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At least 271 records · Page 15

All sources NASA NTRS DOE OSTI

DOE OSTI2022

Gross primary production (GPP) and red solar induced fluorescence (SIF) respond differently to light and seasonal environmental conditions in a subalpine conifer forest

The phenology of montane conifer forests is likely to shift in response to climate change and altered seasonal dynamics of light, temperature, and moisture. Solar-induced fluorescence (SIF) is expected to provide substantial improvement for mapping temporal changes in evergreen gross primary production (GPP) over greenness-based remote sensing indices. The utility of SIF to monitor seasonal changes in the phenology of conifer photosynthesis depends on the degree to which GPP and SIF respond in synchrony to key environmental drivers. However, to what extent SIF and GPP become decoupled by responding differently to the combined effects of light and other environmental conditions remains unknown. The goal of this study was to characterize the responses of GPP and SIFred to a suite of environmental drivers at the half-hour time scale and determine how these relationships change across seasons. We analyzed one year of tower-based SIFred and eddy covariance-derived GPP data from a conifer forest at Niwot Ridge, Colorado. We compared the light responses of GPP and SIFred across the year, finding that SIFred increased in response to light earlier in the year than did GPP. The light response of GPP had a positive temperature dependence in spring, and this dependency reversed in summer due to increased evaporative demand, while the light response of SIFred was less temperature dependent. Using artificial neural network ensemble analysis, we found that from spring to summer, SIFred did not exhibit a parallel response to the seasonally dynamic temperature and moisture controls on GPP. In summer SIFred was not correlated with canopy conductance, suggesting that SIF is less sensitive to stomatal control than GPP. Furthermore, our results suggest that, in conifers, photosystems begin to activate in spring prior to when water becomes available for photosynthesis, presenting a challenge for the use of SIF as a phenological indicator in conifer forests.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Development of a large-mass, low-threshold detector system with simultaneous measurements of athermal phonons and scintillation light

For this work, we have combined two low-threshold detector technologies to develop a large-mass, low-threshold detector system that simultaneously measures the athermal phonons in a sapphire detector while an adjacent silicon high-voltage detector detects the scintillation light from the sapphire detector. This detector system could provide event-by-event discrimination between electron and nuclear events due to the difference in their scintillation light yield. While such systems with simultaneous phonon and light detection have been demonstrated earlier with smaller detectors, our system is designed to provide a large detector mass with high amplification for the limited scintillation light. Future work will focus on at least an order of magnitude improvement in the light collection efficiency by having a highly reflective detector housing and custom phonon mask design to maximize light collection by the silicon high-voltage detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

Absolute light yield of the EJ-204 plastic scintillator

The absolute light yield of a scintillator, defined as the number of scintillation photons produced per unit energy deposited, is a useful quantity for scintillator development, research, and applications. Yet, literature data on the absolute light yield of organic scintillators are limited. The goal of this work is to assess the suitability of the EJ-204 plastic scintillator from Eljen Technology to serve as a reference standard for measurements of the absolute light yield of organic scintillators. Four EJ-204 samples were examined: two manufactured approximately four months prior and stored in high-purity nitrogen, and two aged approximately eleven years and stored in ambient air. The scintillator response was measured using a large-area avalanche photodiode calibrated using low energy $γ$-ray and X-ray sources. The product of the quantum efficiency of the photodetector and light collection efficiency of the housing was characterized using an experimentally-benchmarked optical photon simulation. The average absolute light yield of the fresh samples, 9100 ± 400 photons per MeV, is lower than the manufacturer-reported value of 10400 photons per MeV. Moreover, the aged samples demonstrated significantly lower light yields, deviating from the manufacturer specification by as much as 26%. These results are consistent with recent work showcasing environmental aging in plastic scintillators and suggest that experimenters should use caution when deploying plastic scintillators in photon counting applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2021

The Path to Enlightenment: Progress and Opportunities in High Efficiency Halide Perovskite Light-Emitting Devices

Besides the flourishment in photovoltaics, halide perovskites hold great promise to compete with leading contenders among solution-processed emitters, such as organics and semiconductor colloidal nanocrystals, in the field of light emission. Halide perovskites exhibit outstanding optoelectronic properties, including high photoluminescence quantum yields, facile bandgap tunability, narrow emission line widths, and respectable carrier mobilities, promoting them to thrive in versatile light-emitting applications such as light-emitting diodes, lasers, X-ray scintillators, and circularly polarized light sources. Herein, we discuss the underlying physics of light emission in state-of-the-art perovskite light-emitting devices and focus on promising strategies for further improvement of device performance.

42 ENGINEERING↗

DOE OSTI2023

Light-independent regulation of algal photoprotection by CO 2 availability

Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO 2 conditions. When light energy exceeds CO 2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO 2 Concentrating Mechanism (CCM). How light and CO 2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO 2 concentrations and that depletion of CO 2 drives these responses, even in total darkness. High CO 2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3/CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO 2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO 2 levels.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2025

High aspect ratio organic light-emitting diodes

Reliability is particularly challenging for organic light-emitting diodes (OLEDs) used in solid-state lighting applications, because OLED lifetime is inversely proportional to luminance, and most lighting applications demand high luminance. Here we introduce a strategy to overcome this tradeoff by constructing OLEDs on a substrate with sub-mm, high aspect ratio surface texture. By creating more active OLED area per unit lighting panel area, the device current density required to generate a given panel luminance decreases. We validate this approach for fluorescent and phosphorescent OLEDs, demonstrating good thickness uniformity on corrugated substrates with area enhancement factors up to 1.4x using a standard thermal evaporator. Relative to planar controls at the same panel current density, the high aspect ratio devices achieve a 2.7-fold increase in operating lifetime and up to a 40% increase in external light extraction efficiency, indicating that this approach offers a powerful pathway to improve the efficiency and lifetime of OLED lighting.

OLED↗

DOE OSTI2021

The roles of photochemical and non-photochemical quenching in regulating photosynthesis depend on the phases of fluctuating light conditions

We report the induction and relaxation of photochemistry and non-photochemical quenching (NPQ) are not instantaneous and require time to respond to fluctuating environments. There is a lack of integrated understanding on how photochemistry and NPQ influence photosynthesis in fluctuating environments. We measured the induction and relaxation of chlorophyll a fluorescence and gas exchange in poplar and cotton at varying temperatures under saturating and fluctuating lights. When the light shifted from dark to high, the fraction of open reaction centers in photosystem II (q L ) gradually increased while NPQ increased suddenly and then remained stable. Temperature significantly changed the response of q L but not that of NPQ during the dark to high light transition. Increased q L led to higher photosynthesis but their precise relationship was affected by NPQ and temperature. q L was significantly related to biochemical capacity. Thus, q L appears to be a strong indicator of the activation of carboxylase, leading to the similar dynamics between q L and photosynthesis. When the light shifted from high to low intensity, NPQ is still engaged at a high level, causing a stronger decline in photosynthesis. Our finding suggests that the dynamic effects of photochemistry and NPQ on photosynthesis depend on the phases of environmental fluctuations and interactive effects of light and temperature. Across the full spectra of light fluctuation, the slow induction of q L is a more important limiting factor than the slow relaxation of NPQ for photosynthesis in typical ranges of temperature for photosynthesis. The findings provided a new perspective to improve photosynthetic productivity with molecular biology under natural fluctuating environments.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2021

AbacusSummit Halo Light Cone Catalogs

This is a set of halo light cone catalogs from the AbacusSummit suite of cosmological N-body simulations (abacussummit.readthedocs.io/). They are a value-added data product provided by post-processing the simulation output. The main application of the halo light cone catalogs is the construction of realistic mock galaxy catalogues and weak lensing maps on the sky. The algorithm (described in Hadzhiyska et al. 2021) associates CompaSO halos from 29 redshift epochs spanning z = 0.1-2.5 with their particles at the time of light-cone crossing. It then records the halo and particle information into an easily accessible product, which can be read with the CompaSO reader. The 25 base resolution boxes at fiducial cosmology have a halo light cone catalog covering an octant of the sky to z approx 0.8 and about 2000 deg2 extending to z approx 2.4. The huge boxes provide light cone information of the full sky until z approx 2.18 and extend further towards the corners of the box (available until z = 2.25). Galaxy mock catalogs on the sky can be generated easily though the AbacusHOD script providing an extended HOD framework (see Yuan et al. 2021, for details), which has been modified to work with the halo light cone catalogs. The available tracers are luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasi-stellar objects (QSOs).

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Design tradeoffs between traditional hexagonal and emerging cubic In X Ga (1–X) N/GaN-based green light-emitting diodes

Here, we report on the design tradeoffs between traditional hexagonal and emerging cubic In X Ga (1–X) N/GaN -based green (520 nm≤ λ ≤550 nm) light-emitting diodes with special emphasis on the electron blocking layer, number of quantum wells, and thicknesses of quantum wells and barriers. We identified three crucial design rules for cubic green light-emitting diodes: (1) no need for an electron blocking layer; (2) use of a wide quantum well; and (3) choice of thin quantum barriers in multi-quantum well light-emitting diode designs. These design rules increase the internal quantum efficiency of cubic green light-emitting diodes by ~30.5% under 100A/cm 2 injection with respect to traditional designs. Overall, the design rules of cubic light-emitting diodes and their differentiating nature from the traditional, hexagonal ones are crucial for the advent of next-generation cubic light-emitting diodes.

42 ENGINEERING↗

DOE OSTI2022

A Cybersecurity Threat Profile for a Connected Lighting System

In anticipation of improved energy performance and cost savings, cities and building owners are increasingly considering “smart lighting initiatives” that aim to convert their collection of simple luminaires (i.e., lighting fixtures) into an intelligent connected lighting system (CLS) capable of remotely monitoring energy consumption and fault conditions, and possibly implementing adaptive lighting schemes. The U.S. Department of Energy (DOE) has set an national goal of tripling the energy efficiency and demand flexibility of the buildings sector by 2030, relative to 2020 levels 1. It is forecast that connected lighting systems can contribute to that goal by delivering 125 TWh of annual energy savings by 2035 2, equivalent to the annual output of 50 typical (500 MW) power plants. However, these energy savings and the DOE goal are put at significant risk if connected technologies are not adopted due to real or perceived cybersecurity concerns. Connected IoT devices such as these have historically been rife with vulnerabilities which sometimes put security considerations secondary to functionality and operability. What are the cybersecurity threats that will impact these systems, as formerly banal luminaires transition into intelligent connected devices that collect information about themselves, their surrounding environment, and possibly us? In this paper we analyze a threat profile performed on a fault-detection use case for streetlights. A threat profile establishes security requirements, justifies security measures, yields actionable controls, and effectively communicates risk to stakeholders. This effort provides critical information for making threat-based decisions to increase security at a reasonable cost, and can effectively be used by development teams, software architects, and managers to make cybersecurity a part of their ongoing culture of awareness, training, and prevention. This leads to more secure systems and better-understood security. On-premise, cloud, and hybrid architectures with different authentication mechanisms were modeled and later categorized using the Microsoft STRIDE framework. An analysis of the recommended controls for each threat was performed to determine which controls could and should be put in place by manufacturers or third-party suppliers, and which controls need to be left up the end-user to implement. Fifty-seven threats were identified. Among our key findings: (1) 65% (37/57) of the threats did not involve the luminaires, but rather the other components needed to communicate with and manage them; (2) 63% (36/57) of the threats could have been mitigated through manufacturer-implemented defensive techniques or “controls”; and (3) 23% (13/57) of the threats were dependent on the network configuration. Recommendations based on the results of this work are made to key stakeholder groups. Notably, lighting technology developers are advised to address all threats that can be reasonably controlled with baked-in technology solutions (e.g., encryption or authentication controls), and employ some form of secure supply chain management and tracking where other parts (e.g., sensors, microprocessors) of a luminaire must also be built and manufactured with the proper security controls in place. Developers should also review threats involving assets not developed in-house to understand how connectivity with other devices will affect their product during system operation and determine if a compensating control for a defense-in-depth strategy will be needed. Finally, those interested in deploying CLS should compare the differences between cloud and on-premise models to determine which is more suitable for their needs and the abilities of their security team.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2024

Iron Bonding with Light Elements: Implications for Planetary Cores Beyond the Binary System

Light element alloying in iron is required to explain density deficit and seismic wave velocities in Earth’s core. However, the light element composition of the Earth’s core seems hard to constrain as nearly all light element alloying would reduce the density and sound velocity (elastic moduli). The alloying light elements include oxidizing elements like oxygen and sulfur and reducing elements like hydrogen and carbon, yet their chemical effects in the alloy system are less discussed. Moreover, Fe-X-ray Absorption Near Edge Structure (Fe-XANES) fingerprints have been studied for silicate materials with ferrous and ferric ions, while not many X-ray absorption spectroscopy (XAS) studies have focused on iron alloys, especially at high pressures. To investigate the bonding nature of iron alloys in planetary interiors, we presented X-ray absorption spectroscopy of iron–nitrogen and iron–carbon alloys at high pressures up to 50 GPa. Together with existing literature on iron–carbon, –hydrogen alloys, we analyzed their edge positions and found no significant difference in the degree of oxidation among these alloys. Pressure effects on edge positions were also found negligible. Our theoretical simulation of the valence state of iron, alloyed with S, C, O, N, and P also showed nearly unchanged behavior under pressures up to 300 GPa. This finding indicates that the high pressure bonding of iron alloyed with light elements closely resembles bonding at the ambient conditions. We suggest that the chemical properties of light elements constrain which ones can coexist within iron alloys.

Advanced Photon Source↗

DOE OSTI2024

2020 U.S. Lighting Market Characterization

The Lighting Market Characterization report details how many lighting products (lamps and luminaires) were installed in the U.S. as of 2020, where they were installed, and how much energy they consumed. It also highlights key changes in U.S. lighting market characteristics between 2015 and 2020. This is the fourth edition of the LMC report; previous versions were released in 2002, 2012 and 2017. By publishing summary estimates of installed stock and energy use of various general illumination lighting products, these reports help DOE and others plan effective lighting research and development programs based on changing needs.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2024

2020 U.S. Lighting Market Characterization

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2024

2020 U.S. Lighting Market Characterization

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2023

A Membrane-Associated Light-Harvesting Model is Enabled by Functionalized Assemblies of Gene-Doubled TMV Proteins

Photosynthetic light harvesting requires efficient energy transfer within dynamic networks of light-harvesting complexes embedded within phospholipid membranes. Artificial light-harvesting models are valuable tools for understanding the structural features underpinning energy absorption and transfer within chromophore arrays. Here, a method for attaching a protein-based light-harvesting model to a planar, fluid supported lipid bilayer (SLB) is developed. The protein model consists of the tobacco mosaic viral capsid proteins that are gene-doubled to create a tandem dimer (dTMV). Assemblies of dTMV break the facial symmetry of the double disk to allow for differentiation between the disk faces. A single reactive lysine residue is incorporated into the dTMV assemblies for the site-selective attachment of chromophores for light absorption. Further, on the opposing dTMV face, a cysteine residue is incorporated for the bioconjugation of a peptide containing a polyhistidine tag for association with SLBs. The dual-modified dTMV complexes show significant association with SLBs and exhibit mobility on the bilayer. The techniques used herein offer a new method for protein-surface attachment and provide a platform for evaluating excited state energy transfer events in a dynamic, fully synthetic artificial light-harvesting system.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2026

Spatiotemporal 4D Whole-cell Modeling of a Minimal Autotroph Reveals Central Carbon Metabolism Regulated Locally by Protein Megacomplexes via Post-translational Modifications under Light Disturbance

Photosynthetic microorganisms rely on multiple pathways in central carbon metabolism to adapt to fluctuating light and energy availability across diel cycles. Mechanistic insight into the regulatory dynamics of this adaptation requires integrating processes spanning disparate timescales, from rapid redox-dependent post-translational modifications (PTMs) to slower changes in protein expression and metabolic pathway usage. To address this complexity beyond genome-based inference and traditional modeling, we develop a whole-cell four-dimensional (3D + time) model of the marine cyanobacterium Prochlorococcus marinus MED4 that explicitly represents the spatial organization of enzymatic and molecular processes in central carbon metabolism under light perturbation. We employ a perturbation-based research design to experimentally generate time-series, multi-omics measurements that provide molecular descriptors and cryo-ET derived 3D segmented volumes as constraints for this dynamic 4D framework. The integration of experiments and modeling across defined light regimes enables quantitative validation of system-level responses and forecasting under distinct light disturbances. We test the hypothesis that light-dependent redox PTMs regulating the structural assembly of a protein megacomplex, the “dark complex,” modulate metabolic flux at a conserved regulatory node of the Calvin–Benson cycle (CBC) in cyanobacteria. Our model shows that subcellular spatial organization buffers rapid light-induced changes in thylakoid reaction rates, which are followed by redox-PTM-mediated sequestration or release of CBC enzymes in the dark complex, ultimately impacting carbon fixation dynamics within carboxysomes. Comparison with an equivalently parameterized well-mixed stochastic model demonstrates that post-translational regulation not only buffers transcriptional noise and diffusion-driven fluctuations but also stabilizes phenotypic outcomes, underscoring the importance of spatial heterogeneity in phenotypic robustness. This ability to probe adaptive, spatiotemporally resolved mechanisms in photosynthetic machinery and central carbon metabolism addresses a critical gap in genotype-to-phenotype inference and expands modeling and design capabilities for understudied or genetically intractable autotrophs such as P. marinus MED4.

Johnson, Connah G.↗

DOE OSTI2025

Electrochemical growth of polyaniline films controlled with light

Plasmonic environment and light illumination can have significant impacts on electrochemical reactions. We explore the possibility to control electrochemical deposition of polyaniline films on gold substrates with light and study factors affecting film growth. The analysis of light-induced patterns in films exposed to laser light at different intensities and wavelengths reveals that the growth rate increases the light intensity at small intensities and then saturates with the further increase in laser light intensity. The wavelength of illumination does not significantly affect the results. The findings provide opportunities in fabrication of plasmonic structures with specific patterns of electrochromic polymer, which can operate as electrically tunable metasurfaces and plasmonic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Novel white light-emitting CdSe:Mn 2+ synthesized by photo-assisted chemical bath deposition

Nowadays, white light-emitting materials have attracted extensive research due to their potential applications in lighting devices and displaying images. Several semiconductor nanoparticles have been explored to achieve efficient white light emission. In this work, we report on novel white light-emitting CdSe:Mn 2+ thin films synthesized by photo-assisted chemical bath deposition. The effect of varying the Mn 2+ ion concentrations on the thin film structure, morphology, and optical properties was investigated. X-ray powder diffraction results indicated that all the films annealed at 250 degrees C possessed a cubic structure, with crystallite sizes in the range of 1-130 nm. Scanning electron microscopy demonstrated spherical nanoparticles with no significant changes with varying Mn 2+ doping concentrations. Energy dispersive X-ray spectroscopy confirmed the presence of the anticipated elements. The atomic force microscope revealed that the surface roughness has decreased with an increase in Mn 2+ ion concentrations but decreased for 0.7 %Mn 2+ . The UV-Vis absorption spectra showed absorption edges around 600-650 nm. Photoluminescence emission spectra excited at 3.8 eV (325 nm) showed emission bands at around 1.75 eV (709 nm), and 1.88 eV (659 nm), which were attributed to the band-to-band emission, and 4 T 1 ( 4 G)-> 6 A 1 ( 6 S) transitions of Mn 2+ ions, respectively, while emission bands at 2.35 eV (528 nm), and prominent at 3.17 eV (391 nm) were due to the glass substrate. The temperature-dependent luminescence showed a decrease in relative emission intensity with the increase in the operating temperature. The chromaticity colour coordinates showed white light-emitting thin films. These present findings open a new door to developing white light using CdSe thin films.

36 MATERIALS SCIENCE↗