RESUMEN

The objectives of this study were to assess the effects of participating in regular physical activity on the fitness of children with hyperactivity. The study compared a sample of children who were assessed as hyperactive with the same number of children rated as non-hyperactive. The Conners' Rating Scale was used for hyperactivity evaluation, while fitness levels were assessed using a battery of six motor tests prior to and following the completion of the physical exercise programme. The findings indicated that while overall fitness levels of both groups improved, the differences were not statistically significant. However, improvements shown within the group of hyperactive children with regard to coordination of the whole body, trunk strength and agility were statistically significant. Physical activity may be associated with enhanced levels of some aspects of physical fitness.

Asunto(s)

Trastorno por Déficit de Atención con Hiperactividad/fisiopatología , Ejercicio Físico/fisiología , Aptitud Física/fisiología , Preescolar , Femenino , Humanos , Masculino

RESUMEN

We report the implementation and operation of novel superhigh-reflectivity negative-dispersion dielectric mirrors for use in tunable ultrafast laser systems. The mirror structure is divided into two distinct regions: an underlying superhigh-reflectivity dielectric quarter-wavelength stack and an overlying negative-dispersion section consisting of only a few layers and forming simple multiple Gires-Tournois interferometers. The example that we present was designed for operation from 800 to 900 nm and has a near-constant group-delay dispersion of -40 fs(2) and a peak reflectivity greater than 99.99%. We show a comparison of the predicted and the measured mirror performance and application of these mirrors in a mode-locked Ti:sapphire laser tunable from 805 to 915 nm.

RESUMEN

We report the operation of an all-solid-state system for the generation of tunable mid-infrared sub-50-fs pulses. A Ti:sapphire regenerative amplifier, pumped by 10 W of power from 532-nm, diode-pumped, frequency-doubled Nd:YVO(4) lasers, produced 4-muJ energy, sub-50-fs pulses at 800 nm with a 100-kHz repetition rate. This output was used to drive a beta-BaB(2)O(4) optical parametric amplifier followed by a difference-frequency generator based on a AgGaS(2) crystal. Continuous tuning of ultrafast pulses from 2.4m to longer than 12mum was obtained. A performance comparison of difference-frequency generation in type I and type II phase-matched AgGaS(2) is reported.

RESUMEN

We present a cw chromium-doped forsterite laser that permits rapid wavelength tuning over a broad bandwidth and demonstrate the application of this source to frequency-domain ranging and optical tomography. The entire tuning range of 1200 to 1275 nm can be swept in less than 500 micros . This permits frequency-domain ranging to be performed with a scan rate of 2 kHz and an axial resolution of 15 microm .

RESUMEN

The development of techniques for high-speed image acquisition in optical coherence tomography (OCT) systems is essential for suppressing motion artifacts when one is imaging living systems. We describe a new OCT system for performing micrometer-scale, cross-sectional optical imaging at four images/s. To achieve OCT image-acquisition times of less than 1 s, we use a piezoelectric fiber stretcher to vary the reference arm delay. A Kerr-lens mode-locked chromium-doped forsterite laser is employed as the low-coherence source for the highspeed OCT system. Dynamic, motion-artifact-free in vivo imaging of a beating Xenopus laevis (African frog) heart is demonstrated.

RESUMEN

An all-solid-state Kerr-lens mode-locked Cr:forsterite laser operating at 1.28 microm is demonstrated as a shortcoherence-length, high-average-power source for optical coherence tomographic (OCT) imaging. We achieve ultrahigh resolution by spectrally broadening the laser pulses, using self-phase modulation in a dispersionshifted single-mode fiber. OCT imaging with a resolution of 6 microm and a dynamic range of 115 dB is achieved.

RESUMEN

We describe a new design for chromium-doped forsterite lasers based on near-IR (700-800-nm) pumping of a thin (3-mm) crystal. In contrast with pumping at 1.06 microm, near-IR pumping permits the use of shorter crystal lengths, which enable one to develop compact and diode-pumped laser geometries. Near-IR pumping also results in an increased effective figure of merit and tuning performance. Using a Ti:Al(2)O(3) pump laser, we investigated cw laser characteristics over a range of pump wavelengths compatible with diode pumping. Room-temperature cw operation with a tuning range of 1175 to 1375 nm was achieved. Kerr-lens mode-locked operation of this laser was also demonstrated with pulse durations of ~50 fs.

RESUMEN

We describe a new heterodyne nondegenerate pump-probe waveguide measurement technique that permits independent control of wavelengths, pulse widths, and polarizations of the pump and probe pulses in a collinear geometry. This technique provides both time- and spectral-domain information and can be applied to transmission and index measurements alike. We demonstrate this technique for the measurement of gain dynamics in a strained-layer single-quantum-well diode laser.

RESUMEN

We describe the design, fabrication, measurement, and performance of a set of cryogenic millimetersubmillimeter wavelength filters used in a balloonborne bolometric radiometer. The set contains single resonant mesh grids used as dichroic beam splitters, resonant meshes in a double quarter-wave configuration, a commercial inductive grid filter, and high-frequency blocking filters. The resultant system has passbands at λ = 1.73, 1.05, 0.61, 0.44 mm with δλ/λ = 0.23, 0.23, 0.12, 0.06. Limits on high-frequency leakage are deduced from laboratory measurements and from the analysis of flight data. The filter set response to three different sources of radiation is presented to show the method and limitations of our characterization. The key element of the filter system is a resonant periodic array of cross-shaped holes etched in thin aluminum. We give an empirical scaling law for the resonant wavelength as a function of structure parameters for aluminum on 25-µm-thick Mylar. Plots of the transmittance for normally incident radiation and the transmittance and reflectance for a 45° incident radiation are presented.