Flame flickering frequency on a rotating Bunsen burner

The empirical correlation (St^*2/Ri=0.00028Re^*2/3: St^* is the reduced Strouhal number, Ri the Richardson number, Re^* the reduced Reynolds number) proposed by Kostiuk and Cheng [1995. The coupling of conical wrinkled laminar flames with gravity. Combustion and Flame 103, 27-40] for predicting buoyancy-induced flame flickering frequency, has been experimentally investigated under the swirling flow conditions produced by a rotating Bunsen burner, focusing on how the flame flickering frequency changes with increasing swirl number S. Under low swirling conditions up to S≈0.1, the flame flickering frequency f_t did not change and monotonically increased with increasing the bulk flow velocity from the burner tube U. The trend of the data is similar to those obtained by Durox et al. [1995. Some effects of gravity on the behavior of premixed flames. Combustion and Flame 82, 66-74] and Kostiuk and Cheng (1995) and could be fitted well with the empirical correlation Kostiuk and Cheng (1995). However, under high swirling  conditions (S>1), f_t significantly decreased up to ≈80% of that with non-swirling condition, and became insensitive to U. As a result, the data under S>1 could not be correlated by the empirical equation. From results obtained by laser doppler velocimetry (LDV), this inconsistency is due to flow divergence shown by the change in the velocity distribution between the burner exit and the flame tip with burner rotation. A minimum value of the centerline velocity u_j,min between the burner exit and the flame tip fulfills an important role in controlling the flame flickering frequency. The use of this parameter allows the empirical correlation to be extended to the high swirling case by means of a modified empirical correlation St^*2/Ri=0.00028(Re^*exp(-0.64S^1.78))^2/3.     

Effects of sample orientation on nonpiloted ignition of thin poly(methyl methacrylate) sheets by a laser: 2. Experimental results

The effect of the sample orientation angle on frontside (irradiated surface) ignition and subsequent backside (nonirradiated surface) flame appearance over thin poly(methyl methacrylate) (PMMA) sheets having thicknesses of 0.2 and 0.5 mm has been experimentally investigated, using a CO₂ laser as an external radiant source in quiescent normal gravity. The sample orientation angle was varied from θ=−90° (ceiling configuration) to +90° (floor configuration) at intervals of 15° under three different laser powers of 16.0, 17.3, and 26.1 W. The shortest frontside ignition delay time was observed for the ceiling configuration (θ=−90°) and frontside ignition delay time significantly varied with increase in sample orientation angle at a laser power of 16.0 W. As the laser power was increased, frontside ignition was observed at all angles and its delay time became less dependent on the sample orientation angle. The appearance of a backside flame was achieved after the formation of an open hole (due to local consumption of the sample) by two different processes: the onset of laser induced ignition over the backside sample (backside ignition) and a flame traveling from the frontside through an open hole to the backside (backside flame). The former process was observed for a limited number of cases only around the vertical configurations (−30°?θ?30°). The delay time for the appearance of backside flame tended to be longer for sample surfaces facing downward (θ°<0) than for the sample surface facing upward (θ?0°) regardless of the laser power. When the duration of laser irradiation was shortened from 10 to 4 s, as soon as the laser was shut off, the flame on the frontside immediately shrank, moved close to the sample surface, and then traveled rapidly to the backside. Therefore, the delay time of backside flame appearance (about 6 s) became longer with longer duration of laser irradiation after the onset of a frontside flame. The size of the hole (about 4 mm diameter) was large enough for the flame to travel through it, even after 4 s of laser irradiation to sample. These results indicate that the size of the hole appears to be not a critical parameter for the appearance of the backside flame.     

Secretion-recapture process of apolipoprotein E in hepatic uptake of chylomicron remnants in transgenic mice

To investigate the role of apoE in hepatic uptake of chylomicron remnants, we studied chylomicron metabolism in transgenic mice overexpressing apoE in the liver. Plasma clearance of injected 125I-labeled human chylomicrons was fivefold faster in transgenic mice than in controls. Immunohistochemistry demonstrated that apoE was specifically localized at the basolateral surface of hepatocytes from fasted transgenic mice. After injection of a large amount of chylomicrons, the density of the cell surface apoE was markedly reduced and vesicular staining was observed in the cytoplasm, suggesting that the cell surface apoE was used for hepatic endocytosis of chylomicrons and remnants. Polyacrylamide gel analysis of chylomicrons and remnants that had been reisolated from plasma and from liver membrane after the injection of chylomicrons showed the particles to be enriched with apoE mainly after their influx into the liver rather than during their residence in plasma. These results provide strong evidence for the secretion-recapture process of apoE, whereby chylomicron remnants enter the sinusoidal space, acquire apoE molecules, and subsequently are endocytosed. Data from experiments with very low density lipoprotein and LDL showed that this system is specific for chylomicron remnants.     

Nonlinear analysis on dynamic behavior of buoyancy-induced flame oscillation under swirling flow

From the viewpoint of nonlinear dynamics, the dynamic behavior of buoyancy-induced flame oscillation has been experimentally investigated under a swirling flow produced by rotating a cylindrical burner tube. As the rotational Reynolds number increases, the dynamic behavior undergoes a significant transition from periodic oscillation to low-dimensional deterministic chaos, through quasi-periodic oscillation. This is clearly demonstrated by nonlinear time series analysis based on chaos theory. The motion of the vortical structure around the burner tube due to the centrifugal instability associated with a rotating Taylor–Couette flow plays an important role in the onset of low-dimensional deterministic chaos.     

Orbital instability and prediction of a Bunsen flame tip motion with burner rotation

An orbital instability of the unsteady flame tip motion with burner rotation and the possibility of the prediction of the flame tip motion are investigated from the viewpoint of nonlinear dynamics. A rich methane–air mixture of equivalence ratio 1.43 is used. The mean exit velocity from the burner tube, U, is varied from 0.6 to 1.3 m/s, keeping the swirl number S=1.14 constant. The variation in the flame tip motion is quantitatively evaluated by calculating the mean value of a parallel trajectory value Γ. At U0.7 m/s, the value of Γ is estimated to be approximately zero, indicating that periodic motion occurs. As U increases, the trajectory of the attractor becomes complicated and Γ gradually increases. The value of Γ approaches the value of the Fourier-transformed surrogate data with further increase in U. This suggests that the flame tip motion varies from periodic to chaotic due to the influence of phase randomness with increasing U. The short-term forward prediction method, that is based on the orbit of the attractor, first was used. Then the short-term forward prediction method was modified to successfully extend the prediction term. The results suggest that the modified short-term forward prediction method proposed in the present study provides a valid method for predicting the motion of unsteady flames.     

Effect of macrophage colony stimulating factor on the advanced atherosclerosis in Watanabe heritable hyperlipidemic rabbits

We have reported that macrophage colony-stimulating factor (M-CSF) prevents atherosclerosis in young WHHL rabbits (Atherosclerosis 93:245, 1993). In the present study, we injected recombinant human M-CSF (250 micrograms/day) into WHHL rabbits aged 11 months 3 times a week after advanced atherosclerosis was established. After 8 months of treatment, we did not find any significant difference in plasma lipid levels, cholesterol ester content in the aorta or macroscopic atherosclerosis lesion area between M-CSF treated and non-treated rabbits. There was, however, a significant difference in the ratio of intimal to medial thickness (1.08 vs 1.7, p < 0.01). Thus, M-CSF may influence vascular smooth muscle cell function and modify the process of atherosclerosis in advance lesions.     

Bending and creasing virtual paper

We developed a mathematical model to simulate the bending and creasing behavior of paper-like sheets. This model permits interactive deformation of a surface remaining isometric to a plane rectangular sheet. It exhibits some important characteristics of paper behavior, such as the appearance of creases for some shapes of the boundary. Accurately simulating the detailed behavior of paper creases would involve several complex tasks, like employing mechanical shell modeling with possible boundary layer phenomena and studying the dynamics of buckling, or considering paper's plasticity. We do not discuss these difficult problems, instead simply analyzing the creasing phenomenon as a transition between two kinds of applicable surfaces     

p57Kip2 regulates actin dynamics by binding and translocating LIM-kinase 1 to the nucleus

p57Kip2 is the only cyclin-dependent kinase (Cdk) inhibitor shown to be essential for mouse embryogenesis. The fact suggests that p57 has a specific role that cannot be compensated by other Cdk inhibitors. LIM-kinase 1 (LIMK-1) is a downstream effector of the Rho family of GTPases that phosphorylates and inactivates an actin depolymerization factor, cofilin, to induce the formation of actin fiber. Here we demonstrate that p57 regulates actin dynamics by binding and translocating LIMK-1 from the cytoplasm into the nucleus, which in turn results in a reorganization of actin fiber. The central region of p57, a unique feature among the Cdk inhibitors, and the N-terminal region of LIMK-1, which contains the LIM domains were essential for the interaction. Expression of p57, but not p27Kip1 or a p57 mutant, with a deletion in the central region was shown to induce marked reorganization of actin filament and a translocation of LIMK-1. Our findings indicate p57 may act as a key regulator in embryogenesis by bearing two distinct functions, the regulation of cell cycle through binding to Cdks and the regulation of actin dynamics through binding to LIMK-1, both of which should be important in developmental procedure.