This paper explores the implications of reductions in tariffs or transport costs on the rate of innovation in a quality ladders model where Þrms from both countries innovate. If a country raises its tariffs, its wage rises relative to the other country and its Þrms become technology leaders for a larger fraction of products, but the aggregate rate of innovation falls. If transport costs fall sy...

‎an  oriented perfect path double cover (oppdc) of a‎ ‎graph $g$ is a collection of directed paths in the symmetric‎ ‎orientation $g_s$ of‎ ‎$g$ such that‎ ‎each arc‎ ‎of $g_s$ lies in exactly one of the paths and each‎ ‎vertex of $g$ appears just once as a beginning and just once as an‎ ‎end of a path‎. ‎maxov{'a} and ne{v{s}}et{v{r}}il (discrete‎ ‎math‎. ‎276 (2004) 287-294) conjectured that ...

The urban fringe, as a part of an spatial form, plays considerably major role in expansion and shrinking. After decades rapid development, Chinese cities have advanced from simple stage to expansion–shrinking-coexistence stage. In shrinking expansion, the fringe shows different characteristics requirements for specific aspects such planning, land use, landscape, ecological protection, architect...