The NMR of High Temperature Superconductors without Anti-Ferromagnetic Spin Fluctuations

A microscopic theory for the NMR anomalies of the planar Cu and O sites in superconducting La_1.85Sr_0.15CuO_4 is presented that quantitatively explains the observations without the need to invoke anit-ferromagnetic spin fluctuations on the planar Cu sites and its significant discrepancy with the observed incommensurate neutron spin fluctuations. The theory is derived from the recently published ab-initio band structure calculations that correct LDA computations tendency to overestimate the self-coulomb repulsion for the half-filled Cu d_x2-y2 orbital for these ionic systems. The new band structure leads to two bands at the Fermi level with holes in the Cu d_z2 and apical O p_z orbitals in addition to the standard Cu d_x2-y2 and planar O p_sigma orbitals. This band structure is part of a new theory for the cuprates that explains a broad range of experiments and is based upon the formation of Cooper pairs comprised of a k up spin electron from one band and a -k down spin electron from another band (Interband Pairing Model).Comment: In Press, Journal of Physical Chemistry. See also http://www.firstprinciples.com. Minor changes to references and figure readabilit

Operator Evolution via the Similarity Renormalization Group I: The Deuteron

Similarity Renormalization Group (SRG) flow equations can be used to unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate state contributions to low-energy observables while maintaining the natural hierarchy of many-body forces. Analogous flow equations can be used to consistently evolve operators so that observables are unchanged if no approximations are made. The question in practice is whether the advantages of a softer Hamiltonian and less correlated wave functions might be offset by complications in approximating and applying other operators. Here we examine the properties of SRG-evolved operators, focusing in this paper on applications to the deuteron but leading toward methods for few-body systems. We find the advantageous features generally carry over to other operators with additional simplifications in some cases from factorization of the unitary transformation operator.Comment: 33 pages, 19 figures. Improved figures 17 and 18. Expanded comments on OPE in tex

Operator Evolution via the Similarity Renormalization Group I: The Deuteron

Similarity Renormalization Group (SRG) flow equations can be used to unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate state contributions to low-energy observables while maintaining the natural hierarchy of many-body forces. Analogous flow equations can be used to consistently evolve operators so that observables are unchanged if no approximations are made. The question in practice is whether the advantages of a softer Hamiltonian and less correlated wave functions might be offset by complications in approximating and applying other operators. Here we examine the properties of SRG-evolved operators, focusing in this paper on applications to the deuteron but leading toward methods for few-body systems. We find the advantageous features generally carry over to other operators with additional simplifications in some cases from factorization of the unitary transformation operator.Comment: 33 pages, 19 figures. Improved figures 17 and 18. Expanded comments on OPE in tex

Will I? won't I? Why do men who have sex with men present for post-exposure prophylaxis for sexual exposures?

Background: Failures of post-exposure prophylaxis following sexual exposure (PEPSE) to prevent seroconversion have been reported and are often associated with ongoing risk exposure. Understanding why men who have sex with men (MSM) access PEPSE on some occasions and not others may lead to more effective health promotion and disease prevention strategies Methods: A qualitative study design using semi-structured interviews of 15 MSM within 6 months of them initiating PEPSE treatment at an HIV outpatient service in Brighton, UK. Results: PEPSE seeking was motivated by a number of factors: an episode that related to a particular sexual partner and their behaviour; the characteristics of the venue where the risk occurred; the respondent’s state of mind and influences of alcohol and recreational drug use; and their perceived beliefs on the effectiveness of PEPSE. Help was sought in the light of a “one-off” or “unusual” event. Many respondents felt they were less likely to behave in a risky manner following PEPSE. Conclusion: If PEPSE is to be effective as a public health measure, at risk individuals need to be empowered to make improved risk calculations from an increased perception that they could be exposed to HIV if they continue their current behaviour patterns. The concern is that PEPSE was sought by a low number of MSM implying that a greater number are not using the service based on failure to make accurate risk calculations or recognise high-risk scenario

Block Diagonalization using SRG Flow Equations

By choosing appropriate generators for the Similarity Renormalization Group (SRG) flow equations, different patterns of decoupling in a Hamiltonian can be achieved. Sharp and smooth block-diagonal forms of phase-shift equivalent nucleon-nucleon potentials in momentum space are generated as examples and compared to analogous low-momentum interactions ("v_lowk").Comment: 4 pages, 9 figures (pdfLaTeX

The Importance of Static Correlation in the Band Structure of High Temperature Superconductors

Recently we presented a new band structure for La(2-x)Sr(x)CuO(4) and other high temperature superconductors in which a second narrow band was seen to cross the primary band at the Fermi level. The existence of this second Fermi level band is in complete disagreement with the commonly accepted LDA band structure. Yet it provided a crucial piece of physics which led to an explanation for superconductivity and other unusual phenomena in these materials. In this work we present details as to the nature of the failure of conventional methods in deriving the band structure of the cuprates. In particular, we use a number of chemical analogues to describe the problem of static correlation in the band structure calculations and show how this can be corrected with the predictable outcome of a Fermi level band crossing.Comment: The Journal of Physical Chemistry, in press. References and figures updated. See www.firstprinciples.com for more information related to this wor

Supporting Innovative Co-operative Development: The Case of the Nova Scotia Co-operative Development System

In recent years, social science research has increasingly acknowledged the role of the social economy in building sustainable communities, and, around the world, co-operatives are recognized as major actors in the social economy. In Canada, the Nova Scotia Cooperative Council has forged several innovations in the past decade resulting in the development of a co-operative development system unparalleled in Anglophone Canada

Supporting Innovative Co-operative Development: The Case of the Nova Scotia Co-operative Development System

Description The research was initiated in order to contribute to one of the central research goals of BALTA – namely, to highlight “the scope and characteristics of social economy innovations that are achieving demonstrable social and economic results in other regions” in order to provide lessons and insights for strengthening the social economy in BC and Alberta. This research was subsequently used to inform further action research on how to strengthen the co-operative development systems in the provinces of Alberta and British Columbia. The NS-CDS case study looks at 6 main areas of the co-operative development system including: 1. Development Finance 2. Human Resource Development 3. Planning, Advocacy and Research 4. Policy and Governance 5. Community Economic Development 6. Accountability and EvaluationThis research paper was presented to the 2007 Canadian Congress of the Humanities and Social Sciences. It discusses a case study of the recent history of successful innovation and development in the co-operative sector in the province of Nova Scotia, Canada, that has been unparalleled in other parts of Anglophone Canada. The case study looks at the Nova Scotia Co-operative Development System from a systems perspective in order to encompass a wide range of interacting processes that are involved in the Nova Scotia experience. The research identifies success factors in the Nova Scotia experience that might be relevant to co-operative development in other regions.BC-Alberta Social Economy Research Alliance (BALTA) ; Social Sciences and Humanities Research Council of Canada (SSHRC) ; Canadian Centre for Community Renewal (CCCR