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： 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.

关键词： Catalysis   Spline   Mapping   Mechanistic kinetics   Ammonia   Oxidation  

摘要： This paper demonstrates how pre-computed rate data can be used to enable the numerically efficient implementation of mechanistic kinetics in a reactor model for an automotive ammonia slip catalyst. In a pre-processing step the source terms for the gas species are mapped as a function of gas composition and temperature. From this map (80,000 data points), a spline interpolation function is constructed. The spline function approximates the numerical steady state solution of the kinetic model with an average error of less than 1%. Application of the rate mapping procedure results in a speedup of about two orders of magnitude. The spline approximation is implemented in a 2-dimensional model of a monolith reactor channel that includes diffusion in the washcoat layer. Depending on the channel diameter and the washcoat thickness, diffusion limitations in the open channel and in the washcoat can have a significant influence on the NH3 conversion. Surprisingly, the selectivity for the products N-2, N2O and NO is not sensitive to diffusion effects in the gas phase or in the washcoat. (C) 2010 Elsevier B.V. All rights reserved.

关键词： MOLECULAR dynamics   RESEARCH   IONS   IRON ions   HARTREE-Fock approximation   ANGULAR distribution (Nuclear physics)   QUANTUM theory  

摘要： Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) simulations have been performed for aqueous solutions of Fe2+ and Fe3+ ions at the Hartree-Fock level of theory to describe and compare their structural and dynamical behavior. The structural features of both hydrated ions are characterized by radial distribution functions that give the maximum probability of the ion-O distance for Fe2+ and Fe3+ ions at 2.15 and 2.03 angstrom, respectively. The angular distribution functions of both ions prove the octahedral arrangement of six water ligands, whereas the second shells of these ions differ. Both ions show influence on the water molecules beyond the second shells. The structure-forming abilities of both ions are visible from the ligand mean residence times and ion-O stretching frequencies evaluated for both ions. The substantially improved data obtained from these QMCF-MD simulations show better correlation with available experimental results than the conventional quantum mechanics/molecular mechanics molecular dynamics (QM/MM MD) approaches with one hydration shell treated by quantum mechanics.

关键词： collagen structure   stem cell   mechanical properties   in vitro test   tendon  

摘要： A cell-collagen construct is commonly used to investigate the phenomenon of wound healing and to estimate the variables for tissue engineering. The purpose of this study was to assess the effects of cell concentration and collagen concentration on the contraction kinetics and mechanical properties of bone marrow stromal cell (BMSC) seeded collagen lattices. To investigate the effects of both variables on the contraction kinetics, the construct contraction was monitored up to 13 days. Incremental stress relaxation tests were carried out after a 2-week incubation to obtain the stress strain profiles, which were subsequently assessed in a quasilinear viscoelastic (QLV) model. During contraction, aligned BMSCs were observed first in the interior portion of the ring, followed by the middle portion and finally in the exterior portion. Constructs seeded with a higher initial cell concentration (higher than 1 x 10(5) cells/mL) or lower initial collagen concentration (lower than 2 mg/mL) exhibited faster contraction, higher ultimate stress, and superior elasticity and reduced relaxation behavior (p < 0.05). The cell-collagen model was successfully used to yield information regarding the initial cell concentration and the initial collagen concentration on contraction kinetics and mechanical behavior, which may have possible application in tissue engineering. (C) 2009 Wiley Periodicals, Inc. J Biomed Mater Res 93A: 1132-1139, 2010

关键词： 水下电动机械手   牛顿-欧拉法   水动力学模型   仿真  

摘要： 运用牛顿-欧拉递推算法对机械手进行动力学分析,在此基础上运用单摆动杆水动力方程建立了机械手的水动力学模型,最后对其进行动力学仿真验证。

关键词： 液压动力头   地质探矿   岩心钻机   机械厂   山东省   现场会   施工   装配车间  

标准号: NF E88-051/IN1-2010