Kinetics of copolyurethane network formation

Cure kinetics for the formation of copolyurethane networks of various compositions based on hydroxy-terminated polybutadiene (HTPB), poly(12-hydroxy stearic acid-co-TMP) ester polyol(PEP), and different isocyanates has been studied through viscosity build up during the cure reaction. The viscosity(N)—time (t) plots conform to the equation N = ae^bt, where a and b are empirical constants, dependent on the composition and the nature of the polyols and the isocyanates. The rate constants (k) for viscosity build up, evaluated from the slopes of dN/dt versus N plots at different temperatures, were found to vary significantly from 0.0073 to 0.25 min⁻¹; and the activation energies for gelation were found to be in the range 20 to 40 kJ mol⁻¹. The results have been interpreted in terms of the dependence of the rate constants on structural characteristics of the prepolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1795–1801, 1997     

为集成和成本而战

我们如今所看到的最大的一个变革,就是市场现在成为了一个实施、分析并模拟的圈子.现在已经有5～6个分区叠合成了一个.由于65nm节点上芯片的复杂性,它不再是一堆工具或者点解决方案.     

Furfural hydrogenation over carbon‐supported copper

Furfural hydrogenation over copper dispersed on three forms of carbon – activated carbon, diamond and graphitized fibers – were studied. Only hydrogenation of the C=O bond to form either furfuryl alcohol or 2‐methyl furan occurred at temperatures from 473 to 573 K. Reduction at 573 K gave the most active catalysts, all three catalysts had activation energies of 16 kcal/mol, and turnover frequencies were 0.018–0.032 s^-1 based on the number of Cu⁰ + Cu⁺ sites, which were counted by N₂O adsorption at 363 K and CO adsorption at 300 K, respectively. The Cu/activated carbon catalyst showed no deactivation during 10 h on stream, in contrast to the other two catalysts. A simple Langmuir–Hinshelwood model invoking two types of sites was able to fit all kinetic data quite satisfactorily, thus it was consistent with the presence of both Cu⁰ and Cu⁺ sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rotating anisotropic disc of uniform strength

A procedure to design a constant thickness composite disc of uniform strength by radially tailoring the anisotropic elastic constants is proposed. A special case of an isotropic disc with radially varying modulus is also examined. Analytical results are also compared with FEM calculations for two cases of radially varying anisotropy and for an isotropic disc with variable modulus.     

Global performance evaluation of image features for visual servo control

The performance of a visual servo control system depends on the set of image features used in the control loop. Although some local performance measures have been used for evaluating the image features, their usage in the process of feature selection requires on-line computation that is difficult to realize in real-time, especially with a large number of candidate features. In this article, we introduce a global measure for evaluating the performance of image features for visual servo tasks. This measure can be computed off-line and it takes into account several desirable properties of the image features, including minimization of singularities in the image Jacobian, linearity of feature variation, and maximization of feature resolution. For a given kinematic and imaging model of a robot/camera setup, the measure can be used for a variety of visual servo tasks. A numerical approximation scheme is presented along with several computed examples to illustrate the utility of this measure. © 1996 John Wiley & Sons, Inc.     

Energy and chemicals from rice husk

Rice husk is the only agro residue having maximum siliceous ash content and available in dry form. The present work on rice husk describes processes for producing controlled carbon-silica mixtures in amorphous form, electronic-grade potassium silicate and activated carbon.

Rice husk is first pyrolised in a reactor at less than 973 K to obtain the char which is subsequently heated and activated with steam at 1073–1173 K for about 1 h in another reactor. The char is leached with HCl. Analysis of the leached char indicates that it is amorphous in nature and contains mainly 40% carbon and 56% silica with small quantities of volatile matter. The utility of the material as filler for reinforcement of rubbers is tested. Test results show that a tenfold increase in tensile strength and modulus of elasticity can be achieved with 100 phr.

In another development, the leached char is digested with 10–15% KOH solution in the temperature range of 303–373 K for about 1–10 h. It is found that electronic-grade potassium silicate could be easily produced compared to the conventional method of fusion of sand with alkali at 1273–1473 K. The residue from this process is a good-quality activated carbon. A process flowsheet is presented for producing these chemicals with energy recovery aspects from rice husk.     

Influence of the dislocation density on the performance ofheteroepitaxial indium phosphide solar cells

The authors point out that heteroepitaxial indium phosphide solar cells developed to date have low efficiency due to misfit dislocations. Dislocations act as recombination centers and strongly influence the solar cell performance. Calculations have been made to study the dependence of heteroepitaxial InP solar cell efficiency on dislocation density. The effects of surface recombination velocity and cell emitter thickness are also considered. Calculated results are compared with the available experimental results on representative InP solar cells. It is shown that heteroepitaxial InP cells with over 20% AM0 efficiency could be fabricated if dislocation density can be reduced to <10⁵ cm^-2 and the surface recombination velocity reduced to <10⁵ cm/s