Evidence of beneficial role of inclined piles: observations and summary of numerical analyses

The behaviour under seismic loading of inclined piles embedded in two idealized soil profiles, a homogeneous and a non-homogenous “Gibson” soil, is analysed with 3D finite elements. Two structures, modeled as single-degree-of-freedom oscillators, are studied: (1) a tall slender superstructure (H _st = 12 m) whose crucial loading is the overturning moment, and (2) a short structure (H _st = 1 m) whose crucial loading is the shear force. Three simple two-pile group are studied: (a) one comprising a vertical pile and a pile inclined at 25°, (b) one consisting of two piles symmetrically inclined at 25°, and (c) a group of two vertical piles. The influence of key parameters is analysed and non-dimensional diagrams are presented to illustrate the role of raked piles on pile and structure response. It is shown that this role can be beneficial or detrimental depending on a number of factors, including the slenderness of the superstructure and the type of pile-to-cap connection.     

A review of adverse effects of damping in seismic isolation

In this paper the question of possible adverse effects of damping in seismic isolation because of higher mode response is investigated by means of simple models with a few degrees of freedom (DOF). In particular the second mode response of a 2 DOF system is examined in detail for both viscous and hysteretic (e.g. friction or elastoplastic) damping devices. Qualitative and approximate quantitative estimates are obtained by neglecting the influence of the modal coupling terms, due to viscous damping or friction forces, on the first mode response. It is shown that additional viscous damping has a diminishing effect on base displacement, storey shear force and floor spectra values in the vicinity of the first mode resonance. However, a significant amplification of the floor spectra values near the higher mode frequencies may occur. In accordance with the results of previous works, compared with the viscous damping case, hysteretic damping amplifies moderately the first storey shear force and significantly the upper storeys shear force. It also results, in a much more pronounced amplification of the floor spectral values than viscous damping, in the vicinity of the higher eigenfrequencies. However, the higher modes' response is milder if a realistic velocity dependence of the friction coefficient is taken into account. Copyright © 2007 John Wiley & Sons, Ltd.     

Greek archaeomagnetic intensities: Some aspects of reliability and geophysical implications

Archaeointensity results from Greece for the last 2000 yr have been obtained using thermal and alternating field (AF) demagnetisation techniques. Most of the samples consisted of tiles and bricks derived from Byzantine churches which were epigraphically dated. The accuracy of the dating of the samples (to within a few years) and the comparison of the two techniques for measuring geomagnetic intensity combine to provide a good basis from which to derive meaningful conclusions — i.e. (i) About 70% of the archaeointensity measurements, made by the two methods, were highly compatible, differing less than ±7% from their mean. In 60% of the cases, the AF technique yielded higher palaeointensity results than that for thermal demagnetization. The results for the thermal and AF techniques are discussed in accordance with reliability criteria and attention is drawn to the reliability of archaeointensity data in general. (ii) An overall similarity of the intensity trend was observed for the last 400 years between the AF, the thermal demagnetization and a modelled intensity curve derived from the spherical harmonic coefficients since AD 1600. (iii) A decrease of intensity amounting to 40% is noted in the new data for the period since AD 400, and (iv) a non-dipole disturbance was noted at around AD 1300 in southern Greece, where the intensity changed by about 30% within a period of 30 years or so.     

Cost/benefit analysis of a benthic monitoring programme of organic benthic enrichment using different sampling and analysis methods

To investigate the combined effects of decreasing taxonomic resolution (i.e. species, family, phylum), the use of different mesh-size (1.0 mm and 0.5 mm) and the type of samplers used (van Veen vs. corers taken by divers) on the quality of data obtained, a comparative study was undertaken with the overall aim of identifying cost efficient methods for routinely monitoring the ecological change caused by Mediterranean fish farming. The results clearly showed that information loss was relatively low as data were aggregated at higher taxonomic levels, particularly up to the level of family or even order. It was also found that the extra information gained by sieving samples through a 0.5 mm sieve did not improve the ability to distinguish the potentially impacted sites from the control stations. Finally, it was found that a relatively large proportion of the available information concerning the community structure such as abundance, biomass or diversity is lost when sampling is carried out with corers. A cost/benefit ratio analysis for the two sampling and the two sieving methods showed minimal values for the van Veen samples (for both sieve fractions) at the family level, indicating that analysis at this level gives the best balance between precision of the results and decrease in taxonomic effort. However, if the time needed to sort the samples is included in the analysis, then samples taken with corers using a 0.5 mm sieve and identified to families seems like a good compromise between precision and cost.     

Periodic variation ofδ 18O values from V28–239 pacific ocean deep-sea core

Spectral analysis of ¹⁸O values from V28–239 pacific ocean deep-sea core has revealed periodicities which correspond to those calculated for the eccentricity (400 and 100 Kyrs), the obliquity (41 Kyrs) and the climatic precession (23 and 19 Kyrs) as well as secondary ones spanning between 16 Kyrs to 1 million years. The methods of spectrum analysis applied were the maximum entropy, fourier and the successive approximations, where the periodicities are located and their amplitude defined.The significance and stationarity of the detected periods was examined by various tests as well as employing an evolutionary pseudosonogram.The dominant 100 Kyrs and 50 Kyrs periods are present throughout all the interval, the 30 Kyrs is at low variance during 1.2 to 2 million years interval, the precessional signal is not stationary and appears at about 600 Kyrs to 1820 Kyrs.This study shows the necessity of applying various spectral analysis techniques and several tests to extract the optimum of spectral information and also to test the stationarity of certain periodicities, especially when implied mechanisms of climatic cause and variability are involved.Deceased.     

Assessing water erosion in Mediterranean tree crops using GIS techniques and field measurements: the effect of climate change

In this work, a dynamic GIS modeling approach is presented that incorporates: a) geoinformatic techniques, b) 55-year historical meteorological data, and c) field measurements, in order to estimate soil erosion risk in intensively cultivated regions. The proposed GIS-based modeling approach includes the estimation of soil erosion rates due to surface water flow under current and future climate change scenarios A2 and B1 for the years 2030 and 2050. The soil erosion was estimated using the Universal Soil Loss Equation (USLE). The proposed soil erosion model was validated using field measurements at different sites of the study area. The results show that an extended part of the study area is under intense erosion with the mean annual loss to be 4.85 t/ha year⁻¹. Moreover, an increase in rainfall intensity, especially for scenario B1, can generate a significant increase (32.44 %) in soil loss for the year 2030 and a much more (50.77 %) for the year 2050 in comparison with the current conditions. Regarding the scenario A2, a slight decrease (1.85 %) in soil loss was observed for the year 2030, while for 2050 the results show an adequate increase (7.31 %) in comparison with the present. All these approaches were implemented at one of the most productive agricultural areas of Crete in Greece dominated by olive and citrus crops.

     

Dependence of the aurora borealis occurrences on the solar-terrestrial parameters

The recent measurements made by satellites of the aurorae in connection with solar phenomena have increased interest in auroral research. In the present investigation, we establish that, for the 20th solar cycle, the occurrence of visual discrete aurorae A, deduced from a complete set of data, is significantly related to the sunspot numbers R _z, the number of flares F (of importance 1) the solar wind streams derived from solar coronal holes H, and the geomagnetic index A _p.By employing the theory of residues it has been found that A correlates significantly well with the above indices. Accuracies of the order of 75–94% were found for geomagnetic latitudes in the range of 54 –63 N.The A-R _zrelationship was investigated in particular for the period 1897–1951. For this period spectrum analysis of A annual values revealed the existence of 3–4 yr and 8–10 yr periodicities of significances 95% and 99%; respectively.Research Associate.     

A preliminary study of the relationship between large earthquakes and precipitation for the region of Athens,Greece

The annual rainfall data of Athens rain gauge stations, for the last 119 years, is compared with the occurrence of large (M 6) earthquakes along the fault and thrust systems in the vicinity of Athens and interesting correlations have been observed.This preliminary investigation reveals the possible occurrence of a large earthquake in the region of Athens till 1993.     

Calculation of radar signal delays in the vicinity of the Sun due to the contribution of a Yukawa correction term in the gravitational potential

There has been a renewed interest in the recent years in the possibility of deviations from the predictions of Newton’s “inverse-square law” of universal gravitation. One of the reasons for renewing this interest lies in various theoretical attempts to construct a unified elementary particle theory, in which there is a natural prediction of new forces over macroscopic distances. Therefore the existence of such a force would only coexist with gravity, and in principle could only be detected as a deviation from the inverse square law, or in the “universality of free fall” experiments. New experimental techniques such that of Sagnac interferometry can help explore the range of the Yukawa correction λ≥10¹⁴ m where such forces might be present. It may be, that future space missions might be operating in this range which has been unexplored for very long time. To study the effect of the Yukawa correction to the gravitational potential and its corresponding signal delay in the vicinity of the Sun, we use a spherically symmetric modified space time metric where the Yukawa correction its added to the gravitational potential. Next, the Yukawa correction contribution to the signal delay is evaluated. In the case where the distance of closest approach is much less than the range λ, it results to a signal time delay that satisfies the relation t(b<λ)≅37.7t(b=λ).