Santiago J. Pérez-Ruiz

Pulsed Photoacoustic: A Reliable Technique to Investigate Diffuse Phase Transitions and Associated Phenomena in Ferroelectrics

Often permittivity against T curves do not provide a conclusive characterisation of dielectric features of ferroelectric materials. Particularly, when permittivity is obtained from impedance measurements, where to experimental data is gradually lost at high frequencies when the temperature rises. Here we show how a combination of permittivity measurements and photoacoustic experiments can give a much more complete characterization of the ferro-paraelectric phase transitions and associated phenomena than those obtained from permittivity data alone. Peaked correlation curves, obtained from photoacoustic experiments were interpreted to be a manifestation of large enough microscopic variations of the compressibility as the temperature changed. On one hand, using a classical ferroelectric (BaTiO 3 ) and a well-recognized relaxor (Ba(Ti 0.65 Zr 0.35 )O 3 ) the main differences between their photoacoustic response are established. On the other hand, dielectric and photoacoustic results from the compounds Bi 2 WO 6 and Bi 2 [Ta 0.1 W 0.9 ]O 6 − δ , were combined to characterize the temperature dependence of their dielectric behavior. Results provide evidence of the presence of a diffuse phase transition in Bi 2 WO 6 at 660°C similar to that corresponding to relaxor behavior. Additionally the occurrence of a classical ferro-paraelectric phase transition above 900°C was found. This last phenomenon is detectable only by photoacoustic experiments. In Bi 2 [Ta 0.1 W 0.9 ]O 6 − δ the presence of a well defined transition was not detected. Dielectric determinations throughout ac measurements were carried out in the frequency interval 5 Hz-13 MHz. A pulsed Nd:YAG laser (10 Hz, 5 ns pulse width) was used to perform the photoacoustic experiments, where the out-coming signal was detected by a piezoelectric transducer. Dielectric and photoacoustic experiments were performed in a temperature interval from 250°C up to 1000°C.

Modified acoustic transmission tube apparatus incorporating an active downstream termination

Current techniques for measuring normal incidence sound transmission loss with a modified impedance tube, or transmission tube, require setting up two different absorbing termination loads at the end of the downstream tube [ASTM E2611-09, Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method (American Society for Testing and Materials, West Conshohocken, 2009)]. The process of physically handling the two required passive absorbing loads is a possible source of measurement errors, which are mainly due to changes in sample test position, or in test setup re-assembly, between measurements. In this paper, a modified transmission tube apparatus is proposed for non-intrusively changing the downstream acoustic load by means of a combined passive-active termination. It provides a controlled variable sound absorption which simplifies the setup of standard two-load techniques, without the need of physically handling the apparatus during the tests. This virtually eliminates the risk of errors associated with the physical manipulation of the two passive terminations. Transmission loss measurements in some representative test conditions are reported, showing improvements over current implementations, in reducing by approximately 50% the measurement variations associated with the setup of the two required absorbing terminations. Measurement results agree within 0.4 dB (maximum difference in high resolution broadband), and 0.04 dB (mean difference in 1/3-octave bands), with those obtained using standard passive two-load methods.

Lexical tonal discrimination in Zapotec children. A study of the theta rhythm

El zapoteco es un lenguaje hablado principalmente en el estado de Oaxaca, en Mexico, que tiene la caracteristica de ser tonal; es decir, las palabras homofonas que difieren en la altura del fundamental tienen diferente significado. El objetivo de este trabajo fue analizar los cambios del ritmo theta del electroencefalograma en el curso de la discriminacion de palabras bisilabicas homofonas en zapoteco. Metodo: Se empleo el analisis espectral del electroencefalograma durante la discriminacion tonal lexica del lenguaje zapoteco en 12 ninos sanos de 9-16 anos. Resultados: Se observo una mayor potencia relativa theta en la region temporal derecha durante la discriminacion lexica en comparacion con el registro de reposo-ojos abiertos. Tambien se observaron varias correlaciones significativas intra e interhemisfericas con predominio entre la region frontotemporal izquierda y temporal derecha mientras se realizaba la discriminacion tonal lexica. Conclusion: Estos resultados sugieren que hay un mayor compromiso de las redes neuronales en el hemisferio derecho que participan en la discriminacion del lenguaje zapoteco

Discriminación tonal léxica en niños zapotecas. Un estudio del ritmo theta

BACKGROUND Zapotec is a language used mainly in the state of Oaxaca in Mexico of tonal characteristic; homophone words with difference in fundamental frequency with different meanings. Our objective was to analyze changes in the electroencephalographic (EEG) theta rhythm during word discrimination of lexical tonal bi-syllabic homophone word samples of Zapotec. METHODS We employed electroencephalography analysis during lexical tonal discrimination in 12 healthy subjects 9-16 years of age. RESULTS We observed an increase in theta relative power between lexical discrimination and at rest eyes-open state in right temporal site. We also observed several significant intra- and inter-hemispheric correlations in several scalp sites, mainly in left fronto-temporal and right temporal areas when subjects were performing lexical discrimination. CONCLUSIONS Our data suggest more engagement of neural networks of the right hemisphere are involved in Zapotec language discrimination.

Phonological awareness and sinusoidal amplitude modulation in phonological dislexia.

OBJECTIVE Dyslexia is the difficulty of children in learning to read and write as results of neurological deficiencies. The objective was to test the Phonological awareness (PA) and Sinusoidal amplitude modulation (SAM) threshold in children with Phonological dyslexia (PD). METHODS We performed a case-control, analytic, cross sectional study. We studied 14 children with PD and 14 control children from 7 to 11 years of age, by means of PA measurement and by SAM test. The mean age of dyslexic children was 8.39 years and in the control group was 8.15. RESULTS Children with PD exhibited inadequate skills in PA, and SAM. We found significant correlations between PA and SAM at 4 Hertz frequency, and calculated regression equations that predicts between one-fourth and one-third of variance of measurements. CONCLUSION Alterations in PA and SAM found can help to explain basis of deficient language processing exhibited by children with PD.

Thermomechanical and Photophysical Properties of Crystal-Violet-Dye/H2O Based Dissolutions via the Pulsed Laser Photoacoustic Technique

Different thermoelastic parameters, for example, the acoustic attenuation and the speed of sound, are fundamental for instrumental calibration and quantitative characterization of organic-based dissolutions. In this work, these parameters as functions of the concentration of an organic dye (crystal-violet: CV) in distillated water (H2O) based dissolutions are investigated. The speed of sound was measured by the pulsed-laser photoacoustic technique (PLPA), which consists in the generation of acoustic-waves by the optical absorption of pulsed light in a given material (in this case a liquid sample). The thermally generated sound-waves traveling through a fluid are detected with two piezoelectric sensors separated by a known distance. An appropriate processing of the photoacoustic signals allows an adequate data analysis of the generated waves within the system, providing an accurate determination of the speed of sound as function of the dye-concentration. The acoustic attenuation was calculated based on the distance of the two PZT-microphones to an acoustic-source point and performing linear-fitting of the experimental data (RMS-amplitudes) as function of the dye-concentration. An important advantage of the PLPA-method is that it can be implemented with poor or null optical transmitting materials permitting the characterization of the mechanical and concentration/aggregate properties of dissolved organic compounds.

Experience of students of composition and instrument construction at the National School of Music of UNAM in the auditory normalization of timbre with age and with exposure to different instruments

A study of tonal memory using as stimuli synthesized harmonic sounds with a quasi‐square‐wave spectrum has been carried out at ENM. The subjects were young boys and girls (age span=8:1–15:6), starting their musical education at the Cycle for Musical Initiation, and young adults of either sex (age span=13:11−42), with experience of from 1 to 10 years in singing, piano, violin, clarinet, flute, trumpet, saxophone, guitar, percussion, or composition at the regular courses of ENM. While the children were adept in retaining in memory tonal changes of a major or a minor second using the synthesized stimuli, the older students showed much greater difficulty with this test, particularly those whose instrument had a timbre closer to that of the square wave (clarinet or saxophone), or who were undertaking studies of composition. Students of composition or instrument construction at the Instrument Construction Workshop of ENM have embarked on a further analysis of auditory normalization of timbres of diverse synthes...

Further studies of perception of speech and music in children

The present research is a continuation of an investigation carried out at C.C.R.M.A., Stanford University [J. Acoust. Soc. Am. 93, 2403(A) (1993)], on the perception of the pitch of speech and music in children. Experiments sought to determine whether male and female subjects [N=120 (40×3)] 6 to 14 years of age, monolingual speakers of either Spanish, a tongue with prosodic pitch contrasts, or Otomi or Zapotec, Otomanguean tongues with lexical pitch contrasts between words, and having training in singing or in diverse musical instruments would perceive the pitch of speech as they perceived the pitch of musical sounds. Data obtained provide information that Spanish‐speaking subjects at all ages and younger Otomi‐ and Zapotec‐speaking subjects perceived the pitch of samples of their language in a manner that was similar to their perception of the pitch of synthesized musical samples. These results applied irrespective of musical background. On the other hand, older subjects speaking Otomanguean tongues seem...