A bimodal distribution of haze in Pluto’s atmosphere

Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto’s haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan’s haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels ~0.5 Pa and favors a photochemical rather than a dynamical origin for the formation of Titan’s detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.

Bioinspired Self-Shaping Clay Composites for Sustainable Development

Bioinspired self-shaping is an approach used to transform flat materials into unusual three-dimensional (3D) shapes by tailoring the internal architecture of the flat material. Bioinspiration and bioinspired materials have a high potential for fostering sustainable development, yet are often fashioned out of expensive and synthetic materials. In this work, we use bioinspiration to endow clay with self-shaping properties upon drying. The composites created are based on clay and starch, and the internal architecture is built using celery fibers. The viscosity, shrinkage, and bending of the architected composite monolayers are studied for several compositions by measuring penetration depth and using optical characterization methods. Bilayer structures inspired from plants are then processed using a simple hand layup process to achieve bending, twisting, and combinations of those after drying. By layering a mixture of 32 vol% clay, 25.8 vol% starch, and 42.2 vol% water with 40 wt% embedded aligned celery fibers, it is possible to obtain the desired shape change. The work presented here aims at providing a simple method for teaching the concept of bioinspiration, and for creating new materials using only clay and plant-based ingredients. Rejuvenating clay with endowed self-shaping properties could further expand its use. Furthermore, the materials, methods, and principles presented here are affordable, simple, largely applicable, and could be used for sustainable development in the domain of education as well as materials and structures.

Growth and Deformation Simulation of Aluminum Bronze Grains Produced by Electron Beam Additive Manufacturing

When working out 3D building-up modes, it is necessary to predict the material properties of the resulting products. For this purpose, the crystallography of aluminum bronze grains after electron beam melting has been studied by EBSD analysis methods. To estimate the possibility of sample form changes by pressure treatment, we simulated structural changes by the method of molecular dynamics during deformation by compression of individual grains of established growth orientations. The analysis was carried out for free lateral faces and grain deformation in confined conditions. Simulation and experiments on single crystals with free lateral faces revealed the occurrence of stepwise deformation in different parts of the crystal and its division into deformation domains. Each domain is characterized by a shear along a certain slip system with the maximum Schmidt factor. Blocking the shear towards the lateral faces leads to selectivity of the shear along the slip systems that provide the required shape change. Based on the simulation results, the relationship between stress–strain curves and structural characteristics is traced. A higher degree of strain hardening and a higher density of defects were found upon deformation in confined conditions. The deformation of the columnar grains of the built material occurs agreed with the systems with the maximum Schmidt factor.

Photothermal and Reorientational Contributions to the Photomechanical Response of DR1 Azo Dye-Doped PMMA Fibers

This work is a comprehensive experimental and theoretical study aimed at understanding the photothermal and molecular shape-change contributions to the photomechanical effect of polymers doped with azo dyes. Our prototypical system is the azobenzene dye Disperse Red 1 (DR1) doped into poly (methyl methacrylate) (PMMA) polymer formed into optical fibers. We start by determining the thermo-mechanical properties of the materials with a temperature-dependent stress measurement. The material parameters, so determined, are used in a photothermal heating model—with no adjustable parameters—to predict its contribution. The photothermal heating model predicts the observations, ruling out mechanisms originating in light-induced shape changes of the dopant molecules. The photomechanical tensor response along the two principle axes in the uniaxial approximation is measured and compared with another independent theory of photothermal heating and angular hole burning/reorientation. Again, the results are consistent only with a purely thermal response, showing that effects due to light-induced shape changes of the azo dyes are negligible. The measurements are repeated as a function of polymer chain length and the photomechanical efficiencies determined. We find the results to be mostly chain-length independent.

Surface Measurement of a Large Inflatable Reflector in Cryogenic Vacuum

The metrology of membrane structures, especially inflatable, curved, optical surfaces, remains challenging. Internal pressure, mechanical membrane properties, and circumferential boundary conditions imbue highly dynamic slopes to the final optic surface. Here, we present our method and experimental results for measuring a 1 m inflatable reflector’s shape response to dynamic perturbations in a thermal vacuum chamber. Our method uses phase-measuring deflectometry to track shape change in response to pressure change, thermal gradient, and controlled puncture. We use an initial measurement as a virtual null reference, allowing us to compare 500 mm of measurable aperture of the concave f/2, 1-meter diameter inflatable optic. We built a custom deflectometer that attaches to the TVAC window to make full use of its clear aperture, with kinematic references behind the test article for calibration. Our method produces 500 × 500 pixel resolution 3D surface maps with a repeatability of 150 nm RMS within a cryogenic vacuum environment (T = 140 K, P = 0.11 Pa).

Assessment of the Durability of Threaded Joints

The article deals with the determination of the resistance to cyclic loading of the threaded joints of pressure vessels and defective elements according to the failure mechanics criteria. Theoretical and experimental studies do not provide a sufficient basis for the existing calculation methods for the cyclic strength of the threaded joints of pressure vessels. The short crack kinetics in the threaded joints, a shakedown in one of the joint elements of pressure vessels, i.e., in the bolt or stud, has not been studied sufficiently. The calculation methods designed and improved within the study were based on theoretical and experimental investigations and were simplified for convenient application to engineering practice. The findings could be used to investigate the shakedown of studs of a different cross-section with an initiating and propagating crack. Value: the developed model for the assessment of durability of the threaded joints covers the patterns of resistance to cyclic failure (limit states: crack initiation, propagation, final failure) and shakedown (limit states: progressive shape change and plastic failure). Analysis-based solutions of plastic failure conditions and progressive shape change were accurate (the result was reached using a two-sided approach; the solutions were obtained in view of the parameters of the cyclic failure process in the stud (bolt) and based on experimental investigations of the threaded joints).

Autonomous epithelial folding induced by an intracellular mechano–polarity feedback loop

Epithelial tissues form folded structures during embryonic development and organogenesis. Whereas substantial efforts have been devoted to identifying mechanical and biochemical mechanisms that induce folding, whether and how their interplay synergistically shapes epithelial folds remains poorly understood. Here we propose a mechano–biochemical model for dorsal fold formation in the early Drosophila embryo, an epithelial folding event induced by shifts of cell polarity. Based on experimentally observed apical domain homeostasis, we couple cell mechanics to polarity and find that mechanical changes following the initial polarity shifts alter cell geometry, which in turn influences the reaction-diffusion of polarity proteins, thus forming a feedback loop between cell mechanics and polarity. This model can induce spontaneous fold formation in silico, recapitulate polarity and shape changes observed in vivo, and confer robustness to tissue shape change against small fluctuations in mechanics and polarity. These findings reveal emergent properties of a developing epithelium under control of intracellular mechano–polarity coupling.

In-situ X-ray Computed Tomography of Zinc-Air Primary Cells during Discharge: Correlating Discharge Rate to Anode Morphology

Zinc-air batteries are gaining attention as safe battery alternatives, with high theoretical energy densities and a high abundance of their constituent materials. However, barriers to their widespread adoption include the need to improve their cycling lifetime, as well as stability and avoiding degradation mechanisms such as zinc dendrite growth and hydrogen-producing side reactions. X-ray computed tomography (CT) is a widely used technique for the study of batteries. In-situ/operando X-ray CT has been increasingly used to study the zinc anode of zinc-air batteries to evaluate the interesting morphological changes occurring during the reaction from Zn to ZnO during discharge (vice versa during charge). However, several studies have been carried out using synchrotron X-ray sources, which have limited availability for users. In this work, we present a comprehensive study of the discharge of commercial, primary zinc-air batteries using a laboratory based X-ray source for in-situ X-ray CT measurements. Four different discharge rates are investigated (C/30, C/60, C/90 and C/150), with tomograms collected at various stages throughout each discharge. Results confirm that with decreasing C-rate (i.e., decreasing discharge current) a greater volume of zinc is reacted, with average mass utilisations of 17%, 76%, 81% and 87% for C/30, C/60, C/90 and C/150, respectively. Furthermore, quantification using X-ray CT datasets showed that there is a direct correlation between the volume of zinc remaining in the cell and the state of charge (SoC) of the cell, which deviated from linearity for the longer C-rates. Finally, a potential new mechanism for shape change is discussed, where a zinc particle is replaced with a pore of a similar volume. As well as improvements in statistical relevance gained from multiple repeats for each C-rate, the results presented here could be used in both modelling of battery performance, as well as consideration for future anode design concepts.