Structural pounding between adjacent buildings subjected to strong ground motions. Part II: The effect of multiple earthquakes

The effect of collision between adjacent reinforced concrete building frames under multiple earthquakes is investigated in this paper. The four planar frames and the nine different pairs of adjacent reinforced concrete structures of the first companion paper are also examined here, under five real seismic sequences. Such a sequence of earthquakes results in a significant damage accumulation in a structure because any rehabilitation action between any two successive seismic motions cannot be practically materialised because of lack of time. Various parameters are investigated, such as the maximum horizontal displacement of top floor, ductility of columns, permanent displacements and so on. Furthermore, four different separation gaps between the building frames are considered to determine their influence on the behaviour of these frames. It is concluded that in most of the cases, the seismic sequences appear to be detrimental in comparison with the single seismic events. Copyright © 2013 John Wiley & Sons, Ltd.     

Trophic Links in the Plankton in the Low Salinity Zone of a Large Temperate Estuary: Top-down Effects of Introduced Copepods

We investigated trophic relationships involving microzooplankton in the low salinity zone of the San Francisco Estuary (SFE) as part of a larger effort aimed at understanding the dynamics of the food web supporting the endangered delta smelt, Hypomesus transpacificus. We performed 14 cascade experiments in which we manipulated the biomass of a copepod (Limnoithona tetraspina, Pseudodiaptomus forbesi, or Acartiella sinensis) and quantified responses of lower trophic levels including bacterioplankton, phytoplankton, and microzooplankton. Microzooplankton comprised a major food source for copepods; 9 out of 14 experiments showed removal of at least one group of microzooplankton by copepods. In contrast, the impact of copepods on phytoplankton was indirect; increased copepod biomass led to greater growth of phytoplankton in 3 of 14 experiments. Estimated clearance rates on microzooplankton were 4 mL day^?1 for L. tetraspina and 2–6 mL day^?1 for P. forbesi, whereas A. sinensis consumed mainly copepod nauplii. Complex trophic interactions, including omnivory, among copepods, microzooplankton, and different components of the phytoplankton likely obscured clear trends. The food web of the SFE is probably less efficient than previously thought, providing poor support to higher trophic levels; this inefficient food web is almost certainly implicated in the continuing low abundance of fishes, including the delta smelt that use the low salinity zone of the San Francisco Estuary.     

New method for estimating reference evapotranspiration and comparison with alternative methods in a fruit-producing hub in the semi-arid region of Brazil

Theoretical and Applied Climatology - Analysing alternative methods for estimating reference evapotranspiration (ET0) is essential for improving the management of water resources, especially where...     

The causes of land-use and land-cover change: moving beyond the myths

Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and constraints for new land uses are created by local as well as national markets and policies. Global forces become the main determinants of land-use change, as they amplify or attenuate local factors.     

A 300-kyr record of aridity and wind strength in southwestern Africa: inferences from grain-size distributions of sediments on Walvis Ridge, SE Atlantic

The terrigenous fraction of sediments recovered from Walvis Ridge, SE Atlantic Ocean, reveals a history of southwestern African climate of the last 300 kyr. End-member modelling of a data set of grain-size distributions (n=428) results in three end members. The two coarsest end members are interpreted as eolian dust, the third end member as hemipelagic mud. The ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the SE trade winds. Trade winds were intensified during glacials compared to interglacials. Changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern African aridity. Late Quaternary southwestern African climate was relatively arid during the interglacial stages and relatively humid during the glacial stages, owing to meridional shifts in the atmospheric circulation system. During glacials the polar front shifted equatorward, resulting in a northward displacement of the zone of westerlies, causing increased rainfall in southwestern Africa. The equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient, leading to enhanced atmospheric circulation and increased trade-wind intensity.     

The composition of liquid methane-nitrogen aerosols in Titan’s lower atmosphere from Monte Carlo simulations

Molecular level Monte Carlo simulations have been performed with various model potentials for the CH₄-N₂ vapor-liquid equilibrium at conditions prevalent in the atmosphere of Saturn’s moon Titan. With a single potential parameter adjustment to reproduce the vapor-liquid equilibrium at a higher temperature, Monte Carlo simulations are in excellent agreement with available laboratory measurements. The results demonstrate the ability of simple pair potential models to describe phase equilibria with the requisite accuracy for atmospheric modeling, while keeping the number of adjustable parameters at a minimum. This allows for stable extrapolation beyond the range of available laboratory measurements into the supercooled region of the phase diagram, so that Monte Carlo simulations can serve as a reference to validate phenomenological models commonly used in atmospheric modeling. This is most important when the relevant region of the phase diagram lies outside the range of laboratory measurements as in the case of Titan. The present Monte Carlo simulations confirm the validity of phenomenological thermodynamic equations of state specifically designed for application to Titan. The validity extends well into the supercooled region of the phase diagram. The possible range of saturation levels of Titan’s troposphere above altitudes of 7 km is found to be completely determined by the remaining uncertainty of the most recent revision of the Cassini-Huygens data, yielding a saturation of 100 ± 6% with respect to CH₄-N₂ condensation up to an altitude of about 20 km.     

Electron transport and precipitation at Mercury during the MESSENGER flybys: Implications for electron-stimulated desorption

To examine electron transport, energization, and precipitation in Mercury's magnetosphere, a hybrid simulation study has been carried out that follows electron trajectories within the global magnetospheric electric and magnetic field configuration of Mercury. We report analysis for two solar-wind parameter conditions corresponding to the first two MESSENGER Mercury flybys on January 14, 2008, and October 6, 2008, which occurred for similar solar wind speed and density but contrasting interplanetary magnetic field (IMF) directions. During the first flyby the IMF had a northward component, while during the second flyby the IMF was southward. Electron trajectories are traced in the fields of global hybrid simulations for the two flybys. Some solar wind electrons follow complex trajectories at or near where dayside reconnection occurs and enter the magnetosphere at these locations. The entry locations depend on the IMF orientation (north or south). As the electrons move through the entry regions they can be energized as they execute non-adiabatic (demagnetized) motion. Some electrons become magnetically trapped and drift around the planet with energies on the order of 1–10 keV. The highest energy of electrons anywhere in the magnetosphere is about 25 keV, consistent with the absence of high-energy (>35 keV) electrons observed during either MESSENGER flyby. Once within the magnetosphere, a fraction of the electrons precipitates at the planetary surface with fluxes on the order of 10⁹ cm⁻² s⁻¹ and with energies of hundreds of eV. This finding has important implications for the viability of electron-stimulated desorption (ESD) as a mechanism for contributing to the formation of the exosphere and heavy ion cloud around Mercury. From laboratory estimates of ESD ion yields, a calculated ion production rate due to ESD at Mercury is found to be on par with ion sputtering yields.     

Issues with external occultation of a coronagraph

This paper addresses some of the issues related to externally occulted solar coronagraph; vignetting and achievable resolution due to an external occulter. The analytical expression by Evans (J Opt Soc Am 38:1083–1085, 1948) is used to perform the initial calculations. An expression for the vignetting for a given external occulter and field angle is derived. The values obtained with the derived expression are verified with those obtained by ZEMAX an Optical design software. The degradation in angular resolution of the system due to vignetting is also presented and an empirical relation to calculate the normalized resolution for a given amount of vignetting is obtained.     

Digital complex correlator for a C-band polarimetry survey

The international Galactic Emission Mapping project aims to map and characterize the polarization field of the Milky Way. In Portugal it will map the sky polarized emission of the Northern Hemisphere in C-band and provide templates for map calibration and foreground control of microwave space data to be provided by ESA Planck Surveyor mission and later missions. The receiver system is equipped with a novel receiver with a full digital back-end using a low-cost Field Programmable Gate Array without compromising its performance relation. This new digital backend comprises a base-band complex cross-correlator outputting the four Stokes parameters of the incoming polarized radiation. In this document we describe the design and implementation of the complex correlator using the FPGA and the dedicated digitizers at each receiver arm, detailing the method applied at the several algorithm stages. This correlator is suitable for large sky area polarization continuum surveys.