358 research outputs found
Total Chiral Symmetry Breaking during Crystallization: Who needs a "Mother Crystal"?
Processes that can produce states of broken chiral symmetry are of particular
interest to physics, chemistry and biology. Chiral symmetry breaking during
crystallization of sodium chlorate occurs via the production of secondary
crystals of the same handedness from a single "mother crystal" that seeds the
solution. Here we report that a large and "symmetric" population of D- and
L-crystals moves into complete chiral purity disappearing one of the
enantiomers. This result shows: (i) a new symmetry breaking process
incompatible with the hypothesis of a single "mother crystal"; (ii) that
complete symmetry breaking and chiral purity can be achieved from an initial
system with both enantiomers. These findings demand a new explanation to the
process of total symmetry breaking in crystallization without the intervention
of a "mother crystal" and open the debate on this fascinating phenomenon. We
present arguments to show that our experimental data can been explained with a
new model of "complete chiral purity induced by nonlinear autocatalysis and
recycling".Comment: 5 pages, 4 figures, Added reference
Bayesian Methods for Exoplanet Science
Exoplanet research is carried out at the limits of the capabilities of
current telescopes and instruments. The studied signals are weak, and often
embedded in complex systematics from instrumental, telluric, and astrophysical
sources. Combining repeated observations of periodic events, simultaneous
observations with multiple telescopes, different observation techniques, and
existing information from theory and prior research can help to disentangle the
systematics from the planetary signals, and offers synergistic advantages over
analysing observations separately. Bayesian inference provides a
self-consistent statistical framework that addresses both the necessity for
complex systematics models, and the need to combine prior information and
heterogeneous observations. This chapter offers a brief introduction to
Bayesian inference in the context of exoplanet research, with focus on time
series analysis, and finishes with an overview of a set of freely available
programming libraries.Comment: Invited revie
SOPHIE velocimetry of Kepler transit candidates. V. The three hot Jupiters KOI-135b, KOI-204b and KOI-203b (alias Kepler-17b)
We report the discovery of two new transiting hot Jupiters, KOI-135b and
KOI-204b, that were previously identified as planetary candidates by Borucki et
al. 2011, and, independently of the Kepler team, confirm the planetary nature
of Kepler-17b, recently announced by Desert et al. 2011. Radial-velocity
measurements, taken with the SOPHIE spectrograph at the OHP, and Kepler
photometry (Q1 and Q2 data) were used to derive the orbital, stellar and
planetary parameters. KOI-135b and KOI-204b orbit their parent stars in 3.02
and 3.25 days, respectively. They have approximately the same radius,
Rp=1.20+/-0.06 R_jup and 1.24+/-0.07 R_jup, but different masses Mp=3.23+/-0.19
M_jup and 1.02+/-0.07 M_jup. As a consequence, their bulk densities differ by a
factor of four, rho_p=2.33+/-0.36 g.cm^-3 (KOI-135b) and 0.65+/-0.12 g.cm-3
(KOI-204b). Our SOPHIE spectra of Kepler-17b, used both to measure the
radial-velocity variations and determine the atmospheric parameters of the host
star, allow us to refine the characterisation of the planetary system. In
particular we found the radial-velocity semi-amplitude and the stellar mass to
be respectively slightly smaller and larger than Desert et al. These two
quantities, however, compensate and lead to a planetary mass fully consistent
with Desert et al.: our analysis gives Mp=2.47+/-0.10 M_jup and Rp=1.33+/-0.04
R_jup. We found evidence for a younger age of this planetary system, t<1.8 Gyr,
which is supported by both evolutionary tracks and gyrochronology. Finally, we
confirm the detection of the optical secondary eclipse and found also the
brightness phase variation with the Q1 and Q2 Kepler data. The latter indicates
a low redistribution of stellar heat to the night side (<16% at 1-sigma), if
the optical planetary occultation comes entirely from thermal flux. The
geometric albedo is A_g<0.12 (1-sigma).Comment: submitted to Astronomy and Astrophysic
Chiral Crystal Growth under Grinding
To study the establishment of homochirality observed in the crystal growth
experiment of chiral molecules from a solution under grinding, we extend the
lattice gas model of crystal growth as follows. A lattice site can be occupied
by a chiral molecule in R or S form, or can be empty. Molecules form
homoclusters by nearest neighbor bonds. They change their chirality if they are
isolated monomers in the solution. Grinding is incorporated by cutting and
shafling the system randomly. It is shown that Ostwald ripening without
grinding is extremely slow to select chirality, if possible. Grinding alone
also cannot achieve chirality selection. For the accomplishment of
homochirality, we need an enhanced chirality change on crystalline surface.
With this "autocatalytic effect" and the recycling of monomers due to rinding,
an exponential increase of crystal enantiomeric excess to homochiral state is
realized.Comment: 10 pages, 5 figure
Study protocol for First Dental Steps Intervention: feasibility study of a health visitor led infant oral health improvement programme.
BACKGROUND: Dental caries in childhood is a burden on the daily lives of children and their families, and associated with poor oral health in adulthood. In England, dental caries is the most common reason for young children to be admitted to hospital. It is believed that most tooth extractions (due to decay) for children aged 10 years and under, could be avoided with improved prevention and early management. National public health policy recommendations in England include specific oral health initiatives to tackle tooth decay. One of these initiatives is delivered as part of the Healthy Child Programme and includes providing workforce training in oral health, integrating oral health advice into home visits, and the timely provision of fluoride toothpaste. This protocol seeks to assess the delivery of the First Dental Steps intervention and uncertainties related to the acceptability, recruitment, and retention of participants. METHODS: This study seeks to explore the feasibility and acceptability of the First Dental Steps intervention and research methods. First Dental Steps intervention will be delivered in local authority areas in South West England and includes oral health training for health visitors (or community nursery nurses) working with 0-5-year-olds and their families. Further, for vulnerable families, integrating oral health advice and the provision of an oral health pack (including a free flow cup, an age appropriate toothbrush, and 1450 ppm fluoride toothpaste) during a mandated check by a health visitor. In this study five local authority areas will receive the intervention. Interviews with parents receiving the intervention and health visitors delivering the intervention will be undertaken, along with a range of additional interviews with stakeholders from both intervention and comparison sites (four additional local authority areas). DISCUSSION: This protocol was written after the start of the COVID-19 pandemic, as a result, some of the original methods were adjusted specifically to account for disruptions caused by the pandemic. Results of this study will primarily provide evidence on the acceptability and feasibility of both the First Dental Steps intervention and the research methods from the perspective of both families and stakeholders
Detection of Neptune-size planetary candidates with CoRoT data. Comparison with the planet occurrence rate derived from Kepler
[Abridged] Context. The CoRoT space mission has been searching for transiting
planets since the end of December 2006. Aims. We aim to investigate the
capability of CoRoT to detect small-size transiting planets in short-period
orbits, and to compare the number of CoRoT planets with 2 \leq R_p \leq 4
Rearth with the occurrence rate of small-size planets provided by the
distribution of Kepler planetary candidates (Howard et al. 2012). Methods. We
performed a test that simulates transits of super-Earths and Neptunes in real
CoRoT light curves and searches for them blindly by using the LAM transit
detection pipeline. Results. The CoRoT detection rate of planets with radius
between 2 and 4 Rearth and orbital period P \leq 20 days is 59% (31%) around
stars brighter than r'=14.0 (15.5). By properly taking the CoRoT detection rate
for Neptune-size planets and the transit probability into account, we found
that according to the Kepler planet occurrence rate, CoRoT should have
discovered 12 \pm 2 Neptunes orbiting G and K dwarfs with P \leq 17 days in six
observational runs. This estimate must be compared with the validated Neptune
CoRoT-24b and five CoRoT planetary candidates in the considered range of
planetary radii. We thus found a disagreement with expectations from Kepler at
3 \sigma or 5 \sigma, assuming a blend fraction of 0% (six Neptunes) and 100%
(one Neptune) for these candidates. Conclusions. This underabundance of CoRoT
Neptunes with respect to Kepler may be due to several reasons. Regardless of
the origin of the disagreement, which needs to be investigated in more detail,
the noticeable deficiency of CoRoT Neptunes at short orbital periods seems to
indirectly support the general trend found in Kepler data, i.e. that the
frequency of small-size planets increases with increasing orbital periods and
decreasing planet radii.Comment: 10 pages, 7 figures. Accepted for publication in A&
SOPHIE velocimetry of Kepler transit candidates III. KOI-423b: an 18 Mjup transiting companion around an F7IV star
We report the strategy and results of our radial velocity follow-up campaign
with the SOPHIE spectrograph (1.93-m OHP) of four transiting planetary
candidates discovered by the Kepler space mission. We discuss the selection of
the candidates KOI-428, KOI-410, KOI-552, and KOI-423. KOI-428 was established
as a hot Jupiter transiting the largest and the most evolved star discovered so
far and is described by Santerne et al. (2011a). KOI-410 does not present
radial velocity change greater than 120 m/s, which allows us to exclude at 3
sigma a transiting companion heavier than 3.4 Mjup. KOI-552b appears to be a
transiting low-mass star with a mass ratio of 0.15. KOI-423b is a new
transiting companion in the overlapping region between massive planets and
brown dwarfs. With a radius of 1.22 +- 0.11 Rjup and a mass of 18.0 +- 0.92
Mjup, KOI-423b is orbiting an F7IV star with a period of 21.0874 +- 0.0002 days
and an eccentricity of 0.12 +- 0.02. From the four selected Kepler candidates,
at least three of them have a Jupiter-size transiting companion, but two of
them are not in the mass domain of Jupiter-like planets. KOI-423b and KOI-522b
are members of a growing population of known massive companions orbiting close
to an F-type star. This population currently appears to be absent around G-type
stars, possibly due to their rapid braking and the engulfment of their
companions by tidal decay.Comment: 9 pages, 12 figures, accepted in A&
Noise Sources in Photometry and Radial Velocities
The quest for Earth-like, extrasolar planets (exoplanets), especially those
located inside the habitable zone of their host stars, requires techniques
sensitive enough to detect the faint signals produced by those planets. The
radial velocity (RV) and photometric transit methods are the most widely used
and also the most efficient methods for detecting and characterizing
exoplanets. However, presence of astrophysical "noise" makes it difficult to
detect and accurately characterize exoplanets. It is important to note that the
amplitude of such astrophysical noise is larger than both the signal of
Earth-like exoplanets and state-of-the-art instrumentation limit precision,
making this a pressing topic that needs to be addressed. In this chapter, I
present a general review of the main sources of noise in photometric and RV
observations, namely, stellar oscillations, granulation, and magnetic activity.
Moreover, for each noise source I discuss the techniques and observational
strategies which allow us to mitigate their impact.Comment: 11 pages, 2 tables, Lecture presented at the IVth Azores
International Advanced School in Space Sciences on "Asteroseismology and
Exoplanets: Listening to the Stars and Searching for New Worlds"
(arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in
July 201
Special cases : moons, rings, comets, trojans
Non-planetary bodies provide valuable insight into our current under-
standing of planetary formation and evolution. Although these objects are
challeng- ing to detect and characterize, the potential information to be drawn
from them has motivated various searches through a number of techniques. Here,
we briefly review the current status in the search of moons, rings, comets, and
trojans in exoplanet systems and suggest what future discoveries may occur in
the near future.Comment: Invited review (status August 2017
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