneracy of excitonic states and therefore modifies the absorption and emission spectra of the monomer. In the case of J-aggregation, lower energy excitonic states acquire significant oscillator strength, resulting in a characteristic bathochromic shift of the absorption and fluorescence and often superradiant delocalized exciton states.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1994

Phytochrome, plant growth and flowering

Attempts to use artificially lit cabinets to grow plants identical to those growing in sunlight have provided compelling evidence of the importance of light quality for plant growth. Changing the balance of red (R) to far-red (FR) radiation, but with a fixed photosynthetic input can shift the phytochrome photoequilibrium in a plant and generate large differences in plant growth. With FR enrichment the plants elongate, and may produce more leaf area and dry matter. Similar morphogenic responses are also obtained when light quality is altered only briefly (15-30 min) at the end-of-the-day. Conversely, for plants grown in natural conditions the response of plant form to selective spectral filtering has again shown that red and far-red wavebands are important as found by Kasperbauer and coworkers. Also, where photosynthetic photon flux densities (PPFD) of sunlight have been held constant, the removal of far-red alone alters plant growth. With FR depletion plants grown in sunlight are small, more branched and darker green. Here we examine the implications for plant growth and flowering when the far-red composition of incident radiation in plant growth chambers is manipulated.

King, R. W.↗