964 resultados para Indexicals (Semantics)
Resumo:
Context. Turbulent fluxes of angular momentum and heat due to rotationally affected convection play a key role in determining differential rotation of stars. Aims. We compute turbulent angular momentum and heat transport as functions of the rotation rate from stratified convection. We compare results from spherical and Cartesian models in the same parameter regime in order to study whether restricted geometry introduces artefacts into the results. Methods. We employ direct numerical simulations of turbulent convection in spherical and Cartesian geometries. In order to alleviate the computational cost in the spherical runs and to reach as high spatial resolution as possible, we model only parts of the latitude and longitude. The rotational influence, measured by the Coriolis number or inverse Rossby number, is varied from zero to roughly seven, which is the regime that is likely to be realised in the solar convection zone. Cartesian simulations are performed in overlapping parameter regimes. Results. For slow rotation we find that the radial and latitudinal turbulent angular momentum fluxes are directed inward and equatorward, respectively. In the rapid rotation regime the radial flux changes sign in accordance with earlier numerical results, but in contradiction with theory. The latitudinal flux remains mostly equatorward and develops a maximum close to the equator. In Cartesian simulations this peak can be explained by the strong 'banana cells'. Their effect in the spherical case does not appear to be as large. The latitudinal heat flux is mostly equatorward for slow rotation but changes sign for rapid rotation. Longitudinal heat flux is always in the retrograde direction. The rotation profiles vary from anti-solar (slow equator) for slow and intermediate rotation to solar-like (fast equator) for rapid rotation. The solar-like profiles are dominated by the Taylor-Proudman balance.
Resumo:
During their main sequence evolution, massive stars can develop convective regions very close to their surface. These regions are caused by an opacity peak associated with iron ionization. Cantiello et al. (2009) found a possible connection between the presence of sub-photospheric convective motions and small scale stochastic velocities in the photosphere of early-type stars. This supports a physical mechanism where microturbulence is caused by waves that are triggered by subsurface convection zones. They further suggest that clumping in the inner parts of the winds of OB stars could be related to subsurface convection, and that the convective layers may also be responsible for stochastic excitation of non-radial pulsations. Furthermore, magnetic fields produced in the iron convection zone could appear at the surface of such massive stars. Therefore subsurface convection could be responsible for the occurrence of observable phenomena such as line profile variability and discrete absorption components. These phenomena have been observed for decades, but still evade a clear theoretical explanation. Here we present preliminary results from 3D MHD simulations of such subsurface convection.
Resumo:
Pappret conceptualizes parsning med Constraint Grammar på ett nytt sätt som en process med två viktiga representationer. En representation innehåller lokala tvetydighet och den andra sammanfattar egenskaperna hos den lokala tvetydighet klasser. Båda representationer manipuleras med ren finite-state metoder, men deras samtrafik är en ad hoc -tillämpning av rationella potensserier. Den nya tolkningen av parsning systemet har flera praktiska fördelar, bland annat det inåt deterministiska sättet att beräkna, representera och räkna om alla potentiella tillämpningar av reglerna i meningen.
Resumo:
Artikkelissa esitellään uusi julkisen keskustelun tutkimiseen kehitetty analyysimenetelmä, julkisen oikeuttamisen analyysi (JOA). JOA perustuu Luc Boltanskin ja Laurent Thévenot'n oikeuttamisteorian seitsemän "maailman" – inspiraation, kodin, maineen, kansalaisuuden, markkinoiden, teollisuuden ja ekologian – muodostamalle analyysikehikolle. Se tutkii keskusteluissa esiintyvien vaateiden moraalisia oikeutuksia, niiden yhdistelmiä ja tapoja kiistää ja tuomita kiistakumppaneiden oikeutuksia. JOA:n avulla voidaan kvalitatiiviseen tekstianalyysiin yhdistää myös kvantitatiivista luokittelua, jolloin menetelmä soveltuu suurtenkin aineistojen analyysiin. JOA:n käyttöä havainnollistetaan artikkelissa kahden tutkimusesimerkin avulla. Ensimmäinen esimerkki käsittelee Helsingin Sanomissa globalisaatiosta vuosina 1999–2005 käydyn keskustelun osapuolten, erityisesti kansalaisyhteiskunnan sekä taloudellisen ja poliittisen eliitin, argumentteja ja niille annettuja oikeutuksia. Tämän esimerkin kautta kuvataan erilaisten oikeuttamisyhdistelmien ilmaisuvoimaa yhteiskunnallisten kiistakysymysten moraalisten ulottuvuuksien analysoimisessa. Toinen esimerkki keskittyy paikallisiin kiistoihin Suomessa ja Ranskassa tarkastelemalla kansalaisten ja kaupungin edustajien esittämiä oikeutuksia paikallislehdistössä. Tämä esimerkki osoittaa JOA:n vahvuudet vertailevan tutkimuksen työkaluna.
Resumo:
Abstract. Peat surface CO2 emission, groundwater table depth and peat temperature were monitored for two years along transects in an Acacia plantation on thick tropical peat (>4 m) in Sumatra, Indonesia. A total of 2300 emission measurements were taken at 144 locations. The autotrophic root respiration component of the CO2 emission was separated from heterotrophic emissions caused by peat oxidation in three ways: (i) by comparing CO2 emissions within and beyond the tree rooting zone, (ii) by comparing CO2 emissions with and without peat trenching (i.e. cutting any roots remaining in the peat beyond the tree rooting zone), and (iii) by comparing CO2 emissions before and after Acacia tree harvesting. On average, the contribution of root respiration to daytime CO2 emission is 21 % along transects in mature tree stands. At locations 0.5 m from trees this is up to 80 % of the total emissions, but it is negligible at locations more than 1.3 m away. This means that CO2 emission measurements well away from trees are free of any root respiration contribution and thus represent only peat oxidation emission. We find daytime mean annual CO2 emission from peat oxidation alone of 94 t ha−1 yr−1 at a mean water table depth of 0.8 m, and a minimum emission value of 80 t ha−1 yr−1 after correction for the effect of diurnal temperature fluctuations, which resulted in a 14.5 % reduction of the daytime emission. There is a positive correlation between mean long-term water table depths and peat oxidation CO2 emission. However, no such relation is found for instantaneous emission/water table depth within transects and it is clear that factors other than water table depth also affect peat oxidation and total CO2 emissions. The increase in the temperature of the surface peat due to plantation development may explain over 50 % of peat oxidation emissions.