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Étienne Guyon nous a quittés en juillet dernier. Au cours de sa carrière, il a eu une diversité impressionnante d’activités liées aux sciences comme aux lettres, à la recherche comme à l’enseignement et à la diffusion scientifique.

Although bending a sheet of paper is an easy operation, stretching is more limited and it leads to rupture and tears. However, well-designed cuts on the sheet can induce a large effective stretchability. This kirigami technique offers a large scope of engineering applications ranging from deployable structures to compliant electronics. We are here interested in the axisymmetric configuration where cuts are designed along concentric circles. Applying an increasing transverse load at the center of the sheet results into a 3D axisymmetric structure of growing amplitude which eventually saturates. We first describe the linear response of the structure and determine the evolution of the deployed shape until its asymptotic geometrical limit. Reversing the problem in the linear regime, we propose, a design procedure for the cuts leading to a desired 3D shape. The structure can also be deployed by inflating an inner balloon. Exploring further the interplay between mechanics and geometry, we finally describe the maximum volume of inflated kirigami structures as a function of the cutting pattern.

Après un rappel historique sur les démonstrations publiques d’expériences scientifiques depuis les cabinets de physique du 18e siècle, cet article présente les leçons expérimentales mises en place à l’ESPCI depuis 2003, qui se sont donné l’objectif de présenter « en direct » la science d’aujourd’hui. Ces conférences, gratuites et ouvertes à tous, qui montrent aussi bien la manipulation d’une chaîne d’ADN que des expériences avec des jeux, sont filmées et mises à disposition sur Canal-U pour les rendre durablement accessibles au public.

Une goutte d'eau déposée à la surface d'un bain d'huile de tournesol forme une lentille liquide flottante. Une goutte d'alcool, au contraire, s'étale à la surface de l'huile. Un mélange d'eau et d'alcool produit un spectaculaire phénomène d'étalement et de fragmentation spontanée.

Les films minces qui revêtent les surfaces de nos objets quotidiens tendent à rompre selon un motif de type « boue séchée #x00BB; sous l’effet d’une contraction du film. Nous décrivons un nouveau mode de rupture d’une couche mince d’épaisseur micrométrique déposée sur un substrat rigide. Ici, lorsque la couche sèche et se craquelle, elle se décolle simultanément, ce qui conduit à des fissures aux motifs étonnamment réguliers comme des spirales ou des allées oscillantes.

The purpose of this study is to analyse the antecedents of employee engagement in family and non-family businesses by using the model developed by Saks (2006). Further, the study examines whether there is a difference in employee engagement between employees in family and non-family firms. A quantitative study is applied through cross-sectional survey method by using online questionnaire for data collection. The final sample consists of 126 participants out of which 68 were employees in family businesses and 58 in non-family businesses. The results gave little support for both hypotheses. The partial support was found in the model of antecedents of employee engagement while no support was found for the difference in employee engagement when it comes to comparison between employees in family and non-family businesses.

Viscosity, which impacts the rate of haemolymph circulation and heat transfer, is one of the transport properties that affects the performance of an insect. Measuring the viscosity of insect fluids is challenging because of the small amount available per specimen. Using particle tracking microrheology, which is well suited to characterise the rheology of the fluid part of the haemolymph, we studied the plasma viscosity in the bumblebee Bombus terrestris. In a sealed geometry, the viscosity exhibits an Arrhenius dependence with temperature, with an activation energy comparable to that previously estimated in hornworm larvae. In an open to air geometry, it increases by 4–5 orders of magnitude during evaporation. Evaporation times are temperature dependent and longer than typical insect haemolymph coagulation times. Unlike standard bulk rheology, microrheology can be applied to even smaller insects, paving the way to characterise biological fluids such as pheromones, pad secretions or cuticular layers.

The effects of chemical dips and edible coatings on firmness and colour of fresh-cut banana (cv. Cavendish) from Madeira Island were investigated. Two calcium salts, calcium chloride and calcium lactate, were first investigated for the effects on firmness during four days of storage at 5°C. Firmness and colour were evaluated after a three-minute chemical dipping or chemical dipping followed by coating and during five days of storage at 5°C. The coatings tested consisted of pectin, alginate, carboxymethylcelullose, carrageenan or chitosan solution. Dip with 1% (w/v) calcium chloride, 0.50% (w/v) ascorbic acid and 0.75% (w/v) cysteine was the most efficient treatment in retarding softening and browning of banana slices. This dip also inhibited yeast growth. According to sensory analysis, the edible shelf life of banana slices dipped in such solution was the longest: five days at 5°C. Carrageenan solution was the significantly (p < 0.05) best coating among the ones studied, in preserving firmness and colour of fresh-cut banana during five days at 5°C.

Abstract—Splash‐form tektites are generally acknowledged to have the form of bodies of revolution. However, no detailed fluid dynamical investigation of their form and stability has yet been undertaken. Here, we review the dynamics and stability of spinning, translating fluid drops with a view to making inferences concerning the dynamic history of tektites. We conclude that, unless the differential speed between the molten tektite and ambient is substantially less than the terminal velocity, molten tektites can exist as equilibrium bodies of revolution only up to sizes of 3 mm. Larger tektites are necessarily non‐equilibrium forms and so indicate the importance of cooling and solidification during flight. An examination of the shapes of rotating, translating drops indicates that rotating silicate drops in air will assume the shapes of bodies of rotation if their rotational speed is 1% or more of their translational speed. This requirement of only a very small rotational component explains why most splash‐form tektites correspond to bodies of revolution. A laboratory model that consists of rolling or tumbling molten metallic drops reproduces all of the known forms of splashform tektites, including spheres, oblate ellipsoids, dumbbells, teardrops, and tori. The laboratory also highlights important differences between rolling drops and tumbling drops in flight. For example, toroidal drops are much more stable in the former than in the latter situation.

We summarize different works devoted to the behaviour of liquids on microtextured solid surfaces. We show in particular how the textures can be used for tuning the wettability of a solid, and discuss the sticking of drops on such surfaces.

The progression of a liquid inside a porous medium often involves two macroscopic fronts: a main one, at the bottom, which saturates the medium; and a much thinner one, ahead, which propagates using the fine structures of the porous material. We discuss here different characteristics of this precursor. We show in particular how it can move faster than the main front, although it follows confined paths. We also describe its dynamics, and compare our results with different experimental situations.

Surface coating is generally achieved by an active operation: painting with a brush; withdrawing from a bath. Porous imbibition constitutes a more passive way: a porous material just put in contact with a reservoir containing a wetting fluid is spontaneously invaded. In this case, the material can eventually be filled by the fluid. If the aim is to coat only the surface of the pores, the liquid excess must be actively removed. We present an experiment in which a liquid train spontaneously moves in a capillary tube because of the trail it leaves behind. From a practical point of view, this system achieves a coating of the tube. The condition required for this motion and a model for its dynamics are presented. We also show how these trains can drive extremely viscous liquid slugs (or even solid bodies) in narrow tubes. We discuss the thickness of the deposited films. Extensions and limits of this system in more complex geometries are finally described, together with special cases such as the deposition of solid films.

An increase in the number of new cases of tuberculosis (TB) combined with poor clinical outcome was identified among HIV-infected injecting drug users attending a large HIV unit in central Lisbon. A retrospective epidemiological and laboratory study was conducted to review all newly diagnosed cases of TB from 1995 to 1996 in the HIV unit. Results showed that from 1995 to 1996, 63% (109/173) of the Mycobacterium tuberculosisisolates from HIV-infected patients were resistant to one or more anti-tuberculosis drugs; 89% (95) of these were multidrug-resistant, i.e., resistant to at least isoniazid and rifampicin. Eighty percent of the multidrug-resistant strains (MDR) available for restriction fragment length polymorphism (RFLP) DNA fingerprinting clustered into one of two large clusters. Epidemiological data support the conclusion that the transmission of MDR-TB occurred among HIV-infected injecting drug users exposed to infectious TB cases on open wards in the HIV unit. Improved infection control measures on the HIV unit and the use of empirical therapy with six drugs once patients were suspected to have TB, reduced the incidence of MDR-TB from 42% of TB cases in 1996 to 11% in 1999.

In this paper, the prototype of an auto-tuning PID regulator for fast processes is presented. The regulator is based on The Logic Cell Arrays technology, which allows the user to reach sampling frequencies higher thаn 20kHz. The auto-tuning procedure relies on preliminary closed-loop experiments with a relay. Experimental results obtained by the use of the prototype for speed control of a DC motor are also reported.

The fall of viscous slugs in vertical capillary tubes is described. Deviations toward Poiseuille law are analyzed by taking into account the dissipation in menisci, together with the existence of a film behind the slug. Slugs are found to fall slower in dry tubes than in prewetted ones, which is quantitatively discussed in term of viscous friction. A criterion for the minimal length of the slug obeying the Poiseuille solution is finally derived.

Projet expérimental mis au point pour l’exposition interactive sur les forces et les formes dans la matière, « Ruptures », présentée au Palais de la découverte jusqu’au 10 novembre 2013 (voir annonce, p. 9).

Reports that aerobics can lead to ear damage. Study of Dr. Michael J. Weintraub; Effect of high-impact aerobics on ears; Development of displaced otoliths; Potentials of aerobics on ear damage.