961 research outputs found
Anisotropic fluid inside a relativistic star
An anisotropic fluid with variable energy density and negative pressure is
proposed, both outside and inside stars. The gravitational field is constant
everywhere in free space (if we neglect the local contributions) and its value
is of the order of , in accordance with MOND model. With
, the acceleration is also constant inside stars but the
value is different from one star to another and depends on their mass and
radius . In spite of the fact that the spacetime is of Rindler type and
curved even far from a local mass, the active gravitational energy on the
horizon is , as for the flat Rindler space, excepting the negative sign.Comment: 9 pages, refs added, new chapter added, no figure
Konjugaatti
Tiivistelmä. Tutkielmassa perehdytään konjugaattiin joka on eräänlainen operaatio abstraktissa algebrassa. Konjugaattia ja sen ominaisuuksia tutkitaan sekä yleisellä tasolla, että erinlaisissa ominaisuuksiltaan eroavissa ryhmissä. Tutkielmassa käydään läpi konjugaatin määritelmän lisäksi siihen liittyviä määritelmiä, kuten konjugaattiluokka, normaali aliryhmä, ryhmän keskus ja tekijäryhmä
Bremsstrahlung Emission of an X -Band Permanent Magnet Minimum-B Quadrupole Electron Cyclotron Resonance Ion Source
Initial Conditions for Vector Inflation
Recently, a model of inflation using non-minimally coupled massive vector
fields has been proposed. For a particular choice of non-minimal coupling
parameter and for a flat FRW model, the model is reduced to the model of
chaotic inflation with massive scalar field. We study the effect of non-zero
curvature of the universe on the onset of vector inflation. We find that in a
curved universe the dynamics of vector inflation can be different from chaotic
inflation, and the fraction of the initial conditions leading to inflationary
solutions is reduced compared with the chaotic inflation case.Comment: 12 pages, 5 figures, version to be published in JCA
Illumination diagnosis for retrieval of reflections from ambient-noise seismic data in the Siilinjärvi mining site, Finland
Reflection seismic methods are becoming popular in mineral exploration, because they allow high-resolution delineation of the exploration targets, even at great depths. Seismic interferometry can be used to retrieve reflections from passive seismic data, removing the need for active seismic sources and, therefore, reducing the cost and environmental impact of exploration. The retrieval of reflections can be challenging, since passive seismic records are typically dominated by surface waves. Therefore, illumination diagnosis, a method which allows the isolation of the portions of the passive data where body-wave signals are stronger, can be a valuable step that improves the quality of the reflections retrieved from seismic interferometry and reduces the overall computational cost of the processing stage. Here, we validate the performance of the method to effectively isolate the portions of the passive data dominated by body waves and apply it on an ambient-noise seismic dataset acquired in the Siilinjärvi mining site in Finland
Does fish farming affect natural Baltic fish communities?
In 1985 and 1986, a SW Finnish archipelago area was monitored for fish (using gillnets and seine), in order to investigate potential effects of salmonid fish farming on natural fish communities (population- and community level, growth and food choice). The results indicate some structural change eg. in total abundance and biomass values (increasing), on species composition (towards moore cyprinid-dominated communities), on growth rate (increasing) and food choice (increased proportions of fish consumed) of perch, and a general shift towards communities dominated by juveniles and small fish in areas influenced by fish farms
Dark energy from modified F(R)-scalar-Gauss-Bonnet gravity
The modified F(R)-scalar-Gauss-Bonnet gravity is proposed as dark energy
model. The reconstruction program for such theory is developed. It is
explicitly demonstrated that the known classical universe expansion history
(deceleration epoch, transition to acceleration and effective quintessence,
phantom or cosmological constant era) may naturally occur in such unified
theory for some (reconstructed) classes of scalar potentials. Gauss-Bonnet
assisted dark energy is also proposed. The possibility of cosmic acceleration
is studied there.Comment: LaTeX, 8 pages, no figure, refs. added, version to appear in Physics
Letters
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