Analysis of seismic dynamical systems

A procedure is presented for the analysis of complex stationary time series for which the Fourier power spectra reveals broadband noise or broadened pulses. We first determine the Hurst exponent from which we may know whether the time series under study is mainly random or if the data points present correlations. If the data are correlated, a chaotic analysis will reveal whether they may be interpreted as a low dimensional nonlinear system (defined by a low correlation dimension and a finite and positive Kolmogorov entropy and largest positive Lyapunov exponent) or as a stochastic process. We have studied three kind of temporal series: inter-event time series of infrasonic pulses recorded at Stromboli volcano, and, S-coda waves and microseisms, that have been recorded at the eastern Pyrenees. Results show that microseisms and Coda waves can be modeled as a low dimensional deterministic system, Correlation dimensions 2.3, 3.2, respectively. At the contrary infrasonic has resulted stochastic. This chaotic character can be attributed to the medium properties. Coda waves with scattering through a fractal distribution of scatters or to multiple reflection inside resonators (for example sedimentary basins) and microseisms as a propagation of wave guide of variable cross section which have the same temporal characteristics as a nonlinear forced oscillator.     

Kinematic Dynamos in the Kerr Metric

It is known that a sharp decrease in the angular velocity of the accretion disk around a black hole could in principle produce a kinematic axisymmetric dynamo, in contrast to the classical situation described by Cowling's antidynamo theorem. Here the effect of a nontrivial poloidal velocity of the disk is studied, showing that a strong gradient of this velocity enhances the possibilities of a working dynamo.     

The Evolution of Star-Forming Galaxies: The SFR Density of the Universe

The evolution of the Star Formation Rate (SFR) density of the Universe as a function of look-back time is a fundamental parameter in order to understand the formation and evolution of galaxies. The current picture, only outlined in the last years, is that the global SFR density has dropped by about an order of magnitude from a redshift of z∼1.5 to the current value at z=0. Because these SFR density studies are now extended to the whole range in redshift, it becomes mandatory to combine data from different SFR tracers. At low redshifts, optical emission lines are the most widely used. Using Hα as current-SFR tracer, the Universidad Complutense de Madrid (UCM) Survey provided the first estimation of the global SFR density in the Local Universe. The Hα flux in emission is directly related to the number of ionizing photons and, modulo IMF, to the total mass of stars formed. Metallic lines like [OII]λ3727 and [OIII]λ5007 are affected by metallicity and excitation. Beyond redshifts z∼0.4, Hα is not observable in the optical and [OII]λ3727 or UV luminosities have to be used. The UCM galaxy sample has been used to obtain a calibration between [OII]λ3727 luminosity and SFR specially suitable for the different types of star-forming galaxies found by deep spectroscopic surveys in redshifts up to z∼1.5. These calibrations, when applied to recent deep redshift surveys confirm the drop of the SFR density of the Universe since z∼1 previously infered in the UV. However, the fundamental parameter that determines galactic evolution is mass, not luminosity. The mass function for local star-forming galaxies is critical for any future comparison with other galaxy populations of different evolutionary status. Hα velocity-widths for UCM galaxies indicate that besides a small fraction of 10¹⁰-10¹¹ M_⊙ starburst nuclei spirals, the majority have dynamical masses in the ∼10⁹ M_⊙ range. A comparison with published data for faint blue galaxies suggests that star-forming galaxies at z∼1 would have SFR per unit mass and burst strengths similar to those at z=0, but being intrinsically more massive. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geography of contamination: The location of industrial waste dumps in Catalonia

The handling of the solid industrial waste (SIW) generated in Catalonia is one of the main problems of industrial and territorial policy confronting the public bodies controlling this area of activity. The most recent estimates in this regard indicate that the annual production of SIW is 1,700,000 tons and that only 300,000 tons are treated.In this situation it is usual for a large number of industries to eliminate their SIW furtively, it is common practice to dump waste in various unprepared areas. In this article we present a series of hypotheses which we believe allow us to understand the logic that guides the siting of a large number of these dumps.In the first place we demonstrate the importance of a series of conditions derived from the same industrial logic, to wit, a) the cost of transporting the SIW to the dumps, b) the industrial decentralization process and the metropolitan development of Catalonia, c) vertical integration and the appearance of companies especially dedicated to the elimination of waste and, d) the development of land use through revaluation of the land and greater possibilities for control forces furtive dumps to be sited in more and more distant areas.Secondly, we examine the role of public bodies in this process, concentrating on the characteristics of the legal system and the real effectiveness of urban controls. Finally, in third place, an explanation is given of research carried out in the Barcelona area which shows the importance of the conditions examined above.     

Integrated and interdisciplinary scientific approach to coastal management

Coastal zones and beach management practices, regulatory decisions, and land use planning activities along coastal zones have historically been made with insufficient information concerning the dynamic coastal environment. In this study we address and integrate an interdisciplinary scientific approach to Coastal Management in a scenario where lack of this information has resulted in the alteration of the natural dune system of the beach of Cala Millor (Mallorca, Balearic Islands, Spain), and also in the perception of the beach retreat and in a parallel way, a risk for the tourism resources. In this work the detailed studies on beach morphodynamics have been developed as a basis for integrating proper beach management, beach natural dynamics and local users and economic agent interests. From this point of view a set of solutions are considered as the basis for a management policy that links beach science and beach use as a tourism resort resource.     

A cyclical period variation detected in the updated orbital period analysis of TV Columbae

Two CCD photometries of the intermediate polar TV Columbae are made for obtaining two updated eclipse timings with high precision. There is an interval time ～17 yr since the last mid-eclipse time observed in 1991. Thus, the new mid-eclipse times might offer an opportunity to check the previous orbital ephemerides. A calculation indicates that the orbital ephemeris derived by Augusteijn et al. (Astron. Astrophys. Suppl. Ser. 107:219, 1994) should be corrected. Based on the proper linear ephemeris (Hellier in Mon. Not. R. Astron. Soc. 264:132, 1993), the new orbital period analysis suggests a cyclical period variation in the O–C diagram of TV Columbae. Using Applegate’s mechanism to explain the periodic oscillation in the O–C diagram, the required energy is larger than the energy that a M0-type star can afford over a complete variation period of ～31.0(±3.0) yr. Thus, the light travel-time effect indicates that the tertiary component in TV Columbae may be a dwarf with a low mass, which is near the lower mass limit of ～0.08M _⊙ as long as the inclination of the third body is high enough.     

Dynamics of negative hydraulic barriers to prevent seawater intrusion

Negative hydraulic barriers that intercept inflowing saltwater by pumping near the coast have been proposed as a corrective measure for seawater intrusion in cases where low heads must be maintained. The main disadvantage of these barriers is that they pump a significant proportion of freshwater, leading to contamination with saltwater at the well. To minimize such mixing, a double pumping barrier system with two extraction wells is proposed: an inland well to pump freshwater and a seawards well to pump saltwater. A three-dimensional variable density flow model is used to study the dynamics of the system. The system performs very efficiently as a remediation option in the early stages. Long-term performance requires a well-balanced design. If the pumping rate is high, drawdowns cause saltwater to flow along the aquifer bottom around the seawater well, contaminating the freshwater well. A low pumping rate at the seawards well leads to insufficient desalinization at the freshwater well. A critical pumping rate at the seawater well is defined as that which produces optimal desalinization at the freshwater well. Empirical expressions for the critical pumping rate and salt mass fraction are proposed. Although pumping with partially penetrating wells improves efficiency, the critical pumping rates remain unchanged.     

Construction of deep tunnel shafts in Mexico city soft clays by the flotation method

The drainage system of Mexico City, one of the largest metropolitan areas in the world, is formed by a large network of interceptors and collectors leading to the main outlet: a 49.3-km-long tunnel with a 6.5 m diameter. To build the access shafts to the tunnels of the system and the deep sumps of the pumping stations in the very soft clays of the lacustrine area of Mexico valley, a technique known as “flotation method” has been commonly used since 1969. The paper presents the main construction steps followed and some aspects of the analysis and design of shafts constructed by this technique. The experience gained obtained after more than 30 shafts have been constructed by this method, and the actual trends in its application are also discussed.     

Landslide susceptibility and hazard assessment in San Ramón Ravine, Santiago de Chile, from an engineering geological approach

Debris flows and soil and rock slides are among the main geological hazards in the mountain foothills of Central Chile. Geological risk associated with the development of landslides, especially debris flows triggered in the basins of ravines that drain into the capital city, Santiago, has increased in time due to accelerated urban expansion. A landslide hazard evaluation in the San Ramón Ravine, located within the foothills of Santiago is presented. Hazard evaluation is based on a methodology that combines the determination of landslide susceptibility calculated by integration of conditioning factors, with the assessment of slope failure and runout probabilities incorporating geotechnical engineering approaches. The methodology is appropriate for medium or subregional scale studies with limited data. The results show that in San Ramón Ravine the landslide hazard consists mainly of debris flows, rock block slides, rock falls and shallow soil slides. Among these, debris flows are the most important due to the urban area that can be affected. Other case studies show that the method can be used in other regions with minor adaptations for territorial planning or for engineering and environmental purposes.