5,638 research outputs found
Installation of horizontal wells in landfilled waste using directional drilling
No full textLeachate levels within a landfill must often be controlled for environmental and/or regulatory reasons by means of pumping from wells. Conventional vertical wells are usually used for this purpose, but there is a perception that they are inefficient. In this paper, the feasibility of using directional drilling to install horizontal wells for leachate control in landfills is investigated with reference to pilot and full scale field trials at Rainham, U.K. The difficulties of well-screen design and installation in a landfilled waste are discussed; the insights gained during trial installation are described; and the effectiveness of three trial wells is assessed with reference to the leachate flow rates and drawdowns achieved, in comparison with conventional vertical wells. It is concluded that the drilling rig used must be sufficiently powerful to cope with the likelihood of at least partial borehole collapse around the well-screen during installation; that the screen slot size can be based on at least the D30 particle size of the waste and a natural filter allowed to develop around the well (provided that the resulting well screen is strong enough); and that as experience with the technology grows, directionally drilled horizontal wells could represent a viable, cost effective alternative to conventional vertical wells for leachate control in landfills
An exact corrected log-likelihood function for Cox's proportional hazards model under measurement error and some extensions
No full textThis paper studies Cox`s proportional hazards model under covariate measurement error. Nakamura`s (1990) methodology of corrected log-likelihood will be applied to the so called Breslow likelihood, which is, in the absence of measurement error, equivalent to partial likelihood. For a general error model with possibly heteroscedastic and non-normal additive measurement error, corrected estimators of the regression parameter as well as of the baseline hazard rate are obtained. The estimators proposed by Nakamura (1992), Kong, Huang and Li (1998) and Kong and Gu (1999) are reestablished in the special cases considered there. This sheds new light on these estimators and justifies them as exact corrected score estimators. Finally, the method will be extended to some variants of the Cox model
Tuning GENIE earth system model components using a Grid enabled data management system
No full textWe present the Grid enabled data management system that has been deployed for the GENIE project and demonstrate its use in tuning studies of an Earth system model. A Matlab client to the
system provides a common environment for the project Virtual Organization to share scripts, binaries and output data. By using tools available in the Geodise toolkits we have scripted the execution of tuning studies which exploit multiple heterogeneous computational resources and use the database repository to steer computation using multi-dimensional optimisation methods
Rapporteur’s report – innovative geotechnologies for energy transition
No full textThe 9th Society for Underwater Technology (SUT) International Conference on Offshore Site Investigation and Geotechnics (OSIG) closed with a Rapporteur’s report given by the author. This paper provides a record of that report, transcribed from a video recording. The presentation slides are shown as Figures.</p
Collaborative study of GENIEfy Earth System Models using scripted database workflows in a Grid-enabled PSE
No full textThe integration of compute and data grids into a common problem solving environment enables collaboration between members of the GENIEfy project. In addition, state-of-the-art optimisation algorithms complement the component framework to provide a comprehensive toolset for Earth system modelling. In this paper, we present for the first time, the application of the non-dominated sorting genetic algorithm (NSGA-II) to perform a multi-objective tuning of a 3D atmosphere model. We then demonstrate how scripted database workflows enable the collective pooling of available resource at distributed client sites to collaboratively progress ensembles of simulations through to completion on the computational grid. A systematic study of the oceanic thermohaline circulation in a hierarchy of 3D atmosphere-ocean-sea-ice models is presented providing evidence for bi-stability in the Atlantic Meridional Overturning Circulation
Multiobjective tuning of GENIE Earth system models
No full textIn order to simulate at the multi-decadal time scale and beyond, climate models rely heavily on parameterisations of physical processes that occur on comparatively small time and spatial scales. A key concern in climate modelling is therefore to find appropriate values for these parameters so that a reasonable climatology is simulated. This is of particularly importance within the GENIE modelling framework where component codes, that are often developed independently, are coupled together to form new Earth system models. In order to produce stable and sensible model output it is almost always necessary to re-tune the parameters of the coupled system. However, as with many design problems, the nonlinear response of a model to its parameters and the often conflicting tuning objectives make this a difficult problem to solve.The general problem of optimising a set of model parameters in order to improve a number of possibly conflicting design objectives is typically approached in one of two ways. One can create a single objective measure of design quality by computing a weighted sum of the individual objectives and seek to find the set of variables that minimise or maximise this measure. Many sophisticated algorithms can be applied to a single objective problem but the weighting factors can be critical in the performance of the optimisation. Alternatively, multiobjective methods can be employed to seek a Pareto set of non-dominated solutions; designs that are superior when all objective measures are considered but that may be inferior when a subset of those objectives are considered. Such a solution set can inform the user of competition in the design goals and allows domain expertise to be applied to select the most appropriate parameter sets for further study.We present the results of applying a multiobjective Non-dominated Sorting Genetic Algorithm (NSGA-II) to tune two models from the GENIE framework. The genie_eb-go-gs (3D frictional geostrophic ocean model, 2D energy moisture balance model and 2D sea-ice) and genie-ig-fi-fi-ml (3D atmosphere, 2D fixed ocean and sea-ice and land surface) models are tuned to appropriate target data sets by minimising multiple measures of model-data mismatch across different physical fields. Grid computing is exploited to perform the large number of concurrent simulations that comprise the generations of the algorithm. Recent advances in the method use Response Surface Modelling (RSM) to provide surrogate models of the underlying objective functions. These RSMs can be searched much more cheaply and extensively to provide considerable performance improvements in the optimisation
An Assessment of MPI Environments for Windows NT
No full textIn this paper we evaluate the MPI environments currently available for Windows NT on the Intel IA32 and Compaq/DEC Alpha architectures. We present benchmark results for low-level communication and for the NAS Parallel Benchmarks to allow comparison with other systems, but our primary interest is determining real application performance and robustness in production cluster environments. For this we use PAFEC-FE, a large FORTRAN code for finite-element analysis. We present results from three MPI implementations, two architectures, and three networking technologies (10 and 100 Mbit/s Ethernet and 1 Gbit/s Myrinet)
DEFRApH - Sample collection and handling procedures
No full textAll chemical and biogeochemical process in the sea are affected by the acidity of the water. Acidity is therefore fundamental property of seawater. The growing concern that the acidity of the oceans might be increasing has revealed weaknesses in our knowledge of this fundamental property and its variation in space and time. In 2008 the DEFRApH project (DEFRA contract ME4133) was initiated to provide this missing information in UK related waters. It required sampling for and analysis of the total inorganic carbon and total alkalinity content of samples. This reports documents the procedures sued for sampling. A companion document Hartman Dumousseaud and Roberts (NOC Internal Document No. 01) describes in detail the analytical procedures used and the calculation of the results
Stability of the thermohaline circulation in different complexities and resolutions of earth system model (abstract of paper presented at 3rd EGU General Assembly)
No full textWe use the GENIE Earth system modelling framework to examine how the stability / hysteresis diagram of the thermohaline circulation (THC) depends on the use of complex (GCM) or simple (energy-moisture balance) atmosphere models and how it varies with ocean resolution.The model versions all use the GOLDSTEIN frictional geostrophic ocean, but with 3 different horizontal resolutions (and 8 depth layers in each case): (i) 36x36 longitudesine (latitude), (ii) 72x72 longitude-sine(latitude), (iii) 64x32 longitude-latitude. To these we have coupled the Reading Intermediate General Circulation Model (IGCM) at T21 resolution with 7 vertical levels. We contrast this with earlier work using an energy-moisture balance model (EMBM) and ocean resolution (i).For each model version, we construct an ensemble of runs in which we vary atmospheric freshwater transport from the Atlantic to Pacific. In some cases we also vary a parameter controlling equator to pole freshwater transport. The resulting ensembles are run toward equilibrium and then restarts are used to search parameter space for regions of THC bi-stability.The resulting hundreds of thousands of years of 3D ocean-atmosphere model integration were achieved by using UK Grid computing resources, including 6 nodes of the National Grid Service, and additional clusters in Norwich, Southampton and Bristol. A specially developed database system was used to execute and manage the runs.The results are expected to shed light on whether a dynamical atmosphere alters or removes the bi-stability of the THC, and whether THC stability is sensitive to ocean resolution
Author Correction:Prefrontal cortical ChAT-VIP interneurons provide local excitation by cholinergic synaptic transmission and control attention (Nature Communications, (2019), 10, 1, (5280), 10.1038/s41467-019-13244-9)
No full textThe original version of this Article contained an error in the spelling of the author Wilma D.J. van de Berg, which was incorrectly given as Wilma D.J. van den Berg. This has now been corrected in both the PDF and HTML versions of the Article.</p
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