Complex dynamics in simple systems with seasonal parameter oscillations

We study systems with periodically oscillating parameters that can give way to complex periodic or non periodic orbits. Performing the long time limit, we can define ergodic averages such as Lyapunov exponents, where a negative maximal Lyapunov exponent corresponds to a stable periodic orbit. By this, extremely complicated periodic orbits composed of contracting and expanding phases appear in a natural way. Employing the technique of $\epsilon$-uncertain points, we find that values of the control parameters supporting such periodic motion are densely embedded in a set of values for which the motion is chaotic. When a tiny amount of noise is coupled to the system, dynamics with positive and with negative non-trivial Lyapunov exponents are indistinguishable. We discuss two physical systems, an oscillatory flow inside a duct and a dripping faucet with variable water supply, where such a mechanism seems to be responsible for a complicated alternation of laminar and turbulent phases.Comment: New version with major change

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Two-dimensional mapping of micro-hardness increase on surface treated steel determined by photothermal deflection microscopy

An optical noncontact technique is presented that provides a two-dimensional map of the hardness of treated steel at the micrometer level. The photodeflection technique for determining the thermal diffusivity is shown to be a useful and rapid way to determine the hardness increase profile in two dimensions with only minor preparation of the sample (flat polish). This is possible due to the strong correlation found for this type of material between the inverse of the diffusivity and the hardness increment after treatment. The diffusivity retrieval is performed by a single measurement of the phase delay between the pump beam and the photodeflection signal thus allowing a rapid scanning of the surface. The surface scans of the hardness performed with this technique showed that anomalous regions can be identified that direct optical or scanning electron microscopy observation do not reveal.Fil: Crossa Archiopoli, Ulises. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Mingolo, Nélida. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Martinez, Oscar Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Belgrano. Facultad de Ciencias Exactas y Naturales; Argentin

Acción para el Fortalecimiento Comunicacional de Red Social en la OSP Fundación Organización Poder Popular

La Fundación Organización Poder Popular es la OSP con la cual se ha realizado el proceso de investigación correspondiente al Diplomado en Construcción de Redes Sociales de Comunicación. Proceso formativo e investigativo, que se formalizó teniendo en cuenta que la fundación se encuentra al servicio de la comunidad desde la orientación de su accionar con solidez en los aspectos teórico- práctico, legislación, política e instrumentos, que fortalezcan las soluciones para las problemáticas sociales y las oportunidades de participación e inclusión en pro del desarrollo social; comprometidos con la educación superior. Se efectuaron acompañamientos significativos, entrevistas, observaciones, donde se identificaron hallazgos importantes, los cuales llevaron a plantear una propuesta con un plan de acción para fortalecer la comunicación eficaz y asertiva.The Popular Power Organization Foundation is the OSP with which the research process corresponding to the Diploma in Construction of Social Communication Networks has been carried out. Formative and investigative process, which was formalized taking into account that the foundation is at the service of the community from the orientation of its actions with solidity in the theoretical-practical aspects, legislation, policy and instruments, that strengthen the solutions for social problems and opportunities for participation and inclusion in favor of social development; committed to higher education. Significant follow-ups, interviews and observations were carried out, where important findings were identified, which led to a proposal with an action plan to strengthen effective and assertive communication

Reliable passive mode locking with slow Q switching

An electro-optic modulator (EOM) has been added to a passive mode-locked Nd:glass laser in order to slow Q-switch the cavity. This guarantees that the laser will work near threshold even if the gain of the laser medium or the losses change from shot to shot. The losses at the EOM are used as the output coupling. This new configuration allows more reliable operation of the system

Photothermal microscopy applied to the characterization of nuclear fuel pellets

The photothermal photodeflection technique is shown to provide information on the homogeneity of fuel pellets, pore distribution, clustering detection of pure urania and gadolinea and to provide a two-dimensional mapping of the thermal diffusivity correlated to the composition of the interdiffused Gadolinium and Uranium oxide. Histograms of the thermal diffusivity distribution become a reliable quantitative way of quantifying the degree of homogeneity and the width of the histogram can be used as a direct measure of the homogeneity. These quantitative measures of the homogeneity of the samples at microscopic levels provides a protocol that can be used as a reliable specification and quality control method for nuclear fuels, substituting with a single test a battery of expensive, time consuming and operator dependent techniques.Fil: Zaldivar Escola, Facundo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Laboratorio de Haces Dirigidos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Martinez, Oscar Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Mingolo, Nelida. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Laboratorio de Haces Dirigidos; ArgentinaFil: Kempf, R.. Comisión Nacional de Energía Atómica; Argentin

Photothermal Microscopy

AbstractAn accessory for a commercial optical microscope was implemented to map the thermal diffusivity of the sample with high spatial resolution. The system is based in the photothermal technique recently developed by the group. It consists in the measurement with a probe laser of the surface curvature induced by the heat delivered by a modulated pump laser. A lock-in detection technique provides the signal amplitude and phase as a function of the modulation frequency. The accessory was mounted on the camera port of a metallographic microscope Olympus BX51. Results obtained on different samples are presented

Magnified expansion and compression of subpicosecond pulses from a frequency-doubled Nd:YLF laser

Includes bibliographical references.Pulses from a mode-locked frequency-doubled Nd:YLF laser have been spectrally broadened and subsequently expanded to more than 200 ps and recompressed to 750 fs by grating compressors with magnifying telescopes. The new design magnifies the time delay dispersion to a factor 10 times larger than achievable with standard compressors of similar size. The design of the system and its sensitivity to the variations in the position of its optical components is analyzed. The scheme will allow efficient amplification of subpicosecond pulses in dye amplifiers.This work was supported by N.S.F.-CONICET U.S.A./Argentina Cooperative Science Program under Grant INT 8802563, and by the National Science Foundation under Grants ECS 870507 and ECS 8606226. M. C. Marconi was supported by a Fellowship from the Universidad Nacional de Buenos Aires and Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina