关键词： Saturation   Peptides and proteins   Molecules   Solvates   Deformation  

摘要： Mechanical stability of the CO2-CH4 heteroclathrate hydrate dominates the geomechanical stability of natural gas hydrate deposits when CO2 replaces CH4 from gas hydrate reservoirs. Here, molecular dynamics simulations were employed to investigate the strain-induced fracture behaviors of the CO2-CH4 heteroclathrate hydrate under mechanical loadings at various temperatures, pressures, and CO2 saturations. Results show that all crystals exhibit brittle fracture behavior, and a crack first develops in the location where hydrogen bonds (HBs) in the hexagonal rings of the large 51262 cages are parallel to the tensile direction. Increasing the temperature or CO2 saturation leads to the decrease in Young's modulus and fracture strength of the CO2-CH4 heteroclathrate hydrate. Particularly, abnormal mechanical strengthening of hydrates is observed when the CO2 saturation is around 0.75, mainly attributed to the coupling of the lattice distortion with the host-guest interaction. HBs are the key factors to dominate the deformation of the CO2-CH4 heteroclathrate hydrate. The slow decrease, rapid decrease, and abrupt increase in HB dynamics are corresponding to the elastic deformation, elastic-plastic deformation, and brittle fracture of the CO2-CH4 heteroclathrate hydrate, respectively. With the further stretching after the brittle fracture, the water bridge made up of water molecules released by broken cages at high temperatures leads to different plasticity than at low temperatures and causes a further reduction of HBs. This work advances the understanding of mechanical stability of the gas hydrate, which is believed to be useful in the risk assessment of CO2 replacing CH4 from natural gas hydrates and the storage of CO2 in gas hydrate reservoirs.

关键词： blends   resins   thermal properties   theory and modeling  

摘要： Increases in rated voltage and power density of high voltage gas insulated switchgears (GIS) impose stringent requirements on the diglycidyl ether of bisphenol A (DGEBA)-anhydride thermoset, which is widely used as insulation materials for high GIS, for higher mechanical and heat-resistant properties. In this paper, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (AOO) was copolymerized with DGEBA -anhydride system to increase the mechanical and thermal properties of the thermosets. Based on the molecular dynamics simulation method, the coefficient of thermal expansion, glass transition temperature (T-g), and modulus of AOO copolymer-modified DGEBA-anhydride thermosets were calculated. The AOO copolymer-modified DGEBA-anhydride thermosets specimens were further experimentally prepared and subjected to differential scanning calorimeter test, TGA test, tensile bending test, and dielectric test. The results of simulation and experiment simultaneously indicated that the T-g and modulus of the DGEBA-anhydride thermoset are enhanced after AOO modification. This is mainly due to the decrease in free volume percentage and mean square displacement of the epoxy cross-linked network structure after the introduction of AOO molecules, which makes the structure more compact and the cross-link density increased. Additionally, the dielectric performances of the thermoset was enhanced by AOO. The excellent thermal, mechanical and dielectric properties of AOO modified DGEBA-anhydride thermoset make it a promising application in the field of high voltage GIS.

关键词： Proteins  

摘要： Amyloid formation is a generic property of many protein/polypeptide chains. A broad spectrum of proteins, despite having diversity in the inherent precursor sequence and heterogeneity present in the mechanism of aggregation produces a common cross beta-spine structure that is often associated with several human diseases. However, a general modeling framework to interpret amyloid formation remains elusive. Herein, we propose a data-driven mathematical modeling approach that elucidates the most probable interaction network for the aggregation of a group of proteins (alpha-synuclein, A beta 42, Myb, and TTR proteins) by considering an ensemble set of network models, which include most of the mechanistic complexities and heterogeneities related to amyloidogenesis. The best-fitting model efficiently quantifies various timescales involved in the process of amyloidogenesis and explains the mechanistic basis of the monomer concentration dependency of amyloid-forming kinetics. Moreover, the present model reconciles several mutant studies and inhibitor experiments for the respective proteins, making experimentally feasible non-intuitive predictions, and provides further insights about how to fine-tune the various microscopic events related to amyloid formation kinetics. This might have an application to formulate better therapeutic measures in the future to counter unwanted amyloidogenesis. Importantly, the theoretical method used here is quite general and can be extended for any amyloid-forming protein.

关键词： Na-montmorillonite   Inorganic salts   Microstructure   Mechanical properties   Molecular dynamics  

摘要： In order to explore the mechanical properties of clay minerals in inorganic salt solution, the macroscopic elastic modulus of Na - montmorillonite and its elastic modulus in different concentrations of inorganic salt solution were calculated by molecular dynamics simulation and Voigt - Reuss - Hill approximate calculation, and the mechanism of inorganic salt inhibiting the hydration of montmorillonite was analyzed. The results show that low concentration of NaCl has the best effect on improving the elastic modulus of montmorillonite. The inhibitory effect on the hydration of montmorillonite is CaCl2 > NaCl > KCl > MgCl2.

关键词： Non-recyclable plastics   Pyrolysis   Isoconversional method   Kinetic study   Zeolite catalyst  

摘要： Post-consumer waste plastics that cannot be mechanically recycled represent a concerning environmental issue. According to the latest available data for Europe, as much as 25% of collected post-consumer waste plastics are landfilled, 43% is energy recovered, and 32% is recycled. One possible way of recovering non-recyclable plastics is pyrolysis, which is considered environmentally friendly technology for obtaining fuel or chemicals from plastic waste. To tackle the challenge of recovering non-recyclable plastics via pyrolysis, it is necessary to determine their actual composition. Visual separation of collected non-recyclable plastics was performed, and Fouriertransform infrared spectroscopy was used to confirm the accuracy of visual separation. A significant amount of plastics labelled as "other" was found. Since the composition of "other" waste plastics has not been sufficiently investigated, relatively few studies on their pyrolysis have been conducted. Therefore, they were characterised and added to the mixture with other found polymer types of non-recyclable plastics. Thermogravimetric analysis was conducted to determine thermochemical behaviour and kinetic parameters required for laboratory pyrolysis investigation. Kinetic analysis was conducted using the Friedman isoconversional model-free method and nonlinear multivariate regression method. The goal of this paper was to analyse the kinetics, determine the product yield and characteristics of the pyrolysis process of non-recyclable plastics over zeolite catalysts. It was found how the decomposition of non-recyclable plastics occurs in two decomposition steps. The activation energy of non-recyclable plastics was 144 kJ/mol in the first stage of decomposition and 262 kJ/mol in the second stage of decomposition. It decreased by 34% and 6.5% after fresh fluid catalytic cracking catalyst was added and 41% and 18.3% with iron-modified Zeolite Socony Mobil-5 catalyst. The yield of condensate was 55% (wax) for the o

关键词： ASPM   Strength characteristics   Hydration kinetics   Microscopic morphology   Hydration product  

摘要： Using fly ash (FA), aeolian sand (AS), cement, and mixing water as filling materials for making the paste-like filling mining can not only effectively control the surface subsidence and solve the "three-underground mining" coal pressure but also solve the environmental problems caused by the solid wastes, so as to realize the sustainable utilization of solid waste. The utilization of a large amount of AS resources can control land desertification, and the sale of aeolian sand can bring considerable economic benefits to Yuyang district. Hence, in this study, different ASPM samples were produced by varying the content of FA (0-30 wt%) and the curing times (3, 7, 14 and 28 days). The mechanical strength test, hydration kinetics test and microscopic test of aeolian sand paste-like materials (ASPM) was studied. The results showed that, according to the typical underground mining, the uniaxial compressive strength (UCS) of the backfill, cured for 28 days, was generally between 0.7 and 2.0 MPa, which can provide good roof support. In this study, the minimum strength of the ASPM reached 4.43 MPa (C-FA0), so the ASPM met the requirements of strength performance. Secondly, the hydration exothermic process of ASPM was divided into five different stages, and the influence of FA content on hydration kinetics was analyzed. For example, in the acceleration stage of ASPM, there was a positive correlation between the FA content, exothermic heat, and exothermic rate. The possible reason was that the particle size of FA was finer than that of AS, and the hydration reaction was more sufficient. In addition, the microscopic morphology and the characteristics of hydration products of ASPM were also studied. It is an important prerequisite for industrial field practice to study the mechanical properties, hydration characteristics and hydration product of ASPM.

关键词： Free energy   Molecular modeling   Reaction mechanisms   Molecules   Chemical calculations  

摘要： Bacteriorhodopsin (BR) transports a proton from intracellular to extracellular (EC) sites through five proton transfers. The second proton transfer is the release of an excess proton stored in BR into the EC medium, and an atomistic understanding of this whole process has remained unexplored due to its ubiquitous environment. Here, fully quantum mechanical (QM) molecular dynamics (MD) and metadynamics (MTD) simulations for this process were performed at the divide-and-conquer density-functional tight-binding level using realistic models (similar to 50000 and similar to 20000 atoms) based on the time-resolved photointermediate structures from an X-ray free electron laser. Regarding the proton storage process, the QM-MD/MTD simulations confirmed the Glu-shared mechanism, in which an excess proton is stored between Glu194 and Glu204, and clarified that the activation occurs by localizing the proton at Glu204 in the photocycle. Furthermore, the QM-MD/MTD simulations elucidated a release pathway from Glu204 through Ser193 to the EC water molecules and clarified that the proton release starts at similar to 250 mu s. In the ubiquitous proton diffusion in the EC medium, the transient proton receptors predicted experimentally were assigned to carboxylates in Glu9 and Glu74. Large-scale QM-MD/MTD simulations beyond the conventional sizes, which provided the above findings and confirmations, were possible by adopting our DCDFTBMD program.

关键词： Fluid dynamics   Electrical properties   Micelles   Insulators   Spectroscopy  

摘要： The rheology of wormlike micelle (WLM) solutions is tunable by engineering the micellar structure and topology. While much is known about how microscopic properties influence the rheological characteristics, questions remain regarding the quantification of fast relaxation processes, including Rouse and rotational modes. These fast processes are challenging to access using mechanical spectroscopy as bending modes dominate high-frequency mechanical measurements. In this work, we demonstrate the use of dielectric spectroscopy (DES) to directly interrogate these fast relaxation modes in solutions containing reverse WLMs. These consist of lecithin solutions in n-decane swollen with water. We develop an equivalent circuit model that separates the fast spectral features from the low-frequency processes and show that this relaxation feature is consistent with a combination of high-frequency Rouse and rotational modes. Further, we show that the low-frequency response is not determined by polymer dynamics alone. These findings demonstrate the potential of DES measurements to describe WLM behavior and pave the way toward in situ measurements under steady and transient shear flow.

关键词： Nanoparticles  

摘要： Fully understanding the mechanism by which nanoparticles (NPs) strengthen polymer matrices is crucial for fabricating high-performance polymer nanocomposites (PNCs). Herein, coarse-grained molecular dynamics simulations were adopted to explicitly investigate the reinforcing effect of a NP network. Our results revealed that increasing the NP-NP interactions induced the self-assembly of NPs into a three-dimensional (3D) network that reinforced the polymer matrix. The reinforcing mechanism of NP-NP interactions was quite different from that of NP-polymer interactions. The latter promoted the orientation of polymer chains to transfer the external stress, while the former distributed the stress throughout the NP network. This work revealed the mechanism by which the NP network reinforced the polymer matrix at the molecular level and also provided guidelines for developing high performance PNCs via interfacial modification.

关键词： 材料成型及控制工程   能源与动力工程   机械电子工程   卓越工程师教育培养计划   国家特色专业   机械设计制造及其自动化   三峡大学   核工程与核技术  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院,学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业,其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业,材料成型及控制工程为第三批卓越工程师教育培养计划专业。