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111.
We present the results of a year-long monitoring campaign on J1819+3845.We interpret the results of this WSRT campaign to
infer critical source parameters such as source lifetime and structure on tens of microarcseconds. The long lifetime of the
source at such high brightness temperatures requires continuous energy injection or exotic emission processes. We have previously
interpreted the extreme scintillation ofJ1819+3845 as due to a relatively nearby (∼ 20 pc) scattering screen. We show this
screen has a velocity w.r.t. the LSR of ∼ 25 kms-1, as measured by the changing scintillation properties throughout the year: the `velocity parallax'.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
112.
Summary
Silica-undersaturated phlogopite schists from the Cackleberry Metamorphics, Arunta Inlier, central Australia, preserve relatively
low-temperature sapphirine-bearing parageneses that developed during low-pressure upper amphibolite facies metamorphism. Peak
metamorphic phlogopite–cordierite–sapphirine assemblages are interpreted to have formed during the same event recorded in
nearby metapelites, at c.3 kbar and 650–700 °C. Initial cooling of the terrain resulted in the breakdown of sapphirine to corundum–chlorite–phlogopite
and corundum–spinel–chlorite assemblages. Further retrogression at greenschist facies conditions resulted in the replacement
of sapphirine by diaspore–chlorite intergrowths. The reaction textures are consistent with a near-isobaric heating-cooling
path at low-pressure, and provide evidence for the stability of sapphirine at c.700 °C at low pressures in rocks of an appropriate Mg- and Fe3+-rich bulk composition.
Received August 15, 2001 accepted December 27, 2001 相似文献
113.
P. B. Tissera R. Domínguez-Tenreiro C. Scannapieco A. Sáiz 《Monthly notices of the Royal Astronomical Society》2002,333(2):327-338
We use cosmological smooth particle hydrodynamical (SPH) simulations to study the effects of mergers in the star formation history of galactic objects in hierarchical clustering scenarios. We find that during some merger events, gaseous discs can experience two starbursts: the first one during the orbital decay phase, owing to gas inflows driven as the satellite approaches, and the second one when the two baryonic clumps collide. A trend for these first induced starbursts to be more efficient at transforming the gas into stars is also found. We detect that systems that do not experience early gas inflows have well-formed stellar bulges and more concentrated potential wells, which seem to be responsible for preventing further gas inward transport triggered by tidal forces. The potential wells concentrate owing to the accumulation of baryons in the central regions and of dark matter as the result of the pulling in by baryons. The coupled evolution of the dark matter and baryons would lead to an evolutionary sequence during which systems with shallower total potential wells suffer early gas inflows during the orbital decay phase that help to feed their central mass concentration, pulling in dark matter and contributing to build up more stable systems. Within this scenario, starbursts triggered by early gas inflows are more likely to occur at early stages of evolution of the systems and to be an important contributor to the formation of stellar bulges. Our results constitute the first proof that bulges can form as the product of collapse, collisions and secular evolution in a cosmological framework, and they are consistent with a rejuvenation of the stellar population in bulges at intermediate z with, at least, 50 per cent of the stars (in SCDM) being formed at high z . 相似文献
114.
We develop a general formalism for analysing parameter information from non-Gaussian cosmic fields. The method can be adapted to include the non-linear effects in galaxy redshift surveys, weak lensing surveys and cosmic velocity field surveys as part of parameter estimation. It can also be used as a test of non-Gaussianity of the cosmic microwave background. Generalizing maximum-likelihood analysis to second order, we calculate the non-linear Fisher information matrix and likelihood surfaces in parameter space. To this order we find that the information content is always increased by including non-linearity. Our methods are applied to a realistic model of a galaxy redshift survey, including non-linear evolution, galaxy bias, shot-noise and redshift-space distortions to second order. We find that including non-linearities allows all of the degeneracies between parameters to be lifted. Marginalized parameter uncertainties of a few per cent will then be obtainable using forthcoming galaxy redshift surveys. 相似文献
115.
A. Greco G. Zimbardo P. Veltri A.L. Taktakishvili L.M. Zelenyi 《Astrophysics and Space Science》2001,277(1-2):35-38
We study the ion dynamics in a magnetic field reversal with a constant electric field and with a model of three dimensional
magnetic turbulence. By computing the mean square displacements in the plane of the current sheet we find superdiffusive and
superballistic transport regimes. Since velocity increases with the length of the free path, we have accelerated Lévyflights.
The possibility to generate power law velocity distribution functions is pointed out, as well as the long memory effects and
non local properties of ion transport.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
116.
G. Vedrenne 《Astrophysics and Space Science》2001,276(1):337-346
In spite of the recent successes of SIGMA, RXTE andCompton GRO, and the launch of INTEGRAL in 2001, a lot ofquestions will stay opened for the next decades in gamma-ray astronomy.In this context we have to think about future instrument concepts whichwill allow a new step in the understanding of high-energy phenomena atwork in many exciting objects: binary systems with compact objects,active galactic nuclei, supernovae and novae, gamma ray bursters...A short overview of these new types of instruments will be given. 相似文献
117.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
118.
G. S. Sahakian 《Astrophysics》1997,40(1):77-82
The problem of the equation of state of cosmic matter is discussed and the constants of integration in the Friedmann solutions
are determined.
Translated from Astrofizika, Vol. 40, No. 1, pp. 117–124, January–March, 1997. 相似文献
119.
J. M. Gregory J. A. Church G. J. Boer K. W. Dixon G. M. Flato D. R. Jackett J. A. Lowe S. P. O'Farrell E. Roeckner G. L. Russell R. J. Stouffer M. Winton 《Climate Dynamics》2001,18(3-4):225-240
Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present
an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes
simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario
IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal
expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might
not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout
the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts
to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the
ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as
much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack
of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need
for detailed analysis and intercomparison in order to understand and reduce the disagreements.
Received: 1 September 2000 / Accepted: 20 April 2001 相似文献
120.
The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment. 相似文献