Results for “explainability” — Page 32

DOE OSTI2016

Ferromagnetic bond of Li{sub 10} cluster: An alternative approach in terms of effective ferromagnetic sites

In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li{sub 10} and Li{sub 8} clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Detector dose response in megavoltage small photon beams. I. Theoretical concepts

Purpose: To explain the reasons for significant quality correction factors in megavoltage small photon fields and clarify the underlying concepts relevant to dosimetry under such conditions. Methods: The validity of cavity theory and the requirement of charged particle equilibrium (CPE) are addressed from a theoretical point of view in the context of nonstandard beams. Perturbation effects are described into four main subeffects, explaining their nature and pointing out their relative importance in small photon fields. Results: It is demonstrated that the failure to meet classical cavity theory requirements, such as CPE, is not the reason for significant quality correction factors. On the contrary, it is shown that the lack of CPE alone cannot explain these corrections and that what matters most, apart from volume averaging effects, is the relationship between the lack of CPE in the small field itself and the density of the detector cavity. The density perturbation effect is explained based on Fano’s theorem, describing the compensating effect of two main contributions to cavity absorbed dose. Using the same approach, perturbation effects arising from the difference in atomic properties of the cavity medium and the presence of extracameral components are explained. Volume averaging effects are also discussed in detail. Conclusions: Quality correction factors of small megavoltage photon fields are mainly due to differences in electron density between water and the detector medium and to volume averaging over the detector cavity. Other effects, such as the presence of extracameral components and differences in atomic properties of the detection medium with respect to water, can also play an accentuated role in small photon fields compared to standard beams.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2016

SU-A-BRA-01: Introduction

Vic Montemayor - No one has been more passionate about improving the quality and effectiveness of the teaching of Medical Physics than Bill Hendee. It was in August of 2008 that the first AAPM Workshop on Becoming a Better Teacher of Medical Physics was held, organized and run by Bill Hendee. This was followed up in July of 2010 with a summer school on the same topic, again organized by Bill. There has been continued interest in alternate approaches to teaching medical physics since those initial gatherings. The momentum established by these workshops is made clear each year in the annual Innovation in Medical Physics Education session, which highlights work being done in all forms of medical physics education, from one-on-one residencies or classroom presentations to large-scale program revisions and on-line resources for international audiences. This symposium, presented on behalf of the Education Council, highlights the work of three finalists from past Innovation in Education sessions. Each will be presenting their approaches to and innovations in teaching medical physics. It is hoped that audience members interested in trying something new in their teaching of medical physics will find some of these ideas and approaches readily applicable to their own classrooms. Rebecca Howell - The presentation will discuss ways to maximize classroom learning, i.e., increasing the amount of material covered while also enhancing students’ understanding of the broader implications of the course topics. Specifically, the presentation will focus on two teaching methodologies, project based learning and flip learning. These teaching methods will be illustrated using an example of graduate medical physics course where both are used in conjunction with traditional lectures. Additionally, the presentation will focus on our experience implementing these methods including challenges that were overcome. Jay Burmeister - My presentation will discuss the incorporation of active learning techniques into a traditional medical physics classroom course. I will describe these techniques and how they were implemented as well as student performance before and after implementation. Student feedback indicated that these course changes improved their ability to actively assimilate the course content, thus improving their understanding of the material. Shahid Naqvi - My talk will focus on ways to help students visualize crucial concepts that lie at the core of radiation physics. Although particle tracks generated by Monte Carlo simulations have served as an indispensable visualization tool, students often struggle to resolve the underlying physics from a simultaneous jumble of tracks. We can clarify the physics by “coding” the tracks, e.g., by coloring the tracks according to their “starting” or “crossing” regions. The regionally-coded tracks when overlaid with dose distributions help the students see the elusive connection between dose, kerma and electronic disequilibrium. Tracks coded according to local energy or energy-loss rate can illustrate the need for stopping power corrections in electron beams and explain the Bragg peak in a proton beam. Coding tracks according to parent interaction type and order can clarify the often misunderstood distinction between primary and scatter dose. The students can thus see the “whole” simultaneously with the “sum of the parts,” which enhances their physical insight and creates a sustainable foundation for further learning. After the presentations the speakers and moderator will be open to questions and discussion with the audience members. Learning Objectives: Be able to explain Project-Based Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain Flipped Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain active-learning strategies for the teaching of Medical Physics. Be able to explain how Monte Carlo simulations can be used to deepen a student’s understanding of radiation physics and dosimetry.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2016

SU-A-BRA-02: Making the Most of a One Hour Lecture with Alternative Teaching Methodologies: Implementing Project-Based and Flipped Learning

Vic Montemayor - No one has been more passionate about improving the quality and effectiveness of the teaching of Medical Physics than Bill Hendee. It was in August of 2008 that the first AAPM Workshop on Becoming a Better Teacher of Medical Physics was held, organized and run by Bill Hendee. This was followed up in July of 2010 with a summer school on the same topic, again organized by Bill. There has been continued interest in alternate approaches to teaching medical physics since those initial gatherings. The momentum established by these workshops is made clear each year in the annual Innovation in Medical Physics Education session, which highlights work being done in all forms of medical physics education, from one-on-one residencies or classroom presentations to large-scale program revisions and on-line resources for international audiences. This symposium, presented on behalf of the Education Council, highlights the work of three finalists from past Innovation in Education sessions. Each will be presenting their approaches to and innovations in teaching medical physics. It is hoped that audience members interested in trying something new in their teaching of medical physics will find some of these ideas and approaches readily applicable to their own classrooms. Rebecca Howell - The presentation will discuss ways to maximize classroom learning, i.e., increasing the amount of material covered while also enhancing students’ understanding of the broader implications of the course topics. Specifically, the presentation will focus on two teaching methodologies, project based learning and flip learning. These teaching methods will be illustrated using an example of graduate medical physics course where both are used in conjunction with traditional lectures. Additionally, the presentation will focus on our experience implementing these methods including challenges that were overcome. Jay Burmeister - My presentation will discuss the incorporation of active learning techniques into a traditional medical physics classroom course. I will describe these techniques and how they were implemented as well as student performance before and after implementation. Student feedback indicated that these course changes improved their ability to actively assimilate the course content, thus improving their understanding of the material. Shahid Naqvi - My talk will focus on ways to help students visualize crucial concepts that lie at the core of radiation physics. Although particle tracks generated by Monte Carlo simulations have served as an indispensable visualization tool, students often struggle to resolve the underlying physics from a simultaneous jumble of tracks. We can clarify the physics by “coding” the tracks, e.g., by coloring the tracks according to their “starting” or “crossing” regions. The regionally-coded tracks when overlaid with dose distributions help the students see the elusive connection between dose, kerma and electronic disequilibrium. Tracks coded according to local energy or energy-loss rate can illustrate the need for stopping power corrections in electron beams and explain the Bragg peak in a proton beam. Coding tracks according to parent interaction type and order can clarify the often misunderstood distinction between primary and scatter dose. The students can thus see the “whole” simultaneously with the “sum of the parts,” which enhances their physical insight and creates a sustainable foundation for further learning. After the presentations the speakers and moderator will be open to questions and discussion with the audience members. Learning Objectives: Be able to explain Project-Based Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain Flipped Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain active-learning strategies for the teaching of Medical Physics. Be able to explain how Monte Carlo simulations can be used to deepen a student’s understanding of radiation physics and dosimetry.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2016

SU-A-BRA-03: Creative Stimulation: A Flexible Hands-On Approach to Building a Deeper Understanding of Critical Concepts in Radiation Physics

Vic Montemayor - No one has been more passionate about improving the quality and effectiveness of the teaching of Medical Physics than Bill Hendee. It was in August of 2008 that the first AAPM Workshop on Becoming a Better Teacher of Medical Physics was held, organized and run by Bill Hendee. This was followed up in July of 2010 with a summer school on the same topic, again organized by Bill. There has been continued interest in alternate approaches to teaching medical physics since those initial gatherings. The momentum established by these workshops is made clear each year in the annual Innovation in Medical Physics Education session, which highlights work being done in all forms of medical physics education, from one-on-one residencies or classroom presentations to large-scale program revisions and on-line resources for international audiences. This symposium, presented on behalf of the Education Council, highlights the work of three finalists from past Innovation in Education sessions. Each will be presenting their approaches to and innovations in teaching medical physics. It is hoped that audience members interested in trying something new in their teaching of medical physics will find some of these ideas and approaches readily applicable to their own classrooms. Rebecca Howell - The presentation will discuss ways to maximize classroom learning, i.e., increasing the amount of material covered while also enhancing students’ understanding of the broader implications of the course topics. Specifically, the presentation will focus on two teaching methodologies, project based learning and flip learning. These teaching methods will be illustrated using an example of graduate medical physics course where both are used in conjunction with traditional lectures. Additionally, the presentation will focus on our experience implementing these methods including challenges that were overcome. Jay Burmeister - My presentation will discuss the incorporation of active learning techniques into a traditional medical physics classroom course. I will describe these techniques and how they were implemented as well as student performance before and after implementation. Student feedback indicated that these course changes improved their ability to actively assimilate the course content, thus improving their understanding of the material. Shahid Naqvi - My talk will focus on ways to help students visualize crucial concepts that lie at the core of radiation physics. Although particle tracks generated by Monte Carlo simulations have served as an indispensable visualization tool, students often struggle to resolve the underlying physics from a simultaneous jumble of tracks. We can clarify the physics by “coding” the tracks, e.g., by coloring the tracks according to their “starting” or “crossing” regions. The regionally-coded tracks when overlaid with dose distributions help the students see the elusive connection between dose, kerma and electronic disequilibrium. Tracks coded according to local energy or energy-loss rate can illustrate the need for stopping power corrections in electron beams and explain the Bragg peak in a proton beam. Coding tracks according to parent interaction type and order can clarify the often misunderstood distinction between primary and scatter dose. The students can thus see the “whole” simultaneously with the “sum of the parts,” which enhances their physical insight and creates a sustainable foundation for further learning. After the presentations the speakers and moderator will be open to questions and discussion with the audience members. Learning Objectives: Be able to explain Project-Based Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain Flipped Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain active-learning strategies for the teaching of Medical Physics. Be able to explain how Monte Carlo simulations can be used to deepen a student’s understanding of radiation physics and dosimetry.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2016

SU-A-BRA-04: Incorporating Active Learning Into Medical Physics Education

Vic Montemayor - No one has been more passionate about improving the quality and effectiveness of the teaching of Medical Physics than Bill Hendee. It was in August of 2008 that the first AAPM Workshop on Becoming a Better Teacher of Medical Physics was held, organized and run by Bill Hendee. This was followed up in July of 2010 with a summer school on the same topic, again organized by Bill. There has been continued interest in alternate approaches to teaching medical physics since those initial gatherings. The momentum established by these workshops is made clear each year in the annual Innovation in Medical Physics Education session, which highlights work being done in all forms of medical physics education, from one-on-one residencies or classroom presentations to large-scale program revisions and on-line resources for international audiences. This symposium, presented on behalf of the Education Council, highlights the work of three finalists from past Innovation in Education sessions. Each will be presenting their approaches to and innovations in teaching medical physics. It is hoped that audience members interested in trying something new in their teaching of medical physics will find some of these ideas and approaches readily applicable to their own classrooms. Rebecca Howell - The presentation will discuss ways to maximize classroom learning, i.e., increasing the amount of material covered while also enhancing students’ understanding of the broader implications of the course topics. Specifically, the presentation will focus on two teaching methodologies, project based learning and flip learning. These teaching methods will be illustrated using an example of graduate medical physics course where both are used in conjunction with traditional lectures. Additionally, the presentation will focus on our experience implementing these methods including challenges that were overcome. Jay Burmeister - My presentation will discuss the incorporation of active learning techniques into a traditional medical physics classroom course. I will describe these techniques and how they were implemented as well as student performance before and after implementation. Student feedback indicated that these course changes improved their ability to actively assimilate the course content, thus improving their understanding of the material. Shahid Naqvi - My talk will focus on ways to help students visualize crucial concepts that lie at the core of radiation physics. Although particle tracks generated by Monte Carlo simulations have served as an indispensable visualization tool, students often struggle to resolve the underlying physics from a simultaneous jumble of tracks. We can clarify the physics by “coding” the tracks, e.g., by coloring the tracks according to their “starting” or “crossing” regions. The regionally-coded tracks when overlaid with dose distributions help the students see the elusive connection between dose, kerma and electronic disequilibrium. Tracks coded according to local energy or energy-loss rate can illustrate the need for stopping power corrections in electron beams and explain the Bragg peak in a proton beam. Coding tracks according to parent interaction type and order can clarify the often misunderstood distinction between primary and scatter dose. The students can thus see the “whole” simultaneously with the “sum of the parts,” which enhances their physical insight and creates a sustainable foundation for further learning. After the presentations the speakers and moderator will be open to questions and discussion with the audience members. Learning Objectives: Be able to explain Project-Based Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain Flipped Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain active-learning strategies for the teaching of Medical Physics. Be able to explain how Monte Carlo simulations can be used to deepen a student’s understanding of radiation physics and dosimetry.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2016

SU-A-BRA-05: Panel Discussion

Vic Montemayor - No one has been more passionate about improving the quality and effectiveness of the teaching of Medical Physics than Bill Hendee. It was in August of 2008 that the first AAPM Workshop on Becoming a Better Teacher of Medical Physics was held, organized and run by Bill Hendee. This was followed up in July of 2010 with a summer school on the same topic, again organized by Bill. There has been continued interest in alternate approaches to teaching medical physics since those initial gatherings. The momentum established by these workshops is made clear each year in the annual Innovation in Medical Physics Education session, which highlights work being done in all forms of medical physics education, from one-on-one residencies or classroom presentations to large-scale program revisions and on-line resources for international audiences. This symposium, presented on behalf of the Education Council, highlights the work of three finalists from past Innovation in Education sessions. Each will be presenting their approaches to and innovations in teaching medical physics. It is hoped that audience members interested in trying something new in their teaching of medical physics will find some of these ideas and approaches readily applicable to their own classrooms. Rebecca Howell - The presentation will discuss ways to maximize classroom learning, i.e., increasing the amount of material covered while also enhancing students’ understanding of the broader implications of the course topics. Specifically, the presentation will focus on two teaching methodologies, project based learning and flip learning. These teaching methods will be illustrated using an example of graduate medical physics course where both are used in conjunction with traditional lectures. Additionally, the presentation will focus on our experience implementing these methods including challenges that were overcome. Jay Burmeister - My presentation will discuss the incorporation of active learning techniques into a traditional medical physics classroom course. I will describe these techniques and how they were implemented as well as student performance before and after implementation. Student feedback indicated that these course changes improved their ability to actively assimilate the course content, thus improving their understanding of the material. Shahid Naqvi - My talk will focus on ways to help students visualize crucial concepts that lie at the core of radiation physics. Although particle tracks generated by Monte Carlo simulations have served as an indispensable visualization tool, students often struggle to resolve the underlying physics from a simultaneous jumble of tracks. We can clarify the physics by “coding” the tracks, e.g., by coloring the tracks according to their “starting” or “crossing” regions. The regionally-coded tracks when overlaid with dose distributions help the students see the elusive connection between dose, kerma and electronic disequilibrium. Tracks coded according to local energy or energy-loss rate can illustrate the need for stopping power corrections in electron beams and explain the Bragg peak in a proton beam. Coding tracks according to parent interaction type and order can clarify the often misunderstood distinction between primary and scatter dose. The students can thus see the “whole” simultaneously with the “sum of the parts,” which enhances their physical insight and creates a sustainable foundation for further learning. After the presentations the speakers and moderator will be open to questions and discussion with the audience members. Learning Objectives: Be able to explain Project-Based Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain Flipped Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain active-learning strategies for the teaching of Medical Physics. Be able to explain how Monte Carlo simulations can be used to deepen a student’s understanding of radiation physics and dosimetry.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2016

SU-A-BRA-00: Education Council Symposium: Revitalizing Your Medical Physics Classroom: Some Examples and Thoughts from the Trenches

Vic Montemayor - No one has been more passionate about improving the quality and effectiveness of the teaching of Medical Physics than Bill Hendee. It was in August of 2008 that the first AAPM Workshop on Becoming a Better Teacher of Medical Physics was held, organized and run by Bill Hendee. This was followed up in July of 2010 with a summer school on the same topic, again organized by Bill. There has been continued interest in alternate approaches to teaching medical physics since those initial gatherings. The momentum established by these workshops is made clear each year in the annual Innovation in Medical Physics Education session, which highlights work being done in all forms of medical physics education, from one-on-one residencies or classroom presentations to large-scale program revisions and on-line resources for international audiences. This symposium, presented on behalf of the Education Council, highlights the work of three finalists from past Innovation in Education sessions. Each will be presenting their approaches to and innovations in teaching medical physics. It is hoped that audience members interested in trying something new in their teaching of medical physics will find some of these ideas and approaches readily applicable to their own classrooms. Rebecca Howell - The presentation will discuss ways to maximize classroom learning, i.e., increasing the amount of material covered while also enhancing students’ understanding of the broader implications of the course topics. Specifically, the presentation will focus on two teaching methodologies, project based learning and flip learning. These teaching methods will be illustrated using an example of graduate medical physics course where both are used in conjunction with traditional lectures. Additionally, the presentation will focus on our experience implementing these methods including challenges that were overcome. Jay Burmeister - My presentation will discuss the incorporation of active learning techniques into a traditional medical physics classroom course. I will describe these techniques and how they were implemented as well as student performance before and after implementation. Student feedback indicated that these course changes improved their ability to actively assimilate the course content, thus improving their understanding of the material. Shahid Naqvi - My talk will focus on ways to help students visualize crucial concepts that lie at the core of radiation physics. Although particle tracks generated by Monte Carlo simulations have served as an indispensable visualization tool, students often struggle to resolve the underlying physics from a simultaneous jumble of tracks. We can clarify the physics by “coding” the tracks, e.g., by coloring the tracks according to their “starting” or “crossing” regions. The regionally-coded tracks when overlaid with dose distributions help the students see the elusive connection between dose, kerma and electronic disequilibrium. Tracks coded according to local energy or energy-loss rate can illustrate the need for stopping power corrections in electron beams and explain the Bragg peak in a proton beam. Coding tracks according to parent interaction type and order can clarify the often misunderstood distinction between primary and scatter dose. The students can thus see the “whole” simultaneously with the “sum of the parts,” which enhances their physical insight and creates a sustainable foundation for further learning. After the presentations the speakers and moderator will be open to questions and discussion with the audience members. Learning Objectives: Be able to explain Project-Based Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain Flipped Learning and how can it be incorporated into a Medical Physics classroom. Be able to explain active-learning strategies for the teaching of Medical Physics. Be able to explain how Monte Carlo simulations can be used to deepen a student’s understanding of radiation physics and dosimetry.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2025

A Unified Interpretation of Variability in Precipitation Isotope Ratios

Abstract Several mechanisms have been proposed to explain why the isotope ratios of precipitation vary in space and time and why they correlate with other climate variables like temperature and precipitation. Here, we argue that this behavior is best understood through the lens of radiative transfer, which treats the depletion of atmospheric vapor transport by precipitation as analogous to the attenuation of light by absorption or scattering. Building on earlier work by Siler et al., we introduce a simple model that uses the equations of radiative transfer to approximate the two-dimensional pattern of the oxygen isotope composition of precipitation ( δ p ) from monthly mean hydrologic variables. The model accurately simulates the spatial and seasonal variability in δ p within a state-of-the-art climate model and permits a simple decomposition of δ p variability into contributions from gradients in evaporation and the length scale of vapor transport. Outside the tropics, δ p is mostly controlled by gradients in evaporation, whose dependence on temperature explains the positive correlation between δ p and temperature (i.e., the temperature effect). At low latitudes, δ p is mostly controlled by gradients in the transport length scale, whose inverse relationship with precipitation explains the negative correlation between δ p and precipitation (i.e., the amount effect). This suggests that the temperature and amount effects are both mostly explained by the variability in upstream rainout, but they reflect distinct mechanisms governing rainout at different latitudes. Significance Statement The isotopic composition of precipitation has long been used to make inferences about past climates based on its observed relationship with precipitation in the tropics and with temperature at higher latitudes. These relationships—known as the “amount effect” and “temperature effect,” respectively—have been attributed to many different mechanisms, most of which are thought to operate at either high or low latitudes but not both. Here, we present a unified framework for interpreting the isotope variability that can explain the latitude dependence of the temperature and amount effects despite making no distinction between high and low latitudes. Although our results are generally consistent with certain interpretations of the amount effect, they suggest that the temperature effect is widely misunderstood.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2013

Enhancing the Representation of Subgrid Land Surface Characteristics in Land Surface Models

Land surface heterogeneity has long been recognized and increasingly incorporated in the land surface modelling. In most existing land surface models, the spatial variability of surface cover is represented as subgrid composition of multiple surface cover types. In this study, we developed a new subgrid classification method (SGC) that accounts for the topographic variability of the vegetation cover. Each model grid cell was represented with a number of elevation classes and each elevation class was further described by a number of vegetation types. The numbers of elevation classes and vegetation types were variable and optimized for each model grid so that the spatial variability of both elevation and vegetation can be reasonably explained given a pre-determined total number of classes. The subgrid structure of the Community Land Model (CLM) was used as an example to illustrate the newly developed method in this study. With similar computational burden as the current subgrid vegetation representation in CLM, the new method is able to explain at least 80% of the total subgrid PFTs and greatly reduced the variations of elevation within each subgrid class compared to the baseline method where a single elevation class is assigned to each subgrid PFT. The new method was also evaluated against two other subgrid methods (SGC1 and SGC2) that assigned fixed numbers of elevation and vegetation classes for each model grid with different perspectives of surface cover classification. Implemented at five model resolutions (0.1°, 0.25°, 0.5°, 1.0° and 2.0°) with three maximum-allowed total number of classes N_class of 24, 18 and 12 representing different computational burdens over the North America (NA) continent, the new method showed variable performances compared to the SGC1 and SGC2 methods. However, the advantage of the SGC method over the other two methods clearly emerged at coarser model resolutions and with moderate computational intensity (N_class = 18) as it explained the most PFTs and elevation variability among the three subgrid methods. Spatially, the SGC method explained more elevation variability in topography-complex areas and more vegetation variability in flat areas. Furthermore, the variability of both elevation and vegetation explained by the new method was more spatially homogeneous regardless of the model resolutions and computational burdens. The SGC method will be implemented in CLM over the NA continent to assess its impacts on simulating land surface processes.

characteristics↗

DOE OSTI2025

Hyperspectral leaf reflectance of grasses varies with evolutionary lineage more than with site

Abstract To predict ecological responses at broad environmental scales, grass species are commonly grouped into two broad functional types based on photosynthetic pathway. However, closely related species may have distinctive anatomical and physiological attributes that influence ecological responses, beyond those related to photosynthetic pathway alone. Hyperspectral leaf reflectance can provide an integrated measure of covarying leaf traits that may result from phylogenetic trait conservatism and/or environmental conditions. Understanding whether spectra‐trait relationships are lineage specific or reflect environmental variation across sites is necessary for using hyperspectral reflectance to predict plant responses to environmental changes across spatial scales. We measured hyperspectral leaf reflectance (400–2400 nm) and 12 structural, biochemical, and physiological leaf traits from five grass‐dominated sites spanning the Great Plains of North America. We assessed if variation in leaf reflectance spectra among grass species is explained more by evolutionary lineage (as captured by tribes or subfamilies), photosynthetic pathway (C 3 or C 4 ), or site differences. We then determined whether leaf spectra can be used to predict leaf traits within and across lineages. Our results using redundancy analysis ordination (RDA) show that grass tribe identity explained more variation in leaf spectra (adjusted R 2 = 0.12) than photosynthetic pathway, which explained little variation in leaf spectra (adjusted R 2 = 0.00). Furthermore, leaf reflectance from the same tribe across multiple sites was more similar than leaf reflectance from the same site across tribes (adjusted R 2 = 0.12 and 0.08, respectively). Across all sites and species, trait predictions based on spectra ranged considerably in predictive accuracies ( R 2 = 0.65 to <0.01), but R 2 was >0.80 for certain lineages and sites. The relationship between Vc max , a measure of photosynthetic capacity, and spectra was particularly promising. Chloridoideae, a lineage more common at drier sites, appears to have distinct spectra‐trait relationships compared with other lineages. Overall, our results show that evolutionary relatedness explains more variation in grass leaf spectra than photosynthetic pathway or site, but consideration of lineage‐ and site‐specific trait relationships is needed to interpret spectral variation across large environmental gradients.

Pau, Stephanie [Department of Geography University↗

DOE OSTI2022

Degradation Reduces Microbial Richness and Alters Microbial Functions in an Australian Peatland

Abstract Peatland ecosystems cover only 3% of the world’s land area; however, they store one-third of the global soil carbon (C). Microbial communities are the main drivers of C decomposition in peatlands, yet we have limited knowledge of their structure and function. While the microbial communities in the Northern Hemisphere peatlands are well documented, we have limited understanding of microbial community composition and function in the Southern Hemisphere peatlands, especially in Australia. We investigated the vertical stratification of prokaryote and fungal communities from Wellington Plains peatland in the Australian Alps. Within the peatland complex, bog peat was sampled from the intact peatland and dried peat from the degraded peatland along a vertical soil depth gradient (i.e., acrotelm, mesotelm, and catotelm). We analyzed the prokaryote and fungal community structure, predicted functional profiles of prokaryotes using PICRUSt, and assigned soil fungal guilds using FUNGuild. We found that the structure and function of prokaryotes were vertically stratified in the intact bog. Soil carbon, manganese, nitrogen, lead, and sodium content best explained the prokaryote composition. Prokaryote richness was significantly higher in the intact bog acrotelm compared to degraded bog acrotelm. Fungal composition remained similar across the soil depth gradient; however, there was a considerable increase in saprotroph abundance and decrease in endophyte abundance along the vertical soil depth gradient. The abundance of saprotrophs and plant pathogens was two-fold higher in the degraded bog acrotelm. Soil manganese and nitrogen content, electrical conductivity, and water table level (cm) best explained the fungal composition. Our results demonstrate that both fungal and prokaryote communities are shaped by soil abiotic factors and that peatland degradation reduces microbial richness and alters microbial functions. Thus, current and future changes to the environmental conditions in these peatlands may lead to altered microbial community structures and associated functions which may have implications for broader ecosystem function changes in peatlands.

Environmental Sciences & Ecology↗

DOE OSTI2018

Microstructural effects in the simulation of creep of concrete

The influence of the microstructure on the visco-elastic properties of concrete is investigated using finite element simulations at the meso-scale. We first derive a constitutive law for the creep of the cement paste which accounts for both recoverable and permanent deformations, as well as the influence of temperature and internal relative humidity. The model is calibrated on a set of experiments at the cement paste scale, and then validated after upscaling to the concrete scale. The model is then applied to study the influence of the microstructure on the macroscopic creep of concrete. We show that materials with finer particles exhibit less creep, and that the anisotropy of creep can be explained with the shape and orientation of the aggregates. Furthermore, the acceleration of the stress relaxation in the presence of damage is explained by the micro-mechanical interaction between the aggregates, the cement paste, and the micro-cracks.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Development of photocatalyst by combined nitrogen and yttrium doping

Graphical abstract: The simulated compensated YN{sub SUB} co-doped TiO{sub 2} model can reasonably explain the experimental observations. Calculation results show that substitutional Y at Ti sites and substitutional N at O sites with an oxygen vacancy give stable configuration, reduced band gap, better visible light absorption and enhance separations of photoexcited charge carriers. The experimental observations confirmed the theoretical findings. - Highlights: • (Y, N) codoped TiO{sub 2} was synthesized by mild one pot hydrothermal method. • The Y doping concentration was varied from 0.01 to 1.38 at%. • 0.05% (Y, N) codoped TiO{sub 2} shows enhanced visible light photocatalytic activity. • Compensated and noncompensated ab-initio calculations were performed. • Calculation results reasonably explained the experimental findings. - Abstract: Titanium dioxide co-doped with yttrium and nitrogen with different yttrium doping concentration has been synthesized by mild one pot hydrothermal method without any post calcination for crystallization. Irrespective of the yttrium doping concentration, all the synthesized samples were composed of pure anatase phase with good crystallinity. And the synthesized co-doped samples have spherical morphology with uniform particle size distribution. The absorption edge of the co-doped TiO{sub 2} was shifted toward visible light region depicting that the intrinsic band gap of TiO{sub 2} was affected by the co-doping. Among the different samples, the co-doped sample with 0.05% yttrium doping concentration exhibits enhanced visible light photocatalytic activity by degradation of methylene blue in aqueous solution. Compensated and non-compensated yttrium–nitrogen co-doped TiO{sub 2} models were simulated using density functional theory to explain the experimental findings. The calculation results show that the compensated yttrium–nitrogen co-doped TiO{sub 2} model may reasonably explain the experimental observations due to its stable configuration, narrowed band gap and enhanced separation of photoexcited carriers.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Atomic Scale Studies of La/Sr Ordering in Colossal Magnetoresistant La 2-2x Sr 1+2x Mn 2 O 7 Single Crystals

To date, it is unclear whether chemical order (or disorder) is in any way connected to double exchange, electronic phase separation, or charge ordering (CO) in manganites. In this work, we carry out an atomic resolution study of the colossal magnetoresistant manganite La 2-2x Sr 1+2x Mn 2 O 7 (LSMO). We combine aberration-corrected electron microscopy and spectroscopy with spectroscopic image simulations, to analyze cation ordering at the atomic scale in real space in a number of LSMO single crystals. We compare three different compositions within the phase diagram: a ferromagnetic metallic material (x=0.36), an insulating, antiferromagnetic charge ordered (AF-CO) compound (x=0.5), which also exhibits orbital ordering, and an additional AF sample (x=0.56). Detailed image simulations are essential to accurately quantify the degree of chemical ordering of these samples. We find a significant degree of long-range chemical ordering in all cases, which increases in the AF-CO range. However, the degree of ordering is never complete nor can it explain the strongly correlated underlying ordering phenomena. Our results show that chemical ordering over distinct crystallographic sites is not needed for electronic ordering phenomena to appear in manganites, and cannot by itself explain the complex electronic behavior of LSMO.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Complex Dependence of Calcite Crack Kinetics on Salinity: The Role of DLVO and Hydration Forces

Abstract Subcritical crack growth (SCG) plays an important role in many geological processes such as delayed earth rupture and rock weathering. The complex dependency of SCG on the in‐crack fluid chemistry, however, is still poorly understood. In this study, we utilize the newly developed surface force‐based fracture theory (SFFT) to elucidate the relative contributions of surface forces and solute transport to the crack growth kinetics of calcite in NaCl solutions. Expanding on Barenblatt's cohesive crack model, SFFT introduces an effective stress intensity at the crack tip that encompasses all the relevant intermolecular forces across the crack in addition to the external far‐field stresses. The nonlinear system of equations portraying the crack opening profile, the solute distribution in a propagating crack, and the crack growth velocity are numerically solved via an implicit scheme. After carefully calibrating the model for calcite‐water systems, the SFFT is used to predict the SCG response of calcite at different NaCl concentrations, based on various hypotheses. These predictions are then compared to existing SCG data from the literature. We demonstrate that the experimentally observed variation of SCG rate with NaCl concentration cannot be explained solely by DLVO forces (electrostatic and Van der Waals interactions). This can be remediated by introducing an exponentially decaying hydration force with a nonlinear, nonmonotonic dependence on NaCl concentration. Furthermore, we demonstrate that accounting for both diffusive and advective transport of ions is important in explaining the absence of a stage‐II SCG response for calcite in electrolyte solutions. Plain Language Summary Subcritical crack growth (SCG) refers to the slow propagation of cracks in materials under a stress below the threshold for catastrophic failure. SCG is a key process in many geological events, for example, delayed earth ruptures and rock weathering. New initiatives such as underground CO 2 and H 2 storage in carbonate reservoirs further call for better understanding of SCG in carbonate minerals subjected to varying fluid chemistry. This study examines the SCG of calcite, a key mineral found in carbonate rocks, intergranular cement in sandstones, and filling material in mineral veins and faults, determining their deformation and strength. A mathematical model is developed to describe how the crack opens and propagates, how solutes (like salts) distribute within the crack, and how the crack surfaces interact with each other. We used the model to predict calcite SCG in water at different salt concentrations and compared it with experimental data. Our results revealed that the hydration force is the dominating factor in determining the complex, non‐linear dependency of SCG on salinity. We also found that both the movement of ions by diffusion and by bulk water flow are crucial for explaining the SCG rates, especially when the cracks grow quickly. Key Points Surface Force‐Based Fracture Theory predicts the complex subcritical crack growth patterns of calcite crystals immersed in NaCl solutions Results highlight the dominant role of hydration forces in altering the fracture behavior of calcite compared to VdW and electric double‐layer forces Advective solute transport explains the absence of stages‐II and ‐III subcritical crack growth responses in solid‐liquid systems

DLVO↗

DOE OSTI2025

Environmental Controls on Water Vapor Deuterium Excess in the Coastal Boundary Layer: An Information Theory Perspective

We use information theory to quantify the environmental controls on water vapor deuterium excess (D-excess) in coastal Southern California from June 2023 through February 2024. Using Shannon entropy, mutual information (MI), and joint mutual information, metrics that capture both linear and nonlinear relationships, we identify the most informative variables and variable combinations governing D-excess across contrasting marine and continental regimes. Relative humidity with respect to sea surface temperature (RHS) is consistently the strongest individual predictor, explaining up to 27% of D-excess variability during marine conditions but only 10% in continental air masses. The Relative humidity(RHS) + sea surface temperature (SST) combination demonstrates synergistic effects, where their joint influence (explaining up to 36% of D-excess variability) exceeds what either variable achieves individually, confirming their coupled influence on deuterium excess. Wind direction complements RHS most effectively during continental conditions. The best three-variable combination (RHS + SST + Planetary Boundary Layer height) explains 38% of D-excess variability in marine air, while no combination exceeds 20% explanatory power during continental periods. Information theory shows that heteroscedasticity in D-excess relationships indicates regime shifts in controlling processes and quantifies fundamental constraints on predictor variables: some environmental factors like surface pressure or water vapor flux contain insufficient information content to explain D-excess variability regardless of their physical relevance. These results highlight the different predictability limits between marine and continental regimes, challenging the adequacy of linear models and providing a rigorous framework for quantifying the information content of isotope-climate relationships with implications for both modern and paleoclimate applications.

information theory↗

DOE OSTI2011

Territorial characteristics of low frequency electrostatic fluctuations in a simple magnetized torus

This paper presents an experimental investigation of turbulence in simple toroidal plasma devices without rotational transform. It is argued that Rayleigh-Taylor (flute interchange) mode may be one of the source mechanisms for the observed turbulence but is not sufficient to explain its observed global characteristics. Taking BETA device as an example, we show that pure Rayleigh-Taylor mode cannot explain (i) the observation of mode maximum at the location other than where density scale length is minimum, (ii) the comparable value of amplitude level of fluctuations in good curvature region, and (iii) the decrease in the mode amplitude with increasing magnetic field. Investigations have revealed that there exists not only poloidal plasma flow but also that it is sheared. Including this effect explains the first observation. However, modification brought about by velocity shear in the Rayleigh-Taylor mode still does not explain our second and third observations. We have taken an approach that since Rayleigh-Taylor is not excited in a good curvature region, it cannot be the source of turbulence there. Nor is it defensible to say that turbulence born in a bad curvature region is carried over through ExB rotation to the good curvature region. Consequently, we have invoked cross-field Simon-Hoh instability for this region. Experimental evidence supporting our proposal is presented. This paper concludes that toroidal devices have simultaneous existence of different self-consistent sources of turbulence in different regions of the device.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗