Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene

Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (C_n, with n = 2, 6–16) in amorphous polystyrene at temperatures from 35 °C to 165 °C, that is, both below and above the polymer glass transition temperature of 100 °C. All the mass uptake results are well described by a simple Fickian model (for t < t_1/2) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n²D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.     

Morphology and mechanical behavior of polypropylene hot plate welds

Polypropylene tensile bars were hot plate welded and analyzed by microscopy and mechanical tests. The welding process caused significant modifications to the microstructure and shape of the bars at the weld zone. The weld morphology was affected by both the welding parameters and the thermal history of the components. Oriented textures, coarse spherulites, voids or sharp notches occurring at the beads are the key morphological factors that affect the weld quality. Weld performance is dependent upon the type of testing method used. A tensile impact test has been shown to be potentially useful for quality control, as the fracture behavior is affected by the overall morphoiogy.     

Porous,Sintered Glass‐Ceramics from Inorganic Polymers Based on Fayalite Slag

The present paper deals with the synthesis of porous, sintered glass‐ceramics obtained at temperatures below 1150°C, originating from inorganic polymers based on fayalite slag. Firing led to the evaporation of water, dehydroxylation, and oxidation of Fe²⁺ above 345°C. For heating >700°C, the Si–O stretching band shifted from the 1160 and 750 cm^?1 to the 1255 and 830 cm^?1 region, due to a structural reorganization of the amorphous phase, whereas Fe–O bands appeared at 550 cm^?1. The final microstructure consisted predominantly of an amorphous phase, hematite, and franklinite. The open porosity and compressive strength decreased and increased, respectively, as the firing temperature increased. The final values suggest properties comparable to that of structural lightweight concrete, still, the materials synthesized herein, are lighter, and made primarily from secondary resources.     

Ceramic Microtubes from Preceramic Polymers

A novel process for the production of ceramic microtubes involving the microextrusion of preceramic polymers was studied. Microtubes with a wide range of inner and outer diameters and several centimeters long were produced from two silicone resins. A coextrusion approach was also used to extend the forming capability of the technique. The addition of carbon black resulted in electrically conductive silicon oxycarbide (SiOC) ceramic microtubes. SiOC microtubes possessed a high bending strength, ranging from ∼30–1100 MPa.     

LAS glass–ceramic scaffolds by three-dimensional printing

Highly porous (>60% open porosity) glass–ceramic scaffolds with remarkable mechanical properties (compression strength of ～15 MPa) were produced by indirect 3D printing. Precursor glass powders were printed into 3D ordered structures and then heat treated to sinter and develop crystalline phases. The final glass–ceramic contained a β-spodumene solid solution together with a secondary phase of lithium disilicate.The precision of the printed geometry and the density of the struts in the scaffold depended on several processing parameters (e.g. powder size and flowability, layer thickness) and were improved by increasing the binder saturation and drying time. Two types of powders with different particle size distribution (PSD) and flowability were used. Powders with a larger PSD, could be processed within a wider range of printing parameters due to their good flowability; however, the printing precision and the struts density were lower compared to the scaffolds printed using the powder in a smaller average PSD.     

Sintered Glass–Ceramics and Glass–Ceramic Matrix Composites from CRT Panel Glass

Sintering with simultaneous crystallization of powdered glass represents an interesting processing route for glass–ceramics, especially originating from wastes. Highly dense glass–ceramic samples may be obtained from a simple and short treatment at a relatively low temperature. In addition, glass–ceramic matrix composites may be obtained by mixing glass with suitable reinforcements. In this work sintered nepheline glass–ceramics, based on panel glass from cathode ray tubes, are illustrated. A limited addition of Al₂O₃ platelets caused a significant improvement in the mechanical properties (elastic modulus, bending strength, microhardness, fracture toughness), already remarkable for the un-reinforced glass–ceramic, compared with traditional nepheline glass–ceramics.     

Cellular and Molecular Signatures of Oxidative Stress in Bronchial Epithelial Cell Models Injured by Cigarette Smoke Extract

Exposure of the airways epithelium to environmental insults, including cigarette smoke, results in increased oxidative stress due to unbalance between oxidants and antioxidants in favor of oxidants. Oxidative stress is a feature of inflammation and promotes the progression of chronic lung diseases, including Chronic Obstructive Pulmonary Disease (COPD). Increased oxidative stress leads to exhaustion of antioxidant defenses, alterations in autophagy/mitophagy and cell survival regulatory mechanisms, thus promoting cell senescence. All these events are amplified by the increase of inflammation driven by oxidative stress. Several models of bronchial epithelial cells are used to study the molecular mechanisms and the cellular functions altered by cigarette smoke extract (CSE) exposure, and to test the efficacy of molecules with antioxidant properties. This review offers a comprehensive synthesis of human in-vitro and ex-vivo studies published from 2011 to 2021 describing the molecular and cellular mechanisms evoked by CSE exposure in bronchial epithelial cells, the most used experimental models and the mechanisms of action of cellular antioxidants systems as well as natural and synthetic antioxidant compounds.     

Surgery of chest wall deformities

The effect of melatonin (MEL) on the nephropathy and the oxidative stress induced by a single and high dose of Adriamycin (AD) has been studied in Wistar male rats. MEL (50 microg/kg/day) was injected intraperitoneally 3 and 7 days, respectively, before and after AD injection (20 mg/kg i.p.). Trunk blood was drawn and triglycerides, total cholesterol, phospholipids, high-density lipoprotein cholesterol, urea, creatinine, total protein, lipoperoxides, and reduced glutathione (GSH) levels and catalase activity (CAT) were determined in serum. In kidney homogenates, lipoperoxides, GSH, and CAT were measured as well as total protein in urine. AD administration resulted in hyperlipidemia and high-grade proteinuria and a marked increase in serum lipoperoxides, urea, and creatinine. In the kidney, the increase in lipoperoxides was accompanied by a significant decrease of GSH and CAT. The efficiency of MEL was specially remarkable in restoring GSH, CAT, and proteinuria to the levels of controls. These results confirm the involvement of free radicals in the pathogenesis of nephrotoxicity induced by AD. Likewise, they show the high antioxidative power of MEL and its marked effect on the prevention and suppression of this nephropathy.     

Roles of symbolic knowledge and problem-information context in solving word problems.

In 4 experiments, the effects of symbolic knowledge (i.e., knowledge about the meaning of mathematical notation) and problem-information context (PIC) on translating relational statements (e.g., "There are 6 times as many students as professors") into math equations were examined. College students were more likely to construct correct equations when symbolic knowledge was presented than they were when they only received a single relational statement. Ss who received a PIC that more closely resembled a complete word problem did better on the equation-writing task than did those who only received a relational statement. Results indicated that the effects of the two factors are not separate. When Ss had the appropriate PIC, performance on the equation-writing task was enhanced because Ss' own memory representations for symbolic knowledge were more accessible. Contextual constraints in the access and use of knowledge in problem solving are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)