1,800 research outputs found
Controlled functional expression of the bacteriocins pediocin PA-1 and bactofencin A in Escherichia coli
peer-reviewedThe bacteriocins bactofencin A (class IId) and pediocin PA-1 (class IIa) are encoded by operons with a similarly clustered gene organization including a structural peptide, an immunity protein, an ABC transporter and accessory bacteriocin transporter protein. Cloning of these operons in E. coli TunerTM (DE3) on a pETcoco-2 derived vector resulted in successful secretion of both bacteriocins. A corresponding approach, involving the construction of vectors containing different combinations of these genes, revealed that the structural and the transporter genes alone are sufficient to permit heterologous production and secretion in this host. Even though the accessory protein, usually associated with optimal disulfide bond formation, was not required for bacteriocin synthesis, its presence did result in greater pediocin PA-1 production. The simplicity of the system and the fact that the associated bacteriocins could be recovered from the extracellular medium provides an opportunity to facilitate protein engineering and the overproduction of biologically-active bacteriocins at industrial scale. Additionally, this system could enable the characterization of new bacteriocin operons where genetic tools are not available for the native producers
A vigorous activity cycle mimicking a planetary system in HD200466
Stellar activity can be a source of radial velocity (RV) noise and can
reproduce periodic RV variations similar to those produced by an exoplanet. We
present the vigorous activity cycle in the primary of the visual binary
HD200466, a system made of two almost identical solar-type stars with an
apparent separation of 4.6 arcsec at a distance of 44+/-2 pc. High precision RV
over more than a decade, adaptive optics (AO) images, and abundances have been
obtained for both components. A linear trend in the RV is found for the
secondary. We assumed that it is due to the binary orbit and once coupled with
the astrometric data, it strongly constrains the orbital solution of the binary
at high eccentricities (e~0.85) and quite small periastron of ~21 AU. If this
orbital motion is subtracted from the primary radial velocity curve, a highly
significant (false alarm probability <0.1%) period of about 1300 d is obtained,
suggesting in a first analysis the presence of a giant planet, but it turned
out to be due to the stellar activity cycle. Since our spectra do not include
the Ca~II resonance lines, we measured a chromospheric activity indicator based
on the Halpha line to study the correlation between activity cycles and
long-term activity variations. While the bisector analysis of the line profile
does not show a clear indication of activity, the correlation between the
Halpha line indicator and the RV measurements identify the presence of a strong
activity cycle.Comment: Accepted on Astronomy and Astrophysics Main Journal 2014, 16 pages,
18 figure
A possibly inflated planet around the bright, young star DS Tuc A
The origin of the observed diversity of planetary system architectures is one
of the main topic of the exoplanetary research. The detection of a
statistically significant sample of planets around young stars allows us to
study the early stages of planet formation and evolution, but only a handful of
them is known so far. In this regard, a considerable contribution is expected
from the NASA TESS satellite, which is now performing a survey of
of the sky to search for short-period transiting planets In its first month of
operations, TESS found a planet candidate with an orbital period of 8.14 days
around a member of the Tuc-Hor young association ( 40 Myr), the G6V main
component of the binary system DS\,Tuc. If confirmed, it would be the first
transiting planet around a young star suitable for radial velocity and/or
atmospheric characterization. We aim to validate the planetary nature of this
companion and to measure its orbital and physical parameters. We obtain
accurate planet parameters by coupling an independent reprocessing of the TESS
light curve with improved stellar parameters and the dilution caused by the
binary companion; we analyse high precision archival radial velocities to
impose an upper limit of about 0.1 M on the planet mass; we finally
rule out the presence of external companions beyond 40 au with adaptive optics
images. We confirm the presence of a young, giant ( R) planet having a not negligible possibility to be inflated (theoretical
mass M) around DS\,Tuc~A. We discuss the feasibility
of mass determination, Rossiter-McLaughlin analysis and atmosphere
characterization, allowed by the brightness of the star.Comment: 12 pages, 11 figures. Accepted for publication in A&
The SPHERE data center: a reference for high contrast imaging processing
The objective of the SPHERE Data Center is to optimize the scientific return
of SPHERE at the VLT, by providing optimized reduction procedures, services to
users and publicly available reduced data. This paper describes our motivation,
the implementation of the service (partners, infrastructure and developments),
services, description of the on-line data, and future developments. The SPHERE
Data Center is operational and has already provided reduced data with a good
reactivity to many observers. The first public reduced data have been made
available in 2017. The SPHERE Data Center is gathering a strong expertise on
SPHERE data and is in a very good position to propose new reduced data in the
future, as well as improved reduction procedures.Comment: SF2A proceeding
Operacionalização de uma planta de pirólise rápida de biomassa com reator de leito fluidizado.
Neste trabalho são discutidos os principais problemas encontrados durante a operação da planta piloto de pirólise rápida de biomassa, pertencente à Universidade Estadual de Campinas- Unicamp, Brasil. Essa planta foi ajustada para a produção de bio-óleo, a partir de resíduos de biomassa de pequeno tamanho. Durante os testes, os principais problemas identificados foram: escoamento de vapores da pirólise pelo sistema de alimentação de biomassa; travamento da rosca de alimentação de biomassa; segregação da biomassa no leito; sinterização do material inerte; acúmulo de biomassa e de carvão vegetal dentro do reator; dificuldade para o aquecimento do inerte e baixa eficiência de recuperação de bio-óleo. Os resultados dos testes exploratórios permitiram definir condições operacionais para possibilitar o trabalho estável do reator, aumentar o conhecimento sobre os fenômenos que ocorrem durante a pirólise rápida em leito fluidizado, além do estabelecimento de faixas operacionais para vários fatores independentes, visando a futuros trabalhos de otimização experimental
The origin of R CrA variability: A complex triple system hosting a disk
R~CrA is the brightest member of the Coronet star forming region and it is
the closest Herbig AeBe star with a spectrum dominated by emission lines. Its
luminosity has been monitored since the end of the 19th century, but the origin
of its variability, which shows a stable period of ~days, is
still unknown. We studied photometric and spectroscopic data for this star to
investigate the nature of the variability of R~CrA. We exploited the fact that
near infrared luminosity of the Herbig AeBe stars is roughly proportional to
the total luminosity of the stars to derive the absorption, and then mass and
age of R~CrA. In addition, we model the periodic modulation of the light curve
as due to partial attenuation of a central binary by a circumbinary disk. This
model reproduces very well the observations. We found that the central object
in R~CrA is a very young (~Myr), highly absorbed (~mag) binary; we obtain masses of ~M and
~M for the two components. We propose that the
secular decrease of the R~CrA apparent luminosity is due to a progressive
increase of the disk absorption. This might be related to precession of a
slightly inclined disk caused by the recently discovered M-dwarf companion.
Thus, R~CrA may be a triple system hosting a disk.Comment: Accepted for publication in A&A. 14 pages, 11 figure
Characterizing HR3549B using SPHERE
Aims. In this work, we characterize the low mass companion of the A0 field
star HR3549. Methods. We observed HR3549AB in imaging mode with the the NIR
branch (IFS and IRDIS) of SPHERE@VLT, with IFS in YJ mode and IRDIS in the H
band. We also acquired a medium resolution spectrum with the IRDIS long slit
spectroscopy mode. The data were reduced using the dedicated SPHERE GTO
pipeline, purposely designed for this instrument. We employed algorithms such
as PCA and TLOCI to reduce the speckle noise. Results. The companion was
clearly visible both with IRDIS and IFS.We obtained photometry in four
different bands as well as the astrometric position for the companion. Based on
our astrometry, we confirm that it is a bound object and put constraints on its
orbit. Although several uncertainties are still present, we estimate an age of
~100-150 Myr for this system, yielding a most probable mass for the companion
of 40-50MJup and T_eff ~300-2400 K. Comparing with template spectra points to a
spectral type between M9 and L0 for the companion, commensurate with its
position on the color-magnitude diagram.Comment: Accepted by A&A, 13 pages, 10 Figures (Figures 9 and 10 degraded to
reduce the dimension
AF Lep b: the lowest mass planet detected coupling astrometric and direct imaging data
Aims. Using the direct imaging technique we searched for low mass companions
around the star AF Lep that presents a significant proper motion anomaly (PMa)
signal obtained from the comparison of Hipparcos and Gaia eDR3 catalogs.
Methods. We observed AF Lep in two epochs with VLT/SPHERE using its subsystems
IFS and IRDIS in the near-infrared (NIR) covering wavelengths ranging from the
Y to the K spectral bands (between 0.95 and 2.3 {\mu}m). The data were then
reduced using the high-contrast imaging techniques angular differential imaging
(ADI) and spectral differential imaging (SDI) to be able to retrieve the signal
from low mass companions of the star. Results. A faint companion was retrieved
at a separation of ~0.335" from the star and with a position angle of ~70.5 deg
in the first epoch and with a similar position in the second epoch. This
corresponds to a projected separation of ~9 au. The extracted photometry
allowed us to estimate for the companion a mass between 2 and 5 MJup. This mass
is in good agreement with what is expected for the dynamic mass of the
companion deduced using astrometric measures (5.2-5.5 MJup). This is the first
companion with a mass well below the deuterium burning limit discovered
coupling direct imaging with PMa measures. Orbit fitting done using the orvara
tool allowed to further confirm the companion mass and to define its main
orbital parameters.Comment: 10 pages, 8 Figures, accepted for publication on A&
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