Name: a robotic platform to study the foreflipper of the california sea lion
Uploaded: 2017-01-10T12:30:00
Description: Watch this Scientific Journal Video about A Robotic Platform to Study the Foreflipper of the California Sea Lion at JoVE.com

The authors would like to thank the George Washington University Facilitating Fund for financial support of the project. Mr. Patel is grateful the George Washington University School of Engineering and Applied Science Summer Undergraduate Program in Engineering Research and the Undergraduate Research award for financial support. Finally, we are grateful to the GWU Center for Biomemetics and Bioinspired Engineering (COBRE) for use of facilities controlled by the center.

1. Digitize a Specimen of a Sea Lion Foreflipper
<ol>
	<li>Scan a specimen of a Sea lion foreflipper.
	<ol>
		<li>Obtain a specimen of a sea lion flipper from a deceased individual (Figure 1a). 
		NOTE: In our case, they were obtained from the Smithsonian Zoological Park in Washington, D.C.</li>
		<li>Hang the foreflipper vertically from its base (where the foreflipper attaches to the animal&#39;s body). This both allows the flipper to be straight when scanned, and exposes the entire surface for scanning.</...

<ol>
	<li>Feldkamp, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Swimming+in+the+California+sea+lion:+Morphometrics,+drag+and+energetics.">Swimming in the California sea lion: Morphometrics, drag and energetics.</a> Journal of Experimental Biology. 131, 117-135 (1987).</li><li>Godfrey, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Additional+observations+of+subaqueous+locomotion+in+the+California+sea+lion+(zalophus+californianus).">Additional observations of subaqueous locomotion in the California sea lion (zalophus californianus).</a> Aquatic Mammals. 11 (2), 53-57 (1985).</li><li>Stelle, L. L., Blake, R. W., Trites, A. 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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+kinematics+of+the+California+sea+lion+foreflipper+during+forward+swimming.">The kinematics of the California sea lion foreflipper during forward swimming.</a> Bioinspiration and Biomimetics. 9 (4), (2014).</li><li>Friedman, C., Joel, B. W., Schult, A. R., Leftwich, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noninvasive+3D+geometry+extraction+of+a+Sea+lion+foreflipper.">Noninvasive 3D geometry extraction of a Sea lion foreflipper.</a> Journal of Aero Aqua Bio-mechanisms. 4 (1), 25-31 (2015).</li><li>Aguilar, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+locomotion+robophysics:+the+study+of+movement+at+the+intersection+of+robotics,+soft+matter+and+dynamical+systems.">A review on locomotion robophysics: the study of movement at the intersection of robotics, soft matter and dynamical systems.</a> Rep Prog Phys. 79 (11), 110001 (2016).</li><li>Holmes, P., Koditschek, D., Guckenheimer, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dynamics+of+legged+locomotion:+models,+analyses,+and+challenges.">The dynamics of legged locomotion: models, analyses, and challenges.</a> Dynamics. 48 (2), 207-304 (2006).</li><li>Mazouchova, N., Umbanhowar, P. B., Goldman, D. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flipper-driven+terrestrial+locomotion+of+a+sea+turtle-inspired+robot.">Flipper-driven terrestrial locomotion of a sea turtle-inspired robot.</a> Bioinspiration &amp; Biomimetics. 8 (2), 026007 (2013).</li><li>Hultmark, M., Leftwich, M. C., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flowfield+measurements+in+the+wake+of+a+robotic+lamprey.">Flowfield measurements in the wake of a robotic lamprey.</a> Experiments in fluids. 43 (5), 683-690 (2007).</li><li>Ijspeert, A. J., Crespi, A., Ryczko, D., Cabelguen, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+swimming+to+walking+with+a+salamander+robot+driven+by+a+spinal+cord+model.">From swimming to walking with a salamander robot driven by a spinal cord model.</a> Science. 315 (5817), 1416-1420 (2007).</li><li>Buchholz, J. H., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+evolution+of+the+wake+structure+produced+by+a+low-aspect-ratio+pitching+panel.">On the evolution of the wake structure produced by a low-aspect-ratio pitching panel.</a> Journal of fluid mechanics. 546, 433-443 (2006).</li><li>Lauder, G. V., Anderson, E. J., Tangorra, J., Madden, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fish+biorobotics:+kinematics+and+hydrodynamics+of+self-propulsion.">Fish biorobotics: kinematics and hydrodynamics of self-propulsion.</a> Journal of Experimental Biology. 210 (16), 2767-2780 (2007).</li><li>Leftwich, M. C., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thrust+production+by+a+mechanical+swimming+lamprey.">Thrust production by a mechanical swimming lamprey.</a> Experiments in fluids. 50 (5), 1349-1355 (2011).</li><li>Leftwich, M. C., Tytell, E. D., Cohen, A. H., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wake+structures+behind+a+swimming+robotic+lamprey+with+a+passively+flexible+tail.">Wake structures behind a swimming robotic lamprey with a passively flexible tail.</a> Journal of Experimental Biology. 215 (3), 416-425 (2012).</li><li>Buchholz, J. H., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+wake+structure+and+thrust+performance+of+a+rigid+low-aspect-ratio+pitching+panel.">The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel.</a> Journal of fluid mechanics. 603, 331-365 (2008).</li><li>Quinn, D. B., Lauder, G. V., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+the+propulsive+performance+of+heaving+flexible+panels.">Scaling the propulsive performance of heaving flexible panels.</a> Journal of fluid mechanics. 738, 250-267 (2014).</li><li>Quinn, D. B., Lauder, G. V., Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+propulsors+in+ground+effect.">Flexible propulsors in ground effect.</a> Bioinspiration &amp; biomimetics. 9 (3), 036008 (2014).</li><li>English, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+anatomy+of+the+hands+of+fur+seals+and+sea+lions.">Functional anatomy of the hands of fur seals and sea lions.</a> American Journal of Anatomy. 147 (1), 1-17 (1976).</li><li>. PRONET-E Quick Start Guide Available from: <a target="_blank" href="https://www.anaheimautomation.com/manuals/servo/L011035%20-%20ProNet%20Quick%20Start%20Guide.pdf">https://www.anaheimautomation.com/manuals/servo/L011035%20-%20ProNet%20Quick%20Start%20Guide.pdf</a> (2014)</li><li>Fish, F. E., Legac, P., Williams, T. M., Wei, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+hydrodynamic+force+generation+by+swimming+dolphins+using+bubble+DPIV.">Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV.</a> Journal of Experimental Biology. 217 (2), 252-260 (2014).</li></ol>

The robotic flipper apparatus will allow us to understand the hydrodynamics of the swimming California sea lion. This includes the basic thrust producing stroke (the &#39;clap&#39;), as well as non-physical variations that animal studies cannot investigate. The robotic flipper has been designed for experimental versatility, thus, step 3&#8212;where the flipper itself is made&#8212;is critical in obtaining the desired results. While this apparatus is, clearly, just a model of the living system, in situ studies of...

While scientists have investigated the basic characteristics of sea lion swimming (energetics, cost of transport, drag coefficient, linear speed and acceleration1-3, we lack information about the fluid dynamics of the system. Without this knowledge, we limit potential high-speed, high-maneuverability engineering applications to body-caudal fin (BCF) locomotion models4. By characterizing a different swimming paradigm, we hope to expand our catalog of design tools, specifically those with the potential to enable quieter, stealthier forms of swimming. Thus, we study the fundamental mechanism of sea lion swimming through direct observation of the California sea lion and laboratory investigations using a robotic sea lion foreflipper5,6 .
To do this, we will employ a commonly used technique for exploring complex biological systems: a robotic platform7. Several locomotion studies&#8212;both of walking8,9 and swimming10&#8212;have been based on either complex11 or highly simplified12 mechanical models of animals. Typically, the robotic platforms retain the essence of the model system, while allowing researchers to explore large parameter spaces13-15. While not always characterizing the entire system, much is learned through these platforms that isolate a single component of a locomotive system. For example, the fundamental functioning of unsteady propulsors, like the back-and-forth sweeping of a caudal fin during carangiform swimming, has been intensely explored through experimental investigations of pitching and/or heaving panels12,16,17,18. In this case, we can isolate certain modes of this complex motion in ways that animal based studies cannot. Those fundamental aspects of propulsion can then be used in the design of vehicles which do not need the biological complexity evolution provides.
In this paper, we present a novel platform for exploring the &#39;clap&#39; phase of the sea lion thrust-producing stroke. Only a single foreflipper&#8212;the &#39;roboflipper&#39;&#8212;is included in the platform. Its geometry is derived exactly from biological scans of a California sea lion (Zalophus californianus) specimen. The roboflipper is actuated to replicate the motion of the animals&#39; derived from previous studies1. This robotic flipper will be used to investigate the hydrodynamic performance of the swimming sea lion and to explore a wider parameter space than animal studies, particularly those of large aquatic mammals, can yield.

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			<td height="63" style="height:63px;">PKS-PRO-E-10 System</td>
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a robotic platform to study the foreflipper of the california sea lion

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;). The kinematics of the sea lion&#39;s propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties&#8212;Reynolds number and tip speed&#8212;of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.

The process described above yields a robotic model of a California sea lion foreflipper. The model can be used in two different ways. One is by actuating the flipper only at the root (Figure 6a). In this case, the driving motor sets the rotational rate of the first joint, but the resulting motion of the flipper is determined by the fluid-structure interaction between the flexible flipper and the surrounding water. Additionally, we can create robotic flipp...

Watch this Scientific Journal Video about A Robotic Platform to Study the Foreflipper of the California Sea Lion at JoVE.com

A Robotic Platform to Study the Foreflipper of the California Sea Lion

A robotic platform is described that will be used to study the hydrodynamic performance&#8212;forces and flowfields&#8212;of the swimming California sea lion. The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;).

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most ...

The overall goal of this procedure is to create a robotic platform to study Sea Lion swimming. This matter can help answer key questions in biofluid dynamics, such as how Sea Lions move the water around them when they swim. The main advantage of this technique is that we can explore Sea Lion locomotion in detail while still being in a controlled laboratory setting.Though this method can provide insight into Sea Lion swimming, it can also be applied to other animal systems, such as dolphins, tuna, whales, and other fish or aquatic mammals. To begin, digitize a specimen of a Sea Lion foreflipper, or obtain it from an alternate source. Print the resulting point cloud at 68 percent of the full size, and use it to create a three-dimensional mold.Design three different pieces to mimic the bone structure of the Sea Lion foreflipper, starting with the base. In the CAD software, click on Sketch, and design the base piece so that it is proportional to the distance between the shoulder joint and the wrist of the specimen Sea Lion flipper. Add knuckles to the base by clicking on Sketch and drawing two circles at both ends of the part, then click on Boss-Extrude to extrude the desire length from the plane of the base piece.Click on the sketch of the smaller circle at the knuckles and click Cut-Extrude to make room for the shaft. To strengthen this joint, click on Fillet to smoothen the sharp joints. Next, design the middle section.Click on Sketch and draw a trapezoid with a height of 2.25 inches and bases of 1.625 and 0.85 inches. Then, click on Extrude and input the extruded length as 0.165 inches to get the basic three-dimensional shape of the middle piece. As with the base, add knuckles on both ends so that they will fit inside the volume of the foreflipper.To accomplish this, make the diameter of the extruded cut 0.125 inches. Then, click on Sketch and create a tower as a rectangle on the base of the model. Extrude the sketch by selecting it, clicking on Boss-Extrude, and setting the thickness of the tower to 0.165 inches.Finally, click on Fillet, and select the model and one edge of the extruded tower to smooth the sharp joint and strengthen where the tower and the base of the middle piece are connected. Make the length of the tip piece proportional to the distance between the knuckle joint and the tip of the longest finger bone of a Sea Lion. Do this by clicking on Sketch and sketching the desired shape on the plane.Once the geometry is designed, click on Extrude to get the basic three-dimensional shape of the tip piece. Next, form the knuckles on both ends by making an extruded cut that is equal to the diameter of the axle, which is shown here as 0.125 inches. Finally, add a tower to the base end of the piece on both sides.Once all of the pieces have been created, 3D print the base, middle, and tip pieces of the flipper. Then, reinforce the knuckles of the middle and tip piece by applying epoxy to the printed bone structures, and laying two layers of three-quarter inch long carbon threads onto the epoxy. Next, drill 05 inch diameter holes through the bottom of each tower, which will be use to thread the Kevlar string.Place all of the bone pieces on a flat table. Align the knuckles of the base and middle pieces, and insert the axle. Then, use the same technique to connect the middle and the tip piece together.Use an adhesive on each end of each axle to ensure that the axle does not move laterally. Next, cut four plastic tubes the length of the base bone piece, and two tubes the length of the middle piece. Also, cut four piece of Kevlar string, each three feet in length.Slide one string through an eight centimeter tube and then, a six centimeter tube. Slide a second string through an eight centimeter tube. Repeat the process with the remaining tubes and strings.Place the tubes on top of the bone structures and use tape to hold them in position temporarily. Using an adhesive, permanently secure the tubes onto the bone structure and then remove the tape. Next, thread the Kevlar string from the tubes through the holes drilled onto the tip and middle pieces.Make a small, secure knot once the string is through the hole. First, measure 200 milliliters of silicone and silicone medium in two different containers. Pour both these liquids into a steel bowl and then add up to ten percent paint thinner.Use a stand mixer to mix the components thoroughly for three to four minutes. If desired, add color at this step to achieve the desired visual effects. Insert a rod into the knuckles of the base part and align it with the knuckles of the flipper mold.When the pegs fit into the cavities of the mold, the bone structure should be perfectly aligned. While holding down on the two parts of the mold, secure the parts by using a clamp for added compression. Then, carefully pour the silicone mixture into the mold, until it reaches the topmost knuckles of the bone structure.Look for oozing of liquid from the bottom hole in the mold as a sign that the mixture is uniformly distributed. Once the oozing liquid is noticed, plug the hole to avoid further outflow of the liquid. Leave the liquid to cure for four hours before removing the flipper robot from the mold.Next, connect the flipper to a motor through a three-pulley system, and mount the flipper to the test system as described in the accompanying text protocol. Set the motion of the flipper by selecting the jogging function on the motor driver. Pressing the up button rotates the flipper clockwise and the down button rotates the flipper anticlockwise.Shown here on the left is a foreflipper from a female California Sea Lion, which was scanned and recreated into this robotic flipper. The digital scanned image shows a wire-frame view of the digital flipper. From this image, one can see that the flipper has an airfoil-like shape that is thicker on the leading edge and is cambered, with its upper surface more convex and its inner surface concave.Once mounted to a recirculating flume, like the one shown here, dye can be injected upstream of the flapping flipper, and the flow pattern can be imaged. Shown here are three points along the flipper cycle. In the right panel, a vortex can be seen around the tip of the flapping robotic flipper.Once mastered, this technique can be done in four and a half hours if it is performed properly. After watching this video, you should have a good understanding of how to create a robotic platform to investigate Sea Lion swimming.

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Research

JoVE Journal

Engineering

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction.

Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Disordered structures offer new mechanisms for forming photonic bandgaps and unprecedented freedom in functional-defect designs. To circumvent the computational challenges of disordered systems, we construct modular macroscopic samples of the new class of PBG materials and use microwaves to characterize their scale-invariant photonic properties, in an easy and inexpensive manner.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). ...

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

An integrated device, incorporating a dye-sensitized solar cell and triplet-triplet annihilation up-conversion unit was produced, affording enhanced light harvesting, from a wider section of the solar spectrum. Under modest irradiation levels a significantly enhanced response to low energy photons was demonstrated, yielding a record figure of merit for dye-sensitized solar cells.

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents ...

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

Wind Tunnel Experiments to Study Chaparral Crown Fires

The present protocol presents a laboratory technique designed to study chaparral crown fire ignition and spread. Experiments were conducted in a low velocity fire wind tunnel where two distinct layers of fuel were constructed to represent surface and crown fuels in chaparral. Chamise, a common chaparral shrub, comprised the live crown layer. The dead fuel surface layer was constructed with excelsior (shredded wood). We developed a methodology to measure mass loss, temperature, and flame height for both fuel layers. Thermocouples placed in each layer estimated temperature. A video camera captured the visible flame. Post-processing of digital imagery yielded flame characteristics including height and flame tilt. A custom crown mass loss instrument developed in-house measured the evolution of the mass of the crown layer during the burn. Mass loss and temperature trends obtained using the technique matched theory and other empirical studies. In this study, we present detailed experimental procedures and information about the instrumentation used. The representative results for the fuel mass loss rate and temperature filed within the fuel bed are also included and discussed.

This protocol describes wind tunnel experiments designed to study the transition of a fire from the ground to the canopy of chaparral shrubs.

The present protocol presents a laboratory technique designed to study chaparral crown fire ignition and spread. Experiments were conducted in a low ...

Design and Implementation of a Bespoke Robotic Manipulator for Extra-corporeal Ultrasound

With the potential for high precision, dexterity, and repeatability, a self-tracked robotic system can be employed to assist the acquisition of real-time ultrasound. However, limited numbers of robots designed for extra-corporeal ultrasound have been successfully translated into clinical use. In this study, we aim to build a bespoke robotic manipulator for extra-corporeal ultrasound examination, which is lightweight and has a small footprint. The robot is formed by five specially shaped links and custom-made joint mechanisms for probe manipulation, to cover the necessary range of motion with redundant degrees of freedom to ensure the patient&#39;s safety. The mechanical safety is emphasized with a clutch mechanism, to limit the force applied to patients. As a result of the design, the total weight of the manipulator is less than 2 kg and the length of the manipulator is about 25 cm. The design has been implemented, and simulation, phantom, and volunteer studies have been performed, to validate the range of motion, the ability to make fine adjustments, mechanical reliability, and the safe operation of the clutch. This paper details the design and implementation of the bespoke robotic ultrasound manipulator, with the design and assembly methods illustrated. Testing results to demonstrate the design features and clinical experience of using the system are presented. It is concluded that the current proposed robotic manipulator meets the requirements as a bespoke system for extra-corporeal ultrasound examination and has great potential to be translated into clinical use.

This paper introduces the design and implementation of a bespoke robotic manipulator for extra-corporeal ultrasound examination. The system has five degrees of freedom with lightweight joints made by 3D printing and a mechanical clutch for safety management.

With the potential for high precision, dexterity, and repeatability, a self-tracked robotic system can be employed to assist the acquisition of real-time ...

Fabric Moisture Uniform Control to Study the Influence of Air Impingement Parameters on Fabric Drying Characteristics

Impinging dryness is now a widely used and effective way for fabric drying due to its high heat and mass transfer coefficient. Previous studies on fabric drying have neglected the contributions of moisture uniformity and diffusion coefficient to the drying process; though, they have recently been shown to have a significant influence on drying characteristics. This report outlines a step-by-step procedure to investigate the effects of air impingement parameters on a fabric&#39;s drying characteristics by controlling the uniformity of its area moisture distribution. A hot air blower unit equipped with an angle adjustable nozzle is used to generate air flow with different velocities and temperatures while the drying process is recorded and analyzed using an infrared thermograph. In addition, a uniform padder is adapted to ensure the fabric&#39;s moisture uniformity. Impinging drying is studied under different initial conditions by changing the air flow temperature, velocity, and direction, then the applicability and suitability of the protocol are evaluated.

Presented here is a protocol that guarantees uniform distribution of initial moisture inside of a fabric and investigates the effects of hot-air thermodynamic parameters (velocity, temperature, and direction) and thickness on the fabric&#39;s drying characteristics (e.g., temperature variation) under the condition of air impingement.

Impinging dryness is now a widely used and effective way for fabric drying due to its high heat and mass transfer coefficient. Previous studies on fabric ...