Adjoint methods in data assimilation for estimating model error

Data assimilation aims to incorporate measured observations into a dynamical system model in order to produce accurate estimates of all the current (and future) state variables of the system. The optimal estimates minimize a variational principle and can be found using adjoint methods. The model equations are treated as strong constraints on the problem. In reality, the model does not represent the system behaviour exactly and errors arise due to lack of resolution and inaccuracies in physical parameters, boundary conditions and forcing terms. A technique for estimating systematic and time-correlated errors as part of the variational assimilation procedure is described here. The modified method determines a correction term that compensates for model error and leads to improved predictions of the system states. The technique is illustrated in two test cases. Applications to the 1-D nonlinear shallow water equations demonstrate the effectiveness of the new procedure.

Numerical-asymptotic boundary integral methods in high-frequency acoustic scattering

In this article we describe recent progress on the design, analysis and implementation of hybrid numerical-asymptotic boundary integral methods for boundary value problems for the Helmholtz equation that model time harmonic acoustic wave scattering in domains exterior to impenetrable obstacles. These hybrid methods combine conventional piecewise polynomial approximations with high-frequency asymptotics to build basis functions suitable for representing the oscillatory solutions. They have the potential to solve scattering problems accurately in a computation time that is (almost) independent of frequency and this has been realized for many model problems. The design and analysis of this class of methods requires new results on the analysis and numerical analysis of highly oscillatory boundary integral operators and on the high-frequency asymptotics of scattering problems. The implementation requires the development of appropriate quadrature rules for highly oscillatory integrals. This article contains a historical account of the development of this currently very active field, a detailed account of recent progress and, in addition, a number of original research results on the design, analysis and implementation of these methods.

A comparative review of dimension reduction methods in approximate Bayesian computation

Approximate Bayesian computation (ABC) methods make use of comparisons between simulated and observed summary statistics to overcome the problem of computationally intractable likelihood functions. As the practical implementation of ABC requires computations based on vectors of summary statistics, rather than full data sets, a central question is how to derive low-dimensional summary statistics from the observed data with minimal loss of information. In this article we provide a comprehensive review and comparison of the performance of the principal methods of dimension reduction proposed in the ABC literature. The methods are split into three nonmutually exclusive classes consisting of best subset selection methods, projection techniques and regularization. In addition, we introduce two new methods of dimension reduction. The first is a best subset selection method based on Akaike and Bayesian information criteria, and the second uses ridge regression as a regularization procedure. We illustrate the performance of these dimension reduction techniques through the analysis of three challenging models and data sets.

Advanced feature selection methods in multinominal dementia classification from structural MRI data

Recent studies showed that features extracted from brain MRIs can well discriminate Alzheimer’s disease from Mild Cognitive Impairment. This study provides an algorithm that sequentially applies advanced feature selection methods for findings the best subset of features in terms of binary classification accuracy. The classifiers that provided the highest accuracies, have been then used for solving a multi-class problem by the one-versus-one strategy. Although several approaches based on Regions of Interest (ROIs) extraction exist, the prediction power of features has not yet investigated by comparing filter and wrapper techniques. The findings of this work suggest that (i) the IntraCranial Volume (ICV) normalization can lead to overfitting and worst the accuracy prediction of test set and (ii) the combined use of a Random Forest-based filter with a Support Vector Machines-based wrapper, improves accuracy of binary classification.

Life before ‘The New Biography’: Modernist biographical methods in the Hogarth Press ‘Books on Tolstoi’ 1920-24

In the early 1920s, before Virginia Woolf wrote her now well-known essays “The New Biography” and “The Art of Biography,” the Hogarth Press published four biographies of Tolstoy. Each of these English translations of Russian works takes a different approach to biographical composition, and as a group they offer multiple and contradictory perspectives on Tolstoy’s character and on the genre of biography in the early twentieth century. These works show that Leonard and Virginia Woolf’s Hogarth Press took a multi-perspectival, modernist approach to publishing literary lives.

Data Assimilation and Inverse Methods in Terms of a Probabilistic Formulation

The weak-constraint inverse for nonlinear dynamical models is discussed and derived in terms of a probabilistic formulation. The well-known result that for Gaussian error statistics the minimum of the weak-constraint inverse is equal to the maximum-likelihood estimate is rederived. Then several methods based on ensemble statistics that can be used to find the smoother (as opposed to the filter) solution are introduced and compared to traditional methods. A strong point of the new methods is that they avoid the integration of adjoint equations, which is a complex task for real oceanographic or atmospheric applications. they also avoid iterative searches in a Hilbert space, and error estimates can be obtained without much additional computational effort. the feasibility of the new methods is illustrated in a two-layer quasigeostrophic model.

Research methods in TESOL and digital literacies

One of the biggest challenges of integrating research in TESOL with research in digital literacies is that the research methodologies of these two traditions have developed out of different ontological and episte- mological assumptions about what is being researched (the object of study), where the research is located (the research site), and who is being researched (the research participants).

Participatory Farm Management methods for assessing the suitability of potential innovations. A case study on green manuring options for tomato producers in Ghana

This paper examines the potential of using Participatory Farm Management methods to examine the suitability of a technology with farmers prior to on-farm trials. A study examining the suitability of green manuring as a technology for use with wet season tomato producers in Ghana is described. Findings from this case-study demonstrate that Participatory Budgeting can be used by farmers and researchers to analyse current cultivation practices, identify the options for including green manures into the system and explore the direct and wider resource implications of the technology. Scored-Causal Diagrams can be used to identify farmers' perceptions of the relative importance of the problem that the technology seeks to address. The use of the methods in this examine evaluation process appears to have the potential to improve the effectiveness and efficiency of the adaptive research process. This ensures that technologies subsequently examined in trials ate relevant to farmers' interests, existing systems and resources, thereby increasing the chances of farmer adoption. It is concluded that this process has potential for use-with other technologies and in other farming systems. (C) 2002 Elsevier Science Ltd. All rights reserved.

Comparative costs of the commercial process in different construction procurement methods

The commercial process in construction projects is an expensive and highly variable overhead. Collaborative working practices carry many benefits, which are widely disseminated, but little information is available about their costs. Transaction Cost Economics is a theoretical framework that seeks explanations for why there are firms and how the boundaries of firms are defined through the “make-or-buy” decision. However, it is not a framework that offers explanations for the relative costs of procuring construction projects in different ways. The idea that different methods of procurement will have characteristically different costs is tested by way of a survey. The relevance of transaction cost economics to the study of commercial costs in procurement is doubtful. The survey shows that collaborative working methods cost neither more nor less than traditional methods. But the benefits of collaboration mean that there is a great deal of enthusiasm for collaboration rather than competition.

Responsible tourism and sustainability: the case of Kumarakom in Kerala, India

This paper discusses the notion of ‘responsible tourism’ and its current use within the tourism literature. We argue that the concept as used currently means everything and therefore adds nothing to the conceptual terrain of tourism trends and nomenclatures. We then introduce our own understanding of the concept arguing that while responsible tourism is linked to sustainability initiatives such as alternative tourism, ecotourism, ethical tourism, green tourism, soft tourism, pro-poor tourism, geo-tourism, integrated tourism, community-based tourism, etc it also demarcates an analytical realm of its own. We suggest that the practical use of the term in areas where it has been adopted (such as South Africa and Kerala for instance) suggests a rather restricted use. We identified this realm as the tourism sector-specific manifestation of the corporate social responsibility (CSR) agenda. Following Flyvberg's [(2006). Five misunderstandings about case-study research. Qualitative Inquiry, 12(2), 219–245] call for exemplars and paradigmatic case studies to advance knowledge in a particular domain, the responsible tourism initiative in Kumarakon, Kerala, is presented. Discussion of the case study traces the particular governance context of Kerala and the position of tourism in the state economy. The responsible tourism initiatives at the state level and local level are then described highlighting the ‘how’ of the implementation and the impact that it has produced. Generic, non-prescriptive principles that could be said to be necessary in some form for the successful translation of responsible tourism principles to practices are then identified. Such an approach is contrasted with one that places faith in the voluntary adoption of ‘responsible’ practices by the private sector on its own. It is argued that responsible tourism can make a contribution to practice provided the conceptual terrain is delineated against other forms of tourism and if research within the terrain can unpack the particular forms of challenges that are thrown up by the delineation itself.

Demonstrating the importance of criteria and sub-criteria in building assessment methods

Building assessment methods have become a popular research field since the early 1990s. An international tool which allows the assessment of buildings in all regions, taking into account differences in climates, topographies and cultures does not yet exist. This paper aims to demonstrate the importance of criteria and sub-criteria in developing a new potential building assessment method for Saudi Arabia. Recently, the awareness of sustainability has been increasing in developing countries due to high energy consumption, pollution and high carbon foot print. There is no debate that assessment criteria have an important role to identify the tool’s orientation. However, various aspects influence the criteria and sub-criteria of assessment tools such as environment, economic, social and cultural to mention but a few. The author provides an investigation on the most popular and globally used schemes: BREEAM, LEED, Green Star, CASBEE and Estidama in order to identify the effectiveness of the different aspects of the assessment criteria and the impacts of these criteria on the assessment results; that will provide a solid foundation to develop an effective sustainable assessment method for buildings in Saudi Arabia. Initial results of the investigation suggest that each country needs to develop its own assessment method in order to achieve desired results, while focusing upon the indigenous environmental, economic, social and cultural conditions. Keywords: Assessment methods, BREEAM, LEED, Green Star, CASBEE, Estidama, sustainability, sustainable buildings, Environment, Saudi Arabia.