17 research outputs found
Limits on the HI content of the dwarf galaxy Hydra II
Sensitive 21cm HI observations have been made with the Green Bank Telescope
toward the newly-discovered Local Group dwarf galaxy Hydra II, which may lie
within the leading arm of the Magellanic Stream. No neutral hydrogen was
detected. Our 5-sigma limit of MHI < 210 solar masses for a 15 km/s linewidth
gives a gas-to-luminosity ratio MHI/L_V < 2.6 x 10^{-2} Mo / Lo. The limits on
HI mass and MHI/L_V are typical of dwarf galaxies found within a few hundred
kpc of the Milky Way. Whatever the origin of Hydra II, its neutral gas
properties are not unusual.Comment: Accepted for publication in Astronomy & Astrophysic
Problems in Sensor Networks: Inference, *Localization, and Motion Estimation
114 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Finally, we introduce a framework to study the development of efficient algorithms in systems with dependent tasks. We use it to identify the structure of the algorithms we designed, and a classification that may be useful in other real-time systems.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
Tracking Objects with Networked Scattered Directional Sensors
We study the problem of object tracking using highly directional sensors—sensors whose field of vision is a line or a line segment. A network of such sensors monitors a certain region of the plane. Sporadically, objects moving in straight lines and at a constant speed cross the region. A sensor detects an object when it crosses its line of sight, and records the time of the detection. No distance or angle measurements are available. The task of the sensors is to estimate the directions and speeds of the objects, and the sensor lines, which are unknown a priori. This estimation problem involves the minimization of a highly nonconvex cost function. To overcome this difficulty, we introduce an algorithm, which we call “adaptive basis algorithm.†This algorithm is divided into three phases: in the first phase, the algorithm is initialized using data from six sensors and four objects; in the second phase, the estimates are updated as data from more sensors and objects are incorporated. The third phase is an optional coordinated transformation. The estimation is done in an “ad-hoc†coordinate system, which we call “adaptive coordinate system.†When more information is available, for example, the location of six sensors, the estimates can be transformed to the “real-world†coordinate system. This constitutes the third phase
Learning Tree-Structured Detection Cascades for Heterogeneous Networks of Embedded Devices
In this paper, we present a new approach to learning cascaded classifiers for
use in computing environments that involve networks of heterogeneous and
resource-constrained, low-power embedded compute and sensing nodes. We present
a generalization of the classical linear detection cascade to the case of
tree-structured cascades where different branches of the tree execute on
different physical compute nodes in the network. Different nodes have access to
different features, as well as access to potentially different computation and
energy resources. We concentrate on the problem of jointly learning the
parameters for all of the classifiers in the cascade given a fixed cascade
architecture and a known set of costs required to carry out the computation at
each node.To accomplish the objective of joint learning of all detectors, we
propose a novel approach to combining classifier outputs during training that
better matches the hard cascade setting in which the learned system will be
deployed. This work is motivated by research in the area of mobile health where
energy efficient real time detectors integrating information from multiple
wireless on-body sensors and a smart phone are needed for real-time monitoring
and delivering just- in-time adaptive interventions. We apply our framework to
two activity recognition datasets as well as the problem of cigarette smoking
detection from a combination of wrist-worn actigraphy data and respiration
chest band data.Comment: arXiv admin note: substantial text overlap with arXiv:1607.0373