Effect of weld composition and microstructure on hydrogen assisted fracture of austenitic stainless steels

The effect of severe hydrogen environments on the tensile fracture behavior of a variety of austenitic stainless steel welds was investigated. In all cases, second phases or particulates common only to the weld microstructure were the origin of fracture initiation in hydrogen. These second phases formed as a result of microsegregation during solidification and/or solid state transformations during cooling or aging. In addition to second phases the weld microstructure matrix phase also influences fracture behavior. The fracture behavior is discussed in terms of localized chemical variations and the presence of second phases, and th interaction of dislocations with internal boundaries.     

Transmission electron microscope observations of the wear tracks of nickel and nickel-based alloys tested in a simulated face seal

The fine structural details of the wear tracks of nickel, nickel-chromium and nickel-molybdenum alloys tested in a simulated face seal apparatus have been observed using transmission electron microscopy. The structures are complex and varied; there are regions of extremely high dislocation density and in all materials recrystallization is prevalent, with a very fine grain size (0.1 μm or less). The nickel-molybdenum alloys had been heat-treated to develop either an ordered or a disordered structure and changes in this due to the wear process showed that in some cases the local interface temperature exceeded 900 °C.     

Microstructural origin of the skeletal ferrite morphology of austenitic stainless steel welds

Scanning transmission electron microscopy (STEM) was conducted on welds exhibiting a variety of skeletal, or vermicular ferrite morphologies in addition to one lathy ferrite morphology. These ferrite morphologies result from primary ferrite solidification followed by a solid state transformation upon cooling. During cooling, a large fraction of the ferrite transforms to austenite leaving a variety of ferrite morphologies. Comparison of composition profiles and alloy partitioning showed both the skeletal and lathy ferrite structures result from a diffusion controlled solid state transformation. However, the overall measured composition profiles of the weld structure are a result of partitioning during both solidification and the subsequent solid state transformation.     

Changes in deposition of phytoplankton constituents in a Ca2+ polluted lake

Systematic reductions in the deposition rate of organic C, N, P, and chlorophyll (Chl) are documented for Ca2+ polluted, culturally eutrophic, Onondaga Lake, NY, based on analyses of weekly sediment trap collections over the May-October interval for 10 years of the 1980-1992 period. Inputs of both nutrient-rich domestic waste and industrial salt waste (including Ca2+) decreased over this period. Constituent ratios of the collected sediment indicate phytoplankton biomass was the dominant source of the deposited organic C, N, and Chl. Substantial decreases in downward fluxes of these constituents occurred starting in 1987: 37, 42, 25, and 54%, on average, for organic C, N, P, and Chl, respectively. These reductions were driven primarily by the decreases in the lake's salinity and Ca2+ concentration, that resulted from the closure of a soda ash manufacturing facility (1986), rather than decreases in water column P concentrations from reductions in domestic waste loading. Three different mechanisms for the decreased deposition, related to the reductions in salinity and Ca2+ concentration, are considered: (i) decrease in coating of phytoplankton with CaCO3 precipitate, (ii) increased grazing of phytoplankton by large cladocerans, and (iii) decreases in coagulation of phytoplankton. The greater loss of phytoplankton biomass through deposition, driven by salt waste inputs from the industry, exacerbated the lake's problem of high primary production. This response is consistent with ecological theory for nutrient saturated phytoplankton growth but has not previously been demonstrated on a whole-lake basis.     

Inferring Phylogenetic Trees Using Answer Set Programming

We describe the reconstruction of a phylogeny for a set of taxa, with a character-based cladistics approach, in a declarative knowledge representation formalism, and show how to use computational methods of answer set programming to generate conjectures about the evolution of the given taxa. We have applied this computational method in two domains: historical analysis of languages and historical analysis of parasite-host systems. In particular, using this method, we have computed some plausible phylogenies for Chinese dialects, for Indo-European language groups, and for Alcataenia species. Some of these plausible phylogenies are different from the ones computed by other software. Using this method, we can easily describe domain-specific information (e.g., temporal and geographical constraints), and thus prevent the reconstruction of some phylogenies that are not plausible. This paper is a revised and extended version of [3].     

Power, Thermal, and Reliability Modeling in Nanometer-Scale Microprocessors

System integration and performance requirements are dramatically increasing the power consumptions and power densities of high-performance microprocessors. High power consumption introduces challenges to various aspects of microprocessor and computer system design. It increases the cost of cooling and packaging design, reduces system reliability, complicates power supply circuitry design, and reduces battery life. Researchers have recently dedicated intensive effort to power-related design problems. Modeling is the essential first step toward design optimization. In this article, the power, thermal and reliability modeling problems are explained and recent advances in their accurate and efficient analysis are surveyed.     

Using Semantic Web Technologies to Analyze Learning Content

The authors demonstrate how to use semantic Web technologies to improve the state-of-the-art in online learning environments and bridge the gap between students on the one hand, and authors or teachers on the other. The ontological framework presented here helps formalize learning object context as a complex interplay of different learning-related elements and shows how we can use semantic annotation to interrelate diverse learning artifacts. On top of this framework, the authors implemented several feedback channels for educators to improve the delivery of future Web-based courses.     

Characterizing the strain rate sensitivity of the tensile mechanical properties of a thermoplastic composite

Thermoplastic composites (TPCs) are being given increased consideration for application in vehicle front-end structural crash components. However, studies on the high strainrate behavior of TPCs have been relatively limited. In this study, the effect of strain rate on the tensile properties of a woven fabric commingled E-glass/polypropylene thermoplastic composite was investigated over a strain-rate range of 10⁻⁴ to 70 s⁻¹. Quasi-static tests were conducted in an electromechanical universal test machine. A specially designed test rig in conjunction with a falling weight drop tower was used for high strain-rate characterization. The experimental results show that the elastic modulus, ultimate strength, and strain to failure increase with increasing strain rate.