This work demonstrates the role of microstructure in the friction and oxidation behavior of the lamellar solid lubricant molybdenum disulfide (MoS). We report on systematic investigations of oxidation and friction for two MoS films with distinctively different microstructures-amorphous and planar/highly-ordered-before and after exposure to atomic oxygen (AO) and high-temperature (250 °C) molecular oxygen. A combination of experimental tribology, molecular dynamics simulations, X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) was used to reveal new insights about the links between structure and properties of these widely utilized low-friction materials. Initially, ordered MoS films showed a surprising resistance to both atomic and molecular oxygens (even at elevated temperature), retaining characteristic low friction after exposure to extreme oxidative environments. XPS shows comparable oxidation of both coatings via AO; however, monolayer resolved compositional depth profiles from HS-LEIS reveal that the microstructure of the ordered coatings limits oxidation to the first atomic layer.

The major limitations of precise evaluation of retinal structures in present clinical situations are the lack of standardization, the inherent subjectivity involved in the interpretation of retinal images, and intra- as well as interobserver variability. While evaluating optic disc deformation in glaucoma, these limitations could be overcome by using advanced digital image analysis techniques to generate precise metrics from stereo optic disc image pairs. A digital stereovision system for visualizing the topography of the optic nerve head from stereo optic disc images is presented. We have developed an algorithm, combining power cepstrum and zero-mean-normalized cross correlation techniques, which extracts depth information using coarse-to-fine disparity between corresponding windows in a stereo pair. The gray level encoded sparse disparity matrix is subjected to a cubic B-spline operation to generate smooth representations of the optic cup/disc surfaces and new three-dimensional (3-D) metrics from isodisparity contours. Despite the challenges involved in 3-D surface recovery, the robustness of our algorithm in finding disparities within the constraints used has been validated using stereo pairs with known disparities. In a preliminary longitudinal study of glaucoma patients, a strong correlation is found between the computer-generated quantitative cup/disc volume metrics and manual metrics commonly used in a clinic. The computer generated new metrics, however, eliminate the subjective variability and greatly reduce the time and cost involved in manual metric generation in follow-up studies of glaucoma.

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Utilizing a novel, hybrid molecular dynamics, Monte Carlo simulation, we report on microstructural changes in a polymer network that arise in response to oscillatory shear deformation. We model telechelic selfassociating polymers as a course-grained, bead−spring system. The stress response of the system is obtained from rheological experiments and is reported as a function of frequency and amplitude in both the linear and nonlinear regimes. The frequency-dependent material properties are then correlated with observed changes in the topological network structure. While only minimal structural variations are observed in the elastic regime, a substantial rearrangement occurs in the low frequency, large amplitude viscous regime. Aggregates tend to break apart, resulting in an increased density of free chains. Additionally, the network tends to break and form larger structural elements with an increase multiplicity of chains bridging between the same two aggregates. ■ INTRODUCTIONAssociating polymers have the unique ability to span a large spectrum of rheological properties, from fluid-like viscosity to near solid-like elastic dynamics. Telechelic polymers are one class of associating polymers. These triblock polymers consist of two differing chemical groups. The backbone has a high molecular weight and is constructed from multiple, repeating units. The two functionalized ends of the molecule, referred to as end groups, are members of a different chemical group and comprise a small fraction of the total molecular weight. In solution, end groups tend to aggregate by gathering into localized domains. At low enough temperatures and at concentrations above the micelle transition, a space spanning network is formed. The nodes of this network consist of aggregates of end groups, while links between aggregates are formed by one or more bridging polymer chains. End groups associate and dissociate from aggregates frequently; therefore, the topological structure within the network exhibits transient behavior.The general fluid thickening characteristics of telechelic polymers have long since had utility as a rheological modifier in industrial applications within coatings 1 such as paints, adhesives, plastics, and sealants. Over the past few decades, they have come into considerable interest in a multitude of fields. Most recently, composite materials, partially composed of telechelic polymers, have found their respective place in medical and biological applications. Examples include a temporary matrix for bone tissue regeneration 2 and an injectable drug delivery method 3,4 along with regenerative tissue engineering for wound dressing. 5 Within these applications a water-soluble polymer is desirable, constructed as a hydrophilic backbone terminated by hydrophobic groups. 6−9 Because of the fact that these materials are primarily water by weight, they can exhibit biocompatible and biodegradable properties. They can also be subject to external parameters such as temperature and pH. 10,11 The behavior of these materials is highly s...

Walker,J. and Garrett,S. and Wilson,M.S., 'Evolving Controllers for Real Robots: A Survey of the Literature', Adaptive Behavior, 2003, volume 11, number 3, pp 179--203, SageFor many years, researchers in the field of mobile robotics have been investigating the use of genetic and evolutionary computation (GEC) to aid the development of mobile robot controllers. Alongside the fundamental choices of the GEC mechanism and its operators, which apply to both simulated and physical evolutionary robotics, other issues have emerged which are specific to the application of GEC to physical mobile robotics. This paper presents a survey of recent methods in GEC-developed mobile robot controllers, focusing on those methods that include a physical robot at some point in the learning loop. It simultaneously relates each of these methods to a framework of two orthogonal issues: the use of a simulated and/or a physical robot, and the use of finite, training phase evolution prior to a task and/or lifelong adaptation by evolution during a task. A list of evaluation criteria are presented and each of the surveyed methods are compared to them. Analyses of the framework and evaluation criteria suggest several possibilities; however, there appear to be particular advantages in combining simulated, training phase evolution (TPE) with lifelong adaptation by evolution (LAE) on a physical robot.Peer reviewe