Thermal diffusion in the IGM of clusters of galaxies

We revisit the phenomenon of elements diffusion in the intergalactic medium (IGM) in clusters of galaxies. The diffusion is driven by gravity, concentration and temperature gradients. The latter cause thermal diffusion, which has been so far ignored in IGM studies. We consider the full problem based on the Burgers' equations and demonstrate that the temperature gradients present in clusters of galaxies may successfully compete with gravity, evacuating metals from cooler regions. Under the combined action of gravity and temperature gradients, complicated metallicity profiles with several peaks and depressions may be formed. For a typical cool core cluster, the thermal diffusion may significantly reduce and even reverse the gravitational sedimentation of metals, resulting in the depression in their abundance in the core. This may have implications for diagnostics of the low temperature plasma in the centers of clusters of galaxies.Comment: 10 pages, 8 figures; accepted to MNRA

What is an Insurrection? Destituent Power and Ontological Anarchy in Agamben and Stirner

The aim of this article is to develop a theoretical understanding of the insurrection as a central concept in radical politics in order to account for contemporary movements and forms of mobilisation that seek to withdraw from governing institutions and affirm autonomous practices and forms of life. I will develop a theory of insurrection by investigating the parallel thinking of Giorgio Agamben and Max Stirner. Starting with Stirner’s central distinction between revolution and insurrection, and linking this with Agamben’s theory of destituent power, I show how both thinkers develop an ontologically anarchic approach to ethics, subjectivity and life that is designed to destitute and profane governing institutions and established categories of politics. However, I will argue that Stirner’s ‘egoistic’ and voluntarist approach to insurrection provides a more tangible and positive way of thinking about political action and agency than Agamben’s at times vague, albeit suggestive, notion of inoperativity

Anarchist education and the paradox of pedagogical authority

This paper interrogates a key feature of anarchist education; focusing on a problem with implications not only for anarchist conceptions of education, but for anarchist philosophy and practice more broadly. The problem is this: if anarchism consists in the principled opposition to all forms of coercive authority, then how is this to be reconciled with situations where justice demands the use of coercion in order to protect some particular good? It seems that anarchist educators are forced to deny coercive authority in principle, whilst at the same time affirming it in practice. This is the paradox of pedagogical authority in anarchist education. Coercive authority is simultaneously impossible and indispensable. Exploring this paradox through a reading of Jacques Derrida’s later work, and, in particular, his conception of justice as requiring openness to the singular situation (Derrida, 1990), I argue that in exercising their authority anarchist educators encounter the aporetic moment in anarchism, experiencing what Derrida calls ‘the ordeal of the undecidable’ (Ibid.). Understood this way, the paradox becomes less an indication of anarchism’s limitations than it does its value. For it is here that the problem of pedagogical authority is treated with the gravity that all questions of justice deserve

Development of a portable electroanalytical system for the stripping voltammetry of metals: Determination of copper in acetic acid soil extracts

The development, characterisation and evaluation of a prototype portable electrochemical trace metal analyser are presented. The instrument is a battery-powered microcontroller-based potentiostat, which implements anodic stripping voltammetry (ASV) at suitable sensor electrodes. It is capable of operating away from the laboratory, in the absence of an external power source and is usable by low-skilled personnel. The distinguishing feature of the instrument is its custom software, which enables sample pre-screening, data processing and sample dilution and standard additions calculations to be carried out. The instrument has been evaluated by application of a methodology for the detection of copper in acetic acid soil extracts, both in the laboratory and in the field. Underpotential deposition staircase anodic stripping voltammetry (UPD-SCASV) of the copper at gold disk electrodes was used as a test method. There was good agreement between the instrument results and those from laboratory-based reference analytical methods for analyses carried out both in the laboratory and in the field