Opin vísindi
Opin vísindi er varðveislusafn vísindaefnis og doktorsritgerða í opnum aðgangi á vegum íslenskra háskóla og Landsbókasafns Íslands - Háskólabókasafns.
Opinn aðgangur að rannsóknaniðurstöðum er í samræmi við 10. gr. laga nr. 3/2003 um opinberan stuðning við vísindarannsóknir sem og kröfur innlendra og erlendra rannsóknasjóða. Markmiðið með opnum aðgangi er að niðurstöður rannsókna séu aðgengilegar sem flestum óhindrað og án endurgjalds á rafrænu formi. Vistun í varðveislusafninu er varanleg og ætlað að tryggja aðgang að vísindaefni íslenskra háskóla í opnum aðgangi um ókomna tíð. Varðveislusafnið Opin vísindi er tengt við rannsóknagáttina IRIS og rannsóknaniðurstöður í opnum aðgangi sem eru skráðar í IRIS eru um leið vistaðar og gerðar aðgengilegar til framtíðar í varðveislusafninu. Með því að safna þessu efni saman í eitt safn verður aðgangur að því einfaldur og þægilegur fyrir alla sem vilja kynna sér það og geta þannig notið þess öfluga vísindastarfs sem fram fer í háskólum landsins.
Varðveislusafnið er OpenAIRE / OpenAIREplus samhæft og samrýmist kröfum sem gerðar eru um birtingu rannsóknaniðurstaðna úr verkefnum sem styrkt eru úr evrópsku rannsóknaáætlununum FP7 og H2020.
Varðveislusafnið notar opna hugbúnaðinn DSpace.
Opinn aðgangur að rannsóknaniðurstöðum er í samræmi við 10. gr. laga nr. 3/2003 um opinberan stuðning við vísindarannsóknir sem og kröfur innlendra og erlendra rannsóknasjóða. Markmiðið með opnum aðgangi er að niðurstöður rannsókna séu aðgengilegar sem flestum óhindrað og án endurgjalds á rafrænu formi. Vistun í varðveislusafninu er varanleg og ætlað að tryggja aðgang að vísindaefni íslenskra háskóla í opnum aðgangi um ókomna tíð. Varðveislusafnið Opin vísindi er tengt við rannsóknagáttina IRIS og rannsóknaniðurstöður í opnum aðgangi sem eru skráðar í IRIS eru um leið vistaðar og gerðar aðgengilegar til framtíðar í varðveislusafninu. Með því að safna þessu efni saman í eitt safn verður aðgangur að því einfaldur og þægilegur fyrir alla sem vilja kynna sér það og geta þannig notið þess öfluga vísindastarfs sem fram fer í háskólum landsins.
Varðveislusafnið er OpenAIRE / OpenAIREplus samhæft og samrýmist kröfum sem gerðar eru um birtingu rannsóknaniðurstaðna úr verkefnum sem styrkt eru úr evrópsku rannsóknaáætlununum FP7 og H2020.
Varðveislusafnið notar opna hugbúnaðinn DSpace.
Nýlega bætt við
Simulation studies of Hopfions in atomistic spin systems
(University of Iceland, School of Engineering and Natural Sciences, Faculty of Physical Sciences; RWTH Aachen University, Faculty of Mathematics, Computer Science and Natural Sciences, 2026) Sallermann, Moritz; Hannes Jónsson; Faculty of Physical Sciences (UI); Raunvísindadeild (HÍ); Department of Mathematics (RWTH-AU); School of Engineering and Natural Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ); Faculty of Mathematics, Computer Science and Natural Sciences (RWTH-AU)
The main protagonists of this thesis, magnetic Hopfions, are threedimensional topological solitons characterized by the Hopf invariant, a quantity that measures the linking number of pre-images of constant magnetization within magnetic textures. These intriguing solitons appear as local, spatially compact, energy minima in bulk magnetic materials featuring competing exchange interactions, making them ideal candidates for exploring fundamental physical phenomena as well as potential building blocks for advanced spintronic devices. However, determining their practical stability and viability in technological applications necessitates an in-depth analysis of their decay mechanisms, especially in environments subject to thermal fluctuations.
In this thesis, we employ an atomistic spin lattice model, concretely a Heisenberg model with competing exchange interactions, to describe the Hopfion, which we investigate by means of atomistic spin dynamics. In particular, we employ harmonic transition state theory (HTST), a powerful and computationally efficient framework, to rigorously assess the lifetime and decay dynamics of Hopfions.
We further extend the conventional HTST approach – as commonly applied to spin systems where only magnetization precession over the transition state is considered – by explicitly incorporating thermal crossings of the transition state. This extension provides a more complete and physically accurate description of thermally activated decay processes, accounting not only for precessional dynamics but also for thermal fluctuations enabling magnetization states to cross the saddle region, thus improving lifetime predictions. A fundamental example where this contribution is, perhaps, felt the most is the reversal of a single spin under the influence of uniaxial anisotropy (think of a hard ferromagnet) – where conventional HTST fails to predict any rate at all.
To accurately quantify these dynamics, we implement computational techniques such as the geodesic nudged elastic band (GNEB) method combined with an adapted dimer method, enabling precise identification of transition states and corresponding energy barriers associated with Hopfion decay. Following common methodology, we locate first-order saddle points on an energy landscape, representing critical states where decay occurs via the nucleation and subsequent propagation of Bloch points. Our investigations reveal a clear dependence of Hopfion stability on their size, relative to the underlying lattice structure, demonstrating that larger Hopfions generally exhibit increased robustness against decay.
Moreover, this research explicitly addresses several critical technical challenges inherent to the computational methods employed. These include (i) the accurate treatment and interpretation of Goldstone modes, which emerge due to inherent symmetry properties of the Hopfion configurations, and (ii) the computational complexity associated with evaluating sparse positive-definite determinants, which is essential for determining entropic pre-factors. By resolving these challenges, our study not only provides quantitative predictions of Hopfion lifetimes but also offers qualitative insights into the interplay between energy and entropy in these topological systems.
Through this comprehensive theoretical and numerical analysis, the work presented in this thesis significantly advances the understanding of the fundamental principles governing Hopfion stability.
Health Behavior and Academic Achievement among Adolescents: The Relative Contribution of Dietary Habits, Physical Activity, BMI and Self-Esteem
(2010) Kristjansson, AL.; Sigfusdottir, ID.; Allegrante, JP.; Department of Psychology
Trends in Physical Activity and Participation in Sport Clubs among Icelandic Adolescents
(2008) Eidsdottir, STH.; Kristjansson, AL.; Sigfusdottir, ID.; Allegrante, JP.; Department of Psychology
Social correlates of cigarette smoking among Icelandic adolescents: a population-based cross-sectional study : A population-based cross-sectional study
(2008) Kristjansson, AL.; Sigfusdottir, ID.; Allegrante, JP.; Helgason, AR.; Department of Psychology
Background. Previous research has shown that between 80 and 90 percent of adult smokers report having started smoking before 18 years of age. Several studies have revealed that multiple social factors influence the likelihood of smoking during adolescence, the period during which the onset of smoking usually occurs. To better understand the social mechanisms that influence adolescent smoking, we analyzed the relationship and relative importance of a broad spectrum of social variables in adolescent smoking in Iceland, a Nordic country with high per-capita income. Methods. We used cross-sectional data from 7,430 14- to 16 year-old students (approximately 81% of all Icelanders in these age cohorts) in the 2006 Youth in Iceland study. The Youth in Iceland studies are designed to investigate the role of several cognitive, behavioral, and social factors in the lives of adolescents, and the data collected are used to inform the design, implementation, and evaluation of substance use prevention programs that are being developed by Icelandic social scientists, policy makers, and practitioners. Results. Our analysis revealed that friends' smoking behavior and attitude toward smoking were strongly associated with adolescent smoking and other tobacco use, as well as alcohol consumption during the previous 30 days. Main protective factors were parent's perceived attitude toward smoking, the quantity of time spent with parents, absence of serious verbal conflict between parents and adolescents, and participation in physical activity. Family structure was related to adolescent smoking to a small extent, but other background factors were not. Conclusion. We conclude that multiple social factors are related to adolescent smoking. Parents and other primary preventive agents need to be informed about the complicated nature of the adolescent social world in order to maximize their impact.
Adolescent Health Behavior, Contentment in School, and Academic Achievement : 5th European Youth Heart Study Symposium
(2008) Kristjánsson, Á. L.; Sigfúsdóttir, I. D.; Allegrante, J. P.; Helgason, Á. R.; Department of Psychology
Flokkar í Opnum vísindum
Veldu flokk til að skoða.
- University of Iceland
- University of Akureyri
- Bifröst University
- Hólar University College
- IRIS
- Agricultural University of Iceland
- National and University Library of Iceland
- Iceland University of the Arts