Swimming eukaryotic microorganisms such as spermatozoa, algae, and ciliates self-propel in viscous fluids using traveling wavelike deformations of slender appendages called flagella. Waves are predominant because Purc...
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Swimming eukaryotic microorganisms such as spermatozoa, algae, and ciliates self-propel in viscous fluids using traveling wavelike deformations of slender appendages called flagella. Waves are predominant because Purcell's scallop theorem precludes time-reversible kinematics for locomotion. Using the calculus of variations on a periodic long-wavelength model of flagellar swimming, we show that the planar flagellar kinematics maximizing the time-averaged propulsive force for a fixed amount of energy dissipated in the surrounding fluid correspond for all times to waves traveling with constant speed, potentially on a curved centerline, with propulsion always in the direction opposite to the wave.
X- linked Hoyeraal - Hreidarsson syndrome ( XL-HHS) is the severe infantile variant of X- linked dyskeratosis congenita ( XL- DC) and both are due to mutations in the DKC1 gene within Xq28. We report a novel missense ...
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X- linked Hoyeraal - Hreidarsson syndrome ( XL-HHS) is the severe infantile variant of X- linked dyskeratosis congenita ( XL- DC) and both are due to mutations in the DKC1 gene within Xq28. We report a novel missense mutation in DKC1 exon 3 ( T113 --> C, Ile38Thr) in a Sardinian infant with XL- HHS in whom the disease was characterized by 'T+B-NK- ' severe combined immunodeficiency and bone marrow failure. He underwent sibling bone marrow transplantation using a conditioning regimen fludarabine, rabbit antithymocyte globulin, low- dose melphalan) selected according to the HHS/ DC phenotype. This was associated with low toxicity, prompt engraftment with adequate immune reconstitution and full donor haemopoiesis.
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