Residual stress effect on the fracture toughness of lithium disilicate glass-ceramics

In glass-ceramics (GCs), on cooling from the crystallization temperature, internal residual stresses are generated due to the difference between the thermal expansion coefficient (TEC) of the crystal phase(s) and the residual glass. These stresses could degrade or promote their mechanical properties. In this work, we varied the magnitude of the residual stresses in lithium silicate GCs by designing their microstructures. The level of internal stresses was measured using (Synchrotron) X-ray diffraction. The effects of anisotropy of thermal expansion, crystal shape, and intensity of the residual stresses were analyzed and compared using theoretical models. We extended the Hsueh-Becher model to include the thermal expansion anisotropy of the orthorhombic lithium disilicate (LS2) crystals. We found that the average residual stresses within the LS2 crystals are compressive or null (−100 to ~0) and highly anisotropic. Most importantly, within the limits of this study, we found no evidence for the influence of (compressive or null) residual stresses on the fracture toughness of the studied GCs. Within the crystal size range from 1 to 5 μm, a highly crystallized volume fraction coupled to relatively large crystals (5 μm) of high elastic modulus improved the glass-ceramic fracture toughness. This result can guide the microstructural design of novel tough GCs.     

Modelling and solving spare parts supply chain network design problems

Spare parts are key operational assets in order to minimise unexpected equipment downtimes that may significantly impact a company’s results. The spare parts supply chain network supports the entire spare parts operations management and it is essential to achieve the planned goals. However, most of the traditional literature on spare parts management has not focused on the underlying supply chain network. Thus, this paper studies the integration of supply chain network design and control with traditional spare parts management. In particular, a generic network optimisation modelling structure is proposed, with simultaneous optimisation of warehouse locations and inventory control decisions, allowing minimising the total costs associated with the spare parts supply chain network. The generic model is specified based on three inventory control policies widely employed in the industry, which are suitable for managing a great variety of spare parts, i.e. (s, Q), (R, s, S) and (S-1, S). Furthermore, a solution approach is proposed based on Generalised Benders Decomposition. Finally, numerical results from a real-world application case in the process industry are shown and discussed.     

Effect of simulated acidic and salty fermentation conditions on kinetic growth parameters and probiotic potential of Lactobacillus acidipiscis and Lactobacillus pentosus

The technological stress during food processing may alter the beneficial interactions of food-associated Lactobacillus on the host. The effect of initial combined acidic (pH 5.0) and osmotic stress (NaCl 5 %, w/v with or without CaCl₂ 0.02 %, w/v) typically present in vegetable fermentations and cheesemaking were investigated. The growth kinetics prediction, hydrophobicity, auto-aggregation, in vitro survival and adhesion were determined in Lactobacillus acidipiscis and Lactobacillus pentosus isolated from a Mexican salty cheese. The growth was modelled with the modified Gompertz equation (R > 0.99; RMSE < 0.01). The lag phase increased (>10 h), and auto-aggregation was reduced. Hydrophobicity and S-layer total proteins varied. Gut survival reduced >4 log 10 units compared to the initial intake. Nevertheless, adhesion remained the same. Hence, combined stress affected the technological and physiological properties of both strains negatively. Further research is needed to identify the effect of the combined stress on the potential bioactivity of the strains.     

Effect of EDTA,sodium, and calcium hypochlorite on the inorganic component of root canal dentin: A SEM analysis

This study evaluated the influence of canal irrigation protocols with 5.25% calcium hypochlorite [Ca(OCl)₂], 5.25% sodium hypochlorite (NaOCl) and 17% EDTA solution on the inorganic component of root canal dentin. Sixty roots were randomly divided into six groups (n = 10): Saline solution (SS) (control); Saline solution (SSE) +17% EDTA; CH ? 5.25% Ca(OCl)₂; CHE ? 5.25% Ca(OCl)₂ + 17% EDTA; SH ? 5.25% NaOCl; SHE ? 5.25% NaOCl +17% EDTA. After canal irrigation, the specimens were longitudinally split and analyzed by scanning electron microscopy (SEM). Dentinal tubules were observed in transverse (middle and apical thirds) direction. The images were classified in scores, according to smear layer removal and peritubular dentin alteration, and data were analyzed by Kruskal–Wallis's test, followed by Dunn's test (α = 0.05). In the middle third, all groups with EDTA presented better removal of the smear layer with higher peritubular dentin alteration (p < .05). In the apical third, this happened only in SHE (p < .05). Ca(OCl)₂ and NaOCl exhibit similar performance to remove smear layer and alteration of the inorganic component in the middle third. In the apical third, NaOCl associated with EDTA showed better performance in smear layer removal.     

Activated Carbon by Potassium Carbonate Activation from Pine Sawdust (Pinus montezumae Lamb.)

Activated carbon (AC) was gained from Pinus montezumae (PM) wood sawdust and chemical activation with K₂CO₃ was used for obtaining activated carbons. Variations in reaction conditions such as temperature, impregnation ratio (IR), and activation time were carried out to study their influence on the specific surface area (SSA) and average pore volume (APV) in AC. Materials were analyzed by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) to determine the functional groups, pore structure, and morphology of pine sawdust and activated carbons. Activated carbons were amorphous in nature with some crystalline regions.     

Mesoporous carbon-containing MoS2 materials formed from the in situ decomposition of tetraalkylammonium thiomolybdates

Molybdenum disulfide with unique mesoporous structure was synthesized from tetraalkylammonium thiometallate precursors in situ decomposed in a batch reactor in the presence of dibenzothiophene (DBT). The precursors used in this study were tetraalkylammonium thiomolybdates with alkyl groups ranging from propyl to octyl. Molybdenum disulfide thus prepared presents high surface area (from 255 up to 329 m²/g), high content of carbon (C/Mo=2.7-4.0) and type IV nitrogen adsorption-desorption isotherms when decomposed from tetrahexyl-, tetraheptyl- or tetraoctylammonium thiomolybdates. The as-formed materials are poorly crystallized with a very weak intensity of the (0 0 2) peak of the 2HMoS₂ structure. Such diffraction patterns are characteristic of exfoliated samples. Characterization by TEM shows a disordered layered structure with no long range order for the MoS₂ catalysts. Therefore, the nature of the alkyl group in the precursor affects both the surface area and the pore size distribution of the final MoS₂ catalysts with a progressive morphological modification up to a mesoporous organization.     

A computational fluid dynamic model of the heat and moisture transfer during beef chilling

The unsteady heat and mass transfer process during beef carcass chilling was modelled for a three-dimensional beef carcass geometry. A three-step method was used to simulate the simultaneous heat and mass transfer process in order to reduce the computational time. In the first step, a steady state simulation of the flow field was conducted. In the second step, the local heat and mass transfer coefficients were calculated. Finally, the third step consists of the simultaneous heat and mass transfer process simulation on the meat carcass only. A separate 1-D grid was used to calculate the moisture diffusion in the meat. The simulation of a 20-h chilling run takes 5 days on a 2.5 GHz Pentium 4 computer. The model allows calculating and predicting the heat load, temperatures, weight loss and water activity. Local variations in the heat and mass transfer coefficients, temperature and water activity were found around the beef carcass. The CFD model gives temperature predictions that agree with experimental data better than any previous model. The weight loss tends to be over-predicted probably due to neglecting the resistance caused by the fat cover.