NONLINEAR SHAKE TABLE IDENTIFICATION AND CONTROL FOR NEAR-FIELD EARTHQUAKE TESTING

The primary focus of a structural shake table system is the accurate reproduction of acceleration records for testing. However, many systems deliver variable and less than optimal performance, particularly when reproducing large near-field seismic events that require extreme table performance. Improved identification and control methods are developed for large hydraulic servo-actuated shake table systems that can exhibit unacceptable tracking response for large, near-field seismic testing. The research is presented in the context of a 5-tonne shake table facility at the University of Canterbury that is of typical design. The system is identified using a frequency response approach that accounts for the actual magnitudes and frequencies of motion encountered in seismic testing. The models and methods developed are experimentally verified and the impact of different feedback variables such as acceleration, velocity and displacement are examined.

The methods show that shake table control in testing large near-field seismic events is often a trade off between accurate tracking and nonlinear velocity saturation of the hydraulic valves that can result in severe acceleration spikes. Control methods are developed to improve performance and include both acceleration and displacement feedback to reduce the acceleration spikes, and record modification, where the reference signal is modified to conform to the shake table's operational parameters. Results show record modification gives exact tracking for near-field ground motions, and optimal system response for reference signals with velocity components greater then the system capabilities. Overall, the research presents a methodology for simple effective identification, modelling, diagnosis and control of structural shake table systems that can be readily generalised and applied to any similar facility.     

The determinants of occupational distribution in Seoul metropolitan area: Comparison of high- and low-skilled occupations

In this study we analyse the spatial distribution patterns of professionals and related workers in high-skilled occupations and elementary workers in low-skilled occupations in the Seoul metropolitan area and explore their geographical factors. Spatial autocorrelation relates to the formation and clustering of hot spots according to each occupational characteristic. Geographic factors affecting the distribution of workplaces and residences in professionals-related occupations and elementary-related occupations act differently for each middle occupational classification. However, some occupations show similar spatial distribution patterns. In particular, we found that industrial economic drivers have influence more significant than other regional factors in determining the distribution of workplace and residence by occupation. The spatial coefficient of geographical adjacency varies with the attributes of each occupation and tends to be larger in professional jobs. Findings from the study will help prepare policies related to local talents for specialisation and advancement of the occupational structure and will be of wider interest.     

Accuracy evaluation of the semi-automatic 3D modeling for historical building information models

It is stated that 3D recording and modeling of heritage buildings entail accurate building models (as-built). However, this paper presents an analysis of the 3D modeling accuracy for the creation of historical building information models (HBIM), considering the complexity and the deformations of historical buildings, using point cloud data and BIM tools. The 3D modeling processes analyzed are based on a three-stage semi-automatic approach leading to the generation of HBIM, including manual and automatic processes. The three stages consist of: (a) optical and terrestrial laser scanning; (b) meshing processes; and finally (c) 3D solid modeling to be assembled into HBIM. Next, this approach analyzed the mesh deformations generated automatically in comparison to the initial point cloud data. The deformations and the accuracy evaluation have been undertaken using different commercial software. Finally, our modeling approach shows that it can improve the accuracy of the 3D models achieved using existing BIM technologies.     

A Simple(R) Model to Predict the Source of Dietary Carbon in Individual Consumers

Quantitative individual human diet reconstruction using isotopic data and a Bayesian approach typically requires the inclusion of several model parameters, such as individual isotopic data, isotopic and macronutrient composition of food groups, diet‐to‐tissue isotopic offsets and dietary routing. In an archaeological context, sparse data may hamper a widespread application of such models. However, simpler models may be proposed to address specific archaeological questions. As a consequence of the intake of marine foods, individuals from the first century ad Roman site of Herculaneum showed well‐defined bone collagen radiocarbon age offsets from the expected terrestrial value. Taking as reference these radiocarbon offsets and using as model input stable isotope data (δ¹³C and δ¹⁵N), the performance of two Bayesian mixing model instances (routed and concentration‐dependent model versus non‐routed and concentration‐independent) was compared to predict the carbon contribution of marine foods to bone collagen. Predictions generated by both models were in good agreement with observed values. The model with higher complexity showed only a slightly better performance in terms of accuracy and precision. This demonstrates that under similar circumstances, a simple Bayesian approach can be applied to quantify the carbon contribution of marine foods to human bone collagen.     

Numerical models of petroleum migration via buoyancy-driven porosity waves in viscously deformable sediments

The apparent ability of petroleum to migrate rapidly through low permeability sediments in sedimentary basins has led to many questions about the manner of its transport. One possible explanation is suggested from observations of the compaction of viscously deformable porous media. These systems have been found in some cases to give rise to regions of locally elevated liquid fraction, in the form of fluid‐filled porosity waves that can ascend at rates much greater than that of the background flow. Previous research on the phenomenon has focused on its implications for magma transport, but recognition of the fact that the compaction of viscous porous media can take place in sedimentary basins has suggested the possibility that porosity waves could similarly be important for hydrocarbon transport. The purpose of the present study was to test this hypothesis by quantifying the transport that would occur as the result of porosity waves initiated during the conversion of kerogen to petroleum. A one‐dimensional numerical model was constructed solving equations for the mechanics of viscous compaction and for the kinetics of reactions describing the formation of petroleum from kerogen. The results showed that porosity waves would develop readily in viscously deformable regions of sedimentary basins, but would not necessarily provide enhanced transport over that of the background flow regime. In order for the waves to achieve this enhanced transport, they must develop high amplitudes, i.e. high porosities relative to the background porous medium. To achieve the high wave amplitudes, the background porosity must be very low in absolute terms. In addition, high kerogen contents are needed in the source layer, and the source layer needs to be buried rapidly to a high temperature region of the oil window. Considerable uncertainty exists as to the value of the matrix shear viscosity of sediments in basins. However, the wave volumetric transport capacity was not found to be significantly altered as a result of variations in the value of this parameter. The physical form of the waves was strongly altered by the matrix shear viscosity, with higher values leading to lower amplitudes and generation frequency, but higher wavelengths. Thus the waves become less recognizable physically at higher values of the matrix shear viscosity. As the waves ascend to higher stratigraphic levels, where the porosity is higher, they gradually lose their physical definition and become absorbed into the background.     

Reconstructing the Space-Time Structure of the HIV/AIDS Epidemic for the Countries of Western Europe

This paper applies a compartmental epidemic modelling system to the estimation of HIV infection transfers between the nations of Western Europe for the period 1973–98. This multiregional model imitates the formation of disease contacts by both local and international travel, where the latter is assumed to have the lower sensitivity to the effects of spatial separation. This system is calibrated in two stages: first, disease parameter sets are found to best fit the timing of recorded AIDS incidence in each nation; and second, these sets are entered into a multiregion setting to identify the travel parameters that support the lags between these series. The outputs include estimates for the first year of HIV incidence in each country and the subsequent pathways of infection transfer that connect these dates. The results indicate the contrasting roles of the southern and northern countries within the continental epidemic and point to national variations in the recent delaying effects on AIDS incidence of drug combination therapies.     

Thermodynamic study of capillary pressure curves based on free energy minimization

This paper presents a new method for pore level network simulation of the distribution of two immiscible phases in a permeable medium. The method requires that the Helmholtz free energy of the system — the medium and the two phases contained within the pore space — be a minimum at all saturation states. We describe the method here and show some typical results from a computer algorithm that implements it. The results include (i) an explanation of the ‘scanning’ behaviour of capillary pressure curves based wholly on the free energy minimization, (ii) predictions of capillary pressure at arbitrary wetting states, including negative capillary pressures, and (iii) illustrations of how the minimized free energy changes along the scanning curves. The method also predicts the known dependency of the capillary pressure on the pore size distribution and interfacial tension. The current work is restricted to two‐dimensional networks, but the free energy minimization appears to be generalizable to three dimensions and to more than two fluid phases. Moreover, functions generated through the minimization, specifically contact areas between the medium surface and the phases, appear to have applications predicting other multiphase petrophysical properties.     

Climate change during the Iron Age in the Shashe-Limpopo Basin,southern Africa

Recent research refines previous interpretations about the role of climatic factors in the development of Mapungubwe. First, the Medieval Warm Epoch started at about AD 1000, rather than 900. At about AD 900, Zhizo people moved into the Shashe-Limpopo Basin, most likely to hunt elephants for the East Coast trade. Secondly, a dry period at about AD 1200–1250 affected farming societies over a wide area. In the Basin, multiple rainmaking episodes occurred at this time. A similar situation took place around Makapansgat and at Great Zimbabwe. Thirdly, Mapungubwe was probably abandoned in AD 1300 because of cooler and drier conditions. At this time, it would have been impossible to maintain floodplain agriculture at the intensity necessary to support the large population. Agricultural failures probably undermined political authority, contributing to Mapungubwe's abandonment and shift in power to Great Zimbabwe. This detailed sequence challenges the re-calibrated climatic series from Makapansgat.     

Abortion and eugenics

The late 1960s and early 1970s saw a revolution within foetal diagnostics. In roughly the same period, legal measures in many countries permitted the termination of pregnancies in cases of suspected foetal abnormalities. Critics have claimed that the resulting abortion policies resemble the old, state‐imposed eugenics of the early 20th century. This article presents some evidence to the contrary. In Norway, which is the article's main topic of concern, so‐called eugenic clauses in the abortion legislation were passed well before the revolution in foetal diagnostics. More importantly, other motives were historically more significant than eugenics for the development of modern Norwegian abortion policies. Consequently, any eugenic effect of these policies should be considered a result of coincidence rather than design – or so the article argues. Brief comparisons with the other Nordic countries are included.