5,366 research outputs found
Wettability-independent droplet transport by \emph{Bendotaxis}
We demonstrate \textit{bendotaxis}, a novel mechanism for droplet
self-transport at small scales. A combination of bending and capillarity in a
thin channel causes a pressure gradient that, in turn, results in the
spontaneous movement of a liquid droplet. Surprisingly, the direction of this
motion is always the same, regardless of the wettability of the channel. We use
a combination of experiments at a macroscopic scale and a simple mathematical
model to study this motion, focussing in particular on the time scale
associated with the motion. We suggest that \emph{bendotaxis} may be a useful
means of transporting droplets in technological applications, for example in
developing self-cleaning surfaces, and discuss the implications of our results
for such applications.Comment: 5 pages, 4 figures. Supplementary Information available on reques
A Bayesian spatio-temporal model of panel design data: airborne particle number concentration in Brisbane, Australia
This paper outlines a methodology for semi-parametric spatio-temporal
modelling of data which is dense in time but sparse in space, obtained from a
split panel design, the most feasible approach to covering space and time with
limited equipment. The data are hourly averaged particle number concentration
(PNC) and were collected, as part of the Ultrafine Particles from Transport
Emissions and Child Health (UPTECH) project. Two weeks of continuous
measurements were taken at each of a number of government primary schools in
the Brisbane Metropolitan Area. The monitoring equipment was taken to each
school sequentially. The school data are augmented by data from long term
monitoring stations at three locations in Brisbane, Australia.
Fitting the model helps describe the spatial and temporal variability at a
subset of the UPTECH schools and the long-term monitoring sites. The temporal
variation is modelled hierarchically with penalised random walk terms, one
common to all sites and a term accounting for the remaining temporal trend at
each site. Parameter estimates and their uncertainty are computed in a
computationally efficient approximate Bayesian inference environment, R-INLA.
The temporal part of the model explains daily and weekly cycles in PNC at the
schools, which can be used to estimate the exposure of school children to
ultrafine particles (UFPs) emitted by vehicles. At each school and long-term
monitoring site, peaks in PNC can be attributed to the morning and afternoon
rush hour traffic and new particle formation events. The spatial component of
the model describes the school to school variation in mean PNC at each school
and within each school ground. It is shown how the spatial model can be
expanded to identify spatial patterns at the city scale with the inclusion of
more spatial locations.Comment: Draft of this paper presented at ISBA 2012 as poster, part of UPTECH
projec
An open-source, stochastic, six-degrees-of-freedom rocket flight simulator, with a probabilistic trajectory analysis approach
Predicting the flight-path of an unguided rocket can help overcome unnecessary risks. Avoiding residential areas or a car-park can improve the safety of launching a rocket significantly. Furthermore, an accurate landing site prediction facilitates recovery. This paper introduces a six-degrees-of-freedom flight simulator for large unguided model rockets that can fly to altitudes of up to 13 km and then return to earth by parachute. The open-source software package assists the user with the design of rockets, and its simulation core models both the rocket flight and the parachute descent in stochastic wind conditions. Furthermore, the uncertainty in the input variables propagates through the model via a Monte Carlo wrapper, simulating a range of possible flight conditions. The resulting trajectories are captured as a Gaussian process, which assists in the statistical assessment of the flight conditions in the face of uncertainties, such as changes in wind conditions, failure to deploy the parachute, and variations in thrust. This approach also facilitates concise presentation of such uncertainties via visualisation of trajectory ensembles
Kepler-91b: a planet at the end of its life. Planet and giant host star properties via light-curve variations
The evolution of planetary systems is intimately linked to the evolution of
their host star. Our understanding of the whole planetary evolution process is
based on the large planet diversity observed so far. To date, only few tens of
planets have been discovered orbiting stars ascending the Red Giant Branch.
Although several theories have been proposed, the question of how planets die
remains open due to the small number statistics. In this work we study the
giant star Kepler-91 (KOI-2133) in order to determine the nature of a
transiting companion. This system was detected by the Kepler Space Telescope.
However, its planetary confirmation is needed. We confirm the planetary nature
of the object transiting the star Kepler-91 by deriving a mass of and a planetary radius of
. Asteroseismic analysis produces a
stellar radius of and a mass of
. We find that its eccentric orbit
() is just away
from the stellar atmosphere at the pericenter. Kepler-91b could be the previous
stage of the planet engulfment, recently detected for BD+48 740. Our
estimations show that Kepler-91b will be swallowed by its host star in less
than 55 Myr. Among the confirmed planets around giant stars, this is the
planetary-mass body closest to its host star. At pericenter passage, the star
subtends an angle of , covering around 10% of the sky as seen from
the planet. The planetary atmosphere seems to be inflated probably due to the
high stellar irradiation.Comment: 21 pages, 8 tables and 11 figure
Retrodiction as a tool for micromaser field measurements
We use retrodictive quantum theory to describe cavity field measurements by
successive atomic detections in the micromaser. We calculate the state of the
micromaser cavity field prior to detection of sequences of atoms in either the
excited or ground state, for atoms that are initially prepared in the excited
state. This provides the POM elements, which describe such sequences of
measurements.Comment: 20 pages, 4(8) figure
The Kinetic Sunyaev-Zel'dovich Effect from Radiative Transfer Simulations of Patchy Reionization
We present the first calculation of the kinetic Sunyaev-Zel'dovich (kSZ)
effect due to the inhomogeneous reionization of the universe based on detailed
large-scale radiative transfer simulations of reionization. The resulting sky
power spectra peak at l=2000-8000 with maximum values of
l^2C_l~1\times10^{-12}. The peak scale is determined by the typical size of the
ionized regions and roughly corresponds to the ionized bubble sizes observed in
our simulations, ~5-20 Mpc. The kSZ anisotropy signal from reionization
dominates the primary CMB signal above l=3000. This predicted kSZ signal at
arcminute scales is sufficiently strong to be detectable by upcoming
experiments, like the Atacama Cosmology Telescope and South Pole Telescope
which are expected to have ~1' resolution and ~muK sensitivity. The extended
and patchy nature of the reionization process results in a boost of the peak
signal in power by approximately one order of magnitude compared to a uniform
reionization scenario, while roughly tripling the signal compared with that
based upon the assumption of gradual but spatially uniform reionization. At
large scales the patchy kSZ signal depends largely on the ionizing source
efficiencies and the large-scale velocity fields: sources which produce photons
more efficiently yield correspondingly higher signals. The introduction of
sub-grid gas clumping in the radiative transfer simulations produces
significantly more power at small scales, and more non-Gaussian features, but
has little effect at large scales. The patchy nature of the reionization
process roughly doubles the total observed kSZ signal for l~3000-10^4 compared
to non-patchy scenarios with the same total electron-scattering optical depth.Comment: 14 pages, 13 figures (some in color), submitted to Ap
Towards virtual machine energy-aware cost prediction in clouds
Pricing mechanisms employed by different service providers significantly influence the role of cloud computing within the IT industry. With the increasing cost of electricity, Cloud providers consider power consumption as one of the major cost factors to be maintained within their infrastructures. Consequently, modelling a new pricing mechanism that allow Cloud providers to determine the potential cost of resource usage and power consumption has attracted the attention of many researchers. Furthermore, predicting the future cost of Cloud services can help the service providers to offer the suitable services to the customers that meet their requirements. This paper introduces an Energy-Aware Cost Prediction Framework to estimate the total cost of Virtual Machines (VMs) by considering the resource usage and power consumption. The VMs’ workload is firstly predicted based on an Autoregressive Integrated Moving Average (ARIMA) model. The power consumption is then predicted using regression models. The comparison between the predicted and actual results obtained in a real Cloud testbed shows that this framework is capable of predicting the workload, power consumption and total cost for different VMs with good prediction accuracy, e.g. with 0.06 absolute percentage error for the predicted total cost of the VM
The equivalence of fluctuation scale dependence and autocorrelations
We define optimal per-particle fluctuation and correlation measures, relate
fluctuations and correlations through an integral equation and show how to
invert that equation to obtain precise autocorrelations from fluctuation scale
dependence. We test the precision of the inversion with Monte Carlo data and
compare autocorrelations to conditional distributions conventionally used to
study high- jet structure.Comment: 10 pages, 9 figures, proceedings, MIT workshop on correlations and
fluctuations in relativistic nuclear collision
Analyzing the House Fly's Exploratory Behavior with Autoregression Methods
This paper presents a detailed characterization of the trajectory of a single
housefly with free range of a square cage. The trajectory of the fly was
recorded and transformed into a time series, which was fully analyzed using an
autoregressive model, which describes a stationary time series by a linear
regression of prior state values with the white noise. The main discovery was
that the fly switched styles of motion from a low dimensional regular pattern
to a higher dimensional disordered pattern. This discovered exploratory
behavior is, irrespective of the presence of food, characterized by anomalous
diffusion.Comment: 20 pages, 9 figures, 1 table, full pape
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