关键词： Vaporization   TG   Kinetic model   Brominated flame retardant  

摘要： Brominated flame retardants are well recognized as being highly effective flame retardants. 4-4'-Isopropylidenebis(2,6-dibromophenol), commonly known as tetrabromobisphenol A, is the brominated flame retardant with the largest production volume and is used to improve fire safety, mainly of laminates in electrical and electronic equipment. A kinetic study of the pyrolysis of TBBA has been carried out to obtain decomposition parameters under different operating conditions and taking into account that TBBA is a compound with a high boiling point and that vaporization occurs simultaneously to decomposition. Dynamic runs and dynamic + isothermal run at different heating rates and using different masses of sample were correlated simultaneously. All TG runs were fitted with a unique set of kinetic parameters that is able to explain all the experiments. Moreover, a simplified detailed kinetic model has been developed and the kinetic parameters obtained satisfactorily reproduce the thermal decomposition of TBBA. (C) 2011 Elsevier B.V. All rights reserved.

关键词： flow   plant biomechanics   vibration  

摘要： The modeling of fluid-structure interactions, such as flow-induced vibrations, is a well-developed field of mechanical engineering. Many methods exist, and it seems natural to apply them to model the behavior of plants, and potentially other cantilever-like biological structures, under flow. Overcoming this disciplinary divide, and the application of such models to biological systems, will significantly advance our understanding of ecological patterns and processes and improve our predictive capabilities. Nonetheless, several methodological issues must first be addressed, which I describe here using two practical examples that have strong similarities: one from agricultural sciences and the other from nuclear engineering. Very similar issues arise in both: individual and collective behavior, small and large space and time scales, porous modeling, standard and extreme events, trade-off between the surface of exchange and individual or collective risk of damage, variability, hostile environments and, in some aspects, evolution. The conclusion is that, although similar issues do exist, which need to be exploited in some detail, there is a significant gap that requires new developments. It is obvious that living plants grow in and adapt to their environment, which certainly makes plant biomechanics fundamentally distinct from classical mechanical engineering. Moreover, the selection processes in biology and in human engineering are truly different, making the issue of safety different as well. A thorough understanding of these similarities and differences is needed to work efficiently in the application of a mechanistic approach to ecology.

关键词： PIEZOELECTRIC devices   THERMOELECTRICITY  

摘要： The article reports that University of Michigan engineers attached piezoelectric harvesters to generate power from the wing movements of green June beetles.

关键词： Chemical kinetics   Activation energy   Friction surface   Copper   CMP  

摘要： A comprehensive model for the copper material removal in a chemical mechanical polishing (CMP) process is presented in which both chemical and mechanical effects are taken into consideration. The chemical effects describing the role of oxidizer, complexing agent come into play through the formation of chemically modified surface layer on the copper surface that, in turn, is removed by mechanical effects. Meanwhile there is also heating of the copper surface due to friction during the polishing process, which additionally decreases chemical activation energy and increases the chemical reaction rate. In addition, the removal rate and the coupled effects of the chemical additives are determined from a close-form equation, making use of the concepts of chemical-mechanical equilibrium and chemical kinetics. The model prediction trends are consistent with the published experimental data. This paper aided the understanding of the mechanism of chemical and mechanical interactions during polishing. Published by Elsevier B.V.

关键词： heating kinetics   substrate   electrospark deposition   coating   steel   hard alloy  

摘要： A method is developed for determining the temperature of the substrate in the area of electrospark deposition. The method is employed during experiments on deposition of two types of electrodes onto steel substrates: carbon steel electrodes and hard-alloy electrodes based on tungsten carbide with 6 wt.% cobalt. It is established that the dependence of substrate temperature on deposition time is defined by the initial structure of the substrate, electrode material, and pressing force on the electrode. Analysis of the data shows that cathode jets are the main working element of the electrospark deposition process.

关键词： Motion equations   Non-holonomic constraints   Minimal coordinates   Coordinate partitioning   Inverse dynamics   Multibody dynamics  

摘要： The basis for any model-based control of dynamical systems is a numerically efficient formulation of the motion equations, preferably expressed in terms of a minimal set of independent coordinates. To this end the coordinates of a constrained system are commonly split into a set of dependent and independent ones. The drawback of such coordinate partitioning is that the splitting is not globally valid since an atlas of local charts is required to globally parameterize the configuration space. Therefore different formulations in redundant coordinates have been proposed. They usually involve the inverse of the mass matrix and are computationally rather complex. In this paper an efficient formulation of the motion equations in redundant coordinates is presented for general non-holonomic systems that is valid in any regular configuration. This gives rise to a globally valid system of redundant differential equations. It is tailored for solving the inverse dynamics problem, and an explicit inverse dynamics solution is presented for general full-actuated systems. Moreover, the proposed formulation gives rise to a non-redundant system of motion equations for non-redundantly full-actuated systems that do not exhibit input singularities.

关键词： cellulose   enzymatic hydrolysis   kinetics model   polymer distribution   substrate structure  

摘要： A mechanistically based kinetic model for the enzymatic hydrolysis of cellulosic biomass has been developed that incorporates the distinct modes of action of cellulases on insoluble cellulose polymer chains. Cellulose depolymerization by an endoglucanase (endoglucanase I, EGI) and an exoglucanase (cellobiohydrolase I, CBHI) is modeled using population-balance equations, which provide a kinetic description of the evolution of a polydisperse distribution of chain lengths. The cellulose substrate is assumed to have enzyme-accessible chains and inaccessible interior chains. EGI is assumed to randomly cleave insoluble cellulose chains. For CBHI, distinct steps for adsorption, complexation, processive hydrolysis, and desorption are included in the mechanistic description. Population-balance models that employ continuous distributions track the evolution of the spectrum of chain lengths, and do not require solving equations for all chemical species present in the reacting mixture, resulting in computationally efficient simulations. The theoretical and mathematical development needed to describe the hydrolysis of insoluble cellulose chains embedded in a solid particle by EGI and CBHI is given in this article (Part I). Results for the time evolution of the distribution of chain sizes are provided for independent and combined enzyme hydrolysis. A companion article (Part II) incorporates this modeling framework to study cellulose conversion processes, specifically, solution kinetics, enzyme inhibition, and cooperative enzymatic action. Biotechnol. Bioeng. 2012;109:665675. (C) 2011 Wiley Periodicals, Inc.

关键词： Polyvinylidene fluoride   Molecular dynamics   alpha-Relaxation   Mechanical and dielectric relaxation   Nuclear magnetic resonance  

摘要： The dynamics of segmental motions in semicrystalline poly(vinylidene fluoride) has been studied by means of dielectric and mechanical spectroscopies and nuclear magnetic resonance method. The relaxation data, obtained from different techniques, over a wide temperature and frequency range, have been analyzed in terms of main-chain segmental motion, described by phenomenological Havriliak-Negami function. The results indicate that the correlations between local conformational transitions in the amorphous phase are intermediate. Good agreement between the experimental and calculated data offers a contribution to the understanding of molecular dynamics in the glassy state of the polymer.

关键词： flocculation   synaeresis   kinetics   dewatering   moisture  

摘要： The authors analyze the kinetics of water removal from the orthokinetically formed floccules by mechanical synaeresis. The floccule moisture and time relationship is established under influence of unbalanced force system. It is found that the mechanical treatment of floccules in coal flotation concentrate at velocity gradient of 3-30 l/s reduces the product moisture by 1.5-2.0%, and the floccules integrity remains undisturbed. This finding allows reducing the concentrate drying cost by 10-15%.

关键词： Amorphous   Carbon nitride   Bonding configurations   Hardness  

摘要： Based on ab initio molecular dynamics method, four amorphous CNx, structures with different stoichiometries (CN0.47, CN0.67, CN0.92, and CN1.3) were generated within a 100-atom supercell. Characterizations of the pair correlation functions, bond length and the fraction of bond types of the amorphous carbon nitrides revealed that the N content in such structures plays a key role in determining the obtained structural networks. The calculations of the cohesive energy give direct evidence that experimentally synthesized amorphous carbon nitride films usually possess low nitrogen concentration. The competition relationship between sp(2) and sp(3) bonds was analyzed by electronic effect and electron density of states. The bonding states, especially the sp(3), affect greatly the hardness of these a-CNx compounds, implying a possible way to enhance the hardness of films via tuning the bonding states. (C) 2011 Elsevier B.V. All rights reserved.