DISCUSSIONS:

The diffusion process on the desk cannot be characterized by a simple diffusion equation. In order to analyze, we have to divide the desktop into two area; the working area and the storage area. The working area is a part of desk where one usually uses to read or write (denoted by W), whereas the storage area is a part where one keeps documents or books or some other staffs (denoted by S). At the beginning of the process, one does not have materials to pile, thereby there is no clear boundary between the working area and storage area.see Fig. 1. Then the documents and books start piling on the right-hand side of the desk with some fluctuation. The working area is the left-hand side of the desk.see Fig. 2. Once a pile has been formed, the boundary between the working area and storage area which is denoted by the dashed line becomes apparent. The storage area slowly grows and intrudes to the working area. There is a minimal size of working space to work and due to the deadline to finish works, there is a pressure which pushes the boundary out to the storage area. The strength of pressure is depending on the importance of tasks at that time. Once the pressure of piling and pressure to work are balanced, then the state on the desk attains to the equilibrium state. The relaxation time from the initial metastable state to the equilibrium state is estimated about three weeks. Notice that due to the photographic measurements, the owner could realize the mess of desk. This measurements thus disturbs the dissipation process. The real relaxation time may be shorter than current experiment. The estimation of the real relaxation time will be left for a future study.