6,532 research outputs found
Developments in GRworkbench
The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. Recently, GRworkbench
has been significantly extended to facilitate numerical experimentation in
analytically-defined space-times. The numerical differential geometric engine
has been rewritten using functional programming techniques, enabling objects
which are normally defined as functions in the formalism of differential
geometry and General Relativity to be directly represented as function
variables in the C++ code of GRworkbench. The new functional differential
geometric engine allows for more accurate and efficient visualisation of
objects in space-times and makes new, efficient computational techniques
available. Motivated by the desire to investigate a recent scientific claim
using GRworkbench, new tools for numerical experimentation have been
implemented, allowing for the simulation of complex physical situations.Comment: 14 pages. To appear A. Moylan, S.M. Scott and A.C. Searle,
Developments in GRworkbench. Proceedings of the Tenth Marcel Grossmann
Meeting on General Relativity, editors M. Novello, S. Perez-Bergliaffa and R.
Ruffini. Singapore: World Scientific 200
The ACIGA Data Analysis programme
The Data Analysis programme of the Australian Consortium for Interferometric
Gravitational Astronomy (ACIGA) was set up in 1998 by the first author to
complement the then existing ACIGA programmes working on suspension systems,
lasers and optics, and detector configurations. The ACIGA Data Analysis
programme continues to contribute significantly in the field; we present an
overview of our activities.Comment: 10 pages, 0 figures, accepted, Classical and Quantum Gravity,
(Proceedings of the 5th Edoardo Amaldi Conference on Gravitational Waves,
Tirrenia, Pisa, Italy, 6-11 July 2003
Pericentromeric organization at the fusion point of mouse Robertsonian translocation chromosomes
In mammals, Robertsonian (Rb) translocation (the joining of two telo/acrocentric chromosomes at their centromere to form a metacentric) is the most effective process in chromosomal evolution leading to speciation; its occurrence also affects human health (through the induction of trisomies) and the fertility of farm animals. To understand the mechanism of Rb translocation, we used the house mouse as a model system and studied the organization of pericentromeric satellite DNAs (satDNA) of telocentrics and Rb chromosomes, both minor and major satDNA. The chromosome-orientation fluorescence in situ hybridization (CO-FISH) technique was used to analyze the major satDNA. To detect the very small amount of minor satDNA, a procedure was developed that combines CO-FISH with primed in situ labeling and conventional FISH and is five times more sensitive than the CO-FISH procedure alone. It was found that both the major and the minor satDNA tandem repeats are oriented head-to-tail in telocentric and Rb chromosomes, and their polarity is always the same relative to the centromere. We suggest that all tandemly repetitive satDNAs in a species probably are locked into such a symmetry constraint as a universal consequence of chromosomal evolution. Rb translocation breakpoints were found localized within the minor satDNA of telocentrics, and these sequences contributed symmetrically to the formation of the centromeric region of the Rb chromosomes. These results are important for an understanding of the geometry of Rb translocations and suggest the study of DNA orientation as a new tool for investigating these rearrangements
Robust Bayesian detection of unmodelled bursts
A Bayesian treatment of the problem of detecting an unmodelled gravitational
wave burst with a global network of gravitational wave observatories reveals
that several previously proposed statistics have implicit biases that render
them sub-optimal for realistic signal populations.Comment: 9 pages, 1 figure, submitted to CQG Amaldi proceedings special issu
The Prevalence and Focus of Medical Education Fellowships Across North America
Medical institutions have established medical education fellowships to equip faculty to meet the challenge of constant educational change and to empower faculty to assume programmatic leadership roles in medical education. The purpose of this study was to determine the prevalence and focus of these programs. [See PDF for complete abstract
"How May I Help You?": Modeling Twitter Customer Service Conversations Using Fine-Grained Dialogue Acts
Given the increasing popularity of customer service dialogue on Twitter,
analysis of conversation data is essential to understand trends in customer and
agent behavior for the purpose of automating customer service interactions. In
this work, we develop a novel taxonomy of fine-grained "dialogue acts"
frequently observed in customer service, showcasing acts that are more suited
to the domain than the more generic existing taxonomies. Using a sequential
SVM-HMM model, we model conversation flow, predicting the dialogue act of a
given turn in real-time. We characterize differences between customer and agent
behavior in Twitter customer service conversations, and investigate the effect
of testing our system on different customer service industries. Finally, we use
a data-driven approach to predict important conversation outcomes: customer
satisfaction, customer frustration, and overall problem resolution. We show
that the type and location of certain dialogue acts in a conversation have a
significant effect on the probability of desirable and undesirable outcomes,
and present actionable rules based on our findings. The patterns and rules we
derive can be used as guidelines for outcome-driven automated customer service
platforms.Comment: 13 pages, 6 figures, IUI 201
Bayesian detection of unmodeled bursts of gravitational waves
The data analysis problem of coherently searching for unmodeled
gravitational-wave bursts in the data generated by a global network of
gravitational-wave observatories has been at the center of research for almost
two decades. As data from these detectors is starting to be analyzed, a renewed
interest in this problem has been sparked. A Bayesian approach to the problem
of coherently searching for gravitational wave bursts with a network of
ground-based interferometers is here presented. We demonstrate how to
systematically incorporate prior information on the burst signal and its source
into the analysis. This information may range from the very minimal, such as
best-guess durations, bandwidths, or polarization content, to complete prior
knowledge of the signal waveforms and the distribution of sources through
spacetime. We show that this comprehensive Bayesian formulation contains
several previously proposed detection statistics as special limiting cases, and
demonstrate that it outperforms them.Comment: 18 pages, 3 figures, revisions based on referee comment
Spectral Line Removal in the LIGO Data Analysis System (LDAS)
High power in narrow frequency bands, spectral lines, are a feature of an
interferometric gravitational wave detector's output. Some lines are coherent
between interferometers, in particular, the 2 km and 4 km LIGO Hanford
instruments. This is of concern to data analysis techniques, such as the
stochastic background search, that use correlations between instruments to
detect gravitational radiation. Several techniques of `line removal' have been
proposed. Where a line is attributable to a measurable environmental
disturbance, a simple linear model may be fitted to predict, and subsequently
subtract away, that line. This technique has been implemented (as the command
oelslr) in the LIGO Data Analysis System (LDAS). We demonstrate its application
to LIGO S1 data.Comment: 11 pages, 5 figures, to be published in CQG GWDAW02 proceeding
The bloodstream differentiation - division of Trypanosoma brucei studied using mitochondrial markers
In the bloodstream of its mammalian host, the African trypanosome Trypanosoma brucei undergoes a life cycle stage differentiation from a long, slender form to a short, stumpy form. This involves three known major events: exit from a proliferative cell cycle, morphological change and mitochondrial biogenesis. Previously, models have been proposed accounting for these events (Matthews & Gull 1994a). Refinement of, and discrimination between, these models has been hindered by a lack of stage-regulated antigens useful as markers at the single-cell level. We have now evaluated a variety of cytological markers and applied them to investigate the coordination of phenotypic differentiation and cell cycle arrest. Our studies have focused on the differential expression of the mitochondrial enzyme dihydrolipoamide dehydrogenase relative to the differentiation-division of bloodstream trypanosomes. The results implicate a temporal order of events: commitment, division, phenotypic differentiation
Targeted search for continuous gravitational waves: Bayesian versus maximum-likelihood statistics
We investigate the Bayesian framework for detection of continuous
gravitational waves (GWs) in the context of targeted searches, where the phase
evolution of the GW signal is assumed to be known, while the four amplitude
parameters are unknown. We show that the orthodox maximum-likelihood statistic
(known as F-statistic) can be rediscovered as a Bayes factor with an unphysical
prior in amplitude parameter space. We introduce an alternative detection
statistic ("B-statistic") using the Bayes factor with a more natural amplitude
prior, namely an isotropic probability distribution for the orientation of GW
sources. Monte-Carlo simulations of targeted searches show that the resulting
Bayesian B-statistic is more powerful in the Neyman-Pearson sense (i.e. has a
higher expected detection probability at equal false-alarm probability) than
the frequentist F-statistic.Comment: 12 pages, presented at GWDAW13, to appear in CQ
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