Energy dissipation in concentrated monodisperse colloidal suspensions of silica particles in polyethylene glycol

Highly concentrated colloidal suspensions exhibit a discontinuous shear-thickening behaviour. The transition from a low to a high viscosity state is associated to a large energy dissipation. This effect could find applications in structural damping while the viscosity increase brings added stiffness. In the present work, highly concentrated suspensions of monodisperse spherical silica particles in polyethylene glycol were selected for their strong thickening at low critical shear rates. Their damping properties were characterized by measuring the energy dissipated per cycle at low frequency (below 2 Hz) during oscillatory tests using a rheometer. The influence of parameters such as particle concentration, size and frequency was investigated. Damping was found to overcome that of benchmark elastomeric materials only in high frequencies and high strain domains

La surveillance phytosanitaire de la forêt en région méditerranéenne

La stratégie de lutte est améliorée par une surveillance permanente dépendant d'un réseau en 3 éléments : observation, technique, administration. L'action des principaux insectes ravageurs et agents pathogènes est évoquée

Polyethylene/Polyhydroxyalkanoates-based Biocomposites and Bionanocomposites

The development of advanced polymer composite materials having superior mechanical properties has opened up new horizons in the field of science and engineering. Polyethylene (PE) is considered one of the most widely used thermoplastics in the world due to its excellent properties which have excellent chemical inertness, low coefficient of friction, toughness, near-zero moisture absorption, ease of processing and electrical properties. Polyhydroxyalkanoates (PHAs) are garnering increasing attention in the biodegradable polymer market because of their promising properties such as high biodegradability in different environments. This chapter covers polyethylene/polyhydroxyalkanoates-based biocomposites and bionanocomposites. It summarizes many of the recent research accomplishments in the area of PE/PHAs-based biocomposites and bionanocomposites such as state-of-the-art regarding different methods of their preparation. Also discussed are different characterization techniques and use of PE/PHAs-based biocomposites and bionanocomposites in biomedical, packaging, structural, military, coating, fire retardant, aerospace and optical applications, along with recycling and lifetime studies

Impact de la transition numérique sur la production de ressentis

International audienceDans le cadre d’une thèse CIFRE avec la startup Comongo, nous présentons un travail de recherche en sciences du langage et humanités numériques sur l’analyse automatique de production de ressentis. Nous avons deux objectifs : définir et évaluer l’image de marque d’un client et l’aider à anticiper les ressentis et les attentes de communication de publics cibles en vue d’améliorer cette image de marque. Dans notre démarche, nous employons le terme d’analyse de ressentis qui se distingue de l’analyse de sentiments ou d’opinions. Nous travaillons sur des productions écrites (des réponses à des questions ouvertes) qui nous permettent de comparer une identité souhaitée d’un client avec une image perçue. Nous cherchons à extraire les ressentis et à effectuer une représentation synthétique de ceux-ci

Etude forêts subnaturelles alpines : observations pathologiques effectuées en 1993 en forêt domaniale du Bois du Chapitre (Hautes Alpes) et en forêt de Sixt (Haute-Savoie)

In the framework of a research agreement between the Department of Agriculture and that of Environment, a multidisciplinar program of research was launched in 1992 by the Cemagref in three subnatural alpine forests. A general characterization of the main cryptogamic diseases found in these forests, depending on the species present was made in 1993. It is summarized in this article. The essential characteristics of disease-agents are presented in the appendix. / Dans le cadre d'une convention de recherches avec le Ministère de l'Agriculture et la Pêche et celui de l'Environnement, un programme d'études pluridisciplinaires a été lancé en 1992 pour le CEMAGREF dans trois forêts subnaturelles alpines. Les travaux en pathologie forestière ont consisté en 1993 en une caractérisation générale des principales maladies cryptogamiques décelées dans ces forêts en fonction des essences représentées et sont résumés dans ce document comprenant en annexe les caractéristiques essentielles des agents pathogènes rencontrés

La lutte chimique contre la rouille courbeuse des pins (Melampsora pinitorqua) : test de différents niveaux d'apport et de concentration de fongicide (F.D. du Thureau du Bard - 1990)

Results of a study conducted in 1989 on the chemical control of the pine blister (Melempsora pinitorqua) have shown that a good control of the disease can be achieved with one treatment of triadimefon (tested with 6 other active fungicides) at the beginning of the sensitivity period (B2 phenological stage). The tests conducted in 1990, the objective of which was to study the influence of concentration, confirm the results obtained in 1989. They also indicated that the smallest amount of triadimefon tested with the smallest amount of solution, in other words, 4 mg of active ingredient per tree, was effective. Finally, our results also indicated that the limit height of infection of the Norway pine is less than 2.5 m. / Les résultats de l'étude effectuée en 1989 sur la lutte chimique contre la rouille courbeuse des pins (Melmpsora pinitorqua) ont montré qu'une bonne maîtrise de la maladie peut être obtenue avec le triadiméfon (testé parmi 6 matières actives fongicides) en un seul traitement préventif effectué au début de la période de sensibilité (stade phénologique B2 des pins). Les essais menés en 1990 qui ont eu pour objectif d'étudier l'influence de la concentration du traitement ont confirmé les résultats 1989 ; ils ont en outre révélé que l'efficacité du triadiméfon est démontrée dès l'utilisation de la plus petite dose testée avec l'apport de solution le plus faible, correspondant à 4mg de m.a.par arbre. Enfin l'étude nous apprend que la hauteur limite d'infection du pin sylvestre se situe au moins à 2,50 m

La cylindrosporiose ou anthracnose du merisier : test d'efficacité de six matières actives fongicides en jeune plantation (Serre-les-Sapins)

This is a summary of chemical control tests conducted against the cylindrosporiosis or anthracnosis of the wild cherry (Blumeriella jaapii (Rehm) V.A -rx). The efficiency of six fungicidal active ingredients (doguadine, dithianon, benomy, flusilazole, teboconazole, and difenoconazole) is tested and the products are compared. This experiment is the same than the one conducted in 1991 on nursery and young plants and during which it was impossible to differentiate among the treatments because of particular climatic conditions (drought) observed that year. The results indicated that all six products are efficient, that tebuconazole and fluviazole are the most efficient active ingredients followed by difénoconazole. All three products, which provide a better protection, belong to the triazole family, the action of which is known on numerous fungi. On the other hand, dithianon exhibited the lowest efficiency. Finally, the different products did not affect plant height. / Cette étude fait le bilan des essais de lutte chimique effectués contre la cylindrosporiose ou anthracnose du merisier (Blumeriella jaapii(Rehm)V.Arx). L'efficacité de six matières actives fongicides (doguadine, dithianon, bénomyl, flusilazole, téboconazole et difénoconazole) a été testée et comparée. Cette expérimentation reprend celle effectuée en 1991 en pépinière et en jeune plantation et pour laquelle le faible niveau de l'attaque consécutif aux conditions climatiques particulières de l'année (sécheresse) n'avait pas permis de différencier les traitements. Les résutats révèlent que les six produits testés sont efficaces ; ils permettent d'établir que le tébuconazzole et le fluviazole sont les deux matières actives les plus performates suivis par le difénoconazole. Ces trois produits, qui entraînent la meilleure protection, se révèlent être de la famille des triazoles dont l'action est reconnue sur de nombreux champignons. Par contre, le dithianon présente l'éfficacité la plus faible. Enfin, la réaction des plants à effet des différents produits n'est pas perceptible à travers leur accroissement en hauteur

Le corps manifestant. La manifestation entre expression et représentation

Bodies In Protest. Demonstration between expression and representation. The article examines the different ways in which demonstrators make use of their body, in an attempt to determine the contribution of actual physical bodies to the notion of demonstration. These usage plays a large part in the unity and cohesion of demonstrators, and are used as means of contentious politics. Eventually, they contribute to shape the demonstration as a specific corporal and political experience, which has to combine the competing logics of expression and representation.RESUME: Cet article s’appuie sur la lecture de textes consacrés à la manifestation et sur des observations réalisées au sein de récentes manifestations parisiennes. En examinant les usages que les manifestants font de leur corps dans les cortèges, il s’agissait d’en savoir plus sur la contribution apportée par les corps à la définition du phénomène manifestant. Les usages observés ont en fait paru relever simultanément de deux logiques concurrentes: celle de l’ «expression» et celle de la «représentation». Parce qu’elles mobilisent toutes deux le corps des manifestants, ces logiques se soutiennent, se nourrissent et se répondent. Mais l’ «expression» et la «représentation» du groupe sollicitent le corps chacune à leur façon: une certaine tension subsiste donc entre elles. Le travail politique à l’oeuvre dans la manifestation pourrait dès lors résider pour une grande part dans la gestion de cette tension.Soutrenon Emmanuel. Le corps manifestant. La manifestation entre expression et représentation. In: Sociétés contemporaines N°31, 1998. pp. 37-58

Essai de lutte chimique contre la rouille courbeuse des pins

Pine blister (Melampsora pinitorqua) raises a serious problems in young plantations (permanent distortions, or bud drying). This study is a summary of chemical control tests conducted in 1989, for the first time, on Norway pines. A comparative study was conducted on the efficiency of six fungicidal active ingredients. The results indicated that a good control can be achieved with only one treatment of triadimefon at the beginning of the sensitivity period. / La rouille courbeuse des pins (Melampsora pinitorqua) pose un sérieux problème dans les jeunes plantations (déformations permanentes ou dessèchements des pousses). Cette étude fait le bilan des essais de lutte chimique réalisés en 1989 pour la première fois sur pin sylvestre ; l'efficacité de six matières actives fongicides a été testée et comparée. Les résultats de cette étude montrent qu'une bonne maîtrise de la maladie peut être obtenue avec un seul traitement préventif à l'aide du triadiméfon effectué au début de la période de sensibilité des pins

Shear Thickening Fluid Impregnated Foam Composites for Vibration Control and Impact Protection

Highly concentrated suspensions of silica particles present shear thickening properties, shifting from a low to a high viscosity state, instantly and reversibly at a critical shear rate. Their viscosity increases by up to 3 orders of magnitude, changing from a honey-like liquid to a brittle solid material. This sharp rise in viscosity is associated with a large absorption of energy that can be used in damping applications. These shear thickening fluids (STF) are among the few passive materials that can simultaneously bring both an increase in damping and in stiffness properties. In mechanical design, this leads potentially to a weight reduction of the overall system. This thesis work is aimed to develop and test a composite material solution for vibration control and impact protection, using STF as the damping element. A main challenge was to overcome the fact that STF are liquid at rest, and very sensitive to their environment. The proposed damping material was therefore constituted of foam impregnated with STF and encapsulated with silicone (STF/foam). A comparison of properties with other damping materials such as Smactane®was emphasized along the thesis. Storage and processing conditions of STF constituted of highly concentrated suspensions were shown to affect their rheological properties similarly to other sensitive parameters such as particle concentration. Rigorous processing methods were thus required to produce STF with defined and stable rheological properties. The use of sonication was preferred to disperse the aggregates of particles in concentrated colloidal suspensions due to the packing of the dry powder. Contact with air or humidity deteriorates the shear thickening properties of STF. Storage of STF in a freezer at −24 ◦C or under nitrogen prevents this. The use of a physical barrier to air and humidity such as silicone to protect STF is also shown to greatly reduce the ageing problem. The energy dissipated during a cyclic strain cycle was used as a measure of the damping property of the STF, and compared to that of other materials. It was measured with dynamic rheological measurements performed on suspensions with variations of particle concentration, size and test frequency. STF were shown to dissipate a large amount of energy during their transition, which increases with the increase of frequency and particle concentration and decrease with the increase of particle size. In specific cases of large strain amplitude, they potentially dissipate more energy than viscoelastic materials such as rubber. An open cell melamine resin foam was used as a lightweight scaffold to provide a three dimensional structure to the STF. The foam distributes the load and locally shears the STF. The shape of the foam is easily adjustable. To impregnate the foam with the STF, a system similar to vacuum infusion was used. The foam was placed under vacuum in a mold and the STF heated at 70 ◦C to reduce its viscosity and shear thickening properties was sucked in the foam with the depressurization. The STF/foam systems were then encapsulated in silicone to protect the STF/foam damping pads from contamination and avoid outgassing. During compression tests at low frequencies and large deformations, we demonstrated that STF could be activated in this type of structure, with mechanical properties comparable to those of a viscous honey-like fluid at rest and silicone when the STF is in the solid state. The same behavior was observed during impact solicitations. STF/foam presents a very low coefficient of restitution and absorbs the shock wave associated with impacts. Shock tests done separately confirm the shock absorption properties of STF/foam even if the STF is not activated. The combination of mechanical and damping properties of the foam/STF systems remain lower than for very high performance damping materials like Smactane®. The reasons are their low mechanical compression and shear properties at rest and the need to overcome a threshold strain or stress to activate the STF. However, the large dissimilarity between the states before and after the transition makes these materials interesting for impact or large strain amplitude applications such as sole for running shoes or several space structures