2-D Code for Simulating a Hollow Gas Puff Z-Pinch

We compare the dynamics of plasma in a hollow gas puff Z-pinch device, obtained with Schlieren pictures, with the predictions of a 2-D MHD Lagrangian code. We show that agreement between the model and experiment require an axially variable line density and width of the injected gas.     

Prediction of site factors by a non‐parametric approach

The problem addressed in this paper is the estimation of the (de)amplification of ground motion at soil sites (compared to rock sites) as a function of the intensity of the ground motion. A non‐parametric empirical approach, called the Conditional Average Estimator (CAE) method, has been used, which is different from all existing approaches. Site factors (SFs) for sites characterized with V_s30 between 180 and 360 m/s were predicted for the peak ground acceleration (PGA) and the spectral accelerations by using a combined database of recorded ground motions. Based on the results of the study, site factors for PGA and selected spectral accelerations are proposed, separately for weaker and stronger ground motions. Comparisons are made with the SFs used in two standards (Eurocode 8 and ASCE 7‐10) and with SFs proposed in the literature, including four Next Generation Attenuation (NGA) ground‐motion prediction equations. The study reveals that (i) SFs depend strongly on the ground‐motion intensity. In the case of stronger ground motions, they decrease with increasing acceleration. (ii) The SFs predicted in this study agree reasonably well with the existing SFs in the case of weak ground motion. For higher intensities of ground motion, they are generally smaller than the existing ones. Copyright © 2014 John Wiley & Sons, Ltd.     

A web‐based methodology for the prediction of approximate IDA curves

A web‐based methodology for the prediction of approximate IDA curves, which consists of two independent processes, is proposed. The result of the first process is a response database of the SDOF model, whereas the second process involves the prediction of approximate IDA curves from the response database by using n‐dimensional linear interpolation. Such an approach enables user‐friendly prediction of the seismic response parameters with high accuracy. In order to demonstrate the capabilities of the proposed methodology, a web application for the prediction of the approximate 16th, 50th and 84th fractile responses of an RC structure was developed. For the presented case study, the response database was computed for a set of 30 ground motion records and the discrete values of six structural parameters. Very good agreement between the computed and the approximated IDA curves of the four‐storey RC building was observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical Study of the First Compression of a Two-Dimensional Pinch

For studying the first compression phase of a Plasma Focus machine, we developed a 2-fluid, time-dependent, 2-D code. The code includes two species (ions and electrons), two temperatures, radiation, thermal conductivity, electrical conductivity, magnetic diffusion, and viscosity and is coupled to an external circuit. In order to get reasonable initial conditions for the pinch phase, a simple 1-D model is used for the run-down phase. Under this somewhat ideal Plasma Focus discharge condition, relatively simple scaling laws are obtained. In particular, for a given machine, the pressure (p_o) of maximum thermonuclear production scales with the charging voltage (V_o) as p_o V_{o 2}; the thermonuclear production (Y_n) at these pressures increases with the current (I_o) as Y_n I_o ⁴ and the mean energy per particle is almost independent of all parameters (note that this means that the converging speed should be almost the same regardless of the machine at the optimum conditions). These laws show a reasonable agreement with experimental data and can be explained with a dimensional analysis.     

Evolution of erythemal and total shortwave solar radiation in Valladolid,Spain: Effects of atmospheric factors

Erythemal ultraviolet (UVER; 280–400 nm) and total shortwave (SW; 305–2800 nm) solar irradiances were recorded from 2000 to 2009 in Valladolid, Spain. UVER and SW values under cloudless conditions are simulated by radiative transfer (TUV 4.6) and empirical models. These model estimations are tested with experimental measurements showing a great agreement (root mean square error around 7%). The aerosol effect on UVER irradiance is determined through a model study. UVER radiation and total ozone column (TOC) temporal evolutions show a negative relationship. TOC accounts for 80% of UVER variance and its radiation amplification factor is 1.1 at zenith of 65°. Cloud effects on solar radiation are shown and quantified by the cloud modification factor. Moreover the enhancement effect cases are analysed. SW radiation proves more sensitive to clouds than UVER. Clouds are seen to attenuate and enhance solar radiation by up to 93% and 22% in the UVER range, respectively.     

Optical Measurements in an Exploding Wire Experiment

We present optical measurements (Shadow and Schlieren pictures) of a 12.5 Joule exploding wire experiment. After performing a large number of shots some sort of time evolution can be reconstructed from the pictures. The pictures were taken during the dark phase (zero current) and the plasma phase. Although the electrical signals are quite reproducible from shot to shot (allowing a good time correlation and indicating that the global dynamics is reproducible) we observed that the individual details are quite different, probably due to the non-uniformity of the wire. We observed a uniform expansion (the volume increases almost linearly with time) with the presence of surface instabilities and there is no evident difference in the density distribution between the dark and the plasma phases. Finally, we derive a mean radius and velocity evolution with time and an approximate energy balance.     

Hysteretic energy dissipation capacity and the cyclic to monotonic drift ratio for rectangular RC columns in flexure

Predictions of energy dissipation capacity and of the deterioration of deformation capacity due to cumulative damage have been made by means of a non‐parametric empirical approach, called the conditional average estimator method, using empirical data on rectangular reinforced concrete columns that failed in flexure. Five input parameters were used: axial load index, index related to confinement, shear span index, concrete compressive strength, and longitudinal reinforcement index. The energy capacity was expressed in three different normalized forms and the deterioration of deformation capacity was defined as the ratio of the cyclic to the monotonic ultimate drift. The longitudinal reinforcement index, the index related to confinement, and the axial load index are the most influential input parameters in the case of energy capacity, whereas the latter two indices exhibit the most significant influence in the case of the drift ratio. Energy capacity decreases with an increasing axial load index, whereas it increases with increasing longitudinal reinforcement and with better confinement. In the case of the shear span index, the trend is more complex. Normal concrete has a higher energy dissipation capacity than high‐strength concrete. Similar trends are observed for the drift ratio, with the exception of the influence of the axial load index, where the trend is opposite. The dispersion of the results is high. Copyright © 2008 John Wiley & Sons, Ltd.     

From cave geomorphology to Palaeolithic human behaviour: speleogenesis,palaeoenvironmental changes and archaeological insight in the Atxurra-Armiña cave (northern Iberian Peninsula)

A detailed geomorphological study was performed in the Atxurra-Armiña cave system (northern Iberian Peninsula) to decode landscape evolution, palaeoenvironmental changes and human use of a cave within an Inner Archaeological Context. The results show an average incision rate of the river of <0.083 mm a^–1 for at least the last 419 ka, with interruptions due to sedimentary inputs. Moreover, allostratigraphic units comprising fluviokarstic deposits at the base and flowstone formation at the top have been shown to be climatically controlled, formed either during glacial–interglacial cycles or during interstadial cycles. Finally, when the cave was used by humans in the Late Magdalenian, the lower entrance was closed, and they must therefore have entered the cave through the upper entrance. To reach the sectors selected to decorate the panels, they probably travelled from the upper cave level, as the current crawlway was wider than today, according to our U/Th dating. Once these visitors reached the panels, the floor in the main gallery would have been around 15 cm lower than at present. However, the morphology of the conduit was similar; this has significant implications for understanding and interpreting the human use of the cave during the Palaeolithic.     

Ground‐motion prediction by a non‐parametric approach

Recently, several new ground‐motion prediction equations (GMPEs) have been developed in the U.S.A. (the NGA project) and elsewhere. Unfortunately, the predictions obtained by using different models still differ considerably, although starting from the same database. In this paper, a non‐parametric approach, called the Conditional Average Estimator (CAE) method, has been used for ground‐motion prediction. The comparison between the CAE results and the predictions obtained by five NGA and one European model suggest that the model predictions depend substantially on the selection of the effective database and on the adopted functional form. Both decisions rely to some extent on judgement, and their influence is especially important at short distances from the source. The differences between the results obtained from the European and NGA databases seem to be of the same or even smaller magnitude than the differences observed between different NGA models, at least at short and moderate distances. Aftershocks in the database generally decrease the median values and increase dispersion. The non‐parametric CAE method has proved to be a simple but powerful tool for ground‐motion prediction, especially in a research environment. It can be used for quick predictions with different databases and different input parameters within the range of available data. It is easy to add to or remove data from the database, and to check the influence of additional input parameters. With availability of high quality data, the non‐parametric approach will become more reliable and more attractive also for practical applications. Copyright © 2010 John Wiley & Sons, Ltd.