Tallinn University of Technology

About: Tallinn University of Technology is a education organization based out in Tallinn, Estonia. It is known for research contribution in the topics: European union & Oil shale. The organization has 3688 authors who have published 10313 publications receiving 145058 citations. The organization is also known as: Tallinn Technical University & Tallinna Tehnikaülikool.

A Review of Demand Side Flexibility Potential in Northern Europe

Abstract: The number of regional and national power systems with a high share of wind and solar power in the world is quickly increasing. The background for this development is improved technology, decreasin ...

A reference architecture for managing dynamic inter-organizational business processes

Abstract: For improving the efficiency and effectiveness of business collaboration, the need emerges to inter-organizationally match e-business services. Recent research activities show heightened attention into that direction with the ecosystems-emergence of service-oriented computing clouds. As this increases the business-, conceptual-, and technical governance complexity, a need exists for using a reference architecture to evaluate and design standard-, and concrete architectures for business-to-business (B2B) collaboration. In this paper, we fill that gap by presenting the eSourcing Reference Architecture eSRA that emerges from B2B-research projects and we check this with a scenario-based validation method. We demonstrate how eSRA enables a quick evaluation of not only research-based B2B-architectures but also of industry application suits. That way, we show the usability and applicability in that with the help of eSRA, system designers directly establish a comprehensive understanding of fundamental B2B concepts and develop higher-quality domain-specific architectures.

Premature failure of an additively manufactured material

Abstract: Additively manufactured metallic materials exhibit excellent mechanical strength. However, they often fail prematurely owing to external defects (pores and unmelted particles) that act as sites for crack initiation. Cracks then propagate through grain boundaries and/or cellular boundaries that contain continuous brittle second phases. In this work, the premature failure mechanisms in selective laser melted (SLM) materials were studied. A submicron structure was introduced in a SLM Ag–Cu–Ge alloy that showed semicoherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. This structure led to a remarkable strength of 410 ± 3 MPa with 16 ± 0.5% uniform elongation, well surpassing the strength-ductility combination of their cast and annealed counterparts. The hierarchical SLM microstructure with a periodic arrangement of precipitates and a high density of internal defects led to a high strain hardening rate and strong strengthening, as evidenced by the fact that the precipitates were twinned and encircled by a high density of internal defects, such as dislocations, stacking faults and twins. However, the samples fractured before necking owing to the crack acceleration along the external defects. This work provides an approach for additively manufacturing materials with an ultrahigh strength combined with a high ductility provided that premature failure is alleviated. An analysis of metallic alloys fabricated through layer-by-layer deposition processes has revealed critical factors in preventing these materials from unexpectedly breaking. In selective laser melting (SLM) technology, thin layers of metal powders are assembled into three-dimensional objects using rapid heating and cooling steps. Zhi Wang from the South China University of Technology in Guangzhou and colleagues now show that the microstructure of a silver-copper-germanium alloy formed through SLM can affect the material’s strength. Using optical and X-ray microscopy, the team found that regularly spaced precipitates formed inside the 3D-printed alloy prevented abrupt atomic sliding movements, giving the material a higher natural strength and good ductility. Fractures that occurred at lower than expected stress levels were identified as arising from errors in the printing process, such as pores and unmelted powder particles. A submicron structure strategy was introduced in a selective laser melted (SLM) Ag-Cu-Ge alloy, showing semi-coherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. It leads to a remarkable strength of ~410 MPa with ~16% ductility, well surpassing the strength-ductility combination of their cast counterparts. The hierarchal SLM microstructure and high density of internal defects leading to a high strain hardening rate and strong strengthening. Premature failure occurred due to the external defects, such as pores and unmelted particles. This work paves a way for additively manufacturing materials towards high strength–ductility synergy.

Toxicity of CuO nanoparticles to yeast Saccharomyces cerevisiae BY4741 wild-type and its nine isogenic single-gene deletion mutants.

Abstract: A suite of eight tentatively oxidative stress response-deficient Saccharomyces cerevisiae BY4741 single-gene mutants (sod1Δ, sod2Δ, yap1Δ, cta1Δ, ctt1Δ, gsh1Δ, glr1Δ, and ccs1Δ) and one copper-vulnerable mutant (cup2Δ) was used to elucidate weather the toxicity of CuO nanoparticles to S. cerevisiae is mediated by oxidative stress (OS). Specifically, sensitivity profiles of mutants’ phenotypes and wild-type (wt) upon exposure to nano-CuO were compared. As controls, CuSO4 (solubility), bulk-CuO (size), H2O2, and menadione (OS) were used. Growth inhibition of wt and mutant strains was studied in rich YPD medium and cell viability in deionized water (DI). Dissolved Cu-ions were quantified by recombinant metal-sensing bacteria and chemical analysis. To wt strain nano-CuO was 32-fold more toxic than bulk-CuO: 24-h IC50 4.8 and 155 mg/L in DI and 643 and >20000 mg/L in YPD, respectively. In toxicant-free YPD medium, all mutants had practically similar growth patterns as wt. However, the mutant strains sod1Δ, sod...