Mechanisms of extensive fracture propagation post-coalescence: A machine learning assisted discovery
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Jin, Yuteng (ORCID:0000000241018894)↗
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Results for “extensions”
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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An extension of Thwaites’ method for turbulent boundary layers
Thwaites developed an approximate method for determining the evolution of laminar boundary layers. The approximation follows from an assumption that the growth of a laminar boundary layer in the presence of pressure gradients could be parameterized solely as a function of the Holstein–Bohlen flow parameter, thus reducing the von Kármán momentum integral to a first-order ordinary differential equation. This method is useful for the analysis of laminar flows, and in computational potential flow solvers to account for the viscous effects. In this work, an approximate method for determining the momentum thickness of a two-dimensional, turbulent boundary layer is proposed following Thwaites’ work. It is shown that the method provides good estimates of the momentum thickness for multiple boundary layers, including both favourable and adverse pressure gradient effects, up to the point of separation. In the limit of high Reynolds numbers, it is possible to derive a criterion for the onset of separation from the proposed model, which is shown to be in agreement with prior empirical observations. The sensitivity of the separation location with respect to upstream perturbations is also analysed through this model for the NASA/Boeing speed bump and the transonic Bachalo–Johnson bump.
17 WIND ENERGY↗
Metallic Borides, La 2 Re 3 B 7 and La 3 Re 2 B 5 , Featuring Extensive Boron–Boron Bonding
We synthesized La 2 Re 3 B 7 and La 3 Re 2 B 5 in single-crystalline form from a molten La/Ni eutectic at 1000°C, in the first example of the flux crystal growth of ternary rare-earth rhenium borides. Both compounds crystallize in their own orthorhombic structure types, with La 2 Re 3 B 7 (space group Pcca) having lattice parameters a = 7.657(2) Å, b = 6.755(1) Å, and c = 11.617(2) Å, and La 3 Re 2 B 5 (space group Pmma) having lattice parameters a = 10.809(2) Å, b = 5.287(1) Å, and c = 5.747(1) Å. Furthermore, the compounds possess three-dimensional framework structures that are built up from rhenium boride polyhedra and boron-boron bonding. La 3 Re 2 B 5 features fairly common B 2 dumbbells, whereas La 2 Re 3 B 7 has unique one-dimensional subunits composed of alternating triangular B3 and trans-B4 zigzag chain fragments. Also observed in La 3 Re 2 B 5 is an unusual coordination of B by an octahedron of La atoms. Electronic band structure calculations predict that La 2 Re 3 B 7 is a semimetal, which is observed in the electrical resistivity data as measured on single crystals, with behavior obeying the Bloch-Grüneisen model and a room-temperature resistivity ρ300K of ~ 375 μΩ cm. The electronic band structure calculations also suggest that La 3 Re 2 B 5 is a regular metal.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Molten Alkali Halide Flux Growth of an Extensive Family of Noncentrosymmetric Rare Earth Sulfides: Structure and Magnetic and Optical (SHG) Properties
Twenty new alkali rare earth thiosilicates and thiogermanates with the general formula ALnTS 4 (A = alkali metal, Ln = lanthanide, and T = Si, Ge) were grown as X-ray diffraction-quality single crystals from molten alkali chloride fluxes. These include KNdSiS4, KPrSiS4, RbLnSiS4 (Ln = Ce, Pr, Nd, Gd, Tb, Dy, and Ho), RbLaGeS 4 , CsLnSiS 4 (Ln = La, Pr, and Nd), and CsLnGeS 4 (La, Ce, Pr, Nd, Eu, Gd, and Tb). Herein, we discuss the use of a molten chloride flux growth approach for the preparation of the title compounds and their structure determination via single-crystal X-ray diffraction. In addition, we comment on the magnetic properties of RbNdSiS 4 , CsNdSiS 4 , CsNdGeS 4 , and CsGdGeS 4 , which were found to be paramagnetic for T = 2–300 K and exhibited negative Weiss temperatures with no obvious antiferromagnetic transition down to 2 K. The optical properties of CsLaGeS 4 and CsNdTS 4 (T = Si, Ge) were measured by UV–vis spectroscopy. Second harmonic generation measurements performed on CsLaGeS 4 confirmed the crystallization of the compound in the noncentrosymmetric orthorhombic space group, P2 1 2 1 2 1 ; CsLaGeS 4 was found to be SHG-active with nearly half the intensity of α-SiO 2 upon irradiation with a Nd:YAG 1064 nm laser, and a semiconductor exhibiting a band gap of 3.60 eV based on UV–vis diffuse reflectance measurements.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Learning from Tomorrow’s Recyclers: Extension of Hands-on Recycled Waste Activity
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
CHARMM-GUI Bicelle Builder : An Extension of Membrane Builder for Modeling and Simulation of Bicelle Systems
Membrane mimetics, such as detergent micelles, nanodiscs, and amphipol complexes, which can provide membrane-like environments while retaining small and soluble features, have been utilized to study membrane proteins. A bicelle, composed of varying lipids and detergents, is a useful membrane mimetic because the lipid-to-detergent ratio, the q-value, can be adjusted to alter the properties of the aggregate, including the thickness and size of the bicelle. However, building a bicelle model for modeling and simulation studies requires nontrivial efforts, even for experts. We introduce CHARMM-GUI Bicelle Builder, a web-based platform that can generate various all-atom bicelle systems via a graphical user interface with all available lipids and detergents in Membrane Builder. To illustrate and validate Bicelle Builder with practical systems, we have modeled and simulated pure bicelles consisting of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids with 1,2-dihexanoyl-sn-glycero-3-phosphocholine (C6DHPC) detergents and protein–bicelle complexes, composed of DMPC with C6DHPC, foscholine-10 (FOS10), and lysophosphatidylcholine-12 (LPC12) detergents. Our simulation results indicate that Bicelle Builder can generate reliable and robust bicelle models with and without proteins that retain DMPC bilayer characteristics. Bicelle Builder is expected to help researchers better understand not only bicelles themselves but also atomistic-level structures of protein–bicelle complexes that are often difficult to access through experimental approaches.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
MLTB: Enhancing Transferability and Extensibility of Density Functional Tight-Binding Theory with Many-body Interaction Corrections
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Extension of structure-reactivity correlations for the hydrogen abstraction reaction to methyl radical and comparison to chlorine atom, bromine atom, and hydroxyl radical
In this study, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp3-hybridized carbon by three electrophilic radicals (X • + HCR 3 → XH + • CR 3 ; X = Cl • , HO • , and Br); the reaction enthalpy effect was represented by the independent variable Δ r H and the polar effect by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH 3 • . In spite of a limited and scattered data base, the resulting least-squares fit [log k 437 (CH 3 • ) = 0.0251(Δ r H) + 0.96(ΣF) 0.56(ΣR) – 19.15] was modestly successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the philicity of CH 3 , may depend on the nature of the substituents.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Development of a Systematic and Extensible Force Field for Peptoids (STEPs)
Peptoids (N-substituted glycines) are a class of biomimetic polymers that have attracted significant attention due to their accessible synthesis and enzymatic and thermal stability relative to their naturally occurring counterparts (polypeptides). While these polymers provide the promise of more robust functional materials via hierarchical approaches, they present a new challenge for computational structure prediction for material design. The reliability of calculations hinges on the accuracy of interactions represented in the force field used to model peptoids. For proteins, structure prediction based on sequence and de novo design has made dramatic progress in recent years; however, these models are not readily transferable for peptoids. Current efforts to develop and implement peptoid-specific force fields are spread out, leading to replicated efforts and a fragmented collection of parameterized sidechains. Here, we developed a peptoid-specific force field containing 70 different side chains, using GAFF2 as starting point. The new model is validated based on the generation of Ramachandran-like plots from DFT optimization compared against force field reproduced potential energy and free energy surfaces as well as the reproduction of equilibrium cis/trans values for some residues experimentally known to form helical structures. In conclusion, equilibrium cis/trans distributions (Kct) are estimated for all parameterized residues to identify which residues have an intrinsic propensity for cis or trans states in the monomeric state.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Predicting Partial Atomic Charges in Metal–Organic Frameworks: An Extension to Ionic MOFs
Molecular simulation is an invaluable tool to predict and understand the usage of metal–organic frameworks (MOFs) for gas storage and separation applications. Accurate partial atomic charges, commonly obtained from density functional theory (DFT) calculations, are often required to model the electrostatic interactions between the MOF and adsorbates, especially when the adsorbates have dipole or quadrupole moments, such as water and CO 2 . Machine learning (ML) models have been previously employed to predict partial charges and avoid the computational cost associated with DFT calculations. However, previous ML models suffer from small training data sets, which limit their scope of application. In this work, we introduce two novel machine learning models, PACMOF2-neutral and PACMOF2-ionic, aimed at predicting the density-derived electrostatic and chemical (DDEC6) partial atomic charges for both neutral and ionic MOFs. These models not only yield DFT-level accuracy at a fraction of the computational cost but also demonstrate a remarkable improvement in prediction of adsorption, as validated with grand canonical Monte Carlo simulations. Furthermore, the robustness and fast computational time of the PACMOF2 models, along with their transferability to other porous materials such as covalent organic frameworks and zeolites, underscores their potential in high-throughput screening of MOFs for diverse applications.
36 MATERIALS SCIENCE↗
Extension of Solvent-Assisted Linker Exchange to Supported Metal–Organic Framework Thin Films
Solvent-assisted linker exchange (SALE) is a common postsynthetic approach used to accommodate metal–organic frameworks (MOFs) for targeted applications. As this technique is relatively untested in immobilized MOF structures, we repeated the generalized SALE approach with ZIF-8 deposited directly onto solid substrates and assessed the results with a variety of techniques, including time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Our methods confirm that the supported films maintain their key structural properties while allowing for linker substitution with foreign species. Alongside experiments, we used computational modeling to quantify the relative energetics of SALE reactions with a variety of linkers. These techniques together reveal that SALE is translatable to immobilized MOFs. Additionally, we recognize how various aspects of the postsynthetic approach can bear consequences for the material’s final micro- and macroscopic properties. Furthermore, the results uncover basic yet critical details needed to inform future efforts to engineer MOF films with functional properties.
Ligands↗
Incorporation of Thioacetate Pendants on a Polyalkenamer Enables High Extensibility
This study focuses on functionalizing polycyclooctene (PCOE) with thioacetate groups using thiol–ene click chemistry. The ethylene thioacetate (EVSA) copolymers produced vary in thioacetate incorporation (4–25 mol %) via a controlled semibatch addition technique with AIBN dosing. Copolymers with 4–14 mol % thioacetate are semicrystalline, while those with 20–25 mol % are amorphous. Increased functionalization correlates with decreased crystallinity and increased stretchability, with the highest functionalization (25 mol %) showing a modulus of 0.045 MPa and 2000% elongation at break. Here, this behavior is due to the pseudoprecise functionalization of the thioacetate pendants and intrinsic cross-linking that occurs during melt processing. Broadband dielectric spectroscopy (BDS) indicates a low activation energy barrier (16 kJ/mol for the β process), suggesting potential self-healing applications.
36 MATERIALS SCIENCE↗