Influence of deterioration modelling on the seismic response of steel moment frames designed to Eurocode 8

This paper assesses the influence of cyclic and in‐cycle degradation on seismic drift demands in moment‐resisting steel frames (MRF) designed to Eurocode 8. The structural characteristics, ground motion frequency content, and level of inelasticity are the primary parameters considered. A set of single‐degree‐of‐freedom (SDOF) systems, subjected to varying levels of inelastic demands, is initially investigated followed by an extensive study on multi‐storey frames. The latter comprises a large number of incremental dynamic analyses (IDA) on 12 frames modelled with or without consideration of degradation effects. A suite of 56 far‐field ground motion records, appropriately scaled to simulate 4 levels of inelastic demand, is employed for the IDA. Characteristic results from a detailed parametric investigation show that maximum response in terms of global and inter‐storey drifts is notably affected by degradation phenomena, in addition to the earthquake frequency content and the scaled inelastic demands. Consistently, both SDOF and frame systems with fundamental periods shorter than the mean period of ground motion can experience higher lateral strength demands and seismic drifts than those of non‐degrading counterparts in the same period range. Also, degrading multi‐storey frames can exhibit distinctly different plastic mechanisms with concentration of drifts at lower levels. Importantly, degrading systems might reach a “near‐collapse” limit state at ductility demand levels comparable to or lower than the assumed design behaviour factor, a result with direct consequences on optimised design situations where over‐strength would be minimal. Finally, the implications of the findings with respect to design‐level limit states are discussed.     

Coulomb corrections to the equation of state of nuclear statistical equilibrium matter: implications for SNIa nucleosynthesis and the accretion-induced collapse of white dwarfs

Coulomb corrections to the equation of state of degenerate matter are usually neglected in high-temperature regimes, owing to the inverse dependence of the plasma coupling constant, Γ, on temperature. However, nuclear statistical equilibrium matter is characterized by a large abundance by mass of large- Z (iron group) nuclei. It is found that Coulomb corrections to the ion ideal gas equation of state of matter in nuclear statistical equilibrium are important at temperatures T ≲5–10×10⁹ K and densities ρ ≳10⁸ g cm⁻³. At a temperature T =8.5×10⁹ K and a density ρ =8×10⁹ g cm⁻³, the neutronization rate is larger by ≳28 per cent when Coulomb corrections are included. However, the conductive velocity of a thermonuclear deflagration wave in C–O drops by ∼16 per cent when Coulomb corrections to the heat capacity are taken into account. The implications for SNIa models and nucleosynthesis, and also for the accretion-induced collapse of white dwarfs, are discussed. Particularly relevant is the result that the minimum density for collapse of a white dwarf to a neutron star is shifted down to 5.5–6×10⁹ g cm⁻³, a value substantially lower than previously thought.     

Evolution of polar coronal holes and sunspots during cycles 21 and 22

A very good correlation between the evolution of polar coronal hole size and sunspot number half a solar cycle later was found by Bravo and Otaola for solar cycle 21. In this paper we use a more complete set of data to reanalyse the relationship for solar cycle 21 and investigate the same relationship for solar cycle 22. We find that the complete set of data for cycle 21 yields a slightly different time shift for the best correlation between sunspots and holes and that the time shift for cycle 22 is different from that of cycle 21. However, because of limited availability of data of cycle 22, we consider it necessary to wait until the end of this cycle in order to decide if the difference is statistically significant or not. We also found that the time between successive peaks of smoothed polar hole area and smoothed sunspot number is the same in both cycles. This may provide a useful tool for the forecasting of future sunspot maxima. The constant of proportionality between polar coronal hole area and sunspot number can be seen to be different in both cycles. We discuss this difference and interpret it in terms of a different magnitude of the polar field strength in the two cycles.     

Different Types of Coronal Mass Ejections At Minimum and Maximum of Solar Activity and Their Relation to Magnetic Field Evolution

Coronal mass ejections (CMEs) are considered to be associated with large-scale, closed magnetic field structures in the corona. These structures change throughout the solar activity cycle following the evolution of the general solar magnetic field. To study the variation of CME characteristics with the evolution of coronal magnetic structures, we compute the 3-D coronal magnetic field at minimum and maximum of activity with a source-surface potential field model. In particular, we study the central latitude distribution of CMEs and the frequency of occurrence of the different CME types in these two periods. We find that most CMEs are indeed associated with large-scale, magnetically closed structures, and their latitudinal distribution follows the solar cycle latitudinal changes of the location of these structures. We also find that different CME types, which constitute different fractions of the total during the maximum and the minimum, are associated with different shapes and orientations of the closed structures at different times of the solar cycle.     

Assessment of the distribution of sponge chips in the sediment of East Pacific Ocean reefs

Sponges are one of the principal agents of bioerosion and sediment production in coral reefs. They generate small carbonate chips that can be found in the sediments, and we investigated whether these could provide a means for assessment of bioerosion applicable to reef monitoring. We tested this hypothesis on samples from 12 Mexican coral reefs distributed along the Pacific coast, where boring sponges were particularly abundant, and quantified the amount of chips in samples of superficial sediment in three grain‐size fractions: fine (<44 μm), medium (44–210 μm) and coarse (>210 μm). The grain‐size distribution varied among reefs, with the majority of the sediment of most reefs being composed of coarse sands, and the medium and fine fractions dominating only at La Entrega and Playa Blanca. All the reefs presented clear evidence of bioerosion by sponges, with the characteristic chips present in the sediment, although at most sites the percentage of chips was very low (from 1% to 3% of the total sediment). Only at La Entrega and Playa Blanca did they constitute a significant fraction of the total sediment (18% and 16%, respectively). While not statistically significant, there was an interesting trend between sponge chips versus sponge abundance that suggests that quantification of the chips in the sediment could be used as a proxy for sponge erosion of the entire community, which cannot be estimated in by laboratory experiments. However, while this methodology could provide an integrated approach to monitor sponge bioerosion, more studies are necessary due to the influence of environmental factors on the transport and deposition of these chips.     

Analyzing the basic features of different complex terrain flows by means of a Doppler Sodar and a numerical model: Some implications for air pollution problems

Summary A variety of programmes and field experiments were carried out in order to develop and evaluate models of transport and diffusion of pollutants in complex terrain areas. As part of this programme, in this study, we have focused our interest on analyzing the basic features of different flow fields and thermal structures developed in a complex area and their relation to air pollution problems. The area is located in the province of Barcelona (in the northeast of Spain) close to a wide industrial zone, thus a pollutant flux could affect this region. In order to carry out the main purpose of this study we have analysed data from a Doppler Sodar (FAS 64) and a network of near surface meteorological and air quality stations. In addition, different dynamical simulations given by a numerical mesoscale model (MM5) are also analyzed. The results show that the main flow fields and thermal structures generated in this area are: sea breeze, slope drainage winds, channelling winds created by terrain constrictions and cool-air accumulation in low-lying regions. This last structure, developed specially in winter time, gives rise to stagnant cold air masses and strong thermic inversions, with average lapse rate of –4 degrees on 100m, which contribute to increase air pollution concentration, especially SO₂. Hourly and daily averaged SO₂ concentration can be higher than 350 and 138µgm^–3 respectively. In addition, as La Plana is located not far from the Mediterranean Sea, during summertime the sea breeze arrives into this zone via its southern entrance, thereby reaching the whole area. The arrival of the sea breeze in to La Plana, which advects pollutants from the nearby industrial area, is the main cause of some of these pollutants, especially ozone and its precursors, attaining high concentrations during afternoon hours. The contribution of the sea breeze is variable, but could represent between a 25% to a 30% of its total value.