55,870 research outputs found
Simulation of EPR and Time Resolved EPR lineshapes in partially ordered phases
No full textSimulation of magnetic resonance spectra of probes in partially ordered glasses requires in principle a numerical integration on the full set of three Euler angles Ohm=(alpha beta gamma) from a laboratory fixed to a molecule fixed reference frame. It is shown that it is possible to manage efficiently this problem by using the algebraic properties of the Wigner matrix elements. This analysis is applied to time resolved EPR (TREPR) spectra of a series of bis-adducts of C-60 in the ordered glass of a nematic liquid crystal solvent. A paramagnetic triplet state is created by light excitation and TREPR spectra are obtained with the external magnetic field set parallel or perpendicular to the director n of the mesophase. The preferred orientation in the mesophase of the triplet state zero field tensor is determined
Preferential Orientation of Fulleropyrrolidine Bisadducts in E7 Liquid Crystal: a Time Resolved EPR Study
No full textIntermolecular electron transfer in merocyanine aggregates studied by optical and transient EPR methods
No full textExcited states of two merocyanine chromophores have been studied by means of optical and magnetic resonance techniques. The dye molecules were dissolved in solvents of different polarity and cast in thin films on quartz surfaces. The optical absorption and emission spectra of both molecules indicate a little charge-transfer character in the S-0-S-1 transition. The cast films contain monomers and H type aggregates. EPR spectra have been obtained by time resolved techniques at low temperature after illumination of the sample. EPR spectra of isolated molecules in frozen solutions are typical of triplet excited states generated by spin-orbit promoted intersystem crossing. Two signals are observed in EPR spectra of the cast films, with a narrow line in emission superimposed on a very weak molecular triplet lineshape. The polarization and lineshape analysis suggest that a radical ion pair with a lifetime of the order of microseconds is formed by intermolecular charge migration following the photoinduced electron-transfer reaction between the donor and acceptor moieties of the chromophore
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
Limb Salvage and Survival in Chronic Limb-Threatening Ischemia: The Need for a Fast-Track Team-Based Approach
No full textChronic limb-threatening ischemia (CLTI) represents the end-stage form of peripheral arterial disease (PAD) and is associated with a very poor prognosis and high risk of limb loss and mortality. It can be considered very similar to a terminal cancer disease, reflecting a large impact on quality of life and healthcare costs. The aim of this study is to offer an overview of the relationship between CLTI, limb salvage, and mortality, with a focus on the need of a fast-track team-based management that is a driver to achieve better survival results. This review can be useful to improve management of this growing impact disease, and to promote the standardisation of care and communication between specialist and non-specialist healthcare professionals
Energy dissipation and flux laws for unsteady turbulence
No full textDirect Numerical Simulations of spatially periodic unsteady turbulence show that the high Reynolds number scalings of the instantaneous energy dissipation rate and interscale energy flux at intermediate wavenumbers are qualitatively different from the well-known cornerstone scalings of equilibrium turbulence where and are time-dependent rms velocity and integral length-scales. Instead, they both scale as where and are length and velocity scales characterizing initial/overall unsteady turbulence conditions
Preferential orientation of fulleropyrrolidine bisadducts in E7 liquid crystal: A time-resolved electron paramagnetic resonance study
No full textThe effect of the orientating potential in the E7 liquid crystal on a series of fulleropyrrolidine bisadducts has been examined. Photoexcited triplet states, populated by spin-orbit promoted intersystem crossing, have been used as spin probes to determine the preferential orientations of the guest molecules in the anisotropic medium. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been applied and spectra with the external magnetic field set parallel or perpendicular to the director n of the mesophase have been measured. Spectrum analysis has enabled us to determine the preferred orientation of n with respect to the principal axis frame of the dipolar interaction and to calculate the order parameters by using the orientational distribution function obtained by spectral simulation. It has been found that the macroscopic order degree induced by the mesophase on the guest molecules varies from one bisadduct to another. Bisadducts with D-2h symmetry have exhibited triplet spectra due to dimers besides those of monomers, The measured zero field splitting parameters and magnetic level populations of the monomer and dimer triplet states have been analyzed, and a structure of the dimer has been postulated
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