Extracting the Green's function from measurements of the energy flux

Existing methods for Green's function extraction give the Green's function from the correlation of field fluctuations recorded at those points. In this work it is shown that the Green's function for acoustic waves can be retrieved from measurements of the integrated energy flux through a closed surface taken from three experiments where two time-harmonic sources first operate separately, and then simultaneously. This makes it possible to infer the Green's function in acoustics from measurements of the energy flux through an arbitrary closed surface surrounding both sources. The theory is also applicable to quantum mechanics where the Green's function can be retrieved from measurement of the flux of scattered particles through a closed surface.     

Optical characterization of 316L stainless steel coated with sol–gel titania

In this work 316L stainless steel substrates were coated with sol–gel derived films by means of the dip-coating technique. Titanium isopropoxide and ethanol were used as chemical precursor and solvent, respectively. The dip-coating step was performed using withdrawal speeds of 6 mm/min, 30 mm/min, and 60 mm/min. Next, the samples were heat treated in air for 30 min at 100 °C, 300 °C, and 400 °C. The processed composites were examined by FTIR and UV–vis spectroscopies. We observed that the materials prepared in this work can exhibit a variety of colors depending on the heat treatment temperature, withdrawal speed, and precursor:solvent molar ratio used in their processing. It is an important finding since this behavior could lead to architectural application of these materials. We believe that the changes observed in the UV–vis spectra and the colors of these samples could be related to the variation of the coating thickness as the processing conditions were modified. FTIR tests revealed that the ratio between the intensities of features ascribed to hydroxyl groups and TiO bonds decreased as the heat treatment temperature was increased. On the other hand, the ratio between bands related to TiOTi and TiO bonds decreased when the heating temperature was raised from 100 °C to 300 °C.     

Synthesis and structural characterization of potato starch sponges

Materials with hierarchical porous structures have attracted great attention over the past years since they have been widely used in many industrial applications. Starch stands out among the materials commonly used as sacrificial templates in environmentally friendly applications. In addition, starch is inexpensive, easy to process, and readily available. In this work we present a structural characterization of sponges prepared by freezing and thawing of a starch gel. Samples obtained in this study were examined by scanning electron microscopy (SEM) and X-ray microtomography (μ-CT). SEM tests revealed that these samples show an open macroporous framework with continuous walls. μ-CT tests revealed that it is possible to tailor the pore structure of these materials by changing the starch concentration in gels used in their processing. We noticed that increasing starch concentration from 15 wt.% to 60 wt.% leads to sponges with porosities ranging from about 28% to over 65%. It was also observed that the higher the starch concentration, the greater the mean pore size of the prepared sponge.     

Statistical characterization of an ensemble of functional neural networks

The Ginzburg-Landau free energy functional with two order parameters has been widely used to describe surfactant adsorption phenomena at the interface between two immiscible fluids such as oil and water. To model surfactant adsorption, additional surfactant related terms are added to the original free energy functional which models an immiscible binary mixture. In this paper, we present a detailed comparison of phase-field models for an immiscible binary mixture with surfactant. In particular, we investigate the effects of mathematical model parameters on equilibrium surfactant profile across the interface between the immiscible binary mixture. Most previous models have severe time-step constraints due to the nonlinear coupling of order parameters. To solve these stability problems, we propose a special case of these models which allows the use of a much larger time-step size. We also apply a type of unconditionally gradient stable scheme and a fast multigrid method to solve the proposed model efficiently and accurately.     

Synthesis and properties of Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanoparticles obtained by a proteic sol–gel method

Iron-doped SnO₂ nanoparticles with chemical formula Sn_1?xFe_xO_2?y (x =?0.02, 0.05 and 0.10 at%) were successfully produced by a proteic sol–gel method. Thermogravimetric analysis and differential scanning calorimetry were performed to investigate the thermal behavior of the precursor powders as well as to select the appropriate calcination temperatures for oxide formation. X-ray absorption near-edge spectroscopy studies were carried out to determine the valence state of the transition metal used as dopant. Structural, morphological, and optical properties of the synthesized materials were studied by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectroscopy. The results confirmed the formation of nanometric spherical particles of single-phased SnO₂ with rutile-type tetragonal structure. Iron doping was accomplished in the form of Fe³⁺ substituting for Sn⁴⁺ in the SnO₂ matrix, with the creation of oxygen vacancies to achieve charge balance. Band gaps of SnO₂ were found to be unaffected by the introduction of iron.     

Synthesis of $$\upalpha $$-amino-1,3-dicarbonyl compounds via Ugi flow chemistry reaction: access to functionalized 1,2,3-triazoles

The Ugi multicomponent reaction has been used as an important synthetic route to obtain compounds with potential biological activity. We present the rapid and efficient synthesis of \(\upalpha \)-amino-1,3-dicarbonyl compounds in moderate to good yields via Ugi flow chemistry reactions performed with a continuous flow reactor. Such \(\upalpha \)-amino-1,3-dicarbonyl compounds can act as precursors for the production of \(\upalpha \)-amino acids via hydrolysis of the ethyl ester group as well as building blocks for the synthesis of novel compounds with the 1,2,3-triazole ring. The \(\upalpha \)-amino acid derivatives of the Ugi flow chemistry reaction products were then used for dipeptide synthesis.