Electronic transport in double-strand poly(dG)-poly(dC) DNA segments

We study the electronic properties of a double-strand quasiperiodic DNA molecule modeled by a one-dimensional effective Hamiltonian, which includes contributions from the nucleobasis system as well as the sugar-phosphate backbone. Our theoretical approach makes use of Dyson's equation together with a transfer-matrix treatment, considering an electronic tight-binding Hamiltonian model to investigate the electronic density of states (DOS) and the electronic transmissivity of sequences of DNA finite segments. To mimic the DNA segments, we consider the finite quasiperiodic sequences of Fibonacci's type, in a poly(dG)-poly(dC) configuration, whose building blocks are the bases guanine G and cytosine C. We compared the electronic transport found for the quasiperiodic structure to those using a sequence of natural DNA, as part of the human chromosome Ch22.     

Photoemission and coincidence studies on gas-phase molecules

This article describes Young’s double-slit experiment using high-energy core-level photoemission from N₂ molecules and experimental identification of interatomic Coulombic decay in Ar₂ dimers after Auger decay using k-resolved electron–ion–ion coincidence spectroscopy, aiming to illustrate the leading edge of gas-phase experiments using synchrotron radiation.     

Cluster growth processes by direct simulation monte carlo method

Thin films obtained by cluster deposition have attracted strong attention both as a new manufacturing technique to realize high-density magnetic recording media and to create systems with unique magnetic properties. Because the film’s features are influenced by the cluster properties during the flight path, the relevant physical scale to be studied is as large as centimeters. In this paper, a new model of cluster growth processes based on a combination of the Direct Simulation Monte Carlo (DSMC) method and the cluster growth model is introduced to examine the effects of experimental conditions on cluster growth by an adiabatic expansion process. From the macroscopic viewpoint, we simulate the behavior of clusters and inert gas in the flight path under different experimental conditions. The internal energy of the cluster, which consists of rotational and vibrational energies, is limited by the binding energy which depends on the cluster size. These internal and binding energies are used as criteria of the cluster growth. The binding energy is estimated by surface and volume terms. Several types of size distribution of generated clusters under various conditions are obtained by the present model. The results of the present numerical simulations reveal that the size distribution is strongly related to the experimental conditions and can be controlled. Received: 23 January 2001 / Accepted: 3 May 2001 / Published online: 30 August 2001     

Exciton formation with interchain couplings in organic polymers

Based on the framework of the tight binding approach and the nonadiabatic dynamics, the formation of an exciton in inter-coupled polymer chains is studied. Both a localized exciton in one single chain and a spread exciton between chains are obtained. It is found that an excited electron-hole pair is more inclined to evolve into a localized exciton, and the long range Coulomb e-e interaction is favorable to the exciton formation. By calculating the formation time of an exciton, we show that the optical response time is faster in a dilute solution than that in a solid film of polymer molecules.     

Co-Adsorption of CO in NO-CO Reaction on a Metal Catalytic Surface Studied by Computer Simulation

The effect of co-adsorption of CO molecules in the NO-CO reaction on a metal catalytic surface like Pt（001） is studied by applying the Langmuir-Hinshelwood mechanism using the Monte Carlo simulations. The system is investigated by two approaches of NO adsorption; dissociatively at two empty surface sites and molecularly at a single vacant site. The elementary steps are the same as those in the conventional Ziff-Gulari-Barshad model. With the additional reaction step of co-adsorption, the sustained production of CO2 is obtained, which has never been seen on a square lattice without introducing additional parameters. The most interesting result is the elimination of continuous second order phase transition, i.e. the production of CO2 starts as soon as the partial pressure of CO departs from zero, which is in accordance with the experimental observations. The effect of co-adsorption probability on the phase diagrams has also been studied.     

Elastic Interaction between a String of Cells and an Individual Cell

The elastic interaction between a string of cells and an individual cell on an elastic substrate is investigated numerically using the force-dipole model. This interaction is found to be of short range, and the cut-off distance is about 1.4 times of the length of the cell. The energy-minimization distance is about half the cellular length. The specific relationship between the cellular reorientation and the cellular position are obtained quantitatively. A critical distance is found, and the cellular orientation has an abrupt change at this transition point.     

Fabrication and characterization of TS-1 films on α-Al2O3 substrates using TiCl3 as titanium source

The continuous and highly intergrown anatase-free TS-1 film was fabricated with TiCl₃ as the titanium source for the first time. The in situ nucleation and secondary growth method was employed to synthesize the TS-1 film. By means of scanning electron microscopy (SEM) images, X-ray diffraction (XRD) patterns, and FT-IR and UV-vis spectra measurements, the resulting film was observed to be anatase-free, continuous and highly intergrown with the MFI-type structure, and the Ti atoms existed only in tetrahedral coordination.     

Minireview: The compact phase in polymers and proteins

Proteins are linear molecules. However, the simple model of a polymer viewed as spheres tethered together does not account for many of the observed characteristics of protein structures. Here we review some recent works tackling this problem. In particular, we will show that there is a growing evidence suggesting that the compact structures of folded proteins are selected in their gross topological features based on geometry and symmetry rather than on sequence consideration. They are poised at the edge of compaction, thus accounting for their flexibility. Different aspects of protein behavior can be rationalized by studying how the energy landscape of a single chain in the marginally compact phase can be modified.     

The effect of diffusion and overhangs/vacancies on the microstructure of zig-zag thin film

Basing on some growth models of thin film, we have investigated the growth mechanism of glancing angle deposition (GLAD) film. The simulation verifies that the overhangs/vacancies also contribute to the columnar growth as well as the self-shadowing effect for GLAD thin film. Besides, we have studied the effect of the deposition rate, surface and bulk diffusions on the microstructure of thin film using the time-dependent Monte Carlo method. The results show that the surface and bulk diffusions can significantly enhance the packing density of thin film in GLAD growth, and the increase of the deposition rate induce the moderate decrease of the packing density.