Practical prototyping

The design of robotic mechanisms is a complex process involving geometric, kinematic, dynamic, tolerance, and stress analyses. In the design of a real system, the construction of a physical prototype is often considered. Indeed, a physical prototype helps the designer to identify the fundamental characteristics and the potential pitfalls of the proposed architecture. However, the design and fabrication of a prototype using traditional techniques is rather long, tedious, and costly. In this context, the availability of rapid prototyping machines can be exploited in order to allow designers of robotic mechanisms to build prototypes rapidly and at a low cost. In the article, the rapid prototyping of mechanisms using a commercially available computer-aided design (CAD) package and a fused deposition modeling (FDM) rapid prototyping machine is presented. A database of lower kinematic pairs (joints) is developed using the CAD package, and parameters of fabrication are determined experimentally for each of the joints. These joints are then used in the design of the prototypes where the links are developed and adapted to the particular geometries of the mechanisms to be built. Also, a procedure is developed to build gears and Geneva mechanisms. Examples of mechanisms are then studied and their design is presented. For each mechanism, the joints are described and the design of the links is discussed. Some of the physical prototypes built using the FDM rapid prototyping machine are shown     

Modelling Temperature,Body Size,Prey Density,and Stream Gradient Impacts on Longitudinal Patterns of Potential Production of Drift‐Feeding Trout

In this study, we modelled idealized stream reaches using empirical hydrodynamic and bioenergetic parameters to predict how rainbow trout production depends on physical and biological variations across a downstream gradient, and we compared these downstream effects in a low and high‐gradient stream reach. We found that longitudinal production potential (i.e. net rate of energetic intake per 100 m of stream length) generally increased with increasing stream size when stream gradient was low. This was not the case, however, for high‐gradient streams, wherein maximum longitudinal production potential was associated with middle or low stream size (Q_MAD = 2.5 to 25 m³ s^?1). Areal production potential (net rate of energetic intake per m² of wetted stream bed) reached a maximum at low stream size (Q_MAD = 2.5 m³ s^?1) with both high and low gradients. We also showed that high stream temperature and low drift density could potentially cause adult rainbow trout to be excluded from stream reaches with high flow. The models presented here have a stronger mechanistic basis for predicting fish production across heterogeneous stream environments and provide more nuanced predictions in response to variation in environmental features than their physical habitat‐based predecessors. Copyright © 2016 John Wiley & Sons, Ltd.     

HYDRAULIC GEOMETRY AND LONGITUDINAL PATTERNS OF HABITAT QUANTITY AND QUALITY FOR RAINBOW TROUT (Oncorhynchus mykiss)

We developed predictions of habitat quantity and quality for three life stages of rainbow trout, Oncorhynchus mykiss, across a range of stream sizes characterized by mean annual discharge of 1 to 50 m³ s^?1. The physical habitat template was created by nesting a reach‐scale two‐dimensional hydrodynamic model (River2D) within a downstream hydraulic geometry system using published coefficients for low‐gradient and high‐gradient watersheds. This provided both longitudinal and transverse estimates of depth and velocity profiles that, when combined with habitat suitability curves for the life stages, resulted in predictions of habitat quantity (weighted usable area) and habitat quality (the proportion of the stream profile that provided useable habitat) for rainbow trout along the stream continuum. Habitat quantity increased asymptotically for all life history stages but increased more rapidly in the low‐gradient watershed. Habitat quality decreased non‐linearly for young‐of‐the‐year and peaked at intermediate stream sizes for juveniles in both low‐gradient and high‐gradient watersheds. Adult habitat quality peaked in the high‐gradient watershed but increased asymptotically in the low‐gradient watershed, presumably due to lower mean velocities at larger stream sizes. Incorporation of transverse variation in depth and velocity in our physical habitat template provides a more realistic representation of habitat quantity and quality than do earlier assessments based on simple modal estimates of depth and velocity. Copyright © 2013 John Wiley & Sons, Ltd.     

The treatment decision-making process: age differences in a sample of women recently diagnosed with nonrecurrent, early-stage breast cancer

This research utilizes retrospective, self-report data collected from a nonprobability sample of women recently diagnosed with nonrecurrent, early-stage breast cancer to better understand how the treatment decision-making process varies with patient age. Three important areas--context, decision-making style, and influencing factors--are examined using bivariate and multivariate analyses. Findings indicate that although patients recalled similar contextual attributes, they reported attitudes, behavior, and considerations that differed by age. Older women were less likely than their younger counterparts to have desired participation in therapy selection, sought out medical information, or considered the possibility of recurrence when making treatment decisions.     

An Investigation of the Failure Mechanisms of a Polymer Matrix Composite Crew Oar

Journal of Failure Analysis and Prevention - Rowing, or crew, is a constantly evolving sport with an impressive history of equipment advancements, including the use of advanced polymer matrix...     

Including scalars in a programming language based on the relationalalgebra

Scalars, arrays, and records, together with associated operations and syntax, have been introduced as special cases of relations into the relational programming system, relix. This permits all of these data types, as well as relations, to be stored persistently. The requirement in most languages that array elements and record fields can be assigned to leads in this case to the general implementation of QT-selectors as l-expressions, with, in particular, systematic interpretations of assignment to projections and selections of relations. The authors discuss the principles and the implementation of this extension to the relational algebra. They take advantage of the very specialized syntax of array access to build a tuned access method, using B-trees and Z-order. The performance results show the advantage of this implementation over the slower implementation required for general QT-selectors     

Static balancing of 3-DOF planar parallel mechanisms

The static balancing of planar 3-DOF parallel mechanisms is addressed in this paper. Static balancing is defined as the set of conditions on mechanism dimensional and inertial parameters which, when satisfied, ensure that the weight of the links does not produce any torque (or force) at the actuators for any configuration of the mechanism, under static conditions. For the mechanisms studied here, conditions for static balancing are obtained, and it is shown that balancing is generally possible, even when the dimensional parameters are imposed, which is a useful property since dimensional parameters are usually obtained from kinematic design or optimization. Then, the conditions for the static balancing of the same mechanisms are derived for designs in which elastic elements are included. Finally, examples of balanced mechanisms are given. A dynamic study is performed     

Large area mapping of southwestern forest crown cover, canopy height, and biomass using the NASA Multiangle Imaging Spectro-Radiometer

A rapid canopy reflectance model inversion experiment was performed using multi-angle reflectance data from the NASA Multi-angle Imaging Spectro-Radiometer (MISR) on the Earth Observing System Terra satellite, with the goal of obtaining measures of forest fractional crown cover, mean canopy height, and aboveground woody biomass for large parts of south-eastern Arizona and southern New Mexico (> 200,000 km²). MISR red band bidirectional reflectance estimates in nine views mapped to a 250 m grid were used to adjust the Simple Geometric-optical Model (SGM). The soil-understory background signal was partly decoupled a priori by developing regression relationships with the nadir camera blue, green, and near-infrared reflectance data and the isotropic, geometric, and volume scattering kernel weights of the LiSparse–RossThin kernel-driven bidirectional reflectance distribution function (BRDF) model adjusted against MISR red band data. The SGM's mean crown radius and crown shape parameters were adjusted using the Praxis optimization algorithm, allowing retrieval of fractional crown cover and mean canopy height, and estimation of aboveground woody biomass by linear rescaling of the dot product of cover and height. Retrieved distributions of crown cover, mean canopy height, and aboveground woody biomass for forested areas showed good matches with maps from the United States Department of Agriculture (USDA) Forest Service, with R² values of 0.78, 0.69, and 0.81, and absolute mean errors of 0.10, 2.2 m, and 4.5 tons acre^- 1 (10.1 Mg ha^- 1), respectively, after filtering for high root mean square error (RMSE) on model fitting, the effects of topographic shading, and the removal of a small number of outliers. This is the first use of data from the MISR instrument to produce maps of crown cover, canopy height, and woody biomass over a large area by seeking to exploit the structural effects of canopies reflected in the observed anisotropy patterns in these explicitly multiangle data.     

Poly[bis(m-chlorophenoxy)phosphazene]. Macromolecular characterization and degradation studies

The macromolecular structures of five poly[bis(m-chlorophenoxy)phosphazene] samples are critically analyzed. There are significant variations in the solubility behavior and physical properties of the polymers. Property differences are attributed mainly to the incomplete nucleophilic substitution of the dichlorophosphazene polymer precursor. All the polymers are found to have high molecular weights and broad, bimodal molecular weight distributions. However, differences in branching are noted and the presence of thermally labile “weak links” on the polymer chain backbones is suspected. At 165°C in static air, the polyphosphazene degrades by a random degradation mechanism and for long exposure times is considerably more stable than polystyrene.     

Corrosion protection assessment of sacrificial coating systems as a function of exposure time in a marine environment

The present investigation assessed the corrosion protection performance of 17 different Zn and Al sacrificial coating system configurations during marine atmospheric exposure at Kure Beach, NC. The coating systems incorporated several conversion coating layers, primers and organic topcoats. Visual observations and electrochemical measurements (including electrochemical impedance spectroscopy, EIS) were made on six different occasions throughout the 20-month exposure time. Milled scribes on each of the coating specimens allowed for defect protection as well as barrier protection to be investigated. A novel corrosion analysis technique utilizing a specialized conducting agar (SCAR) cell enabled impedance measurements to be made on both intact and defect areas. Visual observations, E_oc's, and EIS as a function of atmospheric exposure time provided complementary results. Impedance results were found to be useful in determining a coating's barrier protection and scribe damage analysis accurately represented defect protection.