Optical damage resistance of Mg:Ce:Fe:LiNbO3 crystals

Mg:Ce:Fe:LiNbO₃ crystals were prepared with fixed concentrations of Fe₂O₃ and CeO₂, and differing concentrations of MgO by the Czochralski technique. Their infrared transmission spectra were measured in order to investigate their defect structures and their optical damage resistance was characterized by the photoinduced birefringence change and transmission facula distortion method. The optical damage resistance of Mg:Ce:Fe:LiNbO₃ crystals increases remarkably when the concentration of MgO exceeds a threshold concentration. The dependence of the optical damage resistance on the defect structure of Mg:Ce:Fe:LiNbO₃ crystals is discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Three‐dimensional numerical modelling of free surface flows with non‐hydrostatic pressure

A three‐dimensional numerical model is developed for incompressible free surface flows. The model is based on the unsteady Reynolds‐averaged Navier–Stokes equations with a non‐hydrostatic pressure distribution being incorporated in the model. The governing equations are solved in the conventional sigma co‐ordinate system, with a semi‐implicit time discretization. A fractional step method is used to enable the pressure to be decomposed into its hydrostatic and hydrodynamic components. At every time step one five‐diagonal system of equations is solved to compute the water elevations and then the hydrodynamic pressure is determined from a pressure Poisson equation. The model is applied to three examples to simulate unsteady free surface flows where non‐hydrostatic pressures have a considerable effect on the velocity field. Emphasis is focused on applying the model to wave problems. Two of the examples are about modelling small amplitude waves where the hydrostatic approximation and long wave theory are not valid. The other example is the wind‐induced circulation in a closed basin. The numerical solutions are compared with the available analytical solutions for small amplitude wave theory and very good agreement is obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

Study of the performance of a bloom-forming cyanobacterium (Microcystis aeruginosa) on the biosorption of uranium

Journal of Radioanalytical and Nuclear Chemistry - In order to realize the environmental sustainability, a raw bloom-forming species Microcystis aeruginosa harvested from natural waters without any...     

Simulation of rapidly varying flow using an efficient TVD–MacCormack scheme

An efficient numerical scheme is outlined for solving the SWEs (shallow water equations) in environmental flow; this scheme includes the addition of a five‐point symmetric total variation diminishing (TVD) term to the corrector step of the standard MacCormack scheme. The paper shows that the discretization of the conservative and non‐conservative forms of the SWEs leads to the same finite difference scheme when the source term is discretized in a certain way. The non‐conservative form is used in the solution outlined herein, since this formulation is simpler and more efficient. The time step is determined adaptively, based on the maximum instantaneous Courant number across the domain. The bed friction is included either explicitly or implicitly in the computational algorithm according to the local water depth. The wetting and drying process is simulated in a manner which complements the use of operator‐splitting and two‐stage numerical schemes. The numerical model was then applied to a hypothetical dam‐break scenario, an experimental dam‐break case and an extreme flooding event over the Toce River valley physical model. The predicted results are free of spurious oscillations for both sub‐ and super‐critical flows, and the predictions compare favourably with the experimental measurements. Copyright © 2006 John Wiley & Sons, Ltd.