Flexibility is a particularly important biomechanical property for intracranial vascular stents. To study the flexibility of stent, the following work was carried out by using the finite element method: Four mechanical models were adopted to simulate the bending deformation of stents, and comparative studies were conducted about the distinction between cantilever beam and simply supported beam, as well as the distinction between moment-loading method and displacement-loading method. A complete process as implanting a stent including compressing, expanding and bending was also simulated, for analyzing the effects of compressing and expanding deformation on stent flexibility. At the same time, the effects of the arrangement and the number of bridges on stent flexibility were researched. The results show that: 1. A same flexibility index was obtained from cantilever beam model and simply supported beam model; displacement-loading method is better than moment-loading for simulating the bending deformation of stents. 2. The flexibility of stent with compressing and expanding deformation is lower than that in the initial form. 3. Crossly arranging the neighboring bridges in axial direction, can effectively improve the stent flexibility and reduce the flexibility difference in various bending directions; the bridge number, has proportional non-linear correlation with the stent rigidity as well as the maximum moment required for bending the stent.

Combined structural and textural studies of the quartz veins of the Panasqueira W-Cu-Sn deposit of central Portugal have revealed the presence of coeval forms of crack-seal and cavity-fill mineral textures. The textures result from the dilational and infilling histories of brittle fractures produced within the host rock by the intrusion of pressurised fluids. Crack-seal textures were produced wherever or whenever crystal growth rates matched or were greater than fracture dilation rates, whereas cavity-fill textures developed wherever or whenever dilation rates were quicker than those of crystal growth. Rates of dilation within the blade-like fissures were naturally lowest at the edges, where types of crack-seal textures were produced, and highest in the cores, where cavity-fill texture formed. During propagation the linkage of adjacent echelon blades, by the rupture of the host-rock straps (bridges) between them, enhanced dilation rates and led to the widespread development of cavity-fill textures. Within the composite fissures so produced, environments in which types of crack-seal textures could form were restricted to the fissure margins and to areas where the tensile strain was sympathetically shared between closely spaced fissures. Textures and minerals characteristic of each fracture environment were able to form simultaneously within the fracture system.

Despite the high degree of technological sophistication visible in other aspects of urban engineering, the archaeology of pre-Columbian Mesoamerica has revealed curiously few examples of bridges or formal, permanent water-crossing structures. The ancient city of Cotzumalhuapa, where at least five such structures have been identified, is a notable exception. The author reviews the archaeological and historical evidence for these bridges, and reflects upon the diversity of engineering technologies that they reveal. Although it remains unclear why bridges are absent at many other contemporaneous sites, these examples offer a fascinating glimpse into the urban planning of structured mobility in Mesoamerica.

This paper presents the flow structure under a partially inundated bridge deck measured by using particle image velocimetry (PIV) and flow visualization techniques. The approaching flow was subcritical having Froude number F in the range 0.12 ∼ 0.55. The proximity ratio Pr (= ratio of clearance below the bridge deck h to the total depth of deck D) was varied from 0.57 to 2. Depending upon the Froude number F and proximity ratio Pr, four types of flow structures under the bridge deck were recognized. In flow Type I, the water surface elevation on the downstream side of bridge deck is slightly lower than the counterpart on the upstream side, and the shear layer formed at the bottom of upstream girder continuously fluctuates and touches soffit of all girders. In the case of flow Type II, the water surface on downstream side of bridge deck is lower than that on the upstream side and the shear layer originating from the upstream girder impinges near the third cavity between girders. However, in both the cases, the cavities between the girders are completely occupied by vortices. On the contrary, in the cases of flow Type III and flow Type IV, the flow is separated from the upstream girder edge. However, in flow Type III, the separated flow impinges on successive girders and cavities are partially filled by water; while in flow Type IV, the flow is totally separated from the deck bottom like orifice flow. The phenomena of vortex formation within the cavities are discussed for the cases of flow Type I and flow Type II. Also, for the vertical distribution of mean streamwise velocity in the shear layer below bridge deck, the nonlinear regression equations are developed. Using the distributions of measured mean streamwise velocity within the shear layer below the bridge deck at different streamwise distances, the similarity profile is obtained. The mean velocity deficit (usl – usu) and representative thickness bs are considered as the appropriate characteristic velocity and length scales for developing similarity profile. The proposed characteristic scales provided unique similarity profiles having promising regression coefficient. The similarity profile proposed is suitable for more general case of bridge deck having different bridge girders and even for rectangular block without girder. Further, the turbulence characteristics for the flow below the bridge deck are also presented.