Numerical modelling of the application of capillary barrier systems for prevention of rainfall-induced slope instability

Acta Geotechnica - The most common cause of slope instability is intense or sustained rainfall, which may induce reduction in soil suction, and thus, shear strength. Capillary barrier systems...     

The effect of sideband ratio on line intensity for Herschel/HIFI

The Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory is composed of a set of fourteen double sideband mixers. We discuss the general problem of the sideband ratio (SBR) determination and the impact of an imbalanced sideband ratio on the line calibration in double sideband heterodyne receivers. The HIFI SBR is determined from a combination of data taken during pre-launch gas cell tests and in-flight. The results and some of the calibration artefacts discovered in the gas cell test data are presented here along with some examples of how these effects appear in science data taken in orbit.     

Crustal Electrical Structure and Deep Metallogenic Potential in Northern Wuyi Area (South China), based on Magnetotelluric Data

The northern Wuyi area, which is located in the northern Wuyi metallogenic belt, has superior mineralization conditions. The Pingxiang–Guangfeng–Jiangshan–Shaoxing fault (PSF) extends across the whole region regardless of whether or how the PSF relates to the near-surface mineralization. We carried out an MT survey in the region and obtained a reliable 2D model of the crustal electrical structure to a depth of 30 km. In the resistivity model, we inferred that a continuous high conductivity belt that ranges from the shallow to deep crust is a part of the PSF. Then, we estimated the fluid content and pressure gradient to identify the deep sources of fluid as well as its pattern of motion pattern. Finally, we proposed a model for the deep metallogenic migration processes that combines geological data, fluid content data, pressure gradient data, and the subsurface resistivity model. The model analysis showed that the Jiangnan orogenic belt and the Cathaysia block formed the PSF during the process of com. The deep fluid migrated upward through the PSF to the shallow crust. Therefore, we believe that the PSF is an ore-forming fluid migration channel and that it laid the material basis for large-scale mineralization in the shallow crust.     

To move or not to move: an applied study of veterinary clinic location in Wellington,New Zealand

This paper demonstrates the utility, in an applied context, of a standard Teitz and Bart heuristic for solving location-allocation problems. The example discussed is the location of veterinary clinics in Wellington, New Zealand. A distinct ‘service-poor’ area is identified in southern Wellington suggesting that the existing system of clinics, especially the largest multi-veterinary practice, is vulnerable to intrusion by competitors. A variety of strategies, involving new clinics and clinic relocation are analysed to ascertain alternative courses of action for both existing clinic operators and competitors. The appropriateness of this type of analysis as an aid to decision-making is reflected in the locational response of one practice to protect its share of the market for veterinary services.     

A Critical Comparison of Three Methods for Time-Lapse Time-Shift Calculation

Time-shift, one of the most popular time-lapse seismic attributes, has been widely used in dynamic reservoir characterization by linking it with pressure and geomechanical changes. Therefore, it is important to select appropriate calculation methods according to different time-lapse seismic data quality and time-shift magnitude. To date, there have been various published works comparing different time-shift calculation methods and discussing their advantages and disadvantages. However, most of these comparisons are based only on synthetic tests or single field applications. As the quality of time-lapse seismic data and time-shift magnitude can vary in different fields, one method may not work consistently well for each case. In this paper, a critical comparison of three different time-shift calculation techniques (Hale’s fast cross-correlation, Rickett’s non-linear inversion, and Whitcombe’s correlated leakage method) is provided. The three methods are applied to a set of synthetic data sets that are designed to account for various seismic noise and time-shift magnitudes. They are also applied to four real time-lapse seismic data sets from three North Sea fields. The calculated time-shift results are compared with the input (in synthetic tests) or the real observations from information such as seabed subsidence and compaction (in field applications). Both qualitative and quantitative comparisons are performed. At the end, each of the time-shift methods is evaluated based on different aspects, and the most appropriate method is suggested for each data scenario. All three time-shift methods are found to successfully measure time-shifts. However, Rickett’s non-linear inversion is the most outstanding method, as it gives smooth time-shifts with relatively good accuracy, and the derived time strains are more stable and interpretable.

     

A comparative study of the modelling of cement hydration and cement-rock laboratory experiments

The use of cement and concrete as fracture grouting or as tunnel seals in a geological disposal facility for radioactive wastes creates potential issues concerning chemical reactivity. From a long-term safety perspective, it is desirable to be able model these interactions and changes quantitatively. The ‘Long-term Cement Studies’ (LCS) project was formulated with an emphasis on in situ field experiments with more realistic boundary conditions and longer time scales compared with former experiments. As part of the project programme, a modelling inter-comparison has been conducted, involving the modelling of two experiments describing cement hydration on one hand and cement-rock reaction on the other, with teams representing the NDA (UK), Posiva (Finland), and JAEA (Japan).This modelling exercise showed that the dominant reaction pathways in the two experiments are fairly well understood and are consistent between the different modelling teams, although significant differences existed amongst the precise parameterisation (e.g. reactive surface areas, dependences of rate upon pH, types of secondary minerals), and in some instances, processes (e.g. partition of alkali elements between solids and liquid during cement hydration; kinetic models of cement hydration). It was not conclusive if certain processes such as surface complexation (preferred by some modellers, but not by others) played a role in the cement-rock experiment or not. These processes appear to be more relevant at early times in the experiment and the evolution at longer timescales was not affected. The observed permeability profile with time could not be matched. The fact that no secondary minerals could be observed and that the precipitated mass calculated during the simulations is minor might suggest that the permeability reduction does not have a chemical origin, although a small amount of precipitates at pore throats could have a large impact on permeability.The modelling exercises showed that there is an interest in keeping the numerical models as simple as possible and trying to obtain a reasonable fit with a minimum of processes, minerals and parameters. However, up-scaling processes and model parameterisation to the timescales appropriate to repository safety assessment are of considerable concern. Future modelling exercises of this type should focus on a suitable natural or industrial analogue that might aid assessing mineral-fluid reactions at these longer timescales.     

Estimation of meiobenthic nematode diversity by non-specialists

A methodology is presented for the estimation of nematode diversity using Cairns' technique of sequential comparisons. The accuracy and precision of the method are examined and a test presented for the comparison of diversity estimates.