关键词： 人工心脏瓣膜-患者不匹配   心脏瓣膜   心瓣膜置换术   血流动力学  

摘要： 目的探讨应用不同品牌19 mm机械瓣行单纯主动脉瓣置换术后早期血流动力学变化情况。方法回顾性分析2007年1月至2012年1月北京安贞医院116例单纯主动脉瓣狭窄患者行主动脉瓣置换术后血流动力学变化,其中男61例、女55例,年龄(52±13)岁。根据使用的瓣膜品牌将患者分为3组:***瓣膜组,38例(33%),男20例、女18例,平均年龄(52±15)岁;Carbomedics瓣膜组,40例(34%),男21例、女19例,平均年龄(51±17)岁。On-X瓣膜组,38例(33%),男20例、女18例,平均年龄(55±16)岁。比较患者术前和术后左心室收缩期末内径、左心室舒张期末内径、射血分数(EF)值、室间隔厚度、左心室壁厚度、主动脉瓣瓣上流速、跨瓣压差以及术后有效瓣口面积指数(EOAI)。结果三组患者术前及术后的左心室收缩期末内径、左心室舒张期末内径、EF值、室间隔厚度、左心室壁厚度差异均无统计学意义(P>0.05)。主动脉瓣瓣上流速和跨瓣压差术前、术后有差异有统计学意义。***瓣膜组和Carbomedics瓣膜组患者较On-X瓣膜组患者的术后主动脉瓣瓣上流速[(244.30±33.67)cm/s vs.(249.69±79.13)cm/s vs.(294.83±52.05)cm/s]和跨瓣压差[(27.77±3.33)mm Hg vs.(33.58±18.90)mm Hg vs.(38.56±13.21)mm Hg]明显偏小,其差异有统计学意义。结论运用19 mm机械瓣进行主动脉瓣置换术,***和Carbomedics瓣膜较On-X瓣膜有更好的血流动力学效果。

关键词： Micro-mechanics   Apple   Enzyme degradation   Kinetics   Diffusion  

摘要： The enzymatic texture loss during apple maceration was studied by two micro-mechanical techniques. The first technique consisted of a 5% strain compression cycles at a strain rate of 4.5 x 10(-4) s(-1). The second technique consisted on micro-puncture of the apple parenchyma with a small needle. The first technique led to the peripheral tissues degradation modelling with a first order kinetic reaction or a more pertinent Weibull function. The second technique evidenced that the jagged part of the load vs penetration curve corresponded to an interaction between the needle tip and the turgescent apple texture and the fractal dimension of this jagged part was chosen as the texture parameter. Modelling the enzyme diffusion phenomenon with the second Fick's law and taking into account the model previously established on peripheral tissues allowed the estimation of an equivalent enzyme diffusivity through the apple parenchyma varying between 3.5 x 10(-11) and 5.5 x 10(-11) m(2) s(-1). (c) 2013 Published by Elsevier Ltd.

关键词： mechanical properties   molecular dynamics   nanowires   SiGe   vibrational properties  

摘要： In this work, we examine the vibrational and mechanical properties of clamped-clamped rectangular SixGe1-x and Si/SixGe1-x nanowires (NWs) using molecular dynamics simulations. A virtual atomic force microscope nanotip is used to drive the vibration. The frequency response, the beat vibration phenomenon and the calculation of mechanical properties such as quality factor Q and Young's modulus E are thoroughly analyzed. The influence of added mass and hydrogen passivation on the NW resonator performance is also demonstrated. The decreasing frequency trend with increasing Ge concentration was different for binary alloys and alloy superlattices, while it remained unaffected by the superlattice period. The beat vibration phenomenon driven by a single excitation was observed at elevated temperatures for all studied configurations. The resonance frequency decreases linearly with increasing temperature whereas the Q-factor follows a power law decrease. The Young's modulus E obtained through stress-strain computational experiments is found to be overestimated compared to the classical beam theory. Frequency decreases linearly as more atoms are added to the resonator. For low temperatures, the quality factor of composite Si/Ge resonators increased from 10(4) to 10(5) at T=23K, after performing hydrogen passivation on the NW free surfaces. The frequency shift due to the change in stoichiometry in a Si NW, alongside with representative snapshots of the vibrational behavior.

关键词： POLYAMIDES   NANOCOMPOSITE materials   RESEARCH   TITANIUM dioxide   POLYMERIC nanocomposites   NANOPARTICLE research   DIFFERENTIAL scanning calorimetry   NUCLEATION   CRYSTALLIZATION  

摘要： Titanium dioxide (TiO2) nanoparticles were pretreated with excessive toluene-2,4-diisocyanate (TDI) to synthesize TDI-functionalized TiO2 (TiO2-NCO), and then polymeric nanocomposites consisting of polyamide 6 (PA6) and functionalized-TiO2 nanoparticles were prepared via a melt compounding method. The interfacial interaction between TiO2 nanoparticles and polymeric matrix has been greatly improved due to the isocyanate (NCO) groups at the surface of the functionalized-TiO2 nanoparticles reacted with amino groups (NH2) or carboxyl (COOH) groups of PA6 during the melt compounding and resulted in higher tensile and impact strength than that of pure PA6. The nonisothermal crystallization kinetics of PA6/functionalized TiO2 nanocomposites was investigated by differential scanning calorimetry (DSC). The nonisothermal crystallization DSC data were analyzed by the modified-Avrami (Jeziorny) methods. The results showed that the functionalized-TiO2 nanoparticles in the PA6 matrix acted as effective nucleation agents. The crystallization rate of the nanocomposites obtained was faster than that of the pure PA6. Thus, the presence of functionalized-TiO2 nanoparticles influenced the mechanism of nucleation and accelerated the growth of PA6 crystallites. POLYM. COMPOS., 35:294-300, 2014. (c) 2013 Society of Plastics Engineers

关键词： Polyoxymethylene   recycled carbon fibre   composites   reinforcement   mechanical properties   crystallization kinetics  

摘要： Recycled carbon fibre was employed as a reinforcing material to prepare polyoxymethylene?based composites through a simple melting extrusion. An effective approach was developed to clean and modify the surface of as-received recycled carbon fibre with nitric acid and then with a silane-coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for polyoxymethylene/recycled carbon fibre composites due to the improved interfacial adhesion between fibres and the matrix. The thermal stabilities of the composites were also improved in the presence of recycled carbon fibre. The morphological observation of impact fracture surfaces indicated a good interfacial boding between fibres and matrix. The studies on nonisothermal and isothermal crystallization behaviors showed that recycled carbon fibre acted as a nucleation agent for the crystallization of polyoxymethylene domain in composites; therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of recycled carbon fibre. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of polyoxymethylene?based composites. Derived from a combination of polyoxymethylene and recycled carbon fibre, this study may provide a development guide for sustainable engineering materials with a great potential as well as a low cost for industrial and civil applications.

关键词： Spatial ecology   Patchy landscape   Model reduction   Reaction-diffusion equation   Patch model  

摘要： Reaction-diffusion models for the dynamics of a biological population in a fragmented landscape can incorporate detailed descriptions of movement and behavior, but are difficult to analyze and hard to parameterize. Patch models, on the other hand, are fairly easy to analyze and can be parameterized reasonably well, but miss many details of the movement process within and between patches. We develop a framework to scale up from a reaction-diffusion process to a patch model and, in particular, to determine movement rates between patches based on behavioral rules for individuals. Our approach is based on the mean occupancy time, the mean time that an individuals spends in a certain area of the landscape before it exits that area or dies. We illustrate our approach using several different landscape configurations. We demonstrate that the resulting patch model most closely captures persistence conditions and steady state densities as compared with the reaction-diffusion model.

关键词： Nanocomposites   Plant polymer   Flammability   Thermal stability   Activation energy  

摘要： Melamine formaldehyde-furfuryl alcohol copolymer was impregnated into softwood in combination with 1,3-dimethylol-4,5-dihydroxy ethyleneurea, a crosslinking agent, nanoclay, and a renewable polymer, collected as gum from a local plant (Moringa oleifera) under vacuum condition and polymerized by catalyst heat treatment. Fourier-transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy were used to characterize the nanocomposites. Transmission electron microscopy showed uniform distribution of nanoclay in the composites. The mechanical properties were improved after the addition of plant polymer. The plant polymer had a marked influence on the flammability and thermal stability of the prepared composites. The apparent activation energy was determined by Ozawa-Flynn-Wall's and Vyazovkin methods. The activation energy of the composites decreased up to a certain decomposed fraction thereafter it remained constant. Higher the plant polymer content higher was the activation energy of the prepared composites which indicated a better interfacial adhesion and thermal stability.

关键词： Lignocellulosic wastes   particleboards   properties   residues   Tetra Pak   tropical species  

摘要： Lignocellulosic wastes resulting from agricultural activities as well as Tetra Pak residues from urban centres can cause significant levels of pollution. A possible action to minimize this problem is to use them in the production of particleboards. The purpose of this study was to evaluate the physical, mechanical, and hydration properties of particleboards manufactured with the mixture of woody biomass (Cupressus lusitanica, Gmelina arborea, and Tectona grandis) and either agricultural wastes [pineapple leaves (Ananas comosus) and palm residues (Elaeis guineensis)] or Tetra Pak residues (TP). The results show that the particleboards prepared with TP and woody biomass can reduce the swelling and water absorption in up to 40% and 50% compared with particleboards without TP. Also, these particleboards had increased flexure resistance and shear stress (up to 100%) compared with those without TP. On the contrary, particleboards prepared with pineapple leaves in combination with woody biomass showed the lowest mechanical properties, particularly for tensile strength, hardness, glue-line shear, and nail and screw evaluation.

关键词： Nano-wire   Molecular dynamics simulation   Mechanical properties   Size effect   Tensile test   Surface effect  

摘要： In this study we have used atomistic simulations to investigate the role of surface on the size-dependent mechanical properties of nano-wires. In particular, we have performed computational investigation on single crystal face-centered cubic copper nano-wires with diameters ranging from 2 to 20 nm. The wire axis for all the nano-wires are considered along the [001] direction. Characterization of the initial optimized structures revealed clear differences in interatomic spacing, stress, and potential energy in all the nano-wires. The mechanical properties with respect to wire diameter are evaluated by applying tension along the [001] direction until yielding. We have discussed the stress-strain relationships, Young's modulus, and the variation in potential energy from surface to the center of the wire for all the cases. Our results indicate that the mechanical response (including yield strain, Young's modulus, and resilience) is directly related to the proportion of surface to bulk type atoms present in each nano-wire. Thus the sizedependent mechanical properties of single crystal copper nano-wire within elastic region are attributed to the surface to volume ratio (surface effect). Using the calculated response, we have formulated a mathematical relationship, which predicts the nonlinear correlation between the mechanical properties and the diameter of the wire. (C) 2013 Elsevier B.V. All rights reserved.

关键词： CRYSTALLIZATION -- Kinetics   BLOCK copolymers   TEMPERATURE effect   SEPARATION (Technology)   CRYSTAL growth   MATERIALS -- Mechanical properties  

摘要： Two olefinic blocky copolymers (OBCs) were quenched from different mixing states in the melt, and crystallization kinetics and morphology at various crystallization temperatures (T(c)s) and corresponding mechanical properties were studied. It is observed that, at lower T(c)s, premesophase separation in the melt accelerates crystallization of OBC-A with a weak segregation strength and a larger fraction of the crystalline hard blocks due to enrichment of the hard blocks in the hard-block-rich domains. By contrast, premesophase separation retards crystallization of OBC-B with a stronger segregation strength and lower fraction of the hard blocks because of the prevailing confinement effect at lower T(c)s. Moreover, since the hard blocks dissolved in the soft-block-rich domains can crystallize at lower T(c)s, which can bridge the crystals formed in different hard-block-rich domains, the crystal growth is not restricted. At higher T(c)s, OBC-A crystallizes more slowly from the premesophase-separated melt than that from the homogeneous melt, which is attributed to the weaker crystallizability of the hard blocks dissolved in the soft-block-rich domains and thus the restricted crystal growth. Nevertheless, mesophase separation always takes place prior to crystallization at higher T(c)s for OBC-B because of the faster rate of mesophase separation. Therefore, the mixing state in the melt has little effect on crystallization and morphology of OBC-B at higher T(c)s. It is found that the mechanical properties of OBCs can be regulated in a wide range by alteration of crystallization conditions. Better mechanical properties can be achieved when OBCs crystallize from the homogeneous melt and at a lower T-c.