Pui-Man Lam

Monte Carlo simulation of pulsed laser deposition

Using the Monte Carlo method, we have studied the pulsed laser deposition process at the submonolayer regime. In our simulations, dissociation of an atom from a cluster is incorporated. Our results indicate that the pulsed laser deposition resembles molecular-beam epitaxy at very low intensity, and that it is characteristically different from molecular-beam epitaxy at higher intensity. We have also obtained the island size distributions. The scaling function for the island size distribution for pulsed laser deposition is different from that of molecular-beam epitaxy.

Exact series studies of self-avoiding walks on two-dimensional critical percolation clusters

The author presents results of exact series studies of self-avoiding walks on percolation clusters on the square lattice performed very close to the percolation threshold and estimates the critical exponents nu and gamma defined by the disorder averages of the mean square radius of gyration or the end-to-end distance and the number of self-avoiding walks, respectively. The self-avoiding walk configurations are enumerated exactly up to 35 steps. The result for nu indicates a large increase compared with the self-avoiding walks on fully occupied lattice. The result for gamma , however, indicates a behaviour similar to that on a fully occupied lattice. The result for nu is completely different from that of Lee, Nakanishi and Kim (1989).

A percolation approach to the Kauffman model

A study is made of the spreading of damage in the random but deterministic Kauffman model on the square lattice with the spreading from one edge of the lattice. The critical value of the parameterpc above which the system becomes chaotic is found to bepc≈0.298. The possibility of suppression of the chaotic phase by noise is also studied. It is found that forp⩾pc, an extremely large noise levelg>0.99 is required, if possible at all.

Condensate fraction and momentum distribution of liquid helium

Abstract An expansion is presented which allows practical evaluation of the one-particle density matrix of the ground state of a Bose fluid in terms of its two-body, three-body, … spatial distribution functions.

Excluded volume effect in unzipping DNA with a force

A double stranded DNA molecule when pulled with a force acting on one end of the molecule can become either partially or completely unzipped depending on the magnitude of the force F. For a random DNA sequence, the number M of unzipped base pairs goes as M≈(F − Fc)−2 and diverges at the critical force Fc with an exponent χ = 2. We find that when excluded volume effect is taken into account for the unzipped part of the DNA, the exponent χ = 2 is not changed but the critical force Fc is changed. The force versus temperature phase diagram depends on only two parameters in the model, the persistence length and the denaturation temperature. Furthermore a scaling form of the phase diagram can be found. This scaling form is parameter independent and depends only on the spatial dimension. It applies to all DNA molecules and should provide a useful framework for comparison with experiments.

Monte Carlo simulation of coarsening in a model of submonolayer epitaxial growth

We investigate the effect of coarsening in the Clarke–Vvedensky model of thin film growth, primarily as a model of statistical physics far from equilibrium. We deposit adatoms on the substrate until a fixed coverage is reached. We then stop the deposition and measure the subsequent change in the distribution of the island sizes. We find that for large flux, coarsening in this model is consistent with the Lifshitz–Slyozov law ξ∼t1/3, where ξ is the characteristic linear dimension and t is the time in the coarsening process. We have also calculated the stationary states of the island size distributions at long times and find that these distribution functions are independent of initial conditions. They obey scaling with the universal scaling function agreeing with that obtained by Kandel using the Smolochowsky equation in a cluster coalescence model.

Pairing energy of liquid 4He

Abstract The two-particle density matrix of a Bose system described by a Jastrow wave function displays off-diagonal long-range order associated with strong correlations between pairs of bosons with non-zero momenta ħ q , -ħ q . In conjunction with the zero-momentum condensate, these correlations give rise to a finite contribution to the energy expectation value per particle, which is calculated for liquid 4 He at two values of the density.

Self-avoiding walks on percolation clusters at criticality and lattice animals

AbstractWe use the real-space renormalization group method to study the critical behavior of self-avoiding walks (SAWs) on both site percolation clusters at percolation threshold and site lattice animals in a square lattice. The correlation length exponents of SAWs are found to be

Dynamic scaling theory of the forced translocation of a semi-flexible polymer through a nanopore

\nu _{SAW}^{p^c } = 0.767