Other Networks (other + network)

Distribution by Scientific Domains


Selected Abstracts


A hybrid model of anaerobic E. coli GJT001: Combination of elementary flux modes and cybernetic variables

BIOTECHNOLOGY PROGRESS, Issue 5 2008
Jin Il Kim
Flux balance analysis (FBA) in combination with the decomposition of metabolic networks into elementary modes has provided a route to modeling cellular metabolism. It is dependent, however, on the availability of external fluxes such as substrate uptake or growth rate before estimates can become available of intracellular fluxes. The framework classically does not allow modeling of metabolic regulation or the formulation of dynamic models except through dynamic measurement of external fluxes. The cybernetic modeling approach of Ramkrishna and coworkers provides a dynamic framework for modeling metabolic systems because of its focus on describing regulatory processes based on cybernetic arguments and hence has the capacity to describe both external and internal fluxes. In this article, we explore the alternative of developing hybrid models combining cybernetic models for the external fluxes with the flux balance approach for estimation of the internal fluxes. The approach has the merit of the simplicity of the early cybernetic models and hence computationally facile while also providing detailed information on intracellular fluxes. The hybrid model of this article is based on elementary mode decomposition of the metabolic network. The uptake rates for the various elementary modes are combined using global cybernetic variables based on maximizing substrate uptake rates. Estimation of intracellular metabolism is based on its stoichiometric coupling with the external fluxes under the assumption of (pseudo-) steady state conditions. The set of parameters of the hybrid model was estimated with the aid of nonlinear optimization routine, by fitting simulations with dynamic experimental data on concentrations of biomass, substrate, and fermentation products. The hybrid model estimations were tested with FBA (based on measured substrate uptake rate) for two different metabolic networks (one is a reduced network which fixes ATP contribution to the biomass and maintenance requirement of ATP, and the other network is a more complex network which has a separate reaction for maintenance.) for the same experiment involving anaerobic growth of E. coli GJT001. The hybrid model estimated glucose consumption and all fermentation byproducts to better than 10%. The FBA makes similar estimations of fermentation products, however, with the exception of succinate. The simulation results show that the global cybernetic variables alone can regulate the metabolic reactions obtaining a very satisfactory fit to the measured fermentation byproducts. In view of the hybrid model's ability to predict biomass growth and fermentation byproducts of anaerobic E. coli GJT001, this reduced order model offers a computationally efficient alternative to more detailed models of metabolism and hence useful for the simulation of bioreactors. [source]


PREPROCESSING RULES FOR TRIANGULATION OF PROBABILISTIC NETWORKS,

COMPUTATIONAL INTELLIGENCE, Issue 3 2005
Hans L. Bodlaender
Currently, the most efficient algorithm for inference with a probabilistic network builds upon a triangulation of a network's graph. In this paper, we show that pre-processing can help in finding good triangulations for probabilistic networks, that is, triangulations with a maximum clique size as small as possible. We provide a set of rules for stepwise reducing a graph, without losing optimality. This reduction allows us to solve the triangulation problem on a smaller graph. From the smaller graph's triangulation, a triangulation of the original graph is obtained by reversing the reduction steps. Our experimental results show that the graphs of some well-known real-life probabilistic networks can be triangulated optimally just by preprocessing; for other networks, huge reductions in their graph's size are obtained. [source]


Changes in the interaction of resting-state neural networks from adolescence to adulthood

HUMAN BRAIN MAPPING, Issue 8 2009
Michael C. Stevens
Abstract This study examined how the mutual interactions of functionally integrated neural networks during resting-state fMRI differed between adolescence and adulthood. Independent component analysis (ICA) was used to identify functionally connected neural networks in 100 healthy participants aged 12,30 years. Hemodynamic timecourses that represented integrated neural network activity were analyzed with tools that quantified system "causal density" estimates, which indexed the proportion of significant Granger causality relationships among system nodes. Mutual influences among networks decreased with age, likely reflecting stronger within-network connectivity and more efficient between-network influences with greater development. Supplemental tests showed that this normative age-related reduction in causal density was accompanied by fewer significant connections to and from each network, regional increases in the strength of functional integration within networks, and age-related reductions in the strength of numerous specific system interactions. The latter included paths between lateral prefrontal-parietal circuits and "default mode" networks. These results contribute to an emerging understanding that activity in widely distributed networks thought to underlie complex cognition influences activity in other networks. Hum Brain Mapp 2009. © 2009 Wiley-Liss, Inc. [source]


Functional connectivity of default mode network components: Correlation, anticorrelation, and causality

HUMAN BRAIN MAPPING, Issue 2 2009
Lucina Q. Uddin
Abstract The default mode network (DMN), based in ventromedial prefrontal cortex (vmPFC) and posterior cingulate cortex (PCC), exhibits higher metabolic activity at rest than during performance of externally oriented cognitive tasks. Recent studies have suggested that competitive relationships between the DMN and various task-positive networks involved in task performance are intrinsically represented in the brain in the form of strong negative correlations (anticorrelations) between spontaneous fluctuations in these networks. Most neuroimaging studies characterize the DMN as a homogenous network, thus few have examined the differential contributions of DMN components to such competitive relationships. Here, we examined functional differentiation within the DMN, with an emphasis on understanding competitive relationships between this and other networks. We used a seed correlation approach on resting-state data to assess differences in functional connectivity between these two regions and their anticorrelated networks. While the positively correlated networks for the vmPFC and PCC seeds largely overlapped, the anticorrelated networks for each showed striking differences. Activity in vmPFC negatively predicted activity in parietal visual spatial and temporal attention networks, whereas activity in PCC negatively predicted activity in prefrontal-based motor control circuits. Granger causality analyses suggest that vmPFC and PCC exert greater influence on their anticorrelated networks than the other way around, suggesting that these two default mode nodes may directly modulate activity in task-positive networks. Thus, the two major nodes comprising the DMN are differentiated with respect to the specific brain systems with which they interact, suggesting greater heterogeneity within this network than is commonly appreciated. Hum Brain Mapp, 2009. © 2008 Wiley-Liss, Inc. [source]


Detecting and classifying delay Data Exceptions on communication networks using rule based algorithms

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2005
Tammam Benmusa
Abstract Network performance monitoring is essential for managing a network efficiently and for ensuring reliable operation of the network. Monitored network performance changes reflect events in the network, such as faults, significant changes in usage patterns or planned alterations. Network managers are interested in how and when the performance of a network changes; however it is inefficient to analyse all the data resulting from the monitoring operation manually. In this paper a rule based algorithm to automate detection of the changes in one of the network performance parameters, namely delay, is presented and described in detail. The nature of the delay pattern in a commercial communication network was the key issue in developing this algorithm. The approach was tested with monitored delay data generated from three different networks and showed good results. Also, the algorithm was tested with sets of delay data which have been already input to a previously developed detector based on a different approach, and the results between the two detectors are compared. In addition to a noticeable improvement in detection performance, the new approach provides more generality and independency of the source of the delay data, making the approach generally applicable to other networks. Copyright © 2004 John Wiley & Sons, Ltd. [source]


"A brilliant and many-sided personality": Jessie Margaret Murray, founder of the Medico-Psychological Clinic

JOURNAL OF THE HISTORY OF THE BEHAVIORAL SCIENCES, Issue 2 2009
Elizabeth R. Valentine
This paper outlines the life and career of Jessie Margaret Murray, the moving spirit behind the foundation of the Medico-Psychological Clinic, the first public clinic in Britain to offer psychoanalytic therapy and training in psychoanalysis. Biographical details of Murray and her close friend and collaborator, Julia Turner, are presented, and possible routes by which the two women may have met are explored. Murray's role in the suffragist movement is described, as well as other networks and professional societies in which she was involved, in particular the British Society for the Study of Sex Psychology, and her relationship with Marie Stopes. An account is given of events leading up to the founding of the Clinic, its activities, Murray's death, and other factors contributing to its demise. Finally, the Clinic's heritage and implications of the personalities of Murray and Turner for understanding the subsequent development of psycho-analysis in Britain are considered. [source]


The Gudaga Study: establishing an Aboriginal birth cohort in an urban community

AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 2010
Elizabeth Comino
Abstract Objective: This paper describes the establishment of the Gudaga Study, an Aboriginal birth cohort in south-west Sydney, and our approach to follow-up of participants. The Study describes the health, development, and services use of Aboriginal infants and their mothers. The research team works closely with the local Aboriginal community to implement the research. Methods: All mothers in the maternity ward of an urban hospital were surveyed to identify mothers with an Aboriginal infant. These and some additional mothers identified through other networks were recruited to the study. Results: The number of mothers were surveyed was 2,108. Mothers of Aboriginal infants were younger (25.3 years compared to 28.4 years, p<0.001), less likely to be married (16.1% cf. 58.4%, p<0.001) and to have completed school (63.2% cf. 77.8%, p=0.002) than mothers of non-Aboriginal infants. Of 155 identified mothers of Aboriginal infants, 136 were recruited and 23 through other networks. At 12 months, 85.5% of infants were followed up. Conclusions: This study, to our knowledge, is the first cohort study of this kind on the eastern seaboard of Australia. The study has strong community support and follow-up, contrary to views that Aboriginal people are reluctant to participate in research. These data have national and regional significance. [source]


The Commonwealth as an Economic Network

AUSTRALIAN ECONOMIC HISTORY REVIEW, Issue 3 2001
Paul L. Robertson
Research on the economics and sociology of business networks also sheds light on the development of networks of countries. The British Commonwealth was an important global network, or group of networks, in the mid-twentieth century. Commonwealth members, including Australia and New Zealand, cooperated in the management of the Sterling Area and the Commonwealth Preference Area. Yet Commonwealth members also had links to other networks and other sources of influence including the USA, continental Europe and Japan. During the 1950s and 1960s, there was a gradual change in the network relations of Australia and New Zealand, involving a diminution in the importance of bilateral ties with Britain. [source]