299 research outputs found
Nernst Effect and Anomalous Transport in Cuprates: A Preformed-Pair Alternative to the Vortex Scenario
We address those puzzling experiments in underdoped high
superconductors which have been associated with normal state "vortices" and
show these data can be understood as deriving from preformed pairs with onset
temperature . For uncorrelated bosons in small magnetic fields, and
arbitrary , we present the exact contribution to \textit{all}
transport coefficients. In the overdoped regime our results reduce to those of
standard fluctuation theories (). Semi-quantitative agreement
with Nernst, ac conductivity and diamagnetic measurements is quite reasonable.Comment: 9 pages, 4 figures; Title, abstract and contents modified, new
references added, figures changed, one more figure added; to be published on
PR
The pseudogap state in superconductors: Extended Hartree approach to time-dependent Ginzburg-Landau Theory
It is well known that conventional pairing fluctuation theory at the Hartree
level leads to a normal state pseudogap in the fermionic spectrum. Our goal is
to extend this Hartree approximated scheme to arrive at a generalized mean
field theory of pseudogapped superconductors for all temperatures . While an
equivalent approach to the pseudogap has been derived elsewhere using a more
formal Green's function decoupling scheme, in this paper we re-interpret this
mean field theory and BCS theory as well, and demonstrate how they naturally
relate to ideal Bose gas condensation. Here we recast the Hartree approximated
Ginzburg-Landau self consistent equations in a T-matrix form. This recasting
makes it possible to consider arbitrarily strong attractive coupling, where
bosonic degrees of freedom appear at considerably above . The
implications for transport both above and below are discussed. Below
we find two types of contributions. Those associated with fermionic
excitations have the usual BCS functional form. That they depend on the
magnitude of the excitation gap, nevertheless, leads to rather atypical
transport properties in the strong coupling limit, where this gap (as distinct
from the order parameter) is virtually -independent. In addition, there are
bosonic terms arising from non-condensed pairs whose transport properties are
shown here to be reasonably well described by an effective time-dependent
Ginzburg-Landau theory.Comment: 14 pages, 5 figures, REVTeX4, submitted to PRB; clarification of the
diagrammatic technique added, one figure update
Contribution of Classic and Alternative Effector Pathways in Peanut-Induced Anaphylactic Responses
Food allergy affects approximately 5% of children and is the leading cause of hospitalization for anaphylactic reactions in westernized countries. However, the pathways of anaphylaxis in food allergy are still relatively unknown. We investigated the effector pathways of allergic and anaphylactic responses of different strains of mice in a clinical relevant model of peanut allergy. C3H/HeOuJ, C57BL/6 and BALB/c mice were sensitized by intragastric peanut extract and challenged by intragastric or intraperitoneal injection of peanut. Peanut-specific T cell responses, IgE, IgG1 and IgG2a and mucosal mast cell degranulation were induced to different extent in C3H/HeOuJ, C57BL/6 and BALB/c mice. Interestingly, anaphylactic symptoms after systemic challenge were highest in C3H/HeOuJ followed by C57BL/6 but were absent in BALB/c mice. Mechanistic studies showed that the food allergic systemic anaphylaxis was dependent on platelets, FcRγ and mast cells, and partially dependent on platelet activating factor and monocytes/macrophages, depending on mouse strain. These data demonstrate that in three mouse strains, components of the classic and alternative anaphylactic cascade are differently expressed, leading to differential outcomes in parameters of allergic disease and food induced systemic anaphylaxis
Dose escalations in phase I studies: feasibility of interpreting blinded pharmacodynamic data
Aims During phase I study conduct, blinded data are reviewed to predict the safety of increasing the dose level. The aim of the present study was to describe the probability that effects are observed in blinded evaluations of data in a simulated phase I study design. Methods An application was created to simulate blinded pharmacological response curves over time for 6 common safety/efficacy measurements in phase I studies for 1 or 2 cohorts (6 active, 2 placebo per cohort). Effect sizes between 0 and 3 between-measurement standard deviations (SDs) were simulated. Each set of simulated graphs contained the individual response and mean +/- SD over time. Reviewers (n = 34) reviewed a median of 100 simulated datasets and indicated whether an effect was present. Results Increasing effect sizes resulted in a higher chance of the effect being identified by the blinded reviewer. On average, 6% of effect sizes of 0.5 between-measurement SD were correctly identified, increasing to 72% in 3.0 between-measurement SD effect sizes. In contrast, on average 92-95% of simulations with no effect were correctly identified, with little effect of between-measurement variability in single cohort simulations. Adding a dataset of a second cohort at half the simulated dose did not appear to improve the interpretation. Conclusion Our analysis showed that effect sizes <2x the between-measurement SD of the investigated outcome frequently go unnoticed by blinded reviewers, indicating that the weight given to these blinded analyses in current phase I practice is inappropriate and should be re-evaluated.PharmacologyBiopharmaceutic
Microscopic theory of the pseudogap and Peierls transition in quasi-one-dimensional materials
The problem of deriving from microscopic theory a Ginzburg-Landau free energy
functional to describe the Peierls or charge-density-wave transition in
quasi-one-dimensional materials is considered. Particular attention is given to
how the thermal lattice motion affects the electronic states. Near the
transition temperature the thermal lattice motion produces a pseudogap in the
density of states at the Fermi level. Perturbation theory diverges and the
traditional quasi-particle or Fermi liquid picture breaks down. The pseudogap
causes a significant modification of the coefficients in the Ginzburg-Landau
functional from their values in the rigid lattice approximation, which neglects
the effect of the thermal lattice motion. To appear in Physical Review B.Comment: 21 pages, RevTeX, 5 figures in uuencoded compressed tar fil
Somatotropinoma Infarction During Octreotide Therapy Leading to Bilateral Cavernous Sinus Syndrome
The cyclic somatostatin analog, octreotide, forms the mainstay of medical treatment for acromegaly. In addition to lowering circulating growth hormone levels and shrinking tumor size, octreotide may provide symptomatic relief of headaches associated with growth hormone secreting tumors. The majority of reported complications of octreotide therapy are gastrointestinal and metabolic. The present case illustrates the development of acute bilateral cavernous sinus syndrome with loss of eye movement bilaterally during octreotide therapy. Serial MRI examination suggest tumor infarction as the etiology. The symptoms resolved over 2 months as the tumor shrunk in size and growth hormone was dramatically reduced.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47491/1/11102_2004_Article_324058.pd
Reduction in BACE1 decreases body weight, protects against diet-induced obesity and enhances insulin sensitivity in mice
Insulin resistance and impaired glucose homoeostasis are important indicators of Type 2 diabetes and are early risk factors of AD (Alzheimer's disease). An essential feature of AD pathology is the presence of BACE1 (β-site amyloid precursor protein-cleaving enzyme 1), which regulates production of toxic amyloid peptides. However, whether BACE1 also plays a role in glucose homoeostasis is presently unknown. We have used transgenic mice to analyse the effects of loss of BACE1 on body weight, and lipid and glucose homoeostasis. BACE1−/− mice are lean, with decreased adiposity, higher energy expenditure, and improved glucose disposal and peripheral insulin sensitivity than wild-type littermates. BACE1−/− mice are also protected from diet-induced obesity. BACE1-deficient skeletal muscle and liver exhibit improved insulin sensitivity. In a skeletal muscle cell line, BACE1 inhibition increased glucose uptake and enhanced insulin sensitivity. The loss of BACE1 is associated with increased levels of UCP1 (uncoupling protein 1) in BAT (brown adipose tissue) and UCP2 and UCP3 mRNA in skeletal muscle, indicative of increased uncoupled respiration and metabolic inefficiency. Thus BACE1 levels may play a critical role in glucose and lipid homoeostasis in conditions of chronic nutrient excess. Therefore strategies that ameliorate BACE1 activity may be important novel approaches for the treatment of diabetes
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