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  • Hyvärinen, Heini (2010)
    Johdanto: Ikääntyessä iholla tapahtuva D-vitamiininmuodostus heikkenee ja lihakset ja luusto haurastuvat. Heikko lihaskunto on yhteydessä kaatumisriskiin, ja kaatuminen on yleisin syy vanhusten murtumiin. Monissa tutkimuksissa on osoitettu, että luustovaikutustensa lisäksi D-vitamiinilla on vaikutuksia luurankolihakseen. D-vitamiinihoidon on osoitettu vähentävän kaatumisia, mikä saattaa osin selittyä parantuneen tasapainon kautta. Joissakin tutkimuksissa on havaittu heikko tilastollinen yhteys Dvitamiinin ja kroonisen kivun välillä. D-vitamiinin puutokseen liitettyjä kipuja on esitetty luustoperäisiksi, mutta D-vitamiinin lihasvaikutukset huomioiden ne saattavat olla ainakin osin lihasperäisiä. Tavoitteet: Tämän poikkileikkaustutkimuksen tavoitteena oli tutkia, onko seerumin 25-hydroksi-Dvitamiinipitoisuus (25OHD) yhteydessä lihastoimintoihin itsenäisesti kotona asuvilla reumatauteja sairastavilla yli 50-vuotiailla. Hypoteesina oli, että D-vitamiinin puutos on yhteydessä heikentyneisiin neuromuskulaarisiin lihastoimintoihin, joita tässä tutkimuksessa mitattiin tasapainon perusteella. Aineisto ja menetelmät: Tutkimukseen rekrytoitiin yli 50-vuotiaita, koska tässä kohderyhmässä lihastoimintojen heikentymisen ja D-vitamiinin puutoksen odotettiin olevan yleisiä. Tutkittavien tuli kuitenkin olla kohtalaisen hyväkuntoisia, jotta he jaksaisivat fyysiset testit ja tutkimuksen mahdollisesti aiheuttaman henkisen rasituksen. Siksi lihastoimintojen ongelmia kuvaamaan valittiin polymyalgia rheumaticaa sairastavia, itsenäisesti kotona asuvia ihmisiä. Tutkimukseen osallistui myös joitakin yli 50- vuotiaita fibromyalgiaa ja nivelreumaa sairastavia henkilöitä. Seerumin 25OHD-pitoisuus määritettiin EIA-menetelmällä (IDS, UK). D-vitamiinin yhteyttä tutkittiin tasapainoon (Rombergin vakio tasapainolevyllä) ja lihasvoimaan (puristusvoima molempien käsien parhaan tuloksen keskiarvona, jalkojen nopeusvoima hyppylevyllä), kipuun ja toimintakykyyn. Tilastomenetelminä käytettiin ristiintaulukointia, t-testiä, lineaarista regressiota, logistista regressiota ja Pearsonin korrelaatiota. Tulokset: Tutkimukseen osallistui 47 henkilöä, joista viisi oli miehiä. Potilaat olivat 53-81 -vuotiaita (keski-ikä 70 v) ja hieman ylipainoisia (BMI 28). 25OHD oli keskimäärin 64 nmol/l. Ravitsemustila oli keskimäärin hyvä (MNA-pisteet 24). 25OHD oli alle 50 nmol/l 32 %:lla ja vastaavasti alle 75 nmol/l 74 %:lla tutkittavista. Potilaista 83 % käytti D-vitamiinivalmistetta. 25OHD korreloi positiivisesti ravitsemustilan (MNA) ja käänteisesti tasapainon ja kiputiheyden kanssa. 25OHD, ikä, sukupuoli ja MNA-pisteet selittivät 13,9 % (adjusted r2) huojunnan vaihtelusta ja 14,5 % (r2 Cox & Snell) kiputiheyden vaihtelusta. Ainoastaan 25OHD-pitoisuudella oli tilastollisesti merkitsevä itsenäinen selitysosuus huojuntaan (p = 0,024) ja kiputiheyteen (p = 0,045). Niillä, joilla 25OHD oli vähintään 75 nmol/l, oli 83 % pienempi riski kärsiä päivittäisestä kivusta kuin niillä, joilla 25OHD-pitoisuus oli alle 75 nmol/l. Lihasvoimalla, lihasmassalla ja kivun voimakkuudella ei havaittu yhteyttä D-vitamiinistatukseen. Johtopäätökset: Tässä tutkimuksessa reumatauteja sairastavien yli 50-vuotiaiden potilaiden matalat 25OHD-pitoisuudet olivat yhteydessä tasapainovaikeuksiin ja päivittäisiin kipuihin. Lihasmassa ja lihasvoima eivät olleet yhteydessä D-vitamiinistatukseen. Löydösten pohjalta olisi tulevaisuudessa tarpeen tutkia tarkemmin D-vitamiinikorvaushoidon vaikutuksia tasapainomittareihin ja kiputiheyteen.
  • Kairema, Anna (Helsingin yliopisto, 2013)
    This dissertation brings contribution to two interrelated topics. The first contribution concerns the so-called systems of dyadic cubes in the context of metric spaces. Second contribution is applications to one and two weight norm inequalities for linear and sublinear positive integral operators. Both of the topics are important in harmonic analysis and an ongoing area of study. The main novelties of the presented works consist of improving and extending existing results into more general frameworks. The work consists of four research articles and an introductory part. The first two articles, written in collaboration with T. Hytönen, study systems of dyadic cubes in metric spaces. In the Euclidean space, dyadic cubes are well-known and define a convenient structure with useful covering and intersection properties. Such dyadic structures are central especially in the modern trend of harmonic analysis. In the first article extensions of these structures are constructed in general geometrically doubling metric spaces. These consist of a refinement of existing constructions and a completely new construction of finitely many adjacent dyadic systems which behave like "translates" of a fixed system but without requiring a group structure. In this context, "cubes" are not properly cubes but rather more complicated sets that collectively have properties reminiscent of those in the Euclidean case. However, it is natural to ask what type of sets could or should be regarded cubes. In the second paper, we give a complete answer to this question in the general framework of a geometrically doubling metric space making use of the "plumpness" notion already appeared in the geometric measure theory. From another side; the two latter articles study weighted norm inequalities. Via the new construction of adjacent dyadic systems, weighted estimates for positive integral operators are obtained in a general framework. In the third paper, the two-weight problem is investigated for potential-type operators. Both strong and weak type estimates are characterized by "testing type" conditions: to show the full norm inequality it suffices to test the desired estimate on a specific class of simple test functions only. The results improve some previous results in the sense that the considered ambient space is more general (with more general measures and no additional geometric assumptions) and the testing is over a countable collection of test function only (instead of a significantly larger collection appearing in the previous works on the topic). The main technical novelty of the proof is a decomposition of the operator, along dyadic systems giving rise to certain finitely many "dyadic" versions of the original operator. In the fourth article, the focus is on sharp constant estimates for generalized fractional integral operators. A positive answer and its sharpness are given in the context of a space of homogeneous type. The result is reduced to weak-type inequalities using the results in the third paper. The sharpness requires a construction of functions that locally behave similarly to the basic power functions on the Euclidean space. The result extends a recent Euclidean result. Keywords: dyadic cube, adjacent dyadic systems, metric space, space of homogeneous type, potential type operator, testing condition, weighted norm inequality, sharp bound
  • Luther, Fred (1945)
  • Nyberg, Henri (2006)
    Ekonometrisessa tutkimuksessa dynaamisia binäärisiä aikasarjamalleja on toistaiseksi tutkittu kohtuullisen vähän. Viime vuosina on kuitenkin esitetty useita uusia aikasarjamalleja. Tässä tutkielmassa pääpaino on Kaupin ja Saikkosen (2005) esittämissä probit-malleissa, joissa tarkasteltavan aikasarjan viivästettyjä havaintoja sisältävää ns. dynaamista probit-mallia laajennetaan uudella ns. autoregressiivisella osalla. Tutkielman teoriaosassa tarkastellaan probit-mallien ominaisuuksia, kuten parametrien suurimman uskottavuuden estimointia sekä mallien diagnostiikkaan ja ennustamiseen liittyviä kysymyksiä. Parametrien estimoinnin yhteydessä havainnollistetaan uuden autoregressiivisen osan tuomia muutoksia perinteisiin ns. staattisiin probit-malleihin nähden. Hypoteesien testaamista käsittelevässä kappaleessa esitetään kaksi autoregressiivisen osan tarpeellisuutta testaavaa LM-testiä. Teoreettisia tarkasteluita sovelletaan tutkielman empiriaosassa suhdannesyklien ennakointiin, jossa tavoitteena on ennustaa esiintyneitä taloudellisia taantumajaksoja. Aineistona käytetään Yhdysvaltojen ja Saksan vuodesta 1972 alkavaa kuukausiaineistoa, joka on koottu useista eri lähteistä. Lähdekirjallisuudessa hyödyllisiksi ennakoiviksi taantumaindikaattoreiksi havaittujen tuottokäyrien, eli pitkän ja lyhyen koron erotusten, lisäksi käytetään myös muita selittäviä muuttujia, kuten tarkasteltavaan maahan nähden ulkomaista tuottokäyrää sekä maiden pörssien osaketuottoja. Aivan uutena selittäjänä tarkastellaan maiden välistä korkoeroa. Otoksen sisäisissä ja vuonna 2001 alkaneen viimeisimmän taantumajakson keinotekoisissa otoksen ulkopuolisissa ennusteissa Kaupin ja Saikkosen esittämät uudet ns. dynaaminen autoregressiivinen ja autoregressiivinen malli osoittautuvat käyttökelpoisimmiksi malleiksi. Monissa tutkimuksissa käytetty staattinen malli vaikuttaisi olevan käyttökelpoinen lähinnä pitkissä vuoden pituisissa ennusteissa. Vuoden 2001 taantumaa ennustettaessa parhaimmat mallit antoivat selkeät taantumasignaalit kolmesta kuuteen ehtäviä johtopäätöksiä. Maiden kotimaisen tuottokäyrän ohella myös osaketuotoilla ja ulkomaisella tuottokäyrällä havaitaan tilastollisesti merkitsevää ennustevoimaa. Yhdysvaltojen ja Saksan välinen korkoero näyttäisi olevan hyödyllinen selittäjä Saksan tapauksessa. Tutkielman tärkein lähde on Kaupin ja Saikkosen (2005) artikkeli. Teoriaosan kannalta keskeisiä lähteitä ovat Davidsonin ja MacKinnonin kirja (1993) sekä autoregressiivisen osan LM-testiä esitettäessä heidän artikkelinsa (1984) apumallit. Suhdannesyklisovelluksessa tutkielman kannalta keskeisimpiä ovat Bernardin ja Gerlachin (1998) sekä Estrellan ja Mishkinin (1998) artkuukautta ennen taantumajakson alkua. Ennustetehokkuuden kasvaessa mallien dynaamiset rakenteet muuttavat samalla selittävistä muuttujista tikkelit, joissa käsitellään samoja selittäviä muuttujia kuin tässä tutkimuksessa, mutta staattista probit-mallia käyttäen. Empiiristä osaa varten käytiin lävitse edellä mainittujen lähteiden lisäksi laajasti muita suhdannesyklien ennustamiseen ja korkojen tuottokäyriin liittyviä tutkimuksia.
  • Nyberg, Henri (2007)
    Binäärisiä aikasarjoja on toistaiseksi ekonometrisessa tutkimuksessa tutkittu kohtuullisen vähän. Viime vuosina on kuitenkin esitetty uusia aikasarjamalleja, joissa yksinkertaisinta ns. staattista mallia on laajennettu erilaisilla dynaamisilla rakenteilla. Tutkimuksessa tarkastellaan Yhdysvaltojen ja Saksan taantumajaksojen ennustamista Kaupin ja Saikkosen (2007) esittämiä uusia dynaamisia ns. autoregressiivisen rakenteen sisältäviä malleja käyttäen. Aiemmin käytettyihin malleihin tehtävän vertailun lisäksi usean kuukauden pituisten ennusteiden yhteydessä tutkitaan heidän esittämää uutta ns. iteratiivista ennustemenetelmää aiemmin käytettyyn suoraan menetelmään nähden. Tutkimuksen teoriaosassa tarkastellaan dynaamisten probit-mallien ominaisuuksia, kuten parametrien suurimman uskottavuuden estimointia sekä mallien diagnostiikkaan ja ennustamiseen liittyviä kysymyksiä. Hypoteesien testaamista käsittelevässä luvussa esitetään kaksi autoregressiivisen osan tarpeellisuutta testaavaa LM-testiä. Mallien estimoinneissa sekä estimointijakson ulkopuolelle muodostetuissa ennusteissa ns. autoregressiivisen osan sisältämät mallit osoittautuvat käyttökelpoisimmiksi malleiksi. Parhaimmat mallit antavat mm. selkeät taantumasignaalit ennen vuonna 2001 alkanutta, viimeksi esiintynyttä, taantumajaksoa. Dynaamisen probit-mallin tapauksessa iteratiiviset ennusteet ovat suoria ennusteita parempia. Lyhyen ja pitkän koron välinen erotus, eli tuottokäyrä, on aiempien tutkimusten havaintojen tapaan erityisen hyvä taantumajaksoja ennakoiva selittävä muuttuja. Maiden kotimaisten tuottokäyrien lisäksi myös ulkomaisella tuottokäyrällä sekä maiden osaketuotoilla havaitaan tilastollisesti merkitsevää ennustevoimaa. Yhdysvaltojen ja Saksan välinen korkoero näyttäisi olevan hyödyllinen selittäjä Saksan tapauksessa. Tutkimuksen tärkein lähde on Kaupin ja Saikkosen (2007) artikkeli. Mallien rakentelun ja ennustemenetelmien kannalta myös Chauvetin ja Potterin (2005) artikkeli on merkittävä. Teoriaosan kannalta keskeisiä lähteitä ovat Davidsonin ja MacKinnonin kirja (1993) sekä autoregressiivisen osan LM-testiä esitettäessä heidän artikkelinsa (1984) apumallit. Taantumajaksojen ennustamisessa keskeisimpiä ovat Bernardin ja Gerlachin (1998) sekä Estrellan ja Mishkinin (1998) artikkelit. Korkojen, erityisesti tuottokäyrän, ja osaketuottojen taantumaennustevoimaa on lisäksi tarkasteltu useissa muissakin tutkimuksissa.
  • Nyberg, Henri (2007)
    In the econometric literature, there is not much research on binary time series. However, in the last couple of years, some new binary time series models have been suggested where the traditional static model is extended by different kinds of dynamic structures. In the thesis, the main goal is to forecast the economic recession periods occurred in the United States and Germany. Especially, it is interesting to consider new so called autoregressive models suggested by Kauppi and Saikkonen (2007). They also proposed a new iterative framework for multiperiod forecasts. Iterated multiperiod forecasts are compared with previously used direct forecasts. The parameter estimation of the employed dynamic models can be done by a maximum likelihood method described in the theoretical part of the thesis. Model diagnostics and forecasting procedures are as well considered. Two LM tests for the usefulness of the autoregressive part are also proposed. It is shown that the models with autoregressive part seem to outperform the static probit models in terms of in-sample and out-of-sample predictions. The best forecasting models give the distinct recession signals of the forthcoming recession which started in 2001. In the dynamic probit model with the lagged recession indicator, the iterative forecasts seem to be superior to direct forecasts. Several empirical studies have proposed that the yield curve, which is defined as a spread between long and short term interest rates, is an accurate explanatory variable in recession forecasting. As in previous studies, the domestic yield curve is an important predictor variable in both countries but also the foreign yield curve, stock market returns and, in the case of Germany, the interest rate differential between the United States and Germany are statistically significant predictors in the dynamic probit models. The most important reference is the article of Kauppi and Saikkonen (2007). Chauvet and Potter (2005) have also proposed important model variants and forecasting methods for the binary time series models. Davidson and MacKinnon’s book (1993) and their article (1984) are important references for the theoretical part and especially for the proposed LM tests for the autoregressive part. The articles of Bernard and Gerlach (1998) and Estrella and Mishkin (1998) are important references for the recession forecasting. The forecasting power of the yield curves and the stock returns are also considered in numerous other articles.
  • Karpechko, Alexey (Helsingin yliopisto, 2007)
    Transport plays an important role in the distribution of long-lived gases such as ozone and water vapour in the atmosphere. Understanding of observed variability in these gases as well as prediction of the future changes depends therefore on our knowledge of the relevant atmospheric dynamics. This dissertation studies certain dynamical processes in the stratosphere and upper troposphere which influence the distribution of ozone and water vapour in the atmosphere. The planetary waves that originate in the troposphere drive the stratospheric circulation. They influence both the meridional transport of substances as well as parameters of the polar vortices. In turn, temperatures inside the polar vortices influence abundance of the Polar Stratospheric Clouds (PSC) and therefore the chemical ozone destruction. Wave forcing of the stratospheric circulation is not uniform during winter. The November-December averaged stratospheric eddy heat flux shows a significant anticorrelation with the January-February averaged eddy heat flux in the midlatitude stratosphere and troposphere. These intraseasonal variations are attributable to the internal stratospheric vacillations. In the period 1979-2002, the wave forcing exhibited a negative trend which was confined to the second half of winter only. In the period 1958-2002, area, strength and longevity of the Arctic polar vortices do not exhibit significant long-term changes while the area with temperatures lower than the threshold temperature for PSC formation shows statistically significant increase. However, the Arctic vortex parameters show significant decadal changes which are mirrored in the ozone variability. Monthly ozone tendencies in the Northern Hemisphere show significant correlations (|r|=0.7) with proxies of the stratospheric circulation. In the Antarctic, the springtime vortex in the lower stratosphere shows statistically significant trends in temperature, longevity and strength (but not in area) in the period 1979-2001. Analysis of the ozone and water vapour vertical distributions in the Arctic UTLS shows that layering below and above the tropopause is often associated with poleward Rossby wave-breaking. These observations together with calculations of cross-tropopause fluxes emphasize the importance of poleward Rossby wave breaking for the stratosphere-troposphere exchange in the Arctic.
  • Eloranta, Satu (Helsingin yliopisto, 2013)
    A knowledge base is considered a system that is told information about an external world and that answers questions about this world. Our goal here is to outline knowledge bases that involve both knowledge and beliefs. In previous studies, various kinds of belief change have been studied in isolation, but we want to tie them together. We aim at knowledge bases that could carry the epistemic states of agents, that is, the knowledge and the beliefs that an agent has at any one moment in time. The difference between knowledge and belief is that while knowledge increases monotonically with time, beliefs may at some later point in time turn out to be false. Beliefs may change for various reasons: in belief revision, beliefs are changed when receiving new information about a world that has not changed, while in belief update a change in the world is to be recorded. Different types of change call for different treatments. In belief-change studies, various change types have been characterized by rationality criteria set on each type. The main principles in these criteria are maintaining consistency of beliefs and minimality of change. When dealing with belief change, our approach is to take knowledge as an integrity constraint that should always hold, and we describe how the rationality criteria should be modified accordingly. In our refined rationality criteria, beliefs that are inconsistent with the knowledge of the knowledge base will never be allowed to enter into the knowledge base. In the rationality criteria, a common assumption is that the most recent information is the most reliable, and it has therefore been prioritized over the old beliefs. However, this may not be the case in all circumstances. In order to complete the collection of belief-change types, we propose a new, commutative type of change for entering competing evidence into the knowledge base. The representation theorems that have been given for belief revision indicate that belief revision involves an ordering of disbelief on possible alternative situations, or equivalently, an epistemic entrenchment on logical formulas. A formula less entrenched is more easily given up when eliminating inconsistancies. In view of the changes in the rationality criteria, we also refine the representation theorems. We introduce two finite representations for knowledge bases, one with a finite ordered set of propositional formulas that are satisfiable but pairwise inconsistent with each other, and the other with a finite list of pairwise inconsistent propositional formulas. Both representations involve dynamic orderings of disbelief that have arisen out of the previous change operations. We show that for the knowledge base to satisfy the rationality criteria given for belief revision, the dynamic ordering of disbelief in the knowledge base is vital. The representations and the operators that we introduce in this thesis demonstrate how this ordering of disbelief could be dealt with in various operations.
  • Fornaro, Paolo (2011)
    In recent years, thanks to developments in information technology, large-dimensional datasets have been increasingly available. Researchers now have access to thousands of economic series and the information contained in them can be used to create accurate forecasts and to test economic theories. To exploit this large amount of information, researchers and policymakers need an appropriate econometric model.Usual time series models, vector autoregression for example, cannot incorporate more than a few variables. There are two ways to solve this problem: use variable selection procedures or gather the information contained in the series to create an index model. This thesis focuses on one of the most widespread index model, the dynamic factor model (the theory behind this model, based on previous literature, is the core of the first part of this study), and its use in forecasting Finnish macroeconomic indicators (which is the focus of the second part of the thesis). In particular, I forecast economic activity indicators (e.g. GDP) and price indicators (e.g. consumer price index), from 3 large Finnish datasets. The first dataset contains a large series of aggregated data obtained from the Statistics Finland database. The second dataset is composed by economic indicators from Bank of Finland. The last dataset is formed by disaggregated data from Statistic Finland, which I call micro dataset. The forecasts are computed following a two steps procedure: in the first step I estimate a set of common factors from the original dataset. The second step consists in formulating forecasting equations including the factors extracted previously. The predictions are evaluated using relative mean squared forecast error, where the benchmark model is a univariate autoregressive model. The results are dataset-dependent. The forecasts based on factor models are very accurate for the first dataset (the Statistics Finland one), while they are considerably worse for the Bank of Finland dataset. The forecasts derived from the micro dataset are still good, but less accurate than the ones obtained in the first case. This work leads to multiple research developments. The results here obtained can be replicated for longer datasets. The non-aggregated data can be represented in an even more disaggregated form (firm level). Finally, the use of the micro data, one of the major contributions of this thesis, can be useful in the imputation of missing values and the creation of flash estimates of macroeconomic indicator (nowcasting).
  • Nyman, Thomas (2014)
    Operating System-level Virtualization is virtualization technology based on running multiple isolated userspace instances, commonly referred to as containers, on top of a single operating system kernel. The fundamental difference compared to traditional virtualization is that the targets of virtualization in OS-level virtualization are kernel resources, not hardware. OS-level virtualization is used to implement Bring Your Own Device (BYOD) policies on contemporary mobile platforms. Current commercial BYOD solutions, however, don't allow for applications to be containerized dynamically upon user request. The ability to do so would greatly improve the flexibility and usability of such schemes. In this work we study if existing OS-level virtualization features in the Linux kernel can meet the needs of use cases reliant on such dynamic isolation. We present the design and implementation of a prototype which allows applications in dynamic isolated domains to be migrated from one device to another. Our design fits together with security features in the Linux kernel, allowing the security policy influenced by user decisions to be migrated along with the application. The deployability of the design is improved by basing the solution on functionality already available in the mainline Linux kernel. Our evaluation shows that the OS-level virtualization features in the Linux kernel indeed allow applications to be isolated in a dynamic fashion, although known gaps in the compartmentalization of kernel resources require trade-offs between the security and interoperability to be made in the design of such containers.
  • Antipina, Dina (2013)
    The subject of our research is the behavior of the economy in response to monetary and technology shocks. To understand these issues we use a Dynamic Money-in-the-Utility-Function framework. We implement a non-separable property of the utility function that implies non-neutrality of real money balances. We construct a toy theoretic model with two representative agents who maximize their functions subject to constraints. We analytically solve the model using a method of log-linearization around the steady state and obtain the system of linear equations. We analyze the response of economic equilibrium with respect to implemented shocks using a method of undetermined coefficients and solve a system of linear difference expectation equations. In addition to analytical solution we also present Impulse Response Functions of the model. We compute the impacts of monetary and technology shocks on the model and find that in case of a positive monetary shock expected inflation effect dominates the liquidity effect, while in case of a positive productivity shock income effect dominates substitution effect. The findings regarding the impact of a technology shock contradict the theory of real business cycles that predicts the domination of substitution effect over the income effect
  • Louhivuori, Martti (Helsingin yliopisto, 2007)
    Protein conformations and dynamics can be studied by nuclear magnetic resonance spectroscopy using dilute liquid crystalline samples. This work clarifies the interpretation of residual dipolar coupling data yielded by the experiments. It was discovered that unfolded proteins without any additional structure beyond that of a mere polypeptide chain exhibit residual dipolar couplings. Also, it was found that molecular dynamics induce fluctuations in the molecular alignment and doing so affect residual dipolar couplings. The finding clarified the origins of low order parameter values observed earlier. The work required the development of new analytical and computational methods for the prediction of intrinsic residual dipolar coupling profiles for unfolded proteins. The presented characteristic chain model is able to reproduce the general trend of experimental residual dipolar couplings for denatured proteins. The details of experimental residual dipolar coupling profiles are beyond the analytical model, but improvements are proposed to achieve greater accuracy. A computational method for rapid prediction of unfolded protein residual dipolar couplings was also developed. Protein dynamics were shown to modulate the effective molecular alignment in a dilute liquid crystalline medium. The effects were investigated from experimental and molecular dynamics generated conformational ensembles of folded proteins. It was noted that dynamics induced alignment is significant especially for the interpretation of molecular dynamics in small, globular proteins. A method of correction was presented. Residual dipolar couplings offer an attractive possibility for the direct observation of protein conformational preferences and dynamics. The presented models and methods of analysis provide significant advances in the interpretation of residual dipolar coupling data from proteins.
  • Martikainen, Jani-Petri (Helsingin yliopisto, 2001)
  • Tanskanen, Topi (Helsingin yliopisto, 2008)
    The neural basis of visual perception can be understood only when the sequence of cortical activity underlying successful recognition is known. The early steps in this processing chain, from retina to the primary visual cortex, are highly local, and the perception of more complex shapes requires integration of the local information. In Study I of this thesis, the progression from local to global visual analysis was assessed by recording cortical magnetoencephalographic (MEG) responses to arrays of elements that either did or did not form global contours. The results demonstrated two spatially and temporally distinct stages of processing: The first, emerging 70 ms after stimulus onset around the calcarine sulcus, was sensitive to local features only, whereas the second, starting at 130 ms across the occipital and posterior parietal cortices, reflected the global configuration. To explore the links between cortical activity and visual recognition, Studies II III presented subjects with recognition tasks of varying levels of difficulty. The occipito-temporal responses from 150 ms onwards were closely linked to recognition performance, in contrast to the 100-ms mid-occipital responses. The averaged responses increased gradually as a function of recognition performance, and further analysis (Study III) showed the single response strengths to be graded as well. Study IV addressed the attention dependence of the different processing stages: Occipito-temporal responses peaking around 150 ms depended on the content of the visual field (faces vs. houses), whereas the later and more sustained activity was strongly modulated by the observers attention. Hemodynamic responses paralleled the pattern of the more sustained electrophysiological responses. Study V assessed the temporal processing capacity of the human object recognition system. Above sufficient luminance, contrast and size of the object, the processing speed was not limited by such low-level factors. Taken together, these studies demonstrate several distinct stages in the cortical activation sequence underlying the object recognition chain, reflecting the level of feature integration, difficulty of recognition, and direction of attention.
  • Hoikkala, Laura (Helsingin yliopisto, 2012)
    Dissolved organic matter (DOM) in surface waters originates from allochthonous and autochthonous sources, the latter of which includes exudation by phytoplankton, viral lysis of planktonic organisms and 'sloppy' feeding by zooplankton. The concentration of DOM in seawater exceeds by one to two orders of magnitude that of particulate organic matter. Thus the DOM pool may be crucial to nutrition of pelagic osmotrophs, such as bacteria and algae, which are capable of exploiting dissolved organic substrates. In this thesis, monitoring surveys and laboratory experiments were used to examine the seasonal dynamics of DOM, including interactions of DOM and heterotrophic bacteria, in the Gulf of Finland, northern Baltic Sea, which is rich in allochthonous humic DOM. Despite the large ambient DOM pools and their potentially marked influence in the planktonic food webs and biogeochemical cycles of carbon and nutrients, few investigations in the Baltic Sea have focused on the dynamics of DOM, and information from the Gulf of Finland is almost lacking. In this thesis, seasonal changes in the net pools of dissolved organic C (DOC), N (DON) and P (DOP) were followed along with ambient key physical, chemical and biological variables on a shore-to-open-sea salinity gradient once in January and biweekly during the phytoplankton growth season. Horizontal coverage of these data was complemented with DOM samplings along a transect from the western to the eastern part of the Gulf. Autochthonous DOM accumulated throughout the productive season and the accumulated DOM was N- and P-rich compared with the bulk DOM pool in the surface layer of the Gulf of Finland. Notable DOM accumulation occurred during the actively growing and declining phases of spring and late summer blooms. Total export estimates of surface DOC, DON and DOP by autumn overturn corresponded to about 11 25% of reported annual particulate organic matter sedimentation in our study area. Seasonal variation in the availability of the net DOC and DON pools for bacterial utilization was investigated with incubations of natural bacterial samples for 2 3 wk. The concentrations of labile DOC were low in spring and during the summer minimum period, whereas the pools of labile DON were more variable. The labile DOM accumulated during and after the late summer cyanobacterial bloom, with low C:N ratios. For determination of factors that control the net DOM pools, limitation of bacterial growth by inorganic nutrients (N and P), labile C and temperature was followed in natural surface and deep-water bacterial samples during the main postspring bloom stages of phytoplankton growth. Agreeing with the low degradability of the ambient DOC pool, bacterial production was consistently C-limited in the surface layer, with N or both N and P as the secondary limiting nutrients from spring to early summer and in late summer, respectively. In deep water, bacterial growth showed combined temperature and C limitation. Sunlight induces photochemical transformation of DOM, and the importance of this process to bacterial growth during summer was investigated with samples representing extensive spatial and temporal coverage. In addition, photochemical transformation of refractory DOM and its effects on growth and composition of the microbial community were studied in further detail during a late summer cyanobacterial bloom. Photochemical transformation of DOM generally resulted in increased bacterial production, and photoproduced labile DOC was estimated to support < 10% of the daily bacterial C production in the surface layers during summer. Photochemical transformation of DOM led to clear changes in the composition of the bacterial community, with notable increases in the relative percentage of a few typical freshwater bacteria. The results further indicated that bacterial taxa benefiting from labile photoproducts included specialists growing strictly on the photoproducts of humic matter. The results of this thesis suggest that the C-limited bacterial community is for most of the productive season capable of efficient utilization of the labile C compounds released in the Gulf of Finland. The accumulation of phytoplankton-derived, autochthonous DOC during the productive season and subsequent DOC export to deep water are thus lower than in situations where nutrient-limited bacteria would allow accumulation of labile DOC, decreasing the efficiency of the plankton system in incorporating atmospheric CO2. Nevertheless, accumulation in the DOM pool forms a notable temporary storage of phytoplankton-derived C, N and P. The pool of labile DON, which accounted for up to 95% of the available N in surface water during summer, is a notable nutrient source for the N-limited plankton community. Photochemical transformation of DOM seems to contribute relatively little to the bacterial C demand, which is satisfied by autochthonous DOM released from the plankton food web in the Gulf of Finland. However, photoproduction of labile DOM appears to have notable qualitative effects on the composition of the bacterial community, probably contributing to the success in the Baltic Sea of bacteria originating in freshwater.
  • Rintala, Jukka (Helsingin yliopisto, 2007)
    Farmland bird species have been declining in Europe. Many declines have coincided with general intensification of farming practices. In Finland, replacement of mixed farming, including rotational pastures, with specialized cultivation has been one of the most drastic changes from the 1960s to the 1990s. This kind of habitat deterioration limits the persistence of populations, as has been previously indicated from local populations. Integrated population monitoring, which gathers species-specific information of population size and demography, can be used to assess the response of a population to environment changes also at a large spatial scale. I targeted my analysis at the Finnish starling (Sturnus vulgaris). Starlings are common breeders in farmland habitats, but severe declines of local populations have been reported from Finland in the 1970s and 1980s and later from other parts of Europe. Habitat deterioration (replacement of pasture and grassland habitats with specialized cultivation areas) limits reproductive success of the species. I analysed regional population data in order to exemplify the importance of agricultural change to bird population dynamics. I used nestling ringing and nest-card data from 1951 to 2005 in order to quantify population trends and per capita reproductive success within several geographical regions (south/north and west/east aspects). I used matrix modelling, acknowledging age-specific survival and fecundity parameters and density-dependence, to model population dynamics. Finnish starlings declined by 80% from the end of the 1960s up to the end of the 1980s. The observed patterns and the model indicated that the population decline was due to the decline of the carrying capacity of farmland habitats. The decline was most severe in north Finland where populations largely become extinct. However, habitat deterioration was most severe in the southern breeding areas. The deteriorations in habitat quality decreased reproduction, which finally caused the decline. I suggest that poorly-productive northern populations have been partly maintained by immigration from the highly-productive southern populations. As the southern populations declined, ceasing emigration caused the population extinction in north. This phenomenon was explained with source sink population dynamics, which I structured and verified on the basis of a spatially explicit simulation model. I found that southern Finnish starling population exhibits ten-year cyclic regularity, a phenomenon that can be explained with delayed density-dependence in reproduction.
  • Fordell, Thomas (Helsingin yliopisto, 2007)
    The output of a laser is a high frequency propagating electromagnetic field with superior coherence and brightness compared to that emitted by thermal sources. A multitude of different types of lasers exist, which also translates into large differences in the properties of their output. Moreover, the characteristics of the electromagnetic field emitted by a laser can be influenced from the outside, e.g., by injecting an external optical field or by optical feedback. In the case of free-running solitary class-B lasers, such as semiconductor and Nd:YVO4 solid-state lasers, the phase space is two-dimensional, the dynamical variables being the population inversion and the amplitude of the electromagnetic field. The two-dimensional structure of the phase space means that no complex dynamics can be found. If a class-B laser is perturbed from its steady state, then the steady state is restored after a short transient. However, as discussed in part (i) of this Thesis, the static properties of class-B lasers, as well as their artificially or noise induced dynamics around the steady state, can be experimentally studied in order to gain insight on laser behaviour, and to determine model parameters that are not known ab initio. In this Thesis particular attention is given to the linewidth enhancement factor, which describes the coupling between the gain and the refractive index in the active material. A highly desirable attribute of an oscillator is stability, both in frequency and amplitude. Nowadays, however, instabilities in coupled lasers have become an active area of research motivated not only by the interesting complex nonlinear dynamics but also by potential applications. In part (ii) of this Thesis the complex dynamics of unidirectionally coupled, i.e., optically injected, class-B lasers is investigated. An injected optical field increases the dimensionality of the phase space to three by turning the phase of the electromagnetic field into an important variable. This has a radical effect on laser behaviour, since very complex dynamics, including chaos, can be found in a nonlinear system with three degrees of freedom. The output of the injected laser can be controlled in experiments by varying the injection rate and the frequency of the injected light. In this Thesis the dynamics of unidirectionally coupled semiconductor and Nd:YVO4 solid-state lasers is studied numerically and experimentally.