Tadachika Seno

Traffic jam induced by a crosscut road in a traffic-flow model

A deterministic cellular automaton model is presented to simulate the traffic jam induced by a crosscut road in a two-dimensional traffic flow. The effect of a crosscut road on the traffic flow is investigated by the use of a computer simulation. The traffic jam appears when a shock (discontinuous interface of different car densities) is formed. The condition for shock formation is derived for car densities py and px of the crosscut road and its crossing streets. The phase diagram and the dependence of the traffic flow on the car densities are shown. Also, we study the shock structure and the scaling of its width. The width Δw of the shock scales with the system size L as Δw ≈ L12. We present a self-consistent mean-field theory for the traffic flow.

In-situ Electrokinetic Remediation of Soil and Water in Aquifer Contaminated by Heavy Metal

The electrokinetic method for the remediation of contaminated aquifers is realized by applying a fixed low voltage direct current between an anode and a cathode placed into the contaminated zone. The purge water is injected into the anode well and drawn out from the cathode well with the pollutants. Therefore the application of this method to in-situ remediation of aquifers is relatively simple. This method can be applied effectively to remove heavy metals. These cannot be decomposed by other methods such as bioremediation, although this method can be used also for decontamination of organic chemicals in aquifers. However, the variations of the operational variables of this method have not been made clear, because this method is relatively new and is an inovative technique. In order to investigate the operational variables of electrokinetic remediation, a mathematical model has been constructed based on the physico-chemical transport process of heavy metals in the pore water of a contaminated aquifer. The transport of heavy metals is driven not only by the hydraulic flow due to the purge water, but also by electromigration caused by the electric potential gradient. The electric potential between the anode and the cathode is the important operational variable for electrokinetic remediation. From the numerical simulations using this model it is confirmed that remediation starts from the upstream anode and the heavy metal is gradually transported downstream towards the cathode and is drawn out through the purge water.

Drift-Induced Transition and Growth-Rate Distribution in Diffusion-Limited Aggregation

Morphological changes induced by drift in the diffusion-limited aggregation (DLA) is investigated by using the experimental method of electrodeless reduction of silver ions from a AgNO 3 aqueous solution. The silver metal is grown around the electrodeless copper deposition plate within Hele-Shaw cell under an applied electric field which is induced by the electrodes positioned outside Hele-Shaw cell. The applied electric field induces drifts on the diffusive motion of silver ions. The growth pattern of the silver metal on the circular deposition plate is studied by varying strength of the applied electric field. The characteristic growth patterns appear due to the drift of silver ions. The growth-rate distribution around the circular deposition plate is determined experimentally. It is found that the drift-induced transition between growing and no growin g phases occurs at a position on the circular plate.

Electric current and potential variations during electrokinetic removal of heavy metal from aquifer

The electrokinetic method for the remediation of contaminated aquifers is realized by applying a fixed low voltage direct current between anode and cathode which are set into the contaminated zone. The electric current and electric potential between anode and cathode is the important operational variables for the electrokinetic remediation. However, the variations of these variables have not been cleared, because this method is relatively new and is an inovative technique. Depending on the time variation of the electric curret, the removal process can be divided into the first stage and the second one. In the first stage the electric current increases with time, but in the second stage it is almost unchangeable. The distribution of electric potential between electrodes gradually becomes higher and higher (decrease in electric resistance) with time, although the applied voltage between the electrodes is maintained constant.