First-principles calculations of native defects in tetrahedrally-coordinated isovalent semiconductors

This thesis describes the development, the application and the analysis of the accuracy of state-of-the-art ab initio calculations in the description of intrinsic point defects in technologically important tetrahedrally coordinated isovalent semiconductors. The calculations presented in this thesis are based on the density-functional theory. The effective single-particle equations derived from the density-functional theory in the Kohn-Sham scheme are solved numerically using the plane-wave basis representation of the valence electrons and the pseudopotential description of the core electrons. The use of the plane-wave basis enforces periodic boundary conditions. The calculation of the properties of isolated defects within periodic boundary conditions is customarily referred to as the supercell approximation. The supercell method is analyzed in detail in the thesis, with a special emphasis on the calculation of charged point defects. The developments in the numerical methods presented in this thesis include the implementation of a non-local screened-exchange operator for the improved description of the exchange and correlation energy and a non-uniform charge-compensation scheme for charged point defects in a massively-parallel plane-wave pseudopotential software package. The included papers present the most accurate numerical electronic structure calculations to date for vacancies in silicon and silicon-germanium, and for interstitials in silicon carbide.reviewe

The extratropical transition of Hurricane Ophelia (2017) as diagnosed with a generalized omega equation and vorticity equation

Hurricane Ophelia was a category 3 hurricane which underwent extratropical transition and made landfall in Europe as an exceptionally strong post-tropical cyclone in October 2017. In Ireland, Ophelia was the worst storm in 50 years and resulted in significant damage and even loss of life. In this study, the different physical processes affecting Ophelia’s transformation from a hurricane to a mid-latitude cyclone are studied. For this purpose, we have developed software that uses OpenIFS model output and a system consisting of a generalized omega equation and vorticity equation. By using these two equations, the atmospheric vertical motion and vorticity tendency are separated into the contributions from different physical processes: vorticity advection, thermal advection, friction, diabatic heating, and the imbalance between the temperature and vorticity tendencies. Vorticity advection, which is often considered an important forcing for the development of mid-latitude cyclones, is shown to play a small role in the re-intensification of the low-level cyclone. Instead, our results show that the adiabatic upper-level forcing was strongly amplified by moist processes, and thus, the diabatic heating was the dominant forcing in both the tropical and extratropical phases of Ophelia. Furthermore, we calculated in more detail the diabatic heating contributions from different model parameterizations. We find that the temperature tendency due to the convection scheme was the dominant forcing for the vorticity tendency during the hurricane phase, but as Ophelia transformed into a mid-latitude cyclone, the microphysics temperature tendency, presumably dominated by large-scale condensation, gradually increased becoming the dominant forcing once the transition was complete. Temperature tendencies caused by other diabatic processes, such as radiation, surface processes, vertical diffusion, and gravity wave drag, were found to be negligible in the development of the storm.Hurricane Ophelia was a category 3 hurricane which underwent extratropical transition and made landfall in Europe as an exceptionally strong post-tropical cyclone in October 2017. In Ireland, Ophelia was the worst storm in 50 years and resulted in significant damage and even loss of life. In this study, the different physical processes affecting Ophelia's transformation from a hurricane to a mid-latitude cyclone are studied. For this purpose, we have developed software that uses OpenIFS model output and a system consisting of a generalized omega equation and vorticity equation. By using these two equations, the atmospheric vertical motion and vorticity tendency are separated into the contributions from different physical processes: vorticity advection, thermal advection, friction, diabatic heating, and the imbalance between the temperature and vorticity tendencies. Vorticity advection, which is often considered an important forcing for the development of mid-latitude cyclones, is shown to play a small role in the re-intensification of the low-level cyclone. Instead, our results show that the adiabatic upper-level forcing was strongly amplified by moist processes, and thus, the diabatic heating was the dominant forcing in both the tropical and extratropical phases of Ophelia. Furthermore, we calculated in more detail the diabatic heating contributions from different model parameterizations. We find that the temperature tendency due to the convection scheme was the dominant forcing for the vorticity tendency during the hurricane phase, but as Ophelia transformed into a mid-latitude cyclone, the microphysics temperature tendency, presumably dominated by large-scale condensation, gradually increased becoming the dominant forcing once the transition was complete. Temperature tendencies caused by other diabatic processes, such as radiation, surface processes, vertical diffusion, and gravity wave drag, were found to be negligible in the development of the storm.Peer reviewe

OZO v.1.0 : software for solving a generalised omega equation and the Zwack-Okossi height tendency equation using WRF model output

A software package (OZO, Omega-Zwack-Okossi) was developed to diagnose the processes that affect vertical motions and geopotential height tendencies in weather systems simulated by the Weather Research and Forecasting (WRF) model. First, this software solves a generalised omega equation to calculate the vertical motions associated with different physical forcings: vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term between vorticity and temperature tendencies. After this, the corresponding height tendencies are calculated with the Zwack-Okossi tendency equation. The resulting height tendency components thus contain both the direct effect from the forcing itself and the indirect effects (related to the vertical motion induced by the same forcing) of each physical mechanism. This approach has an advantage compared with previous studies with the Zwack-Okossi equation, in which vertical motions were used as an independent forcing but were typically found to compensate the effects of other forcings. The software is currently tailored to use input from WRF simulations with Cartesian geometry. As an illustration, results for an idealised 10-day baroclinic wave simulation are presented. An excellent agreement is found between OZO and the direct WRF output for both the vertical motion and the height tendency fields. The individual vertical motion and height tendency components demonstrate the importance of both adiabatic and diabatic processes for the simulated cyclone. OZO is an open-source tool for both research and education, and the distribution of the software will be supported by the authors.Peer reviewe

Lähiruoan tie kauppaan ja kuluttajan ostoskoriin – opas lähiruokatuottajille ja kauppiaille

Lähiruoan tie kauppaan ja kuluttajan ostoskoriin – opas lähiruokatuottajille ja kauppiaille Paikallisella ruokatuotannolla on tärkeä merkitys huoltovarmuuden ja aluetalouden kannalta. Paikallisten elintarvikeyritysten kilpailuetuja ovat puhtaat raaka-aineet, tuotteiden jäljitettävyys, vastuulliset ja joustavat toimintatavat sekä mahdollisuudet erikoistua. Paikallinen ruoka, lähiruoka, luo työllisyyden lisäksi myös alueen ruokakulttuuria. Mutta tiedämmekö, mitä erilaiset kuluttajat haluavat ostoskoriinsa? Tuottavatko paikalliset lähiruokatuottajat juuri näitä tuotteita, ja mistä he saavat siitä tietoa? Mistä kauppa löytää näitä paikallisia tuotteita valikoimiinsa? Ovatko pienet elintarvikeyritykset valmiita yhteistyöhön kuluttajien ja kauppojen kanssa? Ovatko kaupat valmiita yhteiseen palvelutarjoamaan pienten elintarvikeyritysten kanssa? Tällä oppaalla haluamme tuoda esiin asioita, jotka vaikuttavat lähiruoan matkaan päivittäistavarakauppaan ja sieltä kuluttajan ostoskoriin. Tuomme oppaassa Hämäläinen lähiruokadialogi – lähiruokaa kestävästi kauppaan ja kuluttajalle -hankkeen tuloksia paikallisten kuluttajien, lähiruokatoimijoiden sekä kauppiaiden näkökulmasta. Tätä maaseuturahaston hanketta toteutettiin ajalla 1.1.2021–31.3.2023 yhteistyössä Hämeen ammattikorkeakoulun, Teknologian tutkimuskeskus VTT Oy:n sekä Kauppavalmennus Oy:n kanssa

Simulating dust emissions and secondary organic aerosol formation over northern Africa during the mid-Holocene Green Sahara period

Paleo-proxy data indicate that a “Green Sahara” thrived in northern Africa during the early- to mid-Holocene (MH; 11 000 to 5000 years before present), characterized by more vegetation cover and reduced dust emissions. Utilizing a state-of-the-art atmospheric chemical transport model, TM5-MP, we assessed the changes in biogenic volatile organic compound (BVOC) emissions, dust emissions and secondary organic aerosol (SOA) concentrations in northern Africa during this period relative to the pre-industrial (PI) period. Our simulations show that dust emissions reduced from 280.6 Tg a−1 in the PI to 26.8 Tg a−1 in the MH, agreeing with indications from eight marine sediment records in the Atlantic Ocean. The northward expansion in northern Africa resulted in an increase in annual emissions of isoprene and monoterpenes during the MH, around 4.3 and 3.5 times higher than that in the PI period, respectively, causing a 1.9-times increase in the SOA surface concentration. Concurrently, enhanced BVOC emissions consumed more hydroxyl radical (OH), resulting in less sulfate formation. This effect counteracted the enhanced SOA surface concentration, altogether leading to a 17 % increase in the cloud condensation nuclei at 0.2 % super saturation over northern Africa. Our simulations provide consistent emission datasets of BVOCs, dust and the SOA formation aligned with the northward shift of vegetation during the “Green Sahara” period, which could serve as a benchmark for MH aerosol input in future Earth system model simulation experiments.Peer reviewe