The main classification and delimitation of the world today is based on socioeconomic and geopolitical principles. The criteria of classification cities in the world are centered on the degree of urbanization. Classification of cities in the world depend on a set of criteria, centered on the degree of urbanization. Urbanization sterns from an individual and corporate efforts to shortens the expenses and time, needed in commuting and transportation from job to job. Sanitation of a city is a topic of paramount importance. A city will more likely have issues relating to political, technical decision if good urbanization and sanitization are not emphasized. This article focused on poor housing systems and slums in Douala, the largest city and commercial center of Cameroon, Africa. This study argued that the inability of the city authorities to deal with sanitation and waste management in Douala has health and social implications. However, the study outlined certain recommendations to remedy the problem associated with poor waste management and sanitations in the city of Douala.

Radiation levels were measured around eight diagnostic centres in Owerri, Imo State Nigeria using a portable Geiger Muller counter model GCA-04. The measurements were taken when the radiation sources (x-ray machines) were operational and non-operational. When the machines were non-operational, the background radiation ranged from 0.63 to 1.48 mSv/yr. When the machines were operational, the radiation levels ranged from 0.82 to 24.28 mSv/yr; this adds between 0.19 to 23.14 mSv/yr to the existing background radiation. The diagnostic centres used in this work have background radiation level below the world average dose limit of 2.16 mSv/yr for natural background radiation. Seven centres had annual dose rates that were below the 1.25mSv/yr dose limit for the public when the radiation source is not on and only one centre had a value still below the dose limit for the public when the radiation source was on. The other centres had higher values of annual dose rate when the safety of the general public is considered both for the cases when the radiation source was operational and non-operational.

Trailer mobile robot consists of a tractor and trailer composed of several sections, the tractor performs driving and steering tasks, and the trailer passively follows the tractor movement, such robot systems are typically used to automate factories, airports, railway stations, shipping docks, nuclear environment and so on, to perform material transport, baggage handling, cargo transport and other tasks.

The main control problem of mobile robot with trailer is path tracking control. The problem has become complicated by the presence of multiple bodywork. The mobile robot with trailer mainly includes the two types of the coupling trailer and the Off-axis trailer, and the Off-axis trailer cannot be converted into chain system, and the Linearization method is adopted or the virtual robot method is constructed. The paper [1] adopts the Linearization method and designs the discontinuous feedback controller for the forward tracking and reversing tracking of the line and the arc for the model Robot and the trailer system. In the paper [2], a virtual robot, which is located at the rear of the trailer and symmetrical with the tractor, is constructed for the system of the trailer, which realizes the tracking control of the original system by controlling the virtual robot. He Zhanbin and Ma Baoli transformed the kinematics equation of the Off-axis trailer mobile robot into a time-state model and designed a linear switched feedback stabilizing controller to ensure that the state of the robot converges to the small neighborhood of the origin in finite time [3]. The internal model principle of Zhou and Ma is used to design the linearization dynamic Feedback Control Law of the system, which ensures that the path tracking error is bounded and finally uniformly bounded [4]. In paper [5], the control problem of tracking any path at the midpoint of the axle with continuous time-varying and possibly changing sign is studied. The designed control law can realize the tracking of a given path by a trailer mobile robot. Because the coupling trailer system can be converted into a general chain system, we usually use the Lyapunov method to study it. In the paper [6], Samson transformed the system into an oblique symmetric chain system by coordinate and output transformations, the control law is designed to track the specified location. A local tracking controller with exponential convergence is proposed based on Lyapunov method by Astolfi, which is used for straight line and arc forward tracking control of this kind of robot [7]. The asymptotically convergent reversing tracking controller is designed for two-body systems based on Lyapunov method [8].

This paper mainly studies the tracking problem of the coupling trailer under the camera. Based on the adaptive sliding mode control, two sliding surfaces are designed, and the corresponding sliding mode variable structure controller is obtained for the chain system. The sliding mode control method is simpler and less computational than other methods, but the disadvantage is that it will cause unnecessary jitter. In this paper, the controller is improved for its jitter problem, and the jitter can be reduced appropriately.