Synthesis and characterization of new 1,1′-diester,diketone, and dinitrile derivatives of 2,2′-biimidazole

Substituted 1,1′-diester, diketone and dinitrile derivatives are prepared from 2,2′-biimidazole. The reactions involved include: Michael addition with halogenated olefins; nucleophilic substitution with ketones, nitriles, and esters; and condensation with amines.     

Optical constants of HNO3/H2O and H2SO4/HNO3/H2O at low temperatures in the infrared region

The complex index of refraction of liquid HNO3/H2O and H2SO4/HNO3/H2O has been obtained at different temperatures and acid concentrations. FT-IR specular reflectance spectra were obtained for 30, 54, and 64 wt % aqueous HNO3 and for four different H2SO4/HNO3/H2O mixtures in the temperature region from 293 to 183 K. The complex index of refraction was obtained from the reflectance spectra with the Kramers-Kronig transformation. The optical constants of the binary and ternary mixtures vary with the acid concentration and the temperature. The results demonstrate that vibrational bands originating from the sulfate species are more sensitive to changes in temperature than the bands originating from vibrations in the nitrate species; only minor changes in the nitrate vibrational bands are observed as the temperature decreases below 248 K.     

Synthesis and x-ray characterization of the [Ir6(CO)15COEt]-Anionic Cluster

The reaction of Ir₆(CO)₁₆ with a mixture of CO, H₂, and ethylene yields the [Ir₆(CO)₁₅COEt]^- anion, which has been shown by X-ray diffraction to contain an octahedral iridium cluster bearing a —bonded acyl group; the arrangement of the 11 terminal and 4 edge-bridging carbonyl groups is different from that found in both the analogous rhodium complex and the parent Ir₆(CO)₁₆ carbonyl.     

Structural assignment of organotin hydrides containing the oxazoline ligand

A series of triorganotin hydrides and diorganotin dihydrides containing the optically active 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand have been characterized by means of the multinuclear low-temperature NMR investigations, the results of which are discussed. In the corresponding organotin hydrides values of the ¹J(¹H-^117/119Sn) couplings appeared to be temperature dependent, supporting an axial/equatorial position of the hydrogen attached to the tin.     

Analytical formulation of the Jacobian matrix for non-linear calculation of the forced response of turbine blade assemblies with wedge friction dampers

A fundamental issue in turbomachinery design is the dynamical stress assessment of turbine blades. In order to reduce stress peaks in the turbine blades at engine orders corresponding to blade natural frequencies, friction dampers are employed. Blade response calculation requires the solution of a set of non-linear equations originated by the introduction of friction damping.

Such a set of non-linear equations is solved using the iterative numerical Newton–Raphson method. However, calculation of the Jacobian matrix of the system using classical numerical finite difference schemes makes frequency domain solver prohibitively expensive for structures with many contact points. Large computation time results from the evaluation of partial derivatives of the non-linear equations with respect to the displacements.

In this work a methodology to compute efficiently the Jacobian matrix of a dynamic system having wedge dampers is presented. It is exact and completely analytical.

The proposed methods have been successfully applied to a real intermediate pressure turbine (IPT) blade under cyclic symmetry boundary conditions with underplatform wedge dampers. Its implementation showed to be very effective, and allowed to achieve relevant time savings without loss of precision.     

Quasi-free contributions in the6Li(d,tp)4He-reaction atE d =0.465 MeV

The⁶Li(d, tp)⁴He reaction was investigated at a bombarding energy ofE _d =0.465 MeV in a kinematically complete experiment. Evidence was found for a quasi-free reaction.     

Contribution to 14 MeV neutron activation analysis using half-lives between 0.55 and 873 milliseconds

A study of the possibility of using half-lives between 0.55 and 873 msec in activation analysis with 14 MeV neutrons is presented here. The cyclic counting method is used: irradiation and detection are repeated several times and counts are memorised during all successive cycles until good final statistics are reached. The theoretical aspect of the cyclic counting method and the influence of neutron pulse shape on the activation results are discussed. The sample is activated and its activity measured in the same geometry: the sample and the scintillation detector are placed close to the target of the neutron generator. An electronic gating system is used to avoid photomultiplier gain fluctuations involved in neutron bombardment. Detection limits are measured for the following elements: Be, B, Al, Ca, As, Zr, In, Tl, Pb, Bi. Work carried out at: Centre d'Etudes Nucleaires de Grenoble, France.