[en] Bars of REBa₂Cu₃O_y superconductor with three different rare earths were prepared by floating zone technique in air. Their nominal composition is (RE_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y (RE=Y, La, Pr, Nd, Sm and Yb). The mixing of these three elements leads to a single phase formation. The physical properties of these systems and their microstructure were studied. All the compositions exhibit a superconducting transition excepted that one containing Pr and substitution of Ba by RE is avoided excepted in the case of RE=La. Only the phase with Nd shows a pronounced fishtail effect and the phase with Sm exhibits a very high J_c value of 70 000 A/cm² in self-field and more than 30 000 A/cm² at 1.7 T

[en] The goal of this parer is to point out and discuss several of the most important points still open in astroparticle physics today. Of course, this parer is not exhaustive because of essentially two reasons: the first due to my knowledge and the second to the reasonable length of the parer. However, I will try to remark those hot points which will be discussed in more details during the workshop. I will outline the following items: 1) Introduction, 2) Cosmology, 3) Clusters of galaxies as γ-ray emitters, 4) Cosmic counterparts of γ-ray sources, 5) Active galactic nuclei and galactic collapsed objects: unified schemes, 6) Relativistic jets, 7) Gamma ray bursts, 8) X-ray binaries, 9) Neutrinos, 10) Some ideas on future missions, 11) Conclusions

[en] ((LRE)_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y bulk superconductor (LRE=Sm, Nd) were textured by the top seeded melt textured growth method in a reduced oxygen atmosphere. Their physical properties and their microstructure were studied. (Sm_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y textured material exhibited a critical temperature of 94 K and critical current densities at 77 K of 50000 A cm^-2 under self field and 20000 A cm^-2 under 2 T. In the case of (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y, an optimal critical temperature of 95 K is reached. Moreover, high critical current density under self field of 60000 A cm^-2 is obtained. This last result has been confirmed by transport measurements. Indeed, critical current densities at 77 K higher than 50000 A cm^-2 have been measured when the applied field was below 2 T

No abstract available

[en] In this paper, the authors analyze some processes producing high-energy X rays and gamma rays from a relativistic plasma, namely: proton-proton interactions for thermal and nonthermal models; and e-e and e-p bremsstrahlung in the thermal case and e-p bremsstrahlung in the nonthermal case. The derived models were used in order to fit experimental data from 3C 273 and Geminga. The authors thermal model fits quite well with the data of 3C 273, but it fails the fit of Geminga experimental points. On the contrary, data of Geminga are fitted very well by their nonthermal model. This result strongly supports the presence of a neutron star as the gamma-ray source in the error box of Geminga

[en] An analysis performed on a sample of 191 extragalactic X-ray sources of different classes (QSOs, Seyfert Galaxies, BL Lac, elliptical and SO, spiral and irregular galaxies) appears to show a general relationship between log z and the logarithm of the 2keV equivalent monochromatic luminosity of the brightest object in a given redshift interval (regardless of the class of the object). This function is almost constant for z#lt#0.001; it has a continuous inflection of about two orders of magnitude between z=0.001 and z=0.01, and at z#gt#0.01, where only AGNs are present, it matches with a straight line, with slope equal to 1.6. It is suggested that such a smooth function implies a physical continuity of these objects. (author)

[en] We have investigated the influence of oxygen excess on structural and physical properties of the Nd₂NiO_4+δ compounds. Using the citrate method and subsequent annealing in air and in a reducing atmosphere a various oxygen-doped compounds were prepared. X-ray diffraction at room temperature shows that structure is strongly oxygen excess dependent. Thus, by increasing δ by up to 0.077, the compounds adopt a tetragonal structure gradually with a biphasic domain between orthorhombic and tetragonal structures. And at higher δ values, the structure becomes orthorhombic. Moreover, Rietveld analysis shows that for δ<0.077 the presence of two crystalline phases with different oxygen excess: it should be the signature of interstitial oxygen, which is distributed in heterogeneous way. The biphasic products are composed of a stoichiometric Nd₂NiO₄ phase (orthorhombic structure) and a tetragonal Nd₂NiO_4.077 phase. Magnetic susceptibility shows a deviation from Curie-Weiss law for lower oxygen excess (δ≤0.077). Moreover, some anomalies in dc magnetic susceptibility curves was observed at 45, 95 and 130 K for δ<0.077. These transitions are connected to the tetragonal phase, and were attributed, respectively, to an antiferromagnetic transition, possible charge ordering and structural transition

[en] The interpretation of many high energy astrophysical phenomena relies on a detailed knowledge of radiation and transport processes in hot plasmas. The understanding of these plasma properties is one of the aims of terrestrial plasma physics. While the microscopic properties of astrophysical plasmas can hardly be determined experimentally, laboratory plasmas are more easily accessible to experimental techniques, but transient phenomena and the interaction of the plasma with boundaries often make the interpretation of measurements cumbersome. This book contains the talks given at the NATO Advanced Research Workshop on astro- and plasma-physics in Vulcano, Sicily, May 29-June 2, 1989. The book focuses on three main areas: radiation transport processes in hot (astrophysical and laboratory) plasmas; magnetic fields; their generation, reconnection and their effects on plasma transport properties; relativistic and ultra-high density plasmas

No abstract available

[en] The temporal behavior of three new events of modulated optical emission from Cyg X1, detected in July this year, is presented