Homoclinic bifurcations in low-Prandtl-number Rayleigh-B\'{e}nard convection with uniform rotation

We present results of direct numerical simulations on homoclinic gluing and ungluing bifurcations in low-Prandtl-number ($0 \leq Pr \leq 0.025$) Rayleigh-B\'{e}nard system rotating slowly and uniformly about a vertical axis. We have performed simulations with \textit{stress-free} top and bottom boundaries for several values of Taylor number ($5 \leq Ta \leq 50$) near the instability onset. We observe a single homoclinic ungluing bifurcation, marked by the spontaneous breaking of a larger limit cycle into two limit cycles with the variation of the reduced Rayleigh number $r$ for smaller values of $Ta (< 25)$. A pair of homoclinic bifurcations, instead of one bifurcation, is observed with variation of $r$ for slightly higher values of $Ta$ ($25 \leq Ta \leq 50$) in the same fluid dynamical system. The variation of the bifurcation threshold with $Ta$ is also investigated. We have also constructed a low-dimensional model which qualitatively captures the dynamics of the system near the homoclinic bifurcations for low rotation rates. The model is used to study the unfolding of bifurcations and the variation of the homoclinic bifurcation threshold with $Pr$.Comment: 6 pages, 7 figures, 1 tabl

Protection from experimental colitis by theaflavin-3,3'-digallate correlates with inhibition of IKK and NF-κB activation

Background and purpose: Inflammatory bowel disease (IBD) is associated with activation of nuclear factor &#954; B (NF-&#954;B) involved in regulating the expression of inducible nitric oxide synthase (iNOS) and proinflammatory cytokine genes. As theaflavin-3,3'-digallate (TFDG), the most potent anti-oxidant polyphenol of black tea, down-regulates NF-&#954;B activation, we investigated if TFDG is beneficial in colonic inflammation by suppressing iNOS and proinflammatory cytokines. Experimental approach: The in vivo efficacy of TFDG was assessed in mice with trinitrobenzene sulfonic acid (TNBS)-induced colitis. Both mRNA and protein levels of proinflammatory cytokines and iNOS were analyzed in colon tissue treated with or without TFDG. NF-&#954;B activation was determined by electrophoretic mobility shift assay and levels of NF-&#954;B inhibitory protein (I&#954;B&#945;) were analyzed by Western blotting. Key results: Oral administration of TFDG (5 mg kg-1 daily i.g.) significantly improved TNBS-induced colitis associated with decreased mRNA and protein levels of TNF-&#945;, IL-12, IFN- and iNOS in colonic mucosa. DNA binding and Western blotting revealed increase in NF-&#954;B activation and I&#954;B depletion in TNBS-treated mice from Day 2 through Day 8 with a maximum at Day 4, which resulted from increased phosphorylation of I&#954;B and higher activity of I&#954;B kinase (IKK). Pretreatment with TFDG markedly inhibited TNBS-induced increases in nuclear localization of NF-&#954;B&#945;, cytosolic IKK activity and preserved I&#954;B&#945; in colon tissue. Conclusions and Implications: TFDG exerts protective effects in experimental colitis and inhibits production of inflammatory mediators through a mechanism that, at least in part, involves inhibition of NF-&#954;B activation

Production of Aluminium-Silicon Carbide Cast Particle Composites Without Magnesium

To produce Al matrix cast particle composites, wettability of the ceramic particles by liquid Al is essential. To improve wettability, elements such as Mg, Ce etc. are added into Al alloy prior to incorporation of the ceramic particles. In other methods,ceramic particles are incorporated into solid-liquid slurry of Al alloy: metalceramic powder compacts are slowly dissolved into the Al alloy or particles are preheated before incorporation into Al alloy.In the present study, silicon carbide and alumina particles were mixed with Al-Cu (50:50) piaster alloy powder in a required proportion to produce Al-4.5 Cu alloy- 15 wt% particle composites by vortex method. Success was achieved to incorporate SiC particles in an Al melt without Mg. whereas in case of alumina particles, the viscosity of the melt was too high after addition of about half of the required amount of particles. The fluidity of the Al alloy-SIC composite melt was sufficient to pour in graphite moulds. The mechanism of this novel approach of production of cast ceramic particle composites by vortex method without Mg is discussed