Lockheed Martin (United States)

Abstract Magnetic reconnection occurs continuously along long X‐lines at the Earth's magnetopause. The maximum magnetic shear model predicts the locations of these long X‐lines for a wide range of upstream solar wind conditions. One of the more perplexing observational results is that these X‐lines appear to be stationary, even in the presence of significant magnetosheath plasma bulk flow. A scenario is developed whereby an X‐line forms at the location predicted by the maximum magnetic shear model, but then immediately propagates with the magnetosheath plasma bulk flow away from this location. Before this X‐line can travel far, a new X‐line forms at the location of the original X‐line. If the X‐line reformation cadence is high enough, then these multiple, propagating X‐lines could appear as a single, quasi‐stationary X‐line. One observational test of this scenario is that a spacecraft crossing the magnetopause poleward of the original X‐line location would always observe multiple X‐lines. Magnetospheric Multiscale observations are used to perform this observational test. Results show that there are multiple X‐lines near the predicted location of the X‐line and therefore, this scenario may have merit.

Energy deposition has long been a popular technique to help improve aerodynamic efficiency particularly in minimizing flow separation and increasing drag reduction. In addition to this, it also has the potential to minimize negative flow features such as local peaks in pressure as well as heating loads. Presented here is a discussion on energy deposition in a hypersonic flow on an 8.4 Degree Wedge, 10 Degree Ramp. This paper compares experiment, computation, and blast wave theory by analyzing the over pressure ratio (Δp/p₀) versus increasing energy per unit length. A secondary analysis examines pressure versus time and flow field visualizations to assess whether the computational model can capture blast wave phenomena. Finally, the paper highlights the similarities and differences among experiment vs. computation, computation vs. theory, and experiment vs. theory. Overall, this investigation finds that computation is able to visually showcase proper blast wave characteristics as ambient pressure is varied. Additionally, computation is able to match both experiment and theory at low energy levels in terms of peak overpressure magnitude and shape. Though divergences in magnitude occur at higher energies and ambient pressures between computation and theory, the general trend remains consistent with blast wave behavior.

High-fidelity progressive failure analyses of composite T-joints, both without and with seeded defects, are performed under pull-off tensile, side-bend, and mixed-shear loading using the Composite Bonded and Bolted Toolkit for Abaqus (CB2ATA). The CB2ATA model employs an advanced continuum damage formulation that incorporates physics-based LaRC04 damage criteria to predict matrix and fiber damage progression in T-joint specimens, along with a mixed-mode cohesive element method to model the initiation and propagation of interface delamination cracks. Given the relatively thick adhesive layer and its nonlinear material behavior, a nonlinear shear constitutive model is explicitly included in the simulation, along with inserted cohesive interfaces between the adhesive layer and the adjacent composite substrates. Feature-driven mesh refinement, accompanied by mesh convergence studies, is used to accurately capture stress concentrations at edges, the noodle region, and locations of seeded defects. A smearing approach based on lumped ply modeling is applied to non-critical regions of the composite skin to further improve computational efficiency. Model verification and validation are performed using Tee-stiffeners without and with Teflon inserts at the throat and tip locations. The tool demonstration is conducted through blind predictions of the load–deflection response, failure load, and damage mechanisms and sequences in T-joints, with the predictions compared against experimental data.

Hot stars born as rapid rotators are expected to induce meridional currents that mix hydrogen from the envelope into the core and return CNO-cycle processed material to the envelope, which should enhance the N at the surface at the expense of C and possibly also O depending on the ambient conditions. But the photospheric C and N abundances could also be influenced by mass transfer in a close binary system which spins up the mass gainer and deposits either processed or unprocessed material to its surface depending on just how much material has been peeled off the mass donor. We focus on the chemical composition of Be star photospheres to infer the present and past evolution of rapidly rotating early B stars. To mitigate the effects of gravity darkening and photospheric line blending on the abundances, we chose 8 Be stars with low vsin i that have good high-resolution FUV spectra in the IUE archive. We carried out a conventional NLTE abundance analysis of selected N iii, N i, and C iii lines in the FUV spectral region. We find clear evidence that the C iii 1176 Å multiplet is weak in the core region in most program stars, suggesting CNO processing. However, in all cases we infer a N abundance that is solar or less, raising a conundrum as to what happened to the “missing C.” Since a similar pattern of weak C yet normal N is also found in the mass gainer in some Algol binaries, there appears to be an emerging challenge to explain this apparent abundance anomaly. We speculate that the excess N from CNO processing might be converted into O (and perhaps on to Ne) by fusion with He in the hot but low-density regions either in the trail of ashes just outside the receding carbon-fusing core, or in He-shell flash regions, of a highly evolved mass loser in its final stage of mass transfer.

Abstract Quasiperiodic fast propagating (QFP) magnetosonic waves have been discovered in the solar corona in the extreme ultraviolet (EUV) since the launch of the Solar Dynamics Observatory (SDO) spacecraft more than a decade ago. The QFP waves are associated with flares and coronal mass ejections, providing information on flare pulsations as well as on the magnetic field by MHD wave seismology. Previous models of QFP waves primarily used idealized magnetic active region (AR) structures. However, more realistic AR numerical models are needed to improve the application of coronal seismology to observations of waves in coronal structures. Here, we extend the previous models by including a realistic magnetic configuration based on an observed coronal AR in a case study using AR 11166, observed on 2011 March 10 by the SDO Atmospheric Imaging Assembly, using potential field extrapolation of the photospheric magnetic field with realistic gravitationally stratified density structure and typical coronal temperature in our resistive 3D MHD model. We aim at reproducing the observed QFP properties, such as directionality, propagation, reflection, nonlinearity, and damping of these waves. We model various forms of excitation of QFPs through time-dependent boundary conditions and localized pulses at the base of the corona. We produce synthetic emission measure maps from the 3D MHD modeling results to facilitate comparison to EUV observations. We find that the present, more realistic model provides better qualitative agreement with observations compared to previous idealized models, improving the study of QFP wave excitation, propagation, and damping in coronal ARs, with potential applications to coronal seismology.

Abstract Predicting the location of magnetopause reconnection remains a major challenge. Existing models often fail to predict the location of the reconnection line seen in global MHD simulations, particularly under northward IMF. This work presents a new X‐line model that identifies a dominant reconnection line by maximizing the reconnection rate on both local and global scales. First, it determines the orientations at the magnetopause that locally maximize the rate and then finds the global path with the highest integrated rate. Across four global MHD simulations with diverse dipole tilts and IMF orientations, the new model was consistently more accurate than both the maximum magnetic shear and the global rate maximization models in predicting the location of the magnetic separator in between the magnetospheric cusps. Crucially, it succeeds for a challenging northward IMF case where previous models have failed. This model suggests the X‐line's location is determined by a fundamental principle of maximizing the conversion of magnetic to plasma energy.

While automation has been increasingly used to process high volumes of satellite remote sensing data, deriving accurate and actionable information from these data streams still requires human analysts. Machine learning algorithms are critical for processing large datasets, whereas well-trained operators are especially effective at synthesizing information from diverse sources and recognizing unique situations that may require different interpretations of the data. Therefore, combining algorithmic strengths with improved operator awareness is critical for reliable and robust data analysis. This research contributes a suite of algorithms that support the visualization, analysis, and characterization of infrared satellite data. The key components of our Collaborative Analyst-Machine Perception system include a probabilistic classifier, a false data filter, a historical track comparison tool, and an online data recommendation system. These components are integrated into an interactive dashboard and trained on synthetic satellite information that emulates operational challenges. We evaluated our application with six United States Space Force satellite operators in a live scenario with simulated real-time data acquisition. We found that the operators rated our application as more usable than current operational systems and that the combined human–machine team was capable of more accurate data characterization than machine learning algorithms alone.