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DOE OSTI2012

Breast Conservation Therapy: The Influence of Molecular Subtype and Margins

Purpose: To evaluate treatment results and prognostic factors, especially margin status and molecular subtype, in early-stage breast cancer patients treated with breast conservation therapy (BCT). Methods and Materials: The records of 1,058 Stage I or II breast cancer patients treated with BCT (surgical excision plus radiotherapy) at Duke University Medical Center, Durham, North Carolina, from 1985-2005 were retrospectively reviewed. Conventional receptor analyses were used as surrogate markers for molecular subtype classification (luminal A, luminal B, Her2 positive, and basal like). Actuarial estimates of overall survival (OS), cause-specific survival (CSS), failure-free survival, and locoregional control (LRC) were computed by use of Kaplan-Meier plots. We analyzed prognostic variables for significance using Cox proportional hazards univariate and multivariate analysis. The study was approved by the Duke University Medical Center Institutional Review Board. Results: The median age of the patients was 56 years (range, 18-89 years). Of the patients, 80% had T1 disease and 66% N0 disease pathologically. With a median follow-up of 9.8 years, an in-breast recurrence developed in 53 patients and 10 patients had nodal failure. For all patients, the 10-year CSS rate was 94%; LRC rate, 94%; and failure-free survival rate, 88%. Luminal A patients had a CSS rate of 95% and LRC rate of 99%. Basal-type patients appeared to do worse, with regard to both CSS rate (74%) and LRC rate (76%), but the numbers were small and the difference was not statistically significant. LRC rates of patients with negative margins (widely negative, close, and extent of margin not known) were virtually identical (93%, 96%, and 94%, respectively). Those with positive margins appeared to fare slightly worse based on LRC rate (88%), but again, the numbers were small and the difference was not statistically significant. Conclusions: BCT remains the treatment of choice for early-stage breast cancer patients irrespective of molecular subtype. Negative margins of excision are desirable, but the width of the negative margin does not influence outcome.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

NASA NTRS1990

A cloudiness transition in a marine boundary layer

Boundary layer cloudiness plays several important roles in the energy budget of the earth. Low level stratocumulus are highly reflective clouds which reduce the net incoming shortwave radiation at the earth's surface. Climatically, the transition to a small area fraction of scattered cumulus clouds occurs as the air flows over warmer water. Although these clouds reflect less sunlight, they still play an important role in the boundary layer equilibrium by transporting water vapor upwards, and enhancing the surface evaporation. The First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) included a marine stratocumulus experiment off the southern California coast from June 29 to July 19, 1987. The objectives of this experiment were to study the controls on fractional cloudiness, and to assess the role of cloud-top entrainment instability (CTEI) and mesoscale structure in determining cloud type. The focus is one research day, July 7, 1987, when coordinated aircraft missions were flown by four research aircraft, centered on a LANDSAT scene at 1830 UTC. The remarkable feature of this LANDSAT scene is the transition from a clear sky in the west through broken cumulus to solid stratocumulus in the east. The dynamic and thermodynamic structure of this transition in cloudiness is analyzed using data from the NCAR Electra. By averaging the aircraft data, the internal structure of the different cloud regimes is documented, and it is shown that the transition between broken cumulus and stratocumulus is associated with a change in structure with respect to the CTEI condition. However, this results not from sea surface temperature changes, but mostly from a transition in the air above the inversion, and the breakup appears to be at a structure on the unstable side of the wet virtual adiabat.

Betts, Alan K.↗

DOE OSTI2018

Upgrading the JET Remote Handling System - 18356

The Joint European Torus (JET) has employed advanced remote-maintenance techniques for over three decades to avoid exposing humans to a potentially hazardous environment and to develop techniques for future power-generating fusion reactors where environments will be too hazardous for any manned maintenance. As a unique application of robotics, virtual reality and operations management systems, JET's remote handling unit, now a part of RACE, has driven the state-of-the-art with each upgrade programme in its history. This conference paper presents the current capabilities of the JET remote handling system, and the future capabilities being delivered by its latest upgrade programme, which makes use of cutting edge advances. RACE (Remote Applications in Challenging Environments) aims to shape the technologies being developed for JET in such a way that they will have wider applications, such as in nuclear decommissioning. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

NASA NTRS2002

Virtual Engineering and Science Team - Reusable Autonomy for Spacecraft Subsystems

In this paper we address the design, development, and evaluation of the Virtual Engineering and Science Team (VEST) tool - a revolutionary way to achieve onboard subsystem/instrument autonomy. VEST directly addresses the technology needed for advanced autonomy enablers for spacecraft subsystems. It will significantly support the efficient and cost effective realization of on-board autonomy and contribute directly to realizing the concept of an intelligent autonomous spacecraft. VEST will support the evolution of a subsystem/instrument model that is probably correct and from that model the automatic generation of the code needed to support the autonomous operation of what was modeled. VEST will directly support the integration of the efforts of engineers, scientists, and software technologists. This integration of efforts will be a significant advancement over the way things are currently accomplished. The model, developed through the use of VEST, will be the basis for the physical construction of the subsystem/instrument and the generated code will support its autonomous operation once in space. The close coupling between the model and the code, in the same tool environment, will help ensure that correct and reliable operational control of the subsystem/instrument is achieved.VEST will provide a thoroughly modern interface that will allow users to easily and intuitively input subsystem/instrument requirements and visually get back the system's reaction to the correctness and compatibility of the inputs as the model evolves. User interface/interaction, logic, theorem proving, rule-based and model-based reasoning, and automatic code generation are some of the basic technologies that will be brought into play in realizing VEST.

Bailin, Sidney C.↗

NASA NTRS2010

Online Planning Algorithm

AVA v2 software selects goals for execution from a set of goals that oversubscribe shared resources. The term goal refers to a science or engineering request to execute a possibly complex command sequence, such as image targets or ground-station downlinks. Developed as an extension to the Virtual Machine Language (VML) execution system, the software enables onboard and remote goal triggering through the use of an embedded, dynamic goal set that can oversubscribe resources. From the set of conflicting goals, a subset must be chosen that maximizes a given quality metric, which in this case is strict priority selection. A goal can never be pre-empted by a lower priority goal, and high-level goals can be added, removed, or updated at any time, and the "best" goals will be selected for execution. The software addresses the issue of re-planning that must be performed in a short time frame by the embedded system where computational resources are constrained. In particular, the algorithm addresses problems with well-defined goal requests without temporal flexibility that oversubscribes available resources. By using a fast, incremental algorithm, goal selection can be postponed in a "just-in-time" fashion allowing requests to be changed or added at the last minute. Thereby enabling shorter response times and greater autonomy for the system under control.

Rabideau, Gregg R.↗

DOE OSTI2024

Transitioning to Hybrid Power Plants

Hybrid power plants are power generation systems that combine two or more types of electricity generation or storage, creating systems where the optimal dispatch provides more benefits that the sum of the individual components can. These plants exemplify the interconnected challenges of grid modernization. On one hand, rapid increase in deployment and enhanced controllability of renewable energy assets is needed to meet clean energy targets, but on the other, increasing electrification makes it more difficult to manage load and growth in the number of endpoints and stakeholders involved with hybrid plants complicates asset management and cybersecurity. This talk will cover trends in hybrid power plant technologies and deployments, identify future prospects for hybrid systems, and discuss the challenges and research opportunities that exist to transition from the traditional power grids of today to smart, distributed, hybrid power grids we may see in the next few decades.

14 SOLAR ENERGY↗

DOE OSTI2021

Progress Report on Performance of A709 and G91 Steels in Sodium

Specimens in six different processing and heat treatment conditions of A709 H58776 were exposed to sodium at 550, 600, and 650°C, respectively for various exposure times. G91 base metal was tested in sodium at 550, 600, and 650°C, and G91 weldment at 550 and 600°C, respectively. Parallel thermal aging experiments were conducted on G91 and A709 to obtain thermal aging data for comparison with sodium exposure results to separate the thermal and sodium effects. The corrosion data obtained on A709 steel continue to show low corrosion rates, which indicate good compatibility of A709 with sodium when oxygen content is controlled. G91 has also shown acceptable corrosion rates over the temperature range of 550-650°C in sodium. Thermal aging or sodium exposures reduced the tensile strength, uniform elongation, and total elongation for A709 ESR, AOD specimens. These specimens consistently showed higher yield stress and tensile strength and lower uniform and total elongations after sodium exposure than after thermal aging under comparable testing conditions. It implies that there was an additional effect of sodium exposure that gave rise to an increase in tensile strength of A709. Dynamic strain aginginduced flow serrations were completely removed by either thermal aging or sodium exposure at 650°C, which imply that carbon or nitrogen in solution was removed from the solution and formed precipitates during aging or sodium exposures. The tensile data ruled out the possibility of decarburization under the sodium exposure conditions. The HOMO specimens behaved somewhat differently from the ESR and AOD specimens in sodium. While thermal aging and sodium exposures at 550 and 600°C decreased the yield stress and the ultimate tensile strength of G91, there was virtually no additional effect resulting from sodium exposures at these two temperatures. In contrast, sodium exposures at 650°C had a drastic effect on the yield stress and the ultimate tensile strength of G91. It is suggested that G91 experienced decarburization in the 650°C sodium environments. Carbon concentrations in sodium in the SMT-1 and SMT-2 loops were determined by a foil equilibration method. The estimated carbon concentration was in the range of 0.8-1.2 ppm in the SMT-1 loop and 0.3-0.7 ppm in the SMT-2 loop. The carbon activity in sodium in the SMT-2 loop was estimated to be 0.03-0.08 at 600°C, and 0.08-0.2 at 550°C. The carbon activity in sodium at 650°C in the SMT-1 loop was 0.04-0.07. Equilibrium simulation of the carburization – decarburization processes was conducted for A709 and G91 steels exposed in sodium environments at temperatures of 550-700°C. The carbon activity-concentration relationship for G91 was re-evaluated by considering four phases in G91, i.e. bcc ferrite, M 23 C 6 , NbC and VC carbides. It was found that the carburization-decarburization process in G91 steel was dictated by M 23 C 6 carbides at high carbon activities, while NbC carbides dominated the process at low carbon activities. Formation of NbC increases the decarburization resistance of G91 steel. It remains to be understood whether the decarburization resistance provided by MC carbides in G91 can be maintained during long-term operations of SFRs. The carbon concentration-activity relationship for A709 was calculated based on the equilibrium of fcc-austenite and M 23 C 6 carbide phase. The calculations showed that A709 decarburizes at 650°C in the SMT-1 loop environments, which is different from the experimental findings. The carbon concentration-activity relationship in A709 was further evaluated by considering four phases, including fcc-austenite, M 23 C 6 , NbC, and TiC carbide phases. TiC is the most stable carbides among the three carbide phases. The carburization-decarburization process in A709 is dictated by M 23 C 6 carbides at high carbon activities and by TiC at low carbon activities. Formation of TiC increases the decarburization resistance of A709 steel. Because of the complexity of the precipitation process in A709 during sodium exposures, detailed characterization of precipitates in sodium-exposed specimens and improved thermodynamic models are needed to understand the carburization-decarburization behavior of A709. Kinetic analysis of carbon transfer will be investigated for G91 and A709 in future work.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS2001

Effects of 2.0-g 1.75-g and 1.5-g Hypergravity on Pregnancy Outcome in Rats (Rattus norvegicus)

In 1995, ten pregnant female rats were launched on the Space Shuttle (STS-70) on Gestational day(G) 11 of their 22-day pregnancy as part of the NASA/NIH.Rodent (R)2 Experiment. Following landing on G20, fetuses were harvested from half of the dams, while the remaining five dams underwent birth. Spaceflight did not interrupt pregnancy, alter litter sizes, or affect body weights or gender ratios of the fetuses or neonates. In the present study we used the NASA/NIH.R2 experimental paradigm to analyze the effects of hypergravity on pregnancy outcome. On G10, time-bred Sprague-Dawley rat dams were assigned to either G20 or Birth conditions, then further assigned to Hypergravity (HG) 2.0-g, HG 1.75-g, HG 1.5-g, Rotational Control (RC, 1.03), or Stationary Control (SC, 1.0-g) treatments. Dams were exposed to continuous centrifugation from G11 through G20, with brief daily stops for animal health checks and maintenance. For both the G20 and Birth dams, comparable litter sizes and litter gender ratios were observed across gravity conditions. However, centrifugation-exposed (HG and RC) fetuses and neonates showed significantly lower body masses (p less than 0.05) relative to SC offspring. HG 2.0-g offspring weighed significantly less than those in all other gravity conditions (p less than 0.05). The observed reductions in offspring body mass at 1.5-g and 1.75-g, can be attributed to the rotational component of centrifugation, rather than to increased gravitational load, whereas 2.0-g hypergravity exposure further exacerbated the gravity centrifugation effect on offspring body mass. Pregnant dams exposed to centrifugation weighed significantly less than SC dams (p less than 0.05), suggesting that centrifugation effects on maternal body mass may contribute to reduced size of the developing offspring. These findings are consistent with previous reports of non-pregnant adult animals suggesting that, whereas spaceflight has virtually no effect on body mass, centrifugation is associated with changes in body weight regulation.

Mills, Nicole A.↗

NASA NTRS1990

Experiments and other methods for developing expertise with design of experiments in a classroom setting

The only way to gain genuine expertise in Statistical Process Control (SPC) and the design of experiments (DOX) is with repeated practice, but not on canned problems with dead data sets. Rather, one must negotiate a wide variety of problems each with its own peculiarities and its own constantly changing data. The problems should not be of the type for which there is a single, well-defined answer that can be looked up in a fraternity file or in some text. The problems should match as closely as possible the open-ended types for which there is always an abundance of uncertainty. These are the only kinds that arise in real research, whether that be basic research in academe or engineering research in industry. To gain this kind of experience, either as a professional consultant or as an industrial employee, takes years. Vast amounts of money, not to mention careers, must be put at risk. The purpose here is to outline some realistic simulation-type lab exercises that are so simple and inexpensive to run that the students can repeat them as often as desired at virtually no cost. Simulations also allow the instructor to design problems whose outcomes are as noisy as desired but still predictable within limits. Also the instructor and the students can learn a great deal more from the postmortum conducted after the exercise is completed. One never knows for sure what the true data should have been when dealing only with real life experiments. To add a bit more realism to the exercises, it is sometimes desirable to make the students pay for each experimental result from a make-believe budget allocation for the problem.

Patterson, John W.↗

NASA NTRS2003

Enhanced Multi-Modal Access to Planetary Exploration

Tomorrow's Interplanetary Network (IPN) will evolve from JPL's Deep-Space Network (DSN) and provide key capabilities to future investigators, such as simplified acquisition of higher-quality science at remote sites and enriched access to these sites. These capabilities could also be used to foster public interest, e.g., by making it possible for students to explore these environments personally, eventually perhaps interacting with a virtual world whose models could be populated by data obtained continuously from the IPN. Our paper looks at JPL's approach to making this evolution happen, starting from improved communications. Evolving space protocols (e.g., today's CCSDS proximity and file-transfer protocols) will provide the underpinning of such communications in the next decades, just as today's rich web was enabled by progress in Internet Protocols starting from the early 1970's (ARPAnet research). A key architectural thrust of this effort is to deploy persistent infrastructure incrementally, using a layered service model, where later higher-layer capabilities (such as adaptive science planning) are enabled by earlier lower-layer services (such as automated routing of object-based messages). In practice, there is also a mind shift needed from an engineering culture raised on point-to-point single-function communications (command uplink, telemetry downlink), to one in which assets are only indirectly accessed, via well-defined interfaces. We are aiming to foster a 'community of access' both among space assets and the humans who control them. This enables appropriate (perhaps eventually optimized) sharing of services and resources to the greater benefit of all participants. We envision such usage to be as automated in the future as using a cell phone is today - with all the steps in creating the real-time link being automated.

interplanetary network (IPN)↗

NASA NTRS1959

Low-Subsonic Static Stability and Damping Derivatives at Angles of Attack From 0 deg to 90 deg for a Model with a Low-Aspect-Ratio Unswept Wing and Two Different Fuselage Forebodies

An investigation has been made in the Langley free-flight tunnel at low-subsonic speed to determine the static stability, control effectiveness, and damping in roll and yaw of a model with a low-aspect-ratio unswept wing and two different fuselage forebodies at angles of attack from 0 deg to 90 deg. Results were obtained with a fuselage configuration having a long pointed nose and a shorter rounded nose. Although the wing stalled at an angle of attack of about 12 deg, maximum lift did not occur until an angle of attack of about 40 deg or 50 deg was obtained. The static longitudinal stability of the model having a short rounded nose was greater than that of the model having a longer pointed nose over the entire angle-of-attack range. The pointed-nose model had large out-of-trim yawing moments above an angle of attack of about 40 deg. Shortening and rounding the nose of the model delayed these out-of-trim yawing moments to slightly higher angles of attack. Both models were directionally unstable above an angle of attack of about 20 deg, but both had positive effective dihedral over virtually the entire angle-of-attack range. At the higher angles of attack the pointed-nose model had generally better damping in roll than that of the rounded-nose model. Both models had very high damping in yaw at an angle of attack of about 50 deg or 60 deg.

Boisseau, Peter C.↗

DOE OSTI2021

Development of the IES Plug-and-Play Framework

This report discusses the status of the flexible plug-and-play framework development currently ongoing that aims to integrate Modelica/Dymola with the Risk Analysis and Virtual ENvironment (RAVEN) software in terms of both Functional Mock-Up Interface (FMI)/Functional Mock-Up Unit (FMU) construction and repository structures that aim to ease the sharing and simulation of complex dynamic models. This report aims to provide an overview of all the performed activities resolving around the deployment of methods, software infrastructures, guidelines and workflow for the construction and usage of models, encapsulated using the FMI/FMU protocols and standards. In particular, the report is organized in three main macro-subjects, which are connected to each other: - FMI/FMU adaptors for modelica models - HYBRID repository new structure and open-source deployment - RAVEN FMI/FMU exporting capabilities and Artificial Intelligence (AI)-based analysis acceleration. The first part of the report discusses the FMI/FMU adaptors that have been created within the HYBRID repository to allow users to quickly export models, such as FMUs. Several examples are shown that highlight the step-by-step process of converting an existing Modelica model into an FMU for use within the Dymola platform. Simulation results demonstrate that, while minor differences may occur, the overall control, trends, and solution integrity are maintained between standard Modelica simulation and FMU simulation results. However, it is worth noting that, for small systems, the FMU results have a slower simulation time than the Modelica only simulation. Using this process, a company can provide models that contain proprietary information to entities without disclosing any of the information about the model that could be considered business sensitive. Such an ability would allow institutions to bypass the necessity of “whitewashing” data. In the second part of the report, the new structure of the HYBRID repository is discussed with a major focus on the series of updates that has been completed. These updates include the addition of Modelica system-level regression tests and software quality assurance documentation that ensure that modifications to the Modelica models do not alter system-level model results. The third and final part of the report aims to report the work that has been performed for the deployment of methods and workflows for the construction of RAVEN AI-based models compliant with the FMI/FMU standard. Such development represents the key for the deployment of the concept of “Flexible ecosystem” since it allows for the replacement of high-fidelity modelica models (or any other FMI/FMU compliant model) with RAVEN generated AI surrogate models. Overall, extensive work has been completed on developing FMUs and FMIs from existing models, understanding the requirements and limitations of FMUs, and open-sourcing the HYBRID repository with an integrated regression system.

42 ENGINEERING↗

DOE OSTI2021

Development of the IES Plug-and-Play Framework

14 SOLAR ENERGY↗

NASA NTRS2000

Dynamics of Molecular Hydrogen in Hypersaline Microbial Mars

Early Earth microbial communities that centered around the anaerobic decomposition of organic molecular hydrogen as a carrier of electrons, regulator of energy metabolism, and facilitator of syntroph'c microbial interactions. The advent of oxygenic photosynthetic organisms added a highly dynamic and potentially dominant term to the hydrogen economy of these communities. We have examined the daily variations of hydrogen concentrations in cyanobacteria-dominated microbial mats from hypersaline ponds in Baja California Sur, Mexico. These mats bring together phototrophic and anaerobic bacteria (along with virtually all other trophic groups) in a spatially ordered and chemically dynamic matrix that provides a good analog for early Earth microbial ecosystems. Hydrogen concentrations in the photic zone of the mat can be three orders of magnitude or more higher than in the photic zone, which are, in turn, an order of magnitude higher than in the unconsolidated sediments underlying the mat community. Within the photic zone, hydrogen concentrations can fluctuate dramatically during the diel (24 hour day-night) cycle, ranging from less than 0.001% during the day to nearly 10% at night. The resultant nighttime flux of hydrogen from the mat to the environment was up to 17% of the daytime oxygen flux. The daily pattern observed is highly dependent on cyanobacterial species composition within the mat, with Lyngbya-dominated systems having a much greater dynamic range than those dominated by Microcoleus; this may relate largely to differing degrees of nitrogen-fixing and fermentative activity in the two mats. The greatest H2 concentrations and fluxes were observed in the absence of oxygen, suggesting an important potential feedback control in the context of the evolution of atmospheric composition. The impact of adding this highly dynamic photosynthetic term to the hydrogen economy of early microbial ecosystems must have been substantial. From an evolutionary standpoint, the H2 generated in mats could have represented a very important new source of electrons and energy - but one that could not be harnessed without substantial adaptation to the highly variable chemistry of the mat surface. In addition, the emergent chemistry of anaerobic communities is often highly dependent on ambient hydrogen concentrations, so that incorporation of these communities into photosynthetic mats could have significantly affected the composition and flux of reduced "biosignature' gases to the environment.

Hoehler, Tori M.↗

DOE OSTI2022

Initial Findings from US Department of Energy’s Better Plants Virtual in-Plant Training on 50001 Ready

Manufacturing facilities use about 35% of the domestic energy in the United States every year. Implementing an effective energy management system (EnMS) is one of the most important approaches to improve energy efficiency. However, the implementation of EnMS is low for many countries (including the US) and even for energy-intensive sectors. The reasons for the low implementation rate of energy management systems had been investigated by multiple researchers, but very few studies have focused on the barriers and challenges of implementing ISO 50001-based energy management systems. To contribute to this understudied area, this paper discusses the implementation and outcomes of the first Better Plants 50001 Ready Virtual In-plant Training. This paper first provides an overview of 50001 Ready and the 50001 Ready Navigator Tool. Then, it provides details on this training event and its outcomes. Finally, it discusses findings from the responses to 40 live polling questions about the status of the 25 tasks of the 50001 Ready Navigator for participating companies, key components of the participating manufacturing companies’ energy management systems, and challenges and barriers that these companies are facing. The findings suggest that although many companies understood the importance of an effective energy management system, about half of them do not understand the required resources for building energy management systems, and most of them have only just begun establishing these systems and need more assistance and resources in multiple areas. More specifically, more assistance is necessary for the following: (1) improving corporate management’s understanding of the time and resources needed to build an EnMS as well as the benefits; (2) creating linear regression models for more accurate energy performance tracking; (3) understanding energy use, collecting and analyzing energy performance data; (4) optimizing equipment operational controls, and creating action plans.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2014

Tritium Breeding Blanket for a Commercial Fusion Power Plant - A System Engineering Assessment

The goal of developing a new source of electric power based on fusion has been pursued for decades. If successful, future fusion power plants will help meet growing world-wide demand for electric power. A key feature and selling point for fusion is that its fuel supply is widely distributed globally and virtually inexhaustible. Current world-wide research on fusion energy is focused on the deuterium-tritium (DT for short) fusion reaction since it will be the easiest to achieve in terms of the conditions (e.g., temperature, density and confinement time of the DT fuel) required to produce net energy. Over the past decades countless studies have examined various concepts for TBBs for both magnetic fusion energy (MFE) and inertial fusion energy (IFE). At this time, the key organizations involved are government sponsored research organizations world-wide. The near-term focus of the MFE community is on the development of TBB mock-ups to be tested on the ITER tokamak currently under construction in Caderache France. TBB concepts for IFE tend to be different from MFE primarily due to significantly different operating conditions and constraints. This report focuses on longer-term commercial power plants where the key stakeholders include: electric utilities, plant owner and operator, manufacturer, regulators, utility customers, and in-plant subsystems including the heat transfer and conversion systems, fuel processing system, plant safety systems, and the monitoring control systems.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

Re-Defining Photovoltaic Efficiency Through Molecule Scale Control. Final Report

The direct conversion of sunlight into electricity represents one of the most important general means for sustainable energy production. Most modern photovoltaic cells are based on some form of semiconductor material such as silicon that is described by a characteristic energy or ''bandgap''. For solar rays with photon energy lower than the bandgap no absorption occurs and thus no energy is generated. For solar rays with photon energy greater than the bandgap, light may be absorbed to create a pair of electrical charges but only one bandgap of energy is created, leaving any additional energy lost as heat. Thus low bandgap materials can use a great part of the spectrum but can lose much of that energy; high bandgap materials fail to capture much of the spectrum. Thus there is a limit to the efficiency of such a solar cell that turns out to be about 32%. This limit is known as the Shockely-Queisser Limit. The Columbia EFRC program is dedicated to exploration of concepts that in principle can provide for efficiencies beyond this limit. One concept that this EFRC has explored for enhancing the efficiency of solar photovoltaic cells is called “Singlet Fission.” In this concept the absorption of light rays with photon energy at least twice the value of the basic bandgap for the system can produce two pairs of electrical charge carriers. If properly implemented this in principle can significantly reduce the energy lost as heat and give rise to solar cell efficiencies greater than the Shockley-Queisser limit. The problem is that there are virtually no materials that can undergo this process effectively. We have developed new materials that have demonstrated singlet fission efficiencies of almost 100%. We understand how these materials work and we have learned how to design many more systems in the future. So far we have only demonstrated the basic capability for efficient singlet fission. Much more work will be required to design and engineer specific materials that can be used practically in a solar cell system. In addition much work will be required to envision and demonstrate effective device structures that can utilize this concept. However these discoveries do provide the basis for an entirely new set of opportunities for more efficient solar energy generation moving beyond the Shockley-Queisser limit. A second part of the EFRC research program has been to investigate the material and device properties of an entirely new set of materials based on two-dimensional sheets (“ultra-thin”) with thicknesses of only one atom, or a single molecule or just a few atoms. These materials can exhibit conducting, insulating, and semiconducting character and thus they can form the basis for entirely new types of electrical devices. Recent fundamental investigations of these materials, at Columbia and elsewhere, demonstrate clearly that the flow of electrical charges in these systems is fundamentally different from the nature of electrical current flow in conventional materials. This fact presents many possibilities for new photovoltaic device concepts. The EFRC research team has achieved world leadership in the creation and understanding of these materials and in developing the fabrication techniques necessary to create useful devices from them. We have developed the basic fabrication methodology to build structures of these materials into complex device structures, layer by layer. Our EFRC research team has pioneered the synthesis and understanding for graphene, perhaps the simplest of these materials. Graphene can function as a highly transparent conducting material, capable of funneling an electrical charge over reasonable distances without significant energy loss. The EFRC program has also pioneered the development of ultra-thin sheets that function in a way analogous to semiconductor materials as well as sheets that act as electrical insulators. These developments therefore enable the construction of solar cells based on totally different physics from conventional cells. Because the electrons in these ultra-thin sheets interact strongly they will exhibit behaviors quite different from conventional materials with potential to operate at efficiencies beyond the Shockley-Queisser limit. In our EFRC program we have laid out many of the fundamental properties of these materials including the development of unique fabrication techniques. We discovered several new effects that demonstrate strong electron coupling. We have demonstrated the first solar cell that can actually generate electrical power at a high basic efficiency from these fundamentally new materials. There is much more science and technology required before these devices can become practical, but there is also very strong activity worldwide to build electronic devices from these materials, thus providing infrastructure and technical capability to develop these concepts.

14 SOLAR ENERGY↗

DOE OSTI2022

Mass Transport Limitations and Kinetic Consequences of Corn Stover Deacetylation

Alkaline pretreatment of herbaceous feedstocks such as corn stover prior to mechanical refining and enzymatic saccharification improves downstream sugar yields by removing acetyl moieties from hemicellulose. However, the relationship between transport phenomena and deacetylation kinetics is virtually unknown for such feedstocks and this pretreatment process. Here, we report the development of an experimentally validated reaction–diffusion model for the deacetylation of corn stover. A tissue-specific transport model is used to estimate transport-independent kinetic rate constants for the reactive extraction of acetate, hemicellulose and lignin from corn stover under representative alkaline conditions (5–7 g L -1 NaOH, 10 wt% solids loadings) and at low to mild temperatures (4–70°C) selected to attenuate individual component extraction rates under differential kinetic regimes. The underlying transport model is based on microstructural characteristics of corn stover derived from statistically meaningful geometric particle and pore measurements. These physical descriptors are incorporated into distinct particle models of the three major anatomical fractions (cobs, husks and stalks) alongside an unsorted, aggregate corn stover particle, capturing average Feret lengths of 917–1239 μm and length-to-width aspect ratios of 1.8–2.9 for this highly heterogeneous feedstock. Individual reaction–diffusion models and their resulting particle model ensembles are used to validate and predict anatomically-specific and bulk feedstock performance under kinetic-controlled vs. diffusion-controlled regimes. In general, deacetylation kinetics and mass transfer processes are predicted to compete on similar time and length scales, emphasizing the significance of intraparticle transport phenomena. Critically, we predict that typical corn stover particles as small as ~2.3 mm in length are entirely diffusion-limited for acetate extraction, with experimental effectiveness factors calculated to be 0.50 for such processes. Debilitatingly low effectiveness factors of 0.021–0.054 are uncovered for cobs—implying that intraparticle mass transfer resistances may impair observable kinetic measurements of this anatomical fraction by up to 98%. These first-reported quantitative maps of reaction vs. diffusion control link fundamental insights into corn stover anatomy, biopolymer composition, practical size reduction thresholds and their kinetic consequences. These results offer a guidepost for industrial deacetylation reactor design, scale-up and feedstock selection, further establishing deacetylation as a viable biorefinery pretreatment for the conversion of lignocellulosics into value-added fuels and chemicals.

09 BIOMASS FUELS↗