Sticking and erosion at carbon-containing plasma-facing materials in fusion reactors

Controlled nuclear fusion is one of the most promising sources of energy for the future. Before this goal can be achieved, one must be able to control the enormous energy densities which are present in the core plasma in a fusion reactor. In order to be able to predict the evolution and thereby the lifetime of different plasma facing materials under reactor-relevant conditions, the interaction of atoms and molecules with plasma first wall surfaces have to be studied in detail. In this thesis, the fundamental sticking and erosion processes of carbon-based materials, the nature of hydrocarbon species released from plasma-facing surfaces, and the evolution of the components under cumulative bombardment by atoms and molecules have been investigated by means of molecular dynamics simulations using both analytic potentials and a semi-empirical tight-binding method. The sticking cross-section of CH3 radicals at unsaturated carbon sites at diamond (111) surfaces is observed to decrease with increasing angle of incidence, a dependence which can be described by a simple geometrical model. The simulations furthermore show the sticking cross-section of CH3 radicals to be strongly dependent on the local neighborhood of the unsaturated carbon site. The erosion of amorphous hydrogenated carbon surfaces by helium, neon, and argon ions in combination with hydrogen at energies ranging from 2 to 10 eV is studied using both non-cumulative and cumulative bombardment simulations. The results show no significant differences between sputtering yields obtained from bombardment simulations with different noble gas ions. The final simulation cells from the 5 and 10 eV ion bombardment simulations, however, show marked differences in surface morphology. In further simulations the behavior of amorphous hydrogenated carbon surfaces under bombardment with D^+, D^+2, and D^+3 ions in the energy range from 2 to 30 eV has been investigated. The total chemical sputtering yields indicate that molecular projectiles lead to larger sputtering yields than atomic projectiles. Finally, the effect of hydrogen ion bombardment of both crystalline and amorphous tungsten carbide surfaces is studied. Prolonged bombardment is found to lead to the formation of an amorphous tungsten carbide layer, regardless of the initial structure of the sample. In agreement with experiment, preferential sputtering of carbon is observed in both the cumulative and non-cumulative simulations

On gravitational fields of stars in f(R) gravity theories

Einstein's general relativity is a classical theory of gravitation: it is a postulate on the coupling between the four-dimensional, continuos spacetime and the matter fields in the universe, and it yields their dynamical evolution. It is believed that general relativity must be replaced by a quantum theory of gravity at least at extremely high energies of the early universe and at regions of strong curvature of spacetime, cf. black holes. Various attempts to quantize gravity, including conceptually new models such as string theory, have suggested that modification to general relativity might show up even at lower energy scales. On the other hand, also the late time acceleration of the expansion of the universe, known as the dark energy problem, might originate from new gravitational physics. Thus, although there has been no direct experimental evidence contradicting general relativity so far - on the contrary, it has passed a variety of observational tests - it is a question worth asking, why should the effective theory of gravity be of the exact form of general relativity? If general relativity is modified, how do the predictions of the theory change? Furthermore, how far can we go with the changes before we are face with contradictions with the experiments? Along with the changes, could there be new phenomena, which we could measure to find hints of the form of the quantum theory of gravity? This thesis is on a class of modified gravity theories called f(R) models, and in particular on the effects of changing the theory of gravity on stellar solutions. It is discussed how experimental constraints from the measurements in the Solar System restrict the form of f(R) theories. Moreover, it is shown that models, which do not differ from general relativity at the weak field scale of the Solar System, can produce very different predictions for dense stars like neutron stars. Due to the nature of f(R) models, the role of independent connection of the spacetime is emphasized throughout the thesis.

Lung structure and function studied by synchrotron radiation

A novel method for functional lung imaging was introduced by adapting the K-edge subtraction method (KES) to in vivo studies of small animals. In this method two synchrotron radiation energies, which bracket the K-edge of the contrast agent, are used for simultaneous recording of absorption-contrast images. Stable xenon gas is used as the contrast agent, and imaging is performed in projection or computed tomography (CT) mode. Subtraction of the two images yields the distribution of xenon, while removing practically all features due to other structures, and the xenon density can be calculated quantitatively. Because the images are recorded simultaneously, there are no movement artifacts in the subtraction image. Time resolution for a series of CT images is one image/s, which allows functional studies. Voxel size is 0.1mm3, which is an order better than in traditional lung imaging methods. KES imaging technique was used in studies of ventilation distribution and the effects of histamine-induced airway narrowing in healthy, mechanically ventilated, and anaesthetized rabbits. First, the effect of tidal volume on ventilation was studied, and the results show that an increase in tidal volume without an increase in minute ventilation results a proportional increase in regional ventilation. Second, spiral CT was used to quantify the airspace volumes in lungs in normal conditions and after histamine aerosol inhalation, and the results showed large patchy filling defects in peripheral lungs following histamine provocation. Third, the kinetics of proximal and distal airway response to histamine aerosol were examined, and the findings show that the distal airways react immediately to histamine and start to recover, while the reaction and the recovery in proximal airways is slower. Fourth, the fractal dimensions of lungs was studied, and it was found that the fractal dimension is higher at the apical part of the lungs compared to the basal part, indicating structural differences between apical and basal lung level. These results provide new insights to lung function and the effects of drug challenge studies. Nowadays the technique is available at synchrotron radiation facilities, but the compact synchrotron radiation sources are being developed, and in relatively near future the method may be used at hospitals.

Molecular dynamics studies of nanoparticle impacts

This thesis concerns the dynamics of nanoparticle impacts on solid surfaces. These impacts occur, for instance, in space, where micro- and nanometeoroids hit surfaces of planets, moons, and spacecraft. On Earth, materials are bombarded with nanoparticles in cluster ion beam devices, in order to clean or smooth their surfaces, or to analyse their elemental composition. In both cases, the result depends on the combined effects of countless single impacts. However, the dynamics of single impacts must be understood before the overall effects of nanoparticle radiation can be modelled. In addition to applications, nanoparticle impacts are also important to basic research in the nanoscience field, because the impacts provide an excellent case to test the applicability of atomic-level interaction models to very dynamic conditions. In this thesis, the stopping of nanoparticles in matter is explored using classical molecular dynamics computer simulations. The materials investigated are gold, silicon, and silica. Impacts on silicon through a native oxide layer and formation of complex craters are also simulated. Nanoparticles up to a diameter of 20 nm (315000 atoms) were used as projectiles. The molecular dynamics method and interatomic potentials for silicon and gold are examined in this thesis. It is shown that the displacement cascade expansionmechanism and crater crown formation are very sensitive to the choice of atomic interaction model. However, the best of the current interatomic models can be utilized in nanoparticle impact simulation, if caution is exercised. The stopping of monatomic ions in matter is understood very well nowadays. However, interactions become very complex when several atoms impact on a surface simultaneously and within a short distance, as happens in a nanoparticle impact. A high energy density is deposited in a relatively small volume, which induces ejection of material and formation of a crater. Very high yields of excavated material are observed experimentally. In addition, the yields scale nonlinearly with the cluster size and impact energy at small cluster sizes, whereas in macroscopic hypervelocity impacts, the scaling 2 is linear. The aim of this thesis is to explore the atomistic mechanisms behind the nonlinear scaling at small cluster sizes. It is shown here that the nonlinear scaling of ejected material yield disappears at large impactor sizes because the stopping mechanism of nanoparticles gradually changes to the same mechanism as in macroscopic hypervelocity impacts. The high yields at small impactor size are due to the early escape of energetic atoms from the hot region. In addition, the sputtering yield is shown to depend very much on the spatial initial energy and momentum distributions that the nanoparticle induces in the material in the first phase of the impact. At the later phases, the ejection of material occurs by several mechanisms. The most important mechanism at high energies or at large cluster sizes is atomic cluster ejection from the transient liquid crown that surrounds the crater. The cluster impact dynamics detected in the simulations are in agreement with several recent experimental results. In addition, it is shown that relatively weak impacts can induce modifications on the surface of an amorphous target over a larger area than was previously expected. This is a probable explanation for the formation of the complex crater shapes observed on these surfaces with atomic force microscopy. Clusters that consist of hundreds of thousands of atoms induce long-range modifications in crystalline gold.

Studies on Binary Time Series Models with Applications to Empirical Macroeconomics and Finance

This thesis studies binary time series models and their applications in empirical macroeconomics and finance. In addition to previously suggested models, new dynamic extensions are proposed to the static probit model commonly used in the previous literature. In particular, we are interested in probit models with an autoregressive model structure. In Chapter 2, the main objective is to compare the predictive performance of the static and dynamic probit models in forecasting the U.S. and German business cycle recession periods. Financial variables, such as interest rates and stock market returns, are used as predictive variables. The empirical results suggest that the recession periods are predictable and dynamic probit models, especially models with the autoregressive structure, outperform the static model. Chapter 3 proposes a Lagrange Multiplier (LM) test for the usefulness of the autoregressive structure of the probit model. The finite sample properties of the LM test are considered with simulation experiments. Results indicate that the two alternative LM test statistics have reasonable size and power in large samples. In small samples, a parametric bootstrap method is suggested to obtain approximately correct size. In Chapter 4, the predictive power of dynamic probit models in predicting the direction of stock market returns are examined. The novel idea is to use recession forecast (see Chapter 2) as a predictor of the stock return sign. The evidence suggests that the signs of the U.S. excess stock returns over the risk-free return are predictable both in and out of sample. The new "error correction" probit model yields the best forecasts and it also outperforms other predictive models, such as ARMAX models, in terms of statistical and economic goodness-of-fit measures. Chapter 5 generalizes the analysis of univariate models considered in Chapters 2 4 to the case of a bivariate model. A new bivariate autoregressive probit model is applied to predict the current state of the U.S. business cycle and growth rate cycle periods. Evidence of predictability of both cycle indicators is obtained and the bivariate model is found to outperform the univariate models in terms of predictive power.

Measurement of the WW+WZ production cross section using a matrix element technique in lepton+jets events

We present a measurement of the $WW+WZ$ production cross section observed in a final state consisting of an identified electron or muon, two jets, and missing transverse energy. The measurement is carried out in a data sample corresponding to up to 4.6~fb$^{-1}$ of integrated luminosity at $\sqrt{s} = 1.96$ TeV collected by the CDF II detector. Matrix element calculations are used to separate the diboson signal from the large backgrounds. The $WW+WZ$ cross section is measured to be $17.4\pm3.3$~pb, in agreement with standard model predictions. A fit to the dijet invariant mass spectrum yields a compatible cross section measurement.

Measurement of W-Boson Polarization in Top-Quark Decay in pp̅ Collisions at √s=1.96 TeV

We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb^-1 of ppbar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c^2, three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f_0) and right-handed (f_+) W bosons yields the model-independent results f_0 = 0.88 \pm 0.11 (stat) \pm 0.06 (syst) and f_+ = -0.15 \pm 0.07 (stat) \pm 0.06 (syst) with a correlation coefficient of -0.59. A measurement of f_0 (f_+) constraining f_+ (f_0) to its standard model value of 0.0 (0.7) yields f_0 = 0.70 \pm 0.07 (stat) \pm 0.04 (syst) (f_+ = -0.01 \pm 0.02 (stat) \pm 0.05 (syst)). All these results are consistent with standard model expectations.

Measurement of the top quark mass and pp̅ →tt̅ cross section in the all-hadronic mode with the CDF II detector

We present a measurement of the top quark mass and of the top-antitop pair production cross section using p-pbar data collected with the CDFII detector at the Tevatron Collider at the Fermi National Accelerator Laboratory and corresponding to an integrated luminosity of 2.9 fb-1. We select events with six or more jets satisfying a number of kinematical requirements imposed by means of a neural network algorithm. At least one of these jets must originate from a b quark, as identified by the reconstruction of a secondary vertex inside the jet. The mass measurement is based on a likelihood fit incorporating reconstructed mass distributions representative of signal and background, where the absolute jet energy scale (JES) is measured simultaneously with the top quark mass. The measurement yields a value of 174.8 +- 2.4(stat+JES) ^{+1.2}_{-1.0}(syst) GeV/c^2, where the uncertainty from the absolute jet energy scale is evaluated together with the statistical uncertainty. The procedure measures also the amount of signal from which we derive a cross section, sigma_{ttbar} = 7.2 +- 0.5(stat) +- 1.0 (syst) +- 0.4 (lum) pb, for the measured values of top quark mass and JES.

Measurement of the Λb0 Lifetime in Λb0→Λc+π- Decays in pp̅ Collisions at √s=1.96 TeV

We report a measurement of the lifetime of the Lambda_b baryon in decays to the Lambda_C+ pi- final state in a sample corresponding to 1.1 fb^-1 collected in p-pbar collisions at sqrt(s) = 1.96 TeV by the CDF II detector at the Tevatron collider. Using a sample of about 3000 fully reconstructed Lambda_b events we measure tau(Lambda_b) = 1.401 +- 0.046 (stat) +- 0.035 (syst) ps (corresponding to c.tau(Lambda_b) = 420.1 +- 13.7 (stat) +- 10.6 (syst) um, where c is the speed of light). The ratio of this result and the world average B^0 lifetime yields tau(Lambda_b)/tau(B^0) = 0.918 +- 0.038 (stat and syst), in good agreement with recent theoretical predictions.

Search for New Bottomlike Quark Pair Decays QQ̅ →(tW∓)(t̅ W±) in Same-Charge Dilepton Events

We report the most restrictive direct limits on masses of fourth-generation down-type quarks b′, and quarklike composite fermions (B or T5/3), decaying promptly to tW∓. We search for a significant excess of events with two same-charge leptons (e, μ), several hadronic jets, and missing transverse energy. An analysis of data from pp̅ collisions with an integrated luminosity of 2.7  fb-1 collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits mb′, mB>338  GeV/c2 and mT5/3>365  GeV/c2 at 95% confidence level.

Search for New Bottomlike Quark Pair Decays QQ̅ →(tW∓)(t̅ W±) in Same-Charge Dilepton Events

We report the most restrictive direct limits on masses of fourth-generation down-type quarks $b^{\prime}$, and quark-like composite fermions ($B$ or $T_{5/3}$), decaying promptly to $t W^{\mp}$. We search for a significant excess of events with two same-charge leptons ($e$, $\mu$), several hadronic jets, and missing transverse energy. An analysis of data from $p\overline{p}$ collisions with an integrated luminosity of 2.7 fb$^{-1}$ collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits $m_{b^{\prime}}, m_{B} >$ 338 $\mathrm{GeV}/c^2$ and $m_{T_{5/3}} >$ 365 $\mathrm{GeV}/c^2$ at 95% confidence level.

Search for Anomalous Production of Events with Two Photons and Additional Energetic Objects at CDF

We present results of a search for anomalous production of two photons together with an electron, muon, $\tau$ lepton, missing transverse energy, or jets using $p\bar{p}$ collision data from 1.1-2.0 fb$^{-1}$ of integrated luminosity collected by the Collider Detector at Fermilab (CDF). The event yields and kinematic distributions are examined for signs of new physics without favoring a specific model of new physics. The results are consistent with the standard model expectations. The search employs several new analysis techniques that significantly reduce instrumental backgrounds in channels with an electron and missing transverse energy.

Lihaluujauhon soveltuvuus sokerijuurikkaan lannoitteeksi

Lihaluujauho muodostaa maatilojen myytävien kasvi- ja eläinperäisten tuotteiden jälkeen tärkeimmän agroekosysteemeistä poispäin suuntautuvan ravinnevirran. Se sisältää runsaasti pääkasvinravinteita typpeä, fosforia ja kalsiumia (N ~8%, P ~5%, Ca yleensä ~10-15% luuaineksen määrästä riippuen), sekä kaliumia n.1% tai alle. Lihaluujauho on todettu tehokkaaksi lannoitteeksi useilla viljelykasveilla ja sen käyttö on sallittu myös luomuviljelyssä EU-alueella. Lihaluujauhoon ja erityisesti sen rehukäyttöön liittyvistä riskeistä merkittävin on TSE-tautien riski (naudan BSE-, lampaiden ja vuohien scrapie-, sekä ihmisen vCJD-taudit). Rehukäyttöä on monissa maissa rajoitettu 1980-luvulla puhjenneen BSE-kriisin myötä. BSE-taudin leviäminen yhdistettiin tilanteeseen, jossa nautaperäistä lihaluujauhoa käytettiin nautaeläinten rehun ainesosana. Myös lihaluujauhon käytössä turkiseläinrehuna saattaa piillä BSE:n tai muun TSE-taudin riski. Oikein käsitellyn lihaluujauhon lannoitekäyttöön ei kuitenkaan näytä tarkastelemieni tutkimusten perusteella sisältyvän huomattavaa TSEriskiä, jos huolehditaan asianmukaisista varotoimista ja menettelyistä sekä tuotteen valmistusprosessissa, että käytettäessä lannoitetta. Lihaluujauhon lannoitekäytön lisääminen edistäisi ruokajärjestelmämme ravinnekierron sulkemista etenkin fosforin osalta. Lihaluujauho on uusiutuva luonnonvara, jonka lannoitekäytöllä voitaisiin korvata huomattava osa lannoiteaineena kulutettavista fosforipitoisista kiviaineista. Sokerijuurikkaan lannoituskokeissa Varsinais-Suomen Kaarinassa vuosina 2008 ja 2009 lihaluujauhokäsittelyt eivät menestyneet aivan yhtä hyvin satotasovertailussa kuin kontrollikäsittelyiden NPK-väkilannoitteet, mutta laatuominaisuuksiltaan (sokeripitoisuus, amino-N, K, ja Na-pitoisuudet) joiltakin osin kontrollikäsittelyjä paremmin. Kokeissa käytetyt lajikkeet olivat ’Jesper’ vuonna 2008 ja ’Lincoln’ vuonna 2009. Käytetty lihaluujauholannoite oli Honkajoki Oy:n Viljo Yleislannoite 8-4-3, joka sisälsi noin 10% kaliumsulfaatin ja kasviperäisten sivutuotteiden seosta. Viljo-lannoitetta käytettiin sekä yksistään, että yhdistettynä 10-25%:iin väkilannoitetta. Vuoden 2009 Viljo-koejäseniin vielä lisättiin kaliumsulfaattilannoitetta (42% K, 18% S), jotta päästiin annetun kaliumin määrässä päästiin lannoitussuosituksen (60 kg K/ha) tasolle. Pelkkä Viljo-lannoite tuotti merkitsevästi alhaisemmat sadot kuin kontrollikäsittelyt molempina vuosina. Kuitenkin kun Viljolannoitteen ohella käytettiin väkilannoitetta (10-25% kasvin typentarpeesta) päästiin varsin lähelle kontrollikäsittelyiden satotasoja. Myös pelkän LLJ-lannoitteen tuottamat satotasot olivat kuitenkin selvästi paremmat kuin Suomen keskimääräiset juurikassadot. Viljo-käsittelyillä oli selvästi positiivinen vaikutus laatutekijöihin amino-N, K ja Na vuonna 2008, mutta vuonna 2009 näiden pitoisuudet jäivät kontrollikäsittelyjen tasolle. Viljo-käsittelyiden sokeripitoisuudet olivat vuonna 2008 kontrollikäsittelyn luokkaa ja Viljo77%+NK1:n osalta kontrollia merkitsevästi paremmat. Vuoden 2009 sokeripitoisuudet olivat kaikilla koejäsenillä erinomaiset, ja käsittelyiden välillä ei ilmennyt merkitseviä eroja. Kokeiden perusteella kaliumsulfaatilla täydennetty lihaluujauho on hyvin toimiva lannoite sokerijuurikkaalla Suomen olosuhteissa, etenkin yhdistettynä väkilannoitteeseen.

Oral health and menopause

Hormone therapy (HT) is widely used to relieve climacteric symptoms in order to increase the well-being of the women. The benefits as well as side-effects of HT are well documented. The principal menopausal oral symptoms are dry mouth (DM) and sensation of painful mouth (PM) due to various causes. Profile studies have indicated that HT users are more health-conscious than non-users. The hypothesis of the present study was that there are differences in oral health between woman using HT and those not using HT. A questionnaire study of 3173 women of menopausal age (50-58 years old) was done to investigate the prevalence of self-assessed sensations of PM and DM. Of those women participating in the questionnaire study, a random sample of 400 (200 using, 200 not using HT) was examined clinically in a 2-year follow-up study. Oral status was recorded according to WHO methods using DMFT and CPITN indices. The saliva flows were measured, salivary total protein, albumin and immunoglobulin concentrations and selected periodontal micro-organisms were analysed, and panoramic tomography of the jaws was taken. The patients filled in a structured questionnaire on their systemic health, medication and health habits. According to our questionnaire study there was no significant difference in the occurrence of self- assessed PM or DM between the HT users and non-users. According to logistic regression analyses, climacteric complaints significantly correlated with the occurrence of PM (p=0.000) and DM (p=0.000) irrespective of the use of HT, indicating that PM and DM are associated with climacteric symptoms in general. There was no difference between the groups in DMFT index values at follow up. The number of filled teeth (FT) showed a significant (p<0.05) increase in the HT group at follow-up. Periodontitis was diagnosed in 79% of HT users at baseline and in 71% at the follow-up. The values for non-HT users were 80% vs. 76%, respectively (Ns.). The mean numbers of ≥ 6 mm deep periodontal pockets were 0.9 ± 1.7 at baseline vs. 1.1 ± 2.1 two years later in the HT group, and 1.0 ± 1.7 vs. 1.2 ± 1.9, respectively, in the non-HT group. In a large Finnish national health survey, the prevalence of peridontitis of women of this age group was lower, but the prevalence of severe periodontitis seemed to be higher than in our study. Salivary albumin, IgG and IgM concentrations decreased in the HT group during the 2-year follow up (p<0.05), possibly indicating an improvement in epithelial integrity. No difference was found in any other salivary parameters or in the prevalence of the periodontal bacteria between or within the groups. In conclusion, the present findings showed that 50 to 58 year old women living in Helsinki have fairly good oral and dental health. The occurrence of PM and DM seemed to be associated with climacteric symptoms in general, and the use of HT did not affect the oral symptoms studied.

Corporate Governance in China (summary section only)

The negative relationship between economic growth and stock market return is not an anomaly according to evidence documented in many economies. It is argued that future economic growth is largely irrelevant for predicting future equity returns, since long-run equity returns depend mainly on dividend yields and the growth of per share dividends. The economic growth does result in a higher standard of living for consumers, but does not necessarily translate into higher returns for owners of the capital. The divergence in performance between the real sector and stock markets appears to support the above argument. However, this thesis strives to offer an alternative explanation to the apparent divergence within the framework of corporate governance. It argues that weak corporate governance standards in Chinese listed firms exacerbated by poor inventor protection results into a marginalized capital market. Each of the three essays in the thesis addresses one particular aspect of corporate governance on the Chinese stock market in a sequential way through gathering empirical evidence on three distinctive stock market activities. The first essay questions whether significant agency conflicts do exist by building a game on rights issues. It documents significant divergence in interests among shareholders holding different classes of shares. The second essay investigates the level of agency costs by examining value of control through constructing a sample of block transactions. It finds that block transactions that transfer ultimate control entail higher premiums. The third essay looks into possible avenues through which corporate governance standards could be improved by investigating the economic consequences of cross-listing on the Chinese stock market. It finds that, by adopting a higher disclosure standard through cross-listings, firms voluntarily commit themselves to reducing information asymmetry, and consequently command higher valuation than their counterparts.