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  • 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.
  • Paloviita, Maritta (Suomen Pankki, 2009)
    The present study examines empirically the inflation dynamics of the euro area. The focus of the analysis is on the role of expectations in the inflation process. In six articles we relax rationality assumption and proxy expectations directly using OECD forecasts or Consensus Economics survey data. In the first four articles we estimate alternative Phillips curve specifications and find evidence that inflation cannot instantaneously adjust to changes in expectations. A possible departure of expectations from rationality seems not to be powerful enough to totally explain the persistence of euro area inflation in the New Keynesian framework. When expectations are measured directly, the purely forward-looking New Keynesian Phillips curve is outperformed by the hybrid Phillips curve with an additional lagged inflation term and the New Classical Phillips curve with a lagged expectations term. The results suggest that the euro area inflation process has become more forward-looking in the recent years of low and stable inflation. Moreover, in low inflation countries, the inflation dynamics have been more forward-looking already since the late 1970s. We find evidence of substantial heterogeneity of inflation dynamics across the euro area countries. Real time data analysis suggests that in the euro area real time information matters most in the expectations term in the Phillips curve and that the balance of expectations formation is more forward- than backward-looking. Vector autoregressive (VAR) models of actual inflation, inflation expectations and the output gap are estimated in the last two articles.The VAR analysis indicates that inflation expectations, which are relatively persistent, have a significant effect on output. However,expectations seem to react to changes in both output and actual inflation, especially in the medium term. Overall, this study suggests that expectations play a central role in inflation dynamics, which should be taken into account in conducting monetary policy.
  • Leppä, Johannes (Helsingin yliopisto, 2012)
    Atmospheric aerosol particles have various climate effects and adverse health effects, which both depend on the size and number concentration of the particles. Freshly-formed particles are not large enough to impact neither health nor climate and they are most susceptible to removal by collisions with larger pre-existing particles. Consequently, the knowledge of both the formation and the growth rate of particles are crucially important when assessing the health and climate effects of atmospheric new particle formation. The purpose of this thesis is to increase our knowledge of the dynamics of neutral and charged aerosol particles with a specific interest towards the particle growth rate and processes affecting the aerosol charging state. A new model, Ion-UHMA, which simulates the dynamics of neutral and charged particles, was developed for this purpose. Simple analytical formulae that can be used to estimate the growth rate due to various processes were derived and used to study the effects of charged particles on the growth rate. It was found that the growth rate of a freshly-formed particle population due to condensation and coagulation could be significantly increased when a considerable fraction of the particles are charged. Finally, recent data-analysis methods that have been applied to the aerosol charging states obtained from the measurements were modified for a charge asymmetric framework. The methods were then tested on data obtained from aerosol dynamics simulations. The methods were found to be able to provide reasonable estimates on the growth rate and proportion of particles formed via ion-induced nucleation, provided that the growth rate is high enough and that the charged particles do not grow much more rapidly than the neutral ones. A simple procedure for estimating whether the methods are suitable for analysing data obtained in specific conditions was provided. In this thesis, the dynamics of neutral and charged aerosol particles were studied in detail. Combined with the current field and chamber measurements of neutral and charged particles, the analytical tools provided here can be used to study the atmospheric new particle formation and growth more comprehensively and, eventually, to decrease the uncertainty related to climate effects of aerosol particles.
  • Skarp, Kari-Pekka (Helsingin yliopisto, 2014)
    The notion of actin in the nucleus has slowly garnered popularity over the decades transforming the protein from an obscure artefact into a target of extreme curiosity in that compartment. Actin has been associated with a whole spectrum of nuclear functions, which directly or undirectly connect the protein with the most important nuclear function, transcription. However, it is currently not known how actin enters the nucleus in the first place and whether the protein is subjected to constitutive transport between the two eukaryotic compartments. The question regarding nucleocytoplasmic shuttling of actin is further complicated by the fact that actin is near the nuclear pore complex size exclusion limit, which sets a physical barrier for passive diffusion but not active transport. To investigate the nature of actin transit between the nucleus and the cytoplasm we developed microscope assays to monitor the shuttling of fluorescently labeled particles in real time in living cells. Using our assays it was possible to quantitate nuclear actin import and export rates. This immediately revealed that actin constantly shuttles in steady state cells. We used fluorescent probes of various sizes to explore the limits of passive vs. active import and found that even if the size of the fluorescent actin construct is increased, it retains the import rate. This suggests an active mechanism is behind the nuclear import of actin, because passively traveling constructs slow down when size increases as shown by controls. Longer observations of nuclear import revealed that nuclear actin exists in at least three pools of different motility and the largest one exhibits retarded exchange rates with the environment. This is consistent with the reports of actin bound to various nuclear complexes, which may render the actins in question less mobile. We were also able to clarify the status of actin export, where two export receptors have been reported. By using a small molecule inhibitor, we showed that CRM1 does not participate in the export of actin, which at least during steady state seems to fall exclusively in the domain of exportin 6. Next we identified the components of active import machinery by using RNAi vs. exportin 6 and suspected import factors. We found that actin is imported in complex with importin 9 and unphosphorylated cofilin and the process is dependent on Ran. We then showed that RNA polymerase II dependent transcription requires a suitable amount of actin in the nucleus or it is disrupted. Finally, we wanted to investigate which cellular features might correlate with the transport rates of actin and how actin shuttling is conducted in cells of varying amount of actin in the 2 nucleus in relation to cytoplasm (N/C ratio). We found that factors such as the size or shape of the nucleus or cytoplasm or the ratio of their sizes does not affect the import or export rates of actin. Instead, we made the surprising discovery the the N/C ratio of actin inversely correlates with both export and import. This means that the fastest shuttling rates can be found in cells with least actin in the nucleus while in cells of high amount of actin in the nucleus, the transport is slow. The latter situation suggests the nucleus is filled actin, which is somehow made export incompetent, perhaps by associating with nuclear complexes. To explore the matter further, we performed studies on the motility of nuclear and cytoplasmic actin pools. However, we found no relation with high N/C ratio of actin and the size of the G-actin pool. This suggests that the primary mode of regulation of nucleocytoplasmic shuttling does not take place through manipulating the size of the global G-actin pool.
  • Hölttä, Teemu (Helsingin yliopisto, 2005)
  • Zhang, Lei (Helsingin yliopisto, 2010)
    Dyslipidaemia, a major risk factor of cardiovascular disease (CVD), is prevalent not only in diabetic patients but also in individuals with impaired glucose tolerance (IGT) or impaired fasting glucose (IFG). The aims of this study were: 1) to investigate lipid levels in relation to glucose in European (Study I) and Asian (Study II) populations without a prior history of diabetes; 2) to study the ethnic difference in lipid profiles controlling for glucose levels (Study III); 3) to estimate the relative risk for cardiovascular mortality (Study IV) and morbidity (Study V) associated with dyslipidaemia in individuals with different glucose tolerance status. Data of 15 European cohorts with 19 476 subjects (I and III) and 13 Asian cohorts with 19 763 individuals (II and III) from 21 countries aged 25-89 years, without a prior history of diabetes at enrollment, representing Asian Indian, Chinese, European, Japanese and Mauritian Indian, were compared. The lipid-CVD relationship was studied in 14 European cohorts of 17 763 men and women which provided with follow-up data on vital status, with 871 CVD deaths occurred during the average 10-year follow-up (IV). The impact of dyslipidaemia on incidence of coronary heart disease (CHD) in persons with different glucose categories (V) was further evaluated in 6 European studies, with 9087 individuals free of CHD at baseline and 457 developed CHD during follow-up. Z-scores of each lipid component were used in the data analysis (I, II, IV and V) to reduce the differences in methodology between studies. Analyses of cardiovascular mortality and morbidity were performed using Cox proportional hazards regression analysis adjusting for potential confounding factors. Within each glucose category, fasting plasma glucose (FPG) levels were correlated with increasing levels of triglycerides (TG), total cholesterol (TC), TC to high-density lipoprotein (HDL) ratio and non-HDL cholesterol (non-HDL-C) (p<0.05 in most of the ethnic groups) and inversely associated with HDL-C (p<0.05 in some, but not all, of the populations). The association of lipids with 2-h plasma glucose (2hPG) followed a similar pattern as that for the FPG, except the stronger association of HDL-C with 2hPG. Compared with Central & Northern (C & N) Europeans, multivariable adjusted odd ratios (95% CIs) for having low HDL-C were 4.74 (4.19-5.37), 5.05 (3.88-6.56), 3.07 (2.15-4.40) and 2.37 (1.67-3.35) in Asian Indian men but 0.12 (0.09-0.16), 0.07 (0.04-0.13), 0.11 (0.07-0.20) and 0.16 (0.08-0.32) in Chinese men who had normoglycaemia, prediabetes, undiagnosed and diagnosed diabetes, respectively. Similar results were obtained for women. The prevalence of low HDL-C remained higher in Asian Indians than in others even in individuals with LDL-C < 3 mmol/l. Dyslipidaemia was associated with increased CVD mortality or CHD incidence in individuals with isolated fasting hyperglycaemia or IFG, but not in those with isolated post-load hyperglycaemia or IGT. In conclusion, hyperglycaemia is associated with adverse lipid profiles in Europeans and Asians without a prior history of diabetes. There are distinct patterns of lipid profiles associated with ethnicity regardless of the glucose levels, suggesting that ethnic-specific strategies and guidelines on risk assessment and prevention of CVD are required. Dyslipidaemia predicts CVD in either diabetic or non-diabetic individuals defined based on the fasting glucose criteria, but not on the 2-hour criteria. The findings may imply considering different management strategies in people with fasting or post-load hyperglycaemia.
  • E. 
    Aho, Lauri E. (1930)
  • E. 
    Lohikoski, Virpi (1998)