Steiner t-designs for large t

One of the most central and long-standing open questions in combinatorial design theory concerns the existence of Steiner t-designs for large values of t. Although in his classical 1987 paper, L. Teirlinck has shown that non-trivial t-designs exist for all values of t, no non-trivial Steiner t-design with t > 5 has been constructed until now. Understandingly, the case t = 6 has received considerable attention. There has been recent progress concerning the existence of highly symmetric Steiner 6-designs: It is shown in [M. Huber, J. Algebr. Comb. 26 (2007), pp. 453-476] that no non-trivial flag-transitive Steiner 6-design can exist. In this paper, we announce that essentially also no block-transitive Steiner 6-design can exist.Comment: 9 pages; to appear in: Mathematical Methods in Computer Science 2008, ed. by J.Calmet, W.Geiselmann, J.Mueller-Quade, Springer Lecture Notes in Computer Scienc

Rapid and highly variable warming of lake surface waters around the globe

Peer reviewed. ©2015. The Authors.This is an open access article under theterms of the Creative CommonsAttribution-NonCommercial-N oDerivsLicense, which permits use and distri-bution in any medium, provided theoriginal work is properly cited, the use isnon-commerc ial and no modificationsor adaptations are made.In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean = 0.34°C decade 1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors —from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decade 1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53°C decade 1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes

Taking risky opportunities in youthful content creation: teenagers' use of social networking sites for intimacy, privacy and self-expression

The explosion in social networking sites such as MySpace, Facebook, Bebo and Friendster is widely regarded as an exciting opportunity, especially for youth.Yet the public response tends to be one of puzzled dismay regarding a generation that, supposedly, has many friends but little sense of privacy and a narcissistic fascination with self-display. This article explores teenagers' practices of social networking in order to uncover the subtle connections between online opportunity and risk. While younger teenagers relish the opportunities to recreate continuously a highly-decorated, stylistically-elaborate identity, older teenagers favour a plain aesthetic that foregrounds their links to others, thus expressing a notion of identity lived through authentic relationships. The article further contrasts teenagers' graded conception of `friends' with the binary classification of social networking sites, this being one of several means by which online privacy is shaped and undermined by the affordances of these sites

Post-humanitarianism: humanitarian communication beyond a politics of pity

This article offers a trajectory of humanitarian communication, which suggests a clear, though not linear, move from emotion-oriented to post-emotional styles of appealing. Drawing on empirical examples, the article demonstrates that the humanitarian sensibility that arises out of these emerging styles breaks with pity and privileges a short-term and low-intensity form of agency, which is no longer inspired by an intellectual agenda but momentarily engages us in practices of playful consumerism. Whereas this move to the post-emotional should be seen as a reaction to a much-criticized articulation between politics and humanitarianism, which relied on ‘universal’ morality and grand emotion, it is also a response to the intensely mediatized global market in which humanitarian agencies operate today. The article concludes by reflecting on the political and ethical ambivalence at the heart of this new style of humanitarian communication, which offers both the tentative promise of new practices of altruism and the threat of cultural narcissism

The surface geology and geomorphology around Gobabeb, Namib Desert, Namibia

This paper serves as a brief review and overview of the surface geology and geomorphology around Gobabeb in the Central Namib Desert. It introduces the major lithologies associated with the Damara Orogen of Precambrian and Cambrian age, followed by Tertiary sandstones and conglomerates and Quaternary Kuiseb valley conglomerates, silts and gravels. To celebrate the 50th anniversary of the Gobabeb research station and the recent designation of the Namib Sand Sea as a world heritage site, we are presenting a map to inform and guide future research and educational activities around Gobabeb. The contrast between an ancient gravel plain to the north, a dynamic aeolian sand sea to the south and ephemeral river environments in between become apparent. These natural laboratories have attracted investigations of contemporary sand dune movement, hyper saline waters, evaporites and duricrusts and ephemeral flooding and recharge processes as well as environmental change and human impacts