Microwave synthesis of large few-layer graphene sheets in aqueous solution of ammonia

Few-layer graphene (FLG) sheets with sizes exceeding several micrometers have been synthesized by exfoliation of expanded graphite in aqueous solution of ammonia under microwave irradiation, with an overall yield approaching 8 wt.%. Transmission electron microscopy (in bright-field and dark-field modes) together with electron diffraction patterns and atomic force microscopy confirmed that this graphene material consisted mostly of mono-, bi- or few-layer graphene (less than ten layers). The high degree of surface reduction was confirmed by X-ray photoelectron and infrared spectroscopies. In addition, the high stability of the FLG in the liquid medium facilitates the deposition of the graphene material onto several substrates via low-cost solution-phase processing techniques, opening the way to subsequent applications of the material.      

Analysis of temperature gradient bifurcation in porous media – An exact solution

The phenomenon of temperature gradient bifurcation in a porous medium is analyzed by studying the convective heat transfer process within a channel filled with a porous medium, with internal heat generation. A local thermal non-equilibrium (LTNE) model is used to represent the energy transport within the porous medium. Exact solutions are derived for both the fluid and solid temperature distributions for two primary approaches (Models A and B) for the constant wall heat flux boundary condition. The Nusselt number for the fluid at the channel wall is also obtained. The effects of the pertinent parameters such as fluid and solid internal heat generations, Biot number and fluid to solid thermal conductivity ratio are discussed. It is shown that the internal heat generation in the solid phase is significant for the heat transfer characteristics. The validity of the one equation model is investigated by comparing the Nusselt number obtained from the LTNE model with that from the local thermal equilibrium (LTE) model. The results demonstrate the importance of utilizing the LTNE model in the present study. The phenomenon of temperature gradient bifurcation for the fluid and solid phases at the wall for Model A is established and demonstrated. In addition, the temperature distributions for Models A and B are compared. A numerical study for the constant temperature boundary condition was also carried out. It was established that the phenomenon of temperature gradient bifurcation for the fluid and solid phases for the constant temperature boundary condition can occur over a given axial region.     

A hybrid particle swarm optimisation for scheduling just-in-time single machine with preemption,machine idle time and unequal release times

This paper addresses preemption in just-in-time (JIT) single–machine-scheduling problem with unequal release times and allowable unforced machine idle time as realistic assumptions occur in the manufacturing environments aiming to minimise the total weighted earliness and tardiness costs. Delay in production systems is a vital item to be focussed to counteract lost sale and back order. Thus, JIT concept is targeted including the elements required such as machine preemption, machine idle time and unequal release times. We proposed a new mathematical model and as the problem is proven to be NP-hard, three meta-heuristic approaches namely hybrid particle swarm optimisation (HPSO), genetic algorithm and imperialist competitive algorithm are employed to solve the problem in larger sizes. In HPSO, cloud theory-based simulated annealing is employed with a certain probability to avoid being trapped in a local optimum. Taguchi method is applied to calibrate the parameters of the proposed algorithms. A number of numerical examples are solved to demonstrate the effectiveness of the proposed approach. The performance of the proposed algorithms is evaluated in terms of relative percent deviation and computational time where the computational results clarify better performance of HPSO than other algorithms in quality of solutions and computational time.     

Designing scalable product families by the radial basis function–high-dimensional model representation metamodelling technique

Product family design is cost-efficient for achieving the best trade-off between commonalization and diversification. However, for computationally intensive design functions which are viewed as black boxes, the family design would be challenging. A two-stage platform configuration method with generalized commonality is proposed for a scale-based family with unknown platform configuration. Unconventional sensitivity analysis and information on variation in the individual variants’ optimal design are used for platform configuration design. Metamodelling is employed to provide the sensitivity and variable correlation information, leading to significant savings in function calls. A family of universal electric motors is designed for product performance and the efficiency of this method is studied. The impact of the employed parameters is also analysed. Then, the proposed method is modified for obtaining higher commonality. The proposed method is shown to yield design solutions with better objective function values, allowable performance loss and higher commonality than the previously developed methods in the literature.     

Synthesis of A<Subscript>2</Subscript>B<Subscript>2</Subscript> miktoarm star copolymers from a new heterobifunctional initiator by combination of ROP and ATRP

Abstract  

A new heterobifunctional initiator, 2,3-bis(2-bromo-2-methylpropionyloxy) succinic acid, was synthesized and used in preparation of A₂B₂ miktoarm star copolymers, (polystyrene)₂(poly(ε-caprolactone))₂, by combination of atom transfer radical polymerization (ATRP) and Controlled ring-opening polymerization (ROP). The structures of products were confirmed by the ¹H NMR, ¹³C NMR, FT–IR, elemental analysis, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). GPC traces show that the obtained polymers have a relatively narrow molecular weight distribution. The compositions of resulting miktoarm star copolymers were very close to theoretical.     

A new layered manufacturing machine with cutting force analysis in tapered end milling

We introduce a new layered manufacturing machine with its associated geometric cutting force model. This machine is designed to build metal parts and is a modified type of commercial layered object manufacturing (LOM) machine. This apparatus uses tapered end mills with different angles instead of laser to cut the layer edges. The proposed machine needs higher stiffness, because cutting action would regularly create more inaccuracy. Consequently, a new force model is considered that takes into account cutting conditions, cutter geometry and combination of tool-workpiece materials. Then, by force and stress analysis cutting-force induced inaccuracy has been evaluated for different components of the machine. Finally, the effectiveness of the machine and its capability to build functional metal parts with different geometries is clearly shown.     

The effect of anisotropic dispersion on the convective mixing in long‐term CO2 storage in saline aquifers

Carbon dioxide storage in deep saline aquifers is considered a possible option to bring greenhouse gas emissions under control. The understanding of the underlying mechanisms, such as convective mixing and associated mechanisms, affecting this mixing may have an impact on the long‐term sequestration process in deep saline aquifers. One of the significant aspects of the flow of miscible species in porous media is velocity dependent dispersion. The effect of dispersion on dissolution of carbon dioxide (CO₂) into brine is investigated by full nonlinear numerical simulations. This study reveals that dispersion may dramatically change the trend of CO₂ dissolution into brine. It was found that the dissolution of CO₂ increases as dispersion strength increases. The mixing pattern also shows three different mechanisms: diffusion, convection, and a highly nonlinear interaction mechanism. However, the medium dispersivity ratios were found to slightly affect the mixing, while having an impact on the fingering pattern. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Numerical simulation of underground coal gasification using the CRIP method

A three‐dimensional simulation of the Underground coal gasification (UCG) process is studied in terms of the heat and mass transport phenomena and chemical kinetics in a coal seam during coal combustion by applying the controlled retracting injection point technique. The STARS module of the Computer Modelling Group software is used in this study. The gas species flow rate, cavity shapes, and temperature profile in the coal seam during gasification are investigated. The main motivation behind this study is to provide a simulation methodology by using a comprehensive porous media flow approach to understand the critical aspects of the UCG process.     

Simulation study and kinetic parameter estimation of underground coal gasification in Alberta reservoirs

A new method is developed for the estimation of chemical reaction kinetics at high-pressure underground coal gasification from the field produced gas composition. This method combines a developed numerical forward model and field data to investigate uncertain parameters. The forward model is developed on the basis of a unique porous media approach that combines the effects of heat, mass transport, and chemical reactions to simulate the underground coal gasification in three-dimensional basis. The chemical reaction kinetics, that is limited to low pressure, is upscaled based on the available experimental data. A comprehensive sensitivity analysis is carried out to estimate the reaction kinetics and investigate the effect of various parameters, such as pressure, temperature, and reaction environment, on the produced gas composition. The novelty of the developed method is in its applicability as well as its ability to generate the chemical reaction kinetics that corresponds to the field under study. The advantage of the proposed technique is that the sensitivity of the model to different kinetic parameters can be investigated by a graphical method.