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An overview of three approaches to scoring written essays by computer
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Arbitrary-order Hilbert spectral analysis for time series possessing scaling statistics: a comparison study with detrended fluctuation analysis and wavelet leaders
In this paper we present an extended version of Hilbert-Huang transform,
namely arbitrary-order Hilbert spectral analysis, to characterize the
scale-invariant properties of a time series directly in an amplitude-frequency
space. We first show numerically that due to a nonlinear distortion,
traditional methods require high-order harmonic components to represent
nonlinear processes, except for the Hilbert-based method. This will lead to an
artificial energy flux from the low-frequency (large scale) to the
high-frequency (small scale) part. Thus the power law, if it exists, is
contaminated. We then compare the Hilbert method with structure functions (SF),
detrended fluctuation analysis (DFA), and wavelet leader (WL) by analyzing
fractional Brownian motion and synthesized multifractal time series. For the
former simulation, we find that all methods provide comparable results. For the
latter simulation, we perform simulations with an intermittent parameter {\mu}
= 0.15. We find that the SF underestimates scaling exponent when q > 3. The
Hilbert method provides a slight underestimation when q > 5. However, both DFA
and WL overestimate the scaling exponents when q > 5. It seems that Hilbert and
DFA methods provide better singularity spectra than SF and WL. We finally apply
all methods to a passive scalar (temperature) data obtained from a jet
experiment with a Taylor's microscale Reynolds number Relambda \simeq 250. Due
to the presence of strong ramp-cliff structures, the SF fails to detect the
power law behavior. For the traditional method, the ramp-cliff structure causes
a serious artificial energy flux from the low-frequency (large scale) to the
high-frequency (small scale) part. Thus DFA and WL underestimate the scaling
exponents. However, the Hilbert method provides scaling exponents
{\xi}{\theta}(q) quite close to the one for longitudinal velocity.Comment: 13 pages, 10 figure
Turbulent transport of material particles: An experimental study of finite size effects
We use an acoustic Lagrangian tracking technique, particularly adapted to
measurements in open flows, and a versatile material particles generator (in
the form of soap bubbles with adjustable size and density) to characterize
Lagrangian statistics of finite sized, neutrally bouyant, particles transported
in an isotropic turbulent flow of air. We vary the size of the particles in a
range corresponding to turbulent inertial scales and explore how the turbulent
forcing experienced by the particles depends on their size. We show that, while
the global shape of the intermittent acceleration probability density function
does not depend significantly on particle size, the acceleration variance of
the particles decreases as they become larger in agreement with the classical
scaling for the spectrum of Eulerian pressure fluctuations in the carrier flow
A dissipative random velocity field for fully developed fluid turbulence
We investigate the statistical properties, based on numerical simulations and
analytical calculations, of a recently proposed stochastic model for the
velocity field of an incompressible, homogeneous, isotropic and fully developed
turbulent flow. A key step in the construction of this model is the
introduction of some aspects of the vorticity stretching mechanism that governs
the dynamics of fluid particles along their trajectory. An additional further
phenomenological step aimed at including the long range correlated nature of
turbulence makes this model depending on a single free parameter that
can be estimated from experimental measurements. We confirm the realism of the
model regarding the geometry of the velocity gradient tensor, the power-law
behaviour of the moments of velocity increments (i.e. the structure functions),
including the intermittent corrections, and the existence of energy transfers
across scales. We quantify the dependence of these basic properties of
turbulent flows on the free parameter and derive analytically the
spectrum of exponents of the structure functions in a simplified non
dissipative case. A perturbative expansion in power of shows that
energy transfers, at leading order, indeed take place, justifying the
dissipative nature of this random field.Comment: 38 pages, 5 figure
Development of a Low-Lift Chiller Controller and Simplified Precooling Control Algorithm - Final Report
KGS Buildings LLC (KGS) and Pacific Northwest National Laboratory (PNNL) have developed a simplified control algorithm and prototype low-lift chiller controller suitable for model-predictive control in a demonstration project of low-lift cooling. Low-lift cooling is a highly efficient cooling strategy conceived to enable low or net-zero energy buildings. A low-lift cooling system consists of a high efficiency low-lift chiller, radiant cooling, thermal storage, and model-predictive control to pre-cool thermal storage overnight on an optimal cooling rate trajectory. We call the properly integrated and controlled combination of these elements a low-lift cooling system (LLCS). This document is the final report for that project
Spatially-Resolved Spectra of the "Teacup" AGN: Tracing the History of a Dying Quasar
The Sloan Digital Sky Survey (SDSS) Galaxy Zoo project has revealed a number
of spectacular galaxies possessing Extended Emission-Line Regions (EELRs), the
most famous being Hanny's Voorwerp galaxy. We present another EELR object
discovered in the SDSS endeavor: the Teacup Active Galactic Nucleus (AGN),
nicknamed for its EELR, which has a handle like structure protruding 15 kpc
into the northeast quadrant of the galaxy. We analyze physical conditions of
this galaxy with long-slit ground based spectroscopy from Lowell, Lick, and
KPNO observatories. With the Lowell 1.8m Perkin's telescope we took multiple
observations at different offset positions, allowing us to recover spatially
resolved spectra across the galaxy. Line diagnostics indicate the ionized gas
is photoionized primarily by the AGN. Additionally we are able to derive the
hydrogen density from the [S II] 6716/6731 ratio. We generated two-component
photoionization models for each spatially resolved Lowell spectrum. These
models allow us to calculate the AGN bolometric luminosity seen by the gas at
different radii from the nuclear center of the Teacup. Our results show a drop
in bolometric luminosity by more than two orders of magnitude from the EELR to
the nucleus, suggesting that the AGN has decreased in luminosity by this amount
in a continuous fashion over 46,000 years, supporting the case for a dying AGN
in this galaxy independent of any IR based evidence. We demonstrate that
spatially resolved photoionization modeling could be applied to EELRs to
investigate long time scale variability.Comment: 38 pages, 11 figures, accepted for publication in the Astrophysical
Journa
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