Multi-Fidelity Gaussian Process Emulation And Its Application In The Study Of Tsunami Risk Modelling

Investigating uncertainties in computer simulations can be prohibitive in terms of computational costs, since the simulator needs to be run over a large number of input values. Building a statistical surrogate model of the simulator, using a small design of experiments, greatly alleviates the computational burden to carry out such investigations. Nevertheless, this can still be above the computational budget for many studies. We present a novel method that combines both approaches, the multilevel adaptive sequential design of computer experiments (MLASCE) in the framework of Gaussian process (GP) emulators. MLASCE is based on the two major approaches: efficient design of experiments, such as sequential designs, and combining training data of different degrees of sophistication in a so-called multi-fidelity method, or multilevel in case these fidelities are ordered typically for increasing resolutions. This dual strategy allows us to allocate efficiently limited computational resources over simulations of different levels of fidelity and build the GP emulator. The allocation of computational resources is shown to be the solution of a simple optimization problem in a special case where we theoretically prove the validity of our approach. MLASCE is compared with other existing models of multi-fidelity Gaussian process emulation. Gains of orders of magnitudes in accuracy for medium-size computing budgets are demonstrated in numerical examples. MLASCE should be useful in a computer experiment of a natural disaster risk and more than a mere tool for calculating the scale of natural disasters. To show MLASCE meets this expectation, we propose the first end-to-end example of a risk model for household asset loss due to a possible future tsunami. As a follow-up to this proposed framework, MLASCE provides a reliable statistical surrogate to a realistic tsunami risk assessment under a restricted computational resource and provides accurate and instant predictions of future tsunami risks

Vehicle path optimisation and controllability on the limit using optimal control techniques

Vehicle behaviour near the limit of adhesion is studied using linear optimal . control techniques and relatively simple vehicle models. Both time-invariant and time-varying approaches are used. Controllability is applied as a post-processing tool to analyse the resultant vehicle behaviour. First, a 4WS controller is developed using a linear time-invariant method, with a reference model control structure. Two handling objectives are defined, which are thought to provide predictable dynamics. Advantages of using a reference model control are clearly shown. With a developed control structure, it is shown that the prescribed target dynamics is achieved, provided tyre forces are available. It is also found that the controller is robust to small changes in the various vehicle parameter values. As a next step, time-varying modelling approach was used in order to better represent the vehicle operating conditions through the various dynamic range, including the limit of adhesion. An iterative vehicle path optimisation problem is formulated using a linear time-varying control approach. The validity of the optimisation method is studied against the steady-state simulation result at the limit of adhesion. It is shown that the method is capable of finding a trajectory in the vicinity of the friction limit, where the front tyres are used fully whilst retaining some margin at the rears. However, a couple of Issues are discovered. First, due to the quadratic nature of the road geometry cost function, the trajectory could get locked if the vehicle runs very close to the edge of the road. Hence, the . optimisation needs to be formulated such that the level of "optimality" on the trajectory remains consistent throughout the manoeuvre at each iteration. Secondly, it is found that inappropriate control demands are produced if the system matrix becomes poorly conditioned near the limit. This results in optimisation failure. In order to understand the mechanism of this failure, controllability of linear timevarying system was analysed and its properties were discussed in detail. First, the calculation methods of the controllability gramian matrix are investigated and some practical limitations are found. The gramian matrix is then used to define an open loop control sequence. It is found that the damping of the system has a significant influence on the control strategy. Subsequently, "the moving controllability window of a fixed time period" is found to provide the most relevant information of changing dynamics through the time. The study showed that the failure of the optimisation in the vicinity of the friction limit was indeed due to lack of controllability and the optimisation method itself was functioning correctly. The vehicle path optimisation problem is then extended to include longitudinal dynamics, enabling simulation of more general manoeuvres. The single corner simulation showed that the optimisation converges to an "out-in-out" path, with iterative solution improving continuously in a first order manner. Simulations with various controller settings showed that the strategy is reasonably robust provided that the changes in parameter settings are kept within a reasonable magnitude. It is also confirmed that the optimisation is able to drive a vehicle close to the limit under different types of operations required, i.e. braking, cornering and acceleration. The study was then performed with slightly more complex road geometry in order to investigate if the· optimisation is capable of prioritising certain· part of the manoeuvre in order to achieve better overall result. Unfortunately, this problem could not be solved successfully. The optimisation concentrated on the latter part of the manoeuvre as it had higher sensitivity to the final cost. This resulted in clearly sub-optimal overall performance. Finally, relatively simple study is conducted to investigate the correlation between various vehicle settings and optimisation results. Using the path optimisation problem formulation, iris found that the more oversteer vehicles are able to achieve better· result with more margin left in rear tyre force capacity. The handling objective functions used for the 4 WS controller is also calculated for the resultant trajectories. It is found that the neutral steer cost had a strong correlation, whereas the linearity cost showed no noticeable correlation. The controllability analysis was applied on the various vehicle settings using step steer simulation. It showed that more understeering vehicle retains higher controllability throughout the dynamics range. It is also found that higher inertia gives better controllability near the limit, however, it gives less controllability at more moderate operating conditions

Rapport: conférence électronique sur l'aviculture en Afrique

Cette conférence électronique, du 3 juillet au 11 août 2008, relance la discussion sur les contraintes de l'aviculture et les solutions à y apporter pour en faire un levier important dans les stratégies de réduction de la pauvreté

Management of environmental issues for sustainable fisheries production from aquaculture in Nigeria

Aquaculture depends largely upon a good aquatic environment. The quality of the aquatic medium determines success to a large extent in aquaculture. The medium is particularly vulnerable to excessive abstraction (i.e surface or groundwater) and contamination from a range of sources (industrial, agricultural or domestic) as well as risks of self-pollution. Environmental management options proffered so far include: improvements in farming performance (especially related to feed and feeding strategies, stocking densities, water quality management, disease prevention and control, use of chemicals, etc.) and in the selection of sites and culturable species, treatment of effluents, sensitivity of recipient waters and enforcement of environmental regulations and guidelines specific to the culture system. There are presently conceptual frameworks for aquatic environment management backed by legal administrative tools to create or enforce rational system for water management, fisheries and aquaculture development strengthened by adaptive institutionalisatio

Photoionization of the Potassium Isoelectronic Sequence: Ca+ and Transition Metal Ions

Photoionization cross section calculations are performed for the ground ([Ne]3s23p63d 2D ) and the first two excited ([Ne]3s23p63d 2D and [Ne]3s23p64s 2S ) states of potassium-like transition metal ions (Sc+2, Ti+3, V+4, Cr+5, Mn+6, Fe+7), along with photoionization calculations for K-like Ca+ ions in the ground ([Ne]3s23p64s 2S ) state and the first two excited ([Ne]3s23p63d 2D and [Ne]3s23p63d 2D ) states. The discrete N-electron final state ion system orbitals are generated using the computer program AUTOSTRUCTURE; 24 configurations are included in the configuration-interaction (CI) calculation for transition metal ions, and 30 configurations for the case of Ca+ ions. The initial and final (N+1)-electron wavefunctions are generated using R-matrix along with photoionization cross sections. In addition to the non-relativistic (LS-coupling) R-matrix, we have used the relativistic (Breit-Pauli) R -matrix method to carry out these calculations to focus on relativistic effects. Relativistic and non-relativistic results are compared to demonstrate the influence of relativistic effects. The prominent 3p → 3d giant resonances are analyzed and identified, and our calculated positions and widths are compared with experimental results for K-like ions such as Ca+, Sc+2 and Ti+3. In the case of lower Z (22 Z 20) ions (Ca+, Sc+2 and Ti+3), the photoionization cross section spectra are dominated by the giant (3p 3d excitation) resonances, while in cases of higher Z (26 Z 23) ions (V+4, Cr+5, Mn+6 and Fe+7), the 3p 3d resonances lie below the ionization threshold, and the cross sections are dominated by 3p53d nd and 3p53d n’s Rydberg series of resonances. Comparison of the Ca+, Sc+2 and Ti3+ results with available theoretical and experimental data shows good agreement

Another America is Possible: The Impact of NAFTA on the U.S. Latino Community and Lessons for Future Trade Agreements

A joint report by Labor Council for Latin American Advancement and Public Citizen's Global Trade Watch. The Labor Council for Latin American Advancement (LCLAA) and Public Citizen celebrate the promise of increased interaction and cross-border cooperation among different nationalities on pressing global concerns. This is why we are concerned about the current model of corporate globalization being fostered by "free trade" agreements such as the North American Free Trade Agreement (NAFTA). Negotiated behind closed doors by unelected and largely unaccountable bureaucrats who represent mainly business interests, these trade agreements invariably fail to promote equitable regional integration and cooperation. Instead, this model of corporate globalization explicitly benefits large multinational corporations at the expense of workers, farmers, immigrants, women, people of color, the environment and democratic governance. As the fastest-growing sector of the U.S. population, Latinos are and will continue to be among the groups most affected by this model of corporate globalization. Whether newcomers from El Salvador or fifth-generation Mexican-Americans, U.S. Latinos are seeing adverse effects on their job security, health and environment. Many are immigrants who left their homelands due to the economic and social devastation caused by the current globalization model. In both the United States and in their countries of origin, Latinos have seen their environment and their livelihoods harmed by the status quo globalization package of free trade, investment and finance liberalization, new protections for foreign investors and intellectual property, and new powers that enable multinational corporations to attack state, local and federal public interest laws. In this report, we examine the impact of NAFTA on Latino communities throughout the United States. Implemented in 1994, NAFTA is the most fully realized version of the corporate globalization model. It is currently being used as the blueprint for other trade and investment agreements that the Bush Administration is pushing in the hemisphere, such as the Central American Free Trade Agreement (CAFTA), the Free Trade Area of the Americas (FTAA) and an array of bilateral free trade agreements with the Andean countries (Bolivia, Colombia, Ecuador and Peru) and Panama. Although we support trade, we feel that NAFTA is not the model to follow and should not be copied in these agreements

Insécurité foncière et phénomène de la pauvreté des populations rurales en Afrique noire : cas du Sud-Est du Togo

In most Third World countries in general and those of sub-Saharan Africa in particular, national development is always conditioned by that of the rural world. Agriculture contributes more than 1/3 of the GDP and employs nearly 70% of the active population. In this context, access to land security for rural producers becomes a fundamental imperative. The land problem in the Southeast Maritime is linked to land access which is not reassuring for farmers who do not have land control due to the behavior of landowners. This article analyzes the different dimensions of land insecurity on the phenomenon of poverty experienced by agricultural producers with temporary cultivation rights on cultivated plots. To achieve this, it used quantitative and qualitative methods based on the administration of the questionnaire and individual interviews with actors such as: lineage communities, farmers, tenant farmers, sharecroppers, opinion leaders, etc. The results showed that the precariousness of land access compromises the development of subsistence agriculture (and therefore the improvement of the food security of the population) by making it extremely difficult to make any long-term investment in techniques allowing, at the same time, better soil conservation and a significant increase in agricultural yields.Dans la plupart des pays du tiers monde en général et ceux d’Afrique sub-saharienne en particulier, le développement national est toujours conditionné par celui du monde rural. L’agriculture contribue pour plus d’un 1/3 du PIB et emploie près de 70% de la population active. Dans ce contexte, la sécurisation foncière des producteurs ruraux devient un impératif fondamental. La problématique foncière dans le Sud-Est Maritime est liée à l’accès au foncier qui n’est pas sécurisant pour les paysans n’ayant pas la maîtrise foncière suite aux comportements des propriétaires des parcelles de terre. Cet article analyse les différentes dimensions de l’insécurité foncière sur le phénomène de pauvreté que vivent les producteurs agricoles ayant un droit de culture temporaire sur les parcelles cultivées. Pour y arriver, il a fait usage des méthodes quantitative et qualitative basées sur l’administration du questionnaire et l’entretien individuel auprès des acteurs tels que : collectivités lignagères, exploitants agricoles, exploitants locataires, exploitants métayers, leaders d’opinion, etc. Les résultats ont démontré que la précarité de l’accès au foncier compromet le développement de l'agriculture vivrière (et donc l'amélioration de la sécurité alimentaire de la population) en rendant extrêmement difficile tout investissement de long terme dans des techniques permettant, à la fois une meilleure conservation des sols et un accroissement significatif des rendements agricoles

Multi-level emulation of tsunami simulations over Cilacap, South Java, Indonesia

Carrying out a Probabilistic Tsunami Hazard Assessment (PTHA) requires a large number of simulations done at a high resolution. Statistical emulation builds a surrogate to replace the simulator and thus reduces computational costs when propagating uncertainties from the earthquake sources to the tsunami inundations. To reduce further these costs, we propose here to build emulators that exploit multiple levels of resolution and a sequential design of computer experiments. By running a few tsunami simulations at high resolution and many more simulations at lower resolutions we are able to provide realistic assessments whereas, for the same budget, using only the high resolution tsunami simulations do not provide a satisfactory outcome. As a result, PTHA can be considered with higher precision using the highest spatial resolutions, and for impacts over larger regions. We provide an illustration to the city of Cilacap in Indonesia that demonstrates the benefit of our approach.</p