Showing papers by "University of Alicante published in 1998"
TL;DR: In this paper, the increasing importance of carbon materials in catalytic processes is analyzed in terms of the most important characteristics of these materials when acting as catalysts or catalyst supports, such as surface area, porosity, chemical inertness and oxygen surface groups.
1,620 citations
TL;DR: In this paper, the storage capability of microporous carbon materials for gaseous hydrogen both theoretically and experimentally was investigated, and it was shown that for low gas pressure a cylindrical geometry like that in carbon nanotubes can exceed the storage density of carbon slitpores owing to capillary forces.
Abstract: We have investigated the storage capability of microporous carbon materials for gaseous hydrogen both theoretically and experimentally. In the grand canonical Monte Carlo calculation the hydrogen molecules are physisorbed by van der Waals interactions with the surface atoms of carbon slitpores and carbon nanotubes. At room temperature the optimum pore geometry is a slitpore consisting of two graphite platelets separated by a distance that corresponds approximately to two times the diameter of a hydrogen molecule. In this case for a storage pressure of 10 MPa a maximum adsorbed hydrogen density of 14 kg/m3 can be reached, which corresponds to a gravimetric storage capacity of 1.3 wt %. Only for low gas pressure a cylindrical geometry like that in carbon nanotubes can exceed the storage density of carbon slitpores owing to capillary forces.
488 citations
TL;DR: In this article, the pore sizes of activated carbons and carbon molecular sieves of different origins and pore size distribution were compared to N2 adsorption at 77 K at subatmospheric pressures.
Abstract: Adsorption of CO2 at 273 K up to 4 MPa has been studied in activated carbons and carbon molecular sieves of different origins and pore size distribution. The materials selected for this study include carbon molecular sieves with a pore size (i.e., pore width) between 0.3 and 0.5 nm, activated carbons with supermicroporosity (pore size between 0.7 and 2 nm), and mesoporous and macroporous activated carbons. The relative fugacities covered in the experiments ranges from 10-4 to nearly 1. Additionally, N2 adsorption at 77 K at subatmospheric pressures has been also done. The experimental conditions used allow us to compare both measurements at similar adsorption potentials, in which both gases adsorb in the different ranges of porosity. The results obtained show that CO2 adsorbs at 273 K in the different ranges of porosity following a mechanism similar to that of N2 at 77 K. CO2 is sensitive to narrow micropores not accessible to N2 at 77 K, and hence, it is an adequate complement to N2 at 77 K. This is espe...
372 citations
TL;DR: In this article, a simple and convenient evaluation of volume of micropores and heterogeneity of the micropore size distribution can be obtained by combining the results from adsorption of N2 at 77 K and CO2 at 273 K.
211 citations
TL;DR: In this paper, the growth of a typical brain tumor was analyzed both dynamically and morphologically, and the fractal dimension of the tumor was found to be 1.21 × 1.05.
Abstract: The growth of a cultivated typical brain tumor is studied in this work. The tumor is analyzed both dynamically and morphologically. We have measured its fractal dimension to be ${d}_{f}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.21\ifmmode\pm\else\textpm\fi{}0.05$. From its dynamical behavior we determine the scaling critical exponents of this circular symmetry system which are compatible with the linear molecular beam epitaxy universality class. A very important feature of tumor profiles is that they are super-rough, which constitutes the first ( $1+1$)-dimensional experiment in literature with super-roughness. The results obtained from the dynamics study make manifest two very surprising features of tumor growth: Its dynamics is mainly due to contour cells and the tendency of an interface cell to duplicate is a function of the local curvature.
192 citations
TL;DR: The most important conditions for the generation of a corporate culture based on technological innovation are discussed in this article, with the support of a large number of empirical and theoretical studies, with the aim of analyzing the origin of a culture based in innovation technology.
190 citations
TL;DR: In this article, a model of "satisficing" behavior in the repeated Prisoners Dilemma is studied, where each player has an aspiration at each date, and takes an action only if the achieved payoff fell below the aspiration level.
188 citations
TL;DR: In this article, two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which has been introduced using both H 2 PtCl 6 in acid media and [Pt(NH 3 ) 4 ]Cl 2 in basic media.
Abstract: Two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which has been introduced using both H 2 PtCl 6 in acid media and [Pt(NH 3 ) 4 ]Cl 2 in basic media. The catalysts have been characterized by H 2 chemisorption at room temperature (after different pre-treatments), temperature-programmed reduction (TPR) and temperature-programmed desorption of adsorbed hydrogen (H 2 -TPD), and their catalytic behavior in the gas-phase hydrogenation of benzene has been determined under differential conditions. TPD profiles of oxygen surface groups in fresh catalysts evidenced the support oxidation by H 2 PtCl 6 , with the occurrence of a CO evolution peak at low temperature (630 K). The presence of oxygen surface groups in the support favors the anchoring of [Pt(NH 3 ) 4 ] 2+ , but does not affect the amount of platinum retained by the support when H 2 PtCl 6 is used as metal precursor. TPR experiments have evidenced that the oxidized support hinders the reduction of the platinum precursor. The catalytic activities in the benzene hydrogenation reaction do not show a direct correlation with dispersion values obtained from hydrogen chemisorption, and it has been related to storage and mobility of hydrogen which is spilt over the support during the reduction treatments.
143 citations
TL;DR: In this paper, the authors analyse soft-sediment deformation structures in Upper Miocene calcarenitic tempestites of the Guadalquivir Basin (Southern Spain) and conclude that liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves.
Abstract: The identification of triggering agents for soft-sedimentation structures is an enigmatic geological problem. Mainly seismic-induced soft-sediment structures have been recognized in ancient sediments, rather than those resulting from storm waves. We analyse soft-sediment deformation structures in Upper Miocene calcarenitic tempestites of the Guadalquivir Basin (Southern Spain). The most common structures are load-casts which vary in height and width from 10 centimetres to several metres. The structures are always restricted to a small part of the stratigraphic sections, in exclusive association with tempestites. The analysed soft-deformation structures are interpreted to be the result of liquidization processes. Chiefly from their inferred depositional environment, and subordinately from the deformation style, we have devised basic criteria to identify the trigger mechanism. In these soft-sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves.
134 citations
TL;DR: Although LASik decreased contrast sensitivity values at low and intermediate spatial frequencies for 1 month after surgery, these values rapidly returned to the preoperative values at 3 months, which suggests that LASIK can improve the quality of vision in eyes with moderate and high myopia.
Abstract: Purpose: To evaluate the effect on contrast sensitivity function of laser in situ keratomileusis (LASIK) for the correction of myopia. Setting. Alicante Institute of Ophthalmology, University of Alicante, Spain. Methods: Fourteen eyes of 10 patients had LASIK to correct myopia ranging from 6.00 to 19.50 diopters (D). Mean preoperative myopia was 10.39 D ± 3.69 (SD). Contrast sensitivity was tested preoperatively and 1, 3, and 6 months postoperatively using the CVS-1000E contrast sensitivity unit (VectorVision). Results: Contrast sensitivity decreased 1 month postoperatively; the decrease was significant only at the low and intermediate spatial frequencies of 3 and 6 cycles per degree (cpd) ( P = .034 and .030, respectively). Starting from the first month, there was rapid recovery of contrast sensitivity and at the third month, no statistically significant decrease at all spatial frequencies. Six months after surgery, there was an increase in contrast sensitivity values at 3, 12, and 18 cpd, although the changes were not significant. Conclusion: Although LASIK decreased contrast sensitivity values at low and intermediate spatial frequencies for 1 month after surgery, these values rapidly returned to the preoperative values at 3 months. The improvement at certain frequencies at 6 months suggests that LASIK can improve the quality of vision in eyes with moderate and high myopia.
134 citations
TL;DR: There were few complications after PRK in 3000 eyes and with proper patient selection, PRK can be considered relatively safe compared with other refractive orocedures.
Abstract: Purpose: To evaluate the results and complications of photorefractive keratectomy (PRK) for myopia. Setting: Alicante Institute of Ophthalmology, University of Alicante, Spain. Methods: This prospective study evaluated the results and complications of the first 3000 cases of PRK performed with a VISX Twenty-Twenty excimer laser. Myopia ranged from −1.0 to −14.0 diopters (D) and astigmatism, from −1.0 to −5.0 D. Follow-up was 2 years. Results: Ten eyes (0.7%) lost two or more lines of best corrected visual acuity 1 year after surgery. Retreatment for undercorrection or regression was done in 7.41% in the low myopia group and 38.69% in the high myopia group. Central islands, which could be detected only on videokeratoscopy, occurred frequently but influenced the refractive and visual outcomes in few cases. Severe haze was present in 17 eyes only after 1 year follow-up. There were no cases of progressive hyperopia. Other complications such as eccentric ablation producing astigmatism (n = 15), delayed re-epithelialization, or recurrent corneal erosion were rare. Conclusion: There were few complications after PRK in 3000 eyes. With proper patient selection, PRK can be considered relatively safe compared with other refractive orocedures.
TL;DR: In this article, the Rutter type model of rainfall interception was adapted for individual shrubs and tested with measured rainfall events showing a good agreement between observed and predicted values for R. sphaerocarpa and for A. cytisoides.
TL;DR: In this paper, thermal loss occurs in three stages, centered around 250°C, 350°C and 550°C producing high quantities of gases, as hydrogen, water, hydrocarbons (C1−C4, both saturated and unsaturated), methanol, chloromethane, carbon dioxide and acetic acid.
TL;DR: In this paper, the reaction of dimethyl or diethylzinc with ketones in the presence of a stoichiometric amount of titanium tetraisopropoxide and a catalytic amount (20 mol %) of camphorsulfonamide derivatives as chiral ligands leads to the formation of the corresponding enantioenriched alcohols with enantiomeric ratios up to 94.5:5.
TL;DR: Morphological changes in the corneal nerves after laser in situ keratomileusis (LASIK) were investigated and the changes were compared with those observed after creation of the keratectomy flap without subsequent photoablation.
TL;DR: In this paper, a kinetic model including a first step of pyrolysis, which assumes three organic fractions not forming residues, and a step of combustion is presented, with activation energy in the range 221-235 kJ/mol, and there exists a dependence of the rate of decomposition on the partial pressure of oxygen.
TL;DR: The platinum-ceria interaction, induced after high temperature reduction of platinum based catalysts, has been used to improve the selectivity towards crotyl alcohol in the gas phase hydrogenation of crotonaldehyde as mentioned in this paper.
TL;DR: In this article, a voltammetry and FTIR-ATR techniques have been employed to investigate polyphenol films formed on platinum surfaces by electrochemical oxidation of phenol.
TL;DR: The 16S-23S spacer regions of two ribosomal operons (rrnA and rrnE) have been sequenced in seven representatives of the Salmonella enterica subspecies and the phylogenetic tree inferred is consistent with those of 16S rRNA or housekeeping genes.
Abstract: The 16S-23S spacer regions of two ribosomal operons (rrnA and rrnE) have been sequenced in seven representatives of the Salmonella enterica subspecies. Isolated nucleotide substitutions were found at the same sites as in Escherichia coli but the number of polymorphic sites was much larger, as could be expected for a more heterogeneous species. Still, as in E. coli, most of the variation found was due to insertions and/or deletions affecting blocks of nucleotides generally located at equivalent regions of the putative secondary structure for both species. Isolated polymorphic sites generated phylogenetic trees generally consistent with the subspecies structure and the accepted relationships among the subspecies. However, the sequences of rrnE put subspecies I closer to E. coli K-12 than to the other S. enterica subspecies. The distribution of polymorphisms affecting blocks of nucleotides was much more random, and the presence of equivalent sequences in distantly related subspecies, and even in E. coli, could reflect relatively frequent horizontal transfer. The smallest 16S-23S spacers in other genera of the family Enterobacteriaceae were also sequenced. As expected, the level of variation was much larger. Still, the phylogenetic tree inferred is consistent with those of 16S rRNA or housekeeping genes.
TL;DR: The results indicate’ that PRK may be an alternative for the correction of pediatric myopic anisometropia and an important aid in treating amblyopia.
Abstract: Purpose: To evaluate the visual results of excimer laser photorefractive keratectomy (PRK) to treat pediatric patients with amblyopic myopic anisometropia in whom conventional amblyopia treatments have failed. Setting: Instituto Oftalmologico de Alicante, University of Alicante, Spain. Methods: Six patients aged 5 to 7 years with amblyopic myopic anisometropia were treated by PRK in the more myopic eye using a VISX Twenty-Twenty excimer laser. Minimum preoperative refraction in the amblyopic eyes ranged from −4.00 to −13.00 diopters and best corrected visual acuity (BCVA), from 20/40 to 20/400. All cases completed a minimum of 2 years follow-up of antiamblyopic treatment. Results: After PRK, preoperative BCVA was maintained without optical correction and complementary refraction resulted in increased BCVA in every case. One patient with high myopia developed severe haze. There were no other significant complications. Conclusion: Our results indicate' that PRK may be an alternative for the correction of pediatric myopic anisometropia and an important aid in treating amblyopia. When other therapies have failed, using PRK in children of the ages in this study must be carefully evaluated; however, our results suggest a beneficial effect.
TL;DR: In this article, a tentative catalytic cycle and mechanistic model are proposed for this new reaction and the best results were obtained when phenones are used as substrates independently of the dialkylzinc reagent.
TL;DR: In this article, a set of adsorption isotherms obtained for a series of the same activated carbon with different burning degrees are compared and discussed, and a test for the characterization methods by Monte Carlo Simulation is designed in order to achieve a better understanding of the observed deviations.
TL;DR: In this article, the kinetics of the global primary thermal decomposition of tanned leather were studied using TG-DTG in strict pyrolysis conditions and with different proportions of oxygen.
TL;DR: During the BENTART 95 Expedition, 24 Agassiz trawls for macrozoobenthos sampling were carried out at depths of 40–850 m, from north of Livingston Island to the Antarctic Peninsula, and a zonation of ascidians, regular sea urchins and ophiuroids was observed, clearly related to depth and substratum type.
Abstract: During the BENTART 95 Expedition, 24 Agassiz trawls for macrozoobenthos sampling were carried out at depths of 40–850 m, from north of Livingston Island to the Antarctic Peninsula. The samples were analysed using a semi-quantitative method, and with the resulting numerical data, transformed into a six-point scale, we constructed a Bray-Curtis similarity matrix. A total of 74,624 specimens, belonging to 38 taxonomic groups, were collected. The most abundant group was Polychaeta Sedentaria, with 36% of the total, whereas the highest relative masses were from Ascidiacea (23%), Echinoidea Regularia (18%) and Ophiuroidea (16%). The maximum number of specimens recorded was 15,600 ind./50 l. Cluster analysis separated stations located in Foster Bay (Deception Island), characterised by low taxonomic richness and high relative mass (average: 26.7 kg). A zonation of ascidians, regular sea urchins and ophiuroids was observed at Deception Island, clearly related to depth and substratum type. The remaining stations were separated into two groups. The first one comprised the shallowest stations (40–130 m), dominated by sessile active filter-feeders, belonging to Ascidiacea, Demospongia and Bryozoa, and probably related to high primary production zones. The second group comprised deeper stations and was dominated by classes exhibiting a diversity of trophic strategies: Ophiuroidea and Asteroidea, to 400 m, and Polychaeta Sedentaria at greater depths.
TL;DR: Results indicate that the wound healing reaction after LASIK takes place only at the periphery of the microkeratome wound, leaving the central optical zone clear.
Abstract: BACKGROUND The aim of this study was to characterize the cell biology of wound healing in rabbit corneas subjected to laser in situ keratomileusis (LASIK). METHODS Rabbit corneas underwent LASIK with various multizone photoablations or only a lamellar keratotomy followed by repositioning of the flap. We looked for indications for an active wound healing process. Immunohistochemistry for the extradomain A cellular fibronectin (EDA-cFn) or tenascin (Tn) and routine histology were examined. RESULTS Four days after LASIK or lamellar keratotomy followed by repositioning of the flap, epithelial plugs and prominent keratocytes as well as Tn and EDA-cFn immunoreactions-indicative of a wound-healing process-appeared in the wound margins. Epithelial plugs were less conspicous, and prominent, presumably activated, keratocytes were no longer identified at the wound margin at 2.5 and 5 months after wounding. However, EDA-cFn and Tn immunoreactivities could still be observed. Only the stromal cells located in the periphery of the flap and in relatively close contact with the epithelium were surrounded by scar tissue expressing immunoreactivity for EDA-cFn or Tn. The central corneal stroma was devoid of scar tissue. CONCLUSION Results indicate that the wound healing reaction after LASIK takes place only at the periphery of the microkeratome wound, leaving the central optical zone clear.
TL;DR: In this article, the performance of tin dioxide electrodes with antimony and platinum was investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction.
Abstract: Doped tin dioxide electrodes have been prepared by a standard spray pyrolysis technique. The electrochemical behaviour of these electrodes has been investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction. Oxygen evolution has been used to study the stability of doped SnO2 electrodes. The SnO2 electrodes doped with antimony and platinum exhibit the highest stability. XPS analysis shows that the oxidation state of Sn, Sb and Pt are +4, +3 and +2, respectively, the probable species being SnO2, Sb2O3 and PtO.
TL;DR: In this paper, the effect of nickel (Ni) on the nutrition of tomato plants (Lycopersicon esculentum M. cv. Marmande) was studied.
Abstract: An experiment was conducted to study the effect of nickel (Ni) on the nutrition of tomato plants (Lycopersicon esculentum M. cv. Marmande). Dry matter weights of roots, shoots, and fruit were also studied. Plants, receiving 5, 15, and 30 mg Ni L‐1, were grown in nutrient solution, and roots, stems plus branches, leaves, and fruit were analyzed at different developmental stages for essential nutrients. The presence of Ni in nutrient medium affected plant growth, decreasing dramatically dry matter yield compared to control plants. This plant reduction was likely due to the disturbances and imbalances of the different essential mineral elements. The general effect was a decrease in the absorption and accumulation of these nutrients. The nitrogen (N) content in the plant increased significantly with increasing Ni treatments, showing a synergetic effect between Ni and N. A positive interaction between Ni and potassium (K) was also found. In this way, high levels of Ni in solution caused an increase in...
TL;DR: In this paper, the authors provide an insight into Sperber and Wilson's relevance theory, an analysis of its situation after ten years, and comments on the theory and its wide implications for the study of communication.
TL;DR: In this paper, the interaction of fast charged particles with a semi-infinite medium is described using both quantum-mechanical and semiclassical dielectric formulations, and interference effects in bulk and surface excitations for some particular trajectories are described.
Abstract: The interaction of fast charged particles with a semi-infinite medium is described using both quantum-mechanical and semiclassical dielectric formulations. We consider the coupling with bulk and surface excitations for arbitrary trajectories of the particle and apply the solutions to several cases of special interest. Interference effects in bulk and surface excitations for some particular trajectories are described. We analyze in detail the process of reflection-electron-energy-loss spectroscopy, obtaining results for the probabilities of multiple bulk- and surface-plasmon excitations. The calculations are compared with available experimental results, showing a good description of the angular dependence of the excitation phenomenon.