Structural investigations on an amorphous Se90Te10 alloy produced by mechanical alloying using EXAFS, cumulant expansion and RMC simulations

We investigated an amorphous Se(90)Te(10) alloy produced by mechanical alloying using two different approaches. First, we used extended x-ray absorption fine structure (EXAFS) spectroscopy and the cumulant expansion method using the Einstein model for the temperature dependence of the cumulants to obtain the cumulants C(*)(1), C(*)(2), and C(*)(3). From these, we found information about the structure of the alloy as well as the thermal and structural disorder, anharmonicity of the effective interatomic pair potentials, thermal expansion of the Se-Se and Se-Te bonds and asymmetry of the partial distribution functions g(Se-Se)(r) and g(Se-Te)(r). The cumulants C(*)(1), C(*)(2), and C(*)(3) also allowed us to reconstruct the g(EXAFS)(ij)(r,T) functions from EXAFS. Then, we made reverse Monte Carlo (RMC) simulations using the total structure factor S(K) obtained from synchrotron x-ray diffraction and the EXAFS oscillations χ(k) on the Se K edge as input data to obtain the g(RMC)(ij)(r) functions. Both methods furnished very similar g(ij)(r) functions, and the structural data obtained from them were also very similar. The results obtained from both methods showed the presence of Se-Te pairs indicating that there is alloying at the atomic level. In addition, we could not find any evidence of the presence of Te clusters in the alloy.     

Thermal and optical studies of an amorphous InSe9 alloy produced by mechanical alloying

In this paper we investigated thermal and optical properties of an amorphous alloy of the In–Se system. The amorphous InSe₉ alloy was produced by mechanical alloying and it was studied using Differential Scanning Calorimetry and microPhotoluminescence spectroscopy techniques, and from them several properties, such as glass transition and crystallization temperatures and energies and the optical gap energy were determined and compared to the values found in other alloys of the In–Se system. This comparison revealed some differences among our alloy produced by mechanical alloying and alloys produced by other techniques, which is a clear indication of the influence of the fabrication technique in their physical properties. The main differences occur in the activation energies associated with the glass transition and crystallization processes and also in the optical gap energy.     

Hypenol,a New Lignan from Hypenia salzmannii

A new lignan, (?)‐secoisolariciresin‐9‐yl 6‐O‐p‐coumaroyl‐β‐D ‐glucopyranoside ( 1 ), named hypenol, along with eleven known compounds, i.e., hyperin, rosmarinic acid, methyl rosmarinate, a mixture of the triterpenes betulinic acid, ursolic acid, and oleanolic acid, glycosylated β‐sitosterol, a mixture of the flavanones sakuranetin and isosakuranetin, hinokinin, and β‐peltatin A dimethyl ether were isolated from the EtOH extract of the leaves of Hypenia salzmannii (Benth. ) Harley . The structures of the compounds were elucidated based on the analysis of spectral data, including MS, 1D‐ and 2D‐NMR, and comparison with data in the literature.     

Advanced mono‐ and multi‐dimensional gas chromatography–mass spectrometry techniques for oxygen‐containing compound characterization in biomass and biofuel samples

A wide variety of biomass, from triglycerides to lignocellulosic‐based feedstock, are among promising candidates to possibly fulfill requirements as a substitute for crude oils as primary sources of chemical energy feedstock. During the feedstock processing carried out to increase the H:C ratio of the products, heteroatom‐containing compounds can promote corrosion, thus limiting and/or deactivating catalytic processes needed to transform the biomass into fuel. The use of advanced gas chromatography techniques, in particular multi‐dimensional gas chromatography, both heart‐cutting and comprehensive coupled to mass spectrometry, has been widely exploited in the field of petroleomics over the past 30 years and has also been successfully applied to the characterization of volatile and semi‐volatile compounds during the processing of biomass feedstock. This review intends to describe advanced gas chromatography–mass spectrometry‐based techniques, mainly focusing in the period 2011–early 2020. Particular emphasis has been devoted to the multi‐dimensional gas chromatography–mass spectrometry techniques, for the isolation and characterization of the oxygen‐containing compounds in biomass feedstock. Within this context, the most recent advances to sample preparation, derivatization, as well as gas chromatography instrumentation, mass spectrometry ionization, identification, and data handling in the biomass industry, are described.     

Synthesis,characterization and thermal behaviour of solid-state compounds of yttrium and lanthanide benzoates

Solid-state Ln(Bz)₃·H₂O compounds where Ln stands for trivalent yttrium or lanthanides and Bz is benzoate have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffractometry, infrared spectroscopy and chemical analysis were used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration, thermal stability and thermal decomposition of the isolated compounds.     

The use of ultrasonic guided waves and wavelets analysis in pipe inspection

One of the main applications of guided waves is for pipe inspection, since its one-dimensional geometry allows inspecting long distances in a short time. As with most configurations (frequency, thickness) ultrasonic waves with many modes of propagation are generated, recent research focuses mostly on the generation and reception of specific modes, mainly by means of sophisticated arrays of transducers. In this paper this problem is addressed with a different approach, by processing ultrasonic signals with a low signal/noise ratio acquired with a single transducer in an pulse–echo configuration. In order to improve the evaluation of results, frequency bandpass filters and wavelet analysis were tested. Results showed that even when very noisy signals are utilized, signal processing improve the signal/noise (S/N) ratio up to 12 dB approximately and enhance the analysis of the results, thus demonstrating its usefulness.     

Analysis of FSS with Dielectric Losses at Millimeter Wave Band Using the Transverse Transmission Line Method

The analysis of periodic structures on isotropic substrates with dielectric losses is presented. Frequency selective surface structures composed by an array of conducting patch elements are considered. This analysis uses the Galerkin method in combination with the transverse transmission line method, in the Fourier domain, to determine the reflection and transmission characteristics of the considered structures. The analysis provides very accurate results compared to those presented by other authors.     

Effective scaling behavior of magnetization and Hamming distance in Ising thin films under a surface field

The recent improvements on the technology for developing high-quality thin magnetic films has renewed the interest in the study of surface effects in both static and dynamic magnetic responses. In this work, we use a Monte-Carlo algorithm with Metropolis dynamics together with a spreading of damage technique to study the interplay between the effects of finite thickness and surface ordering field in thin ferromagnetic Ising (S=1/2) films. We calculate, near the bulk critical temperature and several values of the surface field, the dependence on the film thickness of the average magnetization M and Hamming distance D. We employ a finite size scaling analysis to show that both obey an effective one-parameter scaling but exhibit distinct characteristic surface fields. At their corresponding characteristic surface fields both M and D become roughly thickness independent and we estimate the critical exponent characterizing the behavior of the typical scaling lengths. Received 29 March 1999 and Received in final form 21 April 1999     

Interface thickness of the incompatible polymer system PS/PnBMA as measured by neutron reflectometry and ellipsometry

The techniques of neutron reflectometry and spectroscopic ellipsometry are compared as methods to measure the interface width between immiscible polymers. The interface thickness of the incompatible polymer system of polystyrene (PS) and polyn-butyl methacrylate) (PnBMA) is determined by neutron reflectrometry to (6.4±0.2) nm and (8.6±0.2) nm at temperatures of 120 and 156°C, respectively. Some emphasis is put on the measurement of those values also by spectroscopic ellipsometry using the same materials. A special sample geometry is chosen for ellipsometric measurements to compensate for thickness changes of films during annealing, and the dispersions of PS and PnBMA films are determined. With respect to the determination of the interface widths, however, it turns out that in the available wavelength range of 280 to 700 nm spectroscopic ellipsometry is not sensitive enough to measure the thin interface width between PS and PnBMA films. Neutron reflectivity results obtained for PS/PnBMA are discussed with respect to the Flory-Huggins segment interaction parameter calculated within the approximations of meanfield theory.