Crystallization study of SrSnO3:Fe

Alkaline earth stannates have recently become important materials in ceramic technology due to its application as humidity sensor. In this work, alkaline earth stannates doped with Fe³⁺ were synthesized by the polymeric precursor method, with calcination at 300 °C/7 h and between 400 and 1100 °C/4 h. The powder precursors were characterized by TG/DTA after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, infrared spectroscopy, and UV?Cvis spectroscopy. Results confirmed the formation of the SrSnO₃:Fe with orthorhombic perovskite structure, besides SrCO₃ as secondary phase. Crystallization occurred at 600 °C, being much lower than the crystallization temperature of perovskites synthesized by solid state reaction. The analysis of TG curves indicated that the phase crystallization was preceded by two thermal decomposition steps. Carbonate elimination occurred at two different temperatures, around 800 °C and above 1000 °C.     

Well-posedness for a class of fourth order diffusions for image processing

A number of image denoising models based on higher order parabolic partial differential equations (PDEs) have been proposed in an effort to overcome some of the problems attendant to second order methods such as the famous Perona–Malik model. However, there is little analysis of these equations to be found in the literature. In this paper, methods of maximal regularity are used to prove the existence of unique local solutions to a class of fourth order PDEs for noise removal. The proof is laid out explicitly for two newly proposed fourth order models, and an outline is given for how to apply the techniques to other proposed models.     

Phase retrieval in quantitative x-ray microtomography with a single sample-to-detector distance

Phase retrieval extracts quantitative phase information from x-ray propagation-based phase-contrast images. Notwithstanding inherent approximations, phase retrieval using a single sample-to-detector distance (SDD) is very attractive, because it imposes no setup complications or additional radiation dose compared to absorption-based imaging. Considering the phase-attenuation duality (ε=δ/β, where ε is constant), a simple absorption correction factor is proposed for the modified Bronnikov algorithm in x-ray propagation-based phase-contrast computed tomography (PPCT). Moreover, a practical method for calculating the optimal ε value is proposed, which requires no prior knowledge of the sample. Tests performed on simulation and experimental data successfully distinguished different materials in a quasihomogeneous and weakly absorbing sample from a single SDD-PPCT data point.     

A density-functional study of the possibility of noncollinear magnetism in small Mn clusters using SIESTA and the generalized gradient approximation to exchange and correlation

We investigated the possibility of noncollinear magnetism in small Mn(n) clusters (n=2-6) using the density-functional method SIESTA with the generalized gradient approximation (GGA) to exchange and correlation. The lowest-energy states identified were collinear, with the atomic spin magnetic moments pointing in the same direction, for Mn(2) and Mn(3), and noncollinear for Mn(4), Mn(5) and, most decidedly, Mn(6). These SIESTA/GGA results, which are compared with those of an earlier SIESTA study that used the local spin density approximation, are qualitatively in keeping with the result obtained by VASP/GGA calculations.     

Interfacial and stability study of microbubbles coated with a monostearin/monopalmitin-rich food emulsifier and PEG40 stearate

The stability and presence of micron-scale bubbles (microbubbles) is of considerable interest in environmental, biomedical, and food sciences. Here we show that microbubbles can be formed and stabilized in a solution of low cost food-grade emulsifier (a mixture of saturated long-chain monoglycerides, diglycerides and sodium stearoyl-2-lactylate) in combination with polyethylene glycol (PEG)-40 stearate. Langmuir trough methods and fluorescence microscopy were combined to investigate the surface tension, interfacial elastic modulus, phase behavior and microstructure of monolayer shells coating these microbubbles. Our results strongly suggest that although the PEG40S is necessary to form microbubbles this component, as well as sodium stearoyl-2-lactylate, are "squeezed out" in the form of collapse aggregates. This process leaves a microbubble shell, composed of a condensed-phase low surface tension mono- and diglycerides mixture with some of the PEG40S and SSL2 remaining trapped between the condensed-phase domains. We find that other commercially available emulsifiers, containing unsaturated or bulky components unable to form condensed phases, do not to form or stabilize a microbubble layer, although they may form a foam, a finding that we relate to differences in surface tension.     

Heavy metal separation with polymer inclusion membranes

Using functionalized calix[4]arene carrier 1 in a PIM system, Hg(II) is transported with high selectivity from acidic aqueous source phase solutions of Cd(II), Hg(II) and Pb(II) with high NaNO₃ concentration into aqueous receiving solutions containing EDTA. To gain insight into this transport selectivity, complexation studies of the three heavy metal perchlorate species by ligand 1 were conducted in acetonitrile. Although 1:1 complexation of the divalent heavy metal cation by 1 was observed for Cd(II), the stoichiometries were more complicated for Hg(II) and Pb(II). Selective Hg(II) transport across the PIM is attributed to both the strength and stoichiometry of the metal ion-carrier species forming at the source phase-membrane interphase and its stripping from the membrane into the receiving phase by EDTA.     

Drying and rehydration of DLPC/DSPC symmetric and asymmetric supported lipid bilayers: a combined AFM and fluorescence microscopy study

This work characterizes the impact of lipid symmetry/asymmetry on drying/rehydration reorganization in phase-separated dilauroylphosphatidylcholine (DLPC)/distearoylphosphatidylcholine (DSPC) supported lipid bilayers (SLBs) at the submicron and micron-scale. In addition the prevention of major drying/rehydration reorganization by the use of trehalose is demonstrated. Even though it was found using fluorescence microscopy that micrometer scale structure is preserved in the presence and absence of trehalose upon drying/rehydration, AFM and FRAP experiments successfully revealed major changes in the phase-separated structure such as defects, obstructions, lipid condensation, collapse structures, and complex incomplete DLPC-DSPC mixing/exchange in the absence of trehalose. In the presence of trehalose the membrane preserves its structure at the nanometer scale and mobility. We found that SLBs with asymmetric domain configurations underwent major rearrangements during drying and rehydration, whereas the symmetric domain configuration mainly rearranged during rehydration, that we hypothesize is related to lower transmembrane cohesiveness or lack of anchoring to the substrate in the case of the asymmetric domains.     

NiTiO<Subscript>3</Subscript> nanoparticles encapsulated with SiO<Subscript>2</Subscript> prepared by sol–gel method

NiTiO₃ (NTO) nanoparticles encapsulated with SiO₂ were prepared by the sol–gel method resulting on core-shell structure. Changes on isoelectric point as a function of silica were evaluated by means of zeta potential. The NTO nanoparticles heat treated at 600°C were characterized by X-ray diffraction, transmission electron microscopy (TEM) and energy dispersive X-ray analysis. TEM observations showed that the mean size of NTO is in the range of 2.5–42.5 nm while the thickness of SiO₂ shell attained 1.5–3.5 nm approximately.     

Density functional theory study on the structural and electronic properties of low index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems

The present study is concerned with the structural and electronic properties of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems. Periodic quantum mechanical method with density functional theory at the B3LYP level has been carried out. Relaxed surface energies, structural characteristics and electronic properties of the (110), (010), (101) and (00) low-index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 models are studied. For comparison purposes, the bare rutile TiO2 and SnO2 structures are also analyzed and compared with previous theoretical and experimental data. The calculated surface energy for both rutile TiO2 and SnO2 surfaces follows the sequence (110) < (010) < (101) < (001) and the energy increases as (010) < (101) < (110) < (001) and (010) approximately = (110) < (101) < (001) for SnO2/TiO2/SnO2 and TiO2/SnO2/TiO2 composite systems, respectively. SnO2/TiO2/SnO2 presents larger values of surface energy than the individual SnO2 and TiO2 metal oxides and the TiO2/SnO2/TiO2 system renders surface energy values of the same order that the TiO2 and lower than the SnO2. An analysis of the electronic structure of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 systems shows that the main characteristics of the upper part of the valence bands for all the studied surfaces are dominated by the external layers, i.e., by the TiO2 and the SnO2, respectively, and the topology of the lower part of the conduction bands looks like the core layers. There is an energy stabilization of both valence band top and conduction band bottom for (110) and (010) surfaces of the SnO2/TiO2/SnO2 composite system in relation to their core TiO2, whereas an opposite trend is found for the same surfaces of the TiO2/SnO2/TiO2 composite system in relation to the bare SnO2. The present theoretical results may explain the growth of TiO2@SnO2 bimorph composite nanotape.