285 research outputs found
Inoculation Effects of Cast Iron
The paper presents a solidification sequence of graphite eutectic cells of A and D types, as well as globular and cementite eutectics. The morphology of eutectic cells in cast iron, the equations for their growth and the distances between the graphite precipitations in A and D eutectic types were analyzed. It is observed a critical eutectic growth rate at which one type of eutectic transformed into another. A mathematical formula was derived that combined the maximum degree of undercooling, the cooling rate of cast iron, eutectic cell count and the eutectic growth rate. One type of eutectic structure turned smoothly into the other at a particular transition rate, transformation temperature and transformational eutectic cell count. Inoculation of cast iron increased the number of eutectic cells with flake graphite and the graphite nodule count in ductile iron, while reducing the undercooling. An increase in intensity of inoculation caused a smooth transition from a cementite eutectic structure to a mixture of cementite and D type eutectic structure, then to a mixture of D and A types of eutectics up to the presence of only the A type of eutectic structure. Moreover, the mechanism of inoculation of cast iron was studied
A new notion of solutions to the -Laplacian evolution equation in metric measure spaces
The -Laplacian evolution equation in metric measure spaces has been
studied as the gradient flow in of the -Cheeger energy (for ). In this paper, using the first-order differential structure on a
metric measure space introduced by Gigli, we characterize the subdifferential
in of the -Cheeger energy. This gives rise to a new definition of the
-Laplacian operator in metric measure spaces, which allows us to work with
this operator in more detail. In this way, we introduce a new notion of
solutions to the -Laplacian evolution equation in metric measure spaces. For
, we obtain a Green-Gauss formula similar to the one by Anzellotti for
Euclidean spaces, and use it to characterise the -Laplacian operator and
study the total variation flow. We also study the asymptotic behaviour of the
solutions of the -Laplacian evolution equation, showing that for we have finite extinction time.Comment: 56 page
The evolving spectrum of the planetary nebula Hen 2-260
We analysed the planetary nebula Hen 2-260 using optical spectroscopy and
photometry. We compared our observations with the data from literature to
search for evolutionary changes. The nebular line fluxes were modelled with the
Cloudy photoionization code to derive the stellar and nebular parameters. The
planetary nebula shows a complex structure and possibly a bipolar outflow. The
nebula is relatively dense and young. The central star is just starting ionization (). Comparison of our
observations with literature data indicates a 50% increase of the [OIII] 5007
\AA\ line flux between 2001 and 2012. We interpret it as the result of the
progression of the ionization of . The central star evolves to
higher temperatures at a rate of . The heating rate
is consistent with a final mass of
or for two different sets of
post-AGB evolutionary tracks from literature. The photometric monitoring of Hen
2-260 revealed variations on a timescale of hours or days. The variability may
be caused by pulsations of the star. The temperature evolution of the central
star can be traced using spectroscopic observations of the surrounding
planetary nebula spanning a timescale of roughly a decade. This allows us to
precisely determine the stellar mass, since the pace of the temperature
evolution depends critically on the core mass. The kinematical age of the
nebula is consistent with the age obtained from the evolutionary track. The
final mass of the central star is close to the mass distribution peak for
central stars of planetary nebulae found in other studies. The object belongs
to a group of young central stars of planetary nebulae showing photometric
variability.Comment: accepted for publication in A&
The effects of the metal temperature and wall thickness on flake graphite layer in ductile iron
This article addresses the effect of mold filling and wall thickness on the flake graphite layer in ductile iron. The research was conducted for castings with different wall thickness (3-8 mm) and using molding sand with furan resin. A thermal analysis has been performed along the length of the castings to determine the initial temperature of the metal in the mold cavity and the contact time of the liquid metal with the mold. Results demonstrated the strong influence of the temperature decrease of the metal in the mold cavity on the occurrence and the thickness of the flake graphite in the surface layer in ductile iron
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