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Abstract Capturing extreme surface velocities with >50 km/s dynamic range, which arise in shock physics such as inertial confinement fusion (ICF), is beyond the reach of conventional photon Doppler velocimetry (PDV) systems due to the need for extremely large electrical bandwidth under such conditions. The recent ignition in ICF calls for new velocimetry that can measure velocities exceeding 100 km/s. Time lens PDV (TL-PDV) is a solution where the high frequency beat signal from a conventional PDV system is periodically temporally magnified in the optical domain using a time lens. Here we experimentally demonstrate TL-PDV for the first time, validate the performance over a 74 km/s velocity range with high accuracy using a temporal magnification factor of 7.6, and verify excellent agreement with conventional PDV for laser driven micro-flyer experiments. TL-PDV currently provides the largest velocity dynamic range among PDV systems and is scalable to even higher velocities, which makes it an ideal candidate for material characterization under the most extreme conditions such as optimizing fuel efficiency in ICF experiments.

Abstract Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders’ fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA’s Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures’ preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids.

NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1 σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β , resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

Abstract This paper follows a historical background on requirements‐based strategic armor research, leading to the materials in extreme dynamic environments program presented in Part I, now focusing on the developed technical aspects and state‐of‐the‐art. It starts with some background on dynamic testing techniques and a structural ceramics review. Then, selected armor ceramics research results and relevant single‐grain anisotropic crystal physics, microstructure, and defect mechanics mechanisms: Including pivotal armor ceramics research results prior to the adoption of the strategic research objective (SRO). Next, multiscale characteristics, crystal physics, planar features, anisotropy, and relevant mechanisms will be described. The historic progression/evolution of multiscale lightweight armor ceramics research results will be summarized, including multiscale dynamic deformation and damage characteristics. The focus of the following sections will be on the role of defects, quasi‐plasticity, and anisotropic crystal physics properties, including preexisting single grain synthesis and process‐induced planar features (aka twins) and planar deformation features (PDF); for example, nano‐amorphization in boron carbide. A new model for boron carbide processing planar features will be discussed. A schematic diagram illustrating the hypothetical formation of PDFs in a dynamic event is also presented. An expended canonical equation is introduced, suggesting possible strategies for boron carbide research using the canonical figures of merit approach. Finally, we highlight the efficacy of the materials by design process and approach in a multiscale framework for the simultaneous experimental and theoretical research trajectories guided by the accepted canonical equation.

The development of advanced materials for extreme dynamic environments requires an understanding of the links between the microstructure and the response of the material (i.e., Materials-by-Design). Spall failure significantly limits material performance at high strain rates, but our understanding of the influence of microstructure on spall strength is limited. While models suggest that increasing the static yield strength by adding precipitates or refining grain size can improve the spall strength, it is possible that the associated increase in nucleation sites may have deleterious effects on spall performance. Herein, we examine spall failure of a Magnesium-Aluminum system with precipitation and grain size strengthening through novel high-throughput laser-driven micro-flyer (LDMF) impact experiments. Six microstructures are investigated, four with grain sizes around 2–3 μm and precipitates around 0.5–1 μm, and two that are precipitate-free with grain sizes around 500 μm at six and nine percent Aluminum contents. The LDMF method allows us to detect differences in spall strength with relatively small changes in microstructure. The spall strength is observed to be strongly affected by varying levels of precipitates and consistently shows a notable reduction in average spall strength around 8–19% with the addition of precipitates, with values ranging from 1.22–1.50 GPa. The spall strength is also seen to decrease with the refinement of grain size independent of composition. However, this decrease is small compared to the hundred-fold grain size reduction. While ductile void growth is observed across all samples, greater variability and a further decrease in strength are seen with an increasing numbers of non-uniformly dispersed precipitates.

The conditions which affect twinning in tantalum have been investigated across a range of strain rates and initial dislocation densities. Tantalum samples were subjected to a range of strain rates, from 10−4/s to 103/s under uniaxial stress conditions, and under laser-induced shock-loading conditions. In this study, twinning was observed at 77K at strain rates from 1/s to 103/s, and during laser-induced shock experiments. The effect of the initial dislocation density, which was imparted by deforming the material to different amounts of pre-strain, was also studied, and it was shown that twinning is suppressed after a given amount of pre-strain, even as the global stress continues to increase. These results indicate that the conditions for twinning cannot be represented solely by a critical global stress value, but are also dependent on the evolution of the dislocation density. In addition, the analysis shows that if twinning is initiated, the nucleated twins may continue to grow as a function of strain, even as the dislocation density continues to increase.

More than half of the Indian population depends on agriculture as a source of livelihood. But, India's marginal farmers especially, earn meagre amounts from their harvested yields. This may be attributed partly due to relatively smaller land holdings, and partly due to minimal access to resources that aid with informative price forecasts. In order to alleviate the stress caused by the lack of sound financial planning, this research proposes the utilization of machine learning to predict commodity prices. The solution obtained through such a model would assist farmers in predicting the price and associated estimates can be made with respect to yield, sowing patterns and suitable recommendations for sales. The solution developed in this research is a result of a thorough exploration of the literature in this domain, identification of verified secondary sources for data collection, and proposes a methodology to design a machine learning model that predicts prices for seasonal cash crops specific to the markets of Karnataka. Cotton has been used as the crop of focus in this study. ARIMA and Bayesian ridge regression have been used for predictive analytics, and the results obtained indicate a high correlation between the predicted and actual. [ABSTRACT FROM AUTHOR]

We describe a novel valve-based microfluidic axon injury micro-compression (AIM) platform that enables focal and graded compression of micron-scale segments of single central nervous system (CNS) axons. The device utilizes independently controlled “push-down” injury pads that descend upon pressure application and contact underlying axonal processes. Regulated compressed gas is input into the AIM system and pressure levels are modulated to specify the level of injury. Finite element modeling (FEM) is used to quantitatively characterize device performance and parameterize the extent of axonal injury by estimating the forces applied between the injury pad and glass substrate. In doing so, injuries are normalized across experiments to overcome small variations in device geometry. The AIM platform permits, for the first time, observation of axon deformation prior to, during, and immediately after focal mechanical injury. Single axons acutely compressed (∼5 s) under varying compressive loads (0–250 kPa) were observed through phase time-lapse microscopy for up to 12 h post injury. Under mild injury conditions ( 95 kPa), virtually all axons were instantaneously transected and nearly half (∼46%) of these axons were able to regrow within the imaging period in the absence of exogenous stimulating factors. [ABSTRACT FROM AUTHOR]

In this paper, we present an analytical model to investigate stochastic size effects on the critical stress for the activation of non-basal slip and contraction twinning (CT) in miniaturized hexagonal-close packed (HCP) single crystals. The analysis is based on the basic model developed by Parthasarathy et al (Scr. Mater.56 313–6), but extends it to account for the mechanism-based description of pyramidal slip and CT in HCP metals. The results demonstrate that for a given initial dislocation density, a probabilistic competition exists among CT nucleation, CT growth and pyramidal slip. Based on the stochastic model, we construct a mechanism map that provides regimes of dominant deformation modes that govern the macroscopic yield stress in HCP single crystals. [ABSTRACT FROM AUTHOR]

Although a number of cytoskeletal derangements have been described in the setting of traumatic axonal injury (TAI), little is known of early structural changes that may serve to initiate a cascade of further axonal degeneration. Recent work by the authors has examined conformational changes in cytoskeletal constituents of neuronal axons undergoing traumatic axonal injury (TAI) following focal compression through confocal imaging data taken in vitro and in situ. The present study uses electron microscopy to understand and quantify in vitro alterations in the ultrastructural composition of microtubules and neurofilaments within neuronal axons of rats following focal compression. Standard transmission electron microscopy processing methods are used to identify microtubules, while neurofilament identification is performed using antibody labeling through gold nanoparticles. The number, density, and spacing of microtubules and neurofilaments are quantified for specimens in sham Control and Crushed groups with fixation at