52 research outputs found
Pattern formation of reaction-diffusion system having self-determined flow in the amoeboid organism of Physarum plasmodium
The amoeboid organism, the plasmodium of Physarum polycephalum, behaves on
the basis of spatio-temporal pattern formation by local
contraction-oscillators. This biological system can be regarded as a
reaction-diffusion system which has spatial interaction by active flow of
protoplasmic sol in the cell. Paying attention to the physiological evidence
that the flow is determined by contraction pattern in the plasmodium, a
reaction-diffusion system having self-determined flow arises. Such a coupling
of reaction-diffusion-advection is a characteristic of the biological system,
and is expected to relate with control mechanism of amoeboid behaviours. Hence,
we have studied effects of the self-determined flow on pattern formation of
simple reaction-diffusion systems. By weakly nonlinear analysis near a trivial
solution, the envelope dynamics follows the complex Ginzburg-Landau type
equation just after bifurcation occurs at finite wave number. The flow term
affects the nonlinear term of the equation through the critical wave number
squared. Contrary to this, wave number isn't explicitly effective with lack of
flow or constant flow. Thus, spatial size of pattern is especially important
for regulating pattern formation in the plasmodium. On the other hand, the flow
term is negligible in the vicinity of bifurcation at infinitely small wave
number, and therefore the pattern formation by simple reaction-diffusion will
also hold. A physiological role of pattern formation as above is discussed.Comment: REVTeX, one column, 7 pages, no figur
Self-organized stable pacemakers near the onset of birhythmicity
General amplitude equations for reaction-diffusion systems near to the soft
onset of birhythmicity described by a supercritical pitchfork-Hopf bifurcation
are derived. Using these equations and applying singular perturbation theory,
we show that stable autonomous pacemakers represent a generic kind of
spatiotemporal patterns in such systems. This is verified by numerical
simulations, which also show the existence of breathing and swinging pacemaker
solutions. The drift of self-organized pacemakers in media with spatial
parameter gradients is analytically and numerically investigated.Comment: 4 pages, 4 figure
Flow-distributed spikes for Schnakenberg kinetics
This is the post-print version of the final published paper. The final publication is available at link.springer.com by following the link below. Copyright @ 2011 Springer-Verlag.We study a system of reaction–diffusion–convection equations which combine a reaction–diffusion system with Schnakenberg kinetics and the convective flow equations. It serves as a simple model for flow-distributed pattern formation. We show how the choice of boundary conditions and the size of the flow influence the positions of the emerging spiky patterns and give conditions when they are shifted to the right or to the left. Further, we analyze the shape and prove the stability of the spikes. This paper is the first providing a rigorous analysis of spiky patterns for reaction-diffusion systems coupled with convective flow. The importance of these results for biological applications, in particular the formation of left–right asymmetry in the mouse, is indicated.RGC of Hong Kon
Spatial and temporal variation of polycyclic aromatic hydrocarbons in the arctic atmosphere.
In the first multi-year arctic air sampling program, PAHs were sampled (vapor and particulate) every week at three locations in the Canadian and Russian Arctic. Data are presented here for the years 1992−1994. The geometric mean ∑PAH concentrations (where ∑ = 16 compounds) for 1993 ranged from 249 to 508 pg/m3 for the three sites. Clear seasonality was evident with the highest concentrations oc curring during the colder months of October−April, coinciding with the arctic haze period. PAH concentrations during this period were highest in the order of Dunai (Russian) > Alert (high Arctic) > Tagish (Pacific). Air mass back trajectories computed for February 1994 revealed long-range transport from Eurasia into the high Arctic. Short periods of high concentrations were also evident during the warmer months, most notably at the Tagish site, where elevated levels of retene (a marker for soft wood combustion) matched forest fire records. Initial findings suggest that the gas/particle partitioning of some of the lighter PAHs, examined during the colder haze period, is similar to remote temperate studies and in reasonable agreement to the Junge−Pankow adsorption model
Reduction of Weather-Related Terminal Area Delays in the Free-Flight Era
While much of the emphasis of the free-flight movement has been concentrated on reducing en-route delays, airport capacity is a major bottleneck in the current airspace system, particularly during bad weather. According to the Air Transport Association (ATA) Air Carrier Delay Reports, ground delays (gate-hold, taxi-in, and taxi-out) comprise 75 percent of total delays. It is likely that the projected steady growth in traffic will only exacerbate these losses. Preliminary analyses show that implementation of the terminal area technologies and procedures under development in NASA s Terminal Area Productivity program can potentially save the airlines at least $350M annually in weather-related delays by the year 2005 at Boston Logan and Detroit airports alone. This paper briefly describes the Terminal Area Productivity program, outlines the costhenefit analyses that are being conducted in support of the program, and presents some preliminary analysis results
Characterization of a novel ghrelin cell reporter mouse
Ghrelin is a hormone that influences many physiological processes and behaviors, such as food intake, insulin and growth hormone release, and a coordinated response to chronic stress. However, little is known about the molecular pathways governing ghrelin release and ghrelin cell function. To better study ghrelin cell physiology, we have generated several transgenic mouse lines expressing humanized Renilla reniformis green fluorescent protein (hrGFP) under the control of the mouse ghrelin promoter. hrGFP expression was especially abundant in the gastric oxyntic mucosa, in a pattern mirroring that of ghrelin immunoreactivity and ghrelin mRNA. hrGFP expression also was observed in the duodenum, but not in the brain, pancreatic islet, or testis. In addition, we used fluorescent activated cell sorting (FACS) to collect and partially characterize highly enriched populations of gastric ghrelin cells. We suggest that these novel ghrelin-hrGFP transgenic mice will serve as useful tools to better understand ghrelin cell physiology
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