2,976 research outputs found
Optimization of optical data transmitters for 40-Gb/s lightwave systems using frequency resolved optical gating
The measurement technique of frequency resolved optical gating has been used to optimize the phase of a 40-GHz train of optical pulses generated using a continuous-wave laser gated with an external modulator. This technique will be vital for optimization of optical transmitters to be used in systems operating at 40 Gb/s and beyond, as standard measurement techniques will not suffice to optimize such high-speed systems
Activities and relationships with parents as key ecological assets that encourage personal positive youth development
Scientific literature has shown contextual factors that predict youth development, and family variables are the most important ones. In this study, we propose a model that explains the relation between family variables (relationship with parents and family activities) and Personal Positive Youth Development (assessed through Life satisfaction, Interiority, and Self-control), across different cultures. We recruited 2867 adolescents aged 12–18 years (52% female) from three countries: Spain, Mexico, and Peru. They completed an anonymous questionnaire. We run exploratory and confirmatory factor analyses, and structural equation modelling, testing for invariance across countries and sexes. In all subsamples, positive family relationships were associated with adolescents'' Life Satisfaction. In addition, time invested on family activities was associated with Interiority and with Self-control. However, some differences across cultures and sex were found in the specific associations. Theoretical and practical implications are discussed regarding how to improve adolescent development through family life
Targeting class I histone deacetylases by the novel small molecule inhibitor 4SC-202 blocks oncogenic hedgehog-GLI signaling and overcomes smoothened inhibitor resistance
Aberrant activation of Hedgehog (HH)/GLI signaling is causally involved in numerous human malignancies, including basal cell carcinoma (BCC) and medulloblastoma. HH pathway antagonists targeting smoothened (SMO), an essential effector of canonical HH/GLI signaling, show significant clinical success in BCC patients and have recently been approved for the treatment of advanced and metastatic BCC. However, rapid and frequent development of drug resistance to SMO inhibitors (SMOi) together with severe side effects caused by prolonged SMOi treatment call for alternative treatment strategies targeting HH/GLI signaling downstream of SMO. In this study, we report that 4SC-202, a novel clinically validated inhibitor of class I histone deacetylases (HDACs), efficiently blocks HH/GLI signaling. Notably, 4SC-202 treatment abrogates GLI activation and HH target gene expression in both SMOi-sensitive and -resistant cells. Mechanistically, we propose that the inhibition of HDACs 1/2/3 is crucial for targeting oncogenic HH/GLI signaling, and that class I HDAC inhibitors either in combination with SMOi or as second-line therapy may improve the treatment options for HH-associated malignancies with SMOi resistance
Optimization of 40 Gbit/s transmission systems using frequency resolved optical gating characterization techniques
To achieve multiterabit/s capacities in long-haul transport networks, it is anticipated that wavelength division multiplexed (WDM) systems will be upgraded to operate at line rates of 40 Gbit/s. We have shown that by employing the FROG measurement technique to optimize the generation of optical pulses for use in a 40 Gbit/s soliton transmission link, we ensure that the performance of the overall system using the generated optical pulses is optimum
Comprehensive analysis of HD 105, a young solar system analog
HD 105 is a nearby, pre-main-sequence G0 star hosting a moderately bright debris disk (L dust/L ⋆ ∼ 2.6 × 10‑4). The star and its surroundings might therefore be considered an analog of the young solar system. We refine the stellar parameters based on an improved Gaia parallax distance and identify it as a pre-main-sequence star with an age of 50 ± 16 Myr. The circumstellar disk was marginally resolved by Herschel/PACS imaging at far-infrared wavelengths. Here, we present an archival ALMA observation at 1.3 mm, revealing the extent and orientation of the disk. We also present Hubble Space Telescope (HST)/NICMOS and VLT/SPHERE near-infrared images, where we recover the disk in scattered light at the ≥5σ level. This was achieved by employing a novel annular averaging technique and is the first time this has been achieved for a disk in scattered light. Simultaneous modeling of the available photometry, disk architecture, and detection in scattered light allow better determination of the disk’s architecture, and dust grain minimum size, composition, and albedo. We measure the dust albedo to lie between 0.19 and 0.06, the lower value being consistent with Edgeworth–Kuiper Belt objects
<i>Herschel</i> observations of the debris disc around HIP 92043
Context. Typical debris discs are composed of particles ranging from several micron sized dust grains to km sized asteroidal bodies, and their infrared emission peaks at wavelengths 60-100 μm. Recent Herschel DUNES observations have identified several debris discs around nearby Sun-like stars (F, G and K spectral type) with significant excess emission only at 160 μm.
Aims. We observed HIP 92043 (110 Her, HD 173667) at far-infrared and sub-millimetre wavelengths with Herschel PACS and SPIRE. Identification of the presence of excess emission from HIP 92043 and the origin and physical properties of any excess was undertaken through analysis of its spectral energy distribution (SED) and the PACS images.
Methods. The PACS and SPIRE images were produced using the HIPE photProject map maker routine. Fluxes were measured using aperture photometry. A stellar photosphere model was scaled to optical and near infrared photometry and subtracted from the far-infared and sub-mm fluxes to determine the presence of excess emission. Source radial profiles were fitted using a 2D Gaussian and compared to a PSF model based on Herschel observations of α Boo to check for extended emission.
Results. Clear excess emission from HIP 92043 was observed at 70 and 100 μm. Marginal excess was observed at 160 and 250 μm. Analysis of the images reveals that the source is extended at 160 μm. A fit to the source SED is inconsistent with a photosphere and single temperature black body.
Conclusions. The excess emission from HIP 92043 is consistent with the presence of an unresolved circumstellar debris disc at 70 and 100 μm, with low probability of background contamination. The extended 160 μm emission may be interpreted as an additional cold component to the debris disc or as the result of background contamination along the line of sight. The nature of the 160 μm excess cannot be determined absolutely from the available data, but we favour a debris disc interpretation, drawing parallels with previously identified cold disc sources in the DUNES sample
The SHARDDS survey: limits on planet occurrence rates based on point sources analysis via the Auto-RSM framework
In the past decade, HCI surveys provided new insights about the frequency and
properties of substellar companions at separation larger than 5 au. In this
context, our study aims to detect and characterise potential exoplanets and
brown dwarfs within debris disks, by considering the SHARDDS survey, which
gathers 55 Main Sequence stars with known bright debris disk. We rely on the
AutoRSM framework to perform an in-depth analysis of the targets, via the
computation of detection maps and contrast curves. A clustering approach is
used to divide the set of targets in multiple subsets, in order to reduce the
computation time by estimating a single optimal parametrisation for each
considered subset. The use of Auto-RSM allows to reach high contrast at short
separations, with a median contrast of 10-5 at 300 mas, for a completeness
level of 95%. Detection maps generated with different approaches are used along
with contrast curves, to identify potential planetary companions. A new
planetary characterisation algorithm, based on the RSM framework, is developed
and tested successfully, showing a higher astrometric and photometric precision
for faint sources compared to standard approaches. Apart from the already known
companion of HD206893 and two point-like sources around HD114082 which are most
likely background stars, we did not detect any new companion around other
stars. A correlation study between achievable contrasts and parameters
characterising HCI sequences highlights the importance of the strehl, wind
speed and wind driven halo to define the quality of high contrast images.
Finally, planet detection and occurrence frequency maps are generated and show,
for the SHARDDS survey, a high detection rate between 10 and 100 au for
substellar companions with mass >10MJ
Incidence of debris discs around FGK stars in the solar neighbourhood
Debris discs are a consequence of the planet formation process and constitute
the fingerprints of planetesimal systems. Their solar system's counterparts are
the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide
robust numbers for the incidence of debris discs around FGK stars in the solar
neighbourhood. The full sample of 177 FGK stars with d<20 pc proposed for the
DUNES survey is presented. Herschel/PACS observations at 100 and 160 micron
complemented with data at 70 micron, and at 250, 350 and 500 micron SPIRE
photometry, were obtained. The 123 objects observed by the DUNES collaboration
were presented in a previous paper. The remaining 54 stars, shared with the
DEBRIS consortium and observed by them, and the combined full sample are
studied in this paper. The incidence of debris discs per spectral type is
analysed and put into context together with other parameters of the sample,
like metallicity, rotation and activity, and age.
The subsample of 105 stars with d<15 pc containing 23 F, 33 G and 49 K stars,
is complete for F stars, almost complete for G stars and contains a substantial
number of K stars to draw solid conclusions on objects of this spectral type.
The incidence rates of debris discs per spectral type 0.26 (6 objects with
excesses out of 23 F stars), 0.21 (7 out of 33 G stars) and 0.20 (10 out of 49
K stars), the fraction for all three spectral types together being 0.22 (23 out
of 105 stars). Uncertainties corresponding to a 95% confidence level are given
in the text for all these numbers. The medians of the upper limits of
L_dust/L_* for each spectral type are 7.8E-7 (F), 1.4E-6 (G) and 2.2E-6 (K);
the lowest values being around 4.0E-7. The incidence of debris discs is similar
for active (young) and inactive (old) stars. The fractional luminosity tends to
drop with increasing age, as expected from collisional erosion of the debris
belts.Comment: 31 pages, 15 figures, 10 tables, 2 appendice
Two close binaries across the hydrogen-burning limit in the Praesepe open cluster
We present Keck I/OSIRIS and Keck II/NIRC2 adaptive optics imaging of two
member candidates of the Praesepe stellar cluster (d=186.180.11 pc;
590-790 Myr), UGC J08451066+2148171 (L1.50.5) and UGCS J083019352003293
(no spectroscopic classification). We resolved UGCS J084510662148171 into a
binary system in the near-infrared, with a -band wavelength flux ratio of
0.890.04, a projected separation of 60.31.3 mas (11.20.7 au;
1). We also resolved UGCS J083019352003293 into a binary system with
a flux ratio of 0.460.03 and a separation of 62.50.9 mas. Assuming
zero eccentricity, we estimate minimum orbital periods of 100 years for
both systems. According to theoretical evolutionary models, we derive masses in
the range of 0.074-0.078 M and 0.072-0.076 M for the
primary and secondary of UGCS J084510662148171 for an age of 700100
Myr. In the case of UGCS J083019352003293, the primary is a low-mass star at
the stellar/substellar boundary (0.070-0.078 M) while the companion
candidate might be a brown dwarf (0.051-0.065 M). These are the first
two binaries composed of L dwarfs in Praesepe. They are benchmark systems to
derive the location of the substellar limit at the age and metallicity of
Praesepe, determine the age of the cluster based on the lithium depletion
boundary test, derive dynamical masses, and improve low-mass stellar and
substellar evolutionary models at a well-known age and metallicity.Comment: 12 pages, 5 figures, 3 tables, accepted for publication in MNRA
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