78,028 research outputs found
The Feasibility of Reclaiming Shell Material from Investment Casting
This report examines the feasibility of investment shell component reclamation. Shell material components and their compositions are investigated with an industry survey, a study of the available literature, and analysis of specimen shell materials. physical properties and factors related to the reclamation and reuse of shell materials are described. Well known mineral processing methods are capable of producing concentrates of the various shell components. The theory and techniques of some applicable processes are discussed to assist with the development of reclamation operations. The recommended methods are; comminution by roll crushing, component concentration by screening, gravity settling or heavy medium separation. Aluminosilicate stucco (a major component of many investment shells) can be recovered in a form suitable for reuse as backup stucco. Zircon (a minor component in many shell compositions) -can be concentrated in an impure form, and subsequent caustic liberation treatments can remove the intermixed silica phases. Reuse of such zircon in investment casting may be possible but will require careful qualification testing. Fused and crystalline silica (major components of most shell compositions) are not reusable for investment casting. The feasibility of reclamation will be influenced by individual foundry choices of materials, composition and shell practice.HWRIC Project No. RRT-10NTIS PB92-16219
A proposal for regularly updated review/survey articles: "Perpetual Reviews"
We advocate the publication of review/survey articles that will be updated
regularly, both in traditional journals and novel venues. We call these
"perpetual reviews." This idea naturally builds on the dissemination and
archival capabilities present in the modern internet, and indeed perpetual
reviews exist already in some forms. Perpetual review articles allow authors to
maintain over time the relevance of non-research scholarship that requires a
significant investment of effort. Further, such reviews published in a purely
electronic format without space constraints can also permit more pedagogical
scholarship and clearer treatment of technical issues that remain obscure in a
brief treatment.Comment: This is a draft white paper and we seek comments from the communit
The Parasitoid Complex of First Generation \u3ci\u3eOstrinia Nubilalis\u3c/i\u3e (Lepidoptera: Pyralidae) Larvae in Northwest Ohio
A survey of first generation European corn borer (Ostrinia nubilalis) larvae was conducted during 1997 in six cornfields located in northwestern Ohio in order to determine the larval parasitoid complex utilizing this host. Collected larvae were held under constant conditions until the larvae completed development or parasitoids emerged. The following species were recorded: Eriborus terebrans (Hymenoptera: Ichneumonidae), Macrocentrus grandii (Hymenoptera: Braconidae), Sympiesis viridula (Hymenoptera: Eulophidae), and Lixophaga sp. (Diptera: Tachinidae), Levels of parasitism in the different fields ranged from 14.3 to 83.3%. Future research will include surveys of additional fields and sampling of O. nubilalis over the entire season in the northwest Ohio region
Network Structure, Efficiency, and Performance in WikiProjects
The internet has enabled collaborations at a scale never before possible, but
the best practices for organizing such large collaborations are still not
clear. Wikipedia is a visible and successful example of such a collaboration
which might offer insight into what makes large-scale, decentralized
collaborations successful. We analyze the relationship between the structural
properties of WikiProject coeditor networks and the performance and efficiency
of those projects. We confirm the existence of an overall
performance-efficiency trade-off, while observing that some projects are higher
than others in both performance and efficiency, suggesting the existence
factors correlating positively with both. Namely, we find an association
between low-degree coeditor networks and both high performance and high
efficiency. We also confirm results seen in previous numerical and small-scale
lab studies: higher performance with less skewed node distributions, and higher
performance with shorter path lengths. We use agent-based models to explore
possible mechanisms for degree-dependent performance and efficiency. We present
a novel local-majority learning strategy designed to satisfy properties of
real-world collaborations. The local-majority strategy as well as a localized
conformity-based strategy both show degree-dependent performance and
efficiency, but in opposite directions, suggesting that these factors depend on
both network structure and learning strategy. Our results suggest possible
benefits to decentralized collaborations made of smaller, more tightly-knit
teams, and that these benefits may be modulated by the particular learning
strategies in use.Comment: 11 pages, 5 figures, to appear in ICWSM 201
Social Context Modulates Tolerance For Pragmatic Violations In Binary But Not Graded Judgments
A common method for investigating pragmatic processing and its development in children is to have participants make binary judgments of underinformative (UI) statements such as Some elephants are mammals. Rejection of such statements indicates that a (not-all) scalar implicature has been computed. Acceptance of UI statements is typically taken as evidence that the perceiver has not computed an implicature. Under this assumption, the results of binary judgment studies in children and adults suggest that computing an implicature may be cognitively costly. For instance, children under 7 years of age are systematically more likely to accept UI statements compared to adults. This makes sense if children have fewer processing resources than adults. However, Katsos and Bishop (2011) found that young children are able to detect violations of informativeness when given graded rather than binary response options. They propose that children simply have a greater tolerance for pragmatic violations than do adults. The present work examines whether this pragmatic tolerance plays a role in adult binary judgment tasks. We manipulated social attributes of a speaker in an attempt to influence how accepting a perceiver might be of the speaker’s utterances. This manipulation affected acceptability rates for binary judgments (Experiment 1) but not for graded judgments (Experiment 2). These results raise concerns about the widespread use of binary choice tasks for investigating pragmatic processing and undermine the existing evidence suggesting that computing scalar implicatures is costly
Development of Novel Density Functionals for Thermochemical Kinetics
A new density functional theory (DFT) exchange-correlation functional for the
exploration of reaction mechanisms is proposed. This new functional, denoted
BMK (Boese-Martin for Kinetics), has an accuracy in the 2 kcal/mol range for
transition state barriers but, unlike previous attempts at such a functional,
this improved accuracy does not come at the expense of equilibrium properties.
This makes it a general-purpose functional whose domain of applicability has
been extended to transition states, rather than a specialized functional for
kinetics. The improvement in BMK rests on the inclusion of the kinetic energy
density together with a large value of the exact exchange mixing coefficient.
For this functional, the kinetic energy density appears to correct `back' the
excess exact exchange mixing for ground-state properties, possibly simulating
variable exchange.Comment: J. Chem. Phys., in press (303431JCP, scheduled for August 15, 2004
issue); supplementary data available at
http://theochem.weizmann.ac.il/web/papers/BMK.htm
Contract Governance and the Canadian Public Sector
This essay examines the changing character of public sector work in the Canadian federal public service context. It is based on an empirical examination of various forms of contractual relations currently operative within the Canadian state and on a comparative approach of other western liberal state reform initiatives. We argue that contract governance is an ongoing process involving distinct interrelations between the public and private sectors. In this context, we identify various forms of contract governance and flexibility schemes that have been enfolded and refolded into the conventional structures of governance, and unfolded into a liminal space between the state and civil society through the establishment of nonstandard work and the creation of alternative service delivery programmes
Ligand design for site-selective installation of Pd and Pt centers to generate homo- and heteropolymetallic motifs
The modular synthesis of a series of nitrogen-rich polydentate ligands that feature a common pincer-type framework is reported. These ligands allow for site-selective installation of palladium and platinum to give rise to bi- and trimetallic complexes that have d^(8)–d^(8) interactions
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