[en] A property of hermitian matrices is used by means of which the conditions which the positive definiteness of the spin density matrix implies on the real parts of its elements can be derived in a direct and simple way. For this derivation only the hermiticity is required and it can be applied in practice for any spin, even when interferences are present. (Auth.)

[en] Solidification microstructures and phase selection in ingots and melt-spun ribbons of MoSi₂, MoSi₂-W-Ta and MoSi₂-Al alloys were studied. Rapid quenching from the melt refined the grain size of all alloys by two orders of magnitude compared to the ingots. Zone A microstructures were formed in the wheel side of all alloy ribbons. Addition of an Ta and of Al suppressed the formation of Mo₅Si₃ in the ingots and ribbons. Tungsten exhibited complete solid solubility in MoSi₂. In the ribbons the solubility of Ta in MoSi₂ was extended to 2 at% in Zone A, and in the ingots and zone B of the ribbons hexagonal (C40) TaSi₂ and tetragonal (C11_b) MoSi₂ structures were formed. A fine lamellar microstructure between the C11_b and C40 phases was formed at 1,350 C after 48h. Addition of Al changed dramatically the solidification microstructure which consisted of two phases C40 Mo(Al_0.5Si_0.5)₂ and C54 MoAl_1.3Si_0.7. In the ingots the room temperature hardness decreased with addition of W and Ta and of Al. Addition of Al increased the thermal stability of the MoSi₂-Al alloy

[en] Zinc hot-dip galvanizing is an effective method for the corrosion protection of ferrous materials. A way of improving the results is through the addition of various elements in the zinc melt. In the present work the effect of Ni, Bi, Cr, Mn, Se and Si at concentration of 0.5 or 1.5 wt.% was examined. Coupons of carbon steel St-37 were coated with zinc containing the above-mentioned elements and were exposed in a Salt Spray Chamber (SSC). The micro structure of these coatings was examined with SEM and XRD. In every case the usual morphology was observed, while differences at the thickness and the crystal size of each layer were induced. However the alloying elements were present in the coating affecting its reactivity and, at least in the case of Mn and Cr, improving corrosion resistance

[en] Zinc hot-dip galvanizing is a method for protecting iron and steel against corrosion. Galvanizing with pure Zn or Zn with additions like Ni, Al, Pb and Bi has been extensively studied, but there is a lack of scientific information about other additions. The present work examines the effect of a 0.5 wt% Ti addition in the Zn melt. The samples were exposed to accelerated corrosion in a salt spray chamber (SSC). The microstructure and chemical composition of the coatings were determined by Optical Microscopy, XRD and SEM associated with an EDS Analyzer. The results indicate that the coatings have a typical morphology, while Zn-Ti phases were also detected

[en] Metallic coatings have been proved to reduce the rate of corrosion of steel in various atmospheres. In this work the structure of Al, Cu-Al and Zn thermal sprayed coatings is examined. The as formed coatings are extremely rough, and they are composed of several phases which increase corrosion resistance as it was determined Salt Spray Chamber tests

[en] Four powder mixtures with chemical formula La1+xBa2-xCu3Oy was prepared. The mixtures were heated in free atmosphere, at temperature 850 deg. C for 60h and then at 860 deg. C for 40h. XRD measurements were obtained with CuKa radiation. The samples were characterized with the help of the PDF and refined, using the Rietveld's 'Powder Profile Analysis'. Four phases, same for all the samples, were found: (La,Ba)2CuO4, BaCuO2, LaBa2Cu3O7-d, and BaCO3. The percentages of the tour phases are changed, as the x quantity increases, and varied from 38, 25, 18, 19%, for x=0, to 69, 14, 7, 10%, for x=0.6, respectively

[en] A powder mixture with chemical formula CeBa1.8Pb0.2Cu3Oy was prepared. The mixture was heated in free atmosphere, at temperatures 860 deg. C to 940 deg. C, for 24 to 72h. The samples were measured by X-Ray powder diffraction with CuKa radiation. Each sample was characterized with the help of the PDF and refined, using the Rietveld's ''Powder Profile Analysis''. The first sample (860 deg. C) was identified with the phases: Ba2CeBiO6, CuO and BaCuO2, while all the remaining samples (870 deg. C-940 deg. C) with the phases Ba2CePbO6, CuO and CeO2. The phases Ba2CeBiO6 and Ba2CePbO6 are the main phases with analogous chemical types, but different symmetry. The phase CuO is common in all the samples, while from the remaining phases the BaCuO2 appears only in the first sample and the CeO2 in all, except the first one. The quantity 0.2 of Pb is distributed in the Ba positions, substituting a part of these. The percentages of phases are about 82%, 10% and 8% for the first sample and for all the remaining about 85%, 8% and 7%, respectively with above serious

[en] The methods for the synthesis of the superconducting systems are well known. Usual methods are the classical heating in furnace (oven) known as conventional methods for the ceramic samples. Special extra furnace techniques are used as firing profiles with different heating rates as for example, 5 deg C/min, or N deg C/min or cooling at any rate, too. The unusual methods or non conventional methods begin with films with depositions of components, thin films technology, metallurgical route for synthesis, thin films deposited by sol-gel process on different substrates, sintering, spray deposition, films deposited by spray pyrolysis method, solid-state reaction, thin films by pulsed laser deposition, sol-gel process, composites obtained by in situ spray pyrolysis method, etc. Classical mixture with the general chemical formula Ba_(3-x)Pb_xCa₂Cu₃O_8+d (x=0.2) according to the general Ba-Pb-Ca-Cu-O system, was prepared either with the classical conventional oven and with an microwave oven. (authors)

[en] We determine the internal structure functions of the valons introduced by Hwa and coworkers, using low-psub(t) data and Regge model constraints. Our calibration reaction is the fragmentation process p→π^- observed in 70 GeV/c K⁺p interactions. The fitted valon structure parameters are used to make succesful predictions for various other fragmentation processes (p→π⁺ and p→K⁺). A comparison with experimental data of the DIS νW₂(x)-values implied by this same fit, indicates that soft processes probe the nucleon typically at a Q²-value fo approx. equal to1 GeV². This finding supports the hypothesis that soft hadronic reactions are useful (and often unique) tools to learn about hadron quark structure. (orig.)

[en] The structure of the kaon in terms of valons and quarks is studied. Using the K⁺p → Ksup(n)X data from BEBC experiment at 70 GeV/c, the strange and non-strange quark distributions are determined. The procedure illustrates how the valon model allows the study of hadron structure using low-psub(T) reactions. (orig.)