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81.
Ari Buchalter Raul Jimenez Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》2001,328(2):520-526
We predict the Tully–Fisher (TF) and surface-brightness–magnitude relations for disc galaxies at and discuss the origin of these scaling relations and their scatter. We find that both halo dynamics and the star formation history play important roles, and we show that the variation of the TF relation with redshift can be a potentially powerful discriminator of galaxy-formation models. In particular, the TF relation at high redshift might be used to break parameter degeneracies among galactosynthesis models at , as well as to constrain the redshift distribution of collapsing dark-matter haloes, the star formation history and baryon fraction in the disc and the distribution of halo spins. 相似文献
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Raul Jimenez Benjamin Panter Alan F. Heavens Licia Verde 《Monthly notices of the Royal Astronomical Society》2005,356(2):495-501
Using the spectroscopic sample of the Sloan Digital Sky Survey Data Release 1 (SDSS DR1), we measure how gas was transformed into stars as a function of time and stellar mass: the baryonic conversion tree (BCT). There is a clear correlation between early star formation activity and present-day stellar mass: the more massive galaxies have formed approximately 80 per cent of their stars at z > 1 , while for the less massive ones the value is only approximately 20 per cent. By comparing the BCT with the dark matter merger tree, we find indications that star formation efficiency at z > 1 had to be approximately a factor of two higher than today (∼10 per cent) in galaxies with present-day stellar mass larger than 2 × 1011 M⊙ , if this early star formation occurred in the main progenitor. Therefore, the λ cold dark matter (LCDM) paradigm can accommodate a large number of red objects. On the other hand, in galaxies with present-day stellar mass less than 1011 M⊙ , efficient star formation seems to have been triggered at z ∼ 0.2 . We show that there is a characteristic mass ( M * ∼ 1010 M⊙ ) for feedback efficiency (or lack of star formation). For galaxies with masses lower than this, feedback (or star formation suppression) is very efficient while for higher masses it is not. The BCT, determined here for the first time, should be an important observable with which to confront theoretical models of galaxy formation. 相似文献
85.
Raul Orus Perez 《Journal of Geodesy》2017,91(4):397-407
For single-frequency users of the global satellite navigation system (GNSS), one of the main error contributors is the ionospheric delay, which impacts the received signals. As is well-known, GPS and Galileo transmit global models to correct the ionospheric delay, while the international GNSS service (IGS) computes precise post-process global ionospheric maps (GIM) that are considered reference ionospheres. Moreover, accurate ionospheric maps have been recently introduced, which allow for the fast convergence of the real-time precise point position (PPP) globally. Therefore, testing of the ionospheric models is a key issue for code-based single-frequency users, which constitute the main user segment. Therefore, the testing proposed in this paper is straightforward and uses the PPP modeling applied to single- and dual-frequency code observations worldwide for 2014. The usage of PPP modeling allows us to quantify—for dual-frequency users—the degradation of the navigation solutions caused by noise and multipath with respect to the different ionospheric modeling solutions, and allows us, in turn, to obtain an independent assessment of the ionospheric models. Compared to the dual-frequency solutions, the GPS and Galileo ionospheric models present worse global performance, with horizontal root mean square (RMS) differences of 1.04 and 0.49 m and vertical RMS differences of 0.83 and 0.40 m, respectively. While very precise global ionospheric models can improve the dual-frequency solution globally, resulting in a horizontal RMS difference of 0.60 m and a vertical RMS difference of 0.74 m, they exhibit a strong dependence on the geographical location and ionospheric activity. 相似文献
86.
Raul Q. Feitosa Gilson A.O.P. Costa Guilherme L.A. Mota Kian Pakzad Maria C.O. Costa 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(2):159-170
This paper proposes a new fuzzy cascade multitemporal classification method based on Fuzzy Markov Chains. This method differs from prior fuzzy multitemporal approaches proposed thus far, as the method does not require the knowledge of the true class at an earlier date; instead it uses the attributes of the image object being classified at the earlier date. This method combines the fuzzy, non-temporal, classification of a geographical region at two points in time to provide a single unified result. A transformation law based on class transition possibilities projects the earlier classification onto the later date before combining both results. Performance analysis was conducted upon a sequence of three LANDSAT images from the central region of Brazil using a Genetic Algorithm to estimate transition possibilities. The analysis showed that the increase in performance is highly dependent on whether or not a significant correlation exists between the temporal data sets, as well as on the accuracy of the monotemporal classifier at the earlier date. While the monotemporal approach used in the experiments attained an average class accuracy of approximately 55%, the multitemporal scheme achieved between 65% and 95%. Similar results in terms of overall accuracy were also observed. Furthermore, compared to two alternative cascade multitemporal classification approaches, the proposed method consistently showed better results. 相似文献
87.
The numerical model COBRAS-UC [Losada, I.J., Lara, J.L., Guanche,R., Gonzalez-Ondina, J.M. (2008). Numerical analysis of wave overtopping of rubble mound breakwaters. Coastal Engineering, Vol 55 (1), 47–62.] is used to carry out a two-dimensional analysis of wave induced loads on coastal structures. The model calculates pressure, forces and moments for two different cross-sections corresponding to a low-mound and a conventional rubble-mound breakwater with a crown-wall under regular and irregular incident wave conditions. Predicted results are compared with experimental information provided in Losada et al. [Losada, I.J., Lara, J.L., Guanche,R., Gonzalez-Ondina, J.M. (2008). Numerical analysis of wave overtopping of rubble mound breakwaters. Coastal Engineering, Vol 55 (1), 47–62.] and Lara et al. [Lara, J.L., Losada, I.J., Guanche, R. (2008). “Wave interaction with low mound breakwaters using a RANS model”. Ocean engineering (35), pp 1388–1400; doi:10.1016/j.oceaneng.2008.05.006.] on a 1:20 scale. Good agreement is found, and the differences between both typologies are explained in detail. Additionally, numerical results are also compared with several semi-empirical formulae recommended for design at both the 1:20 model scale and two prototype cross-sections. Results suggest that COBRAS-UC is able to provide realistic stability information that can be used to complete the approach based on currently existing methods and tools. 相似文献
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Ralph Hinsch Charlotte M. Krawczyk Christoph Gaedicke Raul Giraudo Daniel Demuro 《Tectonophysics》2002,355(1-4)
In the area of the Bolivian Orocline, we examine the deformation pattern associated with the active development of a new thrust sheet. A dense grid of reprocessed 2-D seismic lines from hydrocarbon exploration industry is interpreted and a 3-D simplified structural and kinematic model is deduced. In the Boomerang Hills, onlapping Paleozoic and foredeep sediments are detached from the underlying S-dipping basement. They are thrust northeastwards by less than 2 km. Two zones can be differentiated along the Andean deformation front: (1) a W–E to NW–SE striking frontal segment of predominantly orthogonal shortening, comprising a thrust and anticline system; (2) a WSW–ENE striking lateral zone of oblique shortening within a complex system of thin-skinned strike–slip faults and minor folds. The deformation front always follows a pronounced edge in the topography of the top basement surface close to the boundary of the Paleozoic basin. The observed deformation pattern indicates intensified strain partitioning caused by the interaction of contraction direction and basement topography, which provides a near oblique ramp for the onlapping wedge of sediments. The SW–NE thrusting direction is divided into orthogonal and tangential components. These are accommodated by convergent and strike–slip structures, respectively, which sole into a common detachment horizon. The structural evolution of the new thrust sheet in the Bolivian Orocline is primarily controlled by the paleorelief of the Brazilian Shield because: (1) the shape of the basement affects the taper of the thrust wedge and localizes the deformation front and (2) small asperities in/close to the top of the basement promote fault localization. The coincidence of a relatively high basement position and a structural high of the Eastern Cordillera leads to the conclusion that the shape of the Brazilian Shield also controls the structural evolution of the pronounced eastern border of the Bolivian Orocline. 相似文献