The origins of governments: from anarchy to hierarchy

We analyze development trajectories of early civilizations where population size and technology are endogenous, and derive conditions under which such societies optimally ‘switch’ from anarchy to hierarchy – when it is optimal to elect and support a ruler. The ruler provides an efficient level of law and order, but creams off part of society's surplus for his own consumption. Switching to hierarchy occurs if the state of technology exceeds a threshold value, but societies may also be ‘trapped’ at lower levels of technology, perpetuating conditions of anarchy. We present empirical evidence based on the Standard Cross Cultural Sample that support the model's main predictions

Galois theory and Lubin-Tate cochains on classifying spaces

We consider brave new cochain extensions F(BG +,R) → F(EG +,R), where R is either a Lubin-Tate spectrum E n or the related 2-periodic Morava K-theory K n , and G is a finite group. When R is an Eilenberg-Mac Lane spectrum, in some good cases such an extension is a G-Galois extension in the sense of John Rognes, but not always faithful. We prove that for E n and K n these extensions are always faithful in the K n local category. However, for a cyclic p-group C p r, the cochain extension F(BC p r +,E n ) → F(EC p r +, E n ) is not a Galois extension because it ramifies. As a consequence, it follows that the E n -theory Eilenberg-Moore spectral sequence for G and BG does not always converge to its expected target

Misinformation: tech companies are removing ‘harmful’ coronavirus content – but who decides what that means?

The “infodemic” of misinformation about coronavirus has made it difficult to distinguish accurate information from false and misleading advice. The major technology companies have responded to this challenge by taking the unprecedented move of working together to combat misinformation about COVID-19. Part of this initiative involves promoting content from government healthcare agencies and other authoritative sources, and introducing measures to identify and remove content that could cause harm. For example, Twitter has broadened its definition of harm to address content that contradicts guidance from authoritative sources of public health information. Facebook has hired extra fact-checking services to remove misinformation that could lead to imminent physical harm. YouTube has published a COVID-19 Medical Misinformation Policy that disallows “content about COVID-19 that poses a serious risk of egregious harm”. The problem with this approach is that there is no common understanding of what constitutes harm. The different ways these companies define harm can produce very different results, which undermines public trust in the capacity for tech firms to moderate health information. As we argue in a recent research paper, to address this problem these companies need to be more consistent in how they define harm and more transparent in how they respond to it

The Challenges of Responding to Misinformation during a Pandemic: content moderation and the limitations of the concept of harm

Social media have been central in informing people about the COVID-19 pandemic. They influence the ways in which information is perceived, communicated and shared online, especially with physical distancing measures in place. While these technologies have given people the opportunity to contribute to public discussions about COVID-19, the narratives disseminated on social media have also been characterised by uncertainty, disagreement, false and misleading advice. Global technology companies have responded to these concerns by introducing new content moderation policies based on the concept of harm to tackle the spread of misinformation and disinformation online. In this essay, we examine some of the key challenges in implementing these policies in real time and at scale, calling for more transparent and nuanced content moderation strategies to increase public trust and the quality of information about the pandemic consumed online

Outflows at the Edges of an Active Region in a Coronal Hole: A Signature of Active Region Expansion?

Outflows of plasma at the edges of active regions surrounded by quiet Sun are now a common observation with the Hinode satellite. While there is observational evidence to suggest that the outflows are originating in the magnetic field surrounding the active regions, there is no conclusive evidence that reveals how they are driven. Motivated by observations of outflows at the periphery of a mature active region embedded in a coronal hole, we have used a three-dimensional simulation to emulate the active region's development in order to investigate the origin and driver of these outflows. We find outflows are accelerated from a site in the coronal hole magnetic field immediately surrounding the active region and are channelled along the coronal hole field as they rise through the atmosphere. The plasma is accelerated simply as a result of the active region expanding horizontally as it develops. Many of the characteristics of the outflows generated in the simulation are consistent with those of observed outflows: velocities up to 45 km per sec, properties akin to the coronal hole, proximity to the active region's draining loops, expansion with height, and projection over monopolar photospheric magnetic concentrations. Although the horizontal expansion occurs as a consequence of the active region's development in the simulation, expansion is also a general feature of established active regions. Hence, it is entirely possible and plausible that the expansion acceleration mechanism displayed in the simulation is occurring in active regions on the Sun and, in addition to reconnection, is driving the outflows observed at their edges.Comment: 19 pages, 9 figure

Optimization of photomixers and antennas for continuous-wave terahertz emission

We have studied terahertz emission from interdigitated finger photomixers coupled to planar antenna structures. Using both pulsed and continuous-wave excitation, polarization measurements reveal that the antenna design dominates the properties of the radiated output at frequencies below 0.6 THz, while the efficiency at higher frequencies is additionally dependent on the design of the photomixer fingers. We have produced terahertz maps of the device, characterizing the photomixer by measuring the generated power as a function of the excitation position. Together, these measurements have allowed us to understand better the distinct roles of the photomixer and antenna in emission at different fre

Mutations in the Arabidopsis Peroxisomal ABC Transporter COMATOSE Allow Differentiation between Multiple Functions In Planta: Insights from an Allelic Series

COMATOSE (CTS), the Arabidopsis homologue of human Adrenoleukodystrophy protein (ALDP), is required for import of substrates for peroxisomal β-oxidation. A new allelic series and a homology model based on the bacterial ABC transporter, Sav1866, provide novel insights into structure-function relations of ABC subfamily D proteins. In contrast to ALDP, where the majority of mutations result in protein absence from the peroxisomal membrane, all CTS mutants produced stable protein. Mutation of conserved residues in the Walker A and B motifs in CTS nucleotide-binding domain (NBD) 1 resulted in a null phenotype but had little effect in NBD2, indicating that the NBDs are functionally distinct in vivo. Two alleles containing mutations in NBD1 outside the Walker motifs (E617K and C631Y) exhibited resistance to auxin precursors 2,4-dichlorophenoxybutyric acid (2,4-DB) and indole butyric acid (IBA) but were wild type in all other tests. The homology model predicted that the transmission interfaces are domain-swapped in CTS, and the differential effects of mutations in the conserved "EAA motif" of coupling helix 2 supported this prediction, consistent with distinct roles for each NBD. Our findings demonstrate that CTS functions can be separated by mutagenesis and the structural model provides a framework for interpretation of phenotypic data

Pedestrian Solution of the Two-Dimensional Ising Model

The partition function of the two-dimensional Ising model with zero magnetic field on a square lattice with m x n sites wrapped on a torus is computed within the transfer matrix formalism in an explicit step-by-step approach inspired by Kaufman's work. However, working with two commuting representations of the complex rotation group SO(2n,C) helps us avoid a number of unnecessary complications. We find all eigenvalues of the transfer matrix and therefore the partition function in a straightforward way.Comment: 10 pages, 2 figures; eqs. (101) and (102) corrected, files for fig. 2 fixed, minor beautification