Self propulsion of droplets driven by an active permeating gel

We discuss the flow field and propulsion velocity of active droplets, which are driven by body forces residing on a rigid gel. The latter is modelled as a porous medium which gives rise to permeation forces. In the simplest model, the Brinkman equation, the porous medium is characterised by a single length scale $\ell$ --the square root of the permeability. We compute the flow fields inside and outside of the droplet as well as the energy dissipation as a function of $\ell$. We furthermore show that there are optimal gel fractions, giving rise to maximal linear and rotational velocities. In the limit $\ell\to\infty$, corresponding to a very dilute gel, we recover Stokes flow. The opposite limit, $\ell\to 0$, corresponding to a space filling gel, is singular and not equivalent to Darcy's equation, which cannot account for self-propulsion

Ravitegevuse kvaliteedi hindamine

Eesti Arst 2017; 96(8):451–45

Reetina kolesteroolembol – Hollenhorsti naast. Kahe haigusjuhu kirjeldus

Hollenhorsti naastu kirjeldati esimest korda 1961. aastal ning see on reetina arterite valendikus olev kollakaskuldne kolesteroolembol, mis väga sageli on asümptomaatiline, kuid võib arteri täielikult sulgeda. Viimasel juhul põhjustab see eri raskusastmega nägemishäireid. Kuna tegu on enamasti süsteemsest ringest lähtunud emboliga, on sel puhul oluline uurida ka patsiendi üldist tervislikku seisundit, eelkõige (kaela) veresooni. Artiklis on esitatud kahe haigusjuhu kirjeldus.Eesti Arst 2014; 93(3):165–16

Deformations of an active liquid droplet

A fluid droplet in general deforms, if subject to active driving, such as a finite slip velocity or active tractions on its interface. We show that these deformations and their dynamics can be computed analytically in a perturbation theory in the inverse surface tension using an approach based on vector spherical harmonics. In lowest order, the deformation is of first order, yet it affects the flow fields inside and outside of the droplet in zeroth order. Hence a correct description of the flow has to allow for shape fluctuations, even in the limit of large surface tension

Mis on D-vitamiin?

Viimastel aastatel on hakatud tähelepanu pöörama vitamiinide efektiivsele kogusele organismis. On räägitud D-vitamiini liiga väikesest sisaldusest põhjamaade inimeste organismis ning seda defitsiiti on seostatud mitmete haigustega. Ülevaates on lühidalt tutvustatud D-vitamiini metabolismi ning erinevate uurimuste tulemusi, kus on näidatud D-vitamiini olulisust inimorganismis. Vaatamata suurele huvile ning intensiivsele uurimistööle on endiselt vaieldav D-vitamiini optimaalne seerumisisaldus.