The diameter of KPKVB random graphs

We consider a model for complex networks that was recently proposed as a model for complex networks by Krioukov et al. In this model, nodes are chosen randomly inside a disk in the hyperbolic plane and two nodes are connected if they are at most a certain hyperbolic distance from each other. It has been previously shown that this model has various properties associated with complex networks, including a power-law degree distribution and a strictly positive clustering coefficient. The model is specified using three parameters : the number of nodes $N$, which we think of as going to infinity, and $\alpha, \nu > 0$ which we think of as constant. Roughly speaking $\alpha$ controls the power law exponent of the degree sequence and $\nu$ the average degree. Earlier work of Kiwi and Mitsche has shown that when $\alpha < 1$ (which corresponds to the exponent of the power law degree sequence being $< 3$) then the diameter of the largest component is a.a.s.~polylogarithmic in $N$. Friedrich and Krohmer have shown it is a.a.s.~$\Omega(\log N)$ and they improved the exponent of the polynomial in $\log N$ in the upper bound. Here we show the maximum diameter over all components is a.a.s.~$O(\log N)$ thus giving a bound that is tight up to a multiplicative constant.Comment: very minor corrections since the last versio

The Atrocity of Representing Atrocity - Watching Kevin Carter's 'Struggling Girl'

Taking Kevin Carter's famous photograph of a Sudanese 'Struggling Girl' as an example, this article shows by criticizing the work of photography scholar Ariella Azoulay who argues for an ethic, reparative spectatorship that focuses on the social encounters behind the photograph, how discussions about atrocity photography often result in moral debates: discussions that center around the social relations behind photography and blame the photographer, but do not take into account and criticize the photographic representation of the atrocity. By giving an overview of the afterlife of Carter's photograph, the articles shows how such a 'social' focus on photography, easily reaffirms the social inequalities that lies within the practices of atrocity photography.   

What Does it Mean to Teach Interpretively?

The ‘interpretive turn’ has gained traction as a research approach in recent decades in the empirical social sciences. While the contributions of interpretive research and interpretive research methods are clear, we wonder: Does an interpretive perspective lend itself to – or even demand – a particular style of teaching? This question was at the heart of a roundtable discussion we organised at the 2014 Interpretive Policy Analysis (IPA) International Conference. This essay reports on the contours of the discussion, with a focus on our reflections upon what it might mean to teach ‘interpretively’. Prior to outlining these, we introduce the defining characteristics of an interpretive perspective and describe our respective experiences and interests in this conversation. In the hope that this essay might constitute the beginning of a wider conversation, we close it with an invitation for others to respond

De productie en moleculaire verschijningsvorm van radiotoxisch Po-210 in kernfusie- en splijtingsreactoren = The Production and Molecular Occurrence of Radiotoxic Po-210 in Nuclear Fusion and Fission Reactors

In order to counter the climate change, there is a need for a radical revolution in the global energy supply. One of the most realistic scenarios is a substantial shift towards renewable energy sources, supported by a flexible baseload from carbon-free nuclear energy. The main requirements for this new generation of nuclear reactors are intrinsic safety, high fuel efficiency and a minimum amount of (long-lived) radioactive waste. A promising candidate for the near future is the lead (alloy) cooled fast fission reactor. An ideal long-term solution are nuclear fusion reactors, which produce only a small amount of short-lived radioactive waste. A problem that occurs in both these reactor types is the undesired production of the highly radiotoxic polonium-210 isotope. In this PhD thesis, the total production of this isotope in a nuclear fusion reactor is determined using neutron transport and inventory calculations. Next, quantum chemical calculations are performed to predict the molecular form in which Po-210 will occur in both discussed reactor types. Combining both aspects allows to estimate the risk associated with the presence of Po-210 in a nuclear reactor and can help to design efficient Po-210 extraction systems

Contact Changes of Sheared Systems: Scaling, Correlations, and Mechanisms

We probe the onset and effect of contact changes in 2D soft harmonic particle packings which are sheared quasistatically under controlled strain. First, we show that in the majority of cases, the first contact changes correspond to the creation or breaking of contacts on a single particle, with contact breaking overwhelmingly likely for low pressures and/or small systems, and contact making and breaking equally likely for large pressures and in the thermodynamic limit. The statistics of the corresponding strains are near-Poissonian. The mean characteristic strains exhibit scaling with the number of particles N and pressure P, and reveal the existence of finite size effects akin to those seen for linear response quantities. Second, we show that linear response accurately predicts the strains of the first contact changes, which allows us to study the scaling of the characteristic strains of making and breaking contacts separately. Both of these show finite size scaling, and we formulate scaling arguments that are consistent with the observed behavior. Third, we probe the effect of the first contact change on the shear modulus G, and show in detail how the variation of G remains smooth and bounded in the large system size limit: even though contact changes occur then at vanishingly small strains, their cumulative effect, even at a fixed value of the strain, are limited, so that effectively, linear response remains well-defined. Fourth, we explore multiple contact changes under shear, and find strong and surprising correlations between alternating making and breaking events. Fifth, we show that by making a link with extremal statistics, our data is consistent with a very slow crossover to self averaging with system size, so that the thermodynamic limit is reached much more slowly than expected based on finite size scaling of elastic quantities or contact breaking strains

Impacts of project attributes on investment preferences : an empirical cluster analysis of energy conservation investment attitudes

Investment attitude refers to the way managements of firms value attributes of investmentproposals and weigh them in their final appraisal. It seems that among firms in the Netherlands an investment attitude exists that hinders theimplementation of energy conservation projects. Using paired comparison results from a survey on energy conservation, this paper evaluates investmentpreferences of firms by applying a Bradley-Terry model. The impact of project attributes on the investment preference is analysed in order to disclosethe underlying investment attitude and to identify barriers to the advance of energy conservation technologies. A latent class approach is used todetect clusters of firms for which specific barners play a dominant role