Simultaneous reconstruction of outer boundary shape and admittivity distribution in electrical impedance tomography

The aim of electrical impedance tomography is to reconstruct the admittivity distribution inside a physical body from boundary measurements of current and voltage. Due to the severe ill-posedness of the underlying inverse problem, the functionality of impedance tomography relies heavily on accurate modelling of the measurement geometry. In particular, almost all reconstruction algorithms require the precise shape of the imaged body as an input. In this work, the need for prior geometric information is relaxed by introducing a Newton-type output least squares algorithm that reconstructs the admittivity distribution and the object shape simultaneously. The method is built in the framework of the complete electrode model and it is based on the Fr\'echet derivative of the corresponding current-to-voltage map with respect to the object boundary shape. The functionality of the technique is demonstrated via numerical experiments with simulated measurement data.Comment: 3 figure

Nonplanar sensing skins for structural health monitoring based on electrical resistance tomography

Electrical resistance tomography (ERT)-based distributed surface sensing systems, or sensing skins, offer alternative sensing techniques for structural health monitoring, providing capabilities for distributed sensing of, for example, damage, strain, and temperature. Currently, however, the computational techniques utilized for sensing skins are limited to planar surfaces. In this paper, to overcome this limitation, we generalize the ERT-based surface sensing to nonplanar surfaces covering arbitrarily shaped three-dimensional structures; we construct a framework in which we reformulate the image reconstruction problem of ERT using techniques of Riemannian geometry, and solve the resulting problem numerically. We test this framework in series of numerical and experimental studies. The results demonstrate the feasibility of the proposed formulation and the applicability of ERT-based sensing skins to nonplanar geometries.Peer reviewe

Imaging of moisture content in wood using electrical capacitance tomography

http://shop.tuverlag.at/de/the-world-conference-on-timber-engineeringThe current study investigates whether an electrical imaging modality, electrical capacitance tomography (ECT), could provide information on the moisture content in wood. In ECT, a set of electrodes are placed around the surface of the object, and based on electrical capacitance measurements from the surface, the spatial distribution of the electrical permittivity inside the object is reconstructed. In this experimental study, water is infiltrated in a wood sample for 7 days, and ECT measurements are sequentially collected during the absorption of water. The reconstructed ECT images show a constant increase of electrical permittivity in the location of water absorption. The results support the feasibility of ECT for imaging the water content in wood.Peer reviewe

Aerosol formation and growth rates from chamber experiments using Kalman smoothing

Bayesian state estimation in the form of Kalman smoothing was applied to differential mobility analyser train (DMA-train) measurements of aerosol size distribution dynamics. Four experiments were analysed in order to estimate the aerosol size distribution, formation rate, and size-dependent growth rate, as functions of time. The first analysed case was a synthetic one, generated by a detailed aerosol dynamics model and the other three chamber experiments performed at the CERN CLOUD facility. The estimated formation and growth rates were compared with other methods used earlier for the CLOUD data and with the true values for the computer-generated synthetic experiment. The agreement in the growth rates was very good for all studied cases: estimations with an earlier method fell within the uncertainty limits of the Kalman smoother results. The formation rates also matched well, within roughly a factor of 2.5 in all cases, which can be considered very good considering the fact that they were estimated from data given by two different instruments, the other being the particle size magnifier (PSM), which is known to have large uncertainties close to its detection limit. The presented fixed interval Kalman smoother (FIKS) method has clear advantages compared with earlier methods that have been applied to this kind of data. First, FIKS can reconstruct the size distribution between possible size gaps in the measurement in such a way that it is consistent with aerosol size distribution dynamics theory, and second, the method gives rise to direct and reliable estimation of size distribution and process rate uncertainties if the uncertainties in the kernel functions and numerical models are known.Bayesian state estimation in the form of Kalman smoothing was applied to differential mobility analyser train (DMA-train) measurements of aerosol size distribution dynamics. Four experiments were analysed in order to estimate the aerosol size distribution, formation rate, and size-dependent growth rate, as functions of time. The first analysed case was a synthetic one, generated by a detailed aerosol dynamics model and the other three chamber experiments performed at the CERN CLOUD facility. The estimated formation and growth rates were compared with other methods used earlier for the CLOUD data and with the true values for the computer-generated synthetic experiment. The agreement in the growth rates was very good for all studied cases: estimations with an earlier method fell within the uncertainty limits of the Kalman smoother results. The formation rates also matched well, within roughly a factor of 2.5 in all cases, which can be considered very good considering the fact that they were estimated from data given by two different instruments, the other being the particle size magnifier (PSM), which is known to have large uncertainties close to its detection limit. The presented fixed interval Kalman smoother (FIKS) method has clear advantages compared with earlier methods that have been applied to this kind of data. First, FIKS can reconstruct the size distribution between possible size gaps in the measurement in such a way that it is consistent with aerosol size distribution dynamics theory, and second, the method gives rise to direct and reliable estimation of size distribution and process rate uncertainties if the un-certainties in the kernel functions and numerical models are known.Peer reviewe

Quantitative electrical imaging of three-dimensional moisture flow in cement-based materials

The presence of moisture significantly affects the mechanical, hydraulic, chemical, electrical, and thermal properties of cement-based and other porous materials, and therefore, methods for detecting and quantifying the moisture ingress in these materials are needed. Recent research studies have shown that the ingress of moisture in porous materials can be qualitatively imaged with Electrical Impedance Tomography (EIT) – an imaging modality which uses electrical measurements from object’s surface to reconstruct the electrical conductivity distribution inside the object. The aim of this study is to investigate whether EIT could image the three-dimensional volumetric moisture content within cement-based materials quantitatively. For this aim, we apply the so-called absolute imaging scheme to the EIT image reconstruction, and use an experimentally developed model for converting the electrical conductivity distribution to volumetric moisture content. The results of the experimental studies support the feasibility of EIT for quantitative imaging of three-dimensional moisture flows in cement-based materials

"It's called plasticity" : Meters and their significance in Lauri Viita's Betonimylläri

Tutkielman aihe on runomitat, niiden käyttö ja niiden merkitys Lauri Viidan runokokoelmassa Betonimylläri (1947). Tutkielmassa selvitän metriikantutkimuksen keinoin, millaisia mittatyyppejä Viita suosii ja miten eri mittatyyppien käyttö kytkeytyy runojen merkityssisältöön ja tyylilajiin. Runomittojen kuvauksessa hyödynnän Pentti Leinon luomaa kuvausmallia, jonka avulla voidaan esittää runomittojen pohjakaavat ja eri runojen noudattamat mittasäännöt. Viita on eräs merkittävimmistä sotienjälkeisistä runoilijoistamme. Sotienjälkeisessä lyriikassa tapahtuu merkittävä muutos, jossa perinteisen runouden käyttämistä sidotusta mitasta ja riimityksestä luovuttiin. Kokonaan näistä keinoista luopunutta suuntausta kutsutaan 50-luvun modernismiksi. Niistä runoilijoista, jotka eivät luopuneet näistä keinoista vaan pikemminkin uudistivat niiden käyttöä 40-luvun lopussa ja 50-luvun alussa, on käytetty esimerkiksi nimitystä ”välipolven runoilijat”. Tähän sukupolveen kuuluu myös Viita. Tutkimuksessa mielenkiintoni kohdistuu siihen, millä tavalla Viita hyödyntää ja uudistaa mitallisen runouden perinnettä. Analyysistäni selviää, että Viita suosii Betonimyllärissä laskevia mittoja, erityisesti trokeeta. Myös daktyylin osuus on huomattava, mikä on poikkeuksellista suomalaisessa lyriikassa. Suomalaisen lyriikan suosimaa nousevaa mittatyyppiä runokokoelmassa esiintyy suhteellisen vähän. Laskevan mittatyypin suosiminen liittyy Viidan runokielen puheenomaisuuteen: laskevien mittojen avulla runojen rytmi on lähempänä proosakieltä. Viita käyttää joissain runoissa huomionarvoisesti sekaisin nousevaa ja laskevaa mittaa. Tällainen säkeen suunnan muutos motivoituu runon sisällöstä käsin. Esimerkiksi analysoimassani runossa ”Alfhild” vaihdos nousevaan mittaan on samalla vaihdos lyyrisempään tyylilajiin, joka puolestaan liittyy runon puhujan tunnetilan muutokseen ja samastumiseen toiseen henkilöön. Viidalla esiintyy jossain määrin myös tavun laajuuden systemaattista vaihtelua, mikä on erityisesti klassisen runouden piirre. Runossa ”Maailmanparantajalle” tällainen alluusio klassiseen runouteen toimii tulkintani mukaan viittauksena runossa kuvattuun puhujaan ja tämän käyttämään retoriikkaan. Runomitan avulla luodaan mielikuva antiikin retoriikasta. Runossa ”Mylly” puolestaan tavun laajuuden vaihtelu liittyy siinä käytettyyn daktyylimittaan. Laajassa daktyylimittaisessa runossa durationaaliset eli tavun laajuuteen liittyvät piirteet tekevät mitasta joustavamman ja vähemmän monotonisen. Vain tavupainoon perustuvat mittasäännöt rajoittaisivat käyttökelpoisten sanojen määrää. Klassisista runomitoista Viita on lainannut periaatteen, että yhden kolmitavuisen daktyylijalan voi korvata myös kaksitavuinen trokeejalka, mikäli sen tavut ovat laajuudeltaan kyllin pitkiä: pitkätavuinen trokee on kestoltaan samaa luokkaa kuin daktyyli, jossa laskuaseman tavut eivät ole kokopitkiä. Tutkielmassani osoitan, että Viita käyttää mittoja joustavasti runon merkitystä ja tyylilajia silmällä pitäen, ja runoissa liikutaan sidotun ja vapaan mitan välillä riippuen siitä, mikä on runon kannalta tarkoituksenmukaista

Bayesian estimation of seasonal course of canopy leaf area index from hyperspectral satellite data

In this paper, Bayesian inversion of a physically-based forest reflectance model is investigated to estimate of boreal forest canopy leaf area index (LAI) from EO-1 Hyperion hyperspectral data. The data consist of multiple forest stands with different species compositions and structures, imaged in three phases of the growing season. The Bayesian estimates of canopy LAI are compared to reference estimates based on a spectral vegetation index. The forest reflectance model contains also other unknown variables in addition to LAI, for example leaf single scattering albedo and understory reflectance. In the Bayesian approach, these variables are estimated simultaneously with LAI. The feasibility and seasonal variation of these estimates is also examined. Credible intervals for the estimates are also calculated and evaluated. The results show that the Bayesian inversion approach is significantly better than using a comparable spectral vegetation index regression.Peer reviewe