Presse et revues
88 pages
- Aller à la page de la table des matièresI
- SOMMAIRE/SUMMARY
- .......... Page(s) .......... III
- .......... Page(s) .......... 501
- Mécanique des solides et des structures/Mechanics of Solids and Structures
- Mécanique des fluides/Fluid Mechanics
- .......... Page(s) .......... 527
- .......... Page(s) .......... 537
- Chimie de l'état solide et cristallochimie/Solid state chemistry and crystal chemistry
- Chronique de la Chimie/History of Chemistry
- .......... Page(s) .......... 555
- .......... Page(s) .......... 559
- Étoiles/Stars
- CONTENTS
- Mechanics of Solids and Structures
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- The mechanical behaviour of fabrics is studied using biaxial tensile tests. A mechanism prescribes strains to cross specimens with different relations between weft and warp directions. This experiment is well suited to fabrics accounting for their lack of shear stiffness. It allows us to appreciate the influence of the weaving geometry on the global fabric behaviour. The geometrical non-linearities at the mesh level induced by the undulation variations lead to a non-linearity of behaviour of the fabric. This phenomenon is basically biaxial accounting for the interactions ofwarp and weft yarns. The test procedure is detailed, especially optical measurement of the strains and the initial state definition. A macroscopic model is proposed, identified and validated from experimental data.
- Fluid Mechanics
- The spreading rate of supersonic mixing layers decreases rapidly with compressibility. This paper presents a study of a passive enhancement mixing rate device applied to a 0.71 convective Mach number twodimensional mixing layer. The apparatus basically of consists a different design for the geometry of the separative plate trailing edge in order to produce streamwise vortices which increase the mixing. An estimation oft he energy losses and of the mixing efficiency has been established.
- We propose and study a new criterion based on the vorticity field properties, in order to define and characterize more precisely vortices (organized structures) in two-dimensional incompressible flows. This criterion is compared with the Weiss criterion. Analytical derivations and numerical studies bring more insight into dissipation processes and axisymmetrization of elliptical vortex structures.
- Gas, plasmas
- We report here a rotational temperature measurement on OH (A, v = 0). levels. This spectroscopic study is realized on the OH (A - X) transition. The plasma is generated by a non-conventional Very High Voltage (VHV) triggered Dielectric Barrier Discharge (DBD) in argon-water vapour atmospheric mixture. The rotational temperature ofthese levels has been estimated at a very low value (
300 K). A comparison with a synthetical spectrum shows a good agreement.
- Solid state chemistry and crystal chemistry
- The octahedral hexazirconium compound has been structurally characterized by a combined analysis of single-crystal X-ray and time-of-flight (TOF) neutron diffraction data. The space group is tetragonal, I41/a,Z = 8, with lattice constants at 123 K of a = 32.957 (8), c = 15.001 (3) A, V = 16, 294(6)A3. Difference Fourier maps based on the neutron data exhibited negative troughs on the triangular faces of the hexazirconium octahedron which were introduced into the structure as hydrogen atoms. Refinement of the atomic positional and occupancy parameters for the hydrogen atoms resulted in about 0.7 H atoms on each triangular face for a total of 5.47(15) hydrogen atoms per hexazirconium cluster, in good accord with the 1H NMR measurement (5.0) and the theoretical expectation of 5. The Zr - (3H) distances range from 1.8 to 2.1 A.
- is obtained by hydrothermal synthesis using 1,4-diaminobutane as a template. Its structure is related to the ULM-3 type fluorometallophosphates: it is built up from corner-linked units composed of three (PO4) tetrahedra, two (AlO4F) trigonal bipyramids and one (AlO4F2) octahedron. The subnetwork of the 1, 4-diammoniumbutane cations induces a non-centric symmetry. Crystal data: orthorhombic, space group Pbc21, a = 10.023(2)A, b = 18.180(3)A, c = 15.841(3)A, V=2,886.5A3, Z = 8, R(F) = 2.84%, 4,263 observed reflections
- History of Chemistry
- .......... Page(s) .......... 555
- It is recalled that the discovery of artificial radioactivity, allowing the production of a huge number of radioelements, has led to the rapid expansion of the method of radioactive tracers. The method has very important applications in chemistry, industry, biology and medicine.
- Stars
- .......... Page(s) .......... 561
- The paper includes a qualitative study of the N-dimensional (N = 1, 2, 3) Lane-Emden équation, written as a two-dimensional autonomous nonlinear system of ordinary differential equations by using Milne's homological invariant variables. The discussion is made for both positive and negative polytropic indices. At the end, we survey the type of orbits that appear in phase portrait of the system for each value of N and various polytropic indices.
- COMPTES RENDUS DE L'ACADÉMIE DES SCIENCES
- .......... Page(s) .......... III-V
- Mécanique des solides et des structures
- .......... Page(s) .......... 503
- Mécanique des fluides
- Gaz, plasmas
- Chimie de l'état solide et cristallochimie
- Chronique de la Chimie
- .......... Page(s) .......... 555
- .......... Page(s) .......... 559
- Étoiles
- .......... Page(s) .......... 561
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