Tailoring boundary geometry to optimize heat transport in turbulent convection

By tailoring the geometry of the upper boundary in turbulent Rayleigh-B\'enard convection we manipulate the boundary layer -- interior flow interaction, and examine the heat transport using the Lattice Boltzmann method. For fixed amplitude and varying boundary wavelength $\lambda$, we find that the exponent $\beta$ in the Nusselt-Rayleigh scaling relation, $Nu-1 \propto Ra^\beta$, is maximized at $\lambda \equiv \lambda_{\text{max}} \approx (2 \pi)^{-1}$, but decays to the planar value in both the large ($\lambda \gg \lambda_{\text{max}}$) and small ($\lambda \ll \lambda_{\text{max}}$) wavelength limits. The changes in the exponent originate in the nature of the coupling between the boundary layer and the interior flow. We present a simple scaling argument embodying this coupling, which describes the maximal convective heat flux.Comment: 6 pages, 6 figure

Towards a mesoscopic model of water-like fluids with hydrodynamic interactions

We present a mesoscopic lattice model for non-ideal fluid flows with directional interactions, mimicking the effects of hydrogen-bonds in water. The model supports a rich and complex structural dynamics of the orientational order parameter, and exhibits the formation of disordered domains whose size and shape depend on the relative strength of directional order and thermal diffusivity. By letting the directional forces carry an inverse density dependence, the model is able to display a correlation between ordered domains and low density regions, reflecting the idea of water as a denser liquid in the disordered state than in the ordered one

Aspects Of Lipid Metabolism During Rat L(6) Skeletal Myogenesis

The primary objective of this study was to determine the regulating factor(s) responsible for the coordinate changes in lipid metabolism observed as L{dollar}\sb{lcub}6{rcub}{dollar} myoblasts switch from predominantly triacylglycerol (TAG)-synthesizing cells to primarily phospholipid-synthesizing cells during fusion into myotubes (ie. skeletal myogenesis). Myoblasts, but not myotubes, showed a dramatic accumulation of TAG in fatty acid-supplemented growth medium. Both fatty acid oxidation and phospholipid synthesis increased significantly during skeletal myogenesis. Pulse-chase studies showed products of TAG degradation to be used for phospholipid synthesis (prior to oxidation), which resulted in a 4-fold increase in phospholipid content during skeletal myogenesis. A 2-fold increase in calcium content and a transient activation of calcium uptake observed during skeletal myogenesis indicate that phospholipid and calcium metabolism may be interrelated.;In vitro studies of catabolism (TAG-lipase) and synthesis (diacylglycerol acyltransferase, DAGAT) showed that TAG catabolism increased, and TAG synthesis decreased, during skeletal myogenesis. The dominant TAG-lipase was shown to be the lysosomal acid lipase based on its pH optimum, cosedimentation with acid phosphatase, and its marked inhibition by the lysosomotropic agents chloroquine (CQ) and chlorpromazine (CZ). In pulse-chase studies of L{dollar}\sb6{dollar} myoblasts, CQ or CZ prevented the shift of TAG products into phospholipid, implicating the above lipase in the catabolism of endogenously-synthesized TAG. The decrease in DAGAT activity was not due to decreased enzyme or DAG. A cell-permeant cAMP derivative (bt{dollar}\sb2{dollar}-cAMP) and the calcium ionophore (A{dollar}\sb{lcub}23/87{rcub}{dollar}) increased TAG synthesis in differentiating L{dollar}\sb6{dollar} myoblasts without affecting TAG catabolism or phospholipid synthesis. The tumor-promoter 12-O-tetradecanoyl phorbol 13-acetate (TPA), a known activator of protein kinase C (PKC), antagonized these effects. Bt{dollar}\sb2{dollar}-cAMP and A{dollar}\sb{lcub}23/87{rcub}{dollar} decreased, but TPA increased, fatty acid oxidation in both L{dollar}\sb6{dollar} myoblasts and myotubes. These observations suggest that TAG synthesis and fatty acid oxidation may be under hormonal regulation.;Significant increases in phospholipid synthesis, calcium uptake and PIP turnover were observed during calcium-regulated myoblast fusion. A transient activation of PKC, possibly initiated by PIP{dollar}\sb2{dollar} breakdown, was postulated and explored (using TPA and A{dollar}\sb{lcub}23/87{rcub}{dollar}) in relation to the transient increase in phospholipid synthesis observed during skeletal myogenesis. TPA, a known activator of PC synthesis, enhanced {dollar}\sp{lcub}32{rcub}{dollar}P incorporation into PC dramatically, but this observation was likely due to a TPA-activated increase in P{dollar}\sb1{dollar} uptake and PC hydrolysis. TPA did not increase (methyl-{dollar}\sp3{dollar}H) choline incorporation into PC. A{dollar}\sb{lcub}23/87{rcub}{dollar} did not affect PC metabolism but did enhance PIP{dollar}\sb2{dollar} turnover in fusing myoblasts only (ie. not myotubes). Neither PKA, PKC nor calcium appear to be implicated in the activation of phospholipid synthesis during skeletal myogenesis. PIP{dollar}\sb2{dollar} breakdown may play a fundamental role during myoblast fusion. Studies with an L{dollar}\sb6{dollar} myoblast mutant (D1) show that TPA-activated PC hydrolysis plays no role in myoblast fusion. A reported drop in cAMP levels leading to diminished PKA-activated TAG synthesis, in combination with marked increases in phospholipid synthesis and fatty acid oxidation, likely manifest in the previously-described switch in lipid metabolism observed during skeletal myogenesis

Lattice Boltzmann versus Molecular Dynamics simulation of nano-hydrodynamic flows

A fluid flow in a simple dense liquid, passing an obstacle in a two-dimensional thin film geometry, is simulated by Molecular Dynamics (MD) computer simulation and compared to results of Lattice Boltzmann (LB) simulations. By the appropriate mapping of length and time units from LB to MD, the velocity field as obtained from MD is quantitatively reproduced by LB. The implications of this finding for prospective LB-MD multiscale applications are discussed.Comment: 4 pages, 4 figure

Turbulent Transport Processes at Rough Surfaces with Geophysical Applications

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Memory Switches in Chemical Reaction Space

Just as complex electronic circuits are built from simple Boolean gates, diverse biological functions, including signal transduction, differentiation, and stress response, frequently use biochemical switches as a functional module. A relatively small number of such switches have been described in the literature, and these exhibit considerable diversity in chemical topology. We asked if biochemical switches are indeed rare and if there are common chemical motifs and family relationships among such switches. We performed a systematic exploration of chemical reaction space by generating all possible stoichiometrically valid chemical configurations up to 3 molecules and 6 reactions and up to 4 molecules and 3 reactions. We used Monte Carlo sampling of parameter space for each such configuration to generate specific models and checked each model for switching properties. We found nearly 4,500 reaction topologies, or about 10% of our tested configurations, that demonstrate switching behavior. Commonly accepted topological features such as feedback were poor predictors of bistability, and we identified new reaction motifs that were likely to be found in switches. Furthermore, the discovered switches were related in that most of the larger configurations were derived from smaller ones by addition of one or more reactions. To explore even larger configurations, we developed two tools: the “bistabilizer,” which converts almost-bistable systems into bistable ones, and frequent motif mining, which helps rank untested configurations. Both of these tools increased the coverage of our library of bistable systems. Thus, our systematic exploration of chemical reaction space has produced a valuable resource for investigating the key signaling motif of bistability

SUSApp: a mobile app for measuring and comparing questionnaire-based usability assessments

Usability questionnaires are one of the most used methods to measure usability in terms of the user’s subjective satisfaction. However, most of the usability questionnaires do not provide a complete environment to store measurements and compare different usability values of application categories and versions over the long term, which makes it difficult to study the usability of a software product or even the usability of different versions of such products over time, hindering the facility to obtain comparisons and thresholds in usability measurements for different product lines. In this paper we present SUSApp, a tool conceived for the analysis of usability through the SUS (System Usability Scale) questionnaire, which is one of the most popular ones. This tool was conceived for mobile platforms, and it is intended to easily analyze usability by storing and recovering past evaluations, and allowing to statistically compare usability measurements among different software products and applications categories. In addition, a user testing is presented. This has provided acceptable usability results concerning SUSApp in an experiment with real usersThis work has been partially supported by the funding projects «eMadrid-CM», granted by the Madrid Research Council (project code S2013/ICE-2715), and «Flexor» granted by the Spanish Government (project code TIN2014-52129-R

Michaelis-Menten dynamics in protein subnetworks

To understand the behaviour of complex systems it is often necessary to use models that describe the dynamics of subnetworks. It has previously been established using projection methods that such subnetwork dynamics generically involves memory of the past, and that the memory functions can be calculated explicitly for biochemical reaction networks made up of unary and binary reactions. However, many established network models involve also Michaelis-Menten kinetics, to describe e.g. enzymatic reactions. We show that the projection approach to subnetwork dynamics can be extended to such networks, thus significantly broadening its range of applicability. To derive the extension we construct a larger network that represents enzymes and enzyme complexes explicitly, obtain the projected equations, and finally take the limit of fast enzyme reactions that gives back Michaelis-Menten kinetics. The crucial point is that this limit can be taken in closed form. The outcome is a simple procedure that allows one to obtain a description of subnetwork dynamics, including memory functions, starting directly from any given network of unary, binary and Michaelis-Menten reactions. Numerical tests show that this closed form enzyme elimination gives a much more accurate description of the subnetwork dynamics than the simpler method that represents enzymes explicitly, and is also more efficient computationally