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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A transmissive concentrator photovoltaic module with cells directly cooled by silicone oil for solar cogeneration systems

Hybrid concentrator photovoltaic-thermal systems can cogenerate electricity and heat by beam-splitting incoming concentrated light onto photovoltaic cells and a thermal receiver to increase total conversion efficiency and potentially reduce system cost. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. Visible light is collected using infrared-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of 43.3% for light of wavelength λ < 873 nm, while 44.2% of out-of-band light with λ > 873 nm is transmitted through for collection by a thermal receiver. During testing on a dual-axis tracked parabolic concentrator dish at up to 166 suns, cell temperatures were maintained at 119 °C or below via a novel active cooling method. This cooling system strictly flows silicone oil directly across both sides of the cells, without inhibiting optical transmission, as verified through experimentation and simulation. The module was validated outdoors for 572 sun·hrs, and achieved a maximum thermal receiver temperature of 180 °C. 86.1% of incident solar power is collected at 166 suns average concentration collectively among the electrical, cooling, and thermal receiver subsystems. The remaining 13.9% is lost to mirror reflectivity, dish shadowing, receiver reflection, and thermal losses. The ability to directly cool the cells with an inert silicone oil offers the potential for reduced system cost relative to previous transmissive hybrid concentrator photovoltaic-thermal systems, including microfluidic-cooled designs. This solar cogeneration capability is valuable in a wide range of commercial and industrial applications.

14 SOLAR ENERGY↗
DOE OSTI2013

Tunable upconversion emission in Ba{sub 2}YF{sub 7}:Yb{sup 3+}/Er{sup 3+} nanocrystals with different Yb{sup 3+} concentration

Graphical abstract: The emission intensity at 520 nm and 540 nm can be tuned by Yb{sup 3+} concentration. - Highlights: • High concentration of Yb{sup 3+} can be doped into Ba{sub 2}YF{sub 7} without a phase change. • The emission intensity at 520 nm and 540 nm can be tuned by Yb{sup 3+} concentration. • The long lifetime of {sup 4}F{sub 9/2} level makes its populating effective. - Abstract: Ba{sub 2}YF{sub 7}:xYb{sup 3+},0.02Er{sup 3+} nanocrystals with different Yb{sup 3+} concentration (x = 0.2, 0.4, 0.6, 0.8, 0.98) were synthesized via a solvothermal method. Their X-ray diffraction patterns reveal that all the samples are cubic phase without phase change at arbitrary Yb{sup 3+} concentration. Upon excitation of 980 nm laser, these nanocrystals display upconversion emission in the green and red spectral regions. The relative emission intensity at these two regions can be tuned by Yb{sup 3+} concentration. To investigate the effect of Yb{sup 3+} ion, the decay times of 650 nm emission were measured and analyzed. Ba{sub 2}YF{sub 7}:0.6Yb{sup 3+},0.02Er{sup 3+} nanocrystals have the longest lifetime and highest emission intensity among all the samples. We concluded the lifetime of {sup 4}F{sub 9/2} level has an effect on its own population and intensity ratio of red and green emission. Our results show Yb{sup 3+} ion can tune the upconversion emission and improve upconverison emission intensity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Constructing a spatiotemporally coherent long-term PM2.5 concentration dataset over China during 1980–2019 using a machine learning approach

The lack of long-term observations and satellite retrievals of health-damaging fine particulate matter in China has demanded the estimates of historical PM 2.5 (particulate matter less than 2.5 µm in diameter) concentrations. This study constructs a gridded near-surface PM 2.5 concentration dataset across China covering 1980–2019 using the space-time random forest model with atmospheric visibility observations and other auxiliary data. The modeled daily PM2.5 concentrations are in excellent agreement with ground measurements during 2015–2019, with a coefficient of determination of 0.95 and mean relative error of 12%. Besides the atmospheric visibility which explains 30% of total importance of variables in the model, both emissions and meteorological conditions are also essential factors affecting PM2.5 predictions. From 1980 to 2014, the model-predicted PM2.5 concentrations increased constantly with the maximum growth rate of 5–10 µg/m3/decade over eastern China. Due to the clean air actions, PM 2.5 concentrations have decreased effectively at a rate over 50 µg/m 3 /decade in the North China Plain and 20–50 µg/m 3 /decade over eastern China during 2014–2019. The newly generated dataset of 1-degree gridded PM 2.5 concentrations for the past 40 years across China provides a useful means for investigating interannual and decadal environmental and climate impacts related to aerosols.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Characterizing how size distribution and concentration affect echogenicity of ultrasound contrast agents

Here, we investigated the effects of UCA gas bubble size distribution and concentration on the generated ultrasound echogenicity signal. Gas bubble size characterization using Coulter Counter and cryogenic-SEM revealed the hollow structure and rare presence of microbubbles >10 µm in a commercial UCA product, Lumason™. Volume-weighed size and concentration were observed to be more sensitive to changes in UCA bubble stability than number-weighted size and concentration. Size distribution measurements showed that the force (e.g., shaking/agitation energy) used to redisperse the sample did not affect the size distribution, concentration, or echogenicity of the UCA sample. The ultrasound backscattering coefficient (BSC) of size fractionated and serial diluted microbubbles showed that the echogenicity signal correlates most with UCA bubble concentration, especially volume-weighted concentration. Findings from this study may be used to support demonstrating the equivalence of a generic UCA product to the reference listed drug.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Long-term trends in urban NO 2 concentrations and associated paediatric asthma incidence: estimates from global datasets

Combustion-related nitrogen dioxide (NO 2 ) air pollution is associated with paediatric asthma incidence. We aimed to estimate global surface NO 2 concentrations consistent with the Global Burden of Disease study for 1990-2019 at a 1 km resolution, and the concentrations and attributable paediatric asthma incidence trends in 13 189 cities from 2000 to 2019. We scaled an existing annual average NO 2 concentration dataset for 2010-12 from a land use regression model (based on 5220 NO 2 monitors in 58 countries and land use variables) to other years using NO 2 column densities from satellite and reanalysis datasets. We applied these concentrations in an epidemiologically derived concentration-response function with population and baseline asthma rates to estimate NO 2 -attributable paediatric asthma incidence. We estimated that 1.85 million (95% uncertainty interval [UI] 0.93-2.80 million) new paediatric asthma cases were attributable to NO 2 globally in 2019, two thirds of which occurred in urban areas (1.22 million cases; 95% UI 0.60-1.8 million). The proportion of paediatric asthma incidence that is attributable to NO 2 in urban areas declined from 19.8% (1.22 million attributable cases of 6.14 million total cases) in 2000 to 16.0% (1.24 million attributable cases of 7.73 million total cases) in 2019. Urban attributable fractions dropped in high-income countries (-41%), Latin America and the Caribbean (-16%), central Europe, eastern Europe, and central Asia (-13%), and southeast Asia, east Asia, and Oceania (-6%), and rose in south Asia (+23%), sub-Saharan Africa (+11%), and north Africa and the Middle East (+5%). The contribution of NO 2 concentrations, paediatric population size, and asthma incidence rates to the change in NO 2 -attributable paediatric asthma incidence differed regionally. Despite improvements in some regions, combustion-related NO 2 pollution continues to be an important contributor to paediatric asthma incidence globally, particularly in cities. Mitigating air pollution should be a crucial element of public health strategies for children.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Characterizing Airborne Phthalate Concentrations and Dynamics in a Normally Occupied Residence

Phthalate esters, commonly used as plasticizers, can be found indoors in the gas phase, in airborne particulate matter, in dust, and on surfaces. The dynamic behavior of phthalates indoors is not fully understood. In this study, time-resolved measurements of airborne phthalate concentrations and associated gas-particle partitioning data were acquired in a normally occupied residence. The vapor pressure and associated gas-particle partitioning of measured phthalates influenced their airborne dynamic behavior. Concentrations of higher vapor pressure phthalates correlated well with indoor temperature, with little discernible influence from direct occupant activity. Conversely, occupant-related behaviors substantially influenced the concentrations and dynamic behavior of a lower vapor pressure compound, diethylhexyl phthalate (DEHP), mainly through production of particulate matter during cooking events. The proportion of airborne DEHP in the particle phase was experimentally observed to increase under higher particle mass concentrations and lower indoor temperatures in correspondence with theory. Experimental observations indicate that indoor surfaces of the residence are large reservoirs of phthalates. The results also indicate that two key factors influenced by human behavior-temperature and particle mass concentration-cause short-term changes in airborne phthalate concentrations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Concentration-Polarization-Induced Precipitation and Ionic Current Oscillations with Tunable Frequency

At the nanoscale, charges present at the surfaces of liquid–solid interfaces greatly influence the properties of ions and molecules present in the solution, and can lead to nanoscale effects such as ion selectivity, ion current rectification, and modulation of local ionic concentrations. Concentration polarization is another nanoscale phenomenon whereby ion concentrations are enriched at one opening of an ion-selective nanopore and depleted at the other. We demonstrate that when a nanopore is in contact with a weakly soluble salt present at a concentration below its solubility product, concentration polarization can lead to locally enhanced ionic concentrations and precipitation of the salt. Formed precipitates partially or fully occlude the nanopore’s opening as indicated by a measured transient decrease of the nanopore’s conductance. We have confirmed experimental conditions at which the locally created precipitate is either pushed through or dissolved, clearing the pore entrance and allowing the precipitation reaction to occur again. The dynamic process of precipitate formation and dissolution is observed as ion current fluctuations and oscillations with frequencies reaching 200 Hz. The frequency of the system operation exceeds other nanopore-based oscillators by 2 orders of magnitude, which we believe stems from the 30 nm length of the pores examined here, versus ~10 μm long pores reported before.

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

Structure and Ionic Conductivity of Polystyrene-block-poly(ethylene oxide) Electrolytes in the High Salt Concentration Limit

We explore the relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis-(trifluoromethanesulfonyl)imide salt (LiTFSI). Two SEO polymers were studied, SEO(16-16) and SEO(4.9-5.5), over the salt concentration range r = 0.03-0.55. The numbers x and y in SEO(x-y) are the molecular weights of the blocks in kg mol -1 , and the r value is the molar ratio of salt to ethylene oxide moieties. Small-angle X-ray scattering was used to characterize morphology and grain size at 120 °C, differential scanning calorimetry was used to study the crystallinity and the glass transition temperature of the PEO-rich microphase, and ac impedance spectroscopy was used to measure ionic conductivity as a function of temperature. The most surprising observation of our study is that ionic conductivity in the concentration regime 0.11 ≤ r ≤ 0.21 increases in SEO electrolytes but decreases in PEO electrolytes. The maximum in ionic conductivity with salt concentration occurs at about twice the salt concentration in SEO (r = 0.21) as in PEO (r = 0.11). Here, we propose that these observations are due to the effect of salt concentration on the grain structure in SEO electrolytes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of Salt Concentration on the Interfacial Solvation Structure and Early Stage of Solid–Electrolyte Interphase Formation in Ca(BH 4 ) 2 /THF for Ca Batteries

The Ca 2+ solvation structure at the electrolyte/electrode interface is of central importance to understand electroreduction stability and solid–electrolyte interphase (SEI) formation for the novel multivalent Ca battery systems. Here, using an exemplar electrolyte, the concentration-dependent solvation structure of Ca(BH 4 ) 2 -tetrahydrofuran on a gold model electrode has been investigated with various electrolyte concentrations via electrochemical quartz crystal microbalance with dissipation (EQCM-D) and X-ray photoelectron spectroscopy (XPS). For the first time, in situ EQCM-D results prove that the prevalent species adsorbed at the interface is CaBH 4 + across all concentrations. As the salt concentration increases, the number of BH 4 – anions associated with Ca 2+ increases, and much larger solvated complexes such as CaBH 4 + ·4THF or Ca(BH 4 ) 3 – ·4THF form at the interface at high concentrations prior to Ca plating. Different interfacial chemistries lead to the formation of SEIs with different components demonstrated by XPS. High electrolyte concentrations reduce the solvent decomposition and promote the formation of thick, uniform, and inorganic-rich (i.e., CaO) SEI layers, which contribute to improved Ca plating efficiency and current density in electrochemical measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Conductivity-Driven Origin of the Limiting Current in Concentrated Electrolytes

Next-generation electrolyte materials are hindered by their ability to support high currents essential for fast-charge and high-power battery applications. The maximum current supported by an electrolyte, the limiting current, is dictated by the formation of concentration gradients across the electrolyte under an electric field. Most of the literature attributes the onset of the limiting current in concentrated electrolytes to the salt concentration at the positive electrode approaching the solubility limit. Here, in this study, we leverage operando X-ray transmission imaging to measure spatiotemporal salt concentration profiles of a polymer electrolyte in a lithium–indium symmetric cell at a current exceeding the limiting current. The measurement of concentration profiles enables mapping the spatiotemporal electric potential, which comprises an ohmic contribution, governed by conductivity, and an overpotential related to maintaining concentration gradients. We find that a precipitous drop in conductivity at the positive electrode drives the divergence of electric potential, rather than a thermodynamic solubility limit.

Abdo, Emily E. [University of California, Berkeley↗
DOE OSTI2022

Estimating the Likelihood of GHG Concentration Scenarios From Probabilistic Integrated Assessment Model Simulations

The climate scenarios that form the basis for current climate risk assessments have no assigned probabilities, and this impedes the analysis of future climate risks. This paper proposes an approach to estimate the probability of carbon dioxide (CO 2 ) concentration scenarios used in key climate change modeling experiments. It computes the CO 2 emissions compatible with the concentrations prescribed by Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 experiments. The distribution of these compatible cumulative emissions is interpreted as the likelihood of future emissions given a concentration pathway. Using Bayesian analysis, the probability of each pathway can be estimated from a probabilistic sample of future emissions. The approach is demonstrated with five probabilistic CO 2 emission simulation ensembles from four Integrated Assessment Models (IAM), leading to independent estimates of the likelihood of the CO 2 concentration of Representative Concentration Pathways (RCP) and Shared Socioeconomic Pathways (SSP). Results suggest that SSP5-8.5 is unlikely for the second half of the 21st century, but offer no clear consensus on which of the remaining scenarios is most likely. Estimates of likelihoods of CO 2 concentrations associated with RCP and SSP scenarios are affected by sampling errors, differences in emission sources simulated by the IAMs, and a lack of a common experimental framework for IAM simulations. These shortcomings, along with a small IAM ensemble size, limit the applicability of the results presented here. Novel joint IAM and the Earth System Model experiments are needed to deliver actionable probabilistic climate risk assessments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Metabolite concentrations, fluxes and free energies imply efficient enzyme usage

In metabolism, available free energy is limited and must be divided across pathway steps to maintain a negative Δ G throughout. For each reaction, Δ G is log proportional both to a concentration ratio (reaction quotient to equilibrium constant) and to a flux ratio (backward to forward flux). In this paper, we use isotope labeling to measure absolute metabolite concentrations and fluxes in Escherichia coli , yeast and a mammalian cell line. We then integrate this information to obtain a unified set of concentrations and Δ G for each organism. In glycolysis, we find that free energy is partitioned so as to mitigate unproductive backward fluxes associated with Δ G near zero. Across metabolism, we observe that absolute metabolite concentrations and Δ G are substantially conserved and that most substrate (but not inhibitor) concentrations exceed the associated enzyme binding site dissociation constant ( K m or K i ). Finally, the observed conservation of metabolite concentrations is consistent with an evolutionary drive to utilize enzymes efficiently given thermodynamic and osmotic constraints.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Concentrating solar thermoelectric generators with a peak efficiency of 7.4%

Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage, enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck effect, simplifying the system. The highest reported efficiency of STEGs so far is 5.2%. We report experimental measurements of STEGs with a peak efficiency of 9.6% at an optically concentrated normal solar irradiance of 211 kW m -2 , and a system efficiency of 7.4% after considering optical concentration losses. The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600 °C, and combining optical and thermal concentration. Our work suggests that concentrating STEGs have the potential to become a promising alternative solar energy technology.

14 SOLAR ENERGY↗
DOE OSTI2021

SANS quantification of bound water in water-soluble polymers across multiple concentration regimes

Contrast-variation small-angle neutron scattering (CV-SANS) is a widely used technique for quantifying hydration water in soft matter systems, but it is predominantly applied in the dilute regime or for systems with a well-defined structure factor. Here, CV-SANS was used to quantify the number of hydration water molecules associating with three water-soluble polymers with different critical solution temperatures and types of water–solute interactions in dilute, semidilute, and concentrated solution through the exploration of novel methods of data fitting and analysis. Multiple SANS fitting workflows with varying levels of model assumptions were evaluated and compared to give insight into SANS model selection. These fitting pathways ranged from general, model-free algorithms to more standard form and structure factor fitting. In addition, Monte Carlo bootstrapping was evaluated as a method to estimate parameter uncertainty through simulation of technical replicates. The most robust fitting workflow for dilute solutions was found to be form factor fitting without CV-SANS ( i.e. polymer in 100% D 2 O). For semidilute and concentrated solutions, while the model-free approach can be mathematically defined for CV-SANS data, the addition of a structure factor imposes physical constraints on the optimization problem, suggesting that the optimal fitting pathway should include appropriate form and structure factor models. The measured hydration numbers were consistent with the number of tightly bound water molecules associated with each monomer unit, and the concentration dependence of the hydration number was largely governed by the chemistry-specific interactions between water and polymer. Polymers with weaker water–polymer interactions ( i.e. those with fewer hydration water molecules) were found to have more bound water at higher concentrations than those with stronger water–polymer interactions due to the increase in the number of forced water–polymer contacts in the concentrated system. This SANS-based method to count hydration water molecules can be applied to polymers in any concentration regime, which will lead to improved understanding of water–polymer interactions and their impact on materials design.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in a periodically modulated laser field

Based on a one-dimensional Smoluchowski equation we have developed the theory of concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in an interference laser field. The numerical solution of a system of recurrence equations resulting from the Smoluchowski equation after expansion of the microsphere concentration N(z,t) in the harmonic series has allowed us to determine the dependence of the concentration nonlinearity settling time on the intensity of the incident radiation. In the diffusion limit, we have derived the expression for the optical Kerr coefficient, which is found to be 8.5×10{sup −10} cm{sup 2} W{sup −1} for an aqueous suspension of latex microspheres with a radius of 1.17μm and a concentration of 6.5×10{sup 10} cm{sup −3}. Diffraction of a probe wave on a light-induced concentration grating is considered as a method for studying a nonlinear concentration response of an artificial highly efficient nonlinear medium for laser radiation of long pulse duration. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

EVOLUTION OF LOW MASS GALACTIC SUBHALOS AND DEPENDENCE ON CONCENTRATION

We carry out a detailed study of the orbital dynamics and structural evolution of over 6000 subhalos in the Via Lactea II simulation, from infall to present. By analyzing subhalos with masses down to m=4×10{sup 5}M{sub ⊙}, we find that lower mass subhalos, which are not strongly affected by dynamical friction, exhibit behaviors qualitatively different from those found previously for more massive ones. Furthermore, there is a clear trend of subhalos that fell into the host earlier being less concentrated. We show that the concentration at infall characterizes various aspects of subhalo evolution. In particular, tidal effects truncate the growth of less concentrated subhalos at larger distances from the host; subhalos with smaller concentrations have larger infall radii. The concentration at infall is further shown to be a determining factor for the subsequent mass loss of subhalos within the host and also for the evolution of their internal structure in the v{sub max} – r{sub max} plane. Our findings raise the prospects of using the concentration to predict the tidal evolution of subhalos, which will be useful for obtaining analytic models of galaxy formation, as well as for near field cosmology.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

A differentiable model of the evolution of dark matter halo concentration

ABSTRACT We introduce a new model of the evolution of the concentration of dark matter haloes, c(t). For individual haloes, our model approximates c(t) as a power law with a time-dependent index, such that at early times, concentration has a nearly constant value of c ≈ 3–4, and as cosmic time progresses, c(t) smoothly increases. Using large samples of halo merger trees taken from the Bolshoi–Planck and MultiDark Planck 2 cosmological simulations, we demonstrate that our three-parameter model can approximate the evolution of the concentration of individual haloes with a typical accuracy of 0.1 dex for $t\gtrsim 2\, {\rm Gyr}$ for all Bolshoi–Planck and MultiDark Planck 2 haloes of present-day peak mass $M_{0}\gtrsim 10^{11.5}\, {\rm M}_{\odot }$. We additionally present a new model of the evolution of the concentration of halo populations, which we show faithfully reproduces both average concentration growth and the diversity of smooth trajectories of c(t), including capturing correlations with halo mass and halo assembly history. Our publicly available source code, diffprof, can be used to generate Monte Carlo realizations of the concentration histories of cosmologically representative halo populations. diffprof is differentiable due to its implementation in the jax autodiff library, which facilitates the incorporation of our model into existing analytical halo model frameworks.

Stevanovich, Dash↗
DOE OSTI2015

Origin of the crossover between a freezing and a structural transition at low concentration in the relaxor ferroelectric K 1-x Li x TaO 3

The origin of the relaxor behavior in K 1-x Li x TaO 3 (KLT) and other disordered perovskites is now recognized to be due to the reorientation of the polar nanodomains formed by the correlated dipoles of off-center ions. The collective dynamics of these systems evolve through several temperature stages. On decreasing temperature below the so-called Burns temperature T B , individual dipoles become correlated within nanosized regions. On further cooling, the slow dynamics of these polar regions allows local lattice distortions to take place and the formation of polar nanodomains at T* < T B . At still lower temperature, some relaxors undergo a phase transition while others do not. In KLT, there is a critical Li concentration x c = 0.022 above which the system undergoes a structural transition at T c , and below which it freezes in a dipole glass state at T f . To better understand the nature of this critical concentration, the changes that occur upon crossing it and the nature of the dipole glass state, the collective dynamics of KLT have been studied by dielectric spectroscopy and neutron diffraction for two Li concentrations (x = 0.026 and 0.018), close to but straddling the critical concentration x c . Two very different transitional behaviors are observed. Just below this critical concentration, KLT displays critical slowing down and the onset of freezing as seen in hydrogen-bonded molecular ferroelectrics, while just above this concentration, KLT undergoes a first-order structural transition.

36 MATERIALS SCIENCE↗