Search results for "Models"
showing 10 items of 8211 documents
Attractive ion-ion correlation forces and the dielectric approximation.
2016
We analyze the classical problem of the interaction between two charged surfaces separated by a solution containing neutralizing counter-ions. The focus is on obtaining a description where the solvent is treated explicitly rather than through a dielectric approximation as is conventionally done. We summarize the results of three papers where we have used a Stockmayer fluid model in Monte Carlo simulations. It is shown that the attractive ion-ion correlation mechanism is also operating when the solvent is described explicitly. There appears an oscillatory component to the force, but when this is accounted for, there is a semi-quantitative agreement between the continuum model and the model w…
An abundance analysis of the symbiotic star CH Cyg
2005
The photospheric abundances for the cool component of the symbiotic star CH Cyg were calculated for the first time using high-resolution near-infrared spectra and the method of of standard LTE analysis and atmospheric models. The iron abundance for CH Cyg was found to be solar, [Fe/H] = 0.0+/-0.19. The atmospheric parameters and metallicity for CH Cyg are found to be approximately equal to those for nearby field M7 giants. The calculated [C/H] = -0.15, [N/H] = +0.16, [O/H] = -0.07, and the isotopic ratios of 12C/13C and 16O/17O are close to the mean values for single M giants that have experienced the first dredge-up. A reasonable explanation for the absence of barium star-like chemical pec…
Microcalorimeter/EBIT measurements of X-ray spectra of highly charged ions
2001
Spectra of highly charged Ar, Kr, Xe and Fe ions, produced in an Electron Beam Ion Trap (EBIT), have been recorded in a broad X-ray energy band (0.2 keV to 10 keV) with a microcalorimeter detector. The first analysis of the Kr spectra has been completed and most of the spectral lines have been identified as transitions of B- to Al-like Kr. Line intensity ratios of Fe XVII have been measured and compared with theoretical models.
Frequency-modulated atomic force microscopy operation by imaging at the frequency shift minimum: the dip-df mode.
2014
In frequency modulated non-contact atomic force microscopy, the change of the cantilever frequency (Delta f) is used as the input signal for the topography feedback loop. Around the Delta f(z) minimum, however, stable feedback operation is challenging using a standard proportional-integral-derivative (PID) feedback design due to the change of sign in the slope. When operated under liquid conditions, it is furthermore difficult to address the attractive interaction regime due to its often moderate peakedness. Additionally, the Delta f signal level changes severely with time in this environment due to drift of the cantilever frequency f(0) and, thus, requires constant adjustment. Here, we pre…
Lattice Boltzmann versus Molecular Dynamics simulations of nanoscale hydrodynamic flows
2006
A fluid flow in a simple dense liquid, passing an obstacle in a two-dimensional thin film geometry, is simulated by Molecular Dynamics (MD) computer simulation and compared to results of Lattice Boltzmann (LB) simulations. By the appropriate mapping of length and time units from LB to MD, the velocity field as obtained from MD is quantitatively reproduced by LB. The implications of this finding for prospective LB-MD multiscale applications are discussed.
Superparamagnetism in Ising Clusters
1992
Recent experiments on small ferromagnetic clusters have inspired introduction of a number of seemingly quite different theoretical models. We shall argue that all these models show superparamagnetic behaviour above the blocking temperature but below the Curie temperature. In particular, we shall show that Ising clusters display superparamagnetism and introduce a simple correction to the usual tank behaviour of magnetisation which has to be included for very small clusters. We also discuss the dependence of magnetisation on coordination number.
On the anomalous Stark effect in a thin disc-shaped quantum dot
2010
The effect of a lateral external electric field F on an exciton ground state in an InAs disc-shaped quantum dot has been studied using a variational method within the effective mass approximation. We consider that the radial dimension of the disc is very large compared to its height. This situation leads to separating the excitonic Hamiltonian into two independent parts: the lateral confinement which corresponds to a two-dimensional harmonic oscillator and an infinite square well in the growth direction. Our calculations show that the complete description of the lateral Stark shift requires both the linear and quadratic terms in F which explains that the exciton possess nonzero lateral dipo…
Total free energy of a spin-crossover molecular system
2004
The free energy of spin-crossover molecular systems studied so far deal with the inner degrees of freedom of the spin-crossover molecules and a variety of interaction schemes between the molecules in the high spin (HS) and low spin (LS) states. Different types of transition curves, gradual, abrupt, hysteresis, and also two step transitions have been simulated or even satisfactorily fitted to experimental data. However, in the last decade spin transition curves were measured, especially under pressure, which could not be explained within these theoretical models. In this contribution the total free energy of an anharmonic lattice incorporating spin-crossover molecules which have a certain mi…
Linear inverse filtering improves spatial separation of nonlinear brain dynamics: a simulation study.
2000
We examined topographic variations in nonlinear measures based on scalp voltages, which were generated by two simulated current dipoles each placed in a different hemisphere of a spherical volume conductor (three-shell model). Dipole dynamics were that of a three-torus and the x-component of the Lorenz-system and scalp voltage were calculated for a configuration of 29 electrode positions. Although estimates for correlation dimension D2 and Lyapunov exponent L1 were close to the theoretical values for the original time series, the simulated scalp voltage data showed almost no topographic resolution of dipole positions. In order to enhance topographic differentiation, we constructed linear in…
Emulation of n-photon Jaynes Cummings and Anti-Jaynes-Cummings models via parametric modulation of cyclic qutrit
2019
We study a circuit QED setup involving a single cavity mode and a cyclic qutrit whose parameters are time modulated externally. It is shown that in the dispersive regime this system behaves as a versatile platform to implement effective $n$-photon Jaynes-Cummings (JC) and anti-Jaynes-Cummings (AJC) models by suitably setting the modulation frequency. The atomic levels and the cavity Fock states involved in the effective Hamiltonians can be controlled through adjustment of the system parameters, and different JC and AJC interactions can be implemented simultaneously using multitone modulations. Moreover, one can implement some models that go beyond simple JC and AJC-like interaction, such as…