Shape minimization of the dissipated energy in dyadic trees

In this paper, we study the role of boundary conditions on the optimal shape of a dyadic tree in which flows a Newtonian fluid. Our optimization problem consists in finding the shape of the tree that minimizes the viscous energy dissipated by the fluid with a constrained volume, under the assumption that the total flow of the fluid is conserved throughout the structure. These hypotheses model situations where a fluid is transported from a source towards a 3D domain into which the transport network also spans. Such situations could be encountered in organs like for instance the lungs and the vascular networks. Two fluid regimes are studied: (i) low flow regime (Poiseuille) in trees with an arbitrary number of generations using a matricial approach and (ii) non linear flow regime (Navier-Stokes, moderate regime with a Reynolds number 100) in trees of two generations using shape derivatives in an augmented Lagrangian algorithm coupled with a 2D/3D finite elements code to solve Navier-Stokes equations. It relies on the study of a finite dimensional optimization problem in the case (i) and on a standard shape optimization problem in the case (ii). We show that the behaviours of both regimes are very similar and that the optimal shape is highly dependent on the boundary conditions of the fluid applied at the leaves of the tree.Comment: \`a para\^itre dans Discrete Contin. Dyn. Syst. (B

Targeting the poor in Mexico

This report reevaluates PROGRESA's targeting methods since the program began adding beneficiary households through a process called “densification.” The authors first evaluate PROGRESA's accuracy in targeting both at the community and household levels. Second, they evaluate the targeting in terms of its impact on poverty alleviation relative to other feasible methods assuming the same total budget.Education ,Mexico ,

Rationales for Real Estate Leasing versus Owning

In this article, rationales for the widespread existence of commercial real estate leasing are examined. Given the tendency of tenants to abuse property to their own advantage, there must be powerful incentives on the other side to encourage landlords and property managers to participate in the widespread practice of leasing. We suggest that common leasing practices are the consequence of many rationales, including the ability of the landlord to solve free-rider problems in maintaining property desirability and informational asymmetries that exist between landlords and tenants.

Junctional sarcoplasmic reticulum motility in adult mouse ventricular myocytes.

Excitation-contraction (EC) coupling is the coordinated process by which an action potential triggers cardiac myocyte contraction. EC coupling is initiated in dyads where the junctional sarcoplasmic reticulum (jSR) is in tight proximity to the sarcolemma of cardiac myocytes. Existing models of EC coupling critically depend on dyad stability to ensure the fidelity and strength of EC coupling, where even small variations in ryanodine receptor channel and voltage-gated calcium channel-α 1.2 subunit separation dramatically alter EC coupling. However, dyadic motility has never been studied. Here, we developed a novel strategy to track specific jSR units in dissociated adult ventricular myocytes using photoactivatable fluorescent proteins. We found that the jSR is not static. Instead, we observed dynamic formation and dissolution of multiple dyadic junctions regulated by the microtubule-associated molecular motors kinesin-1 and dynein. Our data support a model where reproducibility of EC coupling results from the activation of a temporally averaged number of SR Ca2+ release units forming and dissolving SR-sarcolemmal junctions. These findings challenge the long-held view that the jSR is an immobile structure and provide insights into the mechanisms underlying its motility

Case Report: A young man with progressive weakness, double vision and breathlessness

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