Tracking-error model-based predictive control for mobile robots in real time

In this paper, a model-predictive trajectory-tracking control applied to a mobile robot is presented. Linearized tracking-error dynamics is used to predict future system behavior and a control law is derived from a quadratic cost function penalizing the system tracking error and the control effort. Experimental results on a real mobile robot are presented and a comparison of the control obtained with that of a time-varying state-feedback controller is given. The proposed controller includes velocity and acceleration constraints to prevent the mobile robot from slipping and a Smith predictor is used to compensate for the vision-system dead-time. Some ideas for future work are also discussed.     

Influence of lips on thin-walled sections

Turning the free edge of an unstiffened flange inwards or outwards to form a ‘lip’, can substantially improve the local buckling resistance of a member. The lip is the most common type of edge stiffener used in cold-rolled, thin-walled sections. In this paper the behaviour of plate elements of thin-walled sections stiffened by compound lips (i.e. lips which are folded twice to form ‘lips on the lips’) is examined both theoretically and experimentally. An outline of a series of tests on compound edge-stiffened thin-walled sections of various geometries is given and some load-end compression displacement paths are compared with the theoretical predictions. Reasonably good agreement is obtained between the experimental and theoretical results. Comparisons of the theoretical predictions with experimental results of other researchers are also presented in this paper.     

Mechanical properties of alternating high-low sp3 content thick non-hydrogenated diamond-like amorphous carbon films

Thick non-hydrogenated DLC films (∼ 1μm), consisting of alternating sub-layers of high/low sp³ content, were deposited onto n++ Si substrates using the filtered cathodic vacuum arc method. These films were systematically studied to determine how the changes in composition of the sub-layers would affect the mechanical properties such as intrinsic stress, hardness, friction coefficient, wear rate and surface roughness. Variations of both the ratio of hard to soft layers (from 1:3 to 3:1) and thickness of individual layers (from 12.5nm to 75nm) were studied in detail. The stress of the film was sufficiently lowered (7.8GPa–2.4GPa) by the multilayer approach. The results indicated that although hardness has some correlations with the internal composition of the film, the reduced Young's modulus is largely not affected. Wear and frictional characterizations also showed that the multilayer was a good candidate for many mechanical applications.     

A three-dimensional non-epitaxial atomistic growth model for thin-film deposition: effect of surface mobility

The effect of the atomic mobility on a film surface has been studied by using a three-dimensional atomistic thin-film deposition model which simulates three-dimensional thin-film images, surface profiles and cross-sectional area pictures. In addition, quantitative results of surface RMS roughness, average film thickness, atomic coordination number and its distribution, and solid fraction of the deposited thin films, were obtained from the simulations. When the film surface mobility increased from 0.3 to 3.0, RMS roughness decreased from 6.5 to 1.1, solid fraction increased from 0.27 to 0.56 and average film thickness decreased from 40 to 28, due to the reduction of the voids within the film. The full-width half magnitude of the atomic coordination distribution became narrower indicating the increased degree of crystallization. With increase in surface mobility crossing the boundary to 1.5, the film evolved from a porous or loose columnar structure with voids, to a densely packed fibrous grain structure which can be categorized by the zone structure models.     

Repair evaluation of concrete cracks using surface and through-transmission wave measurements

Surface opening cracks are common defects in large civil structures like bridges. They allow penetration of water or other agents that result in loss of durability earlier than expected. Their repair can be conducted by the injection of epoxy material that seals the crack sides keeping out any aggressive substances in addition to the recovery of strength. In order to evaluate crack parameters before impregnation as well as to determine the final repair effectiveness, a combination of Rayleigh and longitudinal waves is applied. Rayleigh waves demonstrate the filling condition of the material into the shallow layer near the surface while tomography using longitudinal waves through the thickness yields information about the area inside the structure. Wave propagation dispersion features are exploited by the proposed tomography at different frequencies, demonstrating that higher frequencies lead to more accurate characterization.     

An empirical study of software piracy among tertiary institutions in Singapore

We used a survey technique at Singapore's three universities to examine perceptions of software piracy and to attempt to discover its underlying factors. About 500 responses were gathered from students and staff. By means of cluster and factor analysis, we were able to identify three groups that had been influenced by attitudes towards software publishers, general acceptance, convenience, and ethics. A decision tree method linked each pirate profile to demographic and computer-related variables. It showed that, while age was negatively related to software piracy, computer experience or computer usage demonstrated an ambiguous relationship to software piracy. Moreover, older respondents who used university software mainly at their workplace tended to pirate less frequently, while students tended to be pirates more often than university employees. Also Malays were the least frequent pirates in all the Singapore ethnic groups.     

Emergent self-organizing feature map for recognizing road sign images

Road sign recognition system remains a challenging part of designing an Intelligent Driving Support System. While there exist many approaches to classify road signs, none have adopted an unsupervised approach. This paper proposes a way of Self-Organizing feature mapping for recognizing a road sign. The emergent self-organizing map (ESOM) is employed for the feature mapping in this study. It has the capability of visualizing the distance structures as well as the density structure of high-dimensional data sets, in which the ESOM is suitable to detect non-trivial cluster structures. This paper discusses the usage of ESOM for road sign detection and classification. The benchmarking against some other commonly used classifiers was performed. The results demonstrate that the ESOM approach outperforms the others in conducting the same simulations of the road sign recognition. We further demonstrate that the result obtained with ESOM is significantly more superior than traditional SOM which does not take into the boundary effect like ESOM did.