78 research outputs found
General description of electromagnetic radiation processes based on instantaneous charge acceleration in `endpoints'
We present a new methodology for calculating the electromagnetic radiation
from accelerated charged particles. Our formulation --- the `endpoint
formulation' --- combines numerous results developed in the literature in
relation to radiation arising from particle acceleration using a complete, and
completely general, treatment. We do this by describing particle motion via a
series of discrete, instantaneous acceleration events, or `endpoints', with
each such event being treated as a source of emission. This method implicitly
allows for particle creation/destruction, and is suited to direct numerical
implementation in either the time- or frequency-domains. In this paper, we
demonstrate the complete generality of our method for calculating the radiated
field from charged particle acceleration, and show how it reduces to the
classical named radiation processes such as synchrotron, Tamm's description of
Vavilov-Cherenkov, and transition radiation under appropriate limits. Using
this formulation, we are immediately able to answer outstanding questions
regarding the phenomenology of radio emission from ultra-high-energy particle
interactions in both the Earth's atmosphere and the Moon. In particular, our
formulation makes it apparent that the dominant emission component of the
Askaryan Effect (coherent radio-wave radiation from high-energy particle
cascades in dense media) comes from coherent `bremsstrahlung' from particle
acceleration, rather than coherent Vavilov-Cherenkov radiation.Comment: accepted by Phys. Rev. E, new title, some corrections in equations
and references, figure styles updated to match journal policie
Honors Programs Best Practices: Le Moyne College, Gonzaga University, Creighton University, Rockhurst University, Regis University, and Loyola University Maryland
Among-site variability in the stochastic dynamics of East African coral reefs
Coral reefs are dynamic systems whose composition is highly influenced by
unpredictable biotic and abiotic factors. Understanding the spatial scale at
which long-term predictions of reef composition can be made will be crucial for
guiding conservation efforts. Using a 22-year time series of benthic
composition data from 20 reefs on the Kenyan and Tanzanian coast, we studied
the long-term behaviour of Bayesian vector autoregressive state-space models
for reef dynamics, incorporating among-site variability. We estimate that if
there were no among-site variability, the total long-term variability would be
approximately one third of its current value. Thus among-site variability
contributes more to long-term variability in reef composition than does
temporal variability. Individual sites are more predictable than previously
thought, and predictions based on current snapshots are informative about
long-term properties. Our approach allowed us to identify a subset of possible
climate refugia sites with high conservation value, where the long-term
probability of coral cover <= 0.1 was very low. Analytical results show that
this probability is most strongly influenced by among-site variability and by
interactions among benthic components within sites. These findings suggest that
conservation initiatives might be successful at the site scale as well as the
regional scale.Comment: 97 pages, 49 figure
Cosmic Ray Detection at the Murchison Radio-astronomy Observatory – a pathfinder for SKA-Low
We present the status of cosmic-ray detection activities at the Murchison Radio-astronomy Observatory. Using 128 antennas of the Murchison Widefield Array radio telescope in its extended configuration, we detect the radio emission from extensive air showers in the 122--154 MHz range at a rate of slightly less than once per hour, each with an approximate energy of 10 eV. We have developed a bespoke filter inversion to obtain high-time-resolution data from this general-purpose astronomy instrument, and directly capture the radio signal. Our future plans include the implementation of a particle-triggered mode, and expanded operations with the low-frequency component of the Square Kilometre Array, which will have ~100,000 antennas deployed on the same site
Some Issues Related to Integrating Active Flow Control With Flight Control
Time varying control of CL is necessary for integrating AFC and Flight Control (Biasing allows for +/- changes in lift) Time delays associated with actuation are long (APPROX.5.8 c/U) and must be included in controllers. Convolution of input signal with single pulse kernel gives reasonable prediction of lift response
Ensemble-Empirical-Mode-Decomposition based micro-Doppler signal separation and classification
The target echo signals obtained by Synthetic Aperture Radar (SAR) and Ground Moving Target Indicator (GMTI platforms are mainly composed of two parts, the micro-Doppler signal and the target body part signal. The wheeled vehicle and the track vehicle are classified according to the different character of their micro-Doppler signal. In order to overcome the mode mixing problem in Empirical Mode Decomposition (EMD), Ensemble Empirical Mode Decomposition (EEMD) is employed to decompose the original signal into a number of Intrinsic Mode Functions (IMF). The correlation analysis is then carried out to select IMFs which have a relatively high correlation with the micro-Doppler signal. Thereafter, four discriminative features are extracted and Support Vector Machine (SVM) classifier is applied for classification. The experimental results show that the features extracted after EEMD decomposition are effective, with up 90% success rate for classification using one feature. In addition, these four features are complementary in different target velocity and azimuth angles
Development of a cloud-based platform for reproducible science: a case study of an IUCN red list of ecosystems assessment
One of the challenges of computational-centric research is to make the research undertaken reproducible in a form that others can repeat and re-use with minimal effort. In addition to the data and tools necessary to re-run analyses, execution environments play crucial roles because of the dependencies of the operating system and software version used. However, some of the challenges of reproducible science can be addressed using appropriate computational tools and cloud computing to provide an execution environment. Here, we demonstrate the use of a Kepler scientific workflow for reproducible science that is sharable, reusable, and re-executable. These workflows reduce barriers to sharing and will save researchers time when undertaking similar research in the future. To provide infrastructure that enables reproducible science, we have developed cloud-based Collaborative Environment for Ecosystem Science Research and Analysis (CoESRA) infrastructure to build, execute and share sophisticated computation-centric research. The CoESRA provides users with a storage and computational platform that is accessible from a web-browser in the form of a virtual desktop. Any registered user can access the virtual desktop to build, execute and share the Kepler workflows. This approach will enable computational scientists to share complete workflows in a pre-configured environment so that others can reproduce the computational research with minimal effort. As a case study, we developed and shared a complete IUCN Red List of Ecosystems Assessment workflow that reproduces the assessments undertaken by Burns et al. (2015) on Mountain Ash forests in the Central Highlands of Victoria, Australia. This workflow provides an opportunity for other researchers and stakeholders to run this assessment with minimal supervision. The workflow also enables researchers to re-evaluate the assessment when additional data becomes available. The assessment can be run in a CoESRA virtual desktop by opening a workflow in a Kepler user interface and pressing a “start” button. The workflow is pre-configured with all the open access datasets and writes results to a pre-configured folder
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