Reflectance and photoluminescence characterization of CdS and CdSe heteroepitaxial films deposited by laser ablation technique

Optical properties of CdSe and CdS films, deposited on sapphire substrate by means of pulsed laser ablation technique, have been investigated in order to study the effect of such a transparent substrate on the photoluminescence efficiency of the deposited epilayers. CdSe and CdS films present intrinsic (excitonic) emission at low temperature, differently from the same films deposited on quartz. The temperature dependence of the excitonic energy has been analyzed taking into account the contribution of both the thermal dilatation and electron-phonon interaction

Order-of-magnitude speedup for steady states and traveling waves via Stokes preconditioning in Channelflow and Openpipeflow

Steady states and traveling waves play a fundamental role in understanding hydrodynamic problems. Even when unstable, these states provide the bifurcation-theoretic explanation for the origin of the observed states. In turbulent wall-bounded shear flows, these states have been hypothesized to be saddle points organizing the trajectories within a chaotic attractor. These states must be computed with Newton's method or one of its generalizations, since time-integration cannot converge to unstable equilibria. The bottleneck is the solution of linear systems involving the Jacobian of the Navier-Stokes or Boussinesq equations. Originally such computations were carried out by constructing and directly inverting the Jacobian, but this is unfeasible for the matrices arising from three-dimensional hydrodynamic configurations in large domains. A popular method is to seek states that are invariant under numerical time integration. Surprisingly, equilibria may also be found by seeking flows that are invariant under a single very large Backwards-Euler Forwards-Euler timestep. We show that this method, called Stokes preconditioning, is 10 to 50 times faster at computing steady states in plane Couette flow and traveling waves in pipe flow. Moreover, it can be carried out using Channelflow (by Gibson) and Openpipeflow (by Willis) without any changes to these popular spectral codes. We explain the convergence rate as a function of the integration period and Reynolds number by computing the full spectra of the operators corresponding to the Jacobians of both methods.Comment: in Computational Modelling of Bifurcations and Instabilities in Fluid Dynamics, ed. Alexander Gelfgat (Springer, 2018

Nucleosynthesis Calculations for the Ejecta of Neutron Star Coalescences

We present the results of fully dynamical r-process network calculations for the ejecta of neutron star mergers (NSMs). The late stages of the inspiral and the final violent coalescence of a neutron star binary have been calculated in detail using a 3D hydrodynamics code (Newtonian gravity plus backreaction forces emerging from the emission of gravitational waves) and a realistic nuclear equation of state. The found trajectories for the ejecta serve as input for dynamical r-process calculations where all relevant nuclear reactions (including beta-decays depositing nuclear energy in the expanding material) are followed. We find that all the ejected material undergoes r-process. For an initial Ye close to 0.1 the abundance distributions reproduce very accurately the solar r-process pattern for nuclei with A above 130. For lighter nuclei strongly underabundant (as compared to solar) distributions are encountered. We show that this behaviour is consistent with the latest observations of very old, metal-poor stars, despite simplistic arguments that have recently been raised against the possibility of NSM as possible sources of Galactic r-process material.Comment: 5 pages, 2 figures, proceedings of Nuclei in the Cosmos 2000, to be published in Nucl. Phys. A; minor correctio

Real-Time Online Monitoring of the Ion Range by Means of Prompt Secondary Radiations

International audiencePrompt secondary radiations such as gamma rays and protons can be used for ion-range monitoring during ion therapy either on an energy-slice basis or on a pencil-beam basis. We present a review of the ongoing activities in terms of detector developments, imaging, experimental and theoretical physics issues concerning the correlation between the physical dose and hadronic processe

Managing design and designers for strategic renewal

In this article, we propose a framework for understanding how design and designers may contribute to strategic renewal in producers of traditional and hi-tech consumer durables. Building on a study of outstanding innovators in product design, we describe design-driven renewal as a four-phase process stimulated and supported by design, combining continuous product innovation with the periodic revision of the strategic course of the company. For each phase, we discuss the specific role of managers and the most common pitfalls that arise from poor management of the process