High-entropy materials for catalysis: A new frontier
High-entropy materials with compositional and structural complexities introduce a transformative opportunity for catalysis.
36 MATERIALS SCIENCE↗
SEARCH · Engineering Papers
Results for “structural complexity”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Field-controlled dynamics of skyrmions and monopoles
Magnetic monopoles, despite their ongoing experimental search as elementary particles, have inspired the discovery of analogous excitations in condensed matter systems. In chiral condensed matter systems, emergent monopoles are responsible for the onset of transitions between topologically distinct states and phases, such as in the case of transitions from helical and conical phase to A-phase comprising periodic arrays of skyrmions. By combining numerical modeling and optical characterizations, we describe how different geometrical configurations of skyrmions terminating at monopoles can be realized in liquid crystals and liquid crystal ferromagnets. We demonstrate how these complex structures can be effectively manipulated by external magnetic and electric fields. Furthermore, we discuss how our findings may hint at similar dynamics in other physical systems and their potential applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Multiplexed CRISPR-Cas9 mutagenesis of rice PSBS1 noncoding sequences for transgene-free overexpression
Understanding CRISPR-Cas9’s capacity to produce native overexpression (OX) alleles would accelerate agronomic gains achievable by gene editing. To generate OX alleles with increased RNA and protein abundance, we leveraged multiplexed CRISPR-Cas9 mutagenesis of noncoding sequences upstream of the rice PSBS1 gene. We isolated 120 gene-edited alleles with varying non-photochemical quenching (NPQ) capacity in vivo—from knockout to overexpression—using a high-throughput screening pipeline. Overexpression increased OsPsbS1 protein abundance two- to threefold, matching fold changes obtained by transgenesis. Increased PsbS protein abundance enhanced NPQ capacity and water-use efficiency. Across our resolved genetic variation, we identify the role of 5'UTR indels and inversions in driving knockout/knockdown and overexpression phenotypes, respectively. Complex structural variants, such as the 252-kb duplication/inversion generated here, evidence the potential of CRISPR-Cas9 to facilitate significant genomic changes with negligible off-target transcriptomic perturbations. Our results may inform future gene-editing strategies for hypermorphic alleles and have advanced the pursuit of gene-edited, non-transgenic rice plants with accelerated relaxation of photoprotection.
60 APPLIED LIFE SCIENCES↗
Prediction and Biochemical Demonstration of a Catabolic Pathway for the Osmoprotectant Proline Betaine
Through the use of genetic, enzymatic, metabolomic, and structural analyses, we have discovered the catabolic pathway for proline betaine, an osmoprotectant, in Paracoccus denitrificans and Rhodobacter sphaeroides. Genetic and enzymatic analyses showed that several of the key enzymes of the hydroxyproline betaine degradation pathway also function in proline betaine degradation. Metabolomic analyses detected each of the metabolic intermediates of the pathway. The proline betaine catabolic pathway was repressed by osmotic stress and cold stress, and a regulatory transcription factor was identified. We also report crystal structure complexes of the P. denitrificans HpbD hydroxyproline betaine epimerase/proline betaine racemase with l-proline betaine and cis-hydroxyproline betaine.
59 BASIC BIOLOGICAL SCIENCES↗
Distortions in IR Spectra Related to Registration Conditions: II. The Influence of Scattering
We consider distortions of the shapes of absorption bands of strongly scattering samples in the spectra of molecules adsorbed on the surface of dispersed solids. We show that the influence of the scattering on IR spectra of dispersed samples is not reduced merely to a weakening of the intensity of the transmitted light, but, rather, the scattering affects the contour of a spectral band due to changes in the refractive index of the substance in the range of the absorption band. Using carbon dioxide adsorbed on a NaX zeolite as an example, we demonstrate two methods for taking into account the contribution of the scattering to the spectra of surface compounds: the registration of the “diffuse-transmission” spectrum and placing a sample into an immersion liquid, for which liquid oxygen is used. The obtained spectra indicate that, if the zeolite is saturated with the adsorbate, the band of the antisymmetric stretching vibration of CO{sub 2} molecules broadens and reveals a complex structure as a result of the resonant dipole–dipole interaction between adsorbed molecules.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Complementary study of the internal porous silicon layers formed under high-dose implantation of helium ions
The surface layers of Si(001) substrates subjected to plasma-immersion implantation of helium ions with an energy of 2–5 keV and a dose of 5 × 10{sup 17} cm{sup –2} have been investigated using high-resolution X-ray reflectivity, Rutherford backscattering, and transmission electron microscopy. The electron density depth profile in the surface layer formed by helium ions is obtained, and its elemental and phase compositions are determined. This layer is found to have a complex structure and consist of an upper amorphous sublayer and a layer with a porosity of 30–35% beneath. It is shown that the porous layer has the sharpest boundaries at a lower energy of implantable ions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Scattering of particles with internal degrees of freedom
The scattering of particles with a small number of internal degrees of freedom is considered. Billiard formalism is used to study the scattering of two such structurally complex particles. The main scattering characteristics are found. Various types of scattering modes are revealed. In particular, a mode is detected when the velocity of motion of such particles away from each other is higher than their approach velocity before the collision. The scattering of such particles is shown to occur after a finite number of collisions. A generalized Newton law is proposed for the collision of particles with a small number of degrees of freedom, and the form of the effective coefficient of restitution is found.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Holes localized in nanostructures in an external magnetic field: g-factor and mixing of states
The energy spectrum and wave functions of holes in the valence band in semiconductor nanosystems, including quantum wells, quantum wires, and quantum dots, in an external magnetic field are theoretically investigated. The dependence of Zeeman splitting of the hole ground state upon variation in the size-quantization parameters with regard to the complex structure of the valence band and magnetic field-induced mixing of hole states is traced. Analytical formulas for describing the Zeeman effect in the valence band in the limiting cases of a quantum disk, spherically symmetric quantum dot, and quantum wire are presented. It is demonstrated that the g-factor of a hole is extremely sensitive to the hole-state composition (heavy or light hole) and, consequently, to the geometry of the size-quantization potential.
36 MATERIALS SCIENCE↗
MBE growth of ultrathin III–V nanowires on a highly mismatched SiC/Si(111) substrate
The possibility in principle of growing III–V GaAs, AlGaAs, and InAs nanowires (NWs) on a silicon substrate with a nanometer buffer layer of silicon carbide is demonstrated for the first time. The diameter of these NWs is smaller than that of similar NWs grown on a silicon substrate. In particular, the minimum diameter is less than 10 nm for InAs NWs. In addition, it was assumed on the basis of photoluminescence measurements that, when AlGaAs NWs are grown on these substrates, a complex structure is formed due to the self-organized formation of AlGaAs quantum dots with a lower content of aluminum, embedded in the NWs.
36 MATERIALS SCIENCE↗
Isoelectronic Oxygen Centers and Conductivity of CdS Crystals Compared with PbS Crystals
The influence of oxygen on the electrical properties of PbS are well known. The goal of this study is to compare and reveal this phenomenon in CdS(O) single crystals, which we have studied in detail previously. The experiments are performed for CdS single crystals with a known oxygen concentration, deviation from stoichiometry, and definite set of intrinsic point defects. They allow us to confirm the results described for PbS and clarify their nature. It is shown that the phenomenon is based on the capture of free charge carriers— electrons—by acceptor-like isoelectronic O{sub S} centers with the subsequent formation of associates having a complex structure. Previous conclusions on the dissolution mechanism of oxygen in CdS with deviations from stoichiometry are confirmed. Variations in the electrical properties in oxygen-activated PbS(O), similarly to CdS(O), showed that isoelectronic oxygen centers O{sub S} are present in lead sulfide.
36 MATERIALS SCIENCE↗
DReAM: Demand Response Architecture for Multi-level District Heating and Cooling Networks
In this paper, we exploit the inherent hierarchy of heat exchangers in District Heating and Cooling (DHC) networks and propose DReAM, a novel Demand Response (DR) architecture for Multi-level DHC networks. DReAM serves to economize system operation while still respecting comfort requirements of individual consumers. Contrary to many present day DR schemes that work on a consumer level granularity, DReAM works at a level of hierarchy above buildings, i.e. substations that supply heat to a group of buildings. This improves the overall DR scalability and reduce the computational complexity. In the first step of the proposed approach, mathematical models of individual substations and their downstream networks are abstracted into appropriately constructed low-complexity structural forms. In the second step, this abstracted information is employed by the utility to perform DR optimization that determines the optimal heat inflow to individual substations rather than buildings, in order to achieve the targeted objectives across the network. We validate the proposed DReAM framework through experimental results under different scenarios on a test network.
Bhattacharya, Saptarshi↗
High-Pressure Electrides: A Quantum Chemical Perspective
It has long been assumed that all matter will adopt simple close-packed lattices and become metallic under pressure, in accordance with the Thomas–Fermi–Dirac (TFD) model. However, this model struggles to explain pressure-driven complex structural transitions that have been observed in elements, including sodium, challenging our conventional understanding of compressed matter. Moreover, in stark contrast to the TFD model, first-principles calculations suggest that various elements and compounds become electrides under pressure. Electrides, characterized by concentrations of charge density at interstitial regions, can be thought of as ionic compounds where electrons behave as the anions. Though ambient-pressure molecular electrides have been extensively studied via experiments and computations, high-pressure electrides (HPEs) are not well-understood. The identification and characterization of HPEs have been, to date, based purely on theory, including topological analysis of the electron density and the electron localization function. Here, we review these theoretical analysis tools and suggest guidelines that can be used to classify systems as electrides. Moreover, we describe models used to rationalize the electronic structure of HPEs, drawing parallels with ambient-pressure molecular systems, and encourage the development of experimental techniques that provide evidence for the theoretically calculated charge localization.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Direct Simulations of Coupled Transport and Reaction on Nano-Scale X-Ray Computed Tomography Images of Platinum Group Metal-Free Catalyst Cathodes
The nano/micro-scale geometry of polymer electrolyte fuel cell (PEFC) catalyst layers critically affects cell performance. The small length scales and complex structure of these composite layers make it challenging to analyze cell performance and physics at the particle scale by experiment. We present a computational method to simulate transport and chemical reaction phenomena at the pore/particle-scale and apply it to a PEFC cathode with platinum group metal free (PGM-free) catalyst. Here, we numerically solve the governing equations for the physics with heterogeneous oxygen diffusion coefficient and proton conductivity evaluated using the actual electrode structure and ionomer distribution obtained using nano-scale resolution X-ray computed tomography (nano-CT). Using this approach, the oxygen concentration and electrolyte potential distributions imposed by the oxygen reduction reaction are solved and the impact of the catalyst layer structure on performance is evaluated.
36 MATERIALS SCIENCE↗
Vidyut3d: A Non-Equilibrium Plasma Modeling Tool [SWR-24-101]
Vidyut3d is a massively-parallel plasma-fluid solver for low-temperature plasmas (LTPs) that supports both local field (LFA) and local mean energy (LMEA) approximations, as well as complex gas and surface-phase chemistry. The solver supports 2D and 3D domains, and uses AMReX's adaptive mesh refinement capabilities to increase the grid resolution around complex structures (e.g. streamer heads and sheaths) while maintaining a tractable problem size. Vidyut specializes in simulating various types of gas-phase discharges, as well as plasma/surface interactions and surface chemistry (e.g. for plasma-mediated catalysis applications). The solver also supports hybrid CPU/GPU parallelization strategies, and has demonstrated excellent scaling on various HPC architectures for problem sizes consisting of O(100 M) control volumes.
Sitaraman, Hariswaran↗
Evaluating Global Streamflow Simulations by a Physically-based Routing Model Coupled with the Community Land Model
Accurately simulating hydrological processes such as streamflow is important in land surface modeling because they can influence other land surface processes, such as carbon cycle dynamics, through various interaction pathways. This study aims to evaluate the global application of a recently developed Model for Scale Adaptive River Transport (MOSART)coupled with theCommunity Land Model, version 4 (CLM4). To support the global implementation of MOSART, a comprehensive global hydrography dataset has been derived at multiple resolutions from different sources. The simulated runoff fields are first evaluated against the composite runoff map from theGlobal RunoffData Centre (GRDC). The simulated streamflow is then shown to reproduce reasonably well the observed daily andmonthly streamflow at over 1600 of the world’smajor river stations in terms of annual, seasonal, and daily flow statistics. The impacts of model structure complexity are evaluated, and results show that the spatial and temporal variability of river velocity simulated byMOSART is necessary for capturing streamflow seasonality and annual maximum flood. Other sources of the simulation bias include uncertainties in the atmospheric forcing, as revealed by simulations driven by four different climate datasets, and human influences, based on a classification framework that quantifies the impact levels of large dams on the streamflow worldwide.
global evaluation, routing model, community land m↗
Experimental investigation of the crush performance of prepreg platelet molding compound tubes
This work presents an experimental study characterizing the crush performance of hollow cylindrical tubes made with prepreg platelet molding compound (PPMC). PPMC is a composite material system that uses platelets from chopped and slit unidirectional prepreg as the basis for a molding compound. This material system has a higher fiber volume fraction and better mechanical properties than traditional short fiber systems and can be molded into complex geometries unlike continuous fiber systems. As such, this material system shows promise for use with complex structural members in vehicles. The failure morphology and specific energy absorption of the material are evaluated with different thickness-to-diameter geometries and test speeds. In addition, this work investigates how PPMC components compare to traditional continuous fiber components and finds that PPMC performs as well as continuous fiber layups with similar effective laminate stiffnesses.
Materials Science↗
Performance evaluation of the USGS velocity model for the San Francisco Bay Area
In this study, we evaluated the performance of the United States Geological Survey velocity model developed for the San Francisco Bay Area (SFBA), version 21.1. The evaluation was performed through high-resolution three-dimensional physics-based ground motion simulations of seven small-magnitude earthquakes (ranging from magnitude 3.8 to 4.4) that occurred on the eastern side of the San Francisco Bay. The simulations were performed in the frequency range from 0 to 5 Hz with a minimum shear-wave velocity of 250 m/s, which allowed the capture of wave propagation effects of the near-surface soft materials that characterize local basins. Based on the direct comparison of Fourier amplitude spectra between recorded and simulated ground motions for more than 250 stations, we found that the velocity model generally performs well in the frequency range of 0.2–5 Hz. The median value of the Fourier amplitude residuals was found to be near zero for all seven earthquakes. The slight over-prediction of 0.2 log-natural units at frequencies above 3 Hz in our simulations was attributed to the potentially inaccurate representation of the source radiation pattern by a double-couple point source model, and simple representation of shallow small-scale underground structural complexity in the velocity model. Maps of spectral amplitude differences between the simulated and recorded data were used to identify areas responsible for systematic ground motion over-predictions or under-predictions. For example, while some sub-domains over soft sediments show over-prediction patterns, the block east of the Hayward fault is prone to exhibit patterns of under-prediction. These maps can be used to guide future refinements of the SFBA velocity model. Since our simulation methodology allows for the decoupling of the source and wave propagation effects, the ground motion data generated by our simulations can also be used to quantify the epistemic uncertainty due to the velocity model, in empirically based ground motion estimates for the SFBA.
58 GEOSCIENCES↗
Improving 3D reconstruction quality for root phenotyping: assessing the impact of camera calibration and imaging parameters
Arate 3D reconstruction is essential for high-throughput plant phenotyping, particularly for studying complex structures such as root systems. While photogrammetry and Structure from Motion (SfM) techniques have become widely used for 3D root imaging, the camera settings used are often underreported in studies, and the impact of camera calibration on model accuracyccu remains largely underexplored in plant science. In this study, we systematically evaluate the effects of focus, aperture, exposure time, and gain settings on the quality of 3D root models made with a multi-camera scanning system. We show through a series of experiments that calibration significantly improves model quality, with focus misalignment and shallow depth of field (DoF) being the most important factors affecting reconstruction accuracy. Our results further show that proper calibration has a greater effect on reducing noise than filtering it during post-processing, emphasizing the importance of optimizing image acquisition rather than relying solely on computational corrections. This work improves the repeatability and accuracy of 3D root imaging for phenotyping pipelines by giving useful calibration guidelines. This leads to better trait quantification for use in crop research and plant breeding in downstream analysis.
3D reconstruction↗