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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Autolysis and extension of isolated walls from growing cucumber hypocotyls

Walls isolated from cucumber hypocotyls retain autolytic activities and the ability to extend when placed under the appropriate conditions. To test whether autolysis and extension are related, we treated the walls in various ways to enhance or inhibit long-term wall extension ('creep') and measured autolysis as release of various saccharides from the wall. Except for some non-specific inhibitors of enzymatic activity, we found no correlation between wall extension and wall autolysis. Most notably, autolysis and extension differed strongly in their pH dependence. We also found that exogenous cellulases and pectinases enhanced extension in native walls, but when applied to walls previously inactivated with heat or protease these enzymes caused breakage without sustained extension. In contrast, pretreatment of walls with pectinase or cellulase, followed by boiling in methanol to inactivate the enzymes, resulted in walls with much stronger expansin-mediated extension responses. Crude protein preparations from the digestive tracts of snails enhanced extension of both native and inactivated walls, and these preparations contained expansin-like proteins (assessed by Western blotting). Our results indicate that the extension of isolated cucumber walls does not depend directly on the activity of endogenous wall-bound autolytic enzymes. The results with exogenous enzymes suggest that the hydrolysis of matrix polysaccharides may not induce wall creep by itself, but may act synergistically with expansins to enhance wall extension.

NASA Discipline Plant Biology↗
DOE OSTI2019

Using solar availability factors to adjust cool-wall energy savings for shading and reflection by neighboring buildings

The extent to which a solar-reflective “cool” wall can reduce a building's cooling load in summer or increase its heating load in winter scales with the wall's incident solar radiation, or solar availability. We assess how the solar availability at the wall of a central (modeled) building is affected by a neighboring wall across an urban canyon by calculating the central wall's solar availability factor (SAF), defined as the ratio of sunlight incident on the central wall in the presence of the neighboring wall to that incident in the absence of the neighboring wall. Cool-wall heating, ventilation, and air conditioning (HVAC) energy savings simulated for an isolated central building (no neighbors) can be multiplied by SAFs to account for interactions with neighboring walls. Monthly values of SAF were evaluated in 17 climates across the United States, including three in California, for north, east, south, and west central walls, over a wide range of canyon aspect ratio (height/width). Results for four representative aspect ratios—0.2, 1, 2, and 10—are presented. In Fresno, CA, monthly SAF ranges from 0.90 to 0.96 for central walls facing north, east, south, or west when the aspect ratio is 0.2 (two-story single-family homes across a street) and both the central and neighboring walls are conventional (albedo 0.25). Monthly SAFs decrease as aspect ratio rises, falling to 0.06–0.24 at an aspect ratio of 10 (adjacent 10-story buildings on the same side of the street). An example worked for a two-story single-family home in Fresno on the west side of a residential street yields SAFs of 0.47 (north), 0.92 (east), 0.50 (south), and 0.63 (west) to apply to the cool-wall annual HVAC energy savings computed for an isolated central building. Shading and reflection reduce the home's annual HVAC energy cost savings by 31%.

14 SOLAR ENERGY↗
DOE OSTI2023

Engine Operating Conditions, Fuel Property Effects, and Associated Fuel–Wall Interaction Dependencies of Stochastic Preignition

This work for the Coordinating Research Council (CRC) explores dependencies on the opportunity for fuel to impinge on internal engine surfaces (i.e., fuel–wall impingement) as a function of fuel properties and engine operating conditions and correlates these data with measurements of stochastic preignition (SPI) propensity. SPI rates are directly coupled with laser–induced florescence measurements of dye-doped fuel dilution measurements of the engine lubricant, which provides a surrogate for fuel–wall impingement. Literature suggests that SPI may have several dependencies, one being fuel–wall impingement. However, it remains unknown if fuel-wall impingement is a fundamental predictor and source of SPI or is simply a causational factor of SPI. In this study, these relationships on SPI and fuel-wall impingement are explored using 4 fuels at 8 operating conditions per fuel, for 32 total test points. The fuels were directly injected at two different injection timings: an earlier injection timing that initially targets the piston crown and a later injection timing that targets the cylinder liner. At each injection timing, the engine was operated at both 90°C and 70°C coolant and lubricant temperatures, and 185 and 200 kPa absolute intake manifold pressure. This work serves as an exploratory effort to down select conditions and provide initial fuel properties of interest for a secondary study to explore fuel property specific effects on fuel-wall interaction and SPI propensity. Significant findings from this initial operating condition and fuel property exploratory work are: 1. reduced engine operating coolant and lubricant temperatures, along with 2. retarded injection timings were required to increase SPI propensity. Moreover, at these conditions some fuel specific effects were also observed; specifically, increased ethanol content increased measured dye–wall (i.e., fuel–wall) interaction. However, despite increased dye–wall interaction, the increased volatility of the ethanol containing fuels also reduced the estimated fuel retention in the top-ring zone and associated measured SPI propensity. Thus, the findings of this unique approach to explore relationships between fuel-wall impingement and SPI highlight that SPI propensity is more directly proportional to retained fuel, and not simply fuel–wall impingement. Furthermore, fuel retention was found to be directly influenced by complex fuel property and engine operating condition relationships. Either retarded injection timings and/or increased fuel volatility increased fuel wall-impingement, while less volatile fuels and/or reduced coolant temperatures increased fuel retention. Therefore, for a given operating condition, the data highlights that greater volatile fuels exhibit increased fuel wall impingement without increased fuel retention or SPI propensity, while less volatile fuels could exhibit reduced fuel-wall impingement but increased fuel retention and SPI propensity rates.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1986

Drag reducing outer-layer devices in rough wall turbulent boundary layers

The ability of outer-layer devices to reduce wall shear stress over a substantial streamwise distance in rough-wall turbulent boundary layers has been studied experimentally. The devices examined are a pair of thin flat ribbons placed in tandem as well as those having symmetric airfoil sections. The wall conditions examined are smooth, d- and k-type transverse-groove and sandgrain roughnesses. The wall drag is found to be reduced from the respective normal levels in all rough walls. All k-type rough walls exhibit a similar level of relative wall drag reduction which is also smaller than that in a smooth-wall. The d-type rough walls exhibit a transitional behaviour - the relative wall drag reduction drops from the smooth wall level to that of the k-type roughness with increasing roughness Reynolds number. However, the absolute reductions in the local wall shear stress are similar in both the rough and smooth walls. On the other hand, the relative reductions are lower in the rough walls because of a higher reference drag which is caused by the unique presence of a pressure component on which the devices are not as effective.

Bandyopadhyay, P. R.↗
DOE OSTI2014

Electron Tomography of Cryo-Immobilized Plant Tissue: A Novel Approach to Studying 3D Macromolecular Architecture of Mature Plant Cell Walls In Situ

Cost-effective production of lignocellulosic biofuel requires efficient breakdown of cell walls present in plant biomass to retrieve the wall polysaccharides for fermentation. In-depth knowledge of plant cell wall composition is therefore essential for improving the fuel production process. The precise spatial three-dimensional (3D) organization of cellulose, hemicellulose, pectin and lignin within plant cell walls remains unclear to date since the microscopy techniques used so far have been limited to two-dimensional, topographic or low-resolution imaging, or required isolation or chemical extraction of the cell walls. In this paper we demonstrate that by cryo-immobilizing fresh tissue, then either cryo-sectioning or freeze-substituting and resin embedding, followed by cryo- or room temperature (RT) electron tomography, respectively, we can visualize previously unseen details of plant cell wall architecture in 3D, at macromolecular resolution (~2 nm), and in near-native state. Qualitative and quantitative analyses showed that wall organization of cryo-immobilized samples were preserved remarkably better than conventionally prepared samples that suffer substantial extraction. Lignin-less primary cell walls were well preserved in both self-pressurized rapidly frozen (SPRF), cryo-sectioned samples as well as high-pressure frozen, freeze-substituted and resin embedded (HPF-FS-resin) samples. Lignin-rich secondary cell walls appeared featureless in HPF-FS-resin sections presumably due to poor stain penetration, but their macromolecular features could be visualized in unprecedented details in our cryo-sections. While cryo-tomography of vitreous tissue sections is currently proving to be instrumental in developing 3D models of lignin-rich secondary cell walls, here we confirm that the technically easier method of RT-tomography of HPF-FS-resin sections could be used immediately for routine study of low-lignin cell walls. As a proof of principle, we characterized the primary cell walls of a mutant (cob-6) and wild type Arabidopsis hypocotyl parenchyma cells by RT-tomography of HPF-FS-resin sections, and detected a small but significant difference in spatial organization of cellulose microfibrils in the mutant walls.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Large-Eddy Simulation of Flow Over Boeing Gaussian Bump Using Multiagent Reinforcement Learning Wall Model: Preprint

We develop a wall model for large-eddy simulation (LES) that takes into account various pressure-gradient effects using multi-agent reinforcement learning. The model is trained using low-Reynolds-number flow over periodic hills with agents distributed on the wall at various computational grid points. It utilizes a wall eddy-viscosity formulation as the boundary condition to apply the modeled wall shear stress. Each agent receives states based on local instantaneous flow quantities at an off-wall location, computes a reward based on the estimated wall-shear stress, and provides an action to update the wall eddy viscosity at each time step. The trained wall model is validated in wall-modeled LES of flow over periodic hills at higher Reynolds numbers, and the results show the effectiveness of the model on flow with pressure gradients. The analysis of the trained model indicates that the model is capable of distinguishing between the various pressure gradient regimes present in the flow. To further assess the robustness of the developed wall model, simulations of flow over the Boeing Gaussian bump are conducted at a Reynolds number of 2 x 10^6, based on the free-stream velocity and the bump width. The results of mean skin friction and pressure on the bump surface, as well as the velocity statistics of the flow field, are compared to those obtained from equilibrium wall model (EQWM) simulations and published experimental data sets. The developed wall model is found to successfully capture the acceleration and deceleration of the turbulent boundary layer on the bump surface, providing better predictions of skin friction near the bump peak and exhibiting comparable performance to the EQWM with respect to the wall pressure and velocity field. We also conclude that the subgrid-scale model is crucial to the accurate prediction of the flow field, in particular the prediction of separation.

boundary layer↗
DOE OSTI2018

Impact of acidic pH on plant cell wall polysaccharide structure and dynamics: insights into the mechanism of acid growth in plants from solid-state NMR

Acidification of plant primary cell walls causes cell wall expansion and plant growth. To understand how acidic pH affects the molecular structure and dynamics of wall polysaccharides, we have now characterized and compared Arabidopsis thaliana primary cell walls in neutral (pH 6.8) and acidic (pH 4.0) conditions using solid-state NMR spectroscopy. Quantitative 13C solid-state NMR spectra indicate that the pH 4.0 cell wall has neutral galacturonic acid residues in homogalacturonan (HG) and rhamnogalacturonan (RG). 13C INEPT spectra, which selectively detect highly dynamic polymers, indicate that some of the HG and RG chains in the interfibrillar region have become more dynamic in the acidic wall compared to the neutral cell wall, whereas other chains have become more rigid. Consistent with this increased dynamic heterogeneity, C–H dipolar couplings and 2D 13C–13C correlation spectra indicate that some of the HG backbones are partially aggregated in the acidic cell wall. Moreover, 2D correlation spectra measured with long mixing times indicate that the acidic cell wall has weaker cellulose–pectin interactions, and water-polysaccharide 1H spin diffusion data show that cellulose microfibrils are better hydrated at low pH. Taken together, these results indicate a cascade of chemical and conformational changes of wall polysaccharides due to cell wall acidification. These changes start with neutralization of the pectic polysaccharides, which disrupts calcium crosslinking of HG, causes partial aggregation of the interfibrillar HG, weakens cellulose–pectin interactions, and increases the hydration of both cellulose microfibrils and matrix polysaccharides. These molecular-level structural and dynamical changes are expected to facilitate polysaccharide slippage, which underlies cell wall loosening and expansion, and may occur both independent of and as a consequence of protein-mediated wall loosening.

biofuels (including algae and biomass), bio-inspir↗
DOE OSTI2024

An enrichment wall modeling framework for spectral element methods

In the present work, a first-of-its-kind enrichment wall-model is developed within the spectral element method (SEM) framework for large-eddy simulations (LES) of wall-bounded turbulent flows. The method augments the polynomial solution in the wall-adjacent elements with an analytical law-of-the-wall enrichment function representing the mean velocity near the wall. In the solution representation, this enrichment function captures the large gradients in the boundary layer, which allows the polynomial modes to represent the turbulent fluctuations. The enriched solution is able to resolve the shear stress at the wall without any modification to the no-slip wall boundary conditions, which allows for greater accuracy in the near-wall region compared to traditional methods. The enrichment wall modeling approach is implemented in a high-order SEM computational fluid dynamics solver, Nek5000, and its performance is assessed in turbulent channel flow wall-modeled LES for a range of Reynolds numbers. It is demonstrated that the enrichment wall-model improves solution accuracy on under-resolved near-wall grids as compared to traditional shear stress wall-models.

42 ENGINEERING↗
DOE OSTI2021

Life cycle of streaks in the buffer layer of wall-bounded turbulence

In this work, streaks in the buffer layer of wall-bounded turbulence are tracked in time to study their life cycle. Spatially and temporally resolved direct numerical simulation data are used to analyze the strong wall-parallel movements conditioned to low-speed streamwise flow. The analysis of the streaks shows that there is a clear distinction between wall-attached and detached streaks, and that the wall-attached streaks can be further categorized into streaks that are contained in the buffer layer and the ones that reach the outer region. The results reveal that streaks are born in the buffer layer, coalescing with each other to create larger streaks that are still attached to the wall. Once the streak becomes large enough, it starts to meander due to the large streamwise-to-wall-normal aspect ratio, and consequently the elongation in the streamwise direction, which makes it more difficult for the streak to be oriented strictly in the streamwise direction. While the continuous interaction of the streaks allows the superstructure to span extremely long temporal and length scales, individual streak components are relatively small and short-lived. Tall-attached streaks eventually split into wall-attached and wall-detached components. These wall-detached streaks have a strong wall-normal velocity away from the wall, similar to ejections or bursts observed in the literature. Conditionally averaging the flow fields to these split events show that the detached streak has not only a larger wall-normal velocity compared to the wall-attached counterpart, it also has a larger (less negative) streamwise velocity, similar to the velocity field at the tip of a vortex cluster.

42 ENGINEERING↗
NASA NTRS1991

Wall-interference assessment and corrections for transonic NACA 0012 airfoil data from various wind tunnels

A nonlinear, four wall, post-test wall interference assessment/correction (WIAC) code was developed for transonic airfoil data from solid wall wind tunnels with flexibly adaptable top and bottom walls. The WIAC code was applied over a broad range of test conditions to four sets of NACA 0012 airfoil data, from two different adaptive wall wind tunnels. The data include many test points for fully adapted walls, as well as numerous partially adapted and unadapted test points, which together represent many different model/tunnel configurations and possible wall interference effects. Small corrections to the measured Mach numbers and angles of attack were obtained from the WIAC code even for fully adapted data; these corrections generally improve the correlation among the various sets of airfoil data and simultaneously improve the correlation of the data with calculations for a 2-D, free air, Navier-Stokes code. The WIAC corrections for airfoil data taken in fully adapted wall test sections are shown to be significantly smaller than those for comparable airfoil data from straight, slotted wall test sections. This indicates, as expected, a lesser degree of wall interference in the adapted wall tunnels relative to the slotted wall tunnels. Application of the WIAC code to this data was, however, somewhat more difficult and time consuming than initially expected from similar previous experience with WIAC applications to slotted wall data.

Green, Lawrence L.↗
NASA NTRS1991

Effect of Compliant Walls on Secondary Instabilities in Boundary-Layer Transition

For aerodynamic and hydrodynamic vehicles, it is highly desirable to reduce drag and noise levels. A reduction in drag leads to fuel savings. In particular for submersible vehicles, a decrease in noise levels inhibits detection. A suggested means to obtain these reduction goals is by delaying the transition from laminar to turbulent flow in external boundary layers. For hydrodynamic applications, a passive device which shows promise for transition delays is the compliant coating. In previous studies with a simple mechanical model representing the compliant wall, coatings were found that provided transition delays as predicted from the semi-empirical e(sup n) method. Those studies were concerned with the linear stage of transition where the instability of concern is referred to as the primary instability. For the flat-plate boundary layer, the Tollmien-Schlichting (TS) wave is the primary instability. In one of those studies, it was shown that three-dimensional (3-D) primary instabilities, or oblique waves, could dominate transition over the coatings considered. From the primary instability, the stretching and tilting of vorticity in the shear flow leads to a secondary instability mechanism. This has been theoretical described by Herbert based on Floquet theory. In the present study, Herbert's theory is used to predict the development of secondary instabilities over isotropic and non-isotropic compliant walls. Since oblique waves may be dominant over compliant walls, a secondary theory extention is made to allow for these 3-D primary instabilities. The effect of variations in primary amplitude, spanwise wavenumber, and Reynolds number on the secondary instabilities are examined. As in the rigid wall case, over compliant walls the subharmonic mode of secondary instability dominates for low-amplitude primary disturbances. Both isotropic and non-isotropic compliant walls lead to reduced secondary growth rates compared to the rigid wall results. For high frequencies, the non-isotropic wall suppresses the amplification of the secondary instabilities, while instabilities over the isotropic wall may grow with an explosive rate similar to the rigid wall results. For the more important lower frequencies, both isotropic and non-isotropic compliant walls suppress the amplification of secondary instabilities compared to the rigid wall results. The twofold major discovery and demonstration of the present investigation are: (1) the use of passive devices, such as compliant walls, can lead to significant reductions in the secondary instability growth rates and amplification; (2) suppressing the primary growth rates and subsequent amplification enable delays in the growth of the explosive secondary instability mechanism.

Joslin, Ronald D.↗
DOE OSTI2022

Plant Cell Growth and Cell Wall Enlargement

Irreversible cell enlargement begins with cell wall loosening which induces wall stress relaxation, leading to cell water uptake and cell enlargement. Growing cell walls consist of a cohesive network of cellulose microfibrils embedded in hydrophilic pectins and cellulose-binding hemicelluloses. Models of the growing cell wall are provisional hypotheses about how these wall polymers interact to make a strong yet extensible wall. Recent results clarify how wall strength, plasticity and elasticity depend mostly on the stretching, straightening and sliding of cellulose microfibril networks in the wall. Passive sliding of cellulose microfibrils is facilitated by nonenzymic proteins named expansins while various enzymes modify pectins and hemicelluloses, altering their interactions with each other and with cellulose. Growth cessation is correlated with reduced expression of genes that promote wall loosening as well as changes in the direction of cellulose deposition and the structure of matrix polysaccharides, leading to a less extensible cell wall.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

An energy model of droplet impingement on an inclined wall under isothermal and non-isothermal environments

The observation of spray-wall interaction is of great importance to understand the dynamics that occur during fuel impingement onto the chamber wall or piston surfaces in internal combustion engines. It is found that the maximum spreading length of an impinged droplet can provide a quantitative estimation of heat transfer and energy transformation for spray-wall interaction. Furthermore, it influences the air-fuel mixing and hydrocarbon and particle emissions at combusting conditions. In this paper, an analytical model of different droplet-wall impingement conditions is developed in terms of βm (dimensionless maximum spreading length, the ratio of maximum spreading length to initial droplet diameter) to understand the detailed impinging dynamic process. These conditions are grouped as: a single diesel droplet impinging on the wall with different inclined angles (α); cold wall - heated droplet and heated wall - cold droplet impingement when inclined angle of the wall is 0°, respectively. The analytical model is built up based on the energy conservation that considers kinetic energy, gravitation energy, and surface energy before impingement, as well as viscous dissipation, gravitation energy, adhesion energy, deformation energy, and heat energy after impingement. The experimental work of diesel droplet impinging on an inclined wall is performed at a certain range of the Weber number (We of 33 to 420) with various inclined angles (α of 0° to 45°), while for inclined angle is 0°, droplet and wall temperature are varied from 25°C to 150°C to study the effects of the inclined angle and temperature on the temporal evolution of the post-impingement characteristics (i.e. droplet spreading length, dynamic contact angle). The analytical model is validated and evaluated at the aforementioned experimental operating points. The validated model can be employed to predict maximum spreading length of the droplet impinged on the wall. It is further utilized to determine the transition from capillary regime to kinetic regime, then to viscous regime at different inclined angle of the wall.

42 ENGINEERING↗
DOE OSTI2025

Domain Wall Reactions in Multiple-Order Parameter Ferroelectrics

The motion of domain walls is crucial for ferroelectric switching. Conventionally, the switching dynamics is believed to be determined by the motion of one or a few low-energy domain wall types of dominant population. Here, we challenge this conventional idea in multiple-order-parameter ferroelectrics. Using hafnia as example, we show that the multiple-order-parameter nature not only provides various mobile domain walls and defectlike immobile domain walls, but also enables the domain wall reactions. In analogy with chemical reactions where substances react to form new substances, domain walls could also react to form other domain walls during switching. We identify several elementary domain wall reaction types including synthesis, decomposition, and exchange reactions. Domain walls are continually changed by these reactions during switching so that the switching behavior reflects the statistical average of many domain wall types with distinct mobility and stability. These reactions also lead to phenomenon like remanent nuclei and defect-site nucleation that facilitate switching and lower coercive field. Finally, the concept of domain wall reaction is not limited to hafnia but can be generalized to any multiple-order-parameter ferroelectric. As a result, this Letter conceptualizes domain wall reaction, expands the theory of ferroelectric switching, and suggests a practical way for defect engineering to control switching behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Solar-Reflective “Cool” Walls: Benefits, Technologies, and Implementation

Raising the albedo (solar reflectance) of a building’s walls reduces unwanted solar heat gain in the cooling season. This saves electricity and lowers peak power demand by decreasing the need for air conditioning. It can also cool the outside air, which can mitigate the urban heat island effect and also improve air quality by slowing the reactions that produce smog. This project quantified the energy savings, peak demand reduction, urban cooling, and air quality improvements attainable from solar-reflective “cool” walls in California; collaborated with industry to assess the performance of existing cool-wall technologies, and to develop innovative cool-wall solutions; and worked with state and federal government agencies, utilities, and industry to create a cool-wall infrastructure, including application guidelines, a product rating program, incentives, and building code credits. Simulations indicate that cool walls provide annual energy savings, peak demand reduction, annual emission reduction, and summer heat island mitigation benefits comparable to those yielded by cool roofs, and are helpful across California and in most of the southern half of the United States (that is, in U.S. climate zones 1—4). Natural exposure trials conducted at three sites in California and another three sites across the United States indicate that cool-wall materials tend to stay clean and reflective. Significant advances were made in novel cool-wall technologies, such as fluorescent cool pigments that expand the color palette for cool-wall products. We prepared guidelines for the climate- and building-appropriate use of cool walls, convened a stakeholder workshop, and created a working group. Ongoing efforts seek to introduce or expand cool-wall provisions in building energy standards, green building programs, and energy efficiency incentive programs, and to develop a cool-wall product rating system.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Solar-Reflective “Cool” Walls: Benefits, Technologies, and Implementation

Raising the albedo (solar reflectance) of a building’s walls reduces unwanted solar heat gain in the cooling season. This saves electricity and lowers peak power demand by decreasing the need for air conditioning. It can also cool the outside air, which can mitigate the urban heat island effect and also improve air quality by slowing the reactions that produce smog. This project quantified the energy savings, peak demand reduction, urban cooling, and air quality improvements attainable from solar-reflective “cool” walls in California; collaborated with industry to assess the performance of existing cool-wall technologies, and to develop innovative cool-wall solutions; and worked with state and federal government agencies, utilities, and industry to create a cool-wall infrastructure, including application guidelines, a product rating program, incentives, and building code credits. Simulations indicate that cool walls provide annual energy savings, peak demand reduction, annual emission reduction, and summer heat island mitigation benefits comparable to those yielded by cool roofs, and are helpful across California and in most of the southern half of the United States (that is, in U.S. climate zones 1—4). Natural exposure trials conducted at three sites in California and another three sites across the United States indicate that cool-wall materials tend to stay clean and reflective. Significant advances were made in novel cool-wall technologies, such as fluorescent cool pigments that expand the color palette for cool-wall products. We prepared guidelines for the climate- and building-appropriate use of cool walls, convened a stakeholder workshop, and created a working group. Ongoing efforts seek to introduce or expand cool-wall provisions in building energy standards, green building programs, and energy efficiency incentive programs, and to develop a cool-wall product rating system.

utility incentives↗
DOE OSTI2016

Cell Wall Ultrastructure of Stem Wood, Roots, and Needles of a Conifer Varies in Response to Moisture Availability

The composition, integrity, and architecture of the macromolecular matrix of cell walls, collectively referred to as cell wall ultrastructure, exhibits variation across species and organs and among cell types within organs. Indirect approaches have suggested that modifications to cell wall ultrastructure occur in response to abiotic stress; however, modifications have not been directly observed. Glycome profiling was used to study cell wall ultrastructure by examining variation in composition and extractability of non-cellulosic glycans in cell walls of stem wood, roots, and needles of loblolly pine saplings exposed to high and low soil moisture. Soil moisture influenced physiological processes and the overall composition and extractability of cell wall components differed as a function of soil moisture treatments. The strongest response of cell wall ultrastructure to soil moisture was increased extractability of pectic backbone epitopes in the low soil moisture treatment. The higher abundance of these pectic backbone epitopes in the oxalate extract indicate that the loosening of cell wall pectic components could be associated with the release of pectic signals as a stress response. The increased extractability of pectic backbone epitopes in response to low soil moisture availability was more pronounced in stem wood than in roots or needles. Additional responses to low soil moisture availability were observed in lignin associated carbohydrates released in chlorite extracts of stem wood, including an increased abundance of pectic arabinogalactan epitopes. Overall, these results indicate that cell walls of loblolly pine organs undergo changes in their ultrastructural composition and extractability as a response to soil moisture availability and that cell walls of the stem wood are more responsive to low soil moisture availability compared to cell walls of roots and needles. In conclusion, to our knowledge, this is the first direct evidence, delineated by glycomic analyses, that abiotic stress affects cell wall ultrastructure. This study is also unique in that glycome profiling of pine needles has never before been reported.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Intrinsic Conductance of Domain Walls in BiFeO 3

Abstract Ferroelectric domain walls exhibit a number of new functionalities that are not present in their host material. One of these functional characteristics is electrical conductivity that may lead to future device applications. Although progress has been made, the intrinsic conductivity of BiFeO 3 domain walls is still elusive. Here, the intrinsic conductivity of 71° and 109° domain walls is reported by probing the local conductance over a cross section of the BiFeO 3 /TbScO 3 (001) heterostructure. Through a combination of conductive atomic force microscopy, high‐resolution electron energy loss spectroscopy, and phase‐field simulations, it is found that the 71° domain wall has an inherently charged nature, while the 109° domain wall is close to neutral. Hence, the intrinsic conductivity of the 71° domain walls is an order of magnitude larger than that of the 109° domain walls associated with bound‐charge‐induced bandgap lowering. Furthermore, the interaction of adjacent 71° domain walls and domain wall curvature leads to a variation of the charge distribution inside the walls, and causes a discontinuity of potential in the [110] p direction, which results in an alternative conductivity of the neighboring 71° domain walls, and a low conductivity of the 71° domain walls when measurement is taken from the film top surface.

Zhang, Yi↗