Search results for "Zero-Point Energy"
showing 10 items of 20 documents
Zero-point excitation of a circularly moving detector in an atomic condensate and phonon laser dynamical instabilities
2020
We study a circularly moving impurity in an atomic condensate for the realisation of superradiance phenomena in tabletop experiments. The impurity is coupled to the density fluctuations of the condensate and, in a quantum field theory language, it serves as an analog of a detector for the quantum phonon field. For sufficiently large rotation speeds, the zero-point fluctuations of the phonon field induce a sizeable excitation rate of the detector even when the condensate is initially at rest in its ground state. For spatially confined condensates and harmonic detectors, such a superradiant emission of sound waves provides a dynamical instability mechanism leading to a new concept of phonon l…
Spurious finite-size instabilities in nuclear energy density functionals
2013
It is known that some well-established parametrizations of the EDF do not always provide converged results for nuclei and a qualitative link between this finding and the appearance of finite-size instabilities of SNM near saturation density when computed within the RPA has been pointed out. We seek for a quantitative and systematic connection between the impossibility to converge self-consistent calculations of nuclei and the occurrence of finite-size instabilities in SNM for the example of scalar-isovector (S=0, T=1) instabilities of the standard Skyrme EDF. We aim to establish a stability criterion based on computationally-friendly RPA calculations of SNM that is independent on the functi…
Vacuum-ultraviolet absorption of hydrogenated and deuterated silanol groups and interstitial water molecules in amorphousSiO2
2005
Vacuum-ultraviolet (VUV) absorption cross sections of hydrogenated and deuterated silanol groups (SiOX, where $\mathrm{X}=\mathrm{H}$ or D) as well as interstitial water molecules $({\mathrm{X}}_{2}\mathrm{O})$ in amorphous $\mathrm{Si}{\mathrm{O}}_{2}$ $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$ were determined between photon energies of 7 and $8.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The absorption bands for the deuterated species are blueshifted compared to those for the hydrogenated ones by $\ensuremath{\sim}0.1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ as a result of a decrease in the zero-point energy associat…
Near zero energy island with sea wave energy: The case study of Pantelleria in Mediterranean Sea
2016
In this paper the authors present a study of the transition of an energy generation system for a real MV/LV distribution system from one that is "fuel-based" to a "renewables-based" system in particular from sea wave energy, using the data acquired from an innovative generator prototype realized by University of Palermo. The study is carried out for a real islanded network located in the Island of Pantelleria (Mediterranean Sea). The procedures applied in the present article, as well as the main equations used, are the result of previous applications made in different technical fields that show a good replicability [1]-[7].
Are most of the stationary points in a molecular association minima? Application of Fraga's potential to benzene-benzene
1993
The importance of characterizing the stationary points of the intermolecular potential by means of Hessian eigenvalues is illustrated for the calculation of the benzene–benzene interaction using an atom-to-atom pair potential proposed by Fraga (FAAP). Two models, the standard one-center-per atom and another using three-centers-per atom due to Hunter and Sanders, are used to evaluate the electrostatic contributions and the results are compared. It is found in both cases that although using low-gradient thresholds allows optimization procedures to avoid many stationary points that are not true minima computing time considerations makes the usual procedure of using high-gradient thresholds [sa…
Vacuum energy densities of a field in a cavity with a mobile boundary
2015
We consider the zero-point field fluctuations, and the related field energy densities, inside a one-dimensional and a three-dimensional cavity with a mobile wall. The mechanical degrees of freedom of the mobile wall are described quantum mechanically and they are fully included in the overall system dynamics. In this optomechanical system, the field and the wall can interact with each other through the radiation pressure on the wall, given by the photons inside the cavity or even by vacuum fluctuations. We consider two cases: the one-dimensional electromagnetic field and the three-dimensional scalar field, and use the Green's functions formalism, which allows extension of the results obtain…
Vacuum local and global electromagnetic self-energies for a point-like and an extended field source
2013
We consider the electric and magnetic energy densities (or equivalently field fluctuations) in the space around a point-like field source in its ground state, after having subtracted the spatially uniform zero-point energy terms, and discuss the problem of their singular behavior at the source's position. We show that the assumption of a point-like source leads, for a simple Hamiltonian model of the interaction of the source with the electromagnetic radiation field, to a divergence of the renormalized electric and magnetic energy density at the position of the source. We analyze in detail the mathematical structure of such singularity in terms of a delta function and its derivatives. We als…
Muon states in metals: Recent progress
1984
We report on our results in two interesting questions related to muon spin rotation studies in condensed matter: (i) energetics of muons in metals, including lattice relaxation and zero point motion in self-trapping phenomena, and (ii) systematics of Knight shifts and hyperfine fields.
All-Normal Dispersion Photonic-Crystal Fiber for Pulse-Preserving Supercontinuum Generation near 800 nm
2013
All-normal dispersion photonic-crystal fiber is designed for pulse-preserving supercontinuum generation near 800 nm. Supercontinuum generation is analyzed numerically addressing the role of pump pulse energy and offset of the pump wavelength from the zero point of 3d-order dispersion.
Existence of zero-energy impurity states in different classes of topological insulators and superconductors and their relation to topological phase t…
2015
We consider the effects of impurities on topological insulators and superconductors. We start by identifying the general conditions under which the eigenenergies of an arbitrary Hamiltonian H belonging to one of the Altland-Zirnbauer symmetry classes undergo a robust zero energy crossing as a function of an external parameter which can be, for example, the impurity strength. We define a generalized root of \det H, and use it to predict or rule out robust zero-energy crossings in all symmetry classes. We complement this result with an analysis based on almost degenerate perturbation theory, which allows a derivation of the asymptotic low-energy behavior of the ensemble averaged density of st…