1,061 research outputs found
Specialized motor-driven dusp1 expression in the song systems of multiple lineages of vocal learning birds.
Mechanisms for the evolution of convergent behavioral traits are largely unknown. Vocal learning is one such trait that evolved multiple times and is necessary in humans for the acquisition of spoken language. Among birds, vocal learning is evolved in songbirds, parrots, and hummingbirds. Each time similar forebrain song nuclei specialized for vocal learning and production have evolved. This finding led to the hypothesis that the behavioral and neuroanatomical convergences for vocal learning could be associated with molecular convergence. We previously found that the neural activity-induced gene dual specificity phosphatase 1 (dusp1) was up-regulated in non-vocal circuits, specifically in sensory-input neurons of the thalamus and telencephalon; however, dusp1 was not up-regulated in higher order sensory neurons or motor circuits. Here we show that song motor nuclei are an exception to this pattern. The song nuclei of species from all known vocal learning avian lineages showed motor-driven up-regulation of dusp1 expression induced by singing. There was no detectable motor-driven dusp1 expression throughout the rest of the forebrain after non-vocal motor performance. This pattern contrasts with expression of the commonly studied activity-induced gene egr1, which shows motor-driven expression in song nuclei induced by singing, but also motor-driven expression in adjacent brain regions after non-vocal motor behaviors. In the vocal non-learning avian species, we found no detectable vocalizing-driven dusp1 expression in the forebrain. These findings suggest that independent evolutions of neural systems for vocal learning were accompanied by selection for specialized motor-driven expression of the dusp1 gene in those circuits. This specialized expression of dusp1 could potentially lead to differential regulation of dusp1-modulated molecular cascades in vocal learning circuits
Critical dynamics of phase transition driven by dichotomous Markov noise
An Ising spin system under the critical temperature driven by a dichotomous
Markov noise (magnetic field) with a finite correlation time is studied both
numerically and theoretically. The order parameter exhibits a transition
between two kinds of qualitatively different dynamics, symmetry-restoring and
symmetry-breaking motions, as the noise intensity is changed.
There exist regions called channels where the order parameter stays for a
long time slightly above its critical noise intensity. Developing a
phenomenological analysis of the dynamics, we investigate the distribution of
the passage time through the channels and the power spectrum of the order
parameter evolution. The results based on the phenomenological analysis turn
out to be in quite good agreement with those of the numerical simulation.Comment: 27 pages, 12 figure
Fluctuating dynamics at the quasiperiodic onset of chaos, Tsallis q-statistics and Mori's q-phase thermodynamics
We analyze the fluctuating dynamics at the golden-mean transition to chaos in
the critical circle map and find that trajectories within the critical
attractor consist of infinite sets of power laws mixed together. We elucidate
this structure assisted by known renormalization group (RG) results. Next we
proceed to weigh the new findings against Tsallis' entropic and Mori's
thermodynamic theoretical schemes and observe behavior to a large extent richer
than previously reported. We find that the sensitivity to initial conditions
has the form of families of intertwined q-exponentials, of which we determine
the q-indexes and the generalized Lyapunov coefficient spectra. Further, the
dynamics within the critical attractor is found to consist of not one but a
collection of Mori's q-phase transitions with a hierarchical structure. The
value of Mori's `thermodynamic field' variable q at each transition corresponds
to the same special value for the entropic index q. We discuss the relationship
between the two formalisms and indicate the usefulness of the methods involved
to determine the universal trajectory scaling function and/or the ocurrence and
characterization of dynamical phase transitions.Comment: Resubmitted to Physical Review E. The title has been changed slightly
and the abstract has been extended. There is a new subsection following the
conclusions that explains the role and usefulness of the q-statistics in the
problem studied. Other minor changes througout the tex
Influence of severe plastic deformation on the precipitation hardening of a FeSiTi steel
The combined strengthening effects of grain refinement and high precipitated
volume fraction (~6at.%) on the mechanical properties of FeSiTi alloy subjected
to SPD processing prior to aging treatment were investigated by atom probe
tomography and scanning transmission electron microscopy. It was shown that the
refinement of the microstructure affects the precipitation kinetics and the
spatial distribution of the secondary hardening intermetallic phase, which was
observed to nucleate heterogeneously on dislocations and sub-grain boundaries.
It was revealed that alloys successively subjected to these two strengthening
mechanisms exhibit a lower increase in mechanical strength than a simple
estimation based on the summation of the two individual strengthening
mechanisms
A recent appreciation of the singular dynamics at the edge of chaos
We study the dynamics of iterates at the transition to chaos in the logistic
map and find that it is constituted by an infinite family of Mori's -phase
transitions. Starting from Feigenbaum's function for the diameters
ratio, we determine the atypical weak sensitivity to initial conditions associated to each -phase transition and find that it obeys the form
suggested by the Tsallis statistics. The specific values of the variable at
which the -phase transitions take place are identified with the specific
values for the Tsallis entropic index in the corresponding . We
describe too the bifurcation gap induced by external noise and show that its
properties exhibit the characteristic elements of glassy dynamics close to
vitrification in supercooled liquids, e.g. two-step relaxation, aging and a
relationship between relaxation time and entropy.Comment: Proceedings of: Verhulst 200 on Chaos, Brussels 16-18 September 2004,
Springer Verlag, in pres
Nonconcave entropies in multifractals and the thermodynamic formalism
We discuss a subtlety involved in the calculation of multifractal spectra
when these are expressed as Legendre-Fenchel transforms of functions analogous
to free energy functions. We show that the Legendre-Fenchel transform of a free
energy function yields the correct multifractal spectrum only when the latter
is wholly concave. If the spectrum has no definite concavity, then the
transform yields the concave envelope of the spectrum rather than the spectrum
itself. Some mathematical and physical examples are given to illustrate this
result, which lies at the root of the nonequivalence of the microcanonical and
canonical ensembles. On a more positive note, we also show that the
impossibility of expressing nonconcave multifractal spectra through
Legendre-Fenchel transforms of free energies can be circumvented with the help
of a generalized free energy function, which relates to a recently introduced
generalized canonical ensemble. Analogies with the calculation of rate
functions in large deviation theory are finally discussed.Comment: 9 pages, revtex4, 3 figures. Changes in v2: sections added on
applications plus many new references; contains an addendum not contained in
published versio
Effects of acute fatigue on the volitional and magnetically-evoked electromechanical delay of the knee flexors in males and females
Neuromuscular performance capabilities, including those measured by evoked responses, may be adversely affected by fatigue; however, the capability of the neuromuscular system to initiate muscle force rapidly under these circumstances is yet to be established. Sex-differences in the acute responses of neuromuscular performance to exercise stress may be linked to evidence that females are much more vulnerable to ACL injury than males. Optimal functioning of the knee flexors is paramount to the dynamic stabilisation of the knee joint, therefore the aim of this investigation was to examine the effects of acute maximal intensity fatiguing exercise on the voluntary and magnetically-evoked electromechanical delay in the knee flexors of males and females. Knee flexor volitional and magnetically-evoked neuromuscular performance was assessed in seven male and nine females prior to and immediately after: (i) an intervention condition comprising a fatigue trial of 30-seconds maximal static exercise of the knee flexors, (ii) a control condition consisting of no exercise. The results showed that the fatigue intervention was associated with a substantive reduction in volitional peak force (PFV) that was greater in males compared to females (15.0%, 10.2%, respectively, p < 0.01) and impairment to volitional electromechanical delay (EMDV) in females exclusively (19.3%, p < 0.05). Similar improvements in magnetically-evoked electromechanical delay in males and females following fatigue (21%, p < 0.001), however, may suggest a vital facilitatory mechanism to overcome the effects of impaired voluntary capabilities, and a faster neuromuscular response that can be deployed during critical times to protect the joint system
Calibration and applications of the dolomite clumped isotope thermometer to high temperatures
Carbonate clumped isotope paleothermometry is based on the temperature-dependent formation of ^(13)C^(18)O^(16)O_2 ^(2-) ion
groups within solid carbonate minerals. This thermometer has now been calibrated for various synthetic and natural biogenic
and abiogenic minerals (calcite, aragonite and carbonateapatites [e.g., 1, 2]) at temperatures below ~ 50°C. Here we
extend the use of the carbonate clumped isotope thermometer to shallow crustal environments by determining the Δ_(47) values
of CO_2 extracted from natural and synthetic dolomites grown at know temperatures from 25 to 350ºC. The experimental
temperature dependance is not linear in the Δ_(47) vs T^(-2) plot and resembles the predicted theoretical temperature dependence,
both in shape and absolute value [3]. These data for synthetic dolomites overlap the previous calibrations for inorganic
calcite and some forms of biogenic carbonates between 25 and 50˚C, and are consistent with a single trend that also intersects
data for synthetic calcite equilibrated at 1200˚C. These observations suggest that a single temperature dependant
relationship reasonably approximates the calibration for both phases. Data from a variety of slowly-cooled (i.e., over
geological timescales) natural marbles and rapid (i.e., laboratory timescales) heating experiments provide insights
into the kinetics of solid-state ^(13)C-^(18)O bond reordering in carbonates and its closure temperature. More generally, our
new calibration and constraints on high-temperature kinetics have implications for the application of this technique to burial
and metamorphic processes. These issues will be illustrated through estimates of the thermal history and oxygen isotopic
compositions and abundances of pore fluids for several suites of late Neoproterozoic carbonates [e.g., 4]
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