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A New Layer Casting System for Ceramic Laser Rapid Prototyping Apparatus
In the existing Ceramic Laser Fusion system, slurry is fed on the high
temperature surface of the green part; therefore, a part of water infiltrates into the
green block and vaporizes before the process of layer casting. As a result, the slurry
viscosity rises gradually; the quality of the layer surface is not uniform, and the green
part density is uneven. The aim of present study is to develop a new layer casting
system which can solve the problems mentioned above to obtain a green part with
uniform surface quality and density, and to shorten the time-taken of part fabrication.
The first part of the paper illustrates the major requirements and parameters of a slurry
distributor; the second part describes the integration of the slurry feeding device and
layer casting system. The integrated system can feed slurry and cast thin layer
simultaneously; consequently, the drawbacks of the existing system can be eliminated
and the time-taken of the layer casting can be shortened. A variable-frequency drive
(inverter) is used to control the motor speed. The relation between the frequency and
the slurry delivery can be included in the process control program to adjust the
quantity in accordance with the layer thickness; hence, the waste of the slurry can be
reduced.Mechanical Engineerin
Classical Extended Conformal Algebras Associated with Constrained KP Hierarchy
We examine the conformal property of the second Hamiltonian structure of
constrained KP hierarchy derived by Oevel and Strampp. We find that it
naturallygives a family of nonlocal extended conformal algebras. We give two
examples of such algebras and find that they are similar to Bilal's V algebra.
By taking a gauge transformation one can map the constrained KP hierarchy to
Kuperschmidt's nonstandard Lax hierarchy. We consider the second Hamiltonian
structure in this representation. We show that after mapping the Lax operator
to a pure differential operator the second structure becomes the sum of the
second and the third Gelfand-Dickey brackets defined by this differential
operator. We show that this Hamiltonian structure defines the W-U(1)-Kac-Moody
algebra by working out its conformally covariant form.Comment: NHCU-HEP-94-28, 19 pages (Plain TeX
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The Characteristics and Applications of Ceramic Laser Fusion and Ceramic Laser Sintering
The aim of present study is to investigate the possible application of the ceramic parts
which are fabricated with the process of Ceramic Laser Fusion or Ceramic Laser Sintering.
The experimental results reveal: (1) CLF can lead to a reduction in the porosity of the
ceramic part but also can induce micro-cracks. Therefore, this process cannot produce a part
with the required strength by a post-process of infiltration; (2) CLS is capable of fabricating a
ceramic part with high porosity. By adjusting the slurry formulation and varying the scanning
energy, the open porosity can be over 90vol% of the total porosity. After a post-process of
infiltration, the density can be increased to 95%; therefore, CLS can apply to produce a part
with high strength. Because the high open porosity leads to a good permeability, the process
of CLS is suitable for the fabrication of ceramic shell mold.Mechanical Engineerin
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Prospect of Making Ceramic Shell Mold by Ceramic Laser Fusion
Manufacturing prototypical castings by conventional investment casting not only takes
several weeks, but also is prohibitively expensive. Z Corporation in USA, EOS GmbH and
IPT in Germany employ the techniques of 3DP and SLS respectively to make directly ceramic
shell molds for metal castings. Although those techniques dramatically reduce time
expenditure and production cost, each layer cannot be thinner than 50 µm because of using
powder to pave layers. The dimensional accuracy and roughness of the castings still cannot
meet the specification of precision casting. Therefore, in this paper the ceramic laser fusion
(CLF) was used to pave layers. Each layer can be thinner than 25 µm, so that the step effect
can be diminished and the workpiece surface can be smoother; drying time will be shortened
dramatically. Moreover, the inherent solid-state support formed by green portion has the
capability of preventing upward and downward deformation of the scanned cross sections. In
order to make shell mold which meets the roughness requirement (Rq=3.048µm) of the
precision casting, following issues have to be further studied: (1) design a proper ceramic
shell mold structure, (2) design a paving chamber for paving a complete green layer which
can be easily collapsed, (3) cut down drying time, (4) optimize laser scanning process
parameters with the smallest distortion, (5) eliminate sunken area, (6) reduce layer thickness
to less than13µm, (7) control power to guarantee the energy uniformly absorbed by workpiece,
and (8) develop a method which can directly clean green portion in cavity from gate.Mechanical Engineerin
Long-term X-ray Variability of Ultraluminous X-ray Sources
Long-term X-ray modulations on timescales from tens to hundreds of days have
been widely studied for X-ray binaries located in the Milky Way and the
Magellanic Clouds. For other nearby galaxies, only the most luminous X-ray
sources can be monitored with dedicated observations. We here present the first
systematic study of long-term X-ray variability of four ultraluminous X-ray
sources (ESO 243-49 HLX-1, Holmberg IX X-1, M81 X-6, and NGC 5408 X-1)
monitored with Swift. By using various dynamic techniques to analyse their
light curves, we find several interesting low-frequency quasi-periodicities.
Although the periodic signals may not represent any stable orbital modulations,
these detections reveal that such long-term regular patterns may be related to
superorbital periods and structure of the accretion discs. In particular, we
show that the outburst recurrence time of ESO 243-49 HLX-1 varies over time and
suggest that it may not be the orbital period. Instead, it may be due to some
kinds of precession, and the true binary period is expected to be much shorter.Comment: 15 pages, 8 figures; accepted for publication in MNRA
A short note on the presence of spurious states in finite basis approximations
The genesis of spurious solutions in finite basis approximations to operators
which possess a continuum and a point spectrum is discussed and a simple
solution for identifying these solutions is suggested
Morphological study of myelinated and unmyelinated fibres in the sacrococcygeal dorsal roots of the rat
Background: The number and calibre of myelinated and unmyelinated fibres of the sacrococcygeal dorsal roots innervating the tail of rats were studied by means of light and electron microscopy.
Materials and methods: There were an estimated total of 12,500 myelinated and 25,500 unmyelinated dorsal root fibres innervating the tail of a rat.Â
Results: The results showed that from the second sacral (S2) to the fourth sacral (S4) segment, the fibre diameter spectrum of myelinated fibres within each dorsal root was bimodal with two peaks at 5 microns and 10 microns, respectively. The first sacral (S1) segment was composed of numerous smaller-size myelinated fibres, thus forming a right-skewed distribution. The coccygeal (Co) segments showed a unimodal distribution peaking at 10 microns for the first (Co1) segment and gradually shifting to 7 microns for the third (Co3) segment. Overall, there was a continuous relative increase of the larger vs. the smaller myelinated fibres from the sacral to coccygeal segments. The fibre diameter of unmyelinated fibres of all these roots was unimodal with a single peak at 0.5 microns. The ratio of unmy- elinated to myelinated fibre numbers was on average 2.83 for the S1–S2 roots, 1.66 for the S3–S4 roots, and 1.24 for the coccygeal roots.Â
Conclusions: The comparison of the left- and right-side nerve fibres show that there was no significant difference, thus implying a symmetrical sensory innervation of the rat’s tail.
Discovery of X-ray pulsations from "next Geminga" - PSR J1836+5925
We report the X-ray pulsation of ~173.3 ms for the "next Geminga", PSR
J1836+5925, with recent XMM-Newton investigations. The X-ray periodicity is
consistent wtih the gamma-ray ephemeris at the same epoch. The X-ray folded
light curve has a sinusoidal structure which is different from the
double-peaked gamma-ray pulse profile. We have also analysed the X-ray
phase-averaged spectra which shows the X-ray emission from PSR J1836+5925 is
thermal dominant. This suggests the X-ray pulsation mainly originates from the
modulated hot spot on the stellar surface.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ Lette
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