Generalised discrete torsion and mirror symmetry for G_2 manifolds

A generalisation of discrete torsion is introduced in which different discrete torsion phases are considered for the different fixed points or twist fields of a twisted sector. The constraints that arise from modular invariance are analysed carefully. As an application we show how all the different resolutions of the T^7/Z_2^3 orbifold of Joyce have an interpretation in terms of such generalised discrete torsion orbifolds. Furthermore, we show that these manifolds are pairwise identified under G_2 mirror symmetry. From a conformal field theory point of view, this mirror symmetry arises from an automorphism of the extended chiral algebra of the G_2 compactification.Comment: LaTeX, 25 pages, 1 figure; v2: one reference added and comment about higher loop modular invariance corrected, version to be publishe

Survey on team sports-related injury and management in young Hong Kong athletes

This item was digitized by the Internet Archive. Thesis (Ed.D.)--Boston Universit

Test Results for CSTR Test 4

One of the 3 technologies currently being developed for the Savannah River Salt Waste Processing Program is the Small-Tank Tetraphenylborate Process (STTP). This process uses sodium tetraphenylborate to precipitate and remove radioactive Cs from the waste and monosodium titanate to sorb and remove radioactive Sr and actinides. ORNL is demonstrating this process at the 1:4000 scale using a 20-liter continuous-flow stirred tank reactor (CSTR) system. The primary goal of Test 4 was to verify that the STTP process could achieve and maintain the necessary Cs decontamination while TPB was actively decomposing. Even with TPB being decomposed by the off-normal conditions of this test, the decontaimination factor for {sup 137}Cs obtained for the filtrate from the Slurry Concentrating Tank ranged from 47,000 to 646,000, exceeding the WAC standard

Speech Denoising Using Non-Negative Matrix Factorization with Kullback-Leibler Divergence and Sparseness Constraints

Proceedings of: IberSPEECH 2012 Conference, Madrid, Spain, November 21-23, 2012.A speech denoising method based on Non-Negative Matrix Factorization (NMF) is presented in this paper. With respect to previous related works, this paper makes two contributions. First, our method does not assume a priori knowledge about the nature of the noise. Second, it combines the use of the Kullback-Leibler divergence with sparseness constraints on the activation matrix, improving the performance of similar techniques that minimize the Euclidean distance and/or do not consider any sparsification. We evaluate the proposed method for both, speech enhancement and automatic speech recognitions tasks, and compare it to conventional spectral subtraction, showing improvements in speech quality and recognition accuracy, respectively, for different noisy conditions.This work has been partially supported by the Spanish Government grants TSI-020110-2009-103 and TEC2011-26807.Publicad

Water vapour corrosion of rare earth monosilicates for environmental barrier coatings application

Water vapour corrosion resistance of five rare earth monosilicates Y2SiO5, Gd2SiO5, Er2SiO5, Yb2SiO5, and Lu2SiO5 was investigated during testing at 1350 ˚C for up to 166 h in static air with 90% water vapour. Four of the RE-silicates showed little weight gain (0.859 mg cm-2) after 166 h of exposure. Prior to testing the microstrucre consists of equiaxed grains of 4- 7 ± 0.4 µm. XRD analysis showed that after 50 h exposure to water vapour corrosion Y, Er, Yb and Lu-silicates had both mono and disilicates present on their surfaces as a result of the reaction between monosilicate and water vapour to form disilicate, while Gd-silicate has converted completely to G4.67Si3O13 making it less stable for environmental barrier coatings application. The microstructures of corroded Y, Er, Yb and Lu-silicates contain ridges and cracks, while that of Gd-silicate contains rounded grains suggesting melting along with striped contract grains

Oscillation of the tunnel splitting in nanospin systems within the particle mapping formalism

The oscillation of tunnel splitting in the biaxial spin system within magnetic field along the anisotropy axis is analyzed within the particle mapping approach, rather than in the (\theta-\phi) spin coherent-state representation. In our mapping procedure, the spin system is transformed into a particle moving in the restricted $S^1$ geometry whose wave function subjects to the boundary condition involving additional phase shift. We obtain the new topological phase that plays the same role as the Wess-Zumino action in spin coherent-state representation. Considering the interference of two possible trajectories, instanton and anti-instanton, we get the identical condition for the field at which tunneling is quenched, with the previous result within spin coherent-state representation.Comment: 11 pages, 1 figure; Some typographical errors have been correcte

A Semantic Grid Oriented to E-Tourism

With increasing complexity of tourism business models and tasks, there is a clear need of the next generation e-Tourism infrastructure to support flexible automation, integration, computation, storage, and collaboration. Currently several enabling technologies such as semantic Web, Web service, agent and grid computing have been applied in the different e-Tourism applications, however there is no a unified framework to be able to integrate all of them. So this paper presents a promising e-Tourism framework based on emerging semantic grid, in which a number of key design issues are discussed including architecture, ontologies structure, semantic reconciliation, service and resource discovery, role based authorization and intelligent agent. The paper finally provides the implementation of the framework.Comment: 12 PAGES, 7 Figure

The Role of Radioactivities in Astrophysics

I present both a history of radioactivity in astrophysics and an introduction to the major applications of radioactive abundances to astronomy