435 research outputs found
Transit Photometry as an Exoplanet Discovery Method
Photometry with the transit method has arguably been the most successful
exoplanet discovery method to date. A short overview about the rise of that
method to its present status is given. The method's strength is the rich set of
parameters that can be obtained from transiting planets, in particular in
combination with radial velocity observations; the basic principles of these
parameters are given. The method has however also drawbacks, which are the low
probability that transits appear in randomly oriented planet systems, and the
presence of astrophysical phenomena that may mimic transits and give rise to
false detection positives. In the second part we outline the main factors that
determine the design of transit surveys, such as the size of the survey sample,
the temporal coverage, the detection precision, the sample brightness and the
methods to extract transit events from observed light curves. Lastly, an
overview over past, current and future transit surveys is given. For these
surveys we indicate their basic instrument configuration and their planet
catch, including the ranges of planet sizes and stellar magnitudes that were
encountered. Current and future transit detection experiments concentrate
primarily on bright or special targets, and we expect that the transit method
remains a principal driver of exoplanet science, through new discoveries to be
made and through the development of new generations of instruments.Comment: Review chapte
CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk
CoRoT 223992193 is the only known low-mass, pre-main sequence eclipsing
binary that shows evidence of a circumbinary disk. The system displays complex
photometric and spectroscopic variability over a range of timescales and
wavelengths. Using two optical CoRoT runs, and infrared Spitzer 3.6 and 4.5
m observations (simultaneous with the second CoRoT run), we model the
out-of-eclipse light curves. The large scale structure in both CoRoT light
curves is consistent with the constructive and destructive interference of
starspot signals at two slightly different periods. Using the stellar
's, we infer different rotation periods: the primary is consistent with
synchronisation and the secondary is slightly supersynchronous. Comparison of
the raw data to the residuals of our spot model in colour-magnitude space
indicates additional contributions consistent with variable dust emission and
obscuration. We also identify short-duration flux dips preceding secondary
eclipse in all three CoRoT and Spitzer bands. We construct a model of the inner
regions of the binary and propose that these dips could be caused by partial
occultation of the central binary by the accretion stream onto the primary
star. Analysis of 15 VLT/FLAMES H profiles reveal an emission profile
associated with each star: the majority is consistent with chromospheric
emission but higher velocity emission is also seen, which could be due to
prominences or accretion-related phenomena. In addition, simultaneous u and
r-band observations from CFHT/MEGACam reveal a short-lived u-band excess
consistent with either an accretion hot spot or stellar flare. The photometric
and spectroscopic variations are complex but are consistent with the picture of
two active stars possibly undergoing non-steady, low-level accretion; the
system's very high inclination provides a new view of such variability.
[Abridged]Comment: 18 pages, 14 figures, 2 tables. Figures 1 & 2 reproduced from Gillen
et al. (2014) for clarity. Accepted for publication in A&
The pre-main sequence binary HK Ori : Spectro-astrometry and EXPORT data
In this paper we present multi-epoch observations of the pre-main sequence
binary HK Ori. These data have been drawn from the EXPORT database and are
complemented by high quality spectro-astrometric data of the system. The
spectroscopic data appear to be very well represented by a combination of an A
dwarf star spectrum superposed on a (sub-)giant G-type spectrum. The radial
velocity of the system is consistent with previous determinations, and does not
reveal binary motion, as expected for a wide binary. The spectral, photometric
and polarimetric properties and variability of the system indicate that the
active object in the system is a T Tauri star with UX Ori characteristics. The
spectro-astrometry of HK Ori is sensitive down to milli-arcsecond scales and
confirms the speckle interferometric results from Leinert et al. The
spectro-astrometry allows with fair certainty the identification of the active
star within the binary, which we suggest to be a G-type T Tauri star based on
its spectral characteristics.Comment: MNRAS in press 8 pages 7 figure
Oral carcinoma after hematopoietic stem cell transplantation â a new classification based on a literature review over 30 years
BACKGROUND: Patients undergoing hematopoietic stem cell transplantation (HSCT) have a higher risk of developing secondary solid tumors, in particular squamous cell carcinoma, because of several risk factors, including full-body irradiation (TBI), chemotherapy, and chronic graft versus host disease (GVHD). Based on the review presented here, a classification of oral changes is suggested in order to provide a tool to detect high-risk patients. Methods and Results The literature over the last 30 years was reviewed for development of malignoma of the oral cavity after HSCT. Overall, 64 cases were found. In 16 out of 30 cases, the tongue was the primary location, followed by the salivary gland (10 out of 30); 56.4% appeared in a latency time of 5 to 9 years after HSCT. In 76.6%, GVHD was noticed before the occurrence of oral malignancy. Premalignant changes of the oral mucosa were mucositis, xerostomia, and lichenoid changes, developing into erosive form. CONCLUSION: All physicians involved in the treatment of post-HSCT patients should be aware of the increased risk, even after 5 years from the development of oral malignancy, in particular when oral graft versus host changes are visible. In order to develop evidence management and to detect and offer adequate therapy as early as possible in this patient group, multicenter studies, involving oncologists and head and neck surgeons, should be established
CsA can induce DNA double-strand breaks: implications for BMT regimens particularly for individuals with defective DNA repair
Several human disorders mutated in core components of the major DNA double-strand break (DSB) repair pathway, non-homologous end joining (NHEJ), have been described. Cell lines from these patients are characterized by sensitivity to DSB-inducing agents. DNA ligase IV syndrome (LIG4) patients specifically, for unknown reasons, respond particularly badly following treatment for malignancy or BMT. We report the first systematic evaluation of the response of LIG4 syndrome to compounds routinely employed for BMT conditioning. We found human pre-B lymphocytes, a key target population for BMT conditioning, when deficient for DNA ligase IV, unexpectedly exhibit significant sensitivity to CsA the principal prophylaxis for GVHD. Furthermore, we found that CsA treatment alone or in combination with BU and fludarabine resulted in increased levels of DSBs specifically in LIG4 syndrome cells compared to wild-type or Artemis-deficient cells. Our study shows that CsA can induce DSBs and that LIG4 syndrome patient's fail to adequately repair this damage. These DSBs likely arise as a consequence of DNA replication in the presence of CsA. This work has implications for BMT and GVHD management in general and specifically for LIG4 syndrome
CoRoT-22 b: a validated 4.9 RE exoplanet in 10-day orbit
The CoRoT satellite has provided high-precision photometric light curves for
more than 163,000 stars and found several hundreds of transiting systems
compatible with a planetary scenario. If ground-based velocimetric observations
are the best way to identify the actual planets among many possible
configurations of eclipsing binary systems, recent transit surveys have shown
that it is not always within reach of the radial-velocity detection limits. In
this paper, we present a transiting exoplanet candidate discovered by CoRoT
whose nature cannot be established from ground-based observations, and where
extensive analyses are used to validate the planet scenario. They are based on
observing constraints from radial-velocity spectroscopy, adaptive optics
imaging and the CoRoT transit shape, as well as from priors on stellar
populations, planet and multiple stellar systems frequency. We use the fully
Bayesian approach developed in the PASTIS analysis software, and conclude that
the planet scenario is at least 1400 times more probable than any other false
positive scenario. The primary star is a metallic solar-like dwarf, with Ms =
1.099+-0.049 Msun and Rs = 1.136 (+0.038,-0.090) Rsun . The validated planet
has a radius of Rp = 4.88 (+0.17,-0.39) RE and mass less than 49 ME. Its mean
density is smaller than 2.56 g/cm^3 and orbital period is 9.7566+-0.0012 days.
This object, called CoRoT-22 b, adds to a large number of validated Kepler
planets. These planets do not have a proper measurement of the mass but allow
statistical characterization of the exoplanet population
CDK-inhibitor independent cell cycle progression in an experimental haematopoietic stem cell leukaemia despite unaltered Rb-phosphorylation
A CD34-negative haematopoietic progenitor cell line, D064, derived from canine bone marrow stromal cells is able to differentiate into haematopoietic progenitors under the influence of growth factor-mediated signalling. While differentiating, these cells eventually start to express MHC class II molecules (DR homologues) on their surface. The stable transfection of the fibroblast-like wild-type cells with retroviral constructs containing the cDNA for the canine MHC class II DR-genes (DRA and DRB) induces a change in morphology, accelerates cell cycle progression and leads to a loss of anchorage-dependent growth. Transfected cells show features of an immature stem cell leukaemia, such as giant cell formation. In wild-type D064 cells the accumulation of the cyclin-dependent kinase inhibitor (cdki) p27kip-1 induces differentiation, which is dependent upon signalling via the ligand for the tyrosine kinase receptor c-kit (stem cell factor). DR-transfected cells instead apparently grow independently of any growth factor-mediated signals and express high levels of the cdkis p27kip-1 and especially p21waf-1/cip-1, concurrently with accelated cell cycle progression. In contrast to the overexpression of cdkis and despite accelerated cell cycle progression, the expression of the G2/M phase transition kinase p34cdc2 is significantly reduced in DR-transfected and transformed cells as compared to the haematopoietic wild-type cell line D064. This might suggest a possible alternative cell cycle progression pathway in this experimental stem cell leukaemia by by-passing the G0/G1 phase arrest, although retinoblastoma (Rb)-phosphorylation remains unaltered. These results provide evidence that mechanisms normally controlling the cell cycle and early haematopoietic differentiation are disrupted by the constitutive transcription and expression of MHC class II genes (DR) leading to a progression and growth of this experimental stem cell leukaemia independent from cell cycle controlling regulators such as p27 and p21. © 1999 Cancer Research Campaig
Allogeneic transplant outcomes are not affected by body mass index (BMI) in patients with haematological malignancies
Ten-year trends in benzodiazepine use in the Dutch population
Background In the past decades knowledge on adequate treatment of affective disorders and awareness of the negative consequences of long-term benzodiazepine use increased. Therefore, a decrease in benzodiazepine use is expected, particularly in prolonged use. The aim of this study was to assess time trends in benzodiazepine use. Methods and material Data from the Longitudinal Aging Study Amsterdam (LASA) were used to investigate trends in benzodiazepine use between 1992 and 2002 in two population-based samples aged 55-64 years. Differences between the two samples with respect to benzodiazepine use and to sociodemographic, physical health and mental health characteristics were described and tested with chi- square tests and logistic regression analyses. Results Benzodiazepine use remained stable over 10 years, with 7.8% in LASA-1 (n = 874) and 7.9% in LASA-2 (n = 919) (p = 0.90) with a persisting preponderance in women and in people with low education, low income, chronic physical diseases, functional limitations, cognitive impairment, depression, anxiety complaints, sleep problems and when using antidepressants. Long-term use remained high with 70% in 1992 and 80% in 2002 of total benzodiazepine use. Conclusion In the Dutch population aged 55-64, overall benzodiazepine use remained stable from 1992 to 2002, with a high proportion of long-term users, despite the effort to reduce benzodiazepine use and the renewal of the guidelines. More effort should be made to decrease prolonged benzodiazepine use in this middle-aged group, because of the increasing risks with ageing. © The Author(s) 2011
European Project on Osteoarthritis (EPOSA): methodological challenges in harmonization of existing data from five European population-based cohorts on aging
BackgroundThe European Project on OSteoArthritis (EPOSA), here presented for the first time, is a collaborative study involving five European cohort studies on aging. This project focuses on the personal and societal burden and its determinants of osteoarthritis (OA). The aim of the current report is to describe the purpose of the project, the post harmonization of the cross-national data and methodological challenges related to the harmonization process MethodsThe study includes data from cohort studies in five European countries (Germany, Italy, the Netherlands, Spain and the United Kingdom) on older community-dwelling persons aged ? 59 years. The study design and main characteristics of the five cohort studies are described. Post harmonization algorithms are developed by finding a "common denominator" to merge the datasets and weights are calculated to adjust for differences in age and sex distribution across the datasets. ResultsA harmonized database was developed, consisting of merged data from all participating countries. In total, 10107 persons are included in the harmonized dataset with a mean age of 72.8 years (SD 6.1). The female/male ratio is 53.3/46.7%. Some variables were difficult to harmonize due to differences in wording and categories, differences in classifications and absence of data in some countries. The post harmonization algorithms are described in detail in harmonization guidelines attached to this paper. ConclusionsThere was little evidence of agreement on the use of several core data collection instruments, in particular on the measurement of OA. The heterogeneity of OA definitions hampers comparing prevalence rates of OA, but other research questions can be investigated using high quality harmonized data. By publishing the harmonization guidelines, insight is given into (the interpretation of) all post harmonized data of the EPOSA study. <br/
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