Ultrasonic and impulse welding of polylactic acid films

The weldability of polylactic acid (PLA) is examined in this article. Biaxially oriented PLA films of various thicknesses were joined with impulse and ultrasonic welding techniques. Relatively high weld strengths were achieved with impulse welding over a wide range of welding parameters. Ultrasonic welding produced high weld strengths with relatively short cycle times. In detail, ultrasonic welded samples had a weld factor (weld strength/base material strength) of 1 at cycle times of 0.25 sec. The weld factor was significantly lower at shorter weld times and weld times above 0.35 sec. In contrast, 100‐μm thick samples joined by impulse welding for 2–3 sec had a weld factor of 1 and a standard deviation of only ±5%. The peak temperature during the impulse welding was measured to determine the fusion temperatures of the films. Mechanical, thermal, and optical analysis was used to examine the properties of the PLA at various welding and annealing conditions. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Scanning Near-Field Ellipsometry Microscopy: imaging nanomaterials with resolution below the diffraction limit

We introduce a simple Scanning Near-Field Ellipsometer Microscopy (SNEM) setup to address the rapidly increasing need for simple, routine optical imaging techniques with resolution well below the diffraction limit. Our setup is based on the combination of commercially available atomic force microscope (AFM) and ellipsometry equipment with gold-coated AFM tips to obtain near-field optical images with a demonstrated resolution below λ/10. AFM topographical data, obtained in contact mode, and near-field optical data were acquired simultaneously using a combined AFM-ellipsometer. The highly enhanced field due to lightning-rod effects and localized surface plasmons excited at the end of the gold-coated tip allowed us to resolve and identify metallic nanoparticles embedded in poly(methyl methacrylate) as well as microphases in microphase-separated block copolymer films.     

Breaking it down is better: haptic decomposition of complex movements aids in robot-assisted motor learning

Training with haptic guidance has been proposed as a technique for learning complex movements in rehabilitation and sports, but it is unclear how to best deliver guidance-based training. Here, we hypothesized that breaking down a complex movement, similar to a tennis backhand, into simpler parts and then using haptic feedback from a robotic exoskeleton would help the motor system learn the movement. We also examined how the particular form of the decomposition affected learning. Three groups of unimpaired participants trained with the target arm movement broken down in three ways: 1) elbow flexion/extension and the unified shoulder motion independently ("anatomical" decomposition), 2) three component shoulder motions in Euler coordinates and elbow flexion/extension ("Euler" decomposition), or 3) the motion of the tip of the elbow and motion of the hand with respect to the elbow, independently ("visual" decomposition). A control group practiced the same number of movements, but experienced the target motion only, achieving eight times more direct practice with this motion. Despite less experience with the target motion, part training was better, but only when the arm trajectory was decomposed into anatomical components. Varying robotic movement training to include practice of simpler, anatomically-isolated motions may enhance its efficacy.     

An ecological approach to landscape planning using geographic information system technology

This paper describes two research programs that are aimed at developing ecologically-based landscape planning models. The first of these models was developed as part of a more comprehensive landscape planning research program at the University of Massachusetts. The second is an on-going program in forest land planning at the University of Vermont. In addition to an emphasis on ecological values, both projects make extensive use of computerized geographic information systems (GIS) for data storage, analysis and display. The emphasis has been to develop a synthesis of planning procedures, ecological theories and quantitative techniques. Both research efforts were guided by a three-part methodological framework adapted from the work of Eugene Odum. The Massachusetts work generated a two-part classification system. The first part of the classification uses the statistical technique of discriminant analysis to place land uses into five groups, each having similar ecological characteristics. The second part of the classification is based on the physical and environmental characteristics of a site. The biological and denudational potentials of a site are determined from soil characteristics and slope. A comparison of the two classification schemes was made to determine ecological compatibility. The procedures were applied to two communities in Western Massachusetts. The Vermont study was aimed at integrating ecological values into forest land management and planning processes. The research utilized soils and topographic information in the development of an ecologically based forest land suitability model. Forest site index and soil erosion potential were determined using data stored in a computerized geographic information system. Forest site index estimates were made by utilizing an existing, well documented soil-site index regression equation applicable to the Green Mountains of Vermont. Soil erosion potential estimates were made by combining a soil erodability factor (K) with slope. The site index and soil erosion estimates were combined to produce land suitability classes for resource protection, forest management, multiple-use and trade-off. The procedure was applied in the Mad River Valley in Central Vermont. Both the Massachusetts and the Vermont studies are seen as significant contributions toward the integration of ecological factors into processes for landscape planning and resource management.     

Probing the morphology and nanoscale mechanics of single poly(N-isopropylacrylamide) microgels across the lower-critical-solution temperature by atomic force microscopy

Submicrometer-sized particles of poly(N-isopropylacrylamide) (PNIPAM) are synthesized by surfactant-free radical polymerization. The morphology and nanomechanical properties of individual, isolated PNIPAM microgel particles at the silicon/air and silicon/water interfaces, below and above the PNIPAM volume-phase-transition temperature (VPTT), are probed by atomic force microscopy. In air, and in water below the VPTT, the PNIPAM spheres are flattened and adopt a pancakelike shape. Interestingly, above the VPTT the microgels adopt a more spherical form with increased height and decreased width, which is attributed to reduced interactions of the particles with the substrate. The elastic modulus calculated from force-indentation curves obtained for individual microgel spheres reveals that the stiffness of the particle's surface decreases by two orders of magnitude upon swelling in water. Additionally, the modulus of the PNIPAM spheres in water increases by one order of magnitude when crossing the VPTT from the swollen to the collapsed states, indicating a more compact chain packing at the particle surface.     

Correlation of the melt rheological properties with the foaming behavior of immiscible blends of poly(2,6‐dimethyl‐1,4‐phenylene ether) and poly(styrene‐co‐acrylonitrile)

Immiscible blends of poly(2,6‐dimethyl‐1,4‐phenylene ether)/poly(styrene‐co‐acrylonitrile) (PPE/SAN) were batch‐foamed using CO₂ as a blowing agent as a function of foaming temperature, foaming time, and blend composition. Evaluation of the resulting cellular morphology revealed an enhanced foamability of SAN with PPE contents up to 20 wt% as indicated by a similar volume expansion but a significantly reduced mean cell size. This behavior is related to a heterogeneous nucleation activity by the dispersed PPE phase. A further increasing PPE content, however, leads to increasing foam densities as well as nonuniform foam morphologies. The changes in the foaming behavior can be correlated with the melt rheological properties and the corresponding blend morphology. Shear‐rheological investigations revealed an onset of percolation of the dispersed PPE phase between 20 and 40 wt%, and a transition towards cocontinuity at 60 wt%. The materials response under uniaxial elongational flow, as assessed by Rheotens measurements, revealed an increase in elongational viscosity scaling with the PPE content, similar to the shear data. However, the strain hardening behavior was reduced by increasing PPE contents and, at 20 wt%, the drawability revealed a significant drop‐both phenomena limiting the foamability of polymers. In summary, the present study discusses fundamental aspects of foaming immiscible PPE/SAN blends. POLYM. ENG. SCI., 48:2111–2125, 2008. © 2008 Society of Plastics Engineers     

Aqueous Phase Glycerol Reforming by PtMo Bimetallic Nano-Particle Catalyst: Product Selectivity and Structural Characterization

A carbon supported PtMo aqueous phase reforming catalyst for producing hydrogen from glycerol was characterized by analysis of the reaction products and pathway, TEM, XPS and XAS spectroscopy. Operando X-ray absorption spectroscopy (XAS) indicates the catalyst consists of bimetallic nano-particles with a Pt rich core and a Mo rich surface. XAS of adsorbed CO indicates that approximately 25% of the surface atoms are Pt. X-ray photoelectron spectroscopy indicates that there is unreduced and partially reduced Mo oxide (MoO₃ and MoO₂), and Pt-rich PtMo bimetallic nano-particles. The average size measured by transmission electron microscopy of the fresh PtMo nano-particles is about 2?nm, which increases in size to 5?nm after 30?days of glycerol reforming at 31?bar and 503?K. The catalyst structure differs from the most energetically stable structure predicted by density functional theory (DFT) calculations for metallic Pt and Mo atoms. However, DFT indicates that for nano-particles composed of metallic Pt and Mo oxide, the Mo oxide is at the particle surface. Subsequent reduction would lead to the experimentally observed structure. The aqueous phase reforming reaction products and intermediates are consistent with both C?CC and C?COH bond cleavage to generate H₂/CO₂ or the side product CH₄. While the H₂ selectivity at low conversion is about 75%, cleavage of C?COH bonds leads to liquid products with saturated carbon atoms. At high conversions (to gas), these will produced additional CH₄ reducing the H₂ yield and selectivity.     

A Linear Time Algorithm of Computing Hausdorff Distance for Content-based Image Analysis

The Hausdorff distance is a very important metric for various image applications in computer vision including image matching, moving-object detection, tracking and recognition, shape retrieval and content-based image analysis. However, no efficient algorithm has been reported that computes the exact Hausdorff distance in linear time for comparing two images. Very few methods have been proposed to compute the approximate Hausdorff distance with higher approximation error. In this paper, we propose a linear time algorithm for computing the approximated Hausdorff distance with lower approximation error. The proposed method is effective to reduce the processing time, while minimizing the error rate in content-based image processing and analysis.