Low wavenumber Raman scattering of cobalt nanoparticles self‐organized in 3D superlattices far from surface plasmon resonance

We report the first observation of low wavenumber Raman scattering from cobalt nanoparticles under 514.5nm laser excitation. These 7.4nm diameter particles were self‐organized in 3D superlattices, but we assign the Raman signature to vibrations of the individual nanoparticles, according to Lamb's elastic sphere model. We estimate the relative Raman intensity to be around 500 times lower than it would be for silver nanoparticles, but our results demonstrate that surface plasmon–phonon resonance coupling is not mandatory to observe Lamb's modes in metal nanoparticles. Copyright © 2015 John Wiley & Sons, Ltd.     

Third-order laser-field-expansion analysis of the Lorenz–Haken equations

This paper revisits a few aspects of laser-dynamics with a strong-harmonic expansion analysis from which new analytical information, within the intrinsic pulsing regime that characterizes the non-linearly coupled differential Lorenz–Haken equations, is extracted. The analysis is expected to provide clearer insights to the physics involved in the laser-dynamics issue. Carried out to third-order in electric field amplitude, the procedure allows for the derivation of a closed form expression which describes the permanent-oscillation frequency of the unstable periodic state. Comparison between the frequency values evaluated from the literal formula and those obtained through direct numerical simulations shows a realistic fit inside the control parameters space that displays symmetric period-one pulsing solutions.     

Parameter identification of advanced plastic strain rate potentials and impact on plastic anisotropy prediction

In the work presented in this paper, several strain rate potentials are examined in order to analyze their ability to model the initial stress and strain anisotropy of several orthotropic sheet materials. Classical quadratic and more advanced non-quadratic strain rate potentials are investigated in the case of FCC and BCC polycrystals. Different identifications procedures are proposed, which are taking into account the crystallographic texture and/or a set of mechanical test data in the determination of the material parameters.     

Application of strain rate potentials with multiple linear transformations to the description of polycrystal plasticity

This paper reviews a class of anisotropic plastic strain-rate potentials, based on linear transformations of the plastic strain-rate tensor. A new formulation is proposed, which includes former models as particular cases and allows for an arbitrary number of linear transformations, involving an increasing number of anisotropy parameters. The formulation is convex and fully three-dimensional, thus being suitable for computer implementation in finite element codes. The parameter identification procedure uses a micromechanical model to generate evenly distributed reference points in the full space of possible loading modes. Material parameters are determined for several anisotropic, fcc and bcc sheet metals, and the gain in accuracy of the new models is demonstrated. For the considered materials, increasing the number of linear transformations leads to a systematic improvement of the accuracy, up to a number of five linear transformations. The proposed model fits very closely the predictions of the micromechanical model in the whole space of plastic strain-rate directions. The r-values, which are not directly used in the identification procedure, served for the validation of the models and to demonstrate their improved accuracy.     

Spectral-line asymmetry in double-output-cavity lasers

The aim of this work is to show that the output from a double-output laser cavity exhibits distinctive features, manifesting themselves through typical asymmetry in the corresponding spectral-line shapes. Such asymmetry in an inhomogeneously broadened gas laser usually appears with a clear, but unpredictable shift of the maximum intensity level either towards the high or low frequency sides with respect to line centre. In the case of a double-output laser, the spectral profiles show opposite shifts. This means that when the maximum intensity of one output moves towards the high frequency side of the profile, the maximum intensity of the other moves towards the low frequency side. This gives rise to a frequency shift with respect to the Lamb-dip for a classical laser. On the theoretical side, we apply the standard disturbed Gaussian beam model to provide a quantification of the frequency shifts obtained at both sides of the system.     

Optimal Design and Reliability Evaluation of Multi-State Series-Parallel Power Systems

A new approach is introduced for calculating the electrical power system reliability indices. Such as multi-state stationary availability, the expected multi-state capacity, the expected unsupplied demand, the loss of load probability and total failed system probability. A multi-state system consisting of elements combined into a series-parallel structure is considered. When the system consists of elements with different reliability and performance (productivity or capacity) characteristics, its availability, defined as the ability to meet a demand, strongly depends on the selection of components and the system structure design. In this paper we present an ant colony method which treats the more sophisticated and realistic models in which components and systems may assume many states ranging from perfect working to complete failure. The objective is to calculate the different reliability indices by using the new modern technique of Ushakov (UMGF technique). A computer program has been developed to implement the UMGF technique. An illustrative example is presented.