4,271 research outputs found
Phase coherence length and quantum interference patterns at step edges
The accepted approximation used to describe quantum interference patterns at
steps is shown to be incorrect. As a result, electron lifetimes determined
using it are in error by a factor 2.Comment: 3 pages, 1 figur
Two-Electron Photon Emission From Metallic Quantum Wells
Unusual emission of visible light is observed in scanning tunneling
microscopy of the quantum well system Na on Cu(111). Photons are emitted at
energies exceeding the energy of the tunneling electrons. Model calculations of
two-electron processes which lead to quantum well transitions reproduce the
experimental fluorescence spectra, the quantum yield, and the power-law
variation of the intensity with the excitation current.Comment: revised version, as published; 4 pages, 3 figure
Block circulant matrices with circulant blocks, weil sums and mutually unbiased bases, II. The prime power case
In our previous paper \cite{co1} we have shown that the theory of circulant
matrices allows to recover the result that there exists Mutually Unbiased
Bases in dimension , being an arbitrary prime number. Two orthonormal
bases of are said mutually unbiased if
one has that ( hermitian scalar product in ). In this paper we show that the theory of block-circulant matrices with
circulant blocks allows to show very simply the known result that if
( a prime number, any integer) there exists mutually Unbiased
Bases in . Our result relies heavily on an idea of Klimov, Munoz,
Romero \cite{klimuro}. As a subproduct we recover properties of quadratic Weil
sums for , which generalizes the fact that in the prime case the
quadratic Gauss sums properties follow from our results
Evolution of unoccupied resonance during the synthesis of a silver dimer on Ag(111)
Silver dimers were fabricated on Ag(111) by single-atom manipulation using
the tip of a cryogenic scanning tunnelling microscope. An unoccupied electronic
resonance was observed to shift toward the Fermi level with decreasing
atom-atom distance as monitored by spatially resolved scanning tunnelling
spectroscopy. Density functional calculations were used to analyse the
experimental observations and revealed that the coupling between the adsorbed
atoms is predominantly direct rather than indirect via the Ag(111) substrate.Comment: 9 pages, 3 figure
Assessing the Safety and Efficacy of the FDA: The Case of the Prescription Drug User Fee Acts
The US Food and drug Administration (FDA) is estimated to regulate markets accounting for about 20% of consumer spending in the US. This paper proposes a general methodology to evaluate FDA policies, in general, and the central speed-safety tradeoff it faces, in particular. We apply this methodology to estimate the welfare effects of a major piece of legislation affecting this tradeoff, the Prescription Drug User Fee Acts (PDUFA). We find that PDUFA raised the private surplus of producers, and thus innovative returns, by about 13 billion. Dependent on the market power assumed of producers while having patent protection, we find that PDUFA raised consumer welfare between 19 billion; thus the combined social surplus was raised between 31 billions. Converting these economic gains into equivalent health benefits, we find that the more rapid access of drugs on the market enabled by PDUFA saved the equivalent of 180 to 310 thousand life-years. Additionally, we estimate an upper bound on the adverse effects of PDUFA based on drugs submitted during PDUFA I/II and subsequently withdrawn for safety reasons, and find that an extreme upper bound of about 56 thousand life-years were lost. We discuss how our general methodology could be used to perform a quantitative and evidence-based evaluation of the desirability of other FDA policies in the future, particularly those affecting the speed-safety tradeoff.
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