Rotation of split cometary nuclei

A simple model for the rotational motion of split cometary nuclei is studied. A large-amplitude precession is easily excited due to the change of the moments of inertia even if the perturbation is small at the splitting. The damping timescale of the excited precession is widely ranged because of the uncertainty of the physical parameter of cometary nuclei. Another possibility for clarifying the evolution of the short period comets by studying the split cometary nuclei is also discussed

An Experimental Study of Bidding Behavior in Subcontract Auctions

It is commonly observed in practices that prime contractors solicit subcontract bids, prior to submitting their bids in procurement auctions: the auctioneers in subcontract auctions will become bidders in a procurement auction. This point is remarkably different from the standard theory of procurement auction. We presented a simple model of such subcontract auctions and conducted a laboratory experiment to examine the bidding behavior derived theoretically. We observed that in the subcontract auction, (1) subjects bid following the equilibrium bidding function derived theoretically, (2) the revenue equivalence between first-price and second-price mechanisms breaks down, and (3) the first-price mechanism more likely achieves ex post efficient allocations than the second-price mechanism.

Lightcurve of comet Austin(1989c1) and its dust mantle development

Brightness variations of comet Austin(1989c1) were investigated in terms of the variations of water production rate. We translated the visual brightness data into water production rates using Newburn's semi-empirical law. The curve of the water production rates as a function of heliocentric distance was compared with the model calculations that assumed energy balance between the solar incident and vaporization of water. Thermal flow in a dust mantle at a surface of the nucleus is also included in the model. The model calculations including the dust mantle are more favorable for the observed rate than non-dust mantle cases. The extinction after the perihelion passage suggests that the dust mantle developed gradually