Extensional flow of hyaluronic acid solutions in an optimized micofluidic cross-slot device

We utilize a recently developed microfluidic device, the Optimized Shape Cross-slot Extensional Rheometer (OSCER), to study the elongational flow behavior and rheological properties of hyaluronic acid (HA) solutions representative of the synovial fluid (SF) found in the knee joint. The OSCER geometry is a stagnation point device that imposes a planar extensional flow with a homogenous extension rate over a significant length of the inlet and outlet channel axes. Due to the compressive nature of the flow generated along the inlet channels, and the planar elongational flow along the outlet channels, the flow field in the OSCER device can also be considered as representative of the flow field that arises between compressing articular cartilage layers of the knee joints during running or jumping movements. Full-field birefringence microscopy measurements demonstrate a high degree of localized macromolecular orientation along streamlines passing close to the stagnation point of the OSCER device, while micro-particle image velocimetry is used to quantify the flow kinematics. The stress-optical rule is used to assess the local extensional viscosity in the elongating fluid elements as a function of the measured deformation rate. The large limiting values of the dimensionless Trouton ratio, Tr ∼ O(50), demonstrate that these fluids are highly extensional-thickening, providing a clear mechanism for the load-dampening properties of SF. The results also indicate the potential for utilizing the OSCER in screening of physiological SF samples, which will lead to improved understanding of, and therapies for, disease progression in arthritis sufferers

The limit to behavioral inertia and the power of default in voluntary contribution games

It is well documented that people are reluctant to switch from a default option. We experimentally test the robustness of this behavioral inertia in a collective decision-making setting by varying the default option type and the decision-making environment. We examine the impacts of automatic-participation and no-participation default options on subjects’ participation in a public goods provision and their contributions. Two variants of public goods game are employed: the linear and the threshold public goods games. The study shows the evidence of partial stickiness rather than complete stickiness of default options as indicated in empirical studies. Our experimental results square with the evidence of behavioral inertia only when the automatic-participation default is used. This default boosts contributions in the linear public goods game but not in the threshold public goods game. The evidence of partial stickiness is robust to the variation of the game employed, but the effect on contribution is sensitive to it

DIY John Curtin: Uncertain futures for heritage and citizenship in the era of digital friends and foes

This article introduces some of the problems confronting the popularization of national, civic and cultural heritage in the era of complex digital systems and social networks. Taking contemporary knowledge of John Curtin (Australia’s wartime PM) as its point of departure, the discussion explores some of the broader transformations of the conditions of citizenship, communication, heritage and knowledge production, and considers their implications for civic education and the uses of archives. In a novel thought experiment, the article explores some ways in which the figure of ‘John Curtin’ may be repurposed and reinvented for a new kind of DIY civic education based on user-led innovation

Networked learning, stepping beyond the net generation and digital natives

This chapter critically examines the idea that young people have undergone a change in which exposure to digital and networked technologies has caused a step change in the character of a whole generation. The empirical and theoretical basis for this argument is reviewed and critical theoretical perspectives are assessed. Evidence from earlier research is compared and contrasted with evidence gathered from students who are said to be part of the new generation. The chapter explores the consequences of these ideas from the standpoint of networked learning. One aim of the chapter is to suggest ways in which the changes that have taken can be more adequately theorized in relation to the idea of networked learning. Arguments used to support generational change rely on a technological determinism and alternative accounts understand young people as active agents. I suggest ex-panding the notion of the agent to include persons enacting roles in collective or-ganizations. Overall the importance of the debate is that determinist arguments can close down debate and networked learning would be impoverished if this occurs

Efficiency in a forced contribution threshold public good game

We contrast and compare three ways of predicting efficiency in a forced contribution threshold public good game. The three alternatives are based on ordinal potential, quantal response and impulse balance theory. We report an experiment designed to test the respective predictions and find that impulse balance gives the best predictions. A simple expression detailing when enforced contributions result in high or low efficiency is provided

Full Agreement and the Provision of Threshold Public Goods

The experimental evidence suggests that groups are inefficient at providing threshold public goods. This inefficiency appears to reflect an inability to coordinate over how to distribute the cost of providing the good. So, why do groups not just split the cost equally? We offer an answer to this question by demonstrating that in a standard threshold public good game there is no collectively rational recommendation. We also demonstrate that if full agreement is required in order to provide the public good then there is a collectively rational recommendation, namely, to split the cost equally. Requiring full agreement may, therefore, increase efficiency in providing threshold public goods. We test this hypothesis experimentally and find support for it