Determination of low levels of free fibres of chrysotile in contaminated soils by X-ray diffraction and FTIR spectroscopy

A new analytical method for the determination of low levels (0.01–1 wt%) of free fibres of chrysotile in contaminated clayey, sandy and sandy-organic soils is described. The detection limit of 0.01 wt% is reached with an enrichment of free fibres of chrysotile in the sample using a standard laboratory elutriator for sedimentation analysis. The chrysotile quantitative determination is performed both by X-ray powder diffraction, using the internal standard and reference intensity ratio methods, and by Fourier-transform infrared absorption spectroscopy. The procedure can be successfully applied to different soils after removal, by a thermal treatment, of the matrix components which can interfere. This straightforward method fulfils the request of public institutions and private companies for an appropriate quantitative determination of chrysotile-free fibres in contaminated soils.     

A new class of chiral organogermanes derived from C2-symmetric dithiols: synthesis,characterization and stereoselective free radical reactions

A new class of dithiostannanes and dithiogermanes have been prepared from 1,1'-binaphthyl-2,2'-dithiol and 3,3'-bis(trimethylsilyl)-1,1'-binaphtho-2,2'-dithiol. While reduction of 4-butyl-4-chloro-3,5-dithia-4-stanna-cyclohepta[2,1-a;3,4-a']dinaphthalene to the corresponding tin hydride was unsuccessful, 4-tert-butyl-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a']dinaphthalene and 4-tert-butyl-2,6-bis(trimethylsilyl)-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a']dinaphthalene were obtained by reduction of the parent germanium chlorides with NaBH(4) and LiBH(4), respectively. Kinetic constants for hydrogen transfer to a primary alkyl radical were measured for both germanium hydrides. Reduction of alpha-halo carbonyl compounds by these germanium hydrides occurs with moderate ee values (up to 42%), while hydrogermylation of methyl methacrylate occurs with low selectivity (<3/1) for the former hydride but high selectivity (>10/1) for the latter.     

Highly homogeneous circularly polarized RF field for whole body NMR imaging

Conditions for generation of polarized RF fields in cylindrical symmetry by high order coils are presented. Whole body NMR transmitters utilizing this principle would require a current control on a certain number of loops. In the present design this is obtained by feeding each loop by an appropriate linear combination of two in quadrature waves. The development has been experimentally tested by three scaled down experimental prototypes operated at 500 kHz and a good agreement has been found.     

The Feynman propagator from a single path

We show that it is possible to construct the Feynman propagator for a free particle in one dimension, without quantization, from a single continuous space-time path.     

A New Iterative Method for the Computation of the Solutions of Nonlinear Equations

Recently, by Costabile, Gualtieri and Serra (1999), an iterative method was presented for the computation of zeros of C ¹ functions. This method combines the assured convergence of the bisection-like algorithms with a superlinear convergence speed which characterizes Newton-like methods. The order of the method and the cost per iteration is exactly equivalent to the Newton method. In this paper we present a new iterative method for the computation of the zeros of C ¹ functions with the same properties of convergence as the method proposed by Costabile, Gualtieri and Serra (1999) but with order 1+ $\sqrt 2 $ ?2.41 for C ³ functions. Compared with the methods of order 1+ $\sqrt 2 $ presented by Traub (1964), our methods ensure global convergence. Then we consider a generalization of this procedure which gives a class of methods of order (n+ $\sqrt {n^2 + 4} $ )/2, where n is the degree of the approximating polynomial, with one-point iteration functions with memory. Finally a number of numerical tests are performed. The numerical results seem to show that, at least on a set of problems, the new methods work better than the methods proposed, and, therefore, than both the Newton and Alefeld and Potra (1992) methods.     

Balance of mass, momentum, and energy in splintering central collisions for 40Ar up to 115 MeV /Nucleon

For central collisions of (17-115)A MeV 40Ar+Cu, Ag, Au, an overall balance is determined for the average mass, energy, and longitudinal momentum. Light charged particles and fragments are separated into forward-focused and isotropic components in the frame of the heaviest fragment. Energy removal by the isotropic component reaches 1-2 GeV. For such high deposition energies, statistical multifragmentation models predict much more extensive nuclear disassembly than is observed.     

13C NMR spectra of 1,3-oxathiolane, 1,3-oxathiolane 3-oxide and 1,3-oxathiolane 3,3-dioxide derivatives

Carbon-13 nmr spectra of several 1,3-oxathiolane, 1,3-oxathiolane-3-oxide and 1,3-oxathiolane-3,3-dioxide derivatives are reported. Relationships between some stereochemical features and chemical shift are discussed.