Multiple Gradient TLC and Densitometric Analysis of p-Coumaric Acid in Some Medicinal Plants from the Family Solanaceae

JPC – Journal of Planar Chromatography – Modern TLC -     

Temperature dependence of the photoluminescence spectra in AgGaS2

The Silver Gallium Sulfide (AgGaS₂) ternary compound is a wide bandgap semiconductor (about 2.7 eV) whose photoluminescence properties are characterized by excitons and donor-acceptor pairs recombinations. We have performed photoluminescence (PL) measurement exciting with the third harmonic (3.5 eV) of a Nd:YAG laser from room temperature down to 10 K at different excitation power. In this work we report the dependence of the ‘green band’ on the excitation power at various temperatures.     

Reliability in scientific evidence based on multi trace forensic neutron activation analysis

The forensic activation analyst must often evaluate his own results as they relate to certain legal or moral situations, since investigative officers, and courts of law are not usually competent to make judgements of the validity or meaning of scientific data. In providing scientific evidence in court, two criteria for criminal identification must be met: (1) suspect's sample should be similar to sample found at the scene of the crime, (2) samples relared to other people in the same statistical population should not generally match that found at the crime site. When two or more specimens are submitted for comparison by NAA they will usually fall into one of three classes: (a) materials about which we have partial or inconclusive data, (c) materials with an excellent analytical data background. Ideally all cases would fall in category c; in practice, very few. Some examples of cases and/or situations that fall into these three categories in both individual and corporate investigations are given. Research sponsored by U.S. Atomic Energy Commission under contract with Union Carbide Corporation.     

Montecarlo and boltzmann calculations of electron energy distributions in RF fields

Summary Detailed comparisons between Montecarlo and Boltzmann calculations of electron energy distributions in gases acted upon by RF fields are presented. Attention is turned to model gases of special theoretical interest but various calculations have also been made for real gases such as pure CO and He−CO mixtures. The analysis has shown that large discrepancies exist between energy distributions obtained with the two mentioned techniques under conditions of particular physical interest. The discrepancies are found to be the consequence of the two-term approximation and are expected to disappear if an appropriate multiterm solution of the Boltzmann equation is adopted.     

Experimental study of a Back Action Evading device for continuos measurements on a macroscopic harmonic oscillator at the quantum limit level

The Back Action Evading technique is a particular kind of quantum non demolition measurement, first proposed by Caves et al. in 1980 [3]. We present an experimental study to implement the Back Action Evading measurement scheme in monitoring the amplitude of an harmonic oscillator excited by a classical force. Results showing the agreement of our theoretical model with the experimental behaviour of our apparatus in the classical regime are presented. We discuss also the optimization of the performance of our set-up, which should allow to monitor our oscillator in quantum regime even below the standard quantum limit level. Received: 22 March 1996     

Gas-phase ion chemistry of BF3/HN3 mixtures: the first observation of [BFnNxHn-1]+ (n=1, 2; x=1, 3) ions

The gas-phase ion chemistry of BF3/HN3 mixtures was investigated by the joint application of mass spectrometric techniques and theoretical methods. The addition of BF2+ to HN3 led to the first observation of [BFnNxHn-1]+ (n=1, 2; x=1, 3) ions in the gas phase. Consistent with collisionally activated dissociation (CAD) mass spectrometric results, theoretical calculations performed at the B3LYP and CCSD(T) levels identified the F2B-NH-N2+, F2B-NH+, FB-N3+, and FBN+ ions as the most stable isomers on the [BFnNxHn-1]+ (n=1, 2; x=1, 3) potential energy surfaces. The F2B-NH+ and FBN+ ions, characterized by a triplet ground state, are formed from F2B-NH-N2+ and FB-N3+ through a spin-forbidden decomposition process. It is worth noting that F2BNH-N2+ is the protonated form of difluoroboron azide, BF2N3, a neutral molecule that has never been experimentally detected. The application of theoretical and experimental methods allowed evaluation of the unknown PA of BF2N3, whose best theoretical estimate 171.2+/-3 kcal mol-1 at the CCSD(T) level is comparable with the experimental one, 170.1+/-3 kcal mol-1. The main interest of all these ionic species is represented by their possible application in boron nitride (BN) physical and chemical vapor deposition.     

A general procedure for the synthesis of stereochemically pure conduritol derivatives practical also for solid-phase chemistry

A straightforward synthetic protocol apt to synthesize a library constituted by all conduritol stereoisomers in solution phase is described and successfully applied to some polymer-supported substrates. During the solid-phase sequence, an unprecedented rearrangement of a resin-bound sulfone performed under the Ramberg-B?cklund conditions appears of particular interest. Upon treatment with Me(3)Si-I, thiepanes supported on resin are found to undergo regio- and stereospecific ring contraction to a six-membered ring system with traceless cleavage from the solid support.