Showing papers by "Tallinn University of Technology published in 2022"

High Gain DC–AC High-Frequency Link Inverter With Improved Quasi-Resonant Modulation

Abstract: This article presents a high gain pure sine- wave inverter based on the full-bridge dc–ac high-frequency link cycloconverter topology for telecom or general-purpose applications. The improved quasi-resonant modulation method allows reduction of ringing and turn- off losses of the dc-side switches. This is achieved with minimal energy circulation and requires no multi-mode operation or extra auxiliary clamping circuits. The soft switching can be provided even if relatively large lossless snubber capacitors are connected across the input side transistors. Moreover, two of the switches at the ac side operate at fundamental frequency, while the rest feature zero current turn- off . A 48 VDC to 230 VAC, 1.2 kW sine-wave inverter prototype was developed to verify the proposed concept.

Human impacts and their interactions in the Baltic Sea region

Abstract: Abstract. Coastal environments, in particular heavily populated semi-enclosed marginal seas and coasts like the Baltic Sea region, are strongly affected by human activities. A multitude of human impacts, including climate change, affect the different compartments of the environment, and these effects interact with each other. As part of the Baltic Earth Assessment Reports (BEAR), we present an inventory and discussion of different human-induced factors and processes affecting the environment of the Baltic Sea region, and their interrelations. Some are naturally occurring and modified by human activities (i.e. climate change, coastal processes, hypoxia, acidification, submarine groundwater discharges, marine ecosystems, non-indigenous species, land use and land cover), some are completely human-induced (i.e. agriculture, aquaculture, fisheries, river regulations, offshore wind farms, shipping, chemical contamination, dumped warfare agents, marine litter and microplastics, tourism, and coastal management), and they are all interrelated to different degrees. We present a general description and analysis of the state of knowledge on these interrelations. Our main insight is that climate change has an overarching, integrating impact on all of the other factors and can be interpreted as a background effect, which has different implications for the other factors. Impacts on the environment and the human sphere can be roughly allocated to anthropogenic drivers such as food production, energy production, transport, industry and economy. The findings from this inventory of available information and analysis of the different factors and their interactions in the Baltic Sea region can largely be transferred to other comparable marginal and coastal seas in the world.

Robust Stability Analysis of Interval Fractional-Order Plants With Interval Time Delay and General Form of Fractional-Order Controllers

Abstract: This letter aims to investigate the robust stability of an interval fractional-order plant with an interval time delay by a general form of fractional-order controllers. Based on a simple graphical procedure, necessary and sufficient criteria are proposed to analyze the robust stability of an interval fractional-order plant. Then, the idea of “robust stability testing function” is extended to analyze the robust stability of the considered type of systems. Besides, an upper frequency bound is provided which is useful for the simulation purposes and it helps to reduce the computational cost. Finally, two examples are presented to verify the usefulness of the obtained results.

Salinity dynamics of the Baltic Sea

Abstract: Abstract. In the Baltic Sea, salinity and its large variability, both horizontal and vertical, are key physical factors in determining the overall stratification conditions. In addition to that, salinity and its changes also have large effects on various ecosystem processes. Several factors determine the observed two-layer vertical structure of salinity. Due to the excess of river runoff to the sea, there is a continuous outflow of water masses in the surface layer with a compensating inflow to the Baltic in the lower layer. Also, the net precipitation plays a role in the water balance and consequently in the salinity dynamics. The salinity conditions in the sea are also coupled with changes in the meteorological conditions. The ecosystem is adapted to the current salinity level: a change in the salinity balance would lead to ecological stress for flora and fauna, as well as related negative effects on possibilities to carry on sustainable development of the ecosystem. The Baltic Sea salinity regime has been studied for more than 100 years. In spite of that, there are still gaps in our knowledge of the changes in salinity in space and time. An important part of our understanding of salinity is its long-term changes. However, the available scenarios for the future development of salinity are still uncertain. We still need more studies on various factors related to the salinity dynamics. Among others, more knowledge is needed, e.g., from meteorological patterns at various space scales and timescales as well as mesoscale variability in precipitation. Also, updated information on river runoff and inflows of saline water is needed to close the water budget. We still do not understand the water mass exchange accurately enough between North Sea and Baltic Sea and within its sub-basins. Scientific investigations of the complicated vertical mixing processes are additionally required. This paper is a continuation and update of the BACC (Baltic Assessment of Climate Change for the Baltic Sea Region) II book, which was published in 2015, including information from articles issued until 2012. After that, there have been many new publications on the salinity dynamics, not least because of the major Baltic inflow (MBI) which took place in December 2014. Several key topics have been investigated, including the coupling of long-term variations of climate with the observed salinity changes. Here the focus is on observing and indicating the role of climate change for salinity dynamics. New results on MBI dynamics and related water mass interchange between the Baltic Sea and the North Sea have been published. Those studies also included results from the MBI-related meteorological conditions, variability in salinity, and exchange of water masses between various scales. All these processes are in turn coupled with changes in the Baltic Sea circulation dynamics.

Slow-roll inflation in Palatini F(R) gravity

Abstract: We study single field slow-roll inflation in the presence of $F(R)$ gravity in the Palatini formulation. In contrast to metric $F(R)$, when rewritten in terms of an auxiliary field and moved to the Einstein frame, Palatini $F(R)$ does not develop a new dynamical degree of freedom. However, it is not possible to solve analytically the constraint equation of the auxiliary field for a general $F(R)$. We propose a method that allows us to circumvent this issue and compute the inflationary observables. We apply this method to test scenarios of the form $F(R) = R + \alpha R^n$ and find that, as in the previously known $n=2$ case, a large $\alpha$ suppresses the tensor-to-scalar ratio $r$. We also find that models with $F(R)$ increasing faster than $R^2$ for large $R$ suffer from numerous problems.

α-Lipoic Acid Has the Potential to Normalize Copper Metabolism, Which Is Dysregulated in Alzheimer’s Disease

Abstract: Background: Alzheimer’s disease (AD) is an age-dependent progressive neurodegenerative disorder and the most common cause of dementia. The treatment and prevention of AD present immense yet unmet needs. One of the hallmarks of AD is the formation of extracellular amyloid plaques in the brain, composed of amyloid-β (Aβ) peptides. Besides major amyloid-targeting approach there is the necessity to focus also on alternative therapeutic strategies. One factor contributing to the development of AD is dysregulated copper metabolism, reflected in the intracellular copper deficit and excess of extracellular copper. Objective: In the current study, we follow the widely accepted hypothesis that the normalization of copper metabolism leads to the prevention or slowing of the disease and search for new copper-regulating ligands. Methods: We used cell culture, ICP MS, and Drosophila melanogaster models of AD. Results: We demonstrate that the natural intracellular copper chelator, α-lipoic acid (LA) translocates copper from extracellular to intracellular space in an SH-SY5Y-based neuronal cell model and is thus suitable to alleviate the intracellular copper deficit characteristic of AD neurons. Furthermore, we show that supplementation with LA protects the Drosophila melanogaster models of AD from developing AD phenotype by improving locomotor activity of fruit fly with overexpression of human Aβ with Iowa mutation in the fly brain. In addition, LA slightly weakens copper-induced smooth eye phenotype when amyloid-β protein precursor (AβPP) and beta-site AβPP cleaving enzyme 1 (BACE1) are overexpressed in eye photoreceptor cells. Conclusion: Collectively, these results provide evidence that LA has the potential to normalize copper metabolism in AD.

CO2 emission intensity of the Estonian DH sector

Abstract: District heating (DH) widespread in Estonia provides at a national level the most efficient opportunity to achieve the objectives of primary energy efficiency, increasing the percentage of renewable energy and reducing the CO 2 emissions. All previous calculations of CO 2 intensity of Estonian DH were performed only based on statistics published by Eurostat and Statistics Estonia. To increase accuracy of initial data and receive results for specific DH networks the real operational data of main Estonian DH networks were collect for year 2020. Calculations are performed using power bonus calculation method and proportional distribution method. Special attention is paid on CO 2 emission factors of different fuels and energy inputs to the DH systems. One of the main issues discussed is definition of waste heat and applicability of CO 2 emission factors. Depending on the methodology used to calculate the weighted average CO 2 emission factor for DH sector, the factor is either −19.8 kgCO 2 /MWh heat (‘power bonus’ method) or 85.6 kgCO 2 /MWh heat (proportional distribution). Revised and clarified main steps for calculation of DH CO 2 emission factors presented in this article assumed to be used by the members of Estonian Power and Heat Association. Common calculation approach will allow transparent benchmarking of Estonian DH systems and can be used as a good way to inform DH consumers about the CO 2 intensity and sustainability of specific DH networks as well as DH sector in general. • Two main calculation approaches for CO 2 emission factor calculations (the ‘power bonus' method and proportional allocation of CO 2 emissions between electricity and heat) are used. • In DH systems 74.1% of heat is produced from waste heat and renewables. Fossil fuels account for 25.9%. • Average CO 2 emission factor for Estonian DH sector is either −19.8 kgCO 2 /MWh heat (‘power bonus’ method) or 85.6 kgCO 2 /MWh heat (proportional allocation). • In DH systems where heat is produced only by boilers and/or using waste heat (cogenerated heat not used), heat consumption was 26% of total heat consumption, with a average CO 2 emission factor of 33.1 kgCO 2 /MWh heat . • For DH systems with cogeneration, average CO 2 emission factor is either −38.4 kgCO 2 /MWh heat (‘power bonus’ method) or 104 kgCO 2 /MWh heat (proportional allocation).

Energy governance as a commons: Engineering alternative socio-technical configurations

Abstract: Transitioning into a sustainable energy system is becoming ever more pressing as the reality of an anthropogenic ecological crisis becomes difficult to ignore. Due to the complexity of the matter, proposed solutions often address the symptoms of the current socioeconomic configuration rather than its core. To conceptualise possible future energy systems, this Perspective focuses on the disconnect between science and technology and engineering studies. On the one hand, this disconnect leads to social science research that passively critiques rather than contributes to tackling societal issues in practice. On the other, it produces technical work limited by the incumbent conceptualisations of economic activity and organisational configurations around production without capturing the broader social and political dynamics. We thus propose a schema for bridging this divide that uses the “commons” as an umbrella concept. We apply this framework on the hardware aspect of a conceptual energy system, which builds on networked microgrids powered by open-source, lower cost, adaptable, socially responsible and sustainable technology. This Perspective is a call to engineers and social scientists alike to form genuine transdisciplinary collaborations for developing radical alternatives to the energy conundrum.

Auto-generation of Smart Contracts from a Domain-Specific XML-Based Language

Abstract: Smart contracts are a means of facilitating, verifying and enforcing digital agreements. Blockchain technology, which includes an inherent consensus mechanism and programming languages, enables the concept of smart contracts. However, smart contracts written in an existing language, such as Solidity, Vyper, and others, are difficult for domain stakeholders and programmers to understand in order to develop code efficiently and without error, owing to a conceptual gap between the contractual provisions and the respective code. Our study addresses the problem by creating smart legal contract markup language (SLCML), an XML-based smart-contract language with pattern and transformation rules that automatically convert XML code to the Solidity language. In particular, we develop an XML schema (SLCML schema) that is used to instantiate any type of business contract understandable to IT and non-IT practitioners and is processed by computers. To reduce the effort and risk associated with smart contract development, we advocate a pattern for converting SLCML contracts to Solidity smart contracts, a smart contractual oriented computer language. We exemplify and assess our SLCML and transformation approach by defining a dairy supply chain contract based on real-world data.

Assignment of a Synthetic Population for Activity-Based Modeling Employing Publicly Available Data

Abstract: Agent-based modeling has the potential to deal with the ever-growing complexity of transport systems, including future disrupting mobility technologies and services, such as automated driving, Mobility as a Service, and micromobility. Although different software dedicated to the simulation of disaggregate travel demand have emerged, the amount of needed input data, in particular the characteristics of a synthetic population, is large and not commonly available, due to legit privacy concerns. In this paper, a methodology to spatially assign a synthetic population by exploiting only publicly available aggregate data is proposed, providing a systematic approach for an efficient treatment of the data needed for activity-based demand generation. The assignment of workplaces exploits aggregate statistics for economic activities and land use classifications to properly frame origins and destination dynamics. The methodology is validated in a case study for the city of Tallinn, Estonia, and the results show that, even with very limited data, the assignment produces reliable results up to a 500 × 500 m resolution, with an error at district level generally around 5%. Both the tools needed for spatial assignment and the resulting dataset are available as open source, so that they may be exploited by fellow researchers.

Austerity and the use of performance information in the budget process

Abstract: IMPACTUsing evidence from Austria, Ireland and Portugal, the authors show that, although the experience of a fiscal crisis can act as a useful trigger for adopting performance budgeting reforms, the context of fiscal stress and austerity does not offer a fertile ground for implementing reforms. In addition, it can undermine the use of performance information in budgetary decision-making. This article will help policy-makers and practitioners to develop realistic expectations about the impacts of performance budgeting in a climate of austerity and fiscal stress.

Urban Open Platform for Borderless Smart Cities

Abstract: As a network of connected sensors to transform data into knowledge, Urban Platforms have been rooted in several smart city projects. However, this has often resulted in them being no more than IoT dashboards. More recently, there has been an increased interest in supporting the data governance and distributed architecture of Urban Platforms in order to adjust these with the administrative structure in a specific city. In addition, Urban Platforms also deal with data roaming between different stakeholders including other cities, different government levels, companies and citizens. Nevertheless, the first deployments have led to an inflexible “smart cities in a box” approach that does not help with building digital skills and causes vendor lock-in to products that do not scale. There is a need to start with simple and widespread urban services through a collaborative joint cross-border, hands-on effort. In order to meet the level of interoperability, international standards should be adopted. The aim of an Urban Open Platform (UOP), introduced in this paper, is to support not only data acquisition but also various types of data processing: data is aggregated, processed, manipulated and extended within the city context. Conceptually, special attention has been put on scalability, roaming and reliability in urban environments. This article introduces the UOP uniquely in the cross-border data exchange context of two European capital cities, Helsinki and Tallinn, and validates it with 10 real-life urban use cases.

Causes of the extensive hypoxia in the Gulf of Riga in 2018

Abstract: Abstract. The Gulf of Riga is a relatively shallow bay connected to the deeper central Baltic Sea (Baltic Proper) via straits with sills. The decrease in the near-bottom oxygen levels from spring to autumn is a common feature in the gulf, but in 2018, extensive hypoxia was observed. We analyzed temperature, salinity, oxygen, and nutrient data collected in 2018, along with historical data available from environmental databases. Meteorological and hydrological data from the study year were compared with their long-term means and variability. We suggest that pronounced oxygen depletion occurred in 2018 due to a distinct development of vertical stratification. Seasonal stratification developed early and was stronger in spring–summer 2018 than on average due to high heat flux and weak winds. Dominating northeasterly winds in early spring and summer supported the inflow of saltier waters from the Baltic Proper that created an additional deep pycnocline restricting vertical transport between the near-bottom layer (NBL) and the water column above. The estimated oxygen consumption rate in the NBL in spring–summer 2018 was about 1.7 mmolO2m-2h-1, which exceeded the oxygen input to the NBL due to advection and vertical mixing. Such a consumption rate leads to near-bottom hypoxia in all years when vertical mixing in autumn reaches the seabed later than on average according to the long-term (1979–2018) meteorological conditions. The observed increase in phosphate concentrations in the NBL in summer 2018 suggests a significant sediment phosphorus release in hypoxic conditions counteracting the mitigation measures to combat eutrophication. Since climate change projections predict that meteorological conditions comparable to those in 2018 will occur more frequently, extensive hypoxia would be more common in the Gulf of Riga and other coastal basins with similar morphology and human-induced elevated input of nutrients.

Security Issues and Application of Blockchain

Abstract: Blockchain is the most important IT invention in current technology. Blockchain is much secured, easily shared and works with various distributed ledgers. Blockchain is changing the working environment from centralized to decentralize. Blockchain has removed the problem of single point of failure (SPOF). In the blockchain, you can easily track all previous transactions and can validate future transactions. Due to various benefits in blockchain, the number of organizations works on blockchain technology for providing solutions and many others are working on security issues in blockchain like 51% vulnerability, private key security, double spending, criminal activities, transaction leakage, smart contracts and many others.