Polymerization of olefins through heterogeneous catalysis X: Modeling of particle growth and morphology

The development of a detailed model describing particle growth in olefin copolymerization systems is presented. The Multigrain Model considers in detail monomer sorption, mass transfer, and changing porosity within the growing particle, as well as heat and mass transfer across the external film of the particle. The model predicts catalyst performance, including polymerization rates and particle morphology, in different reactor media without parameter adjustment. Internal void fractions are calculated through an examination of the relative growth rates within the growing particle. The model is used to examine the effects of mass transfer limitations, prepolymerization, and nonuniform metal distribution on the particle growth process. Model predictions of morphology show the same trends as observed experimentally.     

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in-service temperatures

In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.     

Effects of fiber surface grafting by functionalized carbon nanotubes on the interfacial durability during cryogenic testing and conditioning of CFRP composites

Carbon fiber reinforced epoxy (CE) composite is ideal for a cryogenic fuel storage tank in space applications due to its unmatched specific strength and modulus. In this article, inter-laminar shear strength (ILSS) of carbon fiber/epoxy (CE) composite is shown to be considerably improved by engineering the interface with carboxyl functionalized multi-walled carbon nanotube (FCNT) using electrophoretic deposition technique. FCNT deposited fibers from different bath concentrations (0.3, 0.5, and 1.0 g/L) were used to fabricate the laminates, which were then tested at room (30°C) and in-situ liquid nitrogen (LN) (−196°C) temperature as well as conditioning for different time durations (0.25, 0.5, 1, 6, and 12 h) followed by immediate RT testing to study the applicability of these engineered materials at the cryogenic environment. A maximum increment in ILSS was noticed at bath concentration of 0.5 g/L, which was ~21% and ~ 17% higher than neat composite at 30°C and − 196°C, respectively. Short-term LN conditioning was found to be detrimental due to developed cryogenic shock, which was further found to be compensated by cryogenic interfacial clamping upon long-term exposure.     

Effect of austenitization on austempering of copper alloyed ductile iron

A ductile iron containing 0.6% copper as the main alloying element was austempered at a fixed austempering temperature of 330 °C for a fixed austempering time of 60 min after austenitization at 850 °C for different austenitization periods of 60, 90, and 120 min. The austempering process was repeated after changing austenitization temperature to 900 °C. The effect of austenitization temperature and time was studied on the carbon content and its distribution in the austenite after austenitization. The effect of austenitization parameters was also studied on austempered microstructure, structural parameters like volume fraction of austenite, X _γ , carbon content C _γ , and X _γ C _γ , and bainitic ferrite needle size, d _α after austempering. The average carbon content of austenite increases linearly with austenitization time and reaches a saturation level. Higher austenitization temperature results in higher carbon content of austenite. As regards the austempered structure, the lowering austenitization temperature causes significant refinement and more uniform distribution of austempered structure, and a decrease in the volume fraction of retained austenite.     

Long-wave interfacial instabilities in a thin electrolyte film undergoing coupled electrokinetic flows: a nonlinear analysis

Spatiotemporal deformations of the free charged surface of a thin electrolyte film undergoing a coupled electrokinetic flow composed of an electroosmotic flow (EOF) on a charged solid substrate and an electrophoretic flow (EPF) at its free surface are explored through linear stability analysis and the long-wave nonlinear simulations. The nonlinear evolution equation for the deforming surface is derived by considering both the Maxwell’s stresses and the hydrodynamic stresses. The electric potential across the film is obtained from the Poisson–Boltzmann equation under the Debye–Hückel approximation. The simulations show that at the charged electrolyte–air interface, the applied electric field generates an EPF similar to that of a large charged particle. The EOF near the solid–electrolyte interface and the EPF at the electrolyte–air interface are in the same (or opposite) directions when the zeta potentials at the two interfaces are of the opposite (or same) signs. The linear and nonlinear analyses of the evolution equation predict the presence of travelling waves, which is strongly modulated by the applied electric field and the magnitude/sign of the interface zeta potentials. The time and length scales of the unstable modes reduce as the sign of zeta potential at the two interfaces is varied from being opposite to same and also with the increasing applied electric field. The increased destabilization is caused by a reverse EPF near the free surface when the interfaces bear the same sign of zeta potentials. Flow reversal by EPF at the free surface occurs at smaller zeta potential of the free surface when the film is thicker because of less influence of the EOF arising at the solid–electrolyte boundary. The amplitude of the surface waves is found to be smaller when the unstable waves travel at a faster speed. The films can undergo pseudo-dewetting when the free surface is almost stationary under the combined influences of EPF and EOF. The free surface instability of the coupled EOF and EPF has some interesting implications in the development of micro/nano fluidic devices involving a free surface.     

Analysis of electro‐optical properties of polymer‐stabilized OCB and the application to TFT‐LCDs

Abstract— A 9‐in. full‐color polymer‐stabilized OCB TFT‐LCD with stable bend alignment in the absence of an electric field was developed. The condition of the polymer stabilization, the characteristics of UV‐curable monomers, and their influence on the configurations of the polymer network in the cell were studied. Possible models of the configuration were proposed and their relationship to the electro‐optical properties was analyzed using a novel simulation method considering the distribution of anchoring effects from both alignment surfaces and the polymer network. It was suggested that a good performance such as high contrast ratio and fast response could be expected in the polymer network originating from newly developed monomers composed of multifunctional LC acrylates due to a relatively weak‐anchoring effect and presumably its localization near the alignment surfaces. By using the newly developed monomers under the optimized polymer‐stabilizing process, a high contrast ratio of 250:1 and fast response nearly equal to that of a conventional OCB cell were achieved.     

Supervised Self-Organization of Homogeneous Swarms Using Ergodic Projections of Markov Chains

This paper formulates a self-organization algorithm to address the problem of global behavior supervision in engineered swarms of arbitrarily large population sizes. The swarms considered in this paper are assumed to be homogeneous collections of independent identical finite-state agents, each of which is modeled by an irreducible finite Markov chain. The proposed algorithm computes the necessary perturbations in the local agents' behavior, which guarantees convergence to the desired observed state of the swarm. The ergodicity property of the swarm, which is induced as a result of the irreducibility of the agent models, implies that while the local behavior of the agents converges to the desired behavior only in the time average, the overall swarm behavior converges to the specification and stays there at all times. A simulation example illustrates the underlying concept.     

A large anisotropic damage theory based on an incremental complementary energy equivalence model

This paper presents a large anisotropic damage theory of continuum damage mechanics. It is developed via a new hypothesis of incremental complementary elastic energy equivalence. This hypothesis is more versatile and accurate if compared to the original hypothesis of total complementary energy equivalence. To model the large damage, we assumed that it occurs as a series of incremental small damage. An expression for the damage effect tensor M(D) for large damage is derived. It is shown that when the damage is small, that is, D _i1, the proposed large damage theory reduces to the small damage model of Chow and Wang [1]. To demonstrate this large damage theory, it is applied to model the following cases: (a) uniaxial tension, (b) pure torsion and (c) elastic perfectly-plastic material behavior. In all three cases, the results clearly show that when the damage is small, Chow and Wang's model is recovered. However, for large damage, there are significant differences in predictions. Since this large damage theory is formulated on the basis of the incremental complementary energy, it is applicable to a wider range of problems.     

An anthropometric survey of Indian schoolchildren aged 3-5 years

Kindergartens of age group 3-5 years, a distinct and small subgroup of Indian schoolchildren, need special emphasis on human factors. The paper presents the results of an anthropometric survey conducted on schoolchildren. These data, previously lacking in India, can be of benefit for the designers of kindergartens. A set of 81 different body dimensions was taken from a sample of 198 children of age group 3-4 years and 4.1-5 years. Simple anthropometric techniques were used to collect the data. Statistical analyses of the data have been presented in a tabular form for designers as well as for non-technical users. It is emphasized that such data have to be developed at the national level, including every ethnic group, or on a regional basis. Designers, manufacturers and importers of goods should have access to these data.     

Large‐Stroke Electrochemical Carbon Nanotube/Graphene Hybrid Yarn Muscles

Artificial muscles are reported in which reduced graphene oxide (rGO) is trapped in the helical corridors of a carbon nanotube (CNT) yarn. When electrochemically driven in aqueous electrolytes, these coiled CNT/rGO yarn muscles can contract by 8.1%, which is over six times that of the previous results for CNT yarn muscles driven in an inorganic electrolyte (1.3%). They can contract to provide a final stress of over 14 MPa, which is about 40 times that of natural muscles. The hybrid yarn muscle shows a unique catch state, in which 95% of the contraction is retained for 1000 s following charging and subsequent disconnection from the power supply. Hence, they are unlike thermal muscles and natural muscles, which need to consume energy to maintain contraction. Additionally, these muscles can be reversibly cycled while lifting heavy loads.