730 research outputs found
Experimental evidence for vibrational resonance and enhanced signal transmission in Chua's circuit
We consider a single Chua's circuit and a system of a unidirectionally
coupled n-Chua's circuits driven by a biharmonic signal with two widely
different frequencies \omega and \Omega, where \Omega >> \omega. We show
experimental evidence for vibrational resonance in the single Chua's circuit
and undamped signal propagation of a low-frequency signal in the system of
n-coupled Chua's circuits where only the first circuit is driven by the
biharmonic signal. In the single circuit, we illustrate the mechanism of
vibrational resonance and the influence of the biharmonic signal parameters on
the resonance. In the n(= 75)-coupled Chua's circuits enhanced propagation of
low-frequency signal is found to occur for a wide range of values of the
amplitude of the high-frequency input signal and coupling parameter. The
response amplitude of the ith circuit increases with i and attains a
saturation. Moreover, the unidirectional coupling is found to act as a low-pass
filter.Comment: 15 pages, 12 figures, Accepted for Publication in International
Journal of Bifurcation and Chao
A mechanism explaining the metamorphoses of KAM islands in nonhyperbolic chaotic scattering
In the context of nonhyperbolic chaotic scattering, it has been shown that the evolution of the KAM islands exhibits four abrupt metamorphoses that strongly affect the predictability of Hamiltonian systems. It has been suggested that these metamorphoses are related to significant changes in the structure of the KAM islands. However, previous research has not provided an explanation of the mechanisms underlying the metamorphoses. Here, we show that they occur due to the formation of a homoclinic or heteroclinic tangle that breaks the internal structure of the main KAM island. We obtain similar qualitative results in a two-dimensional Hamiltonian system and a two-dimensional area-preserving map. The equivalence of the results obtained in both systems suggests that the same four metamorphoses play an important role in conservative systems
Thermal diagnostic of the Optical Window on board LISA Pathfinder
Vacuum conditions inside the LTP Gravitational Reference Sensor must comply
with rather demanding requirements. The Optical Window (OW) is an interface
which seals the vacuum enclosure and, at the same time, lets the laser beam go
through for interferometric Metrology with the test masses. The OW is a
plane-parallel plate clamped in a Titanium flange, and is considerably
sensitive to thermal and stress fluctuations. It is critical for the required
precision measurements, hence its temperature will be carefully monitored in
flight. This paper reports on the results of a series of OW characterisation
laboratory runs, intended to study its response to selected thermal signals, as
well as their fit to numerical models, and the meaning of the latter. We find
that a single pole ARMA transfer function provides a consistent approximation
to the OW response to thermal excitations, and derive a relationship with the
physical processes taking place in the OW. We also show how system noise
reduction can be accomplished by means of that transfer function.Comment: 20 pages, 14 figures; accepted for publication in Class. Quantum Gra
The Role of Noise in the Tumor Dynamics under Chemotherapy Treatment
Dynamical systems modeling tumor growth have been investigated to analyze the dynamics between tumor and healthy cells. Recent theoretical studies indicate that these interactions may lead to different dynamical outcomes under the effect of particular cancer therapies. In the present paper, we derive a system of nonlinear differential equations, in order to investigate solid tumors in vivo, taking into account the impact of chemotherapy on both tumor and healthy cells. We start by studying our model only in terms of deterministic dynamics under the variation of a drug concentration parameter. Later, with the introduction of noise, a stochastic model is used to analyze the impact of the unavoidable random fluctuations. As a result, new insights into noise-induced transitions are provided and illustrated in detail using techniques from dynamical systems and from the theory of stochastic processes. © 2021, The Author(s).The work of IB and LR on the analysis of noise-induced phenomena was supported by Russian Science Foundation (21-11-00062). The work on the deterministic analysis has been financially supported by the Portuguese Foundation for Science and Technology (FCT) under Project No. UID/MAT/04459/2013 (JD) and by the Spanish State Research Agency (AEI) and the European Regional Development Fund (ERDF, EU) under Project No. PID2019-105554GB-I00 (JMS and MAFS)
Stellar populations of galaxies in the ALHAMBRA survey up to . II. Stellar content of quiescent galaxies within the dust-corrected stellar masscolour and the colourcolour diagrams
Our aim is to determine the distribution of stellar population parameters
(extinction, age, metallicity, and star formation rate) of quiescent galaxies
within the rest-frame stellar masscolour and colourcolour diagrams
corrected for extinction up to . These novel diagrams reduce the
contamination in samples of quiescent galaxies owing to dust-reddened galaxies,
and they provide useful constraints on stellar population parameters. We set
constraints on the stellar population parameters of quiescent galaxies
combining the ALHAMBRA multi-filter photo-spectra with our SED-fitting code
MUFFIT, making use of composite stellar population models. The extinction
obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from
the sample of red galaxies. The distributions of stellar population
parameters across these rest-frame diagrams are revealed after the dust
correction and are fitted by the LOESS method to reduce uncertainty effects.
Quiescent galaxy samples defined via classical diagrams are typically
contaminated by a % fraction of DSF galaxies. A significant part of the
galaxies in the green valley are actually obscured star-forming galaxies
(%). Consequently, the transition of galaxies from the blue cloud to
the red sequence, and hence the related mechanisms for quenching, seems to be
much more efficient and faster than previously reported. The rest-frame stellar
masscolour and colourcolour diagrams are useful for constraining
the age, metallicity, extinction, and star formation rate of quiescent galaxies
by only their redshift, rest-frame colours, and/or stellar mass. Dust
correction plays an important role in understanding how quiescent galaxies are
distributed in these diagrams and is key to performing a pure selection of
quiescent galaxies via intrinsic colours.Comment: (37 pages, 29 figures, accepted for publication in A&A
The ALHAMBRA survey: An empirical estimation of the cosmic variance for merger fraction studies based on close pairs
Aims. Our goal is to estimate empirically the cosmic variance that affects merger fraction studies based on close pairs for the first time.
Methods. We compute the merger fraction from photometric redshift close pairs with 10 h-1 kpc ≤ rp ≤ 50 h-1 kpc and Δv ≤ 500 km s-1 and measure it in the 48 sub-fields of the ALHAMBRA survey. We study the distribution of the measured merger fractions that follow a log-normal function and estimate the cosmic variance σv as the intrinsic dispersion of the observed distribution. We develop a maximum likelihood estimator to measure a reliable σv and avoid the dispersion due to the observational errors (including the Poisson shot noise term).
Results. The cosmic variance σv of the merger fraction depends mainly on (i) the number density of the populations under study for both the principal (n1) and the companion (n2) galaxy in the close pair and (ii) the probed cosmic volume Vc. We do not find a significant dependence on either the search radius used to define close companions, the redshift, or the physical selection (luminosity or stellar mass) of the samples.
Conclusions. We have estimated the cosmic variance that affects the measurement of the merger fraction by close pairs from observations. We provide a parametrisation of the cosmic variance with n1, n2, and Vc, σv ∝ n1-0.54Vc-0.48 (n_2/n_1)-0.37 . Thanks to this prescription, future merger fraction studies based on close pairs could properly account for the cosmic variance on their results
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