7,946 research outputs found
Transition from rotating waves to modulated rotating waves on the sphere
We study non-resonant and resonant Hopf bifurcation of a rotating wave in
SO(3)-equivariant reaction-diffusion systems on a sphere. We obtained reduced
differential equations on so(3), the characterization of modulated rotating
waves obtained by Hopf bifurcation of a rotating wave, as well as results
regarding the resonant case. Our main tools are the equivariant center manifold
reduction and the theory of Lie groups and Lie algebras, especially for the
group SO(3) of all rigid rotations on a sphere
The large core limit of spiral waves in excitable media: A numerical approach
We modify the freezing method introduced by Beyn & Thuemmler, 2004, for
analyzing rigidly rotating spiral waves in excitable media. The proposed method
is designed to stably determine the rotation frequency and the core radius of
rotating spirals, as well as the approximate shape of spiral waves in unbounded
domains. In particular, we introduce spiral wave boundary conditions based on
geometric approximations of spiral wave solutions by Archimedean spirals and by
involutes of circles. We further propose a simple implementation of boundary
conditions for the case when the inhibitor is non-diffusive, a case which had
previously caused spurious oscillations.
We then utilize the method to numerically analyze the large core limit. The
proposed method allows us to investigate the case close to criticality where
spiral waves acquire infinite core radius and zero rotation frequency, before
they begin to develop into retracting fingers. We confirm the linear scaling
regime of a drift bifurcation for the rotation frequency and the core radius of
spiral wave solutions close to criticality. This regime is unattainable with
conventional numerical methods.Comment: 32 pages, 17 figures, as accepted by SIAM Journal on Applied
Dynamical Systems on 20/03/1
The ROCK inhibitor Fasudil prevents chronic restraint stress-induced depressive-like behaviors and dendritic spine loss in rat hippocampus
IndexaciĂłn: Web of Science; Scopus.Background: Dendritic arbor simplification and dendritic spine loss in the hippocampus, a limbic structure implicated in mood disorders, are assumed to contribute to symptoms of depression. These morphological changes imply modifications in dendritic cytoskeleton. Rho GTPases are regulators of actin dynamics through their effector Rho kinase. We have reported that chronic stress promotes depressive-like behaviors in rats along with dendritic spine loss in apical dendrites of hippocampal pyramidal neurons, changes associated with Rho kinase activation. The present study proposes that the Rho kinase inhibitor Fasudil may prevent the stress-induced behavior and dendritic spine loss. Methods: Adult male Sprague-Dawley rats were injected with saline or Fasudil (i.p., 10 mg/kg) starting 4 days prior to and maintained during the restraint stress procedure (2.5 h/d for 14 days). Nonstressed control animals were injected with saline or Fasudil for 18 days. At 24 hours after treatment, forced swimming test, Golgi-staining, and immuno-western blot were performed. Results: Fasudil prevented stress-induced immobility observed in the forced swimming test. On the other hand, Fasudiltreated control animals showed behavioral patterns similar to those of saline-treated controls. Furthermore, we observed that stress induced an increase in the phosphorylation of MYPT1 in the hippocampus, an exclusive target of Rho kinase. This change was accompanied by dendritic spine loss of apical dendrites of pyramidal hippocampal neurons. Interestingly, increased pMYPT1 levels and spine loss were both prevented by Fasudil administration. Conclusion: Our findings suggest that Fasudil may prevent the development of abnormal behavior and spine loss induced by chronic stress by blocking Rho kinase activity.https://academic.oup.com/ijnp/article/20/4/336/263217
Multielectron Redox Chemistry of Transition Metal Complexes Supported by a NonâInnocent N3P2 Ligand: Synthesis, Characterization, and Catalytic Properties
A new redoxâactive, diarylamidoâbased ligand (LN3P2) capable of Îș5âN,N,N,P,P chelation has been used to prepare a series of complexes with the general formula [MII(LN3P2)]X, where M = Fe (1; X = OTf), Co (2; X = ClO4), or Ni (3; X = ClO4). The diarylamido core of monoanionic LN3P2 is derived from bis(2âaminoâ4âmethylphenyl)amine, which undergoes condensation with two equivalents of 2â(diphenylphosphanyl)benzaldehyde to provide chelating arms with both arylphosphine and imine donors. Xâray structural, magnetic, and spectroscopic studies indicate that the N3P2 coordination environment generally promotes lowâspin configurations. Three quasiâreversible redox couples between +1.0 and â1.5 V (vs. Fc+/Fc) were observed in voltammetric studies of each complex, corresponding to MII/MIII oxidation, LN3P2âbased oxidation, and MII/MI reduction (in order of highest to lowest potential). Spectroscopic and computational analyses of 3ox â generated via chemical oneâelectron oxidation of 3 â revealed that a stable diarylaminyl radical (LN3P2·) is formed upon oxidation. The ability of the CoII complex (2) to function as an electrocatalyst for H2 generation was evaluated in the presence of weak acids. Moderate activity was observed using 4âtertâbutylphenol as the proton source at potentials below â2.0 V. The insights gained here will assist in the future design of pentadentate mixed N/Pâbased chelates for catalytic processes
Bimetallic Cooperativity in Proton Reduction with an AmidoâBridged Cobalt Catalyst
The bimetallic catalyst [CoII2(L1)(bpy)2]ClO4 (1), in which L1 is an [NNâČ2O2] fused ligand, efficiently reduced H+ to H2 in CH3CN in the presence of 100â
equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94â% after 3â
h of bulk electrolysis at â1.6â
V (vs. Ag/AgCl). This observation allowed the proposal that this bimetallic cooperativity is associated with distance, angle, and orbital alignment of the two Co centers, as promoted by the unique CoâNamidoâCo environment offered by L1. Experimental results revealed that the parent [CoIICoII] complex undergoes two successive metalâbased 1â
eâ reductions to generate the catalytically active species [CoICoI], and DFT calculations suggested that addition of a proton to one CoI triggers a cooperative 1â
eâ transfer by each of these CoI centers. This 2â
eâ transfer is an alternative route to generate a more reactive [CoII(CoIIâHâ)] hydride, thus avoiding the CoIIIâHâ required in monometallic species. This [CoII(CoIIâHâ)] species then accepts another H+ to release H2
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Quantification of waves in lidar observations of noctilucent clouds at scales from seconds to minutes
We present small-scale structures and waves observed in noctilucent clouds (NLC) by lidar at an unprecedented temporal resolution of 30 s or less. The measurements were taken with the Rayleigh/Mie/Raman lidar at the ALOMAR observatory in northern Norway (69 N) in the years 2008-2011. We find multiple layer NLC in 7.9% of the time for a brightness threshold of ÎŽ ÎČ 12 Ă 10-10 m-1 sr-1. In comparison to 10 min averaged data, the 30 s dataset shows considerably more structure. For limited periods, quasi-monochromatic waves in NLC altitude variations are common, in accord with ground-based NLC imagery. For the combined dataset, on the other hand, we do not find preferred periods but rather significant periods at all timescales observed (1 min to 1 h). Typical wave amplitudes in the layer vertical displacements are 0.2 km with maximum amplitudes up to 2.3 km. Average spectral slopes of temporal altitude and brightness variations are-2.01 ± 0.25 for centroid altitude,-1.41 ± 0.24 for peak brightness and-1.73 ± 0.25 for integrated brightness. Evaluating a new single-pulse detection system, we observe altitude variations of 70 s period and spectral slopes down to a scale of 10 s. We evaluate the suitability of NLC parameters as tracers for gravity waves
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