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NASA NTRS1993

Some experiences with Krylov vectors and Lanczos vectors

This paper illustrates the use of Krylov vectors and Lanczos vectors for reduced-order modeling in structural dynamics and for control of flexible structures. Krylov vectors and Lanczos vectors are defined and illustrated, and several applications that have been under study at The University of Texas at Austin are reviewed: model reduction for undamped structural dynamics systems, component mode synthesis using Krylov vectors, model reduction of damped structural dynamics systems, and one-sided and two-sided unsymmetric block-Lanczos model-reduction algorithms.

Craig, Roy R., Jr.↗

NASA NTRS1992

The data acquisition system for the Anglo-Australian Observatory 2-degree field project

The Anglo-Australian Observatory (AAO) is building a system that will provide a two-degree field of view at prime focus. A robot positioner will be used to locate up to 400 optical fibers at pre-determined positions in this field. While observations are being made using one set of 400 fibers, the robot will be positioning a second set of fibers in a background field that can be moved in to replace the first when the telescope is moved to a new position. The fibers feed two spectrographs each with a 1024 square CCD detector. The software system being produced to control this involves Vaxes for overall control and data recording, UNIX workstations for fiber configuration calculations and on-line data reduction, and VME systems running VxWorks for real-time control of critical parts such as the positioner robot. The system has to be able to interact with the observatory's present data acquisition systems, which use the ADAM system. As yet, the real-time parts of ADAM have not been ported to Unix, and so we are having to produce a smaller-scale system that is similar but inherently distributed (which ADAM is not). We are using this system as a testbed for ideas that we hope may eventually influence an ADAM II system. The system we are producing is based on a message system that is designed to be able to handle inter-process and inter-processor messages of any length, efficiently, and without ever requiring a task to block (i.e., be unresponsive to 'cancel' messages, enquiry messages), other than when deliberately waiting for external input - all of which will be through such messages. The essential requirement is that a message 'send' operation should never be able to block. The messages will be hierarchical, self-defining, machine-independent data structures. This allows us to provide very simple monitoring of messages for diagnostic purposes, and allows general purpose interface programs to be written without needing to share precise byte by byte message format definitions. Programs in this system have interfaces defined simply in terms of named actions and their parameters. Real-time control programs are required to be able to handle a number of such actions concurrently; data reduction programs will normally only need to handle one action at a time ('process an image', 'display a spectrum', etc).

Shortridge, K.↗

NASA NTRS2006

An eight-meter inflatable reflectarray antenna and its inflatable/self-rigidizable booms

This paper presents the analysis and test results related to buckling capability, modal characteristics, and thermal expansion coefficient of STR aluminum laminate inflatable/self-rigidizable booms with lengths up to 10 metes. STR booms are fundamental building blocks of space inflatable/self-rigidizable reflectarray antennas. These boom characteristics are essential for analyzing structural integrity, in orbit dynamic response, and in orbit thermal distortion of the 8-mter reflectarray antenna. Distinct advantages of the STR booms will also be identified and presented by this paper.

membranes↗

NASA NTRS2018

Structural Certification of Human-Rated Inflatable Space Structures

This paper details the results of an initial study to develop a certification plan for human-rated inflatable space structures, including guidelines for qualification testing. Habitable softgoods inflatables are multi-layered shell structures that use high-strength webbing, cordage and broadcloth fabric to carry the skin loads of a variety of volumetric shapes and structural architectures. The primary objectives of this study are to define the key parameters that affect these structures and propose a statistically robust approach to defining safety and knockdown factors based on test and analysis. Current NASA standards for habitable inflatable space structures use a factor of safety of 4, which was inherited from airship design criteria. An updated approach to defining a design factor, taking into account material strength variability, load variability in the article, number of test samples, and damage and degradation effects is specified. Accurate analytical modeling of these structures is hindered by the difficulty of obtaining accurate and consistent material data due to load-history- dependent, nonlinear load versus strain behavior. A building block approach to certification is detailed that uses stochastic modeling and statistical test design and analysis to address the unique challenges these high-strength softgoods structures present. Human-rated inflatable modules are a transformative capability for launching much larger habitable volumes into space than is possible with rigid shell structures. This research aims to provide the framework for certifying these structures for future human space exploration missions.

Jones, Thomas C.↗

NASA NTRS1998

Trellises and Trellis-Based Decoding Algorithms for Linear Block Codes: A Recursive Maximum Likelihood Decoding - Part 3

The Viterbi algorithm is indeed a very simple and efficient method of implementing the maximum likelihood decoding. However, if we take advantage of the structural properties in a trellis section, other efficient trellis-based decoding algorithms can be devised. Recently, an efficient trellis-based recursive maximum likelihood decoding (RMLD) algorithm for linear block codes has been proposed. This algorithm is more efficient than the conventional Viterbi algorithm in both computation and hardware requirements. Most importantly, the implementation of this algorithm does not require the construction of the entire code trellis, only some special one-section trellises of relatively small state and branch complexities are needed for constructing path (or branch) metric tables recursively. At the end, there is only one table which contains only the most likely code-word and its metric for a given received sequence r = (r(sub 1), r(sub 2),...,r(sub n)). This algorithm basically uses the divide and conquer strategy. Furthermore, it allows parallel/pipeline processing of received sequences to speed up decoding.

Lin, Shu↗

DOE OSTI2020

High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using 13C NMR Spectroscopy and Computer Simulations

This work demonstrates the first high-resolution comonomer sequencing of Blocky brominated syndiotactic polystyrene (sPS-co-sPS-Br) copolymers based on pentad assign- ments of the quaternary carbon region of the nuclear magnetic resonance spectrum. Copolymers containing p-bromostyrene (Br-Sty) units were prepared in matched sets using postpolymerization bromination methods carried out in the heterogeneous gel state (Blocky) and homogeneous solution state (Random). Quantitative information from the quaternary carbon spectra, heteronuclear multiple bond correlation spectroscopy, electronic structure calculations, and simulated statistically random copolymers was correlated to confirm the carbon resonance assignments for all 20 possible pentad comonomer sequences. Using the experimental pentad sequence prevalences, a computer code was developed to simulate chains with microstructures typical of each sample as a means to visually represent the copolymer blockiness with quantitative precision. Based on the microstructure and distribution of run lengths in these chains, the simulations revealed that the Blocky copolymers contain a high degree of blockiness. By comparing the run lengths in the simulated chains to the average number of styrene units in a crystalline segment of sPS (found by small-angle X-ray scattering), copolymer crystallizability was predicted. For the simulated Blocky B-21% (21 mol % Br-Sty) chain, the probability of randomly selecting a styrene unit in a crystallizable block was 25.8%, while that in the simulated Random R-18% was zero, in excellent agreement with the experimental crystallization behavior measured by differential scanning calorimetry. Additionally, these predictions confirmed that the simulated chains accurately represent the ensemble of chains in their respective copolymer samples. Furthermore, each simulated Blocky chain contained one or more long sPS blocks that paralleled the measured 38-40 styrene units spanning a crystalline segment within the sPS/CCl4 gel. This finding affirmed that the long sPS segments originated from the precise lamellar structure within the heterogeneous gel morphology (i.e., block length is correlated with lamellar thickness). Overall, the ability to tailor the copolymer microstructure through control of the semicrystalline gel morphology opens the door to synthesizing ordered copolymers by postpolymerization functionalization processes with unprecedented levels of compositional control.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Symmetry in Seeded Metal Nanocrystal Growth

Symmetry underpins the structure and function of the world around us and is also captured in modern nanomaterials, where changing the symmetry of a nanocrystal or the interparticle spacing and orientation of nanocrystal building blocks in a superlattice can give new function. However, the synthesis and assembly of nanocrystals have been limited largely to simple compositions and structures. It remains a grand challenge to achieve nanocrystals with compositional and structural complexity while maintaining the monodispersity required for their use. This Account will illustrate through recent examples that seeded methods enable the synthesis of compositionally and structurally complex multimetallic crystals with defined and predictable symmetries for applications in plasmonics and catalysis. This outcome arises because the barrier for heterogeneous nucleation (i.e., seeded) is lower than that of homogeneous nucleation, where seeds can serve as preferential sites for the growth of complex structures and crystal phases. Our analysis begins by considering metal overgrowth from single-crystalline seeds of different shapes and symmetries, where the kinetics of adatom addition to seeds relative to their diffusion across seeds accounts for the expressed nanocrystal shapes. These results are then compared to overgrowth from seeds with different internal structures (i.e., planar defects), where the relationships between nanocrystal size and volumetric strain energy and surface energy are discussed. A major finding from this analysis is that often the underlying symmetry of seeds can be predictably transferred to the final crystals during overgrowth processes. Consequences of this finding are the predictable syntheses of crystals with different hierarchies akin to snowcrystals as well as nanocrystals with complex compositions (e.g., quaternary nanoparticles). Yet, there are subtle aspects to seeded growth that pave a path toward examples where nanocrystal symmetry has been reduced compared to the original seeds in a controlled manner. As we found, both the concentrations of metal precursors and capping agents can impact whether symmetry is transferred or reduced during overgrowth. Examples from our laboratory will be placed in context to other reported strategies for symmetry breaking. As will be argued, understanding what conditions favor symmetry preservation versus symmetry reduction during seeded crystal growth is central to accessing next-generation crystal forms. The Account concludes by outlining synthetic challenges associated with forming nanoscale heterostructures with precise 3-D placement of different materials within a given nanocrystal as well as facet control within different material domain and interface engineering. Furthermore, we envision meeting these challenges through regioselective and chemoselective seeded syntheses for which a foundation is outlined herein.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Role of Intra-Domain Heterogeneity on Ion and Polymer Dynamics in Block Polymer Electrolytes: An Approach for Spatially Resolving Dynamics and Ion Transport

The design of safe and high-performance, nanostructured, block polymer (BP) electrolytes for lithium-ion batteries requires a thorough understanding of the key parameters that govern local structure and dynamics. Yet, the interfaces between microphase separated domains can introduce complexities in this local behavior that can be challenging to quantify. Herein, the local polymer, cation (Li + ), and anion dynamics were described in salt-doped polystyrene block poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) through a quantitative framework that considered the effects of polymer architecture, segmental mixing, chain stretching, and confinement on polymer mobility and ion transport. This framework was validated through nuclear magnetic resonance (NMR) spectroscopy measurements on solid (dry) polymer electrolyte samples. Notably, a mobility transition temperature (T mobility ) was identified through NMR spectroscopy that captured the local dynamics more accurately than the thermal glass transition temperature. Additionally, the approach quantitatively described the mobility gradient across a domain when segmental mixing effects were combined with chain stretching and confinement information, especially at higher segregation strengths – facilitating the assessment of local ion diffusion and conductivity. As a result, spatially averaged local ion diffusion predictions quantitatively matched NMR-measured ion diffusivities in the BP samples, while spatially summed ionic conductivity predictions across a domain qualitatively captured trends in the measured ionic conductivities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Structural Phase Transitions in the van der Waals Ferromagnets Fe x Pd y Te 2

Two-dimensional van der Waals (vdW) magnets are attracting significant attention, both as platforms for studying fundamental magnetic interactions and for the exciting possibility of utilizing them as building blocks in devices and heterostructures, which may lead to new physical phenomena and functionalities. Here, we provide a detailed study of the crystal structure and physical properties of the recently discovered vdW ferromagnet FePd 2 Te 2 . We find this compound has a relatively wide width of formation, and grow single crystals with compositions Fe x Pd y Te 2 where x ranges from 0.9 to 1.1 and y from 1.8 to 2.5, respectively. Temperature-dependent X-ray diffraction and transport measurements reveal that a first-order structural transition occurs in the range of T = 360–420 K, where the critical temperature, modulation wave vector, and corresponding room-temperature crystal structures all depend on chemical composition. Above the transition, the compounds with Pd fraction y > 2 adopt a disordered derivative of the tetragonal FeTe structure, with the Fe layer showing mixed Fe/Pd occupancy and the extra Pd atoms partially occupying interstitial sites. Below 370 K, the structure is incommensurately modulated, likely associated with the complex ordering of Pd/Fe atoms in the metal layers or the interstitial Pd in the vdW gaps. For y < 2, the composition Fe 1.1 Pd 1.8 Te 2 has monoclinic symmetry at room temperature that is consistent with the reported structure of FePd 2 Te 2 . This phase undergoes a structural transition at 420 K for which the high temperature structure is yet to be determined; however, based on the similarities with the y > 2 compounds, we speculate that its T > 420 K structure is also tetragonal. Importantly, the high temperature, symmetry-breaking structural transition observed here provides a likely explanation for the origin of the structural domains previously observed in FePd 2 Te 2 . All compounds investigated in the Fe x Pd y Te 2 series show metallic behavior, with magnetic characterization indicating that they are easy-plane, hard, ferromagnets with T C spanning 98–180 K. Both the critical temperature for the structural transition and the Curie temperature are moderately suppressed with increasing Pd fraction y and corresponding decreasing Fe fraction x, indicating that synthetic control over x and y paves way for the further exploration of these compounds.

crystal structure↗

NASA NTRS1985

Compliant hydrodynamic fluid journal bearing

An air bearing structure is described that prevents destructive bending moments within the top foil. Welds are eliminated by mounting the top bearing foil in the bearing cartridge sleeve without using a space block. Tabs or pins at the end of the top bearing foil are restrained by slots or stops formed in the cartridge sleeve. These structural members are free to move in a direction normal to the shaft while being restrained from movement in the direction of shaft rotation.

Warren, E. L.↗

DOE OSTI2022

Multilayered Ordered Protein Arrays Self-Assembled from a Mixed Population of Virus-like Particles

Biology shows many examples of spatially controlled assembly of cells and biomacromolecules into hierarchically organized structures, to which many of the complex biological functions are attributed. While such biological structures have inspired the design of synthetic materials, it is still a great challenge to control the spatial arrangement of individual building blocks when assembling multiple types of components into bulk materials. Here, in this study, we report self-assembly of multilayered, ordered protein arrays from mixed populations of virus-like particles (VLPs). We systematically tuned the magnitude of the surface charge of the VLPs via mutagenesis to prepare four different types of VLPs for mixing. A mixture of up to four types of VLPs selectively assembled into higher-order structures in the presence of oppositely charged dendrimers during a gradual lowering of the ionic strength of the solution. The assembly resulted in the formation of three-dimensional ordered VLP arrays with up to four distinct layers including a central core, with each layer comprising a single type of VLP. A coarse-grained computational model was developed and simulated using molecular dynamics to probe the formation of the multilayered, core-shell structure. Our findings establish a simple and versatile bottom-up strategy to synthesize multilayered, ordered materials by controlling the spatial arrangement of multiple types of nanoscale building blocks in a one-pot fabrication.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2022

Structural Changes during the Conversion Reaction of Tungsten Oxide Electrodes with Tailored, Mesoscale Porosity

In-plane tungsten oxide nanostructures, including hexagonally patterned cylinders and holes in a matrix, were fabricated via sequential infiltration synthesis (SIS) on self-assembled block copolymer templates. Using the tailored morphology and porosity of these model electrodes with in situ grazing incidence small angle X-ray scattering, the intrinsic structural change of nanoscale active materials during the conversion reaction of WO 3 + 6Li ↔ W + 3 Li 2 O was investigated at controlled electrochemical conditions. Reversible electrode volume expansion and contraction was observed during lithiation and delithiation cycles, respectively. The potential where electrode’s thickness expansion started was ~1.6 V, which is close to thermodynamically expected one for conversion reaction of WO 3 with lithium (1.65 V). The temporal evolution of the electrode volume at constant electrode potentials revealed high overpotential for bulk lithiation and slow conversion reaction kinetics, despite the tailored porosity of the SIS electrodes. Oxide cylinders showed smaller overall electrode thickness change, likely due to unconstrained lateral volume change, as compared to a matrix with holes. On the other hand, better connectivity and guided volume change of the latter electrode morphology provided improved cycling stability. Additionally, heterogeneity in an electrode, from internal pores and density gradients, was found to aggravate the fragmentation of the electrode during conversion reaction. Insights into oxide conversion reaction kinetics and the relationship between electrode mesostructure and cycling behavior obtained from this study can help guide the more rational design of conversion electrode for high performing batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

High-resolution chemical patterns from negative tone resists for the integration of extreme ultraviolet patterns of metal-oxide resists with directed self-assembly of block copolymers

Extreme ultraviolet (EUV) lithography faces significant challenges in designing suitable resist materials that can provide adequate precision, while maintaining economically viable throughput. These challenges in resist materials have led to printing failures and high roughness in EUV patterns, compromising the performance of semiconductor devices. Integrating directed self-assembly (DSA) of block copolymers (BCPs) with EUV lithography offers a promising solution because, while the BCPs register to the EUV-defined chemical guiding pattern, the thermodynamically determined structures of the BCPs automatically rectify defects and roughness in the EUV pattern. Despite the superior resolution of metal-oxide EUV resists (MORs), their application to DSA is limited by the difficulty in converting them into chemical patterns that allow effective transfer of the rectified patterns of DSA films into inorganic materials. To address this challenge, this study introduces a novel strategy for fabricating chemical patterns using hydrogen silsesquioxane (HSQ), a high-resolution negative tone inorganic resist, as a model system for MORs. Initially, a sacrificial Cr pattern is generated from HSQ patterns via reactive ion etching. The sacrificial Cr pattern is converted into a chemical pattern by first grafting a water-soluble polyethylene oxide brush onto the substrate, then wet etching the Cr, and finally grafting nonpolar polystyrene brushes. Assembling polystyrene-block-poly(methyl methacrylate) on these patterns results in structures oriented and registered with the underlying pattern, achieving 24 nm full-pitch resolutions. In conclusion, this approach has the potential to integrate MOR patterns into the DSA process, thereby enabling the generation of high-quality sub-10 nm patterns with high-χ BCPs.

Atomic force microscopy↗

DOE OSTI2024

Structural diversity and clustering of bacterial flagellar outer domains

Supercoiled flagellar filaments function as mechanical propellers within the bacterial flagellum complex, playing a crucial role in motility. Flagellin, the building block of the filament, features a conserved inner D0/D1 core domain across different bacterial species. In contrast, approximately half of the flagellins possess additional, highly divergent outer domain(s), suggesting varied functional potential. In this study, we report atomic structures of flagellar filaments from three distinct bacterial species: Cupriavidus gilardii , Stenotrophomonas maltophilia , and Geovibrio thiophilus . Our findings reveal that the flagella from the facultative anaerobic G. thiophilus possesses a significantly more negatively charged surface, potentially enabling adhesion to positively charged minerals. Furthermore, we analyze all AlphaFold predicted structures for annotated bacterial flagellins, categorizing the flagellin outer domains into 682 structural clusters. This classification provides insights into the prevalence and experimental verification of these outer domains. Remarkably, two of the flagellar structures reported herein belong to a distinct cluster, indicating additional opportunities on the study of the functional diversity of flagellar outer domains. Our findings underscore the complexity of bacterial flagellins and open up possibilities for future studies into their varied roles beyond motility.

Science & Technology - Other Topics↗

NASA NTRS1989

Multi-level bandwidth efficient block modulation codes

The multilevel technique is investigated for combining block coding and modulation. There are four parts. In the first part, a formulation is presented for signal sets on which modulation codes are to be constructed. Distance measures on a signal set are defined and their properties are developed. In the second part, a general formulation is presented for multilevel modulation codes in terms of component codes with appropriate Euclidean distances. The distance properties, Euclidean weight distribution and linear structure of multilevel modulation codes are investigated. In the third part, several specific methods for constructing multilevel block modulation codes with interdependency among component codes are proposed. Given a multilevel block modulation code C with no interdependency among the binary component codes, the proposed methods give a multilevel block modulation code C which has the same rate as C, a minimum squared Euclidean distance not less than that of code C, a trellis diagram with the same number of states as that of C and a smaller number of nearest neighbor codewords than that of C. In the last part, error performance of block modulation codes is analyzed for an AWGN channel based on soft-decision maximum likelihood decoding. Error probabilities of some specific codes are evaluated based on their Euclidean weight distributions and simulation results.

Lin, Shu↗

NASA NTRS2001

Carbon Nanotube Anodes Being Evaluated for Lithium Ion Batteries

The NASA Glenn Research Center is evaluating the use of carbon nanotubes as anode materials for thin-film lithium-ion (Li) batteries. The motivation for this work lies in the fact that, in contrast to carbon black, directed structured nanotubes and nanofibers offer a superior intercalation media for Li-ion batteries. Carbon lamellas in carbon blacks are circumferentially oriented and block much of the particle interior, rendering much of the matrix useless as intercalation material. Nanofibers, on the other hand, can be grown so as to provide 100-percent accessibility of the entire carbon structure to intercalation. These tubes can be visualized as "rolled-up" sheets of carbon hexagons (see the following figure). One tube is approximately 1/10,000th the diameter of a human hair. In addition, the high accessibility of the structure confers a high mobility to ion-exchange processes, a fundamental for the batteries to respond dynamically because of intercalation.

Raffaelle, Ryne P.↗

DOE OSTI2023

Revealing the two-dimensional electronic structure and anisotropic superconductivity in a natural van der Waals superlattice (PbSe) 1.14 NbSe 2

Van der Waals superlattices are important for tailoring the electronic structures and properties of layered materials. Here we report the superconducting properties and electronic structure of a natural van der Waals superlattice (PbSe) 1.14 NbSe 2 . Anisotropic superconductivity with a transition temperature T c = 5.6 ± 0.1 K, which is higher than monolayer NbSe 2 , is revealed by transport measurements on high-quality samples. Angle-resolved photoemission spectroscopy (ARPES) measurements reveal the two-dimensional electronic structure and a charge transfer of 0.43 electrons per NbSe 2 unit cell from the blocking PbSe layer. In addition, polarization-dependent ARPES measurements reveal a significant circular dichroism with opposite contrast at K and K' valleys, suggesting a significant spin-orbital coupling and distinct orbital angular momentum. In conclusion, our work suggests natural van der Waals superlattice as an effective pathway for achieving intriguing properties distinct from both the bulk and monolayer samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Iron telluride ladder compounds: Predicting the structural and magnetic properties of BaFe 2 Te 3

Since the discovery of pressure-induced superconductivity in the two-leg ladder system BaFe 2 X 3 (X=S, Se), with the 3d iron electronic density n=6, quasi-one-dimensional iron-based ladders have attracted considerable attention. In this work, we use density-functional theory to predict that the novel n=6 iron ladder BaFe 2 Se 3 could be stable with a similar crystal structure as BaFe 2 Se 3 . Furthermore, our results also indicate that BaFe2Te3 will display a complex 2×2 block-type magnetic order. Due to the magnetic striction effects of this block order, BaFe2Te3 should be a magnetic noncollinear ferrielectric system with a net polarization 0.31μC/cm2. In summary, the similar electronic density and magnetic ground state of Te- and Se-based ladders indicates both should display similar properties. In particular, the physical and structural similarity with BaFe 2 Se 3 suggests that BaFe 2 Se 3 could become superconducting under high pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗