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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Matter-enhanced transition probabilities in quantum field theory

The relativistic quantum field theory is the unique theory that combines the relativity and quantum theory and is invariant under the Poincaré transformation. The ground state, vacuum, is singlet and one particle states are transformed as elements of irreducible representation of the group. The covariant one particles are momentum eigenstates expressed by plane waves and extended in space. Although the S-matrix defined with initial and final states of these states hold the symmetries and are applied to isolated states, out-going states for the amplitude of the event that they are detected at a finite-time interval T in experiments are expressed by microscopic states that they interact with, and are surrounded by matters in detectors and are not plane waves. These matter-induced effects modify the probabilities observed in realistic situations. The transition amplitudes and probabilities of the events are studied with the S-matrix, S[T], that satisfies the boundary condition at T. Using S[T], the finite-size corrections of the form of 1/T are found. The corrections to Fermi’s golden rule become larger than the original values in some situations for light particles. They break Lorentz invariance even in high energy region of short de Broglie wave lengths. -- Highlights: •S-matrix S[T] for the finite-time interval in relativistic field theory. •S[T] satisfies the boundary condition and gives correction of 1/T . •The large corrections for light particles breaks Lorentz invariance. •The corrections have implications to neutrino experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Examination of lead concentrations in new decorative enamel paints in four countries with different histories of activity in lead paint regulation

Paints with high lead concentrations (ppm) continue to be sold around the world in many developing countries and those with economies in transition representing a major preventable environmental health hazard that is being increased as the economies expand and paint consumption is increasing. Prior lead paint testing had been performed in Brazil and India and these countries were selected to examine the impact of a new regulatory limit in Brazil and the impact of efforts of non-governmental organizations and others to stop the use of lead compounds in manufacturing paints. Armenia and Kazakhstan, in Central Asia, were selected because no information on lead concentration in those regions was available, no regulatory activities were evident and non-governmental organizations in the IPEN network were available to participate. Another objective of this research was to evaluate the lead loading (µg/cm{sup 2}) limit determined by X-Ray Fluorescence (XRF) for areas on toys that are too small to obtain a sample of sufficient size for laboratory analysis. The lead concentrations in more than three-fourths of the paints from Armenia and Kazakhstan exceeded 90 ppm, the limit in the United States, and 600 ppm, the limit in Brazil. The percentages were about one-half as high in Brazil and India. The average concentration in paints purchased in Armenia, 25,000 ppm, is among the highest that has been previously reported, that in Kazakhstan, 15,700 ppm, and India, 16,600, about median. The average concentration in Brazil, 5600 ppm, is among the lowest observed. Paints in Brazil that contained an average of 36,000 ppm before the regulatory limit became effective were below detection (<9 ppm) in samples collected in the current study. The lack of any apparent public monitoring of paint lead content as part of regulatory enforcement makes it difficult to determine whether the regulation was a major factor contributing to the decline in lead use in these paints. Using data from the current study and those available from other studies 24 of 28 paints from major brands in India decreased from high concentrations to 90 ppm or lower. Since lead concentrations in golden yellow paints from these brands were found to decrease to ≤90 ppm, it is possible that all 28 of these paints now contain ≤90 ppm since yellow paints usually have the highest lead concentrations. Other brands in Brazil and India that have been analyzed only one time had lead concentrations up to 59,000 ppm and 134,000 ppm, respectively. Less than one-third of the paints had notations on their labels with information about lead content and these were sometimes inaccurate. The label from one brand indicating “no added lead” contained paint with 134,000 ppm lead, the highest found in this study. Three percent (3 of 98) of the paints with surface lead loading that did not exceed 2 µg/cm{sup 2}, the limit established by the Consumer Product Safety Improvement Act for small areas on toys, contained greater than 90 ppm lead and thus were false negatives. Of the new paint samples that contained ≤600 ppm, 88% contained ≤90 ppm. Of the samples that contained ≤90 ppm, 97% contained ≤45 ppm and 92% contained ≤15 ppm. Based on these data it appears to be technically feasible to manufacture paints containing ≤90 ppm and in many cases to produce paints that have lead concentrations that do not exceed 15 ppm. - Highlights: • Brazilian paints with high lead (avg. 36,000 ppm) contained <9 ppm after regulation. • Lead in major Indian paint brands decreased to low levels by efforts of NGOs/others. • Most paints with lead ≤600 ppm also are ≤90 ppm and many also ≤15 ppm. • At the CPSIA limit of 2 µg Pb/cm{sup 2} for small areas on toys, 3% exceeded 90 ppm lead. • Most paint brands in Armenia and Kazakhstan based/manufactured outside the country.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

The histone demethylase KdmB is part of a trimeric protein complex and mediates virulence and mycotoxin production in Penicillium expansum

Epigenetic modification of chromosome structure has increasingly been associated with alterations in secondary metabolism and sporulation defects in filamentous fungal pathogens. Recently, the epigenetic reader protein SntB was shown to govern virulence, spore production and mycotoxin synthesis in the fruit pathogen Penicillium expansum. Through immunoprecipitation-coupled mass spectrometry, we found that SntB is a member of a protein complex with KdmB, a histone demethylase and the essential protein RpdA, a histone deacetylase. Deletion of kdmB phenocopied some but not all characteristics of the ΔsntB mutant. KdmB deletion strains exhibited reduced lesion development on Golden Delicious apples and this was accompanied by decreased production of patulin and citrinin in host tissue. In addition, ΔkdmB mutants were sensitive to several cell wall stressors which possibly contributed to the decreased virulence observed on apples. In conclusion, slight differences in spore production and germination rates of ΔkdmB mutants in vitro did not impact overall diameter growth in culture.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Primordial black-hole dark matter via warm natural inflation

We report on a study of the natural warm inflationary paradigm (WNI). We show two important new results arise in this model. One is that the observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. The second is that WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the golden window of black-hole mass range (10 -16 - 10 -11 M ⊙ ) where it can account for all of the dark matter content of the universe while satisfying observational constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Photovoltaic system derived data for determining the solar resource and for modeling the performance of other photovoltaic systems

Using performance data from some of the millions of installed photovoltaic (PV) modules with micro-inverters may afford the opportunity to provide ground-based solar resource data critical for developing PV projects. Here, a method was developed to back-solve for the direct normal irradiance (DNI) and the diffuse horizontal irradiance (DHI) from the measured ac power of south-facing PV module/micro-inverter systems. The method was validated using one year of irradiance and PV performance measurements for five PV systems, each with a different tilt/azimuth orientation, and located in Golden, Colorado. Compared to using a measured global horizontal irradiance for PV performance model input, using the back-solved values of DNI and DHI only increased the range of mean bias deviations from measured values by 0.6% for the modeled annual averages of the global tilt irradiance and ac power for the five PV systems. Correcting for angle-of-incidence effects is an important feature of the method to prevent underestimating the solar resource and for modeling the performance of PV systems with more dissimilar PV module orientations. The results for the method were also shown more favorable than the results when using an existing power projection method for estimating the ac power.

14 SOLAR ENERGY↗
DOE OSTI2020

Ambient pressure synthesis and characterization of layered honeycomb Li 2 PdO 3

Single-phase polycrystalline Li 2 PdO 3 has been synthesized at 640°C in oxygen for the first time under ambient pressure. X-ray and neutron diffraction analyses show that the sample possesses a monoclinic layered structure belonging to the C2/m space group. Rietveld refinements of neutron powder diffraction data indicate ~10% Li–Pd site exchange and DIFFaX modelling manifest ~2% stacking faults present within LiPd 2 layers. A band gap of ~2.23 eV was calculated for the golden Li 2 PdO 3 using absorbance measurements. Thermogravimetric analysis of the sample shows that Li 2 PdO 3 is stable up to 730°C under oxygen. Here a Curie tail is observed at low temperature magnetic measurements (T < 50K), yielding an effective moment of 0.038 μ B , possibly due to spin ½ impurities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electric vehicle fast charging infrastructure planning in urban networks considering daily travel and charging behavior

Electric vehicles are a sustainable substitution to conventional vehicles. This work introduces an integrated framework for urban fast charging infrastructure to address the range anxiety issue. A mesoscopic simulation tool is developed to generate trip trajectories, and simulate charging behavior based on various trip attributes. The resulting charging demand is the key input to a mixed-integer nonlinear program that seeks charging station configuration. The model minimizes the total system cost including charging station and charger installation costs, and charging, queuing, and detouring delays. The problem is solved using a decomposition technique incorporating a commercial solver for small networks, and a heuristic algorithm for large-scale networks, in addition to the Golden Section method. The solution quality and significant superiority in the computational efficiency of the decomposition approach are confirmed in comparison with the implicit enumeration approach. Furthermore, the required infrastructure to support urban trips is explored for future market shares and technologies.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2018

Altered myofilament structure and function in dogs with Duchenne muscular dystrophy cardiomyopathy

Aim Duchenne Muscular Dystrophy (DMD) is associated with progressive depressed left ventricular (LV) function. However, DMD effects on myofilament structure and function are poorly understood. Golden Retriever Muscular Dystrophy (GRMD) is a dog model of DMD recapitulating the human form of DMD. Objective The objective of this study is to evaluate myofilament structure and function alterations in GRMD model with spontaneous cardiac failure. Methods and results We have employed synchrotron X-rays diffraction to evaluate myofilament lattice spacing at various sarcomere lengths (SL) on permeabilized LV myocardium. We found a negative correlation between SL and lattice spacing in both sub-epicardium (EPI) and sub-endocardium (ENDO) LV layers in control dog hearts. In the ENDO of GRMD hearts this correlation is steeper due to higher lattice spacing at short SL (1.9 μm). Furthermore, cross-bridge cycling indexed by the kinetics of tension redevelopment (ktr) was faster in ENDO GRMD myofilaments at short SL. We measured post-translational modifications of key regulatory contractile proteins. S-glutathionylation of cardiac Myosin Binding Protein-C (cMyBP-C) was unchanged and PKA dependent phosphorylation of the cMyBP-C was significantly reduced in GRMD ENDO tissue and more modestly in EPI tissue. Conclusions We found a gradient of contractility in control dogs' myocardium that spreads across the LV wall, negatively correlated with myofilament lattice spacing. Chronic stress induced by dystrophin deficiency leads to heart failure that is tightly associated with regional structural changes indexed by increased myofilament lattice spacing, reduced phosphorylation of regulatory proteins and altered myofilament contractile properties in GRMD dogs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

The conservation value of forest fragments in the increasingly agrarian landscape of Sumatra

Throughout the world, tropical rainforests are being destroyed at an alarming rate, reducing many unprotected habitats to small fragments of remnant forests within the cleared landscape. Understanding the best way to provide wildlife habitat amid changing landscapes is essential for land use planning, especially in biodiversity hotspots like Indonesia. However, little is known about the conservation significance and mammalian use of forest fragments in Sumatra. In this study, camera trap surveys were conducted within Bukit Barisan Selatan National Park and five surrounding forest fragments, and species composition metrics were used to compare their use. Twenty-eight species of mammals were found in the forest and 21 in the surrounding fragments. The fragments harbored a subset of the species found within the primary forest, as well as several species not observed in the forest. Critically endangered species such as Sunda pangolin (Manis javanica) and Sumatran tiger (Panthera tigris sumatrae) were found in the fragments, along with species of conservation concern such as marbled cat (Pardofelis marmorata) and Asiatic golden cat (Pardofelis temminickii). The biodiversity found within the fragments suggests that these small patches of remnant forest may be of conservation value to certain mammal species and may facilitate connectivity across the landscape.

biodiversity, tropical forests, mammals↗
DOE OSTI2026

Charge Transport in Solvated Donor–Acceptor Functionalized Peptoids: Molecular Dynamics and Rate Theory

Scalable solar-energy conversion requires photoactive materials that combine the efficiency of natural photosynthetic systems with the stability and processability needed for practical applications. Achieving reliable charge transport in soft, self-assembled organic materials remains challenging, as structural fluctuations and environmental effects strongly influence charge-transfer (CT) rates. Here, we present a broadly applicable computational framework for evaluating CT rates in the condensed phase, combining Fermi’s golden rule rate theory with inputs from all-atom molecular dynamics (MD) simulations and first-principles electronic-structure calculations. The approach does not rely on system-specific parametrization and is applicable to a wide range of soft and disordered materials. We demonstrate the applicability and usefulness of the framework on redox-active peptoids functionalized with iron–porphyrin (Fe–P) complexes, a bioinspired platform with programmable donor–acceptor units and tunable three-dimensional organization. The calculated CT rates exhibit strong sensitivity to molecular conformation, with variations spanning several orders of magnitude. This dependence is shown to arise from the pronounced variation in diabatic electronic coupling with the relative orientations and separations of the Fe–P complexes across the conformational ensemble. The framework provides a consistent route for connecting atomistic structure to CT kinetics in the condensed phase and enables analysis of structure–rate relations in organic semiconducting systems.

Charge transfer↗
DOE OSTI2016

Ultrafast Spectroscopic Signatures of Coherent Electron-Transfer Mechanisms in a Transition Metal Complex

The prevalence of ultrafast electron-transfer processes in light-harvesting materials has motivated a deeper understanding of coherent reaction mechanisms. Kinetic models based on the traditional (equilibrium) form of Fermi’s Golden Rule are commonly employed to understand photoinduced electron-transfer dynamics. These models fail in two ways when the electron-transfer process is fast compared to solvation dynamics and vibrational dephasing. First, electron-transfer dynamics may be accelerated if the photoexcited wavepacket traverses the point of degeneracy between donor and acceptor states in the solvent coordinate. Second, traditional kinetic models fail to describe electron-transfer transitions that yield products which undergo coherent nuclear motions. We address the second point in this work. Transient absorption spectroscopy and a numerical model are used to investigate coherent back-electron-transfer mechanisms in a transition metal complex composed of titanium and catechol, [Ti(cat) 3] 2– . The transient absorption experiments reveal coherent wavepacket motions initiated by the back-electron-transfer process. Model calculations suggest that the vibrationally coherent product states may originate in either vibrational populations or coherences of the reactant. That is, vibrational coherence may be produced even if the reactant does not undergo coherent nuclear motions. Lastly, the analysis raises a question of broader significance: can a vibrational population-to-coherence transition (i.e., a nonsecular transition) accelerate electron-transfer reactions even when the rate is slower than vibrational dephasing?

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Predicting Dexter Energy Transfer Interactions from Molecular Orbital Overlaps

Dexter energy transfer (DET), also known as spin forbidden energy transfer (e.g., 3 D 1 A → 1 D 3 A), is undergoing renewed interest because of its utility in energy science, photocatalysis, and biomedical imaging. The DET reactions enable exciton fission and fusion and have been recently used to facilitate nanoscale imaging of protein assemblies on cell surfaces. While DET and Förster energy transfer rates are often well described using Fermi’s golden rule, the donor–acceptor couplings for DET may be bridge-state-mediated and depend on the electronic structure of and interactions among the donor, bridge, and acceptor. We provide a simple approach to approximate DET couplings using a product of molecular orbital overlap factors. This approach may be used to guide the design of DET systems with targeted energy-transfer kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Theory of Exciton Energy Transfer in Carbon Nanotube Composites

Here, we compute the exciton transfer (ET) rate between semiconducting single-wall carbon nanotubes (SWNTs). We show that the main reasons for the wide range of measured ET rates reported in the literature are (1) exciton confinement in local quantum wells stemming from disorder in the environment and (2) exciton thermalization between dark and bright states due to intratube scattering. The SWNT excitonic states are calculated by solving the Bethe–Salpeter equation using tight-binding basis functions. The ET rates due to intertube Coulomb interaction are computed via Fermi’s golden rule. In pristine samples, the ET rate between parallel (bundled) SWNTs of similar chirality is very high (~10 14 s –1 ), while the ET rate for dissimilar or nonparallel tubes is considerably lower (~10 12 s –1 ). Exciton confinement reduces the ET rate between same-chirality parallel SWNTs by 2 orders of magnitude but has little effect otherwise. Consequently, the ET rate in most measurements will be on the order of 10 12 s –1 , regardless of the tube relative orientation or chirality. Exciton thermalization between bright and dark states further reduces the ET rate to ~10 11 s –1 . The ET rate also increases with increasing temperature and decreases with increasing dielectric constant of the surrounding medium.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Elucidation of Ultrafast Decay, Vibrational Beating, and Slow Decay Processes of Excited Azulene

Azulene’s nonradiative decay dynamics and kinetics from its singlet excited-states were studied using mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) combined with trajectory surface-hopping nonadiabatic molecular dynamics (NAMD) and Fermi’s golden rule (FGR) rate theory. The NAMD dynamics reproduce experimental observations that the S 1 → S 0 decay is accelerated and exhibits a crossover from mono- to biexponential kinetics with increasing excess vibrational energy. Minimum-energy-path analyses reveal a continuous S 1 /S 0 conical-intersection seam slightly above the S 1 minimum, providing readily accessible funnels. Time-resolved normal-mode projections reveal selective energy funneling into C–C stretching modes at 1272, 1528, and 1692 cm –1 . Constructive combinations of the latter two modes appear to promote rapid access to the conical-intersection seam, whereas their beating at ∼ 160 fs imposes a natural limit on the decrease of the decay time upon a further increase of excess energies, suggesting that their interference delays the decay. Here, the FGR rate calculation data for the S 1 → S 0 transition reaffirm that the nonradiative decay proceeds mainly near or through the conical intersection, rather than via simple nonadiabatic derivative coupling around the minimum of S 1 . On the other hand, the FGR rates indicate that S 2 decays predominantly to S 0 , as the S 2 –S 1 vibronic coupling is exceptionally weak, which serves as a primary cause for azulene’s characteristic anti-Kasha emission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Roadmap for Optical Metasurfaces

Metasurfaces have recently risen to prominence in optical research, providing unique functionalities that can be used for imaging, beam forming, holography, polarimetry, and many more, while keeping device dimensions small. Despite the fact that a vast range of basic metasurface designs has already been thoroughly studied in the literature, the number of metasurface-related papers is still growing at a rapid pace, as metasurface research is now spreading to adjacent fields, including computational imaging, augmented and virtual reality, automotive, display, biosensing, nonlinear, quantum and topological optics, optical computing, and more. At the same time, the ability of metasurfaces to perform optical functions in much more compact optical systems has triggered strong and constantly growing interest from various industries that greatly benefit from the availability of miniaturized, highly functional, and efficient optical components that can be integrated in optoelectronic systems at low cost. This creates a truly unique opportunity for the field of metasurfaces to make both a scientific and an industrial impact. Furthermore, the goal of this Roadmap is to mark this “golden age” of metasurface research and define future directions to encourage scientists and engineers to drive research and development in the field of metasurfaces toward both scientific excellence and broad industrial adoption.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Spectrally Selective Mirrors with Combined Optical and Thermal Benefit for Photovoltaic Module Thermal Management

Waste heat generated during daytime operation of a solar module will raise its temperature and reduce cell efficiency. In addition to thermalization and carrier recombination, one major source of excess heat in modules is the parasitic absorption of light with sub-bandgap energy. Parasitic absorption can be prevented if sub-bandgap radiation is reflected away from the module. We report on the design considerations and projected changes to module energy yield for photonic reflectors capable of reflecting a portion of sub-bandgap radiation while maintaining or improving transmission of light with energy greater than the semiconductor bandgap. Using a previously developed, self-consistent opto-electro-thermal finite-element simulation, we calculate the total additional energy generated by a module, including various photonic reflectors, and decompose these benefits into thermal and optical effects. We show that the greatest total energy yield improvement comes from photonic mirrors designed for the outside of the glass, but that mirrors placed between the glass and the encapsulant can have significant thermal benefit. We then show that optimal photonic mirror design requires consideration of all angles of incidence, despite unequal amounts of radiation arriving at each angle. We find that optimized photonic mirrors will be omnidirectional in the sense that they have beneficial performance, regardless of the angle of incidence of radiation. By fulfilling these criteria, photonic mirrors can be used at different geographic locations or different tilt angles than their original optimization conditions with only marginal changes in performance. We show designs that improve energy output in Golden, Colorado by 3.7% over a full year. This work demonstrates the importance of considering real-world irradiance and weather conditions when designing optical structures for solar applications.

14 SOLAR ENERGY↗
DOE OSTI2019

Continuous Wave Resonant Photon Stimulated Electron Energy-Gain and Electron Energy-Loss Spectroscopy of Individual Plasmonic Nanoparticles

The unique optical properties of surface plasmon resonances in nanostructured materials have attracted considerable attention, broadly impacting both fundamental research and applied technologies ranging from sensing and optoelectronics to quantum computing. Electron energy-loss spectroscopy (EELS) in the transmission electron microscope has revealed valuable information about the full plasmonic spectrum of these materials with nanoscale spatial resolution. Here, in this study, we report a novel approach for experimentally accessing the photon-stimulated electron energy-gain and stimulated electron energy-loss responses of individual plasmonic nanoparticles via the simultaneous irradiation of a continuous wave laser and continuous current, monochromated electron probe. Stimulated gain and loss probabilities are equivalent and increase linearly in the low-irradiance range of 0.5 × 10 8 to 4 × 10 8 W/m 2 , above which excessive heating reduces the observed probabilities; importantly in our low-irradiance regime, the photon energy must be tuned in resonance with the plasmon energy for the stimulated gain and loss peaks to emerge. Theoretical modeling based on Fermi’s golden rule elucidates how the plasmon resonantly and coherently shuttles energy quanta between the electron probe and the radiation field and vice versa in stimulated electron energy-loss and -gain events. This study opens a fundamentally new approach to explore the quantum physics of excited-state plasmon resonances that does not rely on high-intensity laser pulses or any modification to the EELS detector.

(scanning) transmission electron microscope ((S)TE↗