Search results for "Coupling"
showing 10 items of 1862 documents
Microscopic theory for the glass transition in a system without static correlations
2002
We study the orientational dynamics of infinitely thin hard rods of length L, with the centers-of-mass fixed on a simple cubic lattice with lattice constant a.We approximate the influence of the surrounding rods onto dynamics of a pair of rods by introducing an effective rotational diffusion constant D(l),l=L/a. We get D(l) ~ [1-v(l)], where v(l) is given through an integral of a time-dependent torque-torque correlator of an isolated pair of rods. A glass transition occurs at l_c, if v(l_c)=1. We present a variational and a numerically exact evaluation of v(l).Close to l_c the diffusion constant decreases as D(l) ~ (l_c-l)^\gamma, with \gamma=1. Our approach predicts a glass transition in t…
Fluctuating hydrodynamics and diffusion in amorphous solids
1994
The fluctuating hydrodynamic description for an isotropic fluid is extended to include the displacement field u, reflecting the freezing of the local structures in an amorphous solid. The fluctuating nonlinear equations for the set of hydrodynamic variables including u has been obtained. The role of u is manifested through its longitudinal part, i.e., \ensuremath{\nabla}\ensuremath{\cdot}u, in terms of which we define the variable c(x,t). It refers to the diffusion of the free volume or vacancies, signifying configurational rearrangements in the amorphous solid. The analysis here shows that one recovers the earlier result obtained by Das and Mazenko [Phys. Rev. A 34, 2265 (1986)] for mode c…
A theoretical study on threshold conditions of modulation instability in oppositely directed couplers
2016
We theoretically investigate threshold conditions to observe modulation instability (MI) in a two-core nonlinear oppositely directed coupler (ODC) with a negative-index material (NIM) channel. Using linear stability analysis, we obtain an expression for the instability gain. The analysis shows, with two discrete instability regions, that the band at lower values of f (ratio of the backward to forward-propagating waves amplitude) is a result of the nonlinear positive index material (PIM) channel while the broader range band is a consequence of the nonlinear NIM channel. Both bands are highly sensitive to system parameters. We demonstrate that MI has a threshold-like condition in the normal d…
Dark sectors with dynamical coupling
2019
Coupled dark matter-dark energy scenarios are modeled via a dimensionless parameter $��$, which controls the strength of their interaction. While this coupling is commonly assumed to be constant, there is no underlying physical law or symmetry that forbids a time-dependent $��$ parameter. The most general and complete interacting scenarios between the two dark sectors should therefore allow for such a possibility, and it is the main purpose of this study to constrain two possible and well-motivated coupled cosmologies by means of the most recent and accurate early and late-time universe observations. We find that CMB data alone prefers $��(z) >0$ and therefore a smaller amount of dark ma…
Dips in the diffuse supernova neutrino background
2014
Scalar (fermion) dark matter with mass in the MeV range coupled to ordinary neutrinos and another fermion (scalar) is motivated by scenarios that establish a link between radiatively generated neutrino masses and the dark matter relic density. With such a coupling, cosmic supernova neutrinos, on their way to us, could resonantly interact with the background dark matter particles, giving rise to a dip in their redshift-integrated spectra. Current and future neutrino detectors, such as Super-Kamiokande, LENA and Hyper-Kamiokande, could be able to detect this distortion.
Magnetic interaction between coupled quantum dots
2000
We study the magnetic coupling in artificial molecules composed of two and four laterally coupled quantum dots. The electronic ground-state configurations of such systems are determined by applying current spin density functional theory which allows to include effects of magnetic fields. While the ground-state of a two-dot molecule with strong enough inter-dot coupling tends to be antiferromagnetic with respect to the spins of the single dot components, we find that a square lattice of four dots has a ferromagnetic ground state.
Entangling two spatially separate cavities
2003
A scheme for the transfer of entanglement among systems via successive coupling with an intermediate system is described. This method is applied to a simple experimental realizable situation for entangling two spatially separated cavities. In this scheme entanglement, initially stored in two modes of the first cavity, is transferred by an atom interacting successively with the cavities, into entanglement between two non resonant modes of the different cavities.
THEORETISCHE UNTERSUCHUNG UBER DIE MEHRFACHAUFSTELLUNG VON GEOPHONEN*
1958
The receiving of seismic waves by multiple geophones (geophone-group) is described by a system of coupled differential equations considering only effective resistances. For so-called symmetrical connections of the geophone-group which are used in practice nearly in all cases, a method can be given for solving this system of differential equations. The solutions so derived are valid for seismic waves of any shape. The calculation takes into account the coupling of the geophones as well as the building-up transient oscillations. A suitable measure of superposition is defined, based on the energy transferred during the receiving of the seismic waves. By this means effects similar to interferen…
Single-step arbitrary control of mechanical quantum states in ultrastrong optomechanics
2015
We describe how ultrastrong interactions in optomechanical systems can be used to force the system ground state to evolve into an arbitrary quantum state of mechanical motion in a completely controlled and deterministic manner. If the target quantum state is a superposition of $N$ Fock states, it can be obtained by applying in single-step $N$ classical optical signals of different frequencies for a common time interval. This protocol can be applied to various strongly interacting quantum systems as trapped ions beyond the Lamb-Dicke regime and cavity QED into the ultrastrong coupling regime.
Unraveling exciton dynamics in amorphous silicon dioxide: Interpretation of the optical features from 8 to 11 eV.
2011
Physical review / B 83, 174201 (2011). doi:10.1103/PhysRevB.83.174201