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In this work the adiabatic collapse of a self-gravitating sphere is studied, by means of a computational simulation carried out with Gadget-2. This package has a simulation archetype for the homologous collapse of a unit sphere, which is represented by a series of concentric spherical shells, where the particles are distributed equidistantly to represent a particles number ni=N = r². Another method has been created based on considering the unit sphere made up of small spheres inside. The problem boils down to packing the small spheres in the best possible way. This problem has been solved in solid state physics, for spherical symmetry the maximum packing factor is given by a Face-Centered Cubic (FCC) type Bravais structure. In this work it is shown that the best way to represent a sphere of gas computationally is by means of an FCC distribution. [ABSTRACT FROM AUTHOR]

This research shows the modification of a zeolite Y and a pillared clay (saponite) by impregnation with different platinum quantities (synthesis of Pt catalysts). The solids were characterized about the chemical composition and texture. The textural characterization reveals important changes in the solids, showing that in the zeolitic catalysts microporosity is formed, whereas in the pillared clay the microporous structures are partially blocked. Fractal dimension (by Avnir-Jaroniec method) indicates that the topographic features of the pillared clay surface are significantly affected due to the modification with platinum, probably as a consequence of platinum clusters formation. [ABSTRACT FROM AUTHOR]

A study of the transport properties in the normal-state of the anisotropic polycrystalline superconductors have been developed. The presence of certain orientation order of the grains in polycrystalline (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductors is modeled taking to account a probability factor of the grain's orientation γ. In addition, the concentration of the pores p, which characterizes the contribution of the porosity to the conductivity's decrease in the polycrystalline superconductor have been introduced. The pores and grains are assumed as oblate ellipsoids with similar dimensions, regarding the value of conductivity in each direction in the case of the grains. The calculation is based on the application of a generalization of the effective-medium theory to the heterogeneous mediums which is denominated Coherent- Potential Approximation (CPA). The results are compared with a current empiric model to low oriented YBa2Cu3O7-δ (YBCO) samples, this enriches their employment and is applied to superconductor ceramics in general. [ABSTRACT FROM AUTHOR]

A calculation of the behavior of the conductance through resonant double barrier (n = 2 cells) and superlattice (n > 2 cells), for systems with uncoupled channels is presented. The numerical calculation was done using III and V semiconductors, such as GaAs and AlAs physical systems. Based on the Multicomponent Scattering Approach the two probe Landauer conductance and the phase time are calculated and interpreted. An oscillatory behavior of the conductance for a superlattice for uncoupled holes is observed, as we expected. This model provides evidences of the classical Hartman prediction for energies under the barrier height for uncoupled heavy and light holes, while a non linear dependence of the phase time with the barrier width, the Ramsauer -- Townsend oscillations, for energies above the barrier is observed. [ABSTRACT FROM AUTHOR]

This is a novel application of a solid-on-solid discrete model for simulating pattern formation occurring in a microstructuring technique, namely laser-induced jet-chemical etching (LJE). Instead of formulating a continuous model including the interaction of all chemical and physical processes, we propose a minimal phenomenological description of the etching process based on two mechanisms: curvature dependent erosion and thermally activated surface diffusion. The simulation allows to represent the main parameters of the system in a probabilistic sense, and reproduces qualitatively the ripple regimes appearing in the LJE experiment [ABSTRACT FROM AUTHOR]

In this research we present the synthesis and characterization study of powder and bulk samples of La0.67Ca0.33MnO3-α (LCMO) manganites, prepared by solid state reactions. The analysis of the reaction was done by Thermogravimetry (TGA) and Differential Thermal Analysis (DTA) measurements, in air atmosphere with temperature increase of 10°C/min from 23°C to 900°C. In the TGA and DTA curves we observed different lost weight regions between 336°C and 705.32°C, due to decomposition of the precursor. Above this latter temperature, the reaction as stable. The final product was 85.17% of the starting mixture. Powder XRD measurements were fitted using Rietveld method. The observed crystalline structure was orthorhombic. The chemical composition by EDX measurements showed the phase of compound. The manganese ions (Mn3+ y Mn4+) content was determined by iodometric titration method. Finally, in the magnetometry measurements using SQUID with external applied field of 400 gauss and cooling without field from 300K to 20K, Curie temperature in the sample was measured (TC-251K). [ABSTRACT FROM AUTHOR]

The investigations in the field of the Physics in Cuba are relatively new compared with this antiquity science and the world practice; their beginnings are in the sixties of the recently concluded century. The pioneer in these investigations has been the Physics School of Havana's University, founded in December 1961, with so many expectations like lacks in material resources and manpower, leaning quickly toward the investigations in Solid State Physics, especially in semiconductors and metals. This work direction was projected toward the national necessities, together to the feasibility to develop this type of investigations in a country with few resources. Through interviews with protagonists and original documents this work expose how the first steps were developed in the investigations in Solid State Physics in Cuba, this efforts can be analyzed from several point of views: the personal formation, the creation of the material base and properly the investigations. The author frame the first steps development period up to 1975, when in Cuba, the IV Latin American Symposium of Solid State Physics has taken place, which means the international recognition of the international scientific community to the work of the Cuban investigators in the sphere of Solid State Physics. [ABSTRACT FROM AUTHOR]

The Irradiation Service is part of the specialized technician-scientist services of the Center of Technological Applications and Nuclear Development it belonging to the Radiobiological Department. It provides a self-shielded laboratory irradiador, PX-γ-30 type with Cobalt 60 sources, it destined for research studies, so much basic as applying, in several branches of the science like the radiobiology, the radiation chemistry, the solid state physics, the medicine, the agriculture and the Pharmaceutical-Medical Industry and besides offering the irradiation service properly with the which have been gotten significant economical outputs. The radiation processing is controlled by means of the dosimetric systems of Fricke, ceric-cerous sulfate, Perspex (Red, Clear and Amber) and dose indicators. [ABSTRACT FROM AUTHOR]

In the present paper, the method used is reported in the literature A. Marcilla and others /9/ and permits the treatment of the experimental data for the physical characterization of the porous solids and to obtain the clearest and most consistent information about the pore distribution, also free of the inherent effects to the operator and without false picks. A wide graphical treatment is used to arrive at more exact conclusions about the complete characterization of a porous solid, such as the activated coals without any appeal to analysis complicated methods. Polinomial functions are used to adjust the experimental data by the method of minimum square. [ABSTRACT FROM AUTHOR]

In this work was made an integral characterisation of the industrial yields from the factory of preserves "La Avispa", situated on the Caney zone, Santiago de Cuba. To now the composition and it's effects (on environment) of the yields was analysed some parameters such as chemistry demand of oxygen (CDO), pH, acidity, refraction index, totals solids, fats, nitrogen, metals and some others. From the analysis of the obtained results was possible made an adequate treatment to them and give it and adequate use for diminishing the damages to the environment. [ABSTRACT FROM AUTHOR]

Synthesis and conductivity characterization of the RE0.5Y0.5Ba2Cu3O7-δ (RE=Sm, Gd, Dy, Ho, Eu, Yb) superconducting materials are reported. Samples were produced by the standard solid state reaction method. The x-ray diffraction data permit to establish the crystalline appropriated distribution of rare earth and yttrium. DC resistivity measurements reveal the improvement of the critical temperature (Tc) when substitution of exact 50-50 mix of rare earth (Sm, Gd, Dy, Ho, Eu, Yb) and Yttrium is performed. The Tc was determined by the criterion of the maximum in the temperature derivative of electrical resistivity for the analyzed samples. [ABSTRACT FROM AUTHOR]

Ultrathin films are an important testing ground of our understanding of magnetic interactions in quasi-twodimensional systems. A formalism that takes into account the discreteness of atomic layer distribution along the growth direction is employed to calculate the dipolar anisotropy energy. Numerical results are presented for close-packed and non-close packed structures. Structural and size effects are investigated. Comparison with effective anisotropy energy allows verify the role of the dipolar interaction in the magnetization switching when the film thickness is changed. [ABSTRACT FROM AUTHOR]

Solid state reaction method was used in order to obtain the composite [NiO][MnCo2O4]. We have made two thermal treatments up to 1000 °C for 16 hours, and a third treatment up to 1300 °C for 30 hours. The obtained sample was analyzed by X-ray diffraction (XRD). A comparison between the difractogram and crystallographics data base showed the presence of NiO and MnCo2O4 phases. Rietveld refinement leads to the values χ² ~ 1.6 y RF ~ 4 %. The mass percentage are 65.93 % of NiO and 34.06 % of MnCo2O4. Both structures has cubic symmetries Fm3m (number 225), with lattice parameters 4.1812 Å and 8.3255 Å respectively. We expect that experimental analysis of the magnetic properties of this composite shows exotic properties like half-metallicity which is frequent in spinels. [ABSTRACT FROM AUTHOR]

Manganites with La2/3Ca1/3Mn1-yFeyO3 (y = 0.01 y 0.03) composition were fabricated, by a solid-state reaction in powder and bulk form, using α-Fe2O3, hematite as a precursor, enriched with 95.06% of 57Fe. The hyperfine parameters obtained from the fits of Mössbauer spectrums, show the presence of Fe3+ in octahedral sites of the compounds. The c-axis parameters calculated from the fits to XRD measurements were (7.686(2) Å and 7.670(3) Å for 1 and 3% of Fe, respectively. Neither impurities nor additional phases were observed. Magnetization measures in function of temperature show a small reduction of transition temperature and magnetization when concentration of Fe increases. [ABSTRACT FROM AUTHOR]

El artículo presenta información acerca del IV Simposio Latinoamericano de Física del Estado Sólido (SLAFES) celebrado en Cuba el 27 de enero al 7 de febrero de 2015. El autor comenta sobre los temas centrales del congreso, incluyendo la metalurgia, la microelectrónica y el magnetismo.