On the reduction of the nearest-neighbor variation for moreaccurate classification and error estimates

In designing the nearest-neighbor (NN) classifier, a method is presented to produce a finite sample size risk close to the asymptotic one. It is based on an attempt to eliminate the first-order effects of the sample size, as well as all higher odd terms. This method uses the 2-NN rule without the rejection option and utilizes a polarization scheme. Simulation results are included as a means of verifying this analysis     

Carbon nanotube growth mechanism switches from tip- to base-growth with decreasing catalyst particle size

The growth of carbon nanotubes by a plasma assisted catalytic chemical vapor deposition was investigated using cobalt, nickel and iron catalyst particles of different sizes. For the three catalysts examined, it was shown that the growth mode switches from “tip-growth” for large particles (>>5 nm) to “base-growth” for smaller ones (<5 nm). While single-walled nanotubes and those with few walls (typically <7 walls) grow from their base, larger multi-walled nanotubes are fed with carbon via their tips which support the catalyst particle. A growth scenario involving two different pathways for carbon diffusion is proposed in order to explain the change in growth mode.     

A fast algorithm for the nearest-neighbor classifier

A fast algorithm that finds the nearest neighbor (NN) of an unknown sample from a design set of labeled samples is proposed. This algorithm requires a quite moderate preprocessing effort and a rather excessive storage, but it accomplishes substantial computational savings during classification. The performance of the algorithm is described and compared to the performance of the conventional one. Results on simulated data are provided to illustrate the computational savings that may be achieved using this fast algorithm     

Integration of a carbon nanotube based electrode in silicon microtechnology to fabricate electrochemical transducers

An original approach was developed and validated for the fabrication of a carbon nanotube (CNT) electrode synthesized directly onto a carbon buffer thin film deposited on a highly doped monocrystalline silicon surface. The buffer layer of amorphous carbon thin film was deposited by physical vapour deposition on the silicon substrate before CNT synthesis. For this purpose, nickel was deposited on the carbon buffer layer by an electrochemical procedure and used as a catalyst for the CNT growth. The CNT synthesis was achieved by plasma enhanced chemical vapour deposition (PECVD) in an electron cyclotron resonance (ECR) plasma chamber using a C(2)H(2)/NH(3) gas mixture. In order to evaluate the electrochemical behaviour of the CNT-based electrode, the carbon layer and the silicon/carbon interface were studied. The resulting buffer layer enhanced the electronic transport from the doped silicon to the CNTs. The electrode surface was studied by XPS and characterized by both SEM and TEM. The electrochemical response exhibited by the resulting electrodes modified with CNTs was also examined by cyclic voltammetry. The whole process was found to be compatible with silicon microtechnology and could be envisaged for the direct integration of microsensors on silicon chips.     

Single- and few-walled carbon nanotubes grown at temperatures as low as 450 degrees c: electrical and field emission characterization

Single-wall (SW-) and few-walled (FW-) carbon nanotubes (CNTs) were synthesized on aluminum/ cobalt coated silicon at temperatures as low as 450 degrees C by plasma enhanced chemical vapor deposition technique (PECVD). The SWCNTs and FWCNTs grow vertically oriented and well separated from each other. The cold field emission studies of as-grown SWCNTs and FWCNTs showed low turn-on field emission threshold voltages, strongly dependent of the nanotubes morphology. Current-voltage curves of individual CNTs, measured by conductive atomic force microscopy (CAFM), showed an electrical resistance of about 90 Komega, that is attributed mainly to the resistance of the contact between the CNTs and the conductive CAFM tip (Au and Pt).     

Wear resistance of coatings in high speed gear hobbing

Coating technology is one means of achieving a crucial enhancement in tool performance, especially in hobs that were among the first tools to be coated on a large scale. Nevertheless only few detailed analysis of wear mechanism have been done on field machines. The bifunctional coatings (combination of a tough, hard and refractory coating and of a self lubricating coating possessing a good thermochemical and abrasion resistance but a lower hardness) are very interesting since it is difficult to get a simple coating showing all these characteristics. The use of bilayer coatings raises several problems especially for dry and high speed cutting. Therefore, in order to investigate the behaviour of these bifunctional coatings, hobs have been coated by physical vapour deposition (PVD) methods. After the elaboration of a procedure for hobs testing, field tests have been performed. Results of tool life tests and investigations on tool wear mechanisms for different coated hobs are presented and discussed. The interesting performance in high speed gear hobbing of sintered high speed steel (HSS) hobs (ASP2052) combined with a (Ti,Al)N+MoS₂ coating is particularly underlined.     

Optimal robust disturbance attenuation for continuous time‐varying systems

In this paper we consider the Optimal robust disturbance attenuation problem (ORDAP) for continuous time‐varying systems subject to time‐varying unstructured uncertainty. We show that for causal (possibly time‐varying) continuous systems, ORDAP is equivalent to finding the smallest fixed point of a ‘two‐disc’ type optimization problem under time‐varying feedback control laws. Duality is applied in the context of nest algebra of causal stable systems, to prove existence of optimal continuous time‐varying controllers. We also show that for time‐invariant nominal plants, time‐varying control laws offer no improvement over time‐invariant feedback control laws. Copyright © 2003 John Wiley & Sons, Ltd.     

On optimal robust disturbance attenuation

In this article, we give an explicit solution to the nonstandard H^∞ problem which includes the optimal robust disturbance attenuation problem and the two-disc problem. The solution depends on an operator which is analogous to the Sarason operator for the standard H^∞ problem, it allows to quantify the optimal performance of feedback systems and provides an explicit formula for the optimal controller. The nonstandard H^∞ problem is perhaps the simplest control problem which deals with significant plant uncertainty. Surprisingly, relatively little work has been done on it despite the large number of papers in the H^∞ control literature.     

Experimental Approach for Evaluating an UAV COTS-Based Embedded Sensors System

Fixed-wing Unmanned Aerial Vehicles (UAVs) are a class of UAVs which present many advantages notably long range of action. However, design of this kind of UAVs requires heavy logistics like outdoor tests, runways and experimented pilots. These constraints impact the development of embedded systems for fixed-wing UAVs. The purpose of this paper is to present an experimental approach for evaluating an embedded sensors system of a micro-fixed-wing UAV. Our idea is to test the sensors system using a vehicle that emulate the behavior of this UAV but without the constraints imposed by flight experimentations. Looking for the best emulation vehicle, first a theoretical and then an experimental study is conducted on a mobile robot and a bicycle models. We also show that, contrary to trend in literature, a mobile robot is not the optimal choice to emulate a fixed-wing UAV.