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Biomedical subjects

J Oviedo

Publications and source records attributed to J Oviedo.

11 recordsLinked to original sources
PubMed2006

Ba adsorption on the stoichiometric and defective TiO(2) (110) surface from first-principles calculations.

A theoretical study on Ba adsorption on the rutile TiO(2) (110) surface has been carried out by means of plane-wave, plane augmented waves potential, density functional theory calculations. A model consisting on a (4 x 1) unit cell, which corresponds to coverage of 0.125 monolayer (ML), has been used and several potential adsorption sites on the stoichiometric surface have been tried. It has been found that the most stable site is with the Ba atom in a position where it is bound to two bridging oxygen atoms and an in-plane oxygen atom forming equivalent bonds (OB site). The adsorption energy is 0.71 eV referred to the formation of Ba bulk and is about 0.3 eV more stable than other adsorption sites. The Ba-surface interaction produces some surface relaxation in all cases. The OB site is stable at moderate temperatures; however, after extensive molecular dynamic calculations it is found that atoms diffuse on the surface by means of a jumping mechanism among several stable positions. The presence of bridging oxygen vacancies does not alter significantly this picture since the adsorption close to defects is not energetically favorable and the atoms tend to move away from vacancies. A strong covalent character has been found in the nature of the bonding, which contrasts with previous suggestions of the existence of Ba(2+) species on the surface. When the coverage is increased to 0.25 ML by adding a Ba atom to the supercell, there is a significant repulsion between Ba atoms that move away from each other to occupy OB sites. Thus, the adsorption energy values per atom diminish. For the stoichiometric surface two equivalent adsorption patterns are found, whereas only one is found for the defective surface.

Journal Article↗
PubMed2005

N2O decomposition on TiO2 (110) from dynamic first-principles calculations.

We have carried out a systematic study of N(2)O dissociation on a TiO(2) (110) surface by means of plane-wave pseudopotential density-functional theory calculations. We have made use of both static and dynamic calculations in order to elucidate N(2)O decomposition mechanisms. We find that dissociation is not favorable on the stoichiometric surface. On the other hand, the presence of oxygen bridging vacancies make the N(2)O decomposition possible. The role of the defective surface is to provide electrons to the adsorbed molecule. We find two channels for decomposition, depending on whether the molecule is adsorbed with the O or the N end of the molecule on a vacancy. The first case is energetically downhill and proceeds spontaneously, leading to N(2) ejection from the surface and vacancy oxidation. The second case relies on the formation of an intermediate bridging configuration of the adsorbed molecule and is hindered by a small energy barrier. In this case, molecule breaking produces N(2) in the gas phase and leaves oxygen adatoms on the surface. We relate our results to recent experimental findings.

Letter↗
PubMed2004

Oxygen vacancies on TiO2 (110) from first principles calculations.

We have carried out a systematic study of oxygen vacancy formation on the TiO2 (110) surface by means of plane-wave pseudopotential density-functional theory calculations. We have used models with the mean number of vacancies per surface unit cell being theta=0.25 and theta=0.5. The study comprises several kind of vacancies within the outermost layers of the surface. The use of a suitable set of technical parameter is often essential in order to get accurate results. We find that the presence of bridging vacancies is energetically favored in accordance to experimental data, although the formation of sub-bridging vacancies might be possible at moderate temperatures. Surprisingly, the spin state of the vacancy has little influence on the results. Atomic displacements are also analyzed and found to be strongly dependent on the particular arrangement of vacancies.

Journal Article↗
PubMed2001

Self-care for the inflammatory bowel disease patient: what can the professional recommend?

The management of patients with inflammatory bowel disease (IBD) continues to present a challenge for gastroenterologists. IBD constitutes a significant burden for the affected individual because of both intestinal and systemic manifestations. The lack of a specific cause and a definitive cure for this condition, as well as the potential for associated malignancy, leave patients unsettled and fearful of the future. Many patients and their families are significantly impaired by the limitations that IBD places on their lives. These limitations are frequently overlooked, and extend well beyond the boundaries of traditional medical practice. Patients often seek to become active participants in the management of their disease. An approach that includes discussion and education on lifestyle issues affecting IBD patients should be part of our routine practice. This article reviews lifestyle and self-care factors relevant to the IBD patient, and what the gastroenterologist can recommend based on current evidence.

Adult↗
PubMed1998

Pituitary tumors in adolescent patients.

We report on a series of 48 patients, ages 14 to 20 year, with hypophyseal adenomas. Of these, 46 (96%) had secreting tumors, 3 had Cushing's disease, 9 had somatotrophinomas, and 34 (29 females and 5 males) had prolactinomas. Thirty cases were diagnosed as intrasellar adenomas (62%) while the remaining eighteen (38%) presented extrasellar expansion. Of 9 acromegalic patients, 7 had typical clinical and biochemical features 2 were exclusively prognatic with normal basal GH levels, but abnormal dynamic tests. Prolactinomas were noninvasive in women and faster growing and more extensive in men. Forty seven patients underwent surgery. Five of these required craniotomy and the rest approached through the sphenoidal bone (TSE). Remission was achieved in Cushing's disease, acromegaly, and female intrasellar prolactinomas. Larger tumors such as nonsecreting adenomas and male prolactinomas showed poor results after undergoing subtotal resections, with persistence of endocrinological disturbances. From our findings it appears that these tumors are aggressive in youth than in adults. Because there was a close relationship between tumor size, invasiveness, and the patients' final outcome, we conclude that early diagnosis and treatment is essential. Frequent complaints in adolescents such as irregular menses, retarded puberty, and growth disorders should be thoroughly investigated and not merely considered as transient or 'functional'.

Acromegaly↗
PubMed1985

Growth rate of secondary hydatid cysts of the brain. Case report.

Bilateral intracerebral hydatid cysts developed in a 14-year-old patient after an infarct of presumed embolic origin in the left frontotemporoparietal region. The average rate of growth of these cysts was about 5 cm per year. This suggests that the growth rate is far from uniform and indeed, particularly in young patients, may be much faster than originally estimated.

Adolescent↗
PubMedDate not supplied

[From "how many" to "why": the utilization of health services from the perspective of the users].

Parallel to the National Health Survey-II, in 1994 a qualitative study was conducted on the patterns and microsocial determinants of health services utilization. The study was conducted in eight urban areas from all over the country among middle class and middle-low class sectors. A total of 192 individual open-ended interviews and eight focus groups were completed among users of health services; 61 service providers both from public and private services were also interviewed. This paper reports the main findings regarding the users' perspective. The first part summarizes the conceptual and methodological design. The second part presents the results from the users' point of view. Individuals distinguish between "becoming sick" and "falling sick"; preventive measures are adopted when becoming sick, in order to avoid falling sick. Another finding refers to the population tendency to add up different and even contradictory curative paradigms, as opposed to the modern medical paradigm which tends to exclude any competing alternative knowledge. A third series of findings refers to the dilemmas that utilizing health services poses for the population, given the high costs, and the low quality that characterize these services, according to the users' point of view. This paper concludes with a series of recommendations for policies, aimed at improving the quality of the health services provided to the population.

Health Behavior↗
PubMedDate not supplied

["We do what we can": health service providers facing the utilization problem].

This study presents the second part of the general results obtained by a qualitative study conducted within the National Health Survey II. The object of this study was to identify main patterns and micro-social determinants which affect the process of selection and utilization of health services in order to propose policies aimed at more equity, quality and efficiency in health service delivery. The study was conducted in urban areas among the middle and middle-low class sectors. A total of 192 individual open-ended interviews and eight focus groups were completed among health users in four cities. Also, 61 service providers both from public and private services were interviewed. Since a previous work reported findings related to health service users, this study focuses only on the results pertaining to health service providers. The first part briefly discusses the study design which allowed to explore the meaning that actors--health service providers--attach to their job and working conditions. The second part presents the main findings. The sense of economic and material precariousness with which health providers from public institutions do their work is among the most important results. Common conflicts between health service users and providers are also mentioned, mainly those which arise from the organizational problems of the health center and from the scarcity of the basic drug stock. The third part reports the main coincidences and divergences between health service users and providers. Some of the divergences may be the reason for the under-utilization of health services. The work concludes with a series of policy recommendations aimed at improving the quality and opportunity of health services provided by public institutions for the needs of the population.

Delivery of Health Care↗