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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

New formation and fate of Isoprene SOA markers revealed by field data-constrained modeling

Particulate 2-methyltetrols (2-MT) and 2-methylglyceric acid (2-MG) are typically used to indicate the abundance of isoprene-derived secondary organic aerosols (SOA). However, their formation and fate are not fully understood. In this study, we showed that particulate 2-MT and 2-MG collected at multiple monitoring sites under a wide range of atmospheric and emission conditions, with concentrations spanning six orders of magnitudes, are well reproduced with an expanded isoprene-SOA scheme implemented into the Community Multiscale Air Quality (CMAQ) model. The scheme considers their three-phase (gas-aqueous-organic phase) partitioning, formation from acid-driven multiphase reactions, and degradation by OH radicals in the gas and aqueous phases. The model results reveal that a non-aqueous formation pathway or direct biogenic emission is needed to supplement the commonly assumed acid-driven multiphase reaction process to explain the observed 2-MT concentrations. This missing pathway contributes to 20–40% of 2-MT in areas with aerosol pH < 2 and more than 70% under less acidic conditions (pH~2–5), such as those encountered in the western US and China. The typical summertime gas-phase photochemical lifetimes of 2-MT and 2-MG are estimated to be 4–6 and 20–30 h, respectively, and their aqueous lifetimes are approximately 20–40 h. Our simulations show that predicted 2-MT is mainly influenced by its aqueous phase loss to OH, but 2-MG is more sensitive to gas phase OH loss due to the preferential partitioning of the two tracers in the aqueous and gas phases, respectively.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Direct path integral estimators for isotope fractionation ratios

Fractionation of isotopes among distinct molecules or phases is a quantum effect which is often exploited to obtain insights on reaction mechanisms, biochemical, geochemical, and atmospheric phenomena. Accurate evaluation of isotope ratios in atomistic simulations is challenging, because one needs to perform a thermodynamic integration with respect to the isotope mass, along with time-consuming path integral calculations. By re-formulating the problem as a particle exchange in the ring polymer partition function, we derive new estimators giving direct access to the differential partitioning of isotopes, which can simplify the calculations by avoiding thermodynamic integration. We demonstrate the efficiency of these estimators by applying them to investigate the isotope fractionation ratios in the gas-phase Zundel cation, and in a few simple hydrocarbons.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Origin of molecular conformational stability: Perspectives from molecular orbital interactions and density functional reactivity theory

To have a quantitative understanding about the origin of conformation stability for molecular systems is still an unaccomplished task. Frontier orbital interactions from molecular orbital theory and energy partition schemes from density functional reactivity theory are the two approaches available in the literature that can be used for this purpose. In this work, we compare the performance of these approaches for a total of 48 simple molecules. We also conduct studies to flexibly bend bond angles for water, carbon dioxide, borane, and ammonia molecules to obtain energy profiles for these systems over a wide range of conformations. We find that results from molecular orbital interactions using frontier occupied orbitals such as the highest occupied molecular orbital and its neighbors are only qualitatively, at most semi-qualitatively, trustworthy. To obtain quantitative insights into relative stability of different conformations, the energy partition approach from density functional reactivity theory is much more reliable. We also find that the electrostatic interaction is the dominant descriptor for conformational stability, and steric and quantum effects are smaller in contribution but their contributions are indispensable. Stable molecular conformations prefer to have a strong electrostatic interaction, small molecular size, and large exchange-correlation effect. This work should shed new light towards establishing a general theoretical framework for molecular stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ergodic theory and visualization. II. Fourier mesochronic plots visualize (quasi)periodic sets

We present an application and analysis of a visualization method for measure-preserving dynamical systems introduced by I. Mezić and A. Banaszuk [Physica D 197, 101 (2004)], based on frequency analysis and Koopman operator theory. This extends our earlier work on visualization of ergodic partition [Z. Levnajić and I. Mezić, Chaos 20, 033114 (2010)]. Our method employs the concept of Fourier time average [I. Mezić and A. Banaszuk, Physica D 197, 101 (2004)], and is realized as a computational algorithms for visualization of periodic and quasi-periodic sets in the phase space. The complement of periodic phase space partition contains chaotic zone, and we show how to identify it. The range of method's applicability is illustrated using well-known Chirikov standard map, while its potential in illuminating higher-dimensional dynamics is presented by studying the Froeschlé map and the Extended Standard Map.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Fractal and multifractal characteristics of swift heavy ion induced self-affine nanostructured BaF{sub 2} thin film surfaces

Fractal and multifractal characteristics of self-affine surfaces of BaF{sub 2} thin films, deposited on crystalline Si 〈1 1 1〉 substrate at room temperature, were studied. Self-affine surfaces were prepared by irradiation of 120 MeV Ag{sup 9+} ions which modified the surface morphology at nanometer scale. The surface morphology of virgin thin film and those irradiated with different ion fluences are characterized by atomic force microscopy technique. The surface roughness (interface width) shows monotonic decrease with ion fluences, while the other parameters, such as lateral correlation length, roughness exponent, and fractal dimension, did not show either monotonic decrease or increase in nature. The self-affine nature of the films is further confirmed by autocorrelation function. The power spectral density of thin films surfaces exhibits inverse power law variation with spatial frequency, suggesting the existence of fractal component in surface morphology. The multifractal detrended fluctuation analysis based on the partition function approach is also performed on virgin and irradiated thin films. It is found that the partition function exhibits the power law behavior with the segment size. Moreover, it is also seen that the scaling exponents vary nonlinearly with the moment, thereby exhibiting the multifractal nature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thermodynamical properties of Strunz’s quantum dissipative models

The existence of the negative of specific heat from quantum dissipative theory is investigated. Strunz’s quantum dissipative model will be used in this studies. The thermodynamical properties will be studied starts out from the thermo-dynamic partition function of the dissipative system. The path integral technique is used to calculate the partition function under consideration. The results shows that the specific heat can be negative if the damping parameter more than a half the oscillator frequency and also occur at low temperatures. For damping factor greater than the frequency of harmonic oscillator then specific heat will oscillate at low temperatures and approaching normal conditions at a high temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Coil–globule transition of a polymer involved in excluded-volume interactions with macromolecules

Polymers adopt extended coil and compact globule states according to the balance between entropy and interaction energies. The transition of a polymer between an extended coil state and compact globule state can be induced by changing thermodynamic force such as temperature to alter the energy/entropy balance. Previously, this transition was theoretically studied by taking into account the excluded-volume interaction between monomers of a polymer chain using the partition function. For binary mixtures of a long polymer and short polymers, the coil-globule transition can be induced by changing the concentration of the shorter polymers. Here, we investigate the transition caused by short polymers by generalizing the partition function of the long polymer to include the excluded-volume effect of short polymers. The coil-globule transition is studied as a function of the concentration of mixed polymers by systematically varying Flory’s χ-parameters. We show that the transition is caused by the interplay between the excluded-volume interaction and the dispersion state of short polymers in the solvent. We also reveal that the same results can be obtained by combining the mixing entropy and elastic energy if the volume of a long polymer is properly defined.

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

Strongly coupled fluid-particle flows in vertical channels. I. Reynolds-averaged two-phase turbulence statistics

Simulations of strongly coupled (i.e., high-mass-loading) fluid-particle flows in vertical channels are performed with the purpose of understanding the fundamental physics of wall-bounded multiphase turbulence. The exact Reynolds-averaged (RA) equations for high-mass-loading suspensions are presented, and the unclosed terms that are retained in the context of fully developed channel flow are evaluated in an Eulerian–Lagrangian (EL) framework for the first time. A key distinction between the RA formulation presented in the current work and previous derivations of multiphase turbulence models is the partitioning of the particle velocity fluctuations into spatially correlated and uncorrelated components, used to define the components of the particle-phase turbulent kinetic energy (TKE) and granular temperature, respectively. The adaptive spatial filtering technique developed in our previous work for homogeneous flows [J. Capecelatro, O. Desjardins, and R. O. Fox, “Numerical study of collisional particle dynamics in cluster-induced turbulence,” J. Fluid Mech. 747, R2 (2014)] is shown to accurately partition the particle velocity fluctuations at all distances from the wall. Strong segregation in the components of granular energy is observed, with the largest values of particle-phase TKE associated with clusters falling near the channel wall, while maximum granular temperature is observed at the center of the channel. The anisotropy of the Reynolds stresses both near the wall and far away is found to be a crucial component for understanding the distribution of the particle-phase volume fraction. In Part II of this paper, results from the EL simulations are used to validate a multiphase Reynolds-stress turbulence model that correctly predicts the wall-normal distribution of the two-phase turbulence statistics.

42 ENGINEERING↗
DOE OSTI2016

Atomic partial charges on CH{sub 3}NH{sub 3}PbI{sub 3} from first-principles electronic structure calculations

We calculated the partial charges in methylammonium (MA) lead-iodide perovskite CH{sub 3}NH{sub 3}PbI{sub 3} in its different crystalline phases using different first-principles electronic charge partitioning approaches, including the Bader, ChelpG, and density-derived electrostatic and chemical (DDEC) schemes. Among the three charge partitioning methods, the DDEC approach provides chemically intuitive and reliable atomic charges for this material, which consists of a mixture of transition metals, halide ions, and organic molecules. The DDEC charges are also found to be robust against the use of hybrid functionals and/or upon inclusion of spin–orbit coupling or dispersive interactions. We calculated explicitly the atomic charges with a special focus on the dipole moment of the MA molecules within the perovskite structure. The value of the dipole moment of the MA is reduced with respect to the isolated molecule due to charge redistribution involving the inorganic cage. DDEC charges and dipole moment of the organic part remain nearly unchanged upon its rotation within the octahedral cavities. Our findings will be of both fundamental and practical importance, as the accurate and consistent determination of the atomic charges is important in order to understand the average equilibrium distribution of the electrons and to help in the development of force fields for larger scale atomistic simulations to describe static, dynamic, and thermodynamic properties of the material.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Evaporation dominates evapotranspiration on Alaska’s Arctic Coastal Plain

The dynamics of evapotranspiration (ET), such as the partitioning to evaporation and transpiration, of polygonal ground on the Arctic Coastal Plain are not well understood. We assessed ET dynamics, including evaporation and transpiration partitioning, created by microtopographic features associated with high- and low-centered polygons. Chamber ET and leaf-level transpiration measurements were conducted in one-week field campaigns in two growing seasons with contrasting weather conditions. We found that ET was greater in the drier and warmer sampling period (2013) compared to the colder and wetter one (2014). Evaporation dominated ET, particularly in the wetter and colder sampling period (>90% in 2014 vs. 80% in 2013). In the 2013 sampling period, wetter and warmer conditions increased ET and the contribution of transpiration to ET. If the soils warm with degrading permafrost, ET and the fraction contributed by transpiration may increase to a certain threshold, when moisture must increase with rising temperatures to further increase these fluxes. While the fraction of transpiration may rise with warmer soils, it is unlikely that transpiration will completely dominate ET. This work highlights the complexities of understanding ET in this dynamic environment and the importance of understanding differences across polygonal ground.

58 GEOSCIENCES↗
DOE OSTI2026

A Maize GT14 Family Glycosyltransferase Affects Cell Wall Composition and Carbohydrate Export from Source Leaves

Sucrose translocation from photosynthetic leaves to distant parts of a plant, such as seeds and roots, is a critical aspect of plant growth and development and a major determinant of crop yield. To identify genes contributing to this process in maize (Zea mays), we isolated four allelic mutants, carbohydrate partitioning defective7, 48, 49 (cpd7, cpd48, cpd49) and a UniformMu insertion (mu1049954), all of which exhibited reduced growth and fertility and hyperaccumulation of starch and soluble sugars in mature leaves. Consistent with carbohydrate accumulation, cpd7 mutants exhibited reduced sucrose export from mature leaves. Cpd7 encodes a Golgi-resident glucuronosyltransferase belonging to the Glycosyltransferase14 (GT14) family, which is involved in decoration of type II arabinogalactan proteins. No previously described GT14 mutants exhibit reduced sucrose transport or carbohydrate partitioning defects. Additionally, we show that mature leaves of cpd7 mutants have reduced cellulose content and an altered cell wall composition. Further, cpd7 mutants exhibit ectopic phloem lignification likely as a compensatory mechanism for reduced cell wall integrity. Collectively, our data suggest that Cpd7 functions to facilitate cell wall development in the phloem, which is required for efficient sucrose export from mature maize leaves.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

True Load Balancing for Matricized Tensor Times Khatri-Rao Product

MTTKRP is the bottleneck operation in algorithms used to compute the CP tensor decomposition. For sparse tensors, utilizing the compressed sparse fibers (CSF) storage format and the CSF-oriented MTTKRP algorithms is important for both memory and computational efficiency on distributed-memory architectures. Existing intelligent tensor partitioning models assume the computational cost of MTTKRP to be proportional to the total number of nonzeros in the tensor. However, this is not the case for the CSF-oriented MTTKRP on distributed-memory architectures. We outline two deficiencies of nonzero-based intelligent partitioning models when CSF-oriented MTTKRP operations are performed locally: failure to encode processors' computational loads and increase in total computation due to fiber fragmentation. We focus on existing fine-grain hypergraph model and propose a novel vertex weighting scheme that enables this model encode correct computational loads of processors. We also propose to augment the fine-grain model by fiber nets for reducing the increase in total computational load via minimizing fiber fragmentation. In this way, the proposed model encodes minimizing the load of the bottleneck processor. In conclusion, parallel experiments with real-world sparse tensors on up to 1024 processors prove the validity of the outlined deficiencies and demonstrate the merit of our proposed improvements in terms of parallel runtimes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Allometric scaling laws linking biomass and rooting depth vary across ontogeny and functional groups in tropical dry forest lianas and trees

There are two theories about how allocation of metabolic products occurs. The allometric biomass partitioning theory (APT) suggests that all plants follow common allometric scaling rules. The optimal partitioning theory (OPT) predicts that plants allocate more biomass to the organ capturing the most limiting resource. In this work, whole-plant harvests of mature and juvenile tropical deciduous trees, evergreen trees, and lianas and model simulations were used to address the following knowledge gaps: (1) Do mature lianas comply with the APT scaling laws or do they invest less biomass in stems compared to trees? (2) Do juveniles follow the same allocation patterns as mature individuals? (3) Is either leaf phenology or life form a predictor of rooting depth? It was found that: (1) mature lianas followed the same allometric scaling laws as trees; (2) juveniles and mature individuals do not follow the same allocation patterns; and (3) mature lianas had shallowest coarse roots and evergreen trees had the deepest. It was demonstrated that: (1) mature lianas invested proportionally similar biomass to stems as trees and not less, as expected; (2) lianas were not deeper-rooted than trees as had been previously proposed; and (3) evergreen trees had the deepest roots, which is necessary to maintain canopy during simulated dry seasons.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

The properties of conformal blocks, the AGT hypothesis, and knot polynomials

Various properties of correlators of the two-dimensional conformal field theory are discussed. Specifically, their relation to the partition function of the four-dimensional supersymmetric theory is analyzed. In addition to being of interest in its own right, this relation is of practical importance. For example, it is much easier to calculate the known expressions for the partition function of supersymmetric theory than to calculate directly the expressions for correlators in conformal theory. The examined representation of conformal theory correlators as a matrix model serves the same purpose. The integral form of these correlators allows one to generalize the obtained results for the Virasoro algebra to more complicated cases of the W algebra or the quantum Virasoro algebra. This provides an opportunity to examine more complex configurations in conformal field theory. The three-dimensional Chern–Simons theory is discussed in the second part of the present review. The current interest in this theory stems largely from its relation to the mathematical knot theory (a rather well-developed area of mathematics known since the 17th century). The primary objective of this theory is to develop an algorithm that allows one to distinguish different knots (closed loops in three-dimensional space). The basic way to do this is by constructing the so-called knot invariants.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Variation in sugarcane biomass composition and enzymatic saccharification of leaves, internodes and roots

The composition of biomass determines its suitability for different applications within a biorefinery system. The proportion of the major biomass fractions (sugar, cellulose, hemicellulose and lignin) may vary in different sugarcane genotypes and growth environments and different parts of the plant. This study investigated the composition of mature and immature internodes, roots and mature leaves of sugarcane. Internodes were found to have a significantly larger alcohol-soluble component than leaves and roots. The primary difference between the immature and mature internodes was the ratio of soluble sugars. In mature tissues, sucrose content was significantly higher, whereas in immature internodal tissues there was lower sucrose and heightened concentrations of reducing sugars. Carbon (C) partitioning in leaf tissues was characterised by low levels of soluble components and high “other” and cell wall fractions. Root tissue had low ratios of soluble fractions relative to their cell wall contents, indicating a lack of storage of soluble carbon. There was no significant difference in the ratio of the major cell wall fractions between the major organ types. Characterisation of individual non-cellulosic monomers indicated leaf and root tissues had significantly higher arabinose and galactose fractions. Significantly larger proportions of syringyl lignin compounds and the hydroxycinnamic compound, p-coumaric acid were observed in mature internodal tissues compared to the other tissue types. Tissue-specific differences in composition were shown to greatly affect the recalcitrance of the cell wall to enzymatic saccharification. Overall, this study displayed clear evidence of the differential partitioning of C throughout the sugarcane plant in specific organs. These organ-specific differences have major implications in their utility as a bioproduct feedstock. For example, the inclusion of trash (leaves) with the culms (internodes) may alter processing efficiency.

09 BIOMASS FUELS↗
DOE OSTI2016

Organ and Tissue-specific Sucrose Transporters. Important Hubs in Gene and Metabolite Networks Regulating Carbon Use in Wood-forming Tissues of Populus

The overall project objective was to probe the relationship between sucrose transporters and plant productivity in the biomass for biofuels woody perennial, Populus. At the time the proposal was written, sucrose transporters had already been investigated in many plant model systems, primarily with respect to the export of photosynthate sucrose from source leaves, and the uptake of sucrose in storage organs and seeds. Preliminary findings by the PI found that in Populus, sucrose transporter genes (SUTs) were well expressed in wood-forming tissues that comprise the feedstock for biofuels production. Because sucrose comprises by far the predominant form in which photosynthate is delivered from source organs to sink organs like roots and wood-forming tissues, SUTs control a gate that nominally at least could impact the allocation or partitioning of sucrose for potentially competing end uses like growth (stem biomass) and storage. In addition, water use might be conditioned by the way in which sucrose is distributed throughout the plant, and/or by the way in which sucrose is partitioned intracellularly. Several dozen transgenic lines were produced in year 1 of the project to perturb the expression ratio of multiple plasma membrane (PM) SUTs (intercellular trafficking), versus the single tonoplast membrane (TM) sucrose transporter that effectively regulates intracellular trafficking of sucrose. It was possible to obtain transgenic lines with dual SUT gene knockdown using the 35S promoter, but not the wood-specific TUA1 promoter. By the end of project year 2, a decision was made to work with the 35S plants while archiving the TUA1 plants. The PhD candidate charged with producing the transgenic lines abandoned the project during its second year, substantially contributing to the decision to operate with just the 35S lines. That student’s interests ranged more toward evolutionary topics, and a report on SUT gene evolution was published (Peng et al 2014).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Numerical experiments with the extended virtual element method for the Laplace problem with strong discontinuities

The virtual element method (VEM) is a stabilized Galerkin formulation on arbitrary polytopal meshes. In the VEM, the basis functions are implicit (virtual) — they are not known nor do they need to be computed within the problem domain. Suitable projection operators are used to decompose the bilinear form at the element-level into two parts: a consistent term that reproduces a given polynomial space and a correction term that ensures stability. In this study, we consider a low-order extended virtual element method (X-VEM) that is in the spirit of the extended finite element method for crack problems. Herein, we focus on the two-dimensional Laplace crack problem. In the X-VEM, we enrich the standard virtual element space with additional discontinuous functions through the framework of partition-of-unity. The nodal basis functions in the VEM are chosen as the partition-of-unity functions, and we study means to stabilize the standard and enriched sub-matrices that constitute the element stiffness matrix. Numerical experiments are performed on the problem of a cracked membrane under mode III loading to affirm the accuracy, and to establish the optimal convergence in energy of the method.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2022

Source Decomposition of Eddy-Covariance CO 2 Flux Measurements for Evaluating a High-Resolution Urban CO 2 Emissions Inventory

We present the comparison of source-partitioned CO2 flux measurements with a high-resolution urban CO 2 emissions inventory (Hestia). Tower-based measurements of CO and 14 C are used to partition net CO 2 flux measurements into fossil and biogenic components. A flux footprint model is used to quantify spatial variation in flux measurements. We compare the daily cycle and spatial structure of Hestia and eddy-covariance derived fossil fuel CO 2 emissions on a seasonal basis. Hestia inventory emissions exceed the eddy-covariance measured emissions by 0.36 µ mol m −2 s −1 (3.2%) in the cold season and 0.62 µ mol m −2 s −1 (9.1%) in the warm season. The daily cycle of fluxes in both products matches closely, with correlations in the hourly mean fluxes of 0.86 (cold season) and 0.93 (warm season). The spatially averaged fluxes also agree in each season and a persistent spatial pattern in the differences during both seasons that may suggest a bias related to residential heating emissions. In addition, in the cold season, the magnitudes of average daytime biological uptake and nighttime respiration at this flux site are approximately 15% and 27% of the mean fossil fuel CO 2 emissions over the same time period, contradicting common assumptions of no significant biological CO 2 exchange in northern cities during winter. This work demonstrates the effectiveness of using trace gas ratios to adapt eddy-covariance flux measurements in urban environments for disaggregating anthropogenic CO 2 emissions and urban ecosystem fluxes at high spatial and temporal resolution.

eddy-covariance flux measurements↗