Lokaliseerunud fotosünteetilised eksitonid

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Peaaegu kogu inimkonna poolt tarbitav toit ja näiteks ka fossiilsed kütused on toodetud elusorganismide poolt kinnipüütud päikesevalguse abil. Elusloodus on suutnud sellel viisil päikeseenergiat koguda juba miljardeid aastaid ja väga suures mastaabis, saades samas hakkama väga väheste vahenditega. See kõik on võimalik tänu elusorgamismide võimele paigutada aatomeid väga täpselt mõnenanomeetrise suurusega struktuurideks. Purpurbakterid on ühed vanimad organismid Maal, kes on võimelised päikesevalgust koguma ja enda toitmiseks kasutama. Bakterid on miljardite aastate jooksul suutnud välja töötada väga keerukaid energiakogumise meetodeid, mida saaks ka inimtehnoloogias kasutada. Nende süsteemide mõistmise keerukus tuleneb nende toimimise aluseks olevast kvantmehaanikast, mis tavaliselt avaldub äärmiselt korrapärastes tingimustes (nagu pooljuhtkristallides) väga madalatel temperatuuridel (nagu heeliumi keemistemperatuuril -270 °C juures). Selles töös proovisime edendada arusaamu purpurbakterite valgust koguvate antennisüsteemide tööpõhimõtete kohta. Me suutsime tõestada, et need väikesed nanostruktuurid suudavad footoneid kinni püüda ja neid kvaasiosakesteks (eksitonideks) muundada. Neid eksitone saab siis transportida ja keemilise energiana salvestada. Tuleb välja, et see on siiski võimalik, kuigi tingimused eluslooduses on väga kaugel tingimustest, mis valitsevad pooljuhtkristallides absoluutse nulltemperatuuri lähedal. Uurimus põhines optilise spektroskoopia ja kvantmehaanilise modelleerimise ühendamisel. Koostatud mudel võimaldab ka seletada erinevusi üksikute valgust koguvate komplekside vahel, mis varem on põhjustanud eksperimentaalsete andmete väärtõlgendamist. Kokkuvõttes jõudsime paremale arusaamale nende komplekside tööst ja loodetavasti saab tulevikus nende tööpõhimõtteid rakendada ka inimkonna energiavajaduse rahuldamisel.Virtually all of the food consumed by humans and, for example, fossil fuels, have been produced by capturing sunlight and storing it as chemical energy in the process of photosynthesis. Living nature has been able to collect solar energy this way for billions of years and in very large scales, managing at the same time to do this with very common chemical elements. This is possible thanks to living nature’s ability to place atoms into complex arrangements on the scale of a few nanometres. Purple bacteria are possibly the oldest organisms on the Earth capable of harvesting the sunlight to feed themselves. During billions of years, bacteria have developed very complex methods for energy capture that could also prove useful in human technology. The complexity in understanding these systems lies in the fact that their operation is based on quantum mechanical effects, which ordinarily exhibit in highly regular systems (such as semiconductor crystals) at extremely low temperatures, such as at the boiling point of liquid helium (-270 °C). In this work, we tried to expand our understanding of the mechanisms behind the functioning of the light-harvesting complexes of purple bacteria. We managed to prove that these small nanostructures are capable of collecting solar photons and forming them into excitons that can then be transported and captured as chemical energy. This happens despite being far from the conditions present at near absolute zero temperature semiconductor crystals. For proving this, we used optical spectroscopy and quantum mechanical modelling. The model developed in this work also explains the microscopic differences between individual light-harvesting complexes, which have earlier caused misunderstanding and misinterpretation of experimental data from these complexes. This all has led to a better understanding of the operation of these complexes and hopefully the models can be used in the future to fulfil humanity’s energy needs

Low Albedo Surfaces of Lava Worlds

Hot super Earths are exoplanets with short orbital periods ($<$ 10 days), heated by their host stars to temperatures high enough for their rocky surfaces to become molten. A few hot super Earths exhibit high geometric albedos ($>$ 0.4) in the Kepler band (420-900 nm). We are motivated to determine whether reflection from molten lava and quenched glasses (a product of rapidly cooled lava) on the surfaces of hot super Earths contributes to the observationally inferred high geometric albedos. We experimentally measure reflection from rough and smooth textured quenched glasses of both basalt and feldspar melts. For lava reflectance values, we use specular reflectance values of molten silicates from non-crystalline solids literature. Integrating the empirical glass reflectance function and non-crystalline solids reflectance values over the dayside surface of the exoplanet at secondary eclipse yields an upper limit for the albedo of a lava-quenched glass planet surface of $\sim$0.1. We conclude that lava planets with solid (quenched glass) or liquid (lava) surfaces have low albedos. The high albedos of some hot super Earths are most likely explained by atmospheres with reflective clouds (or, for a narrow range of parameter space, possibly Ca/Al oxide melt surfaces). Lava planet candidates in TESS data can be identified for follow-up observations and future characterization.Comment: 18 pages, 14 figures, 4 tables, published in Ap

Design of a Scientific-Grade Multispectral Imager for Nanosatellites

Applications in agriculture, land-cover change, and vegetation phenology, to name a few, would benefit from more frequent high-quality remote sensing data. However, ”Landsat-class” satellites are too expensive for such applications. Therefore, there is a need to augment larger Earth observation satellites with nanosatellites that use scientific-grade imaging instruments. This paper presents the design for the scientific-grade multispectral imager Theia. It is designed for a 5% radiometric accuracy at a ground sampling distance of 33 m at a 650 km orbit while keeping the modulation transfer function above 0.13 at the Nyquist frequency. The camera has reflective optics with an aluminium optomechanical design to mitigate stress from thermal expansion. Furthermore, the optical path is covered with a mix of black anodization and Acktar Magic Black to suppress stray-light. The sCMOS sensor is back-side illuminated to increase the radio metric quality of the instrument. Furthermore, the imager has a post-launch calibration system for continuous monitoring of the instrument’s quality. The performance is achieved while fitting inside 0.6 CubeSat Units and weighing about 600 g. However, a trade-off between the modulation transfer function and radio metric quality is presented. Such an imager, when deployed on numerous nanosatellites, can enable new kinds of missions that are otherwise too costly. The project is funded by the European Space Agency

Optical Periscopic Imager for Comets (OPIC) Instrument for the Planned Comet Interceptor Mission

This poster presents an update on the development of the Optical Periscopic Imager for Comets (OPIC) instrument [1], which will be hosted on one of three spacecraft making up the Comet Interceptor ESA-JAXA mission [2]. OPIC is a compact ( \u3c 0.5 kg) monochromic camera for taking images of the nucleus and coma of either a long-period or dynamically new comet, or an interstellar object for mapping, reconstruction and localisation purposes. The camera will operate in a harsh environment with continuous dust impacts throughout its multi-day operation; therefore, the instrument is equipped with a periscope, which protects optics from high-velocity impacts. The probe is spin-stabilised at 4-15 RPM and will be parked in Lagrange point L2 (launched with ARIEL telescope) and depart at a suitable time to intercept a target at velocity 10-70 km/s. The closest approach is approximately 400 km

Experimental Preservation of Muscle Tissue in Quartz Sand and Kaolinite

Siliciclastic sediments of the Ediacaran Period contain exceptionally preserved fossils of macroscopic organisms, including three-dimensional casts and molds commonly found in sandstones and siltstones and some two-dimensional compressions reported in shales. The sporadic and variable associations of these exceptionally preserved macroscopic fossils with pyrite, clay minerals, and microbial fossils and textures complicate our understanding of fossilization processes. This hinders inferences about the evolutionary histories, tissue types, original morphologies, and lifestyles of the enigmatic Ediacara biota. Here, we investigate the delayed decay of scallop muscles buried in quartz sand or kaolinite for 45 days. This process occurs in the presence of microbial activity in mixed redox environments, but in the absence of thick, sealing microbial mats. Microbial processes that mediate organic decay and release the highest concentrations of silica and Fe(II) into the pore fluids are associated with the most extensive tissue decay. Delayed decay and the preservation of thick muscles in sand are associated with less intense microbial iron reduction and the precipitation of iron oxides and iron sulfides that contain Fe(II) or Fe(III). In contrast, muscles buried in kaolinite are coated only by <10 μm-thick clay veneers composed of kaolinite grains and newly formed K- and Fe(II)-rich aluminosilicate phases. Muscles that undergo delayed decay in kaolinite lose more mass relative to the muscles buried in sand and undergo vertical collapse. These findings show that the composition of minerals that coat or precipitate within the tissues and the vertical dimension of the preserved features can depend on the type of sediment that buries the muscles. Similar processes in the zone of oscillating redox likely facilitated the formation of exceptionally preserved macrofossils in Ediacaran siliciclastic sediments

Personaalmeditsiini keskuse loomisest Eestis

Eesti Arst 2023; 102(2):76–7

Experimental Preservation of Muscle Tissue in Quartz Sand and Kaolinite

Siliciclastic sediments of the Ediacaran Period contain exceptionally preserved fossils of macroscopic organisms, including three-dimensional casts and molds commonly found in sandstones and siltstones and some two-dimensional compressions reported in shales. The sporadic and variable associations of these exceptionally preserved macroscopic fossils with pyrite, clay minerals, and microbial fossils and textures complicate our understanding of fossilization processes. This hinders inferences about the evolutionary histories, tissue types, original morphologies, and lifestyles of the enigmatic Ediacara biota. Here, we investigate the delayed decay of scallop muscles buried in quartz sand or kaolinite for 45 days. This process occurs in the presence of microbial activity in mixed redox environments, but in the absence of thick, sealing microbial mats. Microbial processes that mediate organic decay and release the highest concentrations of silica and Fe(II) into the pore fluids are associated with the most extensive tissue decay. Delayed decay and the preservation of thick muscles in sand are associated with less intense microbial iron reduction and the precipitation of iron oxides and iron sulfides that contain Fe(II) or Fe(III). In contrast, muscles buried in kaolinite are coated only by <10 μm-thick clay veneers composed of kaolinite grains and newly formed K- and Fe(II)-rich aluminosilicate phases. Muscles that undergo delayed decay in kaolinite lose more mass relative to the muscles buried in sand and undergo vertical collapse. These findings show that the composition of minerals that coat or precipitate within the tissues and the vertical dimension of the preserved features can depend on the type of sediment that buries the muscles. Similar processes in the zone of oscillating redox likely facilitated the formation of exceptionally preserved macrofossils in Ediacaran siliciclastic sediments

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with -1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.Peer reviewe

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with - 1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.</p