Dynamic Analysis of Unidirectional Pressure Infiltration of Porous Preforms by Pure Metals

Unidirectional pressure infiltration of porous preforms by molten metals is investigated numerically. A phenomenological model to describe fluid flow and transport phenomena during infiltration of fibrous preforms by a metal is formulated. The model describes the dynamics of the infiltration process, the temperature distribution, and solid fraction distribution. The numerical results are compared against classical asymptotic analyses and experimental results. This comparison shows that end effects may become important and render asymptotic results unreliable for realistic samples. Fiber volume fraction and initial temperature appear as the factors most strongly influencing infiltration. Metal superheating affects not only the length of the two-phase zone but also the solid fraction distribution in the two-phase zone. The effect of constant applied pressure, although significant on the infiltration velocity, is almost negligible on the two-phase zone length and on solid fraction distribution. When the initial preform temperature is below the metal melting point, and constant pressure is applied under adiabatic conditions, the flow ceases when sufficient solidification occurs to obstruct it. A comparison with literature experiments proves the model to be an efficient predictive tool in the analysis of infiltration processes for different preform/melt systems

Boson gas in a periodic array of tubes

We report the thermodynamic properties of an ideal boson gas confined in an infinite periodic array of channels modeled by two, mutually perpendicular, Kronig-Penney delta-potentials. The particle's motion is hindered in the x-y directions, allowing tunneling of particles through the walls, while no confinement along the z direction is considered. It is shown that there exists a finite Bose- Einstein condensation (BEC) critical temperature Tc that decreases monotonically from the 3D ideal boson gas (IBG) value $T_{0}$ as the strength of confinement $P_{0}$ is increased while keeping the channel's cross section, $a_{x}a_{y}$ constant. In contrast, Tc is a non-monotonic function of the cross-section area for fixed $P_{0}$. In addition to the BEC cusp, the specific heat exhibits a set of maxima and minima. The minimum located at the highest temperature is a clear signal of the confinement effect which occurs when the boson wavelength is twice the cross-section side size. This confinement is amplified when the wall strength is increased until a dimensional crossover from 3D to 1D is produced. Some of these features in the specific heat obtained from this simple model can be related, qualitatively, to at least two different experimental situations: $^4$He adsorbed within the interstitial channels of a bundle of carbon nanotubes and superconductor-multistrand-wires Nb$_{3}$Sn.Comment: 9 pages, 10 figures, submitte

Actualización de la batería estándar y batería ampliada de pruebas alérgicas de contacto por el Grupo Español de Investigación en Dermatitis de Contacto y Alergia Cutánea (GEIDAC)

After the meeting held by the Spanish Contact Dermatitis and Skin Allergy Research Group (GEIDAC) back in October 2021, changes were suggested to the Spanish Standard Series patch testing. Hydroxyethyl methacrylate (2% pet.), textile dye mixt (6.6% pet.), linalool hydroperoxide (1% pet.), and limonene hydroperoxide (0.3% pet.) were, then, added to the series that agreed upon in 2016. Ethyldiamine and phenoxyethanol were excluded. Methyldibromoglutaronitrile, the mixture of sesquiterpene lactones, and hydroxyisohexyl 3-cyclohexene (Lyral) were also added to the extended Spanish series of 2022. (c) 2024 AEDV. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

NEOTROPICAL XENARTHRANS: a data set of occurrence of xenarthran species in the Neotropics

Xenarthrans – anteaters, sloths, and armadillos – have essential functions for ecosystem maintenance, such as insect control and nutrient cycling, playing key roles as ecosystem engineers. Because of habitat loss and fragmentation, hunting pressure, and conflicts with 24 domestic dogs, these species have been threatened locally, regionally, or even across their full distribution ranges. The Neotropics harbor 21 species of armadillos, ten anteaters, and six sloths. Our dataset includes the families Chlamyphoridae (13), Dasypodidae (7), Myrmecophagidae (3), Bradypodidae (4), and Megalonychidae (2). We have no occurrence data on Dasypus pilosus (Dasypodidae). Regarding Cyclopedidae, until recently, only one species was recognized, but new genetic studies have revealed that the group is represented by seven species. In this data-paper, we compiled a total of 42,528 records of 31 species, represented by occurrence and quantitative data, totaling 24,847 unique georeferenced records. The geographic range is from the south of the USA, Mexico, and Caribbean countries at the northern portion of the Neotropics, to its austral distribution in Argentina, Paraguay, Chile, and Uruguay. Regarding anteaters, Myrmecophaga tridactyla has the most records (n=5,941), and Cyclopes sp. has the fewest (n=240). The armadillo species with the most data is Dasypus novemcinctus (n=11,588), and the least recorded for Calyptophractus retusus (n=33). With regards to sloth species, Bradypus variegatus has the most records (n=962), and Bradypus pygmaeus has the fewest (n=12). Our main objective with Neotropical Xenarthrans is to make occurrence and quantitative data available to facilitate more ecological research, particularly if we integrate the xenarthran data with other datasets of Neotropical Series which will become available very soon (i.e. Neotropical Carnivores, Neotropical Invasive Mammals, and Neotropical Hunters and Dogs). Therefore, studies on trophic cascades, hunting pressure, habitat loss, fragmentation effects, species invasion, and climate change effects will be possible with the Neotropical Xenarthrans dataset

Characterisation of the metal phase in NM/Ce0.68Zr0.32O2 (NM: Pt and Pd) catalysts by hydrogen chemisorption and HRTEM microscopy: a comparative study

Pt and Pd particles supported on a texturally stable Ce0.68Zr0.32O2 mixed oxide were investigated by means of H-2 chemisorption and high-resolution transmission electron microscopy (HRTEM). The comparison of the metal dispersion data as determined by HRTEM with those estimated from H-2 volumetric adsorption reveals that, in the case of Pt catalysts reduced at temperatures below 350 degreesC, the chemisorption isotherms recorded at -80 degreesC provide reliable dispersion data. For catalysts reduced at, or above, 350 degreesC, some platinum deactivation occurred. However, H-2 chemisorption capability was recovered by reoxidation at 427 degreesC and further reduction at 150 degreesC. For catalysts reduced at 700 degreesC or 900 degreesC, the recovery of the platinum chemisorptive capability was only partial, even if a more severe reoxidation treatment (700 degreesC) was applied. To prevent hydride formation, H-2 chemisorption on the Pd/Ce0.68Zr0.32O2 was investigated at low H-2 pressures and at room temperature. Under these experimental conditions, which are often employed for characterizing Pd catalysts, hydrogen spillover cannot be blocked, thus preventing a reliable estimate of the metal dispersion in our ceria-zirconia -supported palladium catalysts

Integration of Adsorption and Photocatalytic Degradation of Methylene Blue Using TiO 2 Supported on Granular Activated Carbon

International audienceAn integrated process was investigated for the degradation of methylene blue (MB); it was based on the combination of adsorption and photocatalysis. A granular activated carbon (C) was considered for adsorption, which involved TiO 2 as a photocatalyst (TiO 2/ C ). The TiO 2/ C was directly obtained by an impregnation method using TiCl 3; it was also calcined under air atmosphere at 500∘C (TiO 2/ C -500). These materials were characterized by TGA, BET, SEM, EDS mapping, SEM-EDS, and their pH PZC were measured. The results obtained showed that activated carbon (C) exhibited the best performances in terms of adsorption. The photocatalytic activity on the degradation of MB in aqueous solution under UV irradiation was tested and compared to that of TiO 2 anatase (TiO2A) and a mixture of carbon with TiO 2 (C―TiO 2). TiO 2/ C -500 catalyst was found to be more active than the other catalysts; the C with high surface area provided sites for adsorption, allowing the migration of the dye to the surface of TiO 2. A synergistic effect between C and TiO 2 was shown, which enhanced the photocatalytic activity by retarding the recombination of photogenerated electron–hole pairs, improving light absorption. © 2016, King Fahd University of Petroleum & Minerals

A comparative study of Bi2WO6, CeO2, and TiO2 as catalysts for selective photo-oxidation of alcohols to carbonyl compounds

Several semiconductors based on ceria or bismuth tungstate were tested for selective oxidation of alcohols to carbonyl compounds in a search for photocatalysts more selective than TiO2. Gas-phase selective photo-oxidation of propan-2-ol to acetone and liquid-phase transformation of 2-buten-1-ol (crotyl alcohol) to 2-butenal (crotonaldehyde) were studied as test reactions. In both processes the highest selectivities were achieved with Bi2WO6-based solids. Further studies on crotyl alcohol transformation evidenced the lower adsorption of the aldehyde on these systems which could minimize the decrease in crotyl alcohol yield observed for TiO2 or CeO2 at high conversions. Incorporation of titania (5% molar) to the Bi2WO6 system increased the reaction rate significantly whereas the aldehyde yield remained highPeer Reviewe

Thermal Stabilization of CexZr1-xO2 oxygen storage promoters by addition of Al2O3: Effect of thermal ageing on textural, structural and morphological properties

Thermal stability and dispersion of CeO2 supported on Al2O3 is greatly improved by insertion of ZrO2 into the CeO2 lattice. It is shown that homogeneous nano-sized CexZr1xO2 solid solutions can be prepared on the Al2O3 surface by using a citrate complexation synthesis method. Investigation of effects of CexZr1xO2 composition and loading of the Ce0.2Zr0.8O2 phase on thermal stability and nanostructure of the prepared materials revealed that strong interactions between supported phase and Al2O3 are induced by the high temperature treatment. High contents of ZrO2, choice of the CexZr1xO2 precursors and loading of the mixed oxide are critical factors leading to nanocomposite systems with high thermal and structural stability, consisting of particles of Ce0.2Zr0.8O2 as small as 9-20 nm in close contact with a q-Al2O3 matrix even after calcination at 1373 K. The enhanced stability of the present materials was confirmed also under hydrothermal conditions

Stabilisation of nanostructured Ce0.2Zr0.8O2 solid solution by impregnation on Al2O3: a suitable way for production of thermally stable oxygen storage/release promoters for three-way catalysts

By impregnating gamma -Al2O3 with cerium/zirconium citrate solutions and subsequent calcination, nanostructured CemZr1-mO2 mixed oxides supported on Al2O3 are obtained, which feature remarkably high oxygen storage even after calcination at 1100 degreesC for 24 h