Menú secundario

Artículos SCI


A thermal study approach to roman age wall painting mortars

Duran, A; Perez-Maqueda, LA; Poyato, J; Perez-Rodriguez, JL
Journal of Thermal Analysis and Calorimetry, 99 (2010) 803-809


Roman ancient mortars have been widely studied, in connection with both diagnosis and application required for restoring. Thermoanalytical experiments performed on mortars from Pompeii and Herculaneum provided a very good understanding of the technology employed. The mortars from Pompeii were obtained by the proper mixing of lime and marble grains while mortars of Herculaneum by lime and silicates compounds. The position of the endothermic peak of calcite decomposition showed important variations in the different samples studied, which was assigned to the different crystallinity and particle sizes. Experiments under CO2 flow confirmed the presence of magnesium calcium carbonates.

Marzo, 2010 | DOI: 10.1007/s10973-009-0667-2

Room-Temperature Reaction of Oxygen with Gold: An In situ Ambient-Pressure X-ray Photoelectron Spectroscopy Investigation

Jiang, P; Porsgaard, S; Borondics, F; Kober, M; Caballero, A; Bluhm, H; Besenbacher, F; Salmeron, M
Journal of the American Chemical Society, 132 (2010) 2858-2859
Materiales y Procesos Catalíticos de Interés Ambiental y Energético


The interaction of O-2 with gold foil and gold nanoparticles grown by thermal deposition on TiO2(110) was studied by in situ ambient pressure X-ray photoelectron spectroscopy at room temperature. No spontaneous dissociation of O-2 was observed either on Au foil or oil Au nanoparticles up to 1 Torr of O-2. X-ray irradiation, however, is very effective in promoting gold oxidation on both surfaces in the presence of O-2. Our results help reconcile recent conflicting experimental observations regarding the activation of molecular oxygen, which is a crucial issue in Au catalyzed oxidation reactions.

Marzo, 2010 | DOI: 10.1021/ja909987j

Microstructural characterization of copper based alloys produced by reactive milling

Palma, R; Sepulveda, A; Zuniga, A; Donoso, E; Dianez, MJ; Criado, JM
Revista de Metalurgia, 46 (1010) 197-205
Reactividad de Sólidos


The micro and nanostructure of Cu-Al, Cu-V and Cu-Ti alloys produced by reactive milling were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Samples with different milling times (t = 0, 10, 20 and 30 h) were considered. The grain size, dislocation density and residual microstrain were evaluated form the XRD data using the Williamson-Hall and Klug-Alexander methods. The evolution of texture as a function of milling time was also studied using XRD. It was found, using TEM, that the grain size and dispersoid size were nanometric in all three alloys considered.

Marzo, 2010 | DOI: 10.3989/revmetalm.2010.v46.i3

Evaluation of Different Dielectric Barrier Discharge Plasma Configurations As an Alternative Technology for Green C-1 Chemistry in the Carbon Dioxide Reforming of Methane and the Direct Decomposition of Methanol

Rico, VJ; Hueso, JL; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physical Chemistry A, 114 (2010) 4009-4016
Nanotecnología en Superficies y Plasma


Carbon dioxide reforming of methane and direct decomposition of methanol have been investigated using dielectric harrier discharges (DBD)) at atmospheric pressure and reduced working temperatures. Two different plasma reactor configurations are compared and especial attention is paid to the influence of the surface roughness of the electrodes oil the conversion yields in the first plasma device. The influence of different filling gap dielectric materials (i.e., Al2O3 of BaTiO3) in the second packed configuration has been also evaluated. Depending on the experimental conditions of applied voltage, residence time of reactants. feed ratios, or factor configuration. different conversion yields are achieved ranging front 20 to 80% in the case of methane and 7-45% for the carbon dioxide. The direct decomposition of methanol reaches 60-100% Under similar experimental conditions. Interestingly, the selectivity toward the production of hydrogen and carbon monoxide is kept almost constant under all the experimental conditions, and the formation of longer hydrocarbon chains of coke is a byproduct is not detected. The maximum efficiency yields are observed for the packed-bed reactor configuration containing alumina for both reaction processes (similar to 1 mol H-2 per kilowatt hour for dry reforming of methane and similar to 4.5 mol H-2, per kilowatt hour for direct decomposition of methanol).

Marzo, 2010 | DOI: 10.1021/jp100346q

Theoretical Analysis of the Performance of One-Dimensional Photonic Crystal-Based Dye-Sensitized Solar Cells

Lozano, G; Colodrero, S; Caulier, O; Calvo, ME; Miguez, H
Journal of Physical Chemistry C, 114 (2010) 3681-3687
Materiales Ópticos Multifuncionales


A simple analytical model that allows designing one-dimensional photonic crystal based dye sensitized solar cells of optimized performance, accounting for the actual optical features of the device, is herein presented. Based on the theoretical description of the effect of coupling such Bragg mirrors to the light harvesting electrode, recently reported experimental values of the spectral dependence of incident photon to current conversion efficiency attained for such Structures are fairly reproduced and rationalized. A thorough analysis or them in terms of the interplay between the effect of the electrode thickness and the characteristics of the Bragg reflection, such as intensity, spectral position, and width, is provided. Predictions on the maximum enhancement factors expected for realistic Structures are also presented.

Marzo, 2010 | DOI: 10.1021/jp9096315

Morphological evolution of pulsed laser deposited ZrO2 thin films

Alvarez, R; Palmero, A; Prieto-Lopez, LO; Yubero, F; Cotrino, J; de la Cruz, W; Rudolph, H; Habraken, FHPM; Gonzalez-Elipe, AR
Journal of Applied Physics, 107 (2010) 54311-54320
Nanotecnología en Superficies y Plasma


Morphological evolution of ZrO2 thin films deposited during pulsed laser deposition of Zr in O-2 atmosphere has been experimentally studied at two different film deposition temperatures, 300 and 873 K. The roughness exponent, alpha, the growth exponent, beta, the coarsening exponent, 1/z, and the exponent defining the evolution of the characteristic wavelength of the surface, p, for depositions at 300 K amounted to beta = 1.0 +/- 0.1, alpha = 0.4 +/- 0.1, 1/z = 0.34 +/- 0.03, and p = 0.49 +/- 0.03, whereas for depositions carried out at 873 K amounted to beta = 0.3 +/- 0.3, alpha = 0.4 +/- 0.2, and 1/z = 0.0 +/- 0.2. Experimental error becomes important due to the flat morphology of the films inherent to the deposition technique. The change in the surface topography with the film temperature has been studied with the help of a simple Monte Carlo model which indicates the existence of two different growth regimes: a shadowing dominated growth, occurring at low temperatures, characterized by calculated values beta = 1.00 +/- 0.04, alpha = 0.50 +/- 0.04, p = 0.46 +/- 0.01, and 1/z = 0.35 +/- 0.02 and a diffusion dominated growth that takes place at high temperatures as well as at low deposition rates, characterized by calculated values beta = 0.15 +/- 0.08, alpha = 0.33 +/- 0.04, and 1/z = 0.33 +/- 0.07. The good agreement obtained between the experimental and simulated parameters is discussed within the frame of the general characteristics of the deposition method.

Marzo, 2010 | DOI: 10.1063/1.3318604

Application of Micro-X-ray Fluorescence Analysis for the Characterization of Industrial Wastes

Alba, MD; Aparicio, P; Benitez, JM; Castro, MA; Diaz, M; Orta, MM
Industrial & Engineering Chemistry Research, 49 (2010) 2348-2352
Materiales de Diseño para la Energía y Medioambiente


The issue of how to improve product quality and product yield in a short period of time is becoming more critical in many industries. Thus, shorter delay times between laboratory analysis and process correction are important in process control. Elimination of sample handling and operator Manipulation is desirable. The present article proposes micro-X-ray fluorescence (mu XRF) as an economical control method for industrial product quality with a minimum time cost. Samples from different industrial processes have been chosen and analyzed by XRF and mu XRF, The results show that the two techniques give similar results and that mu XRF allows the waste to be classified and is able to detect problems in the production process.

Marzo, 2010 | DOI: 10.1021/ie901716w

Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles

Guerrero, E; Munoz-Marquez, MA; Fernandez, A; Crespo, P; Hernando, A; Lucena, R; Conesa, JC
Journal of Applied Physics, 107 (2010) 064303-064309
Materiales Nanoestructurados y Microestructura


In the last years, the number of studies performed by wholly independent research groups that confirm the permanent magnetism, first observed in our research lab, for thiol-capped Au nanoparticles (NPs) has rapidly increased. Throughout the years, the initial magnetometry studies have been completed with element-specific magnetization measurements based on, for example, the x-ray magnetic circular dichroism technique that have allowed the identification of gold as the magnetic moment carrier. In the research work here presented, we have focused our efforts in the evaluation of the magnetic behavior and iron impurities content in the synthesized samples by means of superconducting quantum interference device magnetometry and electron paramagnetic resonance spectrometry, respectively. As a result, hysteresis cycles typical of a ferromagnetic material have been measured from nominally iron-free gold NPs protected with thiol, phosphine, and chlorine ligands. It is also observed that for samples containing both, capped gold NPs and highly diluted iron concentrations, the magnetic behavior of the NPs is not affected by the presence of paramagnetic iron impurities. The hysteresis cycles reported for phosphine-chlorine-capped gold NPs confirm that the magnetic behavior is not exclusively for the metal-thiol system.

Marzo, 2010 | DOI: 10.1063/1.3327414

Mechanosynthesis of Hf1-xZrxB2 Solid Solution and Hf1-xZrxB2/SiC Composite Powders

Aviles, MA; Cordoba, JM; Sayagues, MJ; Alcala, MD; Gotor, FJ
Journal of the American Ceramic Society, 93 (2010) 696-702
Reactividad de Sólidos


The synthesis of solid solutions in the HfB2-ZrB2 system was conducted by mechanically induced self-sustaining reaction (MSR) processes under an inert atmosphere from elemental mixtures of Hf, Zr, and B. The stoichiometry of the Hf1-xZrxB2 solid solution phase was controlled by adjusting the Hf/Zr/B atomic ratio in the starting mixture. Composite materials with SiC were achieved by adding the required amount of SiC to the Hf/Zr/B reactant mixture. The presence of up to 20 vol% of SiC did not inhibit the MSR process. Longer milling times were required to ignite the mixture. Small amounts of the refractory phases ZrC or HfC were observed in the composite powders. The chemical composition, structure, and microstructure of products were studied by X-ray diffraction, scanning and transmission electron microscopy, electron diffraction, and energy-dispersive X-ray spectroscopy. This complete characterization confirmed the formation of P6/mmm hexagonal diboride phases with a submicrometric microstructure. The determination of the chemical composition and lattice parameters ascertained the formation of solid solutions with good chemical homogeneity in the HfB2-ZrB2 system.

Marzo, 2010 | DOI: 10.1111/j.1551-2916.2009.03484.x

Active and Optically Transparent Tetracationic Porphyrin/TiO2 Composite Thin Films

Castillero, P; Sanchez-Valencia, JR; Cano, M; Pedrosa, JM; Roales, J; Barranco, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 2 (2010) 712-721
Nanotecnología en Superficies y Plasma


Fluorescent tetracationic porphyrin (TMPyP) molecules have been incorporated into optically transparent TiO2 thin films acting as a host material. The films, with a columnar structure and open pores, were prepared by electron evaporation at glancing angles (GAPVD). The open porosity of the films has been estimated by measuring a water adsorption isotherm with a quartz crystal monitor. TMPyP molecules were infiltrated in the host thin films by their immersion into water solutions at controlled values of pH. The state of the adsorbed molecules, the infiltration efficiency, and the adsorption kinetics were assessed by analyzing the optical response of the films by UV-vis absorption and fluorescence techniques. The infiltration efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) developed for colloidal oxides. By a quantitative evaluation based on the analysis of the UV spectra, the infiltration process has been described by a Langmuir type adsorption isotherm and an Elovich-like kinetics. The accessibility of the infiltrated molecules in the TMPyP/TiO2 composite films is assessed by following the changes of their optical properties when exposed to the acid vapors and their subsequent recovery with time.

Marzo, 2010 | DOI: 10.1021/am900746q

Spark Plasma Sintering of Ultrafine TiCxN1-x Powders Synthesized by a Mechanically Induced Self-Sustaining Reaction

Borrell, A; Fernandez, A; Torrecillas, R; Cordoba, JM; Aviles, MA; Gotor, FJ
Journal of the American Ceramic Society, 93 (2010) 2252-2256
Reactividad de Sólidos


High-purity, nanometer-sized titanium carbonitride powders, TiCxN1-x, were obtained with a mechanically induced self-sustaining reaction (MSR) in a high-energy planetary ball mill from a mixture of titanium and different carbon precursors under a nitrogen atmosphere. A promising method for developing dense TiCxN1-x materials is the coupling of MSR with the spark plasma sintering (SPS) technique. The powders were sintered at different temperatures to provide a completely dense monolithic ceramic (> 99% theoretical density). In this work, the influence of the carbon precursor and SPS treatment on the material microstructures were studied, and the main mechanical properties of the end material were evaluated.

Marzo, 2010 | DOI: 10.1111/j.1551-2916.2010.03735.x

Seville City Hall Chapter Room ceiling decoration

Duran, A; Robador, MD; de Haro, MCJ; Herrera, LK; Gimena, P; Perez-Rodriguez, JL
Materiales de Construcción, 60 (2010) 83-95


El objetivo de este trabajo es el estudio de diferentes aspectos, como el color, la composición química y las fases mineralógicas presentes en los diferentes materiales que forman la ornamentación del techo de la Sala Capitular del Ayuntamiento de Sevilla, mediante métodos físicos y químicos. Nuestros resultados muestran que el dorado fue realizado sobre una capa de bol previamente depositada sobre una lámina de blanco de plomo que cubría un estrato de calcita. Posteriormente, y probablemente debido a alteraciones en el dorado original, el techo fue de nuevo dorado usando una técnica similar. En el siglo XIX, casi todo el techo, excepto las zonas con inscripciones, fue blanqueado usando una mezcla de calcita y blanco de plomo. Se empleó plata para cubrir la espada del rey Juan I (casetón 27). Finísimas láminas de oro se usaron para decorar los atributos reales: coronas, cinturones, cetros, espadas y rosarios. En diferentes partes de la decoración fueron detectados pigmentos como azurita, malaquita, bermellón y negro de humo. La composición del mortero de la estructura era a base de cal y dolomita molida.

Febrero, 2010 | DOI: 10.3989/mc.2010.45107

In situ spectroscopic detection of SMSI effect in a Ni/CeO2 system: hydrogen-induced burial and dig out of metallic nickel

Caballero, A; Holgado, JP; Gonzalez-delaCruz, VM; Habas, SE; Herranz, T; Salmeron, M
Chemical Communications, 46 (2010) 1097-1099
Materiales y Procesos Catalíticos de Interés Ambiental y Energético


In situ APPES technique demonstrates that the strong metal support interaction effect (SMSI) in the Ni-ceria system is associated with the decoration and burial of metallic particles by the partially reduced support, a phenomenon reversible by evacuation at high temperature of the previously absorbed hydrogen.

Febrero, 2010 | DOI: 10.1039/b920803h

Oxidation State and Local Structure of Ti-Based Additives in the Reactive Hydride Composite 2LiBH(4) + MgH2

Deprez, E; Muñoz-Marquez, MA; Roldan, MA; Prestipino, C; Palomares, FJ; Minella, CB; Bosenberg, U; Dornheim, M; Bormann, R; Fernandez, A
Journal of Physical Chemistry C, 114 (2010) 3309-3317
Materiales Nanoestructurados y Microestructura


Nowadays, the technological utilization of reactive hydride composites (RHC) Lis hydrogen storage materials is limited by their reaction kinetics. However, addition of transition-metal-based additives, for instance titanium isopropoxide (Ti-iso), to the 2LiBH(4)+MgH2 system, results in a significant improvement of sorption kinetics. In this work, the evolution of chemical state and local structure of the Ti-based additive has been investigated by means of X-ray absorption (XAS) and photoemission (XPS) spectroscopy. X-ray absorption near-edge Structure (XANES) its well as extended X-ray absorption fine structure (EXAFS) analysis have been Undertaken at the Ti K-edge. The measurements reveal the formation of a highly dispersed and disordered TiO2-like phase during ball milling. During first desorption reduced titanium oxide and titanium boride are formed and remain stable upon cycling. The Surface analysis performed by XPS shows that the reduction processes of the Ti-based additive during first desorption IS Coupled to the migration of the Ti species front the surface to the bulk of the material. Several factors, related to favoring heterogeneous nucleation of MgB2 and the increase of interfacial area through grain refinement are proposed as potential driving force, among other effects, for the observed kinetic improvement.

Febrero, 2010 | DOI: 10.1021/jp910955r

Lanthanide sorption on smectitic clays in presence of cement leachates

Galunin, E; Alba, MD; Santos, MJ; Abrao, T; Vidal, M
Geochimica et Cosmochimica Acta, 74 (2010) 862-875
Materiales de Diseño para la Energía y Medioambiente


Due to their potential retention capacity, clay minerals have been proposed for use in the engineered barriers for the storage of high-level radioactive actinides in deep geological waste repositories. However, there is still a lack of data on the sorption of actinides in clays in conditions simulating those of the repositories. The present article examines the sorption of two lanthanides (actinide analogues) in a set of smectitic clays (FEBEX bentonite, MX80 bentonite, hectorite, saponite, Otay montmorillonite, and Texas montmorillonite). Distribution coefficients (K-d) were determined in two media: water and 0.02 mol L-1 Ca, the latter representing the cement leachates that may modify the chemical composition of the water in contact with the clay. The K-d values of the lanthanides used in the experiments (La and Lu) varied greatly (25-50 000 L kg(-1)) depending on the ionic medium (higher values in water than in the Ca medium), the initial lanthanide concentration (up to three orders of magnitude decrease inversely with lanthanide concentration), and the examined clay (up to one order of magnitude for the same lanthanide and sorption medium). Freundlich and Langmuir isotherms were used to fit sorption data to allow comparison of the sorption parameters among smectites. The model based on the two-site Langmuir isotherms provided the best fit of the sorption data, confirming the existence of sorption sites with different binding energies. The sites with higher sorption affinity were about 6% of the total sorption capacity in the water medium, and up to 17% in the Ca medium, although in this latter site sorption selectivity was lower. The wide range of K-d values obtained regarding the factors examined indicated that the retention properties of the clays should also be considered when selecting a suitable clay for engineered barriers.

Febrero, 2010 | DOI: 10.1016/j.gca.2009.11.003

Air- and Light-Stable Superhydrophobic Colored Surfaces Based on Supported Organic Nanowires

Borras, A; Groning, P; Sanchez-Valencia, JR; Barranco, A; Espinos, JP; Gonzalez-Elipe, AR
Langmuir, 26 (2010) 1487-1492
Nanotecnología en Superficies y Plasma


In this work, we report oil it new type of superhydrophobic material consisting of supported organic nanowires prepared by vacuum deposition, Different intensely colored surfaces with water contact angles its high its 180 degrees call be Fabricated depending oil the composition. morphology, and density of the nanowires. These surfaces are stable in air and under intense light irradiation. The wettability properties of coatings made of metalloporphyrins and metallophthalocyanines nanowires as well as other heterostructured binary and open core@shell nanowires are studied.

Febrero, 2010 | DOI: 10.1021/la903701j

Complete n-hexane oxidation over supported Mn-Co catalysts

Todorova, S; Kolev, H; Holgado, JP; Kadinov, G; Bonev, C; Pereniguez, R; Caballero, A
Applied Catalysis B-Environmental, 94 (2010) 46-54
Materiales y Procesos Catalíticos de Interés Ambiental y Energético


Two series of Co-Mn samples were prepared by impregnation of silica with aqueous solutions or Co(NO3)(2)center dot 6H(2)O and/or Mn(NO3)(2)center dot 6H(2)O. Cobalt oxide was the predominant phase in one of the series and manganese was used as the promoter. The major component in the second series was manganese oxide and Co was the promoter. The prepared samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) and tested in the reaction of complete n-hexane oxidation. The catalytic activity of both single component cobalt and manganese samples was similar, however, a combination between the two elements changed significantly the activity and this depended on the method of preparation. Catalysts prepared by a common solution of Co- and Mn nitrates manifested a considerable increase in activity as a result of very low crystallinity of the supported metal oxide phases, partial enrichment of the surface with cobalt and uniform distribution of oxide agglomerates on the support.

Febrero, 2010 | DOI: 10.1016/j.apcatb.2009.10.019

Doping level effect on sunlight-driven W,N-co-doped TiO2-anatase photo-catalysts for aromatic hydrocarbon partial oxidation

Kubacka, A; Bachiller-Baeza, B; Colon, G; Fernandez-Garcia, M
Applied Catalysis B-Environmental, 93 (2010) 274-281
Fotocatálisis Heterogénea: Aplicaciones


A series of nanosized W,N-co-doped anatase TiO2 catalysts with different dopant contents has been prepared by a microemulsion method and examined in the sunlight selective photo-oxidation of toluene and styrene. The activity results have been correlated with structural, electronic, and surface examinations of the catalysts done with the help of XRD-Rietveld, N-2 physisorption and NH3 chemisorption-calorimetry, XPS, Infrared, and UV-visible spectroscopies. Irrespective of the reaction, a consistent reaction rate enhancement with respect to titania (nano-TiO2, P25) references and W-doped TiO2 systems is observed for single-phase anatase W,N-co-doped samples. This is likely linked with the decrease of the band gap energy decrease and results from a combined W-N cooperative effect on structural properties of the anatase network. W,N simultaneous presence also makes a drastic effect on selectivity, maximizing the yield to partial oxidation products. This appears related with surface properties of the materials.

Enero, 2010 | DOI: 10.1016/j.apcatb.2009.09.039

Synthesis, characterization, and photoactivity of InTaO4 and In0.9Ni0.1TaO4 thin films prepared by electron evaporation

Rico, VJ; Frutos, F; Yubero, F; Espinos, JP; Gonzales-Elipe, AR
Journal of Vacuum Science & Technology A, 28 (2010) 127-134
Nanotecnología en Superficies y Plasma


InTaO4 and In0.9Ni0.1TaO4 thin films have been prepared by electron evaporation of successive layers of the single oxide components and posterior annealing at T > 800 degrees C. The annealed thin films presented the monoclinic crystallographic structure typical of these mixed oxides. The electrical and optical behaviors of the films, assessed by C-V measurements, surface conductivity as a function of temperature, and UV-vis absorption spectroscopy, indicate that these oxides are wide band gap semiconductors with a variable dielectric constant depending on the annealing conditions. By reflection electron energy loss spectroscopy some electronic states have been found in the gap at an energy that is compatible with the activation energy deduced from the conductivity versus 1/T plots for these oxides. The photoactivity of these materials has been assessed by looking to the evolution of the wetting contact angle as a function of the irradiation time. All the films became superhydrophilic when irradiated with UV light, while the In0.9Ni0.1TaO4 thin films also presented a small partial decrease in wetting angle when irradiated with visible photons.

Enero, 2010 | DOI: 10.1116/1.3273597

Microscopic and spectroscopic techniques for the study of paper supports and textile used in the binding of hispano-arabic manuscripts from Al-Andalus: A transition model in the 15th century

Espejo, T; Duran, A; Lopez-Montes, A; Blanc, R
Journal of Cultural Heritage, 11 (2010) 50-58


This work focuses on the study of paper and textiles used in the binding of a series of manuscripts that share some specific characteristics that lead us to speculate on the possibility of a transitional codicological typology from the Arabic to the Christian book in Al-Andalus during the 15th century. The books we analyzed belong to the collection of the Historical Archive of Malaga, the Archive of Sacromonte Abbey, in Granada, the School of Arabic Studies and the Library of P.P. Escolapios, also in Granada. Paper physical study was performed by microscopic and spectroscopic techniques. A routine and objective method, Fourier Transform Infrared (FTIR) spectroscopy, was employed and proved to be a useful technique for the characterization of cellulosic fibres, main component of paper from the boards and the envelope flap pasteboards, and the fabric lining from the cover. The results of our research will help us to date, identify and study the evolution of the techniques, proving that the materials and innovations of the Italian paper manufacturing processes were perfectly known in the south of modern day Spain, before the Christian Reconquest.

Enero, 2010 | DOI: 10.1016/j.culher.2009.01.007