A model for the degradation of polyimides due to oxidation

Polyimides, due to their superior mechanical behavior at high temperatures, are used in a variety of applications that include aerospace, automobile and electronic packaging industries, as matrices for composites, as adhesives etc. In this paper, we extend our previous model in [S. Karra, K. R. Rajagopal, Modeling the non-linear viscoelastic response of high temperature polyimides, Mechanics of Materials, In press, doi:10.1016/j.mechmat.2010.09.006], to include oxidative degradation of these high temperature polyimides. Appropriate forms for the Helmholtz potential and the rate of dissipation are chosen to describe the degradation. The results for a specific boundary value problem, using our model compares well with the experimental creep data for PMR-15 resin that is aged in air.Comment: 13 pages, 2 figures, submitted to Mechanics of Time-dependent Material

An introductory view on archaeoastronomy

Archaeoastronomy is still a marginalised topic in academia and is described by the Sophia Centre, the only UK institution offering a broader MA containing this field, as ‘the study of the incorporation of celestial orientation, alignments or symbolism in human monuments and architecture’. By many it is associated with investigating prehistoric monuments such as Stonehenge and combining astronomy and archaeology. The following will show that archaeoastronomy is far more than just an interdisciplinary field linking archaeology and astronomy. It merges aspects of anthropology, ethno-astronomy and even educational research, and is possibly better described as cultural astronomy. In the past decades it has stepped away from its quite speculative beginnings that have led to its complete rejection by the archaeology community. Overcoming these challenges it embraced full heartedly solid scientific and statistical methodology and achieved more credibility. However, in recent times the humanistic influences of a cultural context motivate a new generation of archaeoastronomers that are modernising this subject; and humanists might find it better described as post-modern archaeoastronomy embracing the pluralism of today’s academic approach to landscape and ancient people

Ambient particulate pollution and the world-wide prevalence of asthma, rhinoconjunctivitis and eczema in children: Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC)

Objectives: To investigate the effect of ambient particulate matter on variation in childhood prevalence of asthma, rhinoconjunctivitis and eczema. Methods: Prevalences of asthma, rhinoconjunctivitis and eczema obtained in Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC) were matched with city-level estimates of residential PM10 obtained from a World Bank model. Associations were investigated using binomial regression adjusting for GNP per capita and for clustering within country. For countries with more than one centre, a two stage meta-analysis was carried out. The results were compared with a meta-analysis of published multi-centre studies. Results: Annual concentrations of PM₁₀ at city level were obtained for 105 ISAAC centres in 51 countries. After controlling for GNP per capita, there was a weak negative association between PM₁₀ and various outcomes. For severe wheeze in 13-14-year-olds, the OR for a 10 μg/m³ increase in PM₁₀ was 0.92 (95 CI 0.84 to 1.00). In 24 countries with more than one centre, most summary estimates for within-country associations were weakly positive. For severe wheeze in 13-14-year-olds, the summary OR for a 10 μg/m³ increase in PM₁₀ was 1.01 (0.92 to 1.10). This result was close to a summary OR of 0.99 (0.91 to 1.06) obtained from published multi-centre studies. Conclusions: Modelled estimates of particulate matter at city level are imprecise and incomplete estimates of personal exposure to ambient air pollutants. Nevertheless, our results together with those of previous multi-centre studies, suggest that urban background PM₁₀ has little or no association with the prevalence of childhood asthma, rhinoconjunctivitis or eczema either within or between countries

An ecosystem for linked humanities data

The main promise of the digital humanities is the ability to perform scholar studies at a much broader scale, and in a much more reusable fashion. The key enabler for such studies is the availability of suciently well described data. For the eld of socio-economic history, data usually comes in a tabular form. Existing eorts to curate and publish datasets take a top-down approach and are focused on large collections. This paper presents QBer and the underlying structured data hub, which address the long tail of research data by catering for the needs of individual scholars. QBer allows researchers to publish their (small) datasets, link them to existing vocabularies and other datasets, and thereby contribute to a growing collection of interlinked datasets.We present QBer, and evaluate our rst results by showing how our system facilitates two use cases in socio-economic history

Dynamic knowledge integration in socio-technical networks: an interpretive study of intranet use for knowledge integration

A major challenge facing firms competing in electronic business markets is the dynamic integration of knowledge within and beyond the firm, enabled by internet-based infrastructure and emergent fluid socio-technical networks. This paper explores how social actors dynamically employ intranets to integrate formal and informal knowledge within evolving socio-technical networks that emerge, permeate and extend beyond the organisational boundary. The paper presents two case studies that illustrate how static intranets can be useful for dynamically integrating knowledge when they are interwoven with other knowledge channels such as e-mail through which flows the informal knowledge needed to make sense of and situate formal organisational knowledge. The findings suggest that businesses should carefully examine how employees integrate intranets with other channels in their work, and the shaping of knowledge outcomes that flows from such use. There are practical implications for the proper skilling of thepeople who share and integrate knowledge in this way. The paper also provides a framework for dynamic knowledge integration in socio-technical networks, which can help underpin future research in this area.<br /

Measuring poverty cycles in the U.S. 1959–2013

This paper aims to shed light on the nature of poverty as a dynamic process by examining poverty cycles, their magnitudes, and their asymmetry. The designated benchmark country is the USA due to the availability of time series data making comprehensive analyses possible. We use Harding and Pagan (2002) and the Cardinale and Taylor (2009) model to isolate poverty cycles in the U.S. during 1959–2013. Once isolated, we test the poverty cycles for duration dependency, and their synchronization with the U.S. business cycles observed over the same period. We find that poverty dynamics measured through poverty cycles differ for alternative poverty rate indicators. Another critical point is the magnitude of change in the poverty cycles. Prolonged and more volatile poverty cycles have a significant adverse impact on people and families facing them. That is particularly important for policymakers who should rethink poverty policy guidelines aimed at helping people with more volatile poverty cycles first. Our is the first study, to our knowledge, to isolate poverty cycles and focus on their nature. Poverty cycles should attract more attention from policymakers since they more accurately assess nations’ economic well-being than output (GDP)