关键词： Hybrid aerogel materials   DEDMS-TEOS   Nanostructure   Absorption capacity   Swelling   Uniaxial compression  

摘要： This work is a new approach to the study of the structural, mechanical and absorption properties of hybrid organic/inorganic silica-based aerogels. Diethoxydimethylsilane and tetraethoxysilane have been used as precursors. Changes in properties such as specific surface area, porous volume, pore radius, and surface texture and chemistry were researched as a function of the relative organic content. In addition, the absorption properties were tested for different organic liquids. The discrepancy in the absorption mechanisms and the kinetics of pure inorganic and hybrid samples were discussed. It was confirmed that swelling occurs in samples with high organic content, which, in turn, governs the absorption process. Finally, the mechanical behaviour was studied by uniaxial compression. A significant rise of the rupture strain up to 0.45 and a 10-fold decrease in the Young's modulus to 7.8 MPa were measured in the dry samples by increasing the organic content. The mechanical response of the samples after saturation by the absorption of two reference oily liquids, namely, common motor oil and liquid polydimethylsiloxane, was also compared with the behaviour of dry samples. The presence of liquid within the sample reduced the value of the mechanical parameters in almost all cases. Moreover, the inclusion of organic chains also made the wet aerogels highly deformable. In summary, these first results suggest that tuning the organic ratio of the hybrid aerogels allows the control of not only the structural and mechanical properties but also the absorption properties.

关键词： Methanol   Kinetics   Temperature dependence   Mechanical properties   Arrhenius equation   Power transformers   Degree of polymerization   Cellulose degradation  

摘要： This paper reports the temperature-dependence of methanol generation and the tensile index under ageing conditions for two paper/oil systems: one consisting of a standard wood Kraft paper and the other of a thermally-upgraded Kraft paper (TUK). A linear correlation between methanol and the tensile index for these paper/oil systems was observed in a previous study at 170 A degrees C. In the current study, the correlation was extended to a large range of temperatures (150-190 A degrees C). The experimental data were fitted with a modified Calvini's kinetic model, while the Arrhenius equation was used to model the kinetic of changes of the paper's mechanical properties during ageing. Good agreement with the temperature (lnk vs. 1/T) was observed for the rate constants of the chain-end group production, methanol formation, and the decrease of mechanical properties. The Arrhenius equation applied to this data grouping showed activation energy of 130 +/- 29 kJ/mol for the decrease in mechanical strength of the standard Kraft paper, while the value was 118 +/- 55 kJ/mol for the TUK paper. These values are of the same order of magnitude as those obtained in this study and in the literature for the depolymerization of cellulose and the generation of methanol that was reported. This confirmed the close relationship between cellulose depolymerization, methanol generation and the reduction of the paper's mechanical strength during ageing, dominated by the acid hydrolysis mechanism. The results, which can be seen as a benchmark and pave the way to further research, provide an opportunity for applying the proposed correlations to estimate the insulation condition in operating transformers.

关键词： Crystallinity   Kinetics   Monomeric sugar   Lignosulfonates   Sugar degradation   Enzymatic hydrolysis  

摘要： Currently, various chemical-mechanical treatments were widely used in biofuel production to achieve high total sugar yields. However, the interaction between two treatments was scarcely investigated. In this study, we employed a ball milling process to create ultrastructural changes for Douglas-fir (Pseudotsuga menziesii) micronized wood powders. The 0, 30, and 60 min ball milled wood powders resulted in a crystallinity index of 0.41, 0.21, and 0.10 respectively. It was found that the ultrastructural changes accelerate monomeric sugars production without influencing the yield of sugar degradation products. The optimal acid bisulfite treatment time was substantially decreased from 120 min to 40 min as the cellulose crystallinity decreased. Meanwhile, total sugar yield increased from 65% to 92% and had a linear relation with a decrease of the cellulose crystallinity. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： add-my-pet   cohort generation time   competition   consumer-resource dynamics   vital rates   von Bertalanffy growth rate   -rule growth model  

摘要： 1. Integral projection models (IPMs) provide a powerful approach to investigate ecological and rapid evolutionary change in quantitative life-history characteristics and population dynamics. IPMs are constructed from functions that describe the demographic rates - survival, growth and reproduction - in relation to the characteristics of individuals and their environment. Currently, however, demographic rates are estimated using phenomenological regression models that lack a mechanistic representation of the biological processes that give rise to observed demographic variation. This lack of mechanistic underpinning limits the ability of the model to predict future dynamics under novel environmental conditions because the model ingredients pertain to current environmental conditions only. Here, we use dynamic energy budget (DEB) theory to construct DEB-IPMs based on a mechanistic representation of individual life-history trajectories. We derive the demographic functions describing growth and reproduction from a simple DEB growth model. The functions describing mortality and the association between parent and offspring characteristics do not follow DEB theory and hence are estimated from individual-level observations. We apply the DEB-IPM to two contrasting systems: the small, fast-reproducing bulb mite Rhizoglyphus robini and the large, slow-reproducing reef manta ray Manta alfredi. In both cases, predictions of population growth rate, lifetime reproductive success and generation time agree with empirical observations. In case of the bulb mite, predictions and observations even agree across different feeding conditions. If the DEB energetics model is accepted as describing growth and reproduction, DEB-IPMs can be parameterised using easy-to-collect life cycle information (growth rate, length at birth, maturation and old age) making them suitable for data-deficient species. Because species differ only in these DEB parameters, comparative studies of character and popula

关键词： Self-assembled monolayers   Molecular dynamics   Rigid rod statistical mechanics   Alkylthiols   Surface ordering  

摘要： A statistical mechanical model that treats hydrocarbon self-assembled monolayer (SAM) chains as rigid rods is examined to interrogate the mechanisms involved in monolayer ordering. The statistical mechanical predictions are compared to fully atomistic molecular dynamics simulations of SAMs with different packing densities. The monolayer chain order is examined as a function of surface coverage, chain-surface interactions, and chain-chain interactions. Reasonable interaction potentials are deduced from ab initio electronic structure calculations of small model systems. It is found that the chain-surface interaction is the most important parameter in formation of flat-lying monolayer phases, while formation of standing phase monolayers is driven most importantly by increased density of molecules at the surface. A brief discussion of the utility and validity of the rigid rod treatment is given in light of the molecular dynamics results.

关键词： Shear stress   Superhydrophobic   Thrombosis   Turbulence   Blood   Bileaflet mechanical heart valve  

摘要： In this study, we explore how blood-material interactions and hemodynamics are impacted by rendering a clinical quality 25 mm St. Jude Medical Bileaflet mechanical heart valve (BMHV) superhydrophobic (SH) with the aim of reducing thrombo-embolic complications associated with BMHVs. Basic cell adhesion is evaluated to assess blood-material interactions, while hemodynamic performance is analyzed with and without the SH coating. Results show that a SH coating with a receding contact angle (CA) of 160A degrees strikingly eliminates platelet and leukocyte adhesion to the surface. Alternatively, many platelets attach to and activate on pyrolytic carbon (receding CA = 47), the base material for BMHVs. We further show that the performance index increases by 2.5% for coated valve relative to an uncoated valve, with a maximum possible improved performance of 5%. Both valves exhibit instantaneous shear stress below 10 N/m(2) and Reynolds Shear Stress below 100 N/m(2). Therefore, a SH BMHV has the potential to relax the requirement for antiplatelet and anticoagulant drug regimens typically required for patients receiving MHVs by minimizing blood-material interactions, while having a minimal impact on hemodynamics. We show for the first time that SH-coated surfaces may be a promising direction to minimize thrombotic complications in complex devices such as heart valves.

关键词： Atomic Force Microscopy   bitumen   micro-mechanical behaviors   Phase Dynamics Theory   MD simulation  

摘要： Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM) experiments, Phase Dynamics Theory and Molecular Dynamics (MD) Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance.

关键词： Motorized spindle   water-lubricated hydrostatic bearing   rotor dynamics   transfer matrix method  

摘要： The purpose of this paper is to investigate the dynamic performances of a motorized spindle supported on water-lubricated bearings. A modified transfer matrix method considering both of the translational and tilting dynamic coefficients of the bearings is established. The turbulent Reynolds equation is adopted and numerically solved by the perturbation method and the finite difference method, and the dynamic characteristics of the water-lubricated journal bearings are obtained;the effects of the eccentricity ratio, tilting angle, and the rotational speed on the dynamic coefficients of the water-lubricated journal bearings are analyzed. The critical speed, the dynamic stiffness of spindle nose, and unbalance response of the motorized spindle are investigated. Finally, a comparative study of rotor dynamic behaviors between the 32- and the eight-coefficient bearing models is conducted. The numerical predictions obtained by the 32-coefficient bearing models correlate well with the experimental values available in the literature.

关键词： Bisphenol E cyanate ester resin   carbon nanotube   functionalized CNT   computational method   molecular dynamics   nanocomposite   mechanical properties  

摘要： This paper presents molecular dynamics (MD) simulations on the effects of carbon nanotubes (CNTs) without and with chemical functionalization, on the mechanical properties of bisphenol E cyanate ester (BECy) - a potential structural resin. Atomistic models of CNTs, functionalized CNTs (fCNTs), BECy resin, CNT-BECy and fCNT-BECy resins with definite quantity of CNT/fCNT are built. Using these atomistic models, mechanical properties of the above nanosystems are estimated through a computational method involving geometric optimization and equilibration through MD by judiciously establishing various parameters. Adoptability of the approach taken up in this work to model and solve complex nanosystems capturing interactions in the interfacial region between CNT/fCNT and the resin to understand the mechanical behaviour has been highlighted. These investigations have yielded interesting and encouraging results to arrive at optimum quantity of CNTs/fCNTs to be added to achieve enhanced mechanical properties of BECy resin that validate the previous experimental studies carried out by the authors infusing similar quantities of CNTs and fCNTs into BECy.

关键词： Mechanical seal   Pump-out   Self-pumping effect   Numerical analysis  

摘要： A new pump-out hydrodynamic mechanical seal with self-pumping effect is presented based on centrifugal pump's working principle. Results of parametric study show that both of the opening force and leakage rate increase with increasing medium pressure, channel diameter, spiral angle and width ratio of groove to ridge;The opening force increases with decreasing groove number and length ratio of groove to dam while the leakage rate decreases slightly;There exits an optimum groove depth that obtains higher opening force along with lower leakage rate. Moreover, the new mechanical seal can be used in conditions with larger pressure difference.