Nonabelian Gauge Theories on Noncommutative Spaces

In this paper, we describe a method for obtaining the nonabelian Seiberg-Witten map for any gauge group and to any order in theta. The equations defining the Seiberg-Witten map are expressed using a coboundary operator, so that they can be solved by constructing a corresponding homotopy operator. The ambiguities, of both the gauge and covariant type, which arise in this map are manifest in our formalism.Comment: 14 pages, latex, Talk presented at 2001: A Spacetime Odyssey - Michigan Center for Theoretical Physics, some typos correcte

Understanding Language Evolution in Overlapping Generations of Reinforcement Learning Agents

Available from MIT Press via the DOI in this recordUnderstanding how the dynamics of language learning and language change are influenced by the population structure of language users is crucial to understanding how lexical items and grammatical rules become established within the context of the cultural evolution of human language. This paper extends the recent body of work on the development of term-based languages through signalling games by exploring signalling game dynamics in a social population with overlapping generations. Specifically, we present a model with a dynamic population of agents, consisting of both mature and immature language users, where the latter learn from the former's interactions with one another before reaching maturity. It is shown that populations in which mature individuals converse with many partners are more able to solve more complex signalling games. While interacting with a higher number of individuals initially makes it more difficult for language users to establish a conventionalised language, doing so leads to increased diversity within the input for language learners, and that this prevents them from developing the more idiosyncratic language that emerge when agents only interact with a small number of individuals. This, in turn, prevents the signalling conventions having to be renegotiated with each new generation of language users, resulting in the emerging language being more stable over subsequent generations of language users. Furthermore, it is shown that allowing the children of language users to interact with one another is beneficial to the communicative success of the population when the number of partners that mature agents interact with is low

Achieving Compositional Language in a Population of Iterated Learners

Available from MIT Press via the DOI in this recordIterated learning takes place when the input into a particular individual's learning process is itself the output of another individual's learning process. This is an important feature to capture when investigating human language change, or the dynamics of culturally learned behaviours in general. Over the last fifteen years, the Iterated Learning Model (ILM) has been used to shed light on how the population-level characteristics of learned communication arise. However, until now each iteration of the model has tended to feature a single immature language user learning from their interactions with a single mature language user. Here, the ILM is extended to include a population of immature and mature language users. We demonstrate that the structure and make-up of this population influences the dynamics of language change that occur over generational time. In particular, we show that, by increasing the number of trainers from which an agent learns, the agent in question learns a fully compositional language at a much faster rate, and with less training data. It is also shown that, so long as the number of mature agents is large enough, this finding holds even if a learner's trainers include other agents that do not yet posses full linguistic competence.This work was supported by an EPSRC Doctoral Training Centre grant (EP/G03690x/1)

Destructive sampling natural science collections: an overview for museum professionals and researchers

There are many reasons why museum collections may be used for destructive sampling, from DNA and isotope analysis to radiocarbon dating. The process is invasive and destroys a part, or all, of the specimen. This can result in reluctance by museum staff to allow specimens to be used in particular types of scientific research. We will present some of the motivations on both sides, but argue that the benefits of destructive sampling can outweigh the risks. Many analytical methods have improved dramatically in the last 30 years, requiring smaller sample sizes. With a focus on destructive sampling for genetic analysis, we will also present some examples from the literature where DNA from museum and archaeological specimens has greatly aided the reconstruction of a species' evolutionary history as well as enriching our understanding of the object sampled. In addition, we highlight the need for museum staff to understand exactly what researchers are asking for, and for researchers in turn to understand museum procedures. We include an example of a Destructive Sampling Policy and a Destructive Sampling Request Form, for institutions to adapt for their own use

Noncommutative 1-cocycle in the Seiberg-Witten map

We show that the Seiberg-Witten map for a noncommutative gauge theory involves a noncommutative 1-cocycle. The cocycle condition enforces a consistency requirement, which has been previously derived.Comment: 6 pages; email correspondence to R. Jackiw ; missing factors of i inserted, one reference adde

Destructive sampling natural science collections: an overview for museum professionals and researchers

There are many reasons why museum collections may be used for destructive sampling, from DNA and isotope analysis to radiocarbon dating. The process is invasive and destroys a part, or all, of the specimen. This can result in reluctance by museum staff to allow specimens to be used in particular types of scientific research. We will present some of the motivations on both sides, but argue that the benefits of destructive sampling can outweigh the risks. Many analytical methods have improved dramatically in the last 30 years, requiring smaller sample sizes. With a focus on destructive sampling for genetic analysis, we will also present some examples from the literature where DNA from museum and archaeological specimens has greatly aided the reconstruction of a species' evolutionary history as well as enriching our understanding of the object sampled. In addition, we highlight the need for museum staff to understand exactly what researchers are asking for, and for researchers in turn to understand museum procedures. We include an example of a Destructive Sampling Policy and a Destructive Sampling Request Form, for institutions to adapt for their own use

The effect of structure directing agents on the ordering of fluoride ions in pure silica MFI zeolites

The authors would like to thank Keele University and the University of St Andrews for providing a PhD studentship for SLB. PW would like to thank the EPSRC for funding (EP/E041825/1). RJD would like to thank Prof. Colin Fyfe of the University of British Columbia for useful discussions and for providing NMR spectrometer time for initial results.The effect of different sizes of structure directing agents on the ordering of the fluoride ions in pure silica MFI zeolites has been determined using magic angle spinning solid state NMR. By synthesizing fluoride containing pure silica MFI zeolites using methyltributylammonium cations as the structure directing agent, it has been possible to change the type of ordering seen for the fluoride ions at room temperature from the previously reported dynamic to static disorder. An initial mechanism for how this fluoride ordering occurs is suggested based upon the coulombic interaction between the positive charge on the nitrogen and the negative fluoride ion, within the zeolite framework, with different sizes of tetraalkylammonium cations.Publisher PDFPeer reviewe

Deficiency of Prdm13, a dorsomedial hypothalamus-enriched gene, mimics age-associated changes in sleep quality and adiposity

The dorsomedial hypothalamus (DMH) controls a number of essential physiological responses. We have demonstrated that the DMH plays an important role in the regulation of mammalian aging and longevity. To further dissect the molecular basis of the DMH function, we conducted microarray-based gene expression profiling with total RNA from laser-microdissected hypothalamic nuclei and tried to find the genes highly and selectively expressed in the DMH. We found neuropeptide VF precursor (Npvf),PR domain containing 13 (Prdm13), and SK1 family transcriptional corepressor (Skor1) as DMH-enriched genes. Particularly, Prdm13, a member of the Prdm family of transcription regulators, was specifically expressed in the compact region of the DMH (DMC), where Nk2 homeobox 1 (Nkx2-1) is predominantly expressed. The expression of Prdm13 in the hypothalamus increased under diet restriction, whereas it decreased during aging. Prdm13 expression also showed diurnal oscillation and was significantly upregulated in the DMH of long-lived BRASTO mice. The transcriptional activity of the Prdm13 promoter was upregulated by Nkx2-1, and knockdown of Nkx2-1 suppressed Prdm13 expression in primary hypothalamic neurons. Interestingly, DMH-specific Prdm13-knockdown mice showed significantly reduced wake time during the dark period and decreased sleep quality, which was defined by the quantity of electroencephalogram delta activity during NREM sleep. DMH-specific Prdm13-knockdown mice also exhibited progressive increases in body weight and adiposity. Our findings indicate that Prdm13/Nkx2-1-mediated signaling in the DMC declines with advanced age, leading to decreased sleep quality and increased adiposity, which mimic age-associated pathophysiology, and provides a potential link to DMH-mediated aging and longevity control in mammals

Hagedorn transition and chronology protection in string theory

We conjecture chronology is protected in string theory due to the condensation of light winding strings near closed null curves. This condensation triggers a Hagedorn phase transition, whose end-point target space geometry should be chronological. Contrary to conventional arguments, chronology is protected by an infrared effect. We support this conjecture by studying strings in the O-plane orbifold, where we show that some winding string states are unstable and condense in the non-causal region of spacetime. The one-loop string partition function has infrared divergences associated to the condensation of these states.Comment: 40 pages, 11 figures. Expanded discussion on evolution of on-shell modes and added appendi

Towards an explicit expression of the Seiberg-Witten map at all orders

The Seiberg-Witten map links noncommutative gauge theories to ordinary gauge theories, and allows to express the noncommutative variables in terms of the commutative ones. Its explicit form can be found order by order in the noncommutative parameter theta and the gauge potential A by the requirement that gauge orbits are mapped on gauge orbits. This of course leaves ambiguities, corresponding to gauge transformations, and there is an infinity of solutions. Is there one better, clearer than the others ? In the abelian case, we were able to find a solution, linked by a gauge transformation to already known formulas, which has the property of admitting a recursive formulation, uncovering some pattern in the map. In the special case of a pure gauge, both abelian and non-abelian, these expressions can be summed up, and the transformation is expressed using the parametrisation in terms of the gauge group.Comment: 17 pages. Latex, 1 figure. v2: minor changes, published versio