Beam Measurements of a CLOUD (Cosmics Leaving OUtdoor Droplets) Chamber

A striking correlation has recently been observed between global cloud cover and the flux of incident cosmic rays. The effect of natural variations in the cosmic ray flux is large, causing estimated changes in the Earth's energy radiation balance that are comparable to those attributed to greenhouse gases from the burning of fossil fuels since the Industrial Revolution. However a direct link between cosmic rays and cloud formation has not been unambiguously established. We therefore propose to experimentally measure cloud (water droplet) formation under controlled conditions in a test beam at CERN with a CLOUD chamber, duplicating the conditions prevailing in the troposphere. These data, which have never been previously obtained, will allow a detailed understanding of the possible effects of cosmic rays on clouds and confirm, or otherwise, a direct link between cosmic rays, global cloud cover and the Earth's climate. The measurements will, in turn, allow more reliable calculations to be made of the residual effect on global temperatures of the burning of fossil fuels, an issue of profound importance to society. Furthermore, light radio-isotope records indicate a correlation has existed between global climate and the cosmic ray flux extending back over the present inter-glacial and perhaps earlier. This suggests it may eventually become possible to make long-term (10-1,000 year) predictions of changes in the Earth's climate, provided a deeper understanding can be achieved of the ``geomagnetic climate'' of the Sun and Earth that modulates the cosmic-ray flux.Comment: More information and higher resolution drawings at http://cern.ch/Cloud Improved figure qualit

Jim Crace: inventor of worlds

Jim Crace is a novelist who makes no religious claims. He is a maker of worlds that have dark resonances, caught between time and eternity, that have their roots in forms of textuality and language that begin in the Hebrew Bible and may be traced in Christianity through the texts of the desert fathers to the writings of T. E. Lawrence and Gertrude Bell. He is a deceiver whose deceptions reveal truths that are familiar yet strange and mysterious

Generalized Onsager algebras

Let $\mathfrak{g}(A)$ be the Kac-Moody algebra with respect to a symmetrizable generalized Cartan matrix $A$. We give an explicit presentation of the fix-point Lie subalgebra $\mathfrak{k}(A)$ of $\mathfrak{g}(A)$ with respect to the Chevalley involution. It is a presentation of $\mathfrak{k}(A)$ involving inhomogeneous versions of the Serre relations, or, from a different perspective, a presentation generalizing the Dolan-Grady presentation of the Onsager algebra. In the finite and untwisted affine case we explicitly compute the structure constants of $\mathfrak{k}(A)$ in terms of a Chevalley type basis of $\mathfrak{k}(A)$. For the symplectic Lie algebra and its untwisted affine extension we explicitly describe the one-dimensional representations of $\mathfrak{k}(A)$.Comment: 20 pages. v2: typos corrected and references adde

High-speed railway developments and corporate location decisions. The role of accessibility

Accessibility is a major factor that determines the effects of transport infrastructure developments on corporate location decisions. High-speed railways have an impact on accessibility by reducing travel times and increasing comfort. However, little research on its effects on location choices has been carried out so far. Still, high-speed railway infrastructure development is advocated for these effects on regional economy. This research uses interviews among corporate decision makers to determine how a change in accessibility due to new high-speed rail infrastructure is perceived by these corporate decision makers and what impact HST infrastructure has on the location choices of firm branches. Firstly, in-dept interviews are held among recently (re)located firm branches to identify accessibility related factors that play a role in the location decision process. For the in-dept interviews we start from the assumption that for firms three aspects of accessibility by passenger transport systems are of importance: access and accessibility for (1) current and potential employees, (2) current and potential business partners, and (3) current and potential customers. Furthermore, corporate decision makers perceive different transport modes in a distinct way. Hereby for example, the level of comfort of the transport mode can be of importance ? it might be of more importance for business trips than for commuting. In this paper special attention is given to how the accessibility by high-speed trains is perceived. The perception of the accessibility of a certain place will differ among firms, because distinct firms appreciate the several facets of accessibility differently. This depends on the activities that take place in the firm branch, for example how often face-to-face contact with (international) business partners occurs, and on the cost structure of the firm. An improved accessibility will reduce transport costs, but on the other hand better accessible locations are likely to have higher prices of real estate. Probably for firms a trade off exists between these opposite cost effects, based on their characteristics. But beside these ?objective? factors, subjective properties of accessibility might also be of importance to corporate decision makers. Being settled on good accessible transport hubs can contribute to the firm?s image. The interviews shed light on how new high-speed rail infrastructure affects the perception of accessibility by corporate decision makers. By questioning different firm types and sizes it is made clear what types of firms are mostly influenced by this change in accessibility. In a later stage of the research, these factors will be quantified by means of stated preference interviews. The results of these interviews will then be used to improve the way accessibility is embedded in land-use transport interaction models, an important instrument for the ex ante evaluation of transport infrastructure.

Tackling the spread of disinformation Why a co-regulatory approach is the right way forward for the EU. Bertelsmann Stiftung Policy Paper 12 December 2019

In recent years social media platforms have led to an unprecedented increase in the spread of disinformation. Concerns about these new and dynamic ways to spread falsehoods have brought politicians and regulators onto the stage. In this paper Paul-Jasper Dittrich proposes a European co-regulatory approach to tackle disinformation on social media instead of the current self-regulatory approach or direct regulation

An instability of unitary quantum dynamics

Instabilities of equilibrium quantum mechanics are common and well-understood. They are manifested for example in phase transitions, where a quantum system becomes so sensitive to perturbations that a symmetry can be spontaneously broken. Here, we consider the possibility that the time evolution governing quantum dynamics may be similarly subject to an instability, at which its unitarity spontaneously breaks down owing to an extreme sensitivity towards perturbations. We find that indeed such an instability exists, and we explore its immediate consequences. Interpretations of the results both in terms of extreme sensitivity to the influence of environmental degrees of freedom, and in terms of a possible fundamental violation of unitarity are discussed.Comment: 11 pages, 2 figures; Conference proceedings DICE 201

Credal Networks under Epistemic Irrelevance

A credal network under epistemic irrelevance is a generalised type of Bayesian network that relaxes its two main building blocks. On the one hand, the local probabilities are allowed to be partially specified. On the other hand, the assessments of independence do not have to hold exactly. Conceptually, these two features turn credal networks under epistemic irrelevance into a powerful alternative to Bayesian networks, offering a more flexible approach to graph-based multivariate uncertainty modelling. However, in practice, they have long been perceived as very hard to work with, both theoretically and computationally. The aim of this paper is to demonstrate that this perception is no longer justified. We provide a general introduction to credal networks under epistemic irrelevance, give an overview of the state of the art, and present several new theoretical results. Most importantly, we explain how these results can be combined to allow for the design of recursive inference methods. We provide numerous concrete examples of how this can be achieved, and use these to demonstrate that computing with credal networks under epistemic irrelevance is most definitely feasible, and in some cases even highly efficient. We also discuss several philosophical aspects, including the lack of symmetry, how to deal with probability zero, the interpretation of lower expectations, the axiomatic status of graphoid properties, and the difference between updating and conditioning