22,921 research outputs found
Rat cities and beehive worlds: density and design in the modern city
Nestled among E. M. Forster's careful studies of Edwardian social mores is a short story called "The Machine Stops." Set many years in the future, it is a work of science fiction that imagines all humanity housed in giant high-density cities buried deep below a lifeless surface. With each citizen cocooned in an identical private chamber, all interaction is mediated through the workings of "the Machine," a totalizing social system that controls every aspect of human life. Cultural variety has ceded to rigorous organization: everywhere is the same, everyone lives the same life. So hopelessly reliant is humanity upon the efficient operation of the Machine, that when the system begins to fail there is little the people can do, and so tightly ordered is the system that the failure spreads. At the story's conclusion, the collapse is total, and Forster's closing image offers a condemnation of the world they had built, and a hopeful glimpse of the world that might, in their absence, return: "The whole city was broken like a honeycomb. [⋯] For a moment they saw the nations of the dead, and, before they joined them, scraps of the untainted sky" (2001: 123). In physically breaking apart the city, there is an extent to which Forster is literalizing the device of the broken society, but it is also the case that the infrastructure of the Machine is so inseparable from its social structure that the failure of one causes the failure of the other. The city has-in the vocabulary of present-day engineers-"failed badly.
The Factory and The Beehive I. Rotation Periods For Low-Mass Stars in Praesepe
Stellar rotation periods measured from single-age populations are critical
for investigating how stellar angular momentum content evolves over time, how
that evolution depends on mass, and how rotation influences the stellar dynamo
and the magnetically heated chromosphere and corona. We report rotation periods
for 40 late-K to mid-M stars members of the nearby, rich, intermediate-age
(~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200
observations taken by the Palomar Transient Factory of four cluster fields from
2010 February to May. Our measurements indicate that Praesepe's mass-period
relation transitions from a well-defined singular relation to a more scattered
distribution of both fast and slow rotators at ~0.6 Msun. The location of this
transition is broadly consistent with expectations based on observations of
younger clusters and the assumption that stellar-spin down is the dominant
mechanism influencing angular momentum evolution at 600 Myr. However, a
comparison to data recently published for the Hyades, assumed to be coeval to
Praesepe, indicates that the divergence from a singular mass-period relation
occurs at different characteristic masses, strengthening the finding that
Praesepe is the younger of the two clusters. We also use previously published
relations describing the evolution of rotation periods as a function of color
and mass to evolve the sample of Praesepe periods in time. Comparing the
resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and
for kinematically selected young and old field star populations suggests that
stellar spin-down may progress more slowly than described by these relations.Comment: To appear in the ApJ. 18 pages, 12 figures; version with higher
resolution figures available at
http://www.astro.columbia.edu/~marcel/papers/praesepe.pdf. Paper title
inspired by local news; see http://tinyurl.com/redhone
Two 'b's in the Beehive: The Discovery of the First Hot Jupiters in an Open Cluster
We present the discovery of two giant planets orbiting stars in Praesepe
(also known as the Beehive Cluster). These are the first known hot Jupiters in
an open cluster and the only planets known to orbit Sun-like, main-sequence
stars in a cluster. The planets are detected from Doppler shifted radial
velocities; line bisector spans and activity indices show no correlation with
orbital phase, confirming the variations are caused by planetary companions.
Pr0201b orbits a V=10.52 late F dwarf with a period of 4.4264 +/- 0.0070 days
and has a minimum mass of 0.540 +/- 0.039 Mjup, and Pr0211b orbits a V=12.06
late G dwarf with a period of 2.1451 +/- 0.0012 days and has a minimum mass of
1.844 +/- 0.064 Mjup. The detection of 2 planets among 53 single members
surveyed establishes a lower limit on the hot Jupiter frequency of 3.8
(+5.0)(-2.4) % in this metal-rich open cluster. Given the precisely known age
of the cluster, this discovery also demonstrates that, in at least 2 cases,
giant planet migration occurred within 600 Myr after formation. As we endeavor
to learn more about the frequency and formation history of planets,
environments with well-determined properties -- such as open clusters like
Praesepe -- may provide essential clues to this end.Comment: 5 pages, 3 tables, 2 figures. Published in ApJ Letter
Towards dense object tracking in a 2D honeybee hive
From human crowds to cells in tissue, the detection and efficient tracking of
multiple objects in dense configurations is an important and unsolved problem.
In the past, limitations of image analysis have restricted studies of dense
groups to tracking a single or subset of marked individuals, or to
coarse-grained group-level dynamics, all of which yield incomplete information.
Here, we combine convolutional neural networks (CNNs) with the model
environment of a honeybee hive to automatically recognize all individuals in a
dense group from raw image data. We create new, adapted individual labeling and
use the segmentation architecture U-Net with a loss function dependent on both
object identity and orientation. We additionally exploit temporal regularities
of the video recording in a recurrent manner and achieve near human-level
performance while reducing the network size by 94% compared to the original
U-Net architecture. Given our novel application of CNNs, we generate extensive
problem-specific image data in which labeled examples are produced through a
custom interface with Amazon Mechanical Turk. This dataset contains over
375,000 labeled bee instances across 720 video frames at 2 FPS, representing an
extensive resource for the development and testing of tracking methods. We
correctly detect 96% of individuals with a location error of ~7% of a typical
body dimension, and orientation error of 12 degrees, approximating the
variability of human raters. Our results provide an important step towards
efficient image-based dense object tracking by allowing for the accurate
determination of object location and orientation across time-series image data
efficiently within one network architecture.Comment: 15 pages, including supplementary figures. 1 supplemental movie
available as an ancillary fil
The Factory and The Beehive II. Activity and Rotation in Praesepe and the Hyades
Open clusters are collections of stars with a single, well-determined age,
and can be used to investigate the connections between angular-momentum
evolution and magnetic activity over a star's lifetime. We present the results
of a comparative study of the relationship between stellar rotation and
activity in two benchmark open clusters: Praesepe and the Hyades. As they have
the same age and roughly solar metallicity, these clusters serve as an ideal
laboratory for testing the agreement between theoretical and empirical
rotation-activity relations at 600 Myr. We have compiled a sample of
720 spectra --- more than half of which are new observations --- for 516
high-confidence members of Praesepe; we have also obtained 139 new spectra for
130 high-confidence Hyads. We have collected rotation periods () for
135 Praesepe members and 87 Hyads. To compare emission, an indicator
of chromospheric activity, as a function of color, mass, and Rossby number
, we first calculate an expanded set of values, with which we can
obtain the to bolometric luminosity ratio, ,
even when spectra are not flux-calibrated and/or stars lack reliable distances.
Our values cover a broader range of stellar masses and colors (roughly
equivalent to spectral types from K0 to M9), and exhibit better agreement
between independent calculations, than existing values. We find no difference
between the two clusters in their equivalent width or
distributions, and therefore take the merged
and data to be representative of 600-Myr-old stars. Our analysis
shows that activity in these stars is saturated for
. Above that value activity declines as a
power-law with slope , before dropping off rapidly
at ...Comment: 17 pages, 15 figures, Accepted by Ap
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