关键词： Viscoelastic properties   Palm oil   Hazelnut oil   Crystallization kinetics   Avrami model   Oscillation rheology  

摘要： Fat crystal networks result from a crystallization process, forming interlinked crystal aggregates of viscoelastic character. Palm oil-based fat crystal networks, such as chocolate and nougat spreads, often show liquid oil separation during storage because the fat crystal network is too weak to retain the liquid oils trapped within its structure. To explore the relationship between crystallization kinetics and subsequent mechanical properties, i) palm oil from three different geographical origins and with diverging crystallization properties, ii) mixtures of Ghanaian palm oil with gradually increasing additions of hazelnut oil, and iii) blends of Ecuadorian palm oil with palm stearin as a tripalmitin (PPP)-rich fraction were investigated. Kinetic parameters were acquired from an extended Avrami model by isothermal differential scanning calorimetry measurements, and the results combined with the elastic properties measured by oscillation rheology since studying crystallization kinetics alone insufficiently informs about the mechanical/structural properties needed to overcome liquid oil separation. Rate constants of all investigated fats followed bell-shaped curves, with curve progression strongly dependent on the lipid composition. Ameliorating crystallization properties entailed enhanced elastic properties. The higher the maximum rate constants, the higher the elastic modulus and the gel rigidity of the respective fats. However, two different linear regions of elastic modulus versus PPP or solid fat content resulted, depending on whether palm oil was diluted with hazelnut oil or blended with a PPP-rich fraction. Hazelnut oil strongly diluted crystallizable portions of the structuring fat, thereby decreasing the mechanical properties in a power-law fashion, because the fat crystal network became less connected between fat crystal aggregates.

关键词： Bombyx mori   silk fibroin   Biomaterial   Molecular dynamics   Computational materials science   Nanoscale mechanics   beta-Sheet crystallite  

摘要： Bombyx mori silk fibroin (B. mori SF) is a promising biopolymer for use in biomedical applications such as tissue engineered grafts and as a load bearing biopolymer with biocompatible and bioresorbable properties. B. mori SF is a hierarchical bio- macro-molecule made up of amino acid (residue) chains consisting of a crystalline phase and an amorphous phase arranged in a specific order. Understanding about the mechanical behavior of B. mori SF at multiple length scales is of importance when developing tissue grafts, which requires a deeper understanding of the mechanics of its nanostructure. Four phenomenological models of B. mori SF nanostructures were developed, based on crystalline and amorphous phase connectivity. Tensile loading based mechanical behavior analysis of these models were performed using molecular dynamics (MD) simulations and compared with existing results from literature for selection of best performing model. Elastic modulus of similar to 7.4GPa and tensile strength of similar to 340 MPa were obtained for this model. Analysis of results reveals that deformation mechanisms in B. mori SF at nanoscale are a combination of tensile and shear deformations, wherein, the tensile deformation of amorphous region results into excessive extension of B. mori SF, whereas, shear deformation of crystalline region results into a high tensile strength. Overall, this work is instrumental in development of a right computational nanoscale model of SF nanostructure and provides deeper insights into the mechanistic interactions and mechanisms between amorphous and crystalline regions of B. mori SF, which would be useful for further studies of silk based biomaterials.

关键词： Gene regulation   Genomic instability   Long non-coding RNAs   RNA decay  

摘要： Much of the mammalian genome is transcribed, generating long non-coding RNAs (lncRNAs) that can undergo post-transcriptional surveillance whereby only a subset of the non-coding transcripts is allowed to attain sufficient stability to persist in the cellular milieu and control various cellular functions. Paralleling protein turnover by the proteasome complex, lncRNAs are also likely to exist in a dynamic equilibrium that is maintained through constant monitoring by the RNA surveillance machinery. In this Review, we describe the RNA surveillance factors and discuss the vital role of lncRNA surveillance in orchestrating various biological processes, including the protection of genome integrity, maintenance of pluripotency of embryonic stem cells, antibody-gene diversification, coordination of immune cell activation and regulation of heterochromatin formation. We also discuss examples of human diseases and developmental defects associated with the failure of RNA surveillance mechanisms, further highlighting the importance of lncRNA surveillance in maintaining cell and organism functions and health. Mammalian genomes generate long non-coding RNAs, which are degraded by the RNA surveillance machinery. This regulated degradation is vital for various processes, including for genome integrity, stem cell pluripotency and immune cell activation. Consequently, defects in RNA surveillance cause human diseases and developmental disorders.

关键词： Deposition   Nanoindentation   Nanoscratching   Heat   Germanium   Silicon  

摘要： Molecular dynamics (MD) simulations are performed to study the mechanical behavior of SiGe thin film during nanoindentation and nanoscratching processes. The MD simulations of deposition and annealing process are conducted to create the Si80Ge20 thin film deposited on Si(0 0 1) substrate. MD simulations of nanoindentation and nanoscratching processes are carried out to study the influence of the temperature on deformation behaviors and mechanical properties of this material. Moreover, the influences of the scratching depth, tool velocity, and temperature on the deformation behavior during nanoscratching process are also surveyed. It is found that the elastic and plastic deformations occur and the shear transformation zones (STZs) are independently developed in the contact region. The force, hardness, and Young's modulus of the Si80Ge20 thin film deposited on the Si substrate decrease as increasing the temperature during the indentation process. The pile-up, friction force, and normal force grow as increasing the scratching depth. As increasing the scratching speed, the pile-up increase while the normal force and the friction force reduce due to the effect of heat and strain rate are more efficient than the effect of the pile-up. As increasing the temperature, the height of pile-up increases while the normal force and the friction force decrease as a result of a higher temperature leads to softening the workpiece because the thermal expansion causes a reduction of the bonding strength of atoms.

关键词： Perfluorooctanoic acid   Peroxymonosulfate   Photocatalysis   Sulfate radicals   Visible light  

摘要： The global occurrence and adverse environmental impacts of perfluorooctanoic acid (PFOA) have attracted wide attention. This study focused on the PFOA photodegradation by using photocatalyst TiO2 with peroxymonosulfate (PMS) activation. Aqueous PFOA (50 mg L-1) at the pH 3 was treated by TiO2/ PMS under 300 W visible light (400-770 nm) or 32 W UV light (254 nm and 185 nm). The addition of PMS induced a significant degradation of PFOA under powerful visible light compared with sole TiO2. Under visible light, 0.25 g L-1 TiO2 and 0.75 g L-1 PMS in the solution with the initial pH 3 provided optimum condition which achieved 100% PFOA removal within 8 h. Under UV light irradiation at 254 nm and 185 nm wavelength, TiO2/PMS presented excellent performance of almost 100% removal of PFOA within .1.5 h, attributed to the high UV absorbance by the photocatalyst The intermediates analysis showed that PFOA was degraded from a long carbon chain PFOA to shorter chain intermediates in a stepwise manner. Furthermore, scavenger experiments indicated that SO(4)(.-)radicals from PMS and photogenerated holes from TiO2 played an essential role in degrading PFOA. The presence of organic compounds in real wastewater reduced the degradation efficacy of PFOA by 18-35% in visible/TiO2/PMS system. In general, TiO2/PMS could be an ideal and effective photocatalysis system for the degradation of PFOA from wastewater using either visible or UV light source. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Oxidation   Iron(II)   Oxygen   Catalysis   Copper(II)  

摘要： The results of this comparative study have shown that in 1M acid solutions, the differences in reactivity of iron (II) for reduction of oxygen are within about an order of magnitude of each other for the systems studied at 40 degrees C. This applies to both the uncatalysed and copper(II) catalysed systems. The exception is the chloride system in which the rate can be significantly increased by increasing the chloride concentration. The other main conclusion is that although catalysis by copper(II) ions can be significant there exist conditions (iron(II) and (III) concentrations) for which the effect is not that important. Rate equations for both the uncatalysed and catalysed reactions have been derived that apply equally to all the systems studied. Values for the various rate constants have been obtained by analysis of extensive kinetic data in 1M acid solutions at 40 degrees C. A limited electrochemical study has been used to derive values for the equilibrium constant for the reaction involving the iron(III)/iron(II) and copper(II)/copper(I) couples. An attempt has been made to compare relevant constants with previously published data and to derive a mechanism that is consistent with the kinetic results. This study has shown that the use of methanesulfonic acid as an oxidative leaching medium does not offer any advantages and is the least reactive of the systems studied.

关键词： Fluidic catalytic cracking   Deep neural network   Lumped kinetics model   Hybrid model   Artificial intelligence   Machine learning  

摘要： Fluid catalytic cracking (FCC) is one of the most important processes in the renewable energy as well as petrochemical industries. The prediction and understanding-of the FCC performance in a real industrial environment is still challenging, as this is a highly complex process affected by many extremely non-linear and interrelated factors. In this paper, a novel hybrid predictive framework for FCC is developed by integrating a data-driven deep neural network with a physically meaningful lumped kinetic model, powered by orders of magnitude greater number of high-quality data from a modem automated FCC process. The results show that the novel hybrid model exhibits best predictions with regards to all the evaluation criteria such as Mean Absolute Percentage Error, Pearson coefficient, and standard deviation. It indicates that the hybrid data-driven deep learning with mechanistic kinetics model creates a better approach for fast prediction and optimization of complex reaction processes such as FCC. (C) 2020 Institution of Chemical Engineers. Published by Elsevier By. All rights reserved.

关键词： Hydrodynamic cavitation   Giant lipid vesicles   DOPC   Stability   Fluorescein release   Confocal laser microscopy  

摘要： Liposomes are widely applied in research, diagnostics, medicine and in industry. In this study we show for the first time the effect of hydrodynamic cavitation on liposome stability and compare it to the effect of well described chemical, physical and mechanical treatments. Fluorescein loaded giant 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid vesicles were treated with hydrodynamic cavitation as promising method in inactivation of biological samples. Hydrodynamic treatment was compared to various chemical, physical and mechanical stressors such as ionic strength and osmolarity agents (glucose, Na+, Ca2+, and Fe3+), free radicals, shear stresses (pipetting, vortex mixing, rotational shear stress), high pressure, electroporation, centrifugation, surface active agents (Triton X-100, ethanol), microwave irradiation, heating, freezing-thawing, ultrasound (ultrasonic bath, sonotrode). The fluorescence intensity of individual fluorescein loaded lipid vesicles was measured with confocal laser microscopy. The distribution of lipid vesicle size, vesicle fluorescence intensity, and the number of fluorescein loaded vesicles was determined before and after treatment with different stressors. The different environmental stressors were ranked in order of their relative effect on liposome fluorescein release. Of all tested chemical, physical and mechanical treatments for stability of lipid vesicles, the most detrimental effect on vesicles stability had hydrodynamic cavitation, vortex mixing with glass beads and ultrasound. Here we showed, for the first time that hydrodynamic cavitation was among the most effective physico-chemical treatments in destroying lipid vesicles. This work provides a benchmark for lipid vesicle robustness to a variety of different physico-chemical and mechanical parameters important in lipid vesicle preparation and application.

关键词： Humanoid robots   legged robots   biomimetics  

摘要： During the steady gait, humans stabilize their head around the vertical orientation. Although there are sensori-cognitive explanations for this phenomenon, its mechanical effect on the body dynamics remains unexplored. In this study, we take profit from the similarities that human steady gait shares with the locomotion of passive-dynamics robots. We introduce a simplified anthropometric 2D model to reproduce a broad walking dynamics. In a previous study, we showed heuristically that the presence of a stabilized head-neck system has a significant influence on the dynamics of walking. This article gives new insights that lead to understanding this mechanical effect. In particular, we introduce an original cart upper-body model that allows to better understand the mechanical interest of head stabilization when walking, and we study how this effect is sensitive to the choice of control parameters.

关键词： Metal matrix composite (MMC)   Mechanical properties   Molecular dynamics simulation (MD)   Iron-carbon nanotube composites  

摘要： Carbon nanotube (CNT) reinforced composites recently have drawn considerable attention from researchers due to their enormous potential in the automotive and space industries. However, knowledge of the composite's mechanical properties for different conditions is essential before its industrial application. In this study, the mechanical properties of CNT reinforced iron metal matrix composite (CNT-Fe MMC) is investigated by molecular dynamics (MD) simulation under uniaxial tension. Our investigation revealed that adding CNT into iron increases its tensile strength up to 58% and Young's modulus up to 40%. The mixture rule's accuracy to predict stress in the composite at the nanoscale is also studied. We developed a mathematical model to predict the pattern of change of the mechanical properties with the variation of CNT radius and validated this theoretical model with a series of MD simulations. We found that 2.5 angstrom is the optimum radius of CNT for manufacturing composites having maximum strength and stiffness. The strengthening effect of matrix volume percentage for different fiber radius and under different temperatures was also investigated. MD analysis also revealed the initiation and propagation of fracture. This study provides novel insights that should be useful in the fabrication of CNT-Fe MMC for strength-based mechanical applications.