Juan Antonio Martínez Rojas

Physical Analysis of Several Organic Signals for Human Echolocation : Oral Vacuum Pulses

Active human echolocation can be an extremely useful aid for blind people. Active echolocation can be trained with both artificial and organic signals. Organic signals offer some advantages over artificial ones. Very detailed studies of organic signals in animals have been done. However, in the case of humans, the scientific literature is very scarce and not systematic. This is the first paper of a series on the properties of several suitable sounds for human echolocation. In this work, we offer a detailed analysis of these sounds, comparing their merits from a physical point of view. The results of this study have important applications to design systematic and optimized training protocols for accurate echolocation awareness.

Physical Analysis of Several Organic Signals for Human Echolocation: Hand and Finger Produced Pulses

In the first part of this work we studied several oral signals suitable for human echolocation. Palatal clicks were proven to be optimal pulses for this task. In the second part of this series, we analyze, from a physical and psychoacoustical point of view, the sounds produced by hand clapping and finger snapping. One additional sound is studied: a loud sound made by clapping one finger against the vacuum space between fingers near the knuckles. The results of our experiments show that these sounds are fairly good for echolocation. The best one is the knuckle vacuum pulse, due to its extraordinary acoustical properties. This sound has many of the good characteristics of palatal clicks with an even richer content in the high frequency part of the spectrum. Besides, this sound exhibits an interesting symmetry in the ultrasound range, which palatal clicks do not have. Experimenters noticed that, in spite of their sound quality, hand and finger produced pulses were inferior to palatal clicks, mainly due to difficulties in the relative orientation between the head and the hands, without sight clues, lack of reproducibility and muscle fatigue during long sessions. Some people with basic echolocation skills, however, found these sounds useful for distant sources, because they were able to make such pulses louder than palatal clicks.

Study of leaky modes in high contrast Bragg fibres

An accurate full vectorial treatment of the leaky modes in Bragg fibres with high refractive index variations is presented. The model can describe arbitrary functions of the relative permittivity inside the fibre. Boundary conditions are substituted by smooth continuous functions. This allows the use of very precise numerical and analytical approaches to the solutions. As a concrete example, a calculation of leaky modes inside a Bragg fibre with a quadratic periodic variation of its relative permittivity profile is made.

Spectral Biomimetic Technique for Wood Classification Inspired by Human Echolocation

Palatal clicks are most interesting for human echolocation. Moreover, these sounds are suitable for other acoustic applications due to their regular mathematical properties and reproducibility. Simple and nondestructive techniques, bioinspired by synthetized pulses whose form reproduces the best features of palatal clicks, can be developed. The use of synthetic palatal pulses also allows detailed studies of the real possibilities of acoustic human echolocation without the problems associated with subjective individual differences. These techniques are being applied to the study of wood. As an example, a comparison of the performance of both natural and synthetic human echolocation to identify three different species of wood is presented. The results show that human echolocation has a vast potential.

Fractal-based image enhancement techniques inspired by differential interference contrast microscopy

Differential interference contrast microscopy is a very powerful optical technique for microscopic imaging. Inspired by the physics of this type of microscope, we have developed a series of image processing algorithms aimed at the magnification, noise reduction, contrast enhancement and tissue analysis of biological samples. These algorithms use fractal convolution schemes which provide fast and accurate results with a performance comparable to the best present image enhancement algorithms. These techniques can be used as postprocessing tools for advanced microscopy or as a means to improve the performance of less expensive visualization instruments. Several examples of the use of these algorithms to visualize microscopic images of raw pine wood samples with a simple desktop scanner are provided.