2,106,693 research outputs found
Range separated hybrid exchange-correlation functional analyses of W and/or N(S) (co)doped anatase TiO_2
Electronic properties and atomic structures of W, N, S, W/N, and W/S dopings
of anatase TiO_2 have been systematically investigated using the density
functional theory (DFT). The exchange and correlation effects have been treated
with Heyd, Scuseria and Ernzerhof (HSE) hybrid functional. Mixing traditional
semi-local and non-local screened Hartree-Fock (HF) exchange energies, the HSE
method corrects the band gap and also improves the description of anion/cation
derived gap states. Enhanced charge carrier dynamics, observed for W/N codoped
titania, can partly be explained by the passivative modifications of N 2p and W
5d states on its electronic structure. Following this trend we have found an
apparent band gap narrowing of 1.03 eV for W/S codoping. This is due to the
large dispersion of S 3p states at the valance band (VB) top extending its edge
to higher energies and Ti--S--W hybridized states appearing at the bottom of
the conduction band (CB). W/S-TiO_2 might show strong visible light response
comparable to W/N codoped anatase catalysts.Comment: 8 pages, 5 figures and 3 table
An estimate for the average spectral measure of random band matrices
For a class of random band matrices of band width , we prove regularity of
the average spectral measure at scales , and find its
asymptotics at these scales.Comment: 19 pp., revised versio
Eigenvector localization for random band matrices with power law band width
It is shown that certain ensembles of random matrices with entries that
vanish outside a band around the diagonal satisfy a localization condition on
the resolvent which guarantees that eigenvectors have strong overlap with a
vanishing fraction of standard basis vectors, provided the band width
raised to a power remains smaller than the matrix size . For a
Gaussian band ensemble, with matrix elements given by i.i.d. centered Gaussians
within a band of width , the estimate holds.Comment: 30 pages; corrected typo
Development of Lumped Element Kinetic Inductance Detectors for the W-Band
We are developing a Lumped Element Kinetic Inductance Detector (LEKID) array
able to operate in the W-band (75-110 GHz) in order to perform ground-based
Cosmic Microwave Background (CMB) and mm-wave astronomical observations. The
W-band is close to optimal in terms of contamination of the CMB from Galactic
synchrotron, free-free, and thermal interstellar dust. In this band, the
atmosphere has very good transparency, allowing interesting ground-based
observations with large (>30 m) telescopes, achieving high angular resolution
(<0.4 arcmin). In this work we describe the startup measurements devoted to the
optimization of a W-band camera/spectrometer prototype for large aperture
telescopes like the 64 m SRT (Sardinia Radio Telescope). In the process of
selecting the best superconducting film for the LEKID, we characterized a 40 nm
thick Aluminum 2-pixel array. We measured the minimum frequency able to break
CPs (i.e. ) obtaining
GHz, that corresponds to a critical temperature of 1.31 K. This is not suitable
to cover the entire W-band. For an 80 nm layer the minimum frequency decreases
to 93.2 GHz, which corresponds to a critical temperature of 1.28 K; this value
is still suboptimal for W-band operation. Further increase of the Al film
thickness results in bad performance of the detector. We have thus considered a
Titanium-Aluminum bi-layer (10 nm thick Ti + 25 nm thick Al, already tested in
other laboratories), for which we measured a critical temperature of 820 mK and
a cut-on frequency of 65 GHz: so this solution allows operation in the entire
W-band.Comment: 16th International Workshop on Low Temperature Detectors, Grenoble
20-24 July 2015, Journal of Low Temperature Physics, Accepte
Quantum Diffusion and Eigenfunction Delocalization in a Random Band Matrix Model
We consider Hermitian and symmetric random band matrices in
dimensions. The matrix elements , indexed by , are independent, uniformly distributed random variables if \abs{x-y}
is less than the band width , and zero otherwise. We prove that the time
evolution of a quantum particle subject to the Hamiltonian is diffusive on
time scales . We also show that the localization length of an
arbitrarily large majority of the eigenvectors is larger than a factor
times the band width. All results are uniform in the size
\abs{\Lambda} of the matrix.Comment: Minor corrections, Sections 4 and 11 update
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