Using molecular mechanics to predict bulk material properties of fibronectin fibers

The structural proteins of the extracellular matrix (ECM) form fibers with finely tuned mechanical properties matched to the time scales of cell traction forces. Several proteins such as fibronectin (Fn) and fibrin undergo molecular conformational changes that extend the proteins and are believed to be a major contributor to the extensibility of bulk fibers. The dynamics of these conformational changes have been thoroughly explored since the advent of single molecule force spectroscopy and molecular dynamics simulations but remarkably, these data have not been rigorously applied to the understanding of the time dependent mechanics of bulk ECM fibers. Using measurements of protein density within fibers, we have examined the influence of dynamic molecular conformational changes and the intermolecular arrangement of Fn within fibers on the bulk mechanical properties of Fn fibers. Fibers were simulated as molecular strands with architectures that promote either equal or disparate molecular loading under conditions of constant extension rate. Measurements of protein concentration within micron scale fibers using deep ultraviolet transmission microscopy allowed the simulations to be scaled appropriately for comparison to in vitro measurements of fiber mechanics as well as providing estimates of fiber porosity and water content, suggesting Fn fibers are approximately 75% solute. Comparing the properties predicted by single molecule measurements to in vitro measurements of Fn fibers showed that domain unfolding is sufficient to predict the high extensibility and nonlinear stiffness of Fn fibers with surprising accuracy, with disparately loaded fibers providing the best fit to experiment. This work shows the promise of this microstructural modeling approach for understanding Fn fiber properties, which is generally applicable to other ECM fibers, and could be further expanded to tissue scale by incorporating these simulated fibers into three dimensional network models

Russia’s natural resources in the world economy : history, review and reassessment

Russia’s role in the global economic system today, and the Soviet Union’s in the past, is dominated by the export of natural resources, particularly oil and gas. The rents earned from these exports are both a source of strength and weakness, as they link the fortunes of Russia’s domestic economy to the volatility of global resource markets. This paper returns to a major research project conducted through the offices of the Association of American Geographers that resulted in Soviet Natural Resources in the World Economy, published in 1983. The project was first conceived in the aftermath of the resource crisis in the 1970s and concluded in the early 1980s as the Soviet Union sought to increase resource exports to support a failing domestic economy. This paper examines the origins, evolution, and management of this seminal work and presents a re-reading of the book in a contemporary context. We develop some of the key themes of the original project and conclude that it has contemporary relevance, as a reliance upon the resource sector remains a defining characteristic of Russia’s political economy and continues to shape Russia’s role in the global economy. We find that the regional dimension that was so important in the original project remains critical as Russia seeks to extend the resource frontier into new regions in the Arctic and the East and, at the same time, reduce its reliance on European markets – that are both stagnant and hostile – by developing new markets in Asia

Shale development in the US and Canada : a review of engagement practice

Public and stakeholder engagement with shale development is difficult, but essential. We review 26 engagement processes carried out by US and Canadian companies, alliances, government agencies, academics and activists; systematically exploring who participates, the stage at which engagements take place, aims and methods, provision for multiway engagement, and issues of credibility. We find a multitude of actors carrying out engagement using a variety of formats, ranging from barbeque events and town hall meetings to citizen science and in-depth qualitative research. Whilst we find many strengths, we also highlight a number of weaknesses. Much of this engagement does not occur at the earliest stages of development, and rarely asks the most fundamental question -whether shale development should proceed at all- instead commonly focusing on questions of impact minimisation, regulation and gaining support. Furthermore, the majority of activities tend to elicit the responses of interested and affected parties, with much less attention to views of the wider public. We reflect on what may be limiting engagement practice, and discuss how engagement might be improved

It’s déjà vu all over again : COVID-19, the global energy market, and the Russian economy

The COVID-19 pandemic has already disrupted large swathes of the global economy, threatening the growth models of major oil and gas producer countries like Russia. A collapse in oil prices, triggered by the pandemic, once again exposed Russia’s enduring susceptibility to sharp falls in oil and gas prices. We argue that this decline in oil prices came at a time when tectonic shifts in global energy markets had already threatened to reduce the value of future oil and gas revenues. These structural changes were accelerated by the collapse in demand caused by the pandemic. Because the Russian leadership had done little to address the threat posed by the emergence of a new energy order, the economy remained highly dependent on oil and gas sales as the primary source of growth. While measures undertaken since 2014 to reduce the government’s fiscal dependence on high oil prices will help Russia avoid a worst-case outcome of a fiscal or financial crisis, the dependence of other branches of the economy on the energy sector remains high. This has left Russia set once again to experience a deeper recession than that forecast for other energy exporting economies

Vacuum field energy and spontaneous emission in anomalously dispersive cavities

Anomalously dispersive cavities, particularly white light cavities, may have larger bandwidth to finesse ratios than their normally dispersive counterparts. Partly for this reason, their use has been proposed for use in LIGO-like gravity wave detectors and in ring-laser gyroscopes. In this paper we analyze the quantum noise associated with anomalously dispersive cavity modes. The vacuum field energy associated with a particular cavity mode is proportional to the cavity-averaged group velocity of that mode. For anomalously dispersive cavities with group index values between 1 and 0, this means that the total vacuum field energy associated with a particular cavity mode must exceed $\hbar \omega/2$. For white light cavities in particular, the group index approaches zero and the vacuum field energy of a particular spatial mode may be significantly enhanced. We predict enhanced spontaneous emission rates into anomalously dispersive cavity modes and broadened laser linewidths when the linewidth of intracavity emitters is broader than the cavity linewidth.Comment: 9 pages, 4 figure

Tracing the water-energy-food nexus : description, theory and practice

The ‘nexus’ between water, energy and food (WEF) has gained increasing attention globally in research, business and policy spheres. We review the premise of recent initiatives framed around the nexus, examine the challenge of achieving the type of disciplinary boundary crossing promoted by the nexus agenda and consider how to operationalise what has to date been a largely paper exercise. The WEF nexus has been promoted through international meetings and calls for new research agendas. It is clear from the literature that many aims of nexus approaches pre-date the recent nexus agenda; these have encountered significant barriers to progress, including challenges to cross-disciplinary collaboration, complexity, political economy (often perceived to be under-represented in nexus research) and incompatibility of current institutional structures. Indeed, the ambitious aims of the nexus—the desire to capture multiple interdependencies across three major sectors, across disciplines and across scales—could become its downfall. However, greater recognition of interdependencies across state and non-state actors, more sophisticated modelling systems to assess and quantify WEF linkages and the sheer scale of WEF resource use globally, could create enough momentum to overcome historical barriers and establish nexus approaches as part of a wider repertoire of responses to global environmental change

Transition to Turbulence in Shear above the Tropopause

2000 FLORIDA AVE NW, WASHINGTON, USA, DC, 2000

Perivascular epithelioid cell neoplasm of the uterine cervix: an unusual tumor in an unusual location

A 46-year-old woman presented for a second opinion regarding a 3–4 cm mass of the uterine cervix. A prior biopsy had been interpreted as a malignant melanoma of the cervix, resulting in a radical hysterectomy with bilateral salpingooophorectomy. This was to be followed by external beam irradiation and immunotherapy; however, given the rarity of this diagnosis, the patient sought a second opinion at our institution. Further review of the pathological material from the hysterectomy revealed a morphologically benign perivascular epithelioid cell neoplasm rather than a malignant melanoma. Close monitoring of the patient was recommended; she is currently diseasefree more than three years after her initial presentation

Managing transition risk : toward an interdisciplinary understanding of strategies in the oil industry

How actors react to change is a crucial question for social scientists interested in global energy system transformation (EST). The global oil industry's response to the challenges associated with climate change and EST is a particular topic of discussion. Here, we argue for an interdisciplinary approach, bringing together insights from multiple disciplines within the social sciences that study oil companies, to further our understanding of what they are doing and why they are doing it. Although research on the political economy and socio-technical nature of EST has led to important insights, it tends to treat the global oil industry as a monolith with common interests and strategic objectives. We argue that the analytical and conceptual tools provided by the management and business literature can help unpack this ‘black box’. We explain how this is the case by exploring some of these tools and applying them to a novel heuristic, the ‘Transition Strategy Continuum’ that helps categorise and analyse the emerging strategies of the publicly-traded ‘International Oil Companies’ (IOCs). As such, we respond to the call for interdisciplinarity raised in the inaugural issue of this Journal. Ultimately, we want social scientists working on energy to take serious insights from other fields of inquiry that help illuminate the complexities of the task of transformation ahead for the IOCs and other related stakeholders

China’s dash for gas : local challenges and global consequences

The recent 2017–18 “dash for gas” captured global attention, but also exposed critical failings in China’s gas market. The 2019 lull imposed by the Government reflects the need to address local challenges. This paper analyzes the prospects for demand growth and assesses the various ways in which that demand can be met. There is considerable uncertainty surrounding demand growth, with cost competitiveness being the determining factor. Equally, although China has significant natural gas reserves, they are largely unconventional and present significant geological and technical challenges; with domestic production growth failing to keep pace as demand import dependence increases. China’s gas imports are met by pipeline gas from Central Asia and Myanmar and Liquified Natural Gas (LNG) from avariety of countries. The Power of Siberia pipeline started deliveries of Russian in late 2019. However, plans to expand Central Asian imports have disappointed and China may agree to asecond pipeline from Russia or increase its LNG imports. Asimple “gas balance model” is used in the final discussion and conclusions to explore future developments and their consequences for global gas security