Dynamic compression characteristics of layered rock mass of significant strength changes in adjacent layers

Layered rock mass of significant strength changes for adjacent layers is frequently observed in underground excavation,and dynamic loading is a prevalent scenario generated during excavation.In order to improve the driving efficiency and reduce engineering accidents,dynamic compression characteristics of this kind of rock mass should be understood.The dynamic properties of a layered composite rock mass are investigated through a series of rock tests and numerical simulations.The rock mass is artificially made of various proportions of sand,cement and water to control the distinct strength variations at various composite layers separated by parallel bedding planes.All rock specimens are prefabricated in a specially designed mould and then cut into 50 mm in diameter and 50 mm in height for split Hopkinson pressure bar(SHPB)dynamic compression testing.The test results reveal that increasing strain rate causes the increases of peak strength,σ_p,and the corresponding failure strain,ε_p,while the dynamic elastic modulus,E_d,remains almost unchanged.Interestingly,under the same strain rates,Ed of the composite rock specimen is found to decline first and then increase as the dip angle of bedding plane increases.The obtained rock failure patterns due to various dip angles lead to failure modes that could be classified into four categories from our dynamic tests.Also,a series of counterpart numerical simulations has been undertaken,showing that dynamic responses are in good agreement with those obtained from the SHPB tests.The numerical analysis enables us to Iook into the dynamic characteristics of the composite rock mass subjected to a broader range of strain rates and dip angles than these being tested.

Optimal control system of the intermittent bus-only approach

To guarantee bus priority with a minimum impact on car traffic at intersections, an optimal control system of the intermittent bus-only approach （IBA） was proposed. The problems of the existing system are first solved through optimization： the judgment time of the IBA system was advanced to allow a bus to jump car queues if the bus was detected to arrive at the intersection, and the instant that the IBA lane became available to cars was controlled dynamically to increase the capacity of the IBA lane. The total car delay in one cycle was then analyzed quantitatively when implementing the optimal control system. The results show that in comparison with the existing system of the IBA, the car delay is greatly reduced and the probability of a car stopping twice is low after optimizing the IBA system.

A cytoprotective graphene oxide-polyelectrolytes nanoshell for single-cell encapsulation

Graphene oxide(GO)has been increasingly utilized in the fields of food,biomedicine,environment and other fields because of its benign biocompatible.We encapsulated two kinds of GO with different sizes on yeast cells with the assistance of polyelectrolytes poly(styrene sulfonic acid)sodium salt(PSS)and polyglutamic acid(PGA)(termed as Y@GO).The result does not show a significant difference between the properties of the two types of Y@GO(namely Y@GO1 and Y@GO2).The encapsulation layers are optimized as Yeast/PGA/PSS/PGA/GO/PGA/PSS based on the morphology,dispersity,colony-forming unit,and zeta potential.The encapsulation of GO increases the roughness of the yeast.It is proved that the Y@GO increases the survival time and enhance the activity of yeast cells.The GO shell improves the resistance of yeast cells against pH and salt stresses and extends the storage time of yeast cells.