This study was aimed to assess the quality of surface water and groundwater in the Bangangté municipality of West Cameroon with focus on Nenga I, Banekouane I and “quartier 2”. This research was initiated in the selected quarters because the quality of water consumed by the population is only appreciated by its clear appearance. Water samples were collected and analysed using standard methods in the months of December 2013 and April 2014; enabling organoleptic, physico-chemical and bacteriological characteristics to be determined. It was observed from the results obtained that the water samples were contaminated to different extents by phosphates, heavy metals and bacteria. This contamination could be due to lack of disinfection, uncontrolled defeacation  and the use of fungicides for agricultural activities. These water sources contained a high pollution level of iron, lead and chromium with non-detectable chloride content and with an unacceptable pH. Bacteriological investigations revealed that all the analysed samples contained indicators of faecal pollution such as E. coli, Salmonella, Streptococcus, Proteus and Enterobacteria. Consequently, their consumption exposes consumers to health risks, and the public  is thus informed  that  although  the  water  has no odour  and  appears clean,  it  contains  infectious  bacteria and thus  should  be  treated  by  boiling or chlorination prior to consumption.

The distribution of cadmium in different parts of beans and sweet potatoes plants was investigated after the process of phytoextraction. Cadmium which is extremely toxic in relatively low concentrations is highly mobile in the soil-plant system and enters into the food chain easily, where it may provoke both human diseases and well known toxicity effects on animals, microorganisms and plants. Field experiments were carried out with two crops: beans and sweet potato. They were planted in soils contaminated with different cadmium concentrations and in an uncontaminated soil to determine the extent of absorption of cadmium by Phaseoulus vulgaris (beans) and Ipomoea batatas L (sweet potatoes) in soils. Results showed that cadmium absorption by the two plants increased with an increase in the concentration of added cadmium. Within beans and sweet potatoes plants, the maximum Cd content was found in the leaves (43.32 mg kg^-1 for sweet potatoes and 34.75 mg kg^-1for beans). Sweet potatoes had the highest cadmium absorption capacity compared to beans. The cadmium contents in the edible roots of all two plants exceeded the allowable quantities stipulated by various nations (maximum absorption values of 34.16 mg kg^-1 for sweet potatoes and 32.05 mg kg^-1 for beans).  The extent of absorption of cadmium by sweet potatoes and beans plants was compared and the extent to which cadmium can be dangerous to the health if beans and sweet potatoes planted on a soil contaminated with cadmium are consumed was evaluated and some recommendation made on the type of soils good for planting of beans and sweet potatoes. Thus, it can be concluded from the results obtained that plants growing in cadmium-contaminated  soils should be banned as foodstuff and soils with slight cadmium contamination should not be used for growing sweet potato, beans and  any other food crop.

Silk fibroin (SF)-cellulose nanocrystals (C) thin films with various compositions were prepared by a new shearing method utilizing aqueous solutions of both components. The nanocrystals used were supplied by a pilot scale facility located in Edmonton, Alberta. These particles were prepared by sulphuric acid hydrolysis of dissolving pulp. Relatively good homogeneity was obtained with each mixing ratio. Films with higher concentration of silk were characterized with reduced initial thermal stability when compared to the cellulosic control. On the other hand, there was a corresponding improvement in percentage thermal degradation when small quantities of silk were added to the cellulose nanocrystals. The main x-ray diffraction peaks were present in most composites. However, for systems where silk was added to cellulose nanocrystals (10C:S and 5C:S), there was a distinct improvement in the crystallinity index. Finally, the addition of silk (high quantities) to the cellulosic material resulted in a sharp decrease in mechanical properties.

The robust stabilization problem of nonholonomic wheeled mobile robots (WMR) has received a great deal of attention in the past several decades [1,2,3,4,5,6,7]. WMR is a typical nonholonomic mechanical system. It can't use smooth or time invariant state feedback to stabilize the nonholonomic mechanical system because it doesn’t meet the Brockett smooth stabilization conditions [3]. Many scholars took the chained transform [4], synovial control [5], discontinuous feedback [6] and time-varying state feedback [7] and so on to realize the control of mobile robot. In the control of nonholonomic WMR, it is usually assumed that the robot states are available by using sensor measurements. In practice, there are uncertain disturbances of kinematics model. In order to overcome this problem, visual feedback is an important approach to improve the control performance of mobile robots.

Visual feedback is usually lack of depth information [8,9,10]. Therefore, the camera is fixed on the ceiling. In [9], the feedback from uncalibrated and fixed (ceiling-mounted) cameras were used. In [10], the adaptive tracking controllers were developed to achieves asymptotic tracking. Control strategy was proposed based on the image by controlling the stabilization system for mobile robot in polar geometry pole in [11]. The dynamic robust stabilization of mobile robots with uncertain camera parameters was investigated in [12]. In [13], a new method based on time-varying feedback was developed to stabilize the tractor-trailer wheeled robot around the origin. In [14], a new smooth time-varying feedback controllers was proposed to exponentially stabilize the uncertain chained system by using state-scaling and control theories for two cases. 

The contribution of this paper is that a kinematics controller is proposed to stabilize a class of dynamic models of nonholonomic mobile robots in the presence of uncertain disturbance with unknown parameters exponentially in a more general situation. And a torque is proposed by using a computed-torque method to make the actual velocity track the desired one infinite time.

The rest paper is organized as follows. Section 2 introduces the kinematic model and dynamic model of WMR. In section 3, the controllers are designed for WMR and give the proof rigorously. In section 4, the simulation results demonstrate the effectiveness of the proposed strategies. Finally, the major contributions of the paper are summarized in section 5.