Polarity control of GaN epilayers grown on ZnO templates

We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH₃ is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH₃ pre-exposure helps form a Zn₃N₂ layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar.     

Parameter identification and design of a robust attitude controller using <Emphasis Type="Italic">H</Emphasis><Subscript>∞</Subscript> methodology for the raptor E620 small-scale helicopter

Rigorous control synthesis for an unmanned aerial vehicle necessitates the availability of a good, reasonable model for such a vehicle. The work reported in this paper focuses on the modeling of a rotary unmanned aerial vehicle (RUAV) and the development of a robust controller that can handle parameter uncertainties and disturbances. The parameters of the plant model are obtained through the use of the prediction error method with real flight data. The response of the identified linear model shows a good match with the measured flight data. The H _∞ control scheme is applied to obtain a robustly stable controller using the identified model. The proposed controller is analyzed using frequency-domain analysis and time-domain simulations. The performance of the proposed H _∞ controller is better than that of the conventional proportional derivative controller in that the proposed controller has a shorter settling time and less overshoot. Furthermore, the degradation of the proposed controller performance is negligible and stability is maintained when the input gains to the plant are doubled, which demonstrates the good performance and robustness of the controller.     

Robust Fault Diagnosis for Quadrotor UAVs Using Adaptive Thau Observer

A robust Fault Diagnosis (FD) scheme for a real quadrotor Unmanned Aerial Vehicle (UAV) is proposed in this paper. Firstly, a novel Adaptive Thau observer (ATO) is developed to estimate the quadrotor system states and build a set of offset residuals to indicate actuators’ faults. Based on these residuals, some rules of Fault Diagnosis (FD) are designed to detect and isolate the faults as well as estimate the fault offset parameters. Secondly, a synthetic robust optimization scheme is presented to improve Fault Estimation (FE) accuracies, three key issues include modeling uncertainties, and magnitude order unbalances as well as noises are addressed. Finally, a typical fault of rotors is simulated and injected into one of four rotors of the quadrotor, and experiments for the FD scheme have been carried out. Unlike former research works on the FD schemes for quadrotors, our proposed FD scheme based on the ATO can not only detect and isolate the failed actuators, but also estimate the fault severities. Regardless of roughness of the real flying data, the FD results still have sufficient FE accuracies.     

An optimal usage of NO x in a combined Pt/ceramic foam and a wall-flow monolith filter for an effective NO x -assisted soot oxidation

Topics in Catalysis - An NO2-assisted soot oxidation based filter candidate consists of Pt-coated ceramic foam in combination with a wall-flow monolith is proposed to acquire for an optimal usage...     

Simple Robust PID Tuning for Magnetic Levitation Systems Using Model-free Control and $${{\cal H}_\infty}$$ ℋ ∞ Control Strategies

International Journal of Control, Automation and Systems - This paper proposes two control techniques to provide robust tracking for magnetic levitation systems (MLS): model-free control (MFC) and...     

From big smartphone data to worldwide research: The Mobile Data Challenge

This paper presents an overview of the Mobile Data Challenge (MDC), a large-scale research initiative aimed at generating innovations around smartphone-based research, as well as community-based evaluation of mobile data analysis methodologies. First, we review the Lausanne Data Collection Campaign (LDCC), an initiative to collect unique longitudinal smartphone dataset for the MDC. Then, we introduce the Open and Dedicated Tracks of the MDC, describe the specific datasets used in each of them, discuss the key design and implementation aspects introduced in order to generate privacy-preserving and scientifically relevant mobile data resources for wider use by the research community, and summarize the main research trends found among the 100+ challenge submissions. We finalize by discussing the main lessons learned from the participation of several hundred researchers worldwide in the MDC Tracks.     

Human interaction discovery in smartphone proximity networks

Since humans are fundamentally social beings and interact frequently with others in their daily life, understanding social context is of primary importance in building context-aware applications. In this paper, using smartphone Bluetooth as a proximity sensor to create social networks, we present a probabilistic approach to mine human interaction types in real life. Our analysis is conducted on Bluetooth data continuously sensed with smartphones for over one year from 40 individuals who are professionally or personally related. The results show that the model can automatically discover a variety of social contexts. We objectively validated our model by studying its predictive and retrieval performance.     

Modelling concurrency with comtraces and generalized comtraces

Comtraces (combined traces) are extensions of Mazurkiewicz traces that can model the “not later than” relationship. In this paper, we first introduce the novel notion of generalized comtraces, extensions of comtraces that can additionally model the “non-simultaneously” relationship. Then we study some basic algebraic properties and canonical representations of comtraces and generalized comtraces. Finally we analyze the relationship between generalized comtraces and generalized stratified order structures. The major technical contribution of this paper is a proof showing that generalized comtraces can be represented by generalized stratified order structures.     

Transition layer thickness in microlaminar deposits

A theoretical analysis was carried out on the change of composition of a deposit obtained by the dual pulse method of forming laminar metal foils, with transition from a low current to a high current pulse, both in the galvanostatic and the potentiostatic mode of deposition. It was shown that the existence of a transition layer of varying composition between a layer of pure metal 1 and a layer consisting predominantly of the metal 2 is an inherent consequence of the electrochemical process, primarily because of an induction period in the concentration polarization with respect to ions of metal 1. The importance of this transition layer increases as the thickness of the layers of the two metals decreases. Eventually this limits the possibility of obtaining a sharp boundary between the layers, when the nanometre region of layer thickness is reached. Equations are given for calculating the deposition current density and rate of stirring of the electrolyte which provide a deposit of a required level of metal 1 in the layer of metal 2, as well as a required sharpness of the boundary between two layers. Experimental proof of the correctness of the analysis was sought. It was found that significant changes in the properties of the deposit occur in the same range of layer thickness in which the transition of the composition takes places.Nomenclature _c,1, a_c,2 transfer coefficient of the cathodic processes - C interfacial capacitance - C₁, C₂ concentration of the ions of metals 1 and 2 at the interface r - C ₀ ¹ , C ₀ ² concentration of ions of the metals 1 and 2 in solution - D ₁ diffusion coefficient for the diffusion of ions of the metal 1 - E _r,1,E _r,2 reversible potentials of metals 1 and 2, respectively - F the Faraday constant - J ₀ ¹ ,J ₀ ² exchange current density of the metals 1 and 2, respectively - M ₁,M ₂ atomic weights of the metals 1 and 2, respectively - kinematic viscosity of solution - ₁, ₂ densities of the metals 1 and 2 respectively - rotation speed (r.p.s.) - z number of electrons exchanged in the deposition process This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemistry.