A New Cosmic Measuring Stick: Unusually bright type 1a Supernovae

LY13449 - White dwarfs are formed when stars exhaust their nuclear fuel. In this letter, we establish a new upper mass limit of 2.58 solar mass for white dwarfs. This is remarkably deviated from the famous Chandrasekhar's mass limit of 1.44 solar mass. Our result, unlike Chandrasekhar's, is based on the evolution of magnetic field in white dwarfs. This solves the origin of puzzling, unconventional, over-luminous, type Ia supernovae (explosions of white dwarfs), which must have super-Chandrasekhar mass white dwarfs as progenitors, contrary to those having the conventional Chandrasekhar mass. The characteristic nature of luminosity variation with time of type Ia supernovae allows them to be used as a 'standard' for measuring far away distances (standard candle) and understanding the expansion history of the universe. Applying this idea to conventional type Ia supernovae led to the Nobel Prize in Physics in 2011 for the discovery of the accelerating universe. Our discovery, however, more than 80 years after the proposal of Chandrasekhar mass limit, heralds the onset of a paradigm shift, plausibly leading to establish the unconventional supernovae as new standard candles for cosmic distance measurement.

Collective phenomena in Wikipedia: Cooperation and conflict

LU13814 - The process of conflict resolution in Wikipedia, an iconic, collaboratively edited encyclopedia, is described as the result of the competition between direct interactions among editors and their interactions with a globally shared medium, such as a Wikipedia article. Darwin himself wondered on the origin of the noble virtue of human cooperation being difficult to explain by natural selection. Today, information-communication technology has opened up unprecedented opportunities of solving complex tasks as a collective emergent phenomenon involving the cooperation of many individuals across the world. This has enabled such collaborative projects like open software development or the CERN experiments. While this leads to a higher level of synergy, unavoidably conflicts of diverse opinions are generated, signalled in Wikipedia by an unusually high number of edits in an article. Our model of how Wikipedia works reproduces key stylized features of conflict dynamics observed in real-world Wikipedia articles. For example, with a fixed number of editors forming one 'mainstream' and two opposing 'extremist' groups, consensus in the medium's content is only achieved after a long time and it may not correspond to the initial mainstream view. In the case of a dynamic environment where new editors replace older ones, periods of conflict and consensus can alternate indefinitely, depending on the rate of newcomers and the degree of controversy in the article's topic. The understanding of these mechanisms provided by our model opens the way for the improvement of the conditions for value production in collaborative environments.

Cell shape is the key to understanding blood vessel formation

LX13714E - Blood vessel formation is an important process during development, regeneration and disease. Networks of blood vessels are formed by cells that move around and interact with one another. By computationally modeling this collective behavior of cells we show that long, adhesive cells form networks without any long distance forces and we explain how this happens. In experiments, living cells are seeded on a medium, upon which they elongate and form a network that is similar to the networks formed by our model. This network formation has been attributed to long distance forces, either via chemicals secreted by the cells or mechanical forces conducted by the medium. We now show that long cells form groups of aligned cells. When these groups meet they do not merge but form a branch point and in this manner a network is formed. Earlier studies showed that cell elongation is important in network formation; our work explains how cell elongation helps network formation. Furthermore we show that long distance forces are not necessary, although they may act to stabilize the networks. These new insights can help to interpret experimental results and thus benefit the overall understanding of blood vessel formation.