Constituents of Satureia calamintha. Application of Eu(fod)3 to the assignments of the methyl resonances of triterpenes related to 12-ursene

The n.m.r. spectra of triterpenoids related to 12-ursene have been examined using the shift reagent Eu(fod)₃. The assignment of all the methyl resonances has been achieved for ursolic acid derivatives and the corresponding compounds of the 3-epi series, which have not been investigated previously. The additive shielding effects of various substituents on the methyl resonance frequencies have been deduced from the results.     

Electroluminescence in CuGaSe2 single crystals

Electroluminescence has been observed in p-type CuGaSe₂ single crystals. At room temperature these crystals exhibit a resistivity of about 10^?2 Ω cm. The electrominescence has been obtained by minority carrier injection from an indium electrode. Two peaks have been identified in the emission spectrum whose energies are 1.53 and 1.59 eV, respectively. These peaks could be caused by the recombination of injected minority carriers in acceptor centers which are localized in the forbidden gap near the valence band.     

Switching and memory properties of some crystalline layer compounds

La Rivista del Nuovo Cimento (1971-1977) -     

Impact parameter interpretation of proton-proton scattering from a critical review of all ISR data

This paper contains a critical review of all the data produced at the ISR on proton-proton elastic scattering and total cross sections. This coherent and complete set of data is used to compute the impact parameter distribution of the proton-proton inelastic overlap integral. This impact parameter analysis has smaller errors than any other previously made, and confirms the good agreement with the geometrical scaling model while strongly disagreeing with models based on factorizing eikonals. For the first time we find indications of a second contribution to the peripheral rising of the proton-proton cross section in a region around 2.2 fm.     

A possible scheme to obtain e-e- and e+e- collisions at energies of hundreds of GeV

As a contribution to the discussion on very long term developments in the field of high energy physics, it is pointed out that it is possible to devise e^-e^- and e⁺e^- colliding beam machines which are not affected by the large synchrotron losses typical of conventional storage rings. The scheme proposed here makes use of two collinear superconducting linacs which at the same time accelerate and recover the energy fed to the electron and positron beams.     

Correlations of secondaries in events with a forward negative hadron at the ISR

Data obtained from p-p collisions at centre-of-mass energies between 31 and 63 GeV are presented on correlations between momentum analysed forward π^?, K^? and $\text{p}$ and charged particles observed in an omnidirectional hodoscope. The data show that significant correlations are present over the whole rapidity range for all three types of negative particles. The dependence on various kinematic variables suggests a cluster mechanism for the production of particles. In this picture, pions would be produced in clusters emitted in the fragmentation region while K^? and $\text{p}$ emanate from non-leading clusters.     

Solid-phase microextraction and gas chromatography–mass spectrometry for rapid characterisation of semi-hard cheeses

A headspace solid-phase microextraction (HS-SPME) method in combination with gas chromatography–mass spectrometry (GC–MS) has been used for extraction and identification of components of the volatile fraction of Provola dei Nebrodi, a typical semi-hard Sicilian cheese. Cheese samples from different producers and at different ripening stages have been examined. The effects of various conditions (e.g. sample volume, sample headspace volume, sample heating temperature, extraction time, etc.) on extraction efficiency were studied in order to optimise the technique. The technique used made it possible to identify 61 components: fatty acids from C₂ to C₁₄ and their esters, aldehydes, alcohols, methyl ketones, -lactones, aromatic compounds, hydrocarbons and terpenes. The main components were butanoic, hexanoic and octanoic acids. The linear free fatty acids (FFA) from C₂ to C₁₀ were quantified by using the standard addition method. Calibration curves constructed for the FFA spiked into cheese were highly linear with a correlation coefficient R²>0.998. Significant statistical differences (P0.05) were evident for the even-carbon-number fatty acids during ripening.     

Combinatorial optimization - Polyhedra and efficiency: A book review

We review the recent three-volume monograph authored by Alexander Schrijver, Combinatorial Optimization - Polyhedra and Efficiency, Springer-Verlag, 2003, ISBN 3-540-44389-4, 1881 pages (in a slip-case), price: € 89,95 .Received: November 2003, Revised: January 2004, AMS classification: 90C57, 68R10, 05C99     

A solution for transient surface waves of the B-G type in a dissipative piezoelectric crystal

We derive a solution to the problem of shear horizontal electroacoustic surface waves in a piezoelectric half-space. We formulate a time-domain dynamic problem accounting for time dispersion for both electric and elastic fields and use a separation of variables to express the solution in terms of a wave propagator. Transient surface waves of the B-G type are found to propagate with a constant speed and exponentially decay in space. Their amplitude vanishes at large distances from the boundary as the reciprocal of the depth. Dispersive and non dispersive solutions are compared.