Search results for "ongelmat"
showing 10 items of 365 documents
Inverse problems for $p$-Laplace type equations under monotonicity assumptions
2016
We consider inverse problems for $p$-Laplace type equations under monotonicity assumptions. In two dimensions, we show that any two conductivities satisfying $\sigma_1 \geq \sigma_2$ and having the same nonlinear Dirichlet-to-Neumann map must be identical. The proof is based on a monotonicity inequality and the unique continuation principle for $p$-Laplace type equations. In higher dimensions, where unique continuation is not known, we obtain a similar result for conductivities close to constant.
Kokkeja, kajuuttavahteja ja oppilaita : miehistön nuorimmat jäsenet oululaisilla ja raahelaisilla purjealuksilla 1850 - 1860 -luvuilla
2012
Pro gradun tarkoituksena on selvittää oululaisten ja raahelaisten kauppa-alusten miehistön nuorimpien jäsenten merille lähtöä ja urakehitystä ensimmäisen viiden vuoden aikana. Työn tavoitteena on selvittää, minkä ikäisiä olivat nuoret merimiehet, millaiset sosiaaliset lähtökohdat heillä oli, miksi he pestautuivat, millaista elämä oli laivalla ja miten heidän uransa kehittyi jatkossa. Tarkastelu kohdistuu viiden vuoden jaksolle vuosina 1858-1863 ja mahdollisuuksien mukaan joidenkin miesten uraa on seurattu pidemmälti. Tutkimus edustaa kollektiivibiografista ja mikrohistoriallista tutkimusotetta. Tutkittavasta joukosta, 75 nuoresta miehestä, on luotu tietokantoja, joiden avulla selvitetään, m…
Mental Health Status of Healthcare Workers During the COVID-19 Outbreak
2021
Background: The COVID-19 pandemic is a massive health crisis that has exerted enormous physical and psychological pressure. Mental healthcare for healthcare workers (HCWs) should receive serious consideration. This study served to determine the mental-health outcomes of 1,556 HCWs from 45 countries who participated in the COVID-19 IMPACT project, and to examine the predictors of the outcomes during the first pandemic wave. Methods: Outcomes assessed were self-reported perceived stress, depression symptom, and sleep changes. The predictors examined included sociodemographic factors and perceived social support. Results: The results demonstrated that half of the HCWs had moderate levels of pe…
Gambling and gaming during COVID-19 : The role of mental health and social motives in gambling and gaming problems
2022
Background: The uncertain and stressful global situation caused by the COVID-19 pandemic has the potential to cause anxiety and impact people's mental health. Simultaneously, social distancing policies have isolated people from their normal social interactions. These societal changes have inevitably influenced gambling and gaming practices, and many people may have turned to betting or gaming as a means of social exchange. This study examined the influence of COVID-19 anxiety on increased mental health problems and their relationship to gambling and gaming problems. The mediating role of social motives for gambling and gaming was also investigated. Material and methods: Finnish adults (N = …
The associations of indoor environment and psychosocial factors on the subjective evaluation of Indoor Air Quality among lower secondary school stude…
2017
Subjective evaluation of Indoor Air Quality (subjective IAQ) reflects both building-related and psychosocial factors, but their associations have rarely been studied other than on the individual level in occupational settings and their interactions have not been assessed. Therefore, we studied whether schools' observed indoor air problems and psychosocial factors are associated with subjective IAQ and their potential interactions. The analysis was performed with a nationwide sample (N = 195 schools/26946 students) using multilevel modeling. Two datasets were merged: (i) survey data from students, including information on schools' psychosocial environment and subjective IAQ, and (ii) data fr…
Relationship Between Accelerometer-Based Physical Activity, Sedentary Behavior, and Mental Health in Young Finnish Men
2022
Healthy lifestyle behaviors including physical activity (PA) have been recognized to contribute positively to mental health. Most of the evidence on relationship between PA and mental health relies on self-reported PA results. Device-based measures on PA or sedentary behavior (SB) are less frequently used in mental health research. The present study aimed at examining the relationship between mental health and PA/SB measured by accelerometers in young Finnish men. The sample consisted of 409 men (mean age 28 ± 7 years), who participated in the military refresher training in Finland. Self-rated mental health was measured with Mental Health Inventory (MHI-5) and short Warwick-Edinburgh Mental…
Jacobian of solutions to the conductivity equation in limited view
2022
Abstract The aim of hybrid inverse problems such as Acousto-Electric Tomography or Current Density Imaging is the reconstruction of the electrical conductivity in a domain that can only be accessed from its exterior. In the inversion procedure, the solutions to the conductivity equation play a central role. In particular, it is important that the Jacobian of the solutions is non-vanishing. In the present paper we address a two-dimensional limited view setting, where only a part of the boundary of the domain can be controlled by a non-zero Dirichlet condition, while on the remaining boundary there is a zero Dirichlet condition. For this setting, we propose sufficient conditions on the bounda…
The Calderón problem for the fractional Schrödinger equation
2020
We show global uniqueness in an inverse problem for the fractional Schr\"odinger equation: an unknown potential in a bounded domain is uniquely determined by exterior measurements of solutions. We also show global uniqueness in the partial data problem where the measurements are taken in arbitrary open, possibly disjoint, subsets of the exterior. The results apply in any dimension $\geq 2$ and are based on a strong approximation property of the fractional equation that extends earlier work. This special feature of the nonlocal equation renders the analysis of related inverse problems radically different from the traditional Calder\'on problem.
Exponential instability in the fractional Calder\'on problem
2017
In this note we prove the exponential instability of the fractional Calder\'on problem and thus prove the optimality of the logarithmic stability estimate from \cite{RS17}. In order to infer this result, we follow the strategy introduced by Mandache in \cite{M01} for the standard Calder\'on problem. Here we exploit a close relation between the fractional Calder\'on problem and the classical Poisson operator. Moreover, using the construction of a suitable orthonormal basis, we also prove (almost) optimality of the Runge approximation result for the fractional Laplacian, which was derived in \cite{RS17}. Finally, in one dimension, we show a close relation between the fractional Calder\'on pro…
The linearized Calderón problem on complex manifolds
2019
International audience; In this note we show that on any compact subdomain of a Kähler manifold that admits sufficiently many global holomorphic functions , the products of harmonic functions form a complete set. This gives a positive answer to the linearized anisotropic Calderón problem on a class of complex manifolds that includes compact subdomains of Stein manifolds and sufficiently small subdomains of Kähler manifolds. Some of these manifolds do not admit limiting Carleman weights, and thus cannot by treated by standard methods for the Calderón problem in higher dimensions. The argument is based on constructing Morse holo-morphic functions with approximately prescribed critical points.…