In this work we present a characterization of yeast dynamic speckle activity during growth in an isolated agar culture medium. We found that it is possible to detect the growth of the microorganisms even before they turn out to be visible. By observing the time evolution of the speckle activity at different regions of the culture medium we could extract a map of the growth process, which served to analyze how the yeast develops and spreads over the agar's medium. An interesting point of this study concerns with the influence of the laser light on the yeast growth rate. We have found that yeast finds hard to develop at regions with higher laser light illumination, although we used a synchronous system to capture the speckle pattern. The results obtained in this work would serve us as a starting point to fabricate a detector of growing microorganism colonies, with obvious interesting applications in diverse areas.
The aim of this work is to present an experience based on the use of digital images and computer processing techniques for enhanced optics laboratory teaching aids. The use of digital images offers the possibility of analysing some phenomena quantitatively, which would be very difficult to do with the traditional equipment available in teaching labs. In order to obtain high quality teaching material, a number of practical aspects should be taken into account during the process of image acquisition and subsequent analysis. Examples of quantitative experiments are presented; they cover the usual topics at undergraduate level, both geometrical and physical optics and even spectral analysis of the light.
This work seeks to determine the age of a fruit from observation of its dynamic speckle pattern. A mobile speckle pattern originates on the fruit's surface due to the interference of the wavefronts reflected from moving scatterers. For this work we analyzed two series of photographs of a strawberry speckle pattern, at different stages of ripening, acquired with a CMOS camera. The first day, we took ten photographs at an interval of one second. The same procedure was repeated the next day. From each series of images we extracted several statistical descriptors of pixel-to-pixel gray level variation during the observation time. By comparing these values from the first to the second day we noticed a diminution of the speckle activity. This decay demonstrated that after only one day the ripening process of the strawberry can be detected by dynamic speckle pattern analysis. For this study we employed a simple new algorithm to process the data obtained from the photographs. This algorithm allows defining a global mobility index that indicates the evolution of the fruit's ripening.
Metallic structures made of ribbed iron bars (ADN-420) are of common use in sheds and supporting structures. Usually, trusses are constructed with many pieces of ribbed iron bars, combined together through a welding process. Although ribbed iron manufacturers do not recommend this type of structure it is still frequently used. The main weakness of these trusses is the welding point because ribbed iron is not a material suitable for welding. This work presents results obtained from an analysis of welding points between ribbed iron bars extracted from a collapsed truss, by means of conventional (optical) and digital holographic interferometry (HI and DHI, respectively). The experiments were divided in two different series of studies. The first series were performed by HI on metallographic samples while the second series were done by DHI on different welding points. These results were complemented by metallographic analysis made in an external laboratory. DHI indicated that the bars did not have important failures but evidenced defects in one of the welding points under analysis. This information together with metallographic results allowed inferring that the collapse was probably due to an error in the design of the structure, since the iron bars were out of standard compliance.
In this work we have studied the dynamic speckle patterns of mucor fungi colonies, which were inoculated on different samples. We were interested in analyzing the development of fungi colonies in bones, since during the last two years, a series of infections by mucor fungi have been reported on patients from different hospitals in Argentina. Coincidentally, all of these infections appeared on patients that were subjected to a surgical intervention for implantation of a titanium prosthesis. Apparently, the reason of the infection was a deficient sterilization process in conjunction with an accidental contamination. We observed that fungi growth, activity and death can be distinguished by means of the dynamic speckle technique.
The treatment of fresh fruits with different doses of ionizing radiation has been found effective for delaying ripening and,
in this way, to extend shelf life. This preservation method is likely to produce some functional or constitutive changes in
the cellular structure of the fruit. In this work, a test of the effectiveness of fruit irradiation with relatively low doses was
performed by using dynamic speckle imaging. Bananas from a same lot were chosen, being a first series of them
irradiated with different doses of 0.2, 0.4 and 0.6 kGy (Gy = J/kg) and a second series with doses of 0.2, 0.4, 0.6 and 1
kGy. Non irradiated bananas (0 kGy) were considered as the lot reference for contrast. Irradiation was carried out at the
Semi-Industrial Cobalt 60 facility of the Ezeiza Atomic Center, with an activity of 6 × 10<sup>5</sup> Curie and a dose rate of 28.5
Gy/min. The objective of this work is to analyze differences in the maturation process between irradiated and nonirradiated
fruits by means of dynamic speckle pattern evaluation.
Techniques based on holographic interferometry have achieved a mature state of non destructive testing applications in
industry and nowadays they are rising as interesting and promising tools in the field of conservation practices; giving
information about the condition of structural integration of artworks. In the practice of these techniques it is necessary to
generate a relative deformation in the object under study. Depending of the characteristics of the artwork, different
methods may be used to achieve the desired displacement; being thermal excitation by means of filament lamps and
wave sounds generated by speakers the most common. By applying these methods the deformation process usually
involves a large area of the object, which limits the information obtained of a finite region. However, the use of a wave
sound emitter of small dimensions, like a low power monotone buzzer, allows to decrease the affected area and to obtain
information about the structural integrity of localized points of the surface.
In the present study conventional double exposure double way holographic technique based on holographic films was
used to obtain an out of plain deformation pattern caused by a sound emitter in an oil painting which has suffered heavy
structural damage. Optimization of the excitation sound wave characteristics (frequency and amplitude) and the
adjustment and calibration of the experimental set up, in order to obtain precise information about the physical and
mechanical integrity of localized points of the painting are reported.