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Generally annular full tape thickness conductors are formed in single or multiple tape layers, and then stacked to produce an annular solid conductive wall for enclosing an electromagnetic isolation cavity. The conductors may be formed using punch and fill operations, or by flowing conductor-containing material onto the tape edge surfaces that define the interior sidewalls of the cavity.
Abstract not provided.
The structure of the 68 nt sequence with G-quadruplex forming potential within the hTERT promoter is disputed. One model features a structure with three stacked parallel G-quadruplex units, while another features an unusual duplex hairpin structure adjoined to two stacked parallel and antiparallel quadruplexes. We report here the results of an integrated structural biology study designed to distinguish between these possibilities. As part of our study, we designed a sequence with an optimized hairpin structure and show that its biophysical and biochemical properties are inconsistent with the structure formed by the hTERT wild-type sequence. By using circular dichroism, thermal denaturation, nuclear magnetic resonance spectroscopy, analytical ultracentrifugation, small-angle X-ray scattering, molecular dynamics simulations and a DNase I cleavage assay we found that the wild type hTERT core promoter folds into a stacked, three-parallel G-quadruplex structure. The hairpin structure is inconsistent with all of our experimental data obtained with the wild-type sequence. All-atom models for both structures were constructed using molecular dynamics simulations. These models accurately predicted the experimental hydrodynamic properties measured for each structure. We found with certainty that the wild-type hTERT promoter sequence does not form a hairpin structure in solution, but rather folds into a compact stacked three-G-quadruplex conformation.
SPARC facilitates the generation of plausible hypotheses regarding underlying biochemical mechanisms by structurally characterizing protein sequence constraints. Such constraints appear as residues co-conserved in functionally related subgroups, as subtle pairwise correlations (i.e., direct couplings), and as correlations among these sequence features or with structural features. SPARC performs three types of analyses. First, based on pairwise sequence correlations, it estimates the biological relevance of alternative conformations and of homomeric contacts, as illustrated here for death domains. Second, it estimates the statistical significance of the correspondence between directly coupled residue pairs and interactions at heterodimeric interfaces. Third, given molecular dynamics simulated structures, it characterizes interactions among constrained residues or between such residues and ligands that: (a) are stably maintained during the simulation; (b) undergo correlated formation and/or disruption of interactions with other constrained residues; or (c) switch between alternative interactions. We illustrate this for two homohexameric complexes: the bacterial enhancer binding protein (bEBP) NtrC1, which activates transcription by remodeling RNA polymerase (RNAP) containing σ 54 , and for DnaB helicase, which opens DNA at the bacterial replication fork. Based on the NtrC1 analysis, we hypothesize possible mechanisms for inhibiting ATP hydrolysis until ADP is released from an adjacent subunit and for coupling ATP hydrolysis to restructuring of σ 54 binding loops. Based on the DnaB analysis, we hypothesize that DnaB ‘grabs’ ssDNA by flipping every fourth base and inserting it into cavities between subunits and that flipping of a DnaB-specific glutamine residue triggers ATP hydrolysis.
Basaltic ring structures (BRSs) are enigmatic, quasi-circular landforms in eastern Washington State that were first recognized in 1965. They remained a subject of geologic scrutiny through the 1970 s and subsequently faded from the spotlight, but recent Mars Orbiter Camera (MOC) images showing morphologically similar structures in Athabasca Valles, Mars, have sparked renewed interest in BRSs. The only known BRSs occur in the Channeled Scabland, a region where catastrophic Pleistocene floods from glacial Lake Missoula eroded into the Miocene flood basalts of the Columbia Plateau. The geologic setting of the martian ring structures (MRSs) is similar; Athabasca Valles is a young channel system that formed when catastrophic aqueous floods carved into a volcanic substrate. This study investigates the formation of terrestrial BRSs and examines the extent to which they are appropriate analogs for the MRSs in Athabasca Valles.
Specific features of the structure formation in rapidly quenched high-cobalt alloy coatings formed by plasma sputtering have been investigated. The structural state of the investigated coatings has been identified by the X-ray diffraction technique. The sequence and kinetics of structural transformations occurring in the specified time-temperature heating regimes have been examined using differential thermal analysis. It has been established that heat generation and crystallization temperature depend on the conditions of formation of bulk amorphous coatings.
Pectin is generally divided into four distinct structural categories, namely homogalacturonan, xylogalacturonan, rhamnogalacturonan I (RG-I) and rhamnogalacturonan II. While much of the structural diversity of homogalacturonan, xylogalacturonan and rhamnogalacturonan II has been elucidated, the structural features of RG-I are less well understood. In this work, we employed multiple complementary analytical techniques to present a detailed structural analysis of RG-I in the model species Arabidopsis thaliana . Starting with highly purified RG-I from different Arabidopsis tissues, we employed comparative linkage and nuclear magnetic resonance analysis along with mass spectrometry analysis of enzymatically digested RG-I oligosaccharides. Besides the presence of the canonical α-1,5-arabinan, β-1,4-galactan, β-1,6-galactan and arabinogalactan RG-I side chains of varying lengths, we show that a large portion of the β-1,6-galactan is terminated by either 4-O-methyl β-glucuronic acid (GlcA) residues or, to a smaller degree, β-GlcA that lacks the Me-ether group. Importantly, O-acetylation of RG-I GalA residues is a minor modification while 10 % of the backbone Rha residues are 3-O-acetylated, and most of the acetylated Rha is additionally branched with β-galactose substituents. Taken together, the combined results of these different analytical techniques present the most comprehensive structural overview of Arabidopsis thaliana RG-I to date.
Worldwide data inventory of rock features associated with meteorite impact structures, including photomicrographs of petrographic features
For apertures above 50 meters, the high structural stiffness and compact packaging of tetrahedral truss make this concept an attractive candidate for the reflector support structure. Various features of a deployable, foldable, doubly curved tetrahedral truss structure are presented as well as methods used to design the truss geometry and to synchronize deployment of the folding elements. An arc division method for distributing truss nodal locations over a doubly curved reflector surface is shown to decrease differences in surface strut lengths and to increase the geometric similarity of all node condigurations in each strut surface. These features enhance the design of a single node and strut synchronizer mechanism for each surface examined. The folding error resulting from using this approach is minimal.
A wind tunnel experiment has been carried out at the NASA Ames Research Center to analyze the evolution of coherent structures from a boundary layer to a shear layer in a turbulent, backward-facing, step flow. A miniature X-wire/cold-wire probe has been used in conjunction with two arrays of cold wires, one aligned in the plane of main shear and the other in the spanwise direction of the flow, to detect and characterize delta-scale organized structures in the outer regions of the flow and to provide detailed information concerning these structures. Kinematic features of the events associated with the large scale structures were analyzed and topological pictures of the evolving flow, as well as the contributions to the Reynolds shear stress components are presented.
Highlights: • New type of IO hybrid semiconductor has been synthesized and reported. • Inorganic (PbI{sub 4}){sup 2−} nano-ribbons are surrounded by organic entities. • Room-temperature optical exciton and charge-transfer features are reported. • Structural and optical mechanisms are useful in nanoscale electronic devices. - Abstract: Synthesis, structural and optical studies of inorganic–organic (IO) hybrid, 1,2-benzyldiammoniumtetraiodo plumbate (H{sub 3}NC{sub 6}H{sub 4}CH{sub 2}NH{sub 3}) PbI{sub 4} are presented. The titled compound crystallizes into triclinic system of P-1(2) space group with mutually surrounded inorganic (PbI{sub 4}){sup 2−} organic (C{sub 7}H{sub 12}N{sub 2}) entities. These one-dimensional IO hybrids are thermally stable up to 300 °C and show room-temperature exciton along with charge-transfer photoluminescence features. Structural and optical mechanisms are discussed for future applications in nanoscaled optoelectronic devices.
Current density has been perceived to play a critical rule for controlling Li deposition morphology and solid electrolyte interphase (SEI). However, the atomic level mechanism of current density on Li deposition and the SEI remains unclear. In this work, based on cryogenic transmission electron microscopy imaging combined with energy dispersive X-ray spectroscopy and electron energy loss spectroscopy electronic structure analyses, we reveal the atomic level correlation of Li deposition morphology and SEI with current density. We discover that increasing current density leads to increased overpotential for Li nucleation and growth, leading to the transition from growth-limited to nucleation-limited mode for Li dendrite. Independence of current density, the electrochemically deposited Li metal (EDLi) exhibits crystalline whisker-like morphology. The SEI formed at low current density (0.1 mA cm -2 ) is monolithic amorphous; while, a current density of above 2 mA cm -2 leads to a mosaic structured SEI, featuring an amorphous matrix with Li 2 O and LiF dispersoids, and the thickness of the SEI increases with the increase of current density. Uniquely, the Li 2 O particles is spatially located at the top surface of the SEI, while LiF is spatially adjacent to the Li-SEI interface. These results highlight the possible tuning of crucial structural and chemical features of EDLi and SEI through altering deposit conditions and consequently direct correlation with electrochemical performance.
Light-matter interactions are ubiquitous in nature and reside at the heart of innumerable technologies. The cascade of processes that occur when a material absorbs a photon of light are exceedingly complex and are interwoven in both space and time, rendering precise determination of the atomic-scale and ultrafast mechanisms immensely challenging. The advent of methods for generating short pulses of light several decades ago led to major advances in understanding the initial moments of light absorption and the resultant effects, though directly interrogating the response of the atoms within the material continued to prove challenging. More recently, methods for generating ultrashort pulses of X-rays and fast electrons have opened the way to probing photoinduced structural dynamics of a wide range of matter in multiple phases. An especially promising laboratory-scale method is ultrafast electron microscopy (UEM), wherein the modalities of conventional transmission electron microscopes (imaging, diffraction, spectroscopy) are extended into the femtosecond temporal regime. Here, the ultrafast imaging and diffraction modalities of UEM were used to study the transient structural aspects of photoexcitation of semiconducting materials (e.g., spatially-resolved electron-phonon coupling, excitation and emission of acoustic phonons, and discrete nanoscale scattering processes). The project had three main objectives: (1) determination of the excitation mechanisms of dense, hypersonic charge-carrier waves and the spatially mediated means by which they couple to the lattice via coherent phonon emission, especially with UEM imaging, wherein effects of nanoscale structural and morphological features on the coupling and relaxation dynamics are expected to dictate nucleation sites and preferred wave vectors, (2) elucidation of photoinduced acoustic-phonon seeding, emergence, propagation, and decay over nanoscale crystal regions and especially with respect to local strain fields and atomic-scale disruptions in lattice order, and (3) interwoven with the first two were efforts aimed at realizing combined angstrom-femtosecond spatiotemporal imaging with UEM. The outcomes and impacts of this project were the generation of new knowledge with respect to fundamental light-matter interactions and, especially, the spatially-mediated excitation and evolution of the structural response of materials following coherent photoexcitation. Importantly, the spatial and temporal resolutions of the UEM imaging modalities used are well-suited for such studies and enable spatially-resolved mechanisms to be determined as a function of atomic order, structural features, and morphology. In addition, ultrafast crystallographic measurements were used to correlate real- and reciprocal-space dynamics in order to determine atomic-scale preferential wave vectors and ultrafast scattering mechanisms, especially as dictated by specimen boundary conditions. The obtained results, as detailed in peer-reviewed publications and presentations, illustrate the importance of ultrafast, angstrom-scale real-space imaging for developing a comprehensive understanding of energy transport and conversion in materials.
For organic photovoltaic (OPV) cells based on the bulk heterojunction (BHJ) structure, it remains challenging to rationally control the degree of phase separation and percolation within blends of donors and acceptors to secure optimal charge separation and transport. Reported is a bottom-up, supramolecular approach to BHJ OPVs wherein tailored hydrogen bonding (H-bonding) interactions between π-conjugated electron donor molecules encourage formation of vertically aligned donor π-stacks while simultaneously suppressing lateral aggregation; the programmed arrangement facilitates fine mixing with fullerene acceptors and efficient charge transport. The approach is illustrated using conventional linear or branched quaterthiophene donor chromophores outfitted with terminal functional groups that are either capable or incapable of self-complementary H-bonding. When applied to OPVs, the H-bond capable donors yield a twofold enhancement in power conversion efficiency relative to the comparator systems, with a maximum external quantum efficiency of 64%. H-bond promoted assembly results in redshifted absorption (in neat films and donor:C 60 blends) and enhanced charge collection efficiency despite disparate donor chromophore structure. Both features positively impact photocurrent and fill factor in OPV devices. Film structural characterization by atomic force microscopy, transmission electron microscopy, and grazing incidence wide angle X-ray scattering reveals a synergistic interplay of lateral H-bonding interactions and vertical π-stacking for directing the favorable morphology of the BHJ.
Ternary bismuth halides form an interesting functional materials class in the context of the closely related Pb halide perovskite photovoltaics, especially given the significantly reduced toxicity of Bi when compared with Pb. The compounds A 3 Bi 2 I 9 (A = K, Rb, Cs) examined here crystallize in two different structure types: the layered defect-perovskite K 3 Bi 2 I 9 type, and the Cs 3 Cr 2 Cl 9 type. The latter structure type features isolated Bi 2 I 9 3– anions. Here, the crystal structures of the ternary iodides are redetermined and a corrected structural model for Rb 3 Bi 2 I 9 , as established by single crystal X-ray diffraction and solid state 87Rb NMR spectroscopy and supported by density functional theory (DFT) calculations is presented. A variety of facile preparation techniques for single crystals, bulk materials, as well as solution-processed thin films are described. The optical properties and electronic structures are investigated experimentally by optical absorption and ultraviolet photoemission spectroscopy and computationally by DFT calculations. Absolute band positions of the valence and conduction bands of these semiconductors, with excellent agreement of experimental and calculated values, are reported, constituting a useful input for the rational interface design of efficient electronic and optoelectronic devices. The different structural connectivity in the two different structure types, somewhat surprisingly, appears to not impact band positions or band gaps in a significant manner. Computed dielectric properties, including the finding of anomalously large Born effective charge tensors on Bi 3+ , suggest proximal structural instabilities arising from the Bi 3+ 6s 2 lone pair. These anomalous Born effective charges are promising for defect screening and effective charge carrier transport. The structural, electronic, and optical properties of the complex bismuth iodides are to some extent similar to the related lead iodide perovskites. In conclusion, the deeper valence band positions in the complex bismuth iodides point to the need for different choices of hole transport materials for Bi-iodide based solar cell architectures.
The goals and objectives of the project summarized in this viewgraph presentation are the following: (1) Develop and demonstrate verified airframe and cryotank structural design and analysis technologies, including damage tolerance, safety, reliability, and residual strength technologies, robust nonlinear shell and cryotank analysis technologies, high-fidelity analysis and design technologies for local structural detail features and joints, and high-fidelity analysis technologies for sandwich structures; (2) Demonstrate low cost, robust materials and processing, including polymeric matrix composite (PMC) and metallic materials and processing, and refractory composite and metallic hot structures materials and processing; (3) Develop and demonstrate robust airframe structures and validated integrated airframe structural concepts, including low cost fabrication and joining, operations efficient designs and inspection techniques (non-destructive evaluation), scale-up and integrated thermal structure tests, and airframe structures IVHM; (4) Demonstrate low cost, robust repair techniques; and (5) Develop verified integrated airframe structural concepts, including integrated structural concepts.
Integrating thermo-responsive polymer switching materials (TRPS) into lithium-ion batteries (LIBs) has been recognized as one of the most effective strategies to prevent thermal runaway under various abuse scenarios. However, the current methods to obtain TRPS cannot satisfy different practical applications. Herein, we develop a versatile strategy for the preparation of various metal carbides (e.g., tungsten carbide, molybdenum carbide) with controllable hierarchical structure that is featured with surface protrusion structure, which is critical for high conductivity and rapid thermal response. Systematic studies of the phase and morphology evolutions by advanced characterizations illustrate that the reducing agent and reduction rate are critical for developing the specific morphology. In conclusion, by using the above-mentioned carbides as the conductive fillers of TRPS, the resulting TRPS with a specially controlled shape exhibits over 5 order of conductivity improvement compared with common carbides with particulate morphology, in addition to reversible shutdown performance and effective thermal abuse protections toward safe LIB operation.
Abstract We present a dataset of structural relaxations of bulk ternary transition metal dichalcogenides (TMDs) computed via plane-wave density functional theory (DFT). We examined combinations of up to two chalcogenides with seven transition metals from groups 4–6 in octahedral (1T) or trigonal prismatic (2H) coordination. The full dataset consists of 672 unique stoichiometries, with a total of 50,337 individual configurations generated during structural relaxation. Our motivations for building this dataset are (1) to develop a training set for the generation of machine and deep learning models and (2) to obtain structural minima over a range of stoichiometries to support future electronic analyses. We provide the dataset as individual VASP xml files as well as all configurations encountered during relaxations collated into an ASE database with the corresponding total energy and atomic forces. In this report, we discuss the dataset in more detail and highlight interesting structural and electronic features of the relaxed structures.