Browsing by department "Institutionen för fysik"

The most important parameters describing the aerosol particle population are the size, concentration and composition of the aerosol particles. The size and water content of the aerosol particles are dependent of the relative humidity of the ambient air. Hygroscopicity is a measure to describe the water absorption ability of an aerosol particle. Volatility of an aerosol defines how the aerosol particles behave as a function of temperature. A Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) is an instrument for size-selected investigation of particle number concentration, volatility, hygroscopicity and the hygroscopicity of the particle core, i.e. what is left of the particle after the volatilization. While knowing these qualities of aerosol particles, one can predict their behavior in different atmospheric conditions. Volatility and hygroscopicity can also be used for indirect analysis of chemical composition. The aim of this study was to build and characterize a VH-TDMA, and report the results of its field deployment at the California Nexus (CalNex) 2010 measurement campaign. The calibration measurements validated that with the VH-TDMA one can obtain accurate volatility and hygroscopicity measurements for particles between 20 nm and 145 nm. The CalNex 2010 results showed that the instrument is capable in field measurements at varying measurement conditions; and valuable data about hygroscopicty, volatility and the mixing state of several types of aerosols were measured. The data obtained was in line with the observations based on the data measured with other instruments.

The Kara Sea is part of the seasonal sea ice zone in the Arctic, where the warming climate is rapidly changing the sea ice regime. The warm Atlantic water transported through the Barents Sea has a strong influence on the ice conditions in the northern Kara Sea. In this thesis, trends and interannual variability in sea ice conditions in the Kara Sea area studied. For this purpose, coupled sea ice-ocean model NEMO-LIM3 and sea ice concentration datasets derived from passive microwave satellite observations (SMMR, SSM/I and SSMIS) are used. Additionally, the model performance is assessed by comparing its output with the observations. The ice coverage examined in regional and local scales shows negative trends in all months in 1978-2015. The interannual variability of the total ice covered fraction increased in winter and spring when the ice regime shifted from full to partial ice cover over the sea. Meanwhile the variability in summer and autumn decreased. The annual ice free time rapidly extended in the area north of Novaya Zemlya where the warm Atlantic water enters the Kara Sea. The mean sea ice thickness, based on the sea ice-ocean model data in 1997-2015, has become thinner in all months. The model is generally in good agreement with the observations, with the exception of the northern Kara Sea where the model underestimated heat advection. The findings confirm that the sea ice conditions in the Kara Sea have changed towards a new regime with shorter and more variable ice seasons.

Flavour violating processes have never been observed for charged leptons, electron, muon and tau. The existence of charged lepton flavour violating (CLFV) processes is however expected, since flavour is violated by all the other fermions of the standard model (SM). In the standard model the neutrinos are massless, which forbids the mixing of neutrino flavour and also the violation of lepton flavour. The zero mass of the neutrinos in the SM is in conflict with the experimentally observed neutrino oscillations. The standard model has to be extended to include massive neutrinos. The easiest way to explain the neutrino mass is to assume that they acquire masses in the same way as the rest of the SM fermions: in the Higgs mechanism. This way however leads to problems with the naturality of the neutrino Yukawa coupling. One of the most popular methods of generating the neutrino mass is the so called seesaw mechanism (type-I). The standard model, extended with the neutrino masses, allows the charged lepton flavour to be violated. This leads to unobservably small transition rates however. Therefore an observation of charged lepton flavour violating process would be a clear evidence of the existence of new physics beyond the standard model and it's trivial extensions. To have hope of ever observing charged lepton flavour violating processes, there must be an extension of the standard model which produces observable, though small, rates for CLFV processes. One of the most popular extensions of the standard model is the so called minimal supersymmetric standard model (MSSM). The neutrinos are massless in the MSSM, as they are in SM, and therefore CLFV processes are forbidden in the MSSM. Luckily the neutrino masses can be generated via seesaw mechanism in the MSSM as well as in the SM. The MSSM contains more potential sources for CLFV processes than the SM. The extra sources are the soft mass parameters of the sleptons. In supersymmetric models the sleptons couple to the leptons through the slepton-lepton-gaugino-vertices. These generate the CLFV processes at the loop-level. Often the off-diagonal soft terms are assumed zero in the MSSM at the input scale, where the supersymmetry breaks. Experiments are done at much lower electroweak scale. The soft SUSY-breaking terms acquire large radiative corrections as they are run from the input scale down to the electroweak scale. Here the seesaw mechanism kicks in. The seesaw mechanism brings with it the off-diagonal neutrino Yukawa coupling matrices. This allows the off-diagonal slepton mass terms to evolve non-zero at the electroweak scale. In this thesis the charged lepton flavour violation is discussed first in the context of the standard model. Then the CLFV processes, l_i → (l_j γ), l_i → (l_j l_k l_l) and l_i ↔ l_j, are studied in the most general way: in the effective theories. Finally the charged lepton flavour violation is studied in the supersymmetric theories in general and more specifically in the minimal supersymmetric standard model extended with the seesaw mechanism (type-I).

In the upgraded CMS pixel detector (phase II upgrade), the pixel size will become smaller due to the higher occupancy caused by higher luminosity of the LHC. This means that also the bump bonds between the sensor and the read-out circuit will become smaller, which results in smaller gap between the sensor and the ROC. This will increase the probability for electrical sparking that might destroy the ROC, the sensor or both. Jaakko Härkönen has suggested using alumina passivation on the modules for sparking prevention. In this thesis it was studied whether bonding is applicable on a surface having an alumina passivation. It was also of interest, which parameters of the bonder make stronger bonds. Bonding was tested on metal pads with different layer thicknesses of alumina: 0 nm, 10 nm, 15 nm, 20 nm and 25 nm. The strengths of the bonds were tested using the bond pull test. The results indicate that wire-bonding on alumina does well in pull-strength tests, though the bonds are slightly weaker than on surfaces with no alumina. Increasing bonding force seems to weaken the bonds, increasing bonding power, on the other hand seems to make stronger bonds. The conclusion of this thesis is that alumina is a viable choice for passivation, since it does not seem to have a negative effect on the module wire bonding.

This Master’s Thesis deals with stellar magnetic activity, both as it is seen in the Sun, our closest star, and in other, more extreme examples of stellar activity. For the Sun, much higher quality data is available, and for a much longer time, so it remains by far the best studied star, although stars, that are much more magnetically active, have been discovered. This thesis will review the most common forms of magnetic activity, as observed both in the Sun and in other stars. A special focus is given to BY Draconis -type stars. These are young stars, whose photometric brightness variations are caused by large, cool starspots, similar to the sunspots seen on the Sun. A particular BY Draconis -star, V889 Herculis, is analysed in detail, using spectroscopic and photometric methods. From spectroscopy, by the Doppler imaging method, a surface temperature map can be constructed for the star. From photometry, both short-term and long-term variations of the star can be studied. During the 20 years time span of the photometric data, the star seems to have gone through similar activity cycles as the well known 11 year solar cycle. The aim of this thesis is to compare solar and stellar activity in general, and specifically V889 Her to the Sun. Based on the analysis, the basic properties of V889 Her, seen in previous studies, are confirmed: a large polar spot is present on its surface, and there are clear changes in its activity. As the stellar parameters, like mass and surface temperature, of V889 Her are very similar to the Sun, and it is also a single star, the main difference is age. As a young star, V889 Her is still magnetically much more active than the Sun today, but probably it will continue to become more and more similar to the present Sun, losing its high activity with increasing age. Similarly, V889 Her shows us what the Sun most likely was like billions of years ago.

Ioninesteet ovat suoloja, joilla on matala sulamislämpötila (alle noin 100 °C). Niillä on useita hyödyllisiä ominaisuuksia ja lukuisia mahdollisia sovelluksia. Tarkempi tieto ioninesteiden atomitason rakenteesta on kuitenkin tärkeää niiden ominaisuuksien ja mahdollisuuksien ymmärtämiseksi sekä sovellusten kehittämiseksi. Tässä työssä tutkittiin 1-3-dimetyyli-imidazoliumkloridia ([mmim]Cl), joka on molekyylimassaltaan kevyt prototyyppinen ionineste. Tässä tutkielmassa hyödynnettiin epäelastista röntgensirontaa uuden informaation saamiseksi. Epäelastisessa röntgensironnassa fotoni siroaa elektronisysteemistä luovuttaen sekä energiaa että liikemäärää. Fotonin epäelastista sirontaa kutsutaan Compton-sironnaksi, kun energian- ja liikemääränsiirto on suuri. Compton-sirontaa voidaan käyttää aineen atomi- ja molekyylitason rakenteen tutkimisessa, sillä Compton-sirontakokeissa määritettävä suure, Compton-profiili, on herkkä atomien välisen geometrian muutoksille. Mittaustulosten tulkinta on kuitenkin haastavaa ja laskennallisella mallintamisella on siinä suuri rooli. Tässä tutkielmassa laskettiin [mmim]Cl:n neste- ja kidefaasien isotrooppisten Compton-profiilien erotus (erotusprofiili). Tiettyjen oletusten ollessa voimassa Compton-profiili riippuu elektronien liikemäärätiheydestä, joten profiilit voidaan määrittää aineen perustilaa kuvaavien elektronirakennelaskujen avulla. Tässä tutkielmassa elektronirakennelaskuissa käytettiin Kohn-Sham-tiheysfunktionaaliteoriaa, periodisia reunaehtoja ja Gaussisia kantajoukkoja elektronitiloille. Lisäksi laskennan tarkkuuteen vaikuttavia tekijöitä arvioitiin. Liikemäärähilan tiheydellä sekä vaihto-korrelaatiofunktionaalin ja kantajoukon valinnalla havaittiin olevan suuri vaikutus laskettuun erotusprofiiliin. Nämä tekijät olivat selkeästi merkittävämpiä kuin nesterakenteiden äärellisestä määrästä johtuva tilastollinen epätarkkuus. Erotusprofiilin tulkitsemiseksi kiderakenteesta otettuun yhteen [mmim]Cl-ionipariin tehtiin muutoksia käytetyn nesterakenteen perusteella ja tarkasteltiin näiden muutosten vaikutusta Compton-profiiliin. Sekä molekylääristen ionien sisäisen rakenteen että ionien välisen geometrian muutosten havaittiin vaikuttavan merkittävästi laskettuun erotusprofiiliin. Tässä työssä esitetyt tulokset auttavat kokeellisen erotusprofiiliin tulkinnassa ja selittämisessä.

Cytochrome bc1, also known as complex III, is the third enzyme of the electron transfer chain in cellular respiration, which is the main process generating energy in living cells. Complex III operates by oxidizing ubiquinol, and transferring two electrons to cytochrome c, while reducing ubiquinone. The electron transfer is coupled to proton translocation across the inner mitochondrial membrane. Thus, complex III contributes to generation of a proton electrochemical gradient, which is required for the function of ATP synthase. Cardiolipins (CLs), constituting up to 20 mol % of lipids in the inner mitochondrial membrane, have an important role in the structure and dynamics of the membrane, as well as in maintaining the correct function of the whole electron transfer chain. Cardiolipins are especially vulnerable to oxidation by reactive oxygen species (ROS) due to their dimeric structure with four doubly unsaturated acyl chains. Cytochrome bc1 is one of the main producers of ROS in mitochondria, increasing the exposure of tightly bound CLs to oxidation. Oxidative stress and CL oxidation have been associated with, for instance, programmed cell death and aging, and developing Alzheimer's and Parkinson's diseases. The objective of this thesis was to build a new computational model of cytochrome bc1 in a membrane, and to study the lipid interactions of complex III using atomistic molecular dynamics simulations. A model system with a high-resolution structure of complex III, embedded in a multicomponent bilayer mimicking the inner mitochondrial membrane was constructed. Four atomistic simulations of 1 μs each were performed to reveal possible cardiolipin binding sites and to examine the effects of CL oxidation on the complex. Altogether, eight CL binding sites on cytochrome bc1 were found, out of which two have not been suggested previously. The key residues of each binding site were listed, to compare with earlier results, and to identify the new binding sites in detail. In order to investigate the effects of CL oxidation, carboxylic acid and hydroperoxyl groups were attached to the acyl chains of three crystallographically resolved CLs. The oxidized region of the CL tails changed the nature of interactions with the protein and the surrounding water. As the tail was oxidized, the results showed an increase in the number of water molecules surrounding it. Additionally, the oxidized tails were found to affect the configuration of CL by bending the tail towards the lipid headgroup, or by reaching out to the water interface of the opposite leaflet. Normally, the acyl chains of CL mostly interact with the nonpolar residues of the protein. After oxidation, the number of polar and charged amino acids in the vicinity of the acyl chain increased.

An aerosol is a colloid of fine solid particles or liquid droplet, in air or another gas (Hinds, 1999).The total carbon (TC) in carbonaceous aerosols can be divided into Inorganic Carbon (IC), Organic Carbon (OC) and Elemental Carbon (EC).We measured carbonaceous aerosols at theSMEAR II (Station for measuring ecosystem atmosphere relations) in southern Finland based on division of Atmospheric Sciences of University of Helsinki. The measurements were carried out continuously from 2005 using different instruments. We used a thermal-optical method to analyze carbonaceous aerosols at Hyytiälä and examineddiurnal and seasonal variation in EC, OC, TC, OC/EC ratio, black carbon (BC) and organics. We found the mean concentrations of EC and OC estimated using Sunset Lab. OCEC analyzer and BC measured using Magee scientific Aethalometer were 0.22±0.19 µgC/m3, 1.53±0.92µgC/m3 and 0.35±0.30 µg/m3 respectively. Whereas the average concentration of BC measured using MAAP was 0.2±0.2 µg/m3. We also found concentrations of EC and BC to be low in summer and high in winter, whereas, the opposite was true for OC. EC, OC and BC showed no significant diurnal cycle, but clear seasonal cycle in all carbonaceous aerosols was evident. The aerosols mass measured by aerosolmass spectrometer (AMS) showed 58% organics, 28% sulfates, 5% nitrates, 9% ammonium and less than 1% chlorides at Hyytiälä.The primary organic carbon (POC) and secondary organic carbon (SOC) estimated by EC-tracer method contributed 5% and 95% respectively to the OC concentrations at Hyytiälä. The relations between different measurement instruments showed a good agreement.

The goal of this study is to ascertain whether methane (CH4) emissions can be estimated source-wise by utilising stable isotope observations in the CarbonTracker Data Assimilation System (CTDAS). The global CH4 budget is poorly known and there are uncertainties in the spatial and temporal distributions as well as in the magnitude of different sources. In this study CTDAS-13CH4 atmospheric inverse model is developed. CTDAS-13CH4 is based on ensemble Kalman filer (EnKF) and used to estimate CH4 fluxes on a region and weekly resolution by implementing CH4 and δ13C-CH4 observations. Anthropogenic biogenic emissions (rice cultivation, landfills and waste water treatments and enteric fermentation and manure management) and anthropogenic non-biogenic emissions (coal, residential and oil and gas) are optimised. Different emission sources can be identified by using process-specific isotopic signature values, δ13C-CH4, because different processes produce CH4 with different isotopic ratio. Optimisation of anthropogenic biogenic emissions increased the total emissions from the prior in eastern North America by 34%, while the optimisation of anthropogenic non-biogenic emissions increased only by 14%. In western North America the corresponding changes were −39% and 9%, respectively. In western parts of Europe, total emissions from prior increased in anthropogenic biogenic optimisation by 18% and decreased in non-biogenic by 3%. Optimisation of anthropogenic biogenic and non-biogenic emissions in the total CH4 budget did not give complete emission estimates, because the optimisation did not include all emission sources and source-specific δ13C-CH4 values were assumed not to vary regionally. However, the modelled concentrations from the optimisation of anthropogenic non-biogenic emissions agreed with the observations of CH4 concentration and δ13C-CH4 values better. Therefore, one could say that the optimisation of anthropogenic non-biogenic emissions was more successful. This study provides reliable information of the magnitude of anthropogenic biogenic and non-biogenic emissions in regions with sufficient observational coverage. The next step in evaluating the spatial and temporal distributions and magnitude of different CH4 sources will be optimising all emission sources simultaneously in a multi-year simulation.

This thesis aims to cover the central aspects of the current research and advancements in cosmic topology from a topological and observational perspective. Beginning with an overview of the basic concepts of cosmology, it is observed that though a determinant of local curvature, Einstein's equations of relativity do not constrain the global properties of space-time. The topological requirements of a universal space time manifold are discussed, including requirements of space-time orientability and causality. The basic topological concepts used in classification of spaces, i.e. the concept of the Fundamental Domain and Universal covering spaces are discussed briefly. The manifold properties and symmetry groups for three dimensional manifolds of constant curvature for negative, positive and zero curvature manifolds are laid out. Multi-connectedness is explored as a possible explanation for the detected anomalies in the quadrupole and octopole regions of the power spectrum, pointing at a possible compactness along one or more directions in space. The statistical significance of the evidence, however, is also scrutinized and I discuss briefly the bayesian and frequentist interpretation of the posterior probabilities of observing the anomalies in a ΛCDM universe. Some of the major topologies that have been proposed and investigated as possible candidates of a universal manifold are the Poincare Dodecahedron and Bianchi Universes, which are studied in detail. Lastly, the methods that have been proposed for detecting a multi-connected signature are discussed. These include ingenious observational methods like the circles in the sky method, cosmic crystallography and theoretical methods which have the additional advantage of being free from measurement errors and use the posterior likelihoods of models. As of the recent Planck mission, no pressing evidence of a multi connected topology has been detected.