6,414 research outputs found
Global Disk Oscillation Modes in Cataclysmic Variables and Other Newtonian Accretors
Diskoseismology, the theoretical study of small adiabatic hydrodynamical
global perturbations of geometrically thin, optically thick accretion disks
around black holes (and other compact objects), is a potentially powerful probe
of the gravitational field. For instance, the frequencies of the normal mode
oscillations can be used to determine the elusive angular momentum parameter of
the black hole. The general formalism developed by diskoseismologists for
relativistic systems can be readily applied to the Newtonian case of
cataclysmic variables (CVs). Some of these systems (e.g., the dwarf nova SS
Cygni) show rapid oscillations in the UV with periods of tens of seconds and
high coherence. In this paper, we assess the possibility that these dwarf nova
oscillations (DNOs) are diskoseismic modes. Besides its importance in
investigating the physical origin of DNOs, the present work could help us to
answer the following question. To what extent are the similarities in the
oscillation phenomenology of CVs and X-ray binaries (XRBs) indicative of a
common physical mechanism?Comment: 1 figur
Nitrogen Cycle And Ecosystem Services In The Brazilian La Plata Basin: Anthropogenic Influence And Climate Change.
The increasing human demand for food, raw material and energy has radically modified both the landscape and biogeochemical cycles in many river basins in the world. The interference of human activities on the Biosphere is so significant that it has doubled the amount of reactive nitrogen due to industrial fertiliser production (Haber-Bosch), fossil fuel burning and land-use change over the last century. In this context, the Brazilian La Plata Basin contributes to the alteration of the nitrogen cycle in South America because of its huge agricultural and grazing area that meets the demands of its large urban centres - Sao Paulo, for instance - and also external markets abroad. In this paper, we estimate the current inputs and outputs of anthropogenic nitrogen (in kg N.km(-2).yr(-1)) in the basin. In the results, we observe that soybean plays a very important role in the Brazilian La Plata, since it contributes with an annual entrance of about 1.8 TgN due to biological nitrogen fixation. Moreover, our estimate indicates that the export of soybean products accounts for roughly 1.0 TgN which is greater than the annual nitrogen riverine exports from Brazilian Parana, Paraguay and Uruguay rivers together. Complimentarily, we built future scenarios representing changes in the nitrogen cycle profile considering two scenarios of climate change for 2070-2100 (based on IPCC's A2 and B2) that will affect land-use, nitrogen inputs, and loss of such nutrients in the basin. Finally, we discuss how both scenarios will affect human well-being since there is a connection between nitrogen cycle and ecosystem services that affect local and global populations, such as food and fibre production and climate regulation.72691-70
On the symmetry breaking phenomenon
We investigate the problem of symmetry breaking in the framework of dynamical
systems with symmetry on a smooth manifold. Two cases will be analyzed: general
and Hamiltonian dynamical systems. We give sufficient conditions for symmetry
breaking in both cases
Use of a Simulation Model to Develop Feeding Strategies for Cattle at Pasture in Small Scale Dairy Farming Systems in the Highlands of Central Mexico: Methodological Frame Work
Existence, uniqueness and approximation of a doubly-degenerate nonlinear parabolic system modelling bacterial evolution
Accepted versio
Photonic processing of microwave signals
In this paper, recent advances in the implementation of photonic tuneable transversal filters for RF signal processing developed by the Optical Communications Group are described. After a brief introduction to the field and the basic concepts, limiting factors and application of these filters are described in the field. This is based on a distinction between filters based on wavelength tuneable optical taps and others based on the tuneability of the dispersive elements that provide the time delay between samples. Recently developed approaches have also been discussed
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