Network Operation (network + operation)

Distribution by Scientific Domains
Distribution within Engineering

Selected Abstracts

Active coordinated operation of a distribution network system for many connections of distributed generators

Yasuhiro Hayashi
Abstract Recently, the total number of distributed generators (DGs) such as photovoltaic generation system and wind turbine generation system connected to an actual distribution network has increased drastically. The distribution network connected to many distributed generators must be operated keeping reliability of power supply, power quality, and loss minimization. In order to accomplish active distribution network operation to take advantage of many connections of DGs, a new coordinated operation of distribution system with many connections of DGs is necessary. In this paper, the authors propose a coordinated operation of distribution network system connected to many DGs by using newly proposed sectionalizing switch control, sending voltage control, and computation of available DG connection capability. In order to check the validity of the proposed coordinated operation of distribution system, numerical simulations using the proposed coordinated distribution system operation are carried out in a practical distribution network model. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 46,57, 2009; Published online in Wiley InterScience ( DOI 10.1002/eej.20655 [source]

Decision support for network operation in an open power market

Geir Warland
Abstract The Norwegian system operator plans to change from (N-1) to a more flexible cost-based security criterion. The approach is illustrated using a simple example and then compared with alternative decision paradigms. The comparison shows how different paradigms may change ranking of operating alternatives and that the new cost-based criterion still tends to favor alternatives close to (N-1), provided application of a penalty factor giving additional and significant weight on interruption costs. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Generalized window advertising for TCP congestion control,

Mario Gerla
Congestion in the Internet is a major cause of network performance degradation. The Generalized Window Advertising (GWA) scheme proposed in this paper is a new approach for enhancing the congestion control properties of TCP. GWA requires only minor modifications to the existing protocol stack and is completely backward compatible, allowing GWA-hosts to interact with non-GWA hosts without modifications. GWA exploits the notion of end-host-network cooperation, with the congestion level notified from the network to end hosts. It is based on solid control theory results mat guarantee performance and stable network operation. GWA is able to avoid window oscillations and the related fluctuations in offered load and network performance. This makes it more robust to sustained network overload due to a large number of connections competing for the same bottleneck, a situation where traditional TCP implementations fail to provide satisfactory performance. GWA-TCP is compared with traditional TCP, TCP with RED and also ECN using the ns-2 simulator. Results show that in most cases GWA-TCP outperforms the traditional schemes. In particular, when compared with ECN, it provides smoother network operation and increased fairness. [source]

,The National Stream Quality Accounting Network: a flux-based approach to monitoring the water quality of large rivers

Richard P. Hooper
Abstract Estimating the annual mass flux at a network of fixed stations is one approach to characterizing water quality of large rivers. The interpretive context provided by annual flux includes identifying source and sink areas for constituents and estimating the loadings to receiving waters, such as reservoirs or the ocean. Since 1995, the US Geological Survey's National Stream Quality Accounting Network (NASQAN) has employed this approach at a network of 39 stations in four of the largest river basins of the USA: the Mississippi, the Columbia, the Colorado and the Rio Grande. In this paper, the design of NASQAN is described and its effectiveness at characterizing the water quality of these rivers is evaluated using data from the first 3 years of operation. A broad range of constituents was measured by NASQAN, including trace organic and inorganic chemicals, major ions, sediment and nutrients. Where possible, a regression model relating concentration to discharge and season was used to interpolate between chemical observations for flux estimation. For water-quality network design, the most important finding from NASQAN was the importance of having a specific objective (that is, estimating annual mass flux) and, from that, an explicitly stated data analysis strategy, namely the use of regression models to interpolate between observations. The use of such models aided in the design of sampling strategy and provided a context for data review. The regression models essentially form null hypotheses for concentration variation that can be evaluated by the observed data. The feedback between network operation and data collection established by the hypothesis tests places the water-quality network on a firm scientific footing. Published in 2001 by John Wiley & Sons, Ltd. [source]

An adaptive joining mechanism for improving the connection ratio of ZigBee wireless sensor networks

Tien-Wen Sung
Abstract Wireless sensor networks (WSNs) are well suited to many applications, including environment surveillance and target tracking. ZigBee is an IEEE 802.15.4-based standard that is considered suitable for WSNs. The functional operations of a ZigBee network rely on self-organized network connections and the proper deployment of sensor devices. However, the devices comprising a ZigBee network may become isolated from the network after the joining phase due to the configuration constraints of the ZigBee standard. This means that some deployed devices cannot join the network even though they can communicate with other joined nodes. These isolated devices reduce the efficiency of network operation and increase deployment costs. This paper proposes a ZigBee-compatible adaptive joining mechanism with connection shifting schemes to improve the connectivity of ZigBee networks, allowing them to operate at the expected efficiency. Simulation results show that the proposed mechanism significantly improves the join ratio of deployed sensor devices in ZigBee WSNs. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A bi-criterion optimization approach for the design and planning of hydrogen supply chains for vehicle use

AICHE JOURNAL, Issue 3 2010
Gonzalo Guillén-Gosálbez
Abstract In this article, we address the design of hydrogen supply chains for vehicle use with economic and environmental concerns. Given a set of available technologies to produce, store, and deliver hydrogen, the problem consists of determining the optimal design of the production-distribution network capable of satisfying a predefined hydrogen demand. The design task is formulated as a bi-criterion mixed-integer linear programming (MILP) problem, which simultaneously accounts for the minimization of cost and environmental impact. The environmental impact is measured through the contribution to climate change made by the hydrogen network operation. The emissions considered in the analysis are those associated with the entire life cycle of the process, and are quantified according to the principles of Life Cycle Assessment (LCA). To expedite the search of the Pareto solutions of the problem, we introduce a bi-level algorithm that exploits its specific structure. A case study that addresses the optimal design of the hydrogen infrastructure needed to fulfill the expected hydrogen demand in Great Britain is introduced to illustrate the capabilities of the proposed approach. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Optimal design and planning of sustainable chemical supply chains under uncertainty

AICHE JOURNAL, Issue 1 2009
Gonzalo Guillén-Gosálbez
Abstract This article addresses the design of sustainable chemical supply chains in the presence of uncertainty in the life cycle inventory associated with the network operation. The design task is mathematically formulated as a bi-criterion stochastic mixed-integer nonlinear program (MINLP) that simultaneously accounts for the maximization of the net present value and the minimization of the environmental impact for a given probability level. The environmental performance is measured through the Eco-indicator 99, which incorporates the recent advances made in Life Cycle Assessment. The stochastic model is converted into its deterministic equivalent by reformulating the probabilistic constraint required to calculate the environmental impact in the space of uncertain parameters. The resulting deterministic bi-criterion MINLP problem is further reformulated as a parametric MINLP, which is solved by decomposing it into two sub-problems and iterating between them. The capabilities of the proposed model and solution procedure are illustrated through two case studies for which the set of Pareto optimal, or efficient solutions that trade-off environmental impact and profit, are calculated. These solutions provide valuable insights into the design problem and are intended to guide the decision maker towards the adoption of more sustainable design alternatives. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source]

Small-size wireless wide area network loop chip antenna for clamshell mobile phone with hearing-aid compatibility

Wei-Yu Li
Abstract A loop chip antenna with an FR4 chip base suitable for clamshell mobile phone application to achieve wireless wide area network operation and hearing-aid compatibility (HAC) is presented. The loop chip antenna is formed by a loop strip excited by a capacitively coupled feed, all printed on the surfaces of the FR4 chip base to achieve a small size of 1.35 cm3 only. Two resonant loop paths are provided by the antenna and each loop path can generate its 0.5, and 1.0, resonant modes with good impedance matching. The excited loop resonant modes are formed into two wide operating bands for the antenna to cover GSM850/900 and GSM1800/1900/UMTS operations for both the open (talk) and closed (idle) states of the clamshell mobile phone. Furthermore, the loop antenna also excites small surface currents on the two ground planes of the clamshell mobile phone. In this case, weak near-field EM fields in the vicinity of the mobile phone can be generated. Results show that the strengths of the near-field E-field and H-field fall in the M3 or M4 Category, making the clamshell mobile phone with the proposed antenna to be an HAC communication device. The obtained specific absorption rate values in 1-g and 10-g head tissues also meet the limit of 1.6 and 2.0 W/kg, respectively. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2327,2335, 2009; Published online in Wiley InterScience ( DOI 10.1002/mop.24665 [source]

Wireless network analysis using per call measurement data

Michael J. Flanagan
The advent of per call measurement data (PCMD) in Alcatel-Lucent network products has enabled an unprecedented view into code division multiple access (CDMA) network operation at the subscriber level. The timing information available in PCMD records allows for maximum-likelihood estimation of subscriber locations using experimental geo-location analysis software suite (GLASS) tools developed at Alcatel-Lucent. Spatial variations of traffic densities, lost call densities, and other phenomena can now be readily studied to better understand wireless network operation as experienced by subscribers. These types of tools can also incorporate financial and business details regarding subscribers to guide network operation and optimization activities more effectively. © 2007 Alcatel-Lucent. [source]

Von Neuronen zu Netzwerken.

Mathematische Gehirnmodelle
Abstract Obwohl unser Verständnis des Nervensystems große Fortschritte macht, stellen Netzwerke aus Milliarden von Neuronen die Neurobiologie vor eine praktisch unlösbare Aufgabe: Die Aktivität eines Gehirns möglichst vollständig zu erfassen und das Beobachtete detailliert zu verstehen. Die "Computational Neuroscience" versucht Brücken zwischen den Konzepten der Teildisziplinen zu schlagen. Die mathematische Beschreibung von Nervenzellen und neuronalen Netzwerken, sowie die Simulation dieser Systeme in Form von Computermodellen, erlaubt Phänomene zu ergründen, die in biologischen Gehirnen nur unter größten Schwierigkeiten messbar sind. Jüngste Studien konnten unter anderem zeigen, dass erregungsabhängige Veränderungen der elektrischen Leitfähigkeit in Neuronen ein Netzwerk davor bewahren, dass räumlich begrenzte Erregung sich aufschaukelt und als Folge die Aktivität im gesamten Netzwerk zum Erliegen bringt. Dieselbe Eigenschaft führt außerdem dazu, dass ein Netzwerk auch ohne äußere Anregung aktiv bleiben kann , eine wichtige Grundeigenschaft von Gehirnen, deren neuronale Funktionsmechanismen bis heute weitgehend unverstanden sind. Our understanding of the nervous system has made great leaps forward. Yet still, the study of networks of billions of neurons poses an almost insolvable challenge to empirical neurobiology: to capture the activity of a brain as a whole, and to make sense of the observations in detail. Here, "Computational Neuroscience" attempts to build bridges between the concepts of the involved disciplines. The mathematical description of neurons and neuronal networks, as well as the simulation of these systems as computer models, allows fathoming phenomena that could be measured in biological brains only under severe difficulties. In particular, recent studies showed that activity dependent changes of neuronal input resistance can prevent a network from local "explosions" of activity, which otherwise could lead to a complete breakdown of network operation. The same property of neurons also causes a network to remain active when external excitation is switched off. This is an important property of brains, the neuronal mechanisms of which are still widely unknown. [source]