14,540 research outputs found
Effects of antibodies against dynein and tubulin on the stiffness of flagellar axonemes
Antidynein antibodies, previously shown to inhibit flagellar oscillation and active sliding of axonemal microtubules, increase the bending resistance of axonemes measured under relaxing conditions, but not the bending resistance of axonemes measured under rigor conditions. These observations suggest that antidynein antibodies can stabilize rigor cross-bridges between outer-doublet microtubules, by interfering with ATP-induced cross-bridge detachment. Stabilization of a small number of cross-bridge appears to be sufficient to cause substantial inhibition of the frequency of flagellar oscillation. Antitubulin antibodies, previously shown to inhibit flagellar oscillation without inhibiting active sliding of axonemal microtubules, do not increase the static bending resistance of axonemes. However, we observed a viscoelastic effect, corresponding to a large increase in the immediate bending resistance. This immediate bending resistance increase may be sufficient to explain inhibition of flagellar oscillation; but several alternative explanations cannot yet be excluded
Quantum dynamics of non-relativistic particles and isometric embeddings
It is considered, in the framework of constrained systems, the quantum
dynamics of non-relativistic particles moving on a d-dimensional Riemannian
manifold M isometrically embedded in . This generalizes recent
investigations where M has been assumed to be a hypersurface of . We
show, contrary to recent claims, that constrained systems theory does not
contribute to the elimination of the ambiguities present in the canonical and
path integral formulations of the problem. These discrepancies with recent
works are discussed.Comment: Revtex, 14 page
Recommended from our members
Evolutionary conservation in genes underlying human psychiatric disorders
Many psychiatric diseases observed in humans have tenuous or absent analogs in other species. Most notable among these are schizophrenia and autism. One hypothesis has posited that these diseases have arisen as a consequence of human brain evolution, for example, that the same processes that led to advances in cognition, language, and executive function also resulted in novel diseases in humans when dysfunctional. Here, the molecular evolution of the protein-coding regions of genes associated with these and other psychiatric disorders are compared among species. Genes associated with psychiatric disorders are drawn from the literature and orthologous sequences are collected from eleven primate species (human, chimpanzee, bonobo, gorilla, orangutan, gibbon, macaque, baboon, marmoset, squirrel monkey, and galago) and 34 non-primate mammalian species. Evolutionary parameters, including dN/dS, are calculated for each gene and compared between disease classes and among species, focusing on humans and primates compared to other mammals, and on large-brained taxa (cetaceans, rhinoceros, walrus, bear, and elephant) compared to their small-brained sister species. Evidence of differential selection in humans to the exclusion of non-human primates was absent, however elevated dN/dS was detected in catarrhines as a whole, as well as in cetaceans, possibly as part of a more general trend. Although this may suggest that protein changes associated with schizophrenia and autism are not a cost of the higher brain function found in humans, it may also point to insufficiencies in the study of these diseases including incomplete or inaccurate gene association lists and/or a greater role of regulatory changes or copy number variation. Through this work a better understanding of the molecular evolution of the human brain, the pathophysiology of disease, and the genetic basis of human psychiatric disease is gained
Stationary Rotating Strings as Relativistic Particle Mechanics
Stationary rotating strings can be viewed as geodesic motions in appropriate
metrics on a two-dimensional space. We obtain all solutions describing
stationary rotating strings in flat spacetime as an application. These rotating
strings have infinite length with various wiggly shapes. Averaged value of the
string energy, the angular momentum and the linear momentum along the string
are discussed.Comment: 20pages, 7 figure
Statistical characterization of the forces on spheres in an upflow of air
The dynamics of a sphere fluidized in a nearly-levitating upflow of air were
previously found to be identical to those of a Brownian particle in a
two-dimensional harmonic trap, consistent with a Langevin equation [Ojha {\it
et al.}, Nature {\bf 427}, 521 (2004)]. The random forcing, the drag, and the
trapping potential represent different aspects of the interaction of the sphere
with the air flow. In this paper we vary the experimental conditions for a
single sphere, and report on how the force terms in the Langevin equation scale
with air flow speed, sphere radius, sphere density, and system size. We also
report on the effective interaction potential between two spheres in an upflow
of air.Comment: 7 pages, experimen
- …