3,459 research outputs found
Search for high-amplitude Delta Scuti and RR Lyrae stars in Sloan Digital Sky Survey Stripe 82 using principal component analysis
We propose a robust principal component analysis (PCA) framework for the
exploitation of multi-band photometric measurements in large surveys. Period
search results are improved using the time series of the first principal
component due to its optimized signal-to-noise ratio.The presence of correlated
excess variations in the multivariate time series enables the detection of
weaker variability. Furthermore, the direction of the largest variance differs
for certain types of variable stars. This can be used as an efficient attribute
for classification. The application of the method to a subsample of Sloan
Digital Sky Survey Stripe 82 data yielded 132 high-amplitude Delta Scuti
variables. We found also 129 new RR Lyrae variables, complementary to the
catalogue of Sesar et al., 2010, extending the halo area mapped by Stripe 82 RR
Lyrae stars towards the Galactic bulge. The sample comprises also 25
multiperiodic or Blazhko RR Lyrae stars.Comment: 23 pages, 17 figure
Fast, Accurate Thin-Structure Obstacle Detection for Autonomous Mobile Robots
Safety is paramount for mobile robotic platforms such as self-driving cars
and unmanned aerial vehicles. This work is devoted to a task that is
indispensable for safety yet was largely overlooked in the past -- detecting
obstacles that are of very thin structures, such as wires, cables and tree
branches. This is a challenging problem, as thin objects can be problematic for
active sensors such as lidar and sonar and even for stereo cameras. In this
work, we propose to use video sequences for thin obstacle detection. We
represent obstacles with edges in the video frames, and reconstruct them in 3D
using efficient edge-based visual odometry techniques. We provide both a
monocular camera solution and a stereo camera solution. The former incorporates
Inertial Measurement Unit (IMU) data to solve scale ambiguity, while the latter
enjoys a novel, purely vision-based solution. Experiments demonstrated that the
proposed methods are fast and able to detect thin obstacles robustly and
accurately under various conditions.Comment: Appeared at IEEE CVPR 2017 Workshop on Embedded Visio
Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process
Manufacturing superconducting circuits out of ultrathin films is a
challenging task when it comes to patterning complex compounds, which are
likely to be deteriorated by the patterning process. With the purpose of
developing high-T superconducting photon detectors, we designed a novel
route to pattern ultrathin YBCO films down to the nanometric scale. We believe
that our method, based on a specific use of a focused-ion beam, consists in
locally implanting Ga^{3+} ions and/or defects instead of etching the film.
This protocol could be of interest to engineer high-T superconducting
devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to
treat other sensitive compounds.Comment: 13 pages, 7 figure
Witnessing the active assembly phase of massive galaxies since z = 1
We present an analysis of ~60 000 massive (stellar mass M_star > 10^{11}
M_sun) galaxies out to z = 1 drawn from 55.2 deg2 of the United Kingdom
Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) and the Sloan
Digital Sky Survey (SDSS) II Supernova Survey. This is by far the largest
survey of massive galaxies with robust mass estimates, based on infrared
(K-band) photometry, reaching to the Universe at about half its present age. We
find that the most massive (M_star > 10^{11.5} M_sun) galaxies have experienced
rapid growth in number since z = 1, while the number densities of the less
massive systems show rather mild evolution. Such a hierarchical trend of
evolution is consistent with the predictions of the current semi-analytic
galaxy formation model based on Lambda CDM theory. While the majority of
massive galaxies are red-sequence populations, we find that a considerable
fraction of galaxies are blue star-forming galaxies. The blue fraction is
smaller in more massive systems and decreases toward the local Universe,
leaving the red, most massive galaxies at low redshifts, which would support
the idea of active 'bottom-up' formation of these populations during 0 < z < 1.Comment: Accepted for publication in MNRAS; replaced with revised version
(minor changes in results and wordings); MNRAS online early version availabl
High-resolution VLA Imaging of SDSS Stripe 82 at 1.4 GHz
We present a high-resolution radio survey of the Sloan Digital Sky Survey
(SDSS) Southern Equatorial Stripe, a.k.a. Stripe 82. This 1.4 GHz survey was
conducted with the Very Large Array (VLA) primarily in the A-configuration,
with supplemental B-configuration data to increase sensitivity to extended
structure. The survey has an angular resolution of 1.8" and achieves a median
rms noise of 52 microJy/bm over 92 deg^2. This is the deepest 1.4 GHz survey to
achieve this large of an area, filling a gap in the phase space between small,
deep and large, shallow surveys. It also serves as a pilot project for a larger
high-resolution survey with the Expanded Very Large Array (EVLA). We discuss
the technical design of the survey and details of the observations, and we
outline our method for data reduction. We present a catalog of 17,969 isolated
radio components, for an overall source density of ~195 sources/deg^2. The
astrometric accuracy of the data is excellent, with an internal check utilizing
multiply-observed sources yielding an rms scatter of 0.19" in both right
ascension and declination. A comparison to the SDSS DR7 Quasar Catalog further
confirms that the astrometry is well tied to the optical reference frame, with
mean offsets of 0.02" +/- 0.01" in right ascension, and 0.01" +/- 0.02" in
declination. A check of our photometry reveals a small, negative CLEAN-like
bias on the level of 35 microJy. We report on the catalog completeness, finding
that 97% of FIRST-detected quasars are recovered in the new Stripe 82 radio
catalog, while faint, extended sources are more likely to be resolved out by
the resolution bias. We conclude with a discussion of the optical counterparts
to the catalog sources, including 76 newly-detected radio quasars. The full
catalog as well as a search page and cutout server are available online at
http://third.ucllnl.org/cgi-bin/stripe82cutout.Comment: 18 pages, 22, figures. Submitted to AJ, revised to address referee's
comment
Improving construction materials management practices in construction sites
Construction Materials Management is a vital function for improving productivity in construction projects. Poor materials management can often affect the overall construction time, quality and budget. Currently, the construction material management practice in Somalia is believed to be poorly performed. Lack of standardized construction materials management system is one of the key issues facing by the building industry in Mogadishu-Somalia. The aim of this study was to investigate the current practices of material management at construction sites in Mogadishu-Somalia. A questionnaire survey study design was used to explore construction materials management practices. Fifty questionnaires were distributed to project managers, project engineers, site engineers, engineer, and foreman, and they were received and analysed. The following data analysis techniques were used: descriptive statistics were conducted to report sample characteristics, reliability and validity analyses were performed to confirm robustness of the instrument, graphical presentation such as bar charts were developed, and finally Average Mean Index Scale were constructed. The study results reveals that, 46.7% of respondentās organization obtain materials for sites without site requisition by site engineer provisions, while 28.9% of respondentās organization procure materials for sites with site requisition by project manager provisions and 13.3% of respondentās organization procure materials for site by engineer. The results indicated that currently there is no standardized and computerized construction materials management system applied in Somalia. The researcher concluded that all contracting companies are interested in using some techniques of managing construction materials such as creating and updating database for materials categories from local and international suppliers. Finally, researcher recommends to use computerized construction materials management systems to reduce effort and time, and to achieve more accurate results
Neuronal assembly dynamics in supervised and unsupervised learning scenarios
The dynamic formation of groups of neuronsāneuronal assembliesāis believed to mediate cognitive phenomena at many levels, but their detailed operation and mechanisms of interaction are still to be uncovered. One hypothesis suggests that synchronized oscillations underpin their formation and functioning, with a focus on the temporal structure of neuronal signals. In this context, we investigate neuronal assembly dynamics in two complementary scenarios: the first, a supervised spike pattern classification task, in which noisy variations of a collection of spikes have to be correctly labeled; the second, an unsupervised, minimally cognitive evolutionary robotics tasks, in which an evolved agent has to cope with multiple, possibly conflicting, objectives. In both cases, the more traditional dynamical analysis of the systemās variables is paired with information-theoretic techniques in order to get a broader picture of the ongoing interactions with and within the network. The neural network model is inspired by the Kuramoto model of coupled phase oscillators and allows one to fine-tune the network synchronization dynamics and assembly configuration. The experiments explore the computational power, redundancy, and generalization capability of neuronal circuits, demonstrating that performance depends nonlinearly on the number of assemblies and neurons in the network and showing that the framework can be exploited to generate minimally cognitive behaviors, with dynamic assembly formation accounting for varying degrees of stimuli modulation of the sensorimotor interactions
Optospintronics in graphene via proximity coupling
The observation of micron size spin relaxation makes graphene a promising
material for applications in spintronics requiring long distance spin
communication. However, spin dependent scatterings at the contact/graphene
interfaces affect the spin injection efficiencies and hence prevent the
material from achieving its full potential. While this major issue could be
eliminated by nondestructive direct optical spin injection schemes, graphenes
intrinsically low spin orbit coupling strength and optical absorption place an
obstacle in their realization. We overcome this challenge by creating sharp
artificial interfaces between graphene and WSe2 monolayers. Application of a
circularly polarized light activates the spin polarized charge carriers in the
WSe2 layer due to its spin coupled valley selective absorption. These carriers
diffuse into the superjacent graphene layer, transport over a 3.5 um distance,
and are finally detected electrically using BN/Co contacts in a non local
geometry. Polarization dependent measurements confirm the spin origin of the
non local signal
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