Pairing and Phase Coherence in High Temperature Superconductors

Mobile holes in an antiferromagnetic insulator form a slowly fluctuating array of quasi one-dimensional metallic stripes, which induce a spin gap or pseudogap in the intervening Mott-insulating regions. The mobile holes on an individual stripe acquire a spin gap via pair hopping between the stripe and its environment; i.e. via a magnetic analog of the usual superconducting proximity effect. This process is the analog of pairing in conventional superconductors. At non-vanishing stripe densities, Josephson coupling between stripes produces a dimensional crossover to a state with long-range superconducting phase coherence. In contrast to conventional superconductors, the superconducting state is characterised by a high density of (spin) pairs, but the phase stiffness, which is determined by the density and mobility of holes on the stripes, is very low.Comment: 4 pages. Proceedings of MMS-High Temperature Superconductivity, V (1997) To be published in Physica

Phonon and Magnetic Neutron Scattering at 41 Mev in YBa₂Cu₃O₇

We report inelastic neutron scattering measurements at excitation energies Latin small letter h with strokeω~41 meV in YBa2Cu3O7. We separate magnetic and phonon contributions to the scattering cross section by a detailed analysis of the momentum dependence of the scattered intensity. The previously reported broad peak around q=(π/a,π/a) in the normal state can be entirely accounted for by a phonon which primarily involves vibrations of the in-plane oxygen. Magnetic scattering centered around 41 meV and q=(π/a,π/a) appears in the superconducting state only. Theoretical implications of these findings are discussed

PetFMM--A dynamically load-balancing parallel fast multipole library

Fast algorithms for the computation of $N$-body problems can be broadly classified into mesh-based interpolation methods, and hierarchical or multiresolution methods. To this last class belongs the well-known fast multipole method (FMM), which offers O(N) complexity. This paper presents an extensible parallel library for $N$-body interactions utilizing the FMM algorithm, built on the framework of PETSc. A prominent feature of this library is that it is designed to be extensible, with a view to unifying efforts involving many algorithms based on the same principles as the FMM and enabling easy development of scientific application codes. The paper also details an exhaustive model for the computation of tree-based $N$-body algorithms in parallel, including both work estimates and communications estimates. With this model, we are able to implement a method to provide automatic, a priori load balancing of the parallel execution, achieving optimal distribution of the computational work among processors and minimal inter-processor communications. Using a client application that performs the calculation of velocity induced by $N$ vortex particles, ample verification and testing of the library was performed. Strong scaling results are presented with close to a million particles in up to 64 processors, including both speedup and parallel efficiency. The library is currently able to achieve over 85% parallel efficiency for 64 processors. The software library is open source under the PETSc license; this guarantees the maximum impact to the scientific community and encourages peer-based collaboration for the extensions and applications.Comment: 28 pages, 9 figure

Complementary and alternative medicine for rheumatic diseases: a systematic review of randomized controlled trials

To summarize all good quality randomized controlled trials (RCTs) using complementary and alternative medicine (CAM) interventions in patients with rheumatic diseases.A systematic literature review guided by the Preferred Reporting Items for Systematic review and Meta-Analysis (PRISMA) was performed. We excluded non-English language articles and abstract-only publications. Due to the large number of RCTs identified, we only include "good quality" RCTs with Jadad score of five.We identified 60 good quality RCTs using CAM as intervention for patients with rheumatic diseases: acupuncture (9), Ayurvedic treatment (3), homeopathic treatment (3), electricity (2), natural products (31), megavitamin therapies (8), chiropractic or osteopathic manipulation (3), and energy healing therapy (1). The studies do not seem to suggest a particular type of CAM is effective for all types for rheumatic diseases. However, some CAM interventions appear to be more effective for certain types of rheumatic diseases. Acupuncture appears to be beneficial for osteoarthritis but not rheumatoid arthritis. For the other therapeutic modalities, the evidence base either contains too few trials or contains trials with contradictory findings which preclude any definitive summary. There were only minor adverse reactions observed for CAM interventions presented.We identified 60 good quality RCTs which were heterogenous in terms of interventions, disease, measures used to assess outcomes, and efficacy of CAM interventions. Evidence indicates that some CAM therapies may be useful for rheumatic diseases, such as acupuncture for osteoarthritis. Further research with larger sample size is required for more conclusive evidence regarding efficacy of CAM interventions

Perceptions of anti-smoking messages amongst high school students in Pakistan

<p>Abstract</p> <p>Background</p> <p>Surveys have provided evidence that tobacco use is widely prevalent amongst the youth in Pakistan. Several reviews have evaluated the effectiveness of various tobacco control programs, however, few have taken into account the perceptions of students themselves regarding these measures. The aim of this study was to determine the most effective anti-smoking messages that can be delivered to high-school students in Pakistan, based on their self-rated perceptions. It also aimed to assess the impact of pictorial/multi-media messages compared with written health warnings and to discover differences in perceptions of smokers to those of non-smokers to health warning messages.</p> <p>Methods</p> <p>This study was carried out in five major cities of Pakistan in private English-medium schools. A presentation was delivered at each school that highlighted the well-established health consequences of smoking using both written health warnings and pictorial/multi-media health messages. Following the presentation, the participants filled out a graded questionnaire form, using which they rated the risk-factors and messages that they thought were most effective in stopping or preventing them from smoking. The Friedman test was used to rank responses to each of the questions in the form. The Wilcoxon Signed Rank test used to analyze the impact of pictorial/multi-media messages over written statements. The Mann Whitney U test was used to compare responses of smokers with those of non-smokers.</p> <p>Results</p> <p>Picture of an oral cavity cancer, videos of a cancer patient using an electronic voice box and a patient on a ventilator, were perceived to be the most effective anti-smoking messages by students. Addiction, harming others through passive smoking and impact of smoking on disposable incomes were perceived to be less effective messages. Pictorial/multi-media messages were perceived to be more effective than written health warnings. Health warnings were perceived as less effective amongst smokers compared to non-smokers.</p> <p>Conclusion</p> <p>Graphic pictorial/multi-media health warnings that depict cosmetic and functional distortions were perceived as effective anti-smoking messages by English-medium high school students in Pakistan. Smokers demonstrated greater resistance to health promotion messages compared with non-smokers. Targeted interventions for high school students may be beneficial.</p