Abstract:
we re-derive the solution for scattering and diffraction of elastic waves by a single spherical obstacle. a complete catalog for the coefficients in the series' expansions of scattered waves is presented. the classical solution is a superposition of incident and diffracted fields. plane p- or s-waves are assumed. they are expressed as expansions of spherical wave functions which are tested against exact results. the diffracted field is calculated from the analytical enforcing of boundary conditions at the scatterer-matrix interface. the spherical obstacle is a cavity, an elastic inclusion or a fluid-filled zone. a complete set of wave functions is given in terms of spherical bessel and hankel radial functions. legendre and trigonometric functions are used for the angular coordinates. results are shown in time and frequency domains. diffracted displacement amplitudes versus normalized frequency and radiation patterns at low, intermediate and high frequencies are reported. synthetic seismograms for some relevant cases are computed.

Abstract:
We re-derive the solution for scattering and diffraction of elastic waves by a single spherical obstacle. A complete catalog for the coefficients in the series’ expansions of scattered waves is presented. The classical solution is a superposition of incident and diffracted fields. Plane P- or S-waves are assumed. They are expressed as expansions of spherical wave functions which are tested against exact results. The diffracted field is calculated from the analytical enforcing of boundary conditions at the scatterer-matrix interface. The spherical obstacle is a cavity, an elastic inclusion or a fluid-filled zone. A complete set of wave functions is given in terms of spherical Bessel and Hankel radial functions. Legendre and trigonometric functions are used for the angular coordinates. Results are shown in time and frequency domains. Diffracted displacement amplitudes versus normalized frequency and radiation patterns at low, intermediate and high frequencies are reported. Synthetic seismograms for some relevant cases are computed.

Abstract:
we study the multiple scattering of elastic waves by a finite linear array of regularly distributed cylindrical obstacles. the transient response of the system for incident anti-plane shear waves is given in detail. we present an extension of an original solution for rigid cylinders, developed by some of us in 1983. the solution is formally obtained for harmonic excitation and fourier analysis provides the transient response. material properties of the cylindrical inclusions are considered. a 2-d formulation is constructed by superposition of the incident field upon the waves diffracted by each obstacle. the solutions for each obstacle are constructed as expansions of cylindrical wave functions, after imposing continuity conditions for the displacements and tractions at the scatterers matrix interfaces with the aid of graf's addition theorem. thus, the total field can be referred to any cylindrical coordinates. the infinite system is approximated by a finite one and numerical results are obtained for different values of the parameters. various cases of cavities and inclusions are studied. a double effect is produced by different filling materials, f. e. amplification at the incidence side and reductions at the far side, or vice versa. synthetic seismograms and snapshots are computed to illustrate the complex features of wave propagation for this inhomogeneous model.

Abstract:
several crack configurations are considered in order to show the importance of the cracks' geometry on the rayleigh-wave propagation. we use the indirect boundary element method, this numerical technique is based on an integral representation of the diffracted wave field, which has been reduced from somigliana's identity. the method allows us to evaluate the complete displacement field by the superposition of the free field and the diffracted field. it is remarkable that the free field is specified as incident rayleigh- waves, making the assumption of absence of cracks. the diffracted field is obtained from the integral representation by means of the presence of cracks. our results are compared with those previously published. we emphasize the amplitude reduction of rayleigh- waves while the interaction with the cracks take place. conspicuous wave amplification at the crack neighborhood is observed immediately after such interaction. this information may give us a way to characterize crack's depth and orientations from the analysis of the diffracted field.

Abstract:
Several crack configurations are considered in order to show the importance of the cracks’ geometry on the Rayleigh-wave propagation. We use the Indirect Boundary Element Method, this numerical technique is based on an integral representation of the diffracted wave field, which has been reduced from Somigliana′s identity. The method allows us to evaluate the complete displacement field by the superposition of the free field and the diffracted field. It is remarkable that the free field is specified as incident Rayleigh- waves, making the assumption of absence of cracks. The diffracted field is obtained from the integral representation by means of the presence of cracks. Our results are compared with those previously published. We emphasize the amplitude reduction of Rayleigh- waves while the interaction with the cracks take place. Conspicuous wave amplification at the crack neighborhood is observed immediately after such interaction. This information may give us a way to characterize crack’s depth and orientations from the analysis of the diffracted field.

Abstract:
The response of El Ni o Southern Oscillation (ENSO) to solar and volcanic radiative forcings over the past millennium is reanalyzed and extrapolated based on historical data and numerical experiments employing the Zebiak–Cane (ZC) model of the tropical Pacific coupled ocean–atmosphere system. The results suggest a self-similarity of the centennial scale component of the reconstructed ENSO record with a shift in frequencies around 1700 AD when the frequencies almost double. This shift of regime puts forward the non-linearity of ENSO climate with a possible centennial scale forecast, suggesting an ENSO trend toward La Ni a conditions for the next three decades.

Abstract:
Results of seismic response of the stations of the Acelerometric Network of Mexico City located in the hill zone are presented. Seven earthquakes from different seismic sources were analyzed, with magnitudes between 5.9 and 7.3. There is a dependence of the seismic response at hill sites on earthquake magnitude, azimuth, epicentral distance and depth. Subduction earthquakes concentrate their energy at low frequencies (<1 Hz), while intraplate earthquakes have frequencies higher than 1 Hz. We find two significant types of amplification: regional, for sites located to the southwest hill zone over sites located to the north of the city, and local. Stations located in the southwest area show higher amplification with respect to the reference station. The spectral ratios of stations located in the central and southwest part of the hill zone show relative amplifications up to four times higher than stations located in the north area of the city for frequencies between 1 and 3 Hz. These local amplifications may be due to the presence of soft material under the lava flows where the stations are located.

Abstract:
We study the multiple scattering of elastic waves by a finite linear array of regularly distributed cylindrical obstacles. The transient response of the system for incident anti-plane shear waves is given in detail. We present an extension of an original solution for rigid cylinders, developed by some of us in 1983. The solution is formally obtained for harmonic excitation and Fourier analysis provides the transient response. Material properties of the cylindrical inclusions are considered. A 2-D formulation is constructed by superposition of the incident field upon the waves diffracted by each obstacle. The solutions for each obstacle are constructed as expansions of cylindrical wave functions, after imposing continuity conditions for the displacements and tractions at the scatterers matrix interfaces with the aid of Graf’s addition theorem. Thus, the total field can be referred to any cylindrical coordinates. The infinite system is approximated by a finite one and numerical results are obtained for different values of the parameters. Various cases of cavities and inclusions are studied. A double effect is produced by different filling materials, f. e. amplification at the incidence side and reductions at the far side, or vice versa. Synthetic seismograms and snapshots are computed to illustrate the complex features of wave propagation for this inhomogeneous model.

Abstract:
objectives: to asess changes in the serum cholesterol (ct) during acute coronary events (infarction-iam-and unstable angina) in clinical practice, to raise to begin pharmacologic lipid therapy knowing only a lipid profile. methods: lipid clinic database was revised. selection criteria: patients who were sent to the clinic 1 to 3 months after the acute coronary event and who were not begun pharmacologic lipid therapy. results: 56 pacients, 69% with iam. admission ct mean was lower. among 17 who had ct lower than 200 mg/dl during acute phase, 16 had ct higher than 200 in ambulatory lipid profile. the bigger acute phase drop took place between those who had ct higher during ambulatory consultation. conclusions: theses results confirm the ct decrease during iam and reports this reduction happens during unstable angina too. that permits to suggest mostly to begin the lipid lowering drug therapy earlier, even although there was only a lipid vlue known.