关键词： Railway vehicle   mechanical brake   hardware-in-the-loop simulation   hysteresis   pneumatic cylinder dynamics   wheel-slide protection  

摘要： A brake hardware-in-the-loop simulation system for a railway vehicle provides an effective platform for testing the braking performance under various dangerous braking conditions. However, in general, four-brake calipers are required to implement a mechanical brake system for one car. In this article, we implement a brake hardware-in-the-loop simulation system only with one brake caliper and three air tanks accounting for hysteresis and pneumatic cylinder dynamics, ultimately saving installation space and reducing financial budget costs. Since the brake caliper has a high nonlinearity, such as hysteresis resulting from friction and from the precompressed spring of the brake cylinder, we measured the hysteresis of the brake caliper clamping force for a mechanical brake system using loadcells, based on which a mathematical model was constructed for the hysteresis of the clamping force between the brake pad and the disk. Moreover, the pneumatic cylinder dynamics are identified and are implemented in three air tanks, together with hysteresis nonlinearity. The proposed brake hardware-in-the-loop simulation system is applied to the wheel-slide protection simulation of a railway vehicle with an initial speed of 80km/h and demonstrated experimentally accounting for the hysteresis and brake cylinder dynamics.

关键词： DGEBA/TETA (DETDA)   Epoxy resins   Glass transition temperature   Mechanical properties   Molecular dynamics simulation  

摘要： Molecular dynamics (MD) simulations were carried out to predict the thermal and mechanical properties of the cross-linked epoxy system composed of DGEBA resin and the curing agent TETA. To investigate the effects of curing agents, a comprehensive and comparative study was also performed on the thermal and mechanical properties of DGEBA/TETA and DGEBA/DETDA epoxy systems such as density, glass transition temperature (T-g), coefficient of thermal expansion (CTE) and elastic properties of different cross-linking densities and different temperatures. The results indicated that the glass transition temperature of DGEBA/TETA system calculated through density-temperature data, similar to 385-395 degrees K, for the epoxy system with the cross-linking density of 62.5% has a better agreement with the experimental value (T-g, similar to 400 degrees K) in comparison to the value calculated through the variation of cell volume in terms of temperature, 430-440 K. They also indicated that CTE related parameters and elastic properties including Young, Bulk, and shear's moduli, and Poisson's ratio have a relative agreement with the experimental results. Comparison between the thermal and mechanical properties of epoxy systems of DGEBA/TETA and DGEBA/DETDA showed that the DGEBA/DETDA has a higher T-g in all cross linking densities than that of DGEBA/TETA, while higher mechanical properties was observed in the case of DGEBA/TETA in almost all cross linking densities. (C) 2015 Elsevier Inc. All rights reserved.

关键词： Molecular simulation   C-S-H   Uniaxial tension test   Ca/Si ratio  

摘要： Calcium silicate hydrate (C-S-H) gels, the main binding phase of cement paste, determine the mechanical properties of cementitious materials. In order to obtain the cohesive force in C-S-H gel, molecular dynamics was carried out to simulate the uniaxial tension test on C-S-H model along x, y and z direction. Due to the structure and dynamic differences of the layered structure, C-S-H model demonstrates heterogeneous mechanical behavior. The calcium silicate layer, constructed by Ca-O and Si-O ionic-covalent bonds, has stronger cohesive force than that of interlayer H-bond network. In addition, composition influence on mechanical performance has been investigated by variation of the Ca/Si ratio. High calcium content, de-polymerizing the silicate chain structure in C-S-H gel, weakens uniaxial tension strength and elastic modulus in three directions. More water molecules penetration into the defective silicate region further reduces the mechanical properties of C-S-H gel at high Ca/Si ratio. Composition analysis at nano-scale can provide molecular insights on the cementitious materials design with different Ca/Si ratios.

关键词： Micellar hydrogel   Aliphatic hydroxy acid chain extension   Cell encapsulation   Gelation   Degradation   Elasticity  

摘要： Due to their high water content and diffusivity of nutrients and biomolecules, hydrogels are very attractive as a matrix for growth factor immobilization and in situ delivery of cells to the site of regeneration in tissue engineering. The formation of micellar structures at the nanoscale in hydrogels alters the spatial distribution of the reactive groups and affects the rate and extent of crosslinking and mechanical properties of the hydrogel. Further, the degradation rate of a hydrogel is strongly affected by the proximity of water molecules to the hydrolytically degradable segments at the nanoscale. The objective of this review is to summarize the unique properties of micellar hydrogels with a focus on our previous work on star polyethylene glycol (PEG) macromonomers chain extended with short aliphatic hydroxy acid (HA) segments (SPEXA hydrogels). Micellar SPEXA hydrogels have faster gelation rates and higher compressive moduli compared to their non-micellar counterpart. Owing to their micellar structure, SPEXA hydrogels have a wide range of degradation rates from a few days to many months as opposed to non-degradable PEG gels while both gels possess similar water contents. Furthermore, the viability and differentiation of mesenchymal stem cells (MSCs) is enhanced when the cells are encapsulated in degradable micellar SPEXA gels compared with those cells encapsulated in non-micellar PEG gels. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Bent optical fibre   CLSM   confocal fluorescence microscope   elastic moduli   flat-ended tip   mitochondria   mitochondrial activity  

摘要： The cells in the cardiovascular system are constantly subjected to mechanical forces created by blood flow and the beating heart. The effect of forces on cells has been extensively investigated, but their effect on cellular organelles such as mitochondria remains unclear. We examined the impact of nano-Newton forces on mitochondria using a bent optical fibre (BOF) with a flat-ended tip (diameter exceeding 2 m) and a confocal fluorescence microscope. By indenting a single mitochondrion with the BOF tip, we found that the mitochondrial elastic modulus was proportional to the (-1/2) power of the mitochondrial radius in the 9.6-115 kPa range. We stained the mitochondria with a potential-metric dye (TMRE) and measured the changes in TMRE fluorescence intensity. We confirmed that more active mitochondria exhibit a higher frequency of repetitive transient depolarization. The same trend was observed at forces lower than 50 nN. We further showed that the depolarization frequency of mitochondria decreases under an extremely large force (nearly 100 nN). We conclude that mitochondrial function is affected by physical environmental factors, such as external forces at the nano-Newton level. Lay Description The cells in the heart system are constantly influenced by mechanical forces created by blood flow and the beating heart. The effect of forces on cells has been extensively studied, but their effect on cellular organelles such as mitochondria remains unknown. Mitochondrial function is recognized as important for health, disease, and aging in human or animal cells. Therefore, we examined the impact of nano-Newton forces on mitochondria using a bent optical fibre (BOF) with a flat-ended tip (diameter exceeding 2 m) and a confocal laser scanning microscope. In this method, the flat-ended tip of BOF is utilized to apply forces on a single isolated mitochondrion. Simultaneously, to observe the physiological changes in mitochondria depending on mechanical forces, a membrane potential

关键词： ARTERIAL stenosis   AORTIC valve diseases   HEMODYNAMICS   BIOMECHANICS   OUTCOME assessment (Medical care)   LONGITUDINAL method   FOLLOW-up studies (Medicine)  

摘要： ObjectiveThe aim of the present study is to report the early and mid-term clinical and hemodynamic results of a prospective trial investigating the clinical performance of the St. Jude Medical Regent 17mm (SJMR-17) versus St. Jude Medical Hemodynamic Plus 17mm (SJMHP-17). Materials and MethodsBetween January 2000 and August 2013, 20 patients (Group I) with aortic valve (AV) stenosis underwent first time AV replacement with a SJMR-17 and nine patients (Group II) underwent AV replacement with a SJMHP-17. The mean follow-up was 5831 months. ResultsThere was one death in Group I. The end-diastolic IVS thickness and end-systolic posterior left ventricle (LV) wall thickness was reduced significantly in boths groups (p=0.001 and p=0.006 in Group I and p=0.007 and p=0.011 in Group II). The peak and mean transprosthesis gradients (P-TPG and M-TPG) were 29 +/- 6.8mmHg and 17.5 +/- 4.5mmHg in Group I, significantly lower than in Group II (55.2 +/- 19.7mmHg and 28.8 +/- 7.7mmHg). The postoperative left ventricular mass (LVM) and indexed left ventricular mass (LVMi) were reduced significantly in both groups versus the preoperative values. The postoperative LVMi was 114.5 +/- 10.6g/m(2) in Group I versus 127 +/- 8g/m(2) in Group II (p=0.01). With dobutamine, heart rate, left ventricular ejection fraction, cardiac output, transprosthesis peak, and mean gradients increased significantly in both groups, however, the P-TPG and M-TPG were significantly higher in Group II (p=0.026 and p=0.022) despite a non-significant increase of the indexed effective orifice area. ConclusionsThe SJMR-17 can be employed with satisfactory postoperative clinical and hemodynamic outcomes in patients with small aortic annulus, especially in elderly patients offering better outcome than SJMHP-17.

关键词： Area per lipid   Bending modulus   Area compressibility modulus   Spontaneous curvature   Gaussian curvature modulus   CHARMM 36 force field  

摘要： Lipid areas (A(l)), bilayer area compressibilities (K-A), bilayer bending constants (K-C), and monolayer spontaneous curvatures (c(0)) from simulations using the CHARMM36 force field are reported for 12 representative homogenous lipid bilayers. A(l) (or their surrogate, the average deuterium order parameter in the "plateau region" of the chain) agree very well with experiment, as do the K-A. Simulated K-C are in near quantitative agreement with vesicle flicker experiments, but are somewhat larger than K-C from X-ray, pipette aspiration, and neutron spin echo for saturated lipids. Spontaneous curvatures of bilayer leaflets from the simulations are approximately 30% smaller than experimental values of monolayers in the inverse hexagonal phase. Published by Elsevier Ireland Ltd.

关键词： 动力机械   钢结构建筑物   振动位移  

摘要： 在钢结构建筑中,动力机械的合理设计,可以提高机械设备的运作效率。控制好动力机械设备的振动范围,可以减少对建筑物周围居民的影响,降低对邻近设备的干扰,对于提高钢结构建筑的建设具有重要的意义。文章通过分析了钢结构建筑的特点和钢结构建筑中的动力机械,深入的探析了钢结构建筑中动力机械设备的设计和动力机械在钢结构建筑物中的应用。

标准号: LY/T 2569-2015

摘要： 本标准规定了以汽油机为动力的由单人操作的手持式绿篱修剪机(以下简称绿篱修剪机)在设计和结构方面的安全技术要求和试验规程。 本标准给出了消除或减少使用绿篱修剪机所产生的各种危害的方法规定了由生产厂家提供的有关安全操作准则的资料要求。本标准给出了与正常使用绿篱修剪机相关的所有严重危害、危险情况和事件(见第4章)。 本标准适用于发动机排量在80 cm3以下的绿篱修剪机。