Progress in aircraft gas turbine engine development

Aircraft gas turbine engine development

Dimensional Mutation and Spacelike Singularities

I argue that string theory compactified on a Riemann surface crosses over at small volume to a higher dimensional background of supercritical string theory. Several concrete measures of the count of degrees of freedom of the theory yield the consistent result that at finite volume, the effective dimensionality is increased by an amount of order $2h/V$ for a surface of genus $h$ and volume $V$ in string units. This arises in part from an exponentially growing density of states of winding modes supported by the fundamental group, and passes an interesting test of modular invariance. Further evidence for a plethora of examples with the spacelike singularity replaced by a higher dimensional phase arises from the fact that the sigma model on a Riemann surface can be naturally completed by many gauged linear sigma models, whose RG flows approximate time evolution in the full string backgrounds arising from this in the limit of large dimensionality. In recent examples of spacelike singularity resolution by tachyon condensation, the singularity is ultimately replaced by a phase with all modes becoming heavy and decoupling. In the present case, the opposite behavior ensues: more light degrees of freedom arise in the small radius regime. I comment on the emerging zoology of cosmological singularities that results.Comment: 15 pages, harvmac big. v2: 18 pages, harvmac big; added computation of density of states and modular invariance check, enhanced discussion of multiplicity of solutions all sharing the feature of increased density of states, added reference

Don't Panic! Closed String Tachyons in ALE Spacetimes

We consider closed string tachyons localized at the fixed points of noncompact nonsupersymmetric orbifolds. We argue that tachyon condensation drives these orbifolds to flat space or supersymmetric ALE spaces. The decay proceeds via an expanding shell of dilaton gradients and curvature which interpolates between two regions of distinct angular geometry. The string coupling remains weak throughout. For small tachyon VEVs, evidence comes from quiver theories on D-branes probes, in which deformations by twisted couplings smoothly connect non-supersymmetric orbifolds to supersymmetric orbifolds of reduced order. For large tachyon VEVs, evidence comes from worldsheet RG flow and spacetime gravity. For \IC^2/\IZ_n, we exhibit infinite sequences of transitions producing SUSY ALE spaces via twisted closed string condensation from non-supersymmetric ALE spaces. In a $T$-dual description this provides a mechanism for creating NS5-branes via {\it closed} string tachyon condensation similar to the creation of D-branes via {\it open} string tachyon condensation. We also apply our results to recent duality conjectures involving fluxbranes and the type 0 string.Comment: 48 pages, harvmac big; 13 figures. v2: added references; comment on gravity regime added to section 5.2. v3: added reference

An information-based approach to integrating empirical and explanation-based learning

We describe a new approach to integrating explanation-based and empirical learning methods for learning relational concepts. The approach uses an information-based heuristic to evaluate components of a hypothesis that are proposed either by explanation-based or empirical methods. Providing domain knowledge to the integrated system can decrease the amount of search required during learning and increase the accuracy of learned concepts, even when the domain knowledge is incorrect and incomplete and there is noise in the training data

Tension is Dimension

We propose a simple universal formula for the tension of a D-brane in terms of a regularized dimension of the associated conformal field theory statespace.Comment: 18 pages, harvmac (b), one ref added, one typo fixe

Retrofitting O'Raifeartaigh Models with Dynamical Scales

We provide a method for obtaining simple models of supersymmetry breaking, with all small mass scales generated dynamically, and illustrate it with explicit examples. We start from models of perturbative supersymmetry breaking, such as O'Raifeartaigh and Fayet models, that would respect an $R$ symmetry if their small input parameters transformed as the superpotential does. By coupling the system to a pure supersymmetric Yang-Mills theory (or a more general supersymmetric gauge theory with dynamically small vacuum expectation values), these parameters are replaced by powers of its dynamical scale in a way that is naturally enforced by the symmetry. We show that supersymmetry breaking in these models may be straightforwardly mediated to the supersymmetric Standard Model, obtain complete models of direct gauge mediation, and comment on related model building strategies that arise in this simple framework.Comment: 15 pages, harvmac bi

Signal and Noise in Correlation Matrix

Using random matrix technique we determine an exact relation between the eigenvalue spectrum of the covariance matrix and of its estimator. This relation can be used in practice to compute eigenvalue invariants of the covariance (correlation) matrix. Results can be applied in various problems where one experimentally estimates correlations in a system with many degrees of freedom, like in statistical physics, lattice measurements of field theory, genetics, quantitative finance and other applications of multivariate statistics.Comment: 17 pages, 3 figures, corrected typos, revtex style changed to elsar

The response to the Dieudonné affair in France risks demonising French minority groups in the name of tolerance

The French comedian Dieudonné M’Bala M’Bala has caused controversy in France over the alleged anti-Semitism of his performances. Paul A. Silverstein writes on the wider issues related to anti-Semitism in French society, and why Dieudonné has proved so controversial. He argues that while Dieudonné’s supporters deny the accusations of anti-Semitism, they feed into a broader social and institutional context that can make Jewish citizens feel targeted. There is also a danger that in attacking Dieudonné, the French establishment risks demonising other French minority groups who make up many of his supporters

Bruce Maddy-Weitzman, Amazigh Politics in the Wake of the Arab Spring

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Seller Liability Under Section 12(2) of the Securities Act of 1933

This Note discusses which persons courts should deem to be sellers under section 12(2) according to their relationships to the challenged transaction. Part II examines the divergent approaches that courts have developed to identify seller status in the absence of legislative history. Part III analyzes the three major approaches and compares the scope of liability under each analysis. Last, part IV concludes that significant differences exist among these approaches and that courts uniformly should adopt a modified version of the proximate cause-substantial factor analysis ... This part examines each of the three approaches in particular situations and compares the results under each approach. This comparison shows first, that the strict privity approach is too narrow and does not sufficiently meet the needs of purchasers; second, that the aiding and abetting approach is too broad and violates the express language of the statute; and last, that the proximate cause-substantial factor approach is the most reasonable and practicable standard for the courts to employ if properly refined