Comparison of finite-size-scaling functions for 3d O(N) spin models to QCD

We calculate numerically universal finite-size-scaling functions of the magnetization for the three-dimensional O(4) and O(2) spin models. The approach of these functions to the infinite-volume scaling functions is studied in detail on the critical and pseudocritical lines. For this purpose we determine the pseudocritical line in two different ways. We find that the asymptotic form of the finite-size-scaling functions is already reached at small values of the scaling variable. A comparison with QCD lattice data for two flavours of staggered fermions shows a similar finite-size behaviour which is compatible with that of the spin models.Comment: Lattice2001(hightemp), 3 pages, 5 figures, acknowledgements completed, minor typographical errors correcte

The analysis of Polyakov loop and spin correlators in finite volumes

We derive an analytic expression for point to point correlation functions of the Polyakov loop based on the transfer matrix formalism. The contributions from the eigenvalues of the transfer matrix including and beyond the mass gap are investigated both for the $2d$ Ising model and in finite temperature $SU(2)$ gauge theory. We find that the leading matrix element shows similar scaling properties in both models. Just above the critical point we obtain for $SU(2)$ a Debye screening mass $~\mu_D/T\approx4~$, independent of the volume. Sorry, figures are not included and can be sent by ordinary mail.Comment: TALK GIVEN AT THE LATTICE '93 INTERNATIONAL SYMPOSIUM LATTICE FIELD THEORY, DALLAS, USA, OCTOBER 12--16, 1993 3 pages preprint HU BERLIN--IEP--93/5 and BIELEFELD BI-TP--93/63, November 199

External field dependence of the correlation lengths in the three-dimensional O(4) model

We investigate numerically the transverse and longitudinal correlation lengths of the three-dimensional O(4) model as a function of the external field H. In the low-temperature phase we verify explicitly the H^{-1/2}-dependence of the transverse correlation length, which is expected due to the Goldstone modes of the model. On the critical line we find the universal amplitude ratio xi^c_T / xi^c_L = 1.99(1). From our data we derive the universal scaling function for the transverse correlation length. The H-dependencies of the correlation lengths in the high temperature phase are discussed and shown to be in accord with the scaling functions.Comment: 3 pages, 4 figures, Lattice2003(higgs) contribution, espcrc2.st

Entwicklung eines universellen Lambshift-Polarimeters für polarisierte Atomstrahl-Targets wie an ANKE/COSY

Since 1994 a Lamb-shift polarimeter (LSP) for the fast and precise measurement of the polarization of an atomic beam was designed, built and tested at the Institut für Kernphysik of the Universität zu Köln. This universal polarimeter can be used to develop a atomic beam polarized ion source (like for the Cologne SAPIS project) or to measure the polarization of atomic beam targets (jet or storage cell targets, e.g. at COSY-Jülich). This Lamb-shift polarimeter was tested with an unpolarized beam of protons and deuterons at Cologne and, since the beginning of 2001, at the Forschungszentrum (FZ) Jülich with the polarized atomic hydrogen and deuterium beams from the atomic beam source of the polarized gas target at ANKE ($\textbf{A}$pparatus for $\textbf{N}$ucleon and $\textbf{K}$aon $\textbf{E}$jectiles). This polarized intemal storage-cell gas target will be used in the storage ring COSY ($\textbf{Co}$oler \Sy}nchrotron) in 2003. The polarimeter is based an measuring the ratios of Lyman-$\alpha$ transition intensities after Stark quenching of spinfilter selected Zeeman hyperfine states. The nuclear polarization of the atomic beam is deduced by applying the product of several correction factors calculated from known effects. The total correction amounts to between 1.1 and 1.2 depending an the occupation numbers of the hyperfine states. The nuclear polarization of atomic beams of hydrogen and deuterium is determined with an accuracy of $\le$ 1% within a few seconds for beams of $\sim$ 3 $\cdot$ 10$^{16}$ atoms/s in one hyperfine state. Its error is dominated by the systematic errors of the various correction factors and will be lowered to $\approx$ 0.5% using a recently developed new ionizer. The sensitivity of the polarimeter is such that even for a beam intensity reduced to 10% the polarization could be determined reliably. The new ionizer will lower this sensitivity limit to $\le$ 3%. With this sensitivity it appears feasible to measure the polarization in the planned storage cell of ANKE by extracting a small fraction of the atoms. In addition to these studies of the (de)polarization in a storage cell plans are to study the polarization and fraction of recombined molecules H$_{2}$ and especially D$_{2}$ in such a cell (CELGAS project). At Cologne the LSP will be used to develop the atomic beam source for the SAPIS project ($\textbf{S}$tored $\textbf{A}$toms $\textbf{P}$ulsed $\textbf{I}$on $\textbf{S}$ource). The LSP offers itself as a very good instrument for all polarized gas target installations at storage rings

Corrections to Scaling and Critical Amplitudes in SU(2) Lattice Gauge Theory

We calculate the critical amplitudes of the Polyakov loop and its susceptibility at the deconfinement transition of SU(2) gauge theory. To this end we carefully study the corrections to the scaling functions of the observables coming from irrelevant exponents. As a guiding line for determining the critical amplitudes we use envelope equations derived from the finite size scaling formulae for the observables. The equations are then evaluated with new high precision data obtained on N^3 x 4 lattices for N=12,18,26 and 36. We find different correction-to-scaling behaviours above and below the transition. Our result for the universal ratio of the susceptibility amplitudes is C_+/C_-=4.72(11) and agrees perfectly with a recent measurement for the 3d Ising model.Comment: LATTICE98(hightemp

Baadassss Gangstas: The Parallel Influences, Characteristics and Criticisms of the Blaxploitation Cinema and Gangsta Rap Movements

Serving as two of the most visible African American cultural movements, blaxploitation cinema and gangsta rap played essential roles in giving African American artists an outlet to establish a new black identity for mainstream audiences. After exploring the similarities between the cultural and economic conditions that spawned both movements, this essay examines the parallel techniques by which the preeminent entries in both genres established themselves as culturally relevant for African American audiences. These techniques included a reliance on place and space to establish authenticity, as well as employing African American myths and folklore such as the Signifying Monkey and the badman. By establishing themselves as mainstream representations of black identity, the harshest critics and staunchest defenders of both movements came from within the African American community, a clear indication of the important role each would play in establishing a new era of black representation in popular culture

Actors and repertoires of contention

Industrial mining is currently one of the fastest growing sectors of the world economy, particularly in the Global South. The present mining boom is, however, accompanied by numerous conflicts: conflicts over labour relations, over territorial control and access to water and land resources, over the effects on local livelihoods, on gender relations and ecological systems, and over the distribution of profits and tax revenues. In this paper, a typology of mining conflicts is developed, starting with existing case studies of current conflicts over industrial mining in sub-Saharan Africa and building on my own research in Burkina Faso. In contrast to existing typologies, the one presented here is based not on the subjects of the conflicts but on actor constellations: conflicts between trade unions and mining companies; between civil society organisations on the one hand and the state and mining companies on the other; and between artisanal miners and mining companies. I argue that historically shaped socio-ecological and socio-economic conditions, namely the existing land usages, have a crucial effect on the actors and actor constellations in conflicts over mining, and that different actors have different means of engaging in conflict at their disposal, and thus rely on different repertoires of contention when engaging in collective conflicts.Der industrielle Bergbau ist gegenwärtig einer der am stärksten wachsenden Wirtschaftssektoren weltweit, insbesondere im Globalen Süden. Der aktuelle Bergbau-Boom geht mit einer Vielzahl an Konflikten einher: um Arbeitsbeziehungen, um territoriale Kontrolle und den Zugang zu Wasser- und Landressourcen, um die Auswirkungen auf lokale livelihoods, auf Geschlechterverhältnisse und Ökosysteme sowie um die Verteilung der Gewinne und Steuereinnahmen. Dieses Kapitel entwickelt ausgehend von bestehenden Fallstudien zu gegenwärtigen Konflikten um den industriellen Bergbau in Subsahara-Afrika sowie aufbauend auf eigene Forschungen in Burkina Faso eine Typologie von Bergbaukonflikten. Anders als bestehende Typologien konzentriert sich diese nicht auf die Konfliktgegenstände, sondern auf die Akteurskonstellationen der Konflikte: zwischen Gewerkschaften und Unternehmen; zivilgesellschaftlichen Organisationen auf der einen und Staat und Unternehmen auf der anderen Seite; und zwischen Akteuren des handwerklichen und industriellen Bergbaus. Ich argumentiere, dass historisch geformte sozial-ökologische und sozio-ökonomische Bedingungen, insbesondere die bestehenden und vorherigen Formen der Landnutzung, wesentlichen Einfluss auf die Akteurskonstellationen in Konflikten um die Ausweitung des industriellen Bergbaus haben. Die Akteurskonstellationen wiederum bedingen die Mittel des Konfliktaustrags: Unterschiedliche Akteure haben unterschiedliche Mittel zur Verfügung und greifen entsprechend auf unterschiedliche „repertoires of contention“ in kollektiven Konflikten zurück

A nation under our feet : Black Panther, Afrofuturism and the potential of thinking through political structures

In this article, the focus is on Black Panther: a nation under our feet, a comic book series written by American public intellectual Ta-Nehisi Coates. The point of departure is Coates's idea of 'the Mecca', a term he uses in his earlier non-fiction. It refers to a space in which black culture is created in the shadow of collective traumas and memories. We argue that in a nation under our feet the fictional African country of Wakanda functions as a metaphorical Mecca. This version of Wakanda is contextualised in terms of the aesthetics of Afrofuturism and theories on the influence of ideology in comic books. The central focus of the article is how this representation of Wakanda questions the idea of a unified black people and how Wakanda, like the real world Meccas described by Coates, display internal ideological and political struggles among its people. We argue that the various characters in a nation under our feet represent different and conflicting ideological positions. These positions are metaphors for real world political views and in playing out the consequences of these ideologies, Coates explores African and global political structures without didactically providing conclusive answers to complex issues