34,019 research outputs found
Glory revealed in disk-integrated photometry of Venus
Context. Reflected light from a spatially unresolved planet yields unique
insight into the overall optical properties of the planet cover. Glories are
optical phenomena caused by light that is backscattered within spherical
droplets following a narrow distribution of sizes; they are well known on Earth
as localised features above liquid clouds. Aims. Here we report the first
evidence for a glory in the disk-integrated photometry of Venus and, in turn,
of any planet. Methods. We used previously published phase curves of the planet
that were reproduced over the full range of phase angles with model predictions
based on a realistic description of the Venus atmosphere. We assumed that the
optical properties of the planet as a whole can be described by a uniform and
stable cloud cover, an assumption that agrees well with observational evidence.
Results. We specifically show that the measured phase curves mimic the
scattering properties of the Venus upper-cloud micron-sized aerosols, also at
the small phase angles at which the glory occurs, and that the glory contrast
is consistent with what is expected after multiple scattering of photons. In
the optical, the planet appears to be brighter at phase angles of 11-13 deg
than at full illumination; it undergoes a maximum dimming of up to 10 percent
at phases in between. Conclusions. Glories might potentially indicate spherical
droplets and, thus, extant liquid clouds in the atmospheres of exoplanets. A
prospective detection will require exquisite photometry at the small
planet-star separations of the glory phase angles.Comment: In press. Astronomy & Astrophysics. Letter to the Editor; 201
Making Sustainable Agriculture Real in CAP 2020: The Role of Conservation Agriculture
Europe is about to redefine its Common Agriculture Policy (CAP) for the near future. The question is whether this redefinition is more a fine-tuning of the existing CAP or whether thorough changes can be expected. Looking back to the last revision of CAP the most notable change is, undoubtedly, the concern about EU and global food security. The revival of the interest in agricultural production already became evident during the Health Check as a consequence of climbing commodity prices in 2007/08. It is therefore no surprise that “rising concerns regarding both EU and global food security” is the first topic to appear in the list of justifications for the need for a CAP reform. Other challenges mentioned in this list such as sustainable management of natural resources, climate change and its mitigation, improvement of competitiveness to withstand globalization and rising price volatility, etc., while not new are considered worthwhile enough to be maintained and reappraised
Kink stability, propagation, and length scale competition in the periodically modulated sine-Gordon equation
We have examined the dynamical behavior of the kink solutions of the
one-dimensional sine-Gordon equation in the presence of a spatially periodic
parametric perturbation. Our study clarifies and extends the currently
available knowledge on this and related nonlinear problems in four directions.
First, we present the results of a numerical simulation program which are not
compatible with the existence of a radiative threshold, predicted by earlier
calculations. Second, we carry out a perturbative calculation which helps
interpret those previous predictions, enabling us to understand in depth our
numerical results. Third, we apply the collective coordinate formalism to this
system and demonstrate numerically that it accurately reproduces the observed
kink dynamics. Fourth, we report on a novel occurrence of length scale
competition in this system and show how it can be understood by means of linear
stability analysis. Finally, we conclude by summarizing the general physical
framework that arises from our study.Comment: 19 pages, REVTeX 3.0, 24 figures available from A S o
Studying synthesis confinement effects on the internal structure of nanogels in computer simulations
We study the effects of droplet finite size on the structure of nanogel
particles synthesized by random crosslinking of molecular polymers diluted in
nanoemulsions. For this, we use a bead-spring computer model of polymer-like
structures that mimics the confined random crosslinking process corresponding
to irradiation- or electrochemically-induced crosslinking methods. Our results
indicate that random crosslinking under strong confinement can lead to unusual
nanogel internal structures, with a central region less dense than the external
one, whereas under moderate confinement the resulting structure has a denser
central region. We analyze the topology of the polymer networks forming nanogel
particles with both types of architectures, their overall structural
parameters, their response to the quality of the solvent and compare the cases
of non-ionic and ionic systems
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