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Evidence of an oceanic impact and megatsunami sedimentation in Chryse Planitia, Mars
In 1976, NASA's Viking 1 Lander (V1L) was the first spacecraft to operate successfully on the Martian surface. The V1L landed near the terminus of an enormous catastrophic flood channel, Maja Valles. However, instead of the expected megaflood record, its cameras imaged a boulder-strewn surface of elusive origin. We identified a 110-km-diameter impact crater (Pohl) ~ 900 km northeast of the landing site, stratigraphically positioned (a) above catastrophic flood-eroded surfaces formed ~ 3.4 Ga during a period of northern plains oceanic inundation and (b) below the younger of two previously hypothesized megatsunami deposits. These stratigraphic relationships suggest that a marine impact likely formed the crater. Our simulated impact-generated megatsunami run-ups closely match the mapped older megatsunami deposit's margins and predict fronts reaching the V1L site. The site's location along a highland-facing lobe aligned to erosional grooves supports a megatsunami origin. Our mapping also shows that Pohl's knobby rim regionally represents a broader history of megatsunami modification involving circum-oceanic glaciation and sedimentary extrusions extending beyond the recorded megatsunami emplacement in Chryse Planitia. Our findings allow that rocks and soil salts at the landing site are of marine origin, inviting the scientific reconsideration of information gathered from the first in-situ measurements on Mars.
Journal Article
Body Composition in Sport, Exercise and Health
The analysis of body composition (fat, bone and muscle) is an important process throughout the biomedical sciences. This is the first book to offer a clear and detailed introduction to the key methods and techniques in body composition analysis and to explain the importance of body composition data in the context of sport, exercise and health.
With contributions from some of the world's leading body composition specialists, the book goes further than any other in demonstrating the practical and applied value of body composition analysis in areas such as performance sport and weight control in clinical populations. The book pays particular attention to the important concept of change in body composition, and includes discussion of ethical issues in the collection, interpretation and presentation of data, and considerations when working with special populations.
Bridging the gap between research methods and practical application, this book is important reading for advanced students and practitioners working in sport and exercise science, health science, anatomy, nutrition, physical therapy or ergonomics.
eBook
Multi-functional direct shear apparatus for geosynthetic interfaces with its application on various GMB/GCL interfaces
A geosynthetic liner system that consists of geomembrane (GMB) and geosynthetic clay liner (GCL) is vital for landfill stability analysis and it is essential to investigate the shear characteristics of GMB/GCL interface. This paper introduces a new direct shear apparatus for various geosynthetic interfaces with innovative designing, and using this apparatus 48 shear test sets of four GMB/GCL interface types are conducted under a normal stress level of 100–500 kPa and a shear rate of 0.1–100 mm/min. Effects of the surface roughness of GMB and the hydration condition of GCL on the shear stress–displacement relationship and shear strength of interfaces are investigated. Results show that the evolution of physical phenomena from shear deformation of GCL (denoted as shear phase) to frictional slip between GMB and GCL (denoted as friction phase) occurs at the critical state of peak shear strength where GMB/GCL interfaces provide the largest shear resistance. For GMB/hydrated GCL, shear phase can be further divided into pure shear phase and reinforced shear phase by initial peak strength. Thus, phased shear mechanism of GMB/GCL interface is revealed with explanations on physical and mechanical results. Some future prospects on GMB/GCL interfaces are also proposed.
Journal Article
Chimera states in mechanical oscillator networks
The synchronization of coupled oscillators is a fascinating manifestation of self-organization that nature uses to orchestrate essential processes of life, such as the beating of the heart. Although it was long thought that synchrony and disorder were mutually exclusive steady states for a network of identical oscillators, numerous theoretical studies in recent years have revealed the intriguing possibility of “chimera states,” in which the symmetry of the oscillator population is broken into a synchronous part and an asynchronous part. However, a striking lack of empirical evidence raises the question of whether chimeras are indeed characteristic of natural systems. This calls for a palpable realization of chimera states without any fine-tuning, from which physical mechanisms underlying their emergence can be uncovered. Here, we devise a simple experiment with mechanical oscillators coupled in a hierarchical network to show that chimeras emerge naturally from a competition between two antagonistic synchronization patterns. We identify a wide spectrum of complex states, encompassing and extending the set of previously described chimeras. Our mathematical model shows that the self-organization observed in our experiments is controlled by elementary dynamical equations from mechanics that are ubiquitous in many natural and technological systems. The symmetry-breaking mechanism revealed by our experiments may thus be prevalent in systems exhibiting collective behavior, such as power grids, optomechanical crystals, or cells communicating via quorum sensing in microbial populations.
Journal Article
Reinforcement learning for bluff body active flow control in experiments and simulations
We have demonstrated the effectiveness of reinforcement learning (RL) in bluff body flow control problems both in experiments and simulations by automatically discovering active control strategies for drag reduction in turbulent flow. Specifically, we aimed to maximize the power gain efficiency by properly selecting the rotational speed of two small cylinders, located parallel to and downstream of the main cylinder. By properly defining rewards and designing noise reduction techniques, and after an automatic sequence of tens of towing experiments, the RL agent was shown to discover a control strategy that is comparable to the optimal strategy found through lengthy systematically planned control experiments. Subsequently, these results were verified by simulations that enabled us to gain insight into the physical mechanisms of the drag reduction process. While RL has been used effectively previously in idealized computer flow simulation studies, this study demonstrates its effectiveness in experimental fluid mechanics and verifies it by simulations, potentially paving the way for efficient exploration of additional active flow control strategies in other complex fluid mechanics applications.
Journal Article