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Application of Design of Experiments to Extrusion Freeform Fabrication (EFF) of Functional Ceramic Prototypes
Extrusion Freeform Fabrication (EFF) is an adaptation of the Stratasys Fused Deposition
Modeling (FDM) process for the Solid Freeform Fabrication (SFF) of functional ceramic
prototypes. It is a complex process involving many process variables, including parameters that
are operation, machine, materials, and geometry specific. A Taguchi factorial Design of
Experiments (DOE) technique was utilized to study the effects of machine specific process
parameters as well as their interactions based on the mechanical and physical properties of
sintered ceramics specimens. Post-processing software was developed to control and modify these
parameters. This software interface wasdesigned to mimic the Quickslice™ interface for setting
motion parameters based upon the material and the operation. The results of this investigation
provided useful information for the experimental analysis of the machine specific process
parameters. Suitable parameters were selected for the EFF process for fabricating representative
ceramic prototypes. With the optimized parameters, complicated parts were successfully
fabricated using both Kyocera SN282 and Starck M-11 silicon nitride powders.Mechanical Engineerin
Planetary Nebulae with Ultra-Violet Imaging Telescope (UVIT): Far Ultra-violet halo around the Bow Tie nebula (NGC 40)
Context. NGC 40 is a planetary nebula with diffuse X-ray emission, suggesting
an interaction of the high speed wind from WC8 central star (CS) with the
nebula. It shows strong Civ 1550 {\AA} emission that cannot be explained by
thermal processes alone. We present here the first map of this nebula in C IV
emission, using broad band filters on the UVIT.
Aims. To map the hot C IV emitting gas and its correspondence with soft X-ray
(0.3-8 keV) emitting regions, in order to study the shock interaction with the
nebula and the ISM. This also illustrates the potential of UVIT for nebular
studies.
Methods. Morphological study of images of the nebula obtained at an angular
resolution of about 1.3" in four UVIT filter bands that include C IV 1550 {\AA}
and C II] 2326 {\AA} lines and UV continuum. Comparisons with X-ray, optical,
and IR images from literature.
Results. The C II] 2326 {\AA} images show the core of the nebula with two
lobes on either side of CS similar to [N II]. The C IV emission in the core
shows similar morphology and extant as that of diffuse X-ray emission
concentrated in nebular condensations. A surprising UVIT discovery is the
presence of a large faint FUV halo in FUV Filter with {\lambda}eff of 1608
{\AA}. The UV halo is not present in any other UV filter. FUV halo is most
likely due to UV fluorescence emission from the Lyman bands of H2 molecules.
Unlike the optical and IR halo, FUV halo trails predominantly towards
south-east side of the nebular core, opposite to the CS's proper motion
direction.
Conclusions. Morphological similarity of C IV 1550 {\AA} and X-ray emission
in the core suggests that it results mostly from interaction of strong CS wind
with the nebula. The FUV halo in NGC 40 highlights the existence of H2
molecules extensively in the regions even beyond the optical and IR halos.Comment: 4 pages, 5 figures, accepted for publication as a letter in Astronomy
& Astrophysic
Planetary Nebulae with UVIT II: Revelations from FUV vision of Butterfly Nebula NGC 6302
The high excitation planetary nebula, NGC 6302, has been imaged in two
far-ultraviolet (FUV) filters, F169M (Sapphire; {\lambda}: 1608
{\AA}) and F172M (Silica; {\lambda}: 1717 {\AA}) and two NUV
filters, N219M (B15; {\lambda}: 2196 {\AA}) and N279N (N2;
{\lambda}: 2792 {\AA}) with the Ultra Violet Imaging Telescope
(UVIT). The FUV F169M image shows faint emission lobes that extend to about 5
arcmin on either side of the central source. Faint orthogonal collimated
jet-like structures are present on either side of the FUV lobes through the
central source. These structures are not present in the two NUV filters nor in
the FUV F172M filter. Optical and IR images of NGC 6302 show bright emission
bipolar lobes in the east-west direction with a massive torus of molecular gas
and dust seen as a dark lane in the north-south direction. The FUV lobes are
much more extended and oriented at a position angle of 113{\deg}. They and the
jet-like structures might be remnants of an earlier evolutionary phase, prior
to the dramatic explosive event that triggered the Hubble type bipolar flows
approximately 2200 years ago. The source of the FUV lobe and jet emission is
not known, but is likely due to fluorescent emission from H molecules. The
cause of the difference in orientation of optical and FUV lobes is not clear
and, we speculate, could be related to two binary interactions.Comment: 9 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Low frequency radio and X-ray properties of core-collapse supernovae
Radio and X-ray studies of young supernovae probe the interaction between the
supernova shock waves and the surrounding medium and give clues to the nature
and past of the progenitor star. Here we discuss the early emission from type
Ic SN 2002ap and argue that repeated Compton boosting of optical photons by hot
electrons presents the most natural explanation of the prompt X-ray emission.
We describe the radio spectrum of another type Ic SN 2003dh (GRB030329)
obtained with combined GMRT and VLA data. We report on the low frequency radio
monitoring of SN 1995N and our objectives of distinguishing between competing
models of X-ray emission from this SN and the nature of its progenitor by X-ray
spectroscopy. Radio studies on SN 2001gd, SN 2001ig and SN 2002hh are
mentioned.Comment: 5 pages, 4 figures. Uses svmult.cls. To appear in proceedings of IAU
Colloquium 192 "Supernovae (10 years of SN 1993J)", April 2003, Valencia,
Spain, eds. J. M. Marcaide and K. W. Weile
Neutrino Spectroscopy of the Early Phase of Nearby Supernovae
Neutrinos emitted during stellar core collapse up to their trapping phase
carry information about the stage from which the Supernova explosion process
initiates. The dominant emission mechanism is by electron capture on
free protons and f-p shell nuclei and the spectrum of these neutrinos is a
function of the ambient physical conditions within the core as well as the
nuclear equation of state. The number of collapse phase which can be
detected by Super-Kamioka and Sudbury Neutrino Observatory from a Supernova
within 1 kpc, and their generic energy spectra are given.Comment: 9 pages of text and tables plus 2 pages of figures. Accepted for
publication in Phys. Rev. Lett. on 11th Jul., 1997. Please e-mail Comments
etc. to [email protected]
Oscillation Effects On Neutrinos From The Early Phase Of a Nearby Supernova
Neutrinos emitted during stellar core collapse leading to a supernova are
primarily of the electron neutrino type at source which may undergo oscillation
between flavor eigenstates during propagation to an earth-bound detector.
Although the number of neutrinos emitted during the pre-bounce collapse phase
is much smaller than that emitted in the post-bounce phase (in which all
flavors of neutrinos are emitted), a nearby supernova event may nevertheless
register a substantial number of detections from the pre-bounce phase at
SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The
calorimetric measurement of the supernova neutrino fluence from this stage via
the charge current and neutral current detection channels in SNO and the
corresponding distortion of detected spectrum in SK over the no-oscillation
spectrum, can probe information about neutrino mass difference and mixing which
are illustrated here in terms of two- and three-flavor oscillation models
Comparisons of various model fits to the Iron line profile in MCG-6-30-15
The broad Iron line in MCG-6-30-15 is fitted to the Comptonization model
where line broadening occurs due to Compton down-scattering in a highly ionized
optically thick cloud. These results are compared to the disk line model where
the broadening is due to Gravitational/Doppler effects in the vicinity of a
black hole. We find that both models fit the data well and it is not possible
to differentiate between them by fitting only the ASCA data. The best fit
temperature and optical depth of the cloud are found to be kT = 0.54 keV and
from the Comptonization model. This model further suggests that
while the temperature can be assumed to be constant, the optical depth varies
during the observation period. We emphasis an earlier conclusion that
simultaneous broad band data ( keV) can rule out (or confirm) the
Comptonization model.Comment: 4 figures. uses aasms4.sty, accepted by ApJ, email:
[email protected]
A rare case of suture material obstructing the closure mechanism of a prosthetic aortic valve: a case report
Prosthetic aortic valve dysfunction presenting as aortic regurgitation is a complication of mechanical valve replacement. We describe a case of late valve dysfunction caused by an annular suture of excessive length obstructing the closure mechanism of a bileaflet prosthetic valve
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