527 research outputs found
Starspot Jitter in Photometry, Astrometry and Radial Velocity Measurements
Analytical relations are derived for the amplitude of astrometric,
photometric and radial velocity perturbations caused by a single rotating spot.
The relative power of the star spot jitter is estimated and compared with the
available data for Ceti and HD 166435, as well as with numerical
simulations for Ceti and the Sun. A Sun-like star inclined at
i=90\degr at 10 pc is predicted to have a RMS jitter of 0.087 \uas in its
astrometric position along the equator, and 0.38 m s in radial
velocities. If the presence of spots due to stellar activity is the ultimate
limiting factor for planet detection, the sensitivity of SIM Lite to Earth-like
planets in habitable zones is about an order of magnitude higher that the
sensitivity of prospective ultra-precise radial velocity observations of nearby
stars.Comment: accepted in ApJ Letters, Nov. 200
Minimizing follow-up for space-based transit surveys using full lightcurve analysis
One of the biggest challenges facing large transit surveys is the elimination
of false-positives from the vast number of transit candidates. We investigate
to what extent information from the lightcurves can identify blend scenarios
and eliminate them as planet candidates, to significantly decrease the amount
of follow-up observing time required to identify the true exoplanet systems. If
a lightcurve has a sufficiently high signal-to-noise ratio, a distinction can
be made between the lightcurve of a stellar binary blended with a third star
and the lightcurve of a transiting exoplanet system. We perform simulations to
determine what signal-to-noise level is required to make the distinction
between blended and non-blended systems as function of transit depth and impact
parameter. Subsequently we test our method on real data from the first IRa01
field observed by the CoRoT satellite, concentrating on the 51 candidates
already identified by the CoRoT team. About 70% of the planet candidates in the
CoRoT IRa01 field are best fit with an impact parameter of b>0.85, while less
than 15% are expected in this range considering random orbital inclinations. By
applying a cut at b<0.85, meaning that ~15% of the potential planet population
would be missed, the candidate sample decreases from 41 to 11. The lightcurves
of 6 of those are best fit with such low host star densities that the
planet-to-star size ratii imply unrealistic planet radii of R>2RJup. Two of the
five remaining systems, CoRoT1b and CoRoT4b, have been identified as planets by
the CoRoT team, for which the lightcurves alone rule out blended light at 14%
(2sigma) and 31% (2sigma). We propose to use this method on the Kepler database
to study the fraction of real planets and to potentially increase the
efficiency of follow-up.Comment: 13 pages, 11 figures, 2 tables. Accepted for publication in A&
Accretion-Induced Lithium Line Enhancements in Classical T Tauri Stars: RW Aur
It is widely accepted that much of the stochastic variability of T Tauri
stars is due to accretion by a circumstellar disk. The emission line spectrum
as well as the excess continuum emission are common probes of this process. In
this communication, we present additional probes of the circumstellar
environment in the form of resonance lines of low ionization potential
elements. Using a set of 14 high resolution echelle observations of the
classical T Tauri star (CTTS), RW Aur, taken between 1986 and 1996, we
carefully measure the continuum veiling at each epoch by comparing more than
500 absorption lines with those of an appropriate template. This allows us to
accurately subtract out the continuum emission and to recover the underlying
photospheric spectrum. In doing so, we find that selected photospheric lines
are enhanced by the accretion process, namely the resonance lines of LiI and
KI. A resonance line of TiI and a low excitation potential line of CaI also
show weak enhancements. Simple slab models and computed line bisectors lead us
to propose that these line enhancements are markers of cool gas at the
beginning of the accretion flow which provides an additional source of line
opacity. These results suggest that published values of surface lithium
abundances of classical T Tauri stars are likely to be overestimated. This
would account for the various reports of surface lithium abundances in excess
of meteoritic values among the extreme CTTS. Computing LTE lithium abundances
of RW Aur in a low and then high accretion state yields abundances which vary
by one order of magnitude. The low accretion state lithium abundance is
consistent with theoretical predictions for a star of this age and mass while
the high accretion state spectrum yields a super-meteoritic lithium abundance.Comment: 28 pages, 8 figures, accepted by Ap
Evaluation of Microencapsulation of The UFV-AREG1 Bacteriophage in Alginate-Ca Microcapsules using Microfluidic Devices
The indiscriminate use of antibiotics and the emergence of resistant
microorganisms have become a major challenge for the food industry. The purpose
of this work was to microencapsulate the bacteriophage UFV-AREG1 in a calcium
alginate matrix using microfluidic devices and to study the viability and
efficiency of retention. The microcapsules were added to gel of propylene
glycol for use as an antimicrobial in the food industry. The technique showed
the number of the phage encapsulation, yielding drops with an average 100-250
m of diameter, 82.1 2% retention efficiency and stability in the gel
matrix for 21 days. The gel added to the microencapsulated phage showed
efficiency (not detectable on the surface) in reducing bacterial contamination
on the surface at a similar level to antimicrobial chemicals (alcohol 70%).
Therefore, it was possible to microencapsulate bacteriophages in alginate-Ca
and apply the microcapsules in gels for use as sanitizers in the food industry.Comment: 8 pages, 5 figure
Anéis de Ferrara: - 4 Anos Depois
Os anéis intraestromais, nomeadamente o anel de Ferrara, constitui uma importante opção terapêutica das doenças ectásicas da córnea, de origem não inflamatória como o Queratocone. Os autores analisaram os primeiros 30 casos operados no Serviço de Oftalmologia do CHLC relativamente à eficácia, estabilidade e segurança deste procedimento ao longo dos 4 anos. Verificaram estabilidade refractiva, diminuição queratométrica e do equivalente esférico e boa tolerância ao material implantado. Os autores concluem que esta opção terapêutica para o queratocone é segura, reversível, com resultados estáveis que permitem adiar ou evitar a queratoplastia
Compensatory fetal membrane mechanisms between biglycan and decorin in inflammation.
Preterm premature rupture of fetal membranes (PPROM) is associated with infection, and is one of the most common causes of preterm birth. Abnormal expression of biglycan and decorin, two extracellular matrix proteoglycans, leads to preterm birth and aberrant fetal membrane morphology and signaling in the mouse. In humans and mice, decorin dysregulation is associated with inflammation in PPROM. We therefore investigated the link between biglycan and decorin and inflammation in fetal membranes using mouse models of intraperitoneal Escherichia coli injections superimposed on genetic biglycan and decorin deficiencies. We assessed outcomes in vivo as well as in vitro using quantitative PCR, Western blotting, and enzyme-linked immunosorbent assays. Our results suggest that biglycan and decorin compensate for each other in the fetal membranes, but lose the ability to do so under inflammation, leading to decreased latency to preterm birth. Furthermore, our findings suggest that biglycan and decorin play discrete roles in fetal membrane signaling pathways during inflammation, leading to changes in the abundance of MMP8 and collagen α1VI, two components of the fetal membrane extracellular matrix that influence the pathophysiology of PPROM. In summary, these findings underline the importance of biglycan and decorin as targets for the manipulation of fetal membrane extracellular matrix stability in the context of inflammation
Repositório Iscte: Um sistema em melhoria contínua
O Repositório do Iscte, o segundo repositório institucional a nível nacional, emergiu de uma dinâmica de inovação e mudança, com o intuito de se manter e desenvolver numa lógica de melhoria contínua, comum a todos os processos da Biblioteca.
Este short paper relata o processo de trabalho realizado nos últimos dois anos no sentido de dotar o Repositório do Iscte de substanciais melhorias ao nível da sua apresentação estética, conteúdo e funcionalidades de que o utilizador poderá usufruir e, simultaneamente, facilitar as operações de BackOffice por parte dos técnicos da
Biblioteca.
Espera-se que o impacto – ainda não avaliado, por ser demasiado recente – resulte em benefícios consideráveis para este recurso, quer ao nível da qualidade dos metadados, quer de economia de tempo de trabalho necessário à execução das tarefas de curadoria e depósito dos documentos científicos. Estas alterações contribuirão, em última
instância e de uma forma significativa, para aumentar quer a qualidade da informação quer a disseminação da produção científica do Iscte.publicad
Detection of Potential Transit Signals in the First Three Quarters of Kepler Mission Data
We present the results of a search for potential transit signals in the first
three quarters of photometry data acquired by the Kepler Mission. The targets
of the search include 151,722 stars which were observed over the full interval
and an additional 19,132 stars which were observed for only 1 or 2 quarters.
From this set of targets we find a total of 5,392 detections which meet the
Kepler detection criteria: those criteria are periodicity of the signal, an
acceptable signal-to-noise ratio, and a composition test which rejects spurious
detections which contain non-physical combinations of events. The detected
signals are dominated by events with relatively low signal-to-noise ratio and
by events with relatively short periods. The distribution of estimated transit
depths appears to peak in the range between 40 and 100 parts per million, with
a few detections down to fewer than 10 parts per million. The detected signals
are compared to a set of known transit events in the Kepler field of view which
were derived by a different method using a longer data interval; the comparison
shows that the current search correctly identified 88.1% of the known events. A
tabulation of the detected transit signals, examples which illustrate the
analysis and detection process, a discussion of future plans and open,
potentially fruitful, areas of further research are included
Variability of Southern T Tauri Stars I: The Continuum and the H Inverse PCygni Profile of GQ LUPI
We present time series spectrophotometric observations of GQ Lupi, a typical
representative of the YY Ori subgroup of T Tauri stars that show conspicuous
inverse PCygni profiles. The data set consists of 32 exposures taken over 5 and
8 consecutive nights of May and July 1998, respectively, and covers the
spectral range of 3100 \AA~ \AA. The region redward and
next to the Balmer jump varies significantly on a night-to-night basis and the
amplitude of such variability decreases sharply at 4600 \AA. The
Balmer continuum slope indicates that the spectral energy distribution is
governed by a gas of temperature greater than that of the stellar photosphere.
We find an anticorrelation between the veiling and the observed Balmer jump.
The time series of the redward absorption component behaves similarly to the
veiling time series. We model the emitting region by a gas of uniform
temperature and density. The models indicate that the gas densities and the
respective temperatures are strongly anticorrelated. In addition, the model
time series show that the increase in the gas density is mirrored by an
increase of the projected emitting area (filling factor). Large/small gas
densities and filling factors are characterized by high/low observed veiling.
As the accretion rate fades from night-to-night, the observed veiling
decreases, as does the gas density and the total projected emitting area.Comment: 26 pages, 14 postscript figures, ApJ accepte
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