关键词： 丙泊酚   右美托咪定   外科术后机械通气患者   镇静   血流动力学  

摘要： 目的探究右美托咪定与丙泊酚对外科术后机械通气患者镇静效果及血流动力学的影响。方法将我院60例外科手术后机械通气患者作为研究对象,电脑随机将其分成右美托咪定组和丙泊酚组,各30例。右美托咪定组给予右美托咪定治疗,丙泊酚组给予丙泊酚治疗,比较两种方法的镇静效果及对血流动力学的影响。结果镇静30 min后,两组的Ramsay镇静评分对比差异无统计学意义(Z=1.23,P>0.05);右美托咪定组心动过缓(6.67%)、低血压(13.33%)、低血压合并心动过缓(3.33%)发生率分别低于丙泊酚组(30.00%、36.67%、26.67%),两组间对比差异有统计学意义(χ^(2)分别为5.45、4.36、6.41,P均<0.05)。结论给予外科术后机械通气患者右美托咪定或丙泊酚,均有更好的镇静效果,但右美托咪定对于血流动力学的影响较小,更适用于机械通气患者。

关键词： Graphene oxide   Cementitious materials   Molecular dynamics modeling   Nanocomposites   Mechanical properties   Fracture  

摘要： Graphene oxide (GO) cementitious composites have recently attracted considerable interest due to their improved mechanical properties and durability. However, most research is focused on the macroscale performance of these composites with very little experimental and modelling research on the characterization of their nanoscale behavior. This makes the design of these new GO-cementitious composites challenging. In this paper, we present a novel molecular dynamics (MD) model for GO-cementitious nanocomposites to understand their behavior and predict their mechanical and fracture properties. In this model, different numbers of GO nanoplatelets were inserted into the C-S-H structure and a number of nanoscale mechanical parameters and crack bridging mechanism were obtained. The MD simulation results revealed that the addition of GO sheets increased the tensile and compressive strength of C-S-H by roughly 50% and 100%. The MD simulation results also identified a double-peak phenomenon which is an indication of additional plasticity when the intercalated GO/C-S-H structures are subjected to compressive stress. The fracture simulation results showed that the failure mode of the intercalated GO/C-S-H composites was marked by high energy release. The results of fracture simulations with different notch lengths also indicated that the addition of GO could improve the fracture performance due to a good interfacial connection between the GO and the C-S-H gel.

关键词： Glass fibre-epoxy (GF/Epoxy) composite   Diffusion mechanism   Acid   Cross-link density   Free-volume   Mechanical properties  

摘要： Glass Fibre-Epoxy (GF/Epoxy) composites are being the choice of material when exposed to inorganic acids such as sulphuric acid due to its superior corrosion resistance properties. Water diffusion into GF/Epoxy composites is well-reported. However, inter-relation between acid diffusion mechanism and its analogous influence on chemo-mechanical properties is never investigated with greater details. In this work, the transport behaviour of aqueous 10% sulphuric acid solution into GF/Epoxy composite and its complex inter-relations with the cross-linking density, morphology and mechanical properties is presented. The transport of aqueous solution of 10% sulphuric acid in the composite was quantified by gravimetric analysis and confirmed by the Energy Dispersive X-Ray Spectroscopy (EDX). The kinetic parameters were evaluated and compared using Fickian and Langmuir diffusion models, where the Langmuir model described the transport behaviour better. Analysis of thermomechanical properties such as storage modulus is characterised by dynamic mechanical thermal analysis (DMTA). The free volume distributions are estimated using positron annihilation lifetime spectroscopy (PALS). The indication of an increase in cross-link density with the acid exposure is further validated by Fourier-transform infrared spectroscopy (FT-IR) analysis. In the absence of substantial chemical degradation and with increased cross-linking density, the deterioration in the mechanical properties is attributed to the erosion of epoxy resin confirmed by the morphology performing Field Emission Scanning Electron Microscope (FE-SEM) analysis. The acid diffusion mechanism results show promising prospects of selecting and designing GF/Epoxy composites for industrial storage and manufacturing facilities containing aggressive environments (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Bimetals Co-Ce   Dry reforming   Calcium   Mechanism   Kinetic  

摘要： The mechanism and kinetic features of dry reforming with methane (DRM) over Ca promoted 1Co-1Ce/AC-N catalyst was investigated. The mechanistic pathway studies have conducted by FTIR and XPS analysis, structure-activity correlations demonstrated the CH4 and CO2 could adsorb on catalyst active sites and generate intermediate CHx, OH and CHxO, continue to generate CO and H-2 and then desorbed from active sites. Moreover, CH4 could also oxidized by Ce4+ and CO2 reduced by Ce3+, the same content of Ce4+ and Ce3+ on promoted catalyst greatly improved the reaction rate. The kinetic of dry reforming with methane was examined for temperature between 650 and 850 at 800 degrees C. The research was carried out by changing the CH4/CO2 ratios between 0.3 and 3.0. The obtained experiment data were fitted by three typical kinetic models (Power Law, Eley-Rideal and Langmuir-Hinshelwood), the fitting results demonstrated that the best prediction of reforming rates can provided by Langmuir-Hinshelwood model for the reaction temperatures between 650 and 800 degrees C. Moreover, activation energies of methane and carbon dioxide consumption were -117 and -47 kJ/mol, indicating that much higher energy barrier is needed for methane activation compared to carbon dioxide. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： TO2-SiO2 hybrid nanoparticle   Response surface methodology   Mechanical properties   Molecular dynamics simulation  

摘要： In this research, experimental and theoretical method are used to improve and optimized the thermo-mechanical properties of hybrid Epoxy/TiO2/SiO2 nano-Composites. For investigation of the influence of weight percentage of Silica toward Titana in TiO2-SiO2 hybrid nanoparticles on tensile properties of epoxy, the composite was optimized by surface methodology. Thirteen experiments were designed by using design expert commercial software totally. The TiO2-SiO2 hybrid nanoparticles were synthesized by sol-gel method. Then, epoxy/TiO2-SiO2 nanocomposites were prepared by direct mixing method. Four factors as elongation at break (EAB), yield strength (sigma y), ultimate strength (sigma u) and elastic modulus (E) were investigated by using tensile test device. The optimization results showed that the best (EAB), (sigma y), (sigma u) and (E) outcomes are 29.3, 17.72, 17.43 and 4.34% respectively with 14.64% weight percent of Silica in total amount of TiO2-SiO2 0.73% hybrid nanoparticles. In order to investigate the chemical and thermo-mechanical properties of nanocomposite as tensile tests, TGA, XRD, FT-IR, SEM, EDX and DRS analysis were performed. In addition, due to the high reliability in predicting the reaction among different materials and comparing with the results of experimental work, which is based on polymer-nanoparticle interaction energy, molecular dynamics simulation (MD) were used. The simulations were performed by using materials studio (MS) software. The numerical and analytical results show that the presence of small amount of Silica beside Titanium creates a strong interaction between fillers and epoxy resin.

关键词： electro-responsive materials   multiphysics   polyampholytes   smart materials   stimuli-responsive polymers  

摘要： Multifunctionality in polymers facilitates their application in emerging technologies. Electrical fields are a preferred stimulus because of the speed and ease of application to bulk polymers. While a wide range of electrically triggered actuators are developed, and electrically controlled adhesion between gels is demonstrated, modification of bulk mechanical properties via electrical stimuli remains elusive. Polymers with covalently incorporated ionic charge (polyelectrolytes) should be well suited to achieving this goal since the mechanical properties depend on electrostatic interactions and these charges are intrinsically susceptible to electric fields. Molecular dynamics simulations are utilized here to investigate whether electric fields can modulate the mechanical properties of polyelectrolytes and to understand the governing mechanisms. Mechanical property modulation by electric field is found to be sensitive to the charge distribution-charges must be tightly attached to the polymer backbone, and responsivity is greater if a single backbone contains both positive and negative charges. The dominant mechanisms are reorientation and stretching of the polymer chains, which also elongate the ionic clusters to maintain strong electrostatic interactions throughout deformation. These insights are critical for future experimental realization of polymers with electric field regulated mechanical properties.

关键词： mechanical seal   gap   microgrooves   two-phase flow   pressure distribution   leakage   deformations  

摘要： This paper presents the numerical methods for calculating the hydrodynamic characteristics of a mechanical seal, taking into account the possibility of a phase transition in its gap. In the numerical model, the solutions are used for the flow of both liquid and gas in the microgap of compaction obtained using the finite volume method. Regularities of the influence of the size and taper of the gap, the depth of the microgrooves, the pressure drop and the value of the saturated vapor pressure on the hydrodynamic characteristics of the seal are revealed. A method has been developed for calculating leaks, the stiffness of the lubricant layer, and the friction power in the seal gap, taking into account vaporization and thermal deformations of the sealing rings. Recommendations for the selection of the geometric parameters of the seal are offered. The cause of pulsating seal leakage has been identified. The developed technique is applicable both for cryogenic liquids and for water.

关键词： Thermo-mechanical   Microbeam   Two-dimensional functionally graded   Vibration   Moving load  

摘要： Due to the multi-functional requirements, more and more multi-dimensional functionally graded structures are reported, while their thermo-mechanical performances are still unclear. This paper aims at theoretically examining the thermo-mechanical behaviors of two-dimensional functionally graded (2D-FG) microbeam excited by a moving load. The formulation is established in the framework of the modified couple stress theory in combination with Hamilton's principle, and this problem is numerically solved through the finite element method (FEM). The material properties of the 2D-FG microbeam are treated as temperature-dependent parameters that vary smoothly along with both the axial and thickness directions, and three different thermal loads including the uniform, linear, and nonlinear temperature rises are taken into account. Both the fundamental frequency and the dynamic transverse deflection are analyzed with consideration of different axial and thickness gradient indexes, thermal load types, temperature rise amplitudes, and small scale parameters. The conclusion obtained in this paper can serve as a guideline for assessing the thermal performance of microstructures subjected to a moving load.

关键词： Azo dye   Providencia rettgeri   Cosubstrate   Whole-genome sequencing   Biodegradation mechanism  

摘要： Azo dyes pose hazards to ecosystems and human health and the cosubstrate strategy has become the focus for the bioremediation of azo dyes. Herein, Brilliant Crocein (BC), a model pollutant, was biodegraded by Providencia rettgeri domesticated from activated sludge. Additional ethanol, as a cosubstrate, could accelerate P. rettgeri growth and BC biodegradation, as reflected by the Gompertz models. This phenomenon was attributed to the smaller metabolites and greater number of potential pathways observed under the synergistic effect of ethanol. Genomic analysis of P. rettgeri showed that functional genes related to azo bond cleavage, redox reactions, ring opening and hydrolysis played crucial roles in azo dye biodegradation. Furthermore, the mechanism proposed was that ethanol might stimulate the production of additional reducing power via the expression of related genes, leading to the cleavage of azo bonds and aromatic rings. However, biodegradation without ethanol could only partly cleave the azo bonds.

关键词： adhesion   interfaces   mechanical properties   molecular dynamics   Nanocomposites  

摘要： Molecular dynamics (MD) simulations were adopted to compare the enhanced mechanical and tribological properties of nitrile rubber composites reinforced by different functionalized graphene sheets. Functional groups such as hydroxyl (-OH), carboxyl (-COOH), and ester (-COOCH3) were adopted. The constant strain method was applied to measure the mechanical properties of graphene/nitrile rubber composites. Sandwiched molecular models were developed to investigate the tribological properties of graphene/nitrile rubber composites by applying a shear load. The MD simulation results showed that the incorporation of functionalized graphene enhanced the Young's modulus, bulk modulus, and shear modulus of the nitrile rubber matrix. In addition, the coefficient of friction and abrasion rate of the functionalized graphene/nitrile rubber composites decreased. The mechanisms for the interfacial interactions between the functionalized graphene and nitrile rubber matrix were determined by calculating the mean square displacement of rubber chains, binding energy, and the radial distribution function between functional groups and polar atoms in the rubber matrix, respectively. The results of the atomistic simulations indicated that stronger interfacial interactions and better stability and dispersion of graphene in rubber matrices can be obtained by introducing functionalized graphene. Owing to the combination of hydrogen bonding and strong van der Waals interactions, the COOH-functionalized graphene behaves the best effect on the enhancement of mechanical and tribological properties of the nitrile rubber composites.