关键词： Aspiration pneumonia   Microbiota   Anaerobes   Mechanical ventilation   Dynamics  

摘要： Background: The emergence of multi-drug resistant pathogens is an urgent health-related problem, and the appropriate use of antibiotics is imperative. It is often difficult to identify the causative bacteria in patients with aspiration pneumonia because tracheal aspirate contains contaminants of oral bacteria. We investigated the dynamics of microbiota in mechanically ventilated patients with aspiration pneumonia to develop a treatment strategy. Methods: Twenty-two intubated patients with aspiration pneumonia were recruited. Saliva and tracheal aspirate of the subjects were collected at three time points: (A) within 2 h after intubation, (B) just before administration of antibiotics, and (C) 48-72 h after administration of antibiotics. The microbiota in each specimen was analyzed by using the 16S rRNA gene clone library sequencing method. Bacterial floras of the samples were analyzed by principal component analysis. Results: Principal component analysis based on the composition of genus revealed that although the changes of microbiota in the saliva from (A) to (B) were not clear, the composition of anaerobes in the tracheal aspirate (B) was lower than (A). In fact, the reduction of anaerobes, not in the saliva but in the tracheal aspirate from (A) to (B), was confirmed by incident rate ratios estimated by a multilevel Poisson regression model (p < 0.001). The extent of decrease in anaerobes was fully dependent on the time difference between the sampling of tracheal aspirate (A) and (B)-in particular, over 3 h of mechanical ventilation. This indicates that the alterations of microbiota (involving the reduction of anaerobes in the lower respiratory tract) occurred during mechanical ventilation prior to the administration of antibiotics. After the administration of antibiotics, Enterobacter spp., Corynebacterium spp., Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, and Granulicatera adiacens were predominantly detected in the tracheal aspirate (C)

关键词： Alkali content   Cement clinker   Compressive strength   Ion concentration   Electrical resistivity  

摘要： The work aims to investigate the effect of alkali content in Portland cement on its hydration kinetics and mechanical properties. Four kinds of cement clinkers with different alkali content were chosen, and K2SO4 was added to adjust the alkali content of cement. The heat release of hydration, non-evaporable water content, electrical resistivity of the pastes and compressive strength of cements were tested. The hydration products, ion concentrations and pH value of the pore solution were analyzed. The results show that the alkali in cement accelerates the hydration at early ages but suppresses its hydration at later ages. Alkali addition increases the main heat evolution of cement with low alkali content and shortens the induction period of cement with high alkali content. The dissolution of C3S and the formation of Ca(OH)(2) are promoted by alkali addition, but the formation of AFt is suppressed. Alkali addition is detrimental to the enhancement of the compressive strength of cement at later ages, the effect on the compressive strength at early ages is related to the total alkali content in cement. A positive effect is present in cement with low alkali content, the effect is negative in cement with high alkali content. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Monolayers   Energy   Nanoflakes   Molecules   Two dimensional materials  

摘要： We investigated the rotational and translational dynamics of hydrogen-passivated, black phosphorene and blue phosphorene nanoflakes of diverse size and geometry anchored to graphene, black phosphorene, blue phosphorene, and MoS2 monolayer substrates. The optimized attractive interaction energy between each nanoflake and monolayer substrates are harmonic for small angular displacements, leading to libration frequencies. We showed that the relevant dynamical parameters and resulting libration frequencies, which vary with the size/geometry of nanoflakes, as well as with the type of substrate, can be monitored by charging, external electric field, pressure, and also by a molecule anchored to the flake. The optimized energy profiles and energy barriers thereof have been calculated in translational and in large angle rotational dynamics. Owing to the weak interaction between the flakes and monolayers the energy barriers are particularly small for incommensurate systems and can renders nearly frictionless rotation and translation, which is crucial for nanoscale mechanics. Even if small for particular combined nanoflake + monolayer heterostructures, the energy band gaps exhibit variations with angular and linear displacements of nanoflakes. However, these band gaps undergo considerable reduction under pressure. With tunable dynamics, electronic structure, and low friction coefficients, individual or periodically repeating nanoflakes on a monolayer substrate constitute critical composite structures offering the design of novel detectors, nanomechanical, electromechanical, and electronic devices.

关键词： Solution chemistry   Metals   Pyrroles   Molecules   Ions  

摘要： To the best of our knowledge, the current study based on ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) is the first to explore the difference in the hydration behavior between Mn(II)- and Mg(II)-associated porphyrins (Mn(II)-POR and Mg(II)-POR) in aqueous solution. The simulation study highlights similar and dissimilar characteristics of the structural, dynamical, and thermodynamical properties of these closely related metals bound to porphyrins in aqueous solution. The structural analysis is based on radial and angular distribution functions, coordination number distributions, and angular-radial distributions. Both hydrated systems demonstrate similar pentacoordinated structures formed via the axial coordination of one water molecule to the metal ion in addition to the four nitrogen atoms of the porphyrin ring. However, in the case of Mn(II)-POR, the formation of a distorted square pyramidal geometry was observed. It was envisaged as a weak coordination of the water molecule to the Mn(II) atom and thus higher atomic fluctuation for all atoms in contrast to that for the hydrated Mg(II)-POR The dynamical data in terms of the mean residence times, velocity autocorrelation function, free energy, and other parameters revealed the difference in the metal binding effect because the Mn(II) atom was observed to inhibit H-bond formation more than the presence of Mg(II) atoms in the core of the porphyrin. The current study thus highlights the significant differences in the structural and dynamical properties of Mn(II)- and Mg(II)-associated porphyrin systems.

关键词： dual-ion batteries   graphite   ion solvation   liquid electrolyte   low-temperature batteries  

摘要： Improving the extremely low temperature operation of rechargeable batteries is vital to the operation of electronics in extreme environments, where systems capable of high-rate discharge are in short supply. Herein, we demonstrate the holistic design of dual-graphite batteries, which circumvent the sluggish ion-desolvation process found in typical lithium-ion batteries during discharge. These batteries were enabled by a novel electrolyte, which simultaneously provides high electrochemical stability and ionic conductivity at low temperature. The dual-graphite cells, when compared to industry-type graphite parallel to LiCoO2 full-cells demonstrated an 11 times increased capacity retention at -60 degrees C for a 10 C discharge rate, indicative of the superior kinetics of the "dual-ion" storage mechanism. These trends are further supported by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) measurements at reduced temperature. This work provides a new design strategy for extreme low-temperature batteries.

关键词： Monolayers  

摘要： In this paper, the mechanical behaviors of recently synthesized monolayer ternary transitional metal dichalogenides (TMDs) MoS2xTe2(1 - x) (0 < x < 1) under tensile loading are studied by classical molecular dynamics simulations. Particular attention is paid to the fundamental mechanical properties such as Young's modulus and fracture behaviors of monolayer MoS2xTe2(1 - x). Our results show that Young's modulus of monolayer MoS2xTe2(1 - x) remains almost unchanged when the stoichiometric coefficient x is in the range of 0-0.4 but increases apparently when x increases from 0.4 to 1. In terms of their fracture behaviors, the alloyed ternary TMDs are found to show a ductile fracture feature, which is distinctly different from the brittle fracture behavior observed in their pristine binary TMD counterparts. The ultimate strength of alloyed ternary TMDs is found to be much lower than that of the pristine binary TMDs, which is attributed to the unaccommodated deformation caused by the stress concentration between Te atoms and nearby S atoms. The influence of loading direction and temperature on the aforementioned mechanical properties is also examined. It is found that Young's modulus and the ultimate strength of monolayer MoS2xTe2(1 - x) generally decrease with increasing temperature due to the temperature-induced softening effect. In the biaxial tensile test, Young's modulus and ultimate strength are found to be isotropic. The aforementioned mechanical parameters of monolayer MoS2xTe2(1 - x) under biaxial loading are significantly smaller than those under uniaxial loading. The present work is expected to significantly expand the knowledge of the mechanics of ternary TMDs and facilitate their applications in bandgap engineering. Published under license by AIP Publishing.

关键词： 船舶   动力设备   噪声数据   远程监测  

摘要： 船舶动力设备作为船舶动力发生核心单元,其设备运行的稳定尤为重要。其中,动力设备运行过程中的噪声数据,可直接作为监测判定船舶动力设备故障与否的重要信息源。在对噪声源监测过程中发现,传统的动力设备噪声监测方法,对噪声数据源单频信号通道支持计算缺乏逻辑支撑,导致数据分析无法接入网络,完成远端的监测执行,不利于噪声数据的远端综合分析与大数据化的指挥调度。为此,提出船舶动力机械设备噪声数据远程监测方法。1)通过对现有噪声数据监测算法的数学建模,得到单频通道下的噪声信号频谱特征规律;2)根据单频噪声信道频谱规律计算得出单频信道的逻辑函数;3)引入EEDM单频噪声信道特征逻辑算法,对噪声单频信道逻辑进行优化计算,实现对远程执行协议逻辑的支持,完成动力设备噪声数据的远程检测;4)通过仿真实验证明提出方法的有效性。

关键词： 化学机械研抛   超声振动   流场   动力学仿真   空化效应   微射流   气含率   反应自由基  

摘要： 为研究保持环超声振动对抛光试件和抛光垫间流场性能的影响,利用COMSOL Multiphysics软件分别针对实体研抛盘和有孔抛光垫,对研抛区流体进行了有限元建模与仿真,分析了试件保持环超声振动的频率、振幅对研抛区流体的速度、压力及气含率分布的影响规律。仿真结果表明:超声振动会使流体的速度与压力剧烈变化,在保持环振子下方产生极强的微射流,而试件下方的流速变化较为平缓;随着超声频率或振幅的增加,流体内的最大速度、最大压力以及最大气含率线性增加。和实体研抛盘相比,使用打孔抛光垫后,抛光试件下方流体最大速度减小数十倍,变化更加平稳,而最大压力却增大了百余倍,试件底面处的最大气含率也有所增大,空化效应更加强烈,更有利于在抛光过程中生成化学反应自由基与提高材料去除率。

关键词： 机械臂   动力学模型   仿真分析  

摘要： 通过分析Brokk60机器人机械臂上各个铰链之间以及铰链与机械臂之间的位置关系,建立公共坐标系和机械臂上的连体坐标系,推导出机械臂的雅可比矩阵。对各个铰链之间的受力关系进行分析研究,结合液压缸活塞上力平衡方程,以笛卡尔坐标系为基础建立该机器人的动力学模型。同时还利用ADAMS软件对机械臂在匀速和变加速两种状况下的运动进行仿真分析,得出机械臂各关节铰的受力、力矩以及各质心加速度情况,并以此绘制出曲线图。