It is reported that a surface model of Polyakov strings undergoes a first-order phase transition between smooth and crumpled (or branched polymer) phases. The Hamiltonian of the model contains the Gaussian term and a deficit angle term corresponding to the weight of the integration measure dX in the partition function. PACS. 64.60.-i General studies of phase transitions -68.60.-p Physical properties of thin films, nonelectronic -87.16.Dg Membranes, bilayers, and vesicles
The Nambu-Goto model is investigated by using the canonical Monte Carlo simulations on fixed connectivity surfaces of spherical topology. Three distinct phases are found: crumpled, tubular, and smooth. The crumpled and the tubular phases are smoothly connected, and the tubular and the smooth phases are connected by a discontinuous transition. The surface in the tubular phase forms an oblong and one-dimensional object similar to a one-dimensional linear subspace in the Euclidean three-dimensional space R3 . This indicates that the rotational symmetry inherent in the model is spontaneously broken in the tubular phase, and it is restored in the smooth and the crumpled phases.
In this paper, several numerical simulations of framed structures were performed to identify the specific structural cause of the high-speed total collapse of the World Trade Center (WTC) towers, which occurred during the 9/11 terrorist attacks. A full-scale aircraft impact simulation of the WTC tower 2 was conducted to examine the dynamic unloading phenomena that occurred in the core columns during impact, which may have caused the destruction of the splices between column sections. Fire-induced progressive collapse analyses of a high-rise tower with an outrigger truss system were carried out to qualitatively demonstrate the effects of fire patterns and structural parameters on the behavior of this tower's collapse. In general, the tower remained standing for a longer period of time due to the catenary action of the outrigger truss system only if the load paths in the tower were protected and if the member connections were strong enough. However, in these analyses, the collapse speed never reached a value as high as that of the free fall observed in the WTC collapse, which occurred while the splices between column sections still retained their tensile strength. From these results, it is evident that the high-speed collapse of the WTC towers might have been caused by an inherent weakness in their member connections in addition to the destruction directly caused by the aircraft impact.
Acontrolled explosion technique using high explosives has been developed in recent years. Although the blast demolition technique increases work eMcienCy , it poses a high risk of damaging neighboring bu皿 山 ngs , especially in urban areas . It also requ 面es high levels of knowledge and experience
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