The present study focuses on two aspects of heavy metals and radionuclide fluxes to lake Annecy: a long term. secular evolution by analysing dated sediment cores, and a short term, seasonal evolution through the analysis of settling particles collected by sediment traps. Compared to background values prior to 1900, sediment cores reveal a two-fold (Cd, Cu, Zn) to a four-fold (Pb) increase in heavy metal concentration after the 40s, and a smaller decrease after the 70s except for Cu, which does not decrease. Sediment traps moored from April 1998 to November 2000 record strong variations of particles (range: 0.5 - 6.1 g m(-2) d(-1)), organic matter (range 0.03 - 0.27 g m(-2) d(-1)) and carbonate fluxes (range: 0.2 - 4.9 g m(-2) d(-1)). The maximum fluxes are observed at the end of spring and summer, related to increased phytoplankton production. Mean annual heavy metal fluxes (0.014 mug.cm(-2).y(-1) for Cd, 1 mug.cm(-2). y(-1) for Ph and Cu and 2.8 mug.cm(-2).y(-1) for Zn) are lower than those recorded in the surface layers of the sediment cores. No relation has been observed between fluxes of heavy metal and of particles. Comparison of heavy metal fluxes in Lake Annecy with two other peri-alpine lakes show that this lake receive more Cu and Ph of anthropogenic origin, in spite of the sewage collector built around the lake.
This paper refers to the characterization of plane masonry behaviour under the assumption of plane stress. Masonry may be seen as a two-phase (bricks and mortar) periodic anisotropic material with complex macroscopic behaviour due to the possible occurrence of cracking in each of the phases. Non-linear constitutive equations have thus to be used in order to realistically represent masonry structures. Most existing macroscopic models defined for such materials are by essence phenomenological. This leads to weakly motivated frameworks and rather complex models, especially if one wants to account for material symmetry evolution due to cracking. The aim of this paper is to identify a simple set of damage mechanics variables for the constituents that could be used in homogenization procedures to infer the overall behaviour of the material from its mesostructural features (geometrical arrangement and mechanical properties of the constituents). Based on unit cell computations, it is shown that scalar damage mesomodels allow to obtain realistic damage patterns encountered in experiments. Results suggest that at the meso-scale, it is possible to use a scalar damage model for the individual phases which naturally leads to the desired anisotropy evolution into the macroscopic descriptions. This macroscopic anisotropy evolution is illustrated using a numerical homogenization procedure to identify the degraded stiffness associated to damage patterns. The influence of variations in the constituent characteristics is also correctly captured as illustrated for some of the loading schemes.
The temperature dependence of the relaxation rates in YbCl 3 .6H 2 O up to 45 K can be explained by the Raman pro cess if phonon dispersion is considered. The analysis of the measured Mossbauer spectra has been performed by means of the field up-down model. It is pointed out that there are found "dispersionlike" terms in the spectra in addition to the usual Lorentzians.
The electric quadrupole and magnetic hyperfine interactions rneasured from the 161Dy Mössbauer resonance in crystalline Dy(OH)3 and from the 166Er resonance in crystalline Ho(OH)3 and Er(OH)3 are interpreted using the crystal field and molecular exchange field model . The crystal field parameters established from previous optical spectroscopy results account weIl for these hyperfine parameters. The crystal-field and magnetic properties of these ferromagnetic insulators are described weIl within the model.
For superparamagnetic particles the consideration of the precession of magnetization vector leads to the asymmetry and broadening of lines.
The temperature dependence of the zero field Mössbauer spectrum of [ϕ4As]2 [Fe(N3)5] il has been determined over the range 300 K to 1.60 K and exhibits the effects of paramagnetic relaxation broadening and magnetic hyperfine splitting (Hn ~ 486 kG à 4,2 K) at low temperatures corresponding to a negative zero field splitting, D ~ -1 cm-l. These results are consistent with the isolated trigonal bipyramidal Fe(N3)52- anion known to be present in this compound and slow spin-spin relaxation between highly separated (11 Å or greater) metal centers. D<0 is further confirmed in a novel temperature dependence of the magnetic moment of the polycrystalline powder such that at very low temperatures (<10K) the powder behaves as an oriented single crystal species for which µ|| > µ⊥ with [Formula: see PDF file] at ~5 K. The X and Q band ESR spectra of the system over the range 300 to 3.6 K indicate a typical axial Fe3+ compound but with slight rhombicity of the local FeN5 coordination environment.
Mössbauer measurements have been done for 2% 57Fe at A site in NiCr2O4. Spectra in a finite temperature range around the distortion temperature have shown that the transition has the characteristics of the first order one, and that cubic regions and tetragonal regions coexist with strong interactions between them. From an anomalous spectrum at 4.2 K a plausible spin configuration for Fe2+ spins has been proposed.
Mössbauer relaxation measurements have been made on 170Yb3+ in DyAlO3, TbAlO3 and HoAlO3. In DyAlO3 and TbAlO3 between 30 K and TN and in HoAlO3 between 30 and 10K conventional temperature inde pendent spin-spin driven relaxation is observed. In HoAlO3 below 10K, the relaxation rate is tempe rature dependent. This behaviour is interpreted in terms of coupling between Yb3+ and the collective excitations of the two singlet level ground states of the Ho3+ ions.
Mossbauer spectra of 57 Fe in LaNi 1-x Fe x O 3 (x = 0.05, 0.1, 0.2) were measured from 2K to room temperature. Isomer shift and the distribution of hyperfine magnetic fields were obtained as a function of temperature. The value of the isomer shift (≈0.34 mm/s) is the characteristic one for the Fe 3+ ions, while the value of the hyperfine field (≈400 kOe) extrapolated to OK is rather smaller than the expected value for the high spin state Fe3+ ions. In the spe~imen with x = 0.05, the magnetic moments of iron ions seem to be frozen in a random manner at low temperatures.
We present here a new ultrasonic diagnosis technique in natural, porous rocks. This method, based on the ultrasonic velocity changes, allows us to measure the transient spacial distribution of two liquids (water and oil) in a sandstone.
We present measurements of ul t rasonic damping and veloci ty, carried out in the Smectic A and Smectic C phases of te rephtha l -b is -p-p ' -buty lani l ine (TBBA), showing that conventional hydrodynamics does not apply in the smectic-phases of l iqu idc rys t a l s . The Smectic A and Smectic C phases of l iquid c rys ta l s consist of equidistant fluid layers stacked one on top of the other (cf. f ig . 1 ) . These phases thus present a solid type s t ructure in the direct ion which i s perpendicular to the layers , and are considered to be the prototypes of one-dimensional so l ids . Fig. 1 Schematic representation of the Smectic A (1-a) and Smectic C (1-b) phases, and of the layer-undulation mode (1-c) , which i s the principal deformation of the smectic phases. In the Smectic A phase, the molecules (the direct ion of or ientat ion of which i s represented by the vector n) are pa ra l l e l to the normal to the layers , whereas in the smectic C phase, they are inclined at an angle <f in re la t ion to t h i s normal. This notion of one-dimensional order i s not, however, completely rigorous, since the LandauPeier ls calculat ion l\l predicts that posi t ion-f luctuat ions of the layers wil l prevent a perfect long-range order from becoming establ ished. This r e s u l t , suggesting that these are large-amplitude f luctuat ions , was long seen as nothing more than a mere s c i e n t i f i c cur ios i ty , and the theories applied used the well-established concepts of conventional systems, even though the va l id i ty of such concepts for smectic phases has never been proven. The influence of layer-f luctuat ions has been examined recently / 2 , 3 / . These new theories predict that such f luctuat ions do in fact play an essent ia l r o l e , and notably that they lead to v i scos i t i e s which, at low frequency f, diverge as 1/f, instead of remaining constant, as in conventional hydrodynamics. This behaviour, predicted by Hazenko, Ramaswamy and Toner Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990208 C2-34 COLLOQUE DE PHYSIQUE (MRT), is the result of a non-linear (anharmonic) coupling between the velocity field and the thermally excited layer-undulation modes / 3 / . A remarkable consequence of the l/f-type behaviour of the viscosities is the modification of the attenuation a of the ultrasound waves, which is thus written : where a is the conventional attenuation term and b/f that associated with the anharmonic effects. Measuring the attenuation of the ultrasound waves as a function of frequency therefore constitutes a direct means of testing the theory. It should be pointed out that terms a and b are dependent on the angle 0 between the direction of sound-propagation and the normal to the smectic layers. To be more precise the term b is written where K, is the constant associated with the undulation mode of the layers, and A, B, C, elastic constants of the compound, which can be determined from velocity measurements by the equation A characteristic example of the results obtained in the Smectic A phase of Terephthal-bis-pp'-Butylaniline (TBBA) is given in fig.2.
Dynamic properties of grain boundaries (GBs), as reviewed in the present report, include diffusion along stationary and migrating boundaries, various boundary diffusion-controlled solid-state processes and mechanism of GB migration. Applicability of different GB diffusivity measurement techniques, influence of diffusion direction and misorientation angle on diffusivity and extent of agreement between experimental results and theoretical computations have been discussed. Relevant features of discontinuous type of transformations pertaining to GB migration and diffusion have been highlighted. Diffusion data for stationary and migrating boundaries in Ni-In system are presented for a suitable comparison. Finally, a new mechanism has been proposed for the migration of GBs on the basis of some recent experimental results.
Self diffusion and diffusion of CO and Fe solutes, which diffuse interstitially in the bulk were measured in grain boundaries of a-Zr within a wide temperature range by the radiotracer technique. The main result is the extremely large difference of eight orders in magnitude in P = s6Dgb between fast solute and self diffusivity in the boundaries. This difference can only be explained by strong solute segregations together with very large solute grain boundary diffusion coefficients D,b, which are a t least four decades larger than grain boundary self diffusion coefficients in a-Zr. A vacancy mechanism cannot account any more for such a difference. It is therefore assumed that CO and Fe diffuse interstitially in a-Zr grain boundaries.
L'interaction d'une onde ultrasonore avec un systeme bi-couche constitue d'une plaque d'acier doux anisotrope et d'une couche de colle est etudie experimentalement et theoriquement. Les proprietes d'anisotropie de la plaque metallique sont demontres a partir des courbes de dispersion des vitesses des modes de Lamb d'ordre zero. L'amplitude des modes A0 et S0 est mesuree par analyse spectrale des signaux reflechis. Les variations d'amplitude de ces signaux en fonction du produit Fd (ou F est la frequence ultrasonore et d l'epaisseur de la plaque) sont analysees theoriquement et interpretes physiquement. Les resultats sont ensuite etendus au cas d'un systeme bi-couche constitue par une couche de colle deposee sur la plaque. L'influence de la couche de colle, non visible sur les courbes de dispersion, est mise en evidence sur l'amplitude des coefficients de reflexion.
R&um6 : Les modkles thermodynamiques classiques ne permettent pas une description rkaliste de la skgrkgation intergranulaire, car ils ne prennent pas en compte les diffkrences entre les caractkristiques CnergCtiques et gComCtriques des diffkrents sites effectifs de skgrCgation. Dans cet article, nous proposons un nouveau modele thermodynamique Cchappant B la critique prCcCdente et permettant de calculer la concentration intergranulaire en solute, en fonction de la structure de l'interface et de la tempkrature. On donne aussi une mCthode de calcul de la tension interfaciale en fonction de 1'Cnergie intergranulaire. Summary : Existent thermodynamic models do not allow a realistic description of segregation. The major reason for this is that classical models of segregation do not take into account the differences between the energetic and geometrical characteristics among the different effective segregation sites. In this paper we propose a new thermodynamical model which suppress mentioned problem and enables a determination of interface solute concentration depending on interface structure and temperat1xe.A method for calculation of grain boundary tension as a function of grain boundary energy is also described.
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. MODÉLISATION UNIDIMENSIONNELLE POUR LA DÉTECTION PAR ULTRASONS DES DÉFAUTS DANS UN MULTICOUCHE PÉRIODIQUE Ph. Gatignol
Par apport de charges, en qualité et quantité choisies, dans une résine il est possible de faire varier les caractéristiques acoustiques (atténuation, vitesses de propagation, masse volumique) du composite ainsi créé.L'étude de cette propriété nous permet d'envisager la fabrication de matériaux adaptés à la simulation des fonds marins.Abstract -Acoustic characteristics(attenuation,propagation velocities, density) of a polyester can be modified by filling it by inclusions(small elastic particles).This property is used to realize materials modeling ocean bottom properties. 1-INTRODUCTIONDans le but d'une transposition de l'étude de la propagation par petit fond dans une grande cuve océanique, il s'agit de réaliser des fonds synthétiques simulant le plus exactement possible les couches réelles des sous sols marins.En réalité, en mer, les fonds marins répondent à ce schéma type :
A broad goal of many few body physics experiments at intermediate energies is to identify shortcomings of our "conventional" descriptions based on nucleons, nucleon resonances and mesons. Fkom these shortcomings it is often hoped to glean some evidence for the contributions of quarks and gluons. In addition one establishes specific oals for particular reaction channels, which upon realization furthers the empiric3 understanding of that channel, and in some small way also contributes to the above broad goal. Studies of the set of reactions involving the n-NN system must take into account the fact that this system is composed of a coupled set of reactions and that what is learned from one channel improves our understanding of the other coupled channels.
