Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Astronomi astrofysik och kosmologi) "

Sökning: hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Astronomi astrofysik och kosmologi)

Sortera/gruppera träfflistan
  • Linder, Cedric, et al. (författare)
  • The overlooked challenge of learning to extrapolate three-dimensionality
  • 2013
  • Ingår i: Book of Abstracts. - : Charles University.
  • Konferensbidrag (refereegranskat)abstract
    • Learning astronomy has many learning challenges due to the highly diverse, conceptual, and theoretical thinking used in the discipline. One taken for granted challenge is the learning to extrapolate three-dimensionality. Although we have the ability to see our surroundings in threedimensional terms, beyond a distance of about 200m this ability quickly becomes very limited. So, when looking up at the night sky, learning to discern critical features that are embedded in dimensionality does not come easily. There have been several articles addressing how fruitful 3D simulations are for astronomy education, but they do not address what students discern, nor the nature of that discernment. Taking the concept of discernment to be about noticing something and assigning meaning to it, our research question is: In terms of dimensionality, what do astronomy/physics students and professors discern when engaging with a simulated video flythrough of our Galaxy and beyond?A web-based questionnaire was designed using links to video clips drawn from a well-regarded simulation-video of travel through our galaxy and beyond. 137 physics and astronomy university students and teaching professors, who were drawn from nine countries, completed the questionnaire. The descriptions provided by them were used to formulate six categories of discernment in relation to multidimensionality. These results are used to make the case that astronomy learning that aims at developing the ability to extrapolate three-dimensionality needs to be grounded in the creation of meaningful motion parallax experiences. Teaching and learning implications are discussed.
  • Eriksson, Urban, et al. (författare)
  • Limits of ultra-high-precision optical astrometry : stellar surface structures
  • 2007
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:3, s. 1389-1400
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. To investigate the astrometric effects of stellar surface structures as a practical limitation to ultra-high-precision astrometry (e.g. in the context of exoplanet searches) and to quantify the expected effects in different regions of the HR-diagram. Methods. Stellar surface structures (spots, plages, granulation, non-radial oscillations) are likely to produce fluctuations in the integrated flux and radial velocity of the star, as well as a variation of the observed photocentre, i.e. astrometric jitter. We use theoretical considerations supported by Monte Carlo simulations (using a starspot model) to derive statistical relations between the corresponding astrometric, photometric, and radial velocity effects. Based on these relations, the more easily observed photometric and radial velocity variations can be used to predict the expected size of the astrometric jitter. Also the third moment of the brightness distribution, interferometrically observable as closure phase, contains information about the astrometric jitter. Results. For most stellar types the astrometric jitter due to stellar surface structures is expected to be of the order of 10 micro-AU or greater. This is more than the astrometric displacement typically caused by an Earth-size exoplanet in the habitable zone, which is about 1-4 micro-AU for long-lived main-sequence stars. Only for stars with extremely low photometric variability (< 0.5 mmag) and low magnetic activity, comparable to that of the Sun, will the astrometric jitter be of the order of 1 micro-AU, sufficient to allow the astrometric detection of an Earth-sized planet in the habitable zone. While stellar surface structure may thus seriously impair the astrometric detection of small exoplanets, it has in general a negligible impact on the detection of large (Jupiter-size) planets and on the determination of stellar parallax and proper motion. From the starspot model we also conclude that the commonly used spot filling factor is not the most relevant parameter for quantifying the spottiness in terms of the resulting astrometric, photometric and radial velocity variations.
  • Eriksson, Urban, et al. (författare)
  • Tell me what you see : Differences in what is discerned when professors and students view the same disciplinary semiotic resource
  • 2014
  • Ingår i: The 5th international 360° conference: Encompassing the Multimodality of Knowledge, May 8-10 2014, Aarhus.
  • Konferensbidrag (refereegranskat)abstract
    • Traditionally, astronomy and physics have been viewed as difficult subjects to master. The movement from everyday conceptions of the world around us to a disciplinary interpretation is fraught with pitfalls and problems. What characterises a disciplinary insider’s discernment of phenomena in astronomy and how does it compare to the views of newcomers to the field? In this paper we report on a study into what students and professors discern (cf. Eriksson et al, in press) from the same disciplinary semiotic resource and use this to propose an Anatomy of Disciplinary Discernment (ADD) as an overarching characterization of disciplinary learning.Students and professors in astronomy and physics were asked to describe what they could discern from a simulation video of travel through our Galaxy and beyond (Tully, 2012). In all, 137 people from nine countries participated. The descriptions were analysed using a hermeneutic, constant comparison approach (Seebohm, 2004; Strauss, 1987). Analysis culminated in the formulation of five hierarchically arranged, qualitatively different categories of discernment. This ADD modelling of the data consists of one non-disciplinary category and four levels of disciplinary discernment: Identification, Explanation, Appreciation, and Evaluation. Our analysis demonstrates a clear relationship between educational level and the level of disciplinary discernment.The analytic outcomes of the study suggest that teachers may create more effective learning environments by explicitly crafting their teaching to support the discernment of various aspects of disciplinary semiotic resources in order to facilitate the crossing of boundaries in the ADD model.
  • Eriksson, Urban, et al. (författare)
  • What do teachers of astronomy need to think about?
  • 2013
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Learning astronomy has exciting prospects for many students; learning about the stars in the sky, the planets, galaxies, etc., is often very inspiring and sets the mind on the really big aspects of astronomy as a science; the Universe. At the same time, learning astronomy can be a challenging endeavor for many students. One of the most difficult things to come to understand is how big the Universe is. Despite seeming trivial, size and distances, together with the three-dimensional (3D) structure of the Universe, probably present some of the biggest challenges in the teaching and learning of astronomy (Eriksson, Linder, Airey, & Redfors, in preparation; Lelliott & Rollnick, 2010). This is the starting point for every astronomy educator. From here, an educationally critical question to ask is: how can we best approach the teaching of astronomy to optimize the potential for our students attaining a holistic understanding about the nature of the Universe? Resent research indicates that to develop students’ understanding about the structure of the Universe, computer generated 3D simulations can be used to provide the students with an experience that other representations cannot easily provide (Eriksson et al., in preparation; Joseph, 2011). These simulations offer disciplinary affordance* through the generation of motion parallax for the viewer. Using this background we will present the results of a recent investigation that we completed looking at what students’ discern (notice with meaning) about the multidimensionality of the Universe. Implications for astronomy education will be discussed and exemplified. *[T]he inherent potential of [a] representation to provide access to disciplinary knowledge (Fredlund, Airey, & Linder, 2012, p. 658) Eriksson, U., Linder, C., Airey, J., & Redfors, A. (in preparation). Who needs 3D when the Universe is flat? Fredlund, T., Airey, J., & Linder, C. (2012). Exploring the role of physics representations: an illustrative example from students sharing knowledgeabout refraction. European Journal of Physics, 33(3), 657. Joseph, N. M. (2011). Stereoscopic Visualization as a Tool For Learning Astronomy Concepts. (Master of Science), Purdue University, Purdue University Press Journals. Lelliott, A., & Rollnick, M. (2010). Big Ideas: A review of astronomy education research 1974--2008. International Journal of Science Education, 32(13), 1771–1799
  • Li, Wenxian, 1989-, et al. (författare)
  • HFSZEEMAN95 : A program for computing weak and intermediate magnetic-field- and hyperfine-induced transition rates
  • 2020
  • Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 253
  • Tidskriftsartikel (refereegranskat)abstract
    • Hfszeeman95 is an updated and extended Fortran 95 version of the Hfszeeman program (Andersson and Jönsson, 2008). Given relativistic atomic state functions generated by the Grasp2018 package (Fischer et al., 2019), Hfszeeman95 together with the accompanying Matlab/GNU Octave program Mithit allows for: (1) the computation and plotting of Zeeman energy splittings of magnetic fine- and hyperfine structure substates as functions of the strength of an external magnetic field, (2) the computation of transition rates between different magnetic fine- and hyperfine structure substates in the presence of an external magnetic field and rates of hyperfine-induced transitions in the field free limit, (3) the synthesization of spectral profiles for transitions obtained from (2). With the new features, Hfszeeman95 and the accompanying Matlab/GNU Octave program Mithit are useful for the analysis of observational spectra and to resolve the complex features due to the splitting of the fine and hyperfine levels.
  • Blesneag, Stefan, et al. (författare)
  • Matter field Kahler metric in heterotic string theory from localisation
  • 2018
  • Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :4
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose an analytic method to calculate the matter field Kahler metric in heterotic compactifications on smooth Calabi-Yau three-folds with Abelian internal gauge fields. The matter field Kahler metric determines the normalisations of the N = 1 chiral superfields, which enter the computation of the physical Yukawa couplings. We first derive the general formula for this Kahler metric by a dimensional reduction of the relevant supergravity theory and find that its T-moduli dependence can be determined in general. It turns out that, due to large internal gauge flux, the remaining integrals localise around certain points on the compactification manifold and can, hence, be calculated approximately without precise knowledge of the Ricci-flat Calabi-Yau metric. In a final step, we show how this local result can be expressed in terms of the global moduli of the Calabi-Yau manifold. The method is illustrated for the family of Calabi-Yau hypersurfaces embedded in P-1 x P-3 and we obtain an explicit result for the matter field Kahler metric in this case.
  • Scott, Pat, 1982- (författare)
  • Searches for Particle Dark Matter : Dark stars, dark galaxies, dark halos and global supersymmetric fits
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation cross-section of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordially-produced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.
  • Aartsen, M. G., et al. (författare)
  • Computational techniques for the analysis of small signals in high-statistics neutrino oscillation experiments
  • 2020
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 977
  • Tidskriftsartikel (refereegranskat)abstract
    • The current and upcoming generation of Very Large Volume Neutrino Telescopes - collecting unprecedented quantities of neutrino events - can be used to explore subtle effects in oscillation physics, such as (but not restricted to) the neutrino mass ordering. The sensitivity of an experiment to these effects can be estimated from Monte Carlo simulations. With the high number of events that will be collected, there is a trade-off between the computational expense of running such simulations and the inherent statistical uncertainty in the determined values. In such a scenario, it becomes impractical to produce and use adequately-sized sets of simulated events with traditional methods, such as Monte Carlo weighting. In this work we present a staged approach to the generation of expected distributions of observables in order to overcome these challenges. By combining multiple integration and smoothing techniques which address limited statistics from simulation it arrives at reliable analysis results using modest computational resources.
  • Abbasi, R., et al. (författare)
  • A convolutional neural network based cascade reconstruction for the IceCube Neutrino Observatory
  • 2021
  • Ingår i: Journal of Instrumentation. - : IOP Publishing. - 1748-0221 .- 1748-0221. ; 16:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Continued improvements on existing reconstruction methods are vital to the success of high-energy physics experiments, such as the IceCube Neutrino Observatory. In IceCube, further challenges arise as the detector is situated at the geographic South Pole where computational resources are limited. However, to perform real-time analyses and to issue alerts to telescopes around the world, powerful and fast reconstruction methods are desired. Deep neural networks can be extremely powerful, and their usage is computationally inexpensive once the networks are trained. These characteristics make a deep learning-based approach an excellent candidate for the application in IceCube. A reconstruction method based on convolutional architectures and hexagonally shaped kernels is presented. The presented method is robust towards systematic uncertainties in the simulation and has been tested on experimental data. In comparison to standard reconstruction methods in IceCube, it can improve upon the reconstruction accuracy, while reducing the time necessary to run the reconstruction by two to three orders of magnitude.
  • Abbasi, R., et al. (författare)
  • Graph Neural Networks for low-energy event classification & reconstruction in IceCube
  • 2022
  • Ingår i: Journal of Instrumentation. - : IOP Publishing Ltd. - 1748-0221 .- 1748-0221. ; 17:11
  • Tidskriftsartikel (refereegranskat)abstract
    • IceCube, a cubic-kilometer array of optical sensors built to detect atmospheric and astrophysical neutrinos between 1 GeV and 1 PeV, is deployed 1.45 km to 2.45 km below the surface of the ice sheet at the South Pole. The classification and reconstruction of events from the in-ice detectors play a central role in the analysis of data from IceCube. Reconstructing and classifying events is a challenge due to the irregular detector geometry, inhomogeneous scattering and absorption of light in the ice and, below 100 GeV, the relatively low number of signal photons produced per event. To address this challenge, it is possible to represent IceCube events as point cloud graphs and use a Graph Neural Network (GNN) as the classification and reconstruction method. The GNN is capable of distinguishing neutrino events from cosmic-ray backgrounds, classifying different neutrino event types, and reconstructing the deposited energy, direction and interaction vertex. Based on simulation, we provide a comparison in the 1 GeV-100 GeV energy range to the current state-of-the-art maximum likelihood techniques used in current IceCube analyses, including the effects of known systematic uncertainties. For neutrino event classification, the GNN increases the signal efficiency by 18% at a fixed background rate, compared to current IceCube methods. Alternatively, the GNN offers a reduction of the background (i.e. false positive) rate by over a factor 8 (to below half a percent) at a fixed signal efficiency. For the reconstruction of energy, direction, and interaction vertex, the resolution improves by an average of 13%-20% compared to current maximum likelihood techniques in the energy range of 1 GeV-30 GeV. The GNN, when run on a GPU, is capable of processing IceCube events at a rate nearly double of the median IceCube trigger rate of 2.7 kHz, which opens the possibility of using low energy neutrinos in online searches for transient events.
Skapa referenser, mejla, bekava och länka
Typ av publikation
tidskriftsartikel (6058)
konferensbidrag (892)
doktorsavhandling (265)
forskningsöversikt (132)
annan publikation (107)
bokkapitel (73)
visa fler...
licentiatavhandling (72)
konstnärligt arbete (48)
rapport (36)
bok (16)
proceedings (redaktörskap) (8)
recension (5)
samlingsverk (redaktörskap) (2)
visa färre...
Typ av innehåll
refereegranskat (6834)
övrigt vetenskapligt (790)
populärvet., debatt m.m. (90)
Reimer, O. (270)
Reimer, A. (255)
Becherini, Yvonne (195)
Bregeon, J. (194)
Ackermann, M. (193)
Conrad, Jan (179)
visa fler...
Katz, U. (177)
Funk, S. (176)
Lemoine-Goumard, M. (176)
Lohse, T. (174)
Longo, F. (174)
Grondin, M. -H (169)
Mizuno, T. (165)
Bulik, T. (163)
Quirrenbach, A. (162)
Giglietto, N. (162)
Mazziotta, M. N. (160)
Morselli, A. (160)
Fontaine, G. (159)
Hofmann, W. (159)
Boisson, C. (157)
Giebels, B. (154)
Khelifi, B. (154)
Moulin, E. (154)
de Naurois, M. (154)
Stawarz, L. (153)
Wagner, S. J. (153)
Fusco, P. (153)
Loparco, F. (153)
Spinelli, P. (153)
Glicenstein, J. F. (152)
Guiriec, S. (152)
Kosack, K. (151)
Moderski, R. (151)
Schwanke, U. (151)
Venter, C. (151)
Lamanna, G. (150)
Lenain, J. -P (150)
Niemiec, J. (150)
Ostrowski, M. (150)
Rudak, B. (150)
Sol, H. (150)
Zech, A. (150)
Bastieri, D. (150)
Egberts, K. (149)
Ohm, S. (149)
Renaud, M. (149)
Rieger, F. (149)
van Eldik, C. (149)
Ajello, M. (149)
visa färre...
Stockholms universitet (2887)
Uppsala universitet (2199)
Lunds universitet (1682)
Kungliga Tekniska Högskolan (1506)
Linnéuniversitetet (381)
Umeå universitet (137)
visa fler...
Luleå tekniska universitet (133)
Högskolan i Halmstad (79)
Malmö universitet (70)
Chalmers tekniska högskola (53)
Högskolan Kristianstad (39)
Karlstads universitet (22)
Linköpings universitet (18)
Jönköping University (16)
Högskolan Dalarna (14)
RISE (11)
Örebro universitet (10)
Göteborgs universitet (6)
Mittuniversitetet (6)
Högskolan Väst (3)
Mälardalens universitet (2)
Naturhistoriska riksmuseet (2)
Blekinge Tekniska Högskola (2)
Konstfack (1)
Karolinska Institutet (1)
visa färre...
Engelska (7618)
Svenska (90)
Danska (5)
Spanska (1)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (7714)
Teknik (85)
Samhällsvetenskap (50)
Humaniora (11)
Medicin och hälsovetenskap (3)


Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy