A simple model for DNA denaturation

Following Poland and Scheraga, we consider a simplified model for the denaturation transition of DNA. The two strands are modeled as interacting polymer chains. The attractive interactions, which mimic the pairing between the four bases, are reduced to a single short range binding term. Furthermore, base-pair misalignments are forbidden, implying that this binding term exists only for corresponding (same curvilinear abscissae) monomers of the two chains. We take into account the excluded volume repulsion between monomers of the two chains, but neglect intra-chain repulsion. We find that the excluded volume term generates an effective repulsive interaction between the chains, which decays as $1/r^{d-2}$. Due to this long-range repulsion between the chains, the denaturation transition is first order in any dimension, in agreement with previous studies.Comment: 10 page

Deposition of Aluminum-Doped ZnO Films by ICP-Assisted Sputtering

Inductively coupled plasma (ICP) assisted DC sputter deposition was used for the deposition of Al-doped ZnO (AZO or ZnO:Al) thin films. With increasing ICP RF power, film properties including deposition rate, crystallinity, transparency, and resistivity were improved. To understand the plasma-surface interaction, several plasma diagnostics were performed. Heat fluxes to the substrate were measured by thermal probes, number densities of sputtered metallic atom species were measured by absorption spectroscopy using hollow cathode lamps (HCL) and light emitting diodes (LEDs), and neutral gas temperatures were measured by external cavity diode laser (ECDL) absorption spectroscopy. As a result, it was revealed that the high-density ICP heated the substrate through a high heat flux to the substrate, resulting in a high-quality film deposition without the need for intentional substrate heating. The heat flux to the substrate was predominantly contributed by the plasma charged species, not by the neutral Ar atoms which were also significantly heated in the ICP. The substrate position where the highest quality films were obtained was found to coincide with the position where the substrate heat flux took the maximum value

Gas flow in microchannels - A lattice Boltzmann method approach

Gas flow in microchannels can often encounter tangential slip motion at the solid surface even under creeping flow conditions. To simulate low speed gas flows with Knudsen numbers extending into the transition regime, alternative methods to both the Navier-Stokes and direct simulation Monte Carlo approaches are needed that balance computational efficiency and simulation accuracy. The lattice Boltzmann method offers an approach that is particularly suitable for mesoscopic simulation where details of the molecular motion are not required. In this paper, the lattice Boltzmann method has been applied to gas flows with finite Knudsen number and the tangential momentum accommodation coefficient has been implemented to describe the gas-surface interactions. For fully-developed channel flows, the results of the present method are in excellent agreement with the analytical slip-flow solution of the Navier-Stokes equations, which are valid for Knudsen numbers less than 0.1. The present paper demonstrates that the lattice Boltzmann approach is a promising alternative simulation tool for the design of microfluidic devices