Synthesis of One-Dimensional And Two-Dimensional Carbon Based Nanomaterials

Particular physical and chemical properties of carbon based nanomaterials (CBNs) have promised and exhibited great applications in manufacturing various nanodevices such as electron field emitters, sensors, one-dimensional conductors, supercapacitors, reinforcing fibres, hydrogen storage devices, and catalyst support for fuel cells electrodes. Despite these amazing technical progresses, many challenges still remain in the development of synthesis methods suitable for commercial applications and fabricating novel functional nanostructures with complex architecture. In this Ph.D. thesis, one-dimensional (1D), two-dimensional (2D) carbon nanostructures, and 1D/2D hybrid of carbon nanostructures have been synthesized using various chemical vapour deposition (CVD) methods. The objective of this work is to explore the potential of various CVD methods, including specially-designed CVD techniques, such as modified spray pyrolysis, plasma enhanced CVD, and magnetron sputtering deposition. By making use of these innovative methods, high density regular and nitrogen-doped nanotubes, graphite nanosheets and assemblies have been successfully obtained on conducting and semiconducting substrates. For the modified spray pyrolysis method, systematic investigation of regular carbon nanotubes (CNTs) was conducted in terms of optimizing various experimental parameters such as hydrocarbon source, temperature, and catalyst in order to control the quality and structure of CBNs. Doping of nitrogen into carbon nanotubes was also systematically studied to enhance their electrical and mechanical properties. Interestingly, a novel structure of multi-branched nitrogen doped CNTs has been achieved by this modified spray pyrolysis method. By employing the plasma assisted CVD/sputtering hybrid system, selective growth of single and few walled CNTs have been realized. The device has also been able to produce 2D carbon nanostructures of nanosheets and a hybrid of nanosheets suspended on vertical aligned CNTs. Based on the magnetron sputtering deposition method, carbon nanowalls have been synthesized without any catalyst addition. Morphology, microstructure, and vibration properties of the CBNs were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Carbon nanomaterials, grown in high densities on conducting and semiconducting substrates, promise great potential in building various nanodevices with different electron conducting requirements. In addition, CBNs provide a very high surface area for the support of platinum particles for use in hydrogen fuel cell electrodes

Equivariant Schr\"odinger Maps in two spatial dimensions

We consider equivariant solutions for the Schr\"odinger map problem from $\mathbb{R}^{2+1}$ to $\mathbb{S}^2$ with energy less than $4\pi$ and show that they are global in time and scatter

Online weight estimation in a robotic gripper arm

This paper presents a novel methodology for online, fast and accurate weight estimation technique in a robotic gripper arm. The laboratory setup is inspired from several real life applications of weight estimation in moving cranes, e.g. loading containers in a shipyard, iron scrapping in steel industry, etc. The weight needs to be estimated within a specified time interval and within a tolerance interval for accuracy. The results indicate that the proposed method is suitable for this kind of application and an improvement of 30% has been achieved compared to the current state of work

Global Schr\"{o}dinger maps

We consider the Schr\"{o}dinger map initial-value problem in dimension two or greater. We prove that the Schr\"{o}dinger map initial-value problem admits a unique global smooth solution, provided that the initial data is smooth and small in the critical Sobolev space. We prove also that the solution operator extends continuously to the critical Sobolev space.Comment: 60 page

Design and practical implementation of a fractional order proportional integral controller (FOPI) for a poorly damped fractional order process with time delay

One of the most popular tuning procedures for the development of fractional order controllers is by imposing frequency domain constraints such as gain crossover frequency, phase margin and iso-damping properties. The present study extends the frequency domain tuning methodology to a generalized range of fractional order processes based on second order plus time delay (SOPDT) models. A fractional order PI controller is tuned for a real process that exhibits poorly damped dynamics characterized in terms of a fractional order transfer function with time delay. The obtained controller is validated on the experimental platform by analyzing staircase reference tracking, input disturbance rejection and robustness to process uncertainties. The paper focuses around the tuning methodology as well as the fractional order modeling of the process' dynamics

An analytic approach for the evolution of the static/flowing interface in viscoplastic granular flows

International audienceObserved avalanche flows of dense granular material have the property to present two possible behaviours: static (solid) or flowing (fluid). In such situation, an important challenge is to describe mathematically the evolution of the physical interface between the two phases. In this work we derive analytically a set of equations that is able to manage the dynamics of such interface, in the thin-layer regime where the flow is supposed to be thin compared to its downslope extension. It is obtained via an asymptotics starting from an incompressible viscoplastic model with Drucker-Prager yield stress, in which we have to make several assumptions. Additionally to the classical ones that are that the curvature of the topography, the width of the layer, and the viscosity are small, we assume that the internal friction angle is close to the slope angle (meaning that the friction and gravity forces compensate at leading order), the velocity is small (which is possible because of the previous assumption), and the pressure is convex with respect to the normal variable. This last assumption is for the stability of the double layer static/flowing configuration. A new higher-order non-hydrostatic nonlinear coupling term in the pressure allows us to close the asymptotic system. The resulting model takes the form of a formally overdetermined initial-boundary problem in the variable normal to the topography, set in the flowing region only. The extra boundary condition gives the information on how to evolve the static/flowing interface, and comes out from the continuity of the velocity and shear stress across it. The model handles arbitrary velocity profiles, and is therefore more general than depth-averaged models

Predictive control of anaerobic digestion of wastewater sludge: a feasibility study

C

Viscoplastic modeling of granular column collapse with pressure-dependent rheology

International audienceA mechanical and numerical model of dry granular flows is proposed that quantitatively reproduce laboratory experiments of granular column collapse over inclined planes. The rheological parameters are directly derived from the experiments.The so-called \mu(I) rheology is reformulated in the framework of Drucker-Prager plasticity with the yield stress and viscosity \eta(||D||,p) depending on both the pressure p and the norm of the strain rate tensor ||D||. The granular domain, velocities, stress deviator and pressure fields are calculated using a finite element method based on an iterative decomposition-coordination formulation coupled with the augmented Lagrangian method. 2-D simulations using this model well reproduce the dynamics and deposits of collapsing granular columns. The flow is essentially located in a surface layer behind the front, whereas it is distributed over the whole depth near the front where basal sliding occurs. The computed runout distances and slopes of the deposits agree very well with the values found in the experiments. Using an easily calculated order of magnitude approximation of the mean viscosity during the flow (\eta = 1 Pa s here), we show that a Drucker-Prager rheology with a constant viscosity gives results very similar to the \mu(I) rheology and agrees with experimental height profiles, while significantly reducing the computational cost. Within the range of viscosities 0.1 < \eta < 1 Pa s, the dynamics and deposits are very similar. The observed slumping behavior therefore appears to be mainly due to the flow/no-flow criterion and to the associated strain-independent part of the "flowing constitutive relation" (i.e. related to plastic effects). However, the results are very different when an unrealistically large value of viscosity (10 Pa s) is used