Enhancing saccharification of Agave tequilana bagasse by oxidative delignification and enzymatic synergism for the production of hydrogen and methane

Agave tequilana bagasse is a suitable lignocellulosic residue for energy production. However, the presence of lignin and the heterogeneous structure of hemicellulose may hinder the availability of polysaccharides. In this work, the pretreatment of A. tequilana bagasse with alkaline hydrogen peroxide (AHP) followed by enzymatic saccharification with hemicellulases and cellulases was assessed for the removal of lignin and extraction of fermentable sugars, respectively. Results of the AHP pretreatment indicated that it is possible to attain up to 97% delignification and recover 88% of cellulose and hemicellulose after only 1.5 h of treatment. Regarding the saccharification process, the total sugar yield and productivity were both increased by 2-fold using an enzymatic mixture (cellulases + hemicellulases) compared to single enzyme hydrolysis (cellulases), evidencing synergism. Further evaluation of the hydrolyzates as substrate for hydrogen and methane production, resulted in yields 1.5 and 3.6-times (215.14 ± 13 L H₂ and 393.4 ± 13 L CH₄ per kg bagasse, respectively) superior to those obtained with hydrolyzates of non-pretreated bagasse processed with a single enzyme. Overall, using AHP pretreatment and subsequent hydrolysis with enzymatic mixtures improves the saccharification of A. tequilana bagasse enhancing the production of hydrogen and methane.     

Growth and adhesion of hot filament chemical vapor deposited diamond coatings on surface modified high speed steel

Diamond coatings were deposited by hot filament chemical vapor deposition on high speed steel substrates. Iron boride diffusion barrier and WC–Co layers were used as interlayers. At high deposition pressure, the quality of the diamond deposits is poor due to the extensive formation of graphitic deposits. At low pressure, diamond films of better quality were obtained, but their adhesion to the substrate was insufficient. A two-step deposition process at low pressure was developed. In a first deposition step performed at high methane percentage, a high nucleation density was achieved. In a second deposition step, the methane percentage was reduced to achieve continuous, dense, and adherent diamond layers on borided or WC–Co coated high speed steel substrates. Adhesion of these diamond layers on the surface modified high speed steel substrates was tested based on reciprocating sliding tests.     

Surface acoustic wave characterization of a thin, rough polymer film

Laser generated surface acoustic waves (SAW) in a heterodyne diffraction scheme is a powerful technique for elastic characterization of thin films and it is frequently used on samples of high optical quality. We show that the method can also be effectively used in difficult conditions, on rough samples. Measurements are presented on a 3 µm thick film of polymer, spin-coated on steel, and on the same sample after addition of an aluminum coating. The experimental data are interpreted using a model assuming a stack of perfect layers. The analyses show good consistency within the SAW results for both configurations, and consistency with nano-indentation results, cross-validating both approaches.     

Effect of sliding wear on tribocorrosion behaviour of stainless steels in a Ringer's solution

The dependence of the tribocorrosion of stainless steels AISI 304L and SS 3M^® orthodontic archwires sliding against corundum in a Ringer's solution on applied normal force, and sliding velocity, has been investigated using in situ electrochemical noise measurements. Applied normal force and sliding velocity were found to greatly affect current and potential during fretting-corrosion. An increase in normal force and sliding velocity induce an increase in current and a decrease in potential accelerating the depassivation rate of the tested stainless steels. The fluctuations in potential and current during fretting-corrosion are more pronounced at increasing sliding frequency than at increasing applied normal force. Sliding wear affects the repassivation behaviour of the tested materials by increasing the anodic current in the wear track area.     

Tribological behaviour and internal stress of diamond coating deposited with a stationary d.c. plasma jet

A diamond coating was produced by a stationary d.c. plasma jet in a confined circular area. Using scanning electron microscopy, optical microscopy, laser profilometry and Raman spectroscopy, it was found that the diamond coated area is inhomogeneous with respect to morphology, purity, thickness, and internal stress. Surrounding the diamond coated central area, an amorphous carbon rich area was identified. The morphologically distinct regions were evaluated separately in a fretting wear test against a corundum counterbody. The frictional behaviour was observed to be dependent on the morphology and structure of the coating and the diamond crystal size and orientation in the diamond coated area. No evidence of any fretting wear damage was found in the diamond coated area, whereas a lot of fretting induced scratches were observed in the amorphous carbon rich area. The presence of wear debris was clearly observed in the fretting contacts both inside and outside the diamond coated area.     

Structural basis for the recognition of carbohydrates by human galectin-7

Knowledge about carbohydrate recognition domains of galectins, formerly known as S-type animal lectins, is important in understanding their role(s) in cell-cell interactions. Here we report the crystal structure of human galectin-7 (hGal-7), in free form and in the presence of galactose, galactosamine, lactose, and N-acetyl-lactosamine at high resolution. This is the first structure of a galectin determined in both free and carbohydrate-bound forms. The structure shows a fold similar to that of the prototype galectins -1 and -2, but has greater similarity to a related galectin molecule, Gal-10. Even though the carbohydrate-binding residues are conserved, there are significant changes in this pocket due to shortening of a loop structure. The monomeric hGal-7 molecule exists as a dimer in the crystals, but adopts a packing arrangement considerably different from that of Gal-1 and Gal-2, which has implications for carbohydrate recognition.