[en] The present report explains the phenomenon of Critical heat flux. The study of this physical phenomenon is carried out during the boiling of a liquid and is of supreme importance for the calculation and operation of a nuclear reactor even in the moderns generators of steam (thermoelectric and nucleoelectrics), industrial cooling and in all those industrial process that use a liquid subject to sources of heating and to conditions of work excessively high (temperatures and pressures) so that stay in operation in an appropriate manner and sure. Once well-known this value, the equipment used in these process works with a maximum heat that is smaller than the Critical Heat Flux. The study of the Critical Heat Flux has achieved important advances in the last years, mainly for the enormous obligation that in this moment involved the safety to world level, this has forced to researchers and designers of this type of equipment to center their attention in the obtaining of a correlation which of general way explains it. In this reports two correlations will be compared that they contribute to the evaluation of the Critical Heat Flux in annulus and that they try to be generals in this type of geometry, the Shah correlation's and the Katto correlation's. The same as most of the correlations, these have been calculated so that the fluid of work is water, although they have also been proven with others fluids. The results obtained in this report only will show the degree of advance which the investigation of this phenomenon has achieved in annulus and to low amounts of flow of liquid, like which they are in the Experimental Heat Transfer Circuit located in the Department of Physics of the National Institute of Nuclear Research. (Author)

[en] In this thesis project we present the results on the generation of laser-induced periodic surface structures (LIPSS) in thin bismuth films. The films were deposited by the pulsed laser ablation technique on glass substrates, using two wavelengths: 1064 nm and 532 nm. Polycrystalline bismuth films were obtained with preferential orientation in the direction (003), a characteristic that depends on the plasma parameters. The deposits were morphologically and structurally characterized by profilometry, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and micro Raman spectroscopy. Subsequently, the films were irradiated in punctual areas with the same laser used for ablation and both wavelengths. The fluence and pulses number were determined and those were kept constant in all the experiments. The irradiated areas were characterized by atomic force microscopy and micro Raman spectroscopy. The results show the periodic structuring on surface of bismuth films in the irradiated areas. A difference is observed in the LIPSS recorded on the polycrystalline films with respect to the oriented films. The grooves are much more parallel in the textured films, unlike the LIPSS in polycrystalline films that are seen in a corrugated form. There is also a difference in the width and height of the grooves. Finally, it was determined that there is a limit on the thickness of the films from which it is possible to generate LIPSS. (Author)

[en] Currently the most common used methods for removing PTFE rich coatings on metal substrates are: grinding, pyrolysis, chemical processes or a combination of these. While effective, all present serious difficulties. In this paper the use of laser ablation to remove PTFE rich coatings, which have previously been applied to sheets of aluminum magnesium alloy EN AW-5251 H34, is proposed. For this purpose the values of the yield strength, tensile strength, percent elongation, impact energy retained and hardness are analyzed. Equally, the grain size distribution at the microstructural level, the ASTM average grain size and distribution of constituent particles have been evaluated. Measurements were performed to three successive stages of application and laser coating removal. Moreover, the previous set of properties have been determined for the same substrates and stages but using pyrolysis to remove the coating. Comparison of the results shows that the removal by laser ablation does not cause any reduction in the properties of the substrates and may become an industrial alternative to traditional disposal procedures. (Author)

[en] The instrumental activation analysis is a technique relatively quickly that help to know the elemental composition of materials. It is used mainly in the trace elements determination but in the case of major elements it is necessary to make some considerations as the different nuclear reactions carried out due to the neutron flux is a mixture of thermal and fast neutrons. This could be interpreted for the presence and or erroneous quantification about some elements. In this work, is described the way in which was analyzed a container piece with approximately a 85% of aluminium. The elements Zn, Mn, Sb, Ga, Cu, Cl and Sm were determined. (Author)

[en] Textile industry is an important activity that provides considerable benefits to people, but unfortunately dyeing of yarn and cloth produces pollution of water, a resource that is valuable and scarce. Dyeing of textiles fibers is an inefficient process, in view of the fact that approximately ten percent of total dye is thrown to municipal sewage. Although different treatment systems are applied to wastewater, dyes are resistant to physical, chemical and biological factors because of the way they are designed. (Author)

[en] The removal of manganese from aqueous solutions on synthetic alumina and natural kaolinite was investigated in batch experiments as a function of pH. Experiments were carried out by using the radiotracer ⁵⁶Mn, produced by neutron activation. Theoretical analysis of manganese removal was performed considering the existence of a single type of surface sites, denoted as ≡ SOH°. The uptake of manganese on kaolinite is similar to that on alumina, indicating that adsorption occurred on the variable-charged aluminol sites. Adsorption experiments suggest that ≡ AlOH° group is the most probable edge site for complexing manganese cations through mononuclear surface complexes (≡ AlOMn⁺) and (≡ AlOMnOH). (author)

[en] Higher derivative field theories with interactions raise serious doubts about their validity due to severe energy instabilities. In many cases the implementation of a direct perturbation treatment to excise the dangerous negative-energies from a higher derivative field theory may lead to violations of Lorentz and other symmetries. In this work we study a perturbative formulation for higher derivative field theories that allows the construction of a low-energy effective field theory being a genuine perturbations over the ordinary-derivative theory and having a positive-defined Hamiltonian. We show that some discrete symmetries are recovered in the low-energy effective theory when the perturbative method to reduce the negative-energy degrees of freedom from the higher derivative theory is applied. In particular, we focus on the higher derivative Maxwell-Chern-Simons model which is a Lorentz invariant and parity-odd theory in 2+1 dimensions. The parity violation arises in the effective action of QED₃ as a quantum correction from the massive fermionic sector. We obtain the effective field theory which remains Lorentz invariant, but parity invariant to the order considered in the perturbative expansion.

[en] We construct a perturbative expansion of the scalar sector in the Myers-Pospelov model, up to second order in the Lorentz violating parameter and taking into account its higher-order time derivative character. This expansion allows us to construct an hermitian positive-definite Hamiltonian which provides a correct basis for quantization. Demanding that the modified normal frequencies remain real requires the introduction of an upper bound in the magnitude |k| of the momentum, which is a manifestation of the effective character of the model. The free scalar propagator, including the corresponding modified dispersion relations, is also calculated to the given order, thus providing the starting point to consider radiative corrections when interactions are introduced

No abstract available

[en] Short communication