3,317 research outputs found
Air cavities at the inner cylinder of turbulent Taylor-Couette flow
Air cavities, i.e. air layers developed behind cavitators, are seen as a
promising drag reducing method in the maritime industry. Here we utilize the
Taylor-Couette (TC) geometry, i.e. the flow between two concentric,
independently rotating cylinders, to study the effect of air cavities in this
closed setup, which is well-accessible for drag measurements and optical flow
visualizations. We show that stable air cavities can be formed, and that the
cavity size increases with Reynolds number and void fraction. The streamwise
cavity length strongly depends on the axial position due to buoyancy forces
acting on the air. Strong secondary flows, which are introduced by a
counter-rotating outer cylinder, clearly decrease the stability of the
cavities, as air is captured in the Taylor rolls rather than in the cavity.
Surprisingly, we observed that local air injection is not necessary to sustain
the air cavities; as long as air is present in the system it is found to be
captured in the cavity. We show that the drag is decreased significantly as
compared to the case without air, but with the geometric modifications imposed
on the TC system by the cavitators. As the void fraction increases, the drag of
the system is decreased. However, the cavitators itself significantly increase
the drag due to their hydrodynamic resistance (pressure drag): In fact, a net
drag increase is found when compared to the standard smooth-wall TC case.
Therefore, one must first overcome the added drag created by the cavitators
before one obtains a net drag reduction.Comment: 14 pages, 13 figure
The influence of wall roughness on bubble drag reduction in Taylor-Couette turbulence
We experimentally study the influence of wall roughness on bubble drag
reduction in turbulent Taylor-Couette flow, i.e.\ the flow between two
concentric, independently rotating cylinders. We measure the drag in the system
for the cases with and without air, and add roughness by installing transverse
ribs on either one or both of the cylinders. For the smooth wall case (no ribs)
and the case of ribs on the inner cylinder only, we observe strong drag
reduction up to and , respectively, for a void fraction of
. However, with ribs mounted on both cylinders or on the outer
cylinder only, the drag reduction is weak, less than , and thus quite
close to the trivial effect of reduced effective density. Flow visualizations
show that stable turbulent Taylor vortices --- large scale vortical structures
--- are induced in these two cases, i.e. the cases with ribs on the outer
cylinder. These strong secondary flows move the bubbles away from the boundary
layer, making the bubbles less effective than what had previously been observed
for the smooth-wall case. Measurements with counter-rotating smooth cylinders,
a regime in which pronounced Taylor rolls are also induced, confirm that it is
really the Taylor vortices that weaken the bubble drag reduction mechanism. Our
findings show that, although bubble drag reduction can indeed be effective for
smooth walls, its effect can be spoiled by e.g.\ biofouling and omnipresent
wall roughness, as the roughness can induce strong secondary flows.Comment: 10 pages, 5 figure
Effects of Substituents on the Length of Central C(sp^3)-C(sp^3) Bond in Anthracene Photodimers and Related Molecules
Effects of substituents on the lengths of the central C–C single bond in the butterfly-shaped anthracene photodimers (1)–(7) and lepidopterenes (8) are studied. X-Ray analysis of the photodimer (10) of 9,10-difluoroanthracene gave a C(9)–C(10′) bond length of 1.631 (3)Å. An attempt to re-determine molecular structure of the photoisomer (5) of [2.2](9,10) anthracenophane (12) by neutron diffraction analysis is also reported [C(9)–C(10′): obs. 1.64(1), calc. 1.63(1)Å]. The D_2 structure that had been proposed for the minimum-energy conformation of (5) is questioned and the D_(2h) symmetric conformation is suggested on the basis of the diffraction results and MNDO calculations. The experimentally determined distances of the long central C–C bonds in these butterfly compounds including dianthronyl (9) are well reproduced by MNDO calculations with a standard deviation of 0.013 Å. Small but significant further elongation of the central C–C bond by up to 0.07 Å resulting from annulation of cyclobutane or cyclopentane ring in anthracene photodimers and from remote chlorine substitution in lepidopterene are interpreted in terms of the increased π→σ^* orbital interaction
Controlling secondary flow in Taylor-Couette turbulence through spanwise-varying roughness
Highly turbulent Taylor-Couette flow with spanwise-varying roughness is
investigated experimentally and numerically (direct numerical simulations (DNS)
with an immersed boundary method (IBM)) to determine the effects of the spacing
and axial width of the spanwise varying roughness on the total drag and
{on} the flow structures. We apply sandgrain roughness, in the form of
alternating {rough and smooth} bands to the inner cylinder. Numerically, the
Taylor number is and the roughness width is varied between
, where is the gap width. Experimentally,
we explore and .
For both approaches the radius ratio is fixed at , with
and the radius of the inner and outer cylinder respectively. We
present how the global transport properties and the local flow structures
depend on the boundary conditions set by the roughness spacing .
Both numerically and experimentally, we find a maximum in the angular momentum
transport as function of . This can be atributed to the
re-arrangement of the large-scale structures triggered by the presence of the
rough stripes, leading to correspondingly large-scale turbulent vortices.Comment: 20 pages, 7 figures, draft for JF
The role of human cytochrome P450 2E1 in liver inflammation and fibrosis.
Cytochrome P450 2E1 (CYP2E1) plays an important role in alcohol and toxin metabolism by catalyzing the conversion of substrates into more polar metabolites and producing reactive oxygen species. Reactive oxygen species-induced oxidative stress promotes hepatocyte injury and death, which in turn induces inflammation, activation of hepatic stellate cells, and liver fibrosis. Here, we analyzed mice expressing only the human CYP2E1 gene (hCYP2E1) to determine differences in hCYP2E1 versus endogenous mouse Cyp2e1 function with different liver injuries. After intragastric alcohol feeding, CYP2E1 expression was induced in both hCYP2E1 and wild-type (Wt) mice. hCYP2E1 mice had greater inflammation, fibrosis, and lipid peroxidation but less hepatic steatosis. In addition, hCYP2E1 mice demonstrated increased expression of fibrogenic and proinflammatory genes but decreased expression of de novo lipogenic genes compared to Wt mice. Lipidomics of free fatty acid, triacylglycerol, diacylglycerol, and cholesterol ester species and proinflammatory prostaglandins support these conclusions. Carbon tetrachloride-induced injury suppressed expression of both mouse and human CYP2E1, but again hCYP2E1 mice exhibited greater hepatic stellate cell activation and fibrosis than Wt controls with comparable expression of proinflammatory genes. By contrast, 14-day bile duct ligation induced comparable cholestatic injury and fibrosis in both genotypes. Conclusion: Alcohol-induced liver fibrosis but not hepatic steatosis is more severe in the hCYP2E1 mouse than in the Wt mouse, demonstrating the use of this model to provide insight into the pathogenesis of alcoholic liver disease. (Hepatology Communications 2017;1:1043-1057)
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Tumor promoter TPA activates Wnt/β-catenin signaling in a casein kinase 1-dependent manner.
The tumor promoter 12-O-tetra-decanoylphorbol-13-acetate (TPA) has been defined by its ability to promote tumorigenesis on carcinogen-initiated mouse skin. Activation of Wnt/β-catenin signaling has a decisive role in mouse skin carcinogenesis, but it remains unclear how TPA activates Wnt/β-catenin signaling in mouse skin carcinogenesis. Here, we found that TPA could enhance Wnt/β-catenin signaling in a casein kinase 1 (CK1) ε/δ-dependent manner. TPA stabilized CK1ε and enhanced its kinase activity. TPA further induced the phosphorylation of LRP6 at Thr1479 and Ser1490 and the formation of a CK1ε-LRP6-axin1 complex, leading to an increase in cytosolic β-catenin. Moreover, TPA increased the association of β-catenin with TCF4E in a CK1ε/δ-dependent way, resulting in the activation of Wnt target genes. Consistently, treatment with a selective CK1ε/δ inhibitor SR3029 suppressed TPA-induced skin tumor formation in vivo, probably through blocking Wnt/β-catenin signaling. Taken together, our study has identified a pathway by which TPA activates Wnt/β-catenin signaling
Developmental Transcriptomic Analysis of the Cave-Dwelling Crustacean, Asellus aquaticus
Cave animals are a fascinating group of species often demonstrating characteristics including reduced eyes and pigmentation, metabolic efficiency, and enhanced sensory systems. Asellus aquaticus, an isopod crustacean, is an emerging model for cave biology. Cave and surface forms of this species differ in many characteristics, including eye size, pigmentation, and antennal length. Existing resources for this species include a linkage map, mapped regions responsible for eye and pigmentation traits, sequenced adult transcriptomes, and comparative embryological descriptions of the surface and cave forms. Our ultimate goal is to identify genes and mutations responsible for the differences between the cave and surface forms. To advance this goal, we decided to use a transcriptomic approach. Because many of these changes first appear during embryonic development, we sequenced embryonic transcriptomes of cave, surface, and hybrid individuals at the stage when eyes and pigment become evident in the surface form. We generated a cave, a surface, a hybrid, and an integrated transcriptome to identify differentially expressed genes in the cave and surface forms. Additionally, we identified genes with allele-specific expression in hybrid individuals. These embryonic transcriptomes are an important resource to assist in our ultimate goal of determining the genetic underpinnings of the divergence between the cave and surface forms
Catastrophic phase inversion in high-Reynolds number turbulent Taylor--Couette flow
Emulsions are omnipresent in the food industry, health care, and chemical
synthesis. In this Letter the dynamics of meta-stable oil-water emulsions in
highly turbulent () Taylor--Couette
flow, far from equilibrium, is investigated. By varying the oil-in-water void
fraction, catastrophic phase inversion between oil-in-water and water-in-oil
emulsions can be triggered, changing the morphology, including droplet sizes,
and rheological properties of the mixture, dramatically. The manifestation of
these different states is exemplified by combining global torque measurements
and local in-situ laser induced fluorescence (LIF) microscopy imaging. Despite
the turbulent state of the flow and the dynamic equilibrium of the oil-water
mixture, the global torque response of the system is found to be as if the
fluid were Newtonian, and the effective viscosity of the mixture was found to
be several times bigger or smaller than either of its constituents.Comment: 5 pages, 4 figure
Rough wall turbulent Taylor-Couette flow: the effect of the rib height
In this study, we combine experiments and direct numerical simulations to
investigate the effects of the height of transverse ribs at the walls on both
global and local flow properties in turbulent Taylor-Couette flow. We create
rib roughness by attaching up to 6 axial obstacles to the surfaces of the
cylinders over an extensive range of rib heights, up to blockages of 25% of the
gap width. In the asymptotic ultimate regime, where the transport is
independent of viscosity, we emperically find that the prefactor of the
scaling (corresponding to the drag coefficient
being constant) scales with the number of ribs and by the rib
height . The physical mechanism behind this is that the dominant
contribution to the torque originates from the pressure forces acting on the
rib which scale with rib height. The measured scaling relation of is slightly smaller than the expected scaling, presumably
because the ribs cannot be regarded as completely isolated but interact. In the
counter-rotating regime with smooth walls, the momentum transport is increased
by turbulent Taylor vortices. We find that also in the presence of transverse
ribs these vortices persist. In the counter-rotating regime, even for large
roughness heights, the momentum transport is enhanced by these vortices.Comment: 18 pages, 9 figure
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