Vacuum field correlations and three-body Casimir-Polder potential with one excited atom

The three-body Casimir-Polder potential between one excited and two ground-state atoms is evaluated. A physical model based on the dressed field correlations of vacuum fluctuations is used, generalizing a model previously introduced for three ground-state atoms. Although the three-body potential with one excited atom is already known in the literature, our model gives new insights on the nature of non-additive Casimir-Polder forces with one or more excited atoms.Comment: 9 page

Dynamical Casimir-Polder energy between an excited and a ground-state atom

We consider the Casimir-Polder interaction between two atoms, one in the ground state and the other in its excited state. The interaction is time-dependent for this system, because of the dynamical self-dressing and the spontaneous decay of the excited atom. We calculate the dynamical Casimir-Polder potential between the two atoms using an effective Hamiltonian approach. The results obtained and their physical meaning are discussed and compared with previous results based on a time-independent approach which uses a non-normalizable dressed state for the excited atom.Comment: 11 page

Dynamical Casimir-Polder force between an excited atom and a conducting wall

We consider the dynamical atom-surface Casimir-Polder force in the nonequilibrium configuration of an atom near a perfectly conducting wall, initially prepared in an excited state with the field in its vacuum state. We evaluate the time-dependent Casimir-Polder force on the atom and find that it shows an oscillatory behavior from attractive to repulsive both in time and in space. We also investigate the asymptotic behavior in time of the dynamical force and of related local field quantities, showing that the static value of the force, as obtained by a time-independent approach, is recovered for times much longer than the time scale of the atomic self-dressing but shorter than the atomic decay time. We then discuss the evolution of global quantities such as atomic and field energies and their asymptotic behavior. We also compare our results for the dynamical force on the excited atom with analogous results recently obtained for an initially bare ground-state atom. We show that new relevant features are obtained in the case of an initially excited atom, for example, much larger values of the dynamical force with respect to the static one, allowing for an easier way to single out and observe the dynamical Casimir-Polder effect

Effect of boundaries on vacuum field fluctuations and radiation-mediated interactions between atoms

In this paper we discuss and review several aspects of the effect of boundary conditions and structured environments on dispersion and resonance interactions involving atoms or molecules, as well as on vacuum field fluctuations. We first consider the case of a perfect mirror, which is free to move around an equilibrium position and whose mechanical degrees of freedom are treated quantum mechanically. We investigate how the quantum fluctuations of the mirror's position affect vacuum field fluctuations for both a one-dimensional scalar and electromagnetic field, showing that the effect is particularly significant in the proximity of the moving mirror. This result can be also relevant for possible gravitational effects, since the field energy density couples to gravity. We stress that this interaction-induced modification of the vacuum field fluctuations can be probed through the Casimir-Polder interaction with a polarizable body, thus allowing to detect the effect of the mirror's quantum position fluctuations. We then consider the effect of an environment such as an isotropic photonic crystal or a metallic waveguide, on the resonance interaction between two entangled identical atoms, one excited and the other in the ground state. We discuss the strong dependence of the resonance interaction with the relative position of the atomic transition frequency with the gap of the photonic crystal in the former case, and with the cut-off frequency of waveguide in the latter.Comment: 8 pages, 2 figures, Proceedings of the Eighth International Workshop DICE 2016 Spacetime - Matter - Quantum Mechanic

Validation of an Emission Model for a Marine Diesel Engine with Data from Sea Operations

In this study, a model is developed to simulate the dynamics of an internal combustion engine, and it is calibrated and validated against reliable experimental data, making it a tool that can effectively be adopted to conduct emission predictions. In this work, the Ricardo WAVE software is applied to the simulation of a particular marine diesel engine, a four-stroke engine used in the maritime field. Results from the bench tests are used for the calibration of the model. Finally, the calibration of the model and its validation with full-scale data measured at sea are presented. The prediction includes not only the classic engine operating parameters for a comparison with surveys but also an estimate of nitrogen oxide emissions, which are compared with similar results obtained with emission factors. The calibration of the model made it possible to obtain an overlap between the simulation results and real data with an average error of approximately 7% on power, torque, and consumption. The model provides encouraging results, suggesting further applications, such as in the study on transient conditions, coupling of the engine model with the ship model for a complete simulation of the operating conditions, and optimization studies on consumption and emissions. The availability of the emission data during the sea trial and validated simulation results are the strengths and novelties of this work

Optimal force evaluation for isotonic fatigue characterization in mouse Tibialis Anterior muscle

Skeletal muscle fatigue is most often studied as a response to repeated stimulations in isometric conditions and it is usually quantified as the progressive loss of force generating capability over time. However, physical dynamic activity is based on the shortening of skeletal muscles. Therefore, the condition that best mimics body movements is the isotonic one, in which muscle is allowed to shorten against a constant load. In the literature, the isotonic fatigue test is performed allowing the muscle to lift a load corresponding to one-third of the maximal isometric force (reference optimal force), as best representative of the force at which the tissue develops its maximum power. The goal of this study was to devise a new testing protocol in which each muscle was tested for isotonic fatigue by shortening against its own optimal force, i.e. the force at which it really developed the maximum power. Our hypothesis was that testing all the muscle at a standard reference value would introduce significant errors in the parameters associated to muscle fatigue and in their variance. The proposed protocol was based on the real-time measurement of the maximum power a muscle was able to generate through the application of the after-load technique and a mathematical interpolation to the Hill's equation, that therefore allowed to determine the experimental optimal force to be applied during the fatigue test. Experimental results showed that the muscles tested with the experimental optimal force had a fatigue time significantly lower than the control muscles tested with the reference optimal force. A decrease, even if not statistically significant, was also measured for the power and work generated during the fatigue test. Of note, for all these parameters a huge decrease in the measurement variance was reported, confirming that a precise assessment of the muscle experimental optimal force was needed to increase the accuracy of the measurements. On the other hand, the application of the protocol proposed in this work required an increase in the test duration, due to the application of the after-load technique, and a real time measurement of the power generated by the tissue

Stem Cell Populations and Regenerative Potential in Chronic Inflammatory Lung Diseases

Several acute and chronic inflammatory pathologies of the lung are accompanied by structural modifications of airway mucosa that vary depending on the severity, duration and type of the disease. These morphological changes, that determine organ dysfunction, are not always reversible. Indeed, the cycle of injury and repair, influencing airway wall regeneration, may sometimes break off and an exacerbation of the pathology may occur. The mechanisms at the base of airway remodelling during inflammation have been widely studied and numerous evidences indicate that the molecular dialogue among the cells of the mucosa has an essential role in orchestrating cell differentiation and tissue repair. In this review, we revise old notions on pulmonary morphology at the light of some of the most recent discoveries concerning stem cell differentiation, tissue homeostasis and organ regeneration of the lung

Spatial correlations of vacuum fluctuations and the Casimir-Polder potential

We calculate the Casimir-Polder intermolecular potential using an effective Hamiltonian recently introduced. We show that the potential can be expressed in terms of the dynamical polarizabilities of the two atoms and the equal-time spatial correlation of the electric field in the vacuum state. This gives support to an interesting physical model recently proposed in the literature, where the potential is obtained from the classical interaction between the instantaneous atomic dipoles induced and correlated by the vacuum fluctuations. Also, the results obtained suggest a more general validity of this intuitive model, for example when external boundaries or thermal fields are present.Comment: 7 page