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At least 847 records · Page 47

Degradation of Anion Exchange Membranes by Cation Elimination: Impact on Water Uptake, Nanostructure, and Ionic Mobility

Anion exchange membranes (AEMs) are an attractive platform for fuel cell and electrolysis technologies since they enable the use of cheaper, nonplatinum group metal electrodes and components. However, the widespread adoption of AEM-based devices is limited by chemical degradation of the AEM in the highly alkaline medium of operation. Experimental studies report three major pathways of degradation, including substitution (S N 2), elimination (E2), and backbone cleavage. The decline in membrane performance is likely due to a cumulative effect of several pathways, which has proven to be difficult to disentangle through experiments. Here we use coarse-grained molecular simulations to isolate the impact of E2 degradation, where cationic sites are replaced by an alkene group, on AEM water uptake, nanoscale morphology, structure of the ion-conducting channels, water mobility, and ionic conductivity. Our studies focus on the well-studied model AEM polyphenylene oxide with tetraalkylammonium cationic sites (PPO-TMA). We find that about half of the hydrophobic groups resulting from the degradation retract into the hydrophobic domains of the membrane. The reduction in ion exchange capacity (IEC) and the hydrophobicity of the alkene groups decrease both the equilibrium water uptake (%WU) and the number of water molecules per cation (λ) of the membrane. Interestingly, the evolution of λ with the IEC seems to follow that of undegraded PPO-TMA membranes. Additionally, we ascribe this to the similarity between the structure of the degraded monomer and the neutral one in the polymer. We conclude that most of the performance losses originate in the lower hydration of the degraded membrane.

36 MATERIALS SCIENCE↗

Energy landscape in protein folding and unfolding

Protein folding represents an open question in science, and the free-energy landscape framework is one way to describe it. In particular, the role played by water in the processes is of special interest. To clarify these issues we study, during folding–unfolding, the temperature evolution of the magnetization for hydrophilic and hydrophobic groups of hydrated lysozyme using NMR spectroscopy. Our findings confirm the validity of the theoretical scenario of a process dominated by different energetic routes, also explaining the water role in the protein configuration stability. Here, we also highlight that the protein native state limit is represented by the water singular temperature that characterizes its compressibility and expansivity and is the origin of the thermodynamical anomalies of its liquid state.

59 BASIC BIOLOGICAL SCIENCES↗

A Report on the Activities, Publications, and Pending Research of a DHS/DOD Sponsored Postdoctoral Research Associate at Los Alamos National Laboratory

Since beginning at Los Alamos National Laboratory in February of 2012, I have been working as a DHS/DNDO Postdoctoral Research Associate under the mentorship of Lav Tandon and Khalil Spencer (NA-22 and mass spectrometry). The focus of these efforts, in addition to pursuing training and qualifications, has principally been the application of Thermal Ionization Mass Spectrometry (TIMS) methods to the characterization of actinide systems of interest in nuclear forensics research. Recently pursued initiatives have included the adaptation of modified total evaporation (MTE) strategies to current group methods and the preliminary development of TIMS-based uranium age-dating approaches; each of these points is discussed below, along with future plans.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Deterministic Calibration of MFiX-PIC, Part 1: Settling Bed

The Particle-in-cell (PIC) numerical approach for modeling granular solids in fluid flow has gained significant interest in recent years. Valued for its often shorter time-to-solution, the PIC formulation relies on modeling statistical groupings of particles called parcels in cooperation with a solids stress model to affect local solids velocity. This is in contrast to the discrete element model (DEM) where every particle in a system is modelled individually and directly coupled to local solids velocity through Newtonian mechanics. The U.S. Department of Energy (DOE), National Energy Technology Laboratory (NETL) develops and maintains Multiphase Flow with Interphase eXchanges (MFiX), a collection of open-source computational fluid dynamics (CFD) solvers. Included in the MFiX suite are traditional two-fluid model (TFM) and DEM solvers, and a recently added PIC solver (NETL, 2021). In general, PIC methodologies offer an accuracy trade-off in lieu of computational speed; and therefore, it is important to assess the credibility of MFiX-PIC simulations. For this purpose, a systematic verification, validation and uncertainty quantification (VVUQ) effort was initiated at NETL to assess the new PIC solver

42 ENGINEERING↗

The Integrated Basin-Scale Opportunity Assessment Initiative: Pilot Assessment for the Deschutes River Basin

In 2010, the U.S. Department of Energy’s (DOE’s) Wind and Water Power Technologies Office provided funding to Pacific Northwest National Laboratory, Oak Ridge National Laboratory (ORNL), and Argonne National Laboratory to develop an approach for assessing a river basin as an integrated system within the context of existing uses and environmental conditions to identify opportunities for sustainable hydropower development and environmental improvements. Called the Integrated Basin-Scale Opportunity Assessment Initiative (BSOA Initiative), the project is one of seven action items of the March 24, 2010 Memorandum of Understanding (MOU) for Sustainable Hydropower. Early efforts of the BSOA Initiative focused on forming a National Steering Committee, identifying potential basins for opportunity assessments, methodologies for stakeholder engagement, existing and needed analytical tools, barriers to the opportunity assessment process, and significant data gaps. One of the key outcomes was identifying a need for better collaborative decision-making tools that can be used by stakeholders. In response to this need, the Basin-Scale Project Team chose a scenario-based modeling approach for assessing hydropower, environmental, and other water-use opportunities. The approach involved the development of a daily hydrologic model for the Upper Deschutes River and Lower Crooked River subbasins to simulate alternative water management scenarios. Two example scenarios were constructed to demonstrate the use of the hydrologic model to explore three management goals in the Deschutes Basin: 1) increasing hydropower assets by adding new generation at existing dams or diversions and in existing irrigation canals or conduits, 2) increasing instream flows to benefit fish and aquatic ecosystems, and 3) maintaining existing water uses (primarily irrigation). Actions to achieve these goals were simulated by incrementally increasing minimum flow requirements during the storage season and reducing water demands during the irrigation season, while simulating hydropower generation at non-powered dams and in irrigation canals. As part of the effort to demonstrate scenario-based modeling, the project team also developed a web-based data-visualization interface for synthesizing modeling results. The interface allows users to view model results in raw form (daily flow) or in the form of value-based metrics that are based on specific information needs expressed by stakeholders (e.g., how often flow exceeds a conservation flow target at a certain location). In addition to the modeling efforts, 29 potential hydropower sites (14 non-powered dams, 15 canal/conduit sites) were evaluated for their technical and economic feasibility using ORNL’s Hydropower Energy and Economic Assessment tool. Results of the feasibility assessment indicated that eight of the sites (four non-powered dams, four canals/conduits) may be feasible and could add approximately 19 megawatts (MW) of hydroelectric capacity in the basin and generate over 78 gigawatt-hours (GWh) of energy per year. The approach presented here is intended to encourage consideration of methods that emphasize exploration of a range of potential management actions that may achieve a better balance among multiple, and often conflicting, management goals. It is important to consider the approach as an iterative and collaborative process focused on moving debates beyond agreement about an exact target that is acceptable to all parties to a discussion of how stakeholders can better understand how achieving their goals interacts with the achievement of goals by other stakeholder groups. By exploring the results of the model in this way, stakeholders are more likely to narrow the bounds of interest so that more in-depth analysis can be completed.

13 HYDRO ENERGY↗

Thermal Characterization of Acid Treated Anion Exchange Resins

Anion exchange is a chemical separation and purification technique in which a solid phase ion exchanging material (i.e., anion exchange resin beads) interchanges its anions with the desired anions from a solution phase. Typical anion exchange resins (e.g., Bio-Rad AG 1-X8 strongly basic anion exchange resin) consist of a polymer resin bead of cross-linked polystyrene with quaternary ammonium functional groups (Figure 1). Anion exchange occurs at the resin functional groups by exchange of the counter ion of the quaternary ammonium (typically chloride or nitrate) for the anionic species of interest. Other resin polymers have been developed—such as cross-linked vinylpyridine/divinylbenzene utilized in Reillex HPQ anion exchange resin—to improve the resins’ resistance against degradation by oxidizing agents, strong acids, and radiation. Anion exchange is performed for the separation of transuranic (TRU) elements throughout the Department of Energy complex. At the Los Alamos National Laboratory (LANL), production scale quantities of these resins are handled at the Chemistry and Metallurgy Research Facility, the Plutonium Facility, and the Transuranic Waste Facility. Spent anion exchange resin will eventually be disposed of as TRU waste. This has prompted concerns regarding its safe disposal under potential hazard scenarios, in particular a thermal excursion of a TRU waste drum. There is a concern that a potential thermal excursion of a TRU waste drum containing anion exchange resin previously contacted with nitric acid may result in energetic side reactions and pressure buildup due to resin degradation by nitric acid and heat. Therefore, the objective of the experiments described in this report was to gather qualitative and quantitative data to support decisions regarding the thermal stability and safe disposal strategy of nitric acid treated anion exchange resins utilized in TRU processing operations.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

IS THE LINE-LIKE OPTICAL AFTERGLOW SED OF GRB 050709 DUE TO A FLARE?

Recently, Jin et al. reanalyzed the optical observation data of GRB 050709 and reported a line-like spectral energy distribution (SED) component observed by the Very Large Telescope at t ∼ 2.5 days after the trigger of the burst, which had been interpreted as a broadened line signal arising from a macronova dominated by an iron group. In this work, we show that an optical flare origin of such a peculiar optical SED is still possible. Interestingly, even in such a model, an “unusual” origin of the late-time long-lasting Hubble Space Telescope F 814 W -band emission is still needed and a macronova/kilonova is the natural interpretation.

79 ASTRONOMY AND ASTROPHYSICS↗

Practical applications of surface analytic tools in tribology

A brief description of many of the widely used tools is presented. Of this list, those which have the highest applicability for giving elemental and/or compound analysis for problems of interest in tribology along with being truly surface sensitive (that is less than 10 atomic layers) are presented. The latter group is critiqued in detail in terms of strengths and weaknesses. Emphasis is placed on post facto analysis of experiments performed under real conditions (e.g., in air with lubricants). It is further indicated that such equipment could be used for screening and quality control.

Ferrante, J.↗

Structure and functions of water-membrane interfaces and their role in proto-biological evolution

Among the most important developments in proto-biological evolution was the emergence of membrane-like structures. These are formed by spontaneous association of relatively simple amphiphilic molecules that would have been readily available in the primordial environment. The resulting interfacial regions between water and nonpolar interior of the membrane have several properties which made them uniquely suitable for promoting subsequent evolution. They can (1) selectively attract organic material and mediate its transport, (2) serve as simple catalysts for chemical reactions, and (3) promote the formation of trans-membrane electrical and chemical gradients which could provide energy sources for proto-cells. Understanding the structure of interfaces, their interactions with organic molecules and molecular mechanisms of their functions is an essential step to understanding proto-biological evolution. In our computer simulation studies, we showed that the structure of water at interfaces with nonpolar media is significantly different from that in the bulk. In particular, the average surface dipole density points from the vapor to the liquid. As a result, negative ions can approach the interface more easily than positive ions. Amphiphilic molecules composed of hydrocarbon conjugated rings and polar substituents (e.g., phenol) assume at the interface rigid orientations in which polar groups are buried in water while hydrocarbon parts are located in the nonpolar environment. These orientational differences are of special interest in connection with the ability of some of these molecules to efficiently absorb photons. Flexible molecules with polar substituents often adopt at interfaces conformations different from those in the bulk aquaeous solution and in the gas phase. As a result, in many instances both specificity and kinetics of chemical reactions in which these molecules can participate is modified by the presence of surfaces. Of special interest is the mechanism by which polar molecules are transferred across interface between water and a nonpolar medium. Our recent study showed that simple ionophores bind ions by the same mechanisms as ion channels and carriers from modern cells.

Pohorille, A.↗

Design and development of experimental facilities for short duration, low-gravity combustion and fire experiments

This report contains the results of three projects conducted by undergraduate students from Worcester Polytechnic Institute at the NASA's Lewis Research Center under a NASA Award NCC3-312. The students involved in these projects spent part of the summer of 1993 at the Lewis Research Center (LeRC) under the direction of Dr. Howard Ross, head of the Combustion group and other NASA engineers and scientists. The Principal Investigator at Worcester Polytechnic Institute was Professor Vahid Motevalli. Professor Motevalli served as the principal project advisor for two of the three projects which were in Mechanical Engineering. The third project was advised by Professor Duckworth of Electrical and Computer Engineering, while Professor Motevalli acted as the co-advisor. These projects provided an excellent opportunity for the students to participate in the cutting edge research and engineering design, interact with NASA engineers and gain valuable exposure to a real working environment. Furthermore, the combustion group at LeRC was able to forward their goals by employing students to work on topics of immediate use and interest such as experimental research projects planned for the space shuttle, the future space station, or to develop demonstration tools to educate the public about LeRC activities.

Motevalli, Vahid↗

Discussion on selected symbiotic stars

Because of its large variety of aspects, the symbiotic phenomenon is not very suitable for a statistical treatment. It is also not clear whether symbiotic stars really represent a homogeneous group of astrophysical objects or a collection of objects of different natures but showing similar phenomena. However we are especially interested in the symbiotic phenomenon, i.e., in those physical processes occurring in the atmosphere of each individual object and in their time dependence. Such a research can be performed through the detailed analysis of individual objects. This study should be done for a time long enough to cover all the different phases of their activity, in all the spectral ranges. Since the typical time scale of the symbiotic phenomena is up to several years and decades, this represents a problem since, for instance, making astronomy outside the visual region is a quite new field of research. It was a fortunate case that a few symbiotic stars (Z And, AG Dra, CH Cyg, AX Per, and PU Vul) had undergone remarkable light variations (or 'outbursts') in recent years, which could have been followed in the space ultraviolet with IUE, and simultaneously in the optical and IR with ground-based telescopes. But, in general, the time coverage of most of the symbiotic objects is too short to have a complete picture of their behavior. In this regard, one should recall Mayall's remark about the light curve of Z And: 'Z Andromedae is another variable that shows it will require several hundred years of observations before a good analysis can be made of its variations'. This pessimistic remark should be considered as a note of caution for those involved in the interpretation of the observations. We shall discuss a number of individual symbiotic stars for which the amount of observational data is large enough to draw a rather complete picture of their general behavior and to make consistent models. We shall especially illustrate the necessary steps toward an empirical model and take the discussion of the individual objects as a useful occasion to describe different techniques of diagnosis.

Viotti, Roberto↗

Cure Chemistry of Phenylethynyl Terminated Oligomers

The ability to process high performance polymers into quality, void-free composites has been significantly advanced using oligomers terminated with reactive groups which cure or crosslink at elevated temperature without the evolution of volatile byproducts. Several matrix resin systems of considerable interest to the aerospace community utilize phenylethynyl-terminated imide (PETI) technology to achieve this advantage. The present paper addresses the cure chemistry of PETI oligomers. The thermal cure of a low molecular weight model compound was studied using a variety of analytical techniques including differential scanning calorimetry, Fourier transform infrared spectroscopy, and liquid chromatography-mass spectroscopy. The studies indicate an extremely complex cure process. Many stable products were isolated and this paper reports current work on identification of those products. The intent of this research is to provide fundamental insight into the molecular structure of the cured PETI engineering materials so that performance and durability can be more fully assessed.

Wood, Karen H.↗

Toward a Systematic Approach for Selection of NASA Technology Portfolios

There is an important need for a consistent analytical foundation supporting the selection and monitoring of R&D tasks that support new system concepts that enable future NASA missions. This capability should be applicable at various degrees of abstraction, depending upon whether one is interested in formulation, development, or operations. It should also be applicable to a single project, a program comprised of a group of projects, an enterprise typically including multiple programs, and the overall agency itself. Emphasis here is on technology selection and new initiatives, but the same approach can be generalized to other applications, dealing, for example, with new system architectures, risk reduction, and task allocation among humans and machines. The purpose of this paper is to describe one such approach, which is in its early stages of implementation within NASA programs, and to discuss several illustrative examples.

return on investment↗

Characterizing GEO Titan IIIC Transtage Fragmentations using Ground-Based and Telescopic Measurements

In a continued effort to better characterize the geosynchronous orbit (GEO) environment, NASA's Orbital Debris Program Office (ODPO) utilizes various ground-based optical assets to acquire photometric and spectral data of known debris associated with fragmentations in or near GEO. The Titan IIIC Transtage upper stage is known to have fragmented four times. Two of the four fragmentations were in GEO while the Transtage fragmented a third time in GEO transfer orbit. The forth fragmentation occurred in low Earth orbit. To better assess and characterize these fragmentations, the NASA ODPO acquired a Titan Transtage test and display article previously in the custody of the 309th Aerospace Maintenance and Regeneration Group (AMARG) in Tucson, Arizona. After initial inspections at AMARG demonstrated that it was of sufficient fidelity to be of interest, the test article was brought to NASA Johnson Space Center (JSC) to continue material analysis and historical documentation. The Transtage has undergone two separate spectral measurement campaigns to characterize the reflectance spectroscopy of historical aerospace materials. These data have been incorporated into the NASA Spectral Database, with the goal of using telescopic data comparisons for potential material identification. A Light Detection and Ranging (LIDAR) system scan also has been completed and a scale model has been created for use in the Optical Measurement Center (OMC) for photometric analysis of an intact Transtage, including bidirectional reflectance distribution function (BRDF) measurements. An historical overview of the Titan IIIC Transtage, the current analysis that has been done to date, and the future work to be completed in support of characterizing the GEO and near GEO orbital debris environment will be discussed in the subsequent presentation.

Cowardin, Heather↗

TPSAS-NF1676L-30451-DND

The fundamental laws of the physics of fluid flow in the continuum regime are embedded in a somewhat "simple" set of partial differential equations describing the transport of mass, momentum, energy, and/orentropy. These basic equations can be manipulated to construct other important physical quantities such as vorticity that help further elucidate flow physics. Additionally, these equations can be nondimensionalized to identify important nondimensional groups governing compressible, reacting fluid flows, most prominently Reynolds, Mach, Froude, Prandtl, Lewis, Schmidt, Damkohler, and Zeldovich numbers. In this lecture, we present these governing equations and discuss the significance of the different terms and nondimensional groups. Furthermore, since these equations cannot be solved directly on current supercomputers for turbulent flows at Reynolds numbers of engineering interest, a scale reduction by averaging or filtering is introduced, which leads to a "closure" problem. The closure is then provided by introducing some common models. The current introduction is by no means complete, but it and the references herein may serve as a good starting point for learning about the most common approaches to turbulent reacting flows.

Tomasz (Tom) G Drozda↗

Photochemistry of Pyrimidine in Astrophysical Ices: Formation of Nucleobases and Other Prebiotic Species

Nucleobases are N-heterocycles that are the informational subunits of DNA and RNA. They are divided into two molecular groups: pyrimidine bases (uracil, cytosine, and thymine) and purine bases (adenine and guanine). Nucleobases have been detected in meteorites, and their extraterrestrial origin confirmed by isotopic measurements. Although no N-heterocycles have ever been observed in the ISM, the positions of the 6.2- m interstellar emission features suggest a population of such molecules is likely to be present. However, laboratory experiments have shown that the ultraviolet (UV) irradiation of pyrimidine in ices of astrophysical relevance such as H2O, NH3, CH3OH, CH4, CO, or combinations of these at low temperature (less than or equal to 20 K) leads to the formation of several pyrimidine derivatives including the nucleobases uracil and cytosine, as well as precursors such as 4(3H)-pyrimidone and 4-aminopyrimidine. Quantum calculations on the formation of 4(3H)-pyrimidone and uracil from the irradiation of pyrimidine in pure H2O ices are in agreement with their experimental formation pathways.10 In those residues, other species of prebiotic interest such as urea as well as the amino acids glycine and alanine could also be identified. However, only very small amounts of pyrimidine derivatives containing CH3 groups could be detected, suggesting that the addition of methyl groups to pyrimidine is not an efficient process. For this reason, the nucleobase thymine was not observed in any of the samples. In this work, we study the formation of nucleobases and other photo-products of prebiotic interest from the UV irradiation of pyrimidine in ices containing H2O, NH3, CH3OH, and CO, mixed in astrophysical proportions.

Nuevo, Michel↗

Physics-based dimension reduction in uncertainty quantification for radiative transfer

We present a physics-based methodology for quantifying the uncertainty in a given quantity of interest (QOI) that is contributed by uncertainties in opacities in radiation transport problems. Typically, opacities are tabulated as a function of density, temperature, and photon energy group. The size of this table makes a study of uncertainties at this level challenging because of the well-known 'curse of dimensionality.' We address this by studying uncertain parameters in the underlying physical model that generates the opacity tables. At this level, there are fewer uncertain parameters but still too many to analyze directly through computationally expensive radiation transport simulations. In order to explore this large uncertain parameter space, we develop two simplified radiation transport problems that are much less computationally demanding than the target problem of interest. An emulator is created for each QOI for each simplified problem using Bayesian Multivariate Adaptive Regression Splines (BMARS). This emulator is used to create a functional relationship between the QOIs and the uncertain parameters. Sensitivity analysis is performed using the emulator to determine which parameters contribute significantly to the uncertainty. This physics-based screening process reduces the dimension of the parameter space that is then studied via the computationally expensive radiation transport calculation to generate distributions of quantities of interest. Results of this research demonstrate that the QOIs for the target problem agree for varying screening criteria determined by the sensitivity analysis, and the QOIs agree well for varying Latin Hypercube Design (LHD) sample sizes for the uncertain space. (authors)

97 MATHEMATICS AND COMPUTING↗

Highly Coupled Heterobicycle‐Fused Porphyrin Dimers: Excitonic Coupling and Charge Separation with Coordinated Fullerene, C 60

Abstract Porphyrin dimers have been widely explored and studied owing to their importance in photosynthetic systems. A vast variety of dimers linked by different groups and at different angles have been synthesized and studied; however, the means by which to synthesize rigidly fused porphyrins with direct conjugation of the chromophores remains limited. Such a class of porphyrins may possess interesting properties that unconjugated or stacked dimers may not exhibit. In this study, bisbenzimidazole‐fused porphyrin dimers and their mono‐ and bis−zinc derivatives are synthesized and characterized. As a consequence of excitonic coupling, these dimers exhibit a split Soret band irrespective of the metal ion in the porphyrin cavity. Steady‐state fluorescence and excitation spectra followed by femtosecond transient absorption spectral studies of the heterometallated dimer, (free‐base and zinc porphyrin) reveals the occurrence of efficient singlet‐singlet energy transfer (>95 % efficiency and rate constant >10 12 s −1 ) within the dyad. Further, donor‐acceptor conjugates were formed by metal‐ligand axial coordination of phenyl imidazole functionalized C 60 and were characterized by a variety of physicochemical techniques. Excited state charge separation from both singlet and triplet excited states of ZnP in the conjugates has been established. The lifetime of the final charge‐separated state was in the 30–40 μs range revealing charge stabilization. Interestingly, no charge separation in the conjugate derived from the heterometallated dimer was observed wherein excitation transfer dominated the process. The present study brings out the importance of the rigid π‐spacer connecting porphyrin dimers in governing the energy and electron transfer events when coupled with an electron acceptor.

Chemistry↗