5,908 research outputs found
How to Mix Molecules with Mathematics
In this paper we develop two methods to calculate thermodynamic properties of mixtures. Starting point are the basic assumptions that also form the basis for the COSMO-RS model. In this approach, the individual molecules are represented by their geometrical shape with an electrical charge density on their surfaces. Next, the surface is split up into surface segments each with its own charge. In COSMO-RS a strong reduction is introduced by treating the segments as if they are completely independent. In the present study we take into account that the coupling between two patches is essentially dependent on the charge distribution on neighboring segments and on the local geometrical structure of the surface. Two approaches are followed. The first one points out how the model
equations, which comprise the optimization of the entropy and conservation of internal energy, can efficiently be solved in general, thus also if the dependency between segments and the local geometry is included in the expression for the coupling energy between segments. In the second method the configuration with maximal entropy and prescribed energy is sought via simulation. Successive molecular configurations of the mixture are simulated and updated via a genetic algorithm to optimize the entropy. The second method is more time consuming but very general
Jet-torus connection in radio galaxies: Relativistic hydrodynamics and synthetic emission
High-resolution Very-Long-Baseline Interferometry observations of active
galactic nuclei have revealed asymmetric structures in the jets of radio
galaxies. These asymmetric structures may be due to internal asymmetries in the
jet, could be induced by the different conditions in the surrounding ambient
medium including the obscuring torus, or a combination of the two. In this
paper we investigate the influence of the ambient medium (including the
obscuring torus) on the observed properties of jets from radio galaxies. We
performed special-relativistic hydrodynamic (RHD) simulations of over-pressured
and pressure-matched jets using the special-relativistic hydrodynamics code
\texttt{Ratpenat}, which is based on a second-order accurate finite-volume
method and an approximate Riemann solver. Using a newly developed emission code
to compute the electromagnetic emission, we have investigated the influence of
different ambient medium and torus configurations on the jet structure and
subsequently computed the non-thermal emission produced by the jet and the
thermal absorption due to the torus. To better compare the emission simulations
with observations we produced synthetic radio maps, taking into account the
properties of the observatory. The detailed analysis of our simulations shows
that the observed asymmetries can be produced by the interaction of the jet
with the ambient medium and by the absorption properties of the obscuring
torus.Comment: 14 pages, 17 figures, submitted to A&
Improving photon-hadron discrimination based on cosmic ray surface detector data
The search for photons at EeV energies and beyond has considerable
astrophysical interest and will remain one of the key challenges for ultra-high
energy cosmic ray (UHECR) observatories in the near future. Several upper
limits to the photon flux have been established since no photon has been
unambiguously observed up to now. An improvement in the reconstruction
efficiency of the photon showers and/or better discrimination tools are needed
to improve these limits apart from an increase in statistics. Following this
direction, we analyze in this work the ability of the surface parameter Sb,
originally proposed for hadron discrimination, for photon search.
Semi-analytical and numerical studies are performed in order to optimize Sb
for the discrimination of photons from a proton background in the energy range
from 10^18.5 to 10^19.6 eV. Although not shown explicitly, the same analysis
has been performed for Fe nuclei and the corresponding results are discussed
when appropriate. The effects of different array geometries and the
underestimation of the muon component in the shower simulations are analyzed,
as well as the Sb dependence on primary energy and zenith angle.Comment: 9 pages, 19 Figures. Accepted in Astroparticle Physics on May 31th,
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Searching for low mass objects around nearby dMe radio stars
Nearby M-dwarfs are best suited for searches of low mass companions. VLBI
phase-referencing observations with sensitive telescopes are able to detect
radio star flux-densities of tenths of mJy as well as to position the star on
the sky with submilliarcsecond precision. We have initiated a long-term
observational program, using EVN telescopes in combination with NASA DSN
dishes, to revisit the kinematics of nearby, single M dwarfs. The precision of
the astrometry allows us to search for possible companions with masses down to
1 Jupiter mass. In this contribution we report preliminary results of the first
observation epochs, in which we could detect some of the radio stars included
in our program.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E.,
Porcas R.W., Lobanov A.P., & Zensus J.A. (eds.), MPIfR, Bonn, Germany, p.
255-258 (2002). 4 pages, 3 figures, needs evn2002.cl
Effects of noise on hysteresis and resonance width in graphene and nanotubes resonators
We investigate the role that noise plays in the hysteretic dynamics of a
suspended nanotube or a graphene sheet subject to an oscillating force. We find
that not only the size but also the position of the hysteresis region in these
systems can be controlled by noise. We also find that nano-resonators act as
noise rectifiers: by increasing the noise in the setup, the resonance width of
the characteristic peak in these systems is reduced and, as a result, the
quality factor is increased.Comment: 15 pages, 6 figures. Sent to PRB (in revision
Spatial Tools for Integrated and Inclusive Landscape Governance: Toward a New Research Agenda
Participatory spatial tools—community mapping, PGIS, and others—find increasing resonance among research and non-governmental organizations to make stakeholder claims and community perspectives explicit for more inclusive landscape governance. In this paper, we situate the use of participatory spatial tools in debates on integrated landscape approaches and inclusive development. We show that using such spatial tools is not new but argue that their application for inclusive landscape governance requires a new research agenda that focuses on expanding the scope of application of the tools, improving the inclusivity of the processes, and developing new technologies
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