Virtual testing environment tools for railway vehicle certification

This paper describes the work performed in Work Package 6 of the European project DynoTRAIN. Its task was to investigate the effects that uncertainties present within the track and running conditions have on the simulated behaviour of a railway vehicle. Methodologies and frameworks for using virtual simulation and statistical tools, in order to reduce both the cost and time required for the certification of new or modified railway vehicles, were proposed. In particular, the project developed a virtual test track (VTT) toolkit that is capable of both generating a series of test tracks based on measurements, which can be used in vehicle virtual testing using computer simulation models, and also automatically handling the output results. The toolkit is compliant with prEN14363: 2013. The VTT was used as an experimental tool to analyse cross-correlations between track data (input) and matching vehicle response (output) based on data recorded using a test train. This paper discusses the issues encountered in the process and suggests avenues for future developments and potential use in the context of European cross-acceptance. The VTT offers benefits to the areas of design development and regulatory certification

Observational study on risk factors determining residual dizziness after successful benign paroxysmal positional vertigo treatment: The role of subclinical BPPV

After successful treatment for benign paroxysmal positional vertigo, many patients may complain of residual dizziness. Possible explanations may be the persistence of otolith into canal insufficient to provoke noticeable nystagmus, utricular dysfunction and undiagnosed coexisting vestibular disorder. We conducted a prospective observational case-control study, focusing on the role of risk factors in determining residual dizziness after BPPV treatment. In the present study, 148 patients were recruited and residual dizziness was documented in the 57.5% of the cohort. Among patients with residual dizziness 36 had subclinical BPPV and after retreatment, although nystagmus was not clinically evident, there was resolution of dizziness. We conclude that residual otoliths may play a role in determining post-maneuver residual dizziness that is often linked to subclinical BPPV; this conclusion is also supported by the high prevalence of BPPV recurrence in patients with residual dizziness, as confirmed by our analysis. The main cause appears to be linked with dispersed otolith in semicircular canals

Fluctuations in the Ensemble of Reaction Pathways

The dominant reaction pathway (DRP) is a rigorous framework to microscopically compute the most probable trajectories, in non-equilibrium transitions. In the low-temperature regime, such dominant pathways encode the information about the reaction mechanism and can be used to estimate non-equilibrium averages of arbitrary observables. On the other hand, at sufficiently high temperatures, the stochastic fluctuations around the dominant paths become important and have to be taken into account. In this work, we develop a technique to systematically include the effects of such stochastic fluctuations, to order k_B T. This method is used to compute the probability for a transition to take place through a specific reaction channel and to evaluate the reaction rate

Sudden transition between classical and quantum decoherence

We study the dynamics of quantum and classical correlations in the presence of nondissipative decoherence. We discover a class of initial states for which the quantum correlations, quantified by the quantum discord, are not destroyed by decoherence for times t < \bar{t}. In this initial time interval classical correlations decay. For t > \bar{t}, on the other hand, classical correlations do not change in time and only quantum correlations are lost due to the interaction with the environment. Therefore, at the transition time \bar{t} the open system dynamics exhibits a sudden transition from classical to quantum decoherence regime.Comment: version accepted for publication by Physical Review Letter

Experimental Studies of Bulk Optically Controlled GaAs Switches Utilizing Fast Infrared Quenching

This dissertation describes some of the properties of copper-compensated, silicon-doped GaAs (Cu:Si:GaAs) with the purpose of demonstrating the feasibility of the Bulk Optically Controlled Switch (BOSS) concept. The BOSS concept involves the excitation of electrons or holes from selected deep centers in the band gap of a bulk Cu:Si:GaAs photoconductor. The conductivity of the Cu:Si:GaAs crystal can be increased or decreased on command by irradiating the crystal with laser light of different wavelengths in the infrared. Photoconductivities as large as 1 (Ω cm)-1 were measured to persist for microseconds after illumination by a 7 ns laser pulse with wavelength λ= 1064 nm. Strong optical quenching of this photoconductivity over a nanosecond time scale has been observed during illumination with a second laser pulse of wavelength λ \u3e 1500 nm. During the conduction phase, currents as large as 10 kA/cm2 have been measured after the crystal withstood fields as large as 19 kV/cm. Dark conductivities of GaAs crystals grown with a silicon doping density of 5 x 1016 cm-3 have been measured after copper diffusion to range from 1.5 x 10-2 (Ω cm)-1 to as low as 1.4 x 106 (Ω cm)-1. These differences are interpreted to be the result of controlled compensation of the crystal resulting in the conversion of the crystal from strongly n-type (undercompensated) to weakly p-type (overcompensated). The actual level of compensation at thermal equilibrium is shown to have an important effect on the photoconductivity properties of the crystal

The impact of early aging on visual perception of space and time.

Visual perception of space and time has been shown to rely on context dependency, an inferential process by which the average magnitude of a series of stimuli previously experienced acts as a prior during perception. This article aims to investigate the presence and evolution of this phenomenon in early aging. Two groups of participants belonging to two different age ranges (Young Adults: average age 28.8 years old; Older Adults: average age 62.8 years old) participated in the study performing a discrimination and a reproduction task, both in a spatial and temporal conditions. In particular, they were asked to evaluate lengths in the spatial domain and interval durations in the temporal one. Early aging resulted to be associated to a general decline of the perceptual acuity, which is particularly evident in the temporal condition. The context dependency phenomenon was preserved also during aging, maintaining similar levels as those exhibited by the younger group in both space and time perception. However, the older group showed a greater variability in context dependency among participants, perhaps due to different strategies used to face a higher uncertainty in the perceptual process

Sudden death and sudden birth of entanglement in common structured reservoirs

We study the exact entanglement dynamics of two qubits in a common structured reservoir. We demonstrate that, for certain classes of entangled states, entanglement sudden death occurs, while for certain initially factorized states, entanglement sudden birth takes place. The backaction of the non-Markovian reservoir is responsible for revivals of entanglement after sudden death has occurred, and also for periods of disentanglement following entanglement sudden birth.Comment: 4 pages, 2 figure

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