4,347 research outputs found
Probing the superconducting condensate on a nanometer scale
Superconductivity is a rare example of a quantum system in which the
wavefunction has a macroscopic quantum effect, due to the unique condensate of
electron pairs. The amplitude of the wavefunction is directly related to the
pair density, but both amplitude and phase enter the Josephson current : the
coherent tunneling of pairs between superconductors. Very sensitive devices
exploit the superconducting state, however properties of the {\it condensate}
on the {\it local scale} are largely unknown, for instance, in unconventional
high-T cuprate, multiple gap, and gapless superconductors.
The technique of choice would be Josephson STS, based on Scanning Tunneling
Spectroscopy (STS), where the condensate is {\it directly} probed by measuring
the local Josephson current (JC) between a superconducting tip and sample.
However, Josephson STS is an experimental challenge since it requires stable
superconducting tips, and tunneling conditions close to atomic contact. We
demonstrate how these difficulties can be overcome and present the first
spatial mapping of the JC on the nanometer scale. The case of an MgB film,
subject to a normal magnetic field, is considered.Comment: 7 pages, 6 figure
Cosmic Calibration: Constraints from the Matter Power Spectrum and the Cosmic Microwave Background
Several cosmological measurements have attained significant levels of
maturity and accuracy over the last decade. Continuing this trend, future
observations promise measurements of the statistics of the cosmic mass
distribution at an accuracy level of one percent out to spatial scales with
k~10 h/Mpc and even smaller, entering highly nonlinear regimes of gravitational
instability. In order to interpret these observations and extract useful
cosmological information from them, such as the equation of state of dark
energy, very costly high precision, multi-physics simulations must be
performed. We have recently implemented a new statistical framework with the
aim of obtaining accurate parameter constraints from combining observations
with a limited number of simulations. The key idea is the replacement of the
full simulator by a fast emulator with controlled error bounds. In this paper,
we provide a detailed description of the methodology and extend the framework
to include joint analysis of cosmic microwave background and large scale
structure measurements. Our framework is especially well-suited for upcoming
large scale structure probes of dark energy such as baryon acoustic
oscillations and, especially, weak lensing, where percent level accuracy on
nonlinear scales is needed.Comment: 15 pages, 14 figure
Two Gap State Density in MgB: A True Bulk Property or A Proximity Effect?
We report on the temperature dependence of the quasiparticle density of
states (DOS) in the simple binary compound MgB2 directly measured using
scanning tunneling microscope (STM). To achieve high quality tunneling
conditions, a small crystal of MgB2 is used as a tip in the STM experiment. The
``sample'' is chosen to be a 2H-NbSe2 single crystal presenting an atomically
flat surface. At low temperature the tunneling conductance spectra show a gap
at the Fermi energy followed by two well-pronounced conductance peaks on each
side. They appear at voltages V mV and V mV. With rising temperature both peaks disappear at the Tc of the bulk
MgB2, a behavior consistent with the model of two-gap superconductivity. The
explanation of the double-peak structure in terms of a particular proximity
effect is also discussed.Comment: 4 pages, 3 figure
Scanning Tunneling Spectroscopy on the novel superconductor CaC6
We present scanning tunneling microscopy and spectroscopy of the newly
discovered superconductor CaC. The tunneling conductance spectra, measured
between 3 K and 15 K, show a clear superconducting gap in the quasiparticle
density of states. The gap function extracted from the spectra is in good
agreement with the conventional BCS theory with = 1.6 0.2
meV. The possibility of gap anisotropy and two-gap superconductivity is also
discussed. In a magnetic field, direct imaging of the vortices allows to deduce
a coherence length in the ab plane 33 nm
Review of the Refeeding Syndrome
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142310/1/ncp0625.pd
Weighted Sobolev spaces of radially symmetric functions
We prove dilation invariant inequalities involving radial functions,
poliharmonic operators and weights that are powers of the distance from the
origin. Then we discuss the existence of extremals and in some cases we compute
the best constants.Comment: 38 page
Harmonic maps from degenerating Riemann surfaces
We study harmonic maps from degenerating Riemann surfaces with uniformly
bounded energy and show the so-called generalized energy identity. We find
conditions that are both necessary and sufficient for the compactness in
and modulo bubbles of sequences of such maps.Comment: 27 page
CD4+CD25−Foxp3− Th1 cells are the source of IL-10–mediated immune suppression in chronic cutaneous leishmaniasis
Nonhealing forms of leishmaniasis in humans are commonly associated with elevated levels of the deactivating cytokine IL-10, and in the mouse, normally chronic infections can be cleared in the absence of IL-10. Using a Leishmania major strain that produces nonhealing dermal lesions in a T helper type 1 (Th1) cell–polarized setting, we have analyzed the cellular sources of IL-10 and their relative contribution to immune suppression. IL-10 was produced by innate cells, as well as CD4+CD25+Foxp3+ and CD4+CD25−Foxp3− T cells in the chronic lesion. Nonetheless, only IL-10 production by antigen-specific CD4+CD25−Foxp3− T cells, the majority of which also produced IFN-γ, was necessary for suppression of acquired immunity in Rag−/− reconstituted mice. Surprisingly, Rag−/− mice reconstituted with naive CD4+ T cells depleted of natural T regulatory cells developed more severe infections, associated with elevated levels of IL-10 and, especially, Th2 cytokines in the site. The data demonstrate that IL-10–producing Th1 cells, activated early in a strong inflammatory setting as a mechanism of feedback control, are the principal mediators of T cell–derived IL-10–dependent immune suppression in a chronic intracellular infection
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