Co-evolution as a computational and cognitive model of design

Co-evolutionary design has been developed as a computational model that assumes two parallel search spaces: the problem space and the solution space. The design process iteratively searches each space using the other space as the basis for a fitness function when evaluating the alternatives. Co-evolutionary design can also be developed as a cognitive model of design by characterizing the way in which designers iteratively search for a design solution, making revisions to the problem specification. This paper presents the computational model of co-evolutionary design and then describes a protocol study of human designers looking for evidence of co-evolution of problem specifications and design solutions. The study shows that co-evolutionary design is a good cognitive model of design and highlights the similarities and differences between the computational model and the cognitive model. The results show that the two kinds of co-evolutionary design complement each other, having strengths in different aspects of the design process. Electronic Publication     

A physically based approach to granular media mechanics: grain-scale experiments,initial results and implications to numerical modeling

It is generally appreciated that the mechanical behavior of granular media depends fundamentally on the interaction of the constituent particles, and that the validity of numerical models of granular media would be greatly improved with knowledge of the grain-scale mechanics. However, most supporting experimental work has been conducted on highly idealized materials, and a limited amount of information exists on grain-scale force–displacement relationships for naturally occurring materials. To address this shortcoming, we are conducting a program that integrates laboratory experiments on grains of naturally occurring aggregate with the discrete element modeling method, with the goal of relating the grain-scale physical and mechanical properties of granular media to bulk behavior. The paper describes the equipment and methods that have been developed to conduct close-loop controlled, grain-scale experiments under monotonic and cyclic loading conditions, and presents results from an initial set of experiments on unbonded grains. The implications of the grain-scale results to the discrete element model are discussed. Discussions center on the applicability of a physically based approach to the mechanics of granular media in general. In light of future exploration missions and the resulting need to predict the mechanical properties of lunar and planetary regoliths, the paper examines the potential usefulness of our physically based approach to the problem of predicting the behavior of the types of materials found in those environments.     

Nickel and chromium cycles: Stocks and flows project part IV

Nickel and chromium are essential ingredients in alloys increasingly important for energy-efficient, environmentally friendly modern technology. Quantitative assessment of the flows of these metals through the world economy from resource extraction to final disposal informs resource policy, energy planning, environmental science, and waste management. This article summarizes the worldwide technological cycles of nickel and chromium in 2000. Stainless steel is the major use of these metals, but they serve numerous other special needs, as in superalloys for high-temperature service, as plating materials, and in coinage. Because they are used primarily in alloys, novel recycling issues arise as their use becomes more widespread. “... the great New York and St. Louis double track, nickel plated railroad...” — Norwalk, Ohio, Chronicle 10 March 1881 announces arrival of surveyors for the future Nickel Plate Railway “Later [1911] I formed an alloy of Iron and Chromium, which showed remarkable resistance to rust and tarnish ... [It was] rediscovered by an Englishman named Brearley, in 1914.” —Elwood Haynes to Stephen F. Roberts, 17 January 1925     

Influence of the silicon surface treatment by plasma etching and scratching on the nucleation of diamond grown in HFCVD - a comparative study

A comparative study for the nucleation of diamond was carried out using surface treatment like (i) surface scratching with 1 μm diamond paste and (ii) surface etching using chlorine plasma at different RF powers (50, 100 and 150 W). Atomic force microscopic study shows variation in roughness from 31 nm to 110 nm. Scratching results in random scratches, whereas plasma etches a surface uniformly. Scanning electron microscopic observations show well faceted crystallites with a predominance of angular shaped grains corresponding to 〈100〉 and 〈110〉 crystallite surfaces for the scratched as well as plasma etched substrate. Surface etching at 150 W plasma power results in a better growth in comparison with 50 and 100 W plasma powers. Chlorine-radical is found responsible for the changes in the growth morphology. Raman spectroscopy shows a sharp peak at 1,332 cm⁻¹ and a peak at ∼1,580 cm⁻¹ for both samples.     

Effects of partial recrystallization on high-cycle fatigue deformation and crack generation of a nitrogen-strengthened 32Mn-7Cr austenitic steel at liquid-nitrogen temperature

To achieve higher fatigue resistance against subsurface crack generation, both the refinement of grain structure and the introduction of mobile dislocations on various slip systems have been shown to be effective in the 32Mn-7Cr austenitic steel. A novel treatment which consisted of cold grooved rolling and partial recrystallization was introduced to modify the microstructure. High-cycle fatigue properties and fatigue-crack generation were investigated for both the solution-treated (ST) and the partially recrystallized (PR) materials at 77 K. The PR material displayed higher fatigue strength than the ST material, especially in the high-cycle regime. No subsurface crack generation was detected for the PR material; however, it appeared in the lower peak stress and/or in the longer-life range for the ST material. Intergranular facets formed a subsurface crack initiation site in the ST material. Since the dislocation structure that developed in the fatigued PR material assisted homogeneous and multidirectional plastic deformation, the localized deformation and/or the stress concentration at the grain boundaries by coplanar arrays were believed to be relieved. Therefore, intergranular cracking due to incompatibility at a grain boundary may disappear.     

A criterion for atomicity revisited

Concurrent and reactive programs are specified by their behaviours in the presence of a nondeterministic environment. In a natural way, this gives a specification (ARW) of an atomic variable in the style of Abadi and Lamport. Several implementations of atomic variables by lower level primitives are known. A few years ago, we formulated a criterion to prove the correctness of such implementations. The proof of correctness of the criterion itself was based on Lynch’s definition of atomicity by serialization points. Here, this criterion is reformulated as a specification HRW in the formal sense. Simulations from HRW to ARW and vice versa are constructed. These now serve as a constructive proof of correctness of the criterion. Eternity variables are used in the simulation from HRW to ARW. We propose so-called gliding simulations to deal with the problems that appear when occasionally the concrete implementation needs fewer steps than the abstract specification.     

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.      

Equilibrium and crystallographic measurements of the binary tetrahydrofuran and helium clathrate hydrates

Clathrate compounds are crystalline materials formed by a physical interaction between host and relatively light guest molecules. Various types of nano-sized cages surrounded by host frameworks exist in the highly unique crystalline structures and free guest molecules are entrapped in an open host-guest network. Recently, we reported two peculiar phenomena, swapping and tuning, naturally occurring in the hydrate cages. Helium, one of the smallest light guest molecules, must be the challengeable material in the sense of physics and moreover possesses versatile applications in the field of superconductivity technology and thermonuclear industry. In this regard, we attempted for the first time to synthesize helium hydrates at moderate temperature and pressure conditions. According to inclusion phenomena, helium itself normally cannot form clathrate hydrates due to being too small molecularly without the help of hydrate former molecules (sI, sII, and sH formers). In this study, the hydrate equilibria of the binary clathrate hydrate containing tetrahydrofuran, helium, and water were determined at 2, 3, 5.56 THF mol%. Direct volumetric measurements were also carried out to confirm the exact amount of helium captured in the hydrate cages. Finally, the crystalline structure of the formed mixed hydrates was identified by powder X-ray diffraction, resulting in structure II.     

Strength and fracture toughness of nano and micron-silica particles bidispersed epoxy composites: evaluated by fragility parameter

In this study, we discuss the composition effect of 240 nm and 1.56 μm-silica particles on strength and fracture toughness by examining two parameters, fragility and glass transition temperature, that were derived from the thermo-viscoelasticity measurements. Experimental results showed that the composites had a lower fragility with higher strength and fracture toughness as the content of nanoparticles was increased regardless of glass transition temperature. The improvement in mechanical properties from adding nanoparticles was definitely explained by the fragility represented the heterogeneity in polymer matrix, and this was related to the interaction between particles and matrix. The fragility was found to be an effective parameter for evaluating strength and fracture toughness of epoxy composite containing a bidispersion of nano and micron-silica particles.