3,462 research outputs found
Drishti, a volume exploration and presentation tool
Among several rendering techniques for volumetric data, direct volume rendering is a powerful visualization tool for a wide variety of applications. This paper describes the major features of hardware based volume exploration and presentation tool - Drishti. The word, Drishti, stands for vision or insight in Sanskrit, an ancient Indian language. Drishti is a cross-platform open-source volume rendering system that delivers high quality, state of the art renderings. The features in Drishti include, though not limited to, production quality rendering, volume sculpting, multi-resolution zooming, transfer function blending, profile generation, measurement tools, mesh generation, stereo/anaglyph/crosseye renderings. Ultimately, Drishti provides an intuitive and powerful interface for choreographing animations
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Quantifying Dimensional Accuracy of a Mask Projection Micro Stereolithography System
Mask Projection Microstereolithography is capable for fabricating true three-dimensional
microparts and hence, holds promise as a potential micro-fabrication process for micro-machine
components. In this paper, the Mask Projection Micro-Stereolithography (MPµSLA) system
developed at the Rapid Prototyping and Manufacturing Institute at Georgia Institute of
Technology is presented. The dimensional accuracy of the system is improved by reducing its
process planning errors. To this effect, the MPµSLA process is mathematically modeled. In this
paper, the irradiance received by the resin surface is modeled as a function of the imaging system
parameters and the pattern displayed on the dynamic mask. The resin used in the system is
characterized to experimentally determine its working curve. This work enables us to compute
the dimensions of a single layer cured using our system. The analytical model is validated by
curing test layers on the system. The model computes layer dimensions within 5% error.Mechanical Engineerin
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Process Planning to Build Mask Projection Stereolithography Parts with Accurate Vertical Dimensions
Mask Projection Stereolithography (MPSLA) is a high resolution manufacturing process
that builds parts layer by layer in a photopolymer. In this paper, we formulate a process planning
method to cure MPSLA parts with accurate vertical dimensions. To this effect, we have
formulated and validated the “Layer cure” model that models the thickness of a cured layer as a
transient phenomenon, in which, the thickness of the layer being cured increases continuously
throughout the duration of exposure. We have shown that for longer durations of exposures, such
as those common with MPSLA systems, cure depth varies linearly with exposure. We have also
quantified the effect of diffusion of radicals on the cure depth when discrete exposure doses, as
opposed to a single continuous exposure dose, are used to cure layers.
Using this work, we have formulated and validated the “Print through” model that
computes the extra curing that would occur when multiple layers are cured over each other.
We have implemented the Print through model to simulate the profile of a down facing surface
of a test part and validated the simulation result by building the test part on our MPSLA system.Mechanical Engineerin
Jupiter: New estimates of mean zonal flow at the cloud level
In order to reexamine the magnitude differences of the Jovian atmosphere's jets, as determined by Voyager 1 and 2 images, a novel approach is used to ascertain the zonal mean east-west component of motion. This technique is based on digital pattern matching, and is applied on pairs of mapped images to yield a profile of the mean zonal component that reproduces the exact locations of the easterly and westerly jets between + and 60 deg latitude. Results were obtained for all of the Voyager 1 and 2 cylindrical mosaics; the correlation coefficient between Voyagers 1 and 2 in mean zonal flow between + and - 60 deg latitude, determined from violet filter mosaics, is 0.998
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Compensation Zone Approach to Avoid Z Errors in Mask Projection Stereolithography Builds
Print-through results in unwanted polymerization occurring beneath a part cured using
Mask Projection Stereolithography (MPSLA) and thus creates error in its Z dimension. In this
paper, the "Compensation zone approach" is proposed to avoid this error. This approach entails
modifying the geometry of the part to be cured. A volume (Compensation zone) is subtracted
from underneath the CAD model in order to compensate for the increase in the Z dimension that
would occur due to Print-through. Three process variables have been identified: Thickness of
Compensation zone, Thickness of every layer and Exposure distribution across every image used
to cure a layer. Analytical relations have been formulated between these process variables in
order to obtain dimensionally accurate parts. The Compensation zone approach is demonstrated
on an example problem.Mechanical Engineerin
Optimal Embedding of Functions for In-Network Computation: Complexity Analysis and Algorithms
We consider optimal distributed computation of a given function of
distributed data. The input (data) nodes and the sink node that receives the
function form a connected network that is described by an undirected weighted
network graph. The algorithm to compute the given function is described by a
weighted directed acyclic graph and is called the computation graph. An
embedding defines the computation communication sequence that obtains the
function at the sink. Two kinds of optimal embeddings are sought, the embedding
that---(1)~minimizes delay in obtaining function at sink, and (2)~minimizes
cost of one instance of computation of function. This abstraction is motivated
by three applications---in-network computation over sensor networks, operator
placement in distributed databases, and module placement in distributed
computing.
We first show that obtaining minimum-delay and minimum-cost embeddings are
both NP-complete problems and that cost minimization is actually MAX SNP-hard.
Next, we consider specific forms of the computation graph for which polynomial
time solutions are possible. When the computation graph is a tree, a polynomial
time algorithm to obtain the minimum delay embedding is described. Next, for
the case when the function is described by a layered graph we describe an
algorithm that obtains the minimum cost embedding in polynomial time. This
algorithm can also be used to obtain an approximation for delay minimization.
We then consider bounded treewidth computation graphs and give an algorithm to
obtain the minimum cost embedding in polynomial time
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