The Optimum Sowing Time for Plastic-film Corn and the Application of Two Related Theories

There are two main theories, the 'temperature-raising' theory and the 'precipitation-based regulation' theory, which guide the optimum sowing time of the plastic-film corn. The former was applied in the humid or semi-humid ecotope and on irrigated or half-shaded land in the arid and semi-arid ecotopes, while the latter was suitable for the dry-farming land in the semi-arid ecotope. The results of experiments and investigations for many years showed that the corn output was increased by 69.2% when the former theory was applied to guide the optimum sowing time for plastic-film corn in the semi-humid ecotope, and by 60. 0% when the latter theory was applied in the semi-arid ecotope. In the semi-arid ecotope, however, the output was increased only by 15.7% when the former theory was applied, and even dropped by 14.4% when the latter theory was applied.

Yield and mechanical properties of veneer from Brachystegia nigerica

In an effort to find suitable wood from natural forest to meet the demand for veneer products, the yield and tensile strength of veneers produced from Brachystegia nigerica were investigated. Two trees of B. nigerica were separately selected from 10 different natural forest zones while two logs were obtained from each tree. The logs were debarked and steamed in a vat prior to rotary peeling and slicing for veneer production. The optimum steam temperature was determined by considering different temperatures： 50℃, 60℃, 70℃, 80℃ and 90℃ for 24 h. Thereafter, optimum steam time was determined at the optimum temperature by considering durations of 24, 48, 72 and 96 h. The average taper of 0.75 mm per 1.0 m length was recorded for B. nigerica, indicating that the logs were reasonably cylindrical; thereby its logs are good for the production of veneer. The yield ranged from 44% to 61% with an average of 52% of the log input. The tensile strength of the veneer was tested perpendicular to grain and both peeled and sliced veneers had the highest tensile strength between 70℃ and 90℃, suggesting that softening of wood polymers, especially lignin, is between 70℃ and 90℃. The optimum temperature and time for veneer production are 70℃ and 48 h, respectively. Commercial production of veneer from B. nigerica is feasible based on the yield and mechanical properties of the obtained veneer, thereby encouraging the expansion of the scope of its utilization.

Element Conception Related to Lifetime and Maintenance of Pipelines in Service

Introduced in this paper are key issues about the lifetime and maintenance of pipelines in service. Some important conceptions are discussed, namely （1） The lifetime and probabilities of failures （PoF） of pipelines are defined,and their determination and calculation are discussed; （2） The key issues about the maintenance and safety of pipelines are demonstrated, and the optimal maintenance periods of pipelines are calculated.

Research on Robotized Advance Support and Supporting Time for Deep Fully Mechanized Excavation Roadway

To keep coal workers away from the hazardous area with frequent accidents such as the roof fall and rib spalling in an underground coalmine,we put forward the solution with robotized self-moving anchor-supporting unit.The existing research shows that the surrounding rock of the roadway has self-stability,and the early or late support is not conducive to the safe and reliable support of the roadway,so there is a problem of support opportunity.In order to study the supporting effect and the optimal supporting time of the above solution,we established the mechanical coupling model of surrounding rock and advance support,and investigated the surrounding rock deformation and advance support pressure distribution under different reserved roof subsidence by using the numerical simulation software FLAC3D.The results show that the deformation of surrounding rock increases and finally tends to a stable level with the increase of pre settlement of roadway roof,and when the pre settlement of roof is between 8-15 mm,the vertical pressure of the top beam of advance support reaches the minimum value,about 0.58 MPa.Based on the above research,we put forward the optimum supporting time in roadway excavation,and summarized the evaluation method based on the mechanical coupling model of surrounding rock-advance support.

A model of vehicle replacement time with overloading cost constraint

Vehicle replacement time depends mainly on the rate of deterioration.Overloading has been found to be a significant factor of deterioration and cost accumulation.We examined the impact of overloading on vehicle deterioration and its total costs and hence the replacement time of vehicle fleets in Nigeria.The research design was a mixture of field survey and a longitudinal study of vehicle fleets of three transport companies in Benin City,Nigeria.The population of the study consisted of all interstate transport companies in Benin City.Multi-stage sampling was used to select the three transport companies studied.An overloading factor was developed and used to estimate the cost of operating overloaded vehicles.Research data were analysed using discrete dynamic programming,which was implemented using computer software developed through Pascal Programming.Results indicate that overloading significantly precipitates vehicle deterioration,increases operating and total cost and thus affects replacement time of vehicles.

A Markov chain model of mixing kinetics for ternary mixture of dissimilar particulate solids

This paper presents a simple but informative mathematical model to describe the mixing of three dissimilar components of particulate solids that have the tendency to segregate within one another. A nonlinear Markov chain model is proposed to describe the process. At each time step, the exchange of particulate solids between the cells of the chain is divided into two virtual stages. The first is pure stochastic mixing accompanied by downward segregation. Upon the completion of this stage, some of the cells appear to be overfilled with the mixture, while others appear to have a void space. The second stage is related to upward segregation. Components from the overfilled cells fill the upper cells （those with the void space） according to the proposed algorithm. The degree of non-homogeneity in the mixture （the standard deviation） is calculated at each time step, which allows the mixing kinetics to be described. The optimum mixing time is found to provide the maximum homogeneity in the ternary mixture. However, this “common” time differs from the optimum mixing times for individual components. The model is verified using a lab-scale vibration vessel, and a reasonable correlation between the calculated and experimental data is obtained