229 research outputs found
A generalization of the van-der-Pol oscillator underlies active signal amplification in Drosophila hearing
The antennal hearing organs of the fruit fly Drosophila melanogaster boost their sensitivity by an active mechanical process that, analogous to the cochlear amplifier of vertebrates, resides in the motility of mechanosensory cells. This process nonlinearly improves the sensitivity of hearing and occasionally gives rise to self-sustained oscillations in the absence of sound. Time series analysis of self-sustained oscillations now unveils that the underlying dynamical system is well described by a generalization of the van-der-Pol oscillator. From the dynamic equations, the underlying amplification dynamics can explicitly be derived. According to the model, oscillations emerge from a combination of negative damping, which reflects active amplification, and a nonlinear restoring force that dictates the amplitude of the oscillations. Hence, active amplification in fly hearing seems to rely on the negative damping mechanism initially proposed for the cochlear amplifier of vertebrate
Gauge-ball spectrum of the four-dimensional pure U(1) gauge theory
We investigate the continuum limit of the gauge-ball spectrum in the
four-dimensional pure U(1) lattice gauge theory. In the confinement phase we
identify various states scaling with the correlation length exponent . The square root of the string tension also scales with this
exponent, which agrees with the non-Gaussian fixed point exponent recently
found in the finite size studies of this theory. Possible scenarios for
constructing a non-Gaussian continuum theory with the observed gauge-ball
spectrum are discussed. The state, however, scales with a Gaussian
value . This suggests the existence of a second, Gaussian
continuum limit in the confinement phase and also the presence of a light or
possibly massless scalar in the non-Gaussian continuum theory. In the Coulomb
phase we find evidence for a few gauge-balls, being resonances in multi-photon
channels; they seem to approach the continuum limit with as yet unknown
critical exponents. The maximal value of the renormalized coupling in this
phase is determined and its universality confirmed.Comment: 46 pages, 12 figure
A lattice study of 3D compact QED at finite temperature
We study the deconfinement phase transition and monopole properties in the
finite temperature 3D compact Abelian gauge model on the lattice. We predict
the critical coupling as function of the lattice size in a simplified model to
describe monopole binding. We demonstrate numerically that the monopoles are
sensitive to the transition. In the deconfinement phase the monopoles appear in
the form of a dilute gas of magnetic dipoles. In the confinement phase both
monopole density and string tension differ from semiclassical estimates if
monopole binding is neglected. However, the analysis of the monopole clusters
shows that the relation between the string tension and the density of monopoles
in charged clusters is in reasonable agreement with those predictions. We study
the cluster structure of the vacuum in both phases of the model.Comment: 18 pages, 14 EPS figures, LaTeX uses epsfig.st
A doublecortin containing microtubule-associated protein is implicated in mechanotransduction in Drosophila sensory cilia
Mechanoreceptors are sensory cells that transduce mechanical stimuli into electrical signals and mediate the perception of sound, touch and acceleration. Ciliated mechanoreceptors possess an elaborate microtubule cytoskeleton that facilitates the coupling of external forces to the transduction apparatus. In a screen for genes preferentially expressed in Drosophila campaniform mechanoreceptors, we identified DCX-EMAP, a unique member of the EMAP family (echinoderm–microtubule-associated proteins) that contains two doublecortin domains. DCX-EMAP localizes to the tubular body in campaniform receptors and to the ciliary dilation in chordotonal mechanoreceptors in Johnston's organ, the fly's auditory organ. Adult flies carrying a piggyBac insertion in the DCX-EMAP gene are uncoordinated and deaf and display loss of mechanosensory transduction and amplification. Electron microscopy of mutant sensilla reveals loss of electron-dense materials within the microtubule cytoskeleton in the tubular body and ciliary dilation. Our results establish a catalogue of candidate genes for Drosophila mechanosensation and show that one candidate, DCX-EMAP, is likely to be required for mechanosensory transduction and amplification
Direct gating and mechanical integrity of Drosophila auditory transducers require TRPN1
The elusive transduction channels for hearing are directly gated mechanically by the pull of gating springs. We found that the transient receptor potential (TRP) channel TRPN1 (NOMPC) is essential for this direct gating of Drosophila auditory transduction channels and that the channel-spring complex was disrupted if TRPN1 was lost. Our results identify TRPN1 as a mechanical constituent of the fly's auditory transduction complex that may act as the channel and/or gating spring
Series Expansions for three-dimensional QED
Strong-coupling series expansions are calculated for the Hamiltonian version
of compact lattice electrodynamics in (2+1) dimensions, with 4-component
fermions. Series are calculated for the ground-state energy per site, the
chiral condensate, and the masses of `glueball' and positronium states.
Comparisons are made with results obtained by other techniques.Comment: 13 figure
Monopoles, confinement and deconfinement of (2+1)D compact lattice QED in external fields
The compact Abelian model in three space--time dimensions is studied in the
presence of external electromagnetic fields at finite temperatures. We show
that the deconfinement phase transition is independent on the strength of the
external fields. This result is in agreement with our observation that the
external fields create small--size magnetic dipoles from the vacuum which do
not influence the confining properties of the model. Contrary to the
deconfinement phase, the internal field in the direction of the applied
external field is attenuated in the confinement phase, this screening becomes
stronger with decreasing temperature.Comment: 22 pages, 24 EPS figures, LaTeX uses epsfig.st
Path Integral Monte Carlo Approach to the U(1) Lattice Gauge Theory in (2+1) Dimensions
Path Integral Monte Carlo simulations have been performed for U(1) lattice
gauge theory in (2+1) dimensions on anisotropic lattices. We extractthe static
quark potential, the string tension and the low-lying "glueball" spectrum.The
Euclidean string tension and mass gap decrease exponentially at weakcoupling in
excellent agreement with the predictions of Polyakov and G{\" o}pfert and Mack,
but their magnitudes are five times bigger than predicted. Extrapolations are
made to the extreme anisotropic or Hamiltonian limit, and comparisons are made
with previous estimates obtained in the Hamiltonian formulation.Comment: 12 pages, 16 figure
Hamiltonian Study of Improved Lattice Gauge Theory in Three Dimensions
A comprehensive analysis of the Symanzik improved anisotropic
three-dimensional U(1) lattice gauge theory in the Hamiltonian limit is made.
Monte Carlo techniques are used to obtain numerical results for the static
potential, ratio of the renormalized and bare anisotropies, the string tension,
lowest glueball masses and the mass ratio. Evidence that rotational symmetry is
established more accurately for the Symanzik improved anisotropic action is
presented. The discretization errors in the static potential and the
renormalization of the bare anisotropy are found to be only a few percent
compared to errors of about 20-25% for the unimproved gauge action. Evidence of
scaling in the string tension, antisymmetric mass gap and the mass ratio is
observed in the weak coupling region and the behaviour is tested against
analytic and numerical results obtained in various other Hamiltonian studies of
the theory. We find that more accurate determination of the scaling
coefficients of the string tension and the antisymmetric mass gap has been
achieved, and the agreement with various other Hamiltonian studies of the
theory is excellent. The improved action is found to give faster convergence to
the continuum limit. Very clear evidence is obtained that in the continuum
limit the glueball ratio approaches exactly 2, as expected in a
theory of free, massive bosons.Comment: 13 pages, 15 figures, submitted to Phys. Rev.
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