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  • 201.
    Hofner, S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Winds of M-type AGB stars driven by micron-sized grains2008Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 491, nr 2, s. L1-L4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. In view of the recent problem regarding the dynamical modelling of winds of M-type AGB stars (insufficient radiation pressure on silicate grains), some of the basic assumptions of these models need to be re-evaluated critically.Aims. Accepting the conclusion that non-grey effects will force silicate grains to be virtually Fe-free, the viability of driving winds with micron-sized Fe-free silicates, instead of small particles, is examined.

    Methods. Using both simple estimates and detailed dynamical atmosphere and wind models, it is demonstrated that radiation pressure on Fe-free silicate grains is sufficient to drive outflows if the restriction to the small particle limit is relaxed, and prevailing thermodynamic conditions allow grains to grow to sizes in the micrometer range.

    Results. The predicted wind properties, such as mass loss rates and outflow velocities, are in good agreement with observations of M-type AGB stars. Due to a self-regulating feedback between dust condensation and wind acceleration, grain growth naturally comes to a halt at particle diameters of about 1 mu m.

    Conclusions. The most efficient grain sizes to drive winds are in a rather narrow interval around 1 mu m. These values are set by the wavelength range corresponding to the flux maximum in typical AGB stars, and are very similar to interstellar grains.

     

  • 202.
    Holmberg, Madeleine
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Determination of Solar EUV Intensity and Ion Flux from Langmuir Probe Current Characteristics2010Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    This report presents a model to determine the solar Extreme UltraViolet (EUV) intensity and the ion flux in the vicinity of Saturn, by using measurements from the Langmuir probe, a plasma investigation instrument, of the Cassini satellite. The model is based on in situ measurements and does therefore provide an improved estimation of the wanted parameters compared to previously used calculations based only on the EUV flux measured near Earth. The solar EUV and ion flux were determined by analysing and processing the current measurements from the Cassini Langmuir probe in several steps. Initially the time intervals where the measured current were expected to be due only to the photoelectron current was extracted. The photoelectron current is the part of the measured probe current that is only due to electrons ejected from the probe by photons coming from the Sun. The measurements showed a periodic behaviour which was concluded to be due to the attitude of the satellite. This interfering effect was corrected for and the data was then plotted against an EUV index, estimated from a traditionally used proxy of the EUV flux near Earth; the F10.7 solar radio flux index. In agreement with the theory of the photoelectric effect a linear relationship between the EUV flux and the photoelectron current mph was expected. A least square linear fit to the extracted photoelectron current data provided the relation, for the Langmuir probe on Cassini, in the form of the equation mph=0.1842EUV+0.2405, where mph is the photoelectron current in nA and EUV is the EUV index in W/Hzm^2. The derived equation is the result of the study, showing how to estimate the solar EUV flux using the Langmuir probe current measurements. This result was used to derive the other wanted parameter, the ion flux. The derivation was done by calculating the photoelectron current mph at all time and subtracting the result from the total current. The retrieved difference gives the magnitude of the ion current for every measurement.

  • 203. Holopainen, Janne
    et al.
    Zackrisson, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Knebe, Alexander
    Nurmi, Pasi
    Heinamaki, Pekka
    Flynn, Chris
    Gill, Stuart
    Riehm, Teresa
    An analytical model of surface mass densities of cold dark matter haloes - with an application to MACHO microlensing optical depths2008Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 383, nr 2, s. 720-728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The cold dark matter (CDM) scenario generically predicts the existence of triaxial dark matter haloes which contain notable amounts of substructure. However, analytical halo models with smooth, spherically symmetric density profiles are routinely adopted in the modelling of light propagation effects through such objects. In this paper, we address the biases introduced by this procedure by comparing the surface mass densities of actual N-body haloes against the widely used analytical model suggested by Navarro, Frenk and White (NFW). We conduct our analysis in the redshift range of 0.0-1.5. In cluster-sized haloes, we find that triaxiality can cause scatter in the surface mass density of the haloes up to sigma(+) = +60 per cent and sigma(-) = -70 per cent, where the 1 sigma limits are relative to the analytical NFW model given value. Subhaloes can increase this scatter to sigma(+) = +70 per cent and sigma(-) = -80 per cent. In galaxy-sized haloes, the triaxial scatter can be as high as sigma(+) = +80 per cent and sigma(-) = -70 per cent, and with subhaloes the values can change to sigma(+) = +40 per cent and sigma(-) = -80 per cent. We present an analytical model for the surface mass density scatter as a function of distance to the halo centre, halo redshift and halo mass. The analytical description enables one to investigate the reliability of results obtained with simplified halo models. Additionally, it provides the means to add simulated surface density scatter to analytical density profiles. As an example, we discuss the impact of our results on the calculation of microlensing optical depths for massive astrophysical compact halo objects in CDM haloes.

  • 204. Hull, C. M.
    et al.
    Lindström, U.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    dos Santos, L. Melo
    von Unge, R.
    Zabzine, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Topological sigma models with H-flux2008Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 9, s. 057-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the topological theory obtained by twisting the N = (2, 2) supersymmetric nonlinear sigma model with target a bihermitian space with torsion. For the special case in which the two complex structures commute, we show that the action is a Q-exact term plus a quasi-topological term. The quasi-topological term is locally given by a closed two-form which corresponds to a flat gerbe-connection and generalises the usual topological term of the A-model. Exponentiating it gives a Wilson surface, which can be regarded as a generalization of a Wilson line. This makes the quantum theory globally well-defined.

  • 205.
    Höfner, Susanne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk astrofysik.
    Dust Formation and Winds around Evolved Stars The Good, the Bad and the Ugly Cases2009Inngår i: COSMIC DUST - NEAR AND FAR / [ed] Henning T, Grun E, Steinacker J, 2009, Vol. 414, s. 3-21Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cool luminous giants, in particular asymptotic giant branch stars, are among the most important sources of cosmic dust Their extended dynamical atmospheres are places where grains form and initiate outflows driven by radiation pressure, leading to considerable stellar mass loss and the enrichment of the interstellar medium with newly-produced elements This review summarizes the current understanding of dust formation and winds in such stars, sketching a system of criteria for identifying crucial types of dust grains in the range of possible condensates Starting with an overview of the specific conditions for dust formation in cool dynamic atmospheres, the role of grains as wind drivers, as well as their influence on observable properties of cool giants and the circum-stellar environment is discussed in some detail Regarding the literature, special attention is given to current developments, e g, the debate concerning the Fe-content and size of silicate grains in M-type AGB stars which are critical issues for the wind mechanism, or recent advances in spatially resolved observations and 3D modeling of giants and their dusty envelopes

  • 206.
    Höfner, Susanne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Winds of AGB stars: does size matter?2008Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T133, s. 014007-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Asymptotic giant branch (AGB) stars are showing clear signs of significant mass loss through cool stellar winds. These outflows are attributed to the combined effects of pulsation-induced shocks and radiation pressure on dust grains formed in the outer atmospheric layers. This paper gives an overview of the current status of radiation-hydrodynamical modelling of these processes, and presents a toy model that allows analysis of certain features of detailed models, such as the influence of grain size dependent opacities and basic differences in winds of C- and M-type AGB stars.

  • 207.
    Höfner, Susanne
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Bladh, S.
    Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Vicolo Osservatorio 3, I-35122 Padua, Italy..
    Aringer, B.
    Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Vicolo Osservatorio 3, I-35122 Padua, Italy.;Osserv Astron Padova, INAF, Vicolo Osservatorio 5, I-35122 Padua, Italy..
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Dynamic atmospheres and winds of cool luminous giants I. Al2O3 and silicate dust in the close vicinity of M-type AGB stars2016Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 594, artikkel-id A108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. In recent years, high spatial resolution techniques have given valuable insights into the complex atmospheres of AGB stars and their wind-forming regions. They make it possible to trace the dynamics of molecular layers and shock waves, to estimate dust condensation distances, and to obtain information on the chemical composition and size of dust grains close to the star. These are essential constraints for understanding the mass loss mechanism, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust, forming in the cool upper layers of the atmospheres. Aims. Spectro-interferometric observations indicate that Al2O3 condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al2O3 grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. The purpose of this paper is to study the necessary conditions for the formation of Al2O3 and the potential effects on mass loss, using detailed atmosphere and wind models. Methods. We have constructed a new generation of Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth and evaporation for both Al2O3 and Fe-free silicates (Mg2SiO4). The equations describing these dust species are solved in the framework of a frequency-dependent radiation hydrodynamical model for the atmosphere and wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Results. Condensation of Al2O3 at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. We derive an upper limit for the imaginary part of the refractive index k around 10(-3) at these wavelengths. For solar abundances, radiation pressure due to Al2O3 is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al2O3 core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations. Conclusions. Al2O3 grains are promising candidates for explaining the presence of gravitationally bound dust shells close to M-type AGB stars, as implied by both scattered light observations and mid-IR spectro-interferometry. The required level of transparency at near-IR wavelengths is compatible with impurities due to a few percent of transition metals (e.g., Cr), consistent with cosmic abundances. Grains consisting of an Al2O3 core and an Fe-free silicate mantle with total grain radii of about 0.1-1 micron may be more efficient at driving winds by the scattering of stellar photons than pure Fe-free silicate grains.

  • 208.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    A decline rate study of Norwegian oil production2008Inngår i: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 36, nr 11, s. 4262-4271Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Norway has been a very important oil exporter for the world and an important supplier for Europe. Oil was first discovered in the North Sea in late 1960s and the rapid expansion of Norwegian oil production lead to the low oil prices in the beginning of the 1990s. In 2001 Norway reached its peak production and began to decline.

    The Norwegian oil production can be broken up into four subclasses; giant oil fields, smaller oil fields, natural gas liquids and condensate. The production of each subclass was analyzed to find typical behaviour and decline rates. The typical decline rates of giant oil fields were found to be -13% annually. The other subclasses decline equally fast or even faster, especially condensate with typical decline rates of -40% annually. The conclusion from the forecast is that Norway will have dramatically reduced export volume of oil by 2030.

  • 209.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    A review on coal to liquid fuels and its coal consumption2010Inngår i: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 34, nr 10, s. 848-864Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Continued reliance on oil is unsustainable and this has resulted in interest in alternative fuels. Coal-to-Liquids (CTL) can supply liquid fuels and have been successfully used in several cases, particularly in South Africa. This article reviews CTL theory and technology. Understanding the fundamental aspects of coal liquefaction technologies are vital for planning and policy-making, as future CTL systems will be integrated in a much larger global energy and fuel utilization system.

    Conversion ratios for CTL are generally estimated to be between 1-2 barrels/ton coal. This puts a strict limitation on future CTL capacity imposed by future coal production volumes, regardless of other factors such as economics, emissions or environmental concern. Assuming that 10% of world coal production can be diverted to CTL, the contribution to liquid fuel supply will be limited to only a few Mb/d. This prevents CTL from becoming a viable mitigation plan for liquid fuel shortage on a global scale. However, it is still possible for individual nations to derive significant shares of their fuel supply from CTL, but those nations must also have access to equally significant coal production capacities. It is unrealistic to claim that CTL provides a feasible solution to liquid fuels shortages created by peak oil. For the most part, it can only be a minor contributor and must be combined with other strategies.

  • 210.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Historical trends in American coal production and a possible future outlook2009Inngår i: International Journal of Coal Geology, ISSN 0166-5162, E-ISSN 1872-7840, Vol. 78, nr 3, s. 201-216Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The United States has a vast supply of coal, with almost 30% of world reserves and more than 1600 Gt (short) as remaining coal resources. The US is also the world’s second largest coal producer after China and annually produces more than twice as much coal as India, the third largest producer.

    The reserves are concentrated in a few states, giving them a major influence on future production. Historically many states have also shown a dramatic reduction in recoverable coal volumes and this has been closely investigated. Current recoverable estimates may also be too high, especially if further restrictions are imposed. The average calorific value of US coals has decreased from 29.2 MJ/kg in 1950 to 23.6 MJ/kg in 2007 as U.S. production moved to subbituminous western coals. This has also been examined in more detail.

    This study also uses established analysis methods from oil and gas production forecasting, such as Hubbert linearization and logistic curves, to create some possible future outlooks for U.S. coal production. In one case, the production stabilizes at 1400 Mt annually and remains there until the end of the century, provided that Montana dramatically increases coal output. The second case, which ignores mining restrictions, forecasts a maximum production of 2500 Mt annually by the end of the century.

  • 211.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Trends in U.S. recoverable coal supply estimates and future production outlooks2009Inngår i: Twenty Sixth Annual International Pittsburgh Coal Conference: September 20-23, 2009, Pittsburgh: University of Pittsburgh , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The geological coal resource of the U.S. is abundant and proved coal reserves are listed as the world’s largest. However, the reserves are unevenly distributed and located in a small number of states, giving them major influence over future production. A long history of coal mining provides detailed time series of production and reserve estimates, which can be used to identify historical trends. Compilation of data from United States Geological Survey, Energy Information Administration, U.S. Bureau of Mines and others reveal how the recoverable volumes have been decreased since before the 1950s. The exact cause of this reduction is probably a multitude of factors, including depletion, changes in economic conditions, land-use restrictions, environmental protection and social acceptance.

    In reviewing the historical evolution of coal reserves, one can state that the trend here does not point towards any major increases in available recoverable reserves; rather the opposite is true due to restrictions and increased focus on environmental impacts from coal extraction. The development of new even stricter regulations and environmental laws is also a reasonable assumption and this will further limit the amount of recoverable coal. Future coal production will not be entirely determined by what is geologically available, but rather by the fraction of that amount that is practically recoverable. Consequently, the historical trend towards reduced recoverable amounts is likely to continue into the future, with even stricter regulations imposed by increased environmental concern.

    Long-term outlooks can be created in many ways, but ultimately the production must be limited by recoverable volumes since coal is a finite resource. Various models, such as the logistic, Hubbert or Gompertz curves, can be used to provide reasonable long-term outlooks for future production. However, such long-term life-cycle projections should not be used as a substitute for meticulous economic studies to forecast perturbations in coal production over the next few years or decades. Based on a logistic model, using the recoverable reserves as an estimate of what is realistically available for production, results in a coal output of around 1400 Mt by 2030 through the rest of the century.

    The geologic amounts of coal are of much less importance to future production than the practically recoverable volumes. The geological coal supply might be vast, but the important question is how large the share that can be extracted under present restrictions are and how those restrictions will develop in the future. Production limitations might therefore appear much sooner than previously expected.

  • 212.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Trends in U.S. recoverable coal supply estimates and future production outlooks2010Inngår i: Natural Resources Research, ISSN 1520-7439, E-ISSN 1573-8981, Vol. 19, nr 3, s. 189-208Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The geological coal resource of the U.S. is abundant and proved coal reserves are listed as the world’s largest. However, the reserves are unevenly distributed and located in a small number of states, giving them major influence over future production. A long history of coal mining provides detailed time series of production and reserve estimates, which can be used to identify historical trends. In reviewing the historical evolution of coal reserves, one can state that the trend here does not point towards any major increases in available recoverable reserves; rather the opposite is true due to restrictions and increased focus on environmental impacts from coal extraction. Future coal production will not be entirely determined by what is geologically available, but rather by the fraction of that amount that is practically recoverable. Consequently, the historical trend towards reduced recoverable amounts is likely to continue into the future, with even stricter regulations imposed by increased environmental concern.

    Long-term outlooks can be created in many ways, but ultimately the production must be limited by recoverable volumes since coal is a finite resource. The geologic amounts of coal are of much less importance to future production than the practically recoverable volumes. The geological coal supply might be vast, but the important question is how large the share that can be extracted under present restrictions are and how those restrictions will develop in the future. Production limitations might therefore appear much sooner than previously expected.

  • 213.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Hirsch, Robert
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Giant oil field decline rates and their influence on world oil production2009Inngår i: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 37, nr 6, s. 2262-2272Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The most important contributors to the world's total oil production are the giant oil fields. Using a comprehensive database of giant oil field production, the average decline rates of the world's giant oil fields are estimated. Separating subclasses was necessary, since there are large differences between land and offshore fields, as well as between non-OPEC and OPEC fields. The evolution of decline rates over past decades includes the impact of new technologies and production techniques and clearly shows that the average decline rate for individual giant fields is increasing with time. These factors have significant implications for the future, since the most important world oil production base - giant fields - will decline more rapidly in the future, according to our findings. Our conclusion is that the world faces an increasing oil supply challenge, as the decline in existing production is not only high now but will be increasing in the future.

  • 214.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Sivertsson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Validity of the fossil fuel production outlooks in the IPCC Emission Scenarios2010Inngår i: Natural Resources Research, ISSN 1520-7439, E-ISSN 1573-8981, Vol. 19, nr 2, s. 63-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Anthropogenic global warming caused by CO2 emissions is strongly and fundamentally linked to future energy production. The Special Report on Emission Scenarios (SRES) from 2000 contains 40 scenarios for future fossil fuel production and is used by the IPCC to assess future climate change. Previous scenarios were withdrawn after exaggerating one or several trends. This study investigates underlying assumptions on resource availability and future production expectations to determine whether exaggerations can be found in the present set of emission scenarios as well.

    It is found that the SRES unnecessarily takes an overoptimistic stance and that future production expectations are leaning towards spectacular increases from present output levels. In summary, we can only encourage the IPCC to involve more resource experts and natural science in future emission scenarios. The current set, SRES, is biased toward exaggerated resource availability and unrealistic expectations on future production outputs from fossil fuels.

  • 215.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Söderbergh, Bengt
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Future Danish oil and gas export2009Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 34, nr 11, s. 1826-1834Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Denmark possesses only a small share of the exploitation rights to North Sea oil and is a minor producer when compared to Norway and the UK. However, Denmark is still an oil exporter and a very important supplier of oil for certain countries, in particular Sweden.

    A field-by-field analysis of the Danish oil and gas fields, combined with estimated production contribution from new field developments, enhanced oil recovery and undiscovered fields, provides a future production outlook. The conclusion from this analysis is that by 2030 Denmark will no longer be an oil or gas exporter at all. Our results are also in agreement with the Danish Energy Authority’s own forecast, and may be seen as an independent confirmation of their general statements.

    Decreasing Danish oil production, coupled with a rapid decline in Norway’s oil output, will force Sweden to import oil from more distant markets in the future, dramatically reducing Swedish energy security. If no new gas suppliers are introduced to the Swedish grid, then Swedish gas consumption is clearly predestined to crumble alongside declining Danish production. Future hydrocarbon production from Denmark displays a clear link to Sweden’s future energy security.

  • 216.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Söderbergh, Bengt
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Jakobsson, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    The evolution of giant oil field production behaviour2009Inngår i: Natural Resources Research, ISSN 1520-7439, E-ISSN 1573-8981, Vol. 18, nr 1, s. 39-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The giant oil fields of the world are only a small fraction of the total number of fields, but their importance is huge. Over 50% of the world oil production came from giants by 2005 and more than haft of the worlds ultimate reserves are found in giants. Based on this it is reasonable to assume that the future development of the giant oil fields will have a significant impact on the world oil supply.

    In order to better understand the giant fields and their future behaviour one must first understand their history. This study has used a comprehensive database on giant oil fields in order to determine their typical parameters, such as the average decline rate and life-times of giants. The evolution of giant oil field behaviour has been investigated to better understand future behaviour. One conclusion is that new technology and production methods have generally lead to high depletion rate and rapid decline. The historical trend points towards high decline rates of fields currently on plateau production.

    The peak production generally occurs before half the ultimate reserves have been produced in giant oil fields. A strong correlation between depletion-at-peak and average decline rate is also found, verifying that high depletion rate leads to rapid decline. Our result also implies that depletion analysis can be used to rule out unrealistic production expectations from a known reserve, or to connect an estimated production level to a needed reserve base.

  • 217.
    Höök, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Zittel, Werner
    Ludwig Bölkow Systemtechnik GmbH.
    Schindler, Jörg
    Ludwig Bölkow Systemtechnik GmbH.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Global coal production outlooks based on a logistic model2010Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 89, nr 11, s. 3546-3558Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A small number of nations control the vast majority of the world’s coal reserves. The geologically available amounts of coal are vast, but geological availability is not enough to ensure future production since economics and restrictions also play an important role. Historical trends in reserve and resource assessments can provide some insight about future coal supply and provide reasonable limits for modelling. This study uses a logistic model to create long-term outlooks for global coal production. A global peak in coal production can be expected between 2020 and 2050, depending on estimates of recoverable volumes. This is also compared with other forecasts. The overall conclusion is that the global coal production could reach a maximum level much sooner than most observers expect.

  • 218. Hüyük, Tayfun
    et al.
    Di Nitto, Antonio
    Jaworski, Grzegorz
    Gadea, Andrés
    Valiente-Dobón, José Javier
    Nyberg, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärnfysik.
    Palacz, Marcin
    Söderström, Pär-Anders
    Aliaga-Varea, Ramon Jose
    de Angelis, Giacomo
    Ataç, Ay\cse
    Collado, Javier
    Domingo-Pardo, Cesar
    Egea, Javier Francisco
    Erduran, Nizamettin
    Ertürk, Sefa
    de France, Gilles
    Gadea, Rafael
    González, Vicente
    Herrero-Bosch, Vicente
    Ka\cska\cs, Ay\cse
    Modamio, Victor
    Moszynski, Marek
    Sanchis, Enrique
    Triossi, Andrea
    Wadsworth, Robert
    Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA2016Inngår i: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 52, nr 3, artikkel-id 55Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The NEutron Detector Array (NEDA) project aims at the construction of a new high-efficiency compact neutron detector array to be coupled with large $ \gamma$ -ray arrays such as AGATA. The application of NEDA ranges from its use as selective neutron multiplicity filter for fusion-evaporation reaction to a large solid angle neutron tagging device. In the present work, possible configurations for the NEDA coupled with the Neutron Wall for the early implementation with AGATA has been simulated, using Monte Carlo techniques, in order to evaluate their performance figures. The goal of this early NEDA implementation is to improve, with respect to previous instruments, efficiency and capability to select multiplicity for fusion-evaporation reaction channels in which 1, 2 or 3 neutrons are emitted. Each NEDA detector unit has the shape of a regular hexagonal prism with a volume of about 3.23l and it is filled with the EJ301 liquid scintillator, that presents good neutron- $ \gamma$ discrimination properties. The simulations have been performed using a fusion-evaporation event generator that has been validated with a set of experimental data obtained in the 58Ni + 56Fe reaction measured with the Neutron Wall detector array.

  • 219. Izotov, Y. I.
    et al.
    Guseva, G
    Fricke, J
    Papaderos, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    SBS 0335-052E+W: deep VLT/FORS plus UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies2009Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 503, nr 1, s. 61-72Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W. Aims. Our aim is to derive element abundances in different H II regions of this unique system of galaxies and to study spatial abundance variations. Methods. The electron temperature T-e (O III) in all H II regions, except for one, is derived from the [O III] lambda 4363/(lambda 4959+lambda 5007) flux ratio. We determine ionic abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The empirical relations for ionization correction factors are used to derive total abundances of these elements. Results. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different H II regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of similar to 1-2 kpc. Good seeing during FORS observations allowed us to extract spectra of four H II regions in SBS 0335-052W. The oxygen abundance in the brightest region No. 1 of SBS 0335-052W is 7.22 +/- 0.07, consistent with previous determinations. Three other H II regions are much more metal-poor with an unprecedently low oxygen abundance of 12 + log O/H = 7.01 +/- 0.07 (region No. 2), 6.98 +/- 0.06 (region No. 3), and 6.86 +/- 0.14 (region No. 4). These are the lowest oxygen abundances ever derived in emission-line galaxies, supporting earlier conclusions that SBS 0335-052W is the lowest-metallicity emission-line galaxy known. Helium abundances derived for the brightest H II regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485 +/- 0.0012 and 0.2514 +/- 0.0012 for two different sets of He I emissivities. The ratios of neon and sulfur to oxygen abundance are similar to the respective ratios obtained for other emission-line galaxies. On the other hand, the chlorine-to-oxygen abundance ratio in SBS 0335-052E is lower, while the argon-to-oxygen abundance ratio is higher than those in other low-metallicity galaxies. The Fe/O abundance ratios in different regions of SBS 0335-052E are among the highest for emission-line galaxies implying that iron is almost entirely not depleted onto dust grains despite dust being detected in this galaxy in earlier ISO and Spitzer observations. The N/O abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12 + logO/H < 7.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity.

  • 220.
    Jakobsson, Kristofer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Söderbergh, Bengt
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Höök, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    Aleklett, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Globala energisystem.
    How reasonable are oil production scenarios from public agencies?2009Inngår i: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 37, nr 11, s. 4809-4818Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    According to the long term scenarios of the International Energy Agency (IEA) and the U.S. Energy Information Administration (EIA), conventional oil production is expected to grow until at least 2030. EIA has published results from a resource constrained production model which ostensibly supports such a scenario. The model is here described and analyzed in detail. However, it is shown that the model, although sound in principle, has been misapplied due to a confusion of resource categories. A correction of this methodological error reveals that EIA’s scenario requires rather extreme and implausible assumptions regarding future global decline rates. This result puts into question the basis for the conclusion that global "peak oil" would not occur before 2030.

  • 221. Javier Egea, Francisco
    et al.
    Sanchis, Enrique
    Gonzalez, Vicente
    Gadea, Andres
    Maria Blasco, Jose
    Barrientos, Diego
    Dobon, J. J. Valiente
    Tripon, Michel
    Boujrad, Abderrahman
    Houarner, Charles
    Jastrzab, Marcin
    Blaizot, Maria
    Bourgault, Patrice
    de Angelis, Giacomo
    Erduran, M. Nizamettin
    Erturk, Sefa
    De France, Gilles
    Huyuk, Tayfun
    Jaworski, Grzegorz
    Di Nitto, Antonio
    Nyberg, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärnfysik.
    Söderström, Pär-Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärnfysik.
    Palacz, Marcin
    Pipidis, A.
    Tarnowski, R.
    Triossi, Andrea
    Wadsworth, R.
    Design and Test of a High-Speed Flash ADC Mezzanine Card for High-Resolution and Timing Performance in Nuclear Structure Experiments2013Inngår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, nr 5, s. 3526-3531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work describes new electronics for the EX-OGAM2 (HP-Ge detector array) and NEDA (BC501A-based neutron detector array). A new digitizing card with high resolution has been designed for gamma-ray and neutron spectroscopy experiments. The higher bandwidth requirement of the NEDA signals, together with the necessity for accuracy, require a high sampling rate in order to preserve the shape for real-time Pulse Shape Analysis (PSA). The PSA is of paramount importance for the NEDA to discriminate between neutrons and gamma-ray signals. Both high resolution and high speed parameters are often difficult to achieve in a single electronic unit. These constraints, together with the need to build new digitizing electronics to improve performance and flexibility of signal analysis in nuclear physics experiments, led to the development a new FADC mezzanine card. In this work, the design and development are described, including the characterization procedure and the preliminary measurement results.

  • 222.
    Johansson, Niklas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Making Maps and Keeping Logs: Quantum Gravity from Classical Viewpoints2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis explores three different aspects of quantum gravity. First we study D3-brane black holes in Calabi-Yau compactifications of type IIB string theory. Using the OSV conjecture and a relation between topological strings and matrix models we show that some black holes have a matrix model description. This is the case if the attractor mechanism fixes the internal geometry to a conifold at the black hole horizon. We also consider black holes in a flux compactification and compare the effects of the black holes and fluxes on the internal geometry. We find that the fluxes dominate. Second, we study the scalar potential of type IIB flux compactifications. We demonstrate that monodromies of the internal geometry imply as a general feature the existence of long series of continuously connected minima. This allows for the embedding of scenarios such as chain inflation and resonance tunneling into string theory. The concept of monodromies is also extended to include geometric transitions: passing to a different Calabi-Yau topology, performing its monodromies and then returning to the original space allows for novel transformations. All constructions are performed explicitly, using both analytical and numerical techniques, in the mirror quintic Calabi-Yau. Third, we study cosmological topologically massive gravity at the chiral point, a prime candidate for quantization of gravity in three dimensions. The prospects of this scenario depend crucially of the stability of the theory. We demonstrate the presence of a negative energy bulk mode that grows logarithmically toward the AdS boundary. The AdS isometry generators have non-unitary matrix representations like in logarithmic CFT, and we propose that the CFT dual for this theory is logarithmic. In a complementing canonical analysis we also demonstrate the existence of this bulk degree of freedom, and we present consistent boundary conditions encompassing the new mode.

    Delarbeid
    1. 4D black holes and holomorphic factorization of the 0A matrix model
    Åpne denne publikasjonen i ny fane eller vindu >>4D black holes and holomorphic factorization of the 0A matrix model
    Vise andre…
    2005 (engelsk)Inngår i: Journal of High Energy Physics, Vol. 0510, s. 046-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    n this letter, we relate the free energy of the 0A matrix model to the sum of topological and anti-topological string amplitudes. For arbitrary integer multiples of the matrix model self-dual radius we describe the geometry on which the corresponding topological string propagates. This geometry is not the one that follows from the usual ground ring analysis, but in a sense its "holomorphic square root". Mixing of terms for different genus in the matrix model free energy yields one-loop terms compatible with type II strings on compact Calabi-Yau target spaces. As an application, we give an explicit example of how to relate the 0A matrix model free energy to that of a four-dimensional black hole in type IIB theory, compactified on a compact Calabi-Yau. Variables, Legendre transforms, and large classical terms on both sides match perfectly.

    Identifikatorer
    urn:nbn:se:uu:diva-79421 (URN)
    Tilgjengelig fra: 2006-04-10 Laget: 2006-04-10 Sist oppdatert: 2011-01-11
    2. Stability of flux vacua in the presence of charged black
    Åpne denne publikasjonen i ny fane eller vindu >>Stability of flux vacua in the presence of charged black
    2006 (engelsk)Inngår i: JHEP, Vol. 09, s. 069-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this letter we consider a charged black hole in a flux compactification of type IIB string theory. Both the black hole and the fluxes will induce potentials for the complex structure moduli. We choose the compact dimensions to be described locally by a deformed conifold, creating a large hierarchy. We demonstrate that the presence of a black hole typically will not change the minimum of the moduli potential in a substantial way. However, we also point out a couple of possible loop-holes, which in some cases could lead to interesting physical consequences such as changes in the hierarchy.

    Identifikatorer
    urn:nbn:se:uu:diva-20261 (URN)
    Tilgjengelig fra: 2006-12-06 Laget: 2006-12-06 Sist oppdatert: 2011-01-11
    3. The world next door: Results in landscape topography
    Åpne denne publikasjonen i ny fane eller vindu >>The world next door: Results in landscape topography
    2007 (svensk)Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 03, s. 080-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Recently, it has become clear that neighboring multiple vacua might have interesting consequences for the physics of the early universe. In this paper we investigate the topography of the string landscape corresponding to complex structure moduli of flux compactified type IIB string theory. We find that series of continuously connected vacua are common. The properties of these series are described, and we relate the existence of infinite series of minima to certain unresolved mathematical problems in group theory. Numerical studies of the mirror quintic serve as illustrating examples.

    Emneord
    Superstring Vacua, Flux compactifications, dS vacua in string theory
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-13761 (URN)10.1088/1126-6708/2007/03/080 (DOI)000245922000080 ()
    Tilgjengelig fra: 2008-01-25 Laget: 2008-01-25 Sist oppdatert: 2017-12-11bibliografisk kontrollert
    4. Deforming, revolving and resolving: New paths in the string theory landscape
    Åpne denne publikasjonen i ny fane eller vindu >>Deforming, revolving and resolving: New paths in the string theory landscape
    Vise andre…
    2008 (engelsk)Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 02, artikkel-id 016Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper we investigate the properties of series of vacua in the string theory landscape. In particular, we study minima to the flux potential in type IIB compactifications on the mirror quintic. Using geometric transitions, we embed its one-dimensional complex structure moduli space in that of another Calabi-Yau with h1,1 = 86 and h2,1 = 2. We then show how to construct infinite series of continuously connected minima to the mirror quintic potential by moving into this larger moduli space, applying its monodromies, and moving back. We provide an example of such series, and discuss their implications for the string theory landscape

    Emneord
    Superstring Vacua, Flux compactifications
    HSV kategori
    Forskningsprogram
    Teoretisk fysik
    Identifikatorer
    urn:nbn:se:uu:diva-100502 (URN)10.1088/1126-6708/2008/02/016 (DOI)000254764400096 ()
    Tilgjengelig fra: 2009-04-01 Laget: 2009-04-01 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    5. Instability in cosmological topologically massive gravity at the chiral point
    Åpne denne publikasjonen i ny fane eller vindu >>Instability in cosmological topologically massive gravity at the chiral point
    2008 (engelsk)Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 7, s. 134-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We consider cosmological topologically massive gravity at the chiral point with positive sign of the Einstein-Hilbert term. We demonstrate the presence of a negative energy bulk mode that grows linearly in time. Unless there are physical reasons to discard this mode, this theory is unstable. To address this issue we prove that the mode is not pure gauge and that its negative energy is time-independent and finite. The isometry generators L0 and 0 have non-unitary matrix representations like in logarithmic CFT. While the new mode obeys boundary conditions that are slightly weaker than the ones by Brown and Henneaux, its fall-off behavior is compatible with spacetime being asymptotically AdS3. We employ holographic renormalization to show that the variational principle is well-defined. The corresponding Brown-York stress tensor coincides with that of global AdS3. Finally we address possibilities to eliminate the instability and prospects for chiral gravity.

    Emneord
    AdS-CFT Correspondence, Classical Theories of Gravity, Models of Quantum Gravity
    HSV kategori
    Forskningsprogram
    fysik
    Identifikatorer
    urn:nbn:se:uu:diva-100498 (URN)10.1088/1126-6708/2008/07/134 (DOI)000258144100134 ()
    Tilgjengelig fra: 2009-04-01 Laget: 2009-04-01 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    6. Canonical analysis of cosmological topologically massive gravity at the chiral point
    Åpne denne publikasjonen i ny fane eller vindu >>Canonical analysis of cosmological topologically massive gravity at the chiral point
    (engelsk)Manuskript (Annet vitenskapelig)
    Abstract [en]

    Wolfgang Kummer was a pioneer of two-dimensional gravity and a strong advocate of the first order formulation in terms of Cartan variables. In the present work we apply Wolfgang Kummer's philosophy, the `Vienna School approach', to a specific three-dimensional model of gravity, cosmological topologically massive gravity at the chiral point. Exploiting a new Chern-Simons representation we perform a canonical analysis. The dimension of the physical phase space is two per point, and thus the theory exhibits a local physical degree of freedom, the topologically massive graviton.

    HSV kategori
    Forskningsprogram
    fysik
    Identifikatorer
    urn:nbn:se:uu:diva-100501 (URN)
    Tilgjengelig fra: 2009-04-01 Laget: 2009-04-01 Sist oppdatert: 2010-01-14
    7. Consistent boundary conditions for cosmological topologically massive gravity at the chiral point
    Åpne denne publikasjonen i ny fane eller vindu >>Consistent boundary conditions for cosmological topologically massive gravity at the chiral point
    2008 (engelsk)Inngår i: International Journal of Modern Physics D, ISSN 0218-2718, Vol. 17, nr 13-14, s. 2367-2372Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We show that cosmological topologically massive gravity at the chiral point allows not only Brown-Henneaux boundary conditions as consistent boundary conditions, but slightly more general ones which encompass the logarithmic primary found in 0805.2610 as well as all its descendants.

    Emneord
    Cosmological topologically massive gravity, Brown–Henneaux boundary conditions, chiral gravity, gravity in three dimensions, logarithmic CFT, AdS/CFT
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-100493 (URN)10.1142/S0218271808014096 (DOI)000264138700003 ()
    Tilgjengelig fra: 2009-04-01 Laget: 2009-04-01 Sist oppdatert: 2017-12-13bibliografisk kontrollert
  • 223.
    Johnson, M.
    et al.
    Uppsala universitet, The Svedberg-laboratoriet.
    Ruber, R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Ziemann, Volker
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Högenergifysik.
    Braun, H.
    Arrival time measurements of ions accompanying RF breakdown2008Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 595, nr 3, s. 568-571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radio-frequency structures for future normal-conducting linear accelerators are limited in accelerating gradient levels by RF breakdown in the structures due to extreme electric field levels. We report of experiments conducted at the CLIC Test Facility CTF3 where the breakdown is sometimes accompanied by a burst of ions that shows a spectrum consistent with hot coulomb explosions.

  • 224.
    Johnson, Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Hoegenergifysik.
    Ziemann, Volker
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Hoegenergifysik.
    Ruber, Roger
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Hoegenergifysik.
    RF breakdown experiments at the CTF3 Two-beam Test-stand2008Inngår i: Proceedings of the European particle Accelerator Conference EPAC08, 2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The Two-beam Test-stand (TBTS) in the CLIC Test Facility CTF3 offers unique possibilities to

    conduct RF-breakdown related experiments on the accelerating structures and the power extraction

    and transfer structures with beam. We report on the set-up of two such experiments, one for the

    measurement of the transverse kick and the other for the measurement of positive ion currents.

    The purpose of the transverse kick measurements is to determine the effects of a RF-breakdown

    event on the beam. Five BPMs in the TBTS will be used to study the trajectory of a pulse train

    after a RF-breakdown event, with important implications for the operation of CLIC. Ion currents

    ejected from accelerating structures during RF-breakdown events have already been observed at

    the 30 GHz test stand at the present test facility. Results and their implications for RF-breakdown

    physics are presented, as well as plans for similar measurements at the TBTS.

  • 225.
    Johnson, Matthew C
    et al.
    California Institute of Technology.
    Larfors, Magdalena
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Field dynamics and tunneling in a flux landscape2008Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 78, nr 8, s. 0835341-08353423Artikkel i tidsskrift (Fagfellevurdert)
  • 226.
    Johnson, Matthew C
    et al.
    California Institute of Technology.
    Larfors, Magdalena
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Obstacle to populating the string theory landscape2008Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 78, nr 12, s. 1235131-1235135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We construct domain walls and instantons in a class of models with coupled scalar fields, determining, in agreement with previous studies, that many such solutions contain naked timelike singularities. Vacuum bubble solutions of this type do not contain a region of true vacuum, obstructing the ability of eternal inflation to populate other vacua. We determine a criterion that potentials must satisfy to avoid the existence of such singularities and show that many domain wall solutions in type IIB string theory are singular.

  • 227. Jucker, Martin
    et al.
    Pavlenko, Vladimir
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    On the kinetic stability of magnetic structures in electron drift turbulence2007Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 3, s. 032303-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The generation of large-scale magnetic fields in magnetic electron drift mode turbulence is investigated. The mechanism of magnetic Reynolds stress is elucidated with the help of kinetic theory, and a sufficient criterion in the form of Nyquist's criterion for the generation of zonal magnetic fields is developed. This criterion is then applied to a narrow wave packet, where an amplitude threshold due to finite width of the wave spectrum in k space is found.

  • 228. Jucker, Martin
    et al.
    Pavlenko, Vladimir
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    On the modulation stability of magnetic structures in electron drift turbulence2007Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 10, s. 102313-102317Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The generation of large-scale magnetic fields in magnetic electron drift mode turbulence is investigated. In particular, the mechanism of modulational instability caused by three-wave interactions is elucidated and the explicit increment is calculated. Also, a stability criterion similar to the known Lighthill criterion is found.

  • 229.
    Jäderström, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärn- och partikelfysik.
    Fragmentation in Proton-Nucleus Reactions from 100 to 1400 MeV2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The heaviest fragments, recoils, have been studied in proton and deuteron induced 28Si reactions and proton-20Ne reactions at 100-300 MeV per nucleon. Inclusive charge and angular distributions and coincidences between He nuclei and recoils have been compared to two theoretical models, Dubna Cascade Model and JAERI Quantum Molecular Dynamics. The overall agreement was good for the reactions with 28Si, however the angular distributions of He fragments could not be reproduced.

    For the 20Ne reactions the recoil angular distributions were only reproduced for large angles. There was a significant underestimation at small angles and low recoil charge. α-clustering in the bombarding nucleus is a possible explanation for the deviations. In the 100 MeV per nucleon reactions all assumptions of the models may not be valid and the agreement was worst for these reactions.

    In proton-natXe reactions intermediate mass fragments have been studied from 200 to 1400 MeV. Slow ramping was used to scan the energy. Charge distributions and a caloric curve have been compared to Cascade Fragmentation Evaporation Model. Charge distributions showed good agreement for fragments with Z<8 but the heavier fragments were underestimated.

    Delarbeid
    1. Probing the liquid–gas coexistence in p+Xe reactions from 200 to 1400 MeV
    Åpne denne publikasjonen i ny fane eller vindu >>Probing the liquid–gas coexistence in p+Xe reactions from 200 to 1400 MeV
    Vise andre…
    2007 (engelsk)Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 644, nr 4, s. 228-231Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The nuclear equation of state (EOS) is probed from statistical parameters, determined in an excitation function experiment on p + Xe-nat reactions at 200-1400 MeV. Total charge (Z) distributions follow a cascade-[multi]fragmentation-evaporation (CFEM) model well. The caloric curve in regions supposedly dominated by fast processes is compatible with a pure statistical multifragmentation (SMM) process, where the temperature (T)-excitation energy (epsilon*) relation starts in the Fermi liquid phase and progresses into a liquid/gas coexistence region, where it remains up to 1400 MeV. A local peak in T at epsilon* = 2.1 MeV agrees with the idea of sudden fragmentation.

     

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96827 (URN)10.1016/j.physletb.2006.11.049 (DOI)000243801600003 ()
    Tilgjengelig fra: 2008-03-14 Laget: 2008-03-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    2. A detector system for studying nuclear reactions relevant to Single Event Effects
    Åpne denne publikasjonen i ny fane eller vindu >>A detector system for studying nuclear reactions relevant to Single Event Effects
    Vise andre…
    2007 (engelsk)Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 578, nr 2, s. 385-398Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We describe a device to study reactions relevant for the Single Event Effect (SEE) in microelectronics by means of 200 A and 300 A MeV, inverse kinematics, Si+H and Si+D reactions. The work is focused on the possibility to measure Z=2–14 projectile fragments as efficiently as possible. During commissioning and first experiments the fourth quadrant of the CELSIUS storage ring acted as a spectrometer to register fragments in two planes of Si strip detectors in the angular region 0–0.6. A combination of ring-structured and sector-structured Si strip detector planes operated at angles 0.6–1.1. For specific event tagging a Si+ phoswich scintillator wall operated in the range 3.9–11.7 and Si ΔEE telescopes of CHICSi type operated at large angles.

    Emneord
    Single event effects, Fragmentation detectors, Inverse kinematics
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-16747 (URN)10.1016/j.nima.2007.05.318 (DOI)000248930700004 ()
    Tilgjengelig fra: 2008-06-05 Laget: 2008-06-05 Sist oppdatert: 2017-12-08
    3. 200 and 300 MeV/nucleon Nuclear Reactions Responsible for Single-Event Effecrs in Microelectronics
    Åpne denne publikasjonen i ny fane eller vindu >>200 and 300 MeV/nucleon Nuclear Reactions Responsible for Single-Event Effecrs in Microelectronics
    Vise andre…
    Artikkel i tidsskrift (Fagfellevurdert) Submitted
    Identifikatorer
    urn:nbn:se:uu:diva-96829 (URN)
    Tilgjengelig fra: 2008-03-14 Laget: 2008-03-14bibliografisk kontrollert
    4. Inclusive production of recoils in 20Ne + 1H reactions ar 100 and 300 MeV/nucleon
    Åpne denne publikasjonen i ny fane eller vindu >>Inclusive production of recoils in 20Ne + 1H reactions ar 100 and 300 MeV/nucleon
    Vise andre…
    Manuskript (Annet vitenskapelig)
    Identifikatorer
    urn:nbn:se:uu:diva-96830 (URN)
    Tilgjengelig fra: 2008-03-14 Laget: 2008-03-14 Sist oppdatert: 2010-01-13bibliografisk kontrollert
  • 230.
    Jäderström, Henrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärn- och partikelfysik.
    Murin, Yuri
    Babain, Yuri
    Chubarov, Mikhail
    Pljuschev, Vladimir
    Zubkov, Mikhail
    Nomokonov, Peter
    Olsson, Nils
    Blomgren, Jan
    Tippawan, Udomrat
    Zartova, Irina
    Budzanowski, Andrzej
    Czech, Bronislaw