How does flow in a pipe become turbulent?

The transition to turbulence in pipe flow does not follow the scenario familiar from Rayleigh-Benard or Taylor-Couette flow since the laminar profile is stable against infinitesimal perturbations for all Reynolds numbers. Moreover, even when the flow speed is high enough and the perturbation sufficiently strong such that turbulent flow is established, it can return to the laminar state without any indication of the imminent decay. In this parameter range, the lifetimes of perturbations show a sensitive dependence on initial conditions and an exponential distribution. The turbulence seems to be supported by three-dimensional travelling waves which appear transiently in the flow field. The boundary between laminar and turbulent dynamics is formed by the stable manifold of an invariant chaotic state. We will also discuss the relation between observations in short, periodically continued domains, and the dynamics in fully extended puffs.Comment: for the proceedings of statphys 2

Psychosocial Treatment of Children in Foster Care: A Review

A substantial number of children in foster care exhibit psychiatric difficulties. Recent epidemiologi-cal and historical trends in foster care, clinical findings about the adjustment of children in foster care, and adult outcomes are reviewed, followed by a description of current approaches to treatment and extant empirical support. Available interventions for these children can be categorized as either symptom-focused or systemic, with empirical support for specific methods ranging from scant to substantial. Even with treatment, behavioral and emotional problems often persist into adulthood, resulting in poor functional outcomes. We suggest that self-regulation may be an important mediat-ing factor in the appearance of emotional and behavioral disturbance in these children

triangularis

Senecio triangularis Hookerarrow-leaved ragwort;arrow-leaved groundsel;brook ragwortséneçon triangulaireSenecio triangularisApprox. 1 mi. E. of Santiam Ski Lodge, Hwy U.S. 20near a roadside ditch on the edge of a coniferous forestRather commonHerb, 5-8 dm tall, flowers yello

sanguineum

Ribes sanguineum Purshred-flowered currant;pink-flowered currant;winter currant;blood currant;red-flowering currantgadellier sanguinNear Heceta Head, U.S. 101Growing in a loamy soil in a shrub-grass association on a high headland above the ocean.Ulex, Baccharis, GarryaA shrub, 1-1 1/2 m. tall, flowers red-reddish pin

maritima

Triglochin maritima Linnaeusseaside arrowgrass;shore arrowgrass;common bog arrowgrass;arrowgrasstroscart maritimemaritimaSouth of Harney Lake, Malheur National Wildlife Refuge.at edge of hot spring, wet alkali soil4200 feetDistichlis, ScirpusScatteredErect, in clumps, 2-5 dm tall; fruit brow