Discotic liquid crystal (LC) molecules readily form columnar supramolecular structures. Because of molecular mobility in the LC state these columnar assemblies can self-heal structural defects to a certain extent. Therefore, conjugated aromatic molecules of the discotic LC state may exhibit exceptional charge carrier transport properties, and thus are potential active materials for use in optoelectronic devices. In this review, a number of discotic LC materials including benzene, triphenylene, hexabenzocoronene, perylene, and phthalocyanine derivatives are reviewed. The emphases are on the correlation between chemical structure and LC properties and some recent developments in the application of these materials in optoelectronic devices such as organic light-emitting diodes (OLED), organic field-effect transistors (OFET), and photovoltaic cells. In addition, studies related to the dynamics of some discotic LC materials are briefly discussed.
In this paper, a modified projection method is combined with a self-adaptive time step procedure to develop numerical scheme for large eddy simulation (LES) of low Ma number turbulent reactive flows. The projection method introduced by Chorin is modified in this study to satisfy the simulation requirement of low Ma number reactive flow. The time step in this computation is automatically determined according to the time scales of both chemical reaction and turbulent fluctuations. This enables the simulation to capture detailed flow structures with less computational time. Numerical simulation of methane-air jet flames is carried out as an example to validate the developed numerical scheme. The mechanism of a simplified 4-step chemical kinetics is applied for the methane-air reaction. The dynamic model is adopted for the turbulent motion of sub-grid scale (SGS). The dynamic similarity model is used as the SGS model for the reaction rate. The LES results satisfactorily depict the ignition process of the turbulent jet flames and illustrate lucid and detailed coherent structures of the fully developed turbulent reactive jet flow. The LES results also exhibit the mechanism and characteristics of local extinction. The method developed in this study provides an effective way to capture more flow details with less computational time. In addition the method also helps one to investigate the mechanism of ignition and local extinction in jet flames. Copyright (C) 2008 John Wiley & Sons, Ltd.
In this paper, a modified projection method is combined with a self-adaptive time step procedure to develop numerical scheme for large eddy simulation (LES) of low Ma number turbulent reactive flows. The projection method introduced by Chorin is modified in this study to satisfy the simulation requirement of low Ma number reactive flow. The time step in this computation is automatically determined according to the time scales of both chemical reaction and turbulent fluctuations. This enables the simulation to capture detailed flow structures with less computational time. Numerical simulation of methane-air jet flames is carried out as an example to validate the developed numerical scheme. The mechanism of a simplified 4-step chemical kinetics is applied for the methane-air reaction. The dynamic model is adopted for the turbulent motion of sub-grid scale (SGS). The dynamic similarity model is used as the SGS model for the reaction rate. The LES results satisfactorily depict the ignition process of the turbulent jet flames and illustrate lucid and detailed coherent structures of the fully developed turbulent reactive jet flow. The LES results also exhibit the mechanism and characteristics of local extinction. The method developed in this study provides an effective way to capture more flow details with less computational time. In addition the method also helps one to investigate the mechanism of ignition and local extinction in jet flames. Copyright (C) 2008 John Wiley & Sons, Ltd.
In this paper, fusion neutron yields from the Coulomb explosion of (CD4)N clusters under the irradiation of an intense femtosecond laser pulse is optimized by controlling the propagation of the laser pulse in a cluster jet. A correlated study of fusion neutron yields, kinetic energies of deuterons, together with the plasma channels diagnosed by a pump–probe interferometer, is performed. It has been found that by controlling the focal position related to the cluster jet, the plasma defocusing effect can balance with the tight focusing effect of the laser pulse induced by an off-axis parabolic mirror, and results in a cylindrical-shaped and relatively narrow plasma channel crossing the gas jet. The most energetic deuterons and the maximum yields of fusion neutrons are produced at the same time. For better understanding of the experimental results, numerical simulations for the nonlinear propagation of the femtosecond laser pulse in (CD4)N gas-cluster jets are performed. Simulated results show that plasma defocusing and laser attenuation play dominant roles in this case of optimization.