Transition of deformation modes from bending to auxetic compression in origami-based metamaterials for head protection from impact.

For the protection of the human head by energy absorption structures, a soft mechanical response upon contact with the head is required to mitigate the effect of impact, while a hard mechanical response for highly efficient energy absorption is required to stop the movement of the head. This study realized the opposite mechanical properties during head protection by transitioning the deformation mode from bending to auxetic compression. First, non-linear finite element (FE) models were constructed to numerically reproduce the bending behavior. The calculated force responses agreed well with forces in bending tests. Using the FE models, the EA structures with proper transition of deformation modes were designed and installed in the seat headrests of real vehicles. Head protection was evaluated by dynamic loading in sled testing, in which the force on the head of the crash test dummy was measured. The head injury criterion improved from 274 to 155, indicating the superior performance of the tested structures compared to that achieved by energy absorption structures based on steel plates. Moreover, the deformation of auxetic structures prevented neck bending by holding the head. These findings present new possibilities for effectively protecting the human body by mitigating impact, facilitating energy absorption, and ensuring head stability.

Scalable Thermochromic Composite Based on a Ternary Polymer Blend for Temperature-Adaptive Solar Heat Management.

A scalable and durable thermochromic composite is developed for temperature-adaptive solar heat management using a carbon absorber and a thermoresponsive polymer blend consisting of an isolated polycaprolactone phase (PCL) and a continuous phase of miscible poly(methyl methacrylate) and polyvinylidene fluoride. The ternary blend exhibits reversible haze transition originating from the melting and crystallization of PCL. The refractive index matching between the molten PCL and surrounding miscible blend contributes to high-contrast haze switching in the range of 14-91% across the melting temperature of PCL (ca. 55 °C). The solar-absorption-switching properties of the composite are due to the spontaneous light-scattering switching in the polymer blend and the presence of a small amount of carbon black. Spectral measurements indicate that the solar reflectance of the composite sheet varies by 20% between 20 and 60 °C upon lamination with a Ag mirror. Solar heat management using the thermochromic composite is successfully demonstrated under natural sunlight, thereby realizing a temperature-adaptive thermal management system.

Visualization of rapid electron precipitation via chorus element wave-particle interactions.

Chorus waves, among the most intense electromagnetic emissions in the Earth's magnetosphere, magnetized planets, and laboratory plasmas, play an important role in the acceleration and loss of energetic electrons in the plasma universe through resonant interactions with electrons. However, the spatial evolution of the electron resonant interactions with electromagnetic waves remains poorly understood owing to imaging difficulties. Here we provide a compelling visualization of chorus element wave-particle interactions in the Earth's magnetosphere. Through in-situ measurements of chorus waveforms with the Arase satellite and transient auroral flashes from electron precipitation events as detected by 100-Hz video sampling from the ground, Earth's aurora becomes a display for the resonant interactions. Our observations capture an asymmetric spatial development, correlated strongly with the amplitude variation of discrete chorus elements. This finding is not theoretically predicted but helps in understanding the rapid scattering processes of energetic electrons near the Earth and other magnetized planets.

Auroral molecular-emission effects on the atomic oxygen line at 777.4 nm.

One of the representative auroral emission lines that radiates from F-region heights and is measurable on the ground is the 777.4 nm line from excited atomic oxygen. This line has been adopted, along with another E-region emission line, for example 427.8 nm, to estimate the mean energy and total energy flux of precipitating auroral electrons. The influence of emissions from part of the molecular nitrogen band, which mainly radiate from E-region heights, should be carefully evaluated because it might overlap the 777.4 nm atomic oxygen line in the spectrum. We performed statistical analysis of auroral spectrograph measurements that were obtained during the winter of 2016-2017 in Tromsø, Norway, to derive the ratio of the intensity of the 777.4 nm atomic oxygen line to that of the net measurement through a typically used optical filter with a full width at half maximum of a few nm. The ratio had a negative trend against geomagnetic activity, with a primary distribution of 0.5-0.7 and a minimum value of 0.3 for the most active auroral condition in this study. This result suggests that the 30-50% emission intensities measured through the optical filter may be from the molecular nitrogen band.

Structure-Activity Relationship Studies of Pyrimido[5,4-b]indoles as Selective Toll-Like Receptor 4 Ligands.

Previous high throughput screening studies led to the discovery of two novel, nonlipid-like chemotypes as Toll-like receptor 4 (TLR4) agonists. One of these chemotypes, the pyrimido[5,4-b]indoles, was explored for structure-activity relationship trends relative to production of TLR4 dependent cytokines/chemokines, resulting in a semioptimized lead (compound 1) that provided a starting point for further optimization studies. In this report, compounds belonging to three areas of structural modification were evaluated for biological activity using murine and human TLR4 reporter cells, primary murine bone marrow derived dendritic cells, and human peripheral blood mononuclear cells. The compounds bearing certain aryl groups at the C8 position, such as phenyl (36) and ß-naphthyl (39), had potencies significantly greater than compound 1. Compound 36 displayed human TLR4 agonist activity at submicromolar concentrations. The computational analysis suggests that the improved potency of these C8-aryl derivatives may be the result of additional binding interactions at the interface of the TLR4/myeloid differentiation protein-2 (MD-2) complex.