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21	Dynamics of Cilia and Flagella Hilfinger, Andreas 07 February 2006 (has links) Cilia and flagella are hair-like appendages of eukaryotic cells. They are actively bending structures that exhibit regular beat patterns and thereby play an important role in many different circumstances where motion on a cellular level is required. Most dramatic is the effect of nodal cilia whose vortical motion leads to a fluid flow that is directly responsible for establishing the left-right axis during embryological development in many vertebrate species, but examples range from the propulsion of single cells, such as the swimming of sperm, to the transport of mucus along epithelial cells, e.g. in the ciliated trachea. Cilia and flagella contain an evolutionary highly conserved structure called the axoneme, whose characteristic architecture is based on a cylindrical arrangement of elastic filaments (microtubules). In the presence of a chemical fuel (ATP), molecular motors (dynein) exert shear forces between neighbouring microtubules, leading to a bending of the axoneme through structural constraints. We address the following two questions: How can these organelles generate regular oscillatory beat patterns in the absence of a biochemical signal regulating the activity of the force generating elements? And how can the beat patterns be so different for apparently very similar structures? We present a theoretical description of the axonemal structure as an actively bending elastic cylinder, and show that in such a system bending waves emerge from a non-oscillatory state via a dynamic instability. The corresponding beat patterns are solutions to a set of coupled partial differential equations presented herein. info:eu-repo/classification/ddc/530 ddc:530
22	Strategies of Sexual Reproduction in Aphids / Fortpflanzungsstrategien der Sexuellen Generation von Blattläusen Dagg, Joachim 30 October 2002 (has links) No description available. 570 Biowissenschaften, Biologie Mathematics and Computer Science Strategie Kopulationsdauer Spermienkonkurrenz Spermien-Kooperation Marginal Value Theorem Paarungsverhalten Partner-Bewachung Partnerwahl Konkurrenz Geschlechter-Verhältnis Geschlechter-Verteilung springende Gene Transposons; strategy copula duration sperm competition sperm co-operation marginal value theorem courtship mate guarding mate choice mate competition kin competition sex ratio sex allocation jumping genes transposon ancient asexual scandals paradox of sexual reproduction replicator interactor Uroleucon cirsii Uroleucon cichorii Euceraphis betulae Schizolachnus obscurus Rhopalosiphum padi; 42.21 Evolution 42.66 Ethologie 42.67 Fortpflanzung 42.75 Insecta 42.97 Ökologie: Sonstiges

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Dynamics of Cilia and Flagella

Strategies of Sexual Reproduction in Aphids / Fortpflanzungsstrategien der Sexuellen Generation von Blattläusen