Genesis of d'Alembert's paradox and analytical elaboration of the drag problem

We show that the issue of the drag exerted by an incompressible fluid on a body in uniform motion has played a major role in the early development of fluid dynamics. In 1745 Euler came close, technically, to proving the vanishing of the drag for a body of arbitrary shape; for this he exploited and significantly extended existing ideas on decomposing the flow into thin fillets; he did not however have a correct picture of the global structure of the flow around a body. Borda in 1766 showed that the principle of live forces implied the vanishing of the drag and should thus be inapplicable to the problem. After having at first refused the possibility of a vanishing drag, d'Alembert in 1768 established the paradox, but only for bodies with a head-tail symmetry. A full understanding of the paradox, as due to the neglect of viscous forces, had to wait until the work of Saint-Venant in 1846.Comment: 10 pages, 4 figures, Physica D, in pres

Plant breeder's toolbox through history

More than ten thousand years ago people began to cultivate the land and grow different plants. Thus they did not need to wander around to hunt and collect their food. That was the time when plant breeding history began. Wild plants were adapted to become crops when humans began to pick and sow the seeds from the plants with the best properties. They chose plants with for example many seeds that remained long on the plant and thus gave them a lot of food. Through thousands of years, it was in this way that plants bred in agriculture have provided the foundation on which today's plant breeding is based. This method can be called selection breeding, since the selection of properties had not occurred naturally without human intervention. Since then, the plant breeding has evolved to include more advanced tools to modify and combine plant genomes to achieve improved properties of crops for adaptation to human agriculture and quality needs

Paratextes polémiques : la première défense d’Arlequin en Allemagne au XVIIIe siècle

Face au projet normatif de réforme de la comédie littéraire allemande entrepris dès 1725 par J. C. Gottsched, J. C. Krüger propose dans les préfaces à ses traductions de comédies de Marivaux (1747-1749) une voie qui s’avérera fructueuse. En introduisant dans la discussion esthétique allemande le masque d’Arlequin, rénové par Marivaux, comme reflet de la condition humaine, il prône, d’une part, la prise en considération de la sensibilité dans la comédie littéraire et, d’autre part, un nouveau jeu du comédien. Par delà sa propre insertion comme auteur dramatique, acteur et traducteur dans l’espace littéraire allemand, Krüger livre au spectateur allemand des éléments fondamentaux pour former son jugement esthétique.In response to the project of normative reform undertaken within German theatre in 1725 by J.C. Gottsched, J.C. Krüger proposes a promising avenue in his prefaces to the translations of Marivaux's (1747-1749) comedies. By introducing the Harlequin's mask, renewed by Marivaux as a reflection of the human condition, to the discussion on German esthetics, he advocates, on the one hand, the inclusion of sensitivity in literary comedy and on the other hand, a new acting style. Beyond his own importance within German literature as a dramatic author, actor and translator, Krüger delivers to the German spectator the fundamental elements allowing him to further hone his own esthetic judgment

Sexuality, Bodily Experiences and Gender: an Ethnographic Study among People Living with HIV in the Metropolitan Area of Buenos Aires, Argentina

Objectives: To discuss both security and protection approaches related to sexual behavior before HIV emerged as a social problem, as well as to discuss the categories of social construction and hegemony under the imperative of inquiring into gender inequalities

Characterizing an Alternative Chloroplast Outer Membrane Targeting Signal in Arabidopsis thaliana

Chloroplasts are organelles that are unique to plant and algal cells and are the site of photosynthesis. Though chloroplasts contain their own genome, an estimated 95% of chloroplast proteins are encoded in the nucleus, and therefore rely on post-translational targeting to the organelle. The majority of known chloroplast proteins are targeted to the chloroplast interior by cleavable signals at the N-terminal end of preproteins known as transit peptides. The translocon at the outer envelope membrane of chloroplasts (Toc) is a multimeric complex that recognizes and binds N-terminal transit peptides at the cytosolic surface of chloroplasts. Though transit peptides are necessary and sufficient for guiding nuclear-encoded preproteins into the chloroplast interior, the nature of sequence information of transit peptides is not fully understood due to their high divergence in length and composition. Over the last nine years, the number of proteins known or predicted to reside in the chloroplast outer envelope membrane of Arabidopsis has tripled to one hundred and seventeen. Although the functions for some of these outer envelope proteins (OEPs) have been characterized, the precise mechanism of their targeting to the chloroplast outer membrane has not been fully elucidated. Besides Toc75, the targeting mechanisms used by OEPs that have been characterized do not involve an N-terminal transit peptide. The bioinformatics tool ChloroP can be used to predict if amino acid sequences contain an N-terminal transit peptide. Recently, ChloroP analysis and protoplast transient expression assays were used to identify a novel chloroplast targeting signal in the C-terminus of the chloroplast preprotein receptor Toc159 in Bienertia sinuspersici (Lung and Chuong, 2012). Toc159 was also shown to lack a canonical transmembrane domain typically present in OEPs. While the unique C-terminal targeting sequence has been partially characterized in Toc159 (Lung et al., 2014), it left open the question of whether this type of signal is unique to Toc159, or if it is used by other OEPs as well. In the current study, to determine if other OEPs use this novel targeting pathway, ChloroP analysis identified eight potential candidates possessing the putative C-terminal targeting signal in Arabidopsis. Transient protoplast expression assays have been performed on OEP18, the protein predicted with the highest ChloroP score, to determine its subcellular localization and the sequences required for its targeting to chloroplasts. The primary purpose of the current study was to establish whether chloroplast outer membrane proteins other than Toc159 use a similar C-terminal targeting signal. Overall, the data in this thesis suggest that some OEPs other than Toc159, such as OEP18, may use this novel targeting pathway

Multiple representations in calorimetry

The purpose of this study is to explore the use of multiple representational modes as a tool for understanding the concepts of temperature and energy transfer in calorimetry. The focus is placed on which type of representation promotes students\u27 understanding of these concepts, and which representation(s) facilitates translations to other types. This study considers verbal, mathematical, and graphical representations. The statistical analysis of a problem set completed by 111 a freshmen college chemistry students and a semi structured interview on one-to-one basis to 23 students, is used to diagnose students\u27 understanding of calorimetry and the use of representations. Based on these results a model for conceptual understanding is proposed

Meetnet functievervulling bos: eerste resultaten beschikbaar

De statistieken van vroeger zijn de meetnetten van nu. Meetnetten meten en moeten liefst de gegevens aanleveren om beleidsprestaties en ¿effecten te monitoren. Met de resultaten kan nieuw beleid worden ontwikkeld en bestaand beleid geëvalueerd. Vorig jaar is een nieuw meetnet gestart, het Meetnet Functievervulling Bos (MFV-bos). De eerste resultaten zijn onlangs beschikbaar gekomen. Deze bijdrage bevat een korte uitleg over de achtergrond van het MFV-bos en enkele in het oog springende resultate

Metallic Strip Gratings in the Sub-Subwavelength Regime

Metallic strip gratings (MSG) have different applications, ranging from printed circuits to filters in microwave domains. When they are under the influence of an electromagnetic field, evanescent and/or abnormal modes appear in the region between the traces, their utilization leading to the development of new electromagnetic nondestructive evaluation methods. This paper studies the behavior of MSGs in the sub-subwavelength regime when they are excited with TEz or TMz polarized plane waves and the slits are filled with different dielectrics. The appearance of propagating, evanescent and abnormal modes is emphasized using an electromagnetic sensor with metamaterials lens realized with two conical Swiss rolls, which allows the extraction of the information carried by the guided evanescent waves. The evanescent waves, manipulated by the electromagnetic sensor with metamaterial lenses, improve the electromagnetic images so that a better spatial resolution is obtained, exceeding the limit imposed by diffraction. Their theoretical and experimental confirmation opens the perspective for development of new types of sensors working in radio and microwave frequencies