Los laboratorios de enseñanza desde una perspectiva histórica y social

A partir de un estudio de caso (Física en Ingeniería), se indaga la evolución de los laboratorios de enseñanza, desde el marco de las olas históricas. El enfoque es cualitativo, holístico e interpretativo, se analizan procesos desde la perspectiva de los actores sociales involucrados. Se identifican los cambios en los objetivos y actividades planteados, con miras a desarrollar los conocimientos, científico e ingenieril, de los estudiantes. Se reconocen los cambios en los modelos de ciencia y de tecnología, y la influencia de los procesos políticos y sociales sobre la evolución de la enseñanza de la física en carreras de ingeniería. Se destaca la importancia que tiene la realización conveniente de actividades experimentales, para que los estudiantes puedan desarrollar ambos tipos de conocimiento, científico e ingenieril, aun desde los primeros años de su carrera

Isotopic Grand Unification with the Inclusion of Gravity (revised version)

We introduce a dual lifting of unified gauge theories, the first characterized by the isotopies, which are axiom- preserving maps into broader structures with positive-definite generalized units used for the representation of matter under the isotopies of the Poincare' symmetry, and the second characterized by the isodualities, which are anti-isomorphic maps with negative-definite generalized units used for the representation of antimatter under the isodualities of the Poincare' symmetry. We then submit, apparently for the first time, a novel grand unification with the inclusion of gravity for matter embedded in the generalized positive-definite units of unified gauge theories while gravity for antimatter is embedded in the isodual isounit. We then show that the proposed grand unification provides realistic possibilities for a resolution of the axiomatic incompatibilities between gravitation and electroweak interactions due to curvature, antimatter and the fundamental space-time symmetries.Comment: 20 pages, Latex, revised in various details and with added reference

Invariant variational principle for Hamiltonian mechanics

It is shown that the action for Hamiltonian equations of motion can be brought into invariant symplectic form. In other words, it can be formulated directly in terms of the symplectic structure $\omega$ without any need to choose some 1-form $\gamma$, such that $\omega= d \gamma$, which is not unique and does not even generally exist in a global sense.Comment: final version; to appear in J.Phys.A; 17 pages, 2 figure

The Moyal-Lie Theory of Phase Space Quantum Mechanics

A Lie algebraic approach to the unitary transformations in Weyl quantization is discussed. This approach, being formally equivalent to the $\star$-quantization, is an extension of the classical Poisson-Lie formalism which can be used as an efficient tool in the quantum phase space transformation theory.Comment: 15 pages, no figures, to appear in J. Phys. A (2001

Quimioesterilización de Anastrepha fraterculus (Diptera: Tephritidae) con un regulador del crecimiento de insectos

Anastrepha fraterculus is a fruit pest of economic importance in South America and northwestern Argentina. Currently, it is controlled with toxic baits but there is a demand for environmentally acceptable methodologies. The use of inhibitors of the chitin synthesis is proposed as a tool to sterilize adults in the field. The aim of this study was to evaluate the efficacy of different doses of lufenuron to generate chemosterilization in A. fraterculus. Three experiments were performed. In the first two, the product was incorporated into the diet of the adults from emergence to sexual maturity. Treated individuals from one sex were crossed with untreated individuals from the other sex. Eggs were collected and allowed embryonic development. In the third trial, untreated males and females were crossed and allowed to copulate. Subsequently, females were exposed to the product and the eggs were collected. Egg hatch was affected in the three experiments in a dose dependent way. In Experiment 3, the effect of the product was evidenced 48 hours after exposure. Fecundity was also affected when the females were the treated sex. The results show that exposure of adults to lufenuron reduces egg hatch in A. fraterculus encouraging further investigations to adapt this methodology for this species.Fil: Ruiz, J. E.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Santilli, Melisa del Valle. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Cabrera, Debora Carina. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; ArgentinaFil: Vera, M. T.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; ArgentinaFil: de la Vega, M. H.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentin

Organic-Inorganic Hybrid Coatings for Corrosion Protection of Metallic Surfaces

A variety of organic-inorganic hybrids have been designed to act as anticorrosive coatings of metallic substrates. Among them, epoxy-silica and poly(methyl methacrylate) (PMMA)- silica hybrids, prepared by the sol-gel process and deposited onto steel or aluminum alloys, have demonstrated high anticorrosive efficiency combined with high thermal and mechanical resistance. Lignin, carbon nanotubes, and graphene oxide have been incorporated into PMMA-silica hybrids as reinforcement agents, and cerium (IV) as corrosion inhibitor. Both hybrids were characterized in terms of their structural and thermal characteristics using different pectroscopies, microscopies and thermogravimetric analysis. Both hybrids present homogeneous nanostructure composed of highly condensed silica nanodomains covalently bonded to the polymeric phase. The transparent coatings with a thickness of 2–7 μm have low surface roughness, high adhesion to metallic substrates, elevated thermal stability, and excellent barrier behavior. Electrochemical impedance spectroscopy showed for coated samples a high corrosion resistance of up to 50 GΩ cm2 and durability >18 months in saline solution. Further improvement of corrosion resistance, thermal and mechanical stability was achieved by incorporation of lignin, carbon nanotubes, and graphene oxide into PMMA-silica matrix, and a self-healing effect was observed after Ce(IV) addition. The results are compared and discussed with those recently reported for a variety of hybrid coatings

Protective Coatings Based on PMMA–Silica Nanocomposites Reinforced with Carbon Nanotubes

Polymethylmethacrylate–silica hybrids have been prepared using the sol–gel route by the radical polymerization of methyl methacrylate(MMA) using benzoyl peroxide (BPO) as a thermal initiator and 3-(trimethoxysilyl)propyl methacrylate(MPTS) as a coupling agent, followed by acid-catalyzed hydrolytic condensation of tetraethoxysilane (TEOS). Carbon nanotubes (CNTs) were first dispersed either by surfactant addition or by functionalization with carboxyl groups and then added at a carbon (CNT) to silicon (TEOS and MPTS) molar ratio (CCNT/SiHybrid) of 0.05% to two different hybrid matrices prepared at BPO/MMA molar ratios of 0.01 and 0.05. Films of 2–7 μm thickness deposited onto carbon steel by dip-coating were characterized in terms of their microstructure and their mechanical, thermal and anticorrosive behavior. Atomic force microscopy and optical microscopy confirmed that there was a homogeneous dispersion of CNTs in the nanocomposites and that the surfaces of the films were very smooth. X-ray photoelectron spectroscopy (XPS) confirmed the nominal composition of the films while nuclear magnetic resonance showed that the connectivity of the silica network was unaffected by CNT loading. Thermogravimetric analysis and mechanical measurements confirmed an increase of thermal stability, hardness, adhesion and scratch resistance of CNT-loaded coatings relative to those without CNTs. Electrochemical impedance spectroscopy measurements in 3.5% NaCl solution interpreted in terms of equivalent circuits showed that the reinforced hybrid coatings, prepared at the higher BPO/MMA molar ratio used in this work, act as a very efficient anticorrosive barrier, with an impedance modulus up to 109 Ω cm2