151 research outputs found
Renormalization of Coulomb interactions in s-wave superconductor NaCoO
We study the renormalized Coulomb interactions due to retardation effect in
NaCoO. Although the Morel-Anderson's pseudo potential for
orbital is relatively large because the direct Coulomb repulsion
is large, that for interband transition between and
orbitals is very small since the renormalization factor for
pair hopping is square of that for . Therefore, the s-wave
superconductivity due to valence-band Suhl-Kondo mechanism will survive against
strong Coulomb interactions. The interband hopping of Cooper pairs due to shear
phonons is essential to understand the superconductivity in NaCoO.Comment: 2pages, 2figures, Proceedings of ICM in Kyoto, 200
Application of Optimal Control to CPMG Refocusing Pulse Design
We apply optimal control theory (OCT) to the design of refocusing pulses
suitable for the CPMG sequence that are robust over a wide range of B0 and B1
offsets. We also introduce a model, based on recent progress in the analysis of
unitary dynamics in the field of quantum information processing (QIP), that
describes the multiple refocusing dynamics of the CPMG sequence as a dephasing
Pauli channel. This model provides a compact characterization of the
consequences and severity of residual pulse errors. We illustrate the methods
by considering a specific example of designing and analyzing broadband OCT
refocusing pulses of length 10 t180 that are constrained by the maximum
instantaneous pulse power. We show that with this refocusing pulse, the CPMG
sequence can refocus over 98% of magnetization for resonance offsets up to 3.2
times the maximum RF amplitude, even in the presence of +/- 10% RF
inhomogeneity.Comment: 23 pages, 10 figures; Revised and reformatted version with new title
and significant changes to Introduction and Conclusions section
Myasthenia gravis
Myasthenia gravis (MG) is a rare, autoimmune neuromuscular junction disorder. Contemporary prevalence rates approach 1/5,000. MG presents with painless, fluctuating, fatigable weakness involving specific muscle groups. Ocular weakness with asymmetric ptosis and binocular diplopia is the most typical initial presentation, while early or isolated oropharyngeal or limb weakness is less common. The course is variable, and most patients with initial ocular weakness develop bulbar or limb weakness within three years of initial symptom onset. MG results from antibody-mediated, T cell-dependent immunologic attack on the endplate region of the postsynaptic membrane. In patients with fatigable muscle weakness, the diagnosis of MG is supported by: 1. pharmacologic testing with edrophonium chloride that elicits unequivocal improvement in strength; 2. electrophysiologic testing with repetitive nerve stimulation (RNS) studies and/or single-fiber electromyography (SFEMG) that demonstrates a primary postsynaptic neuromuscular junctional disorder; and 3. serologic demonstration of acetylcholine receptor (AChR) or muscle-specific tyrosine kinase (MuSK) antibodies. Differential diagnosis includes congenital myasthenic syndromes, Lambert Eaton syndrome, botulism, organophosphate intoxication, mitochondrial disorders involving progressive external ophthalmoplegia, acute inflammatory demyelinating polyradiculoneuropathy (AIDP), motor neuron disease, and brainstem ischemia. Treatment must be individualized, and may include symptomatic treatment with cholinesterase inhibitors and immune modulation with corticosteroids, azathioprine, cyclosporine, and mycophenolate mofetil. Rapid, temporary improvement may be achieved for myasthenic crises and exacerbations with plasma exchange (PEX) or intravenous immunoglobulin (IVIg). Owing to improved diagnostic testing, immunotherapy, and intensive care, the contemporary prognosis is favorable with less than five percent mortality and nearly normal life expectancy
Understanding American Power:Conceptual clarity, strategic priorities and the decline debate
What does it mean for the United States to be powerful? The prospect of a decline in American power, especially relative to a rising China, has attracted considerable scholarly and political attention. Despite a wealth of data, disagreements persist regarding both the likely trajectory of the US-China balance and the most effective strategy for preserving America’s advantage into the future. This article locates the source of these enduring disputes in fundamental conceptual differences over the meaning of power itself. We map the distinct tracks of argument within the decline debate, showing that competing positions are often rooted in differences of focus rather than disputes over fact. Most fundamental is a divide between analyses dedicated to national capabilities, and others that emphasise mechanisms of relational power. This divide underpins how strategists think about the goal of preserving or extending American power. We therefore construct a typology of competing understandings of what it means for America to be powerful, to show that a strategy suited to bolstering American power according to one definition of that goal may not support, and may even undermine, American power understood in other ways
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