93,402 research outputs found
Anderson-type model for a molecule adsorbed on a metal surface
We investigate a modified Anderson model to study the local density of states
(LDOS) of a molecular wire adsorbed on a metal. Using a self-consistent
mean-field type approach we find an exponential decay of the LDOS along the
molecule. A repulsive on-site interaction on the molecule suppresses the
tunneling and decreases the characteristic decay length.Comment: 7 pages (using europhys.sty), 5 EPS figures, To appear in Europhys.
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Conformal Symmetry and Pion Form Factor: Soft and Hard Contributions
We discuss a constraint of conformal symmetry in the analysis of the pion
form factor. The usual power-law behavior of the form factor obtained in the
perturbative QCD analysis can also be attained by taking negligible quark
masses in the nonperturbative quark model analysis, confirming the recent
AdS/CFT correspondence. We analyze the transition from soft to hard
contributions in the pion form factor considering a momentum-dependent
dynamical quark mass from a nonnegligible constituent quark mass at low
momentum region to a negligible current quark mass at high momentum region. We
find a correlation between the shape of nonperturbative quark distribution
amplitude and the amount of soft and hard contributions to the pion form
factor.Comment: 7 pages, 6 figures, extensively revised, to appear in Phys. Rev.
Paraxial ray optics cloaking
Despite much interest and progress in optical spatial cloaking, a
three-dimensional (3D), transmitting, continuously multidirectional cloak in
the visible regime has not yet been demonstrated. Here we experimentally
demonstrate such a cloak using ray optics, albeit with some edge effects. Our
device requires no new materials, uses isotropic off-the-shelf optics, scales
easily to cloak arbitrarily large objects, and is as broadband as the choice of
optical material, all of which have been challenges for current cloaking
schemes. In addition, we provide a concise formalism that quantifies and
produces perfect optical cloaks in the small-angle (`paraxial') limit
Paraxial full-field cloaking
We complete the `paraxial' (small-angle) ray optics cloaking formalism
presented previously [Choi and Howell, Opt. Express 22, 29465 (2014)], by
extending it to the full-field of light. Omnidirectionality is then the only
relaxed parameter of what may be considered an ideal, broadband, field cloak.
We show that an isotropic plate of uniform thickness, with appropriately
designed refractive index and dispersion, can match the phase over the whole
visible spectrum. Our results support the fundamental limits on cloaking for
broadband vs. omnidirectionality, and provide insights into when anisotropy may
be required
N/P InP homojunction solar cells with an In0.53Ga0.47As contacting layer grown by liquid phase epitaxy
N/P InP homojunction solar cells with an In sub 0.53 Ga sub 0.47 As contacting layer were fabricated by liquid phase epitaxy (LPE). Electron-Beam-Induced-Current (EBIC) measurements were performed on several selected samples. It was found that the background doping level in the base region sometimes results in a deep junction, which greatly affects the cell performance
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