MDL Denoising Revisited

We refine and extend an earlier MDL denoising criterion for wavelet-based denoising. We start by showing that the denoising problem can be reformulated as a clustering problem, where the goal is to obtain separate clusters for informative and non-informative wavelet coefficients, respectively. This suggests two refinements, adding a code-length for the model index, and extending the model in order to account for subband-dependent coefficient distributions. A third refinement is derivation of soft thresholding inspired by predictive universal coding with weighted mixtures. We propose a practical method incorporating all three refinements, which is shown to achieve good performance and robustness in denoising both artificial and natural signals.Comment: Submitted to IEEE Transactions on Information Theory, June 200

Tehomuuntajan kuntoarviointi

Tämä insinöörityö on tehty Fortumin Power Solutions -yksikölle, joka tuottaa asiantuntijapalveluita voimalaitoksen käyttöön ja kunnossapitoon. Työ käsittelee öljyeristeisen tehomuuntajan kuntokartoitusta, ja työssä perehdyttiin tehomuuntajan kunnon tärkeimpiin indikaattoreihin sekä käyttöpaikalla suoritettaviin eri kunnonvalvontamenetelmiin. Työn kokeellisessa osassa perehdyttiin dielektrisen taajuusvastemittauksen eli DFR (Dielectric Frequency Response) -mittauksen menetelmään ja sen soveltuvuuteen muuntajan kunnonvalvonnassa. Työn tulokset pohjautuvat pääosin tähän tarkoitukseen valmistetun mittalaitteen tuloksiin. Mittalaite on kehitetty erityisesti tehomuuntajan paperieristyksen kosteuden, häviökertoimen sekä muuntajaöljyn johtavuuden selvittämiseen. Valmistaja ilmoittaa laitteen soveltuvan muun muassa läpivientieristimille sekä suurjännitekaapeleille, mikä myös käsitellään tässä työssä. Työ tehtiin suorittamalla useita kuntokartoituksia muuntajille eri voimalaitoksilla. Työn tukena on käytetty kentältä saadun kokemuksen lisäksi runsaasti alan materiaalia. Lisäksi materiaalina on käytetty Fortumin sisäisiä asiakirjoja sekä eri asiantuntijoiden kokemuksia. Pääeristykset, muuntajaöljy ja virtatiet ovat tehomuuntajan tärkeimmät kunnonvalvonnan kohteet. Mittaustuloksia analysoidessa tulee kiinnittää huomiota tarkkailuraja-arvojen lisäksi trendiseurantaan. Tuloksia tulee aina käsitellä tapauskohtaisesti. DFR-menetelmällä saadaan paljon tietoa muuntajan pääeristyksen kunnosta, kuten kosteudesta ja ikääntymisestä. Mittaustulokset öljypaperieristeisistä suurjännitekaapeleista olivat hyviä. Tulokset muuntajan läpivientieristimistä ovat toistaiseksi olleet vaihtelevia ulkopuolisten häiriöiden takia. Työn jälkeen tutkimuksia DFR-mittauksen mahdollisuuksista jatketaan ja ratkaisuja yritetään löytää tunnistettuihin ongelmiin.This Bachelor’s thesis was performed for Fortum Power Solutions unit, which provides expert and maintenance services for power plants. This thesis concerns the condition assessments of oil-filled power transformer and introduces the main key indicators of power transformer’s condition. Also the different methods for determining the condition of these indicators in the field are presented. In the experimental part of the project, the Dielectric Frequency Response (DFR) measurement method and its suitability for monitoring the condition of power transformer were studied. The outcome of the study is mainly based on results from an instrument specifically manufactured for this purpose. The instrument is developed especially for determining power transformer main insulation’s moisture content, dissipation factor and transformer’s oil conductivity. The manufacturer also notifies that it is suitable for bushings and high voltage cables, which are also addressed in this thesis. The work was carried out by performing a number of condition assessments for power transformers at various power plants. This study is supported by several researches and the experience gain from practical work. In addition, a lot of data has been collected from Fortum’s internal documents and experiences from various experts. This study shows that main insulation, transformer oil and current paths are the most important key indicators of the condition of the power transformer. Attention should be paid in monitoring of limit values and in the trend monitoring when analyzing the measurement results. The results should always be handled on a case by case basis. DFR-method gives a lot of information about the moisture and aging of the power transformer’s main insulation. The measurement results for the oil-paper-insulated high voltage cables were excellent. Results of the transformer bushings have so far been varied due to external interference. After this study, research on DFR-measurement will be continued and the aim will be in finding solutions for the identified problems

Drought effects on carbon allocation to resin defences and on resin dynamics in old-grown Scots pine

Droughts and other rapid changes in abiotic environmental conditions can predispose trees to damage by pest insects and pathogens. For survival of coniferous trees, functional resin-based defences are essential, and it is important to know how they react to changes in environmental conditions at various time scales. We studied the effects of differing water availabilities on resin-based defences in mature Scots pine (Pinus sylvestris) trees in a naturally drought-prone forest within a long-term irrigation experiment. Our objectives were to understand the effects of long-term drought on carbon allocation to resin production and to analyse its influence on resin flow and pressure in comparison to the shorter-term effects of seasonal drought. We tracked carbon allocation to resin after C-13-pulse labelling experiment in late summer 2017 and compared the observed resin dynamics between drought-exposed control trees and irrigated trees from June to August during the dry hot summer of 2018. Dry control trees showed higher allocation of labelled carbon to resin than irrigated trees. Resin pressure was higher in dry control than in irrigated trees with similar water potentials, and resin flow in June was higher in dry control than in irrigated trees with similar crown transparency. Yet, resin pressures of dry control trees in particular decreased with decreasing water availability from June to August. Resin flow was little affected by short-term changes in water availability and mostly associated with crown transparency. We suggest that because of differing timescales of direct drought effects and changes in allocation patterns, dry conditions may support resin-based defences in the long term, but a drought period decreases resin pressure in the short term.Peer reviewe

Drought effects on volatile organic compound emissions from Scots pine stems

Tree stems have been identified as sources of volatile organic compounds (VOCs) that play important roles in tree defence and atmospheric chemistry. Yet, we lack understanding on the magnitude and environmental drivers of stem VOC emissions in various forest ecosystems. Due to the increasing importance of extreme drought, we studied drought effects on the VOC emissions from mature Scots pine (Pinus sylvestris L.) stems. We measured monoterpenes, acetone, acetaldehyde and methanol emissions with custom-made stem chambers, online PTR-MS and adsorbent sampling in a drought-prone forest over the hot-dry summer of 2018 and compared the emission rates and dynamics between trees in naturally dry conditions and under long-term irrigation (drought release). The pine stems were significant monoterpene sources. The stem monoterpene emissions potentially originated from resin, based on their similar monoterpene spectra. The emission dynamics of all VOCs followed temperature at a daily scale, but monoterpene and acetaldehyde emission rates decreased nonlinearly with drought over the summer. Despite the dry conditions, large peaks of monoterpene, acetaldehyde and acetone emissions occurred in late summer potentially due to abiotic or biotic stressors. Our results highlight the potential importance of stem emissions in the ecosystem VOC budget, encouraging further studies in diverse environments.Peer reviewe

Temporal and Spatial Variation in Scots Pine Resin Pressure and Composition

Resin is a first-line defense in pine trees, but important questions regarding its temporal and spatial variation remain unsolved. Resin pressure varies according to water potential in dry conditions, but in moist conditions, it follows temperature dynamics for a yet unknown reason. Relations between resin composition, resin pressure, and shoot monoterpene emissions are also unquantified. To gain mechanistic understanding on the resin dynamics in a boreal forest, we measured temperature and water potential dependency of Scots pine resin pressure. We attempted to quantify the temperature dependency of resin pressure in terms of three contributions: 1) saturation vapor pressure, 2) thermal expansion, and 3) N2, O2, and CO2 solubility. We also analyzed monoterpene composition in the resin and the shoot emissions of 16 pines with gas chromatography mass spectrometry to study their interrelations. We show that in moist conditions, resin pressure is driven by temperature at a diurnal scale, but also affected by soil water potential at a day-to-day scale. Diurnal temperature dependency was explained by thermal expansion of resin and changes in bubble volume due to changes in gas solubility in resin with temperature. Resin pressures correlated also with total monoterpene and α-pinene content in resin and with total monoterpene and ∆3-carene and terpinolene emissions from shoots.Resin is a first-line defense in pine trees, but important questions regarding its temporal and spatial variation remain unsolved. Resin pressure varies according to water potential in dry conditions, but in moist conditions, it follows temperature dynamics for a yet unknown reason. Relations between resin composition, resin pressure, and shoot monoterpene emissions are also unquantified. To gain mechanistic understanding on the resin dynamics in a boreal forest, we measured temperature and water potential dependency of Scots pine resin pressure. We attempted to quantify the temperature dependency of resin pressure in terms of three contributions: (1) saturation vapor pressure, (2) thermal expansion, and (3) N2, O2, and CO2 solubility. We also analyzed monoterpene composition in the resin and the shoot emissions of 16 pines with gas chromatography mass spectrometry to study their interrelations. We show that in moist conditions, resin pressure is driven by temperature at a diurnal scale, but also affected by soil water potential at a day-to-day scale. Diurnal temperature dependency was explained by thermal expansion of resin and changes in bubble volume due to changes in gas solubility in resin with temperature. Resin pressures correlated also with total monoterpene and α-pinene content in resin and with total monoterpene and Δ3-carene and terpinolene emissions from shoots.Peer reviewe

Is Decreased Xylem Sap Surface Tension Associated With Embolism and Loss of Xylem Hydraulic Conductivity in Pathogen-Infected Norway Spruce Saplings?

Increased abiotic stress along with increasing temperatures, dry periods and forest disturbances may favor biotic stressors such as simultaneous invasion of bark beetle and ophiostomatoid fungi. It is not fully understood how tree desiccation is associated with colonization of sapwood by fungi. A decrease in xylem sap surface tension (sigma(xylem)) as a result of infection has been hypothesized to cause xylem embolism by lowering the threshold for air-seeding at the pits between conduits and disruptions in tree water transport. However, this hypothesis has not yet been tested. We investigated tree water relations by measuring the stem xylem hydraulic conductivity (K-stem), sigma(xylem), stem relative water content (RWCstem), and water potential (psi(stem)), and canopy conductance (g(canopy)), as well as the compound composition in xylem sap in Norway spruce (Picea abies) saplings. We conducted our measurements at the later stage ofEndoconidiophora polonicainfection when visible symptoms had occurred in xylem. Saplings of two clones (44 trees altogether) were allocated to treatments of inoculated, wounded control and intact control trees in a greenhouse. The saplings were destructively sampled every second week during summer 2016. sigma(xylem), K(stem)and RWC(stem)decreased following the inoculation, which may indicate that decreased sigma(xylem)resulted in increased embolism. g(canopy)did not differ between treatments indicating that stomata responded to psi(stem)rather than to embolism formation. Concentrations of quinic acid, myo-inositol, sucrose and alkylphenol increased in the xylem sap of inoculated trees. Myo-inositol concentrations also correlated negatively with sigma(xylem)and K-stem. Our study is a preliminary investigation of the role of sigma(xylem)inE. polonicainfected trees based on previous hypotheses. The results suggest thatE. polonicainfection can lead to a simultaneous decrease in xylem sap surface tension and a decline in tree hydraulic conductivity, thus hampering tree water transport.Peer reviewe

Is Decreased Xylem Sap Surface Tension Associated With Embolism and Loss of Xylem Hydraulic Conductivity in Pathogen-Infected Norway Spruce Saplings?

Increased abiotic stress along with increasing temperatures, dry periods and forest disturbances may favor biotic stressors such as simultaneous invasion of bark beetle and ophiostomatoid fungi. It is not fully understood how tree desiccation is associated with colonization of sapwood by fungi. A decrease in xylem sap surface tension (sigma(xylem)) as a result of infection has been hypothesized to cause xylem embolism by lowering the threshold for air-seeding at the pits between conduits and disruptions in tree water transport. However, this hypothesis has not yet been tested. We investigated tree water relations by measuring the stem xylem hydraulic conductivity (K-stem), sigma(xylem), stem relative water content (RWCstem), and water potential (psi(stem)), and canopy conductance (g(canopy)), as well as the compound composition in xylem sap in Norway spruce (Picea abies) saplings. We conducted our measurements at the later stage ofEndoconidiophora polonicainfection when visible symptoms had occurred in xylem. Saplings of two clones (44 trees altogether) were allocated to treatments of inoculated, wounded control and intact control trees in a greenhouse. The saplings were destructively sampled every second week during summer 2016. sigma(xylem), K(stem)and RWC(stem)decreased following the inoculation, which may indicate that decreased sigma(xylem)resulted in increased embolism. g(canopy)did not differ between treatments indicating that stomata responded to psi(stem)rather than to embolism formation. Concentrations of quinic acid, myo-inositol, sucrose and alkylphenol increased in the xylem sap of inoculated trees. Myo-inositol concentrations also correlated negatively with sigma(xylem)and K-stem. Our study is a preliminary investigation of the role of sigma(xylem)inE. polonicainfected trees based on previous hypotheses. The results suggest thatE. polonicainfection can lead to a simultaneous decrease in xylem sap surface tension and a decline in tree hydraulic conductivity, thus hampering tree water transport.Peer reviewe

Scots Pine Stems as Dynamic Sources of Monoterpene and Methanol Emissions

Funding Information: We are grateful for the funding received from Academy of Finland Center of Excellence program (Grant No. 307331), the University of Helsinki Center for Environment HENVI, the Nordic Center of Excellence CRAICC and the University of Helsinki Doctoral program AGFOREE. Publisher Copyright: © Copyright © 2020 Vanhatalo, Aalto, Chan, Hölttä, Kolari, Rissanen, Kabiri, Hellén and Bäck.The volatile organic compound (VOC) fluxes of living plant compartments other than foliage are poorly known. In this paper we describe for the first time the methanol and monoterpene fluxes from living Scots pine stems in situ, over 4 years at the SMEAR II station in southern Finland. The VOC fluxes from stems were measured online with an automated chamber measurement system. Both methanol and monoterpene emissions showed strong diurnal and seasonal cycles. Methanol emission rates were highest in mid-summer, and coincided with the most intensive period of stem radial growth. Methanol emission rates correlated moderately with the xylem sap flow rate and foliage transpiration rate, which suggests that many simultaneous and overlapping processes are related to methanol transport and production in trees. Monoterpene emissions from stems were highest on the hottest summer days, but also substantial in winter during times when the temperature was above zero °C for several days. Overall, the emissions from stems constitute about 2% of the whole stand monoterpene emissions under normal, non-stressed conditions. This can be used in stand monoterpene emission models as the rough estimate of woody compartment contribution.Peer reviewe