Microsegregation in nodular cast iron and its effect on mechanical properties

A review of the literature pertaining to the mechanical properties, solidification and segregation effects in nodular cast iron has been made. A series of investigations concerning the influence of microsegregation on mechanical properties of :pearlitic, ferritic and austenitic nodular cast iron have then been reported. The influence of section size on the tensile and impact properties of cornmercial purity and refined ferritic nodular cast iron has been studied. It has been shown. that an increase in section caused a decrease in impact transition temperature of the commercial purity material without greatly affecting the impact transition temperature of the purer material. This effect has been related to increased amounts of segregation effects such as cell boundary carbides in heavier sections of the commercial purity material. Microsegregation studies on the materials used in this thesis have been carried out using an electron probe microanalyser. This technique has shown that concentrations of chromium and manganese and depletions of nickel and silicon occurred at eutectic cell boundaries in nodular cast iron and were often associated with brittle carbides in these areas. These effects have been shown to be more prevalent in heavier sections. The nature of segregation during the solidification of nodular cast iron has been studied by quenching samples of nodular iron during the solidification process. Micro-analysis of such samples has shown that segregation of manganese and chromium occurs by a gradual build-up of these elements at the solid/liquid interface. The microstructures of the quenched specimens revealed carbide filaments connecting graphite nodules and areas of quenched liquid. These filaments have been used as evidence for a revised hypothesis for the solidification of nodular cast iron by a liquid diffusion mechanism. A similar series of experiments has been carried out on two high nickel austenitic irons containing 0.5 per cent manganese and 4 per cent manganese respectively. In both these materials a decrease in elongation was experienced with increasing section. This effect was more drastic in the 4 per cent manganese material which also contained much greater amounts of cell boundary carbide in heavy sections. Micro-analysis of samples of the 4 per cent manganese material quenched during solidification revealed that manganese concentrated in the liquid and that nickel concentrated in the solid during solidification. No segregation of silicon occurred in this material. Carbide filaments appeared in the microstructures of these specimens. A discussion of all the above effects in terms of current concepts is included

Public Involvement Tools in Environmental Decision-Making: A Primer for Practitioners

Practitioners are often asked to engage the public with limited resources at their disposal. While scholars encourage the use of more deliberate public participation mechanisms, resource constraints often require practitioners to utilize more limited public involvement tools. This article summarizes the strengths and weaknesses of three public involvement tools: citizen surveys, public hearings/meetings, and stakeholder interviews. This assessment should provide preliminary guidance in utilizing the appropriate public involvement tools when resource and time constraints do not allow for an extensive public deliberation process

Contracting Regimes and Third-Party Governance: A Theoretical Construct for Exploring the Importance of Public Service Motivation of Private Sector Contractors

To date the bulk of public service motivation (PSM) research has focused on demonstrating the differences in public service motivation between public sector and private sector employees, yet no research exist exploring the public service motivation (PSM) of private contractors performing public sector tasks. This article provides a detailed review of the privatization and PSM literature and suggests that PSM among private sector contractors can serve as a mitigating factor in protecting the public interest. This article establishes a set of propositions regarding the role of PSM as a mitigating factor in contracted public services, suggesting that PSM’s level of importance is related to the complexity of job task, number of contractors, and presence of a contracting regime. Lastly, the article recommends future directions in PSM research necessary for testing these propositions

Using Proprietary Databases to Overcome Data Suppression in Industry Cluster Analysis

Extension agents are frequently tasked with determining industry clusters that exist in a region to support economic development. However, data suppression issues recurrently prohibit a comprehensive understanding of heavily concentrated firms in a region, particularly in rural areas. This article discusses the use of North American Industry Classification System codes within the LexisNexis Academic database as a technique for locating data about specific firms and analyzing regional industry clusters. This approach provides a practical and cost-efficient method for Extension agents and other researchers and practitioners to identify clusters and gather firm information in small geographies throughout the United States

Accretion Discs in Blazars

The characteristic properties of blazars (rapid variability, strong polarization, high brightness) are widely attributed to a powerful relativistic jet oriented close to our line of sight. Despite the spectral energy distributions (SEDs) being strongly jet-dominated, a "big blue bump" has been recently detected in sources known as flat spectrum radio quasars (FSRQs). These new data provide a unique opportunity to observationally test coupled jet-disc accretion models in these extreme sources. In particular, as energy and angular momentum can be extracted by a jet magnetically coupled to the accretion disc, the thermal disc emission spectrum may be modified from that predicted by the standard model for disc accretion. We compare the theoretically predicted jet-modified accretion disc spectra against the new observations of the "big blue bump" in FSRQs. We find mass accretion rates that are higher, typically by a factor of two, than predicted by standard accretion disc theory. Furthermore, our results predict that the high redshift blazars PKS 0836+710, PKS 2149-307, B2 0743+25 and PKS 0537-286 may be predominantly powered by a low or moderate spin (a < 0.6) black hole with high mass accretion rates mdot_a ~ 50 - 200 msol/yr, while 3C 273 harbours a rapidly spinning black hole (a = 0.97) with mdot_a ~ 20 msol/yr. We also find that the black hole masses in these high redshift sources must be > 5 * 10^9 msol.Comment: Accepted for publication (17 August 2009) in MNRA

Stacking-Mediated Diffusion of Ruthenium Nanoclusters in Graphite

The diffusion, penetration and intercalation of metallic atomic dopants is an important question for various graphite applications in engineering and nanotechnology. We have performed systematic first-principles calculations of the behaviour of ruthenium nanoclusters on a graphene monolayer and intercalated into a bilayer. Our computational results show that at a sufficiently high density of single Ru atom interstitials, intercalated atoms can shear the surrounding lattice to an AA stacking configuration, an effect which weakens with increasing cluster size. Moreover, the interlayer stacking configuration, in turn, has a significant effect on cluster diffusion. We therefore find different trends in diffusivity as a function of cluster size and interlayer stacking. For monolayer graphene and an AA graphene bilayer, the formation of small clusters generally lowers diffusion barriers, while the opposite behaviour is found for the preferred AB stacking configuration. These results demonstrate that conditions of local impurity concentration and interlayer disregistry are able to regulate the diffusivity of metallic impurities in graphite.Comment: 11 pages, 10 figure

The Gap Analysis Program: A Proactive Approach to Biodiversity Conservation

This article introduces Extension professionals to the U.S. Geological Survey\u27s Gap Analysis Program (GAP). GAP seeks to inform the natural resource policy process by providing land cover, stewardship, and species distribution data to decision makers. GAP data may be used to make land use decisions at different geographic levels. GAP aims to address biodiversity conservation in a proactive manner, paying unique attention to the protection of common species and their habitats. Extension professionals may also find GAP data helpful in education and outreach programs designed to inform the public of the role individuals can play in biodiversity maintenance

Ripplocations in Layered Materials: Sublinear Scaling and Basal Climb

The ripplocation is a crystallographic defect which is unique to layered materials, combining nanoscale delamination with the crystallographic slip of a basal dislocation. Here, we have studied basal dislocations and ripplocations, in single and multiple van der Waals layers, using analytical and computational techniques. Expressions for the energetic and structural scaling factors of surface ripplocations are derived, which are in close correspondence to the physics of a classical carpet ruck. Our simulations demonstrate that the lowest-energy structure of dislocation pile-ups in layered materials is the ripplocation, while large dislocation pile-ups in bulk graphite demonstrate multilayer delamination, curvature and voids. This can provide a concise explanation for the large volumetric expansion seen in irradiated graphite.Comment: 7 pages, 6 figure

Influence of quantum well and barrier composition on the spectral behavior of InGaAs quantum dots-in-a-well infrared photodetectors

We report on the spectral behavior of two different quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition.In₀.₅Ga₀.₅Asquantum dots embedded in an In₀.₁₅Ga₀.₈₅As/GaAsquantum well(QW) or a GaAs/Al0.2Ga0.8AsQW have been incorporated into photodetectors and were characterized. A spectral response in the 3–5μm atmospheric window has been achieved by adopting the GaAs∕Al₀.₂Ga₀.₈AsQW.The Australian Research Council is gratefully acknowledged for the financial support

The Effect of Salt and Pyrophosphate on the Structure of Meat

Our obective was to determine whether or not salt and pyrophosphate have the same effect on the structure of pieces of meat as they have on isolated myofibrils. Blocks of pig M. longissimus dorsi were incubated in solutions of sodium chloride at pH 5.5 or sodium chloride plus sodium pyrophosphate at pH 5.5 or 8.0. The blocks were obtained from fresh (24h post- mortem) or aged (72h post-mor tem) muscle and incubated for 5 or 24h with minimal agitation. There was considerable uptake of water by the tissue especially at the higher pH and longer times. Electron microscopy of the meat incubated in salt plus pyrophosphate at pH 8.0 revealed complete or nearly complete extraction of the A-band to a depth of at least one fibre from the surface. In meat incubated in salt plus pyrophosphate at pH 5.5 the extraction of the A-band was 1 ess complete and appeared to occur only near the surface. In salt alone no extraction of the A-band occurred. Swelling of myofibrils close to the surface could be detected either by a reduction of density or by greater separation of filaments . Break-up of the Z-line, probably due to mechanical disruption imposed by swelling of myofibrils, was a common feature of the salt treatments. Mitochondria near the surface were grossly swollen, especially with salt plus pyrophosphate at pH 8.0 At low pH amorphous material was observed inside and outside the cell membrane, but at high pH filamentous material was present in these areas