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When a fluid system is subject to strong rotation, centrifugal fluid motion is expected, i.e., denser (lighter) fluid moves outward (inward) from (toward) the axis of rotation. Here we demonstrate, both experimentally and numerically, the existence of an unexpected outward motion of warm and lighter vortices in rotating thermal convection. This anomalous vortex motion occurs under rapid rotations when the centrifugal buoyancy is sufficiently strong to induce a symmetry-breaking in the vorticity field, i.e., the vorticity of the cold anticyclones overrides that of the warm cyclones. We show that through hydrodynamic interactions the densely distributed vortices can self-aggregate into coherent clusters and exhibit collective motion in this flow regime. Interestingly, the correlation of the vortex velocity fluctuations within a cluster is scale-free, with the correlation length being proportional ( ≈ 30%) to the cluster length. Such long-range correlation leads to the counterintuitive collective outward motion of warm vortices. Our study brings insights into the vortex dynamics that are widely present in nature.
RESUMO
Brownian motion of particles in fluid is the most common form of collective behavior in physical and biological systems. Here, we demonstrate through both experiment and numerical simulation that the movement of vortices in a rotating turbulent convective flow resembles that of inertial Brownian particles, i.e., they initially move ballistically and then diffusively after certain critical time. Moreover, the transition from ballistic to diffusive behaviors is direct, as predicted by Langevin, without first going through the hydrodynamic memory regime. The transitional timescale and the diffusivity of the vortices can be collapsed excellently onto a master curve for all explored parameters. In the spatial domain, however, the vortices exhibit organized structures, as if they are performing tethered random motion. Our results imply that the convective vortices have inertia-induced memory such that their short-term movement can be predicted and their motion can be well described in the framework of Brownian motions.
RESUMO
AIM: To investigate the expression of Toll like receptor 4(TLR4) on splenocytes and TNF-alpha mRNA, the dynamic changes of CD4(+) CD25(+) regulatory T cell(Treg) and endotoxin(ET) in peripheral blood of burnt rats during the early phase, and to explore the mechanism against inflammatory reaction in intestine-derived infection after burn. METHODS: 64 SD male rats were randomly separated into control group and burn model groups. Rats of burn model group were burnt with vapor under 3 mPa pressure and 108 degrees Celsius temperature for 8 seconds to achieve deep partial-thickness burn, and a 30% total body surface area (TBSA) burn model was made. Rats were sacrificed before and 2, 5, 8, 12, 24, 48 and 72 h after burn, and the TLR4 and TNF-alpha mRNA expression in splenocytes were measured at various intervals by RT-PCR. The expression of TLR4 protein was measured by Western blot, and the percentage of Treg cells in CD4(+) T cells was detected by flow cytometry (FCM), and the LPS concentration of plasma was detected by limulus lysate test. RESULTS: The expression of TLR4 mRNA, TNF-alpha mRNA, TLR4 protein and the levels of Treg, ET were significantly increased at some times points after burn. The expression of TLR4 mRNA and protein reached the peak at 8 h, whereas the TNF-alpha mRNA at 12 h, and Treg and ET at 8 h. The peak values of them were 3.66+/-0.51, 2.27+/-0.19, 1.65+/-0.23, 63.19+/-12.65% and 11.68+/-1.71 Eu/mL respectively, which were of significant difference when compared with the control group (P<0.01). The expression of TLR4 mRNA showed a positive correlation with that of Treg, ET and TNF-alpha mRNA (r=0.898, 0.811, 0.462, P<0.01). CONCLUSION: Treg might play a major role in the process of immune regulation in rats after burn, the mechanism of which may be correlated with the increase of LPS-TLR4 signal transduced by intestine-derived infection.
