11,513 research outputs found
The Royal Birth of 2013: Analysing and Visualising Public Sentiment in the UK Using Twitter
Analysis of information retrieved from microblogging services such as Twitter
can provide valuable insight into public sentiment in a geographic region. This
insight can be enriched by visualising information in its geographic context.
Two underlying approaches for sentiment analysis are dictionary-based and
machine learning. The former is popular for public sentiment analysis, and the
latter has found limited use for aggregating public sentiment from Twitter
data. The research presented in this paper aims to extend the machine learning
approach for aggregating public sentiment. To this end, a framework for
analysing and visualising public sentiment from a Twitter corpus is developed.
A dictionary-based approach and a machine learning approach are implemented
within the framework and compared using one UK case study, namely the royal
birth of 2013. The case study validates the feasibility of the framework for
analysis and rapid visualisation. One observation is that there is good
correlation between the results produced by the popular dictionary-based
approach and the machine learning approach when large volumes of tweets are
analysed. However, for rapid analysis to be possible faster methods need to be
developed using big data techniques and parallel methods.Comment: http://www.blessonv.com/research/publicsentiment/ 9 pages. Submitted
to IEEE BigData 2013: Workshop on Big Humanities, October 201
A Low Dimensional Approximation For Competence In Bacillus Subtilis
The behaviour of a high dimensional stochastic system described by a Chemical
Master Equation (CME) depends on many parameters, rendering explicit simulation
an inefficient method for exploring the properties of such models. Capturing
their behaviour by low-dimensional models makes analysis of system behaviour
tractable. In this paper, we present low dimensional models for the
noise-induced excitable dynamics in Bacillus subtilis, whereby a key protein
ComK, which drives a complex chain of reactions leading to bacterial
competence, gets expressed rapidly in large quantities (competent state) before
subsiding to low levels of expression (vegetative state). These rapid reactions
suggest the application of an adiabatic approximation of the dynamics of the
regulatory model that, however, lead to competence durations that are incorrect
by a factor of 2. We apply a modified version of an iterative functional
procedure that faithfully approximates the time-course of the trajectories in
terms of a 2-dimensional model involving proteins ComK and ComS. Furthermore,
in order to describe the bimodal bivariate marginal probability distribution
obtained from the Gillespie simulations of the CME, we introduce a tunable
multiplicative noise term in a 2-dimensional Langevin model whose stationary
state is described by the time-independent solution of the corresponding
Fokker-Planck equation.Comment: 12 pages, to be published in IEEE/ACM Transactions on Computational
Biology and Bioinformatic
A Direct Measurement of the Mean Occupation Function of Quasars: Breaking Degeneracies between Halo Occupation Distribution Models
Recent work on quasar clustering suggests a degeneracy in the halo occupation
distribution constrained from two-point correlation functions. To break this
degeneracy, we make the first empirical measurement of the mean occupation
function (MOF) of quasars at by matching quasar positions with
groups and clusters identified in the MaxBCG sample. We fit two models to the
MOF, a power law and a 4-parameter model. The number distribution of quasars in
host halos is close to Poisson, and the slopes of the MOF obtained from our
best-fit models (for the power law case) favor a MOF that monotonically
increases with halo mass. The best-fit slopes are and for the power law model and the 4-parameter model, respectively. We
measure the radial distribution of quasars within dark matter halos and find it
to be adequately described by a power law with a slope . We
measure the conditional luminosity function (CLF) of quasars and show that
there is no evidence that quasar luminosity depends on host halo mass, similar
to the inferences drawn from clustering measurements. We also measure the
conditional black hole mass function (CMF) of our quasars. Although the results
are consistent with no dependence on halo mass, we observe a slight indication
of downsizing of the black hole mass function. The lack of halo mass dependence
in the CLF and CMF shows that quasars residing in galaxy clusters have
characteristic luminosity and black hole mass scales.Comment: Matches the ApJ accepted version (11 pages, 8 figures
Identification of Si-vacancy related room temperature qubits in 4H silicon carbide
Identification of microscopic configuration of point defects acting as
quantum bits is a key step in the advance of quantum information processing and
sensing. Among the numerous candidates, silicon vacancy related centers in
silicon carbide (SiC) have shown remarkable properties owing to their
particular spin-3/2 ground and excited states. Although, these centers were
observed decades ago, still two competing models, the isolated negatively
charged silicon vacancy and the complex of negatively charged silicon vacancy
and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] are
argued as an origin. By means of high precision first principles calculations
and high resolution electron spin resonance measurements, we here unambiguously
identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively
charged silicon vacancies. Moreover, we identify the Si-vacancy qubit
configurations that provide room temperature optical readout.Comment: 3 figure
Excitation properties of the divacancy in 4H-SiC
We investigate the quenching of the photoluminescence (PL) from the divacancy
defect in 4H-SiC consisting of a nearest-neighbour silicon and carbon
vacancies. The quenching occurs only when the PL is excited below certain
photon energies (thresholds), which differ for the four different inequivalent
divacancy configurations in 4H-SiC. Refined theoretical ab initio calculation
for the charge-transfer levels of the divacancy show very good agreement
between the position of the (0/-) level with respect to the conduction band for
each divacancy configurations and the corresponding experimentally observed
threshold, allowing us to associate the PL decay with conversion of the
divacancy from neutral to negative charge state due to capture of electrons
photoionized from other defects (traps) by the excitation. Electron
paramagnetic resonance measurements are conducted in dark and under excitation
similar to that used in the PL experiments and shed light on the possible
origin of traps in the different samples. A simple model built on this concept
agrees well with the experimentally-observed decay curves.Comment: 28 pages, 6 figure
A 6-year-old boy presenting with traumatic evisceration following a bicycle handle bar injury: a case report
We report the case of a 6-year-old boy presenting with small bowel evisceration following a fall onto a bicycle handle-bar. His case is presented, a review of the literature performed and interesting photos pre and post-op are presented
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