Synchronization is optimal in non-diagonalizable networks

We consider the problem of maximizing the synchronizability of oscillator networks by assigning weights and directions to the links of a given interaction topology. We first extend the well-known master stability formalism to the case of non-diagonalizable networks. We then show that, unless some oscillator is connected to all the others, networks of maximum synchronizability are necessarily non-diagonalizable and can always be obtained by imposing unidirectional information flow with normalized input strengths. The extension makes the formalism applicable to all possible network structures, while the maximization results provide insights into hierarchical structures observed in complex networks in which synchronization plays a significant role.Comment: 4 pages, 1 figure; minor revisio

Overcoming Data Limitations in Nonparametric Benchmarking: Applying PCA-DEA to Natural Gas Transmission

This paper provides an empirical demonstration for a practical approach of efficiency evaluation against the background of limited data availability in some regulated industries. Here, traditional DEA may result in a lack of discriminatory power when high numbers of variables but only limited observations are available. We apply PCA-DEA for radial efficiency measurement to US natural gas transmission companies in 2007. This allows us to reduce dimensions of the optimization problem while maintaining most of the variation in the original data. Our results suggest that the PCA-DEA methodology reduces the probability of over-estimation of the individual firm-specific performance. It also allows for a large number of original variables without substantially reducing the discriminatory power of the model.Efficiency analysis, DEA, PCA, company regulation, natural gas transmission

Information Super-Diffusion on Structured Networks

We study diffusion of information packets on several classes of structured networks. Packets diffuse from a randomly chosen node to a specified destination in the network. As local transport rules we consider random diffusion and an improved local search method. Numerical simulations are performed in the regime of stationary workloads away from the jamming transition. We find that graph topology determines the properties of diffusion in a universal way, which is reflected by power-laws in the transit-time and velocity distributions of packets. With the use of multifractal scaling analysis and arguments of non-extensive statistics we find that these power-laws are compatible with super-diffusive traffic for random diffusion and for improved local search. We are able to quantify the role of network topology on overall transport efficiency. Further, we demonstrate the implications of improved transport rules and discuss the importance of matching (global) topology with (local) transport rules for the optimal function of networks. The presented model should be applicable to a wide range of phenomena ranging from Internet traffic to protein transport along the cytoskeleton in biological cells.Comment: 27 pages 7 figure

Analysis reuse exploiting taxonomical information and belief assignment in industrial problem solving

To take into account the experience feedback on solving complex problems in business is deemed as a way to improve the quality of products and processes. Only a few academic works, however, are concerned with the representation and the instrumentation of experience feedback systems. We propose, in this paper, a model of experiences and mechanisms to use these experiences. More specifically, we wish to encourage the reuse of already performed expert analysis to propose a priori analysis in the solving of a new problem. The proposal is based on a representation in the context of the experience of using a conceptual marker and an explicit representation of the analysis incorporating expert opinions and the fusion of these opinions. The experience feedback models and inference mechanisms are integrated in a commercial support tool for problem solving methodologies. The results obtained to this point have already led to the definition of the role of ‘‘Rex Manager’’ with principles of sustainable management for continuous improvement of industrial processes in companies

Euro-Mediterranean Supply Chain Developments and Trends in Trade Structures, in the Fresh Fruit and Vegetable Sector

Supply chains for fresh fruit and vegetables, are going through considerable re-shaping phase worldwide. This study analyses the trends which impose those changes and focuses mainly at the wholesale and export trading of the Euro-Mediterranean supply chain (namely, on how fruit and vegetable producer, wholesale and export firms react to the market forces that direct them). Producer organizations and wholesale firms one the one hand of The Netherlands, Germany and other EU member countries, and of Non- EU Member Mediterranean countries, on the other hand, are the subject of this study. Two graphical representation of the Dutch and the German supply chains respectively are presented here as the main instrument to demonstrate the dynamics of the sectors structure, by describing the position, function size and development for the main chain partner in each of the aforementioned markets. The Euro-Med dimension of the fruit and vegetable supply chain, is analyzed by attempting an impact assessment and an estimation of the potential development of further supply chain integration or collaboration between firms in EU member countries and Mediterranean partner countries. The existing policy framework (the CMO for the fruit and vegetable sector of the CAP), is also taken into consideration as it particularly affects the relationships developed between producer organizations and wholesale firms and retail chains.Euro-Med Free Trade analysis, Supply chain restructure, supply chain efficiency, fresh fruit and vegetables trade, vertical coordination, Industrial Organization, International Relations/Trade,

Measurement of the Top Quark Pair Production Cross Section in pbar-p Collisions Using Multijet Final States

We have studied tbar-t production using multijet final states in pbar-p collisions at a center-of-mass energy of 1.8 TeV, with an integrated luminosity of 110.3 pb(-1). Each of the top quarks with these final states decays exclusively to a bottom quark and a W boson, with the W bosons decaying into quark-antiquark pairs. The analysis has been optimized using neural networks to achieve the smallest expected fractional uncertainty on the tbar-t production cross section, and yields a cross section of 7.1 +/- 2.8(stat.) +/- 1.5(syst.) pb, assuming a top quark mass of 172.1 GeV/c^(2). Combining this result with previous D0 measurements, where one or both of the W bosons decay leptonically, gives a tbar t production cross section of 5.9 +/- 1.2(stat) +/- 1.1(syst) pb.Comment: 30 pages, 32 figures; no substative change in revisio

What does the 'New Quality' mean in view of Polish dairy cooperatives?

This paper investigates the relationship between the chosen quality strategy and the vertical co-ordination mechanism of a focal company by using new institutional economics, as well as strategic management approaches. The theoretical findings are tested using evidence from 19 of the largest Polish dairy cooperatives, surveyed in spring 2006. The results show that all co-ops recognise the changing market requirements and are treating food quality as more than plain food safety and the ability to continuously reproduce an ex ante defined set of attributes. However, compared to investor-owned dairies, co-ops are disadvantaged in quality-based competition due to their lower flexibility and access to financial and qualified human resources. To overcome this intense competition, co-ops modify their production profile, which leads to market segmentation. Moreover, the choice of quality strategy is an economic activity, guided by the co-op's profit expectations within the selected market. The chosen quality strategy determines the design of the vertical co-ordination mechanism. Thus, the higher the requirements for the final product, the further quality management systems go beyond a firm's boundaries, and the higher is the intensity of the relationships between the intermediary stages in the dairy chain.network theory, relationship management, quality management, cooperatives, Poland, Agribusiness, Livestock Production/Industries,

An improved multi-parametric programming algorithm for flux balance analysis of metabolic networks

Flux balance analysis has proven an effective tool for analyzing metabolic networks. In flux balance analysis, reaction rates and optimal pathways are ascertained by solving a linear program, in which the growth rate is maximized subject to mass-balance constraints. A variety of cell functions in response to environmental stimuli can be quantified using flux balance analysis by parameterizing the linear program with respect to extracellular conditions. However, for most large, genome-scale metabolic networks of practical interest, the resulting parametric problem has multiple and highly degenerate optimal solutions, which are computationally challenging to handle. An improved multi-parametric programming algorithm based on active-set methods is introduced in this paper to overcome these computational difficulties. Degeneracy and multiplicity are handled, respectively, by introducing generalized inverses and auxiliary objective functions into the formulation of the optimality conditions. These improvements are especially effective for metabolic networks because their stoichiometry matrices are generally sparse; thus, fast and efficient algorithms from sparse linear algebra can be leveraged to compute generalized inverses and null-space bases. We illustrate the application of our algorithm to flux balance analysis of metabolic networks by studying a reduced metabolic model of Corynebacterium glutamicum and a genome-scale model of Escherichia coli. We then demonstrate how the critical regions resulting from these studies can be associated with optimal metabolic modes and discuss the physical relevance of optimal pathways arising from various auxiliary objective functions. Achieving more than five-fold improvement in computational speed over existing multi-parametric programming tools, the proposed algorithm proves promising in handling genome-scale metabolic models.Comment: Accepted in J. Optim. Theory Appl. First draft was submitted on August 4th, 201