343 research outputs found
Increasing the Reliability of Adaptive Quadrature Using Explicit Interpolants
We present two new adaptive quadrature routines. Both routines differ from
previously published algorithms in many aspects, most significantly in how they
represent the integrand, how they treat non-numerical values of the integrand,
how they deal with improper divergent integrals and how they estimate the
integration error. The main focus of these improvements is to increase the
reliability of the algorithms without significantly impacting their efficiency.
Both algorithms are implemented in Matlab and tested using both the "families"
suggested by Lyness and Kaganove and the battery test used by Gander and
Gautschi and Kahaner. They are shown to be more reliable, albeit in some cases
less efficient, than other commonly-used adaptive integrators.Comment: 32 pages, submitted to ACM Transactions on Mathematical Softwar
Spatial methods for event reconstruction in CLEAN
In CLEAN (Cryogenic Low Energy Astrophysics with Noble gases), a proposed
neutrino and dark matter detector, background discrimination is possible if one
can determine the location of an ionizing radiation event with high accuracy.
We simulate ionizing radiation events that produce multiple scintillation
photons within a spherical detection volume filled with liquid neon. We
estimate the radial location of a particular ionizing radiation event based on
the observed count data corresponding to that event. The count data are
collected by detectors mounted at the spherical boundary of the detection
volume. We neglect absorption, but account for Rayleigh scattering. To account
for wavelength-shifting of the scintillation light, we assume that photons are
absorbed and re-emitted at the detectors. Here, we develop spatial Maximum
Likelihood methods for event reconstruction, and study their performance in
computer simulation experiments. We also study a method based on the centroid
of the observed count data. We calibrate our estimates based on training data
Checklists and illustrative financial statements for common interest realty associations: a financial accounting and reporting practice aid, June 1992 edtion
https://egrove.olemiss.edu/aicpa_indev/1734/thumbnail.jp
The Cosmic Linear Anisotropy Solving System (CLASS) IV: Efficient implementation of non-cold relics
We present a new flexible, fast and accurate way to implement massive
neutrinos, warm dark matter and any other non-cold dark matter relics in
Boltzmann codes. For whatever analytical or numerical form of the phase-space
distribution function, the optimal sampling in momentum space compatible with a
given level of accuracy is automatically found by comparing quadrature methods.
The perturbation integration is made even faster by switching to an approximate
viscous fluid description inside the Hubble radius, which differs from previous
approximations discussed in the literature. When adding one massive neutrino to
the minimal cosmological model, CLASS becomes just 1.5 times slower, instead of
about 5 times in other codes (for fixed accuracy requirements). We illustrate
the flexibility of our approach by considering a few examples of standard or
non-standard neutrinos, as well as warm dark matter models.Comment: 23 pages, 8 figures, 3 tables. Matches published version. Code
available at http://class-code.ne
Optimal Power Management Strategy for Energy Storage with Stochastic Loads
In this paper, a power management strategy (PMS) has been developed for the control of energy storage in a system subjected to loads of random duration. The PMS minimises the costs associated with the energy consumption of specific systems powered by a primary energy source and equipped with energy storage, under the assumption that the statistical distribution of load durations is known. By including the variability of the load in the cost function, it was possible to define the optimality criteria for the power flow of the storage. Numerical calculations have been performed obtaining the control strategies associated with the global minimum in energy costs, for a wide range of initial conditions of the system. The results of the calculations have been tested on a MATLAB/Simulink model of a rubber tyre gantry (RTG) crane equipped with a flywheel energy storage system (FESS) and subjected to a test cycle, which corresponds to the real operation of a crane in the Port of Felixstowe. The results of the model show increased energy savings and reduced peak power demand with respect to existing control strategies, indicating considerable potential savings for port operators in terms of energy and maintenance costs
Point Contact Spectroscopy of Superconducting Gap Anisotropy in Nickel Borocarbide Compound LuNi2B2C
Point contacts are used to investigate the anisotropy of the superconducting
energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that
the experimental curves should be described assuming that the superconducting
gap is non-uniformly distributed over the Fermi surface. The largest and the
smallest gaps have been estimated by two-gap fitting models. It is found that
the largest contribution to the point-contact conductivity in the c direction
is made by a smaller gap and, in the ab plane by a larger gap. The deviation
from the one-gap BCS model is pronounced in the temperature dependence of the
gap in both directions. The temperature range, where the deviation occurs, is
for the c direction approximately 1.5 times more than in the ab plane. The
\Gamma parameter, allowing quantitatively estimate the gap anisotropy by
one-gap fitting, in c direction is also about 1.5 times greater than in the ab
plane. Since it is impossible to describe satisfactorily such gap distribution
either by the one- or two-gap models, a continuous, dual-maxima model of gap
distribution over the Fermi surface should be used to describe
superconductivity in this material.Comment: 10 pages, 14 Figs, accepted in PR
Relaxation rates and collision integrals for Bose-Einstein condensates
Near equilibrium, the rate of relaxation to equilibrium and the transport
properties of excitations (bogolons) in a dilute Bose-Einstein condensate (BEC)
are determined by three collision integrals, ,
, and . All three collision integrals
conserve momentum and energy during bogolon collisions, but only conserves bogolon number. Previous works have considered the
contribution of only two collision integrals, and . In this work, we show that the third collision integral makes a significant contribution to the bogolon number
relaxation rate and needs to be retained when computing relaxation properties
of the BEC. We provide values of relaxation rates in a form that can be applied
to a variety of dilute Bose-Einstein condensates.Comment: 18 pages, 4 figures, accepted by Journal of Low Temperature Physics
7/201
Longitudinal quantile regression in presence of informative drop-out through longitudinal-survival joint modeling
We propose a joint model for a time-to-event outcome and a quantile of a
continuous response repeatedly measured over time. The quantile and survival
processes are associated via shared latent and manifest variables. Our joint
model provides a flexible approach to handle informative drop-out in quantile
regression. A general Monte Carlo Expectation Maximization strategy based on
importance sampling is proposed, which is directly applicable under any
distributional assumption for the longitudinal outcome and random effects, and
parametric and non-parametric assumptions for the baseline hazard. Model
properties are illustrated through a simulation study and an application to an
original data set about dilated cardiomyopathies
Time-Frequency Analysis of Superorbital Modulation of X-ray Binary SMC X-1 by Hilbert-Huang Transform
The high-mass X-ray binary (HMXB) SMC X-1 exhibits a superorbital modulation
with a dramatically varying period ranging between ~40 d and ~60 d. This
research studies the time-frequency properties of the superorbital modulation
of SMC X-1 based on the observations made by the All-Sky Monitor (ASM) onboard
the Rossi X-ray Timing Explorer (RXTE).We analyzed the entire ASM database
collected since 1996. The Hilbert-Huang Transform (HHT), developed for
non-stationary and nonlinear time series analysis, was adopted to derive the
instantaneous superorbital frequency. The resultant Hilbert spectrum is
consistent with the dynamic power spectrum while it shows more detailed
information in both the time and frequency domains. The RXTE observations
manifest that the superorbital modulation period was mostly betweenn ~50 d and
~65 d, whenas it changed to ~45 d around MJD 50,800 and MJD 54,000. Our
analysis further indicates that the instantaneous frequency changed in a time
scale of hundreds of days between ~MJD 51,500 and ~MJD 53,500. Based on the
instantaneous phase defined by HHT, we folded the ASM light curve to derive a
superorbital profile, from which an asymmetric feature and a low state with
barely any X-ray emissions (lasting for ~0.3 cycles) were observed. We also
calculated the correlation between the mean period and the amplitude of the
superorbital modulation. The result is similar to the recently discovered
relationship between the superorbital cycle length and the mean X-ray flux for
Her X-1.Comment: 26 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Real structured singular value synthesis using the scaled Popov criterion
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77238/1/AIAA-21537-608.pd
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