An atomistic-continuum hybrid simulation of fluid flows over superhydrophobic surfaces

Recent experiments have found that slip length could be as large as on the order of 1 mu m for fluid flows over superhydrophobic surfaces. Superhydrophobic surfaces can be achieved by patterning roughness on hydrophobic surfaces. In the present paper an atomistic-continuum hybrid approach is developed to simulate the Couette flows over superhydrophobic surfaces in which a molecular dynamics simulation is used in a small region near the superhydrophobic surface where the continuum assumption is not valid and the Navier-Stokes equations are used in a large region for bulk flows where the continuum assumption does hold. These two descriptions are coupled using the dynamic coupling model in the overlap region to ensure momentum continuity. The hybrid simulation predicts a superhydrophobic state with large slip lengths which cannot be obtained by molecular dynamics simulation alone.

Dimensionless Analysis of the Simulation of Bucket Foundations under Dynamic Load

Firstly, the main factors are obtained by use of dimensionless analysis. Secondly, the time scaling factors in centrifuge modeling of bucket foundations under dynamic load are analyzed based on dimensionless analysis and control- ling equation. A simplified method for dealing with the conflict of scaling factors of the inertial and the percolation in sand foundation is presented. The presented method is that the material for experiments is not changed while the effects are modified by perturbation method. Thirdly, the characteristic time of liquefaction state and the characteristic scale of affected zone are analyzed.

The computer simulation of primate (Macaca mulatta) spatial visual delayed response and cerebral prefrontal control function

Cerebral prefrontal function is one of the important aspects in neurobiology. Based on the experimental results of neuroanatomy, neurophysiology, behavioral sciences, and the principles of cybernetics and information theory after constructed a simple model simulating prefrontal control function, this paper simulated the behavior of Macaca mulatta completing delayed tasks both before and after its cerebral prefrontal cortex being damaged. The results indicated that there is an obvious difference in the capacity of completing delayed response tasks for the normal monkeys and those of prefrontal cortex cut away. The results are agreement with experiments. The authors suggest that the factors of affecting complete delayed response tasks might be in information keeping and extracting of memory including information storing, keeping and extracting procedures rather than in information storing process.

Exploring consensus mRNA secondary (folding) structure units by stochastic sampling and folding simulation

It is extremely difficult to explore mRNA folding structure by biological experiments. In this report, we use stochastic sampling and folding simulation to test the existence of the stable secondary structural units of-mRNA, look for the folding units, and explore the probabilistic stabilization of the units. Using this method, We made simulations for all possible local optimum secondary structures of a single strand mRNA within a certain range, and searched for the common parts of the secondary structures. The consensus secondary structure units (CSSUs) extracted from the above method are mainly hairpins, with a few single strands. These CSSUs suggest that the mRNA folding units could be relatively stable and could perform specific biological function. The significance of these observations for the mRNA folding problem in general is also discussed. (c) 2004 Elsevier B.V. All rights reserved.

QtUCP-A program for determining unit-cell parameters in electron diffraction experiments using double-tilt and rotation-tilt holders

A computer program, QtUCP, has been developed based on several well-established algorithms using GCC 4.0 and Qt (R) 4.0 (Open Source Edition) under Debian GNU/Linux 4.0r0. it can determine the unit-cell parameters from an electron diffraction tilt series obtained from both double-tilt and rotation-tilt holders. In this approach, two or more primitive cells of the reciprocal lattice are determined from experimental data, in the meantime, the measurement errors of the tilt angles are checked and minimized. Subsequently, the derived primitive cells are converted into the reduced form and then transformed into the reduced direct primitive cell. Finally all the patterns are indexed and the least-squares refinement is employed to obtain the optimized results of the lattice parameters. Finally, two examples are given to show the application of the program, one is based on the experiment, the other is from the simulation. (C) 2008 Elsevier B.V. All rights reserved.

Polarization effects simulation of AlGaN/GaN heterojunction by using a symbolistic delta-doping layer

Polarization effects in AlGaN/GaN heterojunction are simulated based on a traditional semiconductor device simulator. A delta doping layer is purposely inserted at the interface of the heterojunction in the simulation, so the ionized donors or acceptors can represent polarization-induced positive or negative fixed charges. The free electron distribution of single AlGaN/GaN heterostructures with Ga-face and N-face growth is compared, and the results of the simulation show that carrier confinement takes place only in the former structure. The dependence of sheet density of free electrons at the interface of Ga-face growth AlGaN/GaN on Al composition and the thickness of AlGaN is also investigated. The consistency of simulation results with the experiments and calculations reported by other researchers shows that this method can be effectively used to deal with the polarization effects in the simulation of GaN-based heterojunction devices. (C) 2004 Elsevier Ltd. All rights reserved.

Quantum-dot growth simulation on periodic stress of substrate

InAs quantum dots (QDs) are grown on the cleaved edge of an InxGa1-xAs/GaAs supperlattice experimentally and a good linear alignment of these QDs on the surface of an InxGa1-xAs layer has been realized. The modulation effects of periodic strain on the substrate are investigated theoretically using a kinetic Monte Carlo method. Our results show that a good alignment of QDs can be achieved when the strain energy reaches 2% of the atomic binding energy. The simulation results are in excellent qualitative agreement with our experiments. (C) 2005 American Institute of Physics.

Simulation of polarization effects in AlGaN/GaN heterojunction

A method for introducing polarization effects in the simulation of GaN-based heterojunction devices is proposed. A delta doping layer is inserted at the interface of heterojunction and the ionized donors or acceptors act as polarization induced fixed charges. Thus polarization effects can be taken into account in a traditional device simulator. Ga-face and N-face single AlGaN/GaN heterostructures are simulated, and the simulation results show that carrier confinement takes place only in the former structure while not in the latter one. The sheet density of free electrons at the interface of Ga-face AlGaN/GaN increases with the Al composition and the thickness of AlGaN. The consistence of simulation results with the experiments and calculations reported elsewhere shows that this method can effectively introduce polarization effects in the simulation of GaN-based heterojunction devices.

Kinetic Monte Carlo simulation of semiconductor quantum dot growth

Performing an event-based continuous kinetic Monte Carlo (KMC) simulation, We investigate the growth conditions which are important to form semiconductor quantum dot (QD) in molecular beam epitaxy (MBE) system. The simulation results provide a detailed characterization of the atomic kinetic effects. The KMC simulation is also used to explore the effects of periodic strain to the epitaxy growth of QD. The simulation results are in well qualitative agreement with experiments.

MEASUREMENT AND SIMULATION OF THE TURN-ON DELAY TIME JITTER IN GAIN-SWITCHED SEMICONDUCTOR-LASERS

The turn-on delay time jitter of four different unbiased gain-switched laser types is determined by measuring the temporal probability distribution of the leading edge of the emitted optical pulse. One single-mode 1.5-mu-m distributed feed-back laser and three multimode Fabry-Perot lasers emitting at 750 nm and 1.3-mu-m are investigated. The jitter is found to decrease for all lasers with increasing injection current. For multimode lasers it decreases from 8 ps excited slightly above threshold down to below 2 ps at three times the threshold current. The jitter of the distributed feedback (DFB) laser is a factor of 3-5 larger than the jitter of the three multimode lasers. A new model to predict the turn-on delay time jitter is presented and explains the experiments quantitatively.

Simulation of Banded Spherulite Patterns by Coupled Logistic Map Lattice Model in Three Dimensions

Banded spherulite patterns are simulated in three dimensions by means of a Coupled Logistic map lattice model. The patterns obtained by numerical calculation are consistent with those in experiments. The simulation results also indicate that the hand spacing is decreased with the increase of parameter mu in the Logistic map and increased with the increase of the coupling parameter e for cube lattices, and increased with the increase of the thickness of the lattice for polymer film, which is quite similar to the results in some experiments. Spiral pattern in three dimensions is also shown in this paper, which helps us understand the form of banded spherulite in polymers.

Monte Carlo simulation of the grafting of maleic anhydride onto polypropylene at higher temperature

The graft of maleic anhydride (MAH) onto isotactic polypropylene (iPP) initiated by dicumyl peroxide (DCP) at 190 degreesC was studied by means of the Monte Carlo method. The ceiling temperature theory, i.e., no possibility for the homopolymerization of MA-H to occur at higher temperatures, was used in this study. The simulation results show that most MAH monomers were grafted onto the radical chain ends arising from beta scission at a lower MAH concentration, whereas the amount of MAH monomers attached to the tertiary carbons was much larger than that grafted onto the radical chain ends at a higher MAH concentration for various DCP concentrations. This conclusion gives a good interpretation for the disagreement on the grafting sites along a PP chain. Moreover, it was found that the grafting degree increased considerably up to a peak value; thereafter, it decreased continuously with increasing MA-H concentration. The peak shifted in the lower MAH concentration direction and became lower and lower with increasing DCP concentration. When the DCP concentration was below 0.1 wt %, the peak was hardly observed. Those results are in good agreement with the experiments.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .2. Chemorheological modeling

Chemorheology and corresponding models for an epoxy-terminated poly(phenylene ether ketone) (E-PEK) and 4,4'-diaminodiphenyl sulfone (DDS) system were investigated using a differential scanning calorimeter (DSC) and a cone-and-plate rheometer. For this system, the reported four-parameter chemorheological model and modified WLF chemorheological model can only be used in an isothermal or nonisothermal process, respectively. In order to predict the resin viscosity variation during a stepwise temperature cure cycle actually used, a new model based on the combination of the four-parameter model and the modified WLF model was developed. The combined model can predict the resin viscosity variation during a stepwise temperature cure cycle more accurately than the above two models. In order to simplify the establishment of this model, a new five-parameter chemorheological model was then developed. The parameters in this five-parameter model can be determined through very few rheology and DSC experiments. This model is practicable to describe the resin viscosity variation for isothermal, nonisothermal, or stepwise temperature cure cycles accurately. The five-parameter chemorheological model has also successfully been used in the E-PEK systems with two other curing agents, i.e., the diamine curing agent with the addition of a boron trifluride monoethylamine (BF3-MEA) accelerator and an anhydride curing agent (hexahydrophthalic acid anhydride). (C) 1997 John Wiley & Sons, Inc.

Study on corrosion of steels in marine environment by corrosion simulation device

Three kinds of steels were studied using electrically connected hanging specimen in the corrosion simulation device and offshore long scale hanging specimen. The experimental results obtained by the two methods show that the device can better reflect the offshore corrosion environment. A Ni-Cu-P steel specimen was studied through analysis of the specimen's corrosion products and corrosion types. The surface of the samples before and after the removal of the rust layer produced by these two methods were observed and compared after some experiments. The microstructure of the corrosion products under different marine environments were analyzed and compared through IR. It indicated good correlation between the electrically connected hanging specimen method and the long scale hanging specimen method.