Integrating planning and control for single-bodied wheeled mobile robots

This paper presents an approach to couple path planning and control for mobile robot navigation in a hybrid control framework. We build upon an existing hybrid control approach called sequential composition, in which a set of feedback control policies are prescribed on well-defined domains contained in the robot’s free space. Each control policy drives the robot to a goal set, which lies in the domain of a subsequent policy. Control policies are deployed into the free state space so that when composed among one another, the overall action of the set of control policies drives the robot to perform a task, such as moving from a start to a goal location or patrolling a perimeter. A planner determines the sequence of control policies to be invoked. When control policies defined in this framework respect the low-level dynamics and kinematics of the system, this formal approach guarantees that high-level tasks are either accomplished by a given set of policies, or verifies that the tasks are not achievable with the given policies.     

The effect of lighting changes on simultaneous colour contrast: a new aspect of colour rendition

Among the many metrics used to compute the colour rendition of a light source which have been investigated in recent years, most consider only the spectral power distribution of the light source being tested. To highlight aspects not usually considered in the development of colour rendition metrics, and to propose future directions for alternative approaches consistent with human visual perception, an experiment was conducted to examine colour appearance variations on certain spatial visual content configurations, in other words the effects of illusions under different light sources. Results indicate that stronger simultaneous contrast configurations have a more unpredictable variation in appearance. Therefore, it is proposed that colour spatial distribution should be considered for the future generation of rendering metrics.     

A spatially variant white-patch and gray-world method for color image enhancement driven by local contrast

Starting from the revolutionary Retinex by Land and McCann, several further perceptually inspired color correction models have been developed with different aims, e.g. reproduction of color sensation, robust features recognition, enhancement of color images. Such models have a differential, spatially-variant and non-linear nature and they can coarsely be distinguished between white-patch (WP) and gray-world (GW) algorithms. In this paper we show that the combination of a pure WP algorithm (RSR: Random Spray Retinex) and an essentially GW one (ACE) leads to a more robust and better performing model (RACE). The choice of RSR and ACE follows from the recent identification of a unified spatially-variant approach for both algorithms. Mathematically, the originally distinct non-linear and differential mechanisms of RSR and ACE have been fused using the spray technique and local average operations. The investigation of RACE allowed us to put in evidence a common drawback of differential models: corruption of uniform image areas. To overcome this intrinsic defect, we devised a local and global contrast-based and image-driven regulation mechanism that has a general applicability to perceptually inspired color correction algorithms. Tests, comparisons and discussions are presented.     

Stress‐Enhanced Swelling of Silica: Effect on Strength

From the work of Le Chatelier [1884], it is well known that chemical reactions that exhibit a change in volume are sensitive to the ambient pressure of the reaction. Increasing the pressure will alter the ratio of reaction products to reactants. If the change in volume is constrained to occur at a surface, then such reactions can result in residual stresses that affect the strength of the solid. These effects are applicable to silica glass, which increases in volume when reacting with water. In this paper, we discuss the possibility of using this effect to strengthen silica glass. Using a modification of Le Chatelier's theory to handle applied stresses, we show that water penetration into the surface of silica glass can yield sufficient residual stress to increase the strength of silica glass into the GPa range. Applying these ideas to recent data published by Lezzi et al., we are able to attribute the strengthening they observe to a water/silica reaction under an applied tensile stress.     

A general weight function approach to compute mode-II stress intensity factors and crack paths for slightly curved or kinked cracks in finite bodies

A simple procedure is proposed that allows computing the stress intensity factors for slightly curved and kinked cracks in finite bodies. Basis of the method is the computation of the stress field around a straight crack under externally applied tractions. Then, this auxiliary crack is replaced by the crack of interest. The stress intensity factors are computed from the stresses caused by the auxiliary crack using the weight function technique. In a practical application of the method, mode-II stress intensity factors are computed for the edge-cracked half-space. From the usual crack path condition, K_II = 0, the paths of propagating cracks under biaxial loading and the critical biaxiality ratio for global directional instability are computed. The results are in very good agreement with finite element computations.     

Multistage and tandem mass spectrometry of glycosylated triterpenoid saponins isolated from Bacopa monnieri: comparison of the information content provided by different techniques

Whereas all state-of-the-art techniques in mass spectrometry (MS) have been extensively applied to oligosaccharides derived from glycoproteins, less effort has been devoted to the analysis of smaller glycoconjugates. In the present study, the application of a variety of MS techniques for the analysis of two dammarane-type triterpenoid saponins isolated from B. monnieri is reported. The structural information provided by ESI-ion trap (IT)-, AP-MALDI-IT-, and MALDI-IT/reflectron time-of-flight (RTOF)-MS, all utilizing low-energy collision-induced dissociation (CID), and MALDI-TOF/RTOF-MS, facilitating postsource decay and high-energy CID analysis, was compared. The applied desorption/ionization technique does not influence the fragmentation of identical precursor ions in low-energy CID. All three fragmentation techniques clearly yield the sequence and branching of the glycan moiety as well as the molecular mass of the intact aglycon. Cross-ring cleavage of the branching sugar, which gives some information about the sugar linkages, was mainly observed in low-energy CID. High-energy CID, on the other hand, yielded some additional diagnostic fragment ions from the aglycon moiety. Internal cleavage ions are formed by alternative mechanisms in high-energy CID and are assumed to be diagnostic for some linkages. However, none of the applied MS techniques facilitates the identification of those saponins that differ only by their aglycon moiety (i.e., jujubogenin or pseudojujubogenin).