Showing papers by "University of Extremadura published in 1998"

Hydrodynamics for granular flow at low density

Abstract: The hydrodynamic equations for a gas of hard spheres with dissipative dynamics are derived from the Boltzmann equation. The heat and momentum fluxes are calculated to Navier-Stokes order and the transport coefficients are determined as explicit functions of the coefficient of restitution. The dispersion relations for the corresponding linearized equations are obtained and the stability of this linear description is discussed. This requires consideration of the linear Burnett contributions to the energy balance equation from the energy sink term. Finally, it is shown how these results can be imbedded in simpler kinetic model equations with the potential for analysis of more complex states.

The classroom practice of preservice teachers and their conceptions of teaching and learning science

Abstract: The present article describes research carried out with four student teachers of primary and secondary science education The preservice teachers' conceptions of the learning and teaching of science were analyzed and compared with their classroom practice when teaching science lessons The data gathering procedures included a questionnaire and interviews, both analyzed by means of cognitive maps, and classroom observations during the participants' practice teaching The results did not allow a general correspondence to be established between preservice teachers' conceptions about teaching and learning science and their classroom behavior The implications of the research for teacher education are discussed © 1998 John Wiley & Sons, Inc Sci Ed82:197–214, 1998

The architecture of the atrial musculature between the orifice of the inferior caval vein and the tricuspid valve: the anatomy of the isthmus.

Abstract: Anatomy of Electrophysiologic Isthmus. Introduction: Electrophysiologists recognize a so-called “isthmus” in the right atrium through which passes the reentrant circuit of common atrial flutter. Ablative lesions placed in this narrow channel have proved effective in breaking the circuit. To the best of our knowledge, however, no study has been performed to establish the arrangement and orientation of the atrial myocardial fibers in this crucial area. Methods and Results: We examined 28 normal heart specimens, identifying a quadrilateral area composed of three morphologic sectors between the inferior caval vein and the tricuspid valve confluent superiorly with the triangle of Koch. Within this quadrilateral, there are constant recesses, or sinuses, inferior and lateral to the orifice of the coronary sinus. The inferior isthmus measured an average of 31 ± 4 mm (range 19 to 40). Gross examination identified marked differences in the atrial wall forming the quadrilateral. A smooth anterior component forming the vestibule of the tricuspid valve was found in all the hearts, but variations in the remaining sectors were seen in ten specimens. The usually membranous posterior sector was noticeably muscular in three specimens, while the middle, trabecular sector was more membranous in five specimens. We demonstrated the orientation of the subendocardial atrial fibers by dissection in 14 specimens, revealing a relatively constant overall pattern in eight specimens and variations in fiber orientation in the remaining specimens. Conclusion: There are considerable anatomic variations in the atrial wall that comprises the so-called isthmus. The presence of recesses and membranous areas in some hearts and the variations in arrangement of the subendocardial fibers are relevant in improving understanding of conduction in this area.

Headspace solid phase microextraction for the analysis of volatiles in a meat product: dry-cured Iberian ham.

Abstract: The application of solid-phase microextraction (SPME) combined with gas chromatography/mass spectrometry for the analysis of dry-cured Iberian ham volatile compounds has been studied. To determine the optimal conditions to extract volatile compounds, several extraction times and temperatures conditions were tested. The majority of the 82 volatile compounds tentatively identified coincided with those reported for different types of dry-cured ham in the literature. In addition, SPME successfully extracted high molecular weight compounds, some of them being reported for the first time in this type of meat product. Both extraction time and temperature dramatically increased less volatile compounds' chromatographic area and consequently total area (P < 0.0001). Keywords: Dry-cured Iberian ham; solid-phase microextraction (SPME); gas chromatography/mass spectrometry; volatiles

Breaking the Mold of Discotic Liquid Crystals

Abstract: Small molecules of the indene and pseudoazulene type like 1 and 2 form columnar mesophases! These compounds do not possess peripheral flexible chains like conventional columnar liquid crystals. Instead, polarizable chlorine and sulfur atoms, as well as the polar cyano group, function as unusual soft regions between the rigid columns.

Soil hydrological response under simulated rainfall in the Dehesa land system (Extremadura, SW Spain) under drought conditions

Abstract: Soil hydrology was investigated in the Guadelperalon experimental watershed in order to determine the influence of land use and vegetation cover on runoff and infiltration within the Dehesa land system. Five soil–vegetation units were selected: (1) tree cover, (2) sheep trials, (3) shrub cover, (4) hillslope grass and (5) bottom grass. The results of the simulated rainfall experiments performed at an intensity of 56·6 mm h−1 during one hour on plots of 0·25 m2, and the water drop penetration time test indicate the importance of water repellency in the Dehesa land system under drought conditions. Low infiltration rates (c. 9–44 mm h−1) were found everywhere except at shrub sites and in areas with low grazing pressure. Soil water repellency greatly reduced infiltration, especially beneath Quercus ilex canopies, where fast ponding and greater runoff rates were observed. The low vegetation cover as a consequence of a prolonged drought and grazing pressure, in conjunction with the soil water repellency, induces high runoff rates (15–70 per cent). In spite of this, macropore fluxes were found in different locations, beneath trees, on shrub-covered surfaces, as well as at sites with a dominance of herbaceous cover. Discontinuity of the runoff fluxes due to variations in hydrophobicity causes preferential flows and as a consequence deeper infiltration, especially where macropores are developed. © 1998 John Wiley & Sons, Ltd.

Sexual selection and tail streamers in the barn swallow

Abstract: The functional significance of elongated, narrow tips of the tail feathers of certain birds, so-called tail streamers, has recently been discussed from an aerodynamic point of view, and the effects of sexual selection on such traits have been questioned. We review our long-term field studies using observational and experimental approaches to investigate natural and sexual selection in the barn swallow, Hirundo rustica, which has sexually size-dimorphic outermost tail feathers. Experimental manipulation of the length of the outermost tail feathers has demonstrated sexual selection advantages of tail elongation and disadvantages of tail shortening, with opposite effects for natural selection in terms of foraging efficiency, haematocrit and survival. These findings are contrary to the prediction of a general deterioration from both shortening and elongation, if the tail trait was determined solely by its effects on aerodynamic efficiency and flight manoeuvrability. Patterns of sexual selection in manipulated birds conform with patterns in unmanipulated birds, and selection differentials for different components of sexual selection in manipulated birds are strongly positively correlated with differentials in unmanipulated birds. Age and sex differences in tail length, and geographical patterns of sexual size dimorphism, are also consistent with sexual selection theory, but inconsistent with a purely natural selection advantage of long outermost tail feathers in male barn swallows.

First Identification of Autochthonous Cryptococcus neoformans var. gattii Isolated from Goats with Predominantly Severe Pulmonary Disease in Spain

Abstract: Cryptococcus neoformans var. gattii is associated with Eucalyptus trees growing in various tropical and subtropical regions of the world. The identification of 13 autochthonous strains of C. neoformans var. gattii in Spain is reported. These strains were isolated from lung (10 samples), liver (1 sample), and brain (2 samples) tissue specimens from six goats suffering from predominantly severe pulmonary disease that were autopsied. The animals were members of five different herds of goats grazing in rural areas of the province of Caceres (Extremadura, Spain). Between 1990 and 1994, there were five outbreaks, in which between 2.5 and 12% of the goats were affected. Although respiratory symptoms (pneumonia) associated with cachexia were the predominant clinical picture in all outbreaks, brain and liver involvement was also documented in three of the five outbreaks. Biotyping was performed by culturing the isolates on l-canavanine-glycine-bromothymol blue medium and testing them for the assimilation of d-proline and d-tryptophan. Serotyping by agglutination tests confirmed the characterization of all strains as C. neoformans var. gattii serotype B. This is the first confirmation of the presence of this variety in Spain, with a peculiar ability to produce severe pulmonary and systemic disease in normal goats, particularly in the form of outbreaks of pneumonia in association with cachexia.

Fenton Reagent Advanced Oxidation of Polynuclear Aromatic Hydrocarbons in Water

Abstract: Aqueous oxidation of three polynuclear aromatic hydrocarbons, fluorene, phenanthrene and acenaphthene with the combination of hydrogen peroxide and ferrous ion, Fenton reagent, has been studied The effect of variables such as concentration of both reactants, pH and presence of bicarbonate ion and humic substances has been investigated Products resulting from oxidation have also been identified From experimental results and kinetic data determined the process is confirmed as an advanced oxidation involving the generation of hydroxyl radicals Oxidation rates are even higher than those from other advanced oxidation systems involving ozone, UV radiation and hydrogen peroxide Reactivity is in the following decreasing order: Phenanthrene > Fluorene > Acenaphthene

Evaluation of proteolytic activity of micro‐organisms isolated from dry cured ham

Abstract: In order to determine the possible contribution of micro-organisms to the ripening of meat products, 48 cocci, 18 moulds and 20 yeasts isolated from dry-cured Iberian ham were evaluated for proteolytic activity. Two specific methods were used: the ability to hydrolyse myosin in broth and, for those strains showing high activities, hydrolysis on both myofibrillar and sarcoplasmic proteins on pork slices. Moulds and cocci showed the highest proteolytic activity for myosin in broth. Both myofibrillar and sarcoplasmic proteins were recovered at lower rates from inoculated than from sterile incubated pork. The deepest changes in myofibrillar and sarcoplasmic proteins were originated by one strain each of Penicillium chrysogenum and Staphylococcus xylosus, respectively. Only small changes were observed in the concentrations of free amino acids from inoculated pork slices, except for the samples with P. chrysogenum, where there were increases in all free amino acids. Thus, P. chrysogenum makes a significant contribution to proteolysis during the ripening of dry-cured meat products.

Nomenclature for human DPYD alleles.

Abstract: To standardize DPYD allele nomenclature and to conform with international human gene nomenclature guidelines, an alternative to the current arbitrary system is described. Based on recommendations for human genome nomenclature, we propose that each distinct allele be designed by DPYD followed by an asterisk and an Arabic numeral. The number specifies the key mutation and, where appropriate, a letter following the number indicates an additional mutation on the mutant allele. Criteria for classification as a distinct allele are also presented.

Effects of caffeine withdrawal from the diet on the metabolism of clozapine in schizophrenic patients.

Abstract: Both clozapine (CLZ) and caffeine are CYP1A2 substrates.This study raises the hypothesis of whether caffeine withdrawal from the diet alters the metabolism and/or clinical status of patients receiving CLZ. Seven schizophrenic patients (six men and one woman) receiving monotherapy with CLZ at 271 +/-

Body size and reproductive parameters in the wild boar Sus scrofa

Abstract: Parameters involved in the reproductive performance of wild boar Sus scrofa Linnaeus, 1758, such as fertility rates and litter size, show considerable intrapopulational variability. Inthis work authors analyze a total of 198 femaled, culled by hunting in the Villuercas region (Caceres, Spain), in an area with food suplementary throughout the year.

Occurrence of cell surface arabinogalactan-protein and extensin epitopes in relation to pericycle and vascular tissue development in the root apex of four species

Abstract: Monoclonal antibodies recognizing two classes of developmentally regulated plant cell surface components – arabinogalactan-proteins (AGPs) and extensins – have been used to immunolabel cells at the root apices of four species with different characteristics of pericycle and vascular tissue development. Root apices of pea (Pisum sativum L.), radish (Raphanus sativus L.), carrot (Daucus carota L.) and onion (Allium cepa L.) were immunolabelled with the anti-AGP monoclonal antibodies JIM4 and JIM13 and anti-extensin monoclonal antibodies JIM11, JIM12, JIM19 and JIM20. All of these antibodies recognized subsets of pericycle cells in at least one, but never all, of these species. The restricted patterns of epitope occurrence also reflected vascular cell development. The differences in patterns of antibody recognition in the four species are discussed in relation to the possible roles of these cell surface molecules in cell differentiation and root patterning events.

Metabolism of ropivacaine in humans is mediated by CYP1A2 and to a minor extent by CYP3A4: An interaction study with fluvoxamine and ketoconazole as in vivo inhibitors

Abstract: Background Potential drug-drug interactions can be identified in vitro by exploring the importance of specific cytochrome P450 (CYP) isozymes for drug metabolism. The metabolism of the local anesthetic ropivacaine to 3-hydroxyropivacaine and (S)-2′,6′-pipecoloxylidide was shown in vitro to be dependent on CYP1A2 and 3A4, respectively. In this in vivo model study we quantitated the role of these 2 isozymes for the metabolism of ropivacaine. Methods In a randomized, 3-way crossover study, 12 healthy subjects received a single dose of 40 mg ropivacaine intravenously alone or combined either with 25 mg fluvoxamine as a CYP1A2 inhibitor or with 100 mg ketoconazole as a CYP3A4 inhibitor twice daily for 2 days. Venous plasma and urine samples were collected over 10 hours and 24 hours, respectively. The samples were analyzed for ropivacaine base, 3-hydroxyropivacaine, and (S)-2′,6′-pipecoloxylidide. Results Coadministration with fluvoxamine decreased the mean total plasma clearance of ropivacaine from 354 to 112 mL/min (68%), whereas ketoconazole decreased plasma clearance to 302 mL/min (15%). The relative changes in unbound plasma clearance were similar to the changes in total plasma clearance. The ropivacaine half-life (t½) of 1.9 hours was almost doubled during fluvoxamine administration and the plasma concentration at the end of infusion increased slightly, whereas the corresponding parameters after ketoconazole administration remained unchanged. Coadministration with ketoconazole almost abolished the (S)-2′,6′-pipecoloxylidide concentrations in plasma, whereas fluvoxamine administration increased the (S)-2′,6′-pipecoloxylidide levels. The fraction of dose excreted as 3-hydroxyropivacaine in urine decreased during fluvoxamine administration from 39% to 13%. Conclusions CYP1A2 is the most important isozyme for the metabolism of ropivacaine. Drug-drug interactions with strong inhibitors of this isozyme could be of clinical relevance during repeated administration. A potent inhibitor of CYP3A4 causes a minor decrease in clearance, which should be of no clinical relevance. Clinical Pharmacology & Therapeutics (1998) 64, 484–491; doi:

Increase in a heat-shock protein from blood cells in response of nestling house martins (Delichon urbica) to parasitism: an experimental approach

Abstract: Heat-shock proteins (HSPs) are synthesized by animals and plants in response to various stressors. The level of the HSP60 stress protein was measured from the cell fraction of peripheral blood obtained from nestling house martins (Delichon urbica) to test whether ectoparasitism increased the concentration of stress protein. We assessed HSP from nestlings raised in nests previously treated with an insecticide or infested with 50 martin bugs (Oeciacus hirundinis). In addition, haematozoa infections were checked in blood smears. Nestlings from parasite-infested nests, or nestlings infected with trypanosomes, had increased levels of HSP in their blood cells. Nestling growth as determined from wing length was negatively related to HSP60 levels and within-brood variation in wing length increased with increasing levels of the stress protein independently of treatment and infection by trypanosomes. These results suggest HSPs may play a role in host-parasite interactions, and that they can be used reliably for measuring physiological responses to parasites.

Analysis of midazolam and metabolites in plasma by high-performance liquid chromatography: probe of CYP3A.

Abstract: Hydroxylation of midazolam (MDZ) is mediated almost exclusively by CYP3A isoforms. The authors describe a high-performance liquid chromatography assay involving MDZ, 1'-hydroxymidazolam, and 4-hydroxymidazolam in plasma. The compounds were eluted on an Ultrasphere ODS, 3-microm particle size, 7.5 cm x 4.6 mm reversed-phase column and monitored by ultraviolet absorbance at 254 nm. The composition of the mobile phase was 35.2% acetonitrile:4.8% methanol:60% buffer acetate (vol/vol/vol), 0.1 M, pH 4.7; the flow rate was 1 ml/minute. Calibration curves were linear (coefficients of correlation > 0.99) within the range of concentrations established (20 to 640 nM). Within- and between-day coefficients of variation were consistently better than 8%. The overall recovery was >90% and the lowest detectable concentration was 8 nM. This approach provides a simple, rapid, and sensitive assessment of MDZ and metabolites in plasma, with a very good accuracy and precision, which enables it as an in vivo marker of CYP3A activity in humans.