962 research outputs found
Finite reduction and Morse index estimates for mechanical systems
A simple version of exact finite dimensional reduction for the variational
setting of mechanical systems is presented. It is worked out by means of a
thorough global version of the implicit function theorem for monotone
operators. Moreover, the Hessian of the reduced function preserves all the
relevant information of the original one, by Schur's complement, which
spontaneously appears in this context. Finally, the results are
straightforwardly extended to the case of a Dirichlet problem on a bounded
domain.Comment: 13 pages; v2: minor changes, to appear in Nonlinear Differential
Equations and Application
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η3-Allyl carbonyl complexes of group 6 metals: structural aspects, isomerism, dynamic behaviour and reactivity
Transition metal complexes with π-allylic ligands remain an attractive topic in organometallic chemistry, given the numerousreports of a wide variety of synthetic routes, dynamic behaviour and reactivity, structural (including isomerism),spectroscopic and redox properties, and applications in organic synthesis and catalysis. Surprisingly, despite the considerableinterest in the rich and varied chemistry of this family of organometallic compounds, there is no recent review.
This review is focused on π-allylic representatives of low-cost Group-6 metals bearing one or more carbonyl ligand, the coordination sphere being complemented with η5-cyclopentadienyl (Section 2), chelating ligands, including redox-active α-diimines and various complementary diphosphines (Section 3), and novel anionic amidinate or pyrazolate ligands (Section 4). In Section 1, particular attention is paid to rearrangements of the π-allylic ligand, namely exo and endo isomerism, interconversion mechanisms, fluxionality, and agostic interactions. In addition, the application of multinuclear NMR spectroscopy to the elucidation of such isomerism, and the effect of the metal-centre oxidation state on the bonding, dynamic behaviour and reactivity of the π-allylic ligand are described. The detailed mechanistic description of the synthetic routes and dynamic behaviour of selected representatives of α-diimine complexes in Section 2 is followed by a description of the [M(CO)2(η3-allyl-H,R)(α-diimine)]0/+ fragment as a convenient scaffold for diverse monodentate ligands participating in a range of substitution, insertion, intramolecular migration and C–C coupling reactions – frequently involving also the π-allylic ligand, such as allylic alkylation. Special attention is devoted to selected examples of redox and acid-base reactivity of the α-diimine complexes with emphasis on prospects in electrocatalysis. The amidinate (and
related pyrazolate) ligands treated in Section 4 may directly replace the π-allylic ligand in some cyclopentadienyl complexes (Section 2) or the α-diimine ligand in some dicarbonyl π-allylic complexes (Section 3). The brief description of their synthetic routes is complemented by intriguing examples of fluxionality and characteristic reactivity encountered for these unusual four-electron donor ligands
Numerical Simulations of Dynamos Generated in Spherical Couette Flows
We numerically investigate the efficiency of a spherical Couette flow at
generating a self-sustained magnetic field. No dynamo action occurs for
axisymmetric flow while we always found a dynamo when non-axisymmetric
hydrodynamical instabilities are excited. Without rotation of the outer sphere,
typical critical magnetic Reynolds numbers are of the order of a few
thousands. They increase as the mechanical forcing imposed by the inner core on
the flow increases (Reynolds number ). Namely, no dynamo is found if the
magnetic Prandtl number is less than a critical value .
Oscillating quadrupolar dynamos are present in the vicinity of the dynamo
onset. Saturated magnetic fields obtained in supercritical regimes (either
or ) correspond to the equipartition between magnetic and
kinetic energies. A global rotation of the system (Ekman numbers ) yields to a slight decrease (factor 2) of the critical magnetic
Prandtl number, but we find a peculiar regime where dynamo action may be
obtained for relatively low magnetic Reynolds numbers (). In this
dynamical regime (Rossby number , spheres in opposite direction) at
a moderate Ekman number (), a enhanced shear layer around the inner
core might explain the decrease of the dynamo threshold. For lower
() this internal shear layer becomes unstable, leading to small
scales fluctuations, and the favorable dynamo regime is lost. We also model the
effect of ferromagnetic boundary conditions. Their presence have only a small
impact on the dynamo onset but clearly enhance the saturated magnetic field in
the ferromagnetic parts. Implications for experimental studies are discussed
Shortening of the Short Refractory Periods in Short QT Syndrome.
BACKGROUND: Diagnosis of short QT syndrome (SQTS) remains difficult in case of borderline QT values as often found in normal populations. Whether some shortening of refractory periods (RP) may help in differentiating SQTS from normal subjects is unknown. METHODS AND RESULTS: Atrial and right ventricular RP at the apex and right ventricular outflow tract as determined during standard electrophysiological study were compared between 16 SQTS patients (QTc 324±24 ms) and 15 controls with similar clinical characteristics (QTc 417±32 ms). Atrial RP were significantly shorter in SQTS compared with controls at 600- and 500-ms basic cycle lengths. Baseline ventricular RP were significantly shorter in SQTS patients than in controls, both at the apex and right ventricular outflow tract and for any cycle length. Differences remained significant for RP of any subsequent extrastimulus at any cycle length and any pacing site. A cut-off value of baseline RP <200 ms at the right ventricular outflow tract either at 600- or 500-ms cycle length had a sensitivity of 86% and a specificity of 100% for the diagnosis of SQTS. CONCLUSIONS: Patients with SQTS have shorter ventricular RP than controls, both at baseline during various cycle lengths and after premature extrastimuli. A cut-off value of 200 ms at the right ventricular outflow tract during 600- and 500-ms basic cycle length may help in detecting true SQTS from normal subjects with borderline QT values
Zonal shear and super-rotation in a magnetized spherical Couette flow experiment
We present measurements performed in a spherical shell filled with liquid
sodium, where a 74 mm-radius inner sphere is rotated while a 210 mm-radius
outer sphere is at rest. The inner sphere holds a dipolar magnetic field and
acts as a magnetic propeller when rotated. In this experimental set-up called
DTS, direct measurements of the velocity are performed by ultrasonic Doppler
velocimetry. Differences in electric potential and the induced magnetic field
are also measured to characterize the magnetohydrodynamic flow. Rotation
frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the
magnetic Reynolds number based on measured sodium velocities and on the shell
radius reaching to about 33. We have investigated the mean axisymmetric part of
the flow, which consists of differential rotation. Strong super-rotation of the
fluid with respect to the rotating inner sphere is directly measured. It is
found that the organization of the mean flow does not change much throughout
the entire range of parameters covered by our experiment. The direct
measurements of zonal velocity give a nice illustration of Ferraro's law of
isorotation in the vicinity of the inner sphere where magnetic forces dominate
inertial ones. The transition from a Ferraro regime in the interior to a
geostrophic regime, where inertial forces predominate, in the outer regions has
been well documented. It takes place where the local Elsasser number is about
1. A quantitative agreement with non-linear numerical simulations is obtained
when keeping the same Elsasser number. The experiments also reveal a region
that violates Ferraro's law just above the inner sphere.Comment: Phys Rev E, in pres
In Vitro Efficacy of Essential Oils from Melaleuca Alternifolia and Rosmarinus Officinalis, Manuka Honey-based Gel, and Propolis as Antibacterial Agents Against Canine Staphylococcus Pseudintermedius Strains
Abstract: Essential oils (EOs) and honeybee products (e.g., honey and propolis) are natural mixtures
of dierent volatile compounds that are frequently used in traditional medicine and for pathogen
eradication. The aim of this study was to evaluate the antibacterial properties of tea tree (Melaleuca
alternifolia) EO (TTEO), Rosmarinus ocinalis EO (ROEO), manuka-based gel, and propolis against
23 strains of Staphylococcus pseudintermedius (SP) isolated from canine pyoderma. Antimicrobial
resistance screening was assessed using a panel of nine antimicrobial agents coupled with a PCR
approach. An aromatogram was done for both EOs, using the disk diusion method. The minimum
inhibitory concentration (MIC) was determined for all the compounds. Among the 23 SP strains,
14 (60.9%) were multidrug-resistant (MDR), 11 strains (47.8%) were methicillin-resistant (MRSP),
and 9 (39.1%) were non-MDR. The mean diameter of the inhibition zone for Melaleuca and Rosmarinus
were 24.5 8.8 mm and 15.2 8.9 mm, respectively, resulting as statistically dierent (p = 0.0006).
MIC values of TTEO and ROEO were similar (7.6 3.2% and 8.9 2.1%, respectively) and no
statistical significances were found. Honeybee products showed lower MIC compared to those of EOs,
0.22 0.1% for Manuka and 0.8 0.5% for propolis. These findings reveal a significant antibacterial
eect for all the tested products
Neural Networks Supporting Phoneme Monitoring Are Modulated by Phonology but Not Lexicality or Iconicity: Evidence From British and Swedish Sign Language
Sign languages are natural languages in the visual domain. Because they lack a written
form, they provide a sharper tool than spoken languages for investigating lexicality effects
which may be confounded by orthographic processing. In a previous study, we showed
that the neural networks supporting phoneme monitoring in deaf British Sign Language
(BSL) users are modulated by phonology but not lexicality or iconicity. In the present
study, we investigated whether this pattern generalizes to deaf Swedish Sign Language
(SSL) users. British and SSLs have a largely overlapping phoneme inventory but are
mutually unintelligible because lexical overlap is small. This is important because it means
that even when signs lexicalized in BSL are unintelligible to users of SSL they are usually
still phonologically acceptable. During fMRI scanning, deaf users of the two different sign
languages monitored signs that were lexicalized in either one or both of those languages
for phonologically contrastive elements. Neural activation patterns relating to different
linguistic levels of processing were similar across SLs; in particular, we found no effect of
lexicality, supporting the notion that apparent lexicality effects on sublexical processing
of speech may be driven by orthographic strategies. As expected, we found an effect of
phonology but not iconicity. Further, there was a difference in neural activation between
the two groups in a motion-processing region of the left occipital cortex, possibly driven
by cultural differences, such as education. Importantly, this difference was not modulated
by the linguistic characteristics of the material, underscoring the robustness of the neural
activation patterns relating to different linguistic levels of processing
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