Analysis of complex singularities in high-Reynolds-number Navier-Stokes solutions

Numerical solutions of the laminar Prandtl boundary-layer and Navier-Stokes equations are considered for the case of the two-dimensional uniform flow past an impulsively-started circular cylinder. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions that can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous interactions from a different perspective

Zipf law in the popularity distribution of chess openings

We perform a quantitative analysis of extensive chess databases and show that the frequencies of opening moves are distributed according to a power-law with an exponent that increases linearly with the game depth, whereas the pooled distribution of all opening weights follows Zipf's law with universal exponent. We propose a simple stochastic process that is able to capture the observed playing statistics and show that the Zipf law arises from the self-similar nature of the game tree of chess. Thus, in the case of hierarchical fragmentation the scaling is truly universal and independent of a particular generating mechanism. Our findings are of relevance in general processes with composite decisions.Comment: 5 pages, 4 figure

The Keck Aperture Masking Experiment: Dust Enshrouded Red Giants

While the importance of dusty asymptotic giant branch (AGB) stars to galactic chemical enrichment is widely recognised, a sophisticated understanding of the dust formation and wind-driving mechanisms has proven elusive due in part to the difficulty in spatially-resolving the dust formation regions themselves. We have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture Masking Experiment, resolving all of them in multiple near-infrared bands between 1.5 microns and 3.1 microns. We find 45% of the targets to show measurable elongations that, when correcting for the greater distances of the targets, would correspond to significantly asymmetric dust shells on par with the well-known cases of IRC+10216 or CIT6. Using radiative transfer models, we find the sublimation temperature of 1130 +- 90 K and 1170 +- 60 K for silicates and amorphous carbon respectively, both somewhat lower than expected from laboratory measurements and vastly below temperatures inferred from the inner edge of YSO disks. The fact that O-rich and C-rich dust types showed the same sublimation temperature was surprising as well. For the most optically-thick shells (tau > 2 at 2.2 microns), the temperature profile of the inner dust shell is observed to change substantially, an effect we suggest could arise when individual dust clumps become optically-thick at the highest mass-loss rates.Comment: accepted to Monthly Notices of the Royal Astronomical Societ

Adhesive mechanisms governing interferon-producing cell recruitment into lymph nodes

Natural interferon-producing cells (IPCs) are found in peripheral lymph nodes (PLNs), where they support NK cell, T cell, and B cell responses to pathogens. However, their route of entry and the adhesive mechanisms used to gain access to PLNs remain poorly defined. We report that IPCs can enter PLNs via a hematogenous route, which involves a multistep adhesive process, and that transmigration is enhanced by inflammation. Results indicate that L-selectin on IPCs is required for efficient attachment and rolling on high endothelial venules in vivo in both nonstimulated and inflamed PLNs. IPCs, however, also possess functional ligands for E-selectin that contribute to this process only in the latter case. In conjunction with selectin-mediated adhesion, both β1- and β2-integrins participate in IPC attachment to the inflamed vessel wall, whereas chemotaxis relies in part on the chemokine receptor CCR5. Identification of the adhesive machinery required for IPC trafficking into PLNs may provide opportunities to regulate immune responses reliant on the activity of these cells

Chaos induced coherence in two independent food chains

Coherence evolution of two food web models can be obtained under the stirring effect of chaotic advection. Each food web model sustains a three--level trophic system composed of interacting predators, consumers and vegetation. These populations compete for a common limiting resource in open flows with chaotic advection dynamics. Here we show that two species (the top--predators) of different colonies chaotically advected by a jet--like flow can synchronize their evolution even without migration interaction. The evolution is charaterized as a phase synchronization. The phase differences (determined through the Hilbert transform) of the variables representing those species show a coherent evolution.Comment: 5 pages, 5 eps figures. Accepted for publication in Phys. Rev.

Hydraulic resistance to overland flow on surfaces with partially submerged vegetation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96239/1/wrcr13661.pd

Roughness-induced critical phenomena in a turbulent flow

I present empirical evidence that turbulent flows are closely analogous to critical phenomena, from a reanalysis of friction factor measurements in rough pipes. The data collapse found here corresponds to Widom scaling near critical points, and implies that a full understanding of turbulence requires explicit accounting for boundary roughness

Resonance and frequency-locking phenomena in spatially extended phytoplankton-zooplankton system with additive noise and periodic forces

In this paper, we present a spatial version of phytoplankton-zooplankton model that includes some important factors such as external periodic forces, noise, and diffusion processes. The spatially extended phytoplankton-zooplankton system is from the original study by Scheffer [M Scheffer, Fish and nutrients interplay determines algal biomass: a minimal model, Oikos \textbf{62} (1991) 271-282]. Our results show that the spatially extended system exhibit a resonant patterns and frequency-locking phenomena. The system also shows that the noise and the external periodic forces play a constructive role in the Scheffer's model: first, the noise can enhance the oscillation of phytoplankton species' density and format a large clusters in the space when the noise intensity is within certain interval. Second, the external periodic forces can induce 4:1 and 1:1 frequency-locking and spatially homogeneous oscillation phenomena to appear. Finally, the resonant patterns are observed in the system when the spatial noises and external periodic forces are both turned on. Moreover, we found that the 4:1 frequency-locking transform into 1:1 frequency-locking when the noise intensity increased. In addition to elucidating our results outside the domain of Turing instability, we provide further analysis of Turing linear stability with the help of the numerical calculation by using the Maple software. Significantly, oscillations are enhanced in the system when the noise term presents. These results indicate that the oceanic plankton bloom may partly due to interplay between the stochastic factors and external forces instead of deterministic factors. These results also may help us to understand the effects arising from undeniable subject to random fluctuations in oceanic plankton bloom.Comment: Some typos errors are proof, and some strong relate references are adde

Autoinhibition of the kinesin-2 motor KIF17 via dual intramolecular mechanisms

Kinesin-2 motor KIF17 autoinhibition is visualized in vivo; in the absence of cargo, this homodimer’s C-terminal tail blocks microtubule binding, and a coiled-coil segment blocks motility

Jamming coverage in competitive random sequential adsorption of binary mixture

We propose a generalized car parking problem where cars of two different sizes are sequentially parked on a line with a given probability $q$. The free parameter $q$ interpolates between the classical car parking problem of only one car size and the competitive random sequential adsorption (CRSA) of a binary mixture. We give an exact solution to the CRSA rate equations and find that the final coverage, the jamming limit, of the line is always larger for a binary mixture than for the uni-sized case. The analytical results are in good agreement with our direct numerical simulations of the problem.Comment: 4 pages 2-column RevTeX, Four figures, (there was an error in the previous version. We replaced it (including figures) with corrected and improved version that lead to new results and conclusions