11,474 research outputs found
Spectral characterization of the Nigerian shoreline using Landsat imagery
The challenges of shoreline mapping include the high costs of acquiring up-to-date survey data over the coastal area. As a result, in many developing countries, the shoreline has not been consistently mapped. The variety of methods used for this mapping and the large time differences between the surveys (on the order of decades) could result in inaccuracies in shoreline data. This study presents the development of a shoreline characterization procedure for the Nigerian coastline using satellite remote sensing technology. The study goal is to produce a complete, consistent and continuous shoreline map using publicly available data processed in a GIS environment. A spectral analysis using different satellite bands was conducted to define the land/water boundary and characterize the coastal area around the shoreline. The satellite-derived shorelines were compared to charted shorelines for adequacy and consistency. The procedure was developed based on study sites along the Nigerian coastline. Although the shoreline characterization procedure is developed based on datasets from Nigeria, the procedure should be suitable for use in mapping other developing areas around world
The Arecibo Legacy Fast ALFA Survey: VI. Second HI Source Catalog of the Virgo Cluster Region
We present the third installment of HI sources extracted from the Arecibo
Legacy Fast ALFA extragalactic survey. This dataset continues the work of the
Virgo ALFALFA catalog. The catalogs and spectra published here consist of data
obtained during the 2005 and 2006 observing sessions of the survey. The catalog
consists of 578 HI detections within the range 11h 36m < R.A.(J2000) < 13h 52m
and +08 deg < Dec.(J2000) < +12 deg, and cz_sun < 18000 km/s. The catalog
entries are identified with optical counterparts where possible through the
examination of digitized optical images. The catalog detections can be
classified into three categories: (a) detections of high reliability with S/N >
6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c)
signals of lower S/N which coincide spatially with an optical object and known
redshift. 75% of the sources are newly published HI detections. Of particular
note is a complex of HI clouds projected between M87 and M49 that do not
coincide with any optical counterparts. Candidate objects without optical
counterparts are few. The median redshift for this sample is 6500 km/s and the
cz distribution exhibits the local large scale structure consisting of Virgo
and the background void and the A1367-Coma supercluster regime at cz_sun ~7000
km/s. Position corrections for telescope pointing errors are applied to the
dataset by comparing ALFALFA continuum centroid with those cataloged in the
NRAO VLA Sky Survey. The uncorrected positional accuracy averages
27 arcsec ~(21 arcsec ~median) for all sources with S/N > 6.5 and is of order
~21 arcsec ~(16 arcsec ~median) for signals with S/N > 12. Uncertainties in
distances toward the Virgo cluster can affect the calculated HI mass
distribution.Comment: 25 pages, 1 Table, 8 figures, Accepted by the Astronomical Journa
Methanol Maser Emission from Galactic Center Sources with Excess 4.5 {\mu}m Emission
We present a study of signatures of on-going star formation in a sample of
protostellar objects with enhanced 4.5 {\mu}m emission ('green' sources) near
the Galactic center. To understand how star formation in the Galactic center
region compares to that of the Galactic disk, we used the Expanded Very Large
Array to observe radiatively excited Class II 6.7 GHz CH3OH masers and
collisionally excited Class I 44 GHz CH3OH masers, both tracers of high-mass
star formation, toward a sample of 34 Galactic center and foreground 'green'
sources. We find that 33\pm15% of Galactic center sources are coincident with
6.7 GHz masers, and that 44\pm17% of foreground sources are coincident with 6.7
GHz masers. For 44 GHz masers, we find correlation rates of 27\pm13% and
25\pm13% for Galactic center green sources and foreground green sources,
espectively. Based on these CH3OH maser detection rates, as well as
correlations of green sources with other tracers of star formation, such as 24
{\mu}m emission and infrared dark clouds (IRDCs), we find no significant
difference between the green sources in the Galactic center and those
foreground to it. This suggests that once the star formation process has begun,
the environmental differences between the Galactic center region and the
Galactic disk have little effect on its observational signatures. We do find,
however, some evidence that may support a recent episode of star formation in
the Galactic center region.Comment: 73 pages, 34 figures, 5 tables. Accepted for publication in Ap
A near IR imaging survey of intermediate and high-mass young stellar outflow candidates
We have carried out a near-infrared imaging survey of luminous young stellar
outflow candidates using the United Kingdom Infrared Telescope. Observations
were obtained in the broad band K (2.2 mu) and through narrow band filters at
the wavelengths of H_2 v=1--0 S(1) (2.1218 mu) and Br gamma (2.166 mu) lines.
Fifty regions were imaged with a field of view of 2.2 X 2.2 arcmin^2. Several
young embedded clusters are unveiled in our near-infrared images. 76% of the
objects exhibit H_2 emission and 50% or more of the objects exhibit aligned H_2
emission features suggesting collimated outflows, many of which are new
detections. These observations suggest that disk accretion is probably the
leading mechanism in the formation of stars, at least up to late O spectral
types. The young stellar objects responsible for many of these outflows are
positively identified in our images based on their locations with respect to
the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and
radio sources. The close association of molecular outflows detected in CO with
the H_2 emission features produced by shock excitation by jets from the young
stellar objects suggests that the outflows from these objects are jet-driven.
Towards strong radio emitting sources, H_2 jets were either not detected or
were weak when detected, implying that most of the accretion happens in the
pre-UCHII phase; accretion and outflows are probably weak when the YSO has
advanced to its UCHII stage.Comment: 64 pages, 53 figures, Accepted for publication in the MNRA
CoBe -- Coded Beacons for Localization, Object Tracking, and SLAM Augmentation
This paper presents a novel beacon light coding protocol, which enables fast
and accurate identification of the beacons in an image. The protocol is
provably robust to a predefined set of detection and decoding errors, and does
not require any synchronization between the beacons themselves and the optical
sensor. A detailed guide is then given for developing an optical tracking and
localization system, which is based on the suggested protocol and readily
available hardware. Such a system operates either as a standalone system for
recovering the six degrees of freedom of fast moving objects, or integrated
with existing SLAM pipelines providing them with error-free and easily
identifiable landmarks. Based on this guide, we implemented a low-cost
positional tracking system which can run in real-time on an IoT board. We
evaluate our system's accuracy and compare it to other popular methods which
utilize the same optical hardware, in experiments where the ground truth is
known. A companion video containing multiple real-world experiments
demonstrates the accuracy, speed, and applicability of the proposed system in a
wide range of environments and real-world tasks. Open source code is provided
to encourage further development of low-cost localization systems integrating
the suggested technology at its navigation core
Sensitive VLBI Continuum and H I Absorption Observations of NGC 7674: First Scientific Observations with the Combined Array VLBA, VLA & Arecibo
We present phase-referenced VLBI observations of the radio continuum emission
from, and the H I 21 cm absorption toward, the Luminous Infrared Galaxy NGC
7674. The observations were carried out at 1380 MHz using the VLBA, the phased
VLA, and theArecibo radio telescope. These observations constitute the first
scientific use of the Arecibo telescope in a VLBI observation with the VLBA.
The high- and low-resolution radio continuum images reveal several new
continuum structures in the nuclear region of this galaxy. At ~100 mas
resolution, we distinguish six continuum structures extending over 1.4 arcsec,
with a total flux density of 138 mJy. Only three of these structures were known
previously. All these structures seem to be related to AGN activity. At the
full resolution of the array, we only detect two of the six continuum
structures. Both are composed of several compact components with brightness
temperatures on the order of K. While it is possible that one of these
compact structures could host an AGN, they could also be shock-like features
formed by the interaction of the jet with compact interstellar clouds in the
nuclear region of this galaxy. Complex H I absorption is detected with our VLBI
array at both high and low angular resolution. Assuming that the widest H I
feature is associated with a rotating H I disk or torus feeding a central AGN,
we estimate an enclosed dynamical mass of ~7 x 10^7 M_sun, comparable to the
value derived from the hidden broad H emission in this galaxy. The
narrower H I lines could represent clumpy neutral hydrogen structures in the H
I torus. The detection of H I absorption toward some of the continuum
components, and its absence toward others, suggest an inclined H I disk or
torus in the central region of NGC 7674.Comment: 37 pages, 11 figures. ApJ accepted. To appear in the Nov. 10, 2003
issue of ApJ. Please use the PDF version if the postscript doesn't show the
figure
Massive star formation and feedback in W49A: The source of our Galaxy's most luminous water maser outflow
We present high spatial resolution mid-IR images of the ring of UCHII regions
in W49A obtained at Gemini North, allowing us to identify the driving source of
its powerful H2O maser outflow. These data also confirm our previous report
that several radio sources in the ring are undetected in the mid-IR because
they are embedded deep inside the cloud core. We locate the source of the water
maser outflow at the position of the compact mid-IR peak of source G (source
G:IRS1). This IR source is not coincident with any identified compact radio
continuum source, but is coincident with a hot molecular core, so we propose
that G:IRS1 is a hot core driving an outflow analogous to the wide-angle
bipolar outflow in OMC-1. G:IRS1 is at the origin of a larger bipolar cavity
and CO outflow. The water maser outflow is orthogonal to the bipolar CO cavity,
so the masers probably reside near its waist in the cavity walls. Models of the
IR emission require a massive protostar of 45Msun, 3e5Lsun, and an effective
envelope accretion rate of 1e-3Msun/yr. Feedback from the central star could
potentially drive the H2O maser outflow, but it has insufficient radiative
momentum to have driven the large-scale CO outflow, requiring that this massive
star had an active accretion disk over the past 10^4 yr. Combined with the
spatialy resolved morphology in IR images, G:IRS1 in W49 provides compelling
evidence for a massive protostar that formed by accreting from a disk,
accompanied by a bipolar outflow.Comment: 14 pages, MNRAS accepte
Technologies and solutions for location-based services in smart cities: past, present, and future
Location-based services (LBS) in smart cities have drastically altered the way cities operate, giving a new dimension to the life of citizens. LBS rely on location of a device, where proximity estimation remains at its core. The applications of LBS range from social networking and marketing to vehicle-toeverything communications. In many of these applications, there is an increasing need and trend to learn the physical distance between nearby devices. This paper elaborates upon the current needs of proximity estimation in LBS and compares them against the available Localization and Proximity (LP) finding technologies (LP technologies in short). These technologies are compared for their accuracies and performance based on various different parameters, including latency, energy consumption, security, complexity, and throughput. Hereafter, a classification of these technologies, based on various different smart city applications, is presented. Finally, we discuss some emerging LP technologies that enable proximity estimation in LBS and present some future research areas
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