966 research outputs found
Experimental evidence of flow destabilization in a 2D bidisperse foam
Liquid foam flows in a Hele-Shaw cell were investigated. The plug flow
obtained for a monodisperse foam is strongly perturbed in the presence of
bubbles whose size is larger than the average bubble size by an order of
magnitude at least. The large bubbles migrate faster than the mean flow above a
velocity threshold which depends on its size. We evidence experimentally this
new instability and, in case of a single large bubble, we compare the large
bubble velocity with the prediction deduced from scaling arguments. In case of
a bidisperse foam, an attractive interaction between large bubbles induces
segregation and the large bubbles organize themselves in columns oriented along
the flow. These results allow to identify the main ingredients governing 2D
polydisperse foam flows
Range of rotation of thoracolumbar vertebrae in Japanese macaques
In humans, the range of thoracic vertebral rotation is known to be greater than that of the lumbar vertebrae due to their zygapophyseal orientation and soft tissue structure. However, little is known regarding vertebral movements in non-human primate species, which are primarily quadrupedal walkers. To understand the evolutionary background of human vertebral movements, this study estimated the range of axial rotation of the thoracolumbar spine in macaque monkeys. First, computed tomography (CT) was performed while passively rotating the trunk of whole-body cadavers of Japanese macaques, after which the motion of each thoracolumbar vertebra was estimated. Second, to evaluate the influence of the shoulder girdle and surrounding soft tissues, specimens with only bones and ligaments were prepared, after which the rotation of each vertebra was estimated using an optical motion tracking system. In both conditions, the three-dimensional coordinates of each vertebra were digitized, and the axial rotational angles between adjacent vertebrae were calculated. In the whole-body condition, the lower thoracic vertebrae had a greater range of rotation than did the other regions, similar to that observed in humans. In addition, absolute values for the range of rotation were similar between humans and macaques. However, in the bone–ligament preparation condition, the upper thoracic vertebrae had a range of rotation similar to that of the lower thoracic vertebrae. Contrary to previous speculations, our results showed that the mechanical restrictions by the ribs were not as significant; rather, the shoulder girdle largely restricted the rotation of the upper thoracic vertebrae, at least, in macaques
The relative effects of entry parameters on thermal protection system weight
Shielding a spacecraft from the severe thermal environment of an atmospheric entry requires a sophisticated thermal protection system (TPS). Thermal computer program models were developed for two such TPS designs proposed for the space shuttle orbiter. The multilayer systems, a reusable surface insulation TPS, and a re-radiative metallic skin TPS, were sized for a cross-section of trajectories in the entry corridor. This analysis indicates the relative influence of the entry parameters on the weight of each TPS concept. The results are summarized graphically. The trajectory variables considered were down-range, cross-range, orbit inclination, entry interface velocity and flight path angle, maximum heating rate level, angle of attack, and ballistic coefficient. Variations in cross-range and flight path angle over the ranges considered had virtually no effect on the required entry TPS weight. The TPS weight was significantly more sensitive to variations in angle of attack than to dispersions in the other trajectory considered
Role of Internal Motions and Molecular Geometry on the NMR Relaxation of Hydrocarbons
The role of internal motions and molecular geometry on H NMR relaxation
times in hydrocarbons is investigated using MD (molecular dynamics)
simulations of the autocorrelation functions for in{\it tra}molecular
and in{\it ter}molecular H-H dipole-dipole interactions
arising from rotational () and translational () diffusion, respectively.
We show that molecules with increased molecular symmetry such as neopentane,
benzene, and isooctane show better agreement with traditional hard-sphere
models than their corresponding straight-chain -alkane, and furthermore that
spherically-symmetric neopentane agrees well with the Stokes-Einstein theory.
The influence of internal motions on the dynamics and relaxation of
-alkanes are investigated by simulating rigid -alkanes and comparing with
flexible (i.e. non-rigid) -alkanes. Internal motions cause the rotational
and translational correlation-times to get significantly shorter
and the relaxation times to get significantly longer, especially for
longer-chain -alkanes. Site-by-site simulations of H's along the chains
indicate significant variations in and across the chain,
especially for longer-chain -alkanes. The extent of the stretched (i.e.
multi-exponential) decay in the autocorrelation functions are
quantified using inverse Laplace transforms, for both rigid and flexible
molecules, and on a site-by-site bases. Comparison of measurements
with the site-by-site simulations indicate that cross-relaxation (partially)
averages-out the variations in and across the chain of
long-chain -alkanes. This work also has implications on the role of
nano-pore confinement on the NMR relaxation of fluids in the organic-matter
pores of kerogen and bitumen
Gastric Hyperplastic Polyp Associated with Proliferation of Xanthoma Cells Observed by Magnification Narrow-Band Imaging Endoscopy
A case of gastric hyperplastic polyp with proliferation of xanthoma cells is reported. The patient was a 69-year-old man who visited our hospital for further evaluation of gastric polyps. Endoscopic examination of the upper digestive tract revealed multiple hyperplastic polyps in the gastric antrum. There was a pedunculated polyp with whitish yellow granules, 7 mm in diameter, arising from the greater curvature of the antrum. Magnification narrow-band imaging endoscopy (GIF-H260Z, Olympus) revealed long microcapillaries in the polyp but did not reveal disappearance of the mucosal microstructure or irregular branched capillaries. Endoscopic mucosal resection (EMR) was performed. Histological examination of the specimen revealed the lengthened gastric foveolae in the superficial portion and tight sheet of foamy histiocytes in the lamina propria. Diagnosis of gastric hyperplastic polyp with proliferation of xanthoma cells was made. There was no evidence of malignancy. It is necessary to know that a gastric hyperplastic polyp may associate with gastric xanthoma, although such association is very rare
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