Multi-parameter structural transformations of passive electrical networks and natural frequency assignment

The paper examines the problem of systems redesign within the context of passive electrical networks by considering the problem of multi-parameter changes, their representation and impact on properties such as characteristic frequencies. The general problem area is the modelling of systems, whose structure is not fixed but evolves during the system lifecycle. The specific problem we are addressing is the study of effect of changing the topology of an electrical network that is changing individual elements of the network into elements of different type and value, augmenting / or eliminating parts of the network and developing a framework that allows the study of the effect of such transformations on the natural frequencies. This problem is a special case of the more general network redesign problem. We use the Impedance-Admittance models and we establish a representation of the different types of transformations on such models. For the case of network cardinality preserving transformations, we formulate the natural frequencies assignment problem as a problem of zero assignment of matrix pencils by additive structured transformations and this allows the deployment of the Determinantal Assignment Problem framework for the study of assignment and determination of fixed natural frequencies

System Properties of Implicit Passive Electrical Networks Descriptions

Redesigning systems by changing elements, topology, organization, augmenting the system by the addition of subsystems, or removing parts, is a major challenge for systems and control theory. A special case is the redesign of passive electric networks which aims to change the natural dynamics of the network (natural frequencies) by the above operations leading to a modification of the network. This requires changing the system to achieve the desirable natural frequencies and involves the selection of alternative values for dynamic elements and non-dynamic elements within a fixed interconnection topology and/or alteration of the interconnection topology and possible evolution of the network (increase of elements, branches). The use of state-space or transfer function models does not provide a suitable framework for the study of this problem, since every time such changes are introduced, a new state space or transfer function model has to be recalculated. The use of impedance and admittance modeling, provides a suitable framework for the study of network properties under the process of re-engineering transformations. This paper deals with the fundamental system properties of the impedance-admittance network description which provide the appropriate framework for network re-engineering. We identify the natural topologies expressing the structured transformations linked to the impedance-graph, admittance graph-topology of the network and examine issues such as network regularity, number of finite frequencies and provide characterization of them in terms of the basic network matrices. The implicit network representation introduced provides a natural framework for expressing the different types of re-engineering transformations which can be used for the study of the natural frequencies assignment

Implementation of basic QoS mechanisms on videoconferencing network model

Ovo istraživanje je posljedica višegodišnjeg korištenja videokonferencijske veze te pojave raznih problema koji prate istu. Kašnjenje slike i zvuka, pucanje veze, prekid slike ili zvuka samo su neki od razloga zbog kojih je nastao ovaj rad. U ovom radu pokušava se primjenom mehanizama kvalitete usluge na modelu CARNet-ove mreže poboljšati kvaliteta videokonferencijske veze. Na osnovu dobivenih rezultata simulacije videokonferencijske veze prikazani su grafovi ispuštanja paketa, kašnjenja te ostalih parametara bitnih za videokonferencijsku vezu.This research is the outcome of multiannual use of videoconferencing services and the emersion of various problems that come with videoconferencing applications. Video and audio delay, dropped connection, missing audio or video, are just some of the reasons for creating this paper. In this article quality of videoconferencing link in CARNet network is improved by implementing various QoS mechanisms. The obtained results of the videoconferencing simulation are represented in graphs which display dropped packets, delay and other videoconferencing parameters

Matrix pencil representation of structural transformations of passive electrical networks

The paper examines the problem of systems redesign within the context of passive electrical networks by considering the problem of multi-parameter and topology changes, and their representation. This representation may be used to investigate the impact of such changes on properties such as characteristic frequencies. The general problem area is the modelling of systems, whose structure is not fixed but evolves during the system life-cycle. The specific problem we are addressing is the study of effect of changing the topology of an electrical network that is changing individual elements of the network into elements of different type and value, augmenting / or eliminating parts of the network and developing a framework that allows the study of the effect of such transformations on the natural frequencies. This problem is a special case of the more general network redesign problem. We use the Impedance-Admittance models and we establish a representation of the different types of transformations on such models. The representation of the structural transformations is given in terms of the companion pencil that preserves the natural topologies of the RLC network

A validated methodology for the prediction of heating and cooling energy demand for buildings within the Urban Heat Island: Case-study of London

This is the post-print version of the final paper published in Solar Energy. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.This paper describes a method for predicting air temperatures within the Urban Heat Island at discreet locations based on input data from one meteorological station for the time the prediction is required and historic measured air temperatures within the city. It uses London as a case-study to describe the method and its applications. The prediction model is based on Artificial Neural Network (ANN) modelling and it is termed the London Site Specific Air Temperature (LSSAT) predictor. The temporal and spatial validity of the model was tested using data measured 8 years later from the original dataset; it was found that site specific hourly air temperature prediction provides acceptable accuracy and improves considerably for average monthly values. It thus is a very reliable tool for use as part of the process of predicting heating and cooling loads for urban buildings. This is illustrated by the computation of Heating Degree Days (HDD) and Cooling Degree Hours (CDH) for a West–East Transect within London. The described method could be used for any city for which historic hourly air temperatures are available for a number of locations; for example air pollution measuring sites, common in many cities, typically measure air temperature on an hourly basis.EPSR

Socio-Demographic Changes in the Village and in Agriculture

Autor temelji tekst na analizi vitalnih demografskih podataka o poljoprivrednom i seoskom stanovništvu Jugoslavije (broj stanovnika, natalitet, zagreb, jugoslavija mortalitet, prirodni priraštaj, dobna struktura, stupanj ostarjelosti). Uporište za analizu j interpretaciju podataka nalazi u sociološko-historijskom pristupu fenomenu demografskog razvoja što omogućava da istraži uzroke i posljedice uglavnom nepovoljnih demografskih trendova. Autor smatra da je nužno što prije revitalizirati cjelokupni ruralni prostor i agrarnu proizvodnju, jer će se inače i dalje produbljivati socijalna nesigurnost i raslojavanje seoskog stanovništva. Pledira za znanstveno zasnovanu politiku ruralnog razvoja.The author’s text is based on the analysis of vital demographic data on the agricultural and rural population of Yugoslavia (number of inhabitants, natality, mortality, natural growth in population, age structure, age composition). The source for this analysis and interpretation of data can be found in the sociological-historical approach to the phenomenon of demographic development, which enables the author to examine the causes and consequences of usually unfavourable demographic trends. The author considers that it is necessary to revitalize as soon as possible the total rural area and agrarian production, as otherwise the process of social insecurity and stratification of the rural population will continue. He urges scientifically founded policy for rural development