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DOE OSTI2024

Future North Atlantic tropical cyclone intensities in thermodynamically modified historical environments

Tropical cyclones (TCs) rank as the deadliest and most financially crippling natural disasters in the United States for the last half-century. It is imperative to assess potential shifts in TC intensity within the paradigm of an evolving climate. In this study, we have modeled the intensities of 620 historical TC events in the North Atlantic Basin using the Risk Analysis Framework for Tropical Cyclones (RAFT)'s deep learning intensity model. By applying a thermodynamic warming signal extrapolated from Global Climate Models, we rerun historical events under eight different future climate scenarios, providing a spectrum of potential TC intensity outcomes. One of the future simulations indicates a staggering 43% increase in the number of major hurricanes, underscoring the critical impact of climate change on TC intensity. Additionally, an interactive dashboard has been created to enable users to explore individual storm simulations and understand the influence of future climate signals on environmental conditions of TC development and resulting TC intensities. This dataset and the user-friendly tool offer invaluable resources for systematic exploration of the discrete effects that changes in the air-sea thermodynamic state have on the intensities of TCs.

Climate Change↗

NASA NTRS2017

Intermediate Fidelity Solid State Recorder Modeling for NISAR

At 26Tb/day return average, NISAR (National Aero- nautics and Space Administration (NASA) and the In- dian Space Research Organization (ISRO) Synthetic Aperture Radar) will stress ground station facilities with a variable cadence of data generation observing nearly all of earth's land and ice to produce global time- series maps of cryospheric, solid-Earth and ecosystem phenomena. Between the instrument data generation source and downlink sink lies the primary science data bu er, the SSR (Solid State Recorder). The SSR has deferred, discrete le deletion events that occur only after a le is played back to all required ground segments (sometimes both NASA and ISRO). A forward dispatch, advancing frontier repropagation playback scheduler is proposed as a model of the SSR's greedy playback scheduling behavior. Schedules based on the existing low delity model and new intermediate delity model are compared to assess the impact of deferred, discrete deletion on planning. The low delity model is found to produce unfeasible schedules that exceed SSR capacity, causing 3.87% of all observations in a 12 day simulation to be removed by repair actions.

Doubleday, Joshua R.↗

NASA NTRS2013

Prospective Safety Analysis and the Complex Aviation System

Fatal accident rates in commercial passenger aviation are at historic lows yet have plateaued and are not showing evidence of further safety advances. Modern aircraft accidents reflect both historic causal factors and new unexpected "Black Swan" events. The ever-increasing complexity of the aviation system, along with its associated technology and organizational relationships, provides fertile ground for fresh problems. It is important to take a proactive approach to aviation safety by working to identify novel causation mechanisms for future aviation accidents before they happen. Progress has been made in using of historic data to identify the telltale signals preceding aviation accidents and incidents, using the large repositories of discrete and continuous data on aircraft and air traffic control performance and information reported by front-line personnel. Nevertheless, the aviation community is increasingly embracing predictive approaches to aviation safety. The "prospective workshop" early assessment tool described in this paper represents an approach toward this prospective mindset-one that attempts to identify the future vectors of aviation and asks the question: "What haven't we considered in our current safety assessments?" New causation mechanisms threatening aviation safety will arise in the future because new (or revised) systems and procedures will have to be used under future contextual conditions that have not been properly anticipated. Many simulation models exist for demonstrating the safety cases of new operational concepts and technologies. However the results from such models can only be as valid as the accuracy and completeness of assumptions made about the future context in which the new operational concepts and/or technologies will be immersed. Of course that future has not happened yet. What is needed is a reasonably high-confidence description of the future operational context, capturing critical contextual characteristics that modulate both the likelihood of occurrence of hazards, and the likelihood that those hazards will lead to negative safety events. Heuristics extracted from scenarios, questionnaires, and observed trends from scanning the aviation horizon may be helpful in capturing those future changes in a way conducive to safety assessment. What is also needed is a checklist of potential sources of emerging risk that arise from organizational features that are frequently overlooked. The ultimate goal is to develop a pragmatic, workable method for using descriptions of the future aviation context, to generate valid predictions of safety risks.

prospection↗

NASA NTRS2007

Hybrid Automated Diagnosis of Discrete/Continuous Systems

A recently conceived method of automated diagnosis of a complex electromechanical system affords a complete set of capabilities for hybrid diagnosis in the case in which the state of the electromechanical system is characterized by both continuous and discrete values (as represented by analog and digital signals, respectively). The method is an integration of two complementary diagnostic systems: (1) beacon-based exception analysis for multi-missions (BEAM), which is primarily useful in the continuous domain and easily performs diagnoses in the presence of transients; and (2) Livingstone, which is primarily useful in the discrete domain and is typically restricted to quasi-steady conditions. BEAM has been described in several prior NASA Tech Briefs articles: "Software for Autonomous Diagnosis of Complex Systems" (NPO-20803), Vol. 26, No. 3 (March 2002), page 33; "Beacon-Based Exception Analysis for Multimissions" (NPO-20827), Vol. 26, No. 9 (September 2002), page 32; "Wavelet-Based Real-Time Diagnosis of Complex Systems" (NPO-20830), Vol. 27, No. 1 (January 2003), page 67; and "Integrated Formulation of Beacon-Based Exception Analysis for Multimissions" (NPO-21126), Vol. 27, No. 3 (March 2003), page 74. Briefly, BEAM is a complete data-analysis method, implemented in software, for real-time or off-line detection and characterization of faults. The basic premise of BEAM is to characterize a system from all available observations and train the characterization with respect to normal phases of operation. The observations are primarily continuous in nature. BEAM isolates anomalies by analyzing the deviations from nominal for each phase of operation. Livingstone is a model-based reasoner that uses a model of a system, controller commands, and sensor observations to track the system s state, and detect and diagnose faults. Livingstone models a system within the discrete domain. Therefore, continuous sensor readings, as well as time, must be discretized. To reason about continuous systems, Livingstone uses monitors that discretize the sensor readings using trending and thresholding techniques. In development of the a hybrid method, BEAM results were sent to Livingstone to serve as an independent source of evidence that is in addition to the evidence gathered by Livingstone standard monitors. The figure depicts the flow of data in an early version of a hybrid system dedicated to diagnosing a simulated electromechanical system. In effect, BEAM served as a "smart" monitor for Livingstone. BEAM read the simulation data, processed the data to form observations, and stored the observations in a file. A monitor stub synchronized the events recorded by BEAM with the output of the Livingstone standard monitors according to time tags. This information was fed to a real-time interface, which buffered and fed the information to Livingstone, and requested diagnoses at the appropriate times. In a test, the hybrid system was found to correctly identify a failed component in an electromechanical system for which neither BEAM nor Livingstone alone yielded the correct diagnosis.

Park, Han↗

NASA NTRS1984

Transient vibration test criteria for spacecraft hardware

Transient vibration test criteria, developed for spacecraft hardware, provide a test rationale to verify the capability of the hardware to withstand the low and mid frequency transient vibration environments induced by launch vehicle events. A test method, consisting of a series of discrete frequency, limited cycle, modulated sine wave pulses, was developed to avoid the slow swept sine drawbacks, yet provide a repeatable test that would excite all frequencies. The shape of the waveform is that of the classic response of the mass of a one degree of freedom system when it is base-excited by an exponentially decayed sine wave transient. Criteria were developed to define pulse amplitudes, shapes, and center frequencies from spacecraft loads analyses. Test tolerance criteria were also developed and specified. The transient vibration test criteria were implemented on spacecraft flight hardware and provided a more realistic test simulation (i.e., less conservative) for qualification of spacecraft hardware without risk of undertest.

Kern, D. L.↗

NASA NTRS2004

A Re-programmable Platform for Dynamic Burn-in Test of Xilinx Virtexll 3000 FPGA for Military and Aerospace Applications

Field Programmable Gate Arrays (FPGA) have played increasingly important roles in military and aerospace applications. Xilinx SRAM-based FPGAs have been extensively used in commercial applications. They have been used less frequently in space flight applications due to their susceptibility to single-event upsets. Reliability of these devices in space applications is a concern that has not been addressed. The objective of this project is to design a fully programmable hardware/software platform that allows (but is not limited to) comprehensive static/dynamic burn-in test of Virtex-II 3000 FPGAs, at speed test and SEU test. Conventional methods test very few discrete AC parameters (primarily switching) of a given integrated circuit. This approach will test any possible configuration of the FPGA and any associated performance parameters. It allows complete or partial re-programming of the FPGA and verification of the program by using read back followed by dynamic test. Designers have full control over which functional elements of the FPGA to stress. They can completely simulate all possible types of configurations/functions. Another benefit of this platform is that it allows collecting information on elevation of the junction temperature as a function of gate utilization, operating frequency and functionality. A software tool has been implemented to demonstrate the various features of the system. The software consists of three major parts: the parallel interface driver, main system procedure and a graphical user interface (GUI).

Field Programmable Gate Arrays (FPGA)↗

NASA NTRS2022

A 2D Kaleidoscope of Electron Heat Fluxes Driven by Auroral Electron Precipitation

Electron heat flux is an important value for ionospheric space weather modeling networks. Utilizing the 2D array of Time History of Events and Macroscale Interactions during Substorms all-sky-imager (ASI) observations, Gabrielse et al. (2021, https://doi.org/10.3389/fphy.2021.744298) described a new method that estimates the auroral scale sizes of intense precipitating electron energy fluxes and their mean energies during two substorms on 16 February 2010. These parameters in combination with SuperThermal Electron Transport code were used to develop a new methodology to calculate electron thermal fluxes from data inputs in 2D during one of the substorms at 09:40:00 UT across Canada and Alaska. To test the effect of various precipitation lifetimes on electron heat flux values, boxcar averages ranging from 0 to 900 s were applied to the ASI data. These data are then combined with the newly developed kinetic simulation to determine the thermal fluxes associated with the observed diffuse and discrete precipitation.

Electron precipitation in aurora↗

NASA NTRS1998

Buckling and Damage Resistance of Transversely-Loaded Composite Shells

Experimental and numerical work was conducted to better understand composite shell response to transverse loadings which simulate damage-causing impact events. The quasi-static, centered, transverse loading response of laminated graphite/epoxy shells in a [+/-45(sub n)/O(sub n)](sub s) layup having geometric characteristics of a commercial fuselage are studied. The singly-curved composite shell structures are hinged along the straight circumferential edges and are either free or simply supported along the curved axial edges. Key components of the shell response are response instabilities due to limit-point and/or bifurcation buckling. Experimentally, deflection-controlled shell response is characterized via load-deflection data, deformation-shape evolutions, and the resulting damage state. Finite element models are used to study the kinematically nonlinear shell response, including bifurcation, limit-points, and postbuckling. A novel technique is developed for evaluating bifurcation from nonlinear prebuckling states utilizing asymmetric spatial discretization to introduce numerical perturbations. Advantages of the asymmetric meshing technique (AMT) over traditional techniques include efficiency, robustness, ease of application, and solution of the actual (not modified) problems. The AMT is validated by comparison to traditional numerical analysis of a benchmark problem and verified by comparison to experimental data. Applying the technique, bifurcation in a benchmark shell-buckling problem is correctly identified. Excellent agreement between the numerical and experimental results are obtained for a number of composite shells although predictive capability decreases for stiffer (thicker) specimens which is attributed to compliance of the test fixture. Restraining the axial edge (simple support) has the effect of creating a more complex response which involves unstable bifurcation, limit-point buckling, and dynamic collapse. Such shells were noted to bifurcate into asymmetric deformation modes but were undamaged during testing. Shells in this study which were damaged were not observed to bifurcate. Thus, a direct link between bifurcation and atypical damage could not be established although the mechanism (bifurcation) was identified. Recommendations for further work in these related areas are provided and include extensions of the AMT to other shell geometries and structural problems.

Wardle, Brian L.↗

NASA NTRS2022

Discrete Aurora on the Nightside of Mars: Occurrence Location and Probability

This paper represents the first attempt to predict the occurrence location and probability of discrete electron aurora on the nightside of Mars. We run a 3-D time-dependent magnetohydrodynamic model to characterize the spatial and temporal dynamics of magnetic field and plasma distributions over the course of one planetary rotation. We perform eight simulation cases under solar minimum quiet-solar-wind conditions (four equinox/solstice seasons, each with two interplanetary magnetic field polarities) and in an actual interplanetary coronal mass ejection (ICME) case to assess quiet and space weather situations, respectively. The occurrence of detectable discrete aurora is subject to the combination of the probabilities that (a) the ionosphere is magnetically connected with high altitudes through open field lines and (b) precipitating energy fluxes of >30 eV electrons exceed 0.1 erg/cm2/s. Our results show that during quiet solar activity, discrete aurora occurs likely on small-scale patches embedded inside strong crustal magnetic field regions (with a magnitude greater than 50 nT at 150 km), and the overall chance across the globe is ∼0.77%. The higher probability over strong crustal field regions is attributed to the stronger magnetic field convergence. Modeling shows the occurrence probability dramatically increases during the ICME event, particularly by more than an order of magnitude in weak crustal field regions. Our model results reasonably agree with NASA Mars Atmosphere and Volatile EvolutioN and Mars Express observations. Our study suggests that nightside discrete electron aurora is not caused by the direct entry of magnetosheath plasma in a cusp-like process but due to the recycling of nightside magnetospheric electrons.

Xiaohua Fang↗

DOE OSTI2025

Development of a River Dynamical Core for E3SM to simulate compound flooding on Exascale-class heterogeneous supercomputers

Flooding events pose significant risk to human life, property, and infrastructure. Physically-consistent quantification of altered flood risks in global models requires hyper-resolution (~1 km) or fine flood simulations using two-dimensional (2D) physics schemes, both of which are unavailable in the current generation Earth System Models. Here, in this work, we have developed the River Dynamical Core (RDycore), which is an open-source, 2D shallow water equation (SWE) library for the U.S. Department of Energy's Energy Exascale Earth System Model (E3SM). RDycore uses PETSc and libCEED libraries that allows it to run efficiently on CPUs and GPUs, as well as select a time-integration algorithm at runtime without requiring any code modifications. RDycore achieves spatial error convergence rates for problems with analytical and manufactured solutions similar to those reported previously in the literature, or consistent with the implemented first-order spatial discretization scheme. RDycore's accuracy in predicting flooding for a well-studied dam break problem is comparable to existing SWE models. For a problem with 471 million grid cells, RDycore achieves a speedup of 6.6x and 7.6x on GPUs compared to CPUs when using 320 compute nodes on DOE's Perlmutter and Frontier supercomputers, respectively. The one-way coupling of the RDycore library within E3SM is demonstrated by performing multiple 5-day flooding simulations during Hurricane Harvey driven by five precipitation datasets. The E3SM--RDycore simulations at 30 m spatial resolution accurately simulate maximum water height during the hurricane when benchmarked against a previously published study and achieve a speedup of 15x (Perlmutter) and 21x (Frontier) on GPUs relative to CPUs. The work presented here is the foundational step in providing hardware and algorithmic portability framework for simulating kilometer-scale river dynamics within E3SM.

Flood Simulation↗

NASA NTRS1992

A dynamic study of fragmentation and energy loss during high velocity impact

Research conducted under this contract can be divided into two main areas: hypervelocity (in the range up to 7 km/s) and high velocity (less than 1 km/s). Work in the former was performed at NASA-MSFC using the Light Gas Gun Facility. The lower velocity studies were conducted at Auburn University using the ballistic gun. The emphasis of the project was on the hypervelocity phenomenon especially in the characterization of the debris cloud formed by the primary impact events. Special devices were made to determine the angular distributions of momentum and energy of the debris cloud as a function of impact conditions. After several iteration processes, it was decided to concentrate on the momentum effort. Prototype devices were designed, fabricated, and tested. These devices were based on the conservation of momentum. Distributions of the debris cloud formed were measured by determining the amount of momentum transferred from the debris cloud to strategically placed pendulum measurement devices. The motion of the pendula was monitored using itegrated opto-interrupters. The distribution of momentum in the debris cloud was found to be a strong function of the impact condition. Small projectiles at high velocities were observed to produce finely dispersed debris whereas large projectiles generated discrete particles in the debris. Results also show that the momentum in the forward direction was enhanced due to the impact. This phenomenon of momentum multiplication was also observed in other studies and in computer simulations. It was initially planned to determine the energy distribution using deformation energy in a rod with strain gauges. Results from preliminary studies show that this technique is acceptable but too tedious. A new technique was explored based on measuring the heating effect of the debris cloud using an IR camera. The feasibility and sensitivity was established at Auburn University. This type of energy distribution measurement method can easily be adapted to the gas gun facility at MSFC. The objective of the lower velocity studies at Auburn was to simulate the damage produced in advanced materials by the lower energy debris cloud.

Zee, Ralph H.↗

NASA NTRS2000

X-38 Experimental Aerothermodynamics

The X-38 program seeks to demonstrate an autonomously returned orbital test flight vehicle to support the development of an operational Crew Return Vehicle for the International Space Station. The test flight, anticipated in 2002, is intended to demonstrate the entire mission profile of returning Space Station crew members safely back to earth in the event of medical or mechanical emergency. Integral to the formulation of the X-38 flight data book and the design of the thermal protection system, the aerothermodynamic environment is being defined through a synergistic combination of ground based testing and computational fluid dynamics. This report provides an overview of the hypersonic aerothermodynamic wind tunnel program conducted at the NASA Langley Research Center in support of the X-38 development. Global and discrete surface heat transfer force and moment, surface streamline patterns, and shock shapes were measured on scaled models of the proposed X-38 configuration in different test gases at Mach 6, 10 and 20. The test parametrics include angle of attack from 0 to 50 degs, unit Reynolds numbers from 0.3 x 10 (exp 6) to 16 x 10 (exp 6)/ ft, rudder deflections of 0, 2, and 5 deg. and body flap deflections from 0 to 30 deg. Results from hypersonic aerodynamic screening studies that were conducted as the configuration evolved to the present shape at, presented. Heavy gas simulation tests have indicated that the primary real gas effects on X-38 aerodynamics at trim conditions are expected to favorably influence flap effectiveness. Comparisons of the experimental heating and force and moment data to prediction and the current aerodynamic data book are highlighted. The effects of discrete roughness elements on boundary layer transition were investigated at Mach 6 and the development of a transition correlation for the X-38 vehicle is described. Extrapolation of ground based heating measurements to flight radiation equilibrium wall temperatures at Mach 6 and 10 were made and generally compared to within 50 deg F of flight prediction.

Horvath, Thomas J.↗

NASA NTRS2003

FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identi@ the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral Snapshot (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data were used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and/or a long-system particle in cell simulation to model the magnetically connected region between the two satellites. Results from the study indicate that there are three main drivers of auroral acceleration: (1) field-aligned currents that lead to quasistatic parallel potential drops (parallel electric fields), (2) earthward flow of high-energy plasma beams from the magnetotail into the auroral zone that lead to quasistatic parallel potential drops, and (3) large-amplitude Alfven waves that propagate into the auroral region from the magnetotail. The events examined thus far confm the previously established invariant latitudinal dependence of the drivers and show a strong dependence on magnetic activity. Alfven waves tend to occur primarily at the poleward edge of the auroral region during more magnetically active times and are correlated with intense electron precipitation. At lower latitudes away from the poleward edge of the auroral zone is the primary field-aligned current region which results in the classical field- aligned acceleration associated with the auroral zone (electrons earthward and ion beams tailward). During times of high magnetic activity, high-energy ion beams originating from the magnetotail are observed within, and overlapping, the regions of primary and return field-aligned current. Along the field lines where the high-energy magnetotail ion beams are located, field-aligned acceleration can occur in the auroral zone leading to precipitating electrons and upwelling ionospheric ion beams. Field-aligned currents are present during both quiet and active times, while the Alfven waves and magnetotail ion beams were observed only during more magnetically active events.

Schriver, D.↗

NASA NTRS2002

FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

Schriver, D.↗

NASA NTRS2008

Fast Plasma Instrument for MMS: Simulation Results

Magnetospheric Multiscale (MMS) mission will study small-scale reconnection structures and their rapid motions from closely spaced platforms using instruments capable of high angular, energy, and time resolution measurements. The Dual Electron Spectrometer (DES) of the Fast Plasma Instrument (FPI) for MMS meets these demanding requirements by acquiring the electron velocity distribution functions (VDFs) for the full sky with high-resolution angular measurements every 30 ms. This will provide unprecedented access to electron scale dynamics within the reconnection diffusion region. The DES consists of eight half-top-hat energy analyzers. Each analyzer has a 6 deg. x 11.25 deg. Full-sky coverage is achieved by electrostatically stepping the FOV of each of the eight sensors through four discrete deflection look directions. Data compression and burst memory management will provide approximately 30 minutes of high time resolution data during each orbit of the four MMS spacecraft. Each spacecraft will intelligently downlink the data sequences that contain the greatest amount of temporal structure. Here we present the results of a simulation of the DES analyzer measurements, data compression and decompression, as well as ground-based analysis using as a seed re-processed Cluster/PEACE electron measurements. The Cluster/PEACE electron measurements have been reprocessed through virtual DES analyzers with their proper geometrical, energy, and timing scale factors and re-mapped via interpolation to the DES angular and energy phase-space sampling measurements. The results of the simulated DES measurements are analyzed and the full moments of the simulated VDFs are compared with those obtained from the Cluster/PEACE spectrometer using a standard quadrature moment, a newly implemented spectral spherical harmonic method, and a singular value decomposition method. Our preliminary moment calculations show a remarkable agreement within the uncertainties of the measurements, with the results obtained by the Cluster/PEACE electron spectrometers. The data analyzed was selected because it represented a potential reconnection event as currently published.

Figueroa-Vinas, Adolfo↗

DOE OSTI2026

Data-driven particle dynamics: Structure-preserving coarse-graining for emergent behavior in non-equilibrium systems

Multiscale systems are ubiquitous in science and technology, but are notoriously challenging to simulate as short spatiotemporal scales must be appropriately linked to emergent bulk physics. When expensive high-dimensional dynamical systems are coarse-grained into low-dimensional models, the entropic loss of information leads to emergent physics which are dissipative, history-dependent, and stochastic. To machine learn coarse-grained dynamics from time-series observations of particle trajectories, we propose a framework using the metriplectic bracket formalism that preserves these properties by construction; most notably, the framework guarantees discrete notions of the first and second laws of thermodynamics, conservation of momentum, and a discrete fluctuation-dissipation balance crucial for capturing non-equilibrium statistics. We introduce the mathematical framework abstractly before specializing to a particle discretization. As labels are generally unavailable for entropic state variables, we introduce a novel self-supervised learning strategy to identify emergent structural variables. We validate the method on benchmark systems and demonstrate its utility on two challenging examples: (1) coarse-graining star polymers at challenging levels of coarse-graining while preserving non-equilibrium statistics, and (2) learning models from high-speed video of colloidal suspensions that capture coupling between local rearrangement events and emergent stochastic dynamics. We provide open-source implementations in both PyTorch and LAMMPS, enabling large-scale inference and extensibility to diverse particle-based systems.

Computational Engineering, Finance, and Science (c↗

NASA NTRS1993

Impact damage resistance of composite fuselage structure, part 2

The strength of laminated composite materials may be significantly reduced by foreign object impact induced damage. An understanding of the damage state is required in order to predict the behavior of structure under operational loads or to optimize the structural configuration. Types of damage typically induced in laminated materials during an impact event include transverse matrix cracking, delamination, and/or fiber breakage. The details of the damage state and its influence on structural behavior depend on the location of the impact. Damage in the skin may act as a soft inclusion or affect panel stability, while damage occurring over a stiffener may include debonding of the stiffener flange from the skin. An experiment to characterize impact damage resistance of fuselage structure as a function of structural configuration and impact threat was performed. A wide range of variables associated with aircraft fuselage structure such as material type and stiffener geometry (termed, intrinsic variables) and variables related to the operating environment such as impactor mass and diameter (termed, extrinsic variables) were studied using a statistically based design-of-experiments technique. The experimental design resulted in thirty-two different 3-stiffener panels. These configured panels were impacted in various locations with a number of impactor configurations, weights, and energies. The results obtained from an examination of impacts in the skin midbay and hail simulation impacts are documented. The current discussion is a continuation of that work with a focus on nondiscrete characterization of the midbay hail simulation impacts and discrete characterization of impact damage for impacts over the stiffener.

Dost, Ernest F.↗

DOE OSTI2026

Mechanism of Tyrosine-Driven Deprotonation in Photosystem II Revealed by Multiscale Simulations

Photosystem II (PSII) drives light-induced water oxidation via stepwise redox transitions of its oxygen-evolving complex (OEC), a Mn 4 Ca cluster advancing through five intermediate S-states (S 0 –S 4 ). The S 2 → S 3 transition involves a redox event in which a Mn ion donates an electron to the redox-active tyrosine YZ, coupled to deprotonation of an OEC-bound water ligand─yet the underlying coupling mechanism remains unresolved. Time-resolved serial femtosecond crystallography (TR-SFX) has revealed transient electron density shifts near the redox-active tyrosine Y Z , interpreted as sequential oxidation and reduction, with reduction initiating ∼1 μs after excitation and substantially progressed by 30 μs. However, this interpretation conflicts with kinetics from photothermal beam deflection (PBD), time-resolved X-ray absorption spectroscopy (TR-XAS), and electron paramagnetic resonance (EPR), which place electron transfer at 190–400 μs and proton transfer around 30 μs. Here, we reconcile these discrepancies using quantum mechanics/molecular mechanics (QM/MM) and molecular dynamics (MD) simulations. We show that oxidation of P680 and Y Z breaks the symmetry of the nearby hydrogen bonds involving water molecule W4, displacing Y Z and replicating the TR-SFX features of Y Z and Q165 observed at 1 μs. This local perturbation propagates through a hydrogen-bond network, transmitting the electrostatic signal from Y Z to the E65-E312 dyad and triggering redox-coupled deprotonation via the Cl1 channel. By 30 μs, the hydrogen-bond symmetry is restored through deprotonation of W2 (or alternatively W1), reproducing the disappearance of TR-SFX density differences around Y Z and Q165 without requiring Y Z reduction. Our proposed mechanism also gives molecular insights into the O6* density, assigning it to water reorganization rather than a discrete Ca-bound hydroxide species. Here, our results reveal a detailed atomistic mechanism linking Y Z oxidation to long-range proton release and suggest a functional role for the nearby Cl – ion in proton transfer. More broadly, this study underscores the importance of hydrogen-bond dynamics in mediating redox-driven proton transport and demonstrates how integrative simulations can resolve mechanistic ambiguities.

Deprotonation↗