Power-Law Distributions of Component Size in General Software Systems

This paper begins by modeling general software systems using concepts from statistical mechanics which provide a framework for linking microscopic and macroscopic features of any complex system. This analysis provides a way of linking two features of particular interest in software systems: first the microscopic distribution of defects within components and second the macroscopic distribution of component sizes in a typical system. The former has been studied extensively, but the latter much less so. This paper shows that subject to an external constraint that the total number of defects is fixed in an equilibrium system, commonly used defect models for individual components directly imply that the distribution of component sizes in such a system will obey a power-law Pareto distribution. The paper continues by analyzing a large number of mature systems of different total sizes, different implementation languages, and very different application areas, and demonstrates that the component sizes do indeed appear to obey the predicted power-law distribution. Some possible implications of this are explored.     

Strain rate sensitivity of flow stress at large strains

Measurements of the strain rate sensitivity of flow stress are critically assessed. Results depend on strain and on the range of strain rates employed. Changes in strain hardening and transients in the flow stress are discussed.     

Mechanisms of initial melt/substrate heat transfer pertinent to strip casting

An experimental study of initial solidification of 304 stainless steel melts in direct contact with copper substrates under conditions approximating the meniscus region of a strip caster has highlighted the importance of interfacial heat transfer during the first 30 ms of contact. The mechanisms governing initial heat transfer are strongly influenced by dynamic wetting phenomena. This has been illustrated experimentally by the effects of the buildup and melting of oxide films such as manganese silicates at the interface during successive immersions, by the role of surface active agents such as tellurium in the melt, and by the use of specially designed substrate textures to control contact areas. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Software: What's In It and What's It In?

IEEE Software's new series of Impact columns intends to get a better quantitative insight into the impact of software on various businesses. This introduction describes the reasoning behind the columns. All contributors will be asked to quantify the size (in lines of code or another size measure) and volume (number of copies sold per year or another measure) of their projects. This should allow the software developers to position and compare the experiences coming out of the different industries. We hope to publish three to six columns a year and to solicit submissions as momentum grows. Both engineering managers and business managers are encouraged to submit a column. We've already lined up the first columns with submissions from the mobile phone, computer and automotive industries. Our proposal's wide scope should let us accept contributions from large or small programs, low or high volume projects, open or closed source projects, embedded or commercial-off-the-shelf software, and in-house or outsourced software development.     

Cadmium concentration in durum wheat grain (Triticum turgidum) as influenced by nitrogen rate,seeding date and soil type

BACKGROUND: Cadmium (Cd) is a trace element that has been associated with various human health problems. Cd enters plants, either by direct absorption through leaves or by uptake from soils, allowing Cd into the food chain. Nitrogen (N) fertilizer management is important in optimizing crop yield and protein content of durum wheat, but may influence Cd availability and hence Cd concentration in crops, with the effects being strongly influenced by environmental conditions and crop cultivar. RESULTS: In field studies, Cd and protein concentration in durum wheat grain differed between cultivars and were strongly affected by N application, with only minor effects of N occurring on concentration and uptake of P and Zn. Protein content increased significantly with N application in five of six site‐years, with the response being generally independent of cultivar and seeding data. Cd concentration also increased with N application in five of six seeding dates, with the response being greater in AC Melita than Arcola in three of the six site‐years. There were large differences in Cd concentration from year to year and with seeding date, indicating a strong environmental influence. CONCLUSIONS: This study shows that different cultivars accumulate different levels of Cd in the grain and that seeding date and nitrogen fertilizer management can influence grain Cd concentration, with the magnitude of effects varying with environmental factors. In the future we may be able to manipulate management practices to optimize protein concentration and minimize Cd concentration in durum wheat, which could help to address the health and safety concerns of consumers. © Society of Chemical Industry and Her Majesty the Queen in right of Canada     

Dynamic reactive wetting and its role in hot dip coating of steel sheet with an Al-Zn-Si alloy

The effect of substrate preheat temperature on the dynamic wetting of 55Al-43.4Zn-1.6Si hot dip coating melts on low-carbon steel substrates has been investigated. An experimental apparatus based on the sessile drop technique was developed, which allowed the substrate to be preheated to a different temperature than that of the droplet. The initial wetting and spreading of the molten metal droplet on the substrate was recorded at 1000 frames per second using a high-speed digital camera. Wetting was improved (ϑ decreased from 120 to 25 deg) as the substrate preheat temperature was increased from room temperature and approached the droplet temperature, beyond which the improvement in wetting was negligible. Immersion experiments using a thermocouple instrumented substrate dipped into a coating bath were performed for various substrate preheat temperatures. Interfacial heat fluxes and interfacial resistances were calculated from the temperature responses. The “minimum” interfacial resistance was decreased by an order of magnitude (1 × 10⁻⁴ to 2 × 10⁻⁵ m² K/W) as the substrate preheat temperature was increased from room to bath temperature. The reduction in interfacial resistance was related to the improvement of the initial wetting and the increase in mass transfer of iron atoms from the substrate across the interface. There was an apparent increase in the minimum interfacial resistance for substrate temperatures greater than the bath temperature. This was due to the increased rate of alloy layer formation and the exothermic nature of the Fe-Al interfacial reactions. The significance of these findings was discussed with respect to the mechanism of alloy layer formation at the interface during the initial stages of solid-liquid contact. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Quantifying the heats of coal devolatilization

An experimental apparatus was developed to measure the thermal properties of coal in order to determine the heats of reactions during devolatilization. Samples were continuously heated from room temperature to 1000 °C at a constant heating rate. Measuring the temperature changes at two selected locations within the sample allowed the calculation of the apparent specific heat and thermal conductivity by employing an inverse numerical technique to solve the heat conduction equation. Five major reaction regions of coal devolatilization were detected: dehydration, transition, resolidification, secondary reactions and contraction reactions. The most complex region was the exothermic resolidification reaction, where coking coals exhibited significant differences from the thermal coals due to higher plasticity. Small endothermic reaction related to tar vaporization also appeared in this region, becoming stronger at higher heating rates. The exothermic contraction reactions ranging between 140 and 250 MJ/m³ appeared above 600 °C as a result of the dehydrogenation and reformation of stronger C-C bonds. The effects of the heating rate within the range of 5°C/min to 100 °C/min were also examined, showing a shift of the reaction peaks to higher temperatures at increased heating rates. The thermal conductivity and diffusivity were almost constant until the decomposition point, rapidly increasing at higher temperatures. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Circle approximation using integral B-splines

A method to approximate a circular arc of any sweep angle with integral B-spline curves of any degree is presented. The idea is to interpolate end derivatives as well as some internal points with integral B-splines of given degree and continuity. The critical element is the choice of the right end derivative directions and magnitudes. The points and the derivatives at these locations are sampled uniformly using the trigonometric equation of the circle. The method is very general in that any degree and any level of parametric continuity can be specified.