关键词： 正压呼吸   通气机,机械   血流动力学  

摘要： 目的探讨呼气末正压(PEEP)对低血容量趋势患者行机械通气时血流动力学的影响。方法选择20例伴有低血容量趋势需行机械通气的患者作为研究对象。所有患者均在基础呼吸模式上分别加用PEEP 0、5、10、15 cmH2O,每次持续约30 min。记录所有患者的心率、平均动脉压(MAP)、肺动脉嵌压(PAWP)、每搏指数(SVI)、心排血量(CO)、心指数及体循环血管阻力指数(SVRI)等血流动力学指标,中心静脉压(CVP)、髂总静脉压(CIVP)及ΔCVP等静脉回流梯度指标,吸气峰压(PIP)、气道阻力(RAW)、用吸气暂停键测出平台压(Pplat)、气道平均压力(Pmean)及肺循环血管阻力指数(PVRI)等呼吸力学指标。结果随着PEEP水平的增加,患者心率、PAWP及SVRI均显著增加,而MAP、CO、心指数及SVI则逐渐下降(F=20.311、15.100、32.915、15.100、198.635、435.100、17.000,P均<0.001),且CO于PEEP为5 cmH2O时与PEEP为0 cmH2O时比较,已经出现显著降低[(5.31±0.11)L/min vs.(5.46±0.24)L/min];患者的CVP、CIVP的水平逐渐升高,而ΔCVP逐渐下降(F=47.879、27.578、21.393,P均<0.001);患者的PIP、Pplat、Pmean、PVRI水平均逐渐升高,且PEEP为15 cmH2O时达最高(F=67.152、74.025、818.208、31.141,P均<0.001),而RAW在不同PEEP间比较差异无统计学意义(F=2.082,P=0.131)。结论对有低容量趋势行机械通气的患者,当PEEP≥5 cmH2O即出现CO明显下降,因此对于有低容量趋势患者尽量使用最小PEEP来达到治疗目的。

关键词： 铁路   机械动力设备   维修  

摘要： 介绍了上海机车检修段的设备与车间现状,从四方面分析了实施铁路机械动力设备委外修的原因:新设备新技术自主维修难度大,维修人员与任务量之间矛盾突出,专业技术人才数量少、素质不高,控制设备维修成本。介绍了实施委外修的具体方案与成效,并进行了生产成本对比。最后给出了铁路机械动力设备实施委外修在各阶段的相关建议。

关键词： Mitochondrial fusion   Mitochondria] fission   Mitophagy   MFN2   OPA1   YME1L1   MSTO1   FBXL4   DNM1L   MFF   PINK1   PRKN  

摘要： Mitochondria are dynamic organelles that undergo fusion, fission, movement, and mitophagy. These processes are essential to maintain the normal mitochondrial morphology, distribution, and function. Mitochondrial fusion allows the exchange of intramitochondrial material, whereas the fission process is required to replicate the mitochondria during cell division, facilitate the transport and distribution of mitochondria, and allow the isolation of damaged organelles. Mitochondrial mobility is essential for mitochondrial distribution depending on the cellular metabolic demands. Mitophagy is needed for the elimination of dysfunctional and damaged mitochondria to maintain a healthy mitochondria] population. The mitochondrial dynamic processes are mediated by a number of nuclear-encoded proteins that function in mitochondrial transport, fusion, fission, and mitophagy. Disorders of mitochondrial dynamics are caused by pathogenic variants in the genes encoding these proteins. These diseases have a high clinical variability, and range in severity from isolated optic atrophy to lethal encephalopathy. These disorders include defects in mitochondrial fusion (caused by pathogenic variants in MFN2, OPA1, YME1L1, MSTO1, and FBXL4), mitochondrial fission (caused by pathogenic variants in DNM1L and MFF), and mitochondrial autophagy (caused by pathogenic variants in PINK1 and PRKN). In this review, the molecular machinery and biological roles of mitochondrial dynamic processes are discussed. Subsequently, the currently known diseases related to mitochondrial dynamic defects are presented.

关键词： Redox dynamics   Model   Glutathione   Cysteine   Embryo   Organogenesis  

摘要： Precise control of the glutathione/glutathione disulfide (GSH/GSSG) redox balance is vital for the developing embryo, but regulatory mechanisms are poorly understood. We developed a novel, mechanistic mass-balance model for GSH metabolism in the organogenesis stage (gestational day 10.0-11.13) rat conceptus predicting the dynamics of 8 unique metabolites in 3 conceptal compartments: the visceral yolk sac (VYS), the extra-embryonic fluid (EEF) and the embryo proper (EMB). Our results show that thiol concentrations in all compartments are well predicted by the model. Protein synthesis is predicted to be a major efflux pathway for all amino acid precursors of GSH synthesis and an essential model element. Our model provides quantitative insights in the transport fluxes and enzymatic fluxes needed to maintain thiol redox balances under normal physiological conditions. This is crucial to further elucidate the mechanisms through which chemical exposure can perturb redox homeostasis, causing oxidative stress, and potentially birth defects.

关键词： deformation   ductility   elastic constants   first principles theory   fracture mechanics/toughness  

摘要： In this study, first-principles calculations were performed to study the stability, mechanical property, electronic structure and lattice dynamics of beta-Si-3(C-x,N1-x)(4) silicon carbonitride. The solubility of carbon in beta-Si-3(C-x,N1-x)(4) having a stable structure is shown to be about 15 at.%. Within the limit of solubility, an increase in carbon concentration in beta-Si-3(C-x,N1-x)(4) will lead to a decrease in the Young's modulus and density and an increase in the Poisson's ratio. The study of deformation behavior shows that the most likely slip system of {1100} [0001] is on prismatic plane rather than on basal plane. This feature of beta-Si-3(C-x,N1-x)(4) is similar to WC. In addition, the ductility and fracture toughness of beta-Si-3(C-x,N1-x)(4) can be optimized by controlling the carbon concentration. The improvement in ductility and fracture toughness can be attributed to the formation of metallic bonds by the incorporation of carbon atoms. The lattice dynamics study shows that the structural stability of beta-Si-3(C-x,N1-x)(4) is controlled by energy stability criteria under stress-free condition. In the stressed state, the structural stability of beta-Si-3(C-x,N1-x)(4) is controlled by the elastic stability criteria. Subsequently, the beta-Si-3(C-x,N1-x)(4) solid solution was prepared by self-propagating high-temperature synthesis (SHS), and the carbon-concentration-dependent mechanical properties were consistent with the first-principles calculations. The maximum fracture toughness of 10.4 MPa.m(0.5) was obtained in beta-Si-3(C-x,N1-x)(4) at carbon concentration of 5 wt%, which means that the solid solution toughening can be used as a supplement to crack bridging toughening and phase transition toughening for ceramic toughening. The results obtained in this study reveal that the beta-Si-3(C-x,N1-x)(4) solid solution is a promising candidate for high-speed ceramic bearings.

关键词： Free energy   QM/MM   Ions   Chemical calculations   Hydration  

摘要： A recently proposed thermodynamic integration (TI) approach formulated in the framework of quantum mechanical/molecular mechanical molecular dynamics (QM/MM MD) simulations is applied to study the structure, dynamics, and absolute intrinsic hydration free energy Delta(s) G degrees(M+,wat) of the Li+ ion at a correlated ab initio level of theory. Based on the results, standard values (298.15 K, ideal gas at 1 bar, ideal solute at 1 molal) for the absolute intrinsic hydration free energy G degrees(H+,wat), of the proton, the surface electric potential jump chi degrees(wat) upon entering bulk water, and the absolute single-electrode potential V degrees(H+,wat) of the reference hydrogen electrode are calculated to be -1099.9 +/- 4.2 ***(-1), 0.13 +/- 0.08 V, and 4.28 +/- 0.04 V, respectively, in excellent agreement with the standard values recommended by HUnenberger and Reif on the basis of an extensive evaluation of the available experimental data (-1100 +/- 5 ***(-1), 0.13 +/- 0.10 V, and 4.28 +/- 0.13 V). The simulation results for Li+ are also compared to those for Na+ and K+ from a previous study in terms of relative hydration free energies Delta Delta(s) G degrees(M+,wat) and relative electrode potentials Delta V degrees(M+,wat). The calculated values are found to agree extremely well with the experimental differences in standard conventional hydration free energies Delta Delta(s)G(M+,wat)(center dot) and redox potentials Delta Delta(H) V degrees(M+,wat). The level of agreement between simulation and experiment, which is quantitative within error bars, underlines the substantial accuracy improvement achieved by applying a highly demanding QM/MM approach at the resolution-of -identity second -order Moller-Plesset perturbation (RIMP2) level over calculations relying on purely molecular mechanical or density functional theory (DFT) descriptions. A detailed analysis of the structural and dynamical properties of the Li+ hydrate indicates that a correct descriptio

关键词： DNB/DNB center dot- and DNB/DNB2- model systems   antioxidants   kinetics and mechanism for interactions   cyclic voltammetry   PM3 calculations  

摘要： Here we are presenting complete electrochemical studies on redox activities of 1,2-dinitrobenzene (DNB) in the presence of antioxidants-quercetin, morin, rutin, ascorbic acid and beta-carotene. Bimolecular rate constants (k(2)), antioxidant activities (K-a) and diffusion coefficients (D-o) were evaluated from changes in voltammeric responses and electrochemical parameters in the presence of antioxidant's concentrations. Theoretical charge calculations by PM3 parameterization were done which further justified our experimental electrochemical work and proposed scavenging mechanism. Present findings were also compared in details with our previously reported studies on 1,3- and 1,4-dinitrobenzene systems for their interactions with antioxidants.

关键词： in situ liquid cell TEM   dynamics of self-assembly   cluster growth   Brownian force   van der Waals force   hydrodynamic drag force   and steric hindrance force  

摘要： Superlattice structures formed by nanoparticle (NP) self-assembly have attracted increasing attention due to their potential as a class of nanomaterials with enhanced physicochemical properties tailored by the assembly structure. However, many key questions remain regarding the correlation between the dynamics of individual NPs and emerging superlattice patterns. Here we investigated the self-assembly of gold NPs by employing in situ transmission electron microscopy equipped with direct detection camera capabilities, which enabled us to track the rapid motion of individual nanoparticles in real time. By calculating the contributions of Brownian, van der Waals, hydrodynamic, and steric hindrance forces, we obtained a quantitative evaluation of the competitive interactions that drive the assembly process. Such competition between forces over various separations is critical for the kinetics of cluster growth, leading to the superlattice formation. Brownian motion resulted in the formation of small-sized clusters, whose growth dynamics was characterized as reaction-limited aggregation. Subsequently, at relative short-range particle separations, van der Waals force overrode the Brownian force and dominantly drove the assembly process. When the particles were in close proximity, a delicate balance between van der Waals and steric hindrance forces led to an unexpected dynamic nature of the assembled superlattice. Our study provides a fundamental understanding of coupling energetics and dynamics of NPs involved in the assembly process, enabling the control and design of the structure of nanoparticle superlattices.

关键词： Density functional theory (DFT)   Molecular dynamics (MD)   Single-walled carbon nanotube (SWCNT)   Boron-nitride nanotube (BNNT)   Mechanical properties  

摘要： This study investigates the effect of encapsulating a golden fullerene (Au-32) cluster on the mechanical properties of a single-walled carbon nanotube (SWCNT) and a boron-nitride nanotube (BNNT). First, the geometrical parameters of the nanopeapods were optimized using the density functional theory (DFT) method. The DFT results demonstrated that the strength of interaction between the Au-32 cage and a BNNT was stronger than that between the Au-32 cage and SWCNT. The molecular dynamics (MD) method was then applied to calculate mechanical properties such as Young's modulus, failure stress, and failure strain using a stress-strain plot. The mechanical results indicated that encapsulating the Au-32 cluster reduced the Young's modulus and failure stress of both a SWCNT and BNNT, whereas the failure strain did not observably change. To validate these results, a C-60 cage was inserted inside an SWCNT in the most exothermic situation. The MD calculation indicated that, similar to the effect of Au-32 in the Au-32-nanotube peapod, C-60 reduced the mechanical properties of the SWCNT. (C) 2018 American Society of Civil Engineers.

关键词： Cardiovascular disease   Computer simulation   Mock circulation loop   Lumped parameter   Mechanical circulatory support   Pumps, heart-assist  

摘要： The Virtual Mock Loop, a versatile virtual mock circulation loop, was developed using a lumped-parameter model of the mechanically assisted human circulatory system. Inputs allow specification of a variety of continuous-flow pumps (left, right, or biventricular assist devices) and a total artificial heart that can self-regulate between left and right pump outputs. Hemodynamic inputs were simplified using a disease-based input panel, allowing selection of a combination of cardiovascular disease states, including systolic and diastolic heart failure, stenosis, and/or regurgitation in each of the four valves, and high to low systemic and pulmonary vascular resistance values. The menu-driven output includes a summary of hemodynamic parameters and graphical output of selected flows, pressures, and volumes in the heart's four chambers as well as in the pulmonary artery and aorta. New tools to augment experimental research on implantable heart-assist devices and to increase our understanding of patient-specific pump interactions are in high demand. The purpose of this ongoing study is to demonstrate the use of a system analysis computer simulation to explore and better comprehend the interactions of mechanical circulatory support pumps with a more extensive combination of patient-specific or simulation conditions than can be established by practical experimentation. Usability is an important factor in constructing computer models for research purposes, and among our primary objectives in creating this simulation model were to make it as portable and useful as possible outside the lab environment, by people not involved in the creation of its operational software.