1,071 research outputs found

    The Renormalization Group for Flag Manifolds

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    The renormalization group equations for a class of non--relativistic quantum σ\sigma--models targeted on flag manifolds are given. These models emerge in a continuum limit of generalized Heisenberg antiferromagnets. The case of the SU(3)U(1)×U(1){SU(3)\over U(1)\times U(1)} manifold is studied in greater detail. We show that at zero temperature there is a fixed point of the RG transformations in (2+ε)(2+\varepsilon )--dimensions where the theory becomes relativistic. We study the linearized RG transformations in the vicinity of this fixed point and show that half of the couplings are irrelevant. We also show that at this fixed point there is an enlargement of the global isometries of the target manifold. We construct a discrete non--abelian enlargement of this kind.Comment: 22 page

    Continuous Local Symmetry in Ising-type Models

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    A class of generalized Ising models is examined with a view to extracting a low energy sector comprising Dirac fermions coupled to Yang-Mills vectors. The main feature of this approach is a set of gap equations, covariant with respect to one of the 44-dimensional crystallographic space groups.Comment: 7 pages, latex, IC/94/2

    Mouse tafazzin is required for male germ cell meiosis and spermatogenesis

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    Barth syndrome is an X-linked mitochondrial disease, symptoms of which include neutropenia and cardiac myopathy. These symptoms are the most significant clinical consequences of a disease, which is increasingly recognised to have a variable presentation. Mutation in the Taz gene in Xq28 is thought to be responsible for the condition, by altering mitochondrial lipid content and mitochondrial function. Male chimeras carrying a targeted mutation of Taz on their X-chromosome were infertile. Testes from the Taz knockout chimeras were smaller than their control counterparts and this was associated with a disruption of the progression of spermatocytes through meiosis to spermiogenesis. Taz knockout ES cells also showed a defect when differentiated to germ cells in vitro. Mutant spermatocytes failed to progress past the pachytene stage of meiosis and had higher levels of DNA double strand damage and increased levels of endogenous retrotransposon activity. Altogether these data revealed a novel role for Taz in helping to maintain genome integrity in meiosis and facilitating germ cell differentiation. We have unravelled a novel function for the Taz protein, which should contribute to an understanding of how a disruption of the Taz gene results in the complex symptoms underlying Barth Syndrome

    Dissociative Autoionization in (1+2)-photon Above Threshold Excitation of H2 Molecules

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    We have theoretically studied the effect of dissociative autoionization on the photoelectron energy spectrum in (1+2)-photon above threshold ionization(ATI) of H2 molecules. We have considered excitation from the ground state X-singlet-Sigma-g+(v=0,j) to the doubly excited autoionizing states of singlet-Sigma-u+ and singlet-Pi-u+ symmetry, via the intermediate resonant B-singlet-Sigma-u+(v=5,j) states. We have shown that the photoelectron energy spectrum is oscillatory in nature and shows three distinct peaks above the photoelectron energy 0.7 eV. This feature has been observed in a recent experiment by Rottke et al, J. Phys. B, Vol. 30, p-4049 (1997).Comment: 11 pages and 4 figure

    From Words to Action: Comparing the Disparities Between National Drug Policy and Local Implementation in Tijuana, Mexico and Vancouver, Canada

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    In 2009, Mexico passed a national drug policy reform decriminalizing the possession of small amounts of certain drugs for personal use with the aim of diverting drug-dependent individuals from prison and towards addiction treatment. However, the public health approach codified by the reform has not yet led to a meaningful change in local police practices nor contributed to the meaningful scale-up of harm reduction and addiction treatment services in many Mexican cities. Specifically, in Tijuana, Baja California, there continues to be a variety of local level barriers – including arbitrary police behaviours – that hinder the ability of people who inject drugs (PWID) from accessing vital harm reduction services. This has implications for the growing HIV epidemic in Mexico’s northern border region, given that access to harm reduction interventions has been shown to effectively reduce the risk of HIV infection among PWID. In contrast to the largely enforcement-based local response seen in Tijuana, the municipal Four Pillars approach implemented in Vancouver, Canada in 2001 was passed as a public-health oriented response to the rising prevalence of HIV/AIDS among PWID in the Downtown Eastside of Vancouver. Centered on the balancing of four approaches – harm reduction, treatment, prevention and enforcement – the Four Pillars approach in Vancouver has led to a well-resourced local harm reduction and addiction treatment system. This local emphasis on harm reduction contrasts with the Canadian Conservative federal government’s opposition to harm reduction approaches. However, police-public health partnerships along with strong political support have led to the substantial scale up of harm reduction services as well as the reduction of HIV/AIDS among PWID in Vancouver, unlike what has been observed in Tijuana. This commentary therefore aims to assess the discrepancies between federal policy and local responses to drug-related harms in order to fully understand the impact and implications of national drug policies in shaping local response to drug related harms among populations of PWID. Through a comparison of the drug policy landscape in two cities linked by a large North American drug trafficking route - Tijuana, Mexico and Vancouver, Canada, - this commentary suggests that drug policy reform in and of itself will have little impact at the local level unless it is appropriately resourced and meaningfully supported by key stakeholders

    Lethal Injections: The Law, Science, and Politics of Syringe Access for Injection Drug Users

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    ENSURING THAT INJECTION drug users who cannot or will not stop injecting have access to sterile syringes is an important part of a comprehensive approach to reducing the transmission of viral and bacterial infections associated with injection drug use. I Seen purely in terms of public health science and prevention practice, ensuring syringe access for injection drug users is clearly an appropriate strategy: both evaluation research and experience in the field show that adequate syringe access produces positive health effects without negative social side effects