41,951 research outputs found
The Development of a Fiber Optic Raman Temperature Measurement System for Rocket Flows
A fiberoptic Raman diagnostic system for H2/O2 rocket flows is currently under development. This system is designed for measurement of temperature and major species concentration in the combustion chamber and part of the nozzle of a 100 Newton thrust rocket currently undergoing testing. This paper describes a measurement system based on the spontaneous Raman scattering phenomenon. An analysis of the principles behind the technique is given. Software is developed to measure temperature and major species concentrations by comparing theoretical Raman scattering spectra with experimentally obtained spectra. Equipment selection and experimental approach are summarized. This experimental program is part of a program, which is in progress, to evaluate Navier-Stokes based analyses for this class of rocket
Stellar photometry with Multi Conjugate Adaptive Optics
We overview the current status of photometric analyses of images collected
with Multi Conjugate Adaptive Optics (MCAO) at 8-10m class telescopes that
operated, or are operating, on sky. Particular attention will be payed to
resolved stellar population studies. Stars in crowded stellar systems, such as
globular clusters or in nearby galaxies, are ideal test particles to test AO
performance. We will focus the discussion on photometric precision and accuracy
reached nowadays. We briefly describe our project on stellar photometry and
astrometry of Galactic globular clusters using images taken with GeMS at the
Gemini South telescope. We also present the photometry performed with DAOPHOT
suite of programs into the crowded regions of these globulars reaching very
faint limiting magnitudes Ks ~21.5 mag on moderately large fields of view (~1.5
arcmin squared). We highlight the need for new algorithms to improve the
modeling of the complex variation of the Point Spread Function across the field
of view. Finally, we outline the role that large samples of stellar standards
plays in providing a detailed description of the MCAO performance and in
precise and accurate colour{magnitude diagrams.Comment: 17 pages, 12 figures, SPIE 201
Detection of Dispersed Radio Pulses: A machine learning approach to candidate identification and classification
Searching for extraterrestrial, transient signals in astronomical data sets
is an active area of current research. However, machine learning techniques are
lacking in the literature concerning single-pulse detection. This paper
presents a new, two-stage approach for identifying and classifying dispersed
pulse groups (DPGs) in single-pulse search output. The first stage identified
DPGs and extracted features to characterize them using a new peak
identification algorithm which tracks sloping tendencies around local maxima in
plots of signal-to-noise ratio vs. dispersion measure. The second stage used
supervised machine learning to classify DPGs. We created four benchmark data
sets: one unbalanced and three balanced versions using three different
imbalance treatments.We empirically evaluated 48 classifiers by training and
testing binary and multiclass versions of six machine learning algorithms on
each of the four benchmark versions. While each classifier had advantages and
disadvantages, all classifiers with imbalance treatments had higher recall
values than those with unbalanced data, regardless of the machine learning
algorithm used. Based on the benchmarking results, we selected a subset of
classifiers to classify the full, unlabelled data set of over 1.5 million DPGs
identified in 42,405 observations made by the Green Bank Telescope. Overall,
the classifiers using a multiclass ensemble tree learner in combination with
two oversampling imbalance treatments were the most efficient; they identified
additional known pulsars not in the benchmark data set and provided six
potential discoveries, with significantly less false positives than the other
classifiers.Comment: 13 pages, accepted for publication in MNRAS, ref. MN-15-1713-MJ.R
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