Mise en suspension d'une poudre micronique par effet vortex

National audienceNew materials based on nanotechnology are reaching the market in a wide variety of consumer products. Since these nanostructured materials can be in powder form, a suspending powder system is essential for many purposes: For in vivo inhalation toxicological studies,for workers and consumers protection, for instrumental development widening aerosol measurement spectrum. Different powders suspending systems have been developed like the rotating drum or the single drop. They are used as a reference method to evaluate bulk materials dustiness. Usually cumbersome, these systems need a huge amount of powder (a few hundred grams) and require time-consuming cleaning processes which could be even more tedious when a nanostructured material and/or a toxic powder is used. The aim of this work is to evaluate the behavior of a powder suspending system by vortex effect. This system is very simple and requires a very small amount of powder (a few grams) in a tube [1,2]. It has been set up to study the dustiness under controlled and reproducible conditions. Different tests have been performed with a Al2O3 powder. They allowed not only to characterize the influence of shaking speed and powder mass, but also to measure the particle size and the number concentration as shown on the figures belowLa mise en suspension de poudres est un processus essentiel dans différents domaines : il permet d'étudier la physico-chimie de la phase " aérosol " d'une poudre donnée ; un tel système est indispensable pour mener des études toxicologiques par inhalation in vivo ; dans le domaine de la protection des personnes (travailleur, consommateur) et de l'environnement, il permet d'évaluer l'émissivité potentielle des poudres, et en conséquence d'adapter les mesures de protection ; un tel dispositif facilite également le développement instrumental, en donnant accès à un spectre large d'aérosols. Nous rapportons ici les résultats d'une étude consacrée à la mise en suspension par effet vortex. Ce système est particulièrement simple [2, 3] : il consiste en l'agitation d'une faible quantité de poudre, placée dans un tube à essai. Nos essais ont porté sur une poudre micronique d'alumine. L'aérosol obtenu a été caractérisé en nombre et taille à l'aide de systèmes CNC, SMPS, et APS. Des essais de sensibilité ont été menés en termes de quantité de produit, et de niveau d'agitation. Nous avons relevé une très bonne répétabilité des résultat

Resolving the wave-vector in negative refractive media: The sign of Z\sqrt{Z}

We address the general issue of resolving the wave-vector in complex electromagnetic media including negative refractive media. This requires us to make a physical choice for the sign of a square-root imposed merely by conditions of causality. By considering the analytic behaviour of the wave-vector in the complex plane, it is shown that there are a total of eight physically distinct cases in the four quadrants of two Riemann sheets.Comment: 3 pages, 2 figures, RevTe

Digital forensics and the big data deluge — some concerns based on Ramsey theory

Constructions of science that slowly change over time are deemed to be the basis of the reliability with which scientific knowledge is regarded. A potential paradigm shift based on big data is looming – many researchers believe that massive volumes of data have enough substance to capture knowledge without the theories needed in earlier epochs. Patterns in big data are deemed to be sufficient to make predictions about the future, as well as about the past as a form of understanding. This chapter uses an argument developed by Calude and Longo [6] to critically examine the belief system of the proponents of data-driven knowledge, especially as it applies to digital forensic science. From Ramsey theory it follows that, if data is large enough, knowledge is imbued in the domain represented by the data purely based on the size of the data. The chapter concludes that it is generally impossible to distinguish between true domain knowledge and knowledge inferred from spurious patterns that must exist purely as a function of data size. In addition, what is deemed a significant pattern may be refuted by a pattern that has yet to be found. Hence, evidence based on patterns found in big data is tenuous at best. Digital forensics should therefore proceed with caution if it wants to embrace big data and the paradigms that evolve from and around big data.https://link.springer.com/bookseries/6102hj2021Computer Scienc

The Statistics of the Number of Minima in a Random Energy Landscape

We consider random energy landscapes constructed from d-dimensional lattices or trees. The distribution of the number of local minima in such landscapes follows a large deviation principle and we derive the associated law exactly for dimension 1. Also of interest is the probability of the maximum possible number of minima; this probability scales exponentially with the number of sites. We calculate analytically the corresponding exponent for the Cayley tree and the two-leg ladder; for 2 to 5 dimensional hypercubic lattices, we compute the exponent numerically and compare to the Cayley tree case.Comment: 18 pages, 8 figures, added background on landscapes and reference

“Siel van die mier” : reflections on the battle for ‘scholarly’ intelligence

This essay traces two research programmes in broad strokes. Both programmes start from the same observation — the behaviour of an ant (or termite) colony and the ability of the ant colony to act in a collective manner to achieve goals that the individual ant cannot. For one programme such behaviour is indicative of intelligence; for the other it is indicative of (collective) instinct. The primary intention of the essay is not to assess the claims of intelligence found, but to consider the rationale of the researchers involved in the two programmes for doing such research. It is observed that virtue in one programme is understanding (with the concomitant ability to explain — and, hence, teach), while the primary virtue in the other programme is the utility — and ultimately efficiency — that this may add to human problem solving skills. The two programmes used as illustration are Eugène Marais’s study of termites in the first half of the 20th century and the emergence of artificial intelligence projects that are inspired by ant behaviour in the second half of the 20th century. The essay suggests that the current emphasis of inquiry at tertiary education institutions embraces utility to the extent that it displaces pure insight — and hence the ability to explain and, ultimately, the ability to teach.http://www.td-sa.netam201

Characterization of the blue emission of Tm/Er co-implanted GaN

Comparative studies have been carried out on the cathodoluminescence (CL) and photoluminescence (PL) properties of GaN implanted with Tin and GaN co-implanted with Tin and a low concentration of Er. Room temperature CL spectra were acquired in an electron probe microanalyser to investigate the rare earth emission. The room temperature CL intensity exhibits a strong dependence on the annealing temperature of the implanted samples. The results of CL temperature dependence are reported for blue emission (similar to 477 nm) which is due to intra 4f-shell electron transitions ((1)G(4)-> H-3(6)) associated with Tm3+ ions. The 477 nm blue CL emission is enhanced strongly as the annealing temperature increases up to 1200 degrees C. Blue PL emission has also been observed from the sample annealed at 1200 degrees C. To our knowledge, this is the first observation of blue PL emission from Tin implanted GaN samples. Intra-4f transitions from the D-1(2) level (similar to 465 nm emission lines) of Tm3+ ions in GaN have been observed in GaN:Tm films at temperatures between 20-200 K. We will discuss the temperature dependent Tm3+ emission in both GaN:Tm,Er and GaN:Tm samples

A versatile source of polarisation entangled photons for quantum network applications

We report a versatile and practical approach for generating high-quality polarization entanglement in a fully guided-wave fashion. Our setup relies on a high-brilliance type-0 waveguide generator producing paired photon at a telecom wavelength associated with an advanced energy-time to polarisation transcriber. The latter is capable of creating any pure polarization entangled state, and allows manipulating single photon bandwidths that can be chosen at will over five orders of magnitude, ranging from tens of MHz to several THz. We achieve excellent entanglement fidelities for particular spectral bandwidths, i.e. 25 MHz, 540 MHz and 100 GHz, proving the relevance of our approach. Our scheme stands as an ideal candidate for a wide range of network applications, ranging from dense division multiplexing quantum key distribution to heralded optical quantum memories and repeaters.Comment: 5 figure