Practical analysis of welding processes using finite element analysis.

With advances in commercially available finite element software and computational capability, engineers can now model large-scale problems in mechanics, heat transfer, fluid flow, and electromagnetics as never before. With these enhancements in capability, it is increasingly tempting to include the fundamental process physics to help achieve greater accuracy (Refs. 1-7). While this goal is laudable, it adds complication and drives up cost and computational requirements. Practical analysis of welding relies on simplified user inputs to derive important relativistic trends in desired outputs such as residual stress or distortion due to changes in inputs like voltage, current, and travel speed. Welding is a complex three-dimensional phenomenon. The question becomes how much modeling detail is needed to accurately predict relative trends in distortion, residual stress, or weld cracking? In this work, a HAZ (Heat Affected Zone) weld-cracking problem was analyzed to rank two different welding cycles (weld speed varied) in terms of crack susceptibility. Figure 1 shows an aerospace casting GTA welded to a wrought skirt. The essentials of part geometry, welding process, and tooling were suitably captured lo model the strain excursion in the HAZ over a crack-susceptible temperature range, and the weld cycles were suitably ranked. The main contribution of this work is the demonstration of a practical methodology by which engineering solutions to engineering problems may be obtained through weld modeling when time and resources are extremely limited. Typically, welding analysis suffers with the following unknowns: material properties over entire temperature range, the heat-input source term, and environmental effects. Material properties of interest are conductivity, specific heat, latent heat, modulus, Poisson's ratio, yield strength, ultimate strength, and possible rate dependencies. Boundary conditions are conduction into fixturing, radiation and convection to the environment, and any mechanical constraint. If conductivity, for example, is only known at a few temperatures it can be linearly extrapolated from the highest known temperature to the liquidus temperature. Over the liquidus to solidus temperature the conductivity is linearly increased by a factor of three to account for the enhanced heat transfer due to convection in the weld pool. Above the liquidus it is kept constant. Figure 2 shows an example of this type of approximation. Other thermal and mechanical properties and boundary conditions can be similarly approximated, using known physical material characteristics when possible. Sensitivity analysis can show that many assumptions have a small effect on the final outcome of the analysis. In the example presented in this work, simplified analysis procedures were used to model this process to understand why one set of parameters is superior to the other. From Lin (Ref. 8), mechanical strain is expected to drive HAZ cracking. Figure 3 shows a plot of principal tensile mechanical strain versus temperature during the welding process. By looking at the magnitudes of the tensile mechanical strain in the material's Brittle Temperature Region (BTR), it can be seen that on a relative basis the faster travel speed process that causes cracking results in about three times the strain in the temperature range of the BTR. In this work, a series of simplifying assumptions were used in order to quickly and accurately model a real welding process to respond to an immediate manufacturing need. The analysis showed that the driver for HAZ cracking, the mechanical strain in the BTR, was significantly higher in the process that caused cracking versus the process that did not. The main emphasis of the analysis was to determine whether there was a mechanical reason whether the improved weld parameters would consistently produce an acceptable weld, The prediction of the mechanical strain magnitudes confirms the better process

Ernst Freund as Precursor of the Rational Study of Corporate Law

Gindis, David, Ernst Freund as Precursor of the Rational Study of Corporate Law (October 27, 2017). Journal of Institutional Economics, Forthcoming. Available at SSRN: https://ssrn.com/abstract=2905547, doi: https://dx.doi.org/10.2139/ssrn.2905547The rise of large business corporations in the late 19th century compelled many American observers to admit that the nature of the corporation had yet to be understood. Published in this context, Ernst Freund's little-known The Legal Nature of Corporations (1897) was an original attempt to come to terms with a new legal and economic reality. But it can also be described, to paraphrase Oliver Wendell Holmes, as the earliest example of the rational study of corporate law. The paper shows that Freund had the intuitions of an institutional economist, and engaged in what today would be called comparative institutional analysis. Remarkably, his argument that the corporate form secures property against insider defection and against outsiders anticipated recent work on entity shielding and capital lock-in, and can be read as an early contribution to what today would be called the theory of the firm.Peer reviewe

A new ghost cell/level set method for moving boundary problems:application to tumor growth

In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth

The Long Term Response of Birds to Climate Change: New Results from a Cold Stage Avifauna in Northern England

The early MIS 3 (55–40 Kyr BP associated with Middle Palaeolithic archaeology) bird remains from Pin Hole, Creswell Crags, Derbyshire, England are analysed in the context of the new dating of the site’s stratigraphy. The analysis is restricted to the material from the early MIS 3 level of the cave because the upper fauna is now known to include Holocene material as well as that from the Late Glacial. The results of the analysis confirm the presence of the taxa, possibly unexpected for a Late Pleistocene glacial deposit including records such as Alpine swift, demoiselle crane and long-legged buzzard with southern and/or eastern distributions today. These taxa are accompanied by more expected ones such as willow ptarmigan /red grouse and rock ptarmigan living today in northern and montane areas. Finally, there are temperate taxa normally requiring trees for nesting such as wood pigeon and grey heron. Therefore, the result of the analysis is that the avifauna of early MIS 3 in England included taxa whose ranges today do not overlap making it a non-analogue community similar to the many steppe-tundra mammalian faunas of the time. The inclusion of more temperate and woodland taxa is discussed in the light that parts of northern Europe may have acted as cryptic northern refugia for some such taxa during the last glacial. These records showing former ranges of taxa are considered in the light of modern phylogeographic studies as these often assume former ranges without considering the fossil record of those taxa. In addition to the anomalous combination of taxa during MIS 3 living in Derbyshire, the individuals of a number of the taxa are different in size and shape to members of the species today probably due to the high carrying capacity of the steppe-tundra

Clarifying the effect of biodiversity on productivity in natural ecosystems with longitudinal data and methods for causal inference

Causal effects of biodiversity on ecosystem functions can be estimated using experimental or observational designs - designs that pose a tradeoff between drawing credible causal inferences from correlations and drawing generalizable inferences. Here, we develop a design that reduces this tradeoff and revisits the question of how plant species diversity affects productivity. Our design leverages longitudinal data from 43 grasslands in 11 countries and approaches borrowed from fields outside of ecology to draw causal inferences from observational data. Contrary to many prior studies, we estimate that increases in plot-level species richness caused productivity to decline: a 10% increase in richness decreased productivity by 2.4%, 95% CI [-4.1, -0.74]. This contradiction stems from two sources. First, prior observational studies incompletely control for confounding factors. Second, most experiments plant fewer rare and non-native species than exist in nature. Although increases in native, dominant species increased productivity, increases in rare and non-native species decreased productivity, making the average effect negative in our study. By reducing the tradeoff between experimental and observational designs, our study demonstrates how observational studies can complement prior ecological experiments and inform future ones

Legitimacy intermediation in the multilevel European polity and its collapse in the euro crisis

This essay re-examines the dual – republican and liberal – foundations of democratic legitimacy in the Western traditions of normative political theory. Considered in isolation, the European Union conforms to liberal standards but cannot satisfy republican criteria. Given these conflicting standards, debates on the alleged European democratic deficit have remained inconclusive. Moreover, they have failed to pay sufficient attention to the multilevel character of the European polity and to the normative potential of legitimacy intermediation in its two-step compliance and legitimating relationships. I argue, however, that the capacity of democratic member states to legitimate the exercise of European governing functions is being destroyed in the present euro crisis, and I briefly discuss the implications of this new constellation.In der westlichen Tradition der normativen politischen Theorie beruht demokratische Legitimität auf der doppelten Grundlage republikanischer und liberaler Prinzipien. Für sich betrachtet entspricht die Europäische Union zwar liberalen Kriterien, aber eben nicht den republikanischen Anforderungen. Angesichts so unterschiedlicher Kriterien konnte es auch im Streit über das angebliche europäische Demokratiedefizit keine Einigung geben. Überdies ignorierte diese Diskussion den Mehrebenen-Charakter der europäischen Politik und das normative Potenzial der Legitimationsvermittlung zwischen Union und Bürgern durch die demokratisch verfassten Mitgliedstaaten. Die gegenwärtige Eurokrise allerdings zerstört die Fähigkeit demokratischer Mitgliedstaaten, die Ausübung europäischer Herrschaftsfunktionen zu legitimieren. Der Aufsatz erörtert die Implikationen dieser neuen Konstellation.1 Introduction 2 Legitimacy discourses The republican discourse The liberal discourse Differences 3 Constitutional democracies – and the European Union? 4 Legitimacy intermediation in the multilevel European polity 5 The end of legitimacy intermediation in the euro crisis Monetary Union and the failure of output legitimacy Rescuing the euro through supranational intervention 6 Legitimate supranational government? Input-oriented European legitimacy? 7 Reducing the burden on European legitimacy Reference

The Europeanization of UK Government: From Quiet Revolution to Explicit Step-Change?

In this paper we review - from a UK perspective - how the UK government and its policy process have adapted to European integration. Has adaptation been a quiet revolution, a step-change, or both? In exploring this puzzle we draw upon the conceptual literature of Europeanisation. We employ it to shed light on the longer-term pattern of UK adaptation as well as to put into context the domestic changes currently under way. Although commentators frequently alight upon continued non-membership of the euro as an indicator of the UK's continued incomplete adaptation to integration, we argue that there is a step-change under way in the Europeanisation of UK EU policy making, though not necessarily in its outcomes