Showing papers by "Tallinn University of Technology published in 2001"

Advanced Oxidation Processes: Current Status and Prospects

Abstract: The paper provides an overview of theoretical basis, efficiency, economics, laboratory and pilot plant testing, design and modelling of different advanced oxidation processes (combinations of ozone and hydrogen peroxide with UV radiation and catalysts).

Advanced oxidation processes - current status and prospects

Abstract: The paper provides an overview of theoretical basis, efficiency, economics, laboratory and pilot plant testing, design and modelling of different advanced oxidation processes (combinations of ozone and hydrogen peroxide with UV radiation and catalysts).

Characterization of powder particle morphology

Abstract: Technological properties of powders depend on their granulometry and particle morphology. Most of the image analysis methods provide only average size parameters (diameter, area, perimeter, etc.) which are often inadequate for characterizing the morphology of the particles. For particle abrasivity characterization, angularity factors are more sensitive. This paper studies different parameters for describing the hardmetal powder granulometry and morphology. The main aim is to find numerical descriptors for the shape factors that adequately characterize the hardmetal powders produced by the mechanical method - milling in a disintegrator. For the characterization of the powder particle morphology, irregularity parameter IP (relation of the diameters of the maximum inscribed and minimum circumscribed circles) suits best, taking into account the ellipticity and irregularity of the particle form. For describing the angularity of ground powders, the so-called "spike parameter - quadratic fit" can be used.

Does the Nominal Exchange Rate Regime Matter for Investment

Abstract: This paper analyses the impact of exchange rate uncertainty upon the pattern of investment in different exchange rate regimes (very hard pegs, intermediate regimes, and floats) by means of a unified approach. The comparison of different exchange rate regimes indicates that currency volatility exerts only a small influence upon the level of investment spending. On the other hand, firms turn out to be more cautious about responding to exchange rate shocks in a credible target zone model than in a flexible exchange rate regime or in a target zone model with stochastic realignments.

Carbon dioxide binding in the heterogeneous systems formed by combustion of oil shale 1. carbon dioxide binding at oil shale ash deposits

Abstract: About 95 % of electricity production in the Republic of Estonia is based on the firing of pulverised local solid fuel – oil shale. This process is accompanied by high CO2 emission and followed by the formation of waste alkali ash in huge quantities. Ash is removed by hydrotransport and deposited in wet dumps. A complex of laboratory and field experiments with different ashes and their transport water samples from operating power plant (1610 MW) was carried out. Low activity and low carbonation rate of dry ash were determined as well as a much higher activity of previously hydrated ash, which in favourable conditions could be completely carbonated. An up to 50–60 % degree of carbonation of transport waters by binding CO2 from the air in the production cycle was established. The total amount of CO2 bound from the air and calculated basing on the results of laboratory model experiments reached 37 kg per 1 ton of oil shale burnt in the electricity production. The relative part of bound CO2 formed 20.5 % and 4.2 % from the carbonate and total emission of CO2, respectively. The recommendations to increase the amount of CO2 bound at natural field conditions have been worked out. By implementing them, the amount of bound CO2 could be essentially increased – up to 35–36 and 6– 7 %, respectively.

Heat energy and water consumption in apartment buildings

Abstract: Specific heat energy consumption for space and water heating in typical apartment buildings in Tallinn is described. Hot and cold water consumption data is presented and energy conservation measures in apartment buildings are considered.

HTS materials for AC current transport and fault current limitation

Abstract: The European SUPERPOLI project aims to define a MV fault current limiting power link, and to demonstrate its feasibility by a functional model. It includes the development of two alternative low-AC-loss conductor designs suitable for current limitation: a low-cost composite tubular Bi-2212 conductor with moderate Jc; and a coated tubular Y-123 conductor, presenting a very high J/sub c/. BSCCO tubes are developed by Alcatel HTS (length: 650 mm and diameter: 50 mm) with silver contacts on both ends. These tubes have an effective thickness of the superconducting layer of 1.5 mm. This layer is reinforced by an additional nonsuperconducting layer in order to increase mechanical stability. Based on theoretical simulations, Alcatel HTS seeks to develop tubes with a Jc scattering lower than 2%. The main issue with Y-123 films is to find a way for producing them in long reproducible lengths. A novel high rate PLD technique with a repetition rate of 300 Hz has been developed and used for manufacturing films on large-area substrates, made of flexible stainless steel foils buffered by IBAD. The largest samples prepared are of 34 mm/spl times/1 m in size, and present a Jc of 4000 A/mm/sup 2/ (77 K self-field). For a sample with dimensions of 10 mm/spl times/0.5 m, Jc exceeds 6000 A/mm/sup 2/.

Thermopower Measurements in 4H-SiC and Theoretical Calculations Considering the Phonon Drag Effect

Abstract: The Seebeck coefficient study in a heavily nitrogen-doped n-type 4H-SiC epilayer in the direction perpendicular to c-axis is presented. The Seebeck coefficient steeply increases from 0.56 mV/K to 1.7 mV/K with decreasing temperature in the range 400-80 R. This behavior is explained by the phonon drag effect. An approach to the theoretical modeling of the phonon drag effect is discussed and simulation of the Seebeck coefficient temperature-dependence is displayed.

Transparency analysis of first-order takagi-sugeno systems

Abstract: The primary goal of this paper is to investigate transparency properties of Takagi-Sugeno (TS) systems. TS systems, distinguished by half-linguistic/half-functional rules are exploited in numerous applications today and deserve special attention from transparency viewpoint. The fact that TS systems can be interpreted in terms of local linear models is generally acknowledged. Few authors, however, have been interested with the question if this interpretation can be considered accurate (i.e. if the system is transparent). In this paper, the problem is taken into consideration and transparency measure for 1 order TS systems is introduced. Included are examples of TS modeling demonstrating that transparency and adaptability of TS systems are of somewhat exclusive character.

Linearity restrictions for a class of phase frequency detectors

Abstract: In this paper, the transfer characteristic of a class of phase frequency detectors is analysed and modelled for simulations. It is demonstrated that the reasons of non-linearity of the transfer characteristic may originate both from the charge pump and the logic control unit of the phase frequency detector. Restricted slew rate is found to be one of the main reasons of non- linearity of the charge pump, determining the minimum duration of control signals. For a generalized structure of the control unit, an optimum distribution of gate delays is proposed. Also, some critical aspects of selecting the delays are considered which may cause significant non- linearity with a dead zone and even oscillation of the phase frequency detector. The results of the analysis are verified by transistor level SPICE simulation.

Compararison of geological settings at possible deep harbour sites, north-western saaremaa island

Abstract: The investigations carried out on Tagamoisa Peninsula (north-western Saaremaa Island, West Estonian Archipelago) were aimed at finding the deep harbour site with most favourable hydrogeological and geological conditions. Three possible sites were studied: Undva on the eastern coast of Uudepanga Bay, and Suuriku-Kuriku and Vaigu on the western coast of the Tagalaht Bay. The investigations show that in spite of active shore processes between Suuriku and Kuriku cliffs, geological and hydrogeological conditions for establishing the deep harbour are somewhat more favourable in this area than at Undva (dredging volumes as well as the amount of filling material needed for jetties and quays were not considered). At Undva dredging would be more work- consuming and to obtain fresh high quality drinking water is more complicated. Vaigu is less favourable because in the harbour basin area a thick layer of sand occurs on the seafloor.

Application of orthogonal transformations in the revised simplex method

Abstract: Unlike the classical method, orthogonal transformations are used for computing more precise simplex tables. These transformations are stored as products. With these transformations the basic matrix is turned to the triangular form, which is used instead of the reciprocal matrix. The values of initial and dual variables are found from the triangular system. The performed algorithm MULT is appropriate for solving ill-conditioned problems and it is more labour-consuming than the classical revised simplex method. Examples of solving the ill-conditioned problems are given.

On frequency adaptation in an extended block-adaptive fourier analyser

Abstract: Received 2 May 2001, in revised form 2 October 2001 Abstract. The aim of this work is to form a basis for developing an efficient adaptive multi- frequency adaptation algorithm for an extended block-adaptive Fourier analyser (EBAFA), which performs simultaneously separation and analysis of its input signal's periodic components of different frequencies and waveforms. A brief description of EBAFA is given and several possibilities to improve estimation of differences between fundamental frequencies of signal's periodic components and corresponding resonator groups of EBAFA are considered.

Module level defect simulation in digital circuits

Abstract: A new method for parametric defect modelling is developed for calculating the conditions for activating physical defects in the modules (for example, in library components) of digital circuits. The method affords for the first time the possibility to handle the defects which increase the number of states in the circuit. By using the concept of functional faults, the new method of defect modelling by logic conditions is generalized for hierarchical fault simulation. A method is proposed to find the types of faults that may occur in a real circuit, to determine their probabilities, and to find the input test patterns that detect these faults. A new hierarchical defect- oriented fault simulation method is presented. At the higher (module) level simulation we use the functional fault model, at the lower level the defect/fault relationships in the form of defect coverage table and conditional defect probabilities. Experimental data of the hierarchical defect- oriented simulation for ISCAS'85 benchmarks are presented, which show that classical stuck-at fault based simulation and the test coverage calculation, based on counting defects without considering defect probabilities, may lead to considerable overestimation of results.

Application of structurally synthesized binary decision diagrams for timing simulation of digital circuits

Abstract: Meeting the timing requirements is an important constraint imposed on highly integrated circuits, and the verification of timing of a circuit before manufacturing is one of the critical tasks to be solved by CAD tools. In this paper, we present a novel technique to speed up gate-level timing simulation that is based on Structurally Synthesized Binary Decision Diagrams (SSBDD), which have already found application as an efficient mathematical model to represent digital circuits. The new approach uses path delays instead of gate delays for tree-like subcircuits (macros). Therefore timing waveforms are calculated not for all internal nodes of the gate-level circuit, but only for outputs of macros. The macros are represented by SSBDDs, which enable a fast computation of delays for macros. We show that the speed-up of timing simulation is directly proportional to the average size of macros in the circuit. The new approach to speed up the timing simulation is supported by encouraging experimental results.