No abstract

Purpose -To use distinct element simulation (PFC2D) to investigate the relationships between microparameters and macroproperties of the specimens that are modeled by bonded particles. To determine quantitative relationships between particle level parameters and mechanical properties of the specimens. Design/methodology/approach -A combined theoretical and numerical approach is used to achieve the objectives. First, theoretical formulations are proposed for the relationships between microparameters and macroproperties. Then numerical simulations are conducted to quantify the relationships. Findings -The Young's modulus is mainly determined by particle contact modulus and affected by particle stiffness ratio and slightly affected by particle size. The Poisson's ratio is mainly determined by particle stiffness ratio and slightly affected by particle size. The compressive strength can be scaled by either the bond shear strength or the bond normal strength depending on the ratio of the two quantities.Research limitations/implications -The quantitative relationships between microparameters and macroproperties for parallel-bonded PFC2D specimens are empirical in nature. Some modifications may be needed to model a specific material. The effects of the particle distribution and bond strength distribution of a PFC2D specimen are very important aspects that deserve further investigation. Practical implications -The results will provide guidance for people who use distinct element method, especially the PFC2D, to model brittle materials such as rocks and ceramics. Originality/value -This paper offers some new quantitative relationships between microparameters and macroproperties of a synthetic specimen created using bonded particle model.

The experimental results of low pressure supersonic molecular beam injection (SMBI) fuelling on the HL-2A closed divertor indicate that during the period of pulsed SMBI the power density convected at the target plate surfaces was 0.4 times of that before or after the beam injection. An empirical scaling law used for the SMBI penetration depth for the HL-2A plasma was obtained. The cluster jet injection (CJI) is a new fuelling method which is based on and developed from the experiments of SMBI in the HL-1M tokamak. The hydrogen clusters are produced at liquid nitrogen temperature in a supersonic adiabatic expansion of moderate backing pressure gases into vacuum through a Laval nozzle and are measured by Rayleigh scattering. The measurement results have shown that the averaged cluster size of as large as hundreds of atoms was found at the backing pressures of more than 0.1 MPa. Multifold diagnostics gave coincidental evidence that when there was hydrogen CJI in the HL-2A plasma, a great deal of particles from the jet were deposited at a terminal area rather than uniformly ablated along the injecting path. SMB with clusters, which are like micro-pellets, will be of benefit for deeper fuelling, and its injection behaviour was somewhat similar to that of pellet injection. Both the particle penetration depth and the fuelling efficiency of the CJI were distinctly better than that of the normal SMBI under similar discharge operation. During hydrogen CJI or high-pressure SMBI, a combination of collision and radiative stopping forced the runaway electrons to cool down to thermal velocity due to such a massive fuelling.

Rotary ultrasonic machining (RUM) is a relatively low cost and environmentally benign process for machining of advanced ceramics. Much effort has been made to theoretically and experimentally investigate material removal rate, surface roughness, and tool wear in RUM. However, there is no report on systematic study of edge chipping in RUM drilling of ceramics. This paper presents the results of a study on edge chipping in RUM drilling of advanced ceramics. The study is conducted by an integrated approach, combining designed experiments and FEM (finite element method) analysis. The designed experiments will reveal the main effects as well as interaction effects of process variables (spindle speed, ultrasonic power, feedrate, and grit size) on cutting force and chipping thickness. FEM simulations will provide the stress and strain distributions in the workpiece while being drilled by RUM. Furthermore, the relationship between chipping thickness and cutting force obtained from the FEM simulations will be compared with that obtained from the designed experiments.

It is well known that the control/intervention of some genes in a genetic regulatory network is useful for avoiding undesirable states associated with some diseases like cancer. For this purpose, both optimal finite-horizon control and infinite-horizon control policies have been proposed. Boolean networks (BNs) and its extension probabilistic Boolean networks (PBNs) as useful and effective tools for modelling gene regulatory systems have received much attention in the biophysics community. The control problem for these models has been studied widely. The optimal control problem in a PBN can be formulated as a probabilistic dynamic programming problem. In the previous studies, the optimal control problems did not take into account the hard constraints, i.e. to include an upper bound for the number of controls that can be applied to the captured PBN. This is important as more treatments may bring more side effects and the patients may not bear too many treatments. A formulation for the optimal finite-horizon control problem with hard constraints introduced by the authors. This model is state independent and the objective function is only dependent on the distance between the desirable states and the terminal states. An approximation method is also given to reduce the computational cost in solving the problem. Experimental results are given to demonstrate the efficiency of our proposed formulations and methods.

The described HPLC methods are simple, accurate and selective techniques for separation and quantification of anthraquinones in roots of P. multiflori and other plant samples.

No abstract

No abstract