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Coordination Chemistry of Solvated Metal Ions in Soft Donor Solvents
The structures of hexaammine solvated indium(III) and thallium(III) ions in liquid ammonia solution are determined by EXAFS. Both complexes have regular octahedral coordination geometry with mean In-N and Tl-N bond distances of 2.23(1) and 2.29(2) Å, respectively. Ammine solvated thallium(III) in liquid ammonia is characterized with 205Tl NMR measurements. Solvents such as liquid ammonia, N,N-dimethylthioformamide (DMTF), trialkyl and triphenyl phosphite and phosphine are strong electron pair donors and thereby able to form bonds with a large covalent contribution with strong electron pair acceptors. A survey of reported structures of ammine, DMTF, trialkyl and triphenyl phosphite and phosphine solvated metal ions in the solid state and solution is presented. The M-N and M-S bond distances in ammine and DMTF solvated metal ions are compared with the M-O bond distance in the corresponding metal ion hydrates, expected to form mainly electrostatic interactions with metal ions. The d10 metal ions have high ability to form bonds with a high degree of covalency with increasing ability down the group and with decreasing charge of the metal ion. The difference in M-N and M-O bond distances between ammine solvated and hydrated metal ions with the same coordination geometry decreases significantly with the increasing ability of the metal ion to form bonds with a large covalent contribution. This difference correlates well with the covalent bonding index, γM2*r.
Structure of lunar glasses by Raman and soft X-ray spectroscopy.
X-ray spectra and Raman spectra have been measured from individual particles of lunar glasses. Each particle was analyzed separately by electron microprobe. Silicon emission shifts vary between parent rock types and can be interpreted as a range of Si-O distances from 1.612 to 1.637 A. Aluminum emission shifts relate to the amount of 4- and 6-coordinated Al in the glass. Raman spectra show broadened bands. Certain bands recur in many specimens and relate to the main normative minerals for the glass bulk composition, olivine, pyroxene, and anorthite.
Coronal magnetic structures observing campaign. I - Simultaneous microwave and soft X-ray observations of active regions at the solar limb
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Detailed Post-Soft Impact Progressive Damage Assessment for Hybrid Structure Jet Engines
Currently, certification of engine designs for resistance to bird strike is reliant on physical tests. Predictive modeling of engine structural damage has mostly been limited to evaluation of individual forward section components, such as fan blades within a fixed frame of reference, to direct impact with a bird. Such models must be extended to include interactions among engine components under operating conditions to evaluate the full extent of engine damage. This paper presents the results of a study aim to develop a methodology for evaluating bird strike damage in advanced propulsion systems incorporating hybrid composite/metal structures. The initial degradation and failure of individual fan blades struck by a bird were investigated. Subsequent damage to other fan blades and engine components due to resultant violent fan assembly vibrations and fragmentation was further evaluated. Various modeling parameters for the bird and engine components were investigated to determine guidelines for accurately capturing initial damage and progressive failure of engine components. Then, a novel hybrid structure modeling approach was investigated and incorporated into the crashworthiness methodology. Such a tool is invaluable to the process of design, development, and certification of future advanced propulsion systems.
Subcellular Feature-Based Classification of α and β Cells Using Soft X-ray Tomography
The dysfunction of α and β cells in pancreatic islets can lead to diabetes. Many questions remain on the subcellular organization of islet cells during the progression of disease. Existing three-dimensional cellular mapping approaches face challenges such as time-intensive sample sectioning and subjective cellular identification. To address these challenges, we have developed a subcellular feature-based classification approach, which allows us to identify α and β cells and quantify their subcellular structural characteristics using soft X-ray tomography (SXT). We observed significant differences in whole-cell morphological and organelle statistics between the two cell types. Additionally, we characterize subtle biophysical differences between individual insulin and glucagon vesicles by analyzing vesicle size and molecular density distributions, which were not previously possible using other methods. These sub-vesicular parameters enable us to predict cell types systematically using supervised machine learning. We also visualize distinct vesicle and cell subtypes using Uniform Manifold Approximation and Projection (UMAP) embeddings, which provides us with an innovative approach to explore structural heterogeneity in islet cells. This methodology presents an innovative approach for tracking biologically meaningful heterogeneity in cells that can be applied to any cellular system.
Programmable soft valves for digital and analog control
In soft devices, complex actuation sequences and precise force control typically require hard electronic valves and microcontrollers. Existing designs for entirely soft pneumatic control systems are capable of either digital or analog operation, but not both, and are limited by speed of actuation, range of pressure, time required for fabrication, or loss of power through pull-down resistors. Using the nonlinear mechanics intrinsic to structures composed of soft materials—in this case, by leveraging membrane inversion and tube kinking—two modular soft components are developed: a piston actuator and a bistable pneumatic switch. These two components combine to create valves capable of analog pressure regulation, simplified digital logic, controlled oscillation, nonvolatile memory storage, linear actuation, and interfacing with human users in both digital and analog formats. Three demonstrations showcase the capabilities of systems constructed from these valves: 1) a wearable glove capable of analog control of a soft artificial robotic hand based on input from a human user’s fingers, 2) a human-controlled cushion matrix designed for use in medical care, and 3) an untethered robot which travels a distance dynamically programmed at the time of operation to retrieve an object. This work illustrates pathways for complementary digital and analog control of soft robots using a unified valve design.
The Lunar X-ray Observatory (LXO)
X-ray emission from charge exchange recombination between the highly ionized solar wind and neutral material i n Earth's magnetosheath has complicated x-ray observations of celestial objects with x-ray observatories including ROSAT, Chandra, XMM-Newton, and Suzaku. However, the charge-exchange emission can also be used as an important diagnostic of the solar-wind interacting with the magnetosheath. Soft x-ray observations from low-earth orbit or even the highly eccentric orbits of Chandra and XMM-Newton are likely superpositions of the celestial object of interest, the true extra-solar soft x-ray background, geospheric charge exchange, and heliospheric charge exchange. We show that with a small x-ray telescope placed either on the moon, in a similar vein as the Apollo ALSOP instruments, or at a stable orbit near L1, we can begin t o disentangle the complicated emission structure in the soft x-ray band. Here we present initial results of a feasibility study recently funded by NASA t o place a small x-ray telescope on the lunar surface. The telescope operates during lunar night to observe charge exchange interactions between the solar wind and magnetospheric neutrals, between the solar wind and the lunar atmosphere, and an unobstructed view of the soft x-ray background without the geospheric component.
Long-lived photoinduced polar states in metal halide perovskites
Ferroic polarization in hybrid perovskites is crucial for enhancing photovoltaic performance and developing potential electronic applications. Controlling ferroic polarization with an optical field enables probing of ferroic polarization without the unwanted interface ionic effects caused by electronic contacts. This study employs ultrafast near-infrared photoexcitation to control dynamic structural transitions in soft single crystalline hybrid Cu (II) halide perovskites, achieving a long-lived polar state (beyond 104 s) at room temperature. We probe reversible long-lived polar domains under near-infrared photoexcitation using in-situ second harmonic generation microscopy. Theoretical calculation informs the polar lattice microstrain likely induced by anisotropic structure deformation in octahedral copper halide under near-infrared photoexcitation. The reversible slow structure deformation is further confirmed by in-situ photo-induced X-ray diffraction measurement. This work provides a material platform for understanding, controlling, and probing polarization under photoexcitation. Our methodology enables the identification of previously undiscovered polar phases in ferroelectric halide perovskites.
Experimental studies of adaptive structures for precision performance
An experimental study was made of the adaptive structure concept. Experimental data were obtained for a three-longeron, thirteen-bay truss-type test structure. This test structure can be softly suspended as well as rigidly clamped at the central bay. The load-carrying active member consists of a stack of concentric piezoelectric wafers, an eddy current displacement sensor, and a strain gage force sensor. A bridge (or compound) feedback technique developed in communication engineering is applied to the problem of active damping augmentation in adaptive structures. Using collocated force and velocity feedback around the active member, a desired output mechanical impedance can be implemented to maximize energy absorption by the active members. In addition, large gains can be implemented to linearize the active member's nonlinear behavior. Good agreements with linear finite element analysis was found for both static and dynamic structural responses. An 11 percent damping in the first bending mode was demonstrated in the closed-loop damping experiment.
Determination of the structure and heating mechanisms of coronal loops from soft X-ray observations with the solar probe
High resolution soft X-ray imaging from the solar probe is justified in terms of the expected scientific returns which include the determination of the temperature and density structure of a coronal loop. The advantages of the grazing incidence telescope over the multiple pinhole camera are discussed. An instrument package is described which includes a grazing incidence mirror, a thermal prefilter, a three position filter wheel and a focal plane detector baselined as an 800 by 800 back-illuminated charge coupled device. The structural assembly together with the data processing equipment would draw heavily on the designs being developed for the Solar Polar Mission.
Automated 3D cytoplasm segmentation in soft X-ray tomography
Cells’ structure is key to understanding cellular function, diagnostics, and therapy development. Soft X-ray tomography (SXT) is a unique tool to image cellular structure without fixation or labeling at high spatial resolution and throughput. Fast acquisition times increase demand for accelerated image analysis, like segmentation. Currently, segmenting cellular structures is done manually and is a major bottleneck in the SXT data analysis. This paper introduces ACSeg, an automated 3D cytoplasm segmentation model. ACSeg is generated using semi-automated labels and 3D U-Net and is trained on 43 SXT tomograms of immune T cells, rapidly converging to high-accuracy segmentation, therefore reducing time and labor. Furthermore, adding only 6 SXT tomograms of other cell types diversifies the model, showing potential for optimal experimental design. ACSeg successfully segmented unseen tomograms and is published on Biomedisa, enabling high-throughput analysis of cell volume and structure of cytoplasm in diverse cell types.
The solar/interplanetary event of 14 April 1994 observed by Yohkoh/SXT
The polar crown event of April 14 1994 is one of the largest scale eruptive events observed by the Yohkoh/SXT. Associated with the formation of an arcade of soft X-ray loops at the Sun was the detection of an interplanetary forward/reverse shock event by the Ulysses spacecraft some 4-7 days later. The relationship between the coronal and interplanetary signatures of these events is important if we are to address fully the initialization and consequent acceleration of interplanetary phenomena, such as CMEs and counter-streaming electrons, originating at the Sun. From detailed analysis of the energetics of the arcade formed during the eruption of April 14 1994, we find peak temperatures and emission measures of approximately 5MK and approximately 10(exp 48)cm(exp -3) respectively. The total thermal content of the arcade loop structure observed in soft X-rays is calculated to be some 5 x 10(exp 29) ergs. The development of these parameters as the event proceeds and their relationship to the dynamics of the eruption are investigated. Although spanning a longitudinal range of some 150 degrees the April 14 event displayed the typical helmet streamer structure normally associated with coronal mass ejections These helmet streamers are thought to be related to the global solar magnetic field through the heliospheric current sheet (HCS). The arcade formation, together with the eruption of material into interplanetary space, signifies a large-scale reconfiguration of the coronal magnetic field. We examine the effects of the formation of such a coronal arcade structure on the HCS and discuss the dynamics involved with the passage of a large scale disturbance through the interplanetary magnetic field.
Genetic control of morphological transitions in a coacervating protein template
Nature routinely exploits liquid–liquid phase separation (LLPS) of proteins to control the assembly and mineralization of hybrid materials. Here, we show that fusion of the Car9 silica-binding peptide to an elastin-like polypeptide (ELP) yields temperature- and sequence-programmable soft matter templates for the synthesis of silicified architectures ranging in size from nanometers to micrometers. Specifically, we demonstrate unprecedented control over the diameter of silica nanoparticles (SiNP) in the 30–60 nm range with 4 nm precision, show that a single arginine residue (R4) in the Car9 sequence underpins the transition from micelles to proteinosomes, and find that substitutions in other basic residues modulate electrostatic repulsion and solvation to enable access to kinetically trapped species. These structures, which include interconnected micelles, small (∼200 nm) and large (>5 µm) vesicles, are readily visualized by SEM imaging following silicification. Molecular dynamics (MD) simulations and AlphaFold predictions reveal that mutations in positively charged residues alter interfacial packing, hydration, and conformational freedom of the silica-binding segments. Overall, our results establish sequence and thermal energy as synergistic levers for morphological control across length scales using solid-binding ELPs and establish mineralization as a powerful tool to visualize the structure of dynamic soft matter assemblies.
Active member bridge feedback control for damping augmentation
An active damping augmentation approach using active members in a structural system is described. The problem of maximizing the vibration damping in a lightly damped structural system is considered using the analogy of impedance matching between the load and source impedances in an electrical network. The proposed active damping augmentation approach therefore consists of finding the desired active member impedances that maximize the vibration damping, and designing a feedback control in order to achieve desired active member impedances. This study uses a bridge feedback concept that feeds back a combination of signals from sensors of the axial force and relative velocity across the active member to realize the desired active member impedance. The proposed active damping augmentation approach and bridge feedback concept were demonstrated on a three-longeron softly suspended truss structure.
Cryo-electron tomography related radiation-damage parameters for individual-molecule 3D structure determination
To understand the dynamic structure–function relationship of soft- and biomolecules, the determination of the three-dimensional (3D) structure of each individual molecule (nonaveraged structure) in its native state is sought-after. Cryo-electron tomography (cryo-ET) is a unique tool for imaging an individual object from a series of tilted views. However, due to radiation damage from the incident electron beam, the tolerable electron dose limits image contrast and the signal-to-noise ratio (SNR) of the data, preventing the 3D structure determination of individual molecules, especially at high-resolution. Although recently developed technologies and techniques, such as the direct electron detector, phase plate, and computational algorithms, can partially improve image contrast/SNR at the same electron dose, the high-resolution structure, such as tertiary structure of individual molecules, has not yet been resolved. Here, we review the cryo-electron microscopy (cryo-EM) and cryo-ET experimental parameters to discuss how these parameters affect the extent of radiation damage. This discussion can guide us in optimizing the experimental strategy to increase the imaging dose or improve image SNR without increasing the radiation damage. With a higher dose, a higher image contrast/SNR can be achieved, which is crucial for individual-molecule 3D structure. With 3D structures determined from an ensemble of individual molecules in different conformations, the molecular mechanism through their biochemical reactions, such as self-folding or synthesis, can be elucidated in a straightforward manner.
ROSAT EUV and soft X-ray studies of atmospheric composition and structure in G191-B2B
Previous studies of the hot DA white dwarf GI91-B2B have been unable to determine whether the observed soft X-ray and EUV opacity arises from a stratified hydrogen and helium atmosphere or from the presence of trace metals in the photosphere. New EUV and soft X-ray photometry of this star, made with the ROSAT observatory, when analyzed in conjunction with the earlier data, shows that the stratified models cannot account for the observed fluxes. Consequently, we conclude that trace metals must be a substantial source of opacity in the photosphere of G191-B2B.
Navigating the Expansive Landscapes of Soft Materials: A User Guide for High-Throughput Workflows
Synthetic polymers are highly customizable with tailored structures and functionality, yet this versatility generates challenges in the design of advanced materials due to the size and complexity of the design space. Thus, exploration and optimization of polymer properties using combinatorial libraries has become increasingly common, which requires careful selection of synthetic strategies, characterization techniques, and rapid processing workflows to obtain fundamental principles from these large data sets. Herein, we provide guidelines for strategic design of macromolecule libraries and workflows to efficiently navigate these high-dimensional design spaces. We describe synthetic methods for multiple library sizes and structures as well as characterization methods to rapidly generate data sets, including tools that can be adapted from biological workflows. We further highlight relevant insights from statistics and machine learning to aid in data featurization, representation, and analysis. This Perspective acts as a “user guide” for researchers interested in leveraging high-throughput screening toward the design of multifunctional polymers and predictive modeling of structure–property relationships in soft materials.