Overview of Identification Methods of Mechanical Parameters Based on Full-field Measurements

This article reviews recently developed methods for constitutive parameter identification based on kinematic full-field measurements, namely the finite element model updating method (FEMU), the constitutive equation gap method (CEGM), the virtual fields method (VFM), the equilibrium gap method (EGM) and the reciprocity gap method (RGM). Their formulation and underlying principles are presented and discussed. These identification techniques are then applied to full-field experimental data obtained on four different experiments, namely (i) a tensile test, (ii) the Brazilian test, (iii) a shear-flexural test, and (iv) a biaxial test. Test (iv) features a non-uniform damage field, and hence non-uniform equivalent elastic properties, while tests (i), (ii) and (iii) deal with the identification of uniform anisotropic elastic properties. Tests (ii), (iii) and (iv) involve non-uniform strain fields in the region of interest. Working group “Identification” of the French CNRS research network (GDR 2519) “Mesures de champs et identification en Mécanique des Solides / Full-field Measurements and Identification in Solid Mechanics”.     

Kinetic performance and energy profile in a roller coaster electron transfer chain: a study of modified tetraheme-reaction center constructs

In many electron-transfer proteins, the arrangement of cofactors implies a succession of uphill and downhill steps. The kinetic implications of such arrangements are examined in the present work, based on a study of chimeric photosynthetic reaction centers obtained by expressing the tetraheme subunit from Blastochloris viridis in another purple bacterium, Rubrivivax gelatinosus. Site-directed mutations of the environment of heme c559, which is the immediate electron donor to the primary donor P, induced modifications of this heme's midpoint potential over a range of 400 mV. This resulted in shifts of the apparent midpoint potentials of the neighboring carriers, yielding estimates of the interactions between redox centers. At both extremities of the explored range, the energy profile of the electron-transfer chain presented an additional uphill step, either downstream or upstream from c559. These modifications caused conspicuous changes of the electron-transfer rate across the tetraheme subunit, which became approximately 100-fold slower in the mutants where the midpoint potential of c559 was lowest. A theoretical analysis of the kinetics is presented, predicting a displacement of the rate-limiting step when lowering the potential of c559. A reasonable agreement with the data was obtained when combining this treatment with the rates predicted by electron transfer theory for the individual rate constants.     

Intrachain electron transfer in conducting oligomers and polymers: the mixed valence approach

Organic mixed valence compounds consisting of bisdiarylamino charge-bearing units with an oligothiophene bridge and oligothiophene radical cations have been compared using molecular modeling. The study has been performed with oligomers of 1 to 22 thiophene units. These two series of molecules have several properties in common, and intramolecular Single Electron Transfer (SET) in both series can be described within the same theoretical framework. Conducting oligomer radical cations and slightly doped conducting polymers appear as special cases of the vast ensemble of organic mixed valence compounds. Short oligomers are class III, whereas longer oligomers and conducting polymers are class II. Therefore, doped conducting polymers cannot be correctly modeled using oligomers with a short conjugation length. Experimental evidence extracted from the literature confirms these findings. Single electron transfer theories can thus be used when studying interchain and intrachain electron transfer in slightly doped conducting polymers and in materials consisting of short oligomers. This makes it possible to extract from the UV-vis-near-IR spectra the electron-transfer constant rate along or between the pi-conjugated chain. The main differences among inorganic, organic, and conducting oligomer or polymer mixed valence compounds lies in the H(ab) and lambda values associated with these different series. Inorganic mixed valence compounds have small H(ab) and lambda values; organic mixed valence compounds have large H(ab) and lambda values, whereas conducting oligomers and polymers have large H(ab) but small lambda values. This induces charge delocalization to occur for systems larger than those of inorganic and nitrogen-centered organic mixed valence compounds.     

Heterotopic helicand for designing heterometallic helicates

A new diazine tetratopic helicand, H4L, is obtained from 3-formylsalicylic acid and hydrazine. The reaction between H4L and cobalt(II) perchlorate, iron(III) perchlorate, and sodium carbonate leads to triple-stranded tetranuclear anionic helicates, [L3Co(II)2Fe(III)2]2-, which are connected through Na ions, resulting in chiral coordination polymers, [L3Na2Fe2Co2(H2O)4(EtOH)2].3H2O.     

Electrolytic electrospray ionization mass spectrometry of quaterthiophene-bridged bisporphyrins: beyond the identification tool

Several quaterthiophene-bridged bisporphyrins were analyzed by electrospray ionization mass spectrometry (ESI-MS). The active centers of these molecular assemblies are two porphyrins moieties complexed (Z) or not (H) with a metal ion, typically Zn(2+), and the spacer is a quaterthiophene. The two end-groups were chemically linked to the quaterthiophene spacers by (i) a C--C single bond, (ii) a trans double bond or (iii) a triple bond. The formation of charged species either by protonation ([M + H](+) and [M + 2H](2+)) or electron(s) loss (M(+) and M(2+)), account for the occurrence of electrochemical processes in the basic operation of an electrospray source acting in a non-aqueous solvent. The nature of the observed charged species is correlated with the electro-oxidation properties and proton production by electro-oxidation of residual water. The occurence of these electrochemical reaction is proposed when the electroactivity of the electrosprayed substrates is not sufficient to support the current demand of the ESI source. In this way, the results obtained from the analysed series suggest the occurrence of such a process when the interfacial potential of the metal capillary reaches a value of 0.75 V vs Ag/AgCl. The results of theoretical calculations confirm the importance of the ionization energy with regard to the protonation energy in the course of the ionization reaction. The structural differences at the porphyrin-linker junctions lead to significantly smaller ionization energy in the case of the trans double bond. The MS observation of discharged dimers from molecular assemblies, including two complexed porphyrins ZZ or two free bases HH as end-group and a triple bond as the quaterthiophene-bisporphyrin junction, indicates together with molecular modelling (carried out at the semi-empirical PM3 level), that the planar and symmetric structures favour stacking.     

Preparations and characterizations of bichromophoric systems composed of a ruthenium polypyridine complex connected to a difluoroborazaindacene or a zinc phthalocyanine chromophore

This paper describes the synthesis of a new series of molecules composed of a ruthenium cation liganded by a chloro or a thiocyanato, a 4,4'-(diethoxycarbonyl)-2,2'-bipyridine, and a 2,2':6',2' '-terpyridine substituted in its 4' position by a difluoroborazaindacene or a zinc phthalocyanine. A set of conditions are reported to conveniently synthesize these dyads by a Stille cross-coupling reaction between the trimethyltin derivative of the organic chromophore and the corresponding ruthenium complex with 4'-bromo-2,2':6',2' '-terpyridine and 4,4'-(diethoxycarbonyl)-2,2'-bipyridine. The dyads were studied by UV-visible absorption spectroscopy, steady-state fluorescence, and electrochemistry. The results of these studies indicate strong electronic coupling between the zinc phthalocyanine unit and the ruthenium complex but weakly electronically coupled systems in the case of dyads containing a difluoroborazaindacene unit. The new bichromophoric systems display strong absorbance in the visible spectrum. An efficient quenching of the fluorescence of the organic chromophore by the nearby ruthenium complex was also observed in all of the dyads. In dyads connected to the borazaindacene, excitation spectra indicate efficient photoinduced energy transfer from the borazaindacene to the ruthenium complex.     

Multidimensional gas chromatography for the detailed PIONA analysis of heavy naphtha: hyphenation of an olefin trap to comprehensive two-dimensional gas chromatography

A multidimensional method providing the composition of a heavy naphtha in paraffins, isoparaffins, olefins, naphthenes, and aromatics (PIONA) in the C8-C14 range is presented. The analytical set-up consists in a silver modified silica olefin trap on-line coupled to comprehensive two-dimensional gas chromatography (GC x GC). In this configuration, hydrocarbons are separated, in gaseous state, in two fractions, saturate and unsaturate, each fraction being subsequently analysed by GC or by GC x GC. The resolution between saturates and olefins was found to be improved compared to a single GC x GC run. The characterisation of the olefin trap highlights the benefits and the limits related to the use of that stationary phase as a double bond selective fractionation medium.     

Sulfide oxidation by hydrogen peroxide catalyzed by iron complexes: two metal centers are better than one

Peroxoiron species have been proposed to be involved in catalytic cycles of iron-dependent oxygenases and in some cases as the active intermediates during oxygen-transfer reactions. The catalytic properties of a mononuclear iron complex, [Fe(II)(pb)(2)(CH(3)CN)(2)] (pb=(-)4,5-pinene-2,2'-bipyridine), have been compared to those of its related dinuclear analogue. Each system generates specific peroxo adducts, which are responsible for the oxidation of sulfides to sulfoxides. The dinuclear catalyst was found to be more reactive and (enantio)selective than its mononuclear counterpart, suggesting that a second metal site affords specific advantages for stereoselective catalysis. These results might help for the design of future enantioselective iron catalysts.     

Backward stochastic differential equations on manifolds II

In [1], we have studied a generalization of the problem of finding a martingale on a manifold whose terminal value is known. This article completes the results obtained in the first article by providing uniqueness and existence theorems in a general framework (in particular if positive curvatures are allowed), still using differential geometry tools.     

On the Optical Diagnosis and Sizing of Spherical Coated and Multilayered Particles with phase-Doppler anemometry

After having recalled basic theoretical results concerning the extension of generalized Lorenz-Mie theory to the case of multilayered spheres, results connected with phase-Doppler anemometry are considered, showing the influence of Gaussian beam intensity profiles on the light scattering properties of these particles. Particular emphasis is placed on the case of water-coated carbon core particles, for which the possibility of obtaining simultaneous size measurements of the core and outer diameters is discussed. The sensitivity of the technique to particles with a refractive index profile is also considered, showing that this technique is more sensitive to changes in the average refractive index of the particles than to refractive index profiles, such as produced by high pressure and temperature stresses, at least for the studied geometry.