Search results for "Geophysics"
showing 10 items of 2645 documents
Flare diagnostics from loop modeling of a stellar flare observed with XMM-Newton
2006
Abstract XMM-Newton data of an X-ray flare observed on Proxima Centauri provide detailed and challenging constraints for flare modeling. The comparison of the data with the results of time-dependent hydrodynamic loop modeling of this flare allows us to constrain not only the loop morphology, but also the details of the heating function. The results show that even a complex flare event like this can be described with a relatively few – though constrained – components: two loop systems, i.e., a single loop and an arcade, and two heat components, an intense pulse probably located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The similarity …
VSOP monitoring of the quasar 1928+738
2000
Abstract In the paper we describe the first results from a campaign to monitor the relatively low redshift (z=0.3) circumpolar superluminal quasar 1928+738 with VSOP. The three epochs of data that we have analyzed show that there have been substantial structural changes in this source near the core on the time-scale of a few months.
Shock–cloud interactions in the Vela SNR: preliminary results of an XMM-Newton observation
2004
Abstract The study of the clumpy and irregular features in the X-ray emission of middle-aged supernova remnants shells allows us to shed light on the various characteristic of the interstellar medium, like its structure and composition. We have observed with XMM-Newton a small knot in the Vela SNR, which previous ROSAT studies have indicated as one of the best examples of an interaction between the SNR shock and an isolated cloud. We present preliminary results of this study. Thanks to the combination of good spectral and spatial resolution of the EPIC camera, we have realized maps of the X-ray emission in three different bands, pinpointing the contribution from different spatial regions. W…
Determination of sea surface temperature at large observation angles using an angular and emissivity-dependent split-window equation
2007
Abstract This paper proposes an angular and emissivity-dependent split-window equation that permits the determination of the sea surface temperature (SST) to a reasonable level of accuracy for any observation angle, including large viewing angles at the image edges of satellite sensors with wide swaths. This is the case of the MODIS radiometer both on EOS Terra/Aqua platforms, with observation angles of up to 65° at the surface, for which the split-window equation has been developed in this study. The algorithm takes into account the angular dependence of both the atmospheric correction (due to the increase of the atmospheric optical path with angle) and the emissivity correction (since sea…
Messungen der Himmelsstrahlung und deren Polarisationsgrad während der Sonnenfinsternis am 15.2.1961 in Viareggio (Italien)
1961
On the occasion of the total solar eclipse in Viareggio (Italy) measurements of intensity of sky radiation and polarization have been carried out at 90 degrees vertical distance from the sun. UV-, green- and red-filters have been used. The results showed a diminution of the intensity during the eclipse of about 3 powers of ten. The sky brightness in the point 90 degrees distant during the total eclipse was similar to the brightness when sun is 7 degrees below the horizon. About one minute before the total eclipse the degree of polarization diminuished to zero. — Furthermore photos of nearly the total sky were made using two cameras with wide angle lenses.
Digital rock physics, chemistry, and biology: challenges and prospects of pore-scale modelling approach
2021
Abstract Conventional and unconventional hydrocarbon rocks have complicated pore structures with heterogeneities distributed over various length scales (from nanometre to centimetre or even larger scales). Effective characterization of the properties of such rocks based on their digital twins is a challenging task. Digital rock physics (DRP) can be used to quantify the structural and morphological parameters of rocks directly and predict flow transport properties at the pore scale. Digital rock chemistry (DRC) or biology (DRB) applies when the changes in pore structures are due to interaction with solutes or microbial activities. Fluid–rock interactions or microbial activities complicate fl…
Instabilities in a staircase stratified shear flow
2017
We study stratified shear flow instability where the density profile takes the form of a staircase of interfaces separating uniform layers. Internal gravity waves riding on density interfaces can r...
Self-similarity and scaling of thermal shock fractures
2013
The problem of crack pattern formation due to thermal shock loading at the surface of half-space is solved numerically using two-dimensional boundary element method. The results of numerical simulations with 100-200 random simultaneously growing and interacting cracks are used to obtain scaling relations for crack length and spacing. The numerical results predict that such process of pattern formation with quasi-static crack growth is not stable and at some point the excess energy leads to unstable propagation of one of the longest crack. The onset of instability has also been determined from numerical results.
Illustration of microphysical processes in Amazonian deep convective clouds in the gamma phase space: introduction and potential applications
2017
Abstract. The behavior of tropical clouds remains a major open scientific question, resulting in poor representation by models. One challenge is to realistically reproduce cloud droplet size distributions (DSDs) and their evolution over time and space. Many applications, not limited to models, use the gamma function to represent DSDs. However, even though the statistical characteristics of the gamma parameters have been widely studied, there is almost no study dedicated to understanding the phase space of this function and the associated physics. This phase space can be defined by the three parameters that define the DSD intercept, shape, and curvature. Gamma phase space may provide a commo…
A Non-normal-Mode Marginal State of Convection in a Porous Rectangle
2019
Author's accepted manuscript (postprint). This is a post-peer-review, pre-copyedit version of an article published in Transport in Porous Media. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11242-019-01263-5. The fourth-order Darcy–Bénard eigenvalue problem for onset of thermal convection in a 2D rectangular porous box is investigated. The conventional type of solution has normal-mode dependency in at least one of the two spatial directions. The present eigenfunctions are of non-normal-mode type in both the horizontal and the vertical direction. A numerical solution is found by the finite element method, since no analytical method is known for this non-…