Thermoanalytical studies of imidazole-substituted coordination compounds

Four manganese(II) coordination compounds with bis(1-methylimidazol-2-yl)ketone (BIK) of general formula Mn(BIK)₂X₂ (X = Cl, Br, NO₃, ClO₄) were synthesized and characterized by elemental analysis, by UV–vis, and FTIR spectroscopies to be compared with the literature data. Following our previous thermoanalytical studies on imidazole-substituted coordination compounds, the thermal behavior of the synthesized Mn(II) complexes was investigated using TG and DTG techniques: the thermal profile is characterized by three substantial consecutive releasing steps for all the three complexes and the releasing supposed behavior is confirmed by EGA analysis performed by coupling the TG analyzer to an MS spectrometer. In particular, the first step is ascribed to the release of the two anions, followed by the loss of four methyl groups (side chains of the ligand) and two bridge-carbonyl groups. The residual tetra-imidazole manganese compound decomposes in a final step to give MnO as the final residue. Both the initial decomposition temperatures and the kinetic rate constants associated to the first decomposition step indicated a higher stability of the Mn(BIK)₂Cl₂ complex, the bromide complex being very close to the chloride one (first-step thermal stability: ClO₄ ⁻ <NO₃ ⁻ ≤Br⁻ <Cl⁻). Finally, the three-dimensional diffusion reaction model (D3) was selected to describe the first decomposition step for all the four complexes examined.     

Optimum Specimen Geometry for Accurate Tensile Testing of Superplastic Metallic Materials

The high temperatures and large strain limits associated with superplastic materials amplify the possibility of the tensile test outcomes being sensitive to the shape and size of the specimen geometry. In spite of that, the disparities in the specimen geometries used throughout the numerous efforts on characterising this unique class of materials are rather astonishing. There is an urge to evaluate the dependency of a superplastic tensile test on specimen geometry, before a much-needed universally-adopted standard specimen can be designed; which is the main objective of this comprehensive experimental investigation. More than 20 geometries, covering multiple variations in gauge length, gauge width, grip length and grip width values, are tested at identical conditions, and the corresponding material behaviour is compared in terms of deformation uniformity, material flow and the extracted stress/strain curves. The results reveal the influences of each geometrical parameter, as well as their combined effects, and guide the selection of an optimum specimen geometry for accurate and unified tensile testing of superplastic metallic materials.     

Hecke algebras associated with induced representationsLes algèbres de Hecke associées aux représentations induites

We define the Hecke von Neumann algebra $\text{L}\text{(G,H,σ)}$ associated with a group G, a subgroup H and a unitary representation σ of H. We show that when σ is finite dimensional, $\text{L}\text{(G,H,σ)}$ can be seen as a corner algebra of the tensor product of the group von Neumann algebra of a locally compact group and a matrix algebra. To cite this article: R. Curtis, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 31–35     

Long-term trend in CHF2Cl (HCFC-22) from high spectral resolution infrared solar absorption measurements and comparison with in situ measurements

The average tropospheric volume mixing ratio of CHF₂Cl (HCFC-22) has been retrieved from a time series of high spectral resolution ground-based infrared solar absorption spectra recorded with the McMath Fourier transform spectrometer located at the U.S. National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude) for the time period October 1987–November 2002. The retrievals are based on fits to the well-isolated, unresolved 2ν₆ Q branch at 829.05 cm⁻¹ and the SFIT2 retrieval algorithm. The measured daily averages show a near linear rise per year in the mean tropospheric volume mixing ratio as a function of time with a best fit yielding an average increase rate of (5.66±0.15) parts per trillion (10⁻¹²) by volume per year, corresponding to (6.47±0.17)%yr⁻¹, 1 sigma, at the beginning of the time series. The tropospheric mixing ratios retrieved from the solar spectra have been compared with monthly average surface flask sampling measurements from the Climate Monitoring and Diagnostic Laboratory (CMDL) station at Niwot Ridge, Colorado (40.0°N, 105.5°W, 3013 m altitude), archived measurement from the same location, and early CMDL northern hemisphere Pacific cruise measurements. The average ratio of the retrieved tropospheric mixing ratio relative to the CMDL surface mixing ratio is 1.053 for the overlapping 1987 to 2002 time period. The retrieved mean tropospheric mixing ratio is consistent with the surface measurements within the errors estimated for the remote sensing observations.     

Deforming subdivisions

Subdivisions are continuously deformed subject to three local conditions and shown to retain the global property of being a subdivision. Cell maps, which are introduced, enable elementary arguments.This research is supported in part by the National Science Foundation Grant DMS-8902662.     

Electron ionization-tandem mass spectrometry of glycosphingolipids. I: The identiftcation of compound-specific sequence ions in the collision-induced dissociation spectra of the immonium ions of two isomeric hexaglycosylceramides

A permethylated-reduced hexaglycosylceramide in a complex glycolipid mixture isolated from a unique human tissue has been identified by using tandem mass spectrometry (MS/MS). The mass spectrum of this glycolipid mixture, obtained by using in-beam electron ionization, is very complex, and fragment ions derived from the hexaglycosylceramide cannot be distinguished from other ions. Tandem mass spectrometry using a four-sector mass spectrometer gave the mass spectrum of the immonium ion of the permethylated-reduced hexaglycosykeramide (m / z 1645.8), which is characteristic of its structure. Comparison of this MS/MS spectrum with those of two similarly derivatized blood group hexaglycosylceramide isomers permitted identification of the unknown glycolipid structure.     

Homotopies for computation of fixed points on unbounded regions

Givenf: R ⁿ R ^n* with some conditions, our aim is to compute a fixed pointx f(x) off; hereR ⁿ isn-dimensional Euclidean space andR ^n* is the collection of nonempty subsets ofR ⁿ . A typical application of the algorithm can be motivated as follows: Beginning with the constant mapf ₀:R ⁿ {0} R ⁿ and its fixed pointx ₀ = 0, we deformf _t ast tof f and follow the pathx _t of fixed points off _t . Cluster points of thex _t 's ast are fixed points off. This research was supported in part by Army Research Office-Durham Contract DAHC-04-71-C-0041 and by National Science Foundation Grant GK-5695.