Search results for "fluctuation"
showing 10 items of 357 documents
Dynamical Casimir-Polder forces between an atom and a conducting wall
2008
Electromagnetic field fluctuations near a dielectric half-space and appearance of surface divergences in the ideal conductor limit
2012
The electromagnetic field fluctuations in the vacuum state are considered in the region external to a half-space filled with a homogeneous non-dissipative dielectric. We discuss the appropriate limits to a real and an ideal metal, focusing on the renormalized field fluctuations (equivalent to energy densities) in the proximity of the dielectric-vacuum interface. We show that, whereas in presence of a real conductor the renormalized field fluctuations are finite in any point of space, surface divergences appear at the interface in the ideal conductor limit. The main features of such divergences are discussed in detail. We point out that the behavior of field fluctuations close to the interfa…
Causality and Localization Operators
2005
The evolution of the expectation values of one and two points scalar field operators and of positive localization operators, generated by an istantaneous point source is non local. Non locality is attributed either to zero point vacuum fluctuations, or to non local operations or to the microcausality principle being no satisfied.
Effect of Vestibular Rehabilitation on Spontaneous Brain Activity in Patients With Vestibular Migraine: A Resting-State Functional Magnetic Resonance…
2019
Previous studies have shown that vestibular migraine (VM) is a cerebral disease with recurrent vertigo. Vestibular rehabilitation (VR) is an effective type of physical therapy for minimizing vestibular symptoms, as it improves vestibular compensation in patients with VM. Currently, the cerebral regions that are associated with the pathogenesis of VM are largely unknown. To further understand the underlying mechanisms of VM, we performed resting-state functional magnetic resonance imaging (fMRI) before and after 1 month of VR in 14 patients with VM. The Dizziness Handicap Inventory (DHI), the 36-Item Short-Form Health Survey (SF-36), the Hamilton Depression Scale (HAMD) and the Hamilton Anxi…
Fluctuations and elastic properties of lipid membranes in the gel Lβ′ state: a coarse-grained Monte Carlo study
2010
We study the stress distribution profiles and the height and thickness fluctuations of lipid membranes in the gel L-beta ' state by Monte Carlo simulations of a generic coarse-grained model for lipid membranes, which reproduces many known properties of dipalmitoylphosphatidyncholine (DPPC) bilayers. The results are related to the corresponding properties of fluid membranes, and to theoretical predictions for crystalline and hexatic membranes. One striking observation is that the spontaneous curvature of the monolayers changes sign from the fluid to the gel phase. In the gel-phase, the long-wavelength height fluctuations are suppressed, and the fluctuation spectrum is highly anisotropic. In …
The promise of spintronics for unconventional computing
2021
Novel computational paradigms may provide the blueprint to help solving the time and energy limitations that we face with our modern computers, and provide solutions to complex problems more efficiently (with reduced time, power consumption and/or less device footprint) than is currently possible with standard approaches. Spintronics offers a promising basis for the development of efficient devices and unconventional operations for at least three main reasons: (i) the low-power requirements of spin-based devices, i.e., requiring no standby power for operation and the possibility to write information with small dynamic energy dissipation, (ii) the strong nonlinearity, time nonlocality, and/o…
Fluctuating Interfaces in Liquid Crystals
2008
We review and compare recent work on the properties of fluctuating interfaces between nematic and isotropic liquid-crystalline phases. Molecular dynamics and Monte Carlo simulations have been carried out for systems of ellipsoids and hard rods with aspect ratio 15:1, and the fluctuation spectrum of interface positions (the capillary wave spectrum) has been analyzed. In addition, the capillary wave spectrum has been calculated analytically within the Landau-de Gennes theory. The theory predicts that the interfacial fluctuations can be described in terms of a wave vector dependent interfacial tension, which is anisotropic at small wavelengths (stiff director regime) and becomes isotropic at l…
Disorder and dephasing effects on electron transport through conjugated molecular wires in molecular junctions
2012
Understanding electron transport processes in molecular wires connected between contacts is a central focus in the field of molecular electronics. Especially, the dephasing effect causing tunneling-to-hopping transition has great importance from both applicational and fundamental points of view. We analyzed coherent and incoherent electron transmission through conjugated molecular wires by means of density-functional tight-binding theory within the D'Amato-Pastawski model. Our approach can study explicitly the structure/transport relationship in molecular junctions in a dephasing environmental condition using only single dephasing parameter. We investigated the length dependence and the inf…
Lamb shift of a uniformly accelerated hydrogen atom in the presence of a conducting plate
2009
We investigate the effects of acceleration on the energy-level shifts of a hydrogen atom interacting with the electromagnetic field and in the presence of an infinite perfectly conducting plate. We consider the contributions of vacuum fluctuations and of the radiation reaction field to the Lamb shift, and we discuss their dependence from the acceleration of the atom. We show that, because of the presence of the boundary, both vacuum field fluctuations and radiation reaction field contributions are affected by atomic acceleration. In particular, the effect of the vacuum field fluctuations on the energy-level shifts is not equivalent to that of a thermal field. We also discuss the dependence …
Dielectric relaxation and conductivity in ferroelectric perovskites
1996
Abstract Ferroelectric ABO3 perovskites are usually well known for their high dielectric susceptibility. Under selected impurity substitutions their conductivity may be strongly increased. The interaction between electronic conductivity and lattice polarizability may take place over different length scales. At high temperatures (T > 300 K), this interaction length is macroscopic leading to space charges. At low temperatures (T < 50 K), the polaronic interaction is restricted to a few unit cells. In the special case of SrTiO3, these polaronic excitons are sensitive to the quantum fluctuations which lead to the new concept of quantum polarons.