NMR spectroscopy applied to the Cultural Heritage: a preliminary study on ancient wood characterisation

High and low resolution solid state NMR methods have been applied to characterise a few samples of ancient wood. In an ancient larch wood sample, by applying ¹H low resolution NMR methods as a function of the temperature, the average pore size and its distribution have been determined. In addition, high resolution NMR techniques have allowed addressing of the question of the proximity of water pools to cellulose and lignin. In particular, a model can be hypothesized in which water pools are surrounded by thin layers of amorphous cellulose and/or lignin while the crystalline domains of cellulose surround the layers of amorphous cellulose. Preliminary results obtained using a fully non invasive and portable NMR unilateral relaxometer, the Eureka-Mouse10 (EM10), are reported. This instrumentation is shown to be perfectly suitable for characterizing degradation in ancient wood samples. PACS 76.60 k     

Degradation of historical paper: nondestructive analysis by the NMR-MOUSE

The NMR-MOUSE is a mobile sensor for single-sided NMR inspection of organic materials which takes advantage of the principles of magnetic resonance and inside-out-NMR. Historical books dating from the 17th century were measured at different points by positioning the NMR-MOUSE on the paper. Different degrees of paper degradation can be discriminated from the regularized inverse Laplace transform of the envelope of the acquired echo signals. For the first time the degradation of historical paper was characterized entirely nondestructively by NMR. As a contribution to current preservation efforts, NMR shows great promise for future use in damage assessment of historical documents.     

"Oscillating" metallocene catalysts: what stops the oscillation?

The 150 MHz (13)C NMR microstructural analysis of polypropylene samples produced with two representative "oscillating" metallocene catalysts of largely different steric hindrance, namely [(2-(3,5-di-tert-butyl-4-methoxyphenyl)indenyl)(2)ZrP](+) and [(2-phenylindenyl)(2)ZrP](+) (P = polymeryl), and the implications on the origin of the stereocontrol are presented and discussed in detail. The original mechanistic proposal of an "oscillation" between a rac-like (isotactic-selective) and a meso-like (nonstereoselective) conformation cannot explain the observed polymer configuration. The isotactic-stereoblock nature of the polymers obtained with the former catalyst proves unambiguously that the active cation "oscillates" between the two enantiomorphous rac-like conformations at an average frequency that, even at high propene concentration, is only slightly lower than that of monomer insertion. The less-hindered [(2-phenylindenyl)(2)ZrP](+) gives instead a largely stereoirregular polypropylene, which is the logical consequence of a faster ligand rotation; however, depending on the use conditions (in particular, on the nature of the cocatalyst and the polarity of the solvent), the polymerization products may also contain appreciable amounts of a fairly isotactic fraction. The peculiar microstructure of this fraction, with isotactic blocks of the same relative configuration spanned by very short atactic ones, rules out the possibility that the latter are due to an active species in meso-like conformation and points rather to a conformationally "locked" rac-like species with restricted ring mobility. The hypothesis of a stereorigidity induced by the proximity to a counteranion, which would play the role of the interannular bridge in the rac-bis(indenyl) ansa-metallocenes, was tested by computer modeling on a [rac-(2-phenylindenyl)(2)ZrMe(C(3)H(6))][B(C(6)F(5))(4)] ion couple and found viable.     

Novel microscopic mechanism of intermixing during growth on soft metallic substrates

Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands.     

Trasporti rigidi di vettori,e geometria della retta

Sunto. Si risolve completamente una questione posta da Pia Nalli a fondamento dello studio di certi notevoli trasporti rigidi di vettori (e da lei trattata soltanto in alcuni casi particolari), collegandola alla teoria proiettivo-differenziale delle superficie rigate di un iperspazio. Lavoro eseguito nel Seminario Matematico dell'Università di Bologna, comunicato nel settembre 1948 al III Congresso dell'Unione Matematica Italiana.