A simple multiaxial fatigue criterion for metals

A new simple multiaxial high-cycle fatigue endurance criterion, suitable for situations where the convex hull associated with the stress path approximates well an ellipsoid, is proposed. It considers, as measures of fatigue solicitation: (i) a new definition for the equivalent shear stress amplitude; and (ii) the maximum principal stress along the stress history. Assessment of the resulting criterion for a wide range of in-phase and out-phase cyclic loads shows that it compares very well with experimental data published in the literature. To cite this article: C.A. Gonçalves et al., C. R. Mecanique 332 (2004).

Résumé

On propose un critère simple d'endurance à la fatigue polycyclique, applicable à des situations pour lesquelles l'envelope convexe associé à l'histoire des contraintes s'approche bien d'une ellipse. Le critère considère, comme mesures de solicitation à la fatigue : (i) une nouvelle définition de l'amplitude de contrainte de cisaillement ; et (ii) la contrainte principale maximale au cours de l'histoire de chargement. Pour citer cet article : C.A. Gonçalves et al., C. R. Mecanique 332 (2004).     

8-hydroxyquinoline monomer, water adducts, and dimer. Environmental influences on structure, spectroscopic properties, and relative stability of cis and trans conformers

The low fluorescence quantum yield of 8-hydroxyquinoline cannot be correctly interpreted without knowing the form that such a compound assumes in different environments. The commonly accepted emission-quenching excited-state proton transfer can follow different reaction paths if 8-hydroxyquinoline is dimeric or monomeric or if it exists in the form of cis and trans conformers; in this light, the knowledge of the compound form in a particular environment is basic. We have performed a spectroscopic and computational investigation aimed at the determination of the form of 8-hydroxyquinoline in different solvents. UV-vis, fluorescence, and IR spectral features have been assigned by ab initio computations based on the density functional theory and time-dependent density functional theory; the density functional theory and MP2 computations have been applied to the determination of the relative stability of the dimeric and monomeric cis and trans forms of 8-hydroxyquinoline in different solvents. Molecular dynamics computations have been used to determine the compound behavior in water solutions. According to our results, 8-hydroxyquinoline shows a clear preference for the cis conformation (as dimer or monomer), but, in water solutions, a small fraction of the trans conformation is also present.     

C<Subscript>6</Subscript> dispersion coefficients from reduced dipole pseudospectra

A recently proposed interpolation tech- nique for FDPs is extended to cover static pseudospectra of monomers as well. Reduced 4-term dipole pseudospectra are obtained for the ground states of H, He, , LiH, BeH₂, BH, giving dispersion constants from which highly accurate C₆ dispersion coefficients for all homo- and hetero-dimers are obtained by use of the generalized London formula. Contribution to the Fernando Bernardi Memorial Issue.     

A Simple Route to New Cyclic (Chloroalkyl)phosphane‐, Diphosphane‐, and Aminophosphane Derivatives

The reaction between benzothiadiphosphole and, in sequence, a bis‐Grignard and a chloroalkyl Grignard reagent has been reported. It produced, after treatment of the crude reaction mixture with elemental sulfur, new chloroalkyl cyclic tertiary phosphane sulfides. These compounds have been successfully employed as precursors of new nonsymmetric phosphoamino and diphosphano derivatives.     

Total Syntheses of Casuarine and Its 6‐O‐α‐Glucoside: Complementary Inhibition towards Glycoside Hydrolases of the GH31 and GH37 Families

Selective glucosylation : Total synthesis of naturally occurring casuarine ( 1 ) and the first total synthesis of casuarine 6‐O‐α‐glucoside ( 2 ) were achieved through complete stereoselective nitrone cycloaddition, Tamao–Fleming oxidation and selective α‐glucosylation as key steps. Biological assays of the two compounds proved their strong and selective inhibitory properties towards glucoamylase NtMGAM and trehalase Tre37A, respectively, which place them among the most powerful inhibitors of these enzymes.

     

Analysis of Optical Erasure Efficiency in WDM-PONs Employing Carrier Remodulation

This paper proposes a method to monitor the operation performance of reflective semiconductor optical amplifier (RSOA)-based optical network units (ONUs) in wavelength-reuse wavelength-division-multiplexing passive optical network topologies. For this goal, the optical erasure efficiency of ONU RSOA is numerically evaluated through remote measurements at the optical line terminal site, using the VPI Transmission Maker software. The results show good correlation with the optical erasure behavior of RSOA in the injection power range of –20 to –5 dB, bias current of 50 and 150 mA, and confinement factor of 0.2 and 0.3. As a consequence, this method can be used to qualitatively estimate the optical and electrical features of ONU RSOA from the central office, instead of performing a local direct measurement.     

From concepts to algorithms for the treatment of large amplitude internal motions and unimolecular reactions

The formalism of the large amplitude path Hamiltonian provides a theoretical framework for the study of dynamical problems ranging from anharmonic vibrations to unimolecular reactions. A hierarchy of models at different degrees of sophistication can be elaborated and some of them have been put into practical use through the development of the DiNa package. The simplest level requires just the characterization of all the stationary points encountered along a large amplitude path and their quadratic environments. Perturbation theory can next be used to analyze the role of anharmonicity in the vibrational modulation of physico-chemical observables for semirigid systems. An extension of the same approach to saddle points allows the computation of reliable reaction rates taking into account curvature and tunneling effects. Finally, full characterization of the harmonic valley surrounding the path allows study of vibrational modulation in flexible systems and energy flow between different degrees of freedom during chemical reactions.     

Lipid phosphate phosphatases dimerise,but this interaction is not required for <Emphasis Type="Italic">in vivo</Emphasis> activity

Background  

Lipid phosphate phosphatases (LPPs) are integral membrane proteins believed to dephosphorylate bioactive lipid messengers, so modifying or attenuating their activities. Wunen, a Drosophila LPP homologue, has been shown to play a pivotal role in primordial germ cell (PGC) migration and survival during embryogenesis. It has been hypothesised that LPPs may form oligomeric complexes, and may even function as hexamers. We were interested in exploring this possibility, to confirm whether LPPs can oligomerise, and if they do, whether oligomerisation is required for either in vitroor in vivoactivity.     

Assignment of the molecular absolute configuration through the ab initio Hartree-Fock calculation of the optical rotation: can the circular dichroism data help in reducing basis set requirements?

In this paper the calculation of the optical rotation (OR) of some rigid organic molecules, using the Hartree-Fock method with small (6-31G, DZP) basis sets, has been studied thoroughly to carefully evaluate the scope and limitations of this method, previously introduced by other authors. Calculations on test molecules (compounds 1-13) together with a careful analysis of their CD spectra allow a simple criterion for the reliability of this approach to be formulated: for unsaturated and/or aromatic (i.e., absorbing in the near-UV region) molecules, if the [alpha](D) is quantitatively determined by the lowest energy Cotton effect (at wavelengths >220 nm), then the HF/6-31G result is reliable. The usefulness of this method for the experimental organic chemist has been further demonstrated because the OR (sign and order of magnitude) of compounds 14-19 (i.e., large molecules having considerable interest in organic chemistry), which fulfill the above criterion and for which an extended basis set treatment is not feasible owing to their size, is correctly predicted.