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Biomedical subjects

A San Miguel

Publications and source records attributed to A San Miguel.

17 recordsLinked to original sources
PubMed2006

Adaptive geometric numerical integration for point vortex dynamics.

In this paper we describe a variable stepsize integration method for the Hamiltonian dynamics of point vortices based on the explicit symplectic Zhang and Qin scheme. The adapted method is also explicit and preserves the reversible structure of the flow. In order to check the behavior of this adaptive method a numerical study of the exchange-scattering phenomenon in the three-vortex problem is made. The symmetry of the orbit and the energy evolution are discussed for the exchange-scattering model. A long-term integration of this and other models composed also of three vortices indicates that the adaptive Zhang-Qin method has good properties of efficiency and preservation of the first integrals associated with point vortex systems.

Journal Article↗
PubMed2004

Exceptional ideal strength of carbon clathrates.

We study by means of ab initio calculations the ideal tensile and shear strengths of the C-46 clathrate phase. While its bulk modulus and elastic constants are smaller than in diamond, its strength is found to be in all directions larger than the critical stresses associated with the diamond [111] planes of easy slip. This can be related to the frustration by the clathrate cage structure of the diamond to graphite instability under nonhydrostatic stress conditions [corrected] The criteria for designing strong materials are discussed.

Journal Article↗
PubMed1998

High-focusing Bragg-Crystal polychromator design for energy-dispersive X-ray absorption spectroscopy.

The design of a highly focusing profiled Si(111) Bragg crystal polychromator for dispersive EXAFS (extended X-ray absorption fine structure) experiments is described. The contour of the crystal has been optimized to give the best focus over the full 4-13 keV energy range. The profile optimization has been improved taking into account all the degrees of freedom of the geometry and the results of X-ray tracing simulations. The profile of the crystal has been calculated to take full advantage of the new possibilities given by the undulator source and the optics of beamline ID24 at the European Synchrotron Radiation Facility. Full spot sizes have been measured to be between 20 and 40 microm in the 5-12 keV energy range. These values compare well with X-ray tracing simulations and are the smallest spots ever obtained with energy-dispersive EXAFS optics, keeping, however, a wide enough energy bandpass for most X-ray absorption spectroscopy experiments.

Journal Article↗
PubMed1998

[Genotypes of hepatitis C virus: their relationship with risk factors, the severity of liver disease, and the serologic response].

BACKGROUND: The objective of our study was to ascertain the prevalence of different HCV genotypes between the hepatitis C patients in the health area of Monforte de Lemos, Spain, as well as the possible influence of risk factors on their distribution and their relation with hepatic disease and with the serologic response. PATIENTS AND METHODS: We have studied 128 patients with hepatitis C. Of these, 41 were intravenous drug users (IVDU), 19 had received transfusions, 7 were hemodialyzed and in 61 the risk factors were unknown. Antibodies against HCV were detected by second-generation enzyme immunoassay (EIA) and confirmed by immunoblot. RNA-HCV presence was studied by reverse transcription-PCR (RT-PCR), and a reverse hybridization test of the amplifications was used for the genotyping. RESULTS: Hepatitis C genotypes 1b (46.1 [8.6%]), 1a (23.4 [7.3%]) and 3a (13.3 [5.9%]) were the most frequently encountered genotype. Genotype 1a (48.8 [15.3%]) was the most prevalent genotypes in IVDU patients, while 1b was the most frequent in patients of unknown risk factors (62.3 [12.1%]). Alanine-aminotransferase (ALT) was elevated in 66.6 (17.7%) of patients with genotype 1a, in 87.5 (8.6%) of patients with genotype 1b (p = 0.0367) and in 94.1 (11.2%) of patients with genotype 3a (p = 0.0347). Subtype 1b was present in 6 of 7 cases of cirrhosis (85.7%) and in 7 of 12 cases of active chronic hepatitis (58.3%). No significant statistical differences were observed between the genotypes and the specific IgM response against core antigen of HCV, neither we observed differences in the serologic response against C1, C2, NS3 and NS4 peptides. CONCLUSIONS: Hepatitis C genotypes 1a and 3a were the most prevalent genotypes between IVDU patients while genotype 1b was the most frequent between non-IVDU patients. Genotype 1b was associated to severe liver disease. Percentage of positivity or the reactivity against HCV peptides was independent of the genotype encountered in the patient.

Genotype↗
PubMed1998

A scattering filter for energy-dispersive optics.

A filtering technique to remove parasitic scattering from X-ray absorption spectra that are acquired in energy-dispersive mode has been developed and tested at the European Synchrotron Radiation Facility. The improved set-up removes small-angle scattering of the sample or the windows of sample cells which may spoil the energy resolution or reduce the intensity of prominent features in the absorption spectrum, such as the white line at the Pt L(III) edge. The sample is placed behind the curved monochromator and between two plane perfect crystals in the Bonse-Hart configuration. The dispersion of the Bonse-Hart double-crystal camera is matched to the dispersion of the curved monochromator by inclining the scattering planes of the two optical elements against each other.

Journal Article↗
PubMed1998

Nanosecond-resolved XMCD on ID24 at the ESRF to investigate the element-selective dynamics of magnetization switching of Gd-Co amorphous thin film.

The one-bunch filling mode of the ESRF is combined with a microcoil to generate a pulsed-magnetic-field pump phased with respect to the probe that is given by the bunch of photons emitted each turn (357 kHz). Nanosecond-resolved X-ray magnetic circular dichroism (XMCD) is carried out. Besides the microcoil, the two other key-elements are the energy-dispersive XAS spectrometer, which yields parallel data acquisition, and the diamond-based quarter-wave plate, which tunes the helicity of the photon alternatively left and right.

Journal Article↗
PubMed1998

Clinical evaluation of a commercial ligase-based gene amplification method for detection of Mycobacterium tuberculosis.

The purpose of this study was to evaluate the clinical usefulness of a commercial ligase-based gene amplification method (LCx Mycobacterium tuberculosis test; Abbott Laboratories, USA) for detection of Mycobacterium tuberculosis. The tuberculosis infection rate among clinical samples was 10.6%. The sensitivity, specificity, and positive and negative predictive values were 23.5%, 100%, 100%, and 91.7%, respectively, with the fluorochrome auramine stain; 32.4%, 100%, 100%, and 92.6%, respectively, with culture; and 76.5%, 95.8%, 68.4% and 97.2%, respectively, with the gene amplification method. When only samples from patients without current or previous treatment were studied, the sensitivity was 36.4% with the auramine stain, 63.6% with culture, and 100% with the gene amplification assay. The mean treatment time for culture-negative and assay-negative samples was greater than that of culture-negative and assay-positive samples. The LCx Mycobacterium tuberculosis test is a sensitive method for detection and identification of Mycobacterium tuberculosis. It produces few false-positive results. However, as it can remain positive after the culture becomes negative, it is not recommended for evaluation of treatment efficiency.

Bacteriological Techniques↗
PubMed1998

[Variants of hepatitis C virus in different risk groups. Comparative study of a method for genotyping and another for serotyping].

AIMS: The aim of this study was to know the prevalence of the different variants of HCV in the Health Care area of Monforte de Lemos (Lugo, Spain) and its distribution according to risk factors and to compare the results obtained with one genotyping and one serotyping technique. PATIENTS AND METHODS: Eighty-four patients with hepatitis C were studied, 25 of whom were IVDA, 14 had received blood transfusions, 4 hemodialysis and the risk factor was unknown in 41. The antibodies against HCV were studied by second generation EIA and confirmed by an immunoblot technique. Serotyping was carried out by an ELISA test. Genotyping was undertaken with a reverse hybridation test of the amplification obtained by polymerase chain reaction prior to reverse transcription (RT-PCR). RESULTS AND CONCLUSIONS: The genotypes most frequently observed were 1b (47.6%), 1a (20.2%) and 3 (14.3%). In the IVDA patients the genotypes 1a (40%) and 3 (24%) predominated. The 1b genotype was the most prevalent in the patients of unknown risk (68.3%) and patients with a history of blood transfusion (50%). The prevalence of the different serotypes was similar to that of the corresponding genotypes, with nearly 100% agreement. The number of untypable cases was greater in the serotyping technique (20.2%) than in the genotyping (2.4%). A greater number of mixed infections was detected with serotyping (7 cases, 8.3%) than with genotyping (1 case, 1.2%). Lesser sensitivity of the serotyping test was observed in the patients lacking anti-NS4 antibodies.

Blood Transfusion↗
PubMed1997

Metabolic effects in rats of verapamil alone and in combination with captopril.

The metabolic effects of verapamil alone and in combination with captopril were investigated in rats. Animals received the maximum recommended doses for humans (per kg body weight per day) over a 2-week period. Verapamil had no significant effects on serum biochemistry, but caused a significant increase in serum potassium level and significant reductions in the rates of intestinal absorption of glucose and calcium. Verapamil/captopril had a number of significant effects on serum lipid profile (increased total cholesterol, increased HDL-cholesterol, and reduced LDL-cholesterol), and also provoked an increase in serum alanine amino-transferase activity and in serum glucose levels. The combination treatment caused a significant increase in serum chloride levels, but had no effect on intestinal absorption.

Alanine Transaminase↗
PubMed1996

Metabolic effects of the combination of furosemide and captopril in rat.

Diuretics typically provoke increased serum lipid levels and may provoke increased serum uric acid levels and/or glucose intolerance. Furosemide is widely used as an antihypertensive, but in patients for whom furosemide treatment alone proves insufficient to reduce hypertension, a common procedure is to co-administer the angiotensin-converting-enzyme (ACE) inhibitor captopril. The metabolic effects in rats of joint administration of furosemide (15 mg/kg/day) and captopril (2 mg/kg/day) are evaluated over a two-week period. At the end of this period, the serum levels of lipids, uric acid, bilirubin, proteins and various enzymes were determined as well as the effect of the treatment on intestinal absorption of glucose and calcium. Furosemide/captopril led to an increase in serum albumin and alkaline phosphatase levels, and a decrease in triglyceride levels. The results of this work support the view that this drug combination is suitable for hypertension treatment.

Alanine Transaminase↗
PubMed1993

[Specifications on the lecithin/sphingomyelin ratio (L/S). Updated review].

We review the lecithin/sphingomyelin ratio (L/E) studying the amniotic fluid to value the fetal lung maturity. We compare him with others biological parameters. We consider the modifications arising across pregnancy and in different diseases as well as the factors influencing its results.

Amniotic Fluid↗
PubMed1992

[Mediastinal tuberculosis as a cause of fever of unknown origin].

Tuberculosis is the most frequent cause of fever from unknown etiology. On the other hand, mediastinal tuberculous adenopathy (TBM), without associated pulmonary affection is a rare form of presentation among adults, generally evolving with sustained fever until a thoracic radiology is performed showing mediastinal enlargement. We present a case which started as fever from unknown etiology (FUE), given that, according to the thoracic radiology performed one month after the onset of fever, no mediastinal affection was observed.

Adult↗