2,538 research outputs found
Modeling and Validation of Temperature and Concentration for Rapid Freeze Prototyping
Rapid Freeze Prototyping is a solid freeform fabrication process that uses water as the main build
material in a cold environment to create three-dimensional parts. A eutectic sugar-water solution
(C6H12O6 – H2O) has been used as a sacrificial material in order to create complex 3D parts with
features such as overhangs. A study of the interaction of the build and support materials is
presented in this paper. The temperature of both materials during deposition and subsequent
cooling is modeled using a semi-empirical model and a theoretical model. A concentration
model is used to predict the concentration in the fabricated parts around the interface of the two
materials with predicted temperatures as input. Experiments are conducted to validate both the
temperature and concentration models.Mechanical Engineerin
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Study on Incorporating Support Material in Rapid Freeze Prototyping
Rapid Freeze Prototyping (RFP) is a rapid prototyping method that uses water freezing
into ice to make three-dimensional parts. Each layer of a geometry is deposited and allowed to
freeze before the next layer is added. Using a support material in RFP is a relatively new
addition to the process. Validating the successful use of a support material in conjunction with
the main build material of water is presented in this paper. The support material selected for use
is a eutectic sugar solution. The selection criteria, properties, and characteristics of the support
material are discussed. Of particular interest is the diffusion between the support and main build
material, which must be minimized to an acceptable level for producing good quality,
reproducible, complex parts.Mechanical Engineerin
Historic Wetlands Assessment Using Computerized Microdensitometric Analysis of Aerial Photographs
A technique has been designed and tested that permits the quantitative assessment of historic marsh conditions from black and white aerial photography. Utilizing a computerized scanning and writing Rotating Drum Microdensitometer (RDM) system, baseline marsh data has been derived by combining present day field data with computer analysis of present day and historical aerial photography. Quantitative information on the marsh grasses studied (Spartina alternifora - tall and short growth forms, Salt Hay - a mixture of Spartina patens and Distichlis spicata), their distributional patterns, and surface water locations were established.
The RDM technique relates subtle optical density differences in a film emulsion to actual field conditions. Algorithms are then used to classify and map the marsh variables being studied. In this investigation, photographs were scanned using picture elements (pixels) as small as 25 µm per side. For 1:12,000 scale photographs, this translates to a ground equivalent area of 0.96 square feet.
The RDM system measures the optical density of each pixel and assigns it one of 256 different density levels. This is approximately an order of magnitude greater than the human eye\u27s ability to differentiate subtle shades of gray. Once computer analysis is completed, the RDM system then prints the classification categories on to an emulsion, producing a film image that maps the marsh variables.
Classification maps were produced by the RDM system for two geographically separate saline marshes. Each marsh was in excess of 100 acres. Using a Zoom Transfer Scope, the RDM classification maps were transferred and compared to historic wetland maps produced from manual interpretation of color infrared photographs and then extensively field surveyed. The wetland maps were produced by the New Jersey Department of Environmental Protection.
Except for a few small areas where S. alterniflora was misclassified, vegetative cover classes were correctly classified. The vegetational boundaries and land/water interfaces were located with great accuracy
Genericity and Singularities of Robot Manipulators
The kinematic singularities of robot manipulators are studied from the point of view of the theory of singularities. The notion of a generic\u27\u27 kinematic map, whose singularities form smooth manifolds of prescribed dimension in the joint space of the manipulator, is examined. For three-joint robots, an equivalent algebraic condition for genericity using the Jacobian determinants is derived. This condition lends itself to symbolic computation and is sufficient for the study of decoupled manipulators. Orientation and translation singularities of manipulators are studied in detail. A complete characterization of orientation singularities of robots with any number of joints is given. The translation singularities of the eight possible topologies of three-joint robots are studied and the conditions on the link parameters for nongenericity are determined
Generic Singularities of Robot Manipulators
The singularities of the differential kinematic map, i.e. of the manipulator Jacobian, are considered. The authors first examine the notion of a generic kinematic map, whose singularities form smooth manifolds of prescribed dimension in the joint space of the manipulator. For three-joint robots, an equivalent condition for genericity using determinants is derived. The condition lends itself to symbolic computation and is sufficient for the study of decoupled manipulators, i.e. manipulators that an be separated into a three-joint translating part and a three-joint orienting part. The results are illustrated by analyzing the singularities of two classes of three-joint positioning robots
CORBYS cognitive control architecture for robotic follower
In this paper the novel generic cognitive robot control architecture CORBYS is presented. The objective of the CORBYS architecture is the integration of high-level cognitive modules to support robot functioning in dynamic environments including interacting with humans. This paper presents the preliminary integration of the CORBYS architecture to support a robotic follower. Experimental results on high-level empowerment-based trajectory planning have demonstrated the effectiveness of ROS-based communication between distributed modules developed in a multi-site research environment as typical for distributed collaborative projects such as CORBYS
Supplementation of Beef Cows Grazing Corn Stalk Residue: A Demonstration
Controlling feed costs is imperative for cow-calf producers to remain cost-competitive. During fall and early winter, these projected costs can be significantly reduced by utilizing cornstalks. By effectively grazing corn residues, Iowa cow-calf producers have the opportunity to extend the grazing season and reduce winter feed costs. The ISU distillers’ dry grain (DDG) supplementation demonstration suggests that pregnant beef cows utilizing a strip-grazed system with appropriate supplementation can maintain their body condition scores (BCS) during challenging weather conditions. The supplemented group maintained a 5.7 BCS and the control group lost 0.3 BCS during the 49-day demonstration. The DDG supplemented system was projected to be more cost-competitive ($18.82 per head advantage) than the continuous grazed control group
A Study on Effects of Process Parameters in Rapid Freeze Prototyping
Rapid Freeze Prototyping (RFP) is a relatively new solid freeform fabrication
process, which builds a three-dimensional part according to a CAD model by depositing
and freezing water droplets layer by layer. A study on the effects of RFP process
parameters including the nozzle scanning speed, droplet size, and droplet frequency in
building ice parts with a single-nozzle work head is made. Presented in this paper are the
results of this study which indicate that these process parameters determine the ice layer
thickness and ice line width, which in turn determine the surface roughness and the
waiting time required after depositing each layer of water (i.e. between successive layers)
during the ice part building process.This project is supported by a National Science Foundation Grant (DMI-0128313)
and a Department of Education GAANN Fellowship Grant (P200A010446).Mechanical Engineerin
Estimation of the occupancy of butterflies in diverse biogeographic regions
AimWe explored the extent to which occupancy of butterflies within three biogeographic regions could be explained by vegetation structure and composition, topography and other environmental attributes; whether results were consistent among regions; and whether assumptions of closure were met with assemblage-level sampling designs. LocationChesapeake Bay Lowlands (Virginia), central Great Basin (Nevada) and western Great Basin (Nevada and California) (all USA). MethodsWe applied single-season occupancy models that either assumed closure or relaxed the closure assumption to data from 2013 and 2014 for 13-15 species in each region. ResultsMaximum single-year estimates of detection probabilities ranged from 0.14 to 0.99, and single-year occupancy from 0.28 to 0.98. The assumption of closure was met for a maximum of 54% of the species in a given region and year. Detection probabilities of \u3e90% of the species in each region increased as the categorical abundance of nectar or mud increased. Measures of the dominance or abundance of deciduous woody species and structural heterogeneity were included in the greatest number of occupancy models for the Chesapeake Bay Lowlands, which may in part reflect the intensity of browsing by white-tailed deer (Odocoileus virginianus). Elevation and precipitation were prominent covariates in occupancy models for Great Basin butterflies. Main conclusionsBecause occupancy models do not rely on captures or observations of multiple individuals in a population, they potentially can be applied to a relatively high proportion of the species in an assemblage. However, estimation of occupancy is complicated by taxonomic, temporal and spatial variation in phenology. In multiple, widely divergent ecosystems, all or some associations between covariates and detection probability or occupancy for at least one-third of the species could not be estimated, often because a given species rarely was detected at locations with relatively low or high values of a covariate. Despite their advantages, occupancy models may leave unexplained the environmental associations with the distributions of many species
Characteristics and Optimal Design of Variable Airgap Linear Force Motors
An analytical model for predicting the characteristics of variable airgap linear force motors is developed. the model takes into account magnetic losses including the leakage and fringing effects and the reluctance existing at the contacts between permanent magnets and pole pieces. the model is validated by comparing its predicted characteristics with the results obtained from experiments and a finite element program. with the use of the modelled characteristics, computer programs based on the method of constrained steepest descent with state equations are developed for automating and optimising the design of linear force motors. Numerical studies are made for both minimisation of weight and minimisation of power consumption
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