Strong, monochromatic, coherent and continuous terahertz (THz) radiation was generated from the intrinsic Josephson junctions in a cylindrical stand-alone mesa sandwich structure fabricated from a single crystal of the high-temperature superconductor Bi2Sr2CaCu2O8+δ. By varying the base temperature and the dc bias current-voltage characteristic (IVC) points, the emission frequency is tunable from 0.5 to a record high 2.4 THz observed on two inner IVC branch points. Strong emission power peaks were observed at 1.0 THz and 1.6 THz. This device is hence an excellent candidate to fill the “THz gap” between ∼1.4 and 2.0 THz.
The damage distribution in Adra town (south-eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south-east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short-period microtremor observations were performed in 160 sites on a 100 m × 100 m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1-0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N , where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1-D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Figure 4. Continuous microtremor measurements for stationarity analysis: (a) tunnel site (hard rock) and (b) beach site (soft soil).Figure 12. An example of the methodology followed to simulate ground and building responses during the 1993 earthquake in Adra: (a) E-W component of strong motion record in Adra town; (b) simulated strong motion on sediment soil site with a thickness of 30 m (Case 2); (c)-(e) simulated strong motions at the top of buildings with four, six and eight storeys, respectively; and (f) amplitude spectra of the previous strong motions.
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