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Considerations of internal void generation process by observation of melting and solidification behavior in low temperature laser sintering of PEEK
Laser sintering of PEEK performed below the crystallization temperature has been achieved in
previous study by low temperature process that anchors the part to a rigid base plate to suppress
warpage during processing. However, significant surface roughness and large internal voids are
sometimes generated in the parts built by low temperature process, and there are problems in
stability of parts quality. The purpose of this study is to contribute to quality improvement of
laser sintering of PEEK by low temperature process. It was attempted that clarify the process of
surface roughness and void generation by observing the melting and solidification behavior of
the material during process with a video camera. From these observation results, it was assumed
that the amount of volume change from powder to liquid due to melting and the amount of
shrinkage due to solidification affect part quality such as surface roughness and internal voids.Mechanical Engineerin
Three-dimensional MHD Simulations of Jets from Accretion Disks
We report the results of 3-dimensional magnetohydrodynamic (MHD) simulations
of a jet formation by the interaction between an accretion disk and a large
scale magnetic field. The disk is not treated as a boundary condition but is
solved self-consistently. To investigate the stability of MHD jet, the
accretion disk is perturbed with a non-axisymmetric sinusoidal or random
fluctuation of the rotational velocity. The dependences of the jet velocity
, mass outflow rate , and mass accretion rate
on the initial magnetic field strength in both non-axisymmetric cases are
similar to those in the axisymmetric case. That is, ,
and where is the
initial magnetic field strength. The former two relations are consistent with
the Michel's steady solution, , although
the jet and accretion do not reach the steady state. In both perturbation
cases, a non-axisymmetric structure with appears in the jet, where
means the azimuthal wave number. This structure can not be explained by
Kelvin-Helmholtz instability and seems to originate in the accretion disk.
Non-axisymmetric modes in the jet reach almost constant levels after about 1.5
orbital periods of the accretion disk, while all modes in the accretion disk
grow with oscillation. As for the angular momentum transport by Maxwell stress,
the vertical component, , in the wide range of initial magnetic field
strength.Comment: Accepted for publication in ApJ. The pdf file with high resolution
figures can be downloaded at
http://www.kusastro.kyoto-u.ac.jp/~hiromitu/3j050806.pd
Magnetohydrodynamic jets from different magnetic field configurations
Using axisymmetric MHD simulations we investigate how the overall jet
formation is affected by a variation in the disk magnetic flux profile and/or
the existence of a central stellar magnetosphere. Our simulations evolve from
an initial, hydrostatic equilibrium state in a force-free magnetic field
configuration. We find a unique relation between the collimation degree and the
disk wind magnetization power law exponent. The collimation degree decreases
for steeper disk magnetic field profiles. Highly collimated outflows resulting
from a flat profile tend to be unsteady. We further consider a magnetic field
superposed of a stellar dipole and a disk field in parallel or anti-parallel
alignment. Both stellar and disk wind may evolve in a pair of outflows,
however, a reasonably strong disk wind component is essential for jet
collimation. Strong flares may lead to a sudden change in mass flux by a factor
two. We hypothesize that such flares may eventually trigger jet knots.Comment: 5 pages, 4 figures; proceedings from conference: Protostellar Jets in
Context, held in Rhodes, July 7-12, 200
Optimization of Fueling in Magnetically Confined Plasmas ~ Fueling Optimization Using Hα/Dα Line-emission Measurements in Heliotron J ~
Optimization of Fueling in Magnetically Confined Plasmas ~ Analysis of Neutral Behavior and Optimization of Particle Fueling in Open Magnetic Field Plasmas ~
Optimization of Fueling in Magnetically Confined Plasmas (Fueling Optimization Using Hα /Dα Lineemission Measurements in Heliotron J)
Association between Selected Oral Pathogens and Gastric Precancerous Lesions
We examined whether colonization of selected oral pathogens is associated with gastric precancerous lesions in a cross-sectional study. A total of 119 participants were included, of which 37 were cases of chronic atrophic gastritis, intestinal metaplasia, or dysplasia. An oral examination was performed to measure periodontal indices. Plaque and saliva samples were tested with real-time quantitative PCR for DNA levels of pathogens related to periodontal disease (Porphyromonas gingivalis, Tannerella forsythensis, Treponema denticola, Actinobacillus actinomycetemcomitans) and dental caries (Streptococcus mutans and S. sobrinus). There were no consistent associations between DNA levels of selected bacterial species and gastric precancerous lesions, although an elevated but non-significant odds ratio (OR) for gastric precancerous lesions was observed in relation to increasing colonization of A. actinomycetemcomitans (OR = 1.36 for one standard deviation increase, 95% Confidence Interval = 0.87–2.12), P. gingivalis (OR = 1.12, 0.67–1.88) and T. denticola (OR = 1.34, 0.83–2.12) measured in plaque. To assess the influence of specific long-term infection, stratified analyses by levels of periodontal indices were conducted. A. actinomycetemcomitans was significantly associated with gastric precancerous lesions (OR = 2.51, 1.13–5.56) among those with ≥ median of percent tooth sites with PD≥3 mm, compared with no association among those below the median (OR = 0.86, 0.43–1.72). A significantly stronger relationship was observed between the cumulative bacterial burden score of periodontal disease-related pathogens and gastric precancerous lesions among those with higher versus lower levels of periodontal disease indices (p-values for interactions: 0.03–0.06). Among individuals with periodontal disease, high levels of colonization of periodontal pathogens are associated with an increased risk of gastric precancerous lesions