Investment casting of NiAl single-crystal alloys

Significant progress has been made in the understanding of solidification conditions, microstructure evolution, and defect formation during investment casting of NiAl single crystals. The high liquidus temperatures of NiAl alloys result in a larger dendrite arm spacing than is found in superalloy René N5. Because of their higher thermal conductivities, NiAl alloys have higher cooling rates and lower temperature gradients during solidification than René N5. These differences give NiAl alloys a lower tendency to form freckles and a higher tendency to form equiaxed grains. However, with the aid of process modeling, single crystals of various shapes of NiAl alloys have been produced.     

Characterizing the deformation of cold-rolled copper sheet

An advanced x-ray diffraction technique allows the development of texture components to be monitored and provides supplementary information about the cold work and residual stresses in cold-rolled copper sheet. The new technique confirms the results of an ultrasonic test, except for the ultrasonic test’s sensitivity to grain size. The new x-ray diffraction technique could be adapted to provide in-process, nondestructive evaluation of thin copper sheet, even for material moving at high speeds.     

Issues in the replacement of lead-bearing solders

The use of soft solders, particularly those containing lead, dates back nearly 5,000 years. Solders similar to the materials used to seal the aqueducts of ancient Rome are now an important building block in the manufacture of high-speed computer assemblies. This history attests to the technological versatility of soft solders and, in particular, the solder alloys that contain lead. However, the health effects of prolonged exposure to lead have also been documented; measures to limit human exposure—at the work place and indirectly through the environment—are being considered. The successful introduction of lead-free solders into future electronic products will rely heavily upon their solderability, which can be evaluated by test procedures such as the meniscometer/wetting balance technique and the capillary flow test.     

Processing ceramic-matrix composites using electrophoretic deposition

A novel, cost-effective processing technique for manufacturing ceramic-matrix composites (CMCs) containing two-dimensional woven-fiber reinforcement has been developed. The technique relies on the electrophoretic deposition (EPD) of ceramic sols on/into the fiber preforms to achieve the required impregnation. The laboratory-scale results achieved thus far indicate that the processing approach offers great potential for the manufacture of high-quality, composite products with dual-component oxide matrices for high-temperature structural applications.     

The effects of silicon on the properties of tantalum

The microalloying of tantalum with silicon has been effectively used on a commercial scale. However, data on effects of microalloying on processibility, microstructure and mechanical properties are not readily available. To develop some data, tantalum powder with various levels of silicon (0–50 ppm) was processed under identical conditions. Sheet samples were then annealed at different temperatures and evaluated via microstructural, chemical and mechanical tests. The recrystallization temperature was found to increase with silicon content, most probably as a result of the presence of an intermetallic (Ta₃Si) phase. The mechanical properties of unrecrystallized tantalum are, as expected, significantly different from those of recrystallized tantalum.     

Digital Elevation Model generation for historical landscape analysis based on LiDAR data,a case study in Flanders (Belgium)

This paper discusses the generation of a high precision DEM (Digital Elevation Model) based on high density airborne LiDAR (Light Detection and Ranging) data for an interdisciplinary landscape archaeological study concerning the settlement history and environment in Sandy Flanders, a region to the north of Ghent (Belgium). The objective was to create a detailed topographical surface free of artificial features and topographical artefacts, in the form of a DEM, visualizing the natural and current topography through the implementation of true ground points only. The semi-automatical removal of these features and artefacts was based on topographical vector data, visual interpretations and slope analysis. Ultimately two DEM’s were constructed (1) a TIN (Triangulated Irregular Network) model, whereby the inherent large file format restricts the usability to large scale and (2) a grid model which can be used for small-, medium- and large-scale applications. Both datasets were used as an image that is interpreted using ancillary data from historical sources. Its usefulness is illustrated in a case of field pattern and microfield topography. Starting from this DEM, the approach of this landscape historical study is mainly retrogressive, i.e. starting from the landscape structures and elements that are still present in the contemporary landscape and moving into the past.     

Capturing Global Youth: Mobile Gaming in the U.S., Spain,and the Czech Republic

We adapt the technology acceptance model (TAM) to examine the factors influencing mobile gaming adoption among “global youth.” Our model replaces usefulness with convenience, incorporating visual appeal and escapism as antecedents of fun, and perceived novelty and economic value as antecedents of convenience. Questionnaire surveys were conducted in the U.S., Spain, and the Czech Republic, producing 432 usable responses. In the structural model assessment with the pooled sample, convenience exercises greater effects on attitude toward mobile games than fun, suggesting that the most important driver is probably the capability of being used flexibly at any time and in any place, rather than mere enjoyment. Tests of latent means suggest that most dimensions are perceived more strongly in the Czech Republic.     

Sintering and Electronic Conducting Properties of Lao.7Ca0.3CrO3 Perovskite Synthesized by a Glycine-nitrate Process

La0.7 Ca0.3 CrO3 powder consisting of superfine and uniform particles （ 100-200 nm ） were synthesized using a glycine-nitrate process （ GNP ）. The sintering and electronic conducting properties of La0.7 Ca0.3 CrO3 were invetigated in the sintering temperature range of 1 200-1 450 ℃. The desired morphology of the powder significantly improved its sinterability. La0.7 Ca0.3 CrO3 ceramics sintered at 1 250-1 450 ℃ show high relative densities above 95 % . The ceramics sintered at 1 250-1 400 ℃ have very similar electronic conduct- ing properties, providing electronic conductivities around 55 Ω^-1 cm^-1 at a measuring temperature of 800 ℃ . Further increasing the sintering temperature to 1450 ℃ led to an apparent degradation of electronic conducting properties. This research demonstrates the advantage of the GNP in producing La0.7 Ca0.3 CrO3 with respect to the enhanced sintering properties and superior electronic conducting properties.     

The Effects of Aging Precipitation on the Recrystallization of CuNiSiCr Alloy

The interaction between precipitation and recrystallization and its effect on the properties of the Cu-Ni-Si-Cr alloy during aging were discussed. The results show that the deformation results in much more dispersed precipitation of the phases. The precipitations have accelerating or retarding effects on the recrys allization. On the formation and growth of recrystallization, the precipitated phases are coarsed or dissolved in front of grain boundaries following a re-precipitation in the recrystallization area.     

Comparison between cellular automata and linear feedback shift registers based pseudo-random number generators

A detailed comparison between pseudo-random number generators (PRNGs) based on cellular automata (CA) and linear feedback shift registers (LFSRs) is presented in this paper. Various statistical tests have been applied in order to reveal the advantages and disadvantages of both approaches. Both LFSRs and hybrid additive cellular automata (HACA) produce satisfactory PRNGs. HACA operate at higher speeds than LFSRs with the same characteristic polynomials. Regarding the silicon area, direct comparisons between the two approaches cannot be made since it depends on the PRNG length. However, the inherent modularity of HACA reduces the silicon area occupied by them and, when long feedback paths are used, the silicon area occupied by LFSRs increases.