Generation of k-jets on toric varieties

The notion of a k-convex -support function for a toric variety is introduced. A criterion for a line bundle L to generate k-jets on X is given in terms of the k-convexity of the -support function . Equivalently L is proved to be k-jet ample if and only if the restriction to each invariant curve has degree at least k. Received October 22, 1997; in final form January 12, 1998     

Effects in B–doped KDP crystals irradiated with neutrons of large spectra energy

The results obtained for the r₆₃ electro‐optic coefficient of B‐doped and undoped KDP (KH₂PO₄) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta²⁰¹, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H₃BO₃, Na₂B₄O₇ and Li₂B₄O₇) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 10¹⁰ n/cm² s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lifetimes and transition probabilities of Xe II: Experimental measurements and theoretical calculations

In this work we make an experimental and theoretical investigation of transition probabilities (A) and lifetimes of Xe II. Eighteen A_ij's corresponding to the 6p-6d array were measured using a Laser Produced Plasma (LPP) as the spectroscopic source. The ab initio (AI) and Least Square Fitting (LSF) approaches were used to calculate the atomic parameters. Relativistic corrections and Configuration Interaction (CI) effects have been taken into account using the HFR approach described by Cowan. Whereas the AI parameters corresponding to 6p levels are not very affected by CI effects, several of the 6d levels with J=1/2, 3/2and 5/2 making transitions to the fundamental levels 5p⁵ are affected by CI effects due to both, discrete nd and continuum states, modifying their lifetimes values. An extensive comparison with other measurements and calculations are made. In particular, concerned with branching ratio and forbidden transitions. Received 15 July 1999     

Intercalation of tris-(2,2′-bipyridyl) ruthenium (II) in α- and γ-zirconium phosphate: synthesis, thermal behaviour and X-ray characterization

Intercalation compounds such as the ruthenium trisbipyridyl complex in inorganic layered ion-exchangers (α- and γ-zirconium phosphate) have been synthesized using the batch method. There is no loss of bipyridyl ligand from the metal ion during the exchange of the ruthenium trisbipyridyl complex in these host matrices. The materials obtained are thermally stable up to ~330 °C (γ-phase) or ~380 °C (α-phase). The complex decomposition occurs in one or more steps and at ~600 °C the complex decomposition is complete. The X-ray patterns of ruthenium materials show a new phase with an increase in the interlayer distance with respect to the initial phase. Microanalysis measurements confirm the fact that the ruthenium complex is not modified when exchanged and the complex decomposition depends on its position in the host matrices.     

Investigations by various analytical techniques to the correct classification of archaeological finds and delineation of technological features: Late Roman lamps from Egnatia: From imports to local production

Late Roman oil lamps from the archaeological site of Egnatia (Fasano, Brindisi, Italy) were characterized from physical–chemical, mineralogical and morphological points of view. Atomic Spectroscopy, Scanning Electron Microscopy and X-Ray Diffraction analyses were carried out on ceramic body and coatings with the aim of identifying the provenance of lamps, in order to arrive at a correct archaeological classification of finds and to outline their technological features.The analytical results show that the finds differ in raw materials and in production technology. The statistical multivariate treatment of compositional data of ceramic bodies groups the objects into two macro clusters and, according to a study of their different petrographic features and by a comparison with coeval pottery whose provenance is already known, suggests one group to have been imported from North Africa and the other to have been locally produced. Moreover, chemical results and in-depth archaeological analyses allow us to split the imported lamps into two subgroups, hypothesizing the first group to originate from central Tunisia and the second from the north of the same country.The analytical characterisation of finds, by different complementary techniques, has allowed us to identify the raw materials and the technological solutions used by the ancient potters from Egnatia to produce lamps. The potters made lamps which had an external appearance very similar to that of African prototypes, but which were nevertheless different as they employed the locally available materials.     

ATR and transmission analysis of pigments by means of far infrared spectroscopy

In the field of FTIR spectroscopy, the far infrared (FIR) spectral region has been so far less investigated than the mid-infrared (MIR), even though it presents great advantages in the characterization of those inorganic compounds, which are inactive in the MIR, such as some art pigments, corrosion products, etc. Furthermore, FIR spectroscopy is complementary to Raman spectroscopy if the fluorescence effects caused by the latter analytical technique are considered. In this paper, ATR in the FIR region is proposed as an alternative method to transmission for the analyses of pigments. This methodology was selected in order to reduce the sample amount needed for analysis, which is a must when examining cultural heritage materials. A selection of pigments have been analyzed in both ATR and transmission mode, and the resulting spectra were compared with each other. To better perform this comparison, an evaluation of the possible effect induced by the thermal treatment needed for the preparation of the polyethylene pellets on the transmission spectra of the samples has been carried out. Therefore, pigments have been analyzed in ATR mode before and after heating them at the same temperature employed for the polyethylene pellet preparation. The results showed that while the heating treatment causes only small changes in the intensity of some bands, the ATR spectra were characterized by differences in both intensity and band shifts towards lower frequencies if compared with those recorded in transmission mode. All pigments' transmission and ATR spectra are presented and discussed, and the ATR method was validated on a real case study. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quantum study of Eley-Rideal reaction and collision induced desorption of hydrogen atoms on a graphite surface. I. H-chemisorbed case

Collision induced (CI) processes involving hydrogen atoms on a graphite surface are studied quantum mechanically within the rigid, flat surface approximation, using a time-dependent wave packet method. The Eley-Rideal (ER) reaction and collision induced desorption (CID) cross sections are obtained with the help of two propagations which use different sets of coordinates, a "product" and a "reagent" set. Several adsorbate-substrate initial states of the target H atom in the chemisorption well are considered, and CI processes are studied over a wide range of projectile energy. Results show that (i) the Eley-Rideal reaction is the major reactive outcome and (ii) CID cross sections do not exceed 4 A2 and present dynamic thresholds for low values of the target vibrational quantum number. ER cross sections show oscillations at high energies which cannot be reproduced by classical and quasiclassical trajectory calculations. They are related to the vibrational excitation of the reaction products, which is a rather steep decreasing function of the collision energy. This behavior causes a selective population of the low-lying vibrational states and allows the quantization of the product molecular states to manifest itself in a collisional observable. A peak structure in the CID cross section is also observed and is assigned to the selective population of metastable states of the transient molecular hydrogen.     

An intramolecularly self-templated synthesis of macrocycles: self-filling effects on the formation of prismarenes

Ethyl- and propyl-prism[6]arenes are obtained in high yields and in short reaction times, independent of the nature and size of the solvent, in the cyclization of 2,6-dialkoxynaphthalene with paraformaldehyde. PrS[6]Et or PrS[6]nPr adopt, both in solution and in the solid state, a folded cuboid-shaped conformation, in which four inward oriented alkyl chains fill the cavity of the macrocycle. On these bases, we proposed that the cyclization of PrS[6]Et or PrS[6]nPr occurs through an intramolecular thermodynamic self-templating effect. In other words, the self-filling of the internal cavity of PrS[6]Et or PrS[6]nPr stabilizes their cuboid structure, driving the equilibrium toward their formation. Molecular recognition studies, both in solution and in the solid state, show that the introduction of guests into the macrocycle cavity forces the cuboid scaffold to open, through an induced-fit mechanism. An analogous conformational change from a closed to an open state occurs during the endo-cavity complexation process of the pentamer, PrS[5]. These results represent a rare example of a thermodynamically controlled cyclization process driven through an intramolecular self-template effect, which could be exploited in the synthesis of novel macrocycles.

Ethyl- and propyl-prism[6]arenes are obtained by an intramolecular thermodynamic self-template effect: the self-filling of the internal cavity stabilizes their cuboid structure, driving the equilibrium toward their formation.