10,099 research outputs found
Dynamics of a FitzHugh-Nagumo system subjected to autocorrelated noise
We analyze the dynamics of the FitzHugh-Nagumo (FHN) model in the presence of
colored noise and a periodic signal. Two cases are considered: (i) the dynamics
of the membrane potential is affected by the noise, (ii) the slow dynamics of
the recovery variable is subject to noise. We investigate the role of the
colored noise on the neuron dynamics by the mean response time (MRT) of the
neuron. We find meaningful modifications of the resonant activation (RA) and
noise enhanced stability (NES) phenomena due to the correlation time of the
noise. For strongly correlated noise we observe suppression of NES effect and
persistence of RA phenomenon, with an efficiency enhancement of the neuronal
response. Finally we show that the self-correlation of the colored noise causes
a reduction of the effective noise intensity, which appears as a rescaling of
the fluctuations affecting the FHN system.Comment: 13 pages, 10 figure
Time Horizon and Cooperation in Continuous Time
When subjects interact in continuous time, their ability to cooperate may dramatically increase. In an experiment, we study the impact of different time horizons on cooperation in (quasi) continuous time prisoner's dilemmas. We find that cooperation levels are similar or higher when the horizon is deterministic rather than stochastic. Moreover, a deterministic duration generates different aggregate patterns and individual strategies than a stochastic one. For instance, under a deterministic horizon subjects show high initial cooperation and a strong end-of-period reversal to defection. Moreover, they do not learn to apply backward induction but to postpone defection closer to the end.
Design of a Lambda system for population transfer in superconducting nanocircuits
The implementation of a Lambda scheme in superconducting artificial atoms
could allow detec- tion of stimulated Raman adiabatic passage (STIRAP) and
other quantum manipulations in the microwave regime. However symmetries which
on one hand protect the system against decoherence, yield selection rules which
may cancel coupling to the pump external drive. The tradeoff between efficient
coupling and decoherence due to broad-band colored Noise (BBCN), which is often
the main source of decoherence is addressed, in the class of nanodevices based
on the Cooper pair box (CPB) design. We study transfer efficiency by STIRAP,
showing that substantial efficiency is achieved for off-symmetric bias only in
the charge-phase regime. We find a number of results uniquely due to
non-Markovianity of BBCN, namely: (a) the efficiency for STIRAP depends
essentially on noise channels in the trapped subspace; (b) low-frequency
fluctuations can be analyzed and represented as fictitious correlated
fluctuations of the detunings of the external drives; (c) a simple figure of
merit for design and operating prescriptions allowing the observation of STIRAP
is proposed. The emerging physical picture also applies to other classes of
coherent nanodevices subject to BBCN.Comment: 14 pages, 11 figure
Thermal modeling of terahertz quantum-cascade lasers: comparison of optical waveguides
We compare a set of experimental lattice temperature profiles measured in a surface-emitting terahertz (THz) quantum-cascade laser (QCL) with the results of a 2-D anisotropic heat diffusion model. We evaluate the temperature dependence of the cross-plane thermal conductivity (kappaperp) of the active region which is known to be strongly anisotropic due to its superlattice-like nature. Knowledge of kappaperp and its temperature dependence is crucial in order to improve the temperature performance of THz QCLs and this has been used to investigate the longitudinal lattice temperature distribution of the active region and to compare the thermal properties of metal-metal and semi-insulating surface-plasmon THz optical waveguides using a 3-D anisotropic heat diffusion model
Noise Induced Phenomena in the Dynamics of Two Competing Species
Noise through its interaction with the nonlinearity of the living systems can
give rise to counter-intuitive phenomena. In this paper we shortly review noise
induced effects in different ecosystems, in which two populations compete for
the same resources. We also present new results on spatial patterns of two
populations, while modeling real distributions of anchovies and sardines. The
transient dynamics of these ecosystems are analyzed through generalized
Lotka-Volterra equations in the presence of multiplicative noise, which models
the interaction between the species and the environment. We find noise induced
phenomena such as quasi-deterministic oscillations, stochastic resonance, noise
delayed extinction, and noise induced pattern formation. In addition, our
theoretical results are validated with experimental findings. Specifically the
results, obtained by a coupled map lattice model, well reproduce the spatial
distributions of anchovies and sardines, observed in a marine ecosystem.
Moreover, the experimental dynamical behavior of two competing bacterial
populations in a meat product and the probability distribution at long times of
one of them are well reproduced by a stochastic microbial predictive model.Comment: 23 pages, 8 figures; to be published in Math. Model. Nat. Phenom.
(2016
Farmacoeconomia ed etica: cure sostenibili e rispetto della persona
The scarcity of economic resources today is a fundamental problem in public healthcare. The importance of making well-founded choices for optimal resources allocation concerns also pharmacological treatments and is justified also on ethical grounds, besides the economic, political and/or medical considerations. In fact, a better management, also in economic sense, of the patient and sickness involves the possibility of offering an efficient treatment to all the sick, or at least to as many of them as possible. However, these considerations should always be subordinated to the ethical centrality of the patient, to the protection of his life, his health and his personal dignity, to the extent that life and health are priceless. The goal of ethics in pharmacoeconomics can be summarised in respect for the person, which must remain the end and reference of every therapeutic choice as well as every healthcare policy. The indispensable instruments for the realisation of the above objectives are, amongst others, those already highlighted but which demand further explanation: a) a suitable standard background/training and a multidisciplinary approach for optimising the evaluation procedures and increasing accuracy and verifiableness of the data; b) measures to contrast and disclose the conflict of interest for more transparency and credibility; c) a coherent evaluation of the ethical quality and humanness of the pharmacoeconomic analysis which requires a correct consideration of quality of life and a real respect for persons
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