Search results for "FLUCTUATIONS"
showing 10 items of 167 documents
Physical Origin of Anharmonic Dynamics in Proteins: New Insights From Resolution-Dependent Neutron Scattering on Homomeric Polypeptides
2012
Neutron scattering reveals a complex dynamics in polypeptide chains, with two main onsets of anharmonicity whose physical origin and biological role are still debated. In this study the dynamics of strategically selected homomeric polypeptides is investigated with elastic neutron scattering using different energy resolutions and compared with that of a real protein. Our data spotlight the dependence of anharmonic transition temperatures and fluctuation amplitudes on energy resolution, which we quantitatively explain in terms of a two-site model for the protein-hydration water energy landscape. Experimental data strongly suggest that the protein dynamical transition is not a mere resolution …
Raman and Infrared Spectra of Acoustical, Functional Modes of Proteins from All-Atom and Coarse-Grained Normal Mode Analysis
2018
The directions of the largest thermal fluctuations of the structure of a protein in its native state are the directions of its low-frequency modes (below 1 THz), named acoustical modes by analogy with the acoustical phonons of a material. The acoustical modes of a protein assist its conformational changes and are related to its biological functions. Low-frequency modes are difficult to detect experimentally. A survey of experimental data of low-frequency modes of proteins is presented. Theoretical approaches, based on normal mode analysis, are of first interest to understand the role of the acoustical modes in proteins. In this chapter, the fundamentals of normal mode analysis using all-ato…
Thermal and non-thermal signatures of the Unruh effect in Casimir-Polder forces
2014
We show that Casimir-Polder forces between two relativistic uniformly accelerated atoms exhibit a transition from the short distance thermal-like behavior predicted by the Unruh effect, to a long distance non-thermal behavior, associated with the breakdown of a local inertial description of the system. This phenomenology extends the Unruh thermal response detected by a single accelerated observer to an accelerated spatially extended system of two particles, and we identify the characteristic length scale for this crossover with the inverse of the proper acceleration of the two atoms. Our results are derived separating at fourth order in perturbation theory the contributions of vacuum fluctu…
Reply to "Comment on 'Dispersion Interaction between Two Hydrogen Atoms in a Static Electric Field' "
2020
In their Comment on our Letter Dispersion Interaction between Two Hydrogen Atoms in a Static Electric Field, P. P. Abrantes et al. address one of the main points discussed in our Letter, that is, the possibility to manipulate interatomic interactions through an external static electric field. In our Letter, we have shown that the interaction between two ground-state atoms can be significantly modified, exploiting an external static electric field, and even turned from attractive to repulsive, depending on the strength of the external field and the geometrical configu- ration. In their Comment, Abrantes et al. point out that it is the electrostatic contribution between the electric dipoles i…
Über eine bestimmung der peaklage von reinen und komplexen photopeaks
1966
Abstract To determine the center of photopeaks normally occuring in γ-spectra in complex form, some modified methods are developed for most typical cases: a. single peak and constant background; b. single peak and exponentially decreasing background; c. two overlapping peaks at different distances of energy and varying peak intensities. The statistical fluctuations can be widely eliminated by use of a simple averaging method, so that peak center locations can be evaluated even in the case of relatively small peak intensities. Applying the methods proposed to some cases of strongly overlapping photopeaks, excellent agreement between the theoretical and experimentally obtained values could be…
Surface-directed spinodal decomposition: Lattice model versus Ginzburg-Landau theory
2009
When a binary mixture is quenched into the unstable region of the phase diagram, phase separation starts by spontaneous growth of long-wavelength concentration fluctuations ("spinodal decomposition"). In the presence of surfaces, the latter provide nontrivial boundary conditions for this growth. These boundary conditions can be derived from lattice models by suitable continuum approximations. But the lattice models can also be simulated directly, and thus used to clarify the conditions under which the Ginzburg–Landau type theory is valid. This comparison shows that the latter is accurate only in the immediate vicinity of the bulk critical point, if thermal fluctuations can also be neglecte…
Dynamical Casimir-Polder energy between an excited- and a ground-state atom.
2004
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.
General interpolation scheme for thermal fluctuations in superconductors
2006
We present a general interpolation theory for the phenomenological effects of thermal fluctuations in superconductors. Fluctuations are described by a simple gauge invariant extension of the gaussian effective potential for the Ginzburg-Landau static model. The approach is shown to be a genuine variational method, and to be stationary for infinitesimal gauge variations around the Landau gauge. Correlation and penetration lengths are shown to depart from the mean field behaviour in a more or less wide range of temperature below the critical regime, depending on the class of material considered. The method is quite general and yields a very good interpolation of the experimental data for very…
Notes on the Electroelastic Interaction in Joint Hamiltonian and Stochastic Treatment of Polarization Response
2008
Conventional Landau theory for ferroelectric phase instability is extended by entities accounting for the violation of thermodynamic equilibrium and the impact of thermal fluctuations. The physical content concerns Ginzburg-Landau type model Hamiltonians assigned to the mean field interaction of macroscopically small and microscopically large lattice cells affected by thermal fluctuations. A special topic derived in a systematic way is long range electroelastic interaction formally given by selfconsistent solution of the polarization and strain fields. Test solution for inhomogeneous strain in a slab is presented within the framework of lattice cell picture.
Double-seed stabilization of a continuum generated from fourth-order modulation instability
2013
Summary form only given. Modulation instability (MI) is a ubiquitous process in which a weak field is exponentially amplified through a balance between dispersive and nonlinear effects. In single-mode scalar optical fibers, the positive Kerr nonlinearity phase-mismatch can be compensated by anomalous second-order dispersion, a process known as MI2. But phase-matched solutions can also exist in normal second-order dispersion region, thanks to negative even higher-order terms [1]. This process, that we label MI4, gives rise to a pair of narrow sidebands widely detuned far from the pump. MI may grow spontaneously from broadband noise and is usually the main process involved in the early stages…