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At least 847 records · Page 47

Symmetric U(1) and Z 2 spin liquids on the pyrochlore lattice

The geometrically frustrated three-dimensional pyrochlore lattice has been long predicted to host a quantum spin liquid, an intrinsic long-range entangled state with fractionalized excitations. To date, most proposals for pyrochlore materials have focused on quantum spin ice, a U(1) quantum spin liquid whose only low energy excitations are emergent photons of Maxwell type. Here, we explore the possibility of finding pyrochlore quantum spin liquids whose low energy theories go beyond this standard one. We give a complete classification of symmetric U ( 1 ) and Z 2 spin liquids on the pyrochlore lattice within the projective symmetry group framework for fermionic spinons. We find 18 U ( 1 ) spin liquids and 28 Z 2 spin liquids that preserve pyrochlore space-group symmetry while, upon further imposing time-reversal symmetry, the numbers of classes become 16 and 48, respectively. For each class, the most general symmetry-allowed spinon mean-field Hamiltonian is given. Interestingly, we find that several U(1) spin liquid classes possess an unusual gapless multi-nodal-line structure (“nodal star”) in the spinon bands, which is protected by the projective actions of the threefold rotation and screw symmetries of the pyrochlore space group. Through a simple model, we study the effect of gauge fluctuations on such a nodal star spin liquid and propose that the leading terms in the low temperature specific heat have the scaling form C / T ~ T + T / ln T , in contrast to the form C / T ~ T 2 of the standard U(1) pyrochlore spin liquid with gapped spinons.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Fractal dimension analysis of weight-bearing bones of rats during skeletal unloading

Fractal analysis was used to quantify changes in trabecular bone induced through the use of a rat tail-suspension model to simulate microgravity-induced osteopenia. Fractal dimensions were estimated from digitized radiographs obtained from tail-suspended and ambulatory rats. Fifty 4-month-old male Sprague-Dawley rats were divided into groups of 24 ambulatory (control) and 26 suspended (test) animals. Rats of both groups were killed after periods of 1, 4, and 8 weeks. Femurs and tibiae were removed and radiographed with standard intraoral films and digitized using a flatbed scanner. Square regions of interest were cropped at proximal, middle, and distal areas of each bone. Fractal dimensions were estimated from slopes of regression lines fitted to circularly averaged plots of log power vs. log spatial frequency. The results showed that the computed fractal dimensions were significantly greater for images of trabecular bones from tail-suspended groups than for ambulatory groups (p < 0.01) at 1 week. Periods between 1 and 4 weeks likewise yielded significantly different estimates (p < 0.05), consistent with an increase in bone loss. In the tibiae, the proximal regions of the suspended group produced significantly greater fractal dimensions than other regions (p < 0.05), which suggests they were more susceptible to unloading. The data are consistent with other studies demonstrating osteopenia in microgravity environments and the regional response to skeletal unloading. Thus, fractal analysis could be a useful technique to evaluate the structural changes of bone.

Non-NASA Center↗

Growth Disparity in Sympatric Kokanee Breeding Groups

Abstract Growth is arguably the most important dynamic rate function due to its interaction with survival and recruitment. As such, understanding the mechanisms underlying growth is a primary focus of fisheries research. Kokanee Oncorhynchus nerka in Lake Pend Oreille, Idaho, provide an interesting case study for investigating the factors that influence growth. Early-run and late-run kokanee occur in Lake Pend Oreille, but early-run fish generally grow faster than late-run fish. The observed growth disparity between early- and late-run fish could be due to genetic differences between the two groups. Conversely, a common hatchery practice of slowing growth by reducing feed has been hypothesized to elicit a compensatory growth response in early-run fish and to explain the size difference between breeding groups. Using two different experiments, we tested the hypotheses that (1) early-run kokanee are genetically disposed to grow faster than late-run kokanee at identical water temperatures; and (2) feed restriction elicits a compensatory growth response in early-run kokanee that explains the observed size difference between breeding groups. Estimates of mean FL, weight, Fulton's condition factor (K), and specific growth rate (SGR) were not significantly different (P ≥ 0.05) between early-run and late-run fish in the first experiment. However, water temperature was positively related to mean FL, weight, K, and SGR for both breeding groups. Fish that were subjected to food deprivation exhibited an increased growth rate and obtained weights similar to those of control fish. Overall, our results suggest that early- and late-run fish have similar growth potential, but certain hatchery practices likely provide early-run fish with an initial advantage in growth, size, or both.

Klein, Zachary B.↗

Utilizing Ion-Mobility Data to Estimate Molecular Masses

A method is being developed for utilizing readings of an ion-mobility spectrometer (IMS) to estimate molecular masses of ions that have passed through the spectrometer. The method involves the use of (1) some feature-based descriptors of structures of molecules of interest and (2) reduced ion mobilities calculated from IMS readings as inputs to (3) a neural network. This development is part of a larger effort to enable the use of IMSs as relatively inexpensive, robust, lightweight instruments to identify, via molecular masses, individual compounds or groups of compounds (especially organic compounds) that may be present in specific environments or samples. Potential applications include detection of organic molecules as signs of life on remote planets, modeling and detection of biochemicals of interest in the pharmaceutical and agricultural industries, and detection of chemical and biological hazards in industrial, homeland-security, and industrial settings.

Duong, Tuan↗

Bivalent metal-based MIL-53 analogues: Synthesis, properties and application

Trivalent metal-based MIL-53 (Al{sup 3+}, Cr{sup 3+}, Fe{sup 3+}, In{sup 3+}) compounds are interesting metal–organic frameworks (MOFs) with breathing effect and are promising gas sorption materials. Replacing bridging μ{sub 2}-OH group by neutral ligands such as pyridine N-oxide and its derivatives (PNOs), the trivalent metal-based MIL-53 analogous structures could be extended to bivalent metal systems. The introduction of PNOs and bivalent metal elements endows the frameworks with new structural features and physical and chemical properties. This minireview summarizes the recent development of bivalent metal-based MIL-53 analogues (Mn{sup 2+}, Co{sup 2+}, Ni{sup 2+}), typically, focusing on the synthetic strategies and potential applications based on our own works and literatures. We present the synthetic strategy to achieve structures evolution from single-ligand-walled to double-ligand-walled channel. Properties and application of these new materials in a wide range of potential areas are discussed including thermal stability, gas adsorption, magnetism and liquid-phase separation. Promising directions of this research field are also highlighted. - Graphical abstract: The recent development of bivalent metal-based MIL-53 analogues (Mn{sup 2+}, Co{sup 2+}, Ni{sup 2+}) on their synthetic strategies, properties and potential applications was reviewed. - Highlights: • Structure features of bivalent metal-based MIL-53 analogues are illustrated. • Important properties and application are presented. • Host–guest interactions are main impetus for liquid-phase separation. • Promising directions of bivalent metal-based MIL-53 analogues are highlighted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Three luminescent d{sup 10} metal coordination polymers assembled from a semirigid V-shaped ligand with high selective detecting of Cu{sup 2+} ion and nitrobenzene

Three 2D luminescent coordination polymers with helical frameworks, [ZnL{sub 2}]{sub n} (1) and ([ML{sub 2}]·(H{sub 2}O)){sub n} (M=Zn (2), Cd (3)) (HL=4-((2-methyl-1 H-imidazol-1-yl)methyl)benzoic acid), have been assembled under hydro(solvo)thermal conditions. Complex 1 is in chiral space group and displays a rare 2D→2D 2-fold parallel interpenetrated layer network with two types of chiral double helixes. Interestingly, the single crystal structure analyses indicate the coexistence of enantiomers la and 1b in one pot, while the bulk crystallization of 1 are racemic mixtures based on the CD measurement. 2 and 3 are isostructural, in the structure, there are two kinds of 2D chiral helical-layers which stack in an -ABAB- sequence leading to the overall structure are mesomer and achiral. All compounds display intense luminescence in solid state at room temperature with high chemical and thermal stability. More importantly, 1 has been successfully applied in the detection of Cu{sup 2+} ions in aqueous media and nitrobenzene and the probable detecting mechanism was also discussed. - Graphical abstract: Three luminescent d{sup 10} metal coordination polymers with helical-layer based on 4-((2-methyl-1H-imidazol-1-yl)methyl)benzoic acid have been obtained. Compound 1 shows high selective detecting for Cu{sup 2+} ion in aqueous and nitrobenzene. - Highlights: • Three coordination polymers with chiral helical-layer have been obtained. • 1 Can luminescent detect Cu{sup 2+} ion in aqueous media and nitrobenzene. • Racemic mixture or mesomer compounds can be obtained by controlling the reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Series of coordination polymers based on 4-(5-sulfo-quinolin-8-yloxy) phthalate and bipyridinyl coligands: Structure diversity and properties

Reactions between later metal salts and conjugational N-hetrocyclic sulfonate/ carboxylic acid under the presence of bipyridyl auxiliary ligands afforded a series of manganese, nickel, zinc, silver, cadmium coordination polymers bearing with phenyl pendant arm attached to quinoline skeletons, and they have been characterized by elements analysis, thermogravimetry, infrared spectroscopy and single-crystal X-ray diffraction studying. The series of polymers show interesting structural diversity in coordination environment, dimensions and topologies. They are all built from 2-D networks constructed from metal cluster through sulfonate or carboxylate groups, as the secondary building unit (SBU). The thermalgravimetric analyses show that they display framework stabilities in solid state. Variable-temperature magnetic susceptibility studies reveal the existence of antiferromagnetic interactions between adjacent Mn (II) ions in 1, and ferromagnetic interactions between Ni(II) ions for 2, respectively. The photo-luminescence properties of 3-5 have also been investigated systemically. - Highlights: • A series of coordination polymers based on later transition metal ions have been obtained. • They contain conjugational N-hetrocyclic sulfonate-carboxylic acid and bipyridyl auxiliary ligands. • They have been characterized systemically. • They exhibit structure diversity and interesting properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

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↗