Biomedical subjects

Pedro Andrés

Publications and source records attributed to Pedro Andrés.

8 recordsLinked to original sources

PubMed2006

High spatiotemporal resolution in multifocal processing with femtosecond laser pulses.

We report spatial and temporal dispersion compensation for fan-out of femtosecond pulses with a low-frequency diffraction grating by means of a hybrid diffractive-refractive lens triplet. In this way, we achieve a multifocal light structure with nearly diffraction-limited light spots even for 20 fs pulse duration. The spatial chromatic compensation, which drastically reduces the lateral walk-off of the various spectral components, also allows us to improve the available bandwidth at the dispersion-compensated diffraction orders. In fact, the temporal width of the output pulse is essentially limited by the group-delay dispersion term, which is shown to be small. The high spatiotemporal resolution provided by our proposal permits parallel multifocal processing of materials with femtosecond pulses.

Journal Article↗

PubMed2006

Differential toolbox to shape dispersion behavior in photonic crystal fibers.

We present an analytical procedure to compute the first derivatives of the propagation constants with respect to several structural parameters in photonic crystal fibers (PCFs). From them we can easily evaluate the same derivatives of other directly related magnitudes. The above derivatives provide the trend of the magnitude at issue, which allows us to take advantage of a gradient-based algorithm to shape the properties of the guiding structure. In this way we implement an optimization process to carry out real inverse design in PCFs. We focus our attention on designing PCFs with a specific chromatic dispersion behavior. Likewise, the same approach makes it possible to analyze their fabrication tolerances.

Journal Article↗

PubMed2005

Space-time analogy for partially coherent plane-wave-type pulses.

In this Letter we extend the well-known space-time duality to partially coherent wave fields and, as a limit case, to incoherent sources. We show that there is a general analogy between the paraxial diffraction of quasi-monochromatic beams of limited spatial coherence and the temporal distortion of partially coherent plane-wave pulses in parabolic dispersive media. Next, coherence-dependent effects in the propagation of Gaussian Schell-model pulses are retrieved from that of their spatial counterpart, the Gaussian Schell-model beam. Finally, the last result allows us to present a source linewidth analysis in an optical fiber communication system operating around the 1.55 microm wavelength window.

Journal Article↗

PubMed2005

Analytical evaluation of chromatic dispersion in photonic crystal fibers.

We present a two-dimensional modal approach for the evaluation, in an analytical manner, of chromatic dispersion in any kind of optical fiber. It combines an iterative Fourier technique to compute the propagation constant at any fixed wavelength and an analytical procedure to calculate its derivatives. The proposed formulation takes into account the effective anisotropy of the interfaces and allows us to deal with microstructured fibers, in general, and specifically with realistic photonic crystal fibers (PCFs), including arbitrary spatial refractive-index distributions of dispersive and absorbing materials. This fast and accurate numerical technique is extremely useful for both analysis and design. We show some results of analysis of PCFs with high anisotropy, and we also describe PCFs with new dispersive properties.

Journal Article↗

PubMed2004

Thiamin status during the third trimester of pregnancy and its influence on thiamin concentrations in transition and mature breast milk.

Thiamin deficiency remains an important public health problem in some populations. The aim of the present investigation was to study thiamin status during the third trimester of pregnancy and its influence on the concentration of this vitamin in transition (days 13-14 of lactation) and mature breast milk (day 40 of lactation) in a group of Spanish women. The pregnancies and lactation periods of fifty-one healthy women 18-35 (mean 26.7 (SD 3.7)) years old were monitored. Vitamin intake during the third trimester was determined by recording the consumption of foods over 5 d and of the quantities provided by dietary supplements. Thiamin status during this stage of pregnancy was determined by measuring the activation coefficient of erythrocyte transketolase (alpha-ETK). Milk thiamin content was estimated (in 41% of the subjects) by oxidizing thiamin to thiocrome and measuring fluorescence. Subjects with thiamin intakes above that recommended (group H) had more satisfactory serum alpha-ETK coefficients (1.01 (SD 0.19)) than did those with lower intakes (group L) (1.21 (SD 0.30); P<0.05). Mature milk thiamin concentrations were significantly higher in group H subjects (0.59 (SD 0.44) micromol/l) than group L subjects (0.25 (SD 0.07) micromol/l). Subjects with alpha-ETK coefficients >1.25 in the third trimester had significantly lower mature milk thiamin concentration (0.31 (SD 0.10) micromol/l) than did subjects with more satisfactory alpha-ETK levels at this time (0.55 (SD 0.42) micromol/l; P<0.05). The thiamin status of women can be improved since 25.5% of subjects took less than that recommended and 13.7% showed signs of severe deficiency (alpha-ETK >1.25). The influence of maternal thiamin intake on alpha-ETK coefficients and on mature breast milk thiamin concentration is confirmed.

Adolescent↗

PubMed2004

Smoking and passive smoking as conditioners of folate status in young women.

OBJECTIVE: For women of fertile age, an adequate supply of folate is important for preventing a range of health problems, especially congenital malformations in their offspring. Since congenital deformities are more common in children of mothers who smoke, the objective was to analyse the folate status of smokers, passive smokers and non-smokers. METHODS: Folate intake was monitored in 319 women aged 18-35 (112 smokers, 100 passive smokers and 107 non-smokers) using a three day food record. Serum and erythrocyte folate concentrations were measured by radioimmunoassay. Exposure to tobacco smoke was established by a questionnaire on present and past tobacco consumption, the number of hours in contact with smokers, and by assessing urine cotinine concentrations. RESULTS: The folate intake of smokers (S) (159.1 +/- 65.7 microg/day) and passive smokers (PS) (165.2 +/- 66.6 microg/day) was lower than that of non-smokers (N) (181.7 +/- 72.4 microg/day) (p < 0.05 between S and N). No subject fully met the recommended intake of the vitamin, but S and PS subjects both took less than N subjects (39.8 +/- 16.4% and 41.3 +/- 16.6% compared to 45.4 +/- 18.1% respectively). Serum folate concentrations were also lower in S and PS subjects grouped together (16.6 +/- 5.9 nmol/L) compared to N subjects (18.4 +/- 6.7 nmol/L) (p < 0.05). CONCLUSIONS: None of the studied women took the 400 microg/day of folate recommended. 6.7% had serum folate concentrations of < 9.2 nmol/L. The situation was worse in S and PS subjects, which might contribute to an increased risk of developing certain diseases and to giving birth to children with congenital deformations.

Adolescent↗

PubMed2004

Chromatic compensation of broadband light diffraction: ABCD-matrix approach.

Compensation of chromatic dispersion for the optical implementation of mathematical transformations has proved to be an important tool in the design of new optical methods for full-color signal processing. A novel approach for designing dispersion-compensated, broadband optical transformers, both Fourier and Fresnel, based on the collimated Fresnel number is introduced. In a second stage, the above framework is fully exploited to achieve the optical implementation of the fractional Fourier transform (FRT) of any diffracting screen with broadband illumination. Moreover, we demonstrate that the amount of shift variance of the dispersion-compensated FRT can be tuned continuously from the spatial domain, which is totally space variant, to the spectral domain, which is totally space invariant, with the chromatic correction remaining unaltered.

Journal Article↗

PubMed2002

Cognitive function in elderly people is influenced by vitamin E status.

The aim of this study was to examine associations between vitamin E status and cognitive performance in elderly people. The study subjects were a group of 34 men and 86 women, aged 65-91 y, who were free of significant cognitive impairment. Dietary intake was monitored using a "weighed food record" for 5 consecutive days including a Sunday. Serum levels of alpha-tocopherol and cholesterol were determined by HPLC and colorimetric methods, respectively. The cognitive capacity of subjects was tested using the Pfeiffer's Mental Status Questionnaire (PMSQ). Subjects with vitamin E intakes lower than 50% of those recommended had higher PMSQ scores, demonstrating a greater number of errors in comparison to participants with a greater intake of the vitamin (0.91 +/- 1.22 vs. 0.47 +/- 0.60, respectively, P < 0.05). Subjects who made no errors in the PMSQ test had significantly higher serum alpha-tocopherol concentrations (19.7 +/- 8.6 micromol/L in men and 20.0 +/- 8.4 micromol/L in women) and alpha-tocopherol/cholesterol ratios (3.5 +/- 2.0 micromol/mmol in men 2.9 +/- 1.4 micromol/mmol in women) compared with those who made errors (alpha-tocopherol 15.1 +/- 5.6 micromol/L in men and 14.9 +/- 6.1 micromol/L in women; alpha-tocopherol/cholesterol ratio 2.4 +/- 0.8 and 2.3 +/- 1.3 micromol/mmol in men and women, respectively). This study shows there to be a relationship between vitamin E status and cognitive function, and that vitamin E status could be improved in this population of elderly individuals.

Aged↗