An assumed‐gradient finite element method for the level set equation

The level set equation is a non‐linear advection equation, and standard finite‐element and finite‐difference strategies typically employ spatial stabilization techniques to suppress spurious oscillations in the numerical solution. We recast the level set equation in a simpler form by assuming that the level set function remains a signed distance to the front/interface being captured. As with the original level set equation, the use of an extensional velocity helps maintain this signed‐distance function. For some interface‐evolution problems, this approach reduces the original level set equation to an ordinary differential equation that is almost trivial to solve. Further, we find that sufficient accuracy is available through a standard Galerkin formulation without any stabilization or discontinuity‐capturing terms. Several numerical experiments are conducted to assess the ability of the proposed assumed‐gradient level set method to capture the correct solution, particularly in the presence of discontinuities in the extensional velocity or level‐set gradient. We examine the convergence properties of the method and its performance in problems where the simplified level set equation takes the form of a Hamilton–Jacobi equation with convex/non‐convex Hamiltonian. Importantly, discretizations based on structured and unstructured finite‐element meshes of bilinear quadrilateral and linear triangular elements are shown to perform equally well. Copyright © 2005 John Wiley & Sons, Ltd.     

The inhibitive action of dimethyltin dichloride towards the corrosion of aluminium in hydrochloric acid and sodium hydroxide solutions

The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of dimethyltin dichloride as corrosion inhibitor has been studied using hydrogen evolution and thermometric methods. The two methods gave consistent results. The higher inhibition efficiency of this compound in acidic than in alkaline media may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive. The adsorption of this compound was found to obey Frumkin adsorption isotherm.     

RTNCSU: A COMPUTER PROGRAM FOR CALCULATING THE PARAMETERS OF THE CROSS FLOW FINITE STAGE MODEL FOR THE RESIDENCE TIME DISTRIBUTION IN TUMBLING MILLS FROM TRACER DATA

Based on a least squares method which searches for the best value of the parameters of the cross-flow finite stage model for residence time distributions in tumbling mills, a computer program package is presented for treating either open-circuit or closed-circuit tracer test data taken under various test conditions. The test conditions that are treated include the one and two detector approaches to closed-circuit tracer transient tests with optional perfectly mixed counting sumps in the mill input and/or mill discharge streams. The parameter search technique requires good initial estimates of the parameter values which are provided by the moments of the experimental data. This approach makes the program relatively straightforward to use. Simulated results demonstrating the use of the program are presented.     

A self-binning BIST structure for data communications transceivers

Data communication chips are becoming ubiquitous, and their operating frequencies are constantly increasing. Testing of these devices using customary methods has become increasingly challenging and difficult. An on-chip built-in self-testing (BIST) approach that overcomes such difficulties is proposed in this paper to test the functionality of transceivers on a data communications chip. The proposed BIST is capable of performing functional testing at different speeds, thus facilitating binning of the devices according to their working speeds. The concept has been applied to test a 400 Mbps three-port IEEE 1394a system, implemented in a 0.35 /spl mu/m CMOS technology.     

Deducing ink thickness variations by a spectral prediction model

Most existing techniques for regulating the ink flow in offset presses rely on density measurements carried out on specially printed patches. In the present contribution, we develop a methodology to deduce ink thickness variations from spectral measurements of multichromatic halftone patches located within the printed page. For this purpose, we extend the Clapper‐Yule spectral reflectance prediction model by expressing the transmittance of the colorants composed of superposed inks as a function of the ink transmittances and of fitted ink layer thicknesses. We associate to each ink an ink thickness variation factor. At print time, this ink thickness variation factor can be fitted to minimize a difference metric between predicted reflection spectrum and measured reflection spectrum. The ink thickness variations deduced from multichromatic halftones allow to clearly distinguish between normal ink volume, reduced ink volume, or increased ink volume. This information can then be used for performing control operations on the printing press. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 432–442, 2009     

The effect of lithium oxide on the threshold field of ZnO varistors

Lithium oxide in form of Li₂CO₃ solution is added with contents of 0–200 ppm to two ZnO-based varistors standard formulations, once with Sb₂O₃ and the other without. According to Li₂CO₃ concentration, both threshold field and energy absorption capability evolution are studied. It is found that with the benefit of antimony, the lithium allows reaching high threshold field but concomitantly, low energy absorption capability. Without antimony, threshold fields up to 300 V/mm are attained, associated with a fair energy absorption capability. With 100 ppm of Li₂CO₃, optimum couple of values (315 V/mm; 115 J/cm³) is achieved. With 200 ppm of Li₂CO₃, threshold field exceeds 500 V/mm but energy absorption capability falls below 50 J/cm³. Correlations with SEM microstructures observations suggest that lithium increases voltage barrier height by decreasing donor density and that spinel phases (Zn₇Sb₂O₁₂) have detrimental effects on the electrical absorption capability by limiting the density of current, reducing the effective current path from one ZnO grain to another.     

CMOS Digital Time Amplifiers for High Resolution Timing Measurement

In this paper the concept of time amplification in the digital domain is introduced along with a simple CMOS implementation. The time amplifier is presented in the context of a high resolution time-to-digital converter. The issue of limited linearity of the time amplifier is addressed through the utilization of an efficient calibration technique that allows for the correction of such non-ideality. Experimental data validates the design of a resistively loaded time amplifier with a gain of 182 Second/Second. Also, simulations suggest that the time amplifier can be designed for gains up to a few thousands with input dynamic ranges in excess of a few hundred picoseconds. Also, some figures of merit and performance are introduced along with a discussion on some of the trade-offs involved in the design of a time amplifier.Mourad Oulmane received the B.A.Sc. degree from the University of Constantine, Algeria, in 1995, and the M.A.Sc. degree in physics from the Institut National Polytechnique de Grenoble, France, in 1997, the M.Eng. Degree from McGill University in 2001 where he is pursuing a PhD Degree. His research interests include analog/mixed-signal/RF IC design as well as interconnect and semiconductor technologies design and modeling.Gordon W. Roberts received the B.A.Sc. degree from the University of Waterloo, Canada, in 1983, and the M.A.Sc. and Ph.D. degrees from the University of Toronto, Canada, in 1986 and 1989, respectively, all in electrical engineering. He is currently on leave from McGill University as a co-founder of DFT Microsystems, Inc., where he holds the position of Chief Technical Officer. At McGill University he is a full professor where he holds the James McGill Chair in Electrical and Computer Engineering. He has published numerous papers in scientific journals and conferences, and he has contributed chapters to various industrially focused textbooks. In addition, he has co-written five textbooks related to analog IC design and mixed-signal test for undergraduate and graduate engineering programs. Dr. Roberts has held many administration roles within conference organizations; most recently he was the 2003 program chair of the IEEE International Test Conference. Dr. Roberts is a Fellow of the IEEE.     

Textural variations of acid-treated serpentine

A natural serpentine deposit was subjected to treatment with hydrochloric acid of different concentrations, and for varying times. Changes in the texture parameters were determined from adsorption isotherms of nitrogen. In general, treatment with increasing acid concentrations (up to 25%) leads to an increase in various characteristics of serpentine, i.e. weight loss, dissolved iron oxide, “free” silica, surface area, and pore volume. Prolonged treatment results in only slight changes in such parameters. Solids of high specific surface areas (up to 300 m²/g) and of microporous character (mean pore radii ca 15–20 Å) are obtained.     

Stability limits and NO emissions of premixed swirl ammonia-air flames enriched with hydrogen or methane at elevated pressures

This study reports measurements of stability limits and exhaust NO mole fractions of technically-premixed swirl ammonia-air flames enriched with either methane or hydrogen. Experiments were conducted at different pressures from atmospheric to 5 bar, representative of commercial micro gas turbines. The full range of ammonia fractions in the fuel blend, x_NH3, was considered, from 0 (pure methane or hydrogen) to 1 (pure ammonia), covering very lean (φ = 0.25) to rich (φ = 1.60) equivalence ratios. Results show that increasing pressure widens the range of stable equivalence ratios for pure ammonia-air flames. Regardless of pressure, there is a critical ammonia fraction above which the range of stable equivalence ratios suddenly widens. This is because flashback does not occur anymore when the equivalence ratio is progressively increased towards stoichiometric and rich blowout occurs instead. This critical ammonia fraction increases with pressure and is larger for ammonia-hydrogen than for ammonia-methane. Provided that enough hydrogen is blended with ammonia (x_NH3 < 0.9), flames with very lean equivalence ratios (φ < 0.7) can be stabilized and these yield competitively low NO emissions (<200 ppm), regardless of pressure. For this reason, very lean swirl ammonia-hydrogen-air flames are promising candidates for micro gas turbines. However, N₂O emissions have the potential to be unacceptably large for these operating conditions if heat loss is too large or residence time is too short. As a consequence, the post flame region must be considered carefully. Due to the lower reactivity of methane compared to that of hydrogen, very lean swirl ammonia-methane-air flames could not be stabilized and good NO performance is limited to rich equivalence ratios for ammonia-methane fuel blends. The equivalence ratio above which good NO performance depends on pressure and bulk velocity.     

Prediction of concrete initial setting time in field conditions through multivariate regression analysis

Construction of large concrete structures usually requires pouring multiple batches of concrete mixes along 1 day, which creates setting irregularities that increase the potential of crack development within pours. For the case of bridge decks, it is recommended that the initial concrete material should stay plastic over the entire casting operation of a poured bridge segment. Uniform setting of multiple batches is possible if setting times could be predicted and controlled in field conditions. In this study, more than 70 different Class K concrete mixes were manufactured and cast in field conditions, which provided material characteristics along with environmental data that were used to predict concrete initial setting times through multivariate regression analysis. Two prediction models were achieved, corresponding to the addition of set retarding and set accelerating admixtures, respectively. Validating field tests demonstrated that good predictions of concrete initial setting times can be accomplished with 2% error, when accurate field weather forecasts are available. This work also demonstrates the use of the prediction relations, with the objective of achieving uniform thermo-mechanical properties of a pouring sequence in the field.