45 research outputs found
Double aperture speckle method using a BSO crystal for in plane displacement
No full textSPIE Proceedings Vol. 3572The possibility of using a BSO crystal as a recording medium of specklegrams with carrying frequency fringes, to storage multiple interferograms, for uniform in-plane displacements, is presented. Experimental results are shown.CONICET (Argentina)FundaciOn Antorchas (Argentina)CICPBA (Argentina)Facultad de Ingenierla Universidad Nacional de La Plata (Argentina)COLCIENCIAS (Colombia
Estudio de un conversor óptico fotorrefractivo y sus aplicaciones
No full textObjetivos de la tesis:
- estudiar el registro y reconstrucción de distribuciones unidimensionales (redes de Ronchi) de baja frecuencia, registradas incoherentemente en un conversor óptico fotorrefractivo, sin soporte holográfico y en configuración transversal. En particular, se pretende caracterizar el estado de polarización del haz de lectura producido por la modulación de birrefríngencia inducida en el medio. El interés, en este estudio, es controlar el contraste y así optimizar la imagen reconstruida a la salida del sistema.
- implementar los efectos Talbot y Lau a partir de una red registrada en un cristal fotorrefractivo. Esto ha permitido visualizar estos efectos con características novedosas, propias de la naturaleza del registro y en esta modalidad efectuar un tratamiento unificado de los fenómenos analizados. A su vez, estas características han motivado la implementación fotorrefractiva de los interferómetros Talbot y Lau.Doctor en FísicaUniversidad Nacional de La PlataFacultad de Ciencias Exacta
Generación de campos de <i>speckle</i> mediante un modulador espacial de luz
No full textEn esta tesis se generaron experimentalmente campos de speckle gaussianos con características totalmente controlables de forma digital mediante el empleo de pantallas de cristal líquido como moduladores espaciales de luz (LC-SLM). Para ello, se desarrolló una estrategia que condujo a generar los campos de speckle predichos, no obstante las limitaciones que presentan los SLMs permitiendo superar el desempeño que brindan los difusores físicos. Así, el aporte de estos estudios radica en la posibilidad de generar campos de speckle independientes cuyas propiedades estadísticas se puedan controlar sin desplazamiento o modificación de los componentes del arreglo experimental. Estos logros pueden ser útiles para mejorar procedimientos y optimizar el rendimiento de aquellas aplicaciones que utilicen patrones de speckle y el control de los mismos sea un aspecto clave.Doctor en Ciencias Exactas, área FísicaUniversidad Nacional de La PlataFacultad de Ciencias Exacta
Ageing Behavior of Porous and Dense Asphalt Mixtures in the Field
No full textBitumen ageing is one of the principal factors causing the deterioration of asphalt pavements. As bitumen ages, the pavement loses its ability to relax stresses during loading/unloading and thermal cooling process, thus the risk of cracking increases. Oxidation and ultraviolet (UV) radiation are believed to be the main factors that can cause bitumen ageing during pavement service life. The aim of this study is to evaluate the mechanical behavior of porous and dense asphalt pavements during field ageing. Pavement test sections were constructed in 2014 and are being exposed to actual environmental conditions since then. To investigate the effect of UV radiation on ageing, UV reflective glass-plates were utilized to cover part of the pavement surface. To study the evolution of the pavements’ mechanical properties, asphalt cores were collected from the test sections periodically (at one-year intervals). The changes in the stiffness modulus of the mixtures were determined via cyclic indirect tensile tests. The results show that the effect of mineral aggregate packing, and hence of air-void distribution and connectivity, on the ageing sensitivity (both thermal and UV ageing sensitivity) of the pavements with time was found to be significant, as the changes of the stiffness of the porous mixtures were greater than that of dense mixtures.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pavement Engineerin
Speckle photography with different pupils in a multiple-exposure scheme
No full textThe use of different multiple aperture pupils for recording each image in speckle photography is proposed.
The introduction of suitable spatial frequency carriers, by internally modulating imaged speckles, allows one to selectively isolate or combine the spectral content of different images into spatially separated regions in the Fourier plane. Theoretical and experimental results extend the speckle photography technique to the depic tion of several specklegrams of multiple uniform in plane displacements. In this case, because different pu pils are considered for recording, the cross correlation functions for the amplitudes and intensities in the image plane are calculated on the basis of the statistical properties of the object. Also, the ensemble average inten sity in the Fourier plane is analytically derived, and fringe visibility is investigated
Modulated speckle simulations based on the random-walk model
No full textThe random-walk model is employed to simulate modulated speckle patterns. We demonstrate that the geometrical image approximation fails to describe the modulated speckle pattern. A new approach to analyzing this phenomenon is proposed. The validity of the approximations employed is verified by comparison of the simulation with the experimental results. Speckle metrological applications and phase measurement techniques could be improved by taking advantage of this model
Experimental study of volume speckle in four-wave mixing arrangement
No full textWe study a high frequency modulated speckle pattern in a four-wave mixing arrangement. The three-dimensional nature of the speckles is considered in the phase conjugate reflectivity evaluation which implies to analyze its dependence on the average speckle size. Also, the reflectivity is analyzed in terms of the external applied field, the probe beam ratio, and the pupil aperture diameter of the imaging system that generates the subjective speckle beam
Phase-object analysis with a speckle interferometer
No full textWe describe the characteristics of a double-exposure specklegram obtained through a double-aperture system, by introduction of a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and visibility of the interferometric fringes in the Fourier plane are analyzed. An alternative interferometric technique for phase-object detection is proposed
Experimental Validation of the Dual-Oxidation Routes in Bituminous Binders
No full textOxidative ageing in bituminous materials is considered to be one of the most important factors for distress types in road applications. The increasing interest in oxidative ageing has highlighted the need for a thorough understanding of the oxidation mechanisms at molecular level. This paper offers some insight in the validity of the proposed hypotheses about the oxidation routes of bitumen, the fast- and the slow-rate route, reflecting on previous studies. Fourier-Transform Infrared (FTIR) and Electron Paramagnetic Resonance (EPR) spectroscopy were utilised for this verification. To elucidate the uncertain formation of sulfoxides, an additional surface investigation with Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was performed. The findings of the aforementioned techniques reveal the existence of the oxidation products reported previously and contribute to the understanding of the oxidation mechanisms. Overall, this research strengthens experimentally the hypotheses of the dual-oxidation routes of bitumen.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pavement Engineerin
Mechanisms in Healing of Bitumen and the Impact of Normal Force
No full textDamage in pavements is known to reduce over time when the material is left to rest, this phenomenon is known as healing. It has been shown that healing is an important influence factor in pavement performance. However, an accepted method to assess the healing capability of a pavement is currently not available. Healing of cracks is assumed to be the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of surfaces in contact (intrinsic healing). The paper describes influencing parameters of these two processes. The healing potential of bitumen is assessed using a novel test method. In this method two pieces of bitumen are brought together and left to heal under controlled condi-tions. After healing the amount of healing is assessed by testing the specimens us-ing a direct tensile test. From the results it can be seen that normal force has a sig-nificant impact on the observed healing, indicating that the process of two surfaces coming into contact (wetting) has a significant impact on healing behavior of the bitumen.Pavement Engineerin
