38,817 research outputs found
Context Trees: Augmenting Geospatial Trajectories with Context
Exposing latent knowledge in geospatial trajectories has the potential to
provide a better understanding of the movements of individuals and groups.
Motivated by such a desire, this work presents the context tree, a new
hierarchical data structure that summarises the context behind user actions in
a single model. We propose a method for context tree construction that augments
geospatial trajectories with land usage data to identify such contexts. Through
evaluation of the construction method and analysis of the properties of
generated context trees, we demonstrate the foundation for understanding and
modelling behaviour afforded. Summarising user contexts into a single data
structure gives easy access to information that would otherwise remain latent,
providing the basis for better understanding and predicting the actions and
behaviours of individuals and groups. Finally, we also present a method for
pruning context trees, for use in applications where it is desirable to reduce
the size of the tree while retaining useful information
Optical constants of silicon carbide for astrophysical applications. II. Extending optical functions from IR to UV using single-crystal absorption spectra
Laboratory measurements of unpolarized and polarized absorption spectra of
various samples and crystal stuctures of silicon carbide (SiC) are presented
from 1200--35,000 cm ( 8--0.28 m) and used to improve
the accuracy of optical functions ( and ) from the infrared (IR) to the
ultraviolet (UV). Comparison with previous 6--20 m
thin-film spectra constrains the thickness of the films and verifies that
recent IR reflectivity data provide correct values for in the IR region. We
extract and needed for radiative transfer models using a new
``difference method'', which utilizes transmission spectra measured from two
SiC single-crystals with different thicknesses. This method is ideal for
near-IR to visible regions where absorbance and reflectance are low and can be
applied to any material. Comparing our results with previous UV measurements of
SiC, we distinguish between chemical and structural effects at high frequency.
We find that for all spectral regions, 3C (-SiC) and the polarization of 6H (a type of -SiC) have almost identical
optical functions that can be substituted for each other in modeling
astronomical environments. Optical functions for of 6H SiC
have peaks shifted to lower frequency, permitting identification of this
structure below m. The onset of strong UV absorption for pure
SiC occurs near 0.2 m, but the presence of impurities redshifts the rise
to 0.33 m. Optical functions are similarly impacted. Such large
differences in spectral characteristics due to structural and chemical effects
should be observable and provide a means to distinguish chemical variation of
SiC dust in space.Comment: 46 pages inc. 8 figures and 2 full tables. Also 6 electronic-only
data files. Accepted by Ap
The XMM Cluster Survey: X-ray analysis methodology
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters
using all publicly available data in the XMM-Newton Science Archive. Its main
aims are to measure cosmological parameters and trace the evolution of X-ray
scaling relations. In this paper we describe the data processing methodology
applied to the 5,776 XMM observations used to construct the current XCS source
catalogue. A total of 3,675 > 4-sigma cluster candidates with > 50
background-subtracted X-ray counts are extracted from a total non-overlapping
area suitable for cluster searching of 410 deg^2. Of these, 993 candidates are
detected with > 300 background-subtracted X-ray photon counts, and we
demonstrate that robust temperature measurements can be obtained down to this
count limit. We describe in detail the automated pipelines used to perform the
spectral and surface brightness fitting for these candidates, as well as to
estimate redshifts from the X-ray data alone. A total of 587 (122) X-ray
temperatures to a typical accuracy of < 40 (< 10) per cent have been measured
to date. We also present the methodology adopted for determining the selection
function of the survey, and show that the extended source detection algorithm
is robust to a range of cluster morphologies by inserting mock clusters derived
from hydrodynamical simulations into real XMM images. These tests show that the
simple isothermal beta-profiles is sufficient to capture the essential details
of the cluster population detected in the archival XMM observations. The
redshift follow-up of the XCS cluster sample is presented in a companion paper,
together with a first data release of 503 optically-confirmed clusters.Comment: MNRAS accepted, 45 pages, 38 figures. Our companion paper describing
our optical analysis methodology and presenting a first set of confirmed
clusters has now been submitted to MNRA
Growing a Tree in the Forest: Constructing Folksonomies by Integrating Structured Metadata
Many social Web sites allow users to annotate the content with descriptive
metadata, such as tags, and more recently to organize content hierarchically.
These types of structured metadata provide valuable evidence for learning how a
community organizes knowledge. For instance, we can aggregate many personal
hierarchies into a common taxonomy, also known as a folksonomy, that will aid
users in visualizing and browsing social content, and also to help them in
organizing their own content. However, learning from social metadata presents
several challenges, since it is sparse, shallow, ambiguous, noisy, and
inconsistent. We describe an approach to folksonomy learning based on
relational clustering, which exploits structured metadata contained in personal
hierarchies. Our approach clusters similar hierarchies using their structure
and tag statistics, then incrementally weaves them into a deeper, bushier tree.
We study folksonomy learning using social metadata extracted from the
photo-sharing site Flickr, and demonstrate that the proposed approach addresses
the challenges. Moreover, comparing to previous work, the approach produces
larger, more accurate folksonomies, and in addition, scales better.Comment: 10 pages, To appear in the Proceedings of ACM SIGKDD Conference on
Knowledge Discovery and Data Mining(KDD) 201
Measurement-Based Monitoring and Control in Power Systems with High Renewable Penetrations
Power systems are experiencing rapid changes in their generation mixes because of the increasing integration of inverter-based resources (IBRs) and the retirement of traditional generations. This opens opportunities for a cleaner energy outlook but also poses challenges to the safe operation of the power networks. Enhanced monitoring and control based on the increasingly available measurements are essential in assisting stable operation and effective planning for these evolving systems.
First, awareness of the evolving dynamic characteristics is quintessential for secure operation and corrective planning. A quantified monitoring study that keeps track of the inertial response and primary frequency response is conducted on the Eastern Interconnection (EI) for the past decade with field data. Whereas the inertia declined by at least 10%, the primary frequency response experienced an unexpected increase. The findings unveiled in the trending analysis also led to an improved event MW size estimation method, as well as discussions about regional dynamics.
Experiencing a faster and deeper renewable integration, the Continental Europe Synchronous Area (CESA) system has been threatened by more frequent occurrences of inter-area oscillations during light-load high-renewable periods. A measurement-based oscillation damping control scheme is proposed for CESA with reduced reliance on system models. The design, implementation, and hardware-in-the-loop (HIL) testing of the controller are discussed in detail.
Despite the challenges, the increasing presence of IBRs also brings opportunities for fast and efficient controls. Together with synchronized measurement, IBRs have the potential to flexibly complement traditional frequency and voltage control schemes for improved frequency and voltage recovery. The design, implementation, and HIL testing of the measurement-based frequency and voltage control for the New York State Grid are presented.
In addition to the transmission level development, IBRs deployed in distribution networks can also be valuable assets in emergency islanding situations if controlled properly. A power management module is proposed to take advantage of measurements and automatically control the electric boundaries of islanded microgrids for maximized power utilization and improved frequency regulation. The module is designed to be adaptive to arbitrary non-meshed topologies with multiple source locations for increased flexibility, expedited deployment, and reduced cost
An Input-Process-Output Model of Pilot Core Competencies.
Abstract. The aim of this study was to investigate the relationship between the flight-related core competencies for professional airline pilots and to structuralize them as components in a team performance framework. To achieve this, the core competency scores from a total of 2,560 OPC (Operator Proficiency Check) missions were analyzed. A principal component analysis (PCA) of pilotsâ performance scores across the different competencies was conducted. Four principal components were extracted and a path analysis model was constructed on the basis of these factors. The path analysis utilizing the core competencies extracted adopted an inputâprocessâoutputâ (IPO) model of team performance related directly to the activities on the flight deck. The results of the PCA and the path analysis strongly supported the proposed IPO model. </jats:p
- âŚ