Plasmonic nanoantennas as integrated coherent perfect absorbers on SOI waveguides for modulators and all-optical switches

The performance of plasmonic nanoantenna structures on top of SOI wire waveguides as coherent perfect absorbers for modulators and all-optical switches is explored. The absorption, scattering, reflection and transmission spectra of gold and aluminum nanoantenna-loaded waveguides were calculated by means of 3D finite-difference time-domain simulations for single waves propagating along the waveguide, as well as for standing wave scenarios composed from two counterpropagating waves. The investigated configurations showed losses of roughly 1% and extinction ratios greater than 25 dB for modulator and switching applications, as well as plasmon effects such as strong field enhancement and localization in the nanoantenna region. The proposed plasmonic coherent perfect absorbers can be utilized for ultracompact all-optical switches in coherent networks as well as modulators and can find applications in sensing or in increasing nonlinear effects.Comment: 10 pages, 6 figure

Thermal distortion analysis of a deployable parabolic reflector

A thermal distortion analysis of the ATS-6 Satellite parabolic reflector was performed using NASTRAN level 15.1. The same NASTRAN finite element method was used to conduct a one g static load analysis and a dynamic analysis of the reflector. In addition, a parametric study was made to determine which parameters had the greatest effect on the thermal distortions. The method used to model the construction of the reflector is described and the results of the analyses are presented

An ultrafast reconfigurable nanophotonic switch using wavefront shaping of light in a nonlinear nanomaterial

We demonstrate a new concept for reconfigurable nanophotonic devices exploiting ultrafast nonlinear control of shaped wavefronts in a multimode nanomaterial consisting of semiconductor nanowires. Femtosecond pulsed laser excitation of the nanowire mat is shown to provide an efficient nonlinear mechanism to control both destructive and constructive interference in a shaped wavefront. Modulations of up to 63% are induced by optical pumping, due to a combination of multimode dephasing and induced transient absorption. We show that part of the nonlinear phase dynamics can be inverted to provide a dynamical revival of the wavefront into an optimized spot with up to 18% increase of the peak to background ratio caused by pulsed laser excitation. The concepts of multimode nonlinear switching demonstrated here are generally extendable to other photonic and plasmonic systems and enable new avenues for ultrafast and reconfigurable nanophotonic devices.Comment: 18 pages, 6 figure

An experimental study on timely activation of smoke alarms and their effective notification in typical residential buildings

The volume of smoke alarm sound in rooms (other than room of sound origin) in real houses and smoke alarm activation time in rooms in full-scale model houses using ionization, photoelectric and dual detector smoke alarms were determined in this study. The alarm sound level measurements indicated that the sound level in many locations is likely to be too low to provide reliable notification, particularly for sleeping people, if smoke alarms are not installed in every room. In addition, changing to a lower frequency (520 Hz square wave) alarm would further aid effective notification of building occupants. The smoke alarm activation measurements showed that the time to detection (given a particular smoke source) was influenced by door position (open versus closed), the room in which the fire occurs, the location (room or hallway) of the detector, the type of detector and the smoke alarm manufacturer. Furthermore time to detection is also influenced by the type and form of the material that is burning. It was observed that photoelectric smoke alarms had the highest incidence of non-activation and when they did activate they, on average, took longer to activate than ionization and dual (ionization and photoelectric) smoke alarms over all smoke sources considered in this study. It is concluded that to achieve early detection and provide adequate notification, smoke alarms are necessary in every room and should be interconnected

A Modular Voting Architecture ("Frogs")

We present a “modular voting architecture” in which “vote generation” is performed separately from “vote casting.

L’intervention de la puissance publique dans le contrôle de l’étalement urbain. Deuxième partie : confrontation de la situation belge aux expériences suisses et danoises

Recherche SSTC « Les comportements résidentiels des ménages face à la problématique du développement durable »Les comportements résidentiels des ménages face à la problématique du développement durabl

Covering algorithms, continuum percolation and the geometry of wireless networks

Continuum percolation models in which each point of a two-dimensional Poisson point process is the centre of a disc of given (or random) radius r, have been extensively studied. In this paper, we consider the generalization in which a deterministic algorithm (given the points of the point process) places the discs on the plane, in such a way that each disc covers at least one point of the point process and that each point is covered by at least one disc. This gives a model for wireless communication networks, which was the original motivation to study this class of problems. We look at the percolation properties of this generalized model, showing that an unbounded connected component of discs does not exist, almost surely, for small values of the density lambda of the Poisson point process, for any covering algorithm. In general, it turns out not to be true that unbounded connected components arise when lambda is taken sufficiently high. However, we identify some large families of covering algorithms, for which such an unbounded component does arise for large values of lambda. We show how a simple scaling operation can change the percolation properties of the model, leading to the almost sure existence of an unbounded connected component for large values of lambda, for any covering algorithm. Finally, we show that a large class of covering algorithms, which arise in many practical applications, can get arbitrarily close to achieving a minimal density of covering discs. We also construct an algorithm that achieves this minimal density

Position-dependent shear-induced austenite-martensite transformation in double-notched TRIP and dual-phase steel samples

While earlier studies on transformation-induced-plasticity (TRIP) steels focused on the determination of the austenite-to-martensite decomposition in uniform deformation or thermal fields, the current research focuses on the determination of the local retained austenite-to-martensite transformation behaviour in an inhomogeneous yet carefully controlled shear-loaded region of double-notched TRIP and dual-phase (DP) steel samples. A detailed powder analysis has been performed to simultaneously monitor the evolution of the phase fraction and the changes in average carbon concentration of metastable austenite together with the local strain components in the constituent phases as a function of the macroscopic stress and location with respect to the shear band. The metastable retained austenite shows a mechanically induced martensitic transformation in the localized shear zone, which is accompanied by an increase in average carbon concentration of the remaining austenite due to a preferred transformation of the austenite grains with the lowest carbon concentration. At the later deformation stages the geometry of the shear test samples results in the development of an additional tensile component. The experimental strain field within the probed sample area is in good agreement with finite element calculations. The strain development observed in the low-alloyed TRIP steel with metastable austenite is compared with that of steels with the same chemical composition containing either no austenite (a DP grade) or stable retained austenite (a TRIP grade produced at a long bainitic holding time). The transformation of metastable austenite under shear is a complex interplay between the local microstructure and the evolving strain fields