Microstructure and flow behaviour during backward extrusion of semi-solid 7075 aluminium alloy

The microstructure and flow behaviour during thixo backward extrusion of 7075 aluminium alloy were investigated. Reheating the steel die and the aluminium billet placed into the die at the same time using an induction furnace provides rapidly a very homogeneous microstructure suitable for thixoforming. During thixoextrusion, despite the high solid fraction, the solid globules are weakly connected and slide over each other without any plastic deformation. The flow remains quasi homogeneous resulting in homogeneous induced microstructure of the component.     

The infrared thermography control of the laser welding of amorphous polymers

In laser welding technique, a real-time control of temperature distribution inside the irradiated materials is essential when attempting to optimize the process. For all laser welding methods that operate by the transmission principle, the difficulty of recording the developed temperature at the interface derives from the fact that materials to be welded are in contact throughout the entire process. In the present study, in order to overcome this issue, a contact-free method such the infrared thermography is used for surface temperature measurement. Corroborating this data with a numerical simulation of the temperature field evolution inside the components, an assessment of optimal process parameters is possible. The experimental investigations are made on amorphous polymers, in a typical configuration for through-transmission laser welding. The fine agreement obtained between the experimentally and calculated data, validate the infrared thermography as a non-destructive method for real-time monitoring of the welding process.     

Simultaneous optical signal-to-noise ratio and differential group delay monitoring based on degree of polarization measurements in optical communications systems

We present a simultaneous optical signal-to-noise ratio (OSNR) and differential group delay (DGD) monitoring method based on degree of polarization (DOP) measurements in optical communications systems. For the first time in the literature (to our best knowledge), the proposed scheme is demonstrated to be able to independently and simultaneously extract OSNR and DGD values from the DOP measurements. This is possible because the OSNR is related to maximum DOP, while DGD is related to the ratio between the maximum and minimum values of DOP. We experimentally measured OSNR and DGD in the ranges from 10 to 30 dB and 0 to 90 ps for a 10 Gb/s non-return-to-zero signal. A theoretical analysis of DOP accuracy needed to measure low values of DGD and high OSNRs is carried out, showing that current polarimeter technology is capable of yielding an OSNR measurement within 1 dB accuracy, for OSNR values up to 34 dB, while DGD error is limited to 1.5% for DGD values above 10 ps. For the first time to our knowledge, the technique was demonstrated to accurately measure first-order polarization mode dispersion (PMD) in the presence of a high value of second-order PMD (as high as 2071 ps(2)).     

Ligand Binding Promiscuity of Human Liver Fatty Acid Binding Protein: Structural and Dynamic Insights from an Interaction Study with Glycocholate and Oleate

Human liver fatty acid binding protein (hL‐FABP) has been reported to act as an intracellular shuttle of lipid molecules, thus playing a central role in systemic metabolic homeostasis. The involvement of hL‐FABP in the transport of bile salts has been postulated but scarcely investigated. Here we describe a thorough NMR investigation of glycocholate (GCA) binding to hL‐FABP. The protein molecule bound a single molecule of GCA, in contrast to the 1:2 stoichiometry observed with fatty acids. GCA was found to occupy the large internal cavity of hL‐FABP, without requiring major conformational rearrangement of the protein backbone; rather, this led to increased stability, similar to that estimated for the hL‐FABP:oleate complex. Fast‐timescale dynamics appeared not to be significantly perturbed in the presence of ligands. Slow motions (unlike for other proteins of the family) were retained or enhanced upon binding, consistent with a requirement for structural plasticity for promiscuous recognition.     

On the Determination of the Concentration of Crystal Nuclei in Glasses by DSC

An interesting technique was proposed by Ray et al. over a decade ago to determine the number density of nucleation sites, N_q, or the nucleation rate, I(T), in glasses that exhibit internal nucleation. Their approach is based on the measurement of the areas under the differential scanning calorimetry (DSC) crystallization peaks of partially crystallized glass samples. In this study, we review their method and test a modified equation recently proposed by some of us, which also takes into account the crystal morphology and impingement. We compare N_q obtained with both methods for a Li₂O·2SiO₂ glass. Small glass monoliths were treated at 620°C for different time periods for crystal growth, without any nucleation treatment, and subsequently analyzed by DSC up to 800°C. We thus estimated N_q from the area under the DSC crystallization peaks. The corrected approach resulted in N_q values which were not affected by the pair of growth times chosen, as expected, but the obtained values were two‐ to fivefold lower than those calculated with the Ray model. Taking into account previously reported nucleation rates and the corresponding induction periods as a function of temperature (for specimens of the same glass batch), we estimated the number of nuclei formed during the DSC heating/cooling steps, and also measured them by optical microscopy (OM). Finally, we compared the obtained values from OM with the N_q values determined by the DSC method. The N_q resulting from the original and new equations were approximately two orders of magnitude larger than those experimentally determined for the same glass using optical microscopy. This difference is attributed to the formation of new nuclei during the heating and cooling paths of the DSC runs and to surface crystallization, which are not taken into account in the DSC expressions.     

NbO/Nb2O5 core–shells by thermal oxidation

Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb₂O₅ is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 °C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 °C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours.     

Monitoring pH-dependent conformational changes in aqueous solutions of poly(methacrylic acid)-b-polydimethylsiloxane copolymer based on fluorescence spectra of pyrene and 1,3-bis(1-pyrenyl)propane

Aqueous solutions of poly(methacrylic acid)-b-polydimethylsiloxane copolymer (PMA-b-PDMS), and reference solutions of PMA homopolymer, were studied as a function of pH using fluorescent probes: pyrene (P) and 1,3-bis(1-pyrenyl)propane (P3P). In both polymers the conformational transition of PMA chains at pH>5 was reflected in the sharp increase of the intensity ratio of the first to the third vibronic band in emission spectra of P; an excimer emission appeared for P3P, as well as for P if the probe concentration was higher than its solubility limit in water. The excimer to monomer intensity ratio of both probes is a sensitive indicator of the conformational transitions of polymer chains, but P3P is significantly more sensitive compared to pyrene. The data clearly indicated that the presence of PDMS blocks markedly facilitated the transition, even though the ratio of dimethylsiloxane to methacrylic acid units in the copolymer was low, 1:34. The absence of the P3P excimer emission at pH≈3 was rationalized by assuming that clustering of sections of PMA chains around pyrene moieties imposes an extended conformation of the probe molecule.