Seeing Beyond the Surface -- Structural Dynamics Identification through Multi-View Radiographic Imaging
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Rohe, Daniel Peter [Sandia National Laboratories (↗
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Control and dynamics study for the satellite power system. Volume 1: MPTS/SPS collector dynamic analysis and surface deformation
The basic dynamic properties and performance characteristics of the microwave power transmission satellite antenna were analyzed in an effort to develop criteria, requirements, and constraints for the control and structure design. The vibrational properties, the surface deformation, and the corresponding scan loss under the influence of disturbances are considered.
Wang, S. J.↗
Assessment of Near-Angle Scatter on Exo-Earth Coronagraphy
A first order single surface analysis indicates that, to enable coronagraphic detection and characterization of exo-Earth planets, near angle scatter must be considered when specifying optical surfaces for a potential Habitable World Observatory. Based on arbitrary error budget allocations and using Rayleigh-Rice Vector Scatter Theory, Generalized Harvey-Shack Scalar Scatter Theory, and Greynolds Approximation, ‘placeholder’ specifications for the primary mirror are derived: Static Surface Roughness < 1 nm rms, and Dynamic Surface Roughness < 1 pm PV. These specifications will change once error budget allocations are defined. Analysis does not include scatter from more than just the primary mirror, coating structure, edges, contamination, micrometeoroid impacts, etc.
H. Philip Stahl↗
From bulk to surface: Structure and dynamics of amorphous alumina from deep potential molecular dynamics
Understanding the atomic-scale structure and dynamics of amorphous oxide surfaces is essential for interpreting their chemical reactivity, mechanical stability, and interfacial behavior, yet direct experimental characterization remains challenging. We employ Deep Potential (DP) molecular dynamics to generate large-scale, ab initio -quality models of amorphous Al 2 O 3 bulk glasses and melt-quenched free surfaces, enabling a quantitative analysis of both structure and relaxation dynamics with statistical confidence inaccessible to direct ab initio simulation. The trained DP model reproduces experimental liquid and glass structure, captures the cooling-rate dependence of the bulk glass transition, and corrects systematic biases in the polyhedral populations predicted by widely used classical force fields. At the free surface, mass density recovers to bulk values over ~10 Å, while local coordination requires a slightly wider subsurface region to fully converge. The outermost layer is oxygen-enriched, exhibits altered polyhedral connectivity with contracted Al–O bonds, and hosts a broad population of under-coordinated motifs (notably AlO 3 and OAl 2 ) whose abundances are governed by glass stability. These under-coordinated surface motifs exhibit distinct vibrational signatures and occur as locally paired Lewis acid and Brønsted base sites consistent with bond-valence compensation, yet remain spatially dispersed rather than aggregating into extended clusters. Despite this pronounced structural heterogeneity, surface relaxation and the glass-transition temperature remain comparable to their bulk counterparts, suggesting that the disordered surface is kinetically stable once formed. Together, these results establish a molecular-level picture of amorphous alumina surfaces and demonstrate the capability of machine-learned potentials to resolve structure–property relationships in disordered oxide interfaces.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Liquid oxygen sloshing in Space Shuttle External Tank
This paper describes a numerical simulation of the hydrodynamics within the liquid oxygen tank of the Space Shuttle External Tank during liftoff. Before liftoff, the tank is filled with liquid oxygen (LOX) to approximately 97 percent with the other 3 percent containing gaseous oxygen (GOX) and helium. During liftoff, LOX is drained from the bottom of the tank, and GOX is pumped into the tank's ullage volume. There is a delay of several seconds before the GOX reaches the tank which causes the ullage pressure to decrease for several seconds after liftoff; this pressure 'slump' is a common phenomenon in rocket propulsion. When four slosh baffles were removed from the tank, the ullage gas pressure dropped more rapidly than in all previous flights. The purpose of this analysis was to determine whether the removal of the baffles could have caused the increased pressure 'slump' by changing the LOX surface dynamics. The results show that the LOX surface undergoes very high vertical accelerations (up to 5 g) and, therefore, splashing almost certainly occurs. The number of baffles does not affect the surface if the structural motion is assumed; but, the number of baffles may affect the structural motion of the tank.
Kannapel, M. D.↗
Acoustic characteristics and dynamic structural loading of an ASTOVL aircraft in hover
Measurements of surface dynamic loading and freestream acoustics were made for an ASTOVL model in hover, to quantify the effects of elevated temperature on the acoustic field and surface loading. Data were acquired for a many combinations of operating parameters: model height above the ground plane, nozzle pressure ratio, and jet exit stagnation temperature. For many conditions, strong tones were observed, with amplitudes up to 150 dB. The frequencies of the strongest tones were well predicted by a model assuming feedback between the nozzle exit and the ground plane. The model also accounts for many of the variations in frequency observed with changes in model height, nozzle pressure ratio, and jet temperature. Broadband sound pressure levels up to 170 dB were also recorded. The maximum levels occurred at approximately 3 equivalent jet diameters above the ground plane. For the majority of the cases, the increase in noise due to temperature was less than expected based on free jet correlations.
Mitchell, L. K.↗
The interaction of plume heads with compositional discontinuities in the Earth's mantle
The effects of compositional discontinuities of density and viscosity in the Earth's mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique. Three specific problems are considered: (1) a plume head rising away from a deformable interface, (2) a plume head passing through an interface, and (3) a plume head approaching the surface of the Earth. For the case of a plume attached to a free-surface, the calculated time-dependent plume shapesare compared with experimental results. Two principle modes of plume head deformation are observed: plume head elingation or the formation of a cavity inside the plume head. The inferred structure of mantle plumes, namely, a large plume head with a long tail, is characteristic of plumes attached to their source region, and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high- to low-viscosity region. As a rising plume head approaches the upper mantle, most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle. If the plume head moves from a high- to low-viscosity region, the plume head becomes significantly elongated and, for the viscosity contrasts thought to exist in the Earth, could extend from the 670 km discontinuity to the surface. Plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry. The dynamic surface topography induced by plume heads is bell-shaped when the top of the plume head is at depths greater than about 0.1 plume head radii. As the plume head approaches the surface and spreads, the dynamic topography becomes plateau-shaped. The largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical, and the surface expression of these stresses is likely to be dominated by radial extension. As the plume spreads, compressional stresses on the surface are produced beyond the edges of the plume; consequently, extensional features will be produced above the plume head and may be surrounded by a ring of compressional features.
Manga, Michael↗
Sea surface height variability during 1986-1988 in the tropical Pacific Ocean
A description of the sea surface height variabilities during 1986-1988 in the tropical Pacific Ocean is presented on the basis of Geosat altimeter data and a tropical Pacific Ocean GCM (OGCM) forced with observed winds from Florida State University. Both data sets are validated against in situ sea-level measurements at 12 selected sea-level stations in the equatorial Pacific and were found to be in good agreement with these measurements with correlation coefficients of 0.69 for Geosat and 0.71 for OGCM. The Geosat altimeter data are capable of describing sea surface height variabilities during 1986-1988 in the tropical Pacific, in particular, the seasonal cycle, the 1987 El Nino and 1988 La Nina episodes, and the December 1986 equatorial Kelvin wave event. The OGCM-simulated surface dynamic height is found to be sensitive to different surface wind products.
Chao, YI↗
Fluorophilic Sigma(σ)‐Lock Self‐Healable Copolymers
Abstract Although F‐Containing molecules and macromolecules are often used in molecular biology to increase the binding with Lewis acidic groups by introducing favorable C−F dipoles, there is virtually no experimental evidence and limited understanding of the nature of these interactions, especially their role in synthetic polymeric materials. These studies elucidate the molecular origin of inter‐ and intra‐Chain interactions responsible for self‐healing of F‐Containing copolymers composed of pentafluorostyrene and n‐butyl acrylate units (p(PFS/nBA). Guided by dynamic surface oscillating force (SOF) and spectroscopic measurements supported by molecular dynamics (MD) simulations, these studies show that the reformation of σ‐σ orbitals in −C−F of PFS and CH 3 CH 2 − of nBA units enables the recovery of entropic energy via fluorophilic‐σ‐lock van der Waals forces when PFS/nBA molar ratios are ~50/50. The strength of these interactions determined experimentally for self‐healable PFS/nBA compositions is in the order ~0.3 kcal/mol which primarily comes from fluorophilic‐σ‐lock (~70 %) contributions. These interactions are significantly diminished for non‐self‐healable counterparts. Strongly polarized −C−F σ orbitals create lateral dipolar forces enhancing the affinity towards −C−H orbitals, facilitating energetically favorable interactions. Entropic recovery driven by non‐Covalent bonding offers a valuable tool in designing materials with unique functionalities, particularly self‐healable batteries and energy storage devices.
Gaikwad, Samruddhi↗
Fluorophilic Sigma(σ)‐Lock Self‐Healable Copolymers
Although F-Containing molecules and macromolecules are often used in molecular biology to increase the binding with Lewis acidic groups by introducing favorable C−F dipoles, there is virtually no experimental evidence and limited understanding of the nature of these interactions, especially their role in synthetic polymeric materials. These studies elucidate the molecular origin of inter- and intra-Chain interactions responsible for self-healing of F-Containing copolymers composed of pentafluorostyrene and n-butyl acrylate units (p(PFS/nBA). Guided by dynamic surface oscillating force (SOF) and spectroscopic measurements supported by molecular dynamics (MD) simulations, these studies show that the reformation of σ-σ orbitals in −C−F of PFS and CH 3 CH 2 − of nBA units enables the recovery of entropic energy via fluorophilic-σ-lock van der Waals forces when PFS/nBA molar ratios are ~50/50. The strength of these interactions determined experimentally for self-healable PFS/nBA compositions is in the order ~0.3 kcal/mol which primarily comes from fluorophilic-σ-lock (~70 %) contributions. These interactions are significantly diminished for non-self-healable counterparts. Strongly polarized −C−F σ orbitals create lateral dipolar forces enhancing the affinity towards −C−H orbitals, facilitating energetically favorable interactions. Entropic recovery driven by non-Covalent bonding offers a valuable tool in designing materials with unique functionalities, particularly self-healable batteries and energy storage devices.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ternary and Quaternary Nickel-Iron-Oxide-Based Thin Films as Oxygen Evolution Reaction Catalysts in Alkaline Media
Alkaline water electrolyzers are a promising technology for energy storage and conversion through the electrochemical production of hydrogen, however the slow kinetics of the oxygen evolution reaction (OER) pose a major challenge. The alkaline environment enables the use of non-Pt-group metals as OER catalysts, in particular NiFe-based materials. In this study, Mn and/or Cr were elementally mixed with NiFe to further improve the OER catalyst properties through a controlled, systematic synthesis process involving thin films prepared by electron beam-induced physical vapor deposition (PVD). By exploring both simultaneous co-deposition and serial deposition of the different metals, the OER performance was investigated as a function of both the location of Mn or Cr in the multi-metal NiFe-based catalysts and the difference between surface versus bulk mixing. The distinct differences in the redox dynamics, surface oxidation, and stability of the seven studied catalysts reveal metal Cr- and/or Mn-overlayers as a promising synthesis approach for fine-tuning of catalyst properties and improving the OER performance.
Alkaline Water Electrolysis↗
Semiclassical theory of unimolecular dissociation induced by a laser field
A semiclassical nonperturbative theory of direct photodissociation in a laser field is developed in which photon absorption and dissociation are treated in a unified fashion. This is achieved by visualizing nuclear dynamics as a representative particle moving on electronic-field surfaces. Methods are described for calculating dissociation rates and probabilities by Monte Carlo selection of initial conditions and integration of classical trajectories on these surfaces. This unified theory reduces to the golden rule expression in the weak-field and short-time limits, and predicts nonlinear behavior, i.e., breakdown of the golden rule expression in intense fields. Field strengths above which lowest-order perturbation theory fails to work have been estimated for some systems. Useful physical insights provided by the electronic-field representation have been illustrated. Intense field effects are discussed which are amenable to experimental observation. The semiclassical methods used here are also applicable to multiple-surface dynamics in fieldfree unimolecular and bimolecular reactions.
Yuan, J.-M.↗
Comparison of dynamic isotope power systems for distributed planet surface applications
Dynamic isotope power system (DIPS) alternatives were investigated and characterized for the surface mission elements associated with a lunar base and subsequent manned Mars expedition. System designs based on two convertor types were studied. These systems were characterized parametrically and compared over the steady-state electrical output power range 0.2 to 20 kWe. Three methods of thermally integrating the heat source and the Stirling heater head were considered, depending on unit size. Figures of merit were derived from the characterizations and compared over the parametric range. Design impacts of mission environmental factors are discussed and quantitatively assessed.
Bents, David J.↗
The Dissolution of an Interfween Miscible Liquids
The disappearance of the surface tension of the interface of a binary mixture, measured using the dynamic surface light scattering technique, is slower for a binary mixture of higher density contrast. A comparison with a naive diffusion model, expected to provide a lower limit for the speed of dissolution in the absence of gravity shows that the interfacial surface tension disappears much slower than even by diffusion with the effect becoming much more pronounced when density contrast between the liquid phases is increased. Thus, the factor most likely to be responsible for this anomalously slow dissolution is gravity. A mechanism could be based on the competition between diffusive relaxation and sedimentation at the dissolving interface.
Vlad, D.H.↗
Unravelling chemical pathways of H 2 on Ga 2 O 3 surfaces with spectro-electrochemistry
This work highlights the capability of coupled spectroscopic and electrochemical techniques to probe dynamic surface processes under realistic operating conditions. By simultaneously employing in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and electrochemical impedance spectroscopy (EIS), we elucidate the mechanistic interaction between Ga 2 O 3 and hydrogen under elevated temperatures in a low-oxygen environment. This novel spectro-electrochemical approach allows chemistry to be correlated with the surface charge density of Ga 2 O 3 . Our results reveal a concentration-dependent transition in reaction pathway. At low concentrations, hydrogen reacts with ambient oxygen to form surface hydroxyls. At intermediate concentrations, hydrogen interacts with surface adsorbed oxygen to generate hydroxyl groups along with reducing the surface. Finally, at high H 2 concentrations, hydrogen reduces both hydroxyls and surface oxygen, leading to a highly conductive grain surface. As a result, hydrides form on the reduced Ga 2 O 3 surface. The gained insights are relevant for heterogeneous catalysis and gas sensing.
08 HYDROGEN↗
A Parallelized Oxidation-Driven Surface Recession Framework in DSMC Code, SPARTA
Spacecrafts rely on ablative thermal protection systems (TPS) made of composites consisting of a carbon-based reinforcement and a polymeric matrix. These materials are designed to withstand high-temperature oxidation and surface recession during re-entry into the Earth's atmosphere. However, ablation occurs due to a complex interplay of thermal, mechanical, and chemical factors, making it challenging to determine the individual impact of each on the TPS's overall degradation. In this study, we have developed an ablation model that can leverage a finite rate carbon oxidation model to predict material recession and surface states more accurately. Stochastic PArallel Rarified-gas Time-accurate Analyzer (SPARTA), a direct-simulation Monte Carlo (DSMC) code, is modified to allow oxidation-driven ablation of implicitly defined carbon surfaces. In SPARTA, implicit surfaces are generated from the grid corner point values via a marching cubes algorithm, therefore creating a new set of surface elements every time ablation is performed. The finite-rate oxidation model developed by Gopalan et. al can perform both gas-surface and pure-surface reactions and is now adapted to tally surface data on a per grid cell basis. The ablation functionality was also adjusted so once the reactions have occurred, the number of reactions leading to CO formation can be converted to corner point reduction values; therefore, carbon removal is directly proportional to surface recession. We also briefly discuss some unique challenges associated with parallelizing this dynamic surface state and geometry. Finally, we analyze the performance of this parallelized implicit chemistry model with simple 2D and 3D benchmark cases by producing surface state statistics, area changes over time, and visualization across a range of surface temperatures and processors with and without load-balancing.
DSMC↗
Target Trailing With Safe Navigation for Maritime Autonomous Surface Vehicles
This software implements a motion-planning module for a maritime autonomous surface vehicle (ASV). The module trails a given target while also avoiding static and dynamic surface hazards. When surface hazards are other moving boats, the motion planner must apply International Regulations for Avoiding Collisions at Sea (COLREGS). A key subset of these rules has been implemented in the software. In case contact with the target is lost, the software can receive and follow a "reacquisition route," provided by a complementary system, until the target is reacquired. The programmatic intention is that the trailed target is a submarine, although any mobile naval platform could serve as the target. The algorithmic approach to combining motion with a (possibly moving) goal location, while avoiding local hazards, may be applicable to robotic rovers, automated landing systems, and autonomous airships. The software operates in JPL s CARACaS (Control Architecture for Robotic Agent Command and Sensing) software architecture and relies on other modules for environmental perception data and information on the predicted detectability of the target, as well as the low-level interface to the boat controls.
Wolf, Michael↗
Fundamental chemical physics revealed by scattering reactive open-shell atoms from surfaces
The dynamics of reactive atoms at surfaces are centrally important to areas such as heterogeneous catalysis, corrosion, materials degradation in extreme environments, and plasma etching. Remarkably detailed understanding of dynamical processes at surfaces has been extracted from scattering molecules and inert atoms under well-defined conditions. However, traditional techniques for generating beams of reactive atoms often result in impure mixtures, broad energy distributions, and poorly defined contributions of metastable electronically excited atoms. In this perspective article, we review the state-of-the-art in reactive atom surface scattering with a focus on experiments performed under controlled conditions on well-defined surfaces. We highlight a new technique for controlled state-to-state scattering of polyelectronic atoms from surfaces, based on vacuum ultraviolet photolysis and state-selective ion imaging. The new capabilities provide an avenue for research into the underexplored area of excited state and spin selective chemical dynamics at surfaces.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗