Magnetic Collective Mode Dispersion in High Temperature Superconductors

Recent neutron scattering experiments in the superconducting state of YBCO have been interpreted in terms of a magnetic collective mode whose dispersion relative to the commensurate wavevector has a curvature opposite in sign to a conventional magnon dispersion. The purpose of this article is to demonstrate that simple linear response calculations are in support of a collective mode interpretation, and to explain why the dispersion has the curvature it does.Comment: 3 pages, revtex, 4 encapsulated postscript figure

Polarized beam operation of the Hybrid Spectrometer at the pulsed Spallation Neutron Source

The concept of a neutron Hybrid Spectrometer (HYSPEC) combines the time-of-flight spectroscopy with the focusing Bragg optics and incorporates a polarized beam option. Here we describe the polarization analysis scheme proposed for HYSPEC and quantify its performance via the Monte-Carlo simulations. We find that the broadband supermirror-bender transmission polarizers provide reasonably good polarization analysis capability within about 8-10 meV energy window for scattered neutron energies in the thermal range up to about 25 meV.Comment: Preprint, to appear in Physica B. 10 pages, 4 figure

A Review on Various Techniques and Recent Advances in Polymeric Additives to Mitigate Wax Problems in Crude Oil

Oil and gas industry has long recognized and is continuing to face wax deposition problems, particularly, as more unconventional crudes are being produced. As time goes by, many techniques have been developed to reduce the cost to solve this challenging issue. Polymeric additives, which falls on chemical treatment categories have been extensively used and studied to improve the flow of the crude oil along the pipeline. Nevertheless, the majority of the polymeric additives have dual functions including the use as pour point depressant. This article reviews the various techniques used to improve the flow of crude oil such as mechanical, chemical and thermal treatment, and the recent advances of using polymeric additives to mitigate the wax problems

Effects of dilute Zn impurities on the uniform magnetic susceptibility of YBa2Cu3O{7-delta}

The effects of dilute Zn impurities on the uniform magnetic susceptibility are calculated in the normal metallic state for a model of the spin fluctuations of the layered cuprates. It is shown that scatterings from extended impurity potentials can lead to a coupling of the q~(pi,pi) and the q~0 components of the magnetic susceptibility chi(q). Within the presence of antiferromagnetic correlations, this coupling can enhance the uniform susceptibility. The implications of this result for the experimental data on Zn substituted YBa2Cu3O{7-delta} are discussed.Comment: 4 pages, 4 figure

Spin Susceptibility in Underdoped YBa2Cu3O6+x\bf YBa_2Cu_3O_{6+x}

We report a comprehensive polarized and unpolarized neutron scattering study of the evolution of the dynamical spin susceptibility with temperature and doping in three underdoped single crystals of the \YBCO{6+x} high temperature superconductor: \YBCO{6.5} (Tc = 52 K), \YBCO{6.7} (Tc = 67 K), and \YBCO{6.85} (T_c = 87 K). Theoretical implications of these data are discussed, and a critique of recent attempts to relate the spin excitations to the thermodynamics of high temperature superconductors is given.Comment: minor revisions, to appear in PR

Antibiotics in childhood pneumonia: how long is long enough?

Improved access to healthcare, vaccines and treatment with antibiotics has reduced global mortality from childhood community-acquired pneumonia. However, as respiratory viruses are responsible for most episodes of pneumonia, important questions remain over who should receive these agents and the length of each treatment course. Worldwide concerns with increasing antibiotic resistance in respiratory pathogens and appeals for more prudent antibiotic prescribing provide further urgency to these clinical questions. Unfortunately, guidelines for treatment duration in particular are based upon limited (and often weak) evidence, resulting in national and international guidelines recommending treatment courses for uncomplicated pneumonia ranging from 3 to 10 days. The advantages of shortcourse therapy include a lower risk of developing antibiotic resistance, improved adherence, fewer adverse drug effects, and reduced costs. The risks include treatment failure, leading to increased short- or long-term morbidity, or even death. The initial challenge is how to distinguish between bacterial and non-bacterial causes of pneumonia and then to undertake adequately powered randomised-controlled trials of varying antibiotic treatment durations in children who are most likely to have bacterial pneumonia. Meanwhile, healthcare workers should recognise the limitations of current pneumonia treatment guidelines and remember that antibiotic course duration is also determined by the child’s response to therapy

Spin dynamics of stripes

The spin dynamics of stripes in high-temperature superconductors and related compounds is studied in the framework of a spin-wave theory for a simple spin-only model. The magnon dispersion relation and the magnetic structure factor are calculated for diagonal and vertical stripes. Acoustical as well as optical bands are included in the analysis. The incommensurability and the $\pi$ resonance appear as complementary features of the band structure at different energy scales. The dependence of spin-wave velocities and resonance frequencies on the stripe spacing and coupling is calculated. At low doping, the resonance frequency is found to scale roughly inversely proportional to the stripe spacing. The favorable comparison of the results with experimental data suggests that the spin-only model provides a suitable and simple basis for calculating and understanding the spin dynamics of stripes.Comment: 11 page, 10 figures, pdf version with high-res.pics at http://www.thp.uni-koeln.de/~sts

Competing orders in a magnetic field: spin and charge order in the cuprate superconductors

We describe two-dimensional quantum spin fluctuations in a superconducting Abrikosov flux lattice induced by a magnetic field applied to a doped Mott insulator. Complete numerical solutions of a self-consistent large N theory provide detailed information on the phase diagram and on the spatial structure of the dynamic spin spectrum. Our results apply to phases with and without long-range spin density wave order and to the magnetic quantum critical point separating these phases. We discuss the relationship of our results to a number of recent neutron scattering measurements on the cuprate superconductors in the presence of an applied field. We compute the pinning of static charge order by the vortex cores in the `spin gap' phase where the spin order remains dynamically fluctuating, and argue that these results apply to recent scanning tunnelling microscopy (STM) measurements. We show that with a single typical set of values for the coupling constants, our model describes the field dependence of the elastic neutron scattering intensities, the absence of satellite Bragg peaks associated with the vortex lattice in existing neutron scattering observations, and the spatial extent of charge order in STM observations. We mention implications of our theory for NMR experiments. We also present a theoretical discussion of more exotic states that can be built out of the spin and charge order parameters, including spin nematics and phases with `exciton fractionalization'.Comment: 36 pages, 33 figures; for a popular introduction, see http://onsager.physics.yale.edu/superflow.html; (v2) Added reference to new work of Chen and Ting; (v3) reorganized presentation for improved clarity, and added new appendix on microscopic origin; (v4) final published version with minor change

Models of support for disclosure of HIV status to HIV-infected children and adolescents in resource-limited settings

Introduction: Disclosure of HIV status to HIV-infected children and adolescents is a major care challenge. We describe current site characteristics related to disclosure of HIV status in resource-limited paediatric HIV care settings within the International Epidemiology Databases to Evaluate AIDS (IeDEA) consortium. Methods: An online site assessment survey was conducted across the paediatric HIV care sites within six global regions of IeDEA. A standardized questionnaire was administered to the sites through the REDCap platform. Results: From June 2014 to March 2015, all 180 sites of the IeDEA consortium in 31 countries completed the online survey: 57% were urban, 43% were health centres and 86% were integrated clinics (serving both adults and children). Almost all the sites (98%) reported offering disclosure counselling services. Disclosure counselling was most often provided by counsellors (87% of sites), but also by nurses (77%), physicians (74%), social workers (68%), or other clinicians (65%). It was offered to both caregivers and children in 92% of 177 sites with disclosure counselling. Disclosure resources and procedures varied across geographical regions. Most sites in each region reported performing staff members' training on disclosure (72% to 96% of sites per region), routinely collecting HIV disclosure status (50% to 91%) and involving caregivers in the disclosure process (71% to 100%). A disclosure protocol was available in 14% to 71% of sites. Among the 143 sites (79%) routinely collecting disclosure status process, the main collection method was by asking the caregiver or child (85%) about the child's knowledge of his/her HIV status. Frequency of disclosure status assessment was every three months in 63% of the sites, and 71% stored disclosure status data electronically. Conclusion: The majority of the sites reported offering disclosure counselling services, but educational and social support resources and capacities for data collection varied across regions. Paediatric HIV care sites worldwide still need specific staff members' training on disclosure, development and implementation of guidelines for HIV disclosure, and standardized data collection on this key issue to ensure the long-term health and wellbeing of HIV-infected youth