Experimental investigation of the effect of residual stresses on rapid crack propagation in polyethylene (PE100) pipes

Pipe extruded from polyethylene of strength class PE100 was tested using the ISO 13477 Small Scale Steady State “S4” method, to investigate the effect of frozen‐in stress on rapid crack propagation (RCP). It was found that the lower the residual stress, the lower the S4 critical temperature T_cS4 for RCP. Different experimental thermal treatments were used to independently modify residual stresses and crystallinity, to study the separate effects on RCP. It was found that the effect of crystallinity was less significant than that of residual stresses. It has previously been suggested that the residual stress influence on T_cS4 is determined by the balance of two mechanisms: additional stored strain energy prior to fracture helps to drive the crack, while the closing moment after fracture helps to close the flaring pipe wall. Tests on annealed specimens suggested that the first effect dominates, especially soon after crack initiation. However, the observed effect seems too large to be explained by this mechanism, and we suggest that the observed benefit from annealing may be better explained by a change in crack front shape. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

SUPERCRITICAL EXTRACTION OF LINSEED OIL: ECONOMICAL VIABILITY AND MODELING EXTRACTION CURVES

The aim of the present study was to use supercritical technology to recover linseed oil (Linum usitatissimum L.) using carbon dioxide (alone or modified with ethanol as solvent) to determine the influence of the technique on the chemical composition of the oil obtained, model the kinetic curves of extraction, and estimate the manufacturing cost of the process. The experiments were conducted at 323 K, pressure of 25 MPa, constant solvent flow of 1.7 × 10^?5 kg/s, and extraction time of 5 h. The highest yield was obtained with the addition of cosolvent (28.8%). The SFE process of linseed oil manufacture proved to be economically viable, resulting in a product with a specific cost of 13.21 US$/kg_oil. As to oil composition, the main fatty acids detected were linolenic and oleic acid.     

Potassium-Doped Ni–MgO–ZrO2 Catalysts for Dry Reforming of Methane to Synthesis Gas

Ni/K–MgO–ZrO₂ catalysts for dry reforming of methane, with a range of Mg/Zr ratios and each containing about 10 wt% Ni, were prepared via Ni nitrate impregnation on MgO–ZrO₂ supports synthesized by co-precipitation using K₂CO₃. It was found that a proportion of the potassium of the precipitant remained in the samples and improved the stability of the catalysts in the reaction. It was also shown that reduction of the catalysts at 1,023 K without calcination in air is necessary for stable and high activity; calcination in air at 1,073 K gives a deterioration of the catalytic properties, leading to rapid deactivation during the reaction. The order of the CH₄ conversions of the reduced catalysts after 14 h on stream was as follows: Ni/K–Mg₅Zr₂ ~ Ni/K–Mg ≥ Ni/K–Mg₂Zr₅ ? Ni/K–Zr. A catalyst with 0.95 wt% K on MgO–ZrO₂ with a Mg:Zr mole ratio of 5:2 showed the best resistance to deactivation. Experiments in a microbalance system showed that there was only negligible coke deposition on the surface of this sample. This behaviour was attributed to the presence of Ni nanoparticles with a diameter of less than 10 nm located on a MgO/NiO solid solution shell doped by K ions; this in turn covers a core of tetragonal ZrO₂ and/or a MgO/ZrO₂ solid solution. This conclusion was supported by EDS/TEM, XPS, XRD and H₂ chemisorption measurements.     

Amino acid composition of some Mexican foods

Knowledge of the amino acid composition of foods is essential to calculate their chemical score, which is used to predict protein quality of foods and diets. Though amino acid composition of many foods is reasonably well established, better knowledge is needed on native foods consumed in different regions and countries. This paper presents the amino acid composition of different presentations of raw and processed foods produced and consumed in Mexico. The amino acid composition was determined using Beckman amino acid analyzers (models 116 and 6300). Tryptophan was determined using the Spies and Chambers method. Of the different foods analyzed, some comments are made on native or basic foods in Mexico: Spirulin, where lysine is the limiting amino acid, with a chemical score of 67%, is a good source of tryptophan (1.16g/16 gN); amaranth contains high levels of sulphur amino acids (4.09 to 5.34 g/16gN), with a protein content of 15 g/100g; and pulque, a Pre-Hispanic beverage that contains high levels of tryptophan (2.58 g/16 gN) and sulphur amino acids (2.72 g/16 gN). Finally, insects are good sources of sulphur amino acids and lysine.     

The effect of sodium polymethacrylate on the rheology of the positive paste and performance of the lead-acid battery

Due to its rheological properties, positive lead-acid battery paste can be difficult to spread on lead current collectors accurately and efficiently under industry machinery and setting. Sodium polymethacrylate dispersant was studied as an effective positive paste additive that could lower the yield stress of the paste without affecting paste density and battery performance. Under a four-blade vane rheometer setup, stress growth and oscillatory amplitude strain sweep experiments evaluated the rheological properties of positive paste with the addition of varying amounts of sodium polymethacrylate. Further, the electrochemical effects of sodium polymethacrylate were also evaluated in 2V batteries by testing positive active material utilization and cycle life.     

Chemical Modifications for a Next Generation of Nucleic Acid Aptamers

In the past three decades, in vitro systematic evolution of ligands by exponential enrichment (SELEX) has yielded many aptamers for translational applications in both research and clinical settings. Despite their promise as an alternative to antibodies, the low success rate of SELEX (∼30 %) has been a major bottleneck that hampers the further development of aptamers. One hurdle is the lack of chemical diversity in nucleic acids. To address this, the aptamer chemical repertoire has been extended by introducing exotic chemical groups, which provide novel binding functionalities. This review will focus on how modified aptamers can be selected and evolved, with illustration of some successful examples. In particular, unique chemistries are exemplified. Various strategies of incorporating modified building blocks into the standard SELEX protocol are highlighted, with a comparison of the differences between pre-SELEX and post-SELEX modifications. Nucleic acid aptamers with extended functionality evolved from non-natural chemistries will open up new vistas for function and application of nucleic acids.     

Pore Structure Evolution of Lanthana–Alumina Systems Prepared through Coprecipitation

Pure Al₂O₃ and different compositions of La₂O₃–Al₂O₃ samples have been prepared through coprecipitation. Even after heating at 1300°C, the compositions La₂O₃·11Al₂O₃ and La₂O₃·13Al₂O₃ had higher surface area compared to the pure Al₂O₃ and the La₂O₃·Al₂O₃ composition. Ethanol washing is an effective way for improving the textural stability of pure Al₂O₃ and La₂O₃–Al₂O₃ samples. The effect of steam on the thermal stability of La₂O₃·11Al₂O₃ has also been studied. La₂O₃·11Al₂O₃ sample is found to be stable in steam.     

Dislocations at Prismatic Fracture Surfaces in Sapphire

Single-crystal sapphire exhibits a highly anisotropic fracture behavior. The surfaces of specimens fractured along prismatic planes are wavy, with fractographic features appearing as small areas of contrast under an optical microscope. Optical microscopy, atomic force microscopy, X-ray topography, and confocal microscopy are used to demonstrate a correlation between the areas of contrast and dislocations penetrating the sample surface. The surface features are argued to be a consequence of the stress field surrounding the dislocations, which deflect the crack approximately 10 nm normal to the surface as the crack cuts the dislocations. The lateral extent of measurable surface deflection is of the order of 5 μm. These images can be compared directly to show the equivalence of the position of the dislocations observed by X-ray topography and the surface contrast observed optically.