Potential tuning of porous silicon luminescence

Electrochemical investigations were conducted of the effect of potential on the luminescence of porous silico (PS). The use of liquid contacts allows the potential to be controlled during studies of the photoluminescence (PL) and electroluminescence (EI). The PL and EL of PS samples prepared from n-type substrates is considered. To obtain luminescence from such PS it is necessary to generate holes in the valence band. This is achieved by either photoexcitation or an electrochemical process involving the reduction of persulfate. This paper describes the investigations of the effect of potential on the PL and EL of PS. A mechanism of 'potential tuning' based on electron occupancy and Auger quenching is then proposed.

The transition mechanism of highly-loaded LP turbine blades

A detailed experimental investigation was conducted into the interaction of a converted wake and a separation bubble on the rear suction surface of a highly loaded low-pressure (LP) turbine blade. Boundary layer measurements, made with 2D LDA, revealed a new transition mechanism resulting from this interaction. Prior to the arrival of the wake, the boundary layer profiles in the separation region are inflexional. The perturbation of the separated shear layer caused by the converting wake causes an inviscid Kelvin-Helmholtz rollup of the shear layer. This results in the breakdown of the laminar shear layer and a rapid wake-induced transition in the separated shear layer.

Non-linear photoluminescence from graphene

Graphene is in the focus of research due to its unique electronic and optical properties. Intrinsic graphene is a zero gap semiconductor with a linear dispersion relation for E-k leading to zero-effective-mass electrons and holes described by Fermi-Dirac theory. Since pristine graphene has no bandgap no photoluminescence would be expected. However, recently several groups showed non-linear photoluminescence from pristine graphene putting forward different physical models explaining this remarkable effect [1-3]. © 2011 IEEE.

The fundamental mechanism behind headbox jet break-up

It has previously been shown that MD streaks are created in the headbox jet, which is closely connected to the appearance of waves on the jet surface. The fundamental mechanism behind this break-up is presented. This has been achieved by implementing state-of-the-art methods for determining the characteristics and evolution of hydrody-namic instabilities. The methodology also allows the headbox slice to be designed in order to minimise jet break-up. This possibility has been evaluated in pilot-scale.

Collapse mechanism maps for the hollow pyramidal core of a sandwich panel under transverse shear

The finite element method has been used to develop collapse mechanism maps for the shear response of sandwich panels with a stainless steel core comprising hollow struts. The core topology comprises either vertical tubes or inclined tubes in a pyramidal arrangement. The dependence of the elastic and plastic buckling modes upon core geometry is determined, and optimal geometric designs are obtained as a function of core density. For the hollow pyramidal core, strength depends primarily upon the relative density ρ̄ of the core with a weak dependence upon tube slenderness. At ρ̄ below about 3%, the tubes of the pyramidal core buckle plastically and the peak shear strength scales linearly with ρ̄. In contrast, at ρ̄ above 3%, the tubes do not buckle and a stable shear response is observed. The predictions of the current study are in excellent agreement with previous measurements on the shear strength of the hollow pyramidal core, and suggest that this core topology is attractive from the perspectives of both core strength and energy absorption. © 2011 Elsevier Ltd. All rights reserved.