Biomedical subjects

P Nunez

Publications and source records attributed to P Nunez.

4 recordsLinked to original sources

PubMed2004

Dopant distribution in a Tm(3+)-Yb(3+) codoped silica based glass ceramic: an infrared-laser induced upconversion study.

The optically active dopant distribution in a Tm(3+)-Yb(3+) doped silica based glass ceramic sample has been investigated. A systematic analysis of the upconversion fluorescence of the Tm(3+)-Yb(3+) codoped glass and glass ceramic has been performed at room temperature. Tm(3+) and Yb(3+) single doped glass and glass ceramics have also been included in the study. Upon infrared excitation at 790 nm into the (3)H(4) level of the Tm(3+) ions a blue upconversion emission is observed, which is drastically increased in the Yb(3+) codoped samples. A rate equation model confirmed the energy transfer upconversion mechanism. Based on these results, the temporal dynamic curves of the levels involved in the upconversion process, (3)H(4), (2)F(5/2), and (1)G(4) were interpreted in the glass ceramic samples. The contribution of the optically active Tm(3+) and Yb(3+) ions in the crystalline and in the vitreous phase of the glass ceramic was distinguished and the ratio of Tm(3+) ions in the crystalline phase could be quantified for the 1 mol % Tm(3+)-2.5 mol % Yb(3+) glass ceramic. A surprising result was obtained for that concentration: the main contribution to the upconversion emission of the glass ceramic is due to Tm(3+)-Yb(3+) ions in the vitreous phase.

Journal Article↗

PubMed2002

Ethical guidance on human embryonic and fetal tissue transplantation: a European overview.

This article presents an overview of regulations, guidelines and societal debates in eight member states of the EC about a) embryonic and fetal tissue transplantation (EFTT), and b) the use of human embryonic stem cells (hES cells) for research into cell therapy, including 'therapeutic' cloning. There appears to be a broad acceptance of EFTT in these countries. In most countries guidance has been developed. There is a 'strong' consensus about some of the central conditions for 'good clinical practice' regarding EFTT. International differences concern, amongst others, some of the informed consent issues involved, and the questions whether an intermediary organisation is necessary, whether the methods of abortion may be influenced by the possible use of EFT, and whether EFTT should only be used for the experimental treatment of rare disorders. The potential use of hES cells for research into cell therapy has given a new impetus to the debate about (human) embryo research. The therapeutic prospects with regard to the retrieval and research use of hES cells appear to function as a catalyst for the introduction of less restrictive regulations concerning research with spare embryos, at least in some European countries. It remains to be seen whether the prospect of treating patients suffering from serious disorders with transplants produced by therapeutic cloning will decrease the societal and moral resistance to allowing the generation of embryos for 'instrumental' use.

Bioethics↗

PubMed1999

Incorporation of a GnRH agonist, leuprolide acetate, into regimens with exogenous gonadotropins to produce ovarian stimulation and ovulation in the nonpregnant squirrel monkey.

This study was designed to measure the effects of variations in the length of pretreatment with a GnRH agonist, leuprolide acetate (LA), on subsequent follicular development and ovulation. The hypothesis was that the duration of LA suppression of pituitary function does not adversely affect ovarian response to standardized ovulation induction protocols in squirrel monkeys. The first phase determined the dose and duration of LA needed to achieve a hypogonadal state. One of two groups received daily subcutaneous injections of 50 microg of LA. The other received a single injection of 175 microg of a depot suspension of LA. Sera were assayed for estradiol (E2) and progesterone (P). E2 and P levels increased 2- to 5-fold with peak levels on days 4 and 7, respectively. Suppression of steroid levels took 10 to 15 days in the LA-treated group. Depot-LA did not effectively suppress steroid production. After suppression, females receiving daily LA received five daily injections of hMG to stimulate follicular development. E2 and P increased in these animals. These results suggest that cycling squirrel monkeys have P-secreting capacity throughout the cycle. This may explain how the squirrel monkey is able to accommodate both a short (4-5 day) luteal phase of their 9 day cycle and implantation from 5 to 7 days after ovulation. A second study compared exogenous follicle stimulating hormone (FSH) to endogenous gonadotropins released as a response to LA in ovulation induction. Steroid production and hCG-induced ovulation were assessed. LA treatment was compared to a standard ovulation induction protocol by using a randomized cross-over measures design. There were no differences in E2 and P levels in response to dosages of either LA or hMG. The ovulatory response following LA treatment was not significantly greater than that using FSH. The number of animals with unovulated, large follicles was greater on the FSH protocol (12/18) compared to the LA protocol (3/18). Thus, a single injection of a depot preparation of LA is sufficient to stimulate follicular development and ovulation when followed by an hCG injection. Based on this observation and the data on unovulated large follicles, it is suggested that the ovary responds more readily to endogenous gonadotropins released by LA than to exogenous FSH.

Animals↗

PubMed1977

The dipole layer as a model for scalp potentials.

Estimates are made of the potential field at the scalp and cortical surfaces due to large numbers of synchronously active cortical current sources. The basic model is a dipole layer in an infinite, homogeneous conducting medium. Estimates are made of the effects of various inhomogeneities on the attenuation of potentials. It is shown that these approximate methods seem to illuminate the following questions which are of interest in EEG research: (1) The interpretation of reference recordings in terms of local source currents; (2) The differences in amplitude between scalp and cortical recordings; (3) The differences in frequency spectra between scalp and cortical recordings; (4) The observation that alpha rhythm can be recorded deep in the brain; and (5) The effects of simple inhomogeneities on the attenuation of potentials.

Cerebral Cortex↗