25,098 research outputs found
Study of plate-fin heat exchanger and cold plate for the active thermal control system of Space Station
Plate-fin heat exchangers will be employed in the Active Thermal Control System of Space Station Freedom. During ground testing of prototypic heat exchangers, certain anomalous behaviors have been observed. Diagnosis has been conducted to determine the cause of the observed behaviors, including a scrutiny of temperature, pressure, and flow rate test data, and verification calculations based on such data and more data collected during the ambient and thermal/vacuum tests participated by the author. The test data of a plate-fin cold plate have been also analyzed. Recommendation was made with regard to further tests providing more useful information of the cold plate performance
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Study of Ceramic Slurries for Investment Casting with Ice Patterns
Ice patterns generated by rapid freeze prototyping or a molding process can be used to
make ceramic investment molds for metal castings. Due to the use of ice, the ceramic slurries
must be poured around the pattern and cured at sub-freezing temperatures. Success of this
process depends greatly on the mold strength after the gelation of the slurries. This paper
describes the experimental results of the mold strength after the gelation of the slurries under
different compositions. The parameters considered include mixing time, alumino-silicate vs.
fused silica ratio, volume of binder, and volume of catalyst. The strength of the gelled slurries is
examined by breaking test bars on a four-point bending apparatus. Weibull modulus for each
trial is calculated based on the breaking strength from four-point bend tests. Analysis of variance
for breaking strength and Weibull analysis is performed to evaluate the significance of the effect
of each parameter. The casting of a bolt is used to demonstrate that metal castings of complex
geometry can be fabricated using investment casting with ice patterns.Mechanical Engineerin
Shell Cracking In Investment Casting with Laser Stereolithography Patterns
This paper presents an investigation of ceramic shell cracking during the burnout process
in investment casting with internally webbed laser stereolithography patterns. We hypothesize
that shell cracking will occur when the rupture temperature of the ceramic shell is lower than
both the glass transition temperature of the pattern material and the web· link buckling
temperature. The hypothesis is validated by our experimental observations which confirm the
numerical predictions from our fillite element analysis. This provides a basis for design of the
internal web geometry of a lithography pa.tternand evaluation ofthe burnolltprocesswithsuch a
pattern. We show the shell cracking and web link buckling temperatures to be functiollsofthe
pattern geometry (including the cross~sectional dimensions and span length of the web link) and
the shell thickness.Mechanical Engineerin
The Finite-time Ruin Probabilities of a Bidimensional risk model with Constant Interest Force and correlated Brownian Motions
We follow some recent works to study bidimensional perturbed compound Poisson
risk models with constant interest force and correlated Brownian Motions.
Several asymptotic formulae for three different type of ruin probabilities over
a finite-time horizon are established.
Our approach appeals directly to very recent developments in the ruin theory
in the presence of heavy tails of unidimensional risk models and the dependence
theory of stochastic processes and random vectors.Comment: 25page
Segue: Overviewing Evolution Patterns of Egocentric Networks by Interactive Construction of Spatial Layouts
Getting the overall picture of how a large number of ego-networks evolve is a
common yet challenging task. Existing techniques often require analysts to
inspect the evolution patterns of ego-networks one after another. In this
study, we explore an approach that allows analysts to interactively create
spatial layouts in which each dot is a dynamic ego-network. These spatial
layouts provide overviews of the evolution patterns of ego-networks, thereby
revealing different global patterns such as trends, clusters and outliers in
evolution patterns. To let analysts interactively construct interpretable
spatial layouts, we propose a data transformation pipeline, with which analysts
can adjust the spatial layouts and convert dynamic egonetworks into event
sequences to aid interpretations of the spatial positions. Based on this
transformation pipeline, we developed Segue, a visual analysis system that
supports thorough exploration of the evolution patterns of ego-networks.
Through two usage scenarios, we demonstrate how analysts can gain insights into
the overall evolution patterns of a large collection of ego-networks by
interactively creating different spatial layouts.Comment: Published at IEEE Conference on Visual Analytics Science and
Technology (IEEE VAST 2018
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