Comparative theoretical analysis of continuous wave laser cutting of metals at 1 and 10 um wavelength

We present a derivation and, based on it, an extension of a model originally proposed by V.G. Niziev to describe continuous wave laser cutting of metals. Starting from a local energy balance and by incorporating heat removal through heat conduction to the bulk material, we find a differential equation for the cutting profile. This equation is solved numerically and yields, besides the cutting profiles, the maximum cutting speed, the absorptivity profiles, and other relevant quantities. Our main goal is to demonstrate the model’s capability to explain some of the experimentally observed differences between laser cutting at around 1 and 10 μm wavelengths. To compare our numerical results to experimental observations, we perform simulations for exactly the same material and laser beam parameters as those used in a recent comparative experimental study. Generally, we find good agreement between theoretical and experimental results and show that the main differences between laser cutting with 1- and 10-μm beams arise from the different absorptivity profiles and absorbed intensities. Especially the latter suggests that the energy transfer, and thus the laser cutting process, is more efficient in the case of laser cutting with 1-μm beams.

Shakespeare, the Middle Ages and the Luck of the British: Medievalism and National Identity in The Hollow Crown (2012)

Images of the medieval past have long been fertile soil for the identity politics of subsequent periods. Rather than “authentically” reproducing the Middle Ages, medievalism therefore usually tells us more about the concerns and ideological climate of its own time and place of origin. To dramatise the nascent nation, Shakespeare resorts to medievalism in his history plays. Centuries later, the BBC-produced television mini-serial The Hollow Crown – adapting Shakespeare’s second histories tetralogy – revamps this negotiation of national identity for the “Cultural Olympiad” in the run-up to the 2012 London Olympics. In this context of celebratory introspection, The Hollow Crown weaves a genealogical narrative consisting of the increasingly “glorious” medieval history depicted and “national” Shakespearean heritage in order to valorise 21st-century “Britishness”. Encouraging a reading of the histories as medieval history, the films construct an ostensibly inclusive, liberal-minded national identity grounded in this history. Moreover, medieval kingship is represented in distinctly sentimentalising and humanising terms, fostering emotional identification especially with the no longer ambivalent Hal/Henry V and making him an apt model for present-day British grandeur. However, the fact that the films in return marginalise female, Scottish, Irish and Welsh characters gives rise to doubts as to whether this vision of Shakespeare’s Middle Ages really is, as the producers claimed, “for everybody”.

Jewish life in the middle ages

by Israel Abrahams

Canopy gaps promote selective stem-cutting by small mammals of two dominant tree species in an African lowland forest: the importance of seedling chemistry

Small mammals can impede tree regeneration by injuring seedlings and saplings in several ways. One fatal way is by severing their stems, but apparently this type of predation is not well-studied in tropical rain forest. Here, we report on the incidence of 'stem-cutting' to new, wild seedlings of two locally dominant, canopy tree species monitored in 40 paired forest understorey and gap-habitat areas in Korup, Cameroon following a 2007 masting event. In gap areas, which are required for the upward growth and sapling recruitment of both species, 137 seedlings of the long-lived, light-demanding, fast-growing large tropical tree (Microberlinia bisulcata) were highly susceptible to stem-cutting (83% of deaths) - it killed 39% of all seedlings over a c. 2-y period. In stark contrast, seedlings of the more shade-tolerant, slower-growing tree species (Tetraberlinia bifoliolata) were hardly attacked (4.3%). In the understorey, however, stem-cutting was virtually absent. Across the gap areas, the incidence of stem-cutting of M. bisulcata seedlings showed significant spatial variation that could not be explained significantly by either canopy openness or Janzen-Connell type effects (proximity and basal area of conspecific adult trees). To examine physical and chemical traits that might explain the species difference to being cut, bark and wood tissues were collected from a separate sample of seedlings in gaps (i.e. not monitored for stem-cutting). These analyses suggested that, compared with T. bifoliolata, the lower stem density, higher Mg and K and fatty acid concentrations in bark, and fewer phenolic and terpene compounds in M. bisulcata seedlings made them more palatable and attractive to small-mammal predators, likely rodents. We conclude that selective stem-cutting is a potent countervailing force to the current local canopy dominance of the grove-forming M. bisulcata by limiting the recruitment and abundance of its saplings. Given the ubiquity of gaps and ground-dwelling rodents in pantropical forests, it would be surprising if this form of lethal browsing was restricted to Korup.