Albert Yu-Min Lin

Mechanical strength of abalone nacre: Role of the soft organic layer

The nacreous portion of the abalone shell is composed of calcium carbonate crystals interleaved with layers of viscoelastic proteins. The resulting structure yields unique mechanical properties. In this study, we focus on the thin viscoelastic layers between the tiles and on their role on the mechanical properties of the shell. Both SEM and AFM show that the thin (approximately 30 nm) organic layer is porous, containing holes with diameter of approximately 50 nm. These holes enable the formation of mineral bridges between adjacent tile layers. The mineral bridges play a pivotal role in growth and ensure the maintenance of the same crystallographic relationship through tile growth in the terraced cone mode. The existence of mineral bridges is consistent with the difference between tensile and compressive strength of the abalone. Mechanical tests with loading applied perpendicular to the plane of the organic layers reveal a tensile strength lower than 10 MPa, whereas the compressive strength is approximately 300-500 MPa. These nanoscale bridges have, by virtue of their dimensions (50 nm diameter x 30 nm length), a strength that reaches their theoretical value. The calculated tensile strength based on the theoretical strength predicts a bridge density of approximately 2.25/microm(2). A major conclusion of this investigation is that the role of the organic layer is primarily to subdivide the CaCO(3) matrix into platelets with thickness of 0.5 microm. Its intrinsic effect in providing a glue between adjacent tiles may not be significant.

Structure and mechanical properties of crab exoskeletons

The structure and mechanical properties of the exoskeleton (cuticle) of the sheep crab (Loxorhynchus grandis) were investigated. The crab exoskeleton is a natural composite consisting of highly mineralized chitin-protein fibers arranged in a twisted plywood or Bouligand pattern. There is a high density of pore canal tubules in the direction normal to the surface. These tubules have a dual function: to transport ions and nutrition and to stitch the structure together. Tensile tests in the longitudinal and normal to the surface directions were carried out on wet and dry specimens. Samples tested in the longitudinal direction showed a convex shape and no evidence of permanent deformation prior to failure, whereas samples tested in the normal orientation exhibited a concave shape. The results show that the composite is anisotropic in mechanical properties. Microindentation was performed to measure the hardness through the thickness. It was found that the exocuticle (outer layer) is two times harder than the endocuticle (inner layer). Fracture surfaces after testing were observed using scanning electron microscopy; the fracture mechanism is discussed.

Biological materials: a materials science approach.

The approach used by Materials Science and Engineering is revealing new aspects in the structure and properties of biological materials. The integration of advanced characterization, mechanical testing, and modeling methods can rationalize heretofore unexplained aspects of these structures. As an illustration of the power of this methodology, we apply it to biomineralized shells, avian beaks and feathers, and fish scales. We also present a few selected bioinspired applications: Velcro, an Al2O3-PMMA composite inspired by the abalone shell, and synthetic attachment devices inspired by gecko.

Interfacial shear strength in abalone nacre.

The shear strength of the interface between tiles of aragonite in the nacre of red abalone Haliotis rufescens was investigated through mechanical tensile and shear tests. Dog-bone shaped samples were used to determine the tensile strength of nacre when loaded parallel to the plane of growth; the mean strength was 65 MPa. Shear tests were conducted on a special fixture with a shear gap of 200 microm, approximately 100 microm narrower than the spacing between mesolayers. The shear strength is found to be 36.9+/-15.8 MPa with an average maximum shear strain of 0.3. Assuming the majority of failure occurs through tile pull-out and not through tile fracture, the tensile strength can be converted into a shear strength of 50.9 MPa. Three mechanisms of failure at the tile interfaces are discussed: fracture of mineral bridges, toughening due to friction created through nanoasperities, and toughening due to organic glue. An additional mechanism is fracture through individual tiles.

Combining GeoEye-1 Satellite Remote Sensing, UAV Aerial Imaging, and Geophysical Surveys in Anomaly Detection Applied to Archaeology

This paper describes a method of combined ultra-high resolution satellite imaging, unmanned aerial vehicle (UAV) photography, and sub-surface geophysical investigation for anomaly detection, which was employed in a non-invasive survey of three archaeological sites in Northern Mongolia. The surveyed sites were a Bronze Age burial mound, a Turkish period tomb, and a steppe city fortification of unknown origin. For the satellite survey, 50 cm resolution pan-sharpened imagery was generated through a combination of multispectral and panchromatic data, collected from the GeoEye-1 earth-sensing satellite. The imagery was then used to identify the location of the aforementioned sites in an approximate area of 3000 km2 . Aerial photographs of the sites were obtained with two customized electric-powered UAVs: a fixed flying wing rear-propulsion plane and a multi-propeller “oktokopter” helicopter system. Finally, geophysical investigation was conducted with a GSM-19 Overhouser gradiometer, an EM38 electromagnetometer, and an IDS Detector Duo ground penetrating radar. The satellite imagery and aerial photographs were combined with the geophysical survey results and on-site surface observations to provide insight and contextual information about anomalies in multiple layers of data. The results highlight the effectiveness and robustness of the employed method for archaeological investigation in large, rugged and scarcely populated areas.

Small Unmanned Aerial Vehicle System for Wildlife Radio Collar Tracking

This paper describes a low cost system for tracking wildlife that is equipped with radio collars. Currently, researchers have to physically go into the field with a directional antenna to try to pinpoint the VHF (very high frequency) signal originating from a wildlife tracking collar. Depending on the terrain, it could take an entire day to locate a single animal. To vastly improve upon this traditional approach, the system proposed here utilizes a small fixed-wing aircraft drone with a simple radio on-board, flying an automated mission. Received signal strength is recorded, and used to create a heat map that shows the collars position. A prototype of this system was built using off-the-shelf hardware and custom signal processing algorithms. Initial field tests confirm the systems capabilities and its promise for wildlife tracking.

Crowdsourcing the Unknown: The Satellite Search for Genghis Khan

Massively parallel collaboration and emergent knowledge generation is described through a large scale survey for archaeological anomalies within ultra-high resolution earth-sensing satellite imagery. Over 10K online volunteers contributed 30K hours (3.4 years), examined 6,000 km2, and generated 2.3 million feature categorizations. Motivated by the search for Genghis Khans tomb, participants were tasked with finding an archaeological enigma that lacks any historical description of its potential visual appearance. Without a pre-existing reference for validation we turn towards consensus, defined by kernel density estimation, to pool human perception for “out of the ordinary” features across a vast landscape. This consensus served as the training mechanism within a self-evolving feedback loop between a participant and the crowd, essential driving a collective reasoning engine for anomaly detection. The resulting map led a National Geographic expedition to confirm 55 archaeological sites across a vast landscape. A increased ground-truthed accuracy was observed in those participants exposed to the peer feedback loop over those whom worked in isolation, suggesting collective reasoning can emerge within networked groups to outperform the aggregate independent ability of individuals to define the unknown.

Sensor platforms for multimodal underwater monitoring

Surprisingly little is known about underwater marine environments and ecosystems owing to several factors. One important factor has been the general inability to observe and monitor these massive subsurface ocean spaces. Despite significant advances in sensor, communication and computing technology, underwater sensor platforms are generally inferior to their terrestrial counterparts. Here we highlight several sensor platforms that are currently being used and developed for underwater monitoring applications. We focus on two monitoring applications: 1) observation of whale sharks (Rhincodon typus); and 2) transport, accumulation and dispersion of plankton. In both cases, we describe the need for multimodal underwater sensor platforms to work in a cyber-physical mode, communicating a variety of different sensor data among them systematically to maximize acquisition of data. We think that this will substantially enhance understanding underwater ecosystems.

A virtual excavation: combining 3D immersive virtual reality and geophysical surveying

The projection of multi-layered remote sensing and geophysical survey data into a 3D immersive virtual reality environment for noninvasive archaeological exploration is described. Topography, ultra-high resolution satellite imagery, magnetic, electromagnetic, and ground penetrating radar surveys of an archaeological site are visualized as a single data set within the six-sided (including floor) virtual reality (VR) room known as the StarCAVE. These independent data sets are combined in 3D space through their geospatial orientation to facilitate the detection of physical anomalies from signatures observed across various forms of surface and subsurface surveys. The data types are highly variant in nature and scale, ranging from 2D imagery to massive scale point clouds. As a reference base-layer a site elevation map was produced and used as to normalize and correlate the various forms of collected data within a single volume. Projecting this volume within the StarCAVE facilitates immersive and collaborative exploration of the virtual site at actual scale of the physical site.

Visual analytics of inherently noisy crowdsourced data on ultra high resolution displays

The increasing prevalence of distributed human microtasking, crowdsourcing, has followed the exponential increase in data collection capabilities. The large scale and distributed nature of these microtasks produce overwhelming amounts of information that is inherently noisy due to the nature of human input. Furthermore, these inputs create a constantly changing dataset with additional information added on a daily basis. Methods to quickly visualize, filter, and understand this information over temporal and geospatial constraints is key to the success of crowdsourcing. This paper present novel methods to visually analyze geospatial data collected through crowdsourcing on top of remote sensing satellite imagery. An ultra high resolution tiled display system is used to explore the relationship between human and satellite remote sensing data at scale. A case study is provided that evaluates the presented technique in the context of an archaeological field expedition. A team in the field communicated in real-time with and was guided by researchers in the remote visual analytics laboratory, swiftly sifting through incoming crowdsourced data to identify target locations that were identified as viable archaeological sites.