5,605 research outputs found
The star formation history of the Sculptor Dwarf Irregular Galaxy
[abridged] We study the resolved stellar populations and derive the SFH of
the SDIG, a gas-rich dwarf galaxy member of the NGC7793 subgroup in the
Sculptor group. We construct a CMD using archival HST observations and examine
its stellar content. We derive its SFH using a maximum-likelihood fit to the
CMD. The CMD shows that SDIG contains stars from 10Myr to several Gyr old, as
revealed from the MS, BL, luminous AGB, and RGB stars. The young stars with
ages less than ~250Myr show a spatial distribution confined to its central
regions, and additionally the young MS stars exhibit an off-center density
peak. The intermediate-age and older stars are more spatially extended. SDIG is
dominated by intermediate-age stars with an average age of 6.4Gyr. The average
metallicity inferred is [M/H]\approx -1.5dex. Its SFH is consistent with a
constant SFR, except for ages younger than ~200Myr. The lifetime average SFR is
1.3x10^{-3} Mo/yr. More recently than 100Myr, there has been a burst of SF at a
rate ~2-3 times higher than the average SFR. The inferred recent SFR from CMD
modelling is higher than inferred from the Ha flux of the galaxy; we interpret
this to mean that the upper end of the IMF is not being fully sampled due to
the low SFR. Additionally, an observed lack of bright blue stars in the CMD
could indicate a downturn in SFR on 10^7-yr timescales. A previous SF
enhancement appears to have occurred between 600-1100Myr ago, with amplitude
similar to the most recent 100Myr. Older bursts of similar peak SFR and
duration would not be resolvable with these data. The observed enhancements in
SF suggest that SDIG is able to sustain a complex SFH without the effect of
interactions with its nearest massive galaxy. Integrating the SFR over the
entire history of SDIG yields a total stellar mass 1.77x10^{7}Mo, and a current
V-band stellar mass-to-light ratio 3.2Mo/Lo.Comment: A&A accepted; 10 pages, 9 figure
Self-supervised learning of a facial attribute embedding from video
We propose a self-supervised framework for learning facial attributes by
simply watching videos of a human face speaking, laughing, and moving over
time. To perform this task, we introduce a network, Facial Attributes-Net
(FAb-Net), that is trained to embed multiple frames from the same video
face-track into a common low-dimensional space. With this approach, we make
three contributions: first, we show that the network can leverage information
from multiple source frames by predicting confidence/attention masks for each
frame; second, we demonstrate that using a curriculum learning regime improves
the learned embedding; finally, we demonstrate that the network learns a
meaningful face embedding that encodes information about head pose, facial
landmarks and facial expression, i.e. facial attributes, without having been
supervised with any labelled data. We are comparable or superior to
state-of-the-art self-supervised methods on these tasks and approach the
performance of supervised methods.Comment: To appear in BMVC 2018. Supplementary material can be found at
http://www.robots.ox.ac.uk/~vgg/research/unsup_learn_watch_faces/fabnet.htm
Relationship between perceived and actual quality of data checking
Data quality is critical to reaching correct research conclusions. Researchers attempt to ensure that they have accurate data by checking the data after it has been entered. Previous research has demonstrated that some methods of data checking are better than others, but not all researchers use the best methods. Perhaps researchers continue to use less optimal data checking methods because they mistakenly believe that they are highly accurate. The purpose of this study was to examine the relationship between perceived data quality and actual data quality. A total of 29 participants completed this study. Participants checked that letters and numbers had been entered correctly into the computer using one of three randomly assigned data checking methods. Afterwards, they rated the quality of their data checking method. The sample correlations between perceived and actual data quality were small to moderate and confidence intervals for the population correlations did not include high values. We conclude that the relationship between actual and perceived data quality is not high
Fast Two-Qubit Gates in Semiconductor Quantum Dots using a Photonic Microcavity
Implementations for quantum computing require fast single- and multi-qubit
quantum gate operations. In the case of optically controlled quantum dot qubits
theoretical designs for long-range two- or multi-qubit operations satisfying
all the requirements in quantum computing are not yet available. We have
developed a design for a fast, long-range two-qubit gate mediated by a photonic
microcavity mode using excited states of the quantum dot-cavity system that
addresses these needs. This design does not require identical qubits, it is
compatible with available optically induced single qubit operations, and it
advances opportunities for scalable architectures. We show that the gate
fidelity can exceed 90% in experimentally accessible systems
The effects of tumor growth factors on the growth rate of cell cultures
AbstractA mathematical model of growth control in a cell culture in which Tumor Growth Factors (TGF) diffuse through intercellular spaces and act locally is constructed
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