433 research outputs found
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XV. Assessing the achievability and precision of time-delay measurements
COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed
QSOs aimed at implementing Refsdal's time-delay method to measure cosmological
parameters, in particular H0. Given long and well sampled light curves of
strongly lensed QSOs, time-delay measurements require numerical techniques
whose quality must be assessed. To this end, and also in view of future
monitoring programs or surveys such as the LSST, a blind signal processing
competition named Time Delay Challenge 1 (TDC1) was held in 2014. The aim of
the present paper, which is based on the simulated light curves from the TDC1,
is double. First, we test the performance of the time-delay measurement
techniques currently used in COSMOGRAIL. Second, we analyse the quantity and
quality of the harvest of time delays obtained from the TDC1 simulations. To
achieve these goals, we first discover time delays through a careful inspection
of the light curves via a dedicated visual interface. Our measurement
algorithms can then be applied to the data in an automated way. We show that
our techniques have no significant biases, and yield adequate uncertainty
estimates resulting in reduced chi2 values between 0.5 and 1.0. We provide
estimates for the number and precision of time-delay measurements that can be
expected from future time-delay monitoring campaigns as a function of the
photometric signal-to-noise ratio and of the true time delay. We make our blind
measurements on the TDC1 data publicly availableComment: 11 pages, 8 figures, published in Astronomy & Astrophysic
Impact of the 3D source geometry on time-delay measurements of lensed type-Ia Supernovae
It has recently been proposed that gravitationally lensed type-Ia supernovae
can provide microlensing-free time-delay measurements provided that the
measurement is taken during the achromatic expansion phase of the explosion and
that color light curves are used rather than single-band light curves. If
verified, this would provide both precise and accurate time-delay measurements,
making lensed type-Ia supernovae a new golden standard for time-delay
cosmography. However, the 3D geometry of the expanding shell can introduce an
additional bias that has not yet been fully explored. In this work, we present
and discuss the impact of this effect on time-delay cosmography with lensed
supernovae and find that on average it leads to a bias of a few tenths of a day
for individual lensed systems. This is negligible in view of the cosmological
time delays predicted for typical lensed type-Ia supernovae but not for the
specific case of the recently discovered type-Ia supernova iPTF16geu, whose
time delays are expected to be smaller than a day.Comment: 7 pages, 4 figures, published in A&
The Hubble Constant determined through an inverse distance ladder including quasar time delays and Type Ia supernovae
Context. The precise determination of the present-day expansion rate of the
Universe, expressed through the Hubble constant , is one of the most
pressing challenges in modern cosmology. Assuming flat CDM,
inference at high redshift using cosmic-microwave-background data from Planck
disagrees at the 4.4 level with measurements based on the local
distance ladder made up of parallaxes, Cepheids and Type Ia supernovae (SNe
Ia), often referred to as "Hubble tension". Independent,
cosmological-model-insensitive ways to infer are of critical importance.
Aims. We apply an inverse-distance-ladder approach, combining strong-lensing
time-delay-distance measurements with SN Ia data. By themselves, SNe Ia are
merely good relative distance indicators, but by anchoring them to strong
gravitational lenses one can obtain an measurement that is relatively
insensitive to other cosmological parameters. Methods. A cosmological parameter
estimate is performed for different cosmological background models, both for
strong-lensing data alone and for the combined lensing + SNe Ia data sets.
Results. The cosmological-model dependence of strong-lensing measurements
is significantly mitigated through the inverse distance ladder. In combination
with SN Ia data, the inferred consistently lies around 73-74 km s
Mpc, regardless of the assumed cosmological background model. Our
results agree nicely with those from the local distance ladder, but there is a
>2 tension with Planck results, and a ~1.5 discrepancy with
results from an inverse distance ladder including Planck, Baryon Acoustic
Oscillations and SNe Ia. Future strong-lensing distance measurements will
reduce the uncertainties in from our inverse distance ladder.Comment: 5 pages, 3 figures, A&A letters accepted versio
Individual training at the undergraduate level to promote competence in breaking bad news in oncology
Training medical students in breaking bad news (BBN) in oncology may be key to improve patient care in an area where many physicians tend to be uncomfortable. Given the lack of evidence in the literature, this study aimed to assess empirically the impact of 2 teaching strategies to prepare students for the task of BBN in oncology: one-to-one simulated patient (SP) training with individual feedback (intervention group) vs small-group SP training with collective feedback (comparison group).
Fourth-year students (N = 236) were randomly assigned to the intervention or comparison group. The SP videotaped interviews were analyzed with respect to BBN communication performance, rated using the Calgary-Cambridge checklist of teaching objectives for BBN; verbal interaction behaviors, coded with the Roter interaction analysis system; and 7 nonverbal behaviors.
Students in the intervention group scored significantly higher after than before the training on the overall evaluation of the interview (P < .001) as well as on process skills (P < .001); they also obtained significantly higher scores compared to students in the comparison group on the overall evaluation of the interview (P < .001) and on process skills (P < .001).
This study supports an individualized BBN teaching strategy and contributes to efforts to find the best way to train and reach the largest number of future physicians to improve communication competences in oncology
Holo-like and Druggable Protein Conformations from Enhanced Sampling of Binding Pocket Volume and Shape
Understanding molecular recognition of small molecules by proteins in atomistic detail is key for drug design. Molecular docking is a widely used computational method to mimic ligand-protein association in silico. However, predicting conformational changes occurring in proteins upon ligand binding is still a major challenge. Ensemble docking approaches address this issue by considering a set of different conformations of the protein obtained either experimentally or from computer simulations, e.g., molecular dynamics. However, holo structures prone to host (the correct) ligands are generally poorly sampled by standard molecular dynamics simulations of the apo protein. In order to address this limitation, we introduce a computational approach based on metadynamics simulations called ensemble docking with enhanced sampling of pocket shape (EDES) that allows holo-like conformations of proteins to be generated by exploiting only their apo structures. This is achieved by defining a set of collective variables that effectively sample different shapes of the binding site, ultimately mimicking the steric effect due to the ligand. We assessed the method on three challenging proteins undergoing different extents of conformational changes upon ligand binding. In all cases our protocol generates a significant fraction of structures featuring a low RMSD from the experimental holo geometry. Moreover, ensemble docking calculations using those conformations yielded in all cases native-like poses among the top-ranked ones
Holo-like and Druggable Protein Conformations from Enhanced Sampling of Binding Pocket Volume and Shape
Understanding molecular recognition of small molecules by proteins in atomistic detail is key for drug design. Molecular docking is a widely used computational method to mimic ligand–protein association in silico. However, predicting conformational changes occurring in proteins upon ligand binding is still a major challenge. Ensemble docking approaches address this issue by considering a set of different conformations of the protein obtained either experimentally or from computer simulations, e.g., molecular dynamics. However, holo structures prone to host (the correct) ligands are generally poorly sampled by standard molecular dynamics simulations of the apo protein. In order to address this limitation, we introduce a computational approach based on metadynamics simulations called ensemble docking with enhanced sampling of pocket shape (EDES) that allows holo-like conformations of proteins to be generated by exploiting only their apo structures. This is achieved by defining a set of collective variables ..
Strongly lensed SNe Ia in the era of LSST: observing cadence for lens discoveries and time-delay measurements
The upcoming Large Synoptic Survey Telescope (LSST) will detect many strongly
lensed Type Ia supernovae (LSNe Ia) for time-delay cosmography. This will
provide an independent and direct way for measuring the Hubble constant ,
which is necessary to address the current tension in between
the local distance ladder and the early Universe measurements. We present a
detailed analysis of different observing strategies for the LSST, and quantify
their impact on time-delay measurement between multiple images of LSNe Ia. For
this, we produced microlensed mock-LSST light curves for which we estimated the
time delay between different images. We find that using only LSST data for
time-delay cosmography is not ideal. Instead, we advocate using LSST as a
discovery machine for LSNe Ia, enabling time delay measurements from follow-up
observations from other instruments in order to increase the number of systems
by a factor of 2 to 16 depending on the observing strategy. Furthermore, we
find that LSST observing strategies, which provide a good sampling frequency
(the mean inter-night gap is around two days) and high cumulative season length
(ten seasons with a season length of around 170 days per season), are favored.
Rolling cadences subdivide the survey and focus on different parts in different
years; these observing strategies trade the number of seasons for better
sampling frequency. In our investigation, this leads to half the number of
systems in comparison to the best observing strategy. Therefore rolling
cadences are disfavored because the gain from the increased sampling frequency
cannot compensate for the shortened cumulative season length. We anticipate
that the sample of lensed SNe Ia from our preferred LSST cadence strategies
with rapid follow-up observations would yield an independent percent-level
constraint on .Comment: 25 pages, 22 figures; accepted for publication in A&
Exploration of trade-offs between steady-state and dynamic properties in signaling cycles
In the intracellular signaling networks that regulate important cell processes, the base pattern comprises the cycle of reversible phosphorylation of a protein, catalyzed by kinases and opposing phosphatases. Mathematical modeling and analysis have been used for gaining a better understanding of their functions and to capture the rules governing system behavior. Since biochemical parameters in signaling pathways are not easily accessible experimentally, it is necessary to explore possibilities for both steady-state and dynamic responses in these systems. While a number of studies have focused on analyzing these properties separately, it is necessary to take into account both of these responses simultaneously in order to be able to interpret a broader range of phenotypes. This paper investigates the trade-offs between optimal characteristics of both steady-state and dynamic responses. Following an inverse sensitivity analysis approach, we use systematic optimization methods to find the biochemical and biophysical parameters that simultaneously achieve optimal steady-state and dynamic performance. Remarkably, we find that even a single covalent modification cycle can simultaneously and robustly achieve high ultrasensitivity, high amplification and rapid signal transduction. We also find that the response rise and decay times can be modulated independently by varying the activating- and deactivating-enzyme-to-interconvertible-protein ratios
COSMOGRAIL: XVII. Time delays for the quadruply imaged quasar PG 1115+080
Indexación: Scopus.Acknowledgements. The authors would like to thank R. Gredel for his help in setting up the program at the ESO MPIA 2.2 m telescope, and the anonymous referee for his or her comments on this work. This work is supported by the Swiss National Fundation. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018) and the 2D graphics environment Matplotlib (Hunter 2007). K.R. acknowledge support from PhD fellowship FIB-UV 2015/2016 and Becas de Doctorado Nacional CONICYT 2017 and thanks the LSSTC Data Science Fellowship Program, her time as a Fellow has benefited this work. M.T. acknowledges support by the DFG grant Hi 1495/2-1. G. C.-F. C. acknowledges support from the Ministry of Education in Taiwan via Government Scholarship to Study Abroad (GSSA). D. C.-Y. Chao and S. H. Suyu gratefully acknowledge the support from the Max Planck Society through the Max Planck Research Group for S. H. Suyu. T. A. acknowledges support by the Ministry for the Economy, Development, and Tourism’s Programa Inicativa Científica Milenio through grant IC 12009, awarded to The Millennium Institute of Astrophysics (MAS).We present time-delay estimates for the quadruply imaged quasar PG 1115+080. Our results are based on almost daily observations for seven months at the ESO MPIA 2.2 m telescope at La Silla Observatory, reaching a signal-to-noise ratio of about 1000 per quasar image. In addition, we re-analyze existing light curves from the literature that we complete with an additional three seasons of monitoring with the Mercator telescope at La Palma Observatory. When exploring the possible source of bias we considered the so-called microlensing time delay, a potential source of systematic error so far never directly accounted for in previous time-delay publications. In 15 yr of data on PG 1115+080, we find no strong evidence of microlensing time delay. Therefore not accounting for this effect, our time-delay estimates on the individual data sets are in good agreement with each other and with the literature. Combining the data sets, we obtain the most precise time-delay estimates to date on PG 1115+080, with Δt(AB) = 8.3+1.5 -1.6 days (18.7% precision), Δt(AC) = 9.9+1.1 -1.1 days (11.1%) and Δt(BC) = 18.8+1.6 -1.6 days (8.5%). Turning these time delays into cosmological constraints is done in a companion paper that makes use of ground-based Adaptive Optics (AO) with the Keck telescope. © ESO 2018.https://www.aanda.org/articles/aa/abs/2018/08/aa33287-18/aa33287-18.htm
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