245,150 research outputs found
Period Estimation in Astronomical Time Series Using Slotted Correntropy
In this letter, we propose a method for period estimation in light curves
from periodic variable stars using correntropy. Light curves are astronomical
time series of stellar brightness over time, and are characterized as being
noisy and unevenly sampled. We propose to use slotted time lags in order to
estimate correntropy directly from irregularly sampled time series. A new
information theoretic metric is proposed for discriminating among the peaks of
the correntropy spectral density. The slotted correntropy method outperformed
slotted correlation, string length, VarTools (Lomb-Scargle periodogram and
Analysis of Variance), and SigSpec applications on a set of light curves drawn
from the MACHO survey
A Study on the Integration of a High-Speed Flywheel as an Energy Storage Device in Hybrid Vehicles
The last couple of decades have seen the rise of the hybrid electric vehicle as a compromise between the outstanding specific energy of petrol fuels and its low-cost technology, and the zero tail-gate emissions of the electric vehicle. Despite this, considerable reductions in cost and further increases in fuel economy are needed for their widespread adoption.
An alternative low-cost energy storage technology for vehicles is the high-speed flywheel. The flywheel has important limitations that exclude it from being used as a primary energy source for vehicles, but its power characteristics and low-cost materials make it a powerful complement to a vehicle's primary propulsion system. This thesis presents an analysis on the integration of a high-speed flywheel for use as a secondary energy storage device in hybrid vehicles.
Unlike other energy storage technologies, the energy content of the flywheel has a direct impact on the velocity of transmission. This presents an important challenge, as it means that the flywheel must be able to rotate at a speed independent of the vehicle's velocity and therefore it must be coupled via a variable speed transmission. This thesis presents some practical ways in which to accomplish this in conventional road vehicles, namely with the use of a variator, a planetary gear set or with the use of a power-split continuously variable transmission. Fundamental analyses on the kinematic behaviour of these transmissions particularly as they pertain to flywheel powertrains are presented. Computer simulations were carried out to compare the performance of various transmissions, and the models developed are presented as well.
Finally the thesis also contains an investigation on the driving and road conditions that have the most beneficial effect on hybrid vehicle performance, with a particular emphasis on the effect that the road topography has on fuel economy and the significance of this
Holographic studies of Einsteinian cubic gravity
Einsteinian cubic gravity provides a holographic toy model of a
nonsupersymmetric CFT in three dimensions, analogous to the one defined by
Quasi-topological gravity in four. The theory admits explicit non-hairy AdS
black holes and allows for numerous exact calculations, fully nonperturbative
in the new coupling. We identify several entries of the AdS/CFT dictionary for
this theory, and study its thermodynamic phase space, finding interesting new
phenomena. We also analyze the dependence of R\'enyi entropies for disk regions
on universal quantities characterizing the CFT. In addition, we show that
is given by a non-analytic function of the ECG coupling, and that the
existence of positive-energy black holes strictly forbids violations of the KSS
bound. Along the way, we introduce a new method for evaluating Euclidean
on-shell actions for general higher-order gravities possessing second-order
linearized equations on AdS. Our generalized action involves the very
same Gibbons-Hawking boundary term and counterterms valid for Einstein gravity,
which now appear weighted by the universal charge controlling the
entanglement entropy across a spherical region in the CFT dual to the
corresponding higher-order theory.Comment: 59 pages, 7 figures, 1 table; v4: typos fixe
Modeling Opinion Dynamics: Theoretical analysis and continuous approximation
Frequently we revise our first opinions after talking over with other
individuals because we get convinced. Argumentation is a verbal and social
process aimed at convincing. It includes conversation and persuasion. In this
case, the agreement is reached because the new arguments are incorporated. In
this paper we deal with a simple model of opinion formation with such
persuasion dynamics, and we find the exact analytical solutions for both, long
and short range interactions. A novel theoretical approach has been used in
order to solve the master equations of the model with non-local kernels.
Simulation results demonstrate an excellent agreement with results obtained by
the theoretical estimation.Comment: 15 pages, 3 figure
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