Search results for "POLDER"

Retrieving leaf area index from multi-angular airborne data

2009

This work is aimed to demonstrate the feasibility of a methodology for retrieving bio-geophysical variables whilst at the same time fully accounting for additional information on directional anisotropy. A model-based approach has been developed to deconvolve the angular reflectance into single landcovers reflectances, attempting to solve the inconsistencies of 1D models and linear mixture approaches. The model combines the geometric optics of large scale canopy structure with principles of radiative transfer for volume scattering within individual crowns. The reliability of the model approach to retrieve LAI has been demonstrated using data from DAISEX- 99 campaign at Barrax, Spain. Airborn…

Installazione di un tetto verde multistrato in un tipico ambiente urbano del sud Italia

Il verde pensile è un sistema tecnologico che prevede l’utilizzo della vegetazione come strato superiore della copertura di un edificio, impiegato sia per le sue funzioni ambientali che per le sue caratteristiche estetiche (Cascone, 2019). Infatti, la realizzazione di un tetto verde, oltre al suo intrinseco valore ecologico, consente numerosi vantaggi economici ed ambientali rispetto alle coperture tradizionali (Berardi & Ghaffarianhoseini, 2014). Nel tempo, l’interesse nei confronti dei tetti verdi è sempre più cresciuto, sia per i benefici conseguibili che rispondono a molti degli obiettivi delle diverse politiche nazionali, europee e internazionali per la mitigazione e l’adattamento …

Nonperturbative approach for the electronic Casimir-Polder effect in a one-dimensional semiconductor

2013

We present the electronic Casimir-Polder effect for a system consisting of two impurities on a one-dimensional semiconductor quantum wire. Due to the charge transfer from the impurity to a one-dimensional conduction band, the impurity states are dressed by a virtual cloud of the electron field. The attractive electronic Casimir force arises due to the overlap of the virtual clouds. The Van Hove singularity causes the persistent bound state (PBS) to appear below the band edge even when the bare impurity state energy is above the band edge. Since the decay rate of the virtual cloud of the PBS in space is small, the Casimir force can be of a very long range. While the overlap of the electronic…

Dynamical Casimir-Polder interaction between an atom and surface plasmons

2013

We investigate the time-dependent Casimir-Polder potential of a polarizable two-level atom placed near a surface of arbitrary material, after a sudden change in the parameters of the system. Different initial conditions are taken into account. For an initially bare ground-state atom, the time-dependent Casimir-Polder energy reveals how the atom is "being dressed" by virtual, matter-assisted photons. We also study the transient behavior of the Casimir-Polder interaction between the atom and the surface starting from a partially dressed state, after an externally induced change in the atomic level structure or transition dipoles. The Heisenberg equations are solved through an iterative techni…

Casimir-Polder interaction between an accelerated two-level system and an infinite plate

2007

We investigate the Casimir-Polder interaction energy between a uniformly accelerated two-level system and an infinite plate with Dirichlet boundary conditions. Our model is a two-level atom interacting with a massless scalar field, with a uniform acceleration in a direction parallel to the plate. We consider the contributions of vacuum fluctuations and of the radiation reaction field to the atom-wall Casimir-Polder interaction, and we discuss their dependence on the acceleration of the atom. We show that, as a consequence of the noninertial motion of the two-level atom, a thermal term is present in the vacuum fluctuation contribution to the Casimir-Polder interaction. Finally we discuss the…

Energy-level shifts of a uniformly accelerated atom between two reflecting plates

2011

We discuss the radiative level shifts of a uniformly accelerated atom moving between two infinite reflecting plates and interacting with a massless scalar field in the vacuum state. The atom, supposed to be a two-level system, accelerates in a direction parallel to the conducting plates. We evaluate separately the contributions of vacuum fluctuations and radiation reaction field to the energy shift of the atomic levels, and discuss their dependence on acceleration, atomic position and cavity length.

van der Waals Interaction Energy Between Two Atoms Moving With Uniform Acceleration

2013

We consider the interatomic van der Waals interaction energy between two neutral ground-state atoms moving in the vacuum space with the same uniform acceleration. We assume the acceleration orthogonal to their separation, so that their mutual distance remains constant. Using a model for the van der Waals dispersion interaction based on the interaction between the instantaneous atomic dipole moments, which are induced and correlated by the zero-point field fluctuations, we evaluate the interaction energy between the two accelerating atoms in terms of quantities expressed in the laboratory reference frame. We find that the dependence of the van der Waals interaction between the atoms from the…

Harmonic oscillator model for the atom-surface Casimir-Polder interaction energy

2012

In this paper we consider a quantum harmonic oscillator interacting with the electromagnetic radiation field in the presence of a boundary condition preserving the continuous spectrum of the field, such as an infinite perfectly conducting plate. Using an appropriate Bogoliubov-type transformation we can diagonalize exactly the Hamiltonian of our system in the continuum limit and obtain non-perturbative expressions for its ground-state energy. From the expressions found, the atom-wall Casimir-Polder interaction energy can be obtained, and well-know lowest-order results are recovered as a limiting case. Use and advantage of this method for dealing with other systems where perturbation theory …

A microscopic approach to Casimir and Casimir-Polder forces between metallic bodies

2014

We consider the Casimir-Polder interaction energy between a metallic nanoparticle and a metallic plate, as well as the Casimir interaction energy between two macroscopic metal plates, in terms of the many-body dispersion interactions between their constituents. Expressions for two- and three-body dispersion interactions between the microscopic parts of a real metal are first obtained, both in the retarded and non-retarded limits. These expressions are then used to evaluate, a compare each other, the overall two- and three-body contributions to the macroscopic Casimir-Polder and Casimir force, by summing up the contributions from the microscopic constituents of the bodies (metal nanoparticle…

Dynamical Casimir-Polder potentials in non-adiabatic conditions

2014

In this paper we review different aspects of the dynamical Casimir¿Polder potential between a neutral atom and a perfectly conducting plate under nonequilibrium conditions. In order to calculate the time evolution of the atom¿wall Casimir¿Polder potential, we solve the Heisenberg equations describing the dynamics of the coupled system using an iterative technique. Different nonequilibrium initial states are considered, such as bare and partially dressed states. The partially dressed states considered are obtained by a sudden change of a physical parameter of the atom or of its position relative to the conducting plate. Experimental feasibility of detecting the considered dynamical effects i…