BPS states of curves in Calabi--Yau 3--folds

The Gopakumar-Vafa conjecture is defined and studied for the local geometry of a curve in a Calabi-Yau 3-fold. The integrality predicted in Gromov-Witten theory by the Gopakumar-Vafa BPS count is verified in a natural series of cases in this local geometry. The method involves Gromov-Witten computations, Mobius inversion, and a combinatorial analysis of the numbers of etale covers of a curve.Comment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol5/paper9.abs.html Version 3 is GT version 2 and has corrections to eq (2) on p 295, to 1st eq in Prop 2.1 and the tables on p 39

VXA: A Virtual Architecture for Durable Compressed Archives

Data compression algorithms change frequently, and obsolete decoders do not always run on new hardware and operating systems, threatening the long-term usability of content archived using those algorithms. Re-encoding content into new formats is cumbersome, and highly undesirable when lossy compression is involved. Processor architectures, in contrast, have remained comparatively stable over recent decades. VXA, an archival storage system designed around this observation, archives executable decoders along with the encoded content it stores. VXA decoders run in a specialized virtual machine that implements an OS-independent execution environment based on the standard x86 architecture. The VXA virtual machine strictly limits access to host system services, making decoders safe to run even if an archive contains malicious code. VXA's adoption of a "native" processor architecture instead of type-safe language technology allows reuse of existing "hand-optimized" decoders in C and assembly language, and permits decoders access to performance-enhancing architecture features such as vector processing instructions. The performance cost of VXA's virtualization is typically less than 15% compared with the same decoders running natively. The storage cost of archived decoders, typically 30-130KB each, can be amortized across many archived files sharing the same compression method.Comment: 14 pages, 7 figures, 2 table

Professionalising the college workforce through mentoring and professional learning : a neglected perspective on enhancing quality

This submission contains an Integrative Statement of 23 000 words (including\ud footnotes and references) and a total of six' published items. Together, these form\ud the basis of my application for the award of the degree of PhD by publication.\ud The Integrative Statement attempts to show the coherence of my published work\ud and demonstrates my deep and synoptic'2 understanding of my chosen field. I\ud argue that my work has made a significant contribution to a sector of education\ud that has both been neglected and prone to serial and sometimes disarticulated\ud reforms. I also contend that it is a sector that has generated a dominant discourse\ud of quality improvement through strategies encompassing such elements as\ud competition between institutions (ostensibly driving up standards), stronger\ud regulation and control, and an overarching emphasis on the `auditable'.\ud In such circumstances, there has been a notable neglect of any purposeful focus\ud on the manner in which professionalism may be enhanced, to the benefit both of\ud teachers and their learners. Such professionalism as may derive from collective\ud ways of working and from an engagement with the notion of the 'learning\ud professional' has largely been absent from the policy discourse, at both national\ud and institutional levels. The potential of mentoring to play a central role in a\ud professionalising strategy has been a particular concern for me.\ud The specific and distinctive contribution I claim to have made is in the form of my\ud examination of the ways in which mentoring as a supportive activity for teachers\ud may not only significantly aid in professional formation and the improvement of\ud teaching quality, but also thereby assist in the national policy goal of raising\ud standards of learner achievement. The focus in much of my published work has\ud been on mentors' individual motivation, attributes and skills, broadening out in one\ud particular article to an analysis of institutional factors that appear to have a strong\ud influence on the environment in which mentoring may take place. The content and\ud focus of the items being submitted is thus essentially concerned with professional\ud learning and development, in particular when supported by skilled mentoring\ud within environments that are appropriately resourced and where their 'architecture'\ud and ethos meshes productively with the nature of effective mentoring.\ud Even more broadly, two published items being submitted explore aspects of\ud professional learning. I use the medium of the Integrative Statement to draw out\ud some explicit links between these and the professional challenges being faced by\ud practitioners in the post-compulsory sector. I also in my statement relate important\ud elements of my own writing to a range of relevant literature, demonstrating my\ud engagement with and understanding of perspectives from this literature

The Myth of the Rational Voter: Why Democracies Choose Bad Policies

In theory, democracy is a bulwark against socially harmful policies. In practice, however, democracies frequently adopt and maintain policies that are damaging. How can this paradox be explained? The influence of special interests and voter ignorance are two leading explanations. I offer an alternative story of how and why democracy fails. The central idea is that voters are worse than ignorant; they are, in a word, irrational -- and they vote accordingly. Despite their lack of knowledge, voters are not humble agnostics; instead, they confidently embrace a long list of misconceptions. Economic policy is the primary activity of the modern state. And if there is one thing that the public deeply misunderstands, it is economics. People do not grasp the "invisible hand" of the market, with its ability to harmonize private greed and the public interest. I call this anti-market bias. They underestimate the benefits of interaction with foreigners. I call this anti-foreign bias. They equate prosperity not with production, but with employment. I call this make-work bias. Finally, they are overly prone to think that economic conditions are bad and getting worse. I call this pessimistic bias. In the minds of many, Winston Churchill's famous aphorism cuts the conversation short: "Democracy is the worst form of government, except all those other forms that have been tried from time to time." But this saying overlooks the fact that governments vary in scope as well as form. In democracies the main alternative to majority rule is not dictatorship, but markets. A better understanding of voter irrationality advises us to rely less on democracy and more on the market

Plugging Side-Channel Leaks with Timing Information Flow Control

The cloud model's dependence on massive parallelism and resource sharing exacerbates the security challenge of timing side-channels. Timing Information Flow Control (TIFC) is a novel adaptation of IFC techniques that may offer a way to reason about, and ultimately control, the flow of sensitive information through systems via timing channels. With TIFC, objects such as files, messages, and processes carry not just content labels describing the ownership of the object's "bits," but also timing labels describing information contained in timing events affecting the object, such as process creation/termination or message reception. With two system design tools-deterministic execution and pacing queues-TIFC enables the construction of "timing-hardened" cloud infrastructure that permits statistical multiplexing, while aggregating and rate-limiting timing information leakage between hosted computations.Comment: 5 pages, 3 figure