12 research outputs found
An extended pair tunneling model: studies on bilayer splitting and some superconducting state properties
We consider an extended version of the pair tunneling model including
interlayer single particle hopping (ISPH) as a complementary process to pair
tunneling. The normal state gap, as found in cuprates, is taken to suppress the
effective ISPH in conformity with the experimental observations, and this in
turn enhances the pair tunneling process. The effective ISPH involves a
probability factor P for which we consider two choices and provide
phenomenological arguments in favour of them. We address the issue of bilayer
splitting by calculating the spectral density function and corresponding
photoemission intensity curves and show that our calculations conform with the
absence of bilayer splitting observed in ARPES experiments on Bi2212. We have
also studied the temperature variation of the superconducting gap and ratio of
the superconducting gap to T_c. Our results, obtained for both the choices of
P, are reasonably in good agreement with those from experiments on cuprate
superconductors. A linear T-dependent choice of P, however, yields a precise
match to the experimantal data of the temperature varying superconducting gap.Comment: Latex file, 17 pages, 5 figures (postscript files) include
Landau Transport equations in slave-boson mean-field theory of t-J model
In this paper we generalize slave-boson mean-field theory for model to
the time-dependent regime, and derive transport equations for model, both
in the normal and superconducting states. By eliminating the boson and
constraint fields exactly in the equations of motion we obtain a set of
transport equations for fermions which have the same form as Landau transport
equations for normal Fermi liquid and Fermi liquid superconductor, respectively
with all Landau parameters explicity given. Our theory can be viewed as a
refined version of U(1) Gauge theory where all lattice effects are retained and
strong correlation effects are reflected as strong Fermi-liquid interactions in
the transport equation. Some experimental consequences are discussed.Comment: 19 page
D-wave superconductivity in doped Mott insulators
The effect of proximity to a Mott insulating phase on the charge transport
properties of a superconductor is determined. An action describing the low
energy physics is formulated and different scenarios for the approach to the
Mott phase are distinguished by different variation with doping of the
parameters in the action. A crucial issue is found to be the doping dependence
of the quasiparticle charge which is defined here and which controls the
temperature and field dependence of the electromagnetic response functions.
Presently available data on high-T superconductors are analysed. The
data, while neither complete nor entirely consistent, suggest that neither the
quasiparticle velocity nor the quasiparticle charge vanish as the Mott phase is
approached, in contradiction to the predictions of several widely studied
theories of lightly doped Mott insulators. Implications of the results for the
structure of vortices in high-T superconductors are determined. The
numerical coefficients in the field-dependent specific heat are given for
square and triangular vortex lattices.Comment: 12 pages. No figures. Submitted to JPCS (Proceedings of Chicago SNS
conference
Ordering and manipulation of the magnetic moments in large-scale superconducting pi-loop arrays
Since the discovery of high-transition-temperature (high-Tc) superconductivity in layered copper oxides1, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that NaxCoO2dotyH2O (x 0.35, y 1.3) is a superconductor with a Tc of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-Tc copper oxides, suggesting that the two systems have similar underlying physic
A Prospective, Controlled Evaluation of the Abdominal Reapproximation Anchor Abdominal Wall Closure System in Combination with VAC Therapy Compared with VAC Alone in the Management of an Open Abdomen
Protecting health workers from infectious disease transmission: an exploration of a Canadian-South African partnership of partnerships
Background:
Health workers are at high risk of acquiring infectious diseases at work, especially in low and middle-income countries (LMIC) with critical health human resource deficiencies and limited implementation of occupational health and infection control measures. Amidst increasing interest in international partnerships to address such issues, how best to develop such collaborations is being actively debated. In 2006, a partnership developed between occupational health and infection control experts in Canada and institutions in South Africa (including an institute with a national mandate to conduct research and provide guidance to protect health workers from infectious diseases and promote improved working conditions). This article describes the collaboration, analyzes the determinants of success and shares lessons learned.
Methods:
Synthesizing participant-observer experience from over 9 years of collaboration and 10 studies already published from this work, we applied a realist review analysis to describe the various achievements at global, national, provincial and hospital levels. Expectations of the various parties on developing new insights, providing training, and addressing service needs were examined through a micro-meso-macro lens, focusing on how each main partner organization contributed to and benefitted from working together.
Results:
A state-of-the-art occupational health and safety surveillance program was established in South Africa following successful technology transfer from a similar undertaking in Canada and training was conducted that synergistically benefitted Northern as well as Southern trainees. Integrated policies combining infection control and occupational health to prevent and control infectious disease transmission among health workers were also launched. Having a national (South-South) network reinforced by the international (North–south) partnership was pivotal in mitigating the challenges that emerged.
Conclusions:
High-income country partnerships with experience in health system strengthening – particularly in much needed areas such as occupational health and infection control – can effectively work through strong collaborators in the Global South to build capacity. Partnerships are particularly well positioned to sustainably reinforce efforts at national and sub-national LMIC levels when they adopt a “communities of practice” model, characterized by multi-directional learning. The principles of effective collaboration learned in this “partnership of partnerships” to improve working conditions for health workers can be applied to other areas where health system strengthening is needed.Medicine, Faculty ofOther UBCNon UBCPopulation and Public Health (SPPH), School ofReviewedFacult