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2009


Synthesis of MCM-22 zeolites of different Si/Al ratio and their structural, morphological and textural characterisation


Delitala, C; Alba, MD; Becerro, AI; Delpiano, D; Meloni, D; Musu, E; Ferino, I
Microporous and Mesoporous Materials, 118 (2009) 1-10
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

MCM-22 zeolites with Si/Al in the 9–46 range were synthesised in rotating autoclave and characterised by X-ray diffraction, 1H, 29Si and 27Al magic angle spinning nuclear magnetic resonance, scanning electron microscopy and nitrogen physisorption. For the Si/Al = 21, 30 and 46 samples both X-ray diffraction and scanning electron microscopy revealed the crystallisation of pure MCM-22. Besides the latter, crystals of ferrierite also formed during the synthesis of the Si/Al = 9 sample. Based on the 1H MAS NMR spectra of dehydrated samples, the different proton species present on the MCM-22 samples were determined and quantified. Information about the incorporation of Al ions into the zeolite framework, as well as on the preferential crystallographic sites occupied in dependence on the Si/Al ratio of the sample, was obtained by 27Al MAS NMR spectroscopy. From 29Si MAS NMR spectra, differences in the degree of crystallinity of the samples were assessed, the results being in agreement with the diffraction data. Nitrogen physisorption runs revealed the microporous nature of the adsorbents, with a supermicropore to ultramicropore volume ratio in good agreement, for the best crystallised samples, with the porous structure with supercages and sinusoidal channels of the ideal MCM-22 crystal.


Febrero, 2009 | DOI: 10.1016/j.micromeso.2008.07.047

Liquid-phase thiophene adsorption on MCM-22 zeolites. Acidity, adsorption behaviour and nature of the adsorbed products


Delitala, C; Cadoni, E; Delpiano, D; Meloni, D; Alba, MD; Becerro, AI; Ferino, I
Microporous and Mesoporous Materials, 118 (2009) 11-20
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

The liquid-phase adsorption of thiophene from thiophene/iso-octane solutions has been investigated in batch conditions at room temperature and atmospheric pressure on MCM-22 zeolites with Si/Al in the 9–46 range. Thiophene adsorption was found to occur in two steps whatever the Si/Al ratio of the adsorbent. The presence of ferrierite besides the MCM-22 phase caused a significant loss of the adsorption performance. For pure MCM-22 samples, the Si/Al ratio influenced the adsorption performance. Based on the acid properties of the samples, investigated by adsorption microcalorimetry of ammonia, the adsorption features were interpreted by assuming that positively charged species were originated during the first step; these species underwent successive reaction with weakly adsorbed species formed in the second step, leading to heavy molecular weight organosulphur compounds. Direct evidence for the occurrence of reactive adsorption of thiophene involving its transformation into heavy molecular weight organosulphur compounds was obtained by GC/MS investigation of the nature of the adsorbed material recovered after the adsorption experiments. The peculiar structure of MCM-22 zeolites made possible the formation of long-sized organosulphur compounds. Due to the mechanism by which thiophene is transformed (i.e. progressive addition of other thiophene molecules), the size of the resulting products was found to depend also on the concentration of the weakly adsorbed thiophene molecules able to interact with those already activated through protonation.


Febrero, 2009 | DOI: 10.1016/j.micromeso.2008.08.008

Control over the Structural and Optical Features of Nanoparticle-Based One-Dimensional Photonic Crystals


Calvo, ME; Sanchez-Sobrado, O; Colodrero, S; Miguez, H
Langmuir, 25 (2012) 2443-2448
Materiales Ópticos Multifuncionales

ABSTRACT ▼

Herein we present a detailed analysis of the effect of the spin-coating protocol over the optical properties of nanoparticle-based one-dimensional photonic crystals. Based on these results, we provide a reliable synthetic route to attain high-quality porous multilayers in which the effect of imperfections is minimized and whose Bragg diffraction can be precisely tuned over the entire visible and near-infrared spectrum. We present a systematic study of the effect of the acceleration ramp and final rotation speed over the structural and optical quality of these materials. This allows us to relate the structural variations observed with the different relative importance of fluid flow and solvent evaporation on the thinning of each layer in the stack for the different deposition conditions employed.


Febrero, 2009 | DOI: 10.1021/la8030057

Porosity and microstructure of plasma deposited TiO2 thin films


Borras, A; Sanchez-Valencia, JR; Garrido-Molinero, J; Barranco, A; Gonzalez-Elipe, AR
Microporous and Mesoporous Materials, 118 (2009) 314-324
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

The microstructure of TiO2 thin films prepared by plasma enhanced chemical vapour deposition has been assessed by using water adsorption–desorption isotherms measured by means of a quartz crystal monitor (QCM). Thin films have been deposited by using titanium tetraisopropoxide as a precursor and by changing different experimental parameters of the deposition procedure such as temperature of the substrate, pressure, and gas composition in the plasma. The films were characteristic of different microstructures that, according to their scanning electron micrographs, have been categorized as columnar, homogeneous and crystalline. They also have different refraction indices with values between 1.95 and 2.41. Water and toluene adsorption isotherms have been measured by means of a QCM monitor for the films heated in vacuum to remove the water previously adsorbed in their pores. The analysis of the adsorption-desorption isotherms by means of the so called “t-plots” and the determination of the pore size distribution curves rendered that the three kinds of microstructures presented different kinds of isotherms and water adsorption behaviours. Columnar films consisted of micro- and meso-pores had a very high adsorption hystheresis at low pressures. Homogeneous films only had micropores and presented no adsorption hystheresis. Crystalline films consisted of both micro- and meso-pores but had no adsorption hystheresis at low pressures. A zone scheme has been proposed to account for the microstructure of the films depending on the plasma conditions utilized. The implications of the different water adsorption behaviours of the films for the determination of their refraction indices are discussed.


Febrero, 2009 | DOI: 10.1016/j.micromeso.2008.09.002

Experimental Demonstration of the Mechanism of Light Harvesting Enhancement in Photonic-Crystal-Based Dye-Sensitized Solar Cells


Colodrero, S; Mihi, A; Anta, JA; Ocaña, M; Miguez, H
Journal of Physical Chemistry C, 113 (2012) 1150-1154
Materiales Coloidales - Materiales Ópticos Multifuncionales

ABSTRACT ▼

Herein, we report an experimental analysis of the photogenerated current of very thin and uniform dye-sensitized nanocrytalline titanium oxide (nc-TiO2) electrodes coupled to high-quality one-dimensional photonic crystals. The effect of well-defined optical absorption resonances are detected both in optical spectroscopy and photogenerated current experiments, a clear correspondence between them being established. Our study demonstrates that light trapping within absorbing electrodes is responsible for the absorption enhancement that has previously been reported and unveils the mechanism behind it. We prove that this effect improves significantly the power conversion efficiency of very thin electrodes.


Enero, 2009 | DOI: 10.1021/jp809789s

Influence of the microstructure on the mechanical and tribological behavior of TiC/a-C nanocomposite coatings


Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Thin Solid Films, 517 (2009) 1662-1671
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

The performance of protective thin films is clearly influenced by their microstructure. The objective of this work is to study the influence of the structure of TiC/a-C nanocomposite coatings with a-C contents ranging from ~ 0% to 100% on their mechanical and tribological properties measured by ultramicroindentation and pin-on-disks tests at ambient air, respectively. The microstructure evolves from a polycrystalline columnar structure consisting of TiC crystals to an amorphous and dense TiC/a-C nanocomposite structure when the amount of a-C is increased. The former samples show high hardness, moderate friction and high wear rates, while the latter ones show a decrease in hardness but an improvement in tribological performance. No apparent direct correlation is found between hardness and wear rate, which is controlled by the friction coefficient. These results are compared to the literature and explained according to the different film microstructures and chemical bonding nature. The film stress has also been measured at the macro and micro levels by the curvature and Williamson–Hall methods respectively. Other mechanical properties of the coating such as resilience and toughness were evaluated by estimating the H3/E⁎2 and H/E⁎ ratios and the percentage of elastic work (We). None of these parameters showed a tendency that could explain the observed tribological results, indicating that for self-lubricant nanocomposite systems this correlation is not so simple and that the assembly of different factors must be taken into account.


Enero, 2009 | DOI: 10.1016/j.tsf.2008.09.091

Application of Geographic Information Systems (GIS) in the search for and characterization of raw materials of interest in ceramics and glass


Garzon, E; Garcia, IG; Ruiz-Conde, A; Sanchez-Soto, PJ
Boletín de la Sociedad Española de Cerámica y Vidrio, 48 (2009) 39-44
Materiales Avanzados

ABSTRACT ▼

Optically Active Luminescent Perylene Thin Films Deposited by Plasma Polymerization


Blaszczyk-Lezak, I; Aparicio, FJ; Borras, A; Barranco, A; Alvarez-Herrero, A; Fernandez-Rodriguez, M; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 113 (2009) 12840-12847
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

This work reports about the preparation of plasma polymerized thin films of perylene with thicknesses 30−150 nm and their characterization by different methods and the analysis of their optical properties. Highly absorbent and fluorescent films have been obtained by this method that combines the sublimation of the perylene molecules and their controlled polymerization by the interaction with remote Ar plasma. The polymeric films are very flat with a root mean square (rms) roughness in the range 0.3−0.4 nm. In contrast with the sublimated layers of perylene that present a high scattering of light, the polymerized films depict the well-defined absorption bands in the region 400−450 nm and fluorescence spectra of the perylene molecule at 475 nm. The films are formed by a matrix formed by cross-linked fragments of perylene and intact molecules that confer the observed optical properties to this material. The optical and microstructural characteristics of this type of thin films and the possibility to perform their deposition by using lithographic procedures make them suitable for their integration into photonic components for various applications. A preliminary study of the use of these films as an optical sensor of NO2 is also presented.


Enero, 2009 | DOI: http://pubs.acs.org/doi/abs/10.1021/jp807634j

Luminescent and Optical Properties of Nanocomposite Thin Films Deposited by Remote Plasma Polymerization of Rhodamine 6G


Aparicio, FJ; Borras, A; Blaszczyk-Lezak, I; Groning, P; Alvarez-Herrero, A; Fernandez-Rodriguez, M; Gonzalez-Elipe, AR; Barranco, A
Plasma Processes and Polymers, 6 (2009) 17-26
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Mechanically stable and insoluble fluorescent thin films have been deposited by sublimating Rhodamine 6G laser dye in the downstream region of a low-power microwave ECR plasma using an experimental set-up designed to control the interaction of the dye molecule with the glow discharge. The use of reactive organosilane plasmas allows to control the dye distribution inside the matrix, leading to solid nanocomposite thin films containing non-aggregated dye molecules. The suppression of aggregates is a key issue to avoid fluorescence quenching. The obtained nanocomposite films are interesting because of their strong absorption and high fluorescence emission. In addition, they can be patterned using in situ plasma treatments in order to produce optically functional devices.


Enero, 2009 | DOI: 10.1002/ppap.200800092

General Quantum-Mechanical Study on the Hydrolysis Equilibria for a Tetravalent Aquaion: The Extreme Case of the Po(IV) in Water


Ayala, R; Martinez, JM; Pappalardo, RR; Paez, AM; Marcos, ES
Journal of Physical Chemistry B, 113 (2009) 487-496

ABSTRACT ▼

A systematic study of the different hydrolyzed species derived from the hydrated Po(IV) in water, [Po(H2O)n(OH)m](4−m) for 1 m 4, and 4 m + n 9, has been carried out by means of quantum mechanical computations. The effects of outer solvation shells have been included using a polarizable continuum dielectric model. For a fixed number of hydroxyl groups, the preferred hydration number for the Po(IV) can be determined in terms of Gibbs energy. It is shown that the hydration number (n) systematically decreases with the increase in the number of hydroxyl groups (m) in such a way the total coordination number (n + m) becomes smaller, being 9 in the aquocomplex and 4 in the neutral hydroxo-complex. Free energies for the hydrolysis processes involving Po(IV) complexes and a different number of hydroxyl groups have been computed, revealing the strong tendency toward hydrolysis exhibited by these complexes. The predominant species of Po(IV) in aqueous solutions are ruled by a dynamical equilibrium involving aggregates containing in the first coordination shell OH− groups and water molecules. Although there is not experimental information to check the theoretical predictions, theoretical computations in solution seem to suggest that the most likely clusters are [Po(H2O)5(OH)2]2+ and [Po(H2O)4(OH)2]2+. The geometry of the different clusters is ruled by the trend of hydroxyl groups to be mutually orthogonal and to promote a strong perturbation of the water molecule in trans-position by lengthening the Po−H2O distances and tilting the corresponding bond angle. A general thermodynamic cycle is defined to compute the Gibbs free energy associated to the formation of the different hydrolyzed forms in solution. From it, the estimates of pKa values associated to the different protolytic equilibria are provided and discussed. Comparison of the relative values of pKa along a hydrolysis series with the experimental values for other tetravalent cations supports its consistency.


Enero, 2009 | DOI: 10.1021/jp804957s

Gold nanoparticles on silica monospheres modified by amino groups


Penkova, A; Blanes, JMM; Cruz, SA; Centeno, MA; Hadjiivanov, K; Odriozola, JA
Microporous and Mesoporous Materials, 117 (2009) 530-534
Química de Superficies y Catálisis

ABSTRACT ▼

Silica monospheres with a diameter of 330 nm modified with aminosilane compounds of three different basicities have been prepared. Surface coverage of the silica with an organic compound leads to an increase of the point of zero charge (PZC) of the silica surface from 2.1 to 5.1, 6.5 and 7.2 values, depending on the amine used. From these silicas, gold-containing catalysts have been prepared by a deposition–precipitation method at the same pH as the PZC of the support. The best results have been obtained using 3-(Diethoxymethylsilyl) propylamine as a modifying agent, which has allowed obtaining a good dispersion of the gold particles with an average size of 3.8 nm.


Enero, 2009 | DOI: 10.1016/j.micromeso.2008.07.041



2008


Fabrication, chemical etching, and compressive strength of porous biomimetic SiC for medical implants


Torres-Raya, C; Hernandez-Maldonado, D; Ramirez-Rico, J; Garcia-Ganan, C; de Arellano-Lopez, AR; Martinez-Fernandez, J
Journal of Materials Research, 23 (2008) 3247-3254
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

BioSiC is a biomimetic SiC-based ceramic material fabricated by Si melt infiltration of carbon preforms obtained from wood. The microstructure of bioSiC mimics that of the wood precursor. which can be chosen for tailored properties. When the remaining g unreacted Si is removed. a SiC Material with interconnected porosity is obtained. This porous bioSiC is Under study for its use as a medical Implant material. We have successfully fabricated bioSiC from Sipo wood and Studied the kinetics of Si removal by wet etching. The results suggest that the reaction is diffusion-limited, and the etch rate follows a t(-0.5) law. The etching rate is found to be anisotropic, which can be explained attending to the anisotropy of the pore distribution. The compressive strength was studied as a function of etching, time. and the results show a quadratic dependence with density. In the attainable ran-e of densities, the strength is similar or better than that of human bone.


Diciembre, 2008 | DOI: 10.1557/JMR.2008.0392

Growth and characterization of the ZnO/ZnS bilayer obtained by chemical spray pyrolysis


Lopez, MC; Espinos, JP; Leinen, D; Martin, F; Centeno, SP; Romero, R; Ramos-Barrado, JR
Applied Surface Science, 255 (2008) 2118-2124
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

ZnO/ZnS bilayer antireflection coatings have been prepared by spray pyrolysis using aqueous solutions of zinc acetate and thiourea or zinc chloride and thiourea. The structure, surface morphology, chemical composition and optical transmittance of the bilayer have been examined as a function of the composition of the initial solution. X-ray photoelectron spectroscopy analysis and Ar ion-beam sputter etching was carried out to obtain a depth profile of bilayer. Neither carbon nor other by-products, which could alter the optical transmittance of the bilayer were found in either the interface or bulk. The differences between the bilayers arise from the annealing of the ZnS underlayer, as well as the precursor used to prepare it.


Diciembre, 2008 | DOI: 10.1016/j.apsusc.2008.06.195

Synthesis of Supported Single-Crystalline Organic Nanowires by Physical Vapor Deposition


Borras, A; Aguirre, M; Groening, O; Lopez-Cartes, C; Groening, P
Chemistry of Materials, 20 (2008) 7371-7373
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Characterization of iron oxide-based pigments by synchrotron-based micro X-ray diffraction


Herrera, LK; Cotte, M; de Haro, MCJ; Duran, A; Justo, A; Perez-Rodriguez, JL
Applied Clay Science, 42 (2008) 57-62

ABSTRACT ▼

The characterization of iron in microsamples by conventional X-ray diffraction is difficult due to its low concentration in thin layers and its low reflecting power relative to other phases. Synchrotron radiation can provide unique information because of high intensity, sample penetration, small beam diameter and fast data collection. In this study, micro X-ray diffraction (mu-XRD) data were obtained of two samples taken from wall paintings at San Agustin's Church in Cordoba. Crystalline iron phases such as goethite, lepidocrocite and hematite in the cross-section of the painting thin layers were identified. with a good spatial resolution. Conventional XRD only detected hydrocerussite and cerussite rather than the full range of iron phases found in the mu-XRD experiments. 


Diciembre, 2008 | DOI: 10.1016/j.clay.2008.01.021

Comparative performance of nanocomposite coatings of TiC or TiN dispersed in a-C matrixes


Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Surface & Coatings Technology, 203 (2008) 756-760
Materiales Nanoestructurados y Microestructura - Tribología y Protección de Superficies

ABSTRACT ▼

Titanium carbide (TiC) and nitride (TiN) are two of the most used materials in the field of protective coatings, due to their optimal mechanical and tribological properties. The addition of the second phase can provide extra benefits to the coating, like improved hardness, reduced friction and/or oxidation resistance. In this work, we present two series of coatings in which hard crystalline TiC and TiN phases are mixed at the nanometric level with a soft lubricant phase like amorphous carbon (a-C). Both series of TiC/a-C and TiN/a-C nanocomposite coatings were prepared by double magnetron sputtering of C and Ti(N) targets in a Ar atmosphere (P = 5 x 10(-3) Torr) by changing the power ratio applied to each magnetron. The chemical composition has been measured by electron energy loss spectroscopy, and the phase composition changes gradually from pure C to pure TiC or TiN through nanocomposite structures with variable phase contents. These structures are confirmed by transmission electron microscopy and diffraction techniques. like X-ray diffraction and electron diffraction. The mechanical and tribological properties are found to be mainly controlled by the hard/soft phase ratio present in the coating. The changes in hardness values follow similar trends in both types of nanocomposite samples. Introducing a small amount of TiN or TiC into a-C matrix causes a hardness reduction, but further addition of crystalline phase makes increase the hardness. The best tribological properties are found for nanocomposite coatings (both TiN/a-C and TiC/a-C) with high amount of a-C (> 65%), showing low friction values (f similar to 0.1) and high wear resistance (k about 10(-7) mm(3) N-1 m(-1)). However, coatings with 50-60% a-C show a good compromise between tribological and mechanical properties.


Diciembre, 2008 | DOI: 10.1016/j.surfcoat.2008.08.064

Photocatalytic Degradation of 2,4-Dichlorophenoxyacetic Acid Over ZrO2, Cu/ZrO2 and Fe/ZrO2 Photocatalysts Synthesized by Sol Gel Method


Alvarez, M; Lopez, T; Odriozola, JA; Gonzalez, RD
Journal of Nanoscience and Nanotechnology, 8 (2008) 6414-6418
Química de Superficies y Catálisis

ABSTRACT ▼

Photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid was performed over ZrO2, Cu/ZrO2 and Fe/ZrO2 catalysts prepared by the sol-gel method. The samples were annealed at 400 degrees C. Textural and electronic characterization was carried out using BET and UV-Vis in order to establish the relationship between surface, pore volume and E. with the photoactivity of the materials. The degradation of the acid was followed by UV-Vis spectroscopy. The disappearance of the herbicide in solution follows approximately pseudo-first order kinetics. The apparent rate constants were calculated for the three catalysts. The results reveal that Fe/ZrO2 exhibits the best photoactivity for the degradation of 2,4-dichlorophenoxyacetic acid.


Diciembre, 2008 | DOI: 10.1166/jnn.2008.003

Influence of the Capping Molecule on the Magnetic Behavior of Thiol-Capped Gold Nanoparticles


Crespo, Patricia; Guerrero, Estefania; Angel Munoz-Marquez, Miguel; Hernando, Antonio; Fernandez, Asuncion
IEEE Transactions on Magnetics, 44 (2008) 2768-2771
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

Gold nanoparticles with an average particle size below 3 nm have been synthesized and stabilized with different thiol-derivatized molecules for studying the influence of the capping molecule on the magnetic behavior. Thiolated-alkane chains with different lengths as well as a thiol-containing biomolecule (tiopronin) have been selected as protecting shells for the synthesized NPs. Magnetic characterization indicates that the appearance of a ferromagnetic-like behavior is related not only with the formation of Au-S bonds linking the protective molecules to the nanoparticle surface but also with the formation of the nanoparticle itself as well as with the geometry of the capping molecule. The later seems to determine whether the protective monolayer shell is ordered or not. The simultaneous presence of Au-Au and Au-S bonds together with a reduced particle diameter, and the formation of an ordered monolayer protective shell, have been proved to be key parameters for the ferromagnetic-like behavior exhibited by thiol-functionalized gold NPs.


Noviembre, 2008 | DOI: 10.1109/TMAG.2008.2001990

Kissinger kinetic analysis of data obtained under different heating schedules


Sanchez-Jimenez, PE; Criado, JM; Perez-Maqueda, LA
Journal of Thermal Analysis and Calorimetry, 94 (2008) 427-432
Reactividad de Sólidos

ABSTRACT ▼

The dynamic heating rate method developed by TA Instruments (Hi-ResTM) is a kind of sample controlled thermal analysis in which a linear relationship between the logarithm of the heating rate and the rate of mass change is imposed. It is shown in this paper that the reacted fraction at the maximum reaction rate strongly depends on the parameters selected for the Hi-Res heating algorithm, what invalidates the use of the Kissinger method for analysing Hi-Res data unless that the reaction fits a first order kinetic law. Only in this latter case, it has been demonstrated that it is not required that a constant value of the reacted fraction at the maximum reaction rate is fulfilled for determining the activation energy from the Kissinger method. In such a case the Kissinger plot gives the real activation energy, independently of both the heating schedule used and the value of the reacted fraction, alpha(m), at the maximum.


Noviembre, 2008 | DOI: 10.1007/s10973-008-9200-2

Catalytic growth of carbon nanotubes on stainless steel: Characterization and frictional properties


Abad, MD; Srichez-Lopez, JC; Berenguer-Murcia, A; Golovko, VB; Cantoro, M; Wheatley, AEH; Fernandez, A; Johnson, BFG; Robertson, J
Diamond and Related Materials, 17 (2008) 1853-1857
Materiales Nanoestructurados y Microestructura - Tribología y Protección de Superficies

ABSTRACT ▼

Carbon nanotubes (CNTs) have been grown both on a sample of stainless steel (317-2R) and on the same steel coated with cobalt colloid nanoparticles. Both materials are suitable supports for the growth of vertically aligned carbon nanotubes, although a more sparse growth of significantly thicker carbon nanotubes is observed in the case of the bare steel. We find that carbon nanotubes grown directly on the stainless steel support show very poor tribological behaviour whereas the support using nanoparticles for carbon nanotube growth displayed interesting tribological properties with friction coefficients of approximately 0.1-0.2. The modified CNT material (studied by Raman spectroscopy) adheres to both mating surfaces avoiding direct contact between asperities and plough so the friction and wear processes decrease greatly.


Noviembre, 2008 | DOI: 10.1016/j.diamond.2008.03.021

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