A study on flame interaction between methane/air and nitrogen-diluted hydrogen–air premixed flames

Numerical and experimental studies are conducted to grasp downstream interactions between premixed flames stratified with two different kinds of fuel mixture. The selected fuel mixtures are methane and a nitrogen-diluted hydrogen with composition of 30% H₂ + 70% N₂. Extinction limits are determined for methane/air and (30% H₂ + 70% N₂)/air over the entire range of mixture concentrations. These extinction limits are shown to be significantly modified due to the interaction such that a mixture much beyond the flammability limit can burn with the help of a stronger flame. The lean extinction limit shows both the slanted segments of lower and upper branches due to the strong interaction with Lewis numbers of deficient reactant less than unity, while the rich extinction limit has a square shape due to the weak interaction with Lewis numbers of deficient reactant larger than unity. The regimes of negative flame speed show an asymmetric aspect with a single wing shape. The negative flame always appears only when methane is weak. The extent of interaction depends on the separation distance between the flames, which are the functions of the mixtures’ concentrations, the strain rate, the Lewis numbers, and the preferential diffusions of the penetrated hydrogen from the nitrogen-diluted hydrogen flame. The important role of preferential diffusion effects of hydrogen in the flame interaction is also discussed.     

A 100-dB gain-corrected delta-sigma audio DAC with headphone driver

An oversampled digital-to-analog converter (DAC) with a 100-dB A-weighted dynamic range is presented. It uses a switched-capacitor (SC) array to transfer the sampled charges directly into the headphone driver. The overall DAC gain is precisely controlled by a novel reference stage. A new dynamic element matching algorithm, based on split-set data-weighted averaging (SDWA), is used to improve the dynamic range and to reduce the nonlinearity caused by mismatches in the multibit DAC.     

Effects of urea and curing catalysts added to the strand board core‐layer binder phenol–formaldehyde resin

Effects of adding urea to the strand board core‐layer phenol–formaldehyde (PF) resin were investigated in conjunction with cure‐accelerating catalysts. Ten percent urea based on the liquid resin weight was added at the beginning, at three different middle stages of polymerization, and at the end of PF resin synthesis. No significant cocondensation between the urea and PF resin components occurred as identified by ¹³C NMR analyses, which corroborated well with the curing and strand board bonding performance test results. The various urea addition methods resulted in resins that slightly differ in the various tests due to the urea's temporary holding capacity of formaldehyde. The preferred method of urea addition was found to do it in the later part of PF resin synthesis for convenience, consistency, and slightly better overall performance. Some cure‐accelerating catalysts were shown to reduce the thickness swelling of strand boards. This study showed the usefulness of adding some urea to strand board core‐layer binder PF resins of replacing higher cost phenolic components with lower cost urea. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Properties of Symmetric Fitness Functions

The properties of symmetric fitness functions are investigated. We show that the search spaces obtained from symmetric functions have the zero-correlation structures between fitness and distance. It is also proven that symmetric functions induce a class of the hardest problems in terms of the epistasis variance and its variants. These analyses suggest that the existing quantitative measures cannot discriminate among symmetric functions, which reveals critical limitations of the measures. To take a closer look at the symmetric functions, additional analyses are performed from other viewpoints including additive separability and boundedness. It is shown that additive separability in a symmetric function is closely related to the symmetry of its subfunctions. This elucidates why most of the well-known symmetric fitness functions are additively inseparable. The properties of two-bounded symmetric functions are investigated and they are utilized in designing an efficient algorithm to check additive separability for the two-bounded functions. Throughout this paper, we heavily use the generalized Walsh transform over multary alphabets. Our results have an independent interest as a nontrivial application of the generalized Walsh analysis.     

Selective emitter using porous silicon for crystalline silicon solar cells

This study is devoted to the formation of high–low-level-doped selective emitter for crystalline silicon solar cells for photovoltaic application. We report here the formation of porous silicon under chemical reaction condition. The chemical mixture containing hydrofluoric and nitric acid, with de-ionized water, was used to make porous on the half of the silicon surface of size 125×125 cm. Porous and non-porous areas each share half of the whole silicon surface. H₃PO₄:methanol gives the best deposited layer with acceptable adherence and uniformity on the non-porous and porous areas of the silicon surface to get high- and low-level-doped regions. The volume concentration of H₃PO₄ does not exceed 10% of the total volume emulsion. Phosphoric acid was used as an n-type doping source to make emitter for silicon solar cells. The measured emitter sheet resistances at the high- and low-level-doped regions were 30–35 and 97–474 Ω/□ respectively. A simple process for low- and high-level doping has been achieved by forming porous and porous-free silicon surface, in this study, which could be applied for solar cells selective emitter doping.     

Chemical fixation of carbon dioxide to copolymers bearing cyclic carbonate group

This study is related to the investigation of the chemical fixation of carbon dioxide to copolymers bearing a cyclic carbonate group and their application to polymer blends. In the synthesis of (2-oxo-l,3-dioxolan4-yl) methyl vinyl ether (OVE) from glycidyl vinyl ether (GVE) and CO₂, quaternary ammonium salt catalysts showed good yield of OVE. The results with long alkyl chain and with lower accessibility showed a higher catalytic activity. Mixed catalyst of PEG-4000 and Nal showed higher catalytic activity than Nal alone. The copolymer of OVE and acrylonitrile (AN) was prepared by radical copolymerization in acetonitrile at 60 °C. The monomer reactivity ratios were given as r₁(OVE)=0.36 and r₂(AN)=1.21 in the copolymerization of OVE and AN. The films of poly(OVE-co-AN)/PVC blends were cast from DMF. The poly(OVE-co-AN)/PVC blends showed good miscibility over whole composition ranges.     

A trigonometric formulation of the LMS algorithm for realization on pipelined CORDIC

This paper presents an alternate formulation of the least mean square (LMS) algorithm by using a set of angle variables monotonically related to the filter coefficients. The algorithm updates the angles directly instead of the filter coefficients and relies on quantities that can be realized by simple CORDIC rotations. Two architectures based on pipelined CORDIC unit are proposed which achieve efficiency either in time or in area. Further simplifications result from extending the approach to the sign-sign LMS algorithm. An approximate convergence analysis of the proposed algorithm, along with simulation results showing its convergence characteristics are presented.