Browsing Institutt for teoretisk astrofysikk by Title
Now showing items 137-156 of 495
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(Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2012)We consider issues related to the conformal mapping between the Einstein and Jordan frames in f(R) cosmology. We consider the impact of the conformal transformation on the gauge of a perturbed system and show that unless ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2013)In the first-order formalism of gravitational theories, the spacetime connection is considered as an independent variable to vary together with the metric. However, the metric still generates its Levi-Civita connection ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)© 2017. The American Astronomical Society. All rights reserved.
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(Master thesis / Masteroppgave, 2011)There have been many reports on anomalies in the CMB from different research groups. In this work statistical tests using the gradients of the CMB temperature, applied to the seven year WMAP data, have been investigated. ...
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(Master thesis / Hovedoppgave, 2002)It is believed that the Broad Emission Line Region of Quasars consists of discrete clouds. Due to the suspected small size of a cloud, the radiation from clouds may be strongly amplified by gravitational microlensing. It ...
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(Master thesis / Masteroppgave, 2013)The gravitational redshift in clusters of galaxies can be measured to probe gravity as was first done by Wojtak et al. (2011). Using N -body simulations we are able to analyze the gravitational redshift profiles for the ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)Aims: We investigate the gravitational redshift in clusters of galaxies in the symmetron and Hu-Sawicky f(R) models. The characteristic feature of both models is the screening mechanism that hides the fifth force in dense ...
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(Master thesis / Masteroppgave, 2013)Modified gravity theories are a popular research field in the hope that they could explain some of the unanswered questions in cosmology, for example how the universe starts, evolves and ends. One way to test proposed ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2013)The heating of the Sun's chromosphere remains poorly understood. While progress has been made on understanding what drives the quiet-Sun internetwork chromosphere, chromospheric heating in strong magnetic field regions ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)We use coordinated observations with the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1 m Solar Telescope to identify the disk counterpart of type II spicules in upper-chromospheric and transition region ...
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(Master thesis / Masteroppgave, 2010)
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(Doctoral thesis / Doktoravhandling, 2007)Doktorgradsavhandlingen beskriver et programvarebibliotek utviklet av Øystein Olsen ved Institutt for teoretisk astrofysikk. Programvaren har blitt brukt til å finne regioner med stabile og ustabile baner rundt asteroider ...
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(Master thesis / Masteroppgave, 2011)Spicules are relatively small, narrow and elongated structures that stick out above the edge of the solar disk. They are very dynamic and appear as jets that shoot out into the outer solar atmosphere. Up until recently, ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2016)Aims. We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z = 0.18, which is one of the most powerful gravitational telescopes that nature provides. Methods. Our ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)We present the first results of sunspot oscillations from observations by the Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is identified in both the slit-jaw images and the spectra of several ...
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(Master thesis / Masteroppgave, 2007)
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)We report on observations of recurrent jets by instruments on board the Interface Region Imaging Spectrograph, Solar Dynamics Observatory (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21, recurrent coronal ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)We perform non-LTE inversions in a large set of umbral flashes, including the dark fibrils visible within them, and in the quiescent umbra by using the inversion code NICOLE on a set of full Stokes high-resolution Ca ii ...