Showing papers by "University of Seville published in 1996"

Properties and applications of palygorskite-sepiolite clays

Abstract: The palygorskite-sepiolite group of clay minerals has a wide range of industrial applications derived mainly from its sorptive, rheological and catalytic properties which are based on the fabric, surface area, porosity, crystal morphology, structure and composition of these minerals. For assessing potential industrial uses, the mineralogical and chemical composition of the clay and its basic physical and physico-chemical parameters must be determined. Then some particular properties of commercial interest can be modified and improved by appropriate thermal, mechanical and acid treatments, surface active agents, organo-mineral derivatives formation, etc. In this paper, a revision of the principal characteristics of commercial palygorskite-sepiolite clays is presented, and potential uses are suggested according to these data. New products and applications are being investigated and those concerning environmental protection in particular, are noted. Finally, possible health effects of these elongate clay minerals are discussed. While commercial deposits of palygorskite and sepiolite are rare, these two clay minerals occur relatively frequently in sediments and soils. Both palygorskite and sepiolite clays are so- called 'special clays'. The annual production in the western world for the former is estimated to be around two million tonnes; production comes mainly from the southeastern USA (Miocene deposits in Florida and Georgia), about 1.8 million tonnes in 1989 (Ampian, 1991), and from Senegal, Spain, Australia, India, Turkey, South Africa and France to a much smaller extent. Sepiolite is less abundant than palygors- kite. The former is a typically Spanish mineral; in fact, over 90% of sepiolitic clays are produced in Spain (also from Miocene deposits). Other small operations are in Nevada (USA), Turkey and China. The annual production of sepiolite in Spain is close to 800,000 tonnes (O'Driscoll,

Adsorption of Water on Activated Carbons: A Molecular Simulation Study

Abstract: We report a molecular simulation study for a model of water adsorption on nonporous and porous activated carbons. The grand canonical Monte Carlo method is used, and the temperature is fixed at 300...

Preparation of Silica from Rice Husks

Abstract: Preliminary leaching of rice husks with a solution of hydrochloric acid before their combustion at 600°C is shown to be required to obtain relatively pure silica (∼99.5%) with a high specific surface area (∼260 m2/g) that is maintained even after heating at 800°C. Transmission electron microscopy observations indicate that this material has a homogeneous size distribution of nanometric particles. However, if the leaching with HCl is performed on the white ashes obtained by combustion of the rice husks at 600°C, an amorphous silica with the same purity also is obtained, but its specific surface area decreases to 1 m2/g. This behavior is due to a strong interaction between the silica and the potassium contained in the rice husks, which leads to a dramatic decrease of the specific surface area if K+ cations are not removed prior to the heat treatment at 600°C. This finding leads to a better understanding of the effect of potassium on the morphology of silica.

Male sexual behavior and human papillomavirus DNA: key risk factors for cervical cancer in Spain.

Abstract: Background: It is now established that certain types of human papillomaviruses (HPVs) are the sexually transmitted agents etiologically linked to cervical cancer. Studies assessing the contribution of the male's sexual behavior and genital HPV DNA status to the risk of development of cervical neoplasia in sexual partners have yielded inconsistent results. Purpose: This study evaluates the role of men's sexual behavior and the presence of HPV DNA in the penis on the development of cervical cancer in their sexual partners in Spain, a low-risk area for cervical neoplasia. Methods: Husbands (n = 633) of women participating in two case-control studies of cervical neoplasia were interviewed to obtain information on lifestyle habits, including sexual practices. Cytologic samples were taken from the distal urethra and the surface of the glans penis of 183 husbands of case women and of 171 husbands of control women. These samples were analyzed by a polymerase chain reaction-based system using a generic probe and 25 type-specific probes for the detection and typing of HPV DNA. Serologic specimens were also obtained and analyzed for antibodies to Chlamydia trachomatis, Treponema pallidum, herpes simplex virus type II, and Neisseria gonorrhoeae. Results: The presence of HPV DNA in the husbands' penis conveyed a fivefold risk of cervical cancer to their wives (adjusted odds ratio [OR] for HPV DNA positivity = 4.9; 95% confidence interval [CI] = 1.9-12.6). The risk of cervical cancer was strongly related to HPV type (adjusted OR for HPV type 16 = 9.0; 95% CI = 1.1-77.5), to the husbands' number of extramarital partners (adjusted OR = 11.0; 95% CI = 3.0-40.0; for >21 women versus one), and to the number of prostitutes as extramarital sexual partners (adjusted OR = 8.0; 95% CI = 2.9-22.2; for £10 women versus none). Presence of antibodies to C. trachomatis (adjusted OR = 2.6; 95% CI = 1.4-4.6) and an early age at first sexual intercourse of the husband (adjusted OR = 3.2; 95% CI = 1.7-5.9; for ^15 years versus £21 years) were also associated with cervical neoplasia in the wife. After adjustment for these variables and for the wife's pack-years of smoking, the husband's smoking was moderately associated with cervical cancer in his wife (adjusted OR = 2.5; 95% CI = 1.4-4.4; for >26.2 pack-years versus none). Conclusions: The study supports the role of men as vectors of the HPV types that are related to cervical cancer. Lifetime number of female sexual partners, number of female prostitutes as sexual partners, and detection of HPV DNA in the penis of husbands are all surrogate markers of exposure to HPV during marriage. Implications: Men who report multiple sexual partners or who are carriers of HPV DNA may be vectors of high-risk HPV types and may place their wives at high risk of developing cervical cancer. Prostitutes are an important reservoir of high-risk HPVs. [J Natl Cancer Inst 1996;88:1060-7]

Melatonin reduces nitric oxide synthase activity in rat hypothalamus

Abstract: In this report, rat hypothalamic nitric oxide synthase (NOS) activity is shown to be partially inhibited by physiological concentrations of the pineal hormone melatonin. In vitro studies demonstrate that 1 nM melatonin, which approximates the physiological concentration of the hormone at night, significantly inhibited NOS activity. In vivo studies show that administering melatonin or collecting the hypothalamus from animals at night, when endogenous melatonin levels are elevated, results in a significant decrease of NOS activity. Results also show that calmodulin may be involved in this process since its presence in the incubation medium prevents the inhibitory effect of melatonin on NOS activity.

Synthesis, characterization and photocatalytic properties of iron-doped titania semiconductors prepared from TiO2 and iron(III) acetylacetonate

Abstract: Specimens of iron-doped titania containing different amounts of Fe (0.5–5%) were prepared from TiO2 (Degussa P-25) and Fe(III) acetylacetonate by the wet impregnation method. Samples were characterized by X-ray diffraction analysis, specific surface area (BET) measurements, SEM-EDX, atomic absorption and IR and diffuse reflectance spectra. From the structural point of view, the samples were similar to those obtained with Fe(NO3)3 · 9H2O as the precursor, but with a more homogeneous distribution of iron for each mixed oxide sample on the particle surfaces but not between particles. The photocatalytic activity of these samples under near-UV irradiation was better for oxalic acid degradation than for EDTA, and similar for both types of mixed oxide samples. Mixed oxides showed however lower activity than TiO2. Some photodegradation under visible irradiation, not occurring with TiO2, could be observed for oxalic acid when using 5% Fe-containing samples.

Oxygen sensing by ion channels and chemotransduction in single glomus cells

Abstract: We have monitored cytosolic (Ca 2+) and dopamine release in intact fura- 2-loaded glomus cells with microfluorimetry and a polarized carbon fiber electrode. Exposure to low PO 2 produced a rise of cytosolic (Ca 2+) with two distinguishable phases: an initial period (with PO 2 values between 150 and ~70 mm Hg) during which the in- crease of (Ca 2+) is very small and never exceeds 150-200 nM, and a second phase (with PO 2 below ~70 mm Hg) characterized by a sharp rise of cytosolic (Ca2+). Secretion oc- curs once cytosolic (Ca 2+) reaches a threshold value of 180 + 43 nM. The results dem- onstrate a characteristic relationship between Po 2 and transmitter secretion at the cellu- lar level that is comparable with the relation described for the input (02 tension)-out- put (afferent neural discharges) variables in the carotid body. Thus, the properties of single glomus cells can explain the sensory functions of the entire organ. In whole-cell, patch-clamped cells, we have found that in addition to O2-sensitive K + channels, there are Ca 2+ channels whose activity is also regulated by PO 2. Ca z+ channel activity is inhib- ited by hypoxia, although in a strongly voltage-dependent manner. The average hy- poxic inhibition of the calcium current is 30% -+ 10% at -20 mVbut only 2% + 2% at +30 mV. The differential inhibition of K + and Ca 2+ channels by hypoxia helps to ex- plain why the secretory response of the cells is displaced toward Po 2 values (below ~70 mm Hg) within the range of those normally existing in arterial blood. These data pro- vide a conceptual framework for understanding the cellular mechanisms of 02 chemotransduction in the carotid body.

Homogeneous cooling state of a low-density granular flow

Abstract: This research was partially supported by Grant No. PB96- 0534 from the Direccion General de Investigacion Cientifica y Tecnica (Spain)

Spatial learning and memory deficits after telencephalic ablation in goldfish trained in place and turn maze procedures.

Abstract: The present work investigated whether the fish telencephalon is involved in spatial learning based on place strategies in a manner similar to mammalian hippocampus. Goldfish were trained in a 4-arm maze in a room with relevant spatial cues. Sham and to-be-ablated subjects were trained in each of 4 experimental procedures designed as follows: place, turn, place-turn, and control. After acquisition, complete ablations of both telencephalic hemispheres for the experimental groups were carried out. The results showed that ablation exclusively impaired performance in animals using place strategies; in these, accuracy fell to chance level during both postsurgery retraining and reversal periods. In the other groups, ablation of the telencephalon did not induce any significant deficit. These results suggest that the fish telencephalon plays a crucial role in complex place learning.

N-Monomethyl-arginine and nicotinamide prevent streptozotocin-induced double strand DNA break formation in pancreatic rat islets

Abstract: The impact of short term in vitro exposure to the diabetogenic drug streptozotocin on pancreatic islet glucose metabolism, insulin secretion, DNA fragmentation and cell viability, was studied. Streptozotocin impaired cell viability as well as insulin secretion and the oxidation of glucose. These effects were partially counteracted by inhibition of the inducible form of nitric oxide synthase with N-monomethyl-arginine and by scavenging oxygen free radicals with nicotinamide. Isolated islets underwent double strand DNA fragmentation after 24 h in culture. The degree of DNA breakdown was strongly enhanced by exposure of the islet DNA was obtained with N-monomethyl-arginine and nicotinamide. These data suggest that the generation of reactive oxygen and nitrogen species is involved in the deleterious action of streptozotocin on pancreatic islet tissue. A role for oxygen radicals generated during streptozotocin-induced islet cell damage as possible mediators of the expression of the inducible form of nitric oxide synthase and the scavenging action of nicotinamide on these radicals, is then proposed.

Differential oxygen sensitivity of calcium channels in rabbit smooth muscle cells of conduit and resistance pulmonary arteries.

Abstract: 1. Calcium currents were recorded from smooth muscle cells dispersed from conduit and resistance rabbit pulmonary arteries. We tested the hypothesis that Ca2+ channel activity was regulated by environmental O2 tension. 2. Conduit (proximal) and resistance (distal) myocytes differ in their Ca2+ channel density and responses to low PO2. Ca2+ current density in distal myocytes (20.7 +/- 7.4 pA pF-1, n = 10) is almost twice the value in proximal myocytes (12.6 +/- 5.5 pA pF-1, n = 39). In proximal myocytes, the predominant response to reductions in PO2 is inhibition of the calcium current (n = 12) at membrane potentials below 0 mV, whereas potentiation of current amplitude is observed in distal myocytes (n = 24). 3. Hypoxia also produces opposite shifts in the conductance-voltage relationships along the voltage axis. The average displacements induced by low PO2 are +5.05 +/- 2.98 mV (n = 5) in proximal myocytes and -6.06 +/- 2.45 (n = 10) in distal myocytes. 4. These findings demonstrate longitudinal differences in Ca2+ channel density and O2 sensitivity in myocytes along the pulmonary arterial tree. These results may help to understand the differential reactivity to hypoxia of the pulmonary vasculature: vasodilatation in conduit arteries and vasoconstriction in resistance vessels.

Effects of flavonoids on rat aortic smooth muscle contractility: structure-activity relationships.

Abstract: 1. Flavonoids produced a concentration-dependent relaxation of the contractile responses induced by noradrenaline, KCl, or phorbol 12-myristate-13-acetate in rat aortic rings. Only the flavonoid with three contiguous hydroxyls in B rings (myricetin), at low concentrations, potentiates the contractions evoked by these agonists. 2. The relaxant effects of flavanone on the noradrenaline-induced contractions were potentiated by isoprenaline and those of morin, chrysin, flavanone, and naringenin by sodium nitroprusside. 3. Several mechanisms are implicated in the vasodilatory effects of flavonoids: inhibition of protein kinase C; inhibition of cyclic nucleotide phosphodiesterases; and/or decreased Ca2+ uptake.

Phylogenetic analyses of some extremely halophilic archaea isolated from Dead Sea water, determined on the basis of their 16S rRNA sequences.

Abstract: Twenty-two extremely halophilic aerobic archaeal strains were isolated from enrichments prepared from Dead Sea water samples collected 57 years ago. The isolates were phenotypically clustered into five different groups, and a representative from each group was chosen for further study. Almost the entire sequences of the 16S rRNA genes of these representatives, and of Haloarcula hispanica ATCC 33960, were determined to establish their phylogenetic positions. The sequences of these strains were compared to previously published sequences of 27 reference halophilic archaea (members of the family Halobacteriaceae) and two other archaea, Methanobacterium formicicum DSM 1312 and Methanospirillum hungatei DSM 864. Phylogenetic analysis using approximately 1,400 base comparisons of 16S rRNA-encoding gene sequences demonstrated that the five isolates clustered closely to species belonging to three different genera--Haloferax, Halobacterium, and Haloarcula. Strains E1 and E8 were closely related and identified as members of the species Haloferax volcanii, and strain E12 was closely related and identified as a member of the species Halobacterium salinarum. However, strains E2 and E11 clustered in the Haloarcula branch with Haloarcula hispanica as the closest relative at 98.9 and 98.8% similarity, respectively. Strains E2 and E11 could represent two new species of the genus Haloarcula. However, because strains of these two new species were isolated from a single source, they will not be named until additional strains are isolated from other sources and fully characterized.

A relationship between GC content and coding-sequence length.

Abstract: Since base composition of translational stop codons (TAG, TAA, and TGA) is biased toward a low G+C content, a differential density for these termination signals is expected in random DNA sequences of different base compositions. The expected length of reading frames (DNA segments of sense codons flanked by in-phase stop codons) in random sequences is thus a function of GC content. The analysis of DNA sequences from several genome databases stratified according to GC content reveals that the longest coding sequences—exons in vertebrates and genes in prokaryotes—are GC-rich, while the shortest ones are GC-poor. Exon lengthening in GC-rich vertebrate regions does not result, however, in longer vertebrate proteins, perhaps because of the lower number of exons in the genes located in these regions. The effects on coding-sequence lengths constitute a new evolutionary meaning for compositional variations in DNA GC content.

Osmoprotectants in Halomonas elongata: high-affinity betaine transport system and choline-betaine pathway.

Abstract: The osmoregulatory pathways of the moderately halophilic bacterium Halomonas elongata DSM 3043 have been investigated. This strain grew optimally at 1.5 to 2 M NaCl in M63 glucose-defined medium. It required at least 0.5 M NaCl for growth, which is a higher concentration than that exhibited by the H. elongata type strain ATCC 33173. Externally provided betaine, choline, or choline-O-sulfate (but not proline, ectoine, or proline betaine) enhanced the growth of H. elongata on 3 M NaCl-glucose-M63 plates, demonstrating the utilization of these compounds as osmoprotectants. Moreover, betaine and choline stimulated the growth of H. elongata DSM 3043 over the entire range of salinity, although betaine was more effective than choline at salinities below and above the optimum. We found that H. elongata DSM 3043 has at least one high-affinity transport system for betaine (K(m) = 3.06 microM and Vmax = 9.96 nmol of betaine min(-1) mg of protein(-1)). Competition assays demonstrated that proline betaine and ectoine, but not proline, choline, or choline-O-sulfate, are also transported by the betaine permease. Finally, thin-layer chromatography and 13C-nuclear magnetic resonance analysis showed that exogenous choline was taken up and transformed to betaine by H. elongata, demonstrating the existence of a choline-glycine betaine pathway in this moderately halophilic bacterium.

Cohomology of the complement of a free divisor

Abstract: We prove that if D is a "strongly quasihomogeneous" free divisor in the Stein manifold X, and U is its complement, then the de Rham cohomology of U can be computed as the cohomology of the complex of meromorphic differential forms on X with logarithmic poles along D, with exterior derivative. The class of strongly quasihomogeneous free divisors, introduced here, includes free hyperplane arrangements and the discriminants of stable mappings in Mather's nice dimensions (and in particular the discriminants of Coxeter groups).

Nonlinear electrohydrodynamic waves on films falling down an inclined plane

Abstract: The stability of a perfectly conducting viscous film, falling down an inclined plane, is considered for the case of an applied uniform normal electric field. A highly nonlinear evolution equation for the deformation of the free surface of the film is derived. The study of the linear stability of the system shows the destabilizing effect of the electric forces. A weakly nonlinear analysis leads to a Ginsburg-Landau equation, which predicts that the destabilization induced by the electric field in an otherwise stable film occurs in the form of traveling waves of finite amplitude.

Analysis of 16S rRNA gene sequences of Vibrio costicola strains: description of Salinivibrio costicola gen. nov., comb. nov.

Abstract: The phylogenetic positions of six Vibrio costicola strains were determined by direct sequencing and analysis of their PCR-amplified 16S ribosomal DNAs. A comparative analysis of the sequence data revealed that the moderate halophile V. costicola forms a monophyletic branch that is distinct from other Vibrio species and from moderately halophilic species of other genera. These results complement phenotypic and genotypic data determined previously. The molecular evidence, together with several phenotypic differences, distinguishes V. costicola from species of the genus Vibrio and other species belonging to the gamma subclass of the Proteobacteria and indicates that V. costicola should be placed in a new and separate genus. The name Salinivibrio costicola gen. nov., comb. nov. is proposed for this bacterium. The guanine-plus-cytosine content of the DNA is 49.4 to 50.5 mol%. The type strain of S. costicola is strain NCIMB 701 (= ATCC 33508).

Postfire regeneration of a mediterranean heathland in Southern Spain

Abstract: Fire is a recurrent disturbance in the vegetation of Mediterranean climate regions. Most of the woody species (16 out of 19) in a Mediterranean heathland community, in the Strait of Gibraltar region of southern Spain, sprouted from subterranean vegetative organs after a wild-fire. Dominant sprouters were the prostrated oak Quercus lusitanica, three gorses, Genista tridens, G. tridentata and Stauracanthus boivinii, and a heath, Erica scoparia. About 100 seedlings m-2 of 14 woody species were censused in the first three years after fire. The highest density of seedlings was recorded for heather (Calluna vulgaris), a rockrose (Cistus populifolius subsp. major) and a gorse (Genista triacanthos). Woody vegetation covered up to 85% of the soil surface in the third year after fire. At this stager the community was co-dominated by the sprouters Quercus lusitanica (21%), Genista tridentata (21%) and Stauracanthus boivinii (20%), and the seeder Cistus populifolius subsp. major (20%). A total of 52 herbaceous species, many of them (35) perennials, was recorded, showing a temporal change in species composition. The role of fire influencing community diversity and the consequences for the conservation of heathlands in the Strait of Gibraltar region, are discussed.

Influence of Olive Ripeness on the Concentration of Green Aroma Compounds in Virgin Olive Oil

Abstract: Changes have been demonstrated in the concentration of those volatile compounds responsible for green sensory notes in virgin olive oils obtained from four different varieties at three stages of ripeness. The information corresponding to each volatile compound for each stage of ripeness, after fuzzy filtering of the quantitative data, has been established and the relationship between volatile compounds and green sensory attributes has also been demonstrated by means of principal components analysis, correlation and stepwise linear regression analysis.

Stylar Polymorphisms and the Evolution of Heterostyly in Narcissus (Amaryllidaceae)

Abstract: In outcrossing hermaphrodite plants, the separate functions of pollen dispersal and pollen receipt may interfere with one another so that fitness as a paternal or maternal parent is compromised (van der Pijl, 1978; Bawa and Opler, 1975; Lloyd and Yates, 1982; Lloyd and Webb, 1986; Webb and Lloyd, 1986; Bertin and Newman, 1993; Harder and Barrett, 1995). This is particularly likely in flowers in which the sex organs are close together and mature at the same time. Interference can potentially take several forms, including the obstruction by pistils of efficient pollen dispatch by pollinators, stamens restricting access by pollinators to stigmas, thus reducing pollen deposition, and the deleterious effects of self-pollination on maternal function due to stigmatic, stylar, or ovular clogging. Although there is some experimental evidence for self-pollen interference (Shore and Barrett, 1984; Barrett and Glover, 1985; Bertin and Sullivan, 1988; Palmer et al., 1989; Waser and Price, 1991; Scribailo and Barrett, 1994), the other two forms of pollen-pistil interference have seldom been investigated (see, however, Barrett and Glover, 1985; Kohn and Barrett, 1992a).