3,622 research outputs found
Constraints on the Quasiparticle Density of States in High- Superconductors
In this Letter we present new tunneling data on YBaCuO thin films
by low temperature scanning tunneling spectroscopy. Unusual peak-dip-hump
features, previously reported in BiSrCaCuO, are also
found in YBaCuO. To analyse these common signatures we propose a
new heuristic model in which, in addition to the d-wave symmetry, the gap
function is energy dependent. A simple expression for the quasiparticle density
of states is derived, giving an excellent agreement with the experiment. The
dynamics of the quasiparticle states and the energy scales involved in the
superconducting transition are discussed.Comment: 4 page Letter with 3 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
Nanometer Scale Mapping of the Density of States in an Inhomogeneous Superconductor
Using high speed scanning tunneling spectroscopy, we perform a full mapping
of the quasiparticle density of states (DOS) in single crystals of
BiPbSrCaCuO(2212). The measurements carried out at 5 K showed a complex spatial
pattern of important variations of the local DOS on the nanometer scale.
Superconducting areas are co-existing with regions of a smooth and larger
gap-like DOS structure. The superconducting regions are found to have a minimum
size of about 3 nm. The role of Pb-introduced substitutional disorder in the
observed spatial variations of the local DOS is discussed.Comment: 4 page Letter with 3 figures (2 color figures
Pointwise consistency of the kriging predictor with known mean and covariance functions
This paper deals with several issues related to the pointwise consistency of
the kriging predictor when the mean and the covariance functions are known.
These questions are of general importance in the context of computer
experiments. The analysis is based on the properties of approximations in
reproducing kernel Hilbert spaces. We fix an erroneous claim of Yakowitz and
Szidarovszky (J. Multivariate Analysis, 1985) that the kriging predictor is
pointwise consistent for all continuous sample paths under some assumptions.Comment: Submitted to mODa9 (the Model-Oriented Data Analysis and Optimum
Design Conference), 14th-19th June 2010, Bertinoro, Ital
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
Gifting personal interpretations in galleries
The designers of mobile guides for museums and galleries face three major challenges: fostering rich interpretation, delivering deep personalization, and enabling a coherent social visit. We propose an approach to tackling all three simultaneously by inviting visitors to design an interpretation that is specifically tailored for a friend or loved one that they then experience together. We describe a trial of this approach at a contemporary art gallery, revealing how visitors designed personal and sometimes provocative experiences for people they knew well. We reveal how pairs of visitors negotiated these experiences together, showing how our approach could deliver intense experiences for both, but also required them to manage social risk. By interpreting our findings through the lens of ‘gift giving’ we shed new light on ongoing explorations of interpretation, personalization and social visiting within HCI
The interaction of lean and building information modeling in construction
Lean construction and Building Information Modeling are quite different initiatives, but both are having profound impacts on the construction industry. A rigorous analysis of the myriad specific interactions between them indicates that a synergy exists which, if properly understood in theoretical terms, can be exploited to improve construction processes beyond the degree to which it might be improved by application of either of these paradigms independently. Using a matrix that juxtaposes BIM functionalities with prescriptive lean construction principles, fifty-six interactions have been identified, all but four of which represent constructive interaction. Although evidence for the majority of these has been found, the matrix is not considered complete, but rather a framework for research to
explore the degree of validity of the interactions. Construction executives, managers, designers and developers of IT systems for construction can also benefit from the framework as an aid to recognizing the potential synergies when planning their lean and BIM adoption strategies
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