Three-dimensional Classical Model Research Articles

Frustrated double ionization of atoms in elliptically polarized laser fields

Using a three-dimensional classical model, we theoretically investigate frustrated double ionization (FDI) of atoms in elliptically polarized laser fields. The probability curves of FDI have the same characteristic “knee” shape as that of the double ionization. An analysis of the FDI trajectories shows that more than half of the FDI events are induced by recollision for any laser ellipticity. The FDI events without the recollision can be controlled by the ellipticity. Furthermore, the occurrence of FDI events with recollision can be determined from the shape of the photoelectron momentum distribution in elliptically polarized laser fields.

Frustrated double ionization of atoms in circularly polarized laser fields

We theoretically study frustrated double ionization (FDI) of atoms subjected to intense circularly polarized laser pulses using a three-dimensional classical model. We find a ‘knee’ structure of FDI probability as a function of intensity, which is similar to the intensity dependence of nonsequential double ionization probability. The observation of FDI is more favourable when using targets with low ionization potentials and short driving laser wavelengths. This is attributed to the crucial role of recollision therein, which can be experimentally inferred from the photoelectron momentum distribution generated by FDI. This work provides novel physical insights into FDI dynamics with circular polarization.

An overview of the interatomic correlation moments and the mean square relative atomic displacements in anharmonic crystals

We present an overview of a method developed for the calculation of dynamic interatomic correlations in anharmonic crystals based on the correlative method of unsymmetrized self-consistent field (CUSF). The quadratic correlation momenta and the mean square relative displacements have been calculated for one-, two- and three-dimensional classical models.

Triangular antiferromagnetic Ising model with a transverse field at zero temperature

The ground-state properties of the triangular antiferromagnetic Ising model with Ising constant J in a transverse field h are investigated by a real-space renormalisation group method. For h=0, the known properties (energy=-J, finite entropy, no order) are recovered. For h not=0, the ground state remains highly degenerate, no order exists and the correlation function exhibits power-law behaviour up to (h/J)c approximately=1.41, where a phase transition takes place to a non-degenerate ground state. At h/J=(h/J)c, power-law behaviour is still observed for the correlation function but with a different exponent. Just above this region a gap Delta opens ( Delta approximately ((h/J)-(h/J)c)s with s=0.8) and the coherence length of the correlation function xi diverges as xi varies as ((h/J)-(h/J)c)-v with v=0.8. This corresponds to a three-dimensional classical model where h is replaced by the temperature. In this type of system, where the ground state has a degeneracy proportional to N2/3 it is predicted that a transition will occur at a finite Tc to a low-temperature phase without order but with power-law behaviour for the correlation function, as for the classical XY model in two dimensions.

Atmospheric Diffusion of Particulate Matter Released from an Elevated Continuous Source

Dustfall simulation experiments were conducted to estimate the ground-level deposition pattern. Batches of different size glass microspheres (50–200 μ) were continuously released into the atmosphere from an elevated point source. Samplers were placed at ground level along arcs downwind from the stack and the particles were subsequently identified and counted. Measurements of wind speed, gustiness and temperature gradient were made. The data and data obtained by previous investigators were compared with theory. Two mathematical models were used in the comparison: a three-dimensional classical model by Denisov (comparable to Rounds's two-dimensional solution), and a three-dimensional statistical model by Csanady. Both models assume steady-state conditions, horizontal homogeneity, linear growth relationships for the plume dimensions, and complete particle retention at the ground. It was found that the deposit pattern can be predicted reasonably well by the statistical model but should be restricted to values of f/u and f/σw (u is the mean wind speed, f the particle terminal velocity, and σw the rms value of the vertical velocity fluctuations of the turbulent field) greater than 0.05 and 1.0, respectively. At lower values of these ratios, the statistical model overestimates the maximum deposition and underestimates its location. The classical model, in general, underestimates the maximum deposition by a factor of approximately 1.5.