12,762 research outputs found
Bayesian Model Selection with Future 21cm Observations of The Epoch of Reionisation
We apply Bayesian statistics to perform model selection on different
reionisation scenarios via the Multinest algorithm. Initially, we recover the
results shown by 21CMMC for the parameter estimation of 21cmFAST models. We
proceed to test several toy models of the Epoch of Reionisation (EoR) defined
in contrasting morphology and scale. We find that LOFAR observations are
unlikely to allow model selection even with long integration times. HERA would
require 61 dipoles to perform the same analysis in 1080 hours, and becomes
comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours
of observation to conclusively distinguish between our models. Once model
selection is achievable, an analysis of observational priors is performed
finding that neutral fraction checks at specific redshifts add little to no
inference. We show the difficulties in model selection at the level of
distinguishing fiducial parameters within a model or distinguishing galaxies
with a constant versus power law mass-to-light ratio. Finally, we explore the
use of the Savage-Dickey density ratio to show the redundancy of the parameter
Rmfp within 21cmFAST.Comment: 20 pages, 16 figures - Accepted for publication by MNRA
Single Atom Imaging with an sCMOS camera
Single atom imaging requires discrimination of weak photon count events above
background and has typically been performed using either EMCCD cameras,
photomultiplier tubes or single photon counting modules. sCMOS provides a cost
effective and highly scalable alternative to other single atom imaging
technologies, offering fast readout and larger sensor dimensions. We
demonstrate single atom resolved imaging of two site-addressable single atom
traps separated by 10~m using an sCMOS camera, offering a competitive
signal-to-noise ratio at intermediate count rates to allow high fidelity
readout discrimination (error ) and sub-m spatial resolution for
applications in quantum technologies.Comment: 4 pages, 4 figure
21-cm signatures of residual HI inside cosmic HII regions during reionization
We investigate the impact of sinks of ionizing radiation on the
reionization-era 21-cm signal, focusing on 1-point statistics. We consider
sinks in both the intergalactic medium and inside galaxies. At a fixed filling
factor of HII regions, sinks will have two main effects on the 21-cm
morphology: (i) as inhomogeneous absorbers of ionizing photons they result in
smaller and more widespread cosmic HII patches; and (ii) as reservoirs of
neutral gas they contribute a non-zero 21-cm signal in otherwise ionized
regions. Both effects damp the contrast between neutral and ionized patches
during reionization, making detection of the epoch of reionization with 21-cm
interferometry more challenging. Here we systematically investigate these
effects using the latest semi-numerical simulations. We find that sinks
dramatically suppress the peak in the redshift evolution of the variance,
corresponding to the midpoint of reionization. As previously predicted,
skewness changes sign at midpoint, but the fluctuations in the residual HI
suppress a late-time rise. Furthermore, large levels of residual HI
dramatically alter the evolution of the variance, skewness and power spectrum
from that seen at lower levels. In general, the evolution of the large-scale
modes provides a better, cleaner, higher signal-to-noise probe of reionization.Comment: Minor edits to agree with MNRAS published versio
Development of a general purpose airborne simulator
Variable stability system development for General Purpose Airborne Simulator /GPAS
Safety, the Preface Paradox and Possible Worlds Semantics
This paper contains an argument to the effect that possible worlds semantics renders
semantic knowledge impossible, no matter what ontological interpretation is given
to possible worlds. The essential contention made is that possible worlds semantic
knowledge is unsafe and this is shown by a parallel with the preface paradox
Senstitivty analysis and optimization of nodal point placement for vibration reduction
A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location - for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed
Hybrid Atom--Photon Quantum Gate in a Superconducting Microwave Resonator
We propose a novel hybrid quantum gate between an atom and a microwave photon
in a superconducting coplanar waveguide cavity by exploiting the strong
resonant microwave coupling between adjacent Rydberg states. Using
experimentally achievable parameters gate fidelities are possible on
sub-s timescales for waveguide temperatures below 40 mK. This provides a
mechanism for generating entanglement between two disparate quantum systems and
represents an important step in the creation of a hybrid quantum interface
applicable for both quantum simulation and quantum information processing.Comment: 4 pages, 4 figure
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