[en] In the last few years the interest for application of silicon radiation detectors to the detection of X-rays in the 15-30 keV region has been growing. One of the main reasons of such an interest is the development of devices for medical and biological applications, in particular for the diagnostic radiology of soft tissues. For these applications, to ensure a high detection efficiency is of crucial importance. This leads to the use of ''on purpose'' geometrical arrangements and technological solutions for the detector, as well as the use of specifically designed read-out electronics. In this paper we present results and images obtained with silicon microstrip detectors in a ''pixel-like'' geometry, with the X-ray beam impinging parallel to the strips. An efficiency close to 80% has been obtained for photons of energies around 20 keV. The ongoing developments, concerning the realisation of a dedicated silicon detector for digital radiology at the SYRMEP (synchrotron radiation for medical physics) beam line of the ELETTRA synchrotron radiation facility, are described. (orig.)

[en] Classical solutions for conformal invariant fermion-fermion interaction in two dimensions are given and their invariance properties are discussed. A possible generalization to four dimensions is given and corresponding instanton- and meron-like solutions are found. It turns out that these are a natural generalization of two-dimensional ones

[en] Symmetry properties of various classical solutions to field equations, e.g. meron solutions, have been studied previously. For the more complicated systems endowed with internal degrees of freedom invariance requirements have to be supplemented with compensating operations on these additional variables. This work develops considerations in the case of dilatations when additional degrees of freedom allow solutions which, even if not strictly dilatation invariant, are of the power type. The case of the conformal-invariant interaction of charged particles is considered first. Then the same considerations are applied to a model Lagrangian to describe the interaction of the gravitational field gsub(μnu), of SU(2) gauge vector fields Asub(μ)sup(α), and of a neutral scalar field phi. Properties of the solutions obtained are discussed

[en] We present a new algorithm for charged track pattern recognition in high energy physics experiments. We give Monte Carlo results on performances with variable detector sizes and multiplicities, and in realistic working conditions. (orig.)

[en] The WiZard Collaboration is engaged in a program to study the antimatter components of the cosmic rays. A silicon-tungsten (Si-W) imaging calorimeter has been developed as part of this program. We present its performance and preliminary results, obtained during a balloon flight on September 8, 1993. The flight was dedicated to the measurement of the positron spectrum in the energy range 4-50 GeV and took place from Ft. Sumner, New Mexico. (orig.)

[en] Simple gauge theories like the Higgs model and the scalar QED are studied in flat space-time with topology S¹ x R³. This nontrivial topology modifies the mass spectrum of the fields through vacuum fluctuations. For the Higgs model the critical length below which the spontaneously broken symmetry is restored is evaluated. In scalar QED the one-loop radiative corrections to the free propagators giving rise to the photon mass and shifting the mass of the scalar particles are evaluated. The extension of this mass-generating mechanism to non-Abelian gauge theories is also discussed. (author)

[en] A massive scalar field theory is investigated in Einstein static universe. The vacuum energy density and pressure are evaluated in the free-field case through normal-mode sum renormalization. Then a quartic self-interaction term is added and the renormalized one-loop effective potential is evaluated. It is shown that a spontaneously broken symmetry at the classical level can be restored by the one-loop radiative corrections only if the curvature exceeds a critical value. The critical curvature of Einstein universe is computed. (author)

[en] The one-loop effective potential for conformally invariant flat space-times is evaluated. This is achieved by a suitable rescaling of the fields. In the two-dimensional Rindler and Schwarzschild and in the four-dimensional De Sitter metrics the vacuum energy exhibits a thermal feature. The background temperature is quantitatively fixed by the global space-time geometry and its nontrivial topology. For the lambda phi⁴ theory in the De Sitter metric a dynamically generated mass for the field phi is found. (author)

[en] A model collision operator for the drift Fokker Planck equation for application to quiescent magnetoplasmas in presence of simmetric equilibrium hydromagnetic configurations is given. The main feature of this model, contrarily to approximate collision operators previously proposed by other authors, is that it allows to determine relevant microscopic variables by including first order corrections in terms of a suitable adimensional parameter which yields for the magnetic configuration inhomogeneities

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