182 research outputs found
The Relationship of the Facial Nerve to the Condylar Process: A Cadaveric Study with Implications for Open Reduction Internal Fixation
Introduction. The mandibular condyle is the most common site of mandibular fracture. Surgical treatment of condylar fractures by open reduction and internal fixation (ORIF) demands direct visualization of the fracture. This project aimed to investigate the anatomic relationship of the tragus to the facial nerve and condylar process. Materials and Methods. Twelve fresh hemicadavers heads were used. An extended retromandibular/preauricular approach was utilized, with the incision being based parallel to the posterior edge of the ramus. Measurements were obtained from the tragus to the facial nerve and condylar process. Results. The temporozygomatic division of the facial nerve was encountered during each approach, crossing the mandible at the condylar neck. The mean tissue depth separating the facial nerve from the condylar neck was 5.5 mm (range: 3.5 mm–7 mm, SD 1.2 mm). The upper division of the facial nerve crossed the posterior border of the condylar process on average 2.31 cm (SD 0.10 cm) anterior to the tragus. Conclusions. This study suggests that the temporozygomatic division of the facial nerve will be encountered in most approaches to the condylar process. As visualization of the relationship of the facial nerve to condyle is often limited, recognition that, on average, 5.5 mm of tissue separates condylar process from nerve should help reduce the incidence of facial nerve injury during this procedure
Flowing with Time: a New Approach to Nonlinear Cosmological Perturbations
Nonlinear effects are crucial in order to compute the cosmological matter
power spectrum to the accuracy required by future generation surveys. Here, a
new approach is presented, in which the power spectrum, the bispectrum and
higher order correlations, are obtained -- at any redshift and for any momentum
scale -- by integrating a system of differential equations. The method is
similar to the familiar BBGKY hierarchy. Truncating at the level of the
trispectrum, the solution of the equations corresponds to the summation of an
infinite class of perturbative corrections. Compared to other resummation
frameworks, the scheme discussed here is particularly suited to cosmologies
other than LambdaCDM, such as those based on modifications of gravity and those
containing massive neutrinos. As a first application, we compute the Baryonic
Acoustic Oscillation feature of the power spectrum, and compare the results
with perturbation theory, the halo model, and N-body simulations. The
density-velocity and velocity-velocity power spectra are also computed, showing
that they are much less contaminated by nonlinearities than the density-density
one. The approach can be seen as a particular formulation of the
renormalization group, in which time is the flow parameter.Comment: 20 pages, 7 figures. Matches version published on JCA
Atomic parity non-conservation in francium: The FrPNC experiment at TRIUMF
The FrPNC Collaboration is constructing an on-line laser cooling and trapping apparatus at TRIUMF to measure atomic parity non-conservation (PNC) and nuclear anapole moments in a series of artificially produced francium isotopes. Francium’s simple electronic structure and enhanced parity violation make it a strong candidate for precision measurements of atomic PNC: the optical PNC and anapole-induced PNC effects are expected to be an order of magnitude larger in francium than in cesium. Atomic PNC experiments provide unique high precision tests of the Standard Model’s predictions for neutral current weak interactions at very low energies. Furthermore, precision measurements of nuclear anapole moments probe inter-nucleon weak interactions within the nucleus
Automated reliability assessment for spectroscopic redshift measurements
We present a new approach to automate the spectroscopic redshift reliability
assessment based on machine learning (ML) and characteristics of the redshift
probability density function (PDF).
We propose to rephrase the spectroscopic redshift estimation into a Bayesian
framework, in order to incorporate all sources of information and uncertainties
related to the redshift estimation process, and produce a redshift posterior
PDF that will be the starting-point for ML algorithms to provide an automated
assessment of a redshift reliability.
As a use case, public data from the VIMOS VLT Deep Survey is exploited to
present and test this new methodology. We first tried to reproduce the existing
reliability flags using supervised classification to describe different types
of redshift PDFs, but due to the subjective definition of these flags, soon
opted for a new homogeneous partitioning of the data into distinct clusters via
unsupervised classification. After assessing the accuracy of the new clusters
via resubstitution and test predictions, unlabelled data from preliminary mock
simulations for the Euclid space mission are projected into this mapping to
predict their redshift reliability labels.Comment: Submitted on 02 June 2017 (v1). Revised on 08 September 2017 (v2).
Latest version 28 September 2017 (this version v3
Data Deluge in Astrophysics: Photometric Redshifts as a Template Use Case
Astronomy has entered the big data era and Machine Learning based methods
have found widespread use in a large variety of astronomical applications. This
is demonstrated by the recent huge increase in the number of publications
making use of this new approach. The usage of machine learning methods, however
is still far from trivial and many problems still need to be solved. Using the
evaluation of photometric redshifts as a case study, we outline the main
problems and some ongoing efforts to solve them.Comment: 13 pages, 3 figures, Springer's Communications in Computer and
Information Science (CCIS), Vol. 82
Systematic effects on dark energy from 3D weak shear
We present an investigation into the potential effect of systematics inherent
in multi-band wide field surveys on the dark energy equation of state
determination for two 3D weak lensing methods. The weak lensing methods are a
geometric shear-ratio method and 3D cosmic shear. The analysis here uses an
extension of the Fisher matrix framework to jointly include photometric
redshift systematics, shear distortion systematics and intrinsic alignments. We
present results for DUNE and Pan-STARRS surveys. We show that assuming
systematic parameters are fixed, but possibly biased, results in potentially
large biases in dark energy parameters. We quantify any potential bias by
defining a Bias Figure of Merit. We also show the effect on the dark energy
Figure of Merit of marginalising over each systematic parameter individually.
We find that the largest effect on the Figure of Merit comes from uncertainty
in the photometric redshift systematic parameters. These can reduce the Figure
of Merit by up to a factor of 2 to 4 in both 3D weak lensing methods, if no
informative prior on the systematic parameters is applied. Shear distortion
systematics have a smaller overall effect. Intrinsic alignment effects can
reduce the Figure of Merit by up to a further factor of 2. This, however, is a
worst case scenario. By including prior information on systematic parameters
the Figure of Merit can be recovered to a large extent. We conclude that, as a
rule of thumb, given a realistic current understanding of intrinsic alignments
and photometric redshifts, then including all three primary systematic effects
reduces the Figure of Merit by at most a factor of 2, but that in reality this
factor should be much less. [abridged]Comment: 20 pages, 11 figures, submitted to MNRA
Luminous Red Galaxy Clustering at z~0.7 - First Results using AAOmega
We report on the AAT-AAOmega LRG Pilot observing run to establish the
feasibility of a large spectroscopic survey using the new AAOmega instrument.
We have selected Luminous Red Galaxies (LRGs) using single epoch SDSS
riz-photometry to i<20.5 and z<20.2. We have observed in 3 fields including the
COSMOS field and the COMBO-17 S11 field, obtaining a sample of ~600 redshift
z>=0.5 LRGs. Exposure times varied from 1 - 4 hours to determine the minimum
exposure for AAOmega to make an essentially complete LRG redshift survey in
average conditions. We show that LRG redshifts to i<20.5 can measured in
approximately 1.5hr exposures and present comparisons with 2SLAQ and COMBO-17
(photo-)redshifts. Crucially, the riz selection coupled with the 3-4 times
improved AAOmega throughput is shown to extend the LRG mean redshift from
z=0.55 for 2SLAQ to z=0.681+/- 0.005 for riz-selected LRGs. This extended range
is vital for maximising the S/N for the detection of the baryon acoustic
oscillations (BAOs). Furthermore, we show that the amplitude of LRG clustering
is s_0 = 9.9+/-0.7 h^-1 Mpc, as high as that seen in the 2SLAQ LRG Survey.
Consistent results for the real-space amplitude are found from projected and
semi-projected correlation functions. This high clustering amplitude is
consistent with a long-lived population whose bias evolves as predicted by a
simple ``high-peaks'' model. We conclude that a redshift survey of 360 000 LRGs
over 3000deg^2, with an effective volume some 4 times bigger than previously
used to detect BAO with LRGs, is possible with AAOmega in 170 nights.Comment: 12 pages, 7 figures, 8 tables, minor changes, matches published
versio
Photometric Selection of Emission Line Galaxies, Clustering Analysis and a Search for the ISW effect
We investigate the use of simple colour cuts applied to the SDSS optical
imaging to perform photometric selections of emission line galaxies out to z<1.
From colour-cuts using the SDSS g, r and i bands, we obtain mean photometric
redshifts of z=0.32+-0.08, z=0.44+-0.12 and z=0.65+-0.21. We further calibrate
our high redshift selection using spectroscopic observations with the AAOmega
spectrograph on the 4m Anglo-Australian Telescope (AAT), observing ~50-200
galaxy candidates in 4 separate fields. With just 1-hour of integration time
and with seeing of ~1.6", we successfully determined redshifts for ~65% of the
targeted candidates. We calculate the angular correlation functions of the
samples and find correlation lengths of r0=2.64 h-1 Mpc, r0=3.62 h-1 Mpc and
r0=5.88 h-1 Mpc for the low, mid and high redshift samples respectively.
Comparing these results with predicted dark matter clustering, we estimate the
bias parameter for each sample to be b=0.70, b=0.92 and b=1.46. We calculate
the 2-point redshift-space correlation function at z~0.6 and find a clustering
amplitude of s0=6.4 h-1 Mpc. Finally, we use our photometric sample to search
for the Integrated Sachs-Wolfe signal in the WMAP 5yr data. We cross-correlate
our three redshift samples with the WMAP W, V, Q and K bands and find an
overall trend for a positive signal similar to that expected from models.
However, the signal in each is relatively weak. Combining all three galaxy
samples we find a signal of wTg(<100')=0.20+-0.12 microK in the WMAP W-band, a
significance of 1.7sigma.Comment: 14 pages, 17 figures, submitted to MNRA
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