关键词： 风湿性心脏病   机械瓣   血流动力学  

摘要： 目的评价不同类型机械瓣对二尖瓣置换术后血流动力学的影响。方法本院行二尖瓣置换术96例,分为双叶瓣及倾斜碟瓣两组,比较手术前后及手术1年后两组间血流动力学的超声参数。结果两组术前二维超声参数:各房室内径及主、肺动脉内径、二尖瓣口面积差异均无统计学意义,血流动力学参数中E峰、A峰、平均跨瓣压差(mean pressure gradi-ent,MPG)、肺动脉收缩压差异均无统计学意义;术后10d内的二维超声参数比较:双叶瓣及倾斜碟瓣两组的E峰速分别为(1.43±0.70)m/s和(1.86±0.65)m/s(P<0.05),有效瓣口面积(effective orifice area,EOA)分别为(2.61±0.61)cm^2、(2.31±0.63)cm^2(P<0.05);肺动脉收缩压(pulmonary artery systolic pressure,PASP)分别为(33.9±14.2)mmHg和(32.8±9.4)mmHg(1mmHg=0.133 kPa,P>0.05);MPG分别为(4.76±2.8)mmHg和(5.2±3.7)mmHg(P>0.05)。手术1年后复查,双叶瓣及倾斜碟瓣两组的E峰速分别为(1.48±0.9)m/s和(1.92±0.4)m/s(P<0.05),EOA为(2.52±0.32)cm^2和(2.01±0.2)cm^2(P<0.05),PASP为(33.4±22.5)mmHg和(36.4±24.7)mmHg(P>0.05)。结论双叶机械瓣对风湿性心脏病二尖瓣置换术后血流动力学的影响强于倾斜碟瓣。

关键词： Heavy metal toxicology   Bioaccumulation   Ligands (Biochemistry)   Effect of water pollution on fishes   Effect of water pollution on aquatic organisms   Physiological effects of heavy metals   Heavy metal absorption & adsorption   Chemical affinity  

摘要： Both biotic ligand models (BLM) and bioaccumulation models aim to quantify metal exposure based on mechanistic knowledge, but key factors included in the description of metal uptake differ between the two approaches. Here, we present a quantitative comparison of both approaches and show that BLM and bioaccumulation kinetics can be merged into a common mechanistic framework for metal uptake in aquatic organisms. Our results show that metal-specific absorption efficiencies calculated from BLM-parameters for freshwater fish are highly comparable, i.e. within a factor of 2.4 for silver, cadmium, copper, and zinc, to bioaccumulation-absorption efficiencies for predominantly marine fish. Conditional affinity constants are significantly related to the metal-specific covalent index. Additionally, the affinity constants of calcium, cadmium, copper, sodium, and zinc are significantly comparable across aquatic species, including molluscs, daphnids, and fish. This suggests that affinity constants can be estimated from the covalent index, and constants can be extrapolated across species. A new model is proposed that integrates the combined effect of metal chemodynamics, as speciation, competition, and ligand affinity, and species characteristics, as size, on metal uptake by aquatic organisms. An important direction for further research is the quantitative comparison of the proposed model with acute toxicity values for organisms belonging to different size classes.

关键词： Mechanical stimulation   Inositol (1,4,5)-trisphosphate   Ca2+ response   FRET   Fluorescent biosensor   Spatial dynamics  

摘要： In the present study, the contribution of inositol (1,4,5)-trisphosphate [Ins(1,4,5)P-3] generation on the mechanical-stimulation-induced Ca2+ response was investigated in HSY-EA1 cells. Mechanical stimulation induced a local increase in the cytosolic concentration of Ins(1,4,5)P-3 ([IP3](i)), as indicated by the Ins(1,4,5)P-3 biosensor LIBRAvIII. The area of this increase expanded like an intracellular Ins(1,4,5)P-3 wave as [IP3](i) increased in the stimulated region. A small transient [IP3](i) increase was subsequently seen in neighboring cells. The phospholipase C inhibitor U-73122 abolished these Ins(1,4,5)P-3 responses and resultant Ca2+ releases. The purinergic receptor blocker suramin completely blocked increases in [IP3](i) and the Ca2+ release in neighboring cells, but failed to attenuate the responses in mechanically stimulated cells. These results indicate that generation of Ins(1,4,5)P-3 in response to mechanical stimulation is primarily independent of extracellular ATP. The speed of the mechanical-stimulation-induced [IP3](i) increase was much more rapid than that induced by a supramaximal concentration of ATP (1 mM). The contribution of the Ins(1,4,5)P-3-induced Ca2+ release was larger than that of Ca2+ entry in the Ca2+ response to mechanical stimulation in HSY-EA1 cells.

关键词： Maize   Mechanistic model   Potassium efficiency   Rhizosphere   Sugar beet   Wheat  

摘要： Plant species differ in nutrient uptake efficiency. With a pot experiment, we evaluated potassium (K) uptake efficiency of maize (Zea mays L.), wheat (Triticum aestivum L.), and sugar beet (Beta vulgaris L.) grown on a low-K soil. Sugar beet and wheat maintained higher shoot K concentrations, indicating higher K uptake efficiency. Wheat acquired more K because of a greater root length to shoot dry weight ratio. Sugar beet accumulated more shoot K as a result of a 3- to 4-fold higher K influx as compared to wheat and maize, respectively. Nutrient uptake model NST 3.0 closely predicted K influx when 250 mg K kg(-1) were added to the soil, but under-predicted K influx under low K supply. Sensitivity analysis showed that increasing soil solution K concentration (C-Li) by a factor of 1.6-3.5 or buffer power (b) 10- to 50-fold resulted in 100% prediction of K influx. When both maximum influx (I-max) and b were increased by a factor of 2.5 in maize and wheat and 25 in sugar beet, the model could predict measured K influx 100%. In general, the parameter changes affected mostly calculated K influx of root hairs, demonstrating their possible important role in plant K efficiency.

关键词： Partial derivative of matrix functions   Kronecker product   Lagrangian equations   Robot dynamics   Mechanism dynamics  

摘要： The partial derivatives of scalar functions, vector functions, and matrix functions with respect to a vector variable have many practical applications in the study of dynamics and control of mechanical systems. The paper firstly presents an overview of the matrix calculus related to Kronecker products. Secondly, two theorems establishing the relationship between the time derivative of a matrix and its partial derivative with respect to a vector, and the partial derivative of the product of two matrices with respect to a vector will be presented. Finally, a new matrix form of Lagrangian equations is developed to demonstrate the usefulness of these theorems in the study of dynamics of mechanical systems. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Soybean oil   Poly(3-hydroxyalkanoates)   Elastomer   Autoxidation  

摘要： Microbial bioelastomers prepared by the autoxidation of the unsaturated medium-long chain length co-poly-3-hydroxyalkanoate's (mlcl-PHAs) based on soybean oily acids (Sy) have been reported. Pseudomonas oleovorans were grown on a series of the mixture of octanoic acid (OA) and Sy with the weight ratio of 20:80, 28:72 and 50:50 in order to obtain unsaturated mlcl-copolyesters coded PHO-Sy-2080, PHO-Sy-2872, and PHO-Sy-5050, respectively. The microorganism was also grown on the mixture of Sy and 10-undecenoic acid (UA) with the weight ratio of 50:50 to obtain unsaturated copolyester coded PHU-Sy-5050. The PHAs obtained were characterized by (1)H NMR and GC-MS techniques. Double bond contents of the unsaturated PHAs obtained were varying between 0.8 to 20 mol %. Autoxidation of the unsaturated copolyesters were carried out on exposure to air at room temperature in order to obtain new biomaterials whose mechanical strength was improved. Autoxidation kinetics, shelf life, mechanical and thermal properties of these biomaterials were evaluated.

关键词： MOLECULAR dynamics   EPOXY resins   THERMOPHYSICAL properties   MATERIALS -- Mechanical properties   MOISTURE   ELECTRONIC packaging   CHEMICAL structure   CORRELATION (Statistics)  

摘要： This paper addresses the potential of molecular dynamics simulation for structure-property correlations in epoxy-resins. This is an important topic within a multi-scale framework to lifetime prediction in electronic packaging. For that purpose, epoxy-resins with small systematic variations in chemical structure have been synthesised and then characterised by various thermo-mechanical testing methods. It was found that moisture diffusion showed the greatest response with respect to material and loading parameters such as polarity, free volume, moisture concentration and temperature. Based on a parametric study, modeling approaches of various complexity have been able to show first qualitative but then also quantitative agreement. The paper comments further on the accuracy and limits of the method and correlates the calculations with experimental structural analysis results. (C) 2010 Published by Elsevier Ltd.

关键词： biocontrol   bioinsecticides   entomopathogenic nematodes   bioreactors   hydrodynamics   oxygen transfer conditions  

摘要： This study is the first to describe the evolution of both hydrodynamic and oxygen transfer conditions during the submerged culture of the entomopathogenic nematode Steinernema carpocapsae CABA01 (an indigenous strain isolated within the State of Hidalgo, Mexico), and its symbiotic bacterium, Xenorhabdus nematophila, using an internal-loop mechanically agitated bioreactor of 4.5 L of liquid volume. Concentrations up to 217,306 viable nematodes per mL, with 94% in infective juvenile (IJ) stage (i.e., 204,444 IJ/mL), were achieved in 16 days of bioprocess. The Reynolds number (Re) was used as an index of the actual hydrodynamic conditions, and it varied within the interval 5,150 < Re (dimensionless) < 9,440, involving apparent culture broth viscosity changes from 3 to 5.4 mPa s during the processing. The aeration efficiency was expressed on the basis of the volumetric oxygen transfer coefficient, k(L)a, which varied within the range 0.026 to 0.170 s(-1).

关键词： Mechanical systems   flow control   frequency ranges   flow simulation   Magnetoelectric generators   microactuators   Aerodynamics   Workstations   Activation   Synthetic jet   far-field   Enclosed cavity   design process   frequency response  

摘要： A magneto-mechanical micro-actuator providing an axisymmetric synthetic microjet for active flow control was designed, fabricated and characterized. The micro-actuator consists of an enclosed cavity with a small orifice in one face and a high flexible elastomeric (PDMS) membrane in the opposite one. The membrane vibration is achieved using a magnetic actuation chosen for its capacity for providing large out of plane displacements and forces necessary for the performances aimed for. The paper presents first numerical simulations of the flow performed during the design process in order to identify a general jet formation criterion and optimize the device's performances. The fabrication process of this micro-magneto-mechanical system (MMMS) is then briefly described. The full size of the device, including packaging and actuation, does not exceed 1 cm(3). The evaluation of the performances of the synthetic jet with 600 mu m orifice was performed. The results show that the optimum working point is in the frequency range 400-700 Hz which is in accordance with the frequency response of the magnet-membrane mechanical resonator. In this frequency range, the microjet reaches maximum speeds ranging from 25 m s(-1) to 55 m s(-1) for an electromagnetic power consumption of 500 mW. Finally the axial velocity transient and stream-wise behaviours in the near and far fields are reported and discussed.

关键词： MD simulation   Thermodynamics and mechanical properties   Cu-Pd alloys  

摘要： Molecular dynamics (MD) simulations have been performed to investigate the thermodynamic and mechanical properties of Cu-x% Pd (at%) random alloy, as well as those of the Cu3Pd and CuPd3 ordered alloys, in the temperature range from 200 K up to the melting point. The quantum Sutton-Chen (Q-SC) many-body interatomic potentials have been used to describe the energetics of the Cu and Pd pure metals, and a standard mixing rule has been employed to obtain the potential parameters for the mixed (alloy) states. We have computed the variation of the melting temperature with the concentration of Pd. Furthermore, the variation of the cohesive energy, the order parameter, the thermal expansion coefficient, the density, the isobaric heat capacity, the bulk modulus, and the elastic stiffness constants were also calculated at different temperatures and concentrations for these materials. The computed variations of the thermodynamic and mechanical properties with temperature are fitted to a polynomial function. Our computed results show good agreement with other computational simulations, as well as with the experimental results where they have been available. (C) 2010 Elsevier B.V. All rights reserved.