Shear banding in molecular dynamics of polymer melts

In order to establish constitutive equations for a viscoelastic fluid uniform shear flow is usually required. However, in the last 10 years S. Q. Wang and co-workers have demonstrated that some entangled polymers do not flow with the uniform shear rate as usually assumed, but instead choose to separate into fast and slow flowing regions. This phenomenon, known as shear banding, causes flow instabilities and in principle invalidates all rheological measurements when it occurs. In this Letter we report the first observation of shear banding in molecular dynamics simulations of entangled polymer melts. We show that our observations are in a very good agreement with the phenomenology developed by Fielding and Olmsted. Our findings provide a simple way of validating the empirical macroscopic phenomenology of shear banding. © 2012 American Physical Society

A matter of choice: strategy and discretion in the shadow of World War Two

American policy-makers are predisposed towards the idea of a necessary war of survival, fought with little room for choice. This reflects a dominant memory of World War II that teaches Americans that they live in a dangerously small world that imposes conflict. Critics argue that the ‘choice versus necessity’ schema is ahistorical and mischievous. This article offers supporting fire to those critiques. America’s war against the Axis (1941–45) is a crucial case through which to test the ‘small world’ view. Arguments for war in 1941 pose overblown scenarios of the rise of a Eurasian super-threat. In 1941 conflict was discretionary and not strictly necessary in the interests of national security. The argument for intervention is a closer call that often assumed. This has implications for America’s choices today.

The British ‘failure’ that never was? The Anglo-American ‘productivity gap’ in large-scale interwar retailing—evidence from the department store sector

Interwar British retailing has been characterized as having lower productivity, less developed managerial hierarchies and methods, and weaker scale economies than its US counterpart. This article examines comparative productivity for one major segment of large-scale retailing in both countries—the department store sector. Drawing on exceptionally detailed contemporary survey data, we show that British department stores in fact achieved superior performance in terms of operating costs, margins, profits, and stock-turn. While smaller British stores had lower labour productivity than US stores of equivalent size, TFP was generally higher for British stores, which also enjoyed stronger scale economies. We also examine the reasons behind Britain's surprisingly strong relative performance, using surviving original returns from the British surveys. Contrary to arguments that British retailers faced major barriers to the development of large-scale enterprises, that could reap economies of scale and scope and invest in machinery and marketing to support the growth of their primary sales functions, we find that British department stores enthusiastically embraced the retail ‘managerial revolution’—and reaped substantial benefits from this investment.

A qualified defense of American drone attacks in northwest Pakistan under international humanitarian law

Since the terrorist attacks of September 11, 2001, international law has had to grapple with the fundamental challenges that large-scale violence carried out by non-State actors poses to the traditional inter- State orientation of international law. Questions related to the “adequacy” and “effectiveness” of international humanitarian law, international human rights law and the law related to the use of force have been particularly pronounced. This paper focuses on the international humanitarian law implications of American drone attacks in northwest Pakistan. A highly-advanced modality of modern warfare, armed drones highlight the possibilities, problems, prospects and pitfalls of high-tech warfare. How is the battlefield to be defined and delineated geographically and temporally? Who can be targeted, and by whom? Ultimately, this paper concludes that American drone attacks in northwest Pakistan are not unlawful as such under international humanitarian law, though, like any tactical decision in the context of asymmetric warfare, they should be continuously and closely monitored according to the dictates of law with sensitivity to facts on the ground.

Typification of four North American club-chollas: the names of four Engelmannian species from Mexico and Southwestern United States

The names Opuntia bulbispina, O. clavata, O. emoryi and O. grahamii, originally proposed by George Engelmann between 1848 and 1856, are reviewed and typified after new findings of previously unknown voucher specimens. Original materials collected by some of the collaborators employed by Engelmann during the Mexican Boundary Survey were discovered in a loan from the Torrey Herbarium at the New York Botanical Garden (NY). Many of the materials include fragments of stems and fruits, and others include only sectioned flowers and some seeds. Particularly good descriptions of the species here concerned were published in Engelmann’s “Synopsis of the Cactaceae” in 1857, and exceptional illustrations were produced by Paulus Roetter and printed in “Cactaceae of the Boundary” in 1859. The problems surrounding some previous typifications of these names range from typification of joint lectotypes to illegitimate typifications of illustrations when original material was known to exist. The materials selected for typification were collected by the Mexican Boundary Survey and are lodged at the herbaria of the Missouri Botanical Garden (MO) and the New York Botanical Garden (NY); some are illustrations published by Engelmann.

Did the RAI buy it? The role and limits of American broadcasting in Italy in the Cold War

With a 20 million dollar budget and 1,900 staff Voice of America broadcasted in 45 different languages and Italy was one of its main targets. By looking into what went on behind the microphone, this article addresses the extent to which cultural change was planned and structured transnationally, the interactions and interdependencies operating between Washington and Rome, and how a cooperation was achieved despite the fierce resistance of some of RAI’s executives. This allowed to air programmes produced in New York, and led to the launch of the most popular character of Italian radio and television: Mike Bongiorno.

Are the winters 2010 and 2012 archetypes exhibiting extreme opposite behavior of the North Atlantic jet stream?

The atmospheric circulation over the North Atlantic-European sector experienced exceptional but highly contrasting conditions in the recent 2010 and 2012 winters (November-March; with the year dated by the relevant January). Evidence is given for the remarkably different locations of the eddy-driven westerly jet over the North Atlantic. In the 2010 winter the maximum of the jet stream was systematically between 30ºN and 40ºN (in the ‘south jet regime’), while in the 2012 winter it was predominantly located around 55ºN (north jet regime). These jet features underline the occurrence of either weak flow (2010) or strong and persistent ridges throughout the troposphere (2012). This is confirmed by the very different occurrence of blocking systems over the North Atlantic, associated with episodes of strong cyclonic (anticyclonic) Rossby wave breaking in 2010 (2012) winters. These dynamical features underlie strong precipitation and temperature anomalies over parts of Europe, with detrimental impacts on many socioeconomic sectors. Despite the highly contrasting atmospheric states, mid and high-latitude boundary conditions do not reveal strong differences in these two winters. The two winters were associated with opposite ENSO phases, but there is no causal evidence of a remote forcing from the Pacific sea surface temperatures. Finally, the exceptionality of the two winters is demonstrated in relation to the last 140 years. It is suggested that these winters may be seen as archetypes of North Atlantic jet variability under current climate conditions.

The extreme European summer 2012

The European summer of 2012 was marked by strongly contrasting rainfall anomalies, which led to flooding in northern Europe and droughts and wildfires in southern Europe. This season was not an isolated event, rather the latest in a string of summers characterized by a southward shifted Atlantic storm track as described by the negative phase of the SNAO. The degree of decadal variability in these features suggests a role for forcing from outside the dynamical atmosphere, and preliminary numerical experiments suggest that the global SST and low Arctic sea ice extent anomalies are likely to have played a role and that warm North Atlantic SSTs were a particular contributing factor. The direct effects of changes in radiative forcing from greenhouse gas and aerosol forcing are not included in these experiments, but both anthropogenic forcing and natural variability may have influenced the SST and sea ice changes.

Further clarifying the competition–performance relation: reply to D. W. Johnson et al. (2012)

In their commentary, D. W. Johnson, Johnson, and Roseth (2012) provided some laudatory statements about our article, but they also expressed a number of concerns. The concerns focus on the following issues: types and definitions of competition, our choice of control group, the nature of performance-approach and performance-avoidance goals, the comprehensiveness of the opposing processes model, and performance-approach goals and constructive competition. We respond to each of these issues in turn and conclude with a statement regarding working to build an integrative model of the competition–performance relation (and beyond).

Changes in global net radiative imbalance 1985-2012

Combining satellite data, atmospheric reanalyses and climate model simulations, variability in the net downward radiative flux imbalance at the top of Earth's atmosphere (N) is reconstructed and linked to recent climate change. Over the 1985-1999 period mean N (0.34 ± 0.67 Wm–2) is lower than for the 2000-2012 period (0.62 ± 0.43 Wm–2, uncertainties at 90% confidence level) despite the slower rate of surface temperature rise since 2000. While the precise magnitude of N remains uncertain, the reconstruction captures interannual variability which is dominated by the eruption of Mt. Pinatubo in 1991 and the El Niño Southern Oscillation. Monthly deseasonalized interannual variability in N generated by an ensemble of 9 climate model simulations using prescribed sea surface temperature and radiative forcings and from the satellite-based reconstruction is significantly correlated (r ∼ 0.6) over the 1985-2012 period.