Fixed-order H∞ compensator design

A method is presented for the construction of fixed-order compensators to provide H_∞ norm constraint for linear control systems with exogenous disturbances. The method is based on the celebrated bounded-real lemma that predicates the H_∞ norm constraint via a Riccati inequality. The synthesis of fixed-order controllers whose dimensions are less than the order of a given plant, is demonstrated by a set of sufficient conditions along with a numerical algorithm.     

Lightweight dynamic symmetry breaking

Symmetries in constraint problems present an opportunity for reducing search. This paper presents Lightweight Dynamic Symmetry Breaking, an automatic symmetry breaking method that is efficient enough to be used as a default, since it never yields a major slowdown while often giving major performance improvements. This is achieved by automatically exploiting certain kinds of symmetry that are common, can be compactly represented, easily and efficiently processed, automatically detected, and lead to large reductions in search. Moreover, the method is easy to implement and integrate in any constraint system. Experimental results show the method is competitive with the best symmetry breaking methods without risking poor performance.     

Visual search tree profiling

Understanding how the search space is explored for a given constraint problem – and how it changes for different models, solvers or search strategies – is crucial for efficient solving. Yet programmers often have to rely on the crude aggregate measures of the search that are provided by solvers, or on visualisation tools that can show the search tree, but do not offer sophisticated ways to navigate and analyse it, particularly for large trees. We present an architecture for profiling a constraint programming search that is based on a lightweight instrumentation of the solver. The architecture combines a visualisation of the search tree with various tools for convenient navigation and analysis of the search. These include identifying repeated subtrees, high-level abstraction and navigation of the tree, and the comparison of two search trees. The resulting system is akin to a traditional program profiler, which helps the user to focus on the parts of the execution where an improvement to their program would have the greatest effect.     

Crude oil aggregation by microscopy and dynamic light scattering

This research is focused on establishing a methodology to evaluate the aggregation state of Mexican crude oil solutions from two different sources and SARA compositions, by using Dynamic Light Scattering (DLS). Different crude oil concentrations were established and monitored through time in order to determine their effects on the aggregation state. DLS results indicate that the aggregation state of the studied solutions is influenced by crude oil composition, specifically by the amount of resins. Particle size and elemental analysis of the aggregates were performed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX), respectively. Results from these techniques reveal particulated low-porosity smooth surfaces due to the presence of resin, as well as the determination of the characteristic elements found in asphaltenes. High-Resolution Transmission Electron Microscopy (HTEM) indicated the presence of asphaltene aggregates constituted by nanometric particles and asphaltene stacking as well as ultrafine nanocrystalline-oriented structures.     

Fast iterative computation of optimal two-blockH∞-norm

The two-block H^∞ optimization problem is discussed, in which the most computationally demanding work is the computation of the optimal H^∞ norm denoted by γ₀. The problem of computing γ₀ can be considered as that of finding a γ such that μ(γ) is equal to 1. Some new properties of μ(γ) are revealed and studied. Based on these properties and those found by C.-C. Chu and J. Doyle (1985) and Z.Z. Wang and J.B. Pearson (1984), a very fast computational algorithm for finding γ₀ is proposed     

Challenges to sustainable management of the lakes of Malawi

This paper reviews the management challenges facing Malawi lakes and analyzes the management responses that have been developed to deal with these challenges. Malawi lakes are under considerable stress due to high population growth and increasing levels of poverty which have led to overexploitation of fishery resources. High rates of soil erosion in the lake catchments are increasing siltation of shallow lakes, deltas and embayments, affecting water quality and fish breeding habitats, thereby degrading fish production potential. This review further shows that past and current management approaches have focused on maximizing sustainable yield and have failed to adequately incorporate socio-ecological factors and broader lake catchment processes into fisheries management plans. This, in turn, led to the top-down development of fisheries laws and technical regulations which were difficult to enforce, increased conflict between resource users and fisheries managers, and failed to control fisheries over-exploitation and the collapse of the chambo (tilapia) and cyprinid fisheries. The paper recommends that the fisheries policy should be reviewed to focus on resilience of fisheries, environment and livelihoods. Policy makers should adopt integrated management planning to address the diverse interest of stakeholders in lake basins, as well as the ecological, socio-economic and external factors threatening sustainability of lake ecosystems and livelihoods of dependent communities.     

Convection naturelle a l'interieur d'un diedre. Etude experimentale du transfert de masse a la paroi

The authors review the electrochemical technique utilised and present the experimental correlations between the global average Sherwood and Rayleigh numbers. They compare these results with those obtained for a flat plate under the same condition.     

A robust three phase power flow algorithm for radial distribution systems

An efficient load flow solution technique is required as a part of the distribution automation (DA) system for taking various control and operations decisions. This paper presents an efficient and robust three phase power flow algorithm for application to radial distribution networks. This method exploits the radial nature of the network and uses forward and backward propagation to calculate branch currents and node voltages. The proposed method has been tested to analyse several practical distribution networks of various voltage levels and also having high R/X ratio. The results for a practical distribution feeder are presented for illustration purposes. The application of the proposed method is also extended to find optimum location for reactive power compensation and network reconfiguration for planning and day-to-day operation of distribution networks.