Thin film deposition on a corrugated surface: A molecular dynamics approach

This paper presents the use of molecular dynamics (MD) simulation in the investigation of the surface topography of early-stage film growth on a GMR (giant-magnetoresistance) corrugated structure. The size of the simulated system is limited in order to reduce the computational workload. The numerical model adopts the Morse potential and the Verlet-leapfrog time evolution scheme [R.W. Hockney, 1970; D. Potter, 1972 (Chapter 5). [1]] to describe the atomic interactions which take place between the atoms. The impact energy transferred from the incident atoms to the substrate is modeled by rescaling the atoms within the upper substrate layers. It is found that the important properties of the film-substrate system may be obtained after the deposition of just several atomic layers. The influence of the impact velocity upon the coating parameters is investigated by varying the incident energy of the deposited atoms. The current results indicate that the surface coverage is poor, when atoms are deposited at low incident energies upon a low temperature substrate. At a higher incident energy, the deposited film tends to exhibit a quasi-layer-by-layer growth mechanism, which results in an improved surface coverage. Finally, it is demonstrated that a distinct quasi-fluid behavior is evident on the substrate when the atoms are deposited at high incident energies.     

Geotechnical properties of the soft soil in Guangzhou College City

The paper describes some geotechnical properties of the soft soils in Guangzhou College City, China, which are difficult to both sample and test. Laboratory and in situ tests were carried out to assess the physical and mechanical indices of the soils. The data were statistically analyzed and linear regression undertaken such that equations could be developed by which the geotechnical properties of the soft soils can be predicted. The statistical validity of the degree of correlation confirmed that using these equations, the mechanical indices can be estimated from physical indices determined by routine testing.      

水上地震折射互换法误差分析

在理论上，用源检互换的方法进行折射地震勘探是没有误差的，在某些特殊条件下无法铺设检波器而又必须进行折射地震勘探时它也是唯一的选择，然而，在实际工作中，由于各种因素的影响，其误差是不可忽略的。为此，本文从地震折射运动学的角度对水上地震折射互换法因过河钢丝绳的重量、水的流速和流向、炮点深度等客观因素造成的解释误差进行了分析，揭示了水上地震折射互换法应注意的问题。这对水上地震折射互换法的资料解释进行误差校正提供了理论基础。     

Evolving Fault-Tolerant Neural Networks

In this paper, genetic algorithm is used to help improve the tolerance of feedforward neural networks against an open fault. The proposed method does not explicitly add any redundancy to the network, nor does it modify the training algorithm. Experiments show that it may profit the fault tolerance as well as the generalisation ability of neural networks.     

Novel blood-compatible waterborne polyurethane using chitosan as an extender

A series of novel block polymers of polyurethane (PU) and chitosan have been prepared in two steps. The first step is the preparation of PU prepolymer, obtained from polytetramethylene oxide glycol (PTMO, M_n = 1000), isophrone diisocyanate (IPDI), and 2,2′-dimethylol propionic acid (DMPA), followed by ionizing PU prepolymer with triethylamine (TEA). The second step involves PU chain-extended by water-soluble chitosan of low molecular weight (M_n = 5000) by self-emulsion polymerization method. The sizes of the latex particles, morphology, and copolymer architecture have been characterized by dynamic light scattering (DLS), general tensile test, infrared spectroscopy (IR), surface contact angle measurement, and transmission electron microscopy (TEM). Furthermore, it shows that the addition of chitosan remarkably increases anticoagulative property of PU elastomers confirmed by the recalcification time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of the graft yield of maleic anhydride on the rheological behaviors,mechanical properties,thermal properties,and free volumes of maleic anhydride grafted high‐density polyethylene

The rheological behavior, thermal properties, and molecular mobility of a series of maleic anhydride (MA) grafted high‐density polyethylenes were characterized and evaluated. The rheological behavior was studied with a Haake minilaboratory. The viscosity of the samples in their melt state decreased with an increase in the graft yield, and this could be attributed to the higher molecular mobility for samples with a higher degree of grafting. The thermal properties were investigated with dynamic mechanical analysis and differential scanning calorimetry. Positron annihilation lifetime measurements were used to study the effect of the degree of grafting on the chemical environment and the atomic‐scale free‐volume properties. It was found that the grafted MA group played a significant chemical inhibition role in positronium formation when the graft yield was low. The results also indicated that the higher the degree of grafting was, the broader the free‐volume distribution was. The relationship between the microstructure and rheological behavior is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of branched polyacrylonitrile through self‐condensing vinyl copolymerization

Branched polyacrylonitrile (PAN) was prepared through a self‐condensing vinyl copolymerization of acrylonitrile and 2‐(2‐bromopropionyloxy)ethyl acrylate (BPEA). The branched architecture of the product was confirmed by NMR spectra and the average degree of branching (DB ) was estimated. Through a comparison of the intrinsic viscosity of the product with that of its linear analogue, the contraction factor g′ was calculated. It was found that the viscosity of the branched PAN was obviously lower that that of linear PAN. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal and mechanical properties of epoxy composites reinforced by a natural hydrophobic sand

If a low weight percentage of crude fine fillers can improve properties of polymer materials directly without complicated chemical treatment process involved, it will be significant for many industrial applications. Our previous study indicated that a kind of Cancun natural sand could be an effective filler material for polymer composites. In this current work, the epoxy composites reinforced by this kind of natural sand particles were prepared and thermal and mechanical properties of the composites containing up to 5 wt % of the sand particles were characterized. Results showed that the highest flexural strength appears in the epoxy composite containing 1 wt % sand particles. A damage model was used to interpret the flexural properties, which showed an acceptable agreement with the experimental results. The glass transition temperature, high temperature storage modulus, and dimensional stability of the sand/epoxy composites monotonically increased with the addition of the sand particles. The sand particle/epoxy composites also displayed a noticeable enhancement in thermal conductivity. Theoretical analysis showed that in addition to conduction, other heat transport mechanisms played roles in the improved heat transmission through the composites. As a natural porous micron-scale material, Cancun sand has the potential for applications in cost-effective composites with enhanced mechanical and thermal properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics study of Ti[O(CH2)4OCHCH2]4 initiated ring‐opening polymerization of ε‐caprolactone by differential scanning calorimetry

Chemical shrinkage was used for the in situ measurement of the progressing chemical stabilization reactions and the influence of ozone during the stabilization of polyacrylonitrile. A method for evaluating the activation energy through the sensitivity temperature is presented. The calculated results show that the activation energies were 161.57 kJ/mol in air and 181.23 kJ/mol in ozone-enriched air. Therefore, the chemical reactions were postponed during stabilization in ozone-enriched air. Ozone seemed to act in three ways: first, ozone promoted the formation of the serious skin–core structure. Second, ozone accelerated the chemical reactions and shortened the stabilization time at lower heating rates. Third, ozone postponed the chemical reactions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008