Showing papers by "Tallinn University of Technology published in 2003"

Labour demand in germany: an assessment of non-wage labour costs

Abstract: The data indicate that non-wage labour costs in Germany have reached a record high in recent years From 1972 to 2001, the ratio of non-wage labour costs to direct compensation in West German manufacturing industry rose from 556% to 812% The topic of non-wage labour costs is increasingly being discussed among and between the political parties because non-wage labour costs are likely to have major negative effects on employment We follow the real options approach, which allows us to

How Efficient Is The East German Economy? An Exploration With Micro Data

Abstract: The purpose of this paper is to evaluate the efficiency of the East German economy at the firm level using an unbalanced panel over the transition period 1994 to 1998. We adopt a translog stochastic frontier model to estimate technical efficiency in eastern and western Germany. The results indicate that firms in eastern Germany are significantly less efficient than firms in western Germany. The paper also examines some of the possible correlates of regional variations in firm-level efficiency.

Estonian oil shale resources calculated by gis method

Abstract: A digital map of Estonian oil shale mining was created for joining the data about technological, environmental, and social limitations in the deposit. For evaluating potential resource of oil shale, based on borehole database, its amount, tonnage and energy were calculated. Thereafter the quantity of economical oil shale for power plants and shale oil resource were calculated. Energy rating is the most important factor for determining oil shale reserves in the case of using it for electricity generation. In the case of oil production, data on oil yield and potential resources in oil shale are the most important figures to determine the value of the deposit. Basing on the models, oil resource has been calculated. Resource data can be used for composing master plans for the deposit considering both power generation and oil production. The data can be also used for composing development plans of mines and for logistics calculations.

Estimation of Real Emissions Reduction Caused by Wind Generators

Abstract: The aim is to show that the fuel economy and emissions reduction in the power systems consisting mainly of thermal power plants are not proportional with the electricity production of wind turbines. Participation of thermal power plants in the compensation of fluctuating production of windmills eliminates major part of the expected positive effect of wind energy. A method for calculation of real fuel economy and emissions reduction will be described and some calculation results will be given.

Wastewater treatment in oil shale chemical industry

Abstract: Process water and phenols’ balances for the two processes of oil shale thermal treatment, Kiviter (in vertical retort) and Galoter (with solid heat carrier) were compiled. Options of wastewater treatment in the Kiviter process were analyzed in more detail. Laboratory experiments of biological oxidation of the process water after the dephenolation stage without other effluents and municipal wastewater were carried out. Experiments indicated that the oil shale phenols are generally quite easily degradable when the need for phosphorus is covered by added reagents. The experiments indicated that, compared to conventional aerobic bio-oxidation, the combined process, namely aerobic bio-oxidation with ozonation in re-circulation system, enabled to increase the efficiency of purification at relatively low ozone dosages. Application of ozone at moderate doses (up to 30 mg/L) improved the rate of pollutant removal. Injection of ozone at small dose – 2 mg/L – into the activated sludge in the bioreactor increased the sludge activity: the specific oxygen uptake increased about 15–20%. The biologically treated wastewater can be used as some kind of technological water (cooling water) after chemical precipitation and reduction of sulphate content. It can also been discharged to nature, but only after additional treatment to reduce nitrogen content and after filtration to remove the residual suspended solids.

Precision of oil shale energy rating and oil shale resources

Abstract: The main quality indicator of kukersite is calorific value. Determining of this indicator is time and labor consuming. Using simple quality indicators, such as ash content or burning matter range, has not been adequate enough. The current paper shows that in some cases, when mining technology and structure of extracted material is constant, the quality of oil shale can be evaluated by the content of burning matter. In the case of oil shale resource calculations, the specific weight of the mineral is not measured but evaluated by calorific value. This method does not take into account the relationship between clay and lime minerals in the layers. The deviations from calculated resource figures have been noticed in mining practice. The error of this method is evaluated, and recommendations for recalculating oil shale resources are given.

Reforms and economic growth in transition economies: Complementarity, sequencing and speed

Abstract: Growth regressions have provided important insights into the impact of economic reforms on growth in transition economies. Using principal components to decompose reform variables and construct reform clusters, we address unsettled issues such as the importance of sequencing and reform speed. The results indicate a broad-based reform policy is good for growth, but so is a policy of liberalisation and small-scale privatisation without structural reforms. Conversely, large-scale privatisation without adjoining reforms, market opening without supporting reforms and bank liberalisation without enterprise restructuring affect growth negatively. Swift reform policies allow transition countries to benefit from higher growth for a longer period of time. The speed of reforms otherwise appears to have only limited effects on short-term and medium-term growth.

Geotechnical processes in closed oil shale mines

Abstract: During the years 1998–2001 geotechnical processes in closed underground oil shale mines and opencasts were investigated. In addition to kukersite oil shale deposit, the closed Sillamae uranium (Dictyonema shale) mine was prospected. The main tools and methods included mine plans, aerial photographs and Geographical Information System data. 290 km 2 of underground and 130 km 2 of strip-mined areas were studied. The mining maps of Estonian underground and surface mines were created. The stability of underground mined area, where room-and-pillar method was used, was the main objective of the study. It was studied with the help of aerial photographs, mine drawings, maps of quaternary sediments and mathematical modeling of rock failure. The main results are: 20 % of subsidences remain undiscovered and 42 % of subsidence occurrences have no remarkable influence to the land cover; the probability of subsidence remains and may increase in the case of mine drowning. As several mines will be closed during the next few years, the problems of drowned waste (which were not subjects of this study) are going to be more actual than before: increasing underground water level, pollution of underground water, formation of technogenic water sources, overflooding of reclaimed areas, etc. There are two kinds of oil shale in Estonia: kukersite as the principal one and Dictyonema argillite (black oil shale, alum shale) as uranium shale. Both oil shales are deposited in low depth and their fields are large. Kukersite oil shale deposits cover more than 5 % of Estonian mainland. There are fourteen closed and/or abandoned underground mines (including two Sillamae uranium mines) and nine partly reclaimed kukersite open casts today. The total area of mined-out lands exceeds 400 km 2 that is less then 1 % of the Estonian area. In Estonia since the year 1916 almost 1 billion tonnes kukersite oil shale has been extracted, approximately 2 billion m 3 overburden has been excavated and about 200 million m 2 underground workings have been formed.

Modeling of decomposition and sulphation of oil shale carbonates on the basis of natural limestone

Abstract: Estonian oil shale is characterized by a high content of inorganic matter, calcium carbonate making up 57–75% of the total inorganic part. At combustion temperature the carbonates decompose, and the formed free oxides bind at pulverized firing about 80–85% of SO2 formed during combustion already in the boiler. At fluidized-bed combustion the conditions for SO2 binding are close to optimum, and nearly full capture of SO2 is expectable. Modeling of oxide formation and SO2 binding was the task of the present work. In order to obtain data for mathematical modeling of the decomposition and sulphation processes of oil shale carbonaceous part, series of thermogravimetric experiments accompanied by X-ray and SEM analysis, specific surface and porosity measurements were carried out with some natural limestone samples. Mathematically, the calcination process of limestone samples was satisfactorily described using a random pore distribution model, assuming that only chemical reaction limited the overall decomposition process. An extended unreacted shrinking core model with variable (conversion-dependent) effective diffusivity was applied to the sulphation data. From model calculations the kinetic parameters of the decomposition and binding reactions were determined.

Activity Coefficients of Potassium Dihydrogen Phosphate in Aqueous Solutions at 25°C and in Aqueous Mixtures of Urea and this Electrolyte in the Temperature Range 20–35°C

Abstract: Simple two-parameter Huckel and Pitzer equations were determined for the calculation of the activity and osmotic coefficients of aqueous solutions of potassium dihydrogen phosphate at 25°C up to a molality of the saturated solution (= 1.83 mol kg - 1 ). The isopiestic data measured by Stokes 1945) were used in the parameter estimations. The resulting parameter values were tested with all thermodynamic data found in the literature for this electrolyte at this temperature. In these tests it was observed, that the Huckel equation applies to the data within experimental error up to a molality of 1.0 mol kg - 1 , and the Pitzer equation applies well to the data in the molality range 1.0-1.83 mol kg - 1 but not very well in dilute solutions. Therefore, also a three-parameter Pitzer equation was determined that applies to all data. The activity and osmotic coefficients calculated by these three models were compared to the values suggested by Robinson and Stokes (1959) and to those calculated by the equations of Hamer and Wu (1972) and of Pitzer and Mayorga (1973) for this electrolyte. Solubility measurements of KH 2 PO 4 at 20, 25, 30 and 35°C were made in aqueous urea solutions, and the molality of urea varied in these measurements from 0 to 2.5 mol kg The thermodynamics of these studies were analyzed by using the Pitzer formalism. It was observed that only one interaction parameter between urea molecules and ions (this parameter is linearly dependent on the temperature) was needed to describe almost completely the new solubility data.

Test Time Minimization for Hybrid BIST of Core-Based Systems.

Abstract: This paper presents a solution to the test time minimization problem for core-based systems We assume a hybrid BIST approach, where a test set is assembled, for each core, from pseudorandom test patterns that are generated online, and deterministic test patterns that are generated off-line and stored in the system In this paper we propose an iterative algorithm to find the optimal combination of pseudorandom and deterministic test sets of the whole system, consisting of multiple cores, under given memory constraints, so that the total test time is minimized Our approach employs a fast estimation methodology in order to avoid exhaustive search and to speed-up the calculation process Experimental results have shown the efficiency of the algorithm to find near optimal solutions

Sulphate balance of lakes and shallow groundwater in the vasavere buried valley, northeast estonia *

Abstract: Groundwater is an important component of many water resource systems supplying water for domestic use, industry, and agriculture. Management of a groundwater system, an aquifer, means making such decisions as annual withdrawal of the total quantity of water, location of wells for pumping and for artificial recharge and their rates, and control conditions at aquifer boundaries. The decisions related to groundwater quality are of no less importance. In fact, the quantity and quality problems cannot be separated. In many parts of the country, with the increased withdrawal of groundwater, the quality of groundwater has been continuously deteriorating. In recent years the attention has been focused on groundwater contamination by mine water. A thorough understanding of the system, and the processes that take place in it are needed for modeling procedure. It is important to identify those parts of the system’s behavior that are relevant to the considered problem, while other parts may be neglected. On the basis of this understanding, summarized as a conceptual model of the given problem, a numerical model was constructed. Using the conceptual model the groundwater flow model of the Quaternary aquifer, in the eastern part of oil shale deposit area, in the Vasavere buried valley, was constructed. The infiltration of contaminants grows, and the Quaternary aquifer is polluted by sulphate in a large area of the Vasavere buried valley.

Generalized riesz method and convergence acceleration

Abstract: Several λ‐boundedness propositions for generalized linear methods A = (Ank ), while Ank are specially fixed linear bounded operators from Banach space X into X, are presented These results are proved using necessary and sufficient conditions for inclusion Amλ X ? mμ X

Impact of Phonon Drag Effect on Seebeck Coefficient in p-6H-SiC: Experiment and Simulation

Abstract: The temperature dependence of Seebeck coefficient (S) for p-6H-SiC has been obtained. It increases from 2 up to 5.2 mV/K when temperature decreases from 400 down to 240 K. It is shown that phonon d ...

Diffusion-Welded Al Contacts to p-Type SiC

Abstract: The first experimental results on Diffusion Welding (DW) applied to p-type 6Hand 4HSiC are described. Using the extrapolation method and available measurement apparatus the specific series on-state resistance and current-voltage characteristics of Schottky contacts in comparison with the n-type Schottky contacts were obtained

Modeling of Lattice Heat Conductivity and Thermopower in SiC Considering the Four-Phonon Scattering Processes

Abstract: The lattice heat conductivity in low-doped SiC is studied in the wide temperature range 50÷1200 K in order to estimate the strength coefficient a4P for 4-phonon scattering processes mechanism for later application in both heat conductivity and Seebeck coe fficient models. Heat conductivity calculations confirm the domination of the 4-phonon mechanism and t he secondary role of the 3-phonon Umklapp mechanism. The obtained a4P ≈1.5⋅10 −22 s/K gives very satisfactory result in Seebeck coefficient phonon drag component modeling. Introduction. To achieve accuracy in electrothermal device simulation the rel iabl models for the lattice heat conductivity κL and thermopower (Seebeck coefficient) S are needed. To model these material parameters the phonon transport and relevant scattering proc esses should be analyzed. The phonon flux is determining κL and the partial momentum transfer from phonons to electron and hole subsystems (phonon drag effect) increases remarkably the electron and hole Seebeck coefficient Sn,p values, especially at low temperatures. In SiC, according to the hi g heat conductivity and relatively low carrier mobilities, the phonon drag effect is approximately 5 ÷10 times stronger than in silicon [1]. Respectively in SiC the phonon drag component of the Seebeck coeffici ent typically (except low doped material of 10 15 cm range) dominates over classic diffusion component for all temperature range of practical application [1]. More detailed investigation predicts that parameters κL and S are strongly influenced by the 4phonon scattering processes (4-phonon mechanism). Below we will evaluate the s rength coefficient a4P for 4-phonon mechanism from experimental κL(T) in low-doped 6H-SiC in order to use this a4P later in improved theoretical model of Seebeck coefficient phonon drag component (see [1]) . Theoretical background and model description. The phonon drag effect was predicted theoretically for metals by Gurevich in 1946 [2,3] and then observed experi mentally in semiconductors by Frederikse, Geballe and Hull [4-7]. Frederikse [4] s howed also that the strength of this drag is proportional to the ratio of phonon and carrier mean free paths lph/lcarr which rises rapidly at lower temperatures [8]. Herring in his seminal papers [9,10] analyzed the role of lowenergy (i.e. long-wave, LW) phonons for κL and S and proposed a theory for lph calculation considering the 3-phonon LW mechanism. However, soon it was discovered [6,7] tha t Herring’s model provides obviously too long lph and, therefore, significantly overestimates the phonon drag contribution to the thermopower Sph. Our recent investigations reveal the same situation in the case of SiC [1,8,11], Si and Ge. Herring’s model predicts also too strong te mperature dependence Sph ∼T −3.5 [8,11] what disagrees with the observed experimental results Sph ∼T −1.8 ...−2.5 [1,7,8,12]. This indicates that some important phonon scattering processes reducing lph value have been omitted in Sph modeling. In order to overcome this problem, we decided to consider in the Sph model beside the Herring’s type 3-phonon processes also the 4-phonon processes introduced into the κL analysis by Pomeranchuk [13]. Detailed characterization of 3-phonon and 4-phonon processes is giv n, e.g. in Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 391-394 doi:10.4028/www.scientific.net/MSF.433-436.391 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-12/03/20,10:56:49) [14]. The model of Sph obtained by the summation of the LW acoustic phonon relaxation time reciprocals of Herring’s type 3-phonon processes and the 4-phonon processes i s described in [1] and in Appendix below. At that should be mentioned that distinction of LW acousti c phonons from short-wave phonons is quite necessary, because only LW phonons with wavevector s q<2k, where k is the wavevector of an incident charge carrier, can interact wi th electrons or holes and cause the carrier phonon drag effect. In contrast to the relaxation time of LW 3-phonon processes which is w ell described by the Herring’s theory, the exact theoretical description of 4-phonon processe s i a very difficult and maybe a hopeless task, if quantitatively correct results are nee ded. Therefore we decided to evaluate the parameter a4P for the 4-phonon processes relaxation time τ4P = a4P T ω 2 = a4P (kB/h) 2 T 4 x [15] ( x= hω / kBT is the reduced dimensionless phonon energy) on the basis of the well-known experimental κL data for low-doped samples where impurities, defects and surface r el t d resistive mechanism may be omitted. Thus, limiting ourselves with relatively pure and defect-free crystals at medium and high temperatures, for the lattice heat conductivity κL only two major scattering processes, the 3-phonon Umklapp processes and the above-mentioned 4-phonon processes a re important [15]. It is reasonable to exclude from κL model the Herring’s type 3-phonon processes which may be classified as “normal” processes conserving the phonon subs ystem momentum [15]. The primary role of “resistive” processes and secondary role of “ n rmal” processes may be confirmed by the Callaway’s heat conductivity theory [16]. The Umklapp processes mechanism with the relaxation time τU = auT exp[−θ/(bT)]ω 2 [15], where θ is the Debye temperature (1200K for SiC), is a relatively well d fined quantity except the dimensionless parameter b=1...3 under exponent [15]. The strength parameter au may be calculated by au= hγ 2 /Mθ vs 2 [17], where γ is the Grüneisen factor (which default value is typically 2, but in [18] was proposed γ=1.55 for SiC), M is the crystal elementary cell mass, and vs is the average sound velocity. In present calculations we have used numerical value for au presented by Joshi et al. [15] which is completed by concrete Grüneisen factor: au=(6.1626⋅10 −20 s/K)⋅(γ/2), where γ=1.55. Similarly to [15], here the κL is calculated from energy-dependent partial relaxation times τ4P and τU using the Callaway`s approach [16] and assuming that “resistive” processes dominate over “normal” processes: ( ) , ) ( ) ( ) ( , 1 ) ( 2 ) ( 1 1 4 1 /

Mining block stability analysis for room-and-pillar mining with continuous miner in estonian oil shale mines *

Abstract: Without progressive technology to make mining economically viable, this industry, which provides a significant contribution to Estonia’s economy, can no longer exist. This paper presents a proposal for a comprehensive mining system. Determination of the pillar and roof optimum parameters for new mining technology with continuous miner was the main aim of the present work. The conventional calculation formulas and conditional thickness methods were used to determine the room-and-pillar mining system parameters, which guarantee a long-term stability. The calculation methods used gave excellent results.

Design of a new oil shale surface mine

Abstract: The paper discusses designing of oil shale surface mines covered with relatively thin overburden – thickness less than 10 meters. The main issues to pay attention to at the designing procedure are presented.

Extending Classical Theorem Proving for the Semantic Web.

Abstract: We investigate the applicability of classical resolution-based theorem proving methods for the Semantic Web. We consider several well-known search strategies, propose a general schema for applying resolution provers and propose a new search strategy ”chain resolution” tailored for large ontologies. Chain resolution is an extension of the standard resolution algorithm. The main idea of the extension is to treat binary clauses of the general form A(x)∨B(x) with a special chain resolution mechanism, which is different from standard resolution used otherwise. Chain resolution significantly reduces the size of the search space for problems containing a large number of simple implications, typically arising from taxonomies. Finally we present a compilation-based schema for practical application of resolution-based methods as inference engines for Semantic Web queries.

High-temperature corrosion resistance of the austenitic steels in the presence of chlorine-containing on-tube deposits *1

Abstract: High-temperature corrosion resistance of a number of boiler steels was tested experimentally in laboratory and industrial conditions in the presence of chlorine-containing external deposits. Empirical kinetic equations for calculation of corrosion depth depending on operational time and temperature were established, and the dependence of corrosion resistance of the austenitic steels on the alloying elements ratio Ni/Cr was analyzed.

Modelling of crystal growth in multicomponent solutions

Abstract: The crystal growth model was derived from Maxwell-Stefan equations for the diffusioncontrolled growth regime. As a model system, the ternary potassium dihydrogen phosphate (crystallizing substance)-water (solvent)-urea (foreign substance) system was employed. The thermodynamic model for the present system was successfully derived by the Pitzer method and allowed calculating activity coefficients of each component. The resulting activity-based driving force on each component and other solution properties; mass transfer coefficient, concentration of each component and solution density, were introduced to the Maxwell-Stefan equations. The crystal growth rates were successively determined by solving the Maxwell-Stefan equations. The model was evaluated from single crystal growth measurements. The urea concentrations, supersaturation level and solution velocity were varied. The results showed that experimental and predicted growth rates are in acceptable agreements.

Decider: a system for hierarchical test pattern generation

Abstract: . A hierarchical test pattern generation system that usesregister-transfer level VHDL and gate-level EDIFn etlist descriptionsas inputs is presented in current paper. The main novelty of thehierarchical ATPG tool lies in the fact that it implements internalrepresentatoi nof mixed-leve (rl egister-rtansfer and srtuctural levels)decision dagi ramm odesl T. he system includesa ppropraite inetrfacesto synthesize Decision Diagram (DD) models, a DD based testpattern generator and a fault simulator to evaluate the quality of thegenerated tests. In the paper, the structure of the system ispresented. Additionally re, presentationo f differendt esign abstractionlevels using decision diagrams is explained T. he performance of thesystem is compared to other state-of-the-art tools for sequentialcircuit test generation. Experiments show that thep roposed methodallows to reach high fault coverages for circuits with complexsequential structures in a very short time. 1. Introduction As the degree of integration in VLSI designs has beengrowing over the years, so has the need for automation ofdifferent design tasks. Design automation helps to shortenthe time-to-market cycleand increases significantly designer’sproductivity. Automation was first introduced on the lowerlevels of design tasks, such as placement and routing, andtogether with the growth of design complexities, movedgradually to higher levels, e.g. logic synthesis, high-levelsynthessi (HLS) and hardware/software co-desgi n No. wadaysthe goal is clearly to automate the entire design cycle fromconceptualization to generation of silicon layout [1].During recent years, more-and-more high-level synthesistoolshave b ecome avaialbel T. hese toosla re usedby d esignersto automatically generate Register-Transfer Level (RTL)descriptions from design’s behavioral description. In theRTL descriptions the design is usually partitioned into acontrol part, i.e. a finite state machine, and a datapath partcontaining a network of interconnected functional units(FU). The HLS tools take into account several constraints, asspeed, area, or testability, and allow the designer to quicklycompare the trade-offs between alternative RTLimplementations.With the appearance of high-level synthesis, a number ofautomated test generation approaches [2,3] were introducedthat took advantage of register-transfer level informationwhile generating tests for gate-level faults. Current paperpresents a hierarchical test generation system that operateson RTL and gate-level model descriptions. At present, thesystem utilizes Design Compiler [4] from Synopsys Inc. forlogic-level synthesis. In Figure 1, the basic design flow andthe place of test generation in it is shown.