Extraterrestrial, shock-formed, cage-like nanostructured carbonaceous materials

Shock caused by impacts can convert carbonaceous material to diamond. During this transition, new materials can form that depend on the structure of the starting carbonaceous materials and the shock conditions. Here we report the discovery of cage-like nanostructured carbonaceous materials, including carbon nano-onions and bucky-diamonds, formed through extraterrestrial impacts in the Gujba (CBa) meteorite. The nano-onions are fullerene-type materials and range from 5 to 20 nm; the majority shows a graphitic core-shell structure, and some are characterized by fully curved, onion-like graphitic shells. The core is either filled with carbonaceous material or empty. We show the first, natural, 4 nm sized bucky-diamond, which is a type of carbon nano-onion consisting of multilayer graphitic shells surrounding a diamond core. We propose that the nano-onions formed during shock metamorphism, either the shock or the release wave, of the pre-existing primitive carbonaceous material that included nanodiamonds, poorly ordered graphitic material, and amorphous carbonaceous nanospheres. Bucky-diamonds could have formed either through the high-pressure transformation of nano-onions, or as an intermediate material in the high-temperature transformation of nanodiamond to nano-onion. Impact processing of planetary materials was and is a common process in our solar system, and by extension, throughout extrasolar planetary bodies. Together with our previous discovery of interstratified graphite-diamond in Gujba, our new findings extend the range of nano-structured carbonaceous materials formed in nature. Shock-formed nano-onions and bucky-diamonds are fullerene-type structures, and as such they could contribute to the astronomical 217.5 nm absorption feature.

One-dimensional analyses of striker impact on bar with different general impedance

The particle velocity and stress in the striker and bar generated by the striker impact on a bar with different general impedance are formulated based on one-dimensional assumptions. Departure of the impact-generated stress wave towards the rear end of the striker and arrival of the release wave from the rear to the front of the striker constitute one impact cycle. In cases where Zs ≤ Zb ( Z is the general impedance, and subscripts ‘s’ and ‘b’ denote striker and bar, respectively), only one impact cycle takes place because the striker is stationary or separated from the impact surface after the first impact cycle. As a result, only a single (primary) pulse is observed in the bar and striker. In the case where Zs > Zb, however, multiple impact cycles take place because the striker is compressing the bar continually after the first cycle. As a result, a series of step-wise residual pulses follow the primary pulse in the bar and striker. The magnitudes of the stress and particle velocity in the bar and striker calculated using the formulated equations are quantitatively consistent with the results of the numerical simulations, verifying the formulated one-dimensional equations. The equations formulated in this study may be useful for better understanding the various wave interaction phenomena that take place in a pseudo-one-dimensional impact system and for modifying/designing an impact system.

Малогазовая детонация в низкоплотных механоактивированных порошковых смесях

Experimental data on supersonic self-sustaining propagation of the energy release wave in low-density mechanically activated powder mixtures are analyzed. Various mechanisms that may be responsible for this process are analyzed, and a mechanism for the detonation-like propagation of the reaction in powder mixtures is proposed. It is shown that under certain conditions this process has all the signs of detonation and should be recognized as one of the types of detonation. It is shown that this type of detonation is fundamentally different from the classical "ideal" detonation, for example, in gases: instead of a shock wave, a compaction wave propagates through the powder mixture, in which there is basically no compression of the particle material, but powder compaction occurs due to the mutual rearrangement of particles. In this case, the initiation of a chemical reaction occurs due to the mutual friction of the oxidizer and fuel particles in the powder compaction wave.

Observation of the Velocity Variation of an Explosively-Driven Flat Flyer Depending on the Flyer Width

Lim proposed a theoretical study on the velocity profile of an explosively-driven flat flyer affected by the rarefaction (or release wave) intrusion during the metal’s projection. This work shows somewhat reasonable agreement in a given range. However, this work is limited only in the early stage of detonation (~3 µs), and the larger scaled flyer projection (or extended time duration) behavior is needed for an engineering perspective. As continued work originating from this investigation, the velocity profile of explosively-driven flyers with different widths is studied based on multiple different approaches which include hydrocode simulation, the Gurney model, and Baum’s side loss correction (or effective charge mass approach), followed by a series of field experiments. In this study, the focus is on the observation of the flat flyer velocity (or terminal velocity) variation, depending on the width of the flyers which vary from 12, 25, 50, and 75 mm (or 100 mm). The terminal velocity profile variation, depending on the flyer width, is observed, and a general trend is identified.

Tail walking in a bottlenose dolphin community: the rise and fall of an arbitrary cultural ‘fad’

Social learning of adaptive behaviour is widespread in animal populations, but the spread of arbitrary behaviours is less common. In this paper, we describe the rise and fall of a behaviour called tail walking, where a dolphin forces the majority of its body vertically out of the water and maintains the position by vigourously pumping its tail, in a community of Indo-Pacific bottlenose dolphins ( Tursiops aduncus ). The behaviour was introduced into the wild following the rehabilitation of a wild female individual, Billie, who was temporarily co-housed with trained dolphins in a dolphinarium. This individual was sighted performing the behaviour seven years after her 1988 release, as was one other female dolphin named Wave. Initial production of the behaviour was rare, but following Billie's death two decades after her release, Wave began producing the behaviour at much higher rates, and several other dolphins in the community were subsequently sighted performing the behaviour. Social learning is the most likely mechanism for the introduction and spread of this unusual behaviour, which has no known adaptive function. These observations demonstrate the potential strength of the capacity for spontaneous imitation in bottlenose dolphins, and help explain the origin and spread of foraging specializations observed in multiple populations of this genus.

Incorporating the effects of upstream ice jam releases in the prediction of flood levels in the Hay River delta, Canada

The town of Hay River, located in the Northwest Territories, Canada, is vulnerable to ice jam flooding occurring in the adjacent Hay River delta. The most extreme flooding events have occurred when ice jams in the channels of the delta were pushed downstream towards the mouth at Great Slave Lake. This movement has been linked to incoming waves from ice jam release in the upstream reaches of the Hay River. This study incorporated the effect of an upstream ice jam release wave into the prediction of ice jam caused flood levels in the delta by integrating three one-dimensional models. The method was validated with observed breakup events and then used to simulate various combinations of ice and water conditions in the river and the delta. Multiple linear regression analyses were applied to the results to develop a prediction tool for assessing ice jam flood risk.

Void Nucleation and Growth at Grain Boundaries in Copper Bicrystals With Surface Perturbations

Material failure on the microstructural level is important in determining macroscale behavior. When a material is subjected to dynamic (shock) loading conditions, damage and deformation patterns due to spall failure can provide a basis for connecting micro- to macroscale behavior. By analyzing deformation patterns at and around interfaces and boundaries that are representative of those found in engineering materials at high strain rates, we can develop stronger structures that can withstand impact collisions and rapid crack propagation. The addition of surface perturbations to one side of the samples provides insight on how strain localization occurs during the shock loading process and how the rippled release wave interacts with the boundary. Copper bicrystal samples were grown from two single crystal seeds using the vertical Bridgeman technique. A photolithography process was developed to create periodic surface perturbations on one side of the samples. The square wave ripples had a 150 μm wavelength and 5 μm amplitude. The bicrystals were shocked using laser ablation on the perturbation side at the Trident laser at Los Alamos National Laboratory and monitored using a VISAR (velocity interferometer systems for any reflector) and TIDI (transient imaging displacement interferometry) system. Shock pressures used were around 8–10 GPa. Targets measured 5 mm in diameter and 100 microns thick. The orientations of the grains were [001] and [111] along the shock direction with a 50° misorientation angle for the boundary, which was aligned parallel to the shock direction. Samples were soft recovered and cross-sectioned to perform quantitative characterization of damage using electron backscattering diffraction (EBSD) and Scanning Electron Microscopy (SEM) to gather information on the characteristics of the grain boundary and its surroundings, with emphasis on how the rippled surfaces and material anisotropy affected strain localization and spallation, initial results show that damage indeed localized at the grain boundary and that surface perturbations led to heterogeneity of spall damage distribution in the grain bulks.