Verification and validation of numerical models of the transport of insulation debris

A combination of the two-fluid and drift flux models have been used to model the transport of fibrous debris. This debris is generated during loss of coolant accidents in the primary circuit of pressurized or boiling water nuclear reactors, as high pressure steam or water jets can damage adjacent insulation materials including mineral wool blankets. Fibre agglomerates released from the mineral wools may reach the containment sump strainers, where they can accumulate and compromise the long-term operation of the emergency core cooling system. Single-effect experiments of sedimentation in a quiescent rectangular column and sedimentation in a horizontal flow are used to verify and validate this particular application of the multiphase numerical models. The utilization of both modeling approaches allows a number of pseudocontinuous dispersed phases of spherical wetted agglomerates to be modeled simultaneously. Key effects on the transport of the fibre agglomerates are particle size, density and turbulent dispersion, as well as the relative viscosity of the fluid-fibre mixture.

Data Flow Analysis and the Linear Programming Model

* The research is supported partly by INTAS: 04-77-7173 project, http://www.intas.be

Clogging in subsurface-flow treatment wetlands:measurement, modeling and management

This paper reviews the state of the art in measuring, modeling, and managing clogging in subsurface-flow treatment wetlands. Methods for measuring in situ hydraulic conductivity in treatment wetlands are now available, which provide valuable insight into assessing and evaluating the extent of clogging. These results, paired with the information from more traditional approaches (e.g., tracer testing and composition of the clog matter) are being incorporated into the latest treatment wetland models. Recent finite element analysis models can now simulate clogging development in subsurface-flow treatment wetlands with reasonable accuracy. Various management strategies have been developed to extend the life of clogged treatment wetlands, including gravel excavation and/or washing, chemical treatment, and application of earthworms. These strategies are compared and available cost information is reported. © 2012 Elsevier Ltd.

Primary and Secondary Empirical Values in Network Redimensioning

A model of an overall telecommunication network with virtual circuits switching, in stationary state, with Bernoulli-Poisson-Pascal (BPP) input flow, repeated calls, limited number of homogeneous terminals and 8 types of losses is considered. One of the main problems of network redimensioning is estimation of the traffic offered in the network because it reflects on finding of necessary number of equivalent switching lines on the basis of the consideration of detailed users behavior and target Quality of Service (QoS). The aim of this paper is to find a new solution of Network Redimensioning Task (NRDT) [4], taking into account the inconvenience of necessary measurements, not considered in the previous research [5]. The results are applicable for redimensioning of every (virtual) circuit switching telecommunication system, both for wireline and wireless systems (GSM, PSTN, ISDN and BISDN). For packet - switching networks proposed approach may be used as a comparison basis and when they work in circuit switching mode (e.g. VoIP).

Computer Networks Security Models - A New Approach for Denial-of-Services Attacks Mitigation

Computer networks are a critical factor for the performance of a modern company. Managing networks is as important as managing any other aspect of the company’s performance and security. There are many tools and appliances for monitoring the traffic and analyzing the network flow security. They use different approaches and rely on a variety of characteristics of the network flows. Network researchers are still working on a common approach for security baselining that might enable early watch alerts. This research focuses on the network security models, particularly the Denial-of-Services (DoS) attacks mitigation, based on a network flow analysis using the flows measurements and the theory of Markov models. The content of the paper comprises the essentials of the author’s doctoral thesis.

An Overview of Modelling Bulgarian Wildland Fire Behaviour by Application of a Mathematical Game Method and WRF-Fire Models

This paper presents the main achievements of the author’s PhD dissertation. The work is dedicated to mathematical and semi-empirical approaches applied to the case of Bulgarian wildland fires. After the introductory explanations, short information from every chapter is extracted to cover the main parts of the obtained results. The methods used are described in brief and main outcomes are listed. ACM Computing Classification System (1998): D.1.3, D.2.0, K.5.1.

A New Class of Processes for Formalizing and Generalizing Individual-Based Models: The Semi-Semi-Markov Processes

2000 Mathematics Subject Classification: 60K15, 60K20, 60G20,60J75, 60J80, 60J85, 60-08, 90B15.

Groundwater flow patterns within the Triassic sandstone aquifers, Birmingham, United Kingdom

This paper presents the development of a modelling study for part of the Birmingham area. Restricted access and model resolutions have limited wide applications of some of the previously developed models. The study area covers approximately 221 km2, and is underlain geologically, by a multi-layer setup with varied hydraulic properties. The basal aquifer unit is the Kidderminster sandstone Formation, overlain by the Wildmoor and Bromsgrove sandstone Formations. The presence of the Birmingham fault which acts as low permeability barrier demarcates the eastern and southern boundaries. The western boundary is defined by the presence of crystallised rocks and coal measures, while a groundwater divide defines the northern boundary. The estimated recharge flux is 112 mm/yr. The ranges of calibrated values obtained for horizontal and vertical hydraulic conductivities are 5.787x10-6 - 2.315x10-5  m/s and 5.787x10-8  - 1.157x10-7  m/s, respectively. Corresponding values obtained for the specific yield and specific storage are 0.10 - 0.12, and 1x10 -4 - 5x10 -4. The calculated numerical error is generally much less than 0.1 %. Hydraulic layering within the Permo-Triassic sandstone aquifer is thought to account for the large vertical anisotropy. Although, uncertainties are associated with the use of a simplistic delay approach to characterise the effects of the unsaturated zone, the modelled values are comparable with those obtained in the literature, and the flow pattern predictions appear to be realistic. © Research India Publications.

The development of attenuation compensation models of fluorescence spectroscopy signals

This study examines the effect of blood absorption on the endogenous fluorescence signal intensity of biological tissues. Experimental studies were conducted to identify these effects. To register the fluorescence intensity, the fluorescence spectroscopy method was employed. The intensity of the blood flow was measured by laser Doppler flowmetry. We proposed one possible implementation of the Monte Carlo method for the theoretical analysis of the effect of blood on the fluorescence signals. The simulation is constructed as a four-layer skin optical model based on the known optical parameters of the skin with different levels of blood supply. With the help of the simulation, we demonstrate how the level of blood supply can affect the appearance of the fluorescence spectra. In addition, to describe the properties of biological tissue, which may affect the fluorescence spectra, we turned to the method of diffuse reflectance spectroscopy (DRS). Using the spectral data provided by the DRS, the tissue attenuation effect can be extracted and used to correct the fluorescence spectra.

An empirical study of international private label branding in the food sector in Hungary

Private label branding strategies differ to that of the manufacturer. The study aims to identify optimal private label branding strategies for (a) utilitarian products and (b) hedonistic products, considering the special factors reflected in consumer behavior related to private labels in Hungary. The issue of House of Brands and Branded House strategies are discussed and evaluated in the light of retail business models. Focus group interviews and factor analysis of the survey found differences in branding strategies preferred by consumers for the two product categories. The study also outlines a strong trend in possible private label development based on consumer’s changing attitude in favor of national products.

Nemlineáris dinamika klasszikus növekedési modellekben (Nonlinear dynamics in classical economic growth models)

Ebben a tanulmányban a klasszikus Harrod növekedési modellt nemlineáris kiterjesztéssel, keynesi és schumpeteri tradíciók bevezetésével reprezentatív ügynök modellbe alakítjuk. A híres Lucas kritika igazolásaként megmutatjuk, hogy az intrinsic gazdasági növekedési ütemek trajektóriái vagy egy turbulens káoszba szóródnak szét, vagy egy nagyméretű rendhez vezetnek, ami elsődlegesen a megfelelő fogyasztási függvény típusától függ, s bizonyos paraméterek piaci értékei, pedig csak másodlagos szerepet játszanak. A másik meglepő eredmény empirikus, ami szerint külkereskedelmi többlet, a hazai valuta bizonyos devizapiaci értékei mellett, különös attraktorokat generálhat. _____ In this paper the classical Harrodian growth model is transformed into a representative agent model by its nonlinear extensions and the Keynesian and Schumpeterian traditions. For the proof of the celebrated Lucas critique it is shown that the trajectories of intrinsic economic growth rates either are scattered into a turbulent chaos or lead to a large scale order. It depends on the type of the appropriate consumption function, and the market values of some parameters are playing only secondary role.Another surprising result is empirical: the international trade su±cit may generate strange attractors under some exchange rate values.

Növelhető-e a csőd-előrejelző modellek előre jelző képessége az új klasszifikációs módszerek nélkül? (Can the predictive capacity of bankruptcy forecasting models be increased without new classification methods?)

A Bázel–2. tőkeegyezmény bevezetését követően a bankok és hitelintézetek Magyarországon is megkezdték saját belső minősítő rendszereik felépítését, melyek karbantartása és fejlesztése folyamatos feladat. A szerző arra a kérdésre keres választ, hogy lehetséges-e a csőd-előrejelző modellek előre jelző képességét növelni a hagyományos matematikai-statisztikai módszerek alkalmazásával oly módon, hogy a modellekbe a pénzügyi mutatószámok időbeli változásának mértékét is beépítjük. Az empirikus kutatási eredmények arra engednek következtetni, hogy a hazai vállalkozások pénzügyi mutatószámainak időbeli alakulása fontos információt hordoz a vállalkozás jövőbeli fizetőképességéről, mivel azok felhasználása jelentősen növeli a csődmodellek előre jelző képességét. A szerző azt is megvizsgálja, hogy javítja-e a megfigyelések szélsőségesen magas vagy alacsony értékeinek modellezés előtti korrekciója a modellek klasszifikációs teljesítményét. ______ Banks and lenders in Hungary also began, after the introduction of the Basel 2 capital agreement, to build up their internal rating systems, whose maintenance and development are a continuing task. The author explores whether it is possible to increase the predictive capacity of business-failure forecasting models by traditional mathematical-cum-statistical means in such a way that they incorporate the measure of change in the financial indicators over time. Empirical findings suggest that the temporal development of the financial indicators of firms in Hungary carries important information about future ability to pay, since the predictive capacity of bankruptcy forecasting models is greatly increased by using such indicators. The author also examines whether the classification performance of the models can be improved by correcting for extremely high or low values before modelling.

Neumann versus Leontief. Két modell – két gazdaságkép (Neumann vs Leontief. Two models, two approaches to the economy)

A szerző a tisztán elméleti célokra kifejlesztett Neumann-modellt és a gyakorlati alkalmazások céljára kifejlesztett Leontief-modellt veti össze. A Neumann-modell és a Leontief-modell éves termelési periódust feltételező, zárt, stacionárius változatának hasonló matematikai struktúrája azt a feltételezést sugallja, hogy az utóbbi a Neumann-modell sajátos eseteként értelmezhető. Az egyes modellek közgazdasági tartalmát és feltevéseit részletesen kibontva és egymással összevetve a szerző megmutatja, hogy a fenti következtetés félrevezető, két merőben különböző modellről van szó, nem lehet az egyikből a másikat levezetni. Az ikertermelés és technológiai választék lehetősége a Neumann-modell elengedhetetlen feltevése, az éves termelési periódus feltevése pedig kizárja folyam jellegű kibocsátások explicit figyelembevételét. Mindezek feltevések ugyanakkor idegenek a Leontief-modelltől. A két modell valójában egy általánosabb állomány–folyam jellegű zárt, stacionárius modell sajátos esete, méghozzá azok folyamváltozókra redukált alakja. _____ The paper compares the basic assumptions and methodology of the Von Neumann model, developed for purely abstract theoretical purposes, and those of the Leontief model, designed originally for practical applications. Study of the similar mathematical structures of the Von Neumann model and the closed, stationary Leontief model, with a unit length of production period, often leads to the false conclusion that the latter is just a simplified version of the former. It is argued that the economic assumptions of the two models are quite different, which makes such an assertion unfounded. Technical choice and joint production are indispensable features of the Von Neumann model, and the assumption of unitary length of production period excludes the possibility of taking service flows explicitly into account. All these features are completely alien to the Leontief model, however. It is shown that the two models are in fact special cases of a more general stock-flow stationary model, reduced to forms containing only flow variables.

Empirical study of exchange rates in Brazil, Canada and the Caribbean

This dissertation examines the monetary models of exchange rate determination for Brazil, Canada, and two countries in the Caribbean, namely, the Dominican Republic and Jamaica. With the exception of Canada, the others adopted the floating regime during the past ten years.^ The empirical validity of four seminal models in exchange rate economics were determined. Three of these models were entirely classical (Bilson and Frenkel) or Keynesian (Dornbusch) in nature. The fourth model (Real Interest Differential Model) was a mixture of the two schools of economic theory.^ There is no clear empirical evidence of the validity of the monetary models. However, the signs of the coefficients of the nominal interest differential variable were as predicted by the Keynesian hypothesis in the case of Canada and as predicted by the Chicago theorists in the remaining countries. Moreover, in case of Brazil, due to hyperinflation, the exchange rate is heavily influenced by domestic money supply.^ I also tested the purchasing power parity (PPP) for this same set of countries. For both the monetary as well as the PPP hypothesis, I tested for co-integration and applied ordinary least squares estimation procedure. The error correction model was also used for the PPP model, to determine convergence to equilibrium.^ The validity of PPP is also questionable for my set of countries. Endogeinity among the regressors as well as the lack of proper price indices are the contributing factors. More importantly, Central Bank intervention negate rapid adjustment of price and exchange rates to their equilibrium value. However, its forecasting capability for the period 1993-1994 is superior compared to the monetary models in two of the four cases.^ I conclude that in spite of the questionable validity of these models, the monetary models give better results in the case of the "smaller" economies like the Dominican Republic and Jamaica where monetary influences swamp the other determinants of exchange rate. ^

The role of individualism and collectivism as predictors of attributions for unethical work behavior: An empirical examination across two culturally diverse groups

This dissertation addresses how the cultural dimensions of individualism and collectivism affect the attributions people make for unethical behavior at work. The moderating effect of ethnicity is also examined by considering two culturally diverse groups: Hispanics and Anglos. The sample for this study is a group of business graduate students from two universities in the Southeast. A 20-minute survey was distributed to master's degree students at their classroom and later on returned to the researcher. Individualism and collectivism were operationalized as by a set of attitude items, while unethical work behavior was introduced in the form of hypothetical descriptions or scenarios. Data analysis employed multiple group confirmatory factor analysis for both independent and dependent variables, and subsequently multiple group LISREL models, in order to test predictions. Results confirmed the expected link between cultural variables and attribution responses, although the role of independent variables shifted, due to the moderating effect of ethnicity, and to the nuances of each particular situation. ^