432 research outputs found
Ages for illustrative field stars using gyrochronology: viability, limitations and errors
We here develop an improved way of using a rotating star as a clock, set it
using the Sun, and demonstrate that it keeps time well. This technique, called
gyrochronology, permits the derivation of ages for solar- and late-type main
sequence stars using only their rotation periods and colors. The technique is
clarified and developed here, and used to derive ages for illustrative groups
of nearby, late-type field stars with measured rotation periods. We first
demonstrate the reality of the interface sequence, the unifying feature of the
rotational observations of cluster and field stars that makes the technique
possible, and extends it beyond the proposal of Skumanich by specifying the
mass dependence of rotation for these stars. We delineate which stars it cannot
currently be used on. We then calibrate the age dependence using the Sun. The
errors are propagated to understand their dependence on color and period.
Representative age errors associated with the technique are estimated at ~15%
(plus possible systematic errors) for late-F, G, K, & early-M stars. Ages
derived via gyrochronology for the Mt. Wilson stars are shown to be in good
agreement with chromospheric ages for all but the bluest stars, and probably
superior. Gyro ages are then calculated for each of the active main sequence
field stars studied by Strassmeier and collaborators where other ages are not
available. These are shown to be mostly younger than 1Gyr, with a median age of
365Myr. The sample of single, late-type main sequence field stars assembled by
Pizzolato and collaborators is then assessed, and shown to have gyro ages
ranging from under 100Myr to several Gyr, and a median age of 1.2Gyr. Finally,
we demonstrate that the individual components of the three wide binaries
XiBooAB, 61CygAB, & AlphaCenAB yield substantially the same gyro ages.Comment: 58 pages, 18 color figures, accepted for publication in The
Astrophysical Journal; Age uncertainties slightly modified upon correcting an
algebraic error in Section
Urban Green Parks for Long-term Subjective Well-being: Empirical Relationships between Personal Characteristics, Park Characteristics, Park Use, Sense of Place, and Satisfaction with Life in the Netherlands
As our living environment is becoming increasingly urbanized, this puts the livability, health, and quality of life in cities under pressure. Due to the urbanization process, urban green spaces are under threat of becoming scarce, while it is recognized that these green spaces can positively contribute to the subjective well-being of citizens. It is thus important to maximize the use and benefits derived from green spaces by designing them as positively experienced places. The aim of this research is to gain more empirical insights on the relationships between personal and park characteristics, park use behavior, sense of place, and park visitors’ long-term subjective well-being (i.e., life satisfaction). An online questionnaire was administered to participants in two medium-sized cities in The Netherlands, namely Eindhoven and ‘s-Hertogenbosch. Data were analyzed using a structural equation model. The results of this study show that the appreciation of facilities and the absence of disturbances positively influence the use and sense of place of a park. Furthermore, the findings show that sense of place has a positive influence on life satisfaction. The findings can be used by designers and policy-makers as guidelines to improve existing parks or to design new parks that support the subjective well-being of individuals in The Netherlands
Building the cosmic distance scale: from Hipparcos to Gaia
Hipparcos, the first ever experiment of global astrometry, was launched by
ESA in 1989 and its results published in 1997 (Perryman et al., Astron.
Astrophys. 323, L49, 1997; Perryman & ESA (eds), The Hipparcos and Tycho
catalogues, ESA SP-1200, 1997). A new reduction was later performed using an
improved satellite attitude reconstruction leading to an improved accuracy for
stars brighter than 9th magnitude (van Leeuwen & Fantino, Astron. Astrophys.
439, 791, 2005; van Leeuwen, Astron. Astrophys. 474, 653, 2007).
The Hipparcos Catalogue provided an extended dataset of very accurate
astrometric data (positions, trigonometric parallaxes and proper motions),
enlarging by two orders of magnitude the quantity and quality of distance
determinations and luminosity calibrations. The availability of more than 20000
stars with a trigonometric parallax known to better than 10% opened the way to
a drastic revision of our 3-D knowledge of the solar neighbourhood and to a
renewal of the calibration of many distance indicators and age estimations. The
prospects opened by Gaia, the next ESA cornerstone, planned for launch in June
2013 (Perryman et al., Astron. Astrophys. 369, 339, 2001), are still much more
dramatic: a billion objects with systematic and quasi simultaneous astrometric,
spectrophotometric and spectroscopic observations, about 150 million stars with
expected distances to better than 10%, all over the Galaxy. All stellar
distance indicators, in very large numbers, will be directly measured,
providing a direct calibration of their luminosity and making possible detailed
studies of the impacts of various effects linked to chemical element
abundances, age or cluster membership. With the help of simulations of the data
expected from Gaia, obtained from the mission simulator developed by DPAC, we
will illustrate what Gaia can provide with some selected examples.Comment: 16 pages, 16 figures, Conference "The Fundamental Cosmic Distance
scale: State of the Art and the Gaia perspective, 3-6 May 2011, INAF,
Osservatorio Astronomico di Capodimonte, Naples. Accepted for publication in
Astrophysics & Space Scienc
Novel point mutation in the extracellular domain of the granulocyte colony-stimulating factor (G-CSF) receptor in a case of severe congenital neutropenia hyporesponsive to G-CSF treatment
Severe congenital neutropenia (SCN) is a heterogeneous condition
characterized by a drastic reduction in circulating neutrophils and a
maturation arrest of myeloid progenitor cells in the bone marrow. Usually
this condition can be successfully treated with granulocyte
colony-stimulating factor (G-CSF). Here we describe the identification of
a novel point mutation in the extracellular domain of the G-CSF receptor
(G-CSF-R) in an SCN patient who failed to respond to G-CSF treatment. When
this mutant G-CSF-R was expressed in myeloid cells, it was defective in
both proliferation and survival signaling. This correlated with diminished
activation of the receptor complex as determined by signal transducer and
activator of transcription (STAT) activation, although activation of STAT5
was more affected than STAT3. Interestingly, the mutant receptor showed
normal affinity for ligand, but a reduced number of ligand binding sites
compared with the wild-type receptor. This suggests that the mutation in
the extracellular domain affects ligand-receptor complex formation with
severe consequences for intracellular signal transduction. Together these
data add to our understanding of the mechanisms of cytokine receptor
signaling, emphasize the role of GCSFR mutations in the etiology of SCN,
and implicate such mutations in G-CSF hyporesponsiveness
Raman spectroscopy-based identification of nosocomial outbreaks of the clonal bacterium Escherichia coli
DNA-based techniques are frequently used to confirm the relatedness of putative outbreak isolates. These techniques often lack the discriminatory power when analyzing closely related microbes such as E. coli. Here the value of Raman spectroscopy as a typing tool for E. coli in a clinical setting was retrospectively evaluated
Comparing the effectiveness and costs of Bevacizumab to Ranibizumab in patients with Diabetic Macular Edema: A randomized clinical trial (the BRDME study)
Background: The effectiveness of ranibizumab in the treatment of diabetic macular edema has been proven with large clinical trials. For bevacizumab only two clinical trials have been published and a head-to-head comparison is lacking to date. However, if proved non-inferior to ranibizumab, use of the off-label bevacizumab could reduce costs enormously without a loss in visual acuity. A cost-effectiveness study has been designed to substantiate this hypothesis. Aim: To compare the effectiveness and costs of 1.25 mg of bevacizumab to 0.5 mg ranibizumab given as monthly intravitreal injections during 6 months in patients with diabetic macular edema. It is hypothesized that bevacizumab is non-inferior to ranibizumab regarding its effectiveness. Design: This is a randomized, controlled, double masked, clinical trial in 246 patients in seven academic trial centres in The Netherlands. Outcomes: The primary outcome measure is the change in best-corrected visual acuity (BCVA) in the study eye from baseline to month 6. Secondary outcomes are the proportions of patients with a gain or loss of 15 letters or more or a BCVA of 20/40 or more at 6 months, the change in leakage on fluorescein angiography and the change in foveal thickness by optical coherence tomography at 6 months, the number of adverse events in 6 months, and the costs per quality adjusted life-year of the two treatments
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